Effect of Heat-Affected Zone on Spot Weldability in Automotive Ultra High Strength Steel Sheet

Akihiko Nagasaka, Junya Naito, Shota Chinzei, Tomohiko Hojo, Katsumi Horiguchi, Yuki Shimizu, Takuro Furusawa, Yu Kitahara

Research output: Chapter in Book/Report/Conference proceedingChapter

Abstract

Effect of heat-affected zone (HAZ) on spot weldability in automotive hot stamping (HS) steel sheet was investigated for automotive applications. Tensile test was performed on a tensile testing machine at a crosshead speed of 3 mm/min, using spot welded test specimen (Parallel length: 60 mm, Width: 20 mm, Thickness: 1.4 mm, Tab: 20×20 mm). The spot welding test was carried out using spot welded test specimen with welding current (I) of 6.3 kA to 9.5 kA. Hardness was measured with the dynamic ultra micro Vickers hardness tester. In HS steel, has very high strength of 1 500 MPa, tensile strength (TS) and total elongation (TEl) of the spot welded test specimen of HS steel were lower than those of base metal test specimen. The spot welded test specimen broke in the weld. The Vickers hardnesses (HVs) of base metal and fusion zone of hot stamping steel were around HV500. In addition, the hardness of HAZ was under HV300. The difference of hardness between fusion zone and HAZ was around HV200. The hardness distribution acted as a notch. On the other hand, in dual phase (DP) steel, has low strength of 590 MPa, the TS of spot welded test specimen of DP steel was the same as the base metal test specimen because of the breaking of base metal. The TEl of the spot welded test specimen of DP steel was smaller than that of base metal test specimen. In the spot welded test specimen of DP steel, the hardness of base metal was around HV200 and the fusion zone was around HV500. The hardness distribution did not act as a notch. The difference in hardness between base metal and HAZ acted on a crack initiation at HAZ softening.

Original languageEnglish
Title of host publicationHSLA Steels 2015, Microalloying 2015 and Offshore Engineering Steels 2015 Conference Proceedings
Publisherwiley
Pages489-494
Number of pages6
ISBN (Electronic)9781119223399
ISBN (Print)9781119223306
DOIs
Publication statusPublished - 2015 Nov 6

Keywords

  • Heat-affected zone
  • Hot stamping
  • Spot weldability

ASJC Scopus subject areas

  • Engineering(all)
  • Materials Science(all)

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  • Cite this

    Nagasaka, A., Naito, J., Chinzei, S., Hojo, T., Horiguchi, K., Shimizu, Y., Furusawa, T., & Kitahara, Y. (2015). Effect of Heat-Affected Zone on Spot Weldability in Automotive Ultra High Strength Steel Sheet. In HSLA Steels 2015, Microalloying 2015 and Offshore Engineering Steels 2015 Conference Proceedings (pp. 489-494). wiley. https://doi.org/10.1002/9781119223399.ch58