400 series stainless steel is an alloy of iron and carbon-chromium. This stainless steel has a martensitic structure and iron, so it has normal magnetic properties. 400 series stainless steel has strong resistance to high temperature oxidation, and compared with carbon steel, its physical and mechanical properties are further improved. Most 400 series stainless steels can be heat treated.

The commonly used 400 series stainless steel varieties include 430 type with 18% chromium and 410 and 444 types with 13% chromium, among which type 430 stainless steel is the most used. The 430 type stainless steel model is characterized by low price, low thermal expansion coefficient, and chloride stress corrosion resistance better than the 300 series stainless steel type; however, its disadvantage is that the formability, weldability and tensile strength are lower than that of the 304 type stainless steel model. , therefore, its field of use is limited. Under the same chromium content, in oxidizing media such as atmosphere, fresh water and nitric acid, the corrosion resistance of 400 series stainless steel is the same as that of 300 series stainless steel, and usually the corrosion resistance of 400 series stainless steel is better than that of 200 series stainless steel. . The addition of trace amounts of niobium, titanium, copper and aluminum to the 400 series stainless steel can improve its deep drawing performance, weldability, corrosion resistance and high temperature strength, and can partially replace the 304 type stainless steel model. At present, the 400 series stainless steel varieties after adding the above trace elements are SUS430LX, 430JIL, 444, 445M2, NSS447M1 and so on. In the United States and Japan, these models are widely used in automobile exhaust pipes (type 409 and 410L), washing machine drums (type 430), kitchen utensils, home appliances, medical equipment, water heaters, roof panels, curtain walls and power plant equipment.