Experimental And Numerical Simulation Studies On Laser Heat Treatment Of Steel 7CrSiMnMoV

7CrSiMnMoV steel has good hardenability and high tempering stability,and is suitable for the manufacture of large automotive coverings and other cold work molds.However,the hardness and wear resistance of this material in the as-cast state are low,which makes it difficult to adapt to high stress and high wear working conditions,so it needs to be heat-treated to achieve surface strengthening to improve its hardness and wear resistance.Laser heat treatment process has the advantages of flexible operation,cost saving,green and high efficiency,which is an efficient and clean surface strengthening process for cold work die steel.However,as a new type of cold work die steel,the basic data of 7CrSiMnMoV steel are insufficient at present,and systematic research on the determination of thermal physical parameters,the influence of thermal deformation behavior and laser heat treatment process on the microstructure and properties of the material,and numerical modeling and simulation of laser heat treatment are urgently needed.This paper takes 7CrSiMnMoV steel as the research object,establishes its constitutive model,thermal property parameters,etc.,and investigates the influence law of laser heat treatment on the evolution of material organization and properties,temperature field distribution,etc.through experiments and numerical simulations.A prediction model for the depth of the hardened layer of laser heat treatment was established to realize the optimization of laser process parameters.The main research works are as follows.(1)Hot compression tests of spheroidal annealed state 7CrSiMnMoV cold work die steel were conducted on a Gleeble-3500 thermal simulation testing machine,and the effects of strain rate and deformation temperature on its thermal deformation behavior such as stress-strain,microstructure and its evolution in high temperature deformation were studied,and the Johnson-Cook and Arrhenius models based on the constitutive model of 7CrSiMnMoV steel based on Johnson-Cook and Arrhenius models was established to achieve an accurate description of its thermal deformation behavior,and the study elucidated the recrystallization and phase transformation laws of 7CrSiMnMoV steel during high-temperature thermal compression.(2)Thermal expansion tests with different heating and cooling rates were carried out to study the phase transformation law of 7CrSiMnMoV steel.The critical transformation temperatures of austenite,martensite and bainite phases under different conditions were obtained,and the continuous cooling curves of the material were plotted.It was found that the austenite critical transformation temperature of 7CrSiMnMoV steel increased with the increase of the heating rate.The equation of the complete austenite transformation temperature of this material versus the heating rate was constructed.(3)Laser heat treatment process tests of 7CrSiMnMoV steel at different laser powers and scanning speeds were carried out.The effects of laser heat treatment on the microstructure of the hardened layer and heat affected zone were investigated,and the influence of laser process parameters on the distribution of martensite and residual austenite and grain size were obtained.The effects of laser process parameters on the hardness,wear resistance and corrosion resistance of the heat-treated specimens were investigated.The relationship equation between the hardened layer depth and laser energy density was constructed,and it realized the prediction of the hardened layer depth.The changes of microstructure and properties before and after laser heat treatment were studied to elucidate the laser surface hardening mechanism of 7CrSiMnMoV steel.(4)A finite element analysis model of the laser heat treatment process of 7CrSiMnMoV steel was established based on Abaqus software.The change law of temperature field during laser heat treatment process and the heating rate of laser heat treatment process were studied by simulation.The complete austenite transformation temperature range of 7CrSiMnMoV steel in laser heat treatment was obtained.The response surface-based optimization of the laser heat treatment process parameters was carried out,and the response surface model of the hardened layer depth was established.The model realized the optimization of laser process parameters and provided theoretical guidance for practical production.