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

Fasteners Mechanical Properties Bolts, Screws and Studs


  • 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.

  • 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 sd 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 sd 2 , see Table 9.

        ——FF3: used to determine the performance of finished bolts and screws where d s > d 2 or d sd 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 sd 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 t3 d or
    b 2.0 d

    d 3mm and
    l t3 d and
    b 2.0 d

    d 3mm or
    l t3 d or b 2.0 d

    d 3mm and
    l t3 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 t3.2 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 0d 3 , min and b d and
    l 6.5 d

    d 4.5mm and
    d 03mm and
    b d and
    l d + 26mm

    3 d 4.5mm and d 0d 3 , min and b d and l 6.5 d

    4.5mm d 16mm and d 03mm and
    b d and
    l d + 26mm

    d 16mm and
    d 00.75 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 t55mm

    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 t6 d .

    d For bolts and screws, when measuring Z min , l d + 20mm .

    e For studs, when measuring Z min , l t2 d + 20mm .

    f For bolts and screws, when measuring Z min , l 4 d + 8mm .

    g For studs, when measuring Z min , l t5 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 t3.2 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

    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 sd 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. 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 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  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 s2d _

    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°

    20 d≤39 _ _

        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 .

    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 th1 d .

        For wedge load tests on bolted structural bolts with short thread lengths, the permissible unscrewed thread length l th1 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 :

    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  1H /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. Technical requirements

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

        The tensile strength  R 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 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 sd 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 t3.0 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 th1 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 .

    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 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.</