Research On The Friction And Wear Properties Of 40Cr Steel Treated By Laser Microtexturing And Discrete Hardenin

40Cr steel has good comprehensive performance after hardening and tempering treatment,and is widely used in the manufacture of steering knuckles,rear axles and other parts of automobiles.With the continuous improvement of the requirements of lightweight design of automobiles,the working conditions are becoming more and more severe,especially under high-speed and heavy-load conditions,it is difficult to form a continuous lubricating oil film on the surface of mechanical parts,resulting in severe friction and wear.Based on the lubrication and friction reduction mechanism of laser microtexturing "surface reshape" and the enhanced wear resistance mechanism of laser discrete hardening "surface modification",this paper proposes to apply the laser microtexturing-disctete hardening shape composite treatment technology to 40 Cr steel,in order to By optimizing the surface micro-geometry,its lubricating and anti-friction performance is improved,and the microstructure of the hardened zone is improved,thereby improving its surface hardness and friction and wear performance.The main research work and conclusions are as follows:(1)The COMSOL Multiphysics finite element simulation software is used to numerically simulate the laser microtexture-discrete hardening shape composite treatment process,and the distribution of the temperature field is studied.The influence of the geometrical size of the hardening point and the fusion zone,the calculation results show that with the increase of the laser duration time,the geometrical size of the hardening point and the fusion zone also increases.(2)Micro-dimple textures were prepared on the surface of 40 Cr steel samples by nanosecond pulse laser marking machine.The effects of laser power,pulse repetition times and defocus amount on the geometry and size of micro-dimple textures were discussed.Influence factors of laser process parameters on the quality of micro-dimple textures.The results show that with the increase of laser power,the diameter and depth of the micro-dimple textures increase linearly;with the increase of the pulse repetition times,the increasing rate of the diameter and depth of the micro-dimple textures first remains constant.The diameter and depth of the micro-dimple textures show a trend of first increasing and then decreasing with the increase of the defocus amount.(3)The surface of 40 Cr steel sample was subjected to laser discrete hardening treatment by using the laser multifunctional micromachining system independently developed by our research group.The influence of microstructure and microhardness was discussed,and the evolution law of microstructure in the laser phase transformation zone was discussed.The results show that the laser power,laser duration and defocus amount have a significant effect on the geometry of the hardening point.When the laser power is 400 W,the pulse width is 7.5ms,and the defocus amount is +15mm,the hardening point can obtain good results.The surface morphology of the hardened area can also be obtained with the largest geometric size;the microstructure of the hardened area is mainly composed of acicular martensite with dense structure and extremely high hardness,and the microhardness of the hardened area is greatly improved.(4)The 40 Cr steel samples were subjected to laser microtexturing-hardening composite treatment,and the changes of the surface roughness,microhardness and microstructure of the samples under different process parameters were studied,and the results were compared with the laser microtexturing samples and the laser discrete hardening test.A comparative analysis was carried out.The results show that the larger the texture area ratio,the higher the surface roughness,the higher the absorption rate of laser light,and the larger the geometric size of the hardening point;when the texture area ratio is small,the surface quality of the hardening point is better.Considering factors such as the size of the hardened point,the microhardness,and the surface quality of the laser compound surface,the final form of the laser compound surface is as follows: first,a micro-dimple textured surface with an area ratio of 12.6% is processed,and then a laser discrete hardening treatment was performed,wherein the spacing of the hardened points was 1500 μm.(5)On the Rtec multi-functional friction and wear testing machine,the friction and wear of the 40 Cr specimens treated with laser microtexture,laser discrete hardening and laser microtexture-hardening shape-performance composite treatment were carried out with lean oil lubrication and reciprocating motion by pin-disk type respectively.The friction and wear performance was studied;the wear morphology of the sample surface was analyzed by threedimensional surface profilometer and scanning electron microscope.The results show that compared with the laser microtextured surface and the laser discrete quenched surface,the friction coefficient and wear loss of the laser microtextured-quenched shape-performance composite treatment surface have been greatly reduced,and the wear state has been greatly improved,the friction and wear performance has been further improved.