Effect Of Laser Remelting Parameters On Microstructure And Mechanical Properties Of 70Mn Steel

70Mn steel is a kind of high quality carbon structural steel with good comprehensive mechanical properties.It is mostly used to manufacture wear-resistant and heavy load mechanical parts,such as spring coil,thrust ring,clutch disc,locking ring,bearing and bearing cage.In the working process,this kind of parts will be subject to impact,vibration and other dynamic loads,wear and fatigue,which will lead to the increase of the failure of this kind of parts,resulting in security risks and economic losses.In order to realize the micro diameter laser remelting of 70 Mn steel surface,the "stripe type" remelting unit was prepared on 70 Mn steel surface at different scanning rates and different laser power,and the effects of different laser parameters on the microstructure and mechanical properties of 70 Mn steel were investigated.Firstly,ANSYS software is used to simulate the laser remelting process with 400 W laser power and 10mm/s scanning speed parameters,to obtain the temperature field and stress field in the process,and to improve the laser processing method according to the distribution of temperature field and stress field.The microstructure of the specimens before and after laser remelting was observed.It was found that the microstructure of the specimens changed from spherical pearlite to acicular martensite in the remelting zone.The hardness of the remelting zone and heat affected zone increased from 212.95 HV to 639.91 HV.The average hardness of the specimens increased by 200% after laser surface remelting.Through the introduction of EPPD,the relationship between EPPD of different parameters and the depth,width and depth/width ratio of remelting zone is explored.It is found that reducing the scanning rate and increasing the laser power will increase the EPPD value,and the heat conduction is transformed into heat penetration,resulting in a relatively low depth/width ratio.Through the tensile test and friction and wear test of the specimens before and after laser remelting,it is found that laser remelting reduces the tensile strength and tensile ratio of the specimens,and enhances the yield strength of the specimens.Through the observation and analysis of fracture micro morphology,the reason of tensile weakening is that martensite reduces its plastic and elastic deformation limit and then affects its yield strength;the wear mode of the specimens before and after laser remelting is abrasive wear,and most of the friction coefficient increases,and the average friction coefficient of 400 W laser power and 10mm/s scanning speed is the lowest,which is 0.66 The reason is that the hardness of the remelting zone enhances the wear resistance of the material,and the pits formed by the laser remelting will play the role of collecting debris in the friction and wear,thus protecting the friction and wear between the matrix and the dual parts.