321 Stainless Steel (UNS S32100)
18-8 stabilized with titanium so it can be welded and run hot without sensitizing — the stainless for exhaust, expansion joints and furnace hardware.
What 321 Stainless is.
Type 321 is 304 with titanium added at five times the carbon-plus-nitrogen content. Titanium ties up carbon as titanium carbide, so chromium carbide cannot form when the steel is welded or held in the 800 to 1500 °F range. It keeps its corrosion resistance and creep strength in that range better than 304, which is why it is the standard grade for exhaust systems, bellows, expansion joints and heat-exchanger hardware.
We machine 321 fasteners from certified A276 bar to ASTM F593 Alloy Group 3 conditions, and as ASTM A193 B8T or A320 B8T for pressure bolting.
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 | 17.0 | 19.0 |
| Nickel | Ni | 9.0 | 12.0 |
| Titanium | Ti | 5 × (C+N) | 0.70 |
Values per ASTM A276/A276M-17 Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team.
Mechanical properties.
| Condition and nominal diameter (in.) | Tensile strength, min (ksi) | Yield strength 0.2% offset, min (ksi) | Elongation, min (%) | Reduction of area, min (%) | Hardness |
|---|---|---|---|---|---|
| Condition A (annealed), hot finished — all | 75 | 30 | 40 | 50 | — |
| Condition A, cold finished — ½ and under | 90 | 45 | 30 | 40 | — |
| Condition A, cold finished — over ½ | 75 | 30 | 30 | 40 | — |
Values per ASTM A276/A276M-17 Tables 1 and 2 (verified against the specification). Confirm the edition called out on your purchase order with our estimating team. A276 lists 321 in Condition A only; cold-worked fastener strengths are per F593.
| F593 condition · marking | Nominal diameter (in.) | Tensile strength (ksi) | Yield strength, min (ksi) | Rockwell hardness |
|---|---|---|---|---|
| AF (annealed after forming) · F593J | ¼ to 1½ | 65 to 85 | 20 | B85 max |
| A (annealed) · F593K | ¼ to 1½ | 75 to 100 | 30 | B65 to B95 |
| CW1 (cold worked) · F593L | ¼ to ⅝ | 100 to 150 | 65 | B95 to C32 |
| CW2 (cold worked) · F593M | ¾ to 1½ | 85 to 140 | 45 | B80 to C32 |
| SH1 (strain hardened) · F593J | ¼ to ⅝ | 120 to 160 | 95 | C24 to C36 |
| SH2 (strain hardened) · F593K | ¾ to 1 | 110 to 150 | 75 | C20 to C32 |
| SH3 (strain hardened) · F593L | 1⅛ to 1¼ | 100 to 140 | 60 | B95 to C30 |
| SH4 (strain hardened) · F593M | 1⅜ to 1½ | 95 to 130 | 45 | B90 to C28 |
Values per ASTM F593-24 Table 2, full-size tests (verified against the specification). Yield is 0.2 % offset; hardness is Rockwell. Machined-specimen limits differ slightly.
Specifications that apply.
How 321 Stainless ships from Houston.
- Hex and heavy hex bolts and cap screws
- Full-thread studs and threaded rod
- Socket head cap and set screws
- Hex, jam and lock nuts
- Washers and spacers
- Machined components from certified bar
321 Stainless fasteners we make.
Every item is manufactured to your drawing or standard in 321 Stainless, imperial or metric, with an EN 10204 3.1 certificate.
What is 321 stainless steel?
321 solves the sensitization problem of 304 by chemistry rather than by cutting carbon. Titanium has a stronger affinity for carbon than chromium does, so the carbon in the steel is locked into titanium carbides that form at high temperature and stay put. The chromium remains in solution and the steel resists intergranular attack after welding and after long service in the sensitizing range. Titanium also gives a small gain in creep strength above 1000 °F.
321 or 347?
Both are stabilized 18-8 grades and are often interchangeable. 347 uses niobium, which is a more efficient stabilizer, gives slightly better creep strength and welds with less loss of stabilizer in the arc. 321 is more widely stocked and a little less costly. Aerospace and exhaust work has historically leaned to 321; refinery and power piping to 347.
Testing, certification and marking
- Tensile and hardness tested per lot on the finished product
- Grade or marking symbol F593J to F593M and manufacturer's identification on every piece
- EN 10204 3.1 material test report with heat number and chemistry; 3.2 witness available
- PMI verification and intergranular corrosion testing (ASTM A262) arranged on request
Recent 321 Stainless jobs.
347 Stainless Steel (UNS S34700)
18-8 stabilized with niobium for welded and high-temperature service — the refinery and power-plant stainless for hydrogen, hydrocarbon and steam hardware.
ASTM A276 bar · ASTM F593 bolts304 Stainless Steel (UNS S30400)
The general-purpose 18-8 stainless: 75 ksi annealed bar, cold-worked bolts to 160 ksi, non-magnetic, and resistant to water, food and most mild chemicals.
ASTM A193 / ASME SA-193ASTM A193 Grade B8T Class 1 (321 Stainless)
321 stainless bolting stabilised with titanium — the match for 321 piping and vessels in hot, cyclic and welded service.