Effect Of Q&P Process On Microstructure And Properties Of Low Alloy Wear-resistant Steel

Low alloy wear-resistant steel is an material which is widely used for engineering,mining,metallurgy and electric machinery,because of the low alloy content and good comprehensive performance.However,the current heat treatment of low alloy wear-resistant steel is usually quenching and low temperature tempering process,strength and hardness of the steel are high,but there are also problems of low plasticity and toughness.In order to improve the comprehensive properties further and obtain a good combination of strength and toughness,Q&P(quenching-partitioning)process had been used in this paper.The microstructure was observed by mean of scanning electron microscope and transmission electron microscope;the content of retained austenite and the carbon content were measured and calculated by X-ray diffractometer;the mechanical properties were tested by means of a hardness tester and a universal testing machine.The effect of different Q&P process on the microstructure was studied,and the correlation between different Q&P process-microstructure-mechanical properties was analyzed.The results showed that the microstructure of the wear-resistant steel was consisted of initial martensite,fresh martensite and retained austenite after one-step Q&P or two-step Q&P process.There were two types of retained austenite,one was a thin film of 100-200 nm width,which mainly distributed between martensite laths;the other was a block of 300nm-1 μm,which mainly distributed at the grain boundary.With the increase of quenching temperature,the content of initial martensite decreased and the fresh martensite increased gradually.With the increase of the partitioning temperature,the edge of martensite laths appeared serrated and the laths arranged more regularly after the two-step Q&P process.With the increase of partitioning time,the martensite laths became fragmented and carbide precipitation increased.The bainite began to appear after the two-step Q&P process.The content of retained austenite and the carbon content increased first and then decreased with the increase of partitioning temperature and partitioning time.After two-step Q&P process,the content of retained austenite and the carbon content decreased gradually with the increase of quenching temperature.In contrast,the strength and hardness of the steel treated with two-stepQ&P process are slightly lower than that treated with one-step Q&P process,but better than the one-step Q&P process in terms of elongation and strength-ductility balance.The test steel treated by different processes could obtain similar retained austenite content and mechanical properties.Therefore,in the actual production process of steel,various process routes could be used to reduce the requirements on equipment and process parameters and improve the utilization of existing equipment according to the site conditions.