ASTM A193 Grade B8 Class 1 (304 Stainless)
304 stainless bolting — Class 1 for corrosion resistance and cryogenic-to-1500 °F service, Class 2 strain hardened to 125 ksi for strength.
What A193 B8 Class 1 is.
ASTM A193 Grade B8 covers bolting made from AISI 304 austenitic stainless steel. Class 1 is carbide solution treated and has the modest 75 ksi strength of annealed 304 with the full corrosion resistance and toughness of the alloy from cryogenic temperatures to about 1500 °F. Class 2 is solution treated and then strain hardened, raising tensile strength to 125 ksi in small diameters at the cost of some ductility.
B8 is the go-to stainless grade for atmospheric, water, food and mild chemical exposure. We manufacture B8 studs, bolts and screws from certified 304 and 304L bar, and offer B8A (Class 1A, solution treated after finishing) and B8 Class 2 by size.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.08 |
| Manganese | Mn | — | 2.00 |
| Phosphorus | P | — | 0.045 |
| Sulfur | S | — | 0.030 |
| Silicon | Si | — | 1.00 |
| Chromium | Cr | 18.0 | 20.0 |
| Nickel | Ni | 8.0 | 11.0 |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation in 4D, min (%) | Reduction of area, min (%) | Hardness, max |
|---|---|---|---|---|---|
| Class 1 — all diameters | 75 | 30 | 30 | 50 | 223 HBW / 96 HRB |
| Class 1A (B8A) — all diameters | 75 | 30 | 30 | 50 | 192 HBW / 90 HRB |
Values per ASTM A193/A193M-24, Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. Class 1 sizes ¾ in. and smaller may be 241 HBW / 100 HRB. Strain-hardened Class 2 and 2B properties are on the B8 Class 2 page.
Specifications that apply.
How A193 B8 Class 1 ships from Houston.
- Full-thread studs and stud bolts
- Double-end and tap-end studs
- Hex and heavy hex bolts
- Socket head cap screws
- Threaded rod (cut and rolled thread)
- Machined components from certified bar
A193 B8 Class 1 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8 Class 1, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8?
B8 is the 304 stainless steel grade in ASTM A193. 304 is the basic 18 percent chromium, 8 percent nickel austenitic stainless: non-magnetic in the annealed condition, easily formed and machined, and resistant to a wide range of atmospheric and aqueous corrosion. In A193 it appears in two classes. Class 1 is solution treated and is the normal choice where corrosion resistance and temperature capability matter more than strength. Class 2 is cold worked after solution treatment to roughly the strength of B7 in small sizes, with the strength falling off as diameter increases because cold work cannot penetrate a large bar uniformly.
Class 1, Class 1A and Class 2
- Class 1 (B8): carbide solution treated. 75 ksi tensile, 30 ksi yield, best ductility and temperature range.
- Class 1A (B8A): solution treated after all finishing. Use where the finished part must be free of cold-work effects, for example on cryogenic service.
- Class 2 (B8 Cl.2): solution treated then strain hardened. Up to 125 ksi tensile in ¾ inch and under; properties drop by size and the grade is limited to 1½ inch.
B8 versus B8M
B8M is the 316 stainless equivalent, with 2 to 3 percent molybdenum added for resistance to chlorides and pitting. If the joint sees seawater, brine, deicing salts or chlorinated process water, specify B8M. In fresh water, food service and ordinary atmosphere, B8 is the economical choice and performs identically.
Galling and thread lubrication
Austenitic stainless threads gall readily when run dry under load. Every B8 stud and nut set we ship can be supplied with an anti-seize compound or a PTFE coating, and A194 Grade 8 nuts can be furnished slightly oversize-tapped for coated studs. Silver-plated nuts are a common request on cryogenic and vacuum equipment.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade symbol B8 (or B8A, B8 with class mark) and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- PMI verification and intergranular corrosion testing (ASTM A262) arranged on request
Recent A193 B8 Class 1 jobs.
ASTM A193 Grade B8 Class 2 (304 Strain Hardened)
304 stainless bolting cold worked after solution treatment — 125 ksi tensile in ¾ in. and under, with strength stepping down by diameter to 1½ in.
ASTM A193 / ASME SA-193ASTM A193 Grade B8M Class 1 (316 Stainless)
316 stainless bolting with molybdenum for chloride and pitting resistance — offshore, marine, chemical and coastal plant fasteners.
ASTM A194 / ASME SA-194ASTM A194 Grade 8 (304 Stainless)
304 stainless heavy hex nut for A193 and A320 B8 studs — solution treated, 80 ksi proof load, corrosion resistant from cryogenic to 1500 °F.