Effect Of Carbon Partitioning Process On Microstructure And Mechanical Properties Of B1500HS Steel After Hot Forming

After quenching-partitioning(Q-P)treatment,the composite structure of martensite hard phase and retained austenite soft phase is obtained at room temperature,which makes the steel possess both excellent strength and good plasticity in performance and low production cost.In this paper,the high strength steel B1500 HS is taken as the research object.By means of the combination of numerical simulation and experimental research,the VUSDFLD interface of finite element simulation software Abaqus is redeveloped to simulate the Q-P integrated process and obtain the simulation results of the structure field distribution.According to the simulation results of finite element,the Q-P integrated process experiment is designed to analyze the structure and force of B1500 HS.The feasibility of obtaining high strength and good plasticity workpiece by Q-P process treatment of high strength steel B1500 HS was verified by the influence of chemical properties.The high strength steel B1500 HS was treated by Q-P process with Gleeble thermal simulator.The unidirectional tensile test showed that the tensile strength of the treated specimens was 1299.85 MPa~1519.33 MPa,the plasticity was greatly improved,and the elongation after fracture increased from 6.70% to 11.92%~20.25%.The results of optical microscope metallographic observation and X-ray diffraction analysis show that the microstructure of the specimens treated by Q-P process is composed of lath martensite phase and retained austenite phase.The optimum technological parameters are as follows: partitioning temperature 330 C,partitioning time 30 s,tensile strength 1315.62 MPa,elongation after breaking 20.25%,Strength-plasticity product 26641.31 MPa,and retained austenite phase up to 12.81%.The thermodynamic model of Q-P integrated process is analyzed and programmed.The VUSDFLD interface of Abaqus finite element simulation software is used for secondary development.The structure of Q-P process is simulated and calculated.The structure evolution law of B1500 HS high strength steel treated by Q-P process is obtained.The experimental verification of Q-P integrated process for high strength steel B1500 HS cap-shaped parts shows that the plasticity of high strength steel B1500 HS is greatly improved after Q-P process,the elongation after breaking is 10.27%~18.61%,the tensile strength is 893.19 MPa~1155.71 MPa,the bottom plate strength of cap-shaped parts is the highest,the flange plate strength is the lowest,the flange plate plasticity of cap-shaped parts is the best,the bottom plate is the second,and the side plate is the worst.The microstructure of the alloy is lath martensite,retained austenite and a small amount of bainite.The optimum technological parameters are as follows: distribution temperature 350 C,distribution time 30 s,tensile strength 1021.35 MPa,elongation after breaking 18.61%,and strength-plastic product 1907.3235 MPa.