Research On Damage Behavior And Mechanism Of X12 Steel Based On Modified Bonora Model

Ultra-supercritical high-medium-pressure rotors are the most critical pressured components and high-speed rotating components in the entire ultra-supercritical generator set.Due to their large size and volume,they are usually directly forged with steel ingots.The process of hot forging is complicated,and it has the characteristics of high quality requirements,long manufacturing cycles and high production costs.There are many factors that affect the quality of rotors and it is difficult to control.They are prone to defects and cracks,leading to scrapping of the final product and causing huge economic losses.In the forging process of rotors,damage and cracks are the main factors affecting the quality of rotors.Therefore,it is significant to establish suitable ductile fracture criteria to predict and prevent damage initiation and evolution during ultra-supercritical high-medium pressure rotor forging process.X12Cr Mo WVNb N10-1-1 steel with high strength,high toughness,corrosion resistance and thermal fatigue resistance is a commonly material for ultra-supercritical rotors,has the characteristics of.In this work,a combination of physical simulation and numerical simulation was utilized.Regarding X12 steel as the research object,a damage evolution model considering temperature and strain rate was proposed based on the Bonora damage model.The accuracy and effectiveness of the improved Bonora damage model under different triaxiality were verified.The main research contents include:The Bonora damage model under compressive stress was modified,and a damage model considering temperature and strain rate was proposed.Gleeble thermal simulation testing machine was used to perform the tensile tests on X12 steel at the temperature 950°C?1100°C and strain rate 0.1 s^-1?5 s^-1.By combining numerical simulation and experimental data,the damage parameters?,D_cr,?_th,?_cr in damage model were determined based on multi-objective Genetic algorithm(MOGA)reversely,and established the function relationship between temperature,strain rate and each damage parameter.Then the damage model for predicting the damage evolution during high-temperature deformation was established.The improved Bonora damage model was integrated into the FORGE software by user subroutines.Based on digital image correlation experiments,the accuracy of the model to predict the damage evolution under different triaxiality were verified from multiple perspectives.Besides,the damage mechanism of X12 steel under different triaxiality was analyzed by scanning electron microscope.Finally,the ultra-supercritical high-medium pressure rotor forging test was performed on a 315 ton press machine at a scale of 1:13.5.The forging processes were simulated in the FORGE software,and the damage distributions of the workpiece by the two kinds of stretching process were analyzed,which provides a basis for formulating reasonable process parameters for the ultra-supercritical high and medium pressure rotors.