These are nickel-free stainless steels. They have a varying chromium (Cr) content of 12- 18%, and a small amount of carbon (C), normally less than 0.10%.
Austenitic is the most widely used type of stainless steel, the basic composition is 18% Cr and 8% Ni (Grade 304). If further corrosion resistance is required 2-3% molybdenum (Mo) is added (Grade 316).
Martensitic stainless steels are very hard and strong and contains approximately 12-18% chromium. As they have carbon levels up to 1% they are not as corrosion resistant as Austenitic or Ferritic.
Duplex stainless steel contain relatively high chromium (between 18 and 28%) and moderate amounts of nickel (between 4.5 and 8%). Most duplex steels contain molybdenum in a range of 2.5 – 4%. Duplex may be referred to as ferritic-austenitic stainless steel as they a microstructure of approximately 50% ferritic and 50% austenitic 50%.
Precipitation hardening Stainless Steel have extra elements such as Copper, Niobium and Aluminium in their composition. These types of steel are designed to be machinable and then develop very high strength after fabrication by a single low temperature aging treatment.
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