Preparation And Characterization Of Austenitic Corrosion Resistant Alloy For Leaf Guide Wheel By Powder Metallurgy

As the main working part of submersible electric pump,vane guide wheel is prone to wear and corrosion failure during operation.At present,high nickel cast iron is commonly used in vane guide wheels due to its good wear resistance and corrosion resistance.However,there are some problems in the preparation process of vane guide wheel with high nickel cast iron,such as scarce nickel resource,high cost and uncontrollable casting process.In order to solve the above problems,according to the performance requirements of low cost,high performance austenitic iron base alloy and the characteristics of powder metallurgy technology,powder metallurgy austenitic iron base material was prepared,and its process parameters,alloy composition and microstructure properties were designed and optimized.(1)In order to determine the appropriate sintering temperature,the microstructure,wear mechanism and corrosion mechanism of samples at four sintering temperatures of 1050,1100,1150 and 1200?were studied in this paper.The results showed that melting occurred at 1200?.When the sintering temperature was 1050?,the sintering mechanism was solid phase sintering.At 1100?and 1150?,the mechanism was instantaneous liquid phase sintering.According to the wear morphology,the main wear mechanisms of the three groups of samples were oxidation wear and adhesion wear,and the samples sintered at 1150?showed the best wear resistance.After electrochemical corrosion,a large number of corrosion pits appeared on the corrosion surface of samples sintered at 1050?due to their poor compactness.When the sintering temperature was 1100?,the matrix failure was weakened,but there were still multiple pitting holes on the corroded surface.With the increase of sintering temperature to 1150?,a few corrosion pits could be observed on the corrosion surface of the sample,but the matrix structure had good integrity.Therefore,in conclusion,the sintering temperature of 1150?was the most appropriate sintering temperature range.(2)After preliminary determination of sintering temperature,the alloy composition optimization was designed,according to the nickel equivalent formula.the equivalent amount of Mn was used to replace Ni to reduce the cost.and the effect of the amount of Mn on the material microstructure,physical and mechanical properties,wear resistance and corrosion resistance was analyzed.At the same time,the sintering sample Mn0-P and the traditional sample Mn0-C were compared.The results showed that the morphology,distribution and size of free graphite in sintered samples were significantly different from those in traditional cast iron samples.The graphite in sintered sample was finer and more evenly distributed.In the sintered samples,the addition of Mn promoted the formation of(Fe,Mn)₃C phase.When5wt.%Mn was added to the sintered samples,the wear resistance of the samples was the best.After electrochemical corrosion,when 5wt.%Mn was added,the corrosion resistance of the sample was enhanced.The reason was that(Fe,Mn)₃C phase was formed after the addition of Mn,which reduced the potential difference between the matrix and the second phase.With the increase of 10wt.%Mn,the corrosion resistance of the sample decreased sharply,which might be due to the decrease of a large amount of Ni which reduced the potential of the matrix.Therefore,the sample containing5wt.%Mn showed good wear resistance and the best corrosion resistance.(3)The combination of Mn and N instead of Ni could further strengthen the austenite structure.However,it was difficult to introduce nitrogen into high nickel cast iron and high pressure smelting was needed.The purpose of this paper was to introduce nitrogen into powder metallurgy to stabilize the austenite structure by nitrogen sintering,and to study the microstructure,wear mechanism and corrosion mechanism of sintering under vacuum,argon and nitrogen sintering atmosphere.The results showed that the matrix microstructure of vacuum sintered samples was austenite and pearlite,and that of argon sintered samples and nitrogen sintered samples was austenite.In addition,there were dark gray lumps in the structure of nitrogen sintered samples.Through EPMA microanalysis and TEM analysis,it was confirmed that the gray mass is Mn Si N₂,and the solid solution was 0.5wt.%N in the nitrogen sintered sample.The strengthening mechanism of nitrogen includes solid solution strengthening and precipitation strengthening.The wear mechanism of the three groups of samples was mainly oxidation wear.Nitrogen sintered samples showed good wear resistance,which was due to the enhancement of nitrogen element to austenite solution and Mn Si N₂precipitation,so that their initial hardness was higher,and they could effectively resist the material loss caused by grinding during the wear process.After electrochemical corrosion,the corrosion resistance of nitrogen sintered sample was worse than that of argon sintered sample.The reason was that the formation of Mn Si N₂ caused the loss of Si element in the substrate,thus reducing the electrode potential of the substrate material.Besides,Si O₂ oxide film could not be formed on the surface of the substrate,so the corrosion resistance became worse.In conclusion,among the three sintering atmospheres,nitrogen sintering was the most beneficial to the hardness and wear resistance of the samples.Compared with nitrogen sintering and vacuum sintering,argon sintering had a more favorable effect on the corrosion resistance of the samples.(4)In order to further determine the effect of nitrogen pressure,the effects of nitrogen sintering pressure of 0.05MPa,0.5MPa and 1MPa on the microstructure,wear resistance and corrosion resistance of the samples were studied.The results showed that when the sintering pressure was 0.05 MPa,the nitrogen content in the matrix was0.05wt.%.When the sintering pressure was 0.5 MPa,the nitrogen content of matrix was 0.27wt.%.When the sintering pressure was 1MPa,the nitrogen content of matrix was 0.47wt.%.When the sintering pressure decreased from 1MPa to 0.5MPa,the content of Mn Sin2 phase decreased.When the sintering pressure was 1MPa,the surface of the sample had good integrity and exhibits the best wear resistance.When the sintering pressure decreased from 1MPa to 0.5MPa,the corrosion tendency decreased,the corrosion velocity slowed down,and the corrosion resistance was better.The reason might be that the precipitation amount of Mn Si N₂ decreased.When the sintering pressure continued to decrease to 0.05MPa,the corrosion tendency increased,the corrosion speed became faster and the corrosion resistance became weaker.This might be due to the decrease of N content in the sample leading to the decrease of the potential of the matrix,so the corrosion resistance became worse.In this paper,the microstructure and properties of low nickel austenitic Fe-base alloys prepared by powder metallurgy were studied,which provided a new idea for the preparation of low nickel austenitic cast iron,and also provided a theoretical basis and reference for the preparation of low nickel austenitic cast iron with low cost and good comprehensive properties.