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Metallurgical and Materials Transactions A

, Volume 39, Issue 3, pp 593–603 | Cite as

Transmission Electron Microscopy and Nanoindentation Study of the Weld Zone Microstructure of Diode-Laser-Joined Automotive Transformation-Induced Plasticity Steel

  • J. Chen
  • K. Sand
  • M.S. Xia
  • C. Ophus
  • R. Mohammadi
  • M.L. Kuntz
  • Y. Zhou
  • D. Mitlin
Article

Abstract

We have used transmission electron microscopy (TEM) and nanoindentation to characterize the dominant phases present in the weld zone of a diode-laser-welded transformation-induced plasticity (TRIP) steel, examining the unaffected base metal as a baseline. The microstructure of the base metal consists predominantly of ferrite, retained austenite, martensite, and occasional large carbide particles. The dominant microstructure of the weld zone is of differently oriented packets having a bainitic morphology. The weld also contains allotriomorphic ferrite, idiomorphic ferrite, as well some twinned martensite that is surrounded by austenite. The TEM analysis of the bainitic-morphology packets indicates that they consist of a lath ferrite phase separated by an interlath carbon-enriched retained austenite. In most cases, the orientation relationship (OR) between the lath ferrite and the interlath retained austenite can be approximated as Nishiyama–Wasserman (N-W). We used site-specific nanoindentation to further characterize the packets and the allotriomorphic ferrite, confirming through the hardness values the conclusions reached by TEM. While martensite was regularly present in the base metal, it was only sparsely distributed within the weld zone, boding well for the weld’s mechanical properties.

Keywords

Ferrite Austenite Martensite Bainite Welding Speed 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

We are very grateful to Harry Bhadeshia and Velimir Radmilovic for the critical presubmission reviews of this manuscript. We also thank Ryan O′Hagan, MTS, for assistance with the nanoindentation testing and for very useful discussions. One of the authors (JC) wants to thank Dr. Fu-Gao Wei, National Institute for Materials Science of Japan, for the discussion. This research is financially supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada and AUTO21 Network Centres of Excellence of Canada.

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Copyright information

© THE MINERALS, METALS & MATERIALS SOCIETY and ASM INTERNATIONAL 2008

Authors and Affiliations

  • J. Chen
    • 1
  • K. Sand
    • 1
  • M.S. Xia
    • 2
  • C. Ophus
    • 1
  • R. Mohammadi
    • 1
  • M.L. Kuntz
    • 2
  • Y. Zhou
    • 2
  • D. Mitlin
    • 1
  1. 1.Department of Chemical and Materials EngineeringUniversity of Alberta, and the National Institute for NanotechnologyEdmontonCanada
  2. 2.Department of Mechanical EngineeringUniversity of WaterlooWaterlooCanada

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