Effect of Hydrogen on Spot-Welded Tensile Properties in Automotive Ultrahigh-Strength TRIP-Aided Martensitic Steel Sheet

Akihiko Nagasaka, Tomohiko Hojo, Katsuya Aoki, Hirofumi Koyama, Akihiro Shimizu, Zulhafiz Bin Zolkepeli, Yuki Shibayama, Eiji Akiyama

Research output: Contribution to journalArticlepeer-review

Abstract

Effect of hydrogen on spot-welded tensile properties in ultrahigh-strength TRIP-aided martensitic steel (TM steel) sheet was investigated for automotive applications. Tensile test was performed on a tensile testing machine at a crosshead speed of 1 mm/min (strain rate of 2.8×10- 4/s), using base metal and spot-welded specimens with or without hydrogen charging. The results are as follows. (1) The difference between the tensile strength (TS) of 1 532 MPa for base metal specimen without hydrogen charging and the maximum stress (TS-H) of 1 126 MPa for the base metal specimen with hydrogen charging (ΔTS-H=TS-TS-H) in the TM steel was smaller than that of hot stampted steel (HS1 steel) and superior to that of HS1 steel. On the other hand, the TS-H of 725 MPa for the base metal specimen with hydrogen charging was halved in comparison with the TS of 1 438 MPa for base metal specimen without hydrogen charging in the HS1 steel. It is considered that this was because the retained austenite suppressed the strength reduction due to the hydrogen embrittlement of the TM steel. (2) The amount of hydrogen decreased in the order of the HS1 steel, the TM steel, and the tempered martensitic steel (HS7 steel), and the HS1 steel was the highest. This is thought to be due to the high dislocation density of the HS1 steel. (3) The difference between the maximum stress (TS-W) of the spot-welded specimen without hydrogen charging and the maximum stress (TS-WH) of the spot-welded specimen with hydrogen charging (ΔTSWH= TS-W-TS-WH) in the TM steel and that of the HS1 steel were similar. It was considered that this is partly due to the effect of the stress concentration on heat affected zone (HAZ) softening of the hardness distribution of the spot-weld.

Original languageEnglish
Pages (from-to)2644-2653
Number of pages10
JournalIsij International
Volume61
Issue number10
DOIs
Publication statusPublished - 2021

Keywords

  • Hot stamped steel
  • Hydrogen embrittlement
  • Spot-welded specimen
  • Tensile properties
  • Trip-aided martensitic steel

ASJC Scopus subject areas

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

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