Chromium is a ferrite forming element; chromium can strongly improve the passivation ability of iron. Chromium plays a decisive role in the corrosion resistance of stainless steel. In the definition of stainless steel, it is clearly stipulated that the chromium content is ≥10.5%, which is the main element of the corrosion resistance of stainless steel. The higher the chromium content in the steel, the better the corrosion resistance. This is because the steel can form a stable surface protective film (about 10μm) based on Cr2O3 in the oxidizing medium, that is, passivation occurs, and the chromium oxide Cr2O3 is enriched in this film. This chromium-rich oxide film has good stability in many media, thus improving the corrosion resistance of steel. At the same time, chromium can also effectively increase the electrode potential of the solid solution (ferrite, martensite or austenite), making the electrode potential of the original pure iron (low carbon steel) from negative to positive, so that the steel is not corroded.

In addition, chromium has a very good effect on the mechanical and technological properties of stainless steel. Chromium can improve the hardenability of steel and has been widely used in low alloy structures. This effect of chromium reduces the rate of transformation of austenite to ferrite and carbides, and shifts the austenite isothermal transformation diagram to the right, thereby reducing the critical cooling rate of steel for quenching and increasing the hardenability of steel. Some martensitic stainless steels can obtain martensitic structure by air quenching.

Chromium can improve the oxidation resistance of steel. As the chromium content increases, the oxidation resistance of steel will increase significantly. In martensitic chromium stainless steel, its oxygen resistance is 4 to 9 times higher than that of ordinary steel. The martensitic chromium stainless steel does not have a skin temperature of 700 to 850 ℃.

Chromium tends to form carbides in steel more than manganese and less than tungsten.

Chromium can improve the high temperature strength of steel and the wear resistance of high carbon steel.