Mechanical properties of fasteners Bolts, screws and studs GB /T 3098.1 – 2010

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  Marking system for performance levels, materials

  5 Marking system for performance levels

      The code for the performance grade of bolts, screws and studs consists of two parts of numbers separated by dots (see Tables 1 to 3):

      ——The one or two digits to the left of the dot represents 1/100 of the nominal tensile strength ( R _{m , nominal ), measured in MPa (see Table 3, No. 1);}

      ——The number to the right of the point indicates the nominal yield strength (lower yield strength) ( _{R eL, nominal) or the nominal stress that specifies a non-proportional extension of 0.2% (RP0.2} , _{nominal )} or the nominal _stress that specifies a non-proportional extension of 0.0048d ( R _{Pf , nominal} ) (see Table 3, No. 2 ~ No. 4) and the nominal tensile strength ( R _{m , nominal} ) 10 times the ratio (see Table 1).

  Table 1 Yield-strength ratio

  Click the number on the right	.6	.8	.9
  or	0.6	0.8	0.9

                  Example: The fastener has a nominal tensile strength Rm, nominal = 800 MPa and a yield ratio of 0.8, and its performance grade is marked ‘8.8’.

      If the material properties are the same as grade 8.8, but the actual load-bearing capacity is lower than that of grade 8.8 fastener products (reduced load-bearing capacity), the performance grade should be marked ‘08.8’ (see 10.4).

      The product of the nominal tensile strength and the yield ratio is the nominal yield strength, measured in MPa. Appendix A provides information indicating the relationship between the nominal tensile strength and post-fracture growth rate of each performance grade.

      The marking and labeling of the performance grade of fasteners shall be in accordance with the provisions of 10.3, and for those with reduced load-bearing capacity, the provisions of 10.4 shall be followed.

      If the requirements of Table 2 and Table 3 can be met, the performance level marking system specified in this part can also be used for specifications beyond the standard range (d>39mm).

  6 materials

      Table 2 specifies the chemical composition limits and minimum tempering temperatures of steel for each performance grade of fasteners. The chemical composition should be in accordance with relevant national standards.

      Note. Certain chemical elements are restricted or prohibited by regulations in some countries. This should be noted when referring to relevant countries or regions.

      The requirements for fastener materials in Chapter 4 of GB/T 5267.3 apply to hot-dip galvanized fasteners.

  Table 2 Materials

  Performance level	Materials and heat treatment	Chemical composition limits (smelting analysis %) a					Tempering temperature ℃ min
  		C		P	S	B b
  		min	max	max	max	max
  4.6c , d	Carbon steel or carbon steel with added elements	—	0.55	0.050	0.060	Not specified	—
  4.8d _
  5.6e _		0.13	0.55	0.050	0.060
  5.8 days		—	0.55	0.050	0.060
  6.8 days		0.15	0.55	0.050	0.060
  8.8f _	Carbon steel with added elements (such as boron or manganese or chromium) quenched and tempered or	0.15e _	0.40	0.025	0.025	0.003	425
  	Carbon steel quenched and tempered or	0.25	0.55	0.025	0.025
  	Alloy steel quenched and temperedg	0.20	0.55	0.025	0.025
  9.8f _	Carbon steel with added elements (such as boron or manganese or chromium) quenched and tempered or	0.15e _	0.40	0.025	0.025	0.003	425
  	Carbon steel quenched and tempered or	0.25	0.55	0.025	0.025
  	Alloy steel quenched and temperedg	0.20	0.55	0.025	0.025
  10.9f _	Carbon steel with added elements (such as boron or manganese or chromium) quenched and tempered or	0.20e _	0.55	0.025	0.025	0.003	425
  	Carbon steel quenched and tempered or	0.25	0.55	0.025	0.025
  	Alloy steel quenched and temperedg	0.20	0.55	0.025	0.025
  12.9 f,h,i	Alloy steel quenched and temperedg	0.30	0.50	0.025	0.025	0.003	425
  12.9 f,h,i	Carbon steel with added elements such as boron or manganese or chromium quenched and tempered	0.28	0.50	0.025	0.025	0.003	380
  a In case of dispute, conduct finished product analysis.  b The boron content can reach 0.005%, and non-effective boron is controlled by adding titanium and/or aluminum.  c For grade 4.6 and 5.6 cold heading fasteners, in order to ensure the required plasticity and toughness, it may be necessary to perform heat treatment on the cold heading wire rod or cold heading fastener products.  d These performance classes allow the use of free-cut steels with maximum sulfur, phosphorus and lead contents of: 0.34% sulfur; 0.11% phosphorus; 0.35% lead.  e For boron-added carbon steel with a carbon content less than 0.25%, the minimum manganese content is: 0.6% for grade 8.8; 0.7% for grades 9.8 and 10.9.  f The materials used for these performance levels should have sufficient hardenability to ensure that the core of the thread section of the fastener obtains approximately 90% of the martensite structure in the ‘hardened’ state before tempering.  g These alloy steels should contain at least one of the following elements, with a minimum content of: 0.30% chromium; 0.03% nickel; 0.20% molybdenum; and 0.10% vanadium. When containing two, three or four composite alloy components, the content of the alloying elements shall not be less than 70% of the total content of the individual alloying elements.  h On grade 12.9/12.9 surfaces, no white phosphide accumulation layer that can be detected by metallography is allowed. Removal of the phosphide accumulation layer should be carried out before heat treatment.  i When considering using level 12.9/12.9, caution should be exercised. The capabilities of the fastener manufacturer, service conditions and tightening methods should all be carefully considered. In addition to surface treatment, the use environment may also cause stress corrosion cracking of fasteners.

  7 Mechanical and physical properties

  Fasteners of specified performance levels shall comply with the mechanical and physical properties specified in Tables 3 to 7 at     ambient temperature ^{1 ) .}

      Chapter 8 provides applicable test methods to check whether fasteners comply with the requirements of Tables 3 to 7.

      Note 1: Even if the material properties of the fasteners comply with the requirements of Tables 2 and 3, some types of fasteners will reduce the load-bearing capacity due to size reasons (see 8.2, 9.4 and 9.5).

      Note 2: Although this standard specifies high levels of performance, this does not mean that all levels are applicable to all fasteners. The performance levels specified in product standards can be used as a reference for non-standard fasteners.

  Table 3 Mechanical and physical properties of bolts, screws and studs

  No.	mechanical or physical properties			Performance level
  				4.6	4.8	5.6	5.8	6.8	8.8		9.8d≤16mm _	10.9	12.9/ 12.9
  									d≤16mma _ _	d >16mm b
  1	Tensile strength R m /MPa		Nominal c	400		500		600	800		900	1000	1200
  			min	400	420	500	520	600	800	830	900	1040	1220
  2	Lower yield strength R eL. d /MPa		Nominal c	240	—	300	—	—	—	—	—	—	—
  			min	240	—	300	—	—	—	—	—	—	—
  3	Specifies the stress R P0.2 /MPa for non-proportional extension of 0.2%		Nominal c	—	—	—	—	—	640	640	720	900	1080
  			min	—	—	—	—	—	640	660	720	940	1100
  4	The specified non-proportional extension stress R Pf /MPa of 0.0048d for the physical fastener		Nominal c	—	320	—	400	480	—	—	—	—	—
  			min	—	340e _	—	420e _	480e _	—	—	—	—	—
  5	Guaranteed stress S P f /MPa		Nominal	225	310	280	380	440	580	600	650	830	970
  	Guaranteed stress ratio	S P.nominal /R eL.min or S P.nominal / R P0.2.min or S P.nominal / R Pf.min		0.94	0.91	0.93	0.90	0.92	0.91	0.91	0.90	0.88	0.88
  6	Elongation after fracture of machined specimen A/%		min	22	—	20	—	—	12	12	10	9	8
  7	Sectional shrinkage rate of machined specimen Z/%		min	—					52		48	48	44
  8	Elongation after fracture A f of the actual fastener (see Appendix C)		min	—	0.24	—	0.22	0.20	—	—	—	—	—
  9	Head sturdiness			Must not break or crack
  10	Vickers hardness/HV,F≥98N		min	120	130	155	160	190	250	255	290	320	385
  			max	220g _				250	320	335	360	380	435
  11	Brinell hardness/HBW,F=30D 2		min	114	124	147	152	181	245	250	286	316	380
  			max	209g _				238	316	331	355	375	429
  12	Rockwell hardness/HRB		min	67	71	79	82	89	—
  			max	95.0g _				99.5	—
  	Rockwell hardness/HRC		min	—					22	23	28	32	39
  			max	—					32	34	37	39	44
  13	Surface hardness/HV0.3		max	—					h			h,i	h,j
  l4	Height of undecarburized layer of thread E/mm		min	—					1/2H 1			2/3H 1	3/4H 1
  	Depth of fully decarburized layer of thread G/mm		max	—					0.015
  15	Hardness reduction after retempering/HV		max	—					20
  16	Breaking torque MB/Nm		min	—					According to the provisions of GB/T 3098.13
  17	Absorbed energy K V k,l /J		min	—		27	—		27	27	27	27	m
  18	Surface defects			GB/T 5779.1 n										GB/T 5779.3
  The value a does not apply to bolted structures.  b For bolted structure d≥M12.  c The nominal value specified is only for the needs of the performance level marking system, see Chapter 5.  d In the case where the lower yield strength R eL cannot be measured, it is allowed to measure the stress R P0.2 specifying a non-proportional extension of 0.2% .  eThe R Pf.min values ​​for performance levels 4.8, 5.8 and 6.8 are still under investigation. The values ​​in the table are calculated based on the guaranteed load ratio, not the actual measured values.  fTable 5 and Table 7 specify the guaranteed load values.  gWhen measuring the hardness at the end of the fastener, it should be: 250HV, 238HB or HRB max 99.5 respectively .  h When HV0.3 is used to measure surface hardness and core hardness, the surface hardness of the fastener should not be higher than the core strength by 30 HV units.  iSurface  hardness should not exceed 390 HV.  jSurface hardness should not exceed 435 HV.  The k  test temperature is measured at -20°C, see 9.14.  lApplicable to d ≥16 mm. The  mKV value is still under investigation.  nUpon agreement between the supply and demand parties, GB/T 5779.3 can be used instead of GB/T 5779.1.

                     1) The absorbed energy test should be carried out at -20°C (see 9.14).

  Table 4 Minimum tensile load (coarse thread)

  Thread specification ( d )	Thread nominal stress cross-sectional area A s. Nominal a /mm 2	Performance level
  		4.6	4.8	5.6	5.8	6.8	8.8	9.8	10.9	12.9/ 12.9
  		Minimum tensile load F m.min ( A s . Nominal × R m.min )/ N
  M3	5.03	2010	2110	2510	2620	3020	4020	4530	5230	6140
  M3.5	6.78	2710	2850	3390	3530	4070	5420	6100	7050	8270
  M4	8.78	3510	3690	4390	4570	5270	7020	7900	9130	10700
  M5	14.2	5680	5960	7100	7380	8520	11350	12800	14800	17300
  M6	20.1	8040	8440	10000	10400	12100	16100	18100	20900	24500
  M7	28.9	11600	12100	14400	15000	17300	23100	26100	30100	35300
  M8	36.6	14600b _	15400	18300b _	19000	22000	29200b _	32900	38100b _	44600
  M10	58	23200b _	24400	29000b _	30200	34800	46400b _	52200	60300b _	70800
  M12	84.3	33700	35400	42200	43800	50600	67400C _	75900	87700	103000
  M14	115	46000	48300	57500	59800	69000	92000C _	104000	120000	140000
  M16	157	62800	65900	78500	81600	94000	125000c _	141000	163000	192000
  M18	192	76800	80600	96000	99800	115000	159000	—	200000	234000
  M20	245	98000	103000	122000	127000	147000	203000	—	255000	299000
  M22	303	121000	127000	152000	158000	182000	252000	—	315000	370000
  M24	353	141000	148000	176000	184000	212000	293000	—	367000	431000
  M27	459	184000	193000	230000	239000	275000	381000	—	477000	560000
  M30	561	224000	236000	280000	292000	337000	466000	—	583000	684000
  M33	694	278000	292000	347000	361000	416000	576000	—	722000	847000
  M36	817	327000	343000	408000	425000	490000	678000	—	850000	997000
  M39	976	390000	410000	488000	508000	586000	810000	—	1020000	1200000
  a A s , see 9.1.6.1 for nominal calculation. b Hot-dip galvanized fasteners with  6az thread (GB/T 22029) should be in accordance with the provisions of Appendix A in GB/T 5267.3.  c pair of bolted structures are: 70000N (M12), 95500N (M14) and 130000N (M16).

