Research On Process Of Temperforming On Low Carbon Steel And Low Carbon Microalloyed Steel

The microstructure and mechanical properties of low carbon steel and low carbonmicroalloyed steel subjected to quenching and temperforming were investigated in thiswork.The low carbon steel and low carbon microalloyed steel were quenched in brineand temperformed by rolling at different temperatures at a liner speed of0.8m/s and areduction of50%. Microstructure morphology before and after temperforming wereobserved by optical microscopy (OM) and scanning electron microscopy (SEM). Inaddition, the comparison in microstructure and properties between temperforming andtraditional tempering samples was made.Results show that the microstructure of low carbon steel in quenched samples at800℃，850℃，920℃was lath martensite and ferrite， lath martensite and a littleferrite，lath martensite. The microstructure of low carbon steel in quenched at800℃，850℃，920℃and tempered was strip ferrite and tempered martensite, temperedmartensite and a little network ferrite, needles tempered martensite. The crystal grainsgrow up accompany the temperature rising. The structure has obvious orientation andthe structures distortion with the rolling direct.Compared with traditional austempered process, the process of low carbon inquenching at two-phrase region and temperformed wouldn’t obtain high intensity andstrong plastic structure. When the initial structure was completely martensite wouldobtain high intensity structure. By comparing the mechanical properties of low carbonsteel with different temperforming process, the optimum process can be determined tobe temperforming at450℃after quenched at920℃. The mechanical properties of thesample treated by the optimum process were measured as follows: the tensile strength1121MPa, the yield strength905MPa, the total elongation15%, the yield ratio0.907,the impact energy81.8J. The hardness of the sample was determined to be aboutHV341.The microstructure of low carbon microalloyed steel in quenched samples at920℃was lath martensite. The microstructure of low carbon microalloyed steel in quenched at920℃and tempered was needles tempered martensite. The crystal grains grow upaccompany the temperature rising. As the tempering temperatures was increased, thebreakdown of the martensite takes place at a faster rate. The structure has obvious orientation and the structures distortion with the rolling direct.Compared with traditional austempered process, the process of low carbonmicroalloyed steel in quenching and temperformed would obtain high intensity structure.By comparing the mechanical properties of low carbon microalloyed steel with differenttemperforming process, the optimum process can be determined to be temperforming at400℃after quenched at920℃. The mechanical properties of the sample treated by theoptimum process were measured as follows: the tensile strength1489MPa, the yieldstrength1237MPa, the total elongation8%, the yield ratio0.830,the impactenergy19.2J. The hardness of the sample was determined to be about HV424.Delaminated morphologies of tensile and impact fractures were formed intemperformed samples and the micro-morphologies in region of crack propagationexhibited as micro-dimples. Dimples on the matrix indicated that ductile rupturehappened during fracture process.Compared with low carbon steel, the low carbon microalloyed steel would obtainhigh intensity and poor plastic structure at the same deformation tempering temperature.