Research On 38CrMoAl Steel By Combining Treatment Of Abrasive Water Jet Peening And Plasma Nitriding

Plasma nitriding can effectively improve the hardness,wear resistance and fatigue strength of steel,and has been widely used in modern manufacturing industry.However,there still have some insufficiency in plasma nitriding,such as low penetration rate,long process cycle and shallow layer etc..So we need to constantly explore and improve the related technologies to improve the efficiency of plasma nitriding.Researches on surface deformation pretreatment for nitriding at home and abroad mainly focuses on shot peening,ultrasonic nanocrystal surface modification,surface mechanical abrasive treatment and other pretreatment methods,but there are few studies on combining treatment of abrasive water jet peening and plasma nitriding.In this paper,38CrMoAl steel was used as experimental material to study the effects of combining treatment of abrasive water jet peening and plasma nitriding on the structure and properties of the material.Firstly,the process parameters of plasma nitriding of 38CrMoAl steel are optimized.The optimum process parameters of plasma nitriding are obtained by metallographic analysis,hardness gradient,XRD phase analysis and residual stress of the sample surface.Then,the effect of abrasive water jet peening on the structure and properties of 38CrMoAl quenched and tempered steel was investigated.Finally,38CrMoAl Steel pretreated by abrasive water jet peening under different water pressures was treated by plasma nitriding to explore the effect of abrasive water jet peening on plasma nitriding.The main conclusions are as follows:?1?The temperature has a great influence on the quality of plasma nitriding layer in nitriding process parameters.It is found that the optimum temperature of plasma nitriding for 38CrMoAl steel is about 550 C at 300 Pa atmospheric pressure and 36 h nitriding time.Under the optimum technological parameters,the thickness of the white layer on the surface of the sample is 11?m,the depth of nitriding layer is 405?m,the hardness gradient distribution is smooth transition,and the roughness is acceptable.There has not?phase on the surface of the sample,and the surface phase is composed of Fe_2-3N and Fe₄N phases.?2?The optimum water pressure for abrasive water jet peening is 150 MPa under the conditions of 1 mm diameter of nozzle,10 mm target distance,400 mm/min moving velocity of nozzle and 0.1 mm diameter of stainless steel pellets.Under the optimum experimental parameters,the thickness of hardened layer is the largest,and the residual stress layer depth can be produced at the same time.Meanwhile the surface roughness of the sample is also acceptable.?3?The optimum water pressure of abrasive water jet peening pretreatment for38CrMoAl steel composite treatment is 150 MPa.Under these conditions,both the thickness of white and diffused layers of the composite treated specimens are the largest,reaching 15 and 500?m respectively,and the vein nitrides are the least in the nitriding layer.Compared with the sample treated by 150 MPa abrasive water jet peening,the maximum residual stress and the depth of residual stress increased by 44.7%and 163%respectively.Compared with single plasma nitriding,the maximum residual stress and the depth of residual stress layer of the composite treated specimens are also increased.?4?Abrasive water jet peening can reduce the friction coefficient and improve the wear resistance of the material surface.There have abrasive wear,adhesive wear and oxidation wear in the friction and wear process of matrix and abrasive water jet peening sample.But the matrix has serious adhesive wear and oxidation wear.After plasma nitriding,the wear resistance of the sample is significantly improved.At the same time,the wear resistance of the sample treated by the composite treatment of abrasive water jet peening and plasma nitriding is higher than that of the sample treated by the single plasma nitriding.There are abrasive wear,adhesion wear and oxidation wear in the friction and wear process of single nitriding and composite nitriding treatment samples,among which the single nitriding treatment sample has more severe spalling of white layer.