Study On Microstructure And Properties Of G20CrNi2MoA Heavy Load Railway Bearing Steel By Combining Cold Deformation With Heat Treatment

Bearing is the key components of railway wagon,its special working environment requires that the surface of carburizing bearing steel used in railway bearings must have high strength and wear resistance,and high toughness in the center.In this paper,the G20CrNi2MoA bearing steel has been studied.Firstly,the microstructure of the different heat treatment state was analyzed,and the wear resistance of G20CrNi2MoA carburized bearing steel under different temperature has been studied.By proposing cold deformation-heat treatment deformation-phase transformation controlling method to improve the wear resistance of bearing steel,the microstructure evolution during cold deformation-heat treatment was analyzed in detail,also the evolution of mechanical properties of bearing steel after cold deformation-heat treatment and the mechanism of cold deformation on wear resistance have been studied.A multiphase microstructure composed of acicular martensite,carbides and retained austenite was obainted on the top surface after the carburizing heat treatment,and the lath martensite in the center.After the carburizing heat treatment,the hardeness of the surface is about 59.2HRC,with the increasing of temperature,the average friction coefficient and wear rate increased,thus decreasing the wear resistance.The grain size of G20CrNi2MoA bearing steel could be refined and also the proportion of small angle grain boundaries increased after cold deformation.The pior austenite grain could be refined after the carburizing-quenched;The number of carbides increases and the average diameter of carbides decreases after the second-quenched;The acicular martensite is more refined and the content of the retained austenite has been reduced after the second low-temperature tempering.With the cold deformation increases from 0% to 30%,the carbon content on the top surface increased from0.904wt% to 0.950wt% after the carburizing heat treatment,and the hardness increased from 59.2HRC to 60.6HRC,and a high-carbon zone and a high-hardness layer were formed in the surface layer with a depth of about 0.9mm,the microstructure and toughness for the center changed little.However,when the cold deformation increased from 30% to 45%,due to the increase of deformation resistance by work hardening,the grain size was no longer refined,and the carbon content as well as the microhardness also changed little.Therefore,it is clearly that 30% is a suitable cold deformation for G20CrNi2MoA bearing steel.When the cold deformation increases from 0% to 30%,the average friction coefficient and wear rate decreased,the oxygen atomic percentage of the whole worn surface gradually decreases after the wear tests,also the abrasive wear and fatigue wear are gradually reduced,thus increasing the wear resistance.Analysis of the effect of cold deformation on wear resistance shows that: The main reason for cold deformation to improve the wear resistance of G20CrNi2MoA bearing steel was attributed to the large number as well as the refined average diameter of carbides on the surface,low content of retained austenite and refined acicular martensite.