( J69-1170) DP 鋼およびTRIP 鋼の不均一変形挙動におけるマルテンサイトとベイナイトの寄与Contribution of martensite and bainite to inhomogeneous deformation behavior in DP and TRIP steels

摘要

High strength steels with composite structure such as DP and TRIP steels exhibitmicro-scale inhomogeneous deformation during tensile testing due to the difference in strength andmorphology among the constituent microstructures. The inhomogeneous deformation affects thebehavior of work hardening and fracture. In fact, DIC (Digital Image Correlation) analysis for DPsteel revealed that strain was concentrated into ferrite grains neighboring the hard structure ofmartensite, and the strain concentration provided the nucleation sites of the void (1). However, theinhomogeneous deformation behavior in TRIP steel have been rarely studied so far because TRIPsteel consists of complicated structure including bainite and retained austenite as well as martensite,and their size is too fine to be analyzed in detail by conventional SEM. In this study, DIC analysisusing in-situ tensile testing was applied to DP and TRIP steels produced from a low carbon steel. Inparticular, the plastic deformation behavior of each hard structure, namely, martensite and bainite,was focused, and then, the inhomogeneous local plastic strain distribution developed in the initialdeformation stage was compared between those steels.