ASTM A193 Grade B7 is a standard material specification for chromium-molybdenum alloy steel fasteners for use in high tensile, high temperature and special purpose applications. Grade B7 is a heat-treated chromium-molybdenum alloy steel with minimum tensile requirement of 100 ksi, yield of 75 ksi and maximum hardness of 35 HRC. ASTM A193 specification covers requirements for chemical composition, mechanical properties, hardness, heat-treatment, recommended nuts-washers for Grade B7 fasteners. ASTM A193 Grade B7 is the most widely fastener specifications, commonly found in bolting or piping, pressure vessels, valves, flanges and fittings.
| Element | Alloy Steel |
|---|---|
| Chromium Molybdenum SteelA | |
| CompositionB, % | |
| Carbon | 0.37 - 0.49C |
| Manganese | 0.65 - 1.10 |
| Phosphorus | 0.035 max |
| Sulfur | 0.040 max |
| Silicon | 0.15 - 0.35 |
| Chromium | 0.75 - 1.20 |
| Molybdenum | 0.15 - 0.25 |
A: Typical steel compositions used for this grade include 4140, 4142, 4145, 4140H, 4142H, and
4145H.
B: The intentional addition of Bi, Se, Te, and Pb is not permitted.
C: For bar sizes over 31⁄2 in. [90 mm], inclusive, the carbon content may be 0.50 %, max.
| Diameter, inch. | Tensile Strength, min, ksi |
Yield Strength, min, 0.2% offset, ksi |
Elongation in 4D, min, % |
Reduction of Area, min, % |
Hardness, max |
|---|---|---|---|---|---|
| 2-1⁄2 and under | 125 | 105 | 16 | 50 | 321 HBW or 35 HRC |
| over 2-1⁄2 to 4, inclusive | 115 | 95 | 16 | 50 | 321 HBW or 35 HRC |
| over 4 to 7, inclusive | 100 | 75 | 18 | 50 | 321 HBW or 35 HRC |
Heat Treatment: Quenched & Tempered at 1100º F minimum.
| Nut Specification | Washer Specification |
|---|---|
| ASTM A194 Grade 2H OR ASTM A194 Grade 2HM | ASTM F436 |
| Commonly Produced B7 Fasteners | ||||
|---|---|---|---|---|
| Hex Bolts | Heavy Hex Bolts | Stud Bolts | Hex Screws | Anchor Bolts |
| Eye Bolts | Socket Head Cap Screws | Countersunk Screws | U Bolts | Square Head Bolts |