Standard Specification for Alloy-Steel and Stainless Steel Bolting for High Temperature or High Pressure Service and Other Special Purpose Applications
ASTM A193 specification covers alloy and stainless steel bolting for pressure vessels, valves, flanges, and fittings for high temperature or high pressure service, or other special purpose applications. Several grades are covered, including ferritic steels and austenitic stainless steels designated B5, B6, B7, B8, B8M, etc.
Selection will depend upon design, service conditions, mechanical properties, and high temperature characteristics. This specification is expressed in both inch-pound units
and in SI units; however, unless the purchase order or contract specifies the applicable A193M specification designation (SI units), the inch-pound units shall apply
Bolting Grade B8M
| Grade |
Tensile Class |
Raw Material Description |
| B8M
| Class 1 |
AISI 316 Stainless Steel, Carbide Solution Treated |
| B8M
| Class 2 |
AISI 316 Stainless Steel, Carbide Solution Treated and Strain Hardened |
ASTM A193 Grade B8M Chemical Composition
| Austenitic Steels, Classes 1, 1A, 1D, and 2 |
| Element |
Grade B8M, B8MA, B8M2, B8M3 |
| Carbon, max
| 0.08 |
| Manganese, max
| 2.00 |
| Phosphorus, max
| 0.045 |
| Sulfur, max
| 0.030 |
| Silicon, max
| 1.00 |
| Chromium
| 16.0-18.0 |
| Molybdenum
| 2.00-3.00 |
| Columnium + Tantalum
| -- |
ASTM A193 Grade B8M Mechanical Properties
The material as represented by the
tension specimens shall conform to the requirements at room temperature after heat
treatment. Alternatively, stainless strain hardened fasteners
(Class 2, 2B, and 2C) shall be tested full size after strain
hardening to determine tensile strength and yield strength and
shall conform to the requirements prescribed in Table 2 and 3. Should the results of full size tests conflict with results of
tension specimen tests, full size test results shall prevail.
| Grade |
Diameter |
Tensile Strength |
Yield Strength |
Elongation |
Reduction |
Hardness |
| Grade B8, B8M, Class 1, 1D
| All Diameters |
515 |
205 |
30 |
50 |
223 HBW or 96 HRB |
| Grade B8M, B8MLCuN, Class 2
| M20 and under |
760 |
655 |
15 |
45 |
321 HBW or 35 HRC |
| Grade B8M, B8MLCuN, Class 2
| M20 to M24, inclusive |
690 |
550 |
20 |
45 |
321 HBW or 35 HRC |
| Grade B8M, B8MLCuN, Class 2
| M24 to M30, inclusive |
655 |
450 |
25 |
45 |
321 HBW or 35 HRC |
| Grade B8M, B8MLCuN, Class 2
| M30 to M36, inclusive |
620 |
345 |
30 |
45 |
321 HBW or 35 HRC |
ASTM A193 Grade B8M Marking Requirements
| Class |
Grade |
Grade Symbol |
| Class 1
| B8M |
B8M |
| Class 1B
| B8MN |
B8Y or B8MN |
| Class 1D
| B8M |
B95 |
| Class 2
| B8M |
B8MSH |
Recommended Nuts & Washers
| Bolting Grade |
Nut Grade |
Washer Grade |
| ASTM A193 Grade B8M, B8MA, B8M2, B8M3 |
ASTM A194 Grade 8M, 8MA |
SS 316 |