400 series stainless steel is an alloy of iron, carbon and chromium. Because it does not contain nickel, it is a nickel-free stainless steel, also known as stainless iron. 400 series stainless steel contains martensitic structure and iron, not only has normal magnetic properties, but also has a strong high-temperature oxidation resistance, compared with carbon steel, its physical and mechanical properties have been further improved. And most 400 series stainless steels can be heat treated.
Composition and characteristics
The commonly used 400 series stainless steel varieties are 430, 410, 420, 409L, etc., of which 430 stainless steel is the most used. The chromium content of 430 stainless steel is 18%, which is characterized by cheap price, small thermal expansion coefficient and better resistance to chloride stress corrosion than 300 series stainless steel varieties. However, its shortcomings are relatively obvious: formability, weldability and tensile strength are less than 300 series stainless steel models, so it limits its range of use. The chromium content of 410 and 420 stainless steel is 13%, and their main feature is high hardness.
400 series stainless steel in the same chromium content, in the atmosphere, fresh water and nitric acid such as oxidizing media, its corrosion resistance is the same as 300 series stainless steel, and better than 200 series stainless steel. Adding trace 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.
Steel grade classification
We know that according to the different metallographic organization, stainless steel can be divided into ferrite, martensite and austenite three kinds, and 400 series stainless steel is mainly ferrite and martensite.
Ferritic stainless steel: Chromium content is generally 12% to 30%, usually does not contain nickel, sometimes contains a small amount of Mo, Ti, Nb and other elements, in the use of the state of the matrix structure of ferritic stainless steel. It has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent stress corrosion resistance, etc., and is widely used in the manufacture of parts resistant to atmospheric, water vapor, water and oxidizing acid corrosion. But at the same time, there are some disadvantages such as poor plasticity, post-welding plasticity and corrosion resistance. The application of off-furnace refining technology (AOD or VOD) can greatly reduce the gap elements such as carbon and nitrogen, making it widely used. The common 400 series stainless steel models are 430 and 409L.
Martensitic stainless steel: the chromium content is not less than 12%(generally 12%~18%), the carbon content is high, the use of the state of the structure of martensite, through heat treatment can adjust its mechanical properties of stainless steel. Generally speaking, it is a kind of hardened stainless steel. The common 400 series stainless steel models are 410, 420, 440, 436L.
Scope of application
400 series stainless steel has a wide range of applications, and some relevant application areas are displayed below.
Automobile exhaust system exhaust pipe, silencer, tail pipe, catalyst, etc., the main steel types are 409L, 444, 436L, 439, 441, 429.
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