Steel Base Surface Qpq Salt Bath Composite Processing Technology Research

QPQ technology is a kind of technology which can improve the matrix surface hardness, wear resistance, corrosion resistance, anti-fatigue performance salt bath composite processing.Through the research of QPQ commonly salt, salt and adjust salt nitride reference, and use a lot of repeated experiments, explored a salt bath stability strong base salt TF1has been presented, and developed a restore salt named H1which can adjust bath the concentration of CNO", even through explored which can be decomposed from nit riding salt bath of out of the CN-and the matrix surface in a compact Fe3O4film the oxidation of the salt, and discusses the nit riding time, CNO-concentration, matrix of different heat treatment state carbonitriding layer quality, loose layer thickness, oxidation film level and corrosion resistance of influence, and through the surface hardness test, cross section micro hardness distribution test, OM metallographic observation, XRD phase composition and structure analysis, abrasion resistance testing, mechanical property testing (tensile, impact), polarization curve testing, immersion test and corrosion was observed.The results show that:(1) The salt in620℃Chen after2h CNO-concentration can achieve37%, while in up to48h time the Chen, CNO-concentration down slowly, almost no change, at the same time salt bath liquidity is better, after nit riding loose layer is thinner, loose layer high quality characteristics. Adjust salt can be transformed into carbonate root cyanide root restored CNO-activity, reduce the CN-concentration and improve the liquid surface height purpose, at the same time, to make the work with salt oxidation salt formed on the surface of the corrosion resistance to the density of the strong oxidation film, and can completely decompose from nit riding salt bath brings out CNO-and CN-eatures.(2) the original steel after QPQ treatment from the surface in a compact in turn to Fe3O4oxide film (oxidation layer), then thick about10-35um when Fe between the nitrides carbonitriding layer (including Fe2～3N, also called compound layer)), finally forms including N a-Fe (diffusion layer) interstitial clearance.(3) At the same nit riding temperature and CNO-concentrations of nitrogen with the extension of time, the compound layer thickness increases, total carbonitriding layer thickness increases, loose layer thickness were increased and generate loose layer porous and corrosion resistance is bad, in the same nit riding temperature and nit riding time conditions, the greater the CNO’concentration, the solution of the active N atomic sufficient, speeding up the compound layer formation speed, generating nit riding depth linear increase, in the meantime nit riding composition change to Fe2N change by Fe3N, when salt bath of cyan ate root content is lower in the solution when CNO-concentration decreased to32%the following, N elements into the potential energy will be dropped substantially, the same condition, depth of compounds will be dropped substantially, this time may produce Fe4N needle organization, but when CNO-concentration38%higher, the oxidation of salt bath of increase, this time the salt bath, strong corrosive lead to compound layer of poor quality and loose porous easy form corrosion pores, and generate loose layer are serious, the whole resistance to corrosion dropped substantially, even lower than before treatment.(4)Whether the tempering or temperature tempering steel QPQ treatment in state wear resistance, corrosion resistance and mechanical properties is greatly improved, especially wear resistance is increased the high5-before treatment, six times and conditioning state in QPQ steel test, whether in carbonitriding layer thickness, carburizing layer quality, abrasion resistance and tensile, impact and resistance to corrosion are more tempering state, but also in the QPQ test process to the heart of the hardness difference, suitable for engineering application, and tempering state in treatment of large effect on organization turned their hearts, because QPQ nit riding process is equivalent to a high temperature tempering, so heart department will reduce hardness material, so by heat treatment can improve QPQ nit riding process of materials of the hardness of heart, QPQ nit riding process used in the temperature tempering45#steel sample do not need to be in a time before tempering quenching and tempering treatment.