LEE Jae Hoon POSCO Technical Research Laboratories

Spoluautoři CHO Yeol Rea, CHOO Se Don

In order to reduce the vehicle weight by using thinner materials with higher strength, advanced high strength steels (AHSS) are being recognized as automobile structural materials. For an application of AHSS to complex automotive parts, inferior formability of the steels should overcome in cold forming process. Hot press forming (HPF) steels have been developed currently to satisfy both high strength and good formability in manufacturing of automotive parts. In this study, tensile behavior and bendability relationship of B-bearing HPF steels were investigated to produce the full martensitic materials with outstanding bending properties as well as high tensile strengh. After austenitized at 900°C for 6min and quenched in the closed tool, full martensitic microstructure was obtained in the B-bearing HPF steels with 1.5mm in thickness. It was confirmed that the tensile strength and bending angle of the martensitic steels were signeficantly dependent on the carbon content; however, their bendability was independent on the elongation. It was considered that the tensile properties and bendability of B-bearing martensitic steels are accelerated by the tension-induced work hardening, which is related with dislocation density dependent on carbon content. The dislocation density, which was analysed by a Convolution Multiple Whole Profile (CMWP) procedure and a Warren-Averbach plot based on a Williamson-Hall plot using XRD profiles, will be examined in detail to study the relation between bendability and tensile properties of the steels. In addition, the comparative analysis of XRD results and TEM observations on the dislocation density will be mentioned in this conference.