| Property | 1.4301 (AISI 304) | 1.4401 (AISI 316) |
|---|---|---|
| Chromium (Cr) | 17.5–19.5% | 16.5–18.5% |
| Nickel (Ni) | 8.0–10.5% | 10–13% |
| Molybdenum (Mo) | None | 2.0–2.5% (critical for corrosion resistance) |
| Carbon (C) | ≤0.07% | ≤0.07% |
| Pitting Resistance Equivalent (PREN) | 19–21 (moderate pitting resistance) | 26–30 (significantly improved pitting resistance) |
1.4301:
Performs well in low-concentration chlorides (e.g., fresh water, food contact) but is susceptible to pitting and crevice corrosion in high Cl⁻ environments (e.g., seawater, pool water).
Salt spray test (ASTM B117) lifespan: ~1000 hours in 5% NaCl solution before visible corrosion.
1.4401:
Superior chloride resistance due to Mo. Ideal for marine applications, chemical processing, and offshore equipment.
Pitting potential (ASTM G48) is ~300–500 mV higher than 1.4301, indicating a more stable passive film against Cl⁻ attack.
1.4301:
Oxidizing acids (e.g., nitric acid): Excellent resistance; used in nitric acid storage.
Non-oxidizing acids (e.g., sulfuric, hydrochloric acid): Only resistant to dilute solutions; high-concentration acids cause corrosion.
Alkaline environments: Resistant to strong bases (e.g., NaOH) but may suffer stress corrosion cracking (SCC) in hot, concentrated alkalis.
1.4401:
Non-oxidizing acids: Significantly better resistance than 1.4301 due to Mo; suitable for sulfuric/phosphoric acid processing (e.g., reactor vessels).
Alkaline environments: Similar to 1.4301 but more stable in hot, concentrated alkalis.
1.4301:
Short-term service up to 870°C; long-term exposure (420–870°C) may cause carbide precipitation, leading to intergranular corrosion.
Good oxidation resistance for general high-temperature use (e.g., kitchen appliances).
1.4401:
Wider temperature range (short-term 950°C, long-term 800°C); superior high-temperature oxidation and sulfidation resistance.
Mo improves stability in harsh thermal cycles, making it suitable for heat treatment equipment and boiler components.
| Environment | Recommended Alloy | Rationale |
|---|---|---|
| Food processing/kitchenware | 1.4301 | Cost-effective, meets food-grade standards (e.g., FDA). |
| Marine/offshore | 1.4401 | Excellent seawater resistance, prevents chloride-induced pitting. |
| Chemical processing | 1.4401 | Resistant to acids/alkalis, especially Cl⁻-containing media. |
| Architectural decoration | 1.4301 | Low cost, good aesthetics after polishing. |
| High-temperature components | 1.4401 | Better creep resistance and oxidation stability at elevated temps. |
| Test Method | 1.4301 | 1.4401 |
|---|---|---|
| Salt Spray Test (ASTM B117) | 500–1000 hours (white rust) | 2000–3000 hours (no visible rust) |
| Pitting Potential (ASTM G61) | ~+200 mV (vs SCE) | ~+500 mV (vs SCE) |
| Intergranular Corrosion Risk | Requires solution annealing after welding | Reduced risk with low-carbon variant (1.4404) |
| Sulfuric Acid Resistance (5% H₂SO₄, 25°C) | Corrosion rate: 0.1 mm/year | Corrosion rate: 0.01 mm/year |
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