Stainless Steel 321
Stainless Steel 321 (UNS S32100) is a titanium-stabilised austenitic grade built to resist sensitisation between 425°C and 900°C, with good oxidation resistance in continuous service up to approximately 870°C. Titanium is added at a minimum of five times the total of carbon and nitrogen content. This suppresses intergranular carbide precipitation, so it resists corrosion across weld zones without post-weld heat treatment.
1. Chemical Composition
The table below lists the controlled elemental composition of 321. The titanium stabilisation ratio separates this grade from unstabilised austenitic alloys.
| GRADE | UNS Designation |
C | Mn | P | S | Si | Cr | Ni | Mo | Ti | Cu | Al | Other |
| TP321 | S32100 | 0.080 | 2.00 | 0.045 | 0.030 | 1.00 | 17.0-19.0 | 9.0-12.0 | - | 5(C+N)-0.7 | - | - | N≤0.1 |
Note: Titanium content must be at a minimum of 5x(C+N) to ensure full stabilisation as per ASTM A213/A312 requirements.
2. Mechanical Properties
The following minimum mechanical values apply to 321 in the annealed condition. They reflect the grade's suitability for structural load-bearing in elevated-temperature pressure systems.
| Grade | Condition & Size | Standard | Heat Treating Temp. : min | Tensile Strength Min. MPa |
Yield Strength Min. MPa |
Elongation min. % |
| TP321 | t≤9.5mm | A312 | 1040°C | 515 | 205 | 35 |
3. Equivalent Grade
This table cross-references 321 designations across ASTM, European, Japanese, Chinese, and Russian standards for international material verification and sourcing.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| 321 | S32100 | S32168 | 06Cr18Ni11Ti | SUS321 | X6CrNiTi18-10 | 1.4541 | 08X18H10T |
4. Key Technical Advantages
- Titanium Stabilisation Against Sensitisation: Titanium preferentially forms TiC and TiN precipitates instead of allowing chromium carbide formation at grain boundaries. This prevents sensitisation during elevated-temperature exposure and multi-pass welding.
- Sustained High-Temperature Strength: 321 maintains useful tensile and creep strength at continuous service temperatures up to approximately 870°C, with oxidation resistance extending to 900°C or higher depending on atmosphere and cycling conditions. For applications exceeding 870°C, consult project-specific creep and oxidation data.
- Oxidation Resistance: The 17-19% chromium range produces a stable, adherent oxide layer that resists scaling and oxidising atmospheres at temperatures well above those tolerated by unstabilised 300-series grades.
5. Common Manufacturing Standards
ASTM A312: Standard specification for seamless, welded, and heavily cold-worked austenitic stainless steel pipes — covers TP321 designation.
ASTM A213: Standard specification for seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes — TP321 grade included.
ASTM A269: Standard specification for seamless and welded austenitic stainless steel tubing for general service, applicable to 321.
ASTM A511: Standard specification for seamless stainless steel mechanical tubing — MT321 designation covered.
DIN EN 10216-5: Seamless steel tubes for pressure purposes — stainless steel (Grade 1.4541 equivalent).
JIS G3459: Stainless steel pipes — applicable to SUS321 designation.
GB/T 14976: Seamless stainless steel tubes for fluid transport — covers 06Cr18Ni11Ti designation.
GOST 9940 / 9941: Seamless hot- and cold-formed stainless steel tubes — 08X18H10T equivalent.
Manufacturing Standards Comparison Table:
| Standard | ASTM | EN/DIN | JIS | GB/T | GOST |
| Seamless Pipe | A312 TP321 | EN 10216-5 (1.4541) | G3459 SUS321 | GB/T 14976 | GOST 9940 |
| Seamless Tube | A213 TP321 | EN 10216-5 (1.4541) | G3463 SUS321 | GB/T 13296 | GOST 9941 |
| Welded Tube | A249 TP321 | EN 10217-7 (1.4541) | G3463 SUS321 | GB/T 12771 | — |
6. Primary Applications
- Aerospace Exhaust Systems: Jet engine exhaust manifolds, exhaust liners, and afterburner components that need sustained oxidation resistance at high cyclic temperatures.
- Refinery Process Heaters: Furnace tubes and radiant coils in crude oil distillation and reforming units, where continuous exposure at 600-850°C is the standard operating condition.
- Heat Exchangers in High-Temperature Service: Shell-and-tube heat exchangers in petrochemical plants where sensitisation from weld cycles must be prevented in the heat-affected zone.
- Chemical Plant Flexible Piping: Transfer lines and expansion bellows carrying hot corrosive fluids, where repeated thermal cycling would sensitise unstabilised grades.
- Nuclear Power Auxiliaries: Reactor coolant system auxiliary piping and components in plants where intergranular attack in irradiated weld zones is a design consideration.