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About ASTM A320/A194M Specification
It is known by many of our customers that ASTM A320/A194M covers both inch and metric series carbon alloy steel and stainless steel bolting materials. This includes externally threaded bolts, screws, and studs. The specification is intended for alloy and stainless steel bolting material used in pressure vessels, valves, flanges, and fittings designed for low-temperature service. Bars and wire must be hot-wrought, and the material may undergo further processing by centerless grinding or cold drawing. Austenitic stainless steel, belonging to the 300 series, features austenite—a metallic, non-magnetic allotrope of iron—as its primary phase. These alloys contain chromium and nickel (and sometimes nitrogen and molybdenum). Although they cannot be through-hardened, they can undergo carbide solution treatment or both carbide solution treatment and strain-hardening (the latter being classified as “Class 2”).
Charpy Testing and Specifications for ASTM A320 Fasteners in Low-Temperature Environments
ASTM A320 was specifically designed for exceptional performance in low-temperature environments. These fasteners are typically utilized in valves, flanges, fittings, and pressure vessels. According to ASTM A320 specifications, a minimum Charpy impact value is recommended for all grades, with a few exceptions listed below. The Charpy impact test, also known as the pendulum fracture test, measures the total energy absorbed by a material during fracture, providing an indication of the material’s notch toughness. This test, developed by S. B. Russell and Georges Charpy at the turn of the 20th century, remains a critical method for testing high-grade fasteners and other products.
All materials specified under A320/A320M are required to undergo Charpy testing. The only exceptions where impact tests are not necessary include:
- Carbide solution-treated or strain-hardened grades B8, B8F, B8P, B8M, B8T, and B8LN above -325°F.
- Carbide solution-treated grades B8, B8P, B9C, and B9LN above -425°F.
- Ferritic and austenitic steel grades of bolting with a diameter of 1/2″ and smaller.
The heat treatment conditions for the austenitic stainless steels are as follows:
- Carbide solution-treated (Class 1).
- Carbide solution-treated after finishing (Class 1A).
- Annealed and strain-hardened (Class 2).
All austenitic stainless steels must receive a carbide solution treatment, applicable to each class. For Class 2 materials, this involves heating to ambient temperature, maintaining the temperature to allow chromium carbide to dissolve, and then cooling at a rate adequate to prevent carbide precipitation.
ASTM A320 B8F, B8FA, B8M, B8MA
| IDENTIFICATION | B8F, B8FA | B8M, B8MA | ||||
|---|---|---|---|---|---|---|
| Grade | With Added Sulfur (Type 303) | With Added Selenium (Type 303 Se) | With Added Sulfur (Type 303) | |||
| Element | Range | Tolerance +/- | Range | Tolerance +/- | Range | Tolerance +/- |
| Carbon, max | 0.15 | 0.01 over | 0.15 | 0.01 over | 0.08 | 0.01 over |
| Manganese, max | 2.00 | 0.04 over | 2.00 | 0.04 over | 2.00 | 0.04 over |
| Phosphorus, max | 0.20 | 0.010 over | 0.20 | 0.010 over | 0.045 | 0.010 over |
| Sulfur | 0.15, min | .020 | 0.06, max | 0.010 over | 0.030, max | 0.005 over |
| Silicon, max | 1.00 | 0.05 over | 1.00 | 0.05 over | 1.00 | 0.05 over |
| Nickel | 8.0-10.0 | 0.10 | 8.0-10.0 | 0.10 | 10.0-14.0 | 0.15 |
| Chromium | 17.0-19.0 | 0.20 | 17.0-19.0 | 0.20 | 16.0-18.0 | 0.20 |
| Molybdenum | – | – | 2.00-3.00 | 0.10 | ||
| Selenium | – | 0.15-0.35 | – | – | ||
| Titanium | – | – | – | – |
ASTM A320 TENSILE STRENGTH AND HARDNESS CHART
| GRADE AND CLASS | DIAMETER | HEAT TREATMENT | TENSILE STRENGTH MIN KSI | YIELD STRENGTH 0.2% OFFSET KSI | ELONGATION IN 2IN. MIN, % | REDUCTION OF AREA MIN, % | HARDNESS MAX |
|---|---|---|---|---|---|---|---|
| FERRITIC STEELS | |||||||
| L7, L7A, L7B, L7C, L70, L71, L72, L73 | 2-1/2″ and under | quench and tempered | 125 | 105 | 16 | 50 | |
| L43 | 4″ and under | quench and tempered | 125 | 105 | 16 | 50 | |
| L7M | 2-1/2″ and under | quench and tempered @ 1150F, min | 100 | 80 | 18 | 50 | 235 HB / 99HRB |
| L1 | 1″ and under | quench and tempered | 125 | 105 | 16 | 50 | |
| AUSTENTIC STEELS | |||||||
| CLASS 1: B8, B8C, B8M, B8P, B8F, B8T, B8LN, B8MLN | ALL | carbide solution treated | 75 | 30 | 30 | 50 | 223 HB or 96 HRB |
| CLASS 1A: B8A, B8CA, B8MA, B8PA, B8FA, B8TA, B8LNA, B8MLNA | ALL | carbide solution treated | 75 | 30 | 30 | 50 | 192 HB or 90 HRB |
| CLASS 2: B8, B8C, B8P, B8F, B8T | 3/4″ and under | carbide solution treated and strain hardened | 125 | 100 | 12 | 35 | 321 HB or 35 HRC |
| over 3/4 to 1″ incl | 115 | 80 | 15 | 30 | 321 HB or 35 HRC | ||
| over 1″ to 1-1/4″ incl | 105 | 65 | 20 | 35 | 321 HB or 35 HRC | ||
| over 1-1/4″ to 1-1/2″ incl | 100 | 50 | 28 | 45 | 321 HB or 35 HRC | ||
| CLASS 2: B8M | 3/4″ and under | carbide solution treated and strain hardened | 110 | 95 | 15 | 45 | 321 HB or 35 HRC |
| over 3/4 to 1″ incl | 100 | 80 | 20 | 45 | 321 HB or 35 HRC | ||
| over 1″ to 1-1/4″ incl | 95 | 65 | 25 | 45 | 321 HB or 35 HRC | ||
| over 1-1/4″ to 1-1/2″ incl | 90 | 50 | 30 | 45 | 321 HB or 35 HRC |
ASTM A320 NUT & WASHER COMPATABILITY CHART
| GRADE | NUTS | WASHERS |
|---|---|---|
| L7 | A194 Grade 4 or 7 | F-436 |
| L43 | A194 Grade 4 or 7 | F-436 |
| B8 Class 1 | A194 Grade 8 | 304-SS |
| B8M Class 1 | A194 Grade 8M | 316-SS |
| B8 Class 2 | A194 Grade 8 | 304-SS |
| B8M Class 2 | A194 Grade 8M | 316-SS |
Why C&N Bolt ASTM A320 Grade B8M Stud Bolts?
We stock a large amount of ASTM A320 ASTM A320 Grade B8M Stud Bolts. Call or email us C&N Huitong and Supply today, where our fastener experts can meet all of your fastener needs… Any fasteners / any material.
