Usually, people put the chromium content is more than 12% and nickel content more than 8% of alloy steel is stainless steel. This kind of steel in the atmosphere or in a corrosive medium has certain corrosion resistant ability, and under the high temperature (> 450 ℃) with high strength. Chromium content of 16% ~ 18% of steel called acid steel or acid stainless steel, traditionally known as stainless steel.

More than 12% chromium content in steel, in contact with the oxidizing medium, because of the electrochemical action, fast formation on the surface of a layer of rich chromium passivation membrane, protect the metal from corrosion inside; But in the oxidation corrosion medium, is still not easy to form strong passivation film. In order to improve the corrosion resistant ability of steel, usually increase the proportion of chrome or add can promote passivation of alloying elements, Ni, Mo, Mn, Cu, Nb, Ti, W, Co, etc., these elements not only improves the corrosion resistance of steel, at the same time changed the internal organization and the physical and mechanical properties of steel. Content of these alloying elements in steel is different, different influence on the performance of stainless steel, some magnetic, some nonmagnetic, some can be heat treatment, others can't heat treatment.

Due to the characteristics of stainless steel is, more and more widely used in aviation, aerospace, chemical, petroleum, construction and food industries and daily life. Of the alloying elements had a great influence on cutting processability, some even it is hard to cut.