ASTM A193
Grade B8S
Bolt & Nut Manufacturer
What Is ASTM A193 Grade B8S
ASTM A193 Grade B8S is based on UNS S20910 — a high-manganese, nitrogen-strengthened austenitic stainless steel widely known in industry by its trade name “Nitronic 50” or its UNS-adjacent designation XM-19. Where Grade B8T achieves its distinguishing property through a titanium addition that stabilizes carbon, and Grade B8M achieves chloride resistance through molybdenum, B8S takes an entirely different route to a different goal: strengthening the austenitic matrix itself through nitrogen and manganese in solid solution, rather than relying on cold work or carbide precipitation chemistry.
Chemical composition (wt%, representative): Chromium 20.5–23.5, Nickel 11.5–13.5, Manganese 4.0–6.0, Molybdenum 1.5–3.0, Nitrogen 0.20–0.40, Niobium (Columbium) 0.10–0.30, Vanadium 0.10–0.30, Carbon 0.06 max, balance Iron. The nitrogen content in particular is doing real metallurgical work here — it’s a potent solid-solution strengthener in austenitic stainless, which is precisely why B8S reaches high strength without needing to be cold-worked the way standard B8/B8M grades do to hit comparable numbers.
Why this matters in practice: cold-worked stainless bolting (Class 2 B8/B8M) loses much of its strength advantage at larger diameters, since strain hardening doesn’t penetrate a large section uniformly, and it can be sensitive to sustained elevated temperature. B8S, being strengthened in the annealed condition, doesn’t carry either limitation — and it brings a genuinely useful side benefit: austenitic stainless is notorious for galling and thread seizure during assembly, and nitrogen-strengthened grades like this are specifically recognised for resisting that failure mode.
Where Grade B8S Genuinely Earns Its Cost
High Strength Without Cold Work
Nitrogen and manganese strengthen the austenitic matrix directly, so B8S reaches high strength in the annealed condition — with no strain-hardening size limitation to work around.
Genuine Galling Resistance
Austenitic stainless is notorious for thread seizure on assembly; nitrogen-strengthened grades like B8S are specifically recognised in industry for resisting this failure mode.
Strong Cryogenic Toughness
The alloy retains good toughness at low and cryogenic temperatures, making it a dependable choice for LNG and low-temperature process fastening.
A Correctly Matched System
Supplied as a matched bolting system with ASTM A194 Grade 8S nuts, so the stud and nut share the same nitrogen-strengthened base metallurgy end to end.
Grade B8S vs Cold-Worked B8M Class 2
When a project needs stainless bolting stronger than standard B8/B8M Class 1, the default reach is usually B8M Class 2 — Type 316 stainless, strengthened by cold working. It’s a perfectly valid choice for many applications, but it comes with real trade-offs that cold work introduces: reduced strength retention at larger diameters, sensitivity to sustained elevated temperature, and no particular improvement in galling behaviour. Grade B8S reaches comparable or higher strength through alloy chemistry rather than mechanical processing, and it’s worth understanding what that actually buys you before defaulting to the cold-worked option.
| Property | ASTM A193 B8M Class 2 (Cold-Worked 316) | ASTM A193 B8S (UNS S20910, Annealed) |
|---|---|---|
| Strengthening Mechanism | Cold work / strain hardening | Nitrogen + manganese solid-solution strengthening |
| Condition Required for High Strength | Must be strain-hardened | As-annealed — no cold work needed |
| Strength Retention at Larger Diameters | Reduced — derated above 3/4″ typically | Maintained across a wider size range |
| Sustained Elevated Temperature | Cold work can relax over time | Better strength retention, no cold-work to lose |
| Galling / Thread Seizure Resistance | Standard austenitic — prone to galling | Genuinely improved resistance |
| Cryogenic Toughness | Good | Excellent — a recognised strength of the alloy |
| Relative Material Cost | Moderate | Higher |
Grade B8S Product Range
Stud Bolts
Full-thread and tap-end, ASTM A193 Grade B8S
Hex Bolts
Full metric & imperial range in Grade B8S
Heavy Hex Nuts (A194 Gr.8S)
The matched nut counterpart to B8S stud bolts
Washers
Flat and spring washer profiles in matching grade
Threaded Rod / Continuous Thread Stud
Custom lengths for high-strength process piping joints
Grade B8S Technical Specifications
UNS S20910 Base Alloy (wt%)
- Chromium (Cr) 20.5–23.5
- Nickel (Ni) 11.5–13.5
- Manganese (Mn) 4.0–6.0
- Molybdenum (Mo) 1.5–3.0
- Nitrogen (N) 0.20–0.40
- Iron (Fe) Balance
As-Annealed Condition (typical min)
- Tensile Strength 690 MPa (100 ksi)
- Yield Strength (0.2%) 380 MPa (55 ksi)
- Elongation 35%
- Cold Work Required No
- Galling Resistance Genuinely improved
- Cryogenic Toughness Excellent
Available Dimensions
- Metric Diameter M6 – M64
- Imperial Diameter 1/4″ – 4″
- Stud Length Custom to drawing
- Thread Type UNC / UNF / Metric
- Finish Passivated / As-machined
- Testing MTC / NABL on request
Application Areas
Wherever high strength, galling resistance, or cryogenic service is the deciding factor.
Oil & Gas Valves & Subsea Equipment
valve stems and connectors
Cryogenic & LNG Service
piping and equipment fastening
High-Strength Stainless Bolting
limitations become a problem
Marine & Offshore Fastening
resistant bolting for harsh service
Pump & Compressor Fastening
for repeated maintenance cycles
Chemical Processing
fastening for process equipment
Aerospace & Defense
stainless fastening applications
General High-Strength Industrial
strength & anti-galling critical
Standard Export Documentation
Prepared as standard practice for every Grade B8S shipment.
Mill Test Certificate (MTC)
Heat number, chemical composition, and mechanical property verification for every lot.
Certificate of Conformance
Confirms the shipment matches the purchase order specification and grade in full.
Certificate of Origin (COO)
Confirms India as country of manufacture for destination customs purposes.
Commercial Invoice & Packing List
Itemized value, Incoterm, and detailed carton/weight breakdown for customs clearance.
NABL Accredited Test Reports
Independent mechanical and chemical testing available on request for critical applications.
Bill of Lading
Ocean or air freight shipping document confirming carrier, mode, and consignee details.
Internationally Recognised Standards Coverage
Related Fastener Grades & Materials
ASTM A193 Grade B8T Fasteners
Titanium-stabilized Type 321 stainless, built for sensitization resistance in high-temperature service.
View Grade B8T →Stainless Steel 316 Fasteners
General-purpose stainless bolting for standard chloride-resistant applications.
View SS 316 →Super Duplex Fasteners
High strength and severe chloride resistance for demanding process environments.
View Super Duplex →Hastelloy B-3 Stud Bolts
Nickel-molybdenum alloy fastening for reducing acid and severe corrosion service.
View Hastelloy B-3 →Sourcing Grade
B8S Fasteners?
Size · quantity · condition · service application. Akbar Fasteners Pvt. Ltd. responds within 24 hours with pricing and mill test documentation.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in