Effect Of Mixed Microstructure On Properties Of GCr15 Bearing Steel

In order to meet the requirements of the complex operating ambient and higher performance of future bearings,the research and development of bearing materials is not only to improve the quality of traditional bearing steels,but also to carry out the research and development of many new bearing steels with higher performance.When aiming at the research and development of advanced bearing steel or other materials,it should also be paid attention to effectively improve the material level of ordinary bearing steel.In this paper,through the heat treatment test of GCr15 bearing steel under different conditions,the influence of solid solution and tempering factors on the microstructure and properties of GCr15 bearing steel was firstly investigated,and the optimal solution temperature,solution time and tempering temperature of the final heat treatment were determined.Afterwards,the final heat treatment was carried out,that is,the solution temperatures were 840℃and 860℃,and the holding time was 40 min and 30 min respectively.After the austenitizing stage,the steel was quenched into a salt bath furnace at 200℃and 230℃for isothermal quenching for various times.After cooling to room temperature,it was tempered at 200℃×2.5 h.Rockwell hardness tester and pendulum impact tester were used to test the mechanical properties of the samples,and the microstructure and impact fracture of the samples were observed and analyzed.Moreover,Image Pro Plus software was used to calculate the content of the bainites and undissolved carbides in the samples under different heat treatment conditions.Results show that,with the increase of solution temperature and solution time,the diameter and content of undissolved carbides in the matrix decrease,while the content of lower bainites increases.The hardness of samples increases gradually after solution at 860℃,but decreases after solution at 880℃and 900℃.With the increase of tempering temperature,the diameter and content of undissolved carbides in the matrix decrease.The tempering transformation rate is faster below 200℃,and the content of lower bainites decreases.The hardness of the samples increases first and then decreases,and reaches the maximum hardness of 64.28 HRC at 200℃.The optimal process conditions of M+B isothermal quenching are 840℃×40 min+200℃×2 h,which makes the hardness reach 62.3 HRC,the impact toughness reach 9.28 J/mm~2,and the rotary bending fatigue limit reach 800 MPa.The optimal process conditions of M+B isothermal quenching and tempering are 860℃×30 min+200℃×2 h+ 200℃×2.5 h,which makes the hardness of the steel reach 61.9 HRC,the impact toughness reach 9.93 J/mm~2,and the rotary-bending fatigue limit reach 1030 MPa.