SUS316 vs SUS321 stainless steel: high temperature resistance
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SUS316 vs SUS321 stainless steel：Chemical composition
| Grade | Major Alloying Elements | Carbon Content (C) | Stabilizing Element |
|---|---|---|---|
| SUS316 | Cr (16–18%), Ni (10–14%), Mo (2–3%) | ≤0.08% | - |
| SUS321 | Cr (17–19%), Ni (9–12%), Ti (≥5×C%) | ≤0.08% | Titanium (Ti) |
Core difference:
SUS316 improves corrosion resistance by adding molybdenum (Mo); SUS321 fixes carbon by adding titanium (Ti) to avoid the formation of chromium carbide at high temperature (reducing the risk of intergranular corrosion).
SUS316 vs SUS321 stainless steel：High temperature performance
| Property | SUS316 | SUS321 |
|---|---|---|
| Oxidation Resistance Limit Temperature | 870°C (Short-term: 980°C) | 925°C (Short-term: 1050°C) |
| Continuous Operating Temperature | 650°C (Corrosion-free environment) | 800°C (Stress-bearing environment) |
| Creep Strength (700°C/1000h) | 40 MPa | 65 MPa |
| Intergranular Corrosion Sensitivity | Prone to corrosion in sensitization temperature range (450–850°C) | Excellent resistance due to titanium stabilization treatment |
SUS316 vs SUS321 stainless steel：Corrosion resistance
The addition of molybdenum (Mo) in SUS316 stainless steel enables SUS316 to form a stable oxide film at the grain boundary, especially in acidic environments containing chloride ions (such as seawater and chemical media), its resistance to pitting and crevice corrosion is significantly better than that of ordinary austenitic stainless steel. For example, in a 3.5% NaCl solution, the critical pitting temperature (CPT) of SUS316 can reach 70°C, while that of SUS304 is only 40°C.
Titanium (Ti) in SUS321 stainless steel acts as a stabilizing element, which preferentially fixes carbon by forming TiC to avoid the precipitation of chromium carbide (Cr₂₃C₆) in the sensitization range of 450-850°C. This mechanism enables it to maintain grain boundary corrosion resistance in the welding heat affected zone (HAZ), which is particularly suitable for high-temperature structural parts that require frequent heating.
SUS316 vs SUS321 stainless steel：Welding performance
Welding process
SUS316: TIG welding is recommended, ER316L welding wire is selected, and the interlayer temperature is controlled below 150℃ to avoid sensitization of the heat-affected zone.
SUS321: MIG welding can be used, ER321 welding wire is selected, and no solution treatment is required after welding, but stabilization annealing (850-900℃) is required.
Heat treatment specification
SUS316: Solution treatment (1020-1100℃ water cooling) to eliminate work hardening.
SUS321: Stabilization treatment (850-930℃ air cooling) to promote TiC precipitation and improve high-temperature endurance strength.
