Grade B7 is NOT in ASTM A320
B7 is an ASTM A193 grade. For low-temperature 4140 / 4142 bolting, use ASTM A320 Grade L7.
If you arrived here searching for "ASTM A320 B7" or "A320 Grade B7", note that B7 does not exist as an ASTM A320 grade. Grade B7 is part of the ASTM A193 specification for high-temperature pressure bolting. The ASTM A320 low-temperature equivalent of A193 B7 is ASTM A320 Grade L7, which shares the same AISI 4140 / 4142 chemistry and adds mandatory Charpy V-notch impact testing at -150°F (-101°C).
Why the confusion
ASTM A193 (high-temperature bolting) uses B-prefix grade designations: B5, B7, B7M, B16, B8, B8M, B8C, B8F, B8P, B8T. ASTM A320 (low-temperature bolting) borrows the same B-prefix grades for the austenitic stainless family (B8, B8M, B8C, B8F, B8P, B8T) but uses L-prefix grades for the ferritic / martensitic alloy steels (L7, L7M, L7A, L7B, L7C, L43, L70 to L73, L1). The 4140 / 4142 carbon-molybdenum chemistry of A193 B7 maps to A320 L7, not to an A320 B-prefix grade.
If you intended A193 B7
For high-temperature pressure-vessel bolting in 4140 / 4142 chemistry, specify ASTM A193 Grade B7. The TorqBolt A193 reference site covers that specification.
If you intended A320 low-temperature bolting
For low-temperature bolting in 4140 / 4142 chemistry with Charpy V-notch verification, the correct grade is ASTM A320 Grade L7. For the sour-service variant (NACE MR0175 compliant), see ASTM A320 Grade L7M.
If you intended A320 stainless bolting
ASTM A320 covers these B-prefix austenitic stainless grades:
- A320 Grade B8 (UNS S30400) 304 stainless
- A320 Grade B8M (UNS S31600) 316 stainless
- A320 Grade B8C (UNS S34700) 347 stainless
- A320 Grade B8T (UNS S32100) 321 stainless