The main element that determines the corrosion resistance of stainless steel is chromium. This is because when the steel contains a sufficient amount of chromium, the steel can form a stable surface protective film with Cr2O3 as the matrix in an oxidizing medium; at the same time, chromium can effectively improve the solid solution (ferrite, martensite or austenite Intenite) electrode potential, so that the steel is not corroded.
The electrode potential of chromium to improve steel follows the n/8 rule. That is, when the chromium content reaches n/8 atoms (1/8, 2/8, 3/8... or 12.5%, 25%, 37.5%...), the electrode potential has a jump, and the atomic concentration of chromium accounts for 1/ 8 (ie 12.5%), if calculated by mass, it is 11.7%, so the chromium content of chromium stainless steel is above 12%.
