| QPQ technology was the abbreviations of “Quench—Polish—Quench”,which was called the QPQ salt bath composite processing technology. Theessence of QPQ salt bath composite processing technology is low temperaturesalt bath nitriding+salt bath oxidation or low temperature salt bath ofcarbonitriding+salt bath oxidation. QPQ technology has been widely used inengineering manufacturing, mechanical and automobile industry, in order toenhance wear resistance, fatigue resistance and corrosion resistance. Thistechnology was suitable for low carbon steel, structural steel and cast iron.In this study,45steel and304stainless steel were chosen as theexperimental material. The samples were subjected to nitrided at565℃for60min～150min, and oxidized at430℃for0min～100min. The surfaceproperties were studied to research the influence of nitriding time andoxidation time on45steel and304surfaces. Characterization of modifiedsurface layers was made by means of optical microscopy, microhardness test,X-ray diffractions analysis and SEM.In addition, for the application problems of45steel and304stainlesssteel, wear test were used for analysis the influences of QPQ salt bathtreatment time on wear resistance of45steel and304SS. The method ofimmerse were used to evaluate the corrosion performance of45steel in10%NaCl+3‰H2O2(30℃),10%HCl (30℃)，hot water (90℃) and the hightemperature environment at800℃.The microscopic examinations result showed that the sectionmicrostructure was consists of a thin oxides zone at the external surface, abright zone named compound layer at the subsurface and diffusion layer. Thesurface constitution observed by XRD showed the presence of Fe3O4wasnoticed above the compound layers made up of ε nitrides. The microhardnessmeasurements showed that the maximum microhardness value of630HV0.01was obtained after a120min treatment at565℃, whichwas two times higherthan that of the untreated sample. The friction coefficient and the wear weightloss of45steel samples by QPQ treatment could be reduced.120min was the optimum nitriding time to improve the wear resistance. The corrosionresistance was evaluated by hot-water immersing at90℃and10%NaCl+3‰H2O2(30℃), respectively. The results showed that thecorrosion resistance for45steel could be significantly improved by QPQcomplex salt bath treatment,90min and100min were the optimum nitridingtime and oxidation time, respectively. The test in the process of10%HCl(30℃) and800℃high temperature environment showed that QPQ couldn’timprove the corrosion resistance in these conditions.The results of304ss showed that the micro-hardness reached themaximum of1200HV0.01while nitrided for150min at565℃, which was5times higher than that of untreated sample. The nitrided layer of304SS afterQPQ salt-bath treatment was composed of a very thin film of oxide layer,compound layer and the diffusion zone. The main phase of compound layerwas-Fe2~3N. And the results also showed that the wear resistance of304SScould be significantly improved by QPQ treatment. Among all the studiedparameters, nitriding at565℃for150min resulted in the optimum wearresistance, which was10times higher than that of untreated sample. |
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