2. Stainless steel structure

Stainless steels are iron-based metal alloys, or more precisely steel-based (iron-carbon alloy), which must contain at least 10.5% chromium (according to European standard EN 10088-1), and often other additives such as nickel (or its substitute, manganese), and, to a lesser extent, molybdenum.

Before examining the various equilibrium diagrams, it is useful to recall the allotropic varieties of iron:

• At low temperatures and up to 910°C, iron has a cubic-centered structure, known as α-iron;

• From 910°C, it is transformed into γ-iron, which has a face-centered cubic structure;

• a further transformation takes place at 1,400°C, yielding δ iron with a cubic-centered structure.

These transformations, which are reversible,...