超高強度－高延性複層鋼板実現に向けた複合ナノ／ミクロ組織の変形機構の研究

2016 Fiscal Year Annual Research Report

• Project/Area Number: 16F16359
• Research Institution: The University of Tokyo
• Principal Investigator: 小関 敏彦 東京大学, 大学院工学系研究科(工学部), 教授 (70361532)
• Co-Investigator(Kenkyū-buntansha): SHIN SE-EUN 東京大学, 大学院工学系研究科(工学部), 外国人特別研究員
• Project Period (FY): 2016-11-07 – 2019-03-31
• Keywords: Multilayer steel / Martensite / TRIP steel / TWIP steel / Deformation behavior / Strengthening behavior / In-situ observation / Mechanical properties

Outline of Annual Research Achievements

1.I have successfully achieved by control of composition and heat treatment of multilayered steel samples consisting of high carbon TWIP steel and medium high carbon martensitic steel. To attain ultra-high strength with good ductility multilayer steel composites, heat treatment and tempering are established to obtain an optimal strength-ductility combination. For consistency, the conditions for samples were certainly controlled by a modified equation of tempering parameter.
2.Following the tempering, the mechanical properties such as strength, ductility and hardness are carried out by tensile testing machine and Vicker’s hardness machine. The results of mechanical properties are obtained using three or more tensile tests for each temper condition.
3.Accordingly, the microstructures were observed using optical microscope and scanning electron microscope (SEM) with electron backscatter diffraction (EBSD). I focused on the deformation behavior of multilayer steel composites, especially, martensitic deformation, so in-situ experiments with SEM-EBSD were carried out for all samples.Several results from the microstructural evaluation have been obtained, therefore, the details of crystallographic features also have studied.

Current Status of Research Progress

2: Research has progressed on the whole more than it was originally planned.

Reason

1.Based on my research background of strengthening and deformation behavior of metallic composites is favorable to understand deformation behavior of multilayer steel composites.
2.Although lath martensitic deformation behavior have been reported; however, The understanding of lath martensitic deformation behavior of multilayer steel composites have not well attended.
3.I focus on the details of the effective parameters of the lath martensitic deformation during the tensile deformation, I conduct considerable experiments and figure out the crystallographic characteristics.

Strategy for Future Research Activity

1.I focused on the lath martensitic deformation behavior of multilayer steel composites, therefore, currently I performed considerable in-situ experiments to become proficient at microstructural analysis. Using a recently developed software to aware the crystallographic feature of the materials, I figured out the microstructural evolution during tensile test.
2.The deformation of the metals follows to slip system, so considering slip system of the martensite, the dominant slip system of the samples will be discovered related to lath martensitic deformation.
3.An academic paper will be prepared for publication.