Study Of Q&P Heat Treatment On Microstructure And Properties Of Low Alloy Wear Resistant Steel

Conventional heat treatment of low alloy martensitic wear-resistant steel is quenching and low-temperature tempering process, from which it can get tempered martensite structure which has a good combination of strength and toughness. In order to further improve the comprehensive performance of the material and apply in more high impact and wear working conditions, a novel heat treating process, Quenching and Partitioning (Q&P), has been used. The toughness can be greatly improved by raising the amount of retained austenite while the strength and hardness just have a little losses.In this paper, the microstructure and mechanical properties were studied by using optical microscopy(OM), scanning electron microscopy (SEM), EDS analysis,X-ray diffraction (XRD) and tensile test, the impact toughness test and rockwell hardness. The microstructure and properties have been discussed by comparison between conventional quenching and tempering process and Q&P process.Infullence of quenching temperature, parititioning temperature and time on properities of the steel was studies by using orthogonal experimental. According to the result of orthogonal test, quenching temperature is the most significant influence for impact energy and partitioning time for tensile strength. Different process parameters have little influence on the hardness (The maximum and minimum differs1.8HRC).With the increase of quenching temperature, the impact energy of the material decreased at first and then increased, and the tensile strength gradually decreased; With the prolonging of partitioning time, the impact energy of the material presents the downward trend while the tensile strength increases. In different process parameters, the difference between the maximum impact energy (24J) and minimum(14.2J) is about69.01%; The tensile strength (maximum:1730MPa, minimum:1490MPa) is about16.10%; The rockwell hardness is just3.6%. This shows that Q&P heat treatment process is the most significant influence on toughness.By comparison material performance between the conventional quenching tempering process (250℃tempering) and the optimal Q&P process, the tensile strength of the material after Q&P heat treatment reduced about6.38%and little changes in hardness, while the impact energy increased by43.79%, so the Q&P process can obtain more excellent comprehensive performance.The result of microstructure shows that Material after conventional quenching and tempering process and Q&P Process are typical tempered martensite. With the initial quenching temperature rises, the content of pre-formed martensite microstructure gradually reduced, the martensite lath become organized and its size become gradually larger. Partitioning time mainly affects the interface morphology movement. as partitioning time prolonged, the martensite/austenite interface moves and it interface become bent. Also, Granular carbide appears in the matrix.The appear of carbides shows that addition of Si did not completely inhibit the precipitation of carbides, and higher carbon partitioning temperature and longer partitioning time may be the main reason.Results of X-ray diffraction and magnetic analysis showed that content of retained austenite increased after Q&P Process, and it shows that the content of retained austenite is the most important reason on toughness. The size changes of martensite lath, movement of phase interface, carbide precipitation are also the reason of changes in properties.