ASTM A320 Bolt Material Properties
Alloy Steel & Stainless Steel Bolting for Low-Temperature Service
About
ASTM A320 covers alloy steel and stainless steel bolting materials for low-temperature service, typically for pressure vessels, valves, and flanges operating below -50°F (-46°C). The table below contains data from Table 1 of ASTM A320/A320M, which lists the mechanical requirements.
Common grades include L7 (the low-temperature counterpart to A193 B7), L43, and B8/B8M (stainless steel grades). L-series grades require Charpy impact testing at low temperatures.
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Mechanical Requirements Table
Use the grade filter to look up mechanical properties for a specific bolt grade. Toggle between imperial (ksi, °F) and metric (MPa, °C) units.
| Grade | Class | Diameter Range | Heat Treatment | Tensile (ksi) | Yield (ksi) | Elong. (%) | Red. of Area (%) | Hardness | Temper Temp (°F) |
|---|---|---|---|---|---|---|---|---|---|
| L7,L7A,L7B,L7C,L70,L71,L72,L73 | — | 2½ [65] and under | quenched and tempered | 125 | 105 | 16 | 50 | 321 HBW or 35 HRC | 1100 |
| L43 | — | 4 [100] and under | quenched and tempered | 125 | 105 | 16 | 50 | 321 HBW or 35 HRC | 1100 |
| L7M | — | 2½ [65] and under | quenched and tempered | 100 | 80 | 18 | 50 | 235 HBW or 99 HRB | 1150 |
| L1 | — | 1 [25] and under | quenched and tempered | 125 | 105 | 16 | 50 | — | — |
| B8,B8C,B8M,B8P,B8F,B8T,B8LN,B8MLN | 1 | all diameters | carbide solution treated | 75 | 30 | 30 | 50 | 223 HBW or 96 HRB | — |
| B8A,B8CA,B8MA,B8PA,B8FA,B8TA,B8LNA,B8MLNA | 1A | all diameters | carbide solution treated in the finished condition | 75 | 30 | 30 | 50 | 192 HBW or 90 HRB | — |
| B8,B8C,B8P,B8F,B8T | 2 | ¾ [20] and under | carbide solution treated and strain hardened | 125 | 100 | 12 | 35 | 321 HBW or 35 HRC | — |
| B8,B8C,B8P,B8F,B8T | 2 | over ¾ to 1 [20 to 25], incl | — | 115 | 80 | 15 | 35 | 321 HBW or 35 HRC | — |
| B8,B8C,B8P,B8F,B8T | 2 | over 1 to 1¼ [25 to 32], incl | — | 105 | 65 | 20 | 35 | 321 HBW or 35 HRC | — |
| B8,B8C,B8P,B8F,B8T | 2 | over 1¼ to 1½ [32 to 40], incl | — | 100 | 50 | 28 | 45 | 321 HBW or 35 HRC | — |
| B8M | 2 | ¾ [20] and under | carbide solution treated and strain hardened | 110 | 95 | 15 | 45 | 321 HBW or 35 HRC | — |
| B8M | 2 | over ¾ to 1 [20 to 25], incl | — | 100 | 80 | 20 | 45 | 321 HBW or 35 HRC | — |
| B8M | 2 | over 1 to 1¼ [25 to 32], incl | — | 95 | 65 | 25 | 45 | 321 HBW or 35 HRC | — |
| B8M | 2 | over 1¼ to 1½ [32 to 40], incl | — | 90 | 50 | 30 | 45 | 321 HBW or 35 HRC | — |
Data sourced from ASTM A320/A320M, Table 1 — Mechanical Requirements.
How to Use This Chart
To find the mechanical properties for a specific bolt, select the grade using the dropdown filter above. If a grade has multiple rows, the properties vary by diameter range — find the row that matches your bolt diameter. Use the units toggle to switch between imperial and metric values.
Key columns explained:
- Tensile Strength — the minimum ultimate tensile strength the bolt must achieve.
- Yield Strength — the minimum stress at which the bolt begins to deform permanently (0.2% offset method).
- Elongation (%) — the minimum percentage the bolt can stretch before fracture, measured over 4 diameters.
- Hardness — the maximum allowable hardness (HBW = Brinell, HRC = Rockwell C, HRB = Rockwell B).
Related References
- ASTM A193 — High-temperature bolting material properties
- ASTM A453 — High-temperature special application bolting
- All Bolt Materials — Overview of all bolting material standards