| High Mn steel was widely used in various friction and wear environments due to its high work hardening properties.However,there was no work hardening on the surface of high Mn steel during initial use,and the high Mn steel was not significantly work hardened under low loading,resulting in poor wear resistance.Therefore,it was necessary to improve the friction and wear properties of high Mn steel in the initial use.As a new surface modification technology,laser shock processing(LSP)was widely used in the surface modification treatment of metal components,which can induce the plastic deformation and work hardening,thereby improving the strength,hardness and wear resistance of the material.As the research object,the high Mn steel was treated by LSP in this paper.The effects of different LSP parameters on the surface integrity,friction and wear properties and tensile properties of high Mn steel were studied.The work hardening mechanism under different LSP times was explored,and the purpose of improving the initial wear resistance of high Mn steel was achieved.The main research results of this article are as follows:(1)The high Mn steel was strengthened with different LSP energies and times.The changes in microhardness and surface roughness were measured before and after LSP.The results showed that the surface microhardness of high Mn steel and the depth of the hardened layer both increased with the increase of the LSP energies and times.Besides,the surface roughness increased due to uneven structure on surface caused by LSP.The friction and wear test results of the specimens before and after LSP showed that with the increase of LSP energy and times,the friction coefficient and the specific wear rate both tended to decrease under the same loading.The wear mechanism of the LSP specimens changed from oxidation and delamination wear to abrasive wear.There was a good balance between the surface integrity and the friction and wear properties at 7J 1 time LSP and 5J 3 times LSP,showing high wear resistance.As the loading increased,the friction coefficient of the specimens before and after LSP gradually decreased,and the specific wear rate showed an increasing trend.The main wear mechanism of the LSP specimens changed from abrasive wear to abrasive wear and slight delamination wear.(2)The room temperature tensile test of high Mn steel specimens before and after LSP was conducted,and the results showed that the tensile strength and yield strength were impoved by increasing the LSP energy and times,while the elongation of section was affected slightly.The tensile fracture of the specimen before LSP was a mixed fracture mode of plastic intercrystalline,quasi-cleavage and dimples.With the increase of LSP energy and times,the depth of the LSP affected area increased.Besides,the number of dimples increased in the affected area,and the fracture mode was dimple fracture.(3)The surface microstructure evolution of high Mn steel under different LSP times was studied.The results showed that no deformation-induced martensite was produced after LSP,and the surface grains were significantly refined.When the LSP was applied 1 time,lots of dislocations and dislocation tangles appeared in the surface.When the LSP was applied 2 times,deformation bands and a small number of twins appeared in the high Mn steel.These deformation bands were parallel to each other and divided the matrix into different regions to hinder dislocation movement with twins.When the LSP was applied 3 times,a large number of twins appeared,and the dislocation structures were stacked together to form subgrain boundaries,which interacted with the twins to refine the grains.The work hardening mechanisms of LSP strengthened high Mn steel were dislocation and twins. |
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