Class 1A Low Temperature Fasteners - AISI 347 Solution Treated Grade
ASTM A320/A320M Grade B8CA Class 1A is the columbium (niobium) stabilized AISI 347 (UNS S34700) bolting grade in the Class 1A condition, carbide solution treated in the finished condition for corrosion resistance (Table 1 footnote C, 11.1). Table 3 requires niobium plus tantalum of at least 10 times the carbon content, 1.10 % maximum. Class 1A limits hardness to 192 HBW or 90 HRB with 75 ksi [515 MPa] minimum tensile strength, and Class 1A Grade B8CA is exempt from impact testing above -425°F [-255°C] (6.2.1.1), making B8CA suitable for low temperature pressure vessel, valve, flange, and fitting bolting.
| Grade Symbol | UNS Designation | C, max | Mn, max | P, max | S, max | Si, max | Ni | Cr | Nb E + Ta | |
|---|---|---|---|---|---|---|---|---|---|---|
| ASTM A320 B8CA Class 1A | S34700(347) | Range,% | 0.08 | 2.00 | 0.045 | 0.030 |
1.00 | 9.0- 12.0 | 17.0- 19.0 | 10 × C content, min -1.10 max |
| Product Variation, % Over or Under | 0.01 over | 0.04 over | 0.010 over | 0.005 over | 0.05 over | 0.15 | 0.20 | 0.05 under | ||
| Grade and Class | Diameter, in. [mm] | Heat Treatment | Tensile Strength, min, ksi [MPa] | Yield Strength, min, ksi [MPa] (0.2 % offset) | Elongation in 2 in. or 50 mm, min, % | Reduction of Area, min, % | Hardness, max |
|---|---|---|---|---|---|---|---|
| ASTM A320 B8CA Class 1A | All diameters | carbide solution treated in the finished condition | 75 [515] | 30 [205] | 30 | 50 | 192 HBW or 90 HRB |
