The main role of nickel content in stainless steel is that it changes the crystal structure of the steel. One of the main reasons for the addition of nickel in stainless steel is the formation of austenitic crystal structures, which improve the properties of stainless steels such as plasticity, weldability and toughness, so nickel is called an austenite forming element.
The crystal structure of ordinary carbon steel is called ferrite, which is a body-centered cubic (BCC) structure. The addition of nickel promotes the transformation of the crystal structure from the body-centered cubic (BCC) structure to the face-centered cubic (FCC) structure. For austenite.
However, nickel is not the only element of this nature. Common austenite forming elements are: nickel, carbon, nitrogen, manganese, and copper. The relative importance of these elements in forming austenite is important for predicting the crystal structure of stainless steel.