Study On Heat Treatment Process And Its Precipitation Behavior Of Plastic Die Steel 10Ni3MnCuAl

With the improvement of the quality of industrial products and the increasing size of components,the demand for high-quality,large-section plastic die steel will be enhanced in future.In order to cope with this demand,by means of three-dimensional atom probe?3DAP?,dilatometer,scanning electron microscope?SEM?,transmission electron microscope?TEM?,impact testing machine and other equipments,the heat treatment process,the continuous cooling transformation of austenite and the precipitate pattern in Ni-Al-Cu system of 10Ni3MnCuAl steel were systematically studied,and its toughness,corrosion resistance,polishing performance and microstructure were studied in this thesis.In addition,under the premise of ensuring performance,the cross-section of the production are improved.The main results can be summarized as follows:?1?Its temperature of A_c1,A_c3,M_s,M_f are 687°C,765°C,332°C,214°C,respectively.Granular bainite is appeared when its cooling rate is lower than 0.2°C/s.Under air-cooled and water-cooled conditions,the core cooling rate of 10Ni3MnCuAl steel with a thickness of 1200 mm is greater than 0.01°C/s.?2?During the solution procedure,the mechanical properties of 10Ni3MnCuAl steel increased first and then decreased from 790°C to 910°C which due to the influence of grain size,and its peak hardness appeared at 870°C.At the duration of aging,unmelted carbide or large particle precipitates will have a detrimental effect on the polishing performance and corrosion resistance.Therefore,the optimum heat treatment process is 870°C solution treatment for 2 h and aging at 510°C for 6 h,and its hardness can reach 42-44 HRC.?3?Alloying elements such as Ni,Al,and Cu can improve the performance by the nano-sized precipitates during the aging process of the material.When the aging temperature is too high or the aging time is too long,the precipitates are coarsened and the performance is deteriorated.The precipitated particles B2-NiAl and Cu are spherical or nearly spherical at 540°C for 0.5 h and 2 h,and they are strip-shaped at 100 h.The relative particle radius of the them are similar at each time which are between 1 nm and3 nm.When aging for 2 h at 540°C,the number density of Cu particles is 1.22 times than that of NiAl particles.In the isothermal aging process,the NiAl particles are first precipitated from the solid solution state,and the Cu atoms are first enriched in the NiAl particles,and then precipitated separately.They precipitated in adjacent locations.At 2h of aging,MC-type carbides were present in the microstructure and M₇C₃-type carbides were present in the microstructure at 100 h.The strengthening process of10Ni3MnCuAl steel is the result of NiAl particles dominated,Cu particles supplemented,and all alloying elements such as C,Mn and Mo work together.