Series 400 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 a martensitic structure as well as iron, which not only has normal magnetic properties, but also has a strong resistance to high temperature oxidation, and has further improved physical and mechanical properties compared to carbon steel. And most 400 series stainless steels can be heat treated.
Composition and characteristics
Commonly used 400 series stainless steel varieties are 430, 410, 420, 409L, etc., of which 430 stainless steel is the most used. 430 stainless steel chromium content of 18%, its characteristics are inexpensive, small coefficient of thermal expansion, chloride stress corrosion resistance better than 300 series stainless steel varieties; but its shortcomings are also relatively obvious: forming properties, weldability and tensile strength is less than 300 series stainless steel 410, 420 stainless steel chromium content of 13%, their main feature is high hardness.
400 series stainless steel in the same chromium content, in the atmosphere, fresh water and nitric acid such oxidizing media, its corrosion resistance and 300 series stainless steel, and better than 200 series stainless steel. The addition of trace elements such as niobium, titanium, copper and aluminum can improve its deep-drawn properties, weldability, corrosion resistance and high-temperature strength, and can partially replace the 300 series stainless steel.
Classification of steel grades
We know that according to the different metallographic organization, stainless steel can be divided into ferritic, martensitic and austenitic three, and 400 series stainless steel is mainly ferritic and martensitic.
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 state matrix organization for the ferritic stainless steel. With a large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent stress corrosion resistance, etc., mostly used in the manufacture of atmospheric, water vapor, water and oxidizing acid corrosion resistant parts. But at the same time there is poor plasticity, plasticity and corrosion resistance significantly reduced after welding and other disadvantages. The application of off-furnace refining technology (AOD or VOD) can make carbon, nitrogen and other interstitial elements are greatly reduced, so that it is widely used. Common 400 series stainless steel models are 430, 409L.
Martensitic stainless steel: chromium content of not less than 12% (generally in 12% to 18%), high carbon content, the use of state organization for martensite, through heat treatment can adjust its mechanical properties of stainless steel. In layman's terms, it is a class of hardenable stainless steel. Common 400 series stainless steel models 410, 420, 440, 436L.
Application range
The 400 series stainless steel has a wide range of applications.
The main steel grades are 409L, 444, 436L, 439, 441, 429 for exhaust pipes, silencers, tail pipes, catalytic converters, etc. of automobile exhaust systems.
Washing machine inner drum, the main steel grades are 439, 430, 430J1.
Tableware, kitchen sink, soup serving utensils, composite pot bottom, etc., the main steel grades are 430, 420J1, 420J2, 410s.
Building roofing materials, the main steel grades are 445, 446M.