Stainless steel refers to steel that is resistant to the corrosion of weak corrosive media such as air, steam, and water, as well as chemical corrosive media such as acids, alkalis, and salts. It is also known as stainless acid - resistant steel. In practical use, the steel that is resistant to weak corrosive media is often called stainless steel, and the steel that is resistant to chemical media is called acid - resistant steel. Due to the difference in chemical composition between the two, the former is not necessarily resistant to the corrosion of chemical media, while the latter usually has non - corrosive properties. The corrosion resistance of stainless steel depends on the alloy elements contained in the steel.
Some special steels, such as austenitic stainless steel among stainless steels, have a relatively high content of chromium and nickel (the chromium content is about 18% and Ni is more than 4%) added to the steel. The internal structure of the steel shows a microstructure called austenite. This kind of microstructure is non - magnetic and cannot be attracted by magnets. However, some stainless steels used for making knives and scissors are made of martensitic stainless steel. This kind of stainless steel must undergo heat treatment to change its internal structure. Only after increasing the hardness can it be used to make knives and scissors. But the internal structure of this kind of stainless steel is tempered martensite, which is magnetic and can be attracted by magnets.
