The ASTM A320 specification encompasses the standard that covers high-strength low-alloy steel shapes for bolting material used for pressure valves, flanges, vessels, and fittings for high-temperature applications. For this specification, it covers wire, bars, bolts, studs, stud bolts, and screws. They are mainly used in chemical construction and petroleum applications. Although, this material is often utilized in national coarse thread pitches, but threads are specified 8 threads per inch (tpi) for diameters above 1 inch when being used in traditional applications.
Marking of Ferritic Steels | ||||||||||||||||
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Grade | Grade Symbol | |||||||||||||||
L7 | L7 | |||||||||||||||
L7M | L7M | |||||||||||||||
L70 | L70 | |||||||||||||||
L7A | L7A | |||||||||||||||
L71 | L71 | |||||||||||||||
L7B | L7B | |||||||||||||||
L72 | L72 | |||||||||||||||
L7C | L7C | |||||||||||||||
L73 | L73 | |||||||||||||||
L43 | L43 | |||||||||||||||
L1 | L1 |
Marking of Austenitic Steels | ||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Class | Grade | Grade Symbol | ||||||||||||||
Class 1 | B8
B8C B8M B8F B8P B8T B8LN B8MLN | B8
B8C B8M B8F B8P B8T B8F or B8LN B8G or B8MLN | ||||||||||||||
Class 1A | B8A
B8CA B8MA B8FA B8PA B8TA B8LNA B8MLNA | B8A
B8B or B8CA B8D or B8MA B8FA B8H or B8PA B8J or B8TA B8L or B8LNA B8K or B8MLNA | ||||||||||||||
Class 2 | B8
B8C B8M B8F B8P B8T | B8SH
B8CSH B8MSH B8FSH B8PSH B8TSH |
ASTM A320 Specifications for Mechanical Properties governs the material specification defining mechanical properties, chemical composition, and preferential heat treatment. In addition, it governs product marking, hardness requirements, certifications, and more. ASTM A320 defines both SI (Metric) and inch-pound units.
Class and Grade, Diameter, in. [mm] | Heat Treatment | Minimum Tempering Temperature, F°[C°] | Tensile Strength, min, ksi [Mpa] | Yield Strength, min, 0.2 % offset, ksi | Elongation in 2 in. or 50mm, min, % | Reduction of Area, min, % | Hardness, max |
---|---|---|---|---|---|---|---|
L7, L7A, L7B, L7C, L70, L71, L72, L73 2 1/2 [65] and underA | Quenched and Tempered | 1100 [593] | 125 [860] | 105 [725] | 16 | 50 | 321 HBW or 35 HRC |
L43 4 [100] and underA | Quenched and Tempered | 1100 [593] | 125 [860] | 105 [725] | 16 | 50 | 321 HBW or 35 HRC |
L7M 2 1/2 [65] and underA | Quenched and Tempered | 1150 [620] | 100 [690] | 80 [550] | 18 | 50 | 235 HBW or 99 HRB |
L1 1[25] and underA | Quenched and Tempered | 125 [860] | 105 [725] | 16 | 50 |
Class and Grade, Diameter, in. [mm] | Heat TreatmentB | Tensile Strength, min, ksi | Yield Strength, min, 0.2 % offset, ksi | Elongation in 2in or 50mm, min, % | Reduction of Area, min, % | Hardness, max |
---|---|---|---|---|---|---|
Class 1: B8, B8C, B8M, B8P, B8F, B8T, B8LN, B8MLN, all diameters | Carbide solution treated | 75 [515] | 30 [205] | 30 | 50 | 223 HBWB or 96 HRBC |
Class 1A: B8A, B8CA, B8MA, B8PA, B8FA, B8TA, B8LNA, B8MLNA, all diameters | Carbide Solution Treated in the Finished Condition | 75 [515] | 30 [205] | 30 | 50 | 192 HBW or 90 HRB |
Class 2: B8, B8C, B8P, B8F, B8T: 3/4 [20] and under
over 3/4 to 1 [20 to 25], incl over 1 to 1 1/4 [25 to 32], incl over 1 1/4 to 1 1/2 [32 to 140], incl | Carbide Solution Treated and Strain Hardened | 125 [860]
115 [795] 105 [725] 100 [690] | 100 [690]
80 [550] 65 [450] 50 [345] | 12
15 20 28 | 35
35 35 45 | 321 HBW or 35 HRC
321 HBW or 35 HRC 321 HBW or 35 HRC 321 HBW or 35 HRC |
Class 2: B8M: 3/4 [20] and under
over 3/4 to 1 [20 to 25], incl over 1 to 1 1/4 [25 to 32], incl over 1 1/4 to 1 1/2 [32 to 140], incl | Carbide Solution Treated and Strain Hardened | 110 [760]
100 [690] 95 [655] 90 [620] | 95 [655]
80 [550] 65 [450] 50 [345] | 15
20 25 30 | 45
45 45 45 | 321 HBW or 35 HRC
321 HBW or 35 HRC 321 HBW or 35 HRC 321 HBW or 35 HRC |
AThese 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 be over 200 HBW (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 solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over 3⁄4 in. in diameter.
DFor sizes 3/4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.
