Effects of Al-Si coating structures on bendability and resistance to hydrogen embrittlement in 1.5-GPa-grade hot-press-forming steel

Jisung Yoo, Selim Kim, Min Cheol Jo, Seongwoo Kim, Jinkeun Oh, Sang Heon Kim, Sunghak Lee, Seok Su Sohn

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29 Citations (Scopus)

Abstract

Hot-press-forming (HPF) steels have attracted great attention as automotive reinforcement parts, but are exposed to the potential risk of hydrogen embrittlement (HE) because H introduced easily during HPF processes is hardly de-trapped through the solidified coating. In particular, H seriously deteriorates bendability, which is one of the main properties to be considered. In this study, the Al-Si coating structures were modified to improve H emission by increasing H diffusivity. The effects of coating structures on bendability and H desorption were investigated by interrupted bending tests, H-permeation tests, and thermal desorption analyses according to elapsed time after H-charging. Immersion in an Al-10%Si bath and the subsequent HPF process (930 °C for 6 min) produced a 33 μm-thick multiple coating structure composed of Fe2Al5, FeAl, and ferrite layers. On the other hand, the reduced Al-Si adhesion amount from the dip bath and the increased time and temperature (950 °C for 30 min) produced a 30 µm-thick body-centered-cubic (BCC)-based coating structure composed of FeAl and ferrite layers. The BCC-based crystal structure, reduced Al content in the FeAl layer, and coarsened ferrite grains effectively enhanced H diffusivity and suppressed H-induced degradation. Moreover, the softened FeAl and thick ferrite layers improved bendability by allowing the large strain accommodation of bending deformation. Thus, this work proposes an optimal Al-Si coating design that enhances both bendability and resistance to H-induced degradation for secure HPF steel applications.

Original languageEnglish
Article number117561
JournalActa Materialia
Volume225
DOIs
Publication statusPublished - 2022 Feb 15

Bibliographical note

Funding Information:
This work was supported by the POSCO Technical Research Laboratories, the Korea University Grant for S.S. Sohn, and the Brain Korea 21 FOUR Project for Education and Research Center for Future Materials (F20YY7105002).

Publisher Copyright:
© 2021 Acta Materialia Inc.

Keywords

  • Al-Si coating structure
  • Hot-press-forming steel
  • Hydrogen diffusivity
  • Hydrogen embrittlement
  • Interrupted three-point bending test

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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