Effect Of Rare Earth Ce On Microstructure And Oxidation Resistance Of 21Cr-11Ni Austenitic Stainless Steel

Austenitic heat-resistant steel is widely used in various high-temperature components because of its good corrosion resistance and high-temperature oxidation resistance.However,with the economic and social development of our country and the increasing demand for heat-resistant steel,the working conditions and environment of heat-resistant steel in various application fields are becoming more complicated,and the service range and temperature used are also increasing day by day,so the comprehensive utilization performance of materials at high temperature is improved,In particular,its resistance to high temperature and oxidation has been widely valued.Based on 21Cr-11Ni austenitic heat-resistant stainless steel S30815,two kinds of austenitic heat-resistant steels were prepared.The first experimental steel does not contain cerium,the second experimental steel contains cerium.The other compositions are the same as those of austenitic heat-resistant steel S30815.The existing forms,inclusions and microstructure of rare earth in three kinds of test steels were analyzed,and the oxidation kinetics was studied.The appearance,composition and phase of the oxide film were analyzed by SEM/EDS and XRD.The effect of rare earth on the microstructure and high temperature oxidation resistance of heat-resistant steel was studied,so as to improve the utilization rate of rare earth and the quality of heat-resistant steel.The results show that the existing forms of rare earth are solid solution and inclusion.The total content of Ce in 2#test steel is 84ppm,the solid solution content is74.78ppm and the inclusion content is 9.22ppm;The total content of Ce in S30815 steel is 220ppm,the solid solution content is 210ppm and the inclusion content is 10ppm.Compared with 1#test steel,the morphology of inclusions in 2#test steel and S30815test steel changed,the size and shape of some titanium inclusions decreased,and some edges and corners gradually disappeared and changed into ellipse.By observing the microstructure and measuring the grain size of as cast,hot rolled and cold rolled 1#and2#test steels,it is found that rare earth can refine the grain and make the grain more uniform.The isothermal oxidation kinetics curves of the three tested steels at 800?,850?and 900?conform to the parabolic law,namely Wagner oxidation theory.The results show that a small amount of flake structure oxide is formed in the late oxidation stage of1#sample,and part of flake structure oxide Cr₂O₃is formed in the early oxidation stage of 2#sample and S30815 sample,which is basically covered by closely bonded spinel oxide in the late oxidation stage.It shows that the formation of cerium oxide Cr₂O₃makes the oxide film more compact and more protective.The results show that the main oxidation products of sample 1#are ferronickel and ferrochrome compounds,and the main oxidation products of sample 2#and S30815 are Cr₂O₃.At 900?for 150h,the peak value of Cr₂O₃and Fe₃O₄oxides is the highest and the lowest in S30815.The results show that Ce is beneficial to the formation of protective oxidation product Cr₂O₃,which enhances the oxidation resistance of the sample.