[PO-F1] Poster Session 1

[P1-37] Hydrogen trapping in carbon supersaturated a-iron and its decohesion effect in martensitic steel

^○Wen-Tong Geng^1,2, Vei Wang^1,3, Jin-Xu Li², Nobuyuki Ishikawa⁴, Hajime Kimizuka¹, Kaneaki Tsuzaki^5,6, Shigenobu Ogata^1,6 (1.Department of Mechanical Science and Bioengineering, Osaka University, Japan, 2.University of Science and Technology Beijing, China, 3.Department of Applied Physics, Xi’an University of Technology, China, 4.Steel Research Laboratory, JFE Steel Corporation, Japan, 5.Department of Mechanical Engineering, Kyushu University, Japan)

It is generally accepted that the martensite in steels is more susceptible to hydrogen embrittlement than the ferrite. The atomic-scale mechanism underlying this phenomenon, nevertheless, is not fully understood yet. Our first-principles calculations demonstrate hydrogen is more stable in carbon supersaturated martensite than in a-iron, due to the carbon-induced tetragonality in martensite lattice. The trapped hydrogen leads to remarkable decohesion between (110) planes both inside the martensite and along the martensite/ferrite interface, with the former being more significant than the latter. This decohesion can explain recent precise observations that in martensite/ferrite dual-phase steels the hydrogen-promoted crack was initiated in the martensite region and that in lath martensite steel it propagated not on lath boundaries but showed quasi-cleavage feature along (110) planes at very high hydrogen concentration.