Grade B7M
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ASTM A193 Grade B7M Specification for high tensile bolts, screws, stud bolts, threaded rods, anchor bolts and other externally threaded fasteners, made from chromium-molybdenum alloy steel. ASTM A193 Grade B7M is a standard material specification for chromium-molybdenum alloy steel fasteners for use in high tensile, high temperature and special purpose applications. Grade B7M is a heat-treated chromium-molybdenum alloy steel with minimum tensile requirement of 100 ksi, yield of 75 ksi and maximum hardness of 99 HRB. ASTM A193 specification covers requirements for chemical composition, mechanical properties, hardness, heat-treatment, recommended nuts-washrs for Grade B7M fasteners. The difference between B7 & B7M is the hardness testing requirement for each bolt from a given lot in the latter.
| 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. For the B7M grade, a minimum carbon content of 0.28 % is permitted, provided
that the required tensile properties are met in the section sizes involved; the use of AISI 4130 or 4130H is allowed.
| Diameter, inch. | Tensile Strength, min, ksi |
Yield Strength, min, 0.2% offset, ksi |
Elongation in 4D, min, % |
Reduction of Area, min, % |
Hardness, max |
|---|---|---|---|---|---|
| 4 and under | 100 | 80 | 18 | 50 | 235 HBW or 99 HRB |
| over 4 to 7, inclusive | 100 | 75 | 18 | 50 | 235 HBW or 99 HRB |
Note: To meet the tensile requirements, the Brinell hardness shall be over 200 HBW (93 HRB).
Heat Treatment: Quenched & Tempered at 1100º F minimum.
| Nut Specification | Washer Specification |
|---|---|
| ASTM A194 Grade 2HM | ASTM F436 |
| Commonly Produced B7M 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 |