ASTM A193 Grade B8MLCuN Class 2 (254 SMO Strain Hardened)
6 percent molybdenum super-austenitic bolting cold worked to 110 ksi tensile in ¾ in. and under — seawater-grade corrosion resistance with Class 2 strength.
What A193 B8MLCuN Class 2 is.
ASTM A193 B8MLCuN Class 2 is the strain-hardened version of the 254 SMO grade. The bar is carbide solution treated and then cold reduced, which raises the tensile strength from the annealed minimum to 110 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 B8MLCuN Class 2 studs, bolts and cap screws from strain-hardened certified bar, marked B8JSH, and match them with ASTM A194 8MLCuN nuts. The chemistry, corrosion resistance and companion nut are identical to B8MLCuN Class 1B; only the condition and strength differ.
Chemical composition.
| Element | Symbol | Min % | Max % |
|---|---|---|---|
| Carbon | C | — | 0.020 |
| Manganese | Mn | — | 1.00 |
| Phosphorus | P | — | 0.030 |
| Sulfur | S | — | 0.010 |
| Silicon | Si | — | 0.80 |
| Chromium | Cr | 19.5 | 20.5 |
| Nickel | Ni | 17.5 | 18.5 |
| Molybdenum | Mo | 6.0 | 6.5 |
| Copper | Cu | 0.50 | 1.00 |
| Nitrogen | N | 0.18 | 0.25 |
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 |
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 B8MLCuN Class 2 ships from Houston.
- Full-thread studs and stud bolts
- Hex and heavy hex bolts
- Socket head cap screws
- Hex nuts in the same alloy
- Threaded rod
- Machined components from certified bar
A193 B8MLCuN Class 2 fasteners we make.
Every item is manufactured to your drawing or standard in A193 B8MLCuN Class 2, imperial or metric, with an EN 10204 3.1 certificate.
What is ASTM A193 B8MLCuN Class 2?
B8MLCuN Class 2 is 254 SMO super-austenitic stainless steel, solution treated and then strain hardened to the B8M Class 2 strength table. The alloy's 6 percent molybdenum, copper and nitrogen give it a pitting resistance number near 43, enough for seawater, brine and chlorinated process streams where 316 pits. Cold work adds strength without reducing that resistance, so Class 2 lets a 254 SMO joint use the same bolt loads as an alloy steel one. The grade symbol on the bolt is B8JSH.
Why the strength drops with size
- ¾ in. and under: 110 ksi tensile, 95 ksi yield. Cold work reaches the core of a small bar.
- Over ¾ to 1 in.: 100 ksi tensile, 80 ksi yield.
- Over 1 to 1¼ in.: 95 ksi tensile, 65 ksi yield.
- Over 1¼ to 1½ in.: 90 ksi tensile, 50 ksi yield. The largest size certified as Class 2 for this grade.
Class 2 or Class 1B?
Specify Class 2 when the joint needs bolt strength close to alloy steel and runs below about 800 °F. Specify Class 1B 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 B8JSH 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 B8MLCuN Class 1B (254 SMO, UNS S31254)
254 SMO bolting — a 6 % Mo super austenitic with PREN above 42 for seawater, chlorinated cooling water and flue-gas scrubbers where 316 pits.
ASTM A193 / ASME SA-193ASTM 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.
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.