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

Chinese Journal of Mechanical Engineering

Zhandong Wan¹  Yongqiang Li²  Mingsheng Xia³  Hongqiang Zhang⁴  Wei Guo⁴  Peng Peng⁴  Junliang Xue⁴  Caiwang Tan⁵ 

[1]Department of Mechanical Engineering, Tsinghua University, 100084, Beijing, China

[2]Electrical Engineering Department, Changchun Automobile Industry Institute, 130013, Changchun, China

[3]R&D Center, TANGSTEEL Company, HBIS Group, 063016, Tangshan, China

[4]School of Mechanical Engineering and Automation, Beihang University, 100191, Beijing, China

[5]Shandong Provincial Key Laboratory of Special Welding Technology, Harbin Institute of Technology at Weihai, 264209, Weihai, China

关键词: QP980 steel;    DP980 steel;    Fiber laser welding;    Microstructure evolution;    Tensile properties;    Formability;   

DOI  :  10.1186/s10033-021-00596-x

来源: Springer

【 摘 要 】

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.

【 授权许可】

CC BY