Papers by Keyword: Dual-Phase Steel

Abstract: In this article, the authors have analysed the influence of quenching temperature (T_Q) on the mechanical properties of a dual-phase steel with 0.094 % C and 0.53% Mn. In order to obtain a ferrite-martensite structure, specimens of this material have been the subjected to intercritical quenching that consisted of heating at 750, 770, 790, 810 and 830 ^°C, maintaining for 30 minutes and cooling in water. These specimens have then been subjected to metallographic analysis and tensile test in order to determine the volume fraction of martensite (V_M) in the structure, ultimate tensile strength (R_m), the 0.2% offset yield strength (R_p0.2), the total elongation (A₅) and the R_p0.2/R_m ratio.

Abstract: The plastic deformation behavior of dual-phase (DP) steel is strongly affected by its underlying three-dimensional (3D) microstructural factors such as spatial distribution and morphology of ferrite and martensite phases. In this paper, we present a coupled simulation method by the multi-phase-field (MPF) model and the crystal plasticity fast Fourier transformation (CPFFT) model to investigate the 3D microstructure-dependent plastic deformation behavior of DP steel. The MPF model is employed to generate a 3D digital image of DP microstructure, which is utilized to create a 3D representative volume element (RVE). Furthermore, the CPFFT simulation of tensile deformation of DP steel is performed using the 3D RVE. Through the simulations, we demonstrate the stress and strain partitioning behaviors in DP steel depending on the 3D morphology of DP microstructure can be investigated consistently.

Abstract: The specific volume of alloys can be calculated using Thermo-Calc^® for the problem of diffusion transformation in equilibrium or a single phase. The martensite transformation in a displacive manner can not be treated directly with Thermo-Calc^®. A method to calculate the thermal dilatation curves for a dual-phase steel was established in this research associated with martensitic transformation from ferrite plus austenite after intercritical annealing. The equilibrium phase diagram, martensite starting temperature, as well as transformed martensite fraction have been involved in the calculations. The results showed that the calculated dilatation curves were in accordance with the measured curves by dilatometer, and indicated the reason for the ambiguous volume change in the dual-phase steel owing to its small fraction of austenite associating with martensite transformation.

Abstract: In this study, a U-channel bending test with tension were used to evaluate the surface damage resistance of dual-phase (DP) steel against heat treated Mo-Cr cast iron, and a numerical simulation model of the U-channel bending were developed to analyze the interface contact pressure on formed part that is an important influencing factor of surface damage. Investigation results for two bare steel sheets DP780 and DP590 demonstrate that DP780 steel showed more severe surface damage on formed part, and that for the steel DP780 greater interface contact pressure is induced as a result of effect of larger plastic deformation.

Abstract: Laser weldability was investigated for advanced high-strength steel sheets for automotive applications. Dual-phase steel (DP780) and martensitic steel (MS1300) sheets were employed as base materials; laser-butt and overlap welding experiments were conducted on combinations of steels with similar and dissimilar strength. The tensile strength and metallurgical morphology were analysed for the butt-welded specimens; tensile-shear strength and bead shapes were analysed for the overlap-welded specimens. Even with laser welding, martensite in the heat-affected zone disintegrated and resulted in a softened, heat-affected zone as compared with the base materials. The tensile strength of a butt weldment was determined by the strength of the heat-affected zone. The tensile-shear strength of an overlap weldment was determined by not only the strength of the heat-affected zone but also bead shapes such as blow holes, underfill, and the bead width at the faying surface.