   

  Table 5 Guaranteed load (coarse thread )

  Thread specification ( d )	Nominal stress cross-sectional area of ​​the thread A s , nominal a /mm 2	Performance level
  		4.6	4.8	5.6	5.8	6.8	8.8	9.8	10.9		12.9/ 12.9
  		Guaranteed load F p ( A s , nominal × S p , nominal )/ N
  M3	5.03	1130	1560	1410	1910	2210	2920	3270	4180		4880
  M3.5	6.78	1530	2100	1900	2580	2980	3940	4410	5630		6580
  M4	8.78	1980	2720	2460	3340	3860	5100	5710	7290		8520
  M5	14.2	3200	4400	3980	5400	6250	8230	9230	11800		13800
  M6	20.1	4520	6230	5630	7640	8840	11600	13100	16700		19500
  M7	28.9	6500	8960	8090	11000	12700	16800	18800	24000		28000
  M8	36.6	8240b _	11400	10200b _	13900	16100	21200b _	23800	30400b _		35500
  M10	58	13000b _	18000	16200b _	22000	25500	33700b _	37700	48100b _		56300
  M12	84.3	19000	26100	23600	32000	37100	48900c _	54800	70000		81800
  M14	115	25900	35600	32200	43700	50600	66700c _	74800	95500		112000
  M16	157	35300	48700	44000	59700	69100	91000C _	102000	130000	152000
  M18	192	43200	59500	53800	73000	84500	115000	—	159000	186000
  M20	245	55100	76000	68600	93100	108000	147000	—	203000	238000
  M22	303	68200	93900	84800	115000	133000	182000	—	252000	294000
  M24	353	79400	109000	98800	134000	155000	212000	—	293000	342000
  M27	459	103000	142000	128000	174000	202000	275000	—	381000	445000
  M30	561	126000	174000	157000	213000	247000	337000	—	466000	544000
  M33	694	156000	215000	194000	264000	305000	416000	—	576000	673000
  M36	817	184000	253000	229000	310000	359000	490000	—	678000	792000
  M39	976	220000	303000	273000	371000	429000	586000	—	810000	947000
  a A s , see 9.1.6.1 for nominal calculation. b Hot-dip galvanized fasteners with  6az thread (GB/T 22029) should be in accordance with the provisions of Appendix A in GB/T 5267.3.  c pair of bolted structures are: 50700 N (M12), 68800 N (M14) and 94500 N (M16).

   

  Table 6 Minimum tensile load( fine thread)

  Thread specification ( d ×P)	Nominal stress cross-sectional area of ​​the thread A s , nominal a /mm 2	Performance level
  		4.6	4.8	5.6	5.8	6.8	8.8	9.8	10.9	12.9/ 12.9
  		Minimum tensile load F m , min ( A s , nominal × R m , min )/ N
  M8 ×1	39.2	15700	16500	19600	20400	23500	31360	35300	40800	47800
  M10 ×1.25	61.2	24500	25700	30600	31800	36700	49000	55100	63600	74700
  M10 ×1	64.5	25800	27100	32300	33500	38700	51600	58100	67100	78700
  M12 ×1.5	88.1	35200	37000	44100	45800	52900	70500	79300	91600	107000
  M12 ×1.25	92.1	36800	38700	46100	47900	55300	73700	82900	95800	112000
  M14 ×1.5	125	50000	52500	62500	65000	75000	100000	112000	130000	152000
  M16 ×1.5	167	66800	70100	83500	86800	100000	134000	150000	174000	204000
  M18 ×1.5	216	86400	90700	108000	112000	130000	179000	—	225000	264000
  M20 ×1.5	272	109000	114000	136000	141000	163000	226000	—	283000	332000
  M22 ×1.5	333	133000	140000	166000	173000	200000	276000	—	346000	406000
  M24 ×2	384	154000	161000	192000	200000	230000	319000	—	399000	469000
  M27 ×2	496	198000	208000	248000	258000	298000	412000	—	516000	605000
  M30 ×2	621	248000	261000	310000	323000	373000	515000	—	646000	758000
  M33 ×2	761	304000	320000	380000	396000	457000	632000	—	791000	928000
  M36 ×3	865	346000	363000	432000	450000	519000	718000	—	900000	1055000
  M39 ×3	1030	412000	433000	515000	536000	618000	855000	—	1070000	1260000
  a A s , see 9.1.6.1 for nominal calculation.

  Table 7 Guaranteed load (fine pitch thread)

  Thread specification ( d ×P)	Nominal stress cross-sectional area of ​​the thread A s , nominal a /mm 2	Performance level
  		4.6	4.8	5.6	5.8	6.8	8.8	9.8	10.9	12.9/ 12.9
  		Minimum tensile load F m , min ( A s , nominal × R m , min )/ N
  M8 ×1	39.2	8820	12210	11000	14900	17200	22700	25500	32500	38000
  M10 ×1.25	51.2	13800	19000	17100	23300	26900	35500	39800	50800	59400
  M10x1	64.5	14500	20000	18100	24500	28400	37400	41900	53500	62700
  M12 ×1.5	88.1	19800	27300	24700	33500	38800	51100	57300	73100	85500
  M12 ×1.25	92.1	20700	28600	25800	35000	40500	53400	59900	76400	89300
  M14 ×1.5	125	28100	38800	35000	47500	55000	72500	81200	104000	121000
  M16 ×1.5	167	37600	51800	46800	63500	73500	96900	109000	139000	162000
  M18 ×1.5	216	48600	67000	60500	82100	95000	130000	—	179000	210000
  M20 ×1.5	272	61200	84300	76200	103000	120000	163000	—	226000	264000
  M22 ×1.5	333	74900	103000	93200	126000	1146000	200000	—	276000	323000
  M24 ×2	384	86400	119000	108000	146000	169000	230000	—	319000	372000
  M27 ×2	496	112000	154000	139000	188000	218000	298000	—	412000	481000
  M30 ×2	621	140000	192000	174000	236000	273000	373000	—	515000	602000
  M33 ×2	761	171000	236000	213000	289000	335000	457000	—	632000	738000
  M36 ×3	865	195000	268000	242000	329000	381000	519000	—	718000	839000
  M39 ×3	1030	232000	319000	288000	391000	453000	618000	—	855000	999000
  a A s , see 9.1.6.1 for nominal calculation.

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  Applicability of experimental methods

  8 Applicability of experimental methods

  8.1 General

      Two test series (groups), FF and MP, can test the mechanical and physical properties of fasteners specified in Table 3. The FF group is used for fastener finished product testing, while the MP group is used for fastener material performance testing. The FF and MP groups are further divided into: FF1, FF2, FF3, FF4, MP1 and MP2.

      Due to size and/or load-bearing capacity, some types or specifications of fasteners cannot be tested according to all items in Table 3.

  8.2 Load-bearing capacity of fasteners

  8.2.1 Full load-bearing fasteners

      Fasteners with full load-bearing capacity (standardized or non-standardized) should be subjected to tensile tests on finished fasteners according to FF1, FF2 or MP2:

      a) Breakage should occur within the length of the unscrewed thread or the unthreaded shank;

      b) Its minimum tensile load ( F _m.min ) should comply with the provisions of Table 4 or Table 6.

  8.2.2 Fasteners that reduce load-carrying capacity

      Fasteners (standardized or non-standardized) that reduce load-bearing capacity. Although the material properties comply with the provisions of this section, due to geometric dimensions, if the finished product is subjected to a tensile test according to FF1, FF2 or MP2, it will not meet the load-bearing capacity requirements.

      When tensile tested in accordance with FF3 or FF4, fasteners with reduced load-carrying capacity generally do not break within the length of the unscrewed threads.

      There are two basic types of fasteners whose geometric dimensions reduce the load-carrying capacity compared to the minimum tensile load of the thread:

      a) Head design of bolts or screws: reduced head height bolts with or without external wrenching, or oval head, low cylindrical head or certain countersunk head screws with internal wrenching. FF3 is suitable for this type of fastener (see Table 10).

      b) Special shank design of fasteners: suitable for load-bearing capacities that are not required or not specified in this section, such as waist-shaped shank screws. FF4 is suitable for this type of fastener (see Table 11).

  8.3 Manufacturer’s control

      Fasteners produced in accordance with this section are subject to the ‘implementable tests’ specified in Tables 8 to 11. It should be able to meet the technical requirements in Tables 3 to 7.

      This section does not require the manufacturer to perform testing on each production batch, but it is the manufacturer’s responsibility to choose his own methods, such as process control or inspection, to ensure that each production batch meets all technical requirements.

      In case of dispute, the test methods specified in Chapter 9 should be followed.

  8.4 Supplier’s control

      Suppliers can choose their own methods to control the mechanical and physical properties of the fasteners they provide to meet the requirements specified in Tables 3 to 7.

      In case of dispute, the test methods specified in Chapter 9 should be followed.

  8.5 Purchaser’s control

      The purchaser can follow the test methods in Chapter 9 and select the appropriate test series from 8.6 to control the quality of the delivered fasteners.

      In case of dispute, the test methods specified in Chapter 9 should be followed.

  8.6 Tests that may be performed on fasteners and machined specimens

  8.6.1 General

      According to the test methods specified in Chapter 9, Tables 8 to 13 specify the workability of FF1 to FF4, MP1 and MP2.

      Tables 8 to 11 provide fastener finished product tests, providing FF1 to FF4 test series.

  ——FF1: Used to determine the performance of finished bolts and screws with     standard heads and standard rods or thin rods (with full load-bearing capacity), that is, d _s > d ₂ or d _s ≈ d _{2 , see Table 8.}

  ——FF2: used to measure the performance of finished studs of     standard rods or thin rods (with full load-bearing capacity), that is, d _s > d ₂ or d _s ≈ d _{2 , see Table 9.}

      ——FF3: used to determine the performance of finished bolts and screws where d _s > d ₂ or d _s ≈ d _{2 and reduce the load-bearing capacity. The reasons for the reduced load-bearing capacity are:}

          1) Low head height, with or without external wrench structure;

          2) Flat round head or low cylindrical head with internal wrenching structure;

          3) Some countersunk heads with internal wrenching structures.

          See Table 10.

      ——FF4: Used to determine the performance of finished products of bolts, screws and studs of special design that do not require or do not comply with the load-bearing capacity specified in this part, such as d _s < d ₂ waist-shaped rod fasteners (reduced load-bearing capacity) , see Table 11.

      Tables 12 to 13 provide MP1 and MP2 test series for fastener material performance tests and/or process improvement tests. FF1~FF4 can also be used for this purpose.

      ——MP1: Test used to determine the material properties of fasteners and/or improve the process of machined specimens, see Table 12.

