ASTM A193 Grade B8M3 Stud Bolts (Class 2C)
Strain-hardened ASTM A193 Grade B8M3 (Class 2C) stud bolts — 316-family stainless with 85,000 psi minimum tensile, 65,000 psi yield (60,000 over 2"), 30% elongation and a 60% minimum reduction of area. The high-ductility high-strength B8M class for dynamic, shock and thermal-cycling service.
Last updated: 2026-11
Specifications
B8M3 is how the 316 stud line escapes the annealed grades' 75-ksi ceiling: after solution treatment the fastener is strain-hardened — mechanically deformed — which lifts tensile to 85,000 psi minimum and yield to 65,000 psi (60,000 psi above 2") while the Class 2C requirement holds elongation at 30% minimum and mandates a 60% minimum reduction of area. That reduction-of-area clause is the grade's defining trait per the collected datasheet: it is what lets the stud stretch and absorb energy instead of snapping under shock load, the reason the grade is selected for seismic-prone refinery zones, wave-loaded offshore platforms and thermal-cycling flanges. The same strain-hardening is also the grade's maintenance rule: welding a B8M3 fastener locally anneals the steel and drops the heat-affected zone back to the soft Class 1 baseline (~30 ksi yield), so the strain-hardened properties must be designed around, not welded on. Identification follows the collected marking table — B8M3 or B9H on the head — clamped with A194 8M/8MA nuts, with the batch certified against the EN 10204 3.1 mill-test-certificate practice.
| Standard / class | ASTM A193 Grade B8M3, Class 2C (strain-hardened); stud dimensions per ASME B18.31.2, heavy hex heads per ASME B18.2.1 |
|---|---|
| Material | Molybdenum-alloyed austenitic stainless steel, UNS S31600 — chemistry C max 0.08%, Cr 16.0–18.0%, Ni 10.0–14.0%, Mo 2.00–3.00%, Mn max 2.00%, Si max 1.00%, P/S max 0.045%/0.030% |
| Tensile strength, min | 85,000 psi (585 MPa), all diameters in the collected table |
| Yield strength, min (0.2% offset) | 65,000 psi (450 MPa) — 2" and under (to M48); 60,000 psi (415 MPa) over 2" |
| Elongation | 30% minimum (in 4D) |
| Reduction of area | 60% minimum — the defining Class 2C requirement (vs 35–45% Class 2, 40% Class 2B per the collected comparison) |
| Max hardness | 35 HRC (321 HBW) |
| Grade identification | Marked B8M3 or B9H; weakly magnetic due to the strain-hardening (collected material table) |
| Nut pairing | ASTM A194 Grade 8M / 8MA |
| Class comparison | B8M2 (Class 2B) carries higher yield (75 ksi small-diameter) with 40% reduction of area — suited to static flanged joints; B8M3 trades that yield step for the 60% ductility mandate |
| Welding caveat | Welding locally anneals the strain-hardened section — HAZ reverts toward the Class 1 baseline (~30 ksi yield); do not weld |
| Certification practice | EN 10204 Type 3.1 mill test certificate per the collected vendor practice (ductility, yield, chemistry and heat traceability on the certificate) |
| Heavy hex head dims (sample) | 1/2"–13 TPI: WAF 0.875", head height 0.344"; 3/4"–10: 1.250" / 0.500"; 1"–8: 1.625" / 0.656"; 1-1/2"–8UN: 2.375" / 0.969"; 2"–8UN: 3.125" / 1.281" (ASME B18.2.1 max per collected table) |
| Typical applications | Seismic-prone refinery bolting, offshore platforms under wave impact, extreme thermal-cycling flanges — dynamic joints that need ductility with strength |
Materials
- UNS S31600 molybdenum-alloyed austenitic stainless steel, strain-hardened (Class 2C)
Ordering & documentation
Documents
Shipments are backed by Mill Test Certificate (MTC), Dimensional Report, Salt Spray Test Report on request, with full batch traceability from raw material to finished product. Quality management follows the owner-confirmed compliance list: ISO 9001:2015, RoHS, REACH. Exact document sets are confirmed on the order.
