Analysis And Simulation Study Of Hot Forming For High Strength Steel

Since the21st century, automobiles have quietly come into people’s daily life as ahigh consumer goods. But, with the rising of people’s living standards and human’sattention to the earth’s environment,the requirements of auto’s safety and energy savinghave become more and more strongly. Therefore, high strength steels have widelyapplied in car bodies and spare parts. However,due to the high strength and largeresistance of deformation at room temperature, high strength steels are very difficult tobe formed, so the hot forming technology of high strength steels are coming out. In thehot forming process, the high strength steel blank is firstly heated up to theaustenitization temperature in the furnace and hold for some time, then transferring theblank to the press and subsequently formed and quenched in the mould. Because theresistance of deformation of high strength steels at high temperature becomes verysmall, the blank can be easily formed. Also, during the forming process the blank willbe cooled rapidly by the mould with cooling system and martensitic phasetransformation will occur, after that the strength of the formed blank will be higher.This article presents a research on hot forming technology of high strength steel,including tensile experiment at high temperature, theory of hot forming, the constitutiveequation of high strength steel, simulation of hot forming process, et al.The main works of this dissertation are as follows:1) Research on the mechanical behavior at high temperature of high strength steelBR1500HS.Using Gleeble1500thermal simulator to do the high temperature thermalsimulation tensile test of BR1500HS to get the real stress-strain curve of the material atdifferent temperature and different strain-rates.2) Establishing the mathematical model of high temperature flow stress ofBR1500HS. According to the results of high temperature tensile test, the flow stressmodel was established.3) Setting up a new constitutive equation of BR1500HS and secondarydevelopment of VUMAT subroutine based on Abaqus. According to heat transfer theory,theory of plasticity and martensitic phase transformation kinetics, a new constitutiveequation was set up. In this model, the effect of the temperature and phasetransformation on material’s properties was constitutive equation was set up based onsoftware Abaqus. 4) Numerical simulation of high strength steel hot forming process.The hotforming process of U-shaped part was simulated by the new model and Johnson-Cookmodel. The thickness of the blank and springback after forming by the two models andexperiments are compared, and the new model’s results are closer to the experimentvalues. It indicates that the new model can simulate the hot forming process moreaccurate.