  ——MP2: A test used to determine the material properties and/or process improvement of     finished fasteners with full load-bearing capacity ( d _s > d ₂ or d _s ≈ d _{2 ), see Table 13.}

  8.6.2 Applicability

      The applicability of various test methods to fasteners is as specified in Tables 8 to 13.

  8.6.3 Delivery of test results

      When the purchaser requires delivery of a report including test results (special order), they should follow the provisions of Chapter 9 and select the test method from Tables 8 to 13. Special tests specified by the purchaser should be agreed at the time of ordering.

  Table 8 FF1 test series finished bolts and screws with full load capacity

  No. (See Table 3 )	performance	experiment method		Bar number	Performance level
  					4.6 , 4.8 , 5.6 , 5.8 , 6.8			8.8 , 9.8 , 10.9 , 12.9/ 12.9
  					d ＜3mm or l ＜2.5 d or b ＜2.0 d	d ≥ 3mm and l ≥ 2.5 d and b ≥ 2.0 d		d ＜3mm or l ＜2.5 d or b ＜2.0 d	d ≥ 3mm and l ≥ 2.5 d and b ≥ 2.0 d
  1	Minimum tensile strength R m.min	Wedge load tensile test		9.1	NF	a		NF	a
  		Tensile test		9.2	NF	a		NF	a
  5	Nominal guaranteed stress S P. Nominal	Guaranteed load test		9.6	NF			NF
  8	Minimum elongation after break A f.min	Fastener physical tensile test		9.3	NF	b , d	c , d	NF	b , d
  9	Head sturdiness	Head solidity test d ≤ 10mm	1.5 d ≤ l ＜3 d	9.8
  			l≥3d _ _ _
  10 or 11 or 12	hardness	Hardness test		9.9
  13	Highest surface hardness	Carburization test		9.11	NF	NF
  14	Maximum decarburization layer	Decarbonization test		9.10	NF	NF
  15	Hardness reduction value after tempering	Retempering test		9.12	NF	NF		e	e
  16	Minimum breaking torque M B.min	Torque test 1.6mm ≤ d ≤ 10mm ; b ≥ 1d + 2p		9.13	f	f , g			g
  18	Surface defects	Surface defect inspection		9.15
  a for d ≥ 3mm and l ≥ 2d and b < 2d , see 9.1.5 and 9.2.5 . bValues ​​for classes 4.6 , 5.6 , 8.8 and 10.9 are given in Appendix C. c versus 4.8 , 5.8 and 6.8 . d l ≥ 2.7 d and b ≥ 2.2 d . e In case of dispute, this test is an arbitration test. f GB/T 3098.13 does not specify values ​​for levels 4.6 to 6.8 . g In case of dispute, the tensile test can be used instead.            Implementable: The test can be implemented in accordance with Chapter 9 , but in case of dispute, it should be implemented in accordance with Chapter 9 .           It can only be carried out when it is clearly specified: the test can be carried out in accordance with Chapter 9: as an alternative test for a performance (for example, when the tensile test can be carried out, but the torque test is used), or in the product standard or requirement When ordering, special tests (such as impact tests) may be performed due to requirements.        NF    Not Performable: The test cannot be performed: due to the shape and / or size of the fastener (e.g. too short to be tested, headless), or because the test is only applicable to special types of fasteners ( For example, testing of high temperature treated fasteners).

  Table 9 FF2 test series finished stud products with full load capacity

  No. (See Table 3 )	performance	experiment method	Bar number	Performance level
  				4.6 , 4.8 , 5.6 , 5.8 , 6.8			8.8 , 9.8 , 10.9 , 12.9/ 12.9
  				d ＜3mm or l t＜3 d or b ＜2.0 d	d ≥ 3mm and l t ≥ 3 d and b ≥ 2.0 d		d ＜3mm or l t＜3 d or b ＜2.0 d	d ≥ 3mm and l t ≥ 3 d and b ≥ 2.0 d
  1	Minimum tensile strength R m.min	Tensile test	9.2	NF	a		NF	a
  5	Nominal guaranteed stress S P. Nominal	Guaranteed load test	9.6	NF			NF
  8	Minimum elongation after break A f.min	Fastener physical tensile test	9.3	NF	b , d	b , d	c , d	b , d
  10 or 11 or 12	hardness	Hardness test	9.9
  13	Highest surface hardness	Carburization test	9.11	NF	NF
  14	Maximum decarburization layer	Decarbonization test	9,10	NF	NF
  15	Hardness reduction value after tempering	Retempering test	9.12	NF	NF		e	e
  18	Surface defects	Surface defect inspection	9.15
  a If the bolt breaks within the thread length b m screwed into the metal end , the minimum hardness may be used instead of R m , min , or the tensile strength R m may bemeasured using a machined specimen in accordance with 9.7 . b l t ≥ 3.2 d , b ≥ 2.2 d . cValues ​​for levels 4.6 , 5.6 , 8.8 and 10.9 are given in Appendix C. d for level 4.8 , level 5.8 and level 6.8 . e In case of dispute, this test is an arbitration test.            Implementable: The test can be implemented in accordance with Chapter 9 , but in case of dispute, it should be implemented in accordance with Chapter 9 .           It can only be carried out when it is clearly specified: the test can be carried out in accordance with Chapter 9: as an alternative test for a performance (for example, when the tensile test can be carried out, but the torque test is used), or in the product standard or requirement When ordering, special tests (such as impact tests) may be performed due to requirements.       NF    Not Performable: The test cannot be performed: due to the shape and / or size of the fastener (e.g. too short to be tested, headless), or because the test is only applicable to special types of fasteners ( For example, testing of high temperature treated fasteners).

  Table 10 FF3 test series finished screws with reduced load-bearing capacity due to head design

  No. (See Table 3 )	performance	experiment method	Bar number	Performance level
  				04.6 , 04.8 , 05.6 , 05.8 , 06.8		08.8 , 09.8 , 010.9 , 012.9/ 012.9
  				d ＜3mm or l ＜2.5 d or b ＜2.0 d	d ≥ 3mm and l ≥ 2.5 d and b ≥ 2.0 d	d ＜3mm or l ＜2.5 d or b ＜2.0 d	d ≥ 3mm and l ≥ 2.5 d and b ≥ 2.0 d
  a	Minimum tensile load	Due to the design of the head, the tensile test is always within the length of the unscrewed thread.	9.4	NF	a	NF	a
  10 or 11 or 12	hardness	Hardness test	9.9
  13	Highest surface hardness	Carburization test	9.11	NF	NF
  14	Maximum decarburization layer	Decarbonization test	9.10	NF	NF
  15	Hardness reduction value after tempering	Retempering test	9.12	NF	NF	b	b
  18	Surface defectsb	Surface defect inspection	9.15
  a Minimum tensile load, see relevant product standards. b In case of dispute, this test is an arbitration test.            Implementable: The test can be implemented in accordance with Chapter 9 , but in case of dispute, it should be implemented in accordance with Chapter 9 .           It can only be carried out when it is clearly specified: the test can be carried out in accordance with Chapter 9: as an alternative test for a performance (for example, when the tensile test can be carried out, but the torque test is used), or in the product standard or requirement When ordering, special tests (such as impact tests) may be performed due to requirements.       NF    Not Performable: The test cannot be performed: due to the shape and / or size of the fastener (e.g. too short to be tested, headless), or because the test is only applicable to special types of fasteners ( For example, testing of high temperature treated fasteners).

  Table 11 FF4 test series finished bolts, screws and studs with reduced load-bearing capacity (e.g., waisted rods)

  No. (See Table 3 )	performance	experiment method	Bar number	Performance level
  				04.6 , 05.6		08.8 , 09.8 , 010.9 , 012.9/ 012.9
  				d ＜3mm or waist rod length ＜3 d s or b ＜d	d ≥ 3mm and waist rod length ≥ 3 d s and b ≥ d	d ＜3mm or waist rod length ＜3 d s or b ＜d	d ≥ 3mm and waist rod length ≥ 3 d s and b ≥ d
  1	Minimum tensile strength R m.min	Tensile testing of waisted shank bolts and studs	9.5	NF	a	NF	a
  10 or 11 or 12	hardness	Hardness test	9.9
  13	Highest surface hardness	Carburization test	9.11	NF	NF
  14	Maximum decarburization layer	Decarbonization test	9.10	NF	NF
  15	Hardness reduction value after tempering	Retempering test	9.12	NF	NF	b	b
  18	Surface defects	Surface defect inspection	9.15
  a  R m.min is related to the cross-sectional area of ​​the waist rod, A ds = π /4 d s 2 . b In case of dispute, this test is an arbitration test.            Implementable: The test can be implemented in accordance with Chapter 9 , but in case of dispute, it should be implemented in accordance with Chapter 9 .           It can only be carried out when it is clearly specified: the test can be carried out in accordance with Chapter 9: as an alternative test for a performance (for example, when the tensile test can be carried out, but the torque test is used), or in the product standard or requirement When ordering, special tests (such as impact tests) may be performed due to requirements.       NF    Not Performable: The test cannot be performed: due to the shape and / or size of the fastener (e.g. too short to be tested, headless), or because the test is only applicable to special types of fasteners ( For example, testing of high temperature treated fasteners).

  Table 12 MP1 test series using machined specimens to determine material properties

  No. ( See Table 3)	performance	experiment method	Bar number	Performance level
  				4.6 , 5.6		8.8 , 9.8 , 10.9 , 12.9/ 12.9
  				3 ≤ d ＜4.5mm and d 0＜d 3 , min and b ≥ d and l ≥ 6.5 d	d ≥ 4.5mm and d 0 ≥ 3mm and b ≥ d and l ≥ d + 26mm	3 ≤ d ＜4.5mm and d 0＜d 3 , min and b ≥ d and l ≥ 6.5 d	4.5mm ≤ d ≤ 16mm and d 0 ≥ 3mm and b ≥ d and l ≥ d + 26mm	d ＞16mm and d 0 ≥ 0.75 d s and b ≥ d and l ≥ 5.5 d ＋8mm
  1	Minimum tensile strength R m.min	Tensile test of machined specimens	9.7	a	a	a, b, c	a, d, e	a, f, g
  2	Minimum lower yield strength R eL.min			h	h	NF	NF	NF
  3	Specifies the minimum stress R P0.2.min for non-proportional extension of 0.2%			NF h	NF h
  6	Minimum elongation after break A min
  7	Minimum area reduction Z min			NF	NF
  10 or 11 or 12	hardness	Hardness test	9.9
  13	Highest surface hardness	Carburization test	9.11	NF	NF
  14	Maximum decarburization layer	Decarbonization test	9.10	NF	NF
  17	Minimum absorption capacity K v , min	Impact test d ≥ 16mm and l i or l t ≥ 55mm	9.14	NF	j	NF
  18	Surface defects k	Surface defect inspection	9.15	f
  a If measuring studs, the minimum overall length should be added to the length formula by 1 d . b For bolts and screws, when measuring Z min , l ≥ 5 d . c For studs, when measuring Z min , l t ≥ 6 d . d For bolts and screws, when measuring Z min , l ≥ d + 20mm . e For studs, when measuring Z min , l t ≥ 2 d + 20mm . f For bolts and screws, when measuring Z min , l ≥ 4 d + 8mm . g For studs, when measuring Z min , l t ≥ 5 d + 8mm . h When the lower yield strength R eL cannot be measured , it is allowed to measure the stress R P0.2 specifying a non-proportional extension of 0.2% . iHead height can be included. jOnly for level 5.6 . kImplement inspection before machining.            Implementable: The test can be implemented in accordance with Chapter 9 , but in case of dispute, it should be implemented in accordance with Chapter 9 .           It can only be carried out when it is clearly specified: the test can be carried out in accordance with Chapter 9: as an alternative test for a performance (for example, when the tensile test can be carried out, but the torque test is used), or in the product standard or requirement When ordering, special tests (such as impact tests) may be performed due to requirements.        NF    Not Performable: The test cannot be performed: due to the shape and / or size of the fastener (e.g. too short to be tested, headless), or because the test is only applicable to special types of fasteners ( For example, testing of high temperature treated fasteners).

