| Hot stamping of ultra high strength steel is a new sheet metal forming method for modernautomotive manufacture to adapt to energy crises, environmental deterioration and increasingsafety requirements. It is an advanced technology that can make the strength of parts risesharply by changing the physical chemical properties of material. Its principle is to heat themanganese boron steel plate which has strong harden ability to a temperature above therecrystallization and holding for minutes to make it austenized, then transfer it to the toolsquickly for stamping, after holding for some time the microstructure of workpiece transforms touniform martensite completely. The ultimate tensile strength of the hot stamping part canincrease up to1500MPa from about600MPa before, and the part will get excellent wearresistance and weldability. Hot stamping process is becoming a trend of auto body safety partsforming for its apparent advantages.This paper takes one new type of ultra high strength steels as the objective, combines themethod of test, theory analysis and numerical simulation to develop the following research andobtain related harvest：Based on the analysis of hot stamping process of boron steel, by using the physical thermalsimulated experiment, namely, after the materials becoming fully austenitic phase, the tensiletests are carried out under different temperatures and different strain rates, the true stress-straincurves under different conditions are obtained. Then the influences of formingtemperature,forming speed and their rules on flow stress are analyzed. The multi-factorsdifference analysis is carried out based on the results of thermal simulated experiment, theremarkable factors and their effect degree are confirmed during the hot forming condition ofBoron steel.Research on the flow stress model of ultra high strength boron steel is the predeterminecondition to theoretically analyze the plastic forming process and simulation of metal plasticforming. By anylzing the recent research status of flow stress model and based on the hotphysical simulation test result, a new flow stress model fit for the boron steel in hot stampingprocess is established, which realize the description of hot stamping behavior of boron steel.The hot forming activation energy of the new type boron steel is calculated. Based on the studyon the Z parameter, the steady flow stress model and hot forming equation of boron steel isproposed. By using the finite element simulation analysis technology, the hot stamping process ofapart of B.Pillar, U-shape sample of Ultra high strength boron steel, is simulated. Thetemperature distribution, stress distribution and the effective strain distribution during the hotstamping are obtained, the effects and rule of main process parameters such as initialtemperature of blank and stamping velocity on the hot stamping were analyzed. |
PDF Full Text Request