Improvement of Resistance Against Hydrogen Embrittlement by Carbon Segregation at Prior Austenite Grain Boundary in As-Quenched M K. Okada 1, A. Shibata 1, T. Sasaki 2, H. Matsumiya 3, K. Hono 2 and N. Tsuji 3 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) 2 Research Center for Magnetic and Spintronic Materials, National Institute for Materials Science (NIMS) 3 Department of Materials Science and Engineering, Kyoto University High-strength steels, such as martensitic steels, are highly susceptible to hydrogen embrittlement, so that it is desired to improve their resistance against hydrogen embrittlement for wide application of high-strength steels. The hydrogen-related intergranular fracture occurs mainly along prior austenite grain boundaries (PAGB). Recently, first-principles calculations have revealed that carbon (C) segregation in iron suppressed the reduction of GB cohesive energy by hydrogen. However, it has not yet been verified whether C segregation at PAGB is effective or not in reducing susceptibility to hydrogen embrittlement in martensitic steels. The present study experimentally demonstrated that the resistance against hydrogen embrittlement in martensitic steels can be improved by increasing C segregation at PAGB. Using an Fe-3Mn-0.2C (wt.%) alloy, we successfully increased the carbon segregation at PAGB without changing structural unit size and dislocation density (Non-seg specimen: lower C segregation, Seg specimen: higher C segregation). The ultimate tensile strengths of the uncharged specimens were almost the same (~ 1520 MPa). In contrast, in the hydrogen-charged specimens, the maximum tensile stress was higher in the Seg (1186 MPa) than that in the Non-seg (666 MPa) though the diffusible hydrogen content were similar values (~0.48 wt. ppm). In addition, the fraction of intergranular fracture surface was 11.3% in the Seg, which was significantly reduced from that in the Non-seg (55.5%). Development of Analysis MM-based Techniques and X-Ray Contrast Tomography: Application to Strain Localization Phenomena and Hydrogen-induced Effects on Plasticity in High-strength Steels I. Gutierrez-Urrutia1 and A. Shibata 1 1 Research Center for Structural Materials, National Institute for Materials Science (NIMS) We present a summary of the analysis methods developed in the last years for the characterization of crystal defects (stacking faults, full and partial dislocations) in the SEM by the Electron Channeling Contrast Imaging (ECCI) and Transmitted-forescattered Imaging (t-FSEI) techniques, and the reconstruction of 3D Diffraction Contrast Tomography datasets. The developed methods comprise the establishment of novel technical, methodological and theoretical insights for the understanding of 2D/3D Steel Science. Specific examples applied to the investigation of strain localization phenomena and hydrogen-induced effects on plasticity of high-strength FeMnAlC low-density steels will be given. Poster Presentation ｜NIMS Award Symposium 2023ethods for SE P2 ｜ Characterizationartensitic Steels PP22--1155 PP22--1166 51
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