Sintering Preparation And Properties Of 15Cr Hypoeutectic High Chromium Cast Iron

High chromium cast iron is widely used due to its excellent wear resistance.However,the conventional cast high chromium cast iron has a severe cracking of the base due to the large amount of petal-like carbides,resulting in insufficient toughness of the alloy to limit its wear resistance.Sintering high chromium cast iron can effectively improve the alloy structure and greatly improve the mechanical properties.In addition,the lower cost 15Cr high chromium cast iron has less carbide content and more matrix content and better mechanical properties than 25Cr and 20Cr high chromium cast iron.Therefore,this paper uses supersolids liquid phase vacuum sintering technology to prepare 15Cr hypoeutectic sintered high chromium cast iron.Firstly,the influence of sintering process on the microstructure and mechanical properties of 15Cr hypoeutectic high chromium cast iron was discussed.The microstructure was analyzed by computer quantitative analysis to determine the correlation between microstructure and performance.The results show that the alloy microstructure consists of martensite,M₇C₃ carbide and a small amount of retained austenite.Full-density samples can be obtained by supersolids liquid phase vacuum sintering,and the fine rounded short rod-shaped M₇C₃ type carbides are uniformly distributed along the grain boundary and the subgrain boundary so that the alloy has high hardness and good toughness.The sintering process changes the hardness and toughness of the alloy by affecting the degree of densification of the sintered product and the carbides in the structure.Among them,the optimum sintering temperature of C2.4Cr15 is 1210°C.The alloy density was 7.62g/cm³,the hardness was 59.6HRC,the impact toughness was 11.3J/cm²,and the bending strength was 2506.8MPa.Secondly,the effects of carbon and chromium content on the properties of sintered high chromium cast iron were investigated,and the impact abrasive wear test of 15Cr sintered high chromium cast iron was carried out.The test results show that the carbon content affects the mechanical properties mainly by affecting the carbides in the sintered high chromium cast iron structure.The optimum sintering temperature for C2.7Cr15 is 1200°C.The alloy density was 7.50g/cm³,the hardness was58.38HRC,the impact toughness was 10.45J/cm²,and the bending strength was2251.66MPa.The mechanical properties of sintered high chromium cast iron are obviously better than those of similarly cast high chromium cast iron.The hardness of15Cr hypoeutectic sintered high chromium cast iron is reduced by about 1HRC and3HRC compared with 20Cr and 25Cr,respectively,and the impact toughness is improved by 17.7%and 57%respectively.It is an excellent wear resistant material with higher cost performance.The wear forms of 15Cr sintered high chromium cast iron under different impact energy are mainly cutting wear.There is no periodic spalling wear and its wear resistance is excellent.Finally,the effect of heat treatment on the microstructure and properties of C2.4Cr15 with high comprehensive performance was studied.The results show that the microstructure after quenching is mainly martensite,retained austenite and M₇C₃type carbide.After the alloy is quenched,the carbides are more rounded than the sintered state,and are dispersed in a granular form in the matrix.As the quenching temperature increases,the secondary carbides in the structure first precipitate and then dissolve,and the matrix grains do not change much.The volume fraction of alloy carbides increases first and then decreases with the increase of quenching temperature.The hardness of air quenching and water quenching samples increased first and then decreased,reaching the maximum at 950°C,which were 64.86HRC and64.96HRC respectively.After the air quenching treatment,the strength and toughness of the sample increase first and then decrease with the increase of quenching temperature,reaching the maximum at 900°C,respectively:12.7J/cm²and2641.14MPa;the strength and toughness after water quenching decrease,reaching the maximum at 850°C,9.3J/cm² and 2504.23MPa.The sample after quenching at 900°C of C2.4Cr15 was tempered.As the tempering temperature increases,the secondary carbides precipitate,the primary carbide aggregate grows,and the carbide volume fraction increases.The matrix is transformed from high carbon quenched martensite to a more stable tempered structure.When the tempering temperature is less than 450°C,the hardness of the sample is basically 60-61HRC,and the hardness decreases significantly when the temperature continues to rise.The quenched sample reached a maximum hardness of60.9HRC at 450°C,and the water quenched sample reached a maximum hardness of60.96 HRC at 400°C.As the tempering temperature increases,the strength and toughness of the alloy first decrease and then increase.The air quenching and water quenching samples all reached the maximum mechanical properties at 250°C tempering:air quenching and tempering?11.28J/cm² and 2719.86MPa?,water quenching and tempering?9.4J/cm² and 2591.5MPa?.The best heat treatment process for C2.4Cr15 sintered high chromium cast iron is air cooling after 900°C for 120min.