Research On Liquid Phase Plasma Electrolytic Carbonitriding On Low Carbon Steel

Marine piston pins are used to connect pistons and connecting rods.Being exposed to high temperature environment and bearing large periodic impact loads causes that these piston pins are difficult to form lubricating oil film,thus,poor lubrication conditions leads to friction and wear.These complex and harsh working environments means that the piston pin need to have sufficient rigidity,strength and wear resistance.Therefore,this article selects the common material low-carbon steel for piston.pins as the object.To manufacture the carbonitriding layer on its surface and improve its tribological properties,this article uses the liquid phase plasma electrolysis technology.This article first conducted exploration experiments with electrolytes of different systems,and analyzes the effect of carbonitriding in the experiment which is about low carbon steel under various electrolyte systems.Then devised the experimental plan.Liquid-phase plasma electrolytic carbonitriding treatment was used on low carbon steel at stage voltages creatively.At last,test of the microstructure,composition and tribological properties of the carbonitrided layer and the energy consumption under different modes was explored and compared through the SEM/BSE,XRD,EDS,micro hardness tester,friction and wear testing machine and other equipment.The results show that:Low-carbon steel is carbonitrided in the electrolyte of urea and glycerin system.The reaction process of which was continuous and stable.The thickness of the prepared infiltration layer was uniform and the cost of the experiment was controllable.It is suitable as an electrolyte for experiment.Uniform and dense carbonitriding layers was obtained under experimental conditions,the stage voltage can obviously improve the effect of carbonitriding.The thickness of carbonitriding layers is up to 161.34?m,which is about 130%higher than the existing literature,the hardness of it is more than 800HV,which is about 3 times than hardness of the matrix.There are spherical protrusions,pits,melts and discharge channels on the surface of carbonitriding layer,the spherical protrusions gradually decreased and the surface tended to be flat as the working voltage increased.Carbonitriding layer contained FesC2,Fe3C,Fe2-3N,Fe4N and other phase.Properly increasing the voltage was conducive to the infiltration of C and N elements.Under the experimental conditions,the reaction was dominated by nitriding.In addition to improve the effect of carbonitriding,the experiments under stage voltage could also significantly reduce energy consumption by 3.34%.Friction and wear experiment shows that the samples after carbonitriding had obvious wear resistance and friction reduction effects.The minimum friction coefficient of the samples obtained at the stage voltage conditions was stable at about 0.5,it reduced by about 71%compared with the average friction coefficient of the matrix and the lowest wear scar depth was 10.65?m,which was about 87%lower than the matrix.