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Specifications

ASTM A320

The ASTM A320 specification covers alloy steel and stainless steel bolting materials for low temperature service. This standard covers rolled, forged, or strain hardened bars, bolts, screws, studs, and stud bolts used for pressure vessels, valves, flanges, and fittings.

Here are the most common grades within the ASTM A320 specification. Several other less common grades of ASTM A320 exist, but are not covered below.

A320 Grades

L7 Alloy steel AISI 4140/4142 Quenched and tempered
L43 Alloy steel AISI 4340 Quenched and tempered
B8 Class 1 Stainless steel AISI 304, carbide solution treated
B8M Class 1 Stainless steel AISI 316, carbide solution treated
B8 Class 2 Stainless steel AISI 304, carbide solution treated, strain hardened
B8M Class 2 Stainless steel AISI 316, carbide solution treated, strain hardened

A320 Mechanical Properties

Grade Diameter Tensile, ksi, min Yield, ksi, min Charpy Impact 20-ft-lbf @ temp Elong, %, min RA, %, min
L7 Up to 21/2 125 105 -150° F 16 50
L43 Up to 4 125 105 -150° F 16 50
Class 1: BC, B8C, B8M, B8P, B8F, B8T, B8LN, B8MLN All 75 30 N/A 30 50
Class 1A: B8A, B8CA, B8MA, B8PA, B8FA, B8TA, B8LNA, B8MLNA All 75 30 N/A 30 50
Class 2: B8, B8C, B8P, B8F, B8T Up to 3/4 125 100 N/A 12 35
7/8 - 1 115 80 N/A 15 35
11/8 - 11/4 105 65 N/A 20 35
13/8 - 11/2 100 50 N/A 28 45
Class 2: B8M Up to 3/4 110 95 N/A 15 45
7/8 - 1 100 80 N/A 20 45
11/8 - 11/4 95 65 N/A 25 45
13/8 - 11/2 90 50 N/A 30 45

A320 Chemical Properties

Element L7 (AISI 4140) L43 (AISI 4340) B8 (AISI 304) B8M (AISI 316)
Carbon 0.38 - 0.48% 0.38 - 0.43% 0.08% max 0.08% max
Manganese 0.75 - 1.00% 0.75 - 1.00% 2.00% max 2.00% max
Phosphorus, max 0.035% 0.035% 0.045% 0.045%
Sulfur, max 0.040% 0.040% 0.030% 0.030%
Silicon 0.15 - 0.35% 0.15 - 0.35% 1.00% max 1.00% max
Chromium 0.80 - 1.10% 0.70 - 0.90% 18.0 - 20.0% 16.0 - 18.0%
Nickel 1.65 - 2.00% 8.0 - 11.0% 10.0 - 14.0%
Molybdenum 0.15 - 0.25% 0.20 - 0.30% 2.00 - 3.00%