Nickel is the main alloying element that forms austenite, but the role of nickel can only be fully demonstrated when combined with chromium. If you simply use nickel, in order to obtain a pure austenite single-phase structure in low-carbon nickel steel, the nickel content needs to reach more than 24%. In fact, when the nickel content needs to reach 27%, the corrosion resistance of stainless steel can be significantly improved. Therefore, there is no single nickel as an alloying element in stainless steel. When nickel and chromium are combined, the corrosion resistance of nickel can be significantly improved. For example, adding a small amount of nickel to ferritic stainless steel can transform the metallographic structure from single-phase ferrite to austenite Ten-ferrite dual-phase structure, so that its strength can be improved by heat treatment. If the nickel content is further increased, it becomes a single-phase austenite. For example, after adding 8% nickel to a steel with a chromium content of 18%, a complete austenite structure can be obtained. This is the reason why 18-8 chromium-nickel austenitic stainless steel is widely used, because it has high corrosion resistance, good deformation, weldability, and no magnetism.

Nickel can expand the range of passivation and improve corrosion resistance, especially in non-oxidizing media (such as dilute sulfuric acid).

Nickel has a weaker tendency to form carbides than iron, which can promote graphitization and weakly increase the hardenability of steel. In medium carbon and high carbon steels, when the content reaches the effective content value, austenite tends to remain after quenching.

In addition, adding nickel to chromium stainless steel can improve the corrosion resistance of chromium stainless steel in sulfuric acid, acetic acid, oxalic acid and neutral salts (especially sulfate).