Study On Tempering Treatment And Optimization Of Gas Nitriding Process Of H13 Steel

With the rapid development of economy, aluminium profiles are more and more widely used in building, automobile, shipbuilding, aviation, aerospace and other fields. In the modern production, most of the aluminium profiles are made through extrusion. The extrusion dies work with high temperature spindles directly, under high temperature, pressure, intense friction, etc.The working conditions are extremely poor, so that the moulds can easily fail due to wear and fatigue, the life of moulds are decreased significantly. H13 is the most widely used hot die steel home and abroad. Through appropriate heat treatment and surface hardening treatment, it can have good strength and toughness inside, and high surface hardness, wear resistance, fatigue resistance and other excellent properties outside. In this paper, the effects of tempering treatment conditions before nitriding and nitriding process parameters on inside and nitrided layer were investigated.The tempering is an important heat treatment way for H13 steel. So firstly, the influence of tempering treatment temperature and tempering number on the micro- structure and mechanical properties of H13 steel were investigated by microscopy analysis(OM) and hardness analysis. Secondly, two different procedure of nitriding were tested and analyzed. Thirdly, the effects of tempering conditions on the depth, microstructure, hardness, phase composition of nitrided layer were investigated by electronic microscopy analysis(OM, SEM), microhardness tester, energy dispersive spectrometer(EDS) and X-ray diffractometer(XRD). Finally, many gas nitriding tests trough the orthogonal experimental design were designed, the effects of the various process parameters on the quality of nitrided layer were analyzed and compared comprehensively.The results showed that with the increase of tempering temperature, the hardness of H13 steel increased and then decreased. After quenched under 1030℃, not only with the high temperature(560℃,600℃) tempering, but also with the low temperature (350℃) tempering, H13 steel can achieved appropriate hardness and good toughness. The material owned better properties after tempering twice than once. H13 steel had the thicker nitrided layer, higher surface hardness, better wear resistance after nitriding process No.1 compared to nitriding process No.2. Tempering temperature before nitriding process affected the depth of nitrided layer significantly. With the increase of tempering temperature, the depth of nitrided layer increased. The factors which affected surface hardness and depth of nitrided layer most were nitriding temperature and resolve rate of NH3 respectively. With the increase of nitriding temperature, the surface hardness increased and then decreased. With the increase of resolve rate of NH3, the depth of nitrided layer also increased and then decreased. The optimized heat treatment and nitriding procedure has been obtained, which was tempering at 560℃, nitriding at 535℃for 15h, the resolve rate of NH3 50%. These parameters can provide a reference for the actual production.