Study On Surface Modification Of 316 Stainless Steel And Its Tribological Properties

Austenitic stainless steel has good comprehensive mechanical properties,stable quality,easy processing,welding performance and strong corrosion resistance,which has been widely used in aerospace,marine engineering,medical equipment and many other fields.However,the austenitic stainless steel has low hardness and poor wear resistance,and the parts made from it are prone to wear in actual working conditions.Taking the high water-based hydraulic pump as an example,In the process of matching pair,which easily leads to the wear failure of the friction pair surface,shortens the service life of the matching pair,and then affects the performance of the high water-based hydraulic pump due to the distribution pair made of austenitic stainless steel is limited by factors such as high friction factors and weak surface bearing capacity.Therefore,it is significant to improve the surface properties of austenitic stainless steel and exploring its anti-friction mechanism to be used in the manufacturing sliding friction accessory parts.Compared with the traditional single surface modification technology,this paper adopts the processing idea of“reducing material+adding material”to compound treatment of 316 austenitic stainless steel.Firstly,the surfce of 316stainless steel is shot peened by abrasive water jet.The high-pressure water generated by the high-pressure pump and the sand shot sent out by the pill supply device together violently collide and exchange energy in the mixing chamber.Finally,the abrasive jet is sprayed to the surface of the sample through the nozzle.Based on the theory of non-uniform deformation and cold work hardening,the surface of the samples showed continuous and dense groove texture,and then the surface texture of the sample is treated by plasma nitriding.Finally the surface modified layer obtains a excellent performance.The surface morphology,phase structure and toughness of the duplex treated sample are analyzed.At the same time,the mechanical properties of different surface-treated samples and the tribological behavior and wear mechanism under dry friction and liquid lubrication conditions are studied.The main research contents of this paper are as follows:?1?The work aims to study the effect of abrasive water jet process parameters on the surface properties of 316 stainless steel.Abrasive water jet shot peening is applied to 316 stainless steel samples.The effects of the injection pressure,nozzle movement speed and target distance for the surface roughness,microhardness and residual stress of 316stainless steel are investigated.After abrasive water jet peening treated,the surface of 316stainless steel specimen produced groove texture,the surface roughness increased.Meanwhile the microhardness of specimen improved significantly,and a certain amount of residual stress was introduced on the surface of 316stainless steel.The result show that the injection pressure,nozzle movement speed and target distance had obvious effects on the surface properties of 316stainless steel,which effectively change the surface morphology and properties,and further influence its service life.?2?In order to acquire the best process parameters that affect the comprehensive surface quality of 316 stainless steel.The orthogonal experimental method is used to study the influence of jet pressure,nozzle velocity and target distance on the surface quality.Analysis of the experimental results shows that:the order of the influence of the three factors on the surface roughness is as follows:jet pressure>target distance>nozzle velocity.The order of the influence on the residual compressive stress is as follows:target distance>jet pressure>nozzle velocity.For the comprehensive surface quality,the order is pressure>target distance>nozzle velocity.Based on multi-factor optimization design,taking the signal-to-noise ration as the evaluation index,the best parameter combination for shot peening is obtained:jet pressure as120Mpa,target distance as 20mm,nozzle velocity as 700mm·min^-1,feed 0.3mm.?3?The surface texture-nitriding composite modified layer is obtained by the second treament of plasma nitriding under the optimum combination of process parameters.After duplex treated,the surface of the sample formed continuous compact groove texture and the modified layers consists of Fe₂N,Cr₂N,Cr N and other compounds.The thickness of the nitriding layer is about 10?m.The surface microhaedness?79 HRC?and the roughness?1.10?m?of duplex treated sample were higher than those single surface treated samples.?4?The friction coefficients of all samples fluctuate with different degrees under dry friction condition against Si₃N₄ceramic balls.The friction coefficients of 316SS is than that of texture stainless steel?ST-316SS?,nitriding stainless steel?PN-316SS?,texture-nitriding stainless steel?ST-PN-316SSS?.the friction coefficient of ST-PN-316SS fluctuated around 0.25 and the mass losses was 0.3mg,which were significantly lower than those single surface treated samples,and the wear mechanism are mainly fatigue wear and oxidation wear.Both the higher bearing capacity of the composite modified layer and the reduction of the contact area of the friction pair play a role in reducing friction under dry friction condition.?5?Three different surface modified samples have good anti-friction and anti-wear effects under liquid lubrication conditions.The friction coefficients of the PN-316SS gradually increased and the fluctuation range is larger.At the last,the friction coefficients gradually approached 316SS.The friction coefficients of ST-316SS and ST-PN-316SS are relatively low due to the groove texture storing lubrication fluid and it can be continuously lubricated during sliding.they fail to form complete and continuous wear marks in the whole sliding process.However the wear degree of the ST-PN-316SS is lower than of ST-316SS.