| The content of Cr,Ni,Mo and other alloy elements in super austenitic stainless steel(SASS)is significantly higher than that of conventional austenitic stainless steel.Its matrix is stable austenitic structure and has better high temperature resistance and corrosion resistance.Therefore,SASS is widely used in flue gas desulfurization,papermaking and pulp industry,seawater desalination,pharmaceutical industry and many other fields.However,in the process of heat treatment,high content of alloy elements tend to segregate,resulting in the precipitation of brittle second phase(such as sigma phase and laves,etc.),which leads to hot rolling cracking and delamination in the process of heat treatment,and seriously worsens the hot working performance and corrosion resistance of SSASs.The research shows that the rare earth element cerium(Ce),as a microalloy element,can not only refine the grain,but also inhibit the segregation of Cr,Mo and other alloy elements,so as to inhibit the precipitation behavior of the second phase and refine the size of the second phase.Therefore,the addition of Ce to SASSs can optimize the corrosion resistance of SASSs by regulating the segregation behavior of alloy elements.In this study,in order to solve the problem of the precipitation of the second phase during heat treatment and the decline of corrosion resistance of S31254 super austenitic stainless steel,S31254-Ce containing 0.04 wt.% Ce was prepared.The effects of different heat treatment processes on the second phase dissolution and precipitation behavior of S31254-Ce superalloy steel were investigated by observing the microstructure of samples(metallographic microscope and scanning electron microscope).At the same time,the corrosion resistance of S31254-Ce after heat treatment(potentiodynamic polarization test,impedance spectrum test and double ring potentiodynamic activation test)was tested,and the effects of different heat treatment processes on the corrosion resistance of the test steel were discussed.The following conclusions can be drawn:(1)Firstly,S31254-Ce was heat treated at 1130℃,1150 ℃,1170 ℃,1220℃,1190 ℃and 1250 ℃.The microstructure shows that the second phase in S31254-Ce begins to dissolve at 1170 ℃.With the increase of solution temperature and solution time,the degree of dissolution of the second phase in the sample increase and the grain size also increases.After solid solution treatment at 1190 ℃ for S31254-Ce,not only the second phase dissolved completely,but also the grain size was moderate,which can achieve the best dissolving effect.Solid solution treatment at 1190 ℃,1220 ℃ and 1250 ℃ can completely dissolve the second phase in S31254-Ce.The corrosion resistance of S31254-Ce is the best after solution treatment at 1190 ℃.(2)Secondly,S31254-Ce were aged at different temperatures and times.The microstructure shows that during 800 ～ 1100 ℃ aging treatment,with the increase of aging temperature and time,the number and size of the second phase in S31254-Ce increase,and the precipitation rate of the second phase first increases and then slows down.The particle precipitated with network distribution appeared within the grains,and the precipitation morphology was the most obvious under 860 ℃ aging treatment.After the aging temperature is further increased,the second phase of S31254-Ce was mainly distributed in strips along the grain boundary,gradually evolved from intermittent short strips to continuous strips,and the width also gradually increased.The corrosion resistance of S31254-Ce decreases with the increase of aging temperature.The aging sample treated at 800 ℃ has the best corrosion resistance.(3)The heat treatment process of S31254-Ce was improved.The microscopic results show that air cooling treatment and heat preservation at 300 ℃ are beneficial to inhibit the aging precipitation behavior of S31254-Ce.After the combined treatment,the inhibition effect on the aging precipitation behavior of S31254-Ce was more significant.At the same time,air cooling treatment and heat preservation at 300 ℃ can also significantly improve the pitting corrosion resistance and intergranular corrosion resistance of S31254-Ce after aging,and the combined treatment can improve the corrosion resistance more significantly. |
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