ASTM A276
Type 321 Fasteners
Mumbai · India
What Is ASTM A276 Type 321 Fasteners
ASTM A276 covers stainless and heat-resisting steel bars and shapes, and Type 321 within that standard is an austenitic grade built around one specific problem: carbide precipitation, or “sensitization.” When standard 304 or 316 stainless is held in the 450 to 850°C range — during welding heat-affected zones, or sustained high-temperature service — carbon in the alloy combines with chromium to form chromium carbides at the grain boundaries. That reaction depletes the chromium immediately around the grain boundary, and the depleted zone becomes vulnerable to intergranular corrosion even though the bulk material still contains plenty of chromium.
Type 321 solves this by adding titanium — at a minimum of five times the carbon content — which preferentially combines with carbon to form titanium carbides instead, leaving the chromium in solid solution where it belongs. The result is a grade that can be welded, or held at elevated temperature for extended periods, without the intergranular corrosion risk that makes unstabilized 304 or 316 unsuitable for the same service.
Akbar Fasteners Pvt. Ltd. exports to over 50 countries, and our A276 Type 321 fastener range is manufactured with the same ISO 9001:2015 quality system and full mill test documentation as our stainless, duplex, and nickel alloy range, including our related titanium-stabilized ASTM A193 Grade B8T stud bolt line.
Where Titanium Stabilization Genuinely Earns Its Cost
Resists Weld-Zone Sensitization
Titanium carbide formation protects grain boundaries from chromium depletion during and after welding, unlike unstabilized grades.
Sustained High-Temperature Service
Maintains intergranular corrosion resistance across long-term exposure in the 450–850°C sensitization range, where 304/316 degrade.
Good General Corrosion Resistance
Retains the corrosion resistance of standard 18-8 austenitic stainless in addition to its sensitization protection.
Correct Titanium Content Verified
Every batch tested to confirm titanium meets the 5×carbon minimum stabilization requirement, not just nominal 321 chemistry.
Type 321 vs Type 304 vs Type 347
Standard 304 is fine until sustained heat or welding brings sensitization into play — and even then, the choice isn’t automatically Type 321. Type 347 solves the same carbide problem with niobium instead of titanium, and the two aren’t interchangeable in every application. The comparison below is the one we walk through with buyers before quoting.
| Property | Type 321 | Type 304 | Type 347 |
|---|---|---|---|
| UNS Designation | S32100 | S30400 | S34700 |
| Stabilizing Element | Titanium (5×C min) | None — unstabilized | Niobium/Tantalum (10×C min) |
| Sensitization Resistance | Good | Poor — carbide precipitation risk | Very good — often preferred at highest temps |
| Max Practical Service Temp | ~800°C | ~425–650°C before sensitization risk | ~850–900°C |
| Best Suited For | Aerospace, exhaust, general high-temp welded joints | General corrosion resistance, low/no post-weld heat exposure | Highest-temperature welded piping & pressure equipment |
| Relative Cost | Moderate | Lower | Moderate-High |
ASTM A276 Type 321 Product Range
Type 321 Hex Bolts
Titanium-stabilized hex bolts for welded assemblies exposed to sustained elevated temperature.
Type 321 Nuts
Matching hex and heavy hex nuts manufactured to pair correctly with Type 321 bolts and studs.
Type 321 Stud Bolts
Stud bolts for flanged high-temperature piping and pressure vessel joints requiring sensitization resistance.
Type 321 Washers
Matching washers manufactured to the same titanium-stabilized chemistry for complete joint assemblies.
Type 321 Technical Overview
Alloying Elements
- Chromium 17.0 – 19.0%
- Nickel 9.0 – 12.0%
- Titanium Min. 5× Carbon content
- Carbon (max) 0.08%
- Iron Balance
Property Ranges (annealed condition)
- Tensile Strength 515 MPa min
- Yield Strength 205 MPa min
- Elongation 35% min
- Hardness 217 HB max
- Testing MTC / NABL on request
Available Dimensions
- Metric Diameter M6 – M56
- Imperial Diameter 1/4″ – 3.5″
- Stud Length Custom to drawing
- Thread Type UNC / UNF / Metric
- Finish As-machined / Passivated
Application Areas
Wherever welding or sustained heat rules out unstabilized stainless.
Aerospace & Aviation
high-temperature airframe fastening
Automotive Exhaust Systems
resistant to sensitization
Power Generation Boilers
process equipment fastening
Chemical Processing
fastening at elevated temperature
Furnace & Heat Treatment
in sustained high-heat service
Petrochemical Equipment
process joint fastening
Marine Exhaust & Piping
exposed to heat and salt air
General High-Temp Engineering
welded elevated-temp assemblies
Standard Export Documentation
Prepared as standard practice for every Type 321 fastener shipment.
Mill Test Certificate (MTC)
Heat number, chemical composition confirming titanium stabilization ratio, and mechanical property verification.
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
The stud bolt grade built directly on Type 321’s titanium-stabilized chemistry.
View Grade B8T →ASTM A193 Grade B8 Stud Bolts
The unstabilized Type 304 grade Type 321 was developed to improve upon for sustained heat.
View Grade B8 →Stainless Steel 316 Fasteners
The molybdenum-bearing option for chloride resistance where sensitization isn’t the primary concern.
View SS 316 →High Tensile Bolts Specifications
Carbon and alloy steel property classes for structural and mechanical bolting.
View High Tensile Specs →Welding or Sustained Heat
Rules Out Standard 304?
Tell us the temperature, welding condition, and load — and we’ll confirm whether Type 321 or an alternative titanium-stabilized grade is the right fit. Akbar Fasteners Pvt. Ltd. responds within 24 hours.
Sales: +91 724 0000 733 · Support: +91 800 9315 333 · sales@akbarfasteners.in