ASTM A193 Grade B8 Specification
ASTM A193 Grade B8 specification covers requirements for 304/304L stainless steel bolting material with high tensile properties, for use in high temperature or high-pressure service and other special purpose applications. It is a fastener material specification defining typical chemical composition, mechanical properties, hardness requirement, preferential heat treatment, product marking, certification and other requirements, suitable for bolting used in pressure vessel service, valves, flanges and fittings. ASTM A193 defines both SI (Metric) and inch-pound units.
ASTM A193 Grade B8 is subdivided into 3 property classes with different tensile strength; Class 1, Class 2 & Class 2B. A193 Gr B8 Class 1 is a carbide solution-treated 304 stainless steel bolting material with minimum tensile strength requirement of 75 ksi (515 Mpa), yield 30 ksi (205 Mpa), and maximum hardness of 223 HBW (96 HRB); A193 Gr B8 Class 2 has a minimum tensile requirement of 125 ksi (860 Mpa), yield of 100 ksi (690 Mpa), and maximum hardness of 321 HBW (35 HRC); A193 Gr B8 Class 2B has a minimum tensile requirement of 95 ksi (655 Mpa), yield of 75 ksi (515 Mpa), and maximum hardness of 321 HBW (35 HRC).
Find information on ASTM A193 Grade B8 chemical composition, mechanical properties such as tensile strength; yield strength, hardness, marking requirements and reference product standards.
Chemical Composition
| Elements | Range | Allowed Variation, % |
| Carbon, Max | 0.08% | + 0.01 |
| Manganese, max | 2.00% | + 0.04 |
| Phosphorus, max | 0.045% | + 0.010 |
| Sulfur, max | 0.030% | + 0.005 |
| Silicon, max | 1.00% | + 0.05 |
| Chromium | 18.00 – 20.00% | +/- 0.20 |
| Nickel | 8.00 – 11.00% | +/- 0.15 |
Heat Treatment
| Class | Heat Treatment Procedure |
| Class 1 | Carbide Solution Treatment |
| Class 2 | Carbide Solution Treatment & Strain Hardened |
| Class 2B | Carbide Solution Treatment & Strain Hardened |
Mechanical Properties
Find typical requirement for ASTM A193 Grade B8 Mechanical Properties. Tensile, yield strength and hardness requirement of finished products manufactured to ASTM A193 Grade B8 specification must comply with below requirement.
| Mechanical Requirements, Inch Products | |||||||
|---|---|---|---|---|---|---|---|
| Class | Diameter | Tensile Strength, min, ksi | Yield Strength, min, ksi | Elongation in 4D min, % | Reduction of Area, min, % | Hardness, max | |
| 1 | All Diameters | 75 | 30 | 30 | 50 | 223 HBW | 96 HRB |
| 2 | 3/4 and under | 125 | 100 | 12 | 35 | 321 HBW | 35 HRC |
| Over ¾ to 1, incl. | 115 | 80 | 15 | 35 | |||
| Over 1 to 1-1/4, incl. | 105 | 65 | 20 | 35 | |||
| Over 1-1/4 to 1-1/2, incl. | 100 | 50 | 28 | 45 | |||
| 2B | 2 and under | 95 | 75 | 25 | 40 | 321 HBW | 35 HRC |
| Over 2 to 2-1/2, incl. | 90 | 65 | 30 | 40 | |||
| Over 2-1/2 to 3, incl. | 80 | 55 | 30 | 40 | |||
| Mechanical Requirements, Metric Products | |||||||
|---|---|---|---|---|---|---|---|
| Class | Diameter | Tensile Strength, min, ksi | Yield Strength, min, ksi | Elongation in 4D min, % | Reduction of Area, min, % | Hardness, max | |
| 1 | All Diameters | 515 | 205 | 30 | 50 | 223 HBW | 96 HRB |
| 2 | M20 and under | 860 | 690 | 12 | 35 | 321 HBW | 35 HRC |
| Over M20 to M24, incl. | 795 | 550 | 15 | 35 | |||
| Over M24 to M30, incl. | 725 | 450 | 20 | 35 | |||
| Over M30 to M36, incl. | 690 | 345 | 28 | 45 | |||
| 2B | M48 and under | 655 | 515 | 25 | 40 | 321 HBW | 35 HRC |
| Over M48 to M64, incl. | 620 | 450 | 30 | 40 | |||
| Over M64 to M72, incl. | 550 | 380 | 30 | 40 | |||
ASTM A193 Grade B8 Bolt Markings
| Class | Marking |
|---|---|
| Class 1 | "BPF" Manufacturer's Logo & "B8" Grade Marking |
| Class 2 | "BPF" Manufacturer's Logo & "B8SH" Grade Marking |
| Class 2B | "BPF" Manufacturer's Logo & "B9" Grade Marking |
Reference Standards
| ASTM A194/A194M | Specification for Carbon and Alloy Steel Nuts for Bolts for high pressure or high temperature service, or both. |
| ASTM A320/A320M | Specification for alloy-steel and stainless steel bolting for low temperature service. |
| ASTM A962/A962M | Specification for Common Requirements for Bolting Intended for Use at Any Temperature from Cryogenic to the Creep Range. |
| ASME B18.2.1 | Square and Hex Bolts and Screws. |
| ASME B18.2.3.3M | Metric Heavy Hex Screws |
| ASME B18.3 | Hexagon Socket and Spline Socket Screws |
| ASME B18.3.1M | Metric Socket Head Cap Screws |
| ASTM E709 | Guide of Magnetic Particle Testing. |
| ASTM E112 | Test Methods for Determining Average Grain Size. |
| ASTM E18 | Test Methods for Rockwell Hardness of Metallic Materials. |