  Table 13 MP2 Test Series Determination of Material Properties Using Finished Bolts, Screws and Studs with Full Load Capacity

  No. (See Table 3 )	performance	experiment method	Bar number	Performance level
  				4.6 , 5.6	4.8 , 5.8 , 6.8	8.8 , 9.8 , 10.9 , 12.9/ 12.9
  				d ≥ 3mm or l ≥ 2.7 d a or b ≥ 2.2 d
  1	Minimum tensile strength R m , min	Tensile test of finished fasteners	9.2	d	d	d
  4	Specifies the minimum stress R Pf for non-proportional extension 0.0048 d , min	Fastener physical tensile test	9.3	b		c
  5	Nominal guaranteed stress SP , nominal	Fastener physical guarantee load test	9.6	d	d	d
  8	Minimum elongation after break A f.min	Fastener physical tensile test	9.3	e		e
  10 or 11 or 12	hardness	Hardness test	9.9
  13	Highest surface hardness	Carburization test	9.11	NF	NF
  14	Maximum decarburization layer	Decarbonization test	9.10	NF	NF
  15	Hardness reduction value after tempering	Retempering test	9.12	NF	NF	f
  18	Surface defects	Surface defect inspection	9.15
  The end of a   stud screwed into the body is subject to a higher tensile load than the end screwed into the nut or the fully threaded stud with l t ≥ 3.2 d . b  Table 3 does not specify the minimum stress R Pf with a specified non-proportional extension of 0.0048 d for grades 4.6 and 5.6 . c  has no usable value. d l ≥ 2.5 d and b ≥ 2.0 d .  eThe  reference value of A f is given in Appendix C. f  In case of dispute, this test is the arbitration test.            Implementable: The test can be implemented in accordance with Chapter 9 , but in case of dispute, it should be implemented in accordance with Chapter 9 .           It can only be carried out when it is clearly specified: the test can be carried out in accordance with Chapter 9: as an alternative test for a performance (for example, when the tensile test can be carried out, but the torque test is used), or in the product standard or requirement When ordering, special tests (such as impact tests) may be performed due to requirements.       NF    Not Performable: The test cannot be performed: due to the shape and / or size of the fastener (e.g. too short to be tested, headless), or because the test is only applicable to special types of fasteners ( For example, testing of high temperature treated fasteners).

• 

  experiment method

  9  test methods

  9.1  Wedge load test of finished bolts and screws (excluding studs)

  9.1.1  General provisions

      This test can simultaneously measure:

  ——Tensile strength R _m     of finished bolts and screws .

      —The soundness of the junction between the head and the unthreaded shaft or threaded part.

  9.1.2  Scope of application

      This test is applicable to bolts and screws with or without flange faces and complying with the following provisions:

      — Flat bearing surface or serrated surface;

      ——The load-bearing capacity of the head is stronger than that of the threaded rod;

      ——The load-bearing capacity of the head is stronger than that of the unthreaded rod;

      ——Unthreaded rod diameter d _s > d ₂  or d _s ≈ d ₂ ;

      ——Nominal length l ≥ 2. 5 d ;

      ——Thread length b ≥ 2.0 d ;

  ——Bolt b     of bolted structure < 2 d ;

      ——3 mm ≤ d ≤ 39  mm ; _

      ——All performance levels .

  9. 1. 3  Equipment

      The tensile testing machine should comply with the regulations of GB/  T 16825.1 . Automatic centering devices cannot be used because they have a greater impact on the wedge pad angles specified in Figure 1 and Table 16 .

  9.1.4   Test device

      Clamps, wedge pads and threaded clamps should be as follows:

      ——Hardness: ≥ 45 HRC ;

      ——Threads of internal thread clamps: as specified in Table 14 ;

      ——Through hole diameter d _h : as specified in Table 15 ;

      ——Wedge pad: According to the requirements in Figure 1 , Table 15 and Table 16 .

  Table 14  Threads of Internally Threaded Clamps

  Fastener surface treatment	Thread tolerance
  	Threads of fasteners before surface treatment	Internal thread clamp thread
  Without surface treatment	6h or 6g	6H
  Electroplating according to GB/T 5267.1	6g or 6e or 6f	6H
  According to GB/T 5267.2 electrolytic zinc flake coating	6g or 6e or 6f	6H
  Nut threads according to GB/T 5267.3 hot-dip galvanizing and enlarged tapping size: ——6H ; _ ——6AZ ; _ ——6AX _	6az 6g or 6h 6g or 6h	6H 6AZ 6AX

      The test device should be rigid enough to ensure that bending occurs at the interface of the head with the unthreaded stem or threaded portion.

  
  

  a   Rounding or 45 ° chamfer, see Table 15 .

  Figure 1  Wedge pads for wedge load testing of finished bolts and screws

   

  Table 15  Wedge pad aperture and fillet radius (unit: mm)

  Thread nominal diameter d	d  h a , b		r 1 c	Thread nominal diameter d	d h a , b		r 1 c
  	min	max			min	max
  3	3.4	3.58	0.7	16	17.5	17.77	1.3
  3.5	3.9	4.08	0.7	18	20	20.33	1.3
  4	4.5	4.68	0.7	20	22	22.33	1.6
  5	5.5	5.68	07	22	24	24.33	1.6
  6	6.6	6.82	0.7	24	26	26.33	1.6
  7	7.6	7.82	0.8	27	30	30.33	1.6
  8	9	9.22	0.8	30	33	33.39	1.6
  10	11	11.27	0.8	33	36	36.39	1.6
  12	13.5	13.77	0.8	36	39	39.39	1.6
  14	15.5	15.77	1.3	39	42	42.39	1.6
  aAccording   to GB/T 5277 medium assembly series. b   Square neck bolt, the hole should be able to match the square neck. c   Class C product, rounded cornersr  1Calculate according to the following formula: r  1  =  r max + 0.2 In the formula: r max = ( d a , max –  d a , min ) /2 .

   

  Table 16  Wedge pad angle  α for wedge load test

  Nominal diameter of thread  d /mm	Performance level
  	Length of unthreaded shank of bolt or screw l s ≥ 2d _		Fully threaded screws, bolts or unthreaded shank lengths of screws l s < 2 d
  	4.6 , 4.8 , 5.6 , 5.8 , 6.8 , 8.8 , 9.8 , 10.9	12.9/ 12.9	4.6 , 4.8 , 5.6 , 5.8 , 6.8 , 8.8 , 9.8 , 10.9	12.9/ 12.9
  	α ± 30 ‘
  3 ≤ d ≤ 20	10°	6°	6°	4°
  20 ＜d≤39 _ _	6°	4°	4°	4°

      For finished bolts and screws whose head bearing surface diameter exceeds 1.7 d but fails the wedge load test, the head may be processed to 1.7 d and tested again according to the wedge pad angle specified in Table 16 .

      In addition, for finished bolts and screws whose head bearing surface diameter exceeds 1.9 d , the wedge angle can be reduced from 10 ° to 6° .

  9.1.5   Test procedure

      The test piece shall be a fastener that has passed the inspection of dimensions, etc.

      Place the wedge pad specified in 9.1.4 under the bolt or screw head as shown in Figure 1 . The length of the unscrewed thread l _th ≥ 1 d .

      For wedge load tests on bolted structural bolts with short thread lengths, the permissible unscrewed thread length l _th ≤ 1 d .

  The wedge load tensile test shall be carried out     in accordance with the provisions of GB/T 228 . The separation rate of the testing machine chuck should not exceed 25  mm/min .

      The tensile test should be continued until fracture.

      Measure the ultimate tensile load F _m  .

  9.1.6   Test results

  9.1.6.1   Determination of tensile strength  R _m

  9.1.6.1.1   Method

  Calculate the tensile strength  R _m     from the nominal stress cross-sectional area, A _s , the nominal and ultimate tensile load measured during the test, F _m  :

  R _m  = F _m / A _{s , nominal}

      In the formula:

  A _{s , nominal} =(π/ ⁴ ) ×[( d2 + d3 ) /  ₂ ]  ₂

      In the formula:

      d ₂ ——Basic pitch diameter of external thread ( GB/T  196 );

      d ₃ – Small diameter of external thread, d  ₃ = d  ₁ – H /6 ;

      d ₁ ——Basic diameter of external thread ( GB/T  196 );

      H  ——original triangle height ( GB/T 192 ).

      Nominal stress cross-sectional area A s , the nominal values ​​are given in Table 4 and Table 6 .

  9. 1. 6. 1. 2  Technical requirements

      Bolts and screws should break within the length of the unthreaded or unthreaded shank.

      The tensile strength  R _m  should comply with the requirements in Table 3 . The minimum tensile load  F _{m , min} shall comply with the provisions of Table 4 or Table 6 .

  Note: As the diameter decreases, the difference between the nominal stress cross-sectional area and the effective stress cross-sectional area gradually increases. When the hardness is used for process control, especially for smaller diameters, the hardness value needs to be increased and exceed the minimum hardness specified in Table 3 to achieve the minimum tensile load .

  9.1.6.2  The firmness of the junction betweenthe measuringhead and the rod or threaded part

  Should notbreak at the head.

  Bolts and screws with unthreaded shafts should notbreak at the junction of the head and shaft .

  For fully threaded screws , if the breakage begins within lengththe of the unscrewed thread , it is allowed to extend or expand to the junction betweenthe head and the thread , or enterthe headbefore breaking .

  9.2  Tensile test on finished fasteners to determine tensile strength

  9.2.1  General provisions

  This test is used to determine the tensile strength R _m  offinished fasteners .

  This test can be carried out together with the test specified in9.3 .

  9.2.2  Scope of application

  This test is applicable to fasteners that meet the following requirements :

  ——Bolts and screws headbearing capacity is stronger than that of the threaded shank ;

  ——Bolts and screws headload-bearing capacity is stronger than that of unthreaded rods ;

  ——Unthreadedrod diameter d _s > d ₂ or d _s ≈ d ₂ ;    

  ——The nominal lengthl of bolts and screws ≥ 2.5 d ;

  ——Threadlength b ≥ 2.0 d ;

  ——Bolt structural bolts b < 2 d ;

  ——The total length of the stud l _t ≥ 3.0 d ;

  ——3mm ≤ d ≤ 39 mm ; _

  ——All performance levels .

  9.2.3  Equipment

  The tensile testing machine should comply with the regulations of GB/  T 16825.1 .When installing clampingfasteners , avoid oblique pulling and use automatic centering devices.

  9.2.4  Test device

  Clamps and threaded clamps should comply with the following regulations :

  ——Hardness: ≥ 45  HRC ;

  ——Through hole diameter d _h : as specified in Table 15 ;

  ——Thread of internal thread clamp: as specified in Table 14 .

  9.2.5  Test procedure

  The test piece shall be a fastener that has passed the inspection of dimensions, etc.

  Bolts and screw test pieces should be screwed into the internal thread clamps as shown in Figure 2a ) and Figure 2b ); stud test pieces should be screwed into two internal thread clamps, see Figure 2c ) and Figure 2d ). The effective screwing length of the thread is ≥ 1 d .

  The length of the unscrewed thread l _th ≥ 1 d .

  However, when this test is carried out in conjunction with the test specified in 9.3 , the length of the unscrewed thread l _th =1.2 d .

