AISI 303 free-machining austenitic stainless steel · Solution-treated (Class 1) or strain-hardened (Class 2)
ASTM A320 Grade B8F is an austenitic stainless steel bolting grade specified per ASTM A320/A320M-21 for low-temperature service. Table 3 lists UNS S30300 (303) and UNS S30323 (303Se) for this grade. Manufactured from AISI 303 free-machining austenitic stainless steel. The grade is supplied in Class 1 (solution-treated) or Class 2 (strain-hardened) condition, with Class 2 offering higher tensile strength through controlled cold work. Grade B8F is the free-machining grade: Type 303 with 0.15 % minimum sulfur, or selenium-bearing Type 303Se (Table 3). Grade B8F is intended for stud bolts and hex bolts in pressure vessels, valves, flanges, and fittings for low-temperature service. Grade B8F is equivalent to ASME SA-320 Grade B8F in Section II of the ASME Boiler and Pressure Vessel Code.
| Grade Symbol | UNS Designation | C, max | Mn, max | P, max | S, max | Si, max | Ni | Cr | Se | |
|---|---|---|---|---|---|---|---|---|---|---|
| ASTM A320 B8F | S30300(303) | Range,% | 0.15 | 2.00 | 0.20 | 00.15, min | 1.00 | 8.0 - 10.0 | 17.0- 19.0 | 0.15-0.35 |
| Product Variation, % Over or Under | 0.01 over | 0.04 over | 0.010 over | 0.20 | 0.05 over | 0.10 | 0.20 | ... | ||
| 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 B8F : Class 1 | All diameters | carbide solution treated | 75 [515] | 30 [205] | 30 | 50 | 223 HBWDor 96 HRB |
| ASTM A320 B8F : Class 2 | 3/4 [20] and under | carbide solution treated and strain hardened | 125 [860] | 100 [690] | 12 | 35 | 321 HBW or 35 HRC |
| over 3/4 to 1 [20 to 25], incl | 115 [795] | 80 [550] | 15 | 30 | 321 HBW or 35 HRC | ||
| over 1 to 11/4 [25 to 32], incl | 105 [725] | 65 [450] | 20 | 35 | 321 HBW or 35 HRC | ||
| over 11/4 to 11/2 [32 to 40], inclA | 100 [690] | 50 [345] | 28 | 45 | 321 HBW or 35 HRC |
Section 10.2 of ASTM A320 requires Grade B8F bolts, studs, and stud bolts to be equipped with austenitic alloy nuts to ASTM A194/A194M Grade 8F; impact tests are not required for Grade 8F nuts above -325°F [-200°C]. Washers for austenitic bolting are made of austenitic steel as agreed between manufacturer and purchaser (10.5); ASTM F436 hardened steel washers are specified for ferritic bolting only (10.4). TorqBolt supplies kit-matched A320 B8F + A194 Grade 8F + austenitic washer sets with a single EN 10204 3.1 or 3.2 certificate covering all three components.
TorqBolt’s ASTM A320 Grade B8F stud bolt production route is qualified to NORSOK M-650 for North Sea oil & gas offshore service. Each manufacturing record links heat number, melt analysis, heat-treatment batch, mechanical test, dimensional inspection, surface treatment, and dispatch. Standard certification is EN 10204 Type 3.1 (manufacturer’s test report); Type 3.2 third-party witnessed by Lloyd’s Register, DNV, BV, ABS, or TUV is available on request. The qualification packet covers ASME SA-320 B8F equivalence, NACE MR0175 / ISO 15156-3 sour-service compliance (where applicable), and PED 2014/68/EU for European pressure-equipment buyers.
