| The high-throughput material simulation calculation method and experimental study were combined to study a martensitic heat-resistant stainless steel,which is used for the key components in engine.By studying the effect of long-term aging at650?on microstructure and mechanical properties of the tested steel,the results of the effect of precipitated phase on microstructure and properties was analysised,as well as the growth regularity of precipitated phase in tested steel,the thermodynamic calculation based on software Thermo-Calc and dynamic simulation based on DICTRA were combined to be used in the study of component optimization,and the coarsening simulation results of precipitated phase before and after component optimization were compared.The results are as follows:The microstructure of the tested steel after heat treatment turned lath martensite which contained a small amount of?-Fe.After long-term aging,the microstructure came to recovery,and the martensite lath got widened and the precipitated phase got coarsened.The precipitates in the microstructure after heat treatment were mainly M23C6 carbides and MX,and the Laves phase precipitated during aging,The type of precipitated phase obtained by thermodynamic calculation was in agreement with the qualitative results of XRD in tested steel,and results from Thermo-Calc calculations showed that the precipitation of the?phase during aging was related to the segregation of chromium in the vicinity of grain boundaries.The sharp decrease of strength and hardness within 500 h aging time could be attributed to the combined effects of the coarsening of precipitates and the recovery of microstructure.After the aging time was prolonged,the strength and hardness decreased slowly due to a large number of precipitation of the hard and brittle?phase.The impact energy decreased within 1000 h aging time,which was mainly influenced by the coarsening of Laves phase and the chain-shape distributed M23C6 particles.After the aging time was prolonged,the softening effect by microstructure recovery was enhanced,and the impact energy increased slightly.The plasticity remained unchanged within 500 h aging time,and increased slowly after longer aging time because of the recovery of microstructure.Based on kinetic calculation software DICTRA,the coarsening simulation results of M23C6 and Laves phase were in good agreement with the experimental results.The coarsening rate of M23C6 and Laves phase increased with the increasing of temperature.The growth rate of M23C6 during long-term aging was lower than that of tempering,and the growth of Laves phase was promoted by the nucleation and precipitation of M23C6 at the initial stage of aging.Combined with the analysis of experiment and simulation calculation,by reducing the content of carbon,chromium and nitrogen,as well as replacing part of molybdenum from tungsten,part of niobium from vanadium and part of nickle from cobalt to carry out the component optimization.In the thermodynamic equilibrium state,and after the component optimization,the precipitation of M23C6 decreased by7.37%,the precipitation of Laves phase decreased by 26%,the precipitation of Z phase decreased by 22%,and MX phase precipitated slightly.The precipitation temperature of M23C6,Laves and Z phase decreased,while the precipitation temperature range of MX was obviously enlarged.Besides,the precipitation tendency of?phase decreased obviously.The results of coarsening simulation showed that the particle size of M23C6 was almost unchanged,but the equilibrium volume fraction and quantity density decreased obviously.The quantity density of Laves phase reduced slightly,the particle size and volume fraction of Laves phase decreased significantly.The coarsening rate of M23C6 and Laves phase were both decreased.The optimized control of precipitation growth in this steel was realized,which indicated that the results of the component optimization were reliable. |
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