| High speed steel and cemented carbide are widely used in the field of metal cutting because of their high hardness and good wear resistance.In recent years,with the continuous transformation and upgrading of Chinese manufacturing industry and the continuous emergence of all kinds of high-hardness and difficult-to-machining materials such as titanium alloy,superalloy and ultra-high strength steel,higher requirements for the comprehensive mechanical properties of cutting materials have been put forward.By adding hard phase to the high-speed steel matrix,the high-speed steel matrix composites prepared by powder metallurgy can maintain high strength and toughness and obtain excellent wear resistance and red hardness,which is expected to be a tool material to meet the requirements of high-efficiency sawing.Therefore,based on M42 high speed steel which is widely used in cutting field,this paper uses powder metallurgy vacuum sintering technology to develop WC particle（WCP）reinforced M42high speed steel composite,studies the microstructure and mechanical properties of the composites with different WCP content,and evaluates the effect of subsequent heat treatment,in order to provide reference for the development of high-strength,high-hardness and wear-resistant tool materials.In this paper,firstly,the preparation process of WCP/M42 high speed steel composites was studied,and the suitable ball milling time and pressing pressure were determined to be 12h and 350MPa,respectively.On this basis,the sintering densification law of the composites and the effect of WCP addition on the microstructure and mechanical properties of the composites were studied when the addition amount of WCP was 0～10wt.%.The results show that WCp/M42 high speed steel composites with a relative density of more than 98.5%can be prepared by vacuum sintering technology.The sintering density of the alloy increases at first and then tends to be stable with the increase of sintering temperature.When the sintering temperature is 1230℃and the addition amount of WC is 8wt.%,the relative density of the composite reached 98.93%.The phase composition of sintered composites isα-Fe,M6C carbide,M7C3 carbide and a small amount of M2C carbide,and WC hard phase completely dissolves and then transforms into M6C and M2C carbide during sintering.With the increase of WC addition,the fine and dispersed carbides in the matrix gradually decrease,while the carbides at the grain boundary tend to accumulate and grow,and the hardness of the sintered alloy decreases at first and then increases,and is lower than that of M42 powder high speed steel without WC addition,while the bending strength and impact toughness of the alloy decrease gradually.Furthermore,the subsequent heat treatment strengthening of WCP/M42 high speed steel composites was carried out,and the effects of quenching at 1140℃～1220℃×15min and tempering at 560℃×1h on the microstructure and mechanical properties of the alloy were studied.The results show that the quenched microstructure of the composite is composed of quenched martensite,retained austenite,M6C carbide and MC carbide.After three times tempering,the quenched martensite and retained austenite are transformed into tempered martensite and precipitate dispersed secondary carbides including M7C3.The volume fraction of carbides in the alloy decreases with the increase of quenching temperature,and too high temperature will also lead to the abnormal growth of austenite grains and the coarsening of undissolved carbides,and the precipitation amount of secondary carbides increases with the increase of WC addition,but it also leads to the accumulation and growth of carbides at grain boundaries.By comparing the tempering hardness of the alloy quenched at different temperatures,it is found that the hardness of the alloy is the highest after quenching at1200℃and tempering at 560℃,and increases with the increase of the amount of WC.When the addition amount of WC is 10wt.%,the hardness reaches the maximum value of 66.4HRC,which is as high as 17.7HRC compared with as-sintered.Under this process,the best combination of strength and toughness was obtained when the addition of WC was 8wt.%.The bending strength and impact toughness were1782.47MPa and 2.69J/cm2,respectively,and the hardness was 65HRC. |
