ASTM A193 Grade B8M Class 2 (316 Strain Hardened)
316 stainless bolting cold worked after solution treatment — 110 ksi tensile in ¾ in. and under, with B8M2 and B8M3 classes for diameters to 3 in. and beyond.
What A193 B8M Class 2 is.
ASTM A193 B8M Class 2 is 316 stainless bar that has been carbide solution treated and then strain hardened. The cold work lifts the tensile strength from 75 ksi to 110 ksi in ¾ in. and under, stepping down by size to 90 ksi at 1½ in. A193 adds two large-diameter classes for 316: Class 2B (marked B8M2) to 3 in. and Class 2C (marked B8M3) at 85 ksi with high ductility, listed for 2 in. and under and for over 2 in.
B8M Class 2 gives a chloride-resistant bolt with strength approaching alloy steel, which is why it is common on offshore, coastal and chemical plant flanges. We supply it as studs, bolts and cap screws from strain-hardened certified bar, marked B8MSH, with A194 Grade 8M nuts.
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 | 16.0 | 18.0 |
| Nickel | Ni | 10.0 | 14.0 |
| Molybdenum | Mo | 2.00 | 3.00 |
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 | 110 | 95 | 15 | 45 | 321 HBW / 35 HRC |
| Class 2 — over ¾ to 1 | 100 | 80 | 20 | 45 | 321 HBW / 35 HRC |
| Class 2 — over 1 to 1¼ | 95 | 65 | 25 | 45 | 321 HBW / 35 HRC |
| Class 2 — over 1¼ to 1½ | 90 | 50 | 30 | 45 | 321 HBW / 35 HRC |
| Class 2B (B8M2) — 2 and under | 95 | 75 | 25 | 40 | 321 HBW / 35 HRC |
| Class 2B (B8M2) — over 2 to 2½ | 90 | 65 | 30 | 40 | 321 HBW / 35 HRC |
| Class 2B (B8M2) — over 2½ to 3 | 80 | 55 | 30 | 40 | 321 HBW / 35 HRC |
| Class 2C (B8M3) — 2 and under | 85 | 65 | 30 | 60 | 321 HBW / 35 HRC |
| Class 2C (B8M3) — over 2 | 85 | 60 | 30 | 60 | 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.; Class 2B is listed in size steps to 3 in. and Class 2C for 2 in. and under and over 2 in. Strain-hardened austenitic steel may not show uniform properties through the section, particularly over ¾ in. diameter.
Specifications that apply.
How A193 B8M 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 B8M Class 2 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8M Class 2, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8M Class 2?
B8M Class 2 is 316 stainless steel that has been cold worked after its solution anneal to raise its strength. 316 work-hardens slightly less than 304, so its Class 2 numbers sit about 15 ksi below B8 Class 2 at each size, but it keeps the 2 to 3 percent molybdenum that resists pitting and crevice corrosion in chloride environments. It is the usual answer when a stainless joint on seawater or brine service needs a stronger bolt than annealed 316 can offer.
Class 2, B8M2 and B8M3
- Class 2 (B8MSH): 110 ksi tensile in ¾ in. and under, stepping to 90 ksi at 1½ in. Not certified above 1½ in.
- Class 2B, marked B8M2: 95 ksi to 80 ksi tensile for sizes 2 in. through 3 in.
- Class 2C, marked B8M3: 85 ksi tensile at 65 ksi yield (2 in. and under) or 60 ksi yield (over 2 in.), with 60 percent reduction of area, where ductility matters more than peak strength.
- All three classes carry the same 321 HBW / 35 HRC hardness ceiling and the same 316 chemistry.
Where B8M Class 2 is the wrong choice
Above about 800 °F the cold-worked structure recovers and the strength advantage disappears, so hot flanges should use Class 1 or a stabilized grade. Sour service to NACE MR0175 / ISO 15156 restricts cold-worked austenitic bolting; the annealed Class 1 grades, or a duplex or nickel alloy, are the usual substitutes there. If chlorides are absent, B8 Class 2 offers more strength for less cost.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade symbol B8MSH, B8M2 or B8M3 and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- Hardness checked on the finished product; 321 HBW / 35 HRC maximum
- PMI verification and intergranular corrosion testing (ASTM A262) arranged on request
Recent A193 B8M Class 2 jobs.
ASTM 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 A193 / ASME SA-193ASTM 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 A194 / ASME SA-194ASTM A194 Grade 8M (316 Stainless)
316 stainless heavy hex nut for B8M studs — molybdenum-bearing for chloride and marine service, 80 ksi proof load.