  For the tensile test of bolts for bolted structures with short threads, the length of the unscrewed threads shall be l _th < 1 d , and the tensile test shall be conducted in accordance with the provisions of GB/T 228 . The separation rate of the testing machine chuck should not exceed 25 mm/min .

  The tensile test shall be continued until fracture.

  Measure the ultimate tensile load F _m  .

  Description :

  1 —— Screw into the body end;

  2 —— Screw in the nut end;

  d _h ——pore diameter;

  l _th ——The length of the unscrewed the fastenerthread of in the test fixture .

  
  

  Figure 2  Example of test device

  9.2.6   Test results

  9.2.6.1   Method

  See 9.1.6.1 for the calculation method .

  9.2.6.2  Technicalrequirements

  Fastenersshould break within the length of the unthreadedorunthreaded shank.

  For fully threaded screws , if the breakage begins within lengththe of the unscrewed thread , it is allowed to extend or expand to the junction betweenthe head and the thread , or enter the head before breaking .

  The tensile strengthR _m should comply with the requirements in Table 3 .The minimum tensile loadF _{m , min} shall comply with the provisionsof Table 4 or Table 6 .

  Note: As the diameter decreases, the betweendifference the nominal stress cross- sectional area and the effective stress cross-sectional area gradually increases. When the hardness is used for process control , especially for smaller diameters, the hardness value needs to be increased and exceed the minimum hardness specified in Table 3 to achieve the minimum tensile load.

  9.3   Tensile test on the actual fastener to determine the elongation after break A _f and the 0.004 8 d non -proportional extension stressR _Pf

  9.3.1   General provisions

  This test can simultaneously measure:

  ——Elongation A _f after break of the actual fastener;

  ——The 0.004 8 d non – proportional extension stressR Pf of the actual fastener_.

  This test can be carried out together with the test specified in9.2 .

  9.3.2   Scope of application

  This test is applicable to fasteners that meet the following requirements :

  ——Bolts and screws headbearing capacity is stronger than that of the threaded shank ;

  ——Bolts and screws headload-bearing capacity is stronger than that of unthreaded rods ;

  ——Unthreadedrod diameter d _s > d or d _s ≈ d ;

  ——The nominal lengthl of bolts and screws ≥ 2.7 d ;

  ——Threadlength b ≥ 2.2 d ;

  ——The total length of the stud l _t ≥ 3.2 d ;

  ——The end of the stud screwed into the base body should bear a higher ultimate tensile load than the nut end.

  ——3 mm ≤ d ≤ 39  mm ;

  ——All performance levels .

  9.3.3   Equipment

  The tensile testing machine should comply with the regulations of GB/  T 16825.1 .When installing clampingfasteners , avoid oblique pulling and use automatic centering devices.

  9.3.4  Test device

  Clamps and threaded clamps should comply with the following regulations :

  ——Hardness: ≥ 45  HRC ;

  ——Through hole diameter d _h : as specified in Table 15 ;

  ——Thread of internal thread clamp: as specified in Table 14 .

  The testing device should be rigid enough to avoiddeformation that may affectthe determination of0.004 8 d non-proportional extension loadF _Pf or elongation fracture A _f  .

  9.3.5   Test procedure

  The test piece shall be a fastenerthat has passed the inspection of dimensions, etc.

  Screw the fastenertest piece into the internal thread fixture as shown in Figure 2a ) and Figure 2b ) . Two threaded clamps should be used for stud specimens , see Figure 2c ) and Figure 2d ). The effective threadengagement lengthshould be at least 1 d . For the length of unscrewedthreads subjected to load ,l _th shall be 1.2 d .

  Note: In order to achieve the requirement of l _th = 1.2 d , it is recommended to adopt the following practical method: first, screw the threaded clamp to theend of the thread ; then, unscrew the clamp by a numberof turns equivalent to 1.2 d .

  The tensiletest should be carried out in accordance withthe provisionsof GB/T 228 . When carrying out0.004 8 d non-proportional extension load , F _Pf test , the separation rate of the testing machine chuck should not exceed10 mm/min , and for other tests it should notexceed25  mm/min .

  The tensile loadF can be measureddirectly with the help of a suitable electronic device (such as a microprocessor ), or according to the load– displacement curve ( see GB/T 228 )until fracture. The curvecan be drawn automatically or graphically .

  In order to obtain a more accurate graphicalmeasurement, the scale of the curve should be such that the anglebetween the straight line portion representing the elasticdeformationand the loadaxis is between 30 ° and  45 °.

  9.3.6   Test results

  9.3.6.1   Determination of elongation break A _f

  9.3.6.1.1   Method

  The plastic elongation ΔLP is measureddirectly on an electronic on a load– displacement curve drawngraphically,see _Figure 3 . 

  
  

  a   breaking point.

  Figure 3  Load– displacement curve for measuring the elongation afterfracture A _f

  The inclination ) of the rangeelastic (straight -line part of the curve ) should be measured ;a line parallel to the straight-line part of the elasticdeformationphasein the load– extensioncurve is drawn through the breaking point Line , see line a in Figure 3 . The straight line a that intersects the fracture point and the axis center line of the clamping displacementshould intersect with the elongation coordinate(abscissa) Δ L , and the plastic elongation Δ L _P should be measured , see Figure 3 .

  When there is a dispute , for example, within the rangeelastic of the measurement , when the straightpart has a certain arc , a straight line can be drawn through the two points on the curveequivalent to 0.4 F _P and 0.7 F _P (press again Thisstraight line is drawn parallel tothe breaking point ). F _P is the proof load given in Table 5 and Table 7 .

  Calculate the post-break the physicalelongation fastenerusingthe following formula :

  A _f = Δ L _P /1.2 d 

  9.3.6.1.2   Technicalrequirements

  For Class 4.8 , Class 5.8 and Class 6.8 Af _, the requirements in Table 3 shall be met .

  9.3.6.2   Determination of0.004 8 d _non -proportional extension stressR Pf

  9.3.6.2.1   Method

  R _Pf should be measured directly on the load– displacement curve ,see Figure 4 .

  
  

  Figure 4  Load – displacement curve for determining 0.0048 d non-proportional extension stress R _Pf

  On the axis of the clamping displacement , at a distance equal to 0. 004 8 d , draw a straight line parallel to the inclination angle ofthe elasticrange ( the straight part of the curve ) . The point where this line intersects the curvecorresponds to the loadF _Pf .

  In case of dispute , when measuringthe inclination angle of the load– displacement curve in the rangeelastic , a straight line shall be drawn through two points equivalent to 0.4 F _P and 0.7 F _P intersectingthe curve. F _P is the proof load given in Table 5 and Table 7 .

  Calculate the 0. 004 8 d non-proportional extension stressR _Pf according to the following formula:

  R _Pf = F _Pf / A _{S , nominal}

  In the formula: A S _, the _{nominal name}  is specified in 9.1.6.1 .

  9.3.6.2.2   Technicalrequirements

  There are no definedtechnical requirements.

  Note 1:  The value of R _Pf is under investigation . Forreference, see Table3 ( No. 4 and footnote e ).

  Note 2 : Due to the influence of manufacturing methods and specifications, the yield strengthvalue obtained from the physical test of the fastener instead of the value obtained from the machined specimen is different .

  9.4   Tensile test of bolts and headsscrews

  9.4.1   General provisions

  This test is intended to determine the tensile load on bolts and the lengthscrews the unscrewed thread due toheaddesign (see 8.2 ).

  9.4.2  Scope of application

  This test applies to bolts and provisionsscrews :

  ——Unthreadedrod diameter d _S > d ₂ or d _S  = d ₂ ;

  ——Nominal lengthl ≥ 2.5 d ;

  ——Threadlength b ≥ 2.0 d ;

  ——3 mm ≤ d ≤ 39  mm ;

  ——All performance levels .

  9.4.3   Equipment

  The tensile testing machine should comply with the regulations of GB/  T 16825.1 .When installing clampingfasteners , avoid oblique pulling and use automatic centering devices.

  9.4.4  Test device

  Clamps and threaded clamps should comply with the following regulations :

  ——Hardness: ≥ 45 HRC ;

  ——Through hole diameter d _h  : as specified in Table 15 ;

  ——Thread of internal thread clamp: as specified in Table 14 .

  9.4.5  Test procedure

  The test piece shall be a fastenerthat has passed the inspection of dimensions, etc.

  Screw the fastenertest piece into the internal thread fixture as shown in Figure 2a ) and Figure 2b ) .

  For the lengthof the unscrewed thread l _th ≥ 1 d .

  The tensiletest should be carried out in accordance withthe provisionsof GB/T 228 . The separation rate of the testing machine chuck should not exceed25  mm/min .

  The tensile test shall becontinued until fracture.

  Measure the ultimate tensile loadF _m .

  9.4.6   Technical requirements for test results

  The ultimate tensile loadF _m  should be equal to or greater than the minimum tensile load specified in the corresponding product standards or other technical conditions .

  9.5   Tensiletest of waist rod fasteners

  9.5.1   General provisions

  This test is suitable for determining the tensile strength R _m of waist -shaped rod fasteners( see 8.2 ) .

  9.5.2   Scope of application

  This test is applicable to fasteners that meet the following requirements :

  ——Unthreadedrod diameter d _S < d ₂ ;

  ——The length of the waist-shaped rod is ≥ 3 d _S ( see Figure6  L _C  );

  ——Threadlength b ≥ 1 d ;

  ——3 mm ≤ d ≤ 39  mm ;

  ——4.6 , 5.6 , 8.8 , 9.8 , 10.9 and 12.9 / 12.9 levels . _ _

  9.5.3   Equipment

  The tensile testing machine should comply withtheprovisions of GB/T  16825.1 . When installing clamping fasteners , oblique pulling should be avoided and automatic centering devices can be used .

  9.5.4   Test device

  Clamps and threaded clamps should comply with the following regulations:

  ——Hardness: ≥ 45  HRC ;

  ——Through hole diameter d _h  : as specified in Table 15 ;

  ——Thread of internal thread clamp: as specified in Table 14 .

  9.5.5   Test procedure

  The test piece shall be a fastenerthat has passed the inspection of dimensions, etc.

  Screw the fastenertest piece into the internal thread fixture as shown in Figure 2a ) . Two threaded clamps should be used for stud specimens , see Figure 2c ). The effective threadengagementlengthshould be at least 1 d .

  The tensile test should be carried out in accordance withthe provisionsof GB/T 228 . The separation rate of the testing machine chuck should not exceed 25 mm/min .

  The tensile test shall becontinued until fracture.

  Measure the ultimate tensile load F _m  .

  9.5.6   Test results

  9.5.6.1   Method

  Calculate the tensile strength R _m  based on the cross-sectional area A _ds of the waist-shaped bar and the ultimate tensile load F _m measured in the test ;

  Rm ＝Fm / Ads _{_ _ _}

  In the formula:

  A _ds = ( π /4)  d _S ²

  9.5.6.2   Technical requirements

  Breakage should occur within the waist-shaped rod.

  The tensile strength R _m  should comply with the requirements in Table 3 .

  9.6   Guaranteed load test of finished fasteners

  9.6.1   General provisions

  The guarantee load test consists of two steps:

  ——Implement the specified guarantee load (see Figure 5 );

  – Measure the permanent elongation produced by the proof load.

  9.6.2   Scope of application

  This test is applicable to fasteners that meet the following requirements:

  ——Bolts and screws whose head bearing capacity is stronger than that of the threaded shank;

  ——Bolts and screws whose head load-bearing capacity is stronger than that of unthreaded rods;

  ——Unthreaded rod diameter d _S＞d ₂ or d _S ≈ d ₂ ;

  ——The nominal length l of bolts and screws ≥ 2.5 d ;

  ——Thread length b ≥ 2.0 d ;

  ——The total length of the stud l _t ≥ 3.0 d ;

  ——3 mm ≤ d ≤ 39  mm ;

  ——All performance levels .

