ASTM A320 Specification
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Originally approved in 1948, 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. Like the ASTM A193 specification, unless otherwise specified, the 8UN thread series is specified on fastener larger than 1” in diameter.
Below is a basic summary of a few of the common grades within the ASTM A320 specification. A number of other less common grades of ASTM A320 exist, but not covered in the description below.
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Grades
L7 |
AISI 4140/4142 Quenched and tempered |
|---|---|
L43 |
AISI 4340 Quenched and tempered |
B8 Class 1 |
AISI 304, carbide solution treated |
B8 Class 2 |
AISI 304, carbide solution treated, strain hardened |
B8M Class 1 |
AISI 316, carbide solution treated |
B8M Class 2 |
AISI 316, carbide solution treated, strain hardened |
Mechanical Properties
Grade |
Size |
Tensile ksi, min |
Yield, ksi, min |
Elong, %, min |
RA % min |
Charpy Impact 20-ft-lbf @ temp |
|---|---|---|---|---|---|---|
L7 |
Up to 2-1/2 |
125 |
105 |
16 |
50 |
-150° F |
L43 |
Up to 4 |
125 |
105 |
16 |
50 |
-150° F |
B8 Class 1 |
All |
75 |
30 |
30 |
50 |
N/A |
B8 Class 2 |
Up to 3/4 |
125 |
100 |
12 |
35 |
N/A |
7/8 - 1 |
115 |
80 |
15 |
35 |
N/A |
|
1-1/8 - 1-1/4 |
105 |
65 |
20 |
35 |
N/A |
|
1-3/8 - 1-1/2 |
100 |
50 |
28 |
45 |
N/A |
|
B8M Class 1 |
All |
75 |
30 |
30 |
50 |
N/A |
B8M Class 2 |
Up to 3/4 |
110 |
95 |
15 |
45 |
N/A |
7/8 - 1 |
100 |
80 |
20 |
45 |
N/A |
|
1-1/8 - 1-1/4 |
95 |
65 |
25 |
45 |
N/A |
|
1-3/8 - 1-1/2 |
90 |
50 |
30 |
45 |
N/A |
Material Chemical Composition
Element |
L7 (AISI 4140) |
L43 (AISI 4340) |
B8 (AISI 304) |
B8M (AISI 316) |
|---|---|---|---|---|
Carbon |
0.37 - 0.49% |
0.38 - 0.43% |
0.08% max |
0.08% max |
Manganese |
0.65 - 1.10% |
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 |
0.75 - 1.20% |
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% |
0.02 - 0.30% |
2.00 - 3.00% |
Recommended Nuts & Washer
Bolt Grade |
Nuts |
Washers |
|---|---|---|
L7 |
A194 Grade 4 or 7 |
F436 |
L43 |
A194 Grade 4 or 7 |
F436 |
B8 Class 1 |
A194 Grade 8 |
SS304 |
B8 Class 2 |
A194 Grade 8 |
SS304 |
B8M Class 1 |
A194 Grade 8M |
SS316 |
B8M Class 2 |
A194 Grade 8M |
SS316 |
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