The Difference between Stainless Iron and Stainless Steel—Part Two

Ferritic stainless steel:
Ferritic stainless steel is steel with ferrite structure in use. The chromium content is 11%-30%, and it has a body-centered cubic crystal structure. This kind of steel generally does not contain nickel, and sometimes contains a small amount of elements such as Mo, Ti, Nb, etc. This kind of steel has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent stress corrosion resistance, etc., and is mostly used to manufacture parts resistant to atmospheric, water vapor, water and oxidative acid corrosion. This kind of steel has some disadvantages, such as poor plasticity, obvious decrease of plasticity and corrosion resistance after welding, which limits its application. The application of refining technology outside the furnace (AOD or VOD) can greatly reduce interstitial elements such as carbon and nitrogen, thus making this kind of steel widely used.

Austenitic-ferritic duplex stainless steel:
It is stainless steel with austenite and ferrite structure accounting for about half of each other. Under the condition of low C content, Cr content is 18%-28% and Ni content is 3%-10%. Some steels also contain alloy elements such as Mo, Cu, Si, Nb, Ti and N. This kind of steel has the characteristics of both austenitic and ferritic stainless steel. Compared with ferritic steel, it has higher plasticity and toughness, no brittleness at room temperature, significantly improved intergranular corrosion resistance and weldability, while maintaining the brittleness of ferritic stainless steel at 475℃, high thermal conductivity and superplasticity. Compared with austenitic stainless steel, it has higher strength, intergranular corrosion resistance and chloride stress corrosion resistance. Duplex stainless steel is a nickel-saving stainless steel with excellent corrosion resistance.