Quotation
- The fastener family (ASTM A193 Grade B8M3 Stud Bolts (Class 2C)) plus the standard designation from your drawing — DIN / ISO / JIS / ASTM / ANSI, or a drawing for custom parts.
- Size (diameter and length), thread type (metric or inch), property class or grade, and coating or finish.
- Quantity per size and your target delivery date.
- Destination country, and any required documents (for example a mill test certificate) so the quote includes them.
Sample & supply
Minimum order quantity is 1,000–10,000 pieces depending on size. Stock items run 3–7 days. High-strength and custom parts run 15–25 days. Quantities or variants outside the standard range are confirmed at quotation.
Storage & shipping
Parts are packed for export and shipped factory-direct to buyers in Europe, Asia, the Americas and the Middle East. Store fasteners dry and protected until installation, and keep coated parts in their packaging until use; specific packing and preservation requirements can be stated on the order and confirmed at quotation.
Frequently asked questions
B8M or B8M3 — what does the Class 2C upgrade actually buy?
Yield strength with ductility kept. Standard annealed B8M sits at 75 ksi tensile with a soft yield profile; B8M3 raises tensile to 85,000 psi and yield to 65,000 psi (60,000 above 2") — but the clause that defines it is the 60% minimum reduction of area with 30% elongation, which lets the stud deform and absorb shock energy rather than fracture. Static, well-behaved flanges do fine on annealed B8M. Joints that see earthquake loading, wave impact or relentless thermal cycling are where the Class 2C ductility mandate pays, because in those joints the failure mode being designed against is brittle snap, not slow overload.
Can B8M3 studs be welded or repaired in place?
The collected datasheet is explicit that welding destroys the engineered properties: the arc heat locally anneals the strain-hardened steel, and the heat-affected zone drops back toward the ~30 ksi yield of a Class 1 fastener even though the marking still reads B8M3. A welded-and-marked stud is therefore a silent understrength part. If a joint modification requires welding near the bolting, the practice is to plan for stud replacement afterward — and to insist on the EN 10204 3.1 mill certificate trail so the replacement batch's ductility and yield are documented, not assumed.
Related knowledge
- What Bolt Property Classes 8.8, 10.9 and 12.9 Encode — and When High Strength Stops Being the Right Choice
- Bolt Grade Selection: ISO 898-1 8.8/10.9/12.9 vs ASTM A307 and A325
- 8.8 vs 10.9 vs 12.9 Bolts: Strength, Hardness and Cost — What the Evidence Settles
- Calculating Bolt Preload and Clamp Force: Torque, Friction and Tightening Method
- How to Determine Tightening Torque and Choose a Tightening Method for a Bolted Joint
- Fastener Failure Modes: Which Fatigue, Creep and SCC Controls the Evidence Supports
- Hydrogen Embrittlement in High-Strength Bolts: Which Grades Need Controls, Which Coatings and Baking Schedules Are Acceptable, and What to Require Before the RFQ
Request a Quote
Get factory-direct pricing from the manufacturer.
What to include in your inquiry
- ✓ Standard and property class (e.g. DIN 912, ISO 4762, class 8.8) — or a drawing for custom parts.
- ✓ Sizes, lengths and thread type (metric or inch).
- ✓ Quantity per size and your target delivery date.
- ✓ Destination country, plus any coating or finish requirement.
- ✓ Any documents you need with the shipment (e.g. mill test certificate) so the quote includes them.
- ✓ Your inquiry goes straight to the factory team by email and gets a reply within 24 hours.
- ✓ Factory-direct pricing
- ✓ Standard and custom specifications
- ✓ Factory-direct export to buyers in Europe, Asia, the Americas and the Middle East
- ✓ Full fastener family support