Differences between stainless steel and stainless iron

How to identify stainless steel and stainless iron products? We can identify from their marks. A lot of stainless steel products have their marks on the surface, for example 13-0 and 18-8, the first number means the Chrome content and the second number means nickel content. Like 13-0 which contains only chromium but not nickel, commonly known as "stainless iron"; while 18-8 contains chromium and nickel, which is stainless steel. Or we can judge from their sounds by knocking. We can also use the magnetism method. For the real stainless steel wouldn't be attracted by the magnet, but stainless iron would. Performances of stainless iron and stainless steel are different, but they are significantly better than wrought iron and cast iron cookware when it comes to anti-corrosion ability.

Identification of stainless steel
Austenitic stainless steel
Stainless steel with austenitic structure at normal temperature, when the steel contains about 18% of Cr, 8% -10% of Ni, 0.1% of C, it has stable austenitic structure. Austenitic chromium nickel stainless steel includes the famous 18Cr-8Ni steel and high Cr-Ni series steel that develops from 18Cr-8Ni steel, which increases the Cr, Ni content and adds Mo, Cu, Si, Nb, Ti. Though Austenitic stainless steel is non-magnetic and has high tenacity and plasticity, its strength is low, we can only strengthen it by cold processing instead of phase change. If we add S, Ca, Se, Te, the stainless steel would have good machinability. Besides oxidative and acid resistance, this kind of steel would have sulfuric acid, phosphoric acid, formic acid, acetic acid and urea resistance if the stainless steel contains Mo or Cu. If the steel's carbon content is less than 0.03% or it contains Ti, Ni, the intergranular corrosion resistance can be greatly improved. High silicon austenitic stainless steel concentrated nitric acid has good corrosion resistance. As austenitic stainless steel has a comprehensive and good performance, it is widely used in all walks of life .

Ferritic stainless steel
Stainless steel that mainly contains ferritic organization in the statement of using, its chromium is 11% -30%, which has a body-centered cubic crystal structure. This kind of steel generally has no nickel and sometimes also contains a small amount of Mo, Ti and Nb, which has characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, excellent resistance to stress corrosion. It is used for component that is resistance to vapor, water and oxidization acid corrosion. This sort of steel has disadvantages of poor plasticity, obviously lower plasticity and corrosion after welding, which limits its application. The use of furnace refining technology (AOD or VOD) can make carbon, nitrogen and other interstitial elements greatly reduce, so this type of steel can be widely used.

Austenite-ferrite duplex stainless steel
Austenite-ferrite duplex stainless steel refers to stainless steel which has half austenite and ferrite structure. In the case of low C, it contains 18% -28% of Cr, 3% -10% of Ni, some steel also contain alloy elements like Mo, Cu, Si, Nb, Ti, N, etc. Austenite-ferrite duplex stainless steel has  same characteristics as austenitic and ferritic stainless steel. Compared with the ferrite, austenite-ferrite duplex stainless steel has higher plasticity, tenacity, higher toughness, no room temperature brittleness, resistance to intergranular corrosion and welding performance. At the same time, it still maintain 475 ℃ brittleness and high thermal conductivity with super plasticity, which are ferrite stainless steel's characteristics. Compared with austenitic stainless steel, austenite-ferrite duplex stainless steel has high strength and its resistance to intergranular corrosion and chloride stress corrosion has improved significantly. Duplex stainless steel has excellent resistance to pitting corrosion, which is also Nickel-efficient stainless steel.