Material and Chemical Property Requirements for the ASTM A320 governs minimum and maximum carbon, phosphorus, manganese, sulfur, silicon, chromium, nickel, and molybdenum percent content of steel fasteners within the ASTM A320 specification. The properties also include the minimum tempering temperature requirements.
Ferritic Steels | ||||||||||||||||
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Grade | Description and UNS Designation | Carbon | Manganese | Phosphorous, max | Sulfur, max | Silicon | Nickel | Chromium | Molybdenum | Boron | ||||||
L7, L7M, L70 | Chromium-MolybdenumB | 0.38-0.48C | 0.75-1.00 | 0.035 | 0.040 | 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 | ... | |||||||
L7A, L71 | Carbon-Molybdenum (AISI 4037) | 0.35-0.40 | 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 | ... | |||||||
L7B, L72 | Chromium- Molybdenum (AISI 4137)C | 0.35-0.40 | 0.70-0.90 | 0.035 | 0.040 | 0.15-0.35 | 0.80-1.10 | 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 | ||||||||
L7C, L73 | Nickel-Chromium-Molybdenum (AISI 8740) | 0.38-0.43 | 0.75-1.00 | 0.035 | 0.040 | 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 | ... | |||||||
L43 | Nickel-Chromium-Molybdenum (AISI 4340) | 0.38-0.43 | 0.60-0.85 | 0.035 | 0.040 | 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 | ... | |||||||
L1 | Low-Carbon Boron | 0.17-0.24 | 0.70-1.40 | 0.035 | 0.050 | 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 | Description and UNS Designation | Class | Carbon | Manganese | Phosphorous | Sulfur | Silicon | Nickel | Chromium | NiobiumE + Tantalum | Molybdenum | Selenium | Titanium | Nitrogen | ||
B8, B8A | 304, S30400 | 1, 1A, 2D | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 8.00-11.00 | 18.0-20.0 | ... | ... | ... | ... | ... | ||
Product Variation, % Over or Under | 0.01 | 0.04 | 0.010 | 0.005 | 0.05 | 0.15 | 0.20 | ... | ... | ... | ... | ... | ||||
B8C, B8CA | 347, S31600 | 1, 1A, 2D | 0.08 | 2.00 | 0.045 | 0.030 | 1.00 | 9.00-12.00 | 17.0-19.0 | 10 x carbon content, min. -1.10 max | ... | ... | ... | ... | ||
Product Variation, % Over or Under | 0.01 | 0.04 | 0.010 | 0.005 | 0.05 | 0.2 | 0.05 under | ... | ... | ... | ... | ... | ||||
B8T, B8TA | 321, S32100 | 1, 1A, 2D | 0.08 | 2.00 | 0.045 | 0.030 max | 1.00 | 9.0-12.0 | 17.0-19.0 | ... | ... | ... | 5 x (C+N) min - 0.7 max | 0.10 max | ||
Product Variation, % Over or Under | 0.01 | 0.04 | 0.010 | 0.005 | 0.05 | 0.15 | 0.20 | ... | ... | ... | 0.05 under | 0.01 | ||||
B8P, B8PA | S30500 | 1, 1A, 2D | 0.12 | 2.00 | 0.045 | 0.030, max | 1.00 | 11.0-13.0 | 17.0-19.0 | ... | ... | ... | ... | ... | ||
Product Variation, % Over or Under | 0.01 | 0.04 | 0.010 | 0.005 | 0.05 | 0.15 | 0.20 | ... | ... | ... | ... | ... | ||||
B8F, B8FA | 303, S30300 | 1A, 1B, 2D | 0.15 | 2.00 | 0.20 | 0.15, min. | 1.00 | 8.0-10.0 | 17.0-19.0 | ... | ... | 0.15-0.35 (303Se only) | ... | ... | ||
Product Variation, % Over or Under | 0.01 | 0.04 | 0.010 | 0.020 | 0.05 | 0.10 | 0.20 | ... | ... | 0.03 under (303Se only) | ... | ... | ||||
B8M, B8MA | 316, S31600 | 1A, 1B, 2D | 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 | 0.04 | 0.010 | 0.005 | 0.05 | 0.15 | 0.20 | ... | 0.10 | ... | ... | ... | ||||
B8LN, B8LNA | S30453 | 1, 1A | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 8.0-11.0 | 18.0-20.0 | ... | ... | ... | ... | 0.10-0.16 | ||
Product Variation, % Over or Under | 0.005 | 0.04 | 0.010 | 0.005 | 0.05 | 0.15 | 0.20 | ... | ... | ... | ... | 0.01 | ||||
B8MLN, B8MLNA | 31653 | 1, 1A | 0.03 | 2.00 | 0.045 | 0.030 | 1.00 | 10.0-13.0 | 16.0-18.0 | ... | 2.0-3.0 | ... | ... | 0.10-0.16 | ||
Product Variation, % Over or Under | 0.005 | 0.04 | 0.010 | 0.005 | 0.05 | 0.15 | 0.20 | ... | 0.10 | ... | ... | 0.01 |
AThese 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 be over 200 HBW (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 solution treated and strain hardened. Austenitic steels in the strain-hardened condition may not show uniform properties throughout the section particularly in sizes over 3⁄4 in. in diameter.
DFor sizes 3/4 in. [20 mm] in diameter and smaller, a maximum hardness of 241 HBW (100 HRB) is permitted.