Reason for high strength and good ductility in dual phase steels composed of soft ferrite and hard martensite

38th Risø International Symposium on Materials Science

Terada, Daisuke^1,2 ; Ikeda, Gosuke^2 ; Park, Myeong-Heom^2,3 ; Shibata, Akinobu^2,3 ; Tsuji, Nobuhiro^2,3

Department of Advanced Materials Science and Engineering, Chiba Institute of Technology, Narashino

275-0016, Japan^1

Department of Materials Science and Engineering, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto

606-8501, Japan^2

Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University, Japan^3

关键词: D. digital image correlation (DIC);    Large elongation;    Martensite structures;    Network structures;    Strain distributions;    Strain partitioning;    Strength ductility balance;    Tensile deformation;   

Others  :  https://iopscience.iop.org/article/10.1088/1757-899X/219/1/012008/pdf
DOI  :  10.1088/1757-899X/219/1/012008

来源: IOP

【 摘 要 】

Dual phase (DP) steels in which the microstructures are composed of a soft ferrite phase and a hard martensite phase are known to show good strain-hardening, high strength and large elongation, but reasons for their superior mechanical properties are still unclear. In the present study, two types of DP structures, having either networked martensite or isolated martensite were fabricated in a low-carbon steel by different heat treatment routes, and their tensile deformation behavior was analyzed using the digital image correlation (DIC) technique. It was revealed that the DP specimens having networked martensite microstructures showed a better strength-ductility balance than the DP specimens with isolated martensite structures. The microscopic DIC analysis of identical areas showed that the strain distribution within the DP microstructures was not uniform and the plastic strain was localized in soft ferrite grains. The strain localized regions tended to detour around hard martensite but eventually propagated across the martensite. It was found also from the DIC analysis that the degree of strain partitioning between ferrite and martensite in the networked DP structure was lower than that in the isolated DP structure. The deformation became more homogeneous when the hard phase (martensite) was connected to form a network structure, which could be one of the reasons for the better strength-ductility balance in the networked DP structure compared to that in the isolated DP structure.