ASTM A193 Grade B8C Class 2 (347 Strain Hardened)
Niobium-stabilized 347 bolting cold worked to 125 ksi tensile in ¾ in. and under — strength for moderate-temperature joints that must not sensitize.
What A193 B8C Class 2 is.
ASTM A193 B8C Class 2 is the strain-hardened version of the 347 grade. The bar is carbide solution treated and then cold reduced, which raises the tensile strength from the annealed minimum to 125 ksi in ¾ in. and smaller sizes. Because cold work cannot penetrate a large section evenly, the specification steps the required strength down by diameter and stops at 1½ in.
We supply B8C Class 2 studs, bolts and cap screws from strain-hardened certified bar, marked B8CSH, and match them with ASTM A194 8C nuts. The chemistry, corrosion resistance and companion nut are identical to B8C Class 1; only the condition and strength differ.
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 | 17.0 | 19.0 |
| Nickel | Ni | 9.0 | 12.0 |
| Niobium (columbium) | Nb | 10 × C | 1.10 |
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 2 — ¾ and under | 125 | 100 | 12 | 35 | 321 HBW / 35 HRC |
| Class 2 — over ¾ to 1 | 115 | 80 | 15 | 35 | 321 HBW / 35 HRC |
| Class 2 — over 1 to 1¼ | 105 | 65 | 20 | 35 | 321 HBW / 35 HRC |
| Class 2 — over 1¼ to 1½ | 100 | 50 | 28 | 45 | 321 HBW / 35 HRC |
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 2 is limited to 1½ in. Strain-hardened austenitic steel may not show uniform properties through the section, particularly over ¾ in. diameter.
Specifications that apply.
How A193 B8C Class 2 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 B8C Class 2 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8C Class 2, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8C Class 2?
B8C Class 2 is 347 stainless steel that has been solution treated and then cold worked to raise its strength, following the same size-stepped table as B8 Class 2. The niobium stabilization that makes 347 resistant to sensitization is unaffected by cold work, so the grade suits welded or thermally cycled equipment that also needs a stronger bolt than annealed 347. The cold-worked strength recovers above about 800 °F, so hot flanges should stay with B8C Class 1.
Why the strength drops with size
- ¾ in. and under: 125 ksi tensile, 100 ksi yield. Cold work reaches the core of a small bar.
- Over ¾ to 1 in.: 115 ksi tensile, 80 ksi yield.
- Over 1 to 1¼ in.: 105 ksi tensile, 65 ksi yield.
- Over 1¼ to 1½ in.: 100 ksi tensile, 50 ksi yield. The largest size certified as Class 2 for this grade.
Class 2 or Class 1?
Specify Class 2 when the joint needs bolt strength close to alloy steel and runs below about 800 °F. Specify Class 1 for hot service, for large diameters, for sour service to NACE MR0175 / ISO 15156 where cold-worked austenitic bolting is restricted, and wherever the design only needs the annealed strength. Both classes share one chemistry, so the corrosion performance is the same.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade symbol B8CSH and manufacturer's identification on every piece
- Hardness checked on the finished product; 321 HBW / 35 HRC maximum
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
ASTM A193 Grade B8C Class 1 (347 Stainless)
347 stainless bolting stabilised with niobium against sensitisation — for hot hydrogen, refinery and welded stainless service between 800 and 1500 °F.
ASTM A193 / ASME SA-193ASTM A193 Grade B8T Class 2 (321 Strain Hardened)
Titanium-stabilized 321 bolting cold worked to 125 ksi tensile in ¾ in. and under — a stronger stabilized bolt for welded stainless equipment at moderate temperature.
ASTM A194 / ASME SA-194ASTM A194 Grade 8C (347 Stainless)
347 stainless heavy hex nut for B8C studs — stabilised against sensitisation for hot hydrogen, refinery and welded stainless service.