| As the term "Energy Saving and Emission Reduction" was proposed, people demand more about automobiles:lightweight, improved safety and high crashworthiness. People's desire of that can be achieved by the appearance of Advance High Strength Steel (AHSS) and the associated hot stamping technology. As one type of AHSS—boron steel, which is used for hot forming, also receives extensive attention. This paper employs the boron steel produced by Baosteel—B1500HS as the object of the investigation. The procedure of quenching, uniaxial hot drawing and hot bending were studied, also the properties of sheet steel after quenching, parameters of quenching process, flow behavior at elevated temperature and the springback of hot bending were discussed.Using the tools designed by us, the quenching experiment was conducted under three different cooling mediums—water, copper and iron chopping board with cooling duct, the influence of specimen's austenitizing temperature and holding time to the mechanical property and microstructure was comprehensively investigated. According to the results, the heat treatment parameters of B1500HS boron steel under the condition of solid quenching were proposed. Meanwhile, the influence of cooling medium to final mechanical property of sheet steel after quenching was analysed. Better strength performance will be achieved under the austenitizing temperature of 900 to 950℃with the holding time of 5 min. Different cooling medium did not show dramatic influence to the final mechanical properties of the quenched part.Through the uniaxial hot drawing test, the relationship between forming load, tensile strength at elevated temperature and strain, strain rate, temperature was studied respectively. Also, through this test, we discover that the factors of strain, strain rate and temperature all show significant influence to the flow stress of B1500HS boron steel. Besides that, using least square method, we can get a equation with respect to flow stress and these factors by fitting. The flow stress model of B1500HS boron steel under the condition of 1173K≤T≤1233K,0.033s-1≤ε≤0.067s-1 is Experimental mould was designed, which aims to study the bending formability of B1500HS boron sheet steel at room and elevated temperature. The influence of technological parameters, such as temperature and bending radius and so forth to springback was analysed. It could be concluded that springback angle can be controlled within the range of±0.5°by hot bending process, the rise of temperature benefits the decrease of springback angle, and bending angle which is too small will lead to negative springback and the value of the springback angle will exceed 0.5°.With the help of finite element software—Dyna-form, we conducted the numerical simulation of the springback angle of B1500HS sheet steel under different bending radius and temperature. The comparison between fitting result and experimental data shows that by means of numerical simulation method together with the material loading model selected in this paper, we can forecast the variation of springback angle in the bending process under certain temperature range. Using a software named ABAQUS/CAE, the temperature distribution of the blank during the hot bending process of B1500HS sheet steel was investigated in this paper. The results indicate that the dwell time of 7 s can insure the accomplishment of the martensitic transformation in material. Meanwhile, during the dwelling process, heat always accumulate in the fillet of the bending part. So, adding cooling duct below the fillet of the die is essential. |
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