ASTM A320 is a standard material specification covering alloy and stainless steel bolting materials for pressure vessels, valves, flanges, and fittings for low temperature services. ASTM A320 specification includes chemical composition, mechanical properties, dimensional reference standards, recommended nuts and washers for grades like L7, L43, B8, B8M, B8C, B8T and many others with notch toughness requirements.
Supplementary requirements includes Impact properties and hardness testing of class 2 bolting materials for ASME applications.
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 |
(For all grades, please visit ASTM A320 Grades)
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 |
ASTM A320 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 |
ASTM A320 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] |
ASTM A320 Recommended Nuts & Washers
Reference Standards