Narrow Results

Usage of AHSS may reduce the weight of automobiles and improve the crash safety, consequently, AHSS have been used on automobile increasingly. As the typical representative of AHSS, boron alloyed steels have been the point of focus for the materials choice in hot stamping. In this paper, hot stamped steel produced by Ma Steel is taken as the study object. The CCT curve is measured by Gleeble 3500. In addition, parts are trial produced by hot stamping steel sheet, microstructure observation and micro-hardness test are carried out as well. The parameters of hot stamping are determined and the mechanical properties of the parts made by tested steel meet requirements as well.

Here in this paper, a multiscale framework based on crystal plasticity is proposed coupling with thermal activation mechanism, as well as the continuum damage mechanism. The microscopic hardening phenomenon is revealed by a dislocation density evolution model, which is constructed according to the temperature. The physical-based exponential function of shear strain rate is posed to describe the thermal material behavior replacing the general phenomenological power-law equation. A 3D spatial distribution of stress, strain and damage is presented in the finite element method, parameters of which are previously determined by a RVE calculation and fitting test compared to the experimental data. Finally, some discussions of stress heterogeneity and texture evolution are proposed and conclusions are made.

22MnB5 steel has been widely used for its good formability at high temperature and high strength after quenching. Then, a so-called progressive induction quenching process matched with 22MnB5 has been proposed to make thin-wall welded rectangulartubes. However, about 20 ∼ 45 mm bending deformation occurs in the direction of length. In this paper, in order to reduce the bending deformation of thin-wall welded rectangulartube, the reason of deformation is analyzed firstly. Both the hardness of inner and outer surface and tensile strength of rectangular-tube were measured. The microstructure at weld zone was observed to investigate the effect of weld joint. The relationship of temperature distribution and deformation of rectangular-tube was investigated by means of ABAQUS simulation. From the analysis, it can be seen that although the weld microstructure is large in grain size, it has little influence on the deformation. The cooling rate and nonuniform cooling will cause bending deformation, but the main reason is nonuniform cooling.

Usage of AHSS may reduce the weight of automobiles and improve the crash safety, consequently, AHSS have been used on automobile increasingly. As the typical representative of AHSS, boron alloyed steels have been the point of focus for the materials choice in hot stamping. However, the high strength and low toughness with full martensite microstructure of PHS induced the poor bending quality. In this paper, hot stamped steel 22MnB5 and Nb-V composite micro-alloyed PHS produced by Ma Steel was taken as the study object. The microstructure and mechanical properties and bendability were studied after hot stamping; subsequently experienced tempering process. The results indicate proper tempering treatment process can significantly improve bendability.