Effect Of High Temperature Heat Treatment On Microstructure And Properties Of 60Si2CrVAT Spring Steel

In recent years,great achievements have been made in the high-speed railway construction.60Si2 CrVAT spring steel is a special spring steel for speed-increasing train bogies.Improve its service life and mechanical properties has always been the focus of research.This article mainly simulates the heat treatment process through a hightemperature confocal microscope,and based on this,develops two heat treatment experiments of high-temperature direct quenching and high-temperature cooling quenching.With the help of optical microscope(OM),scanning electron microscope(SEM),electron backscatter diffraction(EBSD)and other methods,studied the microstructure changes of steel under different austenitizing processes and its influence on properties.The results show:Obtained the change of microstructure with austenitizing temperature througth simulating the heat treatment process by confocal microscope.When the austenitizing temperature is low,the microstructure after cooling is a mixture of pearlite and martensite.With the increase of austenitizing temperature,the lamellar spacing of pearlite becomes smaller,the microstructure gradually transforms into martensite completely,and has a tendency of coarsening.The hardness of the sample increases with the increase of temperature.After slow cooling at high temperature,the grain size becomes more uniform.The results of high temperature direct quenching show that the microstructure of the sample coarsens slightly from the edge to the center,and the inhomogeneity increases.With the increase of heating temperature,the austenite grains of the steel decrease slightly and then increase;the overall structure coarsens and the uniformity becomes worse;the strength of the steel increases with the increase of quenching temperature,the elongation after fracture decreases slightly,and the reduction of area is the lowest when the structure is the most uneven.After holding for a period of time in the high temperature stage and then slowly cooled to the target temperature followed by quenching(called quenching after slow cooling),the results shows after holding for 30 minutes at 960?,when the temperature is slowly lowered to the quenching temperature,the segregation and inhomogeneity in the edge,middle and center of the sample decrease.After holding at 990? for 30 minutes and undergoing a large gradient of cooling to the quenching temperature,the structure of the sample has the best uniformity,which can significantly increase the yield strength and tensile strength,and obtain the largest reduction of area.The experimental results show that 60Si2 CrVAT spring steel is slowly cooled to900? after holding for 30 minutes at 990? and then quenched and tempered at 430? for one hour,can obtain excellent comprehensive mechanical properties,so that the tensile strength reaches 1735.3MPa,the yield strength reaches 2118.7MPa,and the elongation after fracture.It is 13.9%,and the reduction of area is 26.9%.