| QPQ technology is a composite processing technology on the material surface. QPQtechnology was applied to65Mn steel, this paper studied the material fatigue strength,corrosion resistance and wear resistance, analysis the influence of mechanism, and thetechnological parameters of QPQ technology was optimized by using orthogonal test methodto get the optimal process parameters.The experimental results showed that:(1) After treated by QPQ,65Mn samples’conditional fatigue strength increased from308MPa to469MPa, increased by52.3%. At thesame stress level, the fatigue life of specimens before and after QPQ treatment wereobediented to the three parameter Weibull distribution. In the QPQ technical parameters,reaction time is the main factors affecting the fatigue strength. The optimal processparameters is: nitriding temperature580℃, reaction time2h, oxidation temperature370℃,reaction time20min. Under the process conditions, the fatigue strength is470MPa.(2) Thesamples’ residual strength degradation model before QPQ treatment is subject to the powerfunction formula, and QPQ treated samples obey exponential formula. The statistical modelof residual strength before and after QPQ treatment are subject to Weibull distribution. Theresidual strength distribution function can be deduced by the static strength distributionfunction, but it need to be revised.(3) QPQ technology can greatly improve the corrosionresistance of the65Mn steel, and the optimal process parameters is: nitriding temperature600℃, reaction time1h, oxidation temperature410℃, reaction time40min. The longestcorrosion time is45h, which is54times of untreated samples, and the minimum corrosionrate is2.02g/(m2h), about16%of the untreated sample.The most important factor whichinfluences corrosion of several process parameters is nitriding temperature.(4) QPQtechnology can greatly improve the wear resistance of the65Mn steel. Under the condition ofoil lubrication,the applied load of100N，the speed of60r/min, the average friction coefficientof QPQ samples is0.0793, which reduces37.7%of quenched and tempered samples, and thewear loss is3.2mg, which reduces71.4%of quenched and tempered samples.(5) The mostimportant factor which influences wear loss and average friction coefficient is nitridingtemperature; QPQ treatment process to obtain the minimum wear loss is: nitridingtemperature570℃, reaction time3h, oxidation temperature330℃, reaction time40min. QPQtreatment process to obtain the minimum friction coefficient is: nitriding temperature570℃,reaction time2h, oxidation temperature410℃, reaction time20min.The mechanism of QPQ treatment effect on the performance of65Mn:(1) After QPQtreatment, layer from outside to inside includes the oxide film, the loose layer, the compoundlayer. The composite permeability layer includes Fe2N phase, Fe8N phase, Mn3O4phase,Fe3O4phase and Mn2N0.86phase from the surface of10um.(2) The improvement of fatiguestrength is mainly due to the compound layer formed by QPQ treatment and the surfaceresidual compressive stress exists on the metal surface. Before QPQ treatment, the samplefracture form is cleavage fracture,and after QPQ treatment the surface strengthening layerfracture form is quasi-cleavage fracture, the fracture form of diffusion layer and the substrate part is cleavage fracture.(3) QPQ technology can greatly improve the corrosion resistance of65Mn steel, because the dual protection of Fe3O4oxide film and nitride layer. The existenceof the porous layer will be conducive to improve the corrosion resistance, but the loose can’tbe too serious. Long oxidation time can cause that it will produce a compressional stress inthe oxide film and the oxide film cracking or fall off, corrosion resistance is reduced.(4) QPQtechnology can greatly improve the wear resistance of65Mn steel. This is mainly because thehardness of compound layer is very high and Fe3O4oxide film which formed in the oxidationprocess can reduce the friction coefficient and improve the fretting wear resistance. |
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