The difference between 201 and 316 stainless steel is substantial, primarily concerning their chemical composition, corrosion resistance, and cost. They represent opposite ends of the spectrum within common austenitic stainless steels regarding performance in corrosive environments.
Composition:
- Type 201: Lower nickel (approx. 3.5-5.5%), higher manganese (approx. 5.5-7.5%), added nitrogen (up to 0.25%), and chromium (approx. 16-18%). Designed as a cost-saving alternative.
- Type 316: Higher nickel (approx. 10-14%), chromium (approx. 16-18%), and crucially, contains molybdenum (approx. 2-3%). Designed for superior corrosion resistance.
Corrosion Resistance: This is the most significant difference. Type 316 stainless steel offers vastly superior corrosion resistance compared to Type 201. The addition of molybdenum in 316 provides excellent protection against pitting and crevice corrosion, especially in chloride-rich environments (like seawater, de-icing salts, and many industrial chemicals). Type 201 has only moderate corrosion resistance and is unsuitable for marine applications or environments with significant chemical exposure; it can rust or pit relatively easily under such conditions. Grade 201 is best suited for mild, indoor, or non-corrosive settings.
Mechanical Properties: Type 201 generally has higher yield strength in the annealed state than Type 316 due to its nitrogen content. Both offer good ductility and toughness typical of austenitic steels.
Cost: Type 201 is significantly less expensive than Type 316 due to its lower nickel content and absence of molybdenum.
Applications:
- Type 201: Indoor decorative items, appliances, cookware, restaurant equipment, automotive trim (in less demanding locations), hose clamps.
- Type 316: Marine hardware, chemical processing equipment, pharmaceutical equipment, food processing in corrosive environments, medical implants, stainless steel tube for aggressive media, coastal architectural elements.
In essence, the choice between 201 and 316 is driven by the required corrosion resistance and budget. If high corrosion resistance, especially against chlorides, is needed, 316 is essential. If cost is paramount and the environment is mild, 201 might suffice.