Microstructure And Properties Of Nitrogen Bearing Stainless Steel

Stainless Bearing steel was used for produce bearing of petrochemical industry and aviation.There are big eutectic carbide in the annealed and quenched microstructure of traditional stainless bearing steel because of large amount of carbon and chromium.That is harmful to steel’s contact fatigue life and corrosion resistance.In this test we produce three kind of stainless bearing steel which the nitrogen content is more than solubility limit under atmospheric pressure to study the material’s basic characteristics and change rules of microstructure and property by using metalloscope,SEM,TEM,XRD,mechanical property test,electrochemical test and so on.The result show that:(1)The nitrogen content of high nitrogen bearing stainless steel is up to0.42%. Annealed microstructure is ferrite+carbide+nitride,Quenched microstructure is martensite+carbide+nitride (low quenching temperature) or martensite+nitride (high quenching temperature).The carbide is M23C6and the nitride is (CrFe)2N1-x.The second phase is small and fine dispersion which the main size is between0.2-1.0μm.Also there is no large eutectic carbides in the annealed and quenched structure.The Hardness is up to58HRC while the steel is quenched between1000℃-1050℃,The steel has a secondary hardening peak when tempered at500℃,the hardness is up to HRC59.5.(2)The content of carbon,nitrogen,chromium have a big effect on the microstructure of high nitrogen bearing stainless steel.The tendency of formation of eutectic carbides is decreased by decreasing the content of carbon,chromium and increasing nitrogen. The turn of solution of second phase at heating stage was determined by content of carbon,nitrogen,Chromium.The carbide would completely dissolved before nitride did when steel contain high content of nitrogen and low content of carbon and chromium,otherwise the nitride would completely dissolved before carbide.(3)The hardness of high nitrogen bearing stainless steel could reach more than HRC58,the tensile strength could reach more than2000MPa.High hardness and strength were obtained through solid solution strengthening, dislocation strengthening refined crystalline strengthening and second phase strengthening.The impact toughness is as same as9Cr18indicate that nitrogen would not damage the impact toughness.(4)High nitrogen bearing stainless steel has an excellent Passivation ability, it mean that high nitrogen stainless bearing steel have higher Pitting corrosion resistance then Traditional stainless bearing steel, The function of nitrogen on.corrosion resistance is stronger than Chromium.