Stainless steel belongs to alloy, and metal material is not metal, because metal belongs to simple substance and stainless steel belongs to mixture. Stainless steel refers to steel resistant to weak corrosive media such as air, steam and water and chemical corrosive media such as acid, alkali and salt, also known as stainless acid-resistant steel.
In practical application, steel resistant to weak corrosive medium is usually called stainless steel, while steel resistant to chemical medium is called acid-resistant steel.
Because of the different chemical composition, the former is not necessarily resistant to the corrosion of chemical media, while the latter is generally stainless. The corrosion resistance of stainless steel depends on the alloying elements contained in the steel.