Chinese Journal of Mechanical Engineering >

2021 , Vol. 34 >Issue 4: 80 - 80

DOI: https://doi.org/10.1186/s10033-021-00596-x

Smart Materials

HAZ Characterization and Mechanical Properties of QP980-DP980 Laser Welded Joints

  • Junliang Xue ,
  • Peng Peng ,
  • Wei Guo ,
  • Mingsheng Xia ,
  • Caiwang Tan ,
  • Zhandong Wan ,
  • Hongqiang Zhang ,
  • Yongqiang Li
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  • 1. School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China;
    2. R&D Center, TANGSTEEL Company, HBIS Group, Tangshan 063016, China;
    3. Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, Weihai 264209, China;
    4. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China;
    5. Electrical Engineering Department, Changchun Automobile Industry Institute, Changchun 130013, China

Received date: 2020-03-20

  Revised date: 2021-04-19

  Online published: 2021-12-21

Supported by

Supported by National Natural Science Foundation of China (Grant Nos. 51871010, 51875129), and Beijing Municipal Natural Science Foundation of China (Grant No. 3202016 3212008)

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Abstract

The QP980-DP980 dissimilar steel joints were fabricated by fiber laser welding. The weld zone (WZ) was fully martensitic structure, and heat-affected zone (HAZ) contained newly-formed martensite and partially tempered martensite (TM) in both steels. The super-critical HAZ of the QP980 side had higher microhardness (~549.5 Hv) than that of the WZ due to the finer martensite. A softened zone was present in HAZ of QP980 and DP980, the dropped microhardness of softened zone of the QP980 and DP980 was Δ 21.8 Hv and Δ 40.9 Hv, respectively. Dislocation walls and slip bands were likely formed at the grain boundaries with the increase of strain, leading to the formation of low angle grain boundaries (LAGBs). Dislocation accumulation more easily occurred in the LAGBs than that of the HAGBs, which led to significant dislocation interaction and formation of cracks. The electron back-scattered diffraction (EBSD) results showed the fraction of LAGBs in sub-critical HAZ of DP980 side was the highest under different deformation conditions during tensile testing, resulting in the failure of joints located at the sub-critical HAZ of DP980 side. The QP980-DP980 dissimilar steel joints presented higher elongation (~11.21%) and ultimate tensile strength (~1011.53 MPa) than that of DP980-DP980 similar steel joints, because during the tensile process of the QP980-DP980 dissimilar steel joint (~8.2% and 991.38 MPa), the strain concentration firstly occurred on the excellent QP980 BM. Moreover, Erichsen cupping tests showed that the dissimilar welded joints had the lowest Erichsen value (~5.92 mm) and the peak punch force (~28.4 kN) due to the presence of large amount of brittle martensite in WZ and inhomogeneous deformation.

Key words： QP980 steel; DP980 steel; Fiber laser welding; Microstructure evolution; Tensile properties; Formability

Cite this article

Junliang Xue , Peng Peng , Wei Guo , Mingsheng Xia , Caiwang Tan , Zhandong Wan , Hongqiang Zhang , Yongqiang Li . HAZ Characterization and Mechanical Properties of QP980-DP980 Laser Welded Joints[J]. Chinese Journal of Mechanical Engineering, 2021 , 34(4) : 80 -80 . DOI: 10.1186/s10033-021-00596-x

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