Characterization of Nickel Free Stainless Steel

Stainless steel is defined as a steel alloy with a minimum of 10.5-11% chromium content. It is produced, basically having three types of structures-ferritic, martensitic and austenitic. Generally, steels contain nickel as one of the alloy that increases its hardenability. But due to high cost and its reactivity with organic matter an alternative i.e. nickel free stainless steels are developed. High-strength austenitic stainless steels can be produced by replacing carbon with nitrogen. Nitrogen has greater solid-solubility than carbon, is a strong austenite stabilizer, potent interstitial solid-solution strengthener, and improves pitting corrosion resistance. The introduction of nitrogen causes linear increase in yield and tensile strength at room temperature. The increase in N2 concentration strengthens the austenitic steels further with the greater planar slip and higher density of deformation twin. The cold deformation of these steels later increases their hardness but at the same time decreases the ductility of these steels. So, these steels are properly heat treated to regain ductility.