400 series stainless steel is an alloy of iron, carbon and chromium. Because it does not contain nickel, it is a nickel-saving stainless steel, also known as stainless steel. 400 series stainless steel contains martensitic structure and iron element, which not only has normal magnetic properties, but also has strong resistance to high temperature oxidation. Compared with carbon steel, its physical and mechanical properties are further improved. And most 400 series stainless steels can be heat treated.

1. Composition and characteristics
The commonly used 400 series stainless steel varieties are 430, 410, 420, 409L, etc., of which 430 stainless steel is used the most. The chromium content of 430 stainless steel is 18%, which is characterized by low price, small thermal expansion coefficient, and chloride stress corrosion resistance better than 300 series stainless steel varieties; but its shortcomings are relatively obvious: formability, weldability and tensile strength. It is smaller than the 300 series stainless steel model, so its scope of use is limited. The chromium content of 410 and 420 stainless steel is 13%, and their main feature is high hardness. 400 series stainless steel has the same corrosion resistance as 300 series stainless steel in oxidizing media such as atmosphere, fresh water and nitric acid under the same chromium content, and is better than 200 series stainless steel. Adding trace amounts of niobium, titanium, copper, aluminum and other elements can improve its deep drawing performance, weldability, corrosion resistance and high temperature strength, and can partially replace 300 series stainless steel.

2. Steel classification
We know that stainless steel can be divided into ferrite, martensite and austenite according to different metallographic structures, while 400 series stainless steel is mainly ferrite and martensite.
Ferritic stainless steel: The chromium content is generally 12% to 30%, usually without nickel, and sometimes with a small amount of Mo, Ti, Nb and other elements, and the matrix structure is ferritic stainless steel in use. It has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, and excellent stress corrosion resistance. However, there are disadvantages such as poor plasticity, significantly reduced post-weld plasticity and corrosion resistance. The application of out-of-furnace refining technology (AOD or VOD) can greatly reduce interstitial elements such as carbon and nitrogen, making it widely used. Common 400 series stainless steel models are 430 and 409L.

Martensitic stainless steel: stainless steel with a chromium content of not less than 12% (usually 12% to 18%), a high carbon content, a martensitic structure in use, and whose mechanical properties can be adjusted by heat treatment. In layman's terms, it is a type of hardenable stainless steel. Common 400 series stainless steel models are 410, 420, 440, and 436L.

3. Scope of application
400 series stainless steel has a wide range of applications. Below I will show you some related application fields. Exhaust pipe, muffler, tail pipe, catalytic converter, etc. of automobile exhaust system, the main steel grades are 409L, 444, 436L, 439, 441, 429.

Washing machine inner barrel, the main steel grades are 439, 430, 430J1

Tableware, kitchen sinks, soup utensils, composite pot bottoms, etc., the main steel grades are 430, 420J1, 420J2, 410s.

Building roofing materials, the main steel grades are 445 and 446M.

Summary: 400 series stainless steel occupies the same important position in our life as 200 and 300 series stainless steel, and is an indispensable good helper in our life. No matter where the weather is hot or cold, they are always ready for every job with their robustness!