Effects Of Variable Temperature Sintering And TiC Particle Reinforcement On The Microstructure And Properties Of 20Cr Hypoeutectic High Chromium Cast Iron

In this paper,based on the urgent need to improve the production process control capability of sintered high chromium cast iron and expand the application prospects,sintered high chromium cast iron(SHCCI)and TiC reinforced sintered high chromium cast iron(TiC-SHCCI)composite were prepared by supersolidus phase liquid phase sintering technology.The effect of variable temperature sintering process and the addition of TiC particles on the microstructure and mechanical properties of sintered high-chromium cast iron and its internal relationship were systematically studied.It is expected to provide a solid foundation for the high-quality and efficient production of sintered high-chromium cast iron.This paper analyzes the chemical composition,phase composition and three-dimensional carbide morphology of the prepared sintered high-chromium cast iron and TiC-SHCCI composite.The physical and mechanical properties such as the density,Rockwell hardness,impact toughness,and bending strength of the corresponding materials were tested.The effect of variable temperature sintering process on the structure and properties of SHCCI was explored;the optimized variable temperature sintering process of sintered high cast iron within the experimental range was obtained.The influence of the amount of reinforced TiC particles on the structure and properties of sintered high cast iron is revealed.The above research results show that:The variable temperature sintering process can increase the sintering temperature range of 20Cr SHCCI.Its maximum sintering temperature is increased from the original 1235?to1255?.The variable temperature sintering process is divided into two stages:high-temperature sintering stage and low-temperature sintering stage.The effect of these two stages on microstructure and performance has its own focus.In the first stage,as the sintering temperature increases,the microstructure of the sintered high-chromium cast iron becomes coarse when the sintering time is the same.By comparing the effects of sintering time and sintering temperature on the volume fraction of carbides in the microstructure,it is found that the high-temperature sintering time has a greater impact than the high-temperature sintering temperature.Therefore,the high-temperature sintering time should be controlled not to exceed 15 min when designing the variable temperature sintering process.In the low-temperature sintering stage,low-temperature sintering can improve the charging and analysis of carbide-forming elements in the matrix of high-chromium cast iron,and the performance shows that the hardness decreases and the toughness increases.Low temperature sintering temperature will significantly affect the precipitation and morphology of carbides.Therefore,if more wear-resistant phases are to be obtained,the sintering temperature should be controlled to be higher when designing a variable temperature sintering process.In this case,more liquid phase is generated so that carbides can be fully precipitated.If HCCI want to improve the carbide morphology and toughness,HCCI should control the sintering temperature to produce only a small amount of liquid phase.Within the test range,the optimized variable temperature sintering process of 20Cr sintered high chromium cast iron is:1255?*5min+1190?*80min.The density,hardness,impact toughness and bending strength of 20Cr sintered high chromium cast iron prepared under this process are:7.53 g/cm³?58.3HRC?7.9 J/cm² and 2180.4 MPa.Through the process of electrolytic extraction and centrifugal separation,M₇C₃ carbide samples in 20Cr sintered high-chromium cast iron were obtained,and it was found that M₇C₃carbides had a hexagonal prism shape.With the extension of the sintering time,the size of the M7C3 carbide becomes larger,and the degree of connection continues to increase.TiC reinforced sintered high-chromium cast iron composite materials with an additive amount of 5wt.%To 40wt.%Were prepared by super solid phase liquid phase sintering technology.As the amount of TiC added increases,the relative density of TiC-SHCCI composites increases first and then decreases.In the microstructure,the size of the matrix phase becomes smaller,and the morphology of the matrix is distributed from larger blocks to smaller islands.At the same time,the size of M₇C₃ carbides in the matrix becomes smaller.From the analysis of the size and distribution of TiC,most TiC can be well combined with adhesion,but a small amount of TiC agglomeration has always existed.From the analysis of the size and distribution of TiC,most TiC particles can be well combined with adhesion,but a small amount of TiC agglomeration has always existed.As the amount of TiC added increases,the hardness of the composite gradually increases.When the mass fraction increases to 30%,the hardness reaches the maximum value of 70.5HRC,and then decreases;the impact toughness continues to decrease.When the TiC mass fraction is 30%,TiC-SHCCI composites have the best comprehensive mechanical properties,and their density,hardness,impact toughness and flexural strength are 6.46g/cm³,70.5HRC and 1.4 J/cm²,respectively.The quenching heat treatment process(1050?×2h+air cooling)improves the hardness of TiC-SHCCI composites with low TiC addition and reduces its impact toughness.This is mainly caused by the increased martensite content in the matrix.