STS321 stainless steel: composition, performance and application analysis
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What is STS321 stainless steel?
STS321 is a stainless steel grade in the Korean Industrial Standard (KS), corresponding to the internationally used 321 stainless steel (321 in the US ASTM standard and 06Cr18Ni10Ti in the Chinese GB standard). It is an austenitic stainless steel that stabilizes carbon by adding titanium (Ti) elements. It has excellent high temperature resistance and intergranular corrosion resistance, and is widely used in scenarios that require service in medium and high temperature environments after welding.
sts321 stainless steel standard
| Country/Region | Standard | Grade |
|---|---|---|
| South Korea | KS D 3503 | STS321 |
| USA | ASTM A240 | 321 / 321H |
| China | GB/T 24511 | 06Cr18Ni10Ti |
| Japan | JIS G4303 | SUS321 |
Differences Between STS321 and 304 Stainless Steel
STS321 contains titanium, which is not present in standard 304. This addition significantly enhances its resistance to intergranular corrosion after welding or long-term exposure to high temperatures, making it suitable for continuous service in the 450–850°C range. In contrast, 304 stainless steel tends to become sensitized within this temperature range, reducing its corrosion resistance.
Physical and Mechanical Properties of STS321 Stainless Steel
Thermal Properties
High-temperature resistance: Can operate continuously at temperatures up to 850°C, with short-term peaks reaching 1000°C.
Offers better high-temperature strength than 304 stainless steel, making it ideal for use in heat exchangers and heating pipelines.
Mechanical Properties (at room temperature)
Tensile strength: ≥520 MPa
Yield strength: ≥205 MPa
Elongation: ≥40%
Excellent toughness and crack resistance after welding.
Formability and Machinability
Austenitic structure provides good plasticity, allowing cold working processes such as bending and drawing.
However, it has a relatively high work hardening rate, so deformation should be carefully controlled.
Corrosion Resistance of STS321 Stainless Steel
Intergranular Corrosion Resistance
Titanium binds carbon, preventing chromium carbide precipitation at grain boundaries in the heat-affected zone (HAZ). This gives 321 stainless steel superior intergranular corrosion resistance compared to unstabilized 304, especially after welding.
General Corrosion Resistance
Performs well in atmospheric, water, and mildly acidic/alkaline environments.
However, it has lower resistance to chloride-induced corrosion (e.g., seawater, salt solutions) than 316 stainless steel, and should not be used in high-chloride environments.
Application Fields of STS321 Stainless Steel
High-Temperature Industrial Equipment
Heating furnace piping, heat treatment fixtures, and heat exchangers used in power plants and chemical reactors.
Automotive Exhaust Systems
Exhaust pipes and catalytic converters, which must endure exhaust gas temperatures between 500–800°C and resist thermal cycling stress.
Welded Structural Components
Components used directly after welding, such as pressure vessels and piping flanges.
Welded pipelines operating at high temperatures (e.g., distillation columns and boiler connection pipes in petrochemical plants).
Titanium addition significantly reduces the risk of post-weld intergranular corrosion, eliminating the need for complex post-weld heat treatments.
