Design And Application Of Electrochemical Stripping In A Gear Steel

The surface quality of fabricated parts directly affects the performance and service life.Metal physics,materials science and fatigue fracture theory have proven that most failures of parts originate from surface cracks.Therefore,surface quality has become a hot research topic.Residual stress is an important indicator of surface quality,residual stress is of great significance for controlling surface quality.18CrNiMo7-6 gear steel has the advantages of high surface strength and good toughness of the core after carburizing quenching,low temperature tempering and finishing.This steel is widely used in the manufacture of high-speed locomotive gears and reducer gears.There will be a certain residual stress in the gear after heat treatment and machining,understanding the distribution of residual stresses in gears and analyzing the failure mechanism of gears will help improve product quality and improve the service life of gears.In this paper,the depth direction corrosion of 18CrNiMo7-6 gear steel is made by electrochemical polishing.This method provides a new way of thinking for measuring the distribution of residual stress and hardness along the direction of depth.The main research content of this article is as follows:(a)Through COMSOL simulations,the effects of voltage,distance between electrodes,and conductivity on the quality of electrochemical polishing were investigated.For the micro surface of the workpiece,the current density is larger and the corrosion rate is faster.For the smooth or concave part,the current density is small and the corrosion rate is relatively slow.(b)Analysis of the effects of traditional corrosion equipment gives the necessity of fixture design.By designing the stripping fixture and the establishment of an electrochemical test platform,the 18CrNiMo7-6 gear steel is stripped in the depth direction has been realized.(c)Through the screening test of electrolyte,current density and polishing time,the electrochemical polishing process parameters suitable for 18CrNiMo7-6 gear steel are as follows:the electrolyte is a mixed solution of phosphoric acid(20%H2SO4 +60%H3PO4 + 20%H2O),the current density is 0.49 A/cm2,the polishing time is 18min-25min.Under this process parameter,the stripping rate of 3.43 ?m/min can be achieved.(d)After stripping,the residual stress and hardness of the sample were measured.The results show that the residual stress in the surface layer is-230 MPa.With the depth of the layer increases,the residual stress changes from compressive stress to tensile stress,and finally stabilizes at about 50 MPa;The hardness fluctuates around 65.8-64.8 HRC with the decrease in depth of 85.86 ?m,with little change in hardness.