ASTM A320 Overview
ASTM A320 is a general material specification that includes alloy steel and stainless steel bolting material applied in low-temperature services. These bolting materials are usually used in pressure vessels, valves, fittings and flanges. The ASTM A320 specification establishes the requirements in terms of chemical composition, mechanical properties, dimensional reference standards, and recommended nuts and washers. It consists of L7, L43, B8, B8M, B8C and B8T, among a few others which demand a notch toughness test.
Another auxiliary requirement contained in the specification is impact testing and hardness testing, particularly on Class 2 bolting materials that are to be used in ASME.
Request QuoteTable of Contents
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 & Strain Hardened |
| B8M | AISI 316 Stainless Steel, Carbide Solution Treated |
| B8M Class 2 | AISI 316 Stainless Steel, Carbide Solution Treated & Strain Hardened |
| B8T | AISI 321 Stainless Steel, Carbide Solution Treated |
| B8T Class 2 | AISI 321 Stainless Steel, Carbide Solution Treated & Strain Hardened |
| B8C | AISI 347 Stainless Steel, Carbide Solution Treated |
Send Your Enquiry
ASTM A320 Chemical Composition
| Element | L7 / L7M | L43 | B8 | B8M | B8T | B8C |
|---|---|---|---|---|---|---|
| Carbon | 0.38–0.48 | 0.38–0.43 | 0.08 max | 0.08 max | 0.08 max | 0.08 max |
| Manganese | 0.75–1.00 | 0.75–1.00 | 2.00 max | 2.00 | 2.00 | 1.00 |
| Phosphorus | 0.035 | 0.035 | 0.045 | 0.045 | 0.045 | 0.040 |
| Sulfur | 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 | 8.0–11.0 |
| 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 × C (min) | — |
ASTM A320 Mechanical Properties
| Grade | Diameter (in.) | Tensile (ksi) | Yield (ksi) | Elongation % | Reduction % | Hardness |
|---|---|---|---|---|---|---|
| B7 | 2.5 & under | 125 | 105 | 16 | 50 | 321 HBW / 35 HRC |
| B7M | 4 & under | 125 | 105 | 16 | 50 | 321 HBW / 35 HRC |
| B16 | 2.5 & under | 100 | 80 | 18 | 50 | 321 HBW / 35 HRC |
| B8 / B8M / B8C / B8T Class 1 | 1" & under | 75 | 30 | 30 | 50 | 223 HBW / 96 HRB |
| B8 / B8C / B8T Class 2 | 3/4 & under | 125 | 100 | 12 | 35 | 321 HBW / 35 HRC |
| 3/4–1 | 115 | 80 | 15 | 30 | 321 HBW / 35 HRC | |
| 1–1¼ | 105 | 65 | 20 | 35 | 321 HBW / 35 HRC | |
| 1¼–1½ | 100 | 50 | 28 | 45 | 321 HBW / 35 HRC | |
| B8M Class 2 | 3/4 & under | 110 | 95 | 15 | 45 | 321 HBW / 35 HRC |
| 3/4–1 | 100 | 80 | 20 | 45 | 321 HBW / 35 HRC | |
| 1–1¼ | 95 | 65 | 25 | 45 | 321 HBW / 35 HRC | |
| 1¼–1½ | 90 | 50 | 30 | 45 | 321 HBW / 35 HRC |
ASTM A320 Impact Test Requirements
| Grade | °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
All Grades Except L1
| Specimen Size (mm) | Avg. of 3 (ft-lbf / J) | One Specimen (ft-lbf / J) |
|---|---|---|
| 10 × 10 | 20 / 27 | 15 / 20 |
| 10 × 7.5 | 16 / 22 | 12 / 16 |
Grade L1
| Specimen Size (mm) | Avg. of 3 (ft-lbf / J) | One Specimen (ft-lbf / J) |
|---|---|---|
| 10 × 10 | 40 / 54 | 30 / 41 |
| 10 × 7.5 | 32 / 44 | 24 / 32 |
ASTM A320 Recommended Nuts & Washers
| Bolt Grade | Nut Grade | Washer Grade |
|---|---|---|
| L7 | ASTM A194 Grade 7 | ASTM F436 Type 1 |
| L7M | ASTM A194 Grade 7M | ASTM F436 Type 1 |
| L43 | ASTM A194 Grade 4 / 7 | ASTM F436 Type 1 |
| B8 | ASTM A194 Grade 8 | AISI 304 |
| B8M | ASTM A194 Grade 8M | AISI 316 |
| B8T | ASTM A194 Grade 8T | AISI 321 |
| B8C | ASTM A194 Grade 8C | AISI 347 |
Reference Standards
| Standard | Description |
|---|---|
| ASTM A194 | Carbon & alloy steel nuts for high pressure/temperature |
| ASTM A194M | Metric equivalent of ASTM A194 |
| ASTM F436 | Hardened steel washers |
| ASTM F436M | Metric hardened steel washers |
| ASME B1.1 | Screw threads |
| ASME B18.2.1 | Bolts & screws dimensions |
| ASME B18.2.2 | Nuts dimensions |
| ASME B18.22.1 | Plain washers |
| DIN 931 | Hex bolts |
| DIN 933 | Hex cap screws |
| DIN 934 | Hex nuts |
ASTM A320 Applications
ASTM A320 bolting materials are widely used in industries where low-temperature strength, toughness, and reliability are critical. These fasteners are specifically designed to perform under extreme cold conditions without loss of mechanical properties.
- Low-temperature pressure vessels and piping systems
- Valves, flanges, and fittings for cryogenic services
- Oil & gas processing plants
- Petrochemical and chemical industries
- LNG and LPG storage tanks
- Power generation equipment
- Offshore platforms and subsea applications
- Heat exchangers and pressure-containing equipment
ASTM A320 bolts, studs, and fasteners ensure safe and durable performance in environments exposed to low temperatures and high pressure.
FAQs About ASTM A320
What is ASTM A320 equivalent to?
ASTM A320 does not have a single direct equivalent because it is specifically designed for low-temperature bolting applications. However, depending on the grade, ASTM A320 materials are often compared with ASTM A193 grades for high-temperature service and ISO or EN bolting standards. The key difference is that ASTM A320 requires mandatory impact testing to ensure notch toughness at low temperatures, which is not always required in equivalent standards.
What is ASTM A320 grade L43 material?
ASTM A320 Grade L43 is a chromium-molybdenum alloy steel that is quenched and tempered. It is designed for low-temperature service where improved toughness and strength are required. Grade L43 offers better low-temperature impact properties compared to standard alloy steel bolting and is commonly used in pressure vessels, valves, and flanges operating in cold environments.
What is ASTM A320 grade L7M material?
ASTM A320 Grade L7M is a quenched and tempered chromium-molybdenum alloy steel with controlled hardness. It is specifically intended for applications where resistance to hydrogen embrittlement and sulfide stress cracking is important. L7M is widely used in oil and gas and sour service applications that operate at low temperatures.
What is ASTM A320 material?
ASTM A320 is a standard specification that covers alloy steel and stainless steel bolting materials intended for low-temperature service. These materials are used in critical applications such as pressure vessels, flanges, valves, and fittings. The specification includes strict requirements for chemical composition, mechanical properties, and impact testing to ensure safe performance in cold environments.