  9.6.3   Equipment

  The tensile testing machine shall comply with the provisions of GB/T  16825.1  .When installing clampingfasteners , avoid oblique pulling and use automatic centering devices .

  9.6.4   Test device

  Clamps and threaded clamps should be as follows :

  ——Hardness: ≥ 45  HRC ;

  ——Through hole diameter d _h  : as specified in Table 15 ;

  ——Thread of internal thread clamp: as specifiedin Table 14 .

  
  

  Description :

  1 —— Load .

  Note: There should be ‘ball – cone ‘ contact between the probe and the center hole at the end of the fastener . Other appropriate methods can also be used.

  Figure 5  Installation example of applying guaranteed load to finished fasteners

  9.6.5   Test procedure

  The test piece shall be a fastenerthat has passed the inspection of dimensions, etc.

  Each end of the test piece should be appropriately processed, as shown in Figure 5 . To measure length ( before and after application of load the fastenershall be placed in a bench-mounted measuringinstrument with a sphericalprobe (or other suitable method) . Gloves or pliers should be used tominimizemeasurement errors due to temperature effects. Measure the total length l ₀ of the fastener before load is applied .

  Screw the fastenertest piece into the threaded fixture as shown in Figure 5 . Two threaded clamps should be used on studs . The effective threadengagement lengthshould be at least 1 d . The lengthl _th of the unscrewed thread should be 1 d .

  Note: In order to meet the requirement of l _{t h} = 1 d , it is recommended to firstscrew the threaded clamp tothe end of the thread; then, unscrew the clamp by a numberof turns equivalent to 1 d .

  Apply the guarantee load specified in Table 5 or Table 7 to the fastener axially .

  The separation rate of the testing machine chuck should not exceed3 mm/min . This guaranteedload should be maintained for 15s .

  After unloading, measurethe total length l ₁ of the fastener. 

  9.6.6   Technical requirements for test results

  After unloading, the total length l ₁ of the fastener should be the same as l ₀ before loading(its tolerance ± 12.5 μ m is the allowablemeasurementerror ) . Certain uncertainties, such as straightness , thread alignment, and measurement errors, can causesignificantfastener elongationwhen proof loads arefirst . In this case, a load that is 3% greater than the values ​​specified inTable 5 and Table 7 can be used , and the test can be carried outagain according to 9.6.5 . If the length after the second unloading (l2 ) is the same as the length before loading(l1 ) (its tolerance ±  _1.25 μm is the allowablemeasurement error) , it should be considered to meet _the requirements of this test .

  9.7   Tensile test of machined specimens

  9.7.1   General provisions

  This test can determine:

  ——Tensile strength R _m ;

  ——Lower yield strength R _eL or 0.2% non-proportional extension stress R _P0.2 ;

  ——The elongation after fracture A of the mechanically processed specimen ;

  ——The area shrinkage Z of the mechanically processed specimen .

  9.7.2  Scope of application

  This test is applicable to fasteners that meet the following requirements:

  a)   Machined specimens made from bolts and screws:

  ——3mm ≤ d ≤ 39mm ; _

  ——Thread length b ≥ 1 d ;

  ——Measurement A : nominal length l ≥ 6 d ₀＋2 r ＋d (see Figure 6 );

  ——Measurement of Z : nominal length l ≥ 4 d ₀ + 2 r + d (see Figure 6 ).

  b ) Machined specimens made from studs:

  ——3mm ≤ d ≤ 39mm ; _

  ——Thread length b ≥ 1 d ;

  ——Measurement A : Total length l _t ≥ 6 d ₀＋2 r ＋d (see Figure 6 );

  ——Measure Z : the total length l _t ≥ 4 d ₀＋2 r ＋d (see Figure 6 ).

  c ) Level 4.6 , Level 5.6 , Level 8.8 , Level 9.8 and Level 12.9/ 12.9 .

  Note: Mechanical processing specimens can be made from bolts or screws whose bearing capacity is reduced due to geometric dimensions and whose head bearing capacity is stronger than the bearing capacity of the cross-sectional area ( S ₀ ) of the specimen, or from unthreaded rods with diameter d _s < Produced from fasteners of d _{2 .}

  Grade 4.8 , 5.8 and 6.8 (cold work hardened) fasteners are subject to physical tensile tests, see 9.3 .

  9.7.3   Equipment

  The tensile testing machine shall comply with the provisions of GB/T 16825.1 . When installing clamping fasteners, avoid oblique pulling and use automatic centering devices.

  9.7.4   Test device

  Clamps and threaded clamps should be as follows :

  ——Hardness: ≥ 45  HRC;

  ——Through hole diameter d _h : as specified in Table 15 ;

  ——Thread of internal thread clamp: as specifiedin Table 14 .

  9.7.5   Mechanical processing test pieces

  Mechanical processing test pieces shouldbe made from fasteners that have passed the dimensional inspection . Figure 6 shows the machined specimen for the tensile test .

  The diameter of the machined test piece should be : d ₀ < d _{3 , min} , and as far as possible : d ₀ ≥ 3  mm .

  For machined specimens with a nominal diameter d > 16 mm and quenched and tempered fasteners , the diameter reduction shall not exceed 25 %ofthe original diameter d (44% of the initial cross-sectional area ). For test pieces made from studs , the minimum thread length at both ends is 1 d .

  9.7.6   Test procedure

  The tensiletest should be carried out in accordance with    the provisionsof GB/T 228  . The separation rate of the testing machine chuck : for the lower yield strengthR _eL or 0.2% non-proportional extension stressR _P0.2 , it should notexceed 10 mm/min , and for other itemsit should not exceed25  mm/min .

      The tensile test shall becontinued until fracture.

      Measure the ultimate tensile loadF _m  .

  

  Description :

  d  —— Nominal diameter of thread .

  d ₀  ——The diameter of the machined specimen ( d ₀ < d _{3, min} , and as far as possible : d 0 _≥ 3mm ) .

  b  —— Thread length ( b ≥ d ).

  L ₀  ——Initial measured length of the machined specimen :

  ——Used to determinethe elongation after fracture of machined specimens : L 0 ₌ 5 d 0 _or ( 5. 65 );

  ——Used to determinethe area shrinkage _of  machined specimens : L ₀ ≥ 3 d 0 .

  L _c  – the length of the straight linesegment of the machined specimen (L ₀ + d ₀ ).

  L _t  ——The total length of the machined specimen ( L _c＋2 r ＋b ).

  S ₀  ——The cross-sectional area of ​​the machined specimen before the tensile test .

  r   —— Corner radius ( r ≥ 4  mm ).

  Figure 6  Mechanical specimen for tensile test

  9.7.7   Test results

  9.7.7.1   Method

  The following properties are measured according to the provisionsof GB/T 228 :

  a )  Tensile strengthR _m , R _m = F _m / S ₀  .

  b )  Lower yield strengthR _eL or 0.2% non-proportional extension stressR _P0.2  .

  c )  The elongation after fracture of the machined specimen , whose L ₀ is at least 5 d ₀  .

  A = ( L _u – L ₀ )/ L ₀ × 100

  Where: L _u is the finalmeasured length of the machined specimen (see GB/T  228 ).

  d )  The area shrinkage the machined specimen , whose L ₀ is at least 3 d ₀

  Z = ( S ₀ – S _u )/ S ₀ × 100

  In the formula: S _u is the cross-sectional area of ​​the machined specimen after fracture .

  9.7.7.2   Technicalrequirements

  The following properties should comply with the requirements of Table 3 :

  ——Minimum tensile strengthR _m ; 

  ——Lower yield strengthR _eL or 0.2% non-proportional extension stressR _P0.2  ;

  ——The elongation after fracture A  of the mechanically processed specimen ;

  ——The area shrinkage the mechanically processed specimen .

  9.8   Headstabilitytest

  9.8.1   General provisions

  This test is used to checkthe solidity of the head and the unthreaded stem or the threaded transition circle. During inspection , hammer the head of the fastenerplaced in the test mold with a specified .

  Note: This test is generally used where the wedge load test cannot be performed because the fastener is too short.

  9.8.2   Scope of application

  This test applies to bolts and provisionsscrews :

  ——The load-bearing capacity ofthe head is stronger than that of the threaded rod ;

  ——Nominal lengthl ≥ 1. 5 d ;

  ——d ≤ 10  mm ; _

  ——All performance levels .

  9.8.3  Test device

  The test mold is shown in Figure 7 and should comply with the following regulations :

  ——Hardness: ≥ 45  HRC ;

  ——Through hole diameter d _h and filletr ₁ are as specified in Table 15 ;

  ——Minimum thickness: ≥ 2 d ;

  ——β angle : as specifiedin Table 17 .

  
  

  a   l ≥ 1.5 d .

  bTest   mold thickness ≥ 2 d .

  Figure 7  Test mold for head robustness test

   

  Table 17  Test mold beta angle for head robustness test

  Performance level	4.6	5.6	4.8	5.8	6.8	8.8	9.8	10.9	12.9/ 12.9
  β	60°		80°

  9.8.4   Test procedure

  The test piece shall be a fastenerthat has passed the inspection of dimensions, etc.

  The test mold shown in Figure 7 should be used for the headsolidity test .

  The test mold should be firmly fixed. Hit the head of the bolt or screw several times with a hand hammer to bend the head at a 90 °-β  angle . The β angle is as specifiedin Table 17 .

  The inspection should be carried out ata magnification of 8 to 10 times .

  9.8.5   Technical requirements for test results

  No cracksshould be found at the transition circle between the head and the unthreaded shank or thread .

  Fully threaded screws shall still be deemed to comply with the requirements of this test even if cracksappearon the first thread , as long as thehead .

  9.9   Hardness test

  9.9.1   General provisions

  This test can determine :

  ——For fasteners that cannot be subjected to tensiletesting :determinethe hardness of the fastener

  – For fasteners capable of tensiletesting (see 9.1 , 9.2 , 9.5 and 9.7 ): determinethe maximum hardness of the fastener .

  Note : There may not be a direct conversion relationship between hardness and tensile strength . In addition consideringto the theoreticalmaximum tensile strength, the maximum hardnessvalue also has other factors (such as avoiding brittle fracture).

  Hardness can be measured on a suitable surface, or on a cross-section of the thread .

  9.9.2   Scope of application

  This test is applicable to fasteners that meet the following requirements :

  ——All specifications ;

  ——All performance levels .

  9.9.3  Test methods

  Hardness can be measured using Vickers , Brinell or Rockwell hardness tests .

  a )  Vickers hardness test

  Vickers hardness test should be in accordance with GB /  T 4340.1 .

  b )  Brinell hardness test

  Brinell hardness test should be in accordance with GB/T 231.1 .

  c )  Rockwell hardness test

  Rockwell hardness test should be in accordance with GB/T 230.1 .

  9.9.4   Test procedure

  9.9.4.1   General provisions

  Fastenersthat have passed the size inspection should be used for hardness testing .

  9.9.4.2  Determination of hardness at thread cross-section

  A cross-section is taken 1d from the end of the threadand should be properly prepared .

  Measure the hardness in the area between 1/2 radius and the axisline , see Figure 8 .

  
  

  illustrate:

  1 ——Fastener axis line;

  2——1 / 2 radius area.

  Figure 8 Hardness measurement within 1/2 radius area

  9.9.4.3   Determination ofhardness on surface

  After removing the surface plating or coating andproperly treating the specimen, measure the hardness on the flat surface unthreadedof the head rod .

  For routine inspection , this method can be used.

