One of the main reasons for adding nickel to stainless steel is to form austenite crystal structure, thus improving the plasticity, weldability and toughness of stainless steel, so nickel is called austenite forming element.
The crystal structure of ordinary carbon steel is called ferrite, which has a body-centered cubic (BCC) structure. The addition of nickel promotes the change of crystal structure from body-centered cubic (BCC) structure to face-centered cubic (FCC) structure, which is called austenite. However, nickel is not the only element with this property.
Common austenite forming elements are: nickel, carbon, nitrogen, manganese and copper. The relative importance of these elements in the formation of austenite is of great significance for predicting the crystal structure of stainless steel.