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    ASTM A320/A320M Bolting Specification

    Alloy Steel & Stainless Steel Bolting for Low Temperature Service

    Scope

    ASTM A320 / A320M specification covers alloy and ferritic and austenitic stainless steel bolting materials and bolting components for pressure vessels, valves, flanges, and fittings for low temperature service. To Meet the Impact Energy Requirements we at TorqBolt use only Ingot Cast Steel which is refined steel, duly killed and mercury free with lower Phosphorous and Sulphur contents with restricted gas elements. Bolting Materials such as Bars and wire rods shall be hot wrought and may be further processed by center less grinding or by cold drawing. Austenitic stainless steel may be carbide solution treated or carbide solution treated and strain-hardened. Bolting type such as Hex Bolts, Heavy Hex Bolts, Studs, Socket Head Cap Screws, Hex Cap Screws, Threaded Rods and Threaded Bars can be manufactured from ¼” to 4” in imperial and M6 to M100 in metric variants both fine threads and coarse threads. Bolting Components up to 6” can be provided at TorqBolt with the same certification. PED 2014/68/EC Certified ASTM/ASME A320/A320M Bolting is available exstock.

    ASTM A320/A320M Chemical Requirements

    Ferritic Steels

    Grade Symbol Description C Mn P,max S,max Si Ni Cr Mo B
    ASTM A320 L7, L7M, L70 Cr - Mo - B Range,% 0.38 - 0.48C 0.75 - 1.00 0.035 0.04 0.15 - 0.35 ... 0.80 - 1.10 0.15 - 0.25 ...
    Product Variation, % Over or Under 0.02 0.04 0.005 over 0.005 over 0.02 ... 0.05 0.02 ...
    ASTM A320 L7A, L71 C - Mo (AISI 4037) Range,% 0.38 - 0.48 0.70 - 0.90 0.035 0.04 0.15 - 0.35 ... ... 0.20- 0.30 ...
    Product Variation, % Over or Under 0.02 0.03 0.005 over 0.005 over 0.02 ... ... 0.02 ...
    ASTM A320 L7B, L72 Cr - Mo (AISI 4137) Range,% 0.35 - 0.40 0.70 - 0.90 0.035 0.04 0.15 - 0.35 ... 080 - 110 0.15 - 0.25 ...
    Product Variation, % Over or Under 0.02 0.03 0.005 over 0.005 over 0.02 ... 0.05 0.02 ...
    ASTM A320 L7C, L73 Ni - Cr - Mo (AISI 8740) Range,% 0.38 - 0.43 0.75 - 1.00 0.035 0.04 0.15 - 0.35 0.40 - 0.70 0.40 - 0.60 0.20- 0.30 ...
    Product Variation, % Over or Under 0.02 0.04 0.005 over 0.005 over 0.02 0.03 0.03 0.02 ...
    ASTM A320 L43 Ni - Cr - Mo (AISI 4340) Range,% 0.38 - 0.43 0.60 - 0.85 0.035 0.04 0.15 - 0.35 1.65 - 2.00 0.70 - 0.90 0.20- 0.30 ...
    Product Variation, % Over or Under 0.02 0.03 0.005 over 0.005 over 0.02 0.05 0.03 0.02 ...
    ASTM A320 L1 Low - C, B Range,% 0.17 - 0.24 0.70 - 1.40 0.035 0.05 0.15 - 0.30 ... ... ... 0.001 - 0.003
    Product Variation, % Over or Under 0.01 0.04 0.005 over 0.005 over 0.02 ... ... ... ...

