Classification of Stainless Steel
Stainless steel vary In their composition from a fairly simple alloy of iron with 11% chromium, to complex alloys that include 30% chromium substantial quantities of nickel and half a dozen other effective elements.
Based on the alloy content and the internal structure , on rapid cooling, stainless steels are classified into three major categories viz: Austenitic,Ferritic and Martensitic.
The Austenitic stainless steel contains 16 to 26% chromium and 6 to 22% nickel. They are non-magnetic and have excellent corrosion resistance. They are not hardenable by heat treatment however they can develop high strength even on light cold working. They have excellent weldability,formability, hygiene factor and cryogenic properties. They are identified in the AISI 300 series.
The Ferritic stainless steel contains 12 to 30% chromium without any nickel. They are ferro-magnetic in nature and generally not hardenable by heat treatment. These steels possess good resistance to corrosion and fair weldability. They are identified in the AISI 400 series.
The Martensitic stainless steel contains 11 to 14% chromium without any nickel, but with a slightly higher carbon content compared to the Austenitic and Ferritic stainless steels. They are ferro-magnetic in nature and hardenable by heat treatment. They possess moderate corrosion resistance, poor weldability and are identifies