With 18% chromium, how much percent of nickel is necessary for stainless steel to be austenitic?

To achieve an austenitic structure in stainless steel, the composition typically requires a specific balance of chromium and nickel. Austenitic stainless steels are primarily characterized by their high chromium content (often above 18%) and a sufficient amount of nickel that stabilizes the face-centered cubic (FCC) austenitic phase at room temperature.

When chromium is at 18%, it generally correlates with the need for approximately 8% nickel to maintain the austenitic structure. This nickel addition helps to enhance corrosion resistance, ductility, and weldability, critical properties of austenitic stainless steels.

Nickel acts as a stabilizer for the austenite phase, preventing the steel from transforming into more brittle phases at lower temperatures. It is also vital to enable the steel to maintain its toughness and corrosion resistance.

If the nickel content were lower than 8%, the steel might not fully develop the desired austenitic structure, potentially leading to other crystallographic phases that are not desirable for applications requiring toughness and ductility. Thus, the 8% nickel addition at 18% chromium is essential to achieve the right balance for an austenitic stainless steel formulation.