Research On Microstructure And Mechanical Properties Of 45Mn Steel For Shipboard Engine Chain Of Laser Surface Quenching Under Different Scanning Modes

High-powered marine equipment in long-term operation at sea,sea air humidity,high salinity is the key reason for the low actual service life of marine equipment engines.As the core parts of high-powered marine equipment engine,the transmission chain is more likely to corrode and wear out,resulting in low engine efficiency or even damage.In view of the difficulty of marine maintenance,high-end equipment chain mainly relies on foreign imports and other problems,the use of direct replacement of the chain,improve the traditional treatment process and other methods have greatly increased the cost of expenditure.In order to solve the above problems,the advanced,efficient and economical laser quenching surface modification technology is proposed to be applied to the surface of the engine chain chain plate to make its surface with high hardness and high wear resistance.In this paper,laser quenching experiments are carried out on the surface of 45 Mn steel of chain plate under different scanning modes to study the changes of hardened layer organization and surface anti-wear and wear reduction performance and mechanism under different process parameters.The results of the study can provide new solutions and theoretical support for solving the problem of wear loss in marine equipment engine chains.Firstly,the effect of single-pass laser quenching on the surface organization and mechanical properties of 45 Mn steel was studied.The effects of key process parameters including laser power,scanning speed and spot diameter on the macroscopic morphology,tissue morphology and surface mechanical properties of the hardened layer were analyzed by orthogonal experiments.The results showed that the best process parameters of single-pass laser quenching were: power 800 w,scanning speed 8mm/s,spot diameter 4 mm;the organization of the phase transformation zone changed from top to bottom from slate-martensite to fine martensite,with cryptocrystalline martensite and residual austenite at the bottom;the surface hardness increased 3.2～3.7 times compared with the untreated substrate,and the wear reduction effect reached 46 %～52 %.Then,based on the single-pass laser quenching process parameters,the 45 Mn steel surface was subjected to multi-pass lap laser quenching to further investigate the mechanism of the effect of lap rate on the quenched surface properties.The lap rate was found to be the primary factor affecting the flatness of the bottom of the multi-pass laser quenched hardened layer,and the optimal process parameters for multi-pass laser quenching were: 40 % lap rate,700 w power,and 10 mm/s scanning speed.the quenched hardened layer was flat;the temper softening in the lap zone was inevitable and widened with the increase of the lap rate;the non-uniform processing method was proposed for the temper softening problem The temper softening in the lap zone was effectively reduced;the friction coefficient of the 40 % lap rate multi-pass laser hardened surface was reduced by 0.0267 compared with the untreated surface,with a 75.1 %wear reduction effect.Finally,tribological and biological theories are combined with laser surface quenching scanning methods to design four discrete surface quenching paths,which are processed based on the optimal process parameters for single-pass laser quenching,and to investigate the effects of different shapes,path intervals,tilt angles,and different working conditions on the friction and wear resistance of the surfaces.The frictional wear performance and mechanism of the discrete laser scanning quenched surfaces were investigated.The optimal process parameters for discrete laser quenching were determined by using the control variable method,combining the average friction coefficient,wear volume and wear morphology: power 800 w,scanning speed 8 mm/s,and a grid-like scanning mode with 0.2 mm interval,with a wear reduction effect of 76.33 %.Wear resistance mechanism.In this paper,by studying the effect of laser quenching key process parameters on the comprehensive performance of the surface under different scanning modes,it is confirmed that laser quenching is a complex processing process with cross influence of multiple factors,and the wear reduction and wear resistance of the quenched surface under different scanning modes are different.The results of this study will provide ideas and theoretical basis in solving the wear resistance problems of engine chains and other components of marine equipment.