Research On Melted Generated Phases Representation And Heat Treatments Influence And Mechanical Properties Of Heat-resistant Steel C12A

Heat-resistant steel C12A is a type of high-alloyed casted steel, served under the environment of high-temperature and high-pressure, and it is used to make cylinder,high-pressure valve bodies and other key components in (ultra) supercritical thermal power units.The material is studied in-depth and make localization early which is a great significance for our nation to develop our (ultra) supercritical thermal power units.In this paper, thermodynamic equilibrium precipitate phases of the heat-resistant steel C12A are analysed,and Gibbs free EnergyΔGof the carbine of different kinds in the five elements Fe-Cr-Ni-V-C system was calculated; The microstructure and the mechanical properties of the casted heat-resistant steel C12A were tested; The influences to C12A on properties and microstructure which was made by different heat treatments process and different tempering temperature were studied; To study the high-temperature mechanical properties,high temperature tensile testing was carried out under the conditions of 550^℃,600^℃,650 ^℃and 700 ^℃, and the fracture scanning was also carried out. All the results show that:The thermodynamic calculations show that in the Fe - Cr - Ni - V - C five elements system,after melted, when the temperature is higher than 1785K, the Gibbs free energyΔGof the precipitates Cr₂₃C₆ is the minimum, then the Cr₇C₃, the precipitates of Cr₂₃C₆,Cr₇C₃,VC etc would also included. As it is under liquid environment, a small amount of cementite would be generated, the mainly precipitates in the matrix are Cr₂₃C₆,Cr₇C₃,Fe₃C,VC and so on. The casting C12A is of a good mechanical properties under normal temperature,and the microstructure is plank martensite; The mechanical properties and microstructure have a great influence on different heat treatment process, the process of normalizing or quenching + tempering in high temperature made it in it's best; Tempering temperature made a great contribution to the mechanical properties of C12A, the plank martensite would reply insufficient if tempering temperature is too low; On the contrary, it would enter the coexistence region,then partly would austenitizing, so the best tempering temperature comes from760 ^℃to 790 ^℃.The anti-soften capability of C12A under high temperature is very well. The properties of tensile strength and plasticity are much significantly higher than that of carbon steel and stainless steel in the same high temperature conditions. Through the fracture scanning, it can be known that the fracture mode under high temperature is ductility.