Surface Strengthening And Wear Resistance Of Inner Hole Of 42CrMo Steel By Ultrasonic Rolling

In the face of increasingly stringent emission regulations,using steel pistons to meet the engine's high explosion pressure requirements has become the best choice for heavy-duty diesel engines at this stage.However,when the steel piston is subjected to alternating impact load and thermal load,problems such as wear and fracture often occur in the pin hole.The ultrasonic rolling process can refine the crystal grains to generate residual compressive stress inside the material,and improve the impact and wear resistance of the material.Therefore,this article will use the ultrasonic rolling technology to process the inner hole of the steel piston material 42CrMo steel,and combine the simulation results to explore the effect of the ultrasonic inner hole rolling on the performance of 42CrMo steel.Improved the design of the inner hole ultrasonic rolling device structure,carried out the 42CrMo steel inner hole ultrasonic rolling orthogonal test,studied the influence of the rolling parameters such as speed,feed and static pressure on the surface shape characteristics,and optimized the rolling parameter.The results show that the unreasonable rotation speed during the rolling process will cause vibration marks on the surface of the sample,and the excessive feed will cause the rolling marks to significantly reduce the ultrasonic rolling effect.The static pressure exceeding a certain range will cause over-rolling on the surface of the workpiece.Affect the quality of the rolling gauge.Using the optimized rolling parameters,the 42CrMo steel inner hole ultrasonic rolling test was carried out,and the surface integrity test and characterization were carried out.The influence of the rolling feed rate on the surface morphology,microhardness,residual stress and microstructure was studied.law.Experiments have found that the smaller the rolling feed rate,the smoother the surface of the material,but the surface of the material will be damaged if the rolling feed rate is too small,causing microcracks.The microhardness value of the material surface decreases with the increase of the rolling feed,and the depth of the affected layer also decreases.Ultrasonic rolling will also cause significant residual compressive stress inside the material,but the number of rolling has no obvious influence on the value of residual stress.From the perspective of the microstructure of the material,the smaller the rolling feed rate,the higher the degree of grain refinement in the material,and the deeper the depth of the influence layer.The finite element simulation of the ultrasonic inner hole rolling process was carried out using Abaqus finite element simulation software.The rolling process is set to four stages of rolling,unloading,external force release and cooling,and the curve of the residual stress of the material with depth is obtained.The simulation results are compared with the experiment to verify the correctness of the finite element model.The results show that the change trend of the residual stress measured by the experiment is consistent with the simulation,and the maximum residual stress value decreases with the increase of the rolling feed.The reciprocating ball-disk dry friction and ring-block sliding friction tests were carried out on the ultrasonic rolling surface of the inner hole,and the influence of the rolling feed rate on the wear resistance of the inner hole surface was studied.According to the results of the dry friction of the ball and disc,the smaller the feed rate,the more serious the over-rolling damage of the material surface after the secondary rolling,and the greater the friction coefficient in the stable wear stage.In the running-in wear stage,with the increase of the number of rolling,the slope of the curve of the friction coefficient with time gradually decreases,indicating that the anti-wear performance of the initial wear stage increases significantly with the increase of the number of rolling.The results of the sliding friction experiment show that when the rolling feed is small,the surface quality of the primary rolling sample and the counter-grinding part are better,but the secondary rolling sample has excessive rolling cracks on the surface,and sticking occurs in the experiment.Knot wear.With the increase of the rolling feed rate,there will be no over-rolling phenomenon on the surface of the secondary rolling sample,and the wear resistance of the material will be significantly improved.