ProCast Simulation Optimization And Experimental Study Of TP347H Steel Die Casting Process

Austenitic heat-resistant steel for high-pressure boilers such as TP347H has excellent high-pressure structural stability and durability,and is widely used in various high-temperature parts of power station boilers.In the metallurgy of domestic austenitic heat-resistant steel,the production process of steel pipes and the application of end users,it is easy to appear that the particles of the precipitated phase containing Nb are large,the yield rate of the steel pipe is low during the steel pipe rolling process,the product quality is low,and the quality of the bend pipe in the construction of the power station is not easy.A series of problems such as guarantee and poor performance at high temperature.This thesis is aimed at the problem of coarse and uneven distribution of primary Nb-containing precipitated phase particles（related to Nb segregation）in the solidification process of TP347H austenitic heat-resistant steel.According to the technical route of thermodynamics,finite element calculation and experiment,aiming at small size The test steel ingots are analyzed by low magnification,metallography,scanning electron microscopy,microbeam fluorescence and XRD.The thermodynamic equilibrium phase diagrams of precipitation and solid solution behavior are calculated based on Thermo-Calc and Jmat Pro software.The temperature field and microstructure of the steel ingot casting process are developed based on ProCast software.Organize finite element simulation and get the following conclusions:There are shrinkage porosity and Nb element segregation in the center of the small-sized test steel ingot.The proportion of equiaxed crystals is small and distributed along the central axis of the ingot;as the N content increases,the equiaxed crystal ratio will increase accordingly.The solidification structure of the small-size test steel ingot obtained by finite element simulation is basically consistent with the low-magnification analysis results;the types of precipitates calculated by thermodynamics are consistent with the XRD qualitative results of the small-size test steel ingots,and the main precipitates are MX phase and M₂₃C₆Wait.By reducing the content of C,N,and Nb in the steel to optimize the composition,the precipitation temperature of the MX phase can be reduced from 1370°C to 1350°C,which is lower than the solidus temperature,and the amount of precipitation is also significantly reduced;The appropriate content of C,N,and Nb is 0.052%,0.006%,and0.52%respectively.The finite element simulation compares the solidification process of industrial-size steel ingots with superheat of 30℃,45℃,60℃and 75℃.It is found that when the superheat is 60℃,the shrinkage cavity and shrinkage porosity in the alloy are the best.The finite element simulation compares the influence laws of superheat,heat transfer coefficient,and N content on the solidification structure of industrial-sized steel ingots.As the degree of superheat increases,the nucleation rate decreases,the columnar crystal region becomes wider,the equiaxed crystal becomes less,and the average grain size increases;the heat transfer coefficient increases,which stimulates the nucleation of non-uniform nucleation particles,and the equiaxed crystal becomes less,The columnar crystals grow up obviously;with the increase of the N element content,the equiaxed crystal area expands and the number of columnar crystals decreases.