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ASTM A320 Specification

ASTM A320 specification covers alloy steel and stainless steel bolting materials grades such as B8, B8M, L7, L7M, L43, B8, B8M, B8C & B8T, etc., for pressure vessels, valves, flanges, and fittings for low- temperature service. The term "bolting material" as used in this specification covers rolled, forged, or strain hardened bars, bolts, screws, studs, and stud bolts. The bars shall be hot- wrought. The material may be further processed by centerless grinding or by cold drawing. Austenitic stainless steel may be solution annealed or annealed and strain-hardened.

ASTM A320 Grades

Grade Raw Material
L7 13% Chromium Ferritic Steel
L7M Chromium Molybdenum Alloy Steel, Quenched & Tempered
L43 Chromium Molybdenum Alloy Steel, Quenched & Tempered
B8 AISI 304 Stainless Steel, Carbide Solution Treated
B8 Class 2 AISI 304 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8M AISI 316 Stainless Steel, Carbide Solution Treated
B8M Class 2 AISI 316 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8T AISI 321 Stainless Steel, Carbide Solution Treated
B8T Class 2 AISI 321 Stainless Steel, Carbide Solution Treated and Strain Hardened
B8C AISI 347 Stainless Steel, Carbide Solution Treated

ASTM A320 Properties

ASTM A320 Chemical Composition

Element Grade L7, L7M Grade L43 Grade B8 Grade B8M Grade B8T Grade B8C
Carbon 0.38 - 0.48 0.38 - 0.43 0.08 max 0.08 max 0.08 max 0.08 max
Manganese, max 0.75 - 1.00 0.75 - 1.00 2.00 max 2.00 2.00 1.00
Phosphorus, max 0.035 0.035 0.045 0.045 0.045 0.040
Sulfur, max 0.040 0.040 0.030 0.030 0.030 0.030
Silicon 0.15 - 0.35 0.15 - 0.35 1.00 max 1.00 1.00 1.00 max
Nickel - 0.40 - 0.70 8.0 - 11.0 10.0 - 14.0 9.0 - 12.0 8.00 - 11.00
Chromium 0.80 - 1.10 0.40 - 0.60 18.0 - 20.0 16.0 - 18.0 17.0 - 19.0 18.0 - 20.0
Molybdenum 0.15 - 0.25 0.20 - 0.30 - 2.0 - 3.0 - -
Titanium - - - - 5 x C, min -

ASTM A320 Mechanical Properties

Grade Diameter, in. Tensile Strength, ksi Yield Strength ksi Elongation, % Reduction, % Hardness
B7 2.5 and under 125 105 16 50 321 HBW or 35 HRC
           
           
B7M 4 and under 125 105 16 50 321 HBW or 35 HRC
           
B16 2.5 and under 100 80 18 50 321 HBW or 35 HRC
           
           
B8, B8M, B8C, B8T Class 1 1" and under 75 30 30 50 223 HBW or 96 HRB
B8, B8C, B8T, Class 2 3/4 and under 125 100 12 35 321 HBW or 35 HRC
Over 3/4 to 1, inclusive 115 80 15 30 321 HBW or 35 HRC
Over 1 to 1 1/4", inclusive 105 65 20 35 321 HBW or 35 HRC
Over 1 1/4" to 1 1/2", inclusive 100 50 28 45 321 HBW or 35 HRC
B8M, Class 2 3/4 and under 110 95 15 45 321 HBW or 35 HRC
over 3/4 to 1, inclusive 100 80 20 45 321 HBW or 35 HRC
over 1 to 1 1/4, inclusive 95 65 25 45 321 HBW or 35 HRC
over 1-1/4" to 1-1/2", inclusive 90 50 30 45 321 HBW or 35 HRC

Impact Test Requirements

Grade Test Temperature
°F °C
L7M, L70, L71, L72, L73 -100 -73
L7, L7A, L7B, L7C -150 -101
L43 -150 -101
L1 -100 -73

Temperature Requirement For Impact Testing

Size of specimen, mm Minimum Impact Value Required for Average of Each Set of Three Specimens, ft.lbf(J) Minimum Impact Value permitted for One Specimen Only of a Set, ft.lbf(J)
All Grade Except L1A
10 by 10 20 [27] 15 [20]
10 by 7.5 16 [22] 12 [16]
Grade L1
10 by 10 40 [54] 30 [41]
10 by 7.5 32 [44] 24 [32]

Recommended Nuts & Washers

Bolt Grade Nut Grade Washer Grade
L7, L7M ASTM A194 Grade 7, 7M ASTM F436
L43 ASTM A194 Grade 4 OR Grade 7 ASTM F436
B8 ASTM A194 Grade 8 SS 304
B8M ASTM A194 Grade 8M SS 316
B8T ASTM A194 Grade 8T SS 321
B8C ASTM A194 Grade 8C SS 347