    Austenitic Steels

    Grade Symbol UNS Designation C, max Mn, max P, max S, max Si, max Ni Cr Mo Se Ti N Nb E  + Ta
    ASTM A320 B8, B8A S30400(304) Range,% 0.08 2.00 0.045
    0.030    		 1.00 8.0-11.0 18.0 - 20.0 ... ... ... ... ...
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 ... ... ... ... ...
    ASTM A320 B8C, B8CA S34700(347) Range,% 0.08 2.00 0.045
    0.030    		 1.00 9.0- 12.0 17.0- 19.0 ... ... ... ... 10 × C content, min -1.10 max
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 ... ... ... ... 0.05 under
    ASTM A320 B8T, B8TA S32100(321) Range,% 0.08 2.00 0.045 0.030, max 1.00 9.0- 12.0 17.0- 19.0 ... ... 5 × (C+N) min -0.7 max 010, max ...
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 ... ... 0.05 under 1 ...
    ASTM A320 B8P, B8PA S30500 Range,% 0.12 2.00 0.045 0.030, max 1.00 11- 13.0 17.0- 19.0 ... ... ... ... ...
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 ... ... ... ... ...
    ASTM A320 B8F, B8FA S30300(303) Range,% 0.15 2.00 0.20 00.15, min 1.00 8.0 - 10.0 17.0- 19.0 ... ... ... ... ...
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.20 0.05 over 0.10 0.20 ... ... ... ... ...
    S30323(303Se) Range,% 0.15 2.00 0.20 0.06, max 1.00 8.0 - 10.0 17.0- 19.0 ... 00.15- 035 ... ... ...
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.010 over 0.05 over 0.10 0.20 ... 0.03 under ... ... ...
    ASTM A320 B8F, B8FA S30300(303) Range,% 0.01 over 0.04 over 0.010 over 0.02 0.05 over 0.1 0.2 . . . . . . . . . ... ...
    Product Variation, % Over or Under 0.15 2 0.2 0.06, max 1 8.0-10.0 17.0-19.0 . . . 0.15-0.35 . . . ... ...
    S30323(303Se) Range,% 0.01 over 0.04 over 0.010 over 0.010 over 0.05 over 0.1 0.2 . . . 0.03 under . . . ... ...
    Product Variation, % Over or Under 0.08 2 0.045 0.030, max 1 10.0-14.0 16.0-18.0 2.00-3.00 . . . . . . ... ...
    ASTM A320 B8M, B8MA S31600(316) Range,% 0.08 2.00 0.045 0.030, max 1.00 10.0 - 14.0 16.0 - 18.0 2.00 - 3.00 ... ... ... ...
    Product Variation, % Over or Under 0.01 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 0.10 ... ... ... ...
    ASTM A320 B8LN, B8LNA S30453 Range,% 0.030 2.00 0.045 0.030 1.00 8.0-11 18.0-20.0 ... ... ... 0.10-0.16 ...
    Product Variation, % Over or Under 0.005 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 ... ... ... 0.01 ...
    ASTM A320 B8MLN, B8MLNA S31653 Range,% 0.030 2.00 0.045 0.030 1.00 10.0-13.0 16.0-18.0 2.00-3.00 ... ... 0.10-0.16 ...
    Product Variation, % Over or Under 0.005 over 0.04 over 0.010 over 0.005 over 0.05 over 0.15 0.20 0.10 ... ... 0.01 ...
    • (A) The intentional addition of Bi, Se, Te, and Pb is not permitted except for Grade B8F, in which selenium is specified and required.
    • (B) Typical steel compositions used for this grade include 4140, 4142, 4140.10- 4140H, 4142H, and 4145H.
    • (C) For the L7M grade, a minimum carbon content of 0.28 % is permitted provided that the required tensile properties are met in the section sizes involved; the use of AISI 4130 or 4130H is allowed.
    • (D) Class 1 are made from solution-treated material. Class 1A products (B8A, B8CA, B8MA, B8PA, B8FA, and B8TA) are solution-treated in the finished condition. Class 2 products are solution-treated and strain-hardened.
    • (E) Niobium and columbium are interchangeable names for the same element and both names are acceptable for use in A01.22 specifications.

    ASTM A320/A320M Mechanical Requirements

    Ferritic Steels

    Property / Parameter ASTM A320 L7, L7A, L7B, L7C, L70, L71, L72, L73
    2½ [65] and underA    		 ASTM A320 L43
    4 [100] and underA    		 ASTM A320 L7M
    2½ [65] and underA    		 ASTM A320 L1
    1 [25] and underA
    Heat Treatment quenched and tempered quenched and tempered quenched and tempered quenched and tempered
    Minimum Tempering Temperature, °F [°C] 1100 [593] 1100 [593] 1150 [620] . . .
    Tensile Strength, min, ksi [MPa] 125 [860] 125 [860] 100 [690] 125 [860]
    Yield Strength, min, ksi [MPa] (0.2% offset) 105 [725] 105 [725] 80 [550] 105 [725]
    Elongation in 2 in. or 50 mm, min, % 16 16 18 16
    Reduction of Area, min, % 50 50 50 50
    Hardness, max 321 HBW or 35 HRC 321 HBW or 35 HRC 235 HBWB or 99 HRB . . .