  9.9.4.4   Test load for determining

  The minimum loadused for Vickers hardness testing is 98 N.

  The test loadfor Brinell hardness is equal to 30 D ² inN.

  9.9.5   Technicalrequirements

  For fasteners that cannot be subjected to tensiletests andbolts forbolted structures with short thread lengths ( for tensile tests , the lengthof the threads with short thread lengths and unscrewed threadsl _th＜1 d ), the The hardness should be within the rangespecified in Table 3 .

  For fasteners that can be subjected to tensiletests , the lengthof unscrewedthreads l _th ≥ 1 d , waist-shaped rod fasteners , and machined test pieces, the hardness should not exceed the maximum valuespecified in Table 3 .

  4. For grade 6 , grade 4.8 , grade 5.6 , grade 5.8 and grade 6.8 fasteners , the hardness shall be measured at the end of the fastener in accordance with the provisions of 9.9.4.3, and shall notexceed the maximumspecified inTable 3 . value .

  For heat-treated fasteners , if the difference in hardness values ​​measured within the 1/2  radius area ( see Figure 8 )is not greater than 30 HV , it is confirmed that the martensite in the material has reached the requirement of 90% ( see Table2 ).

  4. The hardness of grade 8 , 5.8 and 6.8 cold work hardened fasteners shall be measured according tothe provisionsof 9.9.4.2 , and shall be within the hardness rangespecified inTable 3 .

  In case of dispute , the arbitration test shall be conducted in accordance withthe provisions of 9.9.4.2 and Vickers hardnessshall be used .

  9.10   Decarbonization test

  9.10.1   General provisions

  This test can determine the surface decarburization and depth of the decarburization layer of quenched and tempered fasteners ( see Figure 9 ).

  Note: The decarburization layer caused by the heat treatmentprocess exceeding the requirements inTable 3 will reduce the strength of the thread and may cause its failure.

  The state of surface carbon content shall be determined using one of the following two methods :

  ——Metallography;

  ——Hardness method.

  The metallographic method can determinethe depth G of the fully decarburized layer of the thread and the height E of the non-decarburized layer of the thread ( see Figure 9 ).

  The hardness method can measurethe height E of the undecarburized layer of the thread and the micro– hardness method can measure incomplete decarburization ( see Figure 9 ).

  
  

  Description :

  1 – Full decarbonization;

  2 – Incomplete decarburization;

  3 ——Medium diameter line ;

  4 – base metal;

  E – the height of the non-decarburized layer of the thread ;

  G —— The depth of the fully decarburized layer of the thread ;

  H ₁ ——The tooth profile height of the external solidthread .

  Figure 9  Decarburization layer

  9.10.2   Metallography

  9.10.2.1   Scope of application

  This method is applicable to fasteners that meet the following requirements:

  ——All specifications ;

  ——Level 8.8～12.9 / Level 12.9 .

  9.10.2.2  Preparation of test specimens

  Test pieces shall be prepared from fasteners after all heat treatment procedures have been completed and plating or other coatingshave been removed .

  A longitudinal section of the specimen is taken about one nominal diameter ( 1 d ) away from the end of the thread theaxis of the thread . The test piece shall be embedded in plastic or mounted in a fixture. After installation, the surface is ground and polished until ready for metallographic examination .

  Note: Usually, immersion in 3% nitric acid ethanol etching solution (a mixture of concentrated nitric acid and ethanol ) can showthe changes in the metallographic structure caused by decarburization .

  9.10.2.3  Test procedure

  Place the test piece under a microscopeand inspectit at 100x magnification unless otherwiseagreed .

  If the microscopehas a ground glass screen, the degree of decarburization can be measured directly with the aid of a scale . Ifmeasuring with an eyepiece, a microscopewith a crosshair or scale should be used .

  9.10.2.4  Technicalrequirements

  The maximum depth G of the fully decarburized layer shall comply with the technical requirements specified in Table 3 . The height E of the incomplete decarburization layer shall comply with the technicalrequirements specified inTable 18 .

  Table 18  Under the maximum solid condition , the profile height H _{1 of the external thread} andthe minimum height value E _min of the incomplete decarburization layer of the thread

  Pitch Pa _			0.5	0.6	0.7	0.8	1	1.25	1.5	1.75	2	2.5	3	3.5	4
  H 1			0.307	0.368	0.429	0.491	0.613	0.767	0.920	1.074	1.227	1.534	1.840	2.147	2.454
  Performance level	8.8 , 9.8	E min b	0.154	0.184	0.215	0.245	0.307	0.384	0.460	0.537	0.614	0.767	0.920	1.074	1.227
  	10.9		0.205	0.245	0.286	0.327	0.409	0.511	0.613	0.716	0.818	1.023	1.227	1.431	1.636
  	12.9/ 12.9		0.230	0.276	0.322	0.368	0.460	0.575	0.690	0.806	0.920	1.151	1.380	1.610	1.841
  a P < 1.25mm , only metallographic method is used. b  is calculated according to the provisions of No. 14 in Table 3 .

  9.10.3   Hardness method

  9.10.3.1   Scope of application

  This method is applicable to fasteners that meet the following requirements:

  ——Pitch P ≥ 1.25mm ;

  ——Level 8.8～12.9/ Level 12.9 .

  9.10.3.2   Preparation of test specimens

  Test specimens shall be prepared in accordance with 9.10.2.2 , but corrosion and removal of surface coatings are not required.

  9.10.3.3   Test procedure

  Measure the Vickers hardness at points 1 and 2 as shown in Figure 10 , and the test force is 2.942N (Vickers hardness test HV0.3 ).

  
  

  illustrate:

  E ——Height of non-decarburized layer of thread, mm ;  non-decarburized: HV(2) ≥ HV(1)-30                                 

  H ₁ ——Tooth height of external thread under maximum solidcondition , mm ; without decarburization: HV(3) ≥ HV(1)-30                     

  1 , 2 , 3 – measuring point (point 1 );

  4  ——Medium diameter line .

  The value of 0.14 mm given by a only indicates the position of that point on the pitch line . 

  Figure 10  Hardness measurement of decarburization test and carburization test

  9.10.3.4   Technicalrequirements

  The Vickers hardness value at point 2 , HV (2), should be equal to or greater than the Vickers hardness at point 1 , HV(1) minus 30 Vickers units .The height E of the undecarburized layer of the threadshall comply with the technical requirements specified in Table 18 .

  Note: When full decarburization reaches the maximum valuespecified in Table 3 , the hardness measurement method cannot be used.

  9.11   Carbon addition test

  9.11.1   General provisions

  This test is suitable for determiningwhether carburization is formed on the surface of quenched and tempered fasteners the heat treatmentprocess . Forthe evaluation of the carburization state of the surface layer ,the difference between is the decisive indicator .

  Note: Adding carburization is harmful because increasing surface hardness can cause brittle fracture or reduce fatigue resistance. Careshould be taken to distinguish whether the increase in hardness is due to carburization orheat treatment or surface cold work hardening, such as thread rolling after heat treatment.

  One of the following methods can be used to conduct the carburization test :

  ——Measurement of hardness in longitudinal ;

  – Determination of hardness on the surface .

  In case of dispute , and when P ≥ 1. 25 mm , the hardness test specified in 9.11.2 shall be the arbitration test method .

  9.11.2   Determination of hardness in longitudinal section

  9.11.2.1   Scope of application

  This method is applicable to fasteners that meet the following requirements :

  ——Pitch P ≥ 1. 25  mm ;

  ——Level 8.8 ~ 12. 9 / 12. 9 . _

  9.11.2.2   Preparation of test specimens

  Test specimens shall be prepared in accordance with9.10.2.2 , but corrosion and removal of surface coatings are not required .

  9.11.2.3   Test procedure

  Measurethe Vickers hardness at points 1 and 3 as shown in Figure 10 . The test force is : 2. 942 N ( Vickers hardness test HV0. 3 ).

  If the test piece has been used in the test according to 9.10.3.3 , the hardness of point 3 shall be on the threadpitch line andmeasured on the teeth adjacent to the hardness of points 1 and 2 . Perform measurement .

  9.11.2.4   Technicalrequirements

  The Vickers hardness value at point 3 , HV (3), shall be equal to or less than the Vickers hardness value at point 1 , HV(1) plus 30 Vickers units .

  More than30 Vickers units indicates that the carburization has been added . See Table3 ( No. 13 and footnotes h , i and j ) for the hardness regulations of grade 10.9 and grade 12.9 / 12.9 .

  9.11.3   Determination of hardness on surface

  9.11.3.1   Scope of application

  This method is applicable to fasteners that meet the following requirements :

  ——All specifications;

  ——Level 8.8～ Level 12.9/12.9 .

  9.11.3.2   Preparation of test specimens

  Prepare an appropriate flat surface by grinding or polishing the head or end of the fastener to ensure that the original characteristics of the material surface are reproduced and maintained.

  A cross-section is taken 1 d from the end of the thread and suitably prepared.

  9.11.3.3   Test procedure

  Surface hardness shall be determined on the prepared surface.

  Base metal hardness should be measured in cross-section.

  The test force used in measuring the above hardness is: 2.942N (Vickers hardness test HV0.3 ).

  9.11.3.4   Technical requirements

  The surface hardness value should be equal to or less than the base metal hardness value plus 30 Vickers units.

  More than 30 Vickers units indicates carbonization, see Table 3 ( No. 13 and footnote h ). For grade 10.9 or grade 12.9/12.9, the maximum surface hardness should not be greater than 390HV or 435HV .

  9.12   Retempering test

  9.12.1   General provisions

  9.12.2   Scope of application

  This method is applicable to fasteners that meet the following requirements:

  ——All specifications;

  ——Level 8.8～12.9/ Level 12.9 .

  9.12.3   Test procedures

  Determine Vickers hardness in accordance with the provisions of 9.9.4.2 and read three values ​​on a fastener.

  When tempering this fastener, the part temperature should be 10°C lower than the minimum tempering temperature specified in Table 2 and maintained for 30 minutes . After retempering, measure a new three-point Vickers hardness value on the same fastener and in the same area as the first measurement.

  9.12.4   Technical requirements

  Compare the average hardness of the three points before and after re-tempering. After re-tempering, (if sometimes) the hardness decreases and should be less than 20 Vickers hardness.

  9.13  Torque test

  9.13.1   General

  This torque test can determine the breaking torque M _B and is suitable for bolts and screws that cannot be subjected to tensile tests.

  9.13.2   Scope of application

  This test is applicable to fasteners that meet the following requirements :

  ——Bolts and screws headbearing capacity is stronger than that of the threaded shank ;

  ——The diameter of the unthreaded rod d _s > d ₂ or d _s = d ₂ ; 

  ——Threadlength b ≥ 1 d + 2 P  ;

  —— 1. 6 mm ≤ d ≤ 10 mm ;

  ——Level 4.6 ~ 12. 9 / 12. 9 . _

  Note:  GB/T 3098.13 does not specifyvalues ​​for levels 4.6 to 6.8 .

  9.13.3   Test instruments and devices

  See GB/T  3098.13 .

  9.13.4   Test procedure

  The test piece shall be a fastenerthat has passed the inspection of dimensions , etc.

  According to the provisions of GB/T  3098.13 , bolts or screws installed into the test fixture and should have a length ofthread at least 1 d . The lengthl _th of the unscrewed thread from the head to the end of the thread, or from the unthreaded shank to the end of the thread, is at least 2 P . Torque should be applied continuously .

  Note: ISO  898-7:1992 ( GB/T  3098.13-1996, idt ) has been included in the revision plan . A survey of basic research has shown that the values ​​for unscrewed threads and thread engagement lengthsmay be interchanged .

  9.13.5   Test results

  9.13.5.1   Method

  See GB/T  3098.13 .

