Corrosion resistance of stainless steel
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Martensite is a change in the range of chromium content in steel that is about 13% and has a carbon content of 0.1%-0.4%. That is to say, the carbon content is high, and the carbon element reduces the rust resistance in stainless steel, so the rust resistance decreases with the increase of carbon content. And let's talk about martensitic stainless steel. Martensite and ferrite are often referred to as chromium stainless steel, and also called ferrochrome steel. Martensitic stainless steel is quite different from ferritic stainless steel. First, the formation mechanism is different; the carbon element in steel is austenite forming element. Martensite is austenite in high temperature zone and cooled to low temperature (room temperature) as martensite structure, that is to say, martensitic stainless steel has phase transformation. According to the cooling method and cooling rate, the quenching process can have different hardness and strength properties, but the plasticity is low, the cold deformation is poor, and the deformation is easy to crack after deformation. It needs to be annealed in time to eliminate stress treatment. Therefore, martensite can not be delivered after cold deformation.
When the chromium content of ferritic stainless steel is increased to more than 17% or the carbon content is reduced to less than 0.08%, the internal microstructure of ferrite is not phase transition at high temperature to low temperature. With the increase of chromium content, the corrosion resistance is also enhanced, but the deformation and hardening rate of ferritic stainless steel is very low and the deformation stress is low. The strength value can not be increased by cold deformation, but the plasticity is reduced, so that ferritic stainless steel becomes brittle and self cracked. The ferritic stainless steel has low temperature brittleness, which can not be applied to the device under the normal temperature (especially in the winter of the northeast region), and the brittle temperature at 475 degrees C, so the use range is narrow, which makes the use limit. If the content of the ferrite carbon is reduced to less than 0.001%, the nitrogen element in the steel is reduced to less than 0.001%, and the low temperature brittleness can be reduced to below -80 C, and the advantages of no nickel and rust prevention are shown.

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