    Austenitic Steels

    Grade and Class  Diameter, in. [mm] Heat Treatment Minimum Tempering Temperature, °F [°C] Tensile Strength, min, ksi [MPa] Yield Strength, min, ksi [MPa] (0.2 % offset) Elongation in 2 in. or 50 mm, min, % Reduction of Area, min, % Hardness, max
    ASTM A320 B8, B8C, B8M, B8P, B8F, B8T, B8LN, B8MLN : Class 1 All diameters carbide solution treated ... 75 [515] 30 [205] 30 50 223 HBWDor  96 HRB
    ASTM A320 B8A, B8CA, B8MA, B8PA, B8FA, B8TA, B8LNA, B8MLNA : Class 1A All diameters carbide solution treated in the  finished condition ... 75 [515] 30 [205] 30 50 192 HBW or 90  HRB
    ASTM A320 B8, B8C, B8P, B8F, B8T : Class 2 3/4 [20] and under  carbide solution treated and strain  hardened ... 125 [860] 100 [690] 12 35 321 HBW or 35  HRC
    over 3/4 to 1 [20 to 25], incl ... 115 [795] 80 [550] 15 30 321 HBW or 35  HRC
    over 1 to 11/4 [25 to 32], incl ... 105 [725] 65 [450] 20 35 321 HBW or 35  HRC
    over 11/4 to 11/2 [32 to 40], inclA ... 100 [690] 50 [345] 28 45 321 HBW or 35  HRC
    ASTM A320 B8M : Class 2 3/4 [20] and under carbide solution treated and strain  hardened ... 110 [760] 95 [655] 15 45 321 HBW or 35  HRC
    over 3/4 to 1 [20 to 25], incl ... 100 [690] 80 [550] 20 45 321 HBW or 35  HRC
    over 1 to 11/4 [25 to 32], incl ... 95 [655] 65 [450] 25 45 321 HBW or 35  HRC
    over 11/4 to 11/2 [32 to 40], inclA ... 90 [620] 50 [345] 30 45 321 HBW or 35  HRC
    • (A) These upper diameter limits were established on the basis that these were the largest sizes commonly available that consistently met specification property limits. They are not intended as absolute limits beyond which bolting materials could no longer be certified to the specification.
    • (B) To meet the tensile requirements, the Brinell hardness shall not be less than 200 HBW or 93 HRB.
    • (C) Class 1 products are made from solution-treated material. Class 1A products are solution treated in the finished condition for corrosion resistance; heat treatment is critical for enhancing this physical property and meeting the mechanical property requirements. Class 2 products are made from solution-treated material that has been strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the cross section, particularly in sizes over 3/4 in. [20 mm] in diameter.
    • (D) For sizes 3/4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.

    ASTM A320/A320M Impact Test Requirements

    Property / Specimen Condition ASTM A320 L7M, L70, L71, L72, L73 ASTM A320 L7, L7A, L7B, L7C, L43 ASTM A320 L1
    Test Temperature (°F) -100 -150 -100
    Test Temperature (°C) -73 -101 -73
    CVN Specimen Section Size (mm) 10×10
    10×7.5
    10×10    		 10×7.5
    10×10    		 10×7.5
    Min Average Impact Toughness (ft-lbf [J])
    three specimens     		20 [27]
    16 [22]
    20 [27]    		 16 [22]
    40 [54]    		 32 [44]
    Min Single Specimen Value (ft-lbf [J])
    of set of three    		 15 [20]
    12 [16]
    15 [20]    		 12 [16]
    30 [41]    		 24 [32]

    ASTM A320/A320M Bolting Components Marking

    Austenitic Steels

    Grade Class Grade Symbol
    ASTM A320 Grade B8 Class 1 TB B8
    ASTM A320 Grade B8C Class 1 TB B8C
    ASTM A320 Grade B8M Class 1 TB B8M
    ASTM A320 Grade B8F Class 1 TB B8F
    ASTM A320 Grade B8P Class 1 TB B8P
    ASTM A320 Grade B8T Class 1 TB B8T
    ASTM A320 Grade B8LN Class 1 TB B8F or TB B8LN
    ASTM A320 Grade B8MLN Class 1 TB B8G or TB B8MLN
    ASTM A320 Grade B8A Class 1A TB B8A
    ASTM A320 Grade B8CA Class 1A TB B8TB B or TB B8CA
    ASTM A320 Grade B8MA Class 1A TB B8D or TB B8MA
    ASTM A320 Grade B8FA Class 1A TB B8FA
    ASTM A320 Grade B8PA Class 1A TB B8H or TB B8PA
    ASTM A320 Grade B8TA Class 1A TB B8J or TB B8TA
    ASTM A320 Grade B8LNA Class 1A TB B8L or TB B8LNA
    ASTM A320 Grade B8MLNA Class 1A TB B8K or TB B8MLNA
    ASTM A320 Grade B8 Class 2 TB B8SH
    ASTM A320 Grade B8C Class 2 TB B8CSH
    ASTM A320 Grade B8M Class 2 TB B8MSH
    ASTM A320 Grade B8F Class 2 TB B8FSH
    ASTM A320 Grade B8P Class 2 TB B8PSH
    ASTM A320 Grade B8T Class 2 TB B8TSH