  9.13.5.2   Technicalrequirements

  See GB/T  3098.13 .

  In case of dispute , the following test shall prevail :

  ——For bolts and screws that cannot be subjected to tensile test : the hardness test specified in 9.9 is the arbitration test ;

  ——For bolts and screws can be subjected to tensile test : the tensile test is the arbitration test .

  9.14   Impact test of machined specimens

  9.14.1   General provisions

  This test is used to test the toughness of fastener under specified low temperature conditions .Thistest can only be implemented if there is a requirement in the productstandardor .

  9.14.2   Scope of application

  This test is applicable to fasteners that meet the following requirements :

  – Machined specimens made from bolts, screws and studs ;

  ——d ≥ 16  mm ; _

  ——The total length of bolts and screws (including heads ) ≥  55  mm ;

  ——The total length of the stud , l _t ≥ 55  mm ;

  ——Level 5.6 , Level 8.8 , Level 9.8 , Level 10.9 and Level 12.9 / 12.9 .

  9.14.3   Test instruments and devices

  Test instruments and devices should comply with the requirements of GB/T 229 .

  9.14.4   Mechanical processing test pieces

  Test pieces should be made from finished fasteners that have passed inspection of dimensions, etc.

  The machined test piece should comply with the requirements of GB/T 229 (Charpy V -notch test ) .The test piece should be alongthe longitudinal direction of the screw, as close to the surface of the fastener as far away fromthe threaded part as possible. The unnotched side the test piece shall be close to the surface of the fastener

  9.14.5   Test procedure

  The machined test piece should be placed at a constant temperature  of -20 °C, with a pendulum blade radius of 2mm , and tested in accordance with the provisionsof GB/T 229 .

  9.14.6   Technical requirements

  The energy absorbed by the specimen at -20°C should comply  with the requirementsin Table 3 .

  Note: Other test temperatures and absorbed energy values ​​may be specified in relevant product standards or by agreement between the supply and demand parties.

  9.15  Surface defect inspection

  Surface defects of fasteners should be controlled within acceptable limits. The inspection of surface defects of fasteners of grades 4.6 to 10.9 shall be in accordance with the provisions of GB/T 5779.1 . The inspection can also be carried out according to GB/T 5779.3 by agreement between the supply and demand parties .

  The inspection of surface defects of grade 12.9/12.9 fasteners shall be in accordance with the provisions of GB/T 5779.3 .

  In the case of the MP1 series of tests (see Chapter 8 ), inspection of surface defects shall be carried out before machining.

• 

  logo, appendix

  10 signs

  10.1 General

      Only if the technical requirements specified in this part are fully complied with, they may be marked in accordance with the marking system of Chapter 5 and provided with markings in accordance with 10.2 and 10.3 or 10.4.

      Unless otherwise specified in the product standard, the height of the raised logo on the top surface of the head shall not be included in the head height dimension.

  10.2 Manufacturer’s identification mark

      The manufacturer’s identification mark shall be marked on all fastener products bearing the performance grade code during the production process. It is also recommended that fasteners that are not marked with a performance grade be marked with the manufacturer’s identification mark.

      The seller of fasteners using their own identification mark shall also be regarded as the manufacturer’s identification mark.

  10.3 Marking and marking of full load-bearing fasteners

  10.3.1 General

      Fasteners with full load-bearing capacity produced in accordance with the technical requirements of this section shall be marked according to 10.3.2~10.3.4.

      It is specified in 10.3.2 to 10.3.4 that the optional markings allowed shall be determined by the manufacturer.

  10.3.2 Marking code of performance level

      The marking code of the performance level shall be as specified in Table 19.

  Table 19 Marking codes of fasteners with full load-bearing capacity

  Performance level	4.6	4.8	5.6	5.8	6.8	8.8	9.8	10.9	12.9	12.9
  Logo code a	4.6	4.8	5.6	5.8	6.8	8.8	9.8	10.9	12.9	12.9
  The ‘.’ in the  a  sign code can be omitted.

      In the case of small screws, or when the shape of the head does not permit marking according to Table 19, the clock face marking symbols given in Table 20 may be used.

  Table 20 Clock face symbols for bolts and screws with full load-bearing capacity

  Performance level	4.6	4.8	5.6	5.8
  glyph _
  Performance level	6.8	8.8	9.8	10.9	12.9
  glyph _
  a The 12 o’clock position (reference mark) should be marked with the manufacturer’s identification mark, or a dot.  b Use one long dash or two long dashes to indicate the performance level, and use a dot for level 12.9.

  10.3.3   Identification mark

  10.3.3.1   Hexagonal and hexagonal head bolts and screws

      Hexagonal and hexagonal head bolts and screws (including flange face fasteners) shall be marked with the manufacturer’s identification mark and the marking code of the performance class specified in Table 19.

      Marking is required for all performance classes and fasteners with a nominal diameter ≥5mm.

      It is best to use concave or convex characters on the top of the head, or concave characters on the side of the head (see Figure 11). For bolts or screws on the flange surface, when the manufacturing process does not allow marking on the top surface of the head, the mark can be marked on the flange.

  
  

  a Manufacturer’s identification mark.

  b Performance level.

  Figure 11 Examples of markings for hexagonal and hexagonal head bolts and screws

  10.3.3.2 Hexagon socket and hexagon socket head screws

      Hexagon socket and socket head cylindrical head screws shall be marked with the manufacturer’s identification mark and the marking code of the performance level specified in Table 19.

      Marking is required for all performance classes and fasteners with a nominal diameter ≥5mm.

      It is best to use concave characters on the side of the head or concave or convex characters on the top of the head (see Figure 12).

  
  

  Circle 12 Example of marking for hexagon socket head screws

  10.3.3.3 Round head square neck bolts

      Round head square neck bolts shall be marked with the manufacturer’s identification mark and the marking code of the performance level specified in Table 19.

      Marking is required for all performance classes and fasteners with a nominal diameter ≥5mm.

      Mark it with concave or embossed characters on the head (see Figure 13).

  
  

  Figure 13 Example of round head square neck bolt logo

  10.3.3.4 Studs

      Studs shall be marked with the manufacturer’s identification mark and the marking code for the performance level specified in Table 19, or the optional performance level marking symbol specified in Table 21.

      Marks are required for grade 5.6, grade 8.8, grade 9.8, grade 10.9 and grade 12.9/12.9, and studs with nominal diameter ≥5mm.

      The marking shall be made on the unthreaded shank of the stud. If this is not possible, the performance level shall be marked on the threaded nut end of the stud, and the manufacturer’s identification mark may be omitted (see Figure 14).

      For studs with interference fit, the performance level should be marked on the end of the screwed nut, and the manufacturer’s identification mark can be omitted.

  Figure 14 Example of stud mark

   

  Table 21 Optional stud symbols

  Performance level	5.6	8.8	9.8	10.9	12.9
  glyph	—	⚪ a	+	□	△
  a allows the symbol to show only the outline or the entire area to be depressed

  10.3.3.5 Other types of bolts and screws

      According to user requirements, the marking codes specified in 10.3 can also be used for other types of bolts and screws, as well as special fasteners.

      Generally, countersunk head, semi-countersunk head, cylindrical head and pan head screws, or those with similar slotted or cross-recessed shapes, or with internal grooves, or other internal wrenching structures, are not marked.

  10.3.4 Marking of bolts and screws with left-hand thread

      Bolts and screws with left-hand threads with a nominal diameter ≥5 mm shall be marked on the top surface or end of the head according to the symbols specified in Figure 15.

  
  

  Figure 15 Markings of bolts and screws with left-hand thread

      For hexagonal head bolts and screws, the left-hand thread marking specified in Figure 16 can also be used.

  
  

          s——Width across sides;

          k——head height.

  Figure 16 Optional markings for bolts and screws with left-hand thread

  10.4 Marking and marking of fasteners with reduced load-carrying capacity

  10.4.1 General

      Fasteners with reduced load-carrying capacity produced in accordance with this section shall be marked in accordance with the provisions of Table 22, and the rest shall be marked in accordance with the provisions of 10.3.3 and 10.3.4.

      The marking codes specified in Table 19, Table 20 and Table 21 should not be used for fasteners with reduced load-bearing capacity.

      The product standard is fasteners with reduced load-bearing capacity. Even if some specifications can meet the technical requirements of full load-bearing capacity, all specifications of the product should be marked in accordance with Table 22.

  10.4.2 Marking codes for fasteners that reduce load-bearing capacity

      The marking code of fasteners that reduce the load-bearing capacity shall be as specified in Table 22.

  Table 22 Marking codes of fasteners that reduce load-bearing capacity

  Performance level	04.6	04.8	05.6	05.8	06.8	08.8	09.8	010.9	012.9	012.9
  Logo code a	04.6	04.8	05.6	05.8	06.8	08.8	09.8	010.9	012.9	012.9
  The ‘.’ in the  a  sign code can be omitted.

  10.5 Packaging markings

      All types of fasteners and all packages of all specifications should be marked (including stickers or bolt labels). The mark should include the manufacturer and/or distributor’s trademark (or identification mark) and performance level mark code, as well as the production batch number specified in GB/T 90.3.

   

  Appendix A

  (Informative appendix)

  Relationship between tensile strength and elongation after break

      The relationship between tensile strength and elongation after fracture is shown in Table A.1.

  Table A.1 Relationship between tensile strength and elongation after break

  Tensile strength R m,nom /MPa
  			400 500 600 700 800 900 1000 1100 1200 1300
  Elongation after break a A f,min or A min	A f,min	A min
  	0.37	22		4.6
  	0.33	20			5.6
  	0.24			4.8
  	0.22				5.8
  	0.20b _	12c _				6.8		8.8
  	—	10							9.8
  	0.13	9								10.9
  	—	8										12.9/ 12.9
  a A f,min and A min The values ​​in bold are standard values , see Table 3 . b Only applicable to level 6.8 . c only applies to level 8.8 .

   Appendix B

  (Informative appendix)

  Effect of high temperature on mechanical properties of fasteners

      High temperature can change the mechanical properties and working performance of fasteners.

      We know that when the typical service temperature of 150°C is reached, there is no harmful effect on the mechanical properties of fasteners. When the temperature exceeds 150°C and reaches a maximum of 300°C, careful inspection should be carried out to ensure the working performance of the fasteners.

      As the temperature increases, it will gradually show:

      ——For the lower yield strength of the finished fastener, or the stress that specifies a non-proportional extension of 0.2%, or the reduction of the stress that specifies a non-proportional extension of 0.0048d

      ——Reduction in tensile strength.

      Word of experience: Under high-temperature service conditions, when fasteners continue to operate, stress relaxation can occur with higher temperature growth. Stress relaxation will be accompanied by a loss of clamping force.

      Cold work hardened fasteners (4.8, 5.8, 6.8) are more sensitive to stress relaxation than quenched and tempered or stress relieved fasteners.

      Care should be taken when using lead-containing steel for high temperature fasteners. For such fasteners, the risk of liquid metal embrittlement (LME) should be considered when the service temperature is within the melting point range of lead.

      References on ‘Selection and application of steels for high temperature fasteners’ such as EN 10269 and ASTM F 2281.

   AppendixC

  (Informative appendix)

  Elongation Af after actual fastener breakage

      Table 3 only stipulates the minimum elongation after fracture Af,min for the actual bolts, screws and studs of grades 4.8, 5.8 and 6.8. As information, values ​​for other performance classes are given in Table C.1. These values ​​are still under investigation.

  Table C.1 Elongation after break of physical fasteners, Af

  Performance level	4.6	5.6	8.8	9.8	10.9	12.9/ 12.9
  A f,min	0.37	0.33	0.20	—	0.13	—