    Ferritic Steels

    Grade Grade Symbol
    ASTM A320 L1 TB L1
    ASTM A320 L7 TB L7
    ASTM A320 L7A TB L7A
    ASTM A320 L7B TB L7B
    ASTM A320 L7M TB L7M
    ASTM A320 L7C TB L7C
    ASTM A320 L43 TB L43
    ASTM A320 L70 TB L70
    ASTM A320 L71 TB L71
    ASTM A320 L72 TB L72
    ASTM A320 L73 TB L73

    ASTM A320/A320M Supplementary Requirements

    Impact Properties (Supplement S1)

    Supplement S1 requires impact testing on alloys that A320 would normally exempt. In practice, this means Charpy V-notch tests on austenitic stainless grades that are not already covered by the base spec .
    The specific test temperature and minimum energy level are not fixed by A320 but must be agreed between purchaser and manufacturer . (For reference, other grades in A320 require about 20 ft·lb [27 J] at –50 °F for average Charpy energy.) S1 is typically invoked when guaranteed low-temperature toughness is needed in Class 2 stainless steels (e.g. A320 304/316 Class 2) or other austenitics used in cryogenic service. Because the spec leaves the acceptance criterion open, the contract will usually stipulate a target impact energy (for example, 20 ft·lb at 0 °F) to ensure ductile fracture performance.

    Lateral Expansion (Supplement S2)

    Supplement S2 adds a lateral expansion (plastic deformation) criterion to the Charpy test for ferritic steels. In other words, after the standard Charpy impact, the broken specimen’s thickness increase is measured. A320 S2 requires each specimen to show at least 0.015 inch (0.38 mm) of lateral expansion .
    The test temperature is set by the purchaser (typically a low service temperature) . This gauge of expansion complements energy absorption by confirming a ductile fracture mode. (When expansion falls short, it indicates excessive brittleness or cleavage.) In practice, S2 is requested when a project needs explicit proof of fracture ductility in ferritic alloys at cold temperatures. For example, very high-chromium grades like L7-series may struggle to hit 0.015″ at –150 °F, so S2 is less likely used on them; Grade L43 (lower alloy L7 variant) often meets the value more easily

    .

    Hardness Testing of Class 2 Bolting (Supplement S3)

    Supplement S3 imposes a hardness limit (Rockwell C) on Class 2 (strain-hardened) stainless bolts and studs when used in ASME equipment. Specifically, A320 S3 says the maximum hardness at the minor diameter under the threads shall be RC 35 .
    The test is done on a small flat (≥3 mm across) prepared by lightly grinding off the threads . The intent is to cap the strength of cold-worked stainless fasteners so they retain ductility and meet ASME yield limits. Indeed, ASME codes explicitly require A320 S3 on Class 2 parts: for example, an ASME piping Material Data Sheet mandates “Supplementary requirement ASTM A320 S3” for all Class 2 stainless bolting .
    Hardness testing (ASTM E18/F606) is performed at the same frequency as tensile tests. If any sample exceeds 35 HRC, the part is rejected to prevent overly brittle, high-strength material. In practice, S3 is used for pressure-vessel and piping fasteners (boilers, B31.3 process piping, etc.) made from A320 Class 2 alloys.

    Restriction to Ingot Cast Steel (Supplement S4)

    Supplement S4 mandates that only ingot-cast steel be used as the starting material (continuous-cast bar is forbidden) . This is a material quality provision rather than a test. Ingot casting yields a more uniform microstructure and lower segregation than continuous casting, which helps maximize toughness and reduce unknown defects in critical parts. S4 is typically invoked when the utmost steel quality is required (for example, in severe low-temperature or safety-critical applications where the cleaner grain structure of ingot steel is desired). No acceptance test is given in A320 beyond verifying mill certifications; the supplier must simply source ingot-cast bars for the orde

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