Mechanism of the crack formation and suppression in laser-MAG hybrid welded 30CrMnSiA joints
Mechanism of the crack formation and suppression in laser-MAG hybrid welded 30CrMnSiA joints
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DOI：
10.1016/j.jmatprotec.2016.08.033
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发表时间：
2017
影响因子：
6.3
通讯作者：
Z. Lei;Bingwei Li;Long Ni;Yang Yuhe;Si Yang;Peipei Hu
中科院分区：
文献类型：
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作者：
Z. Lei;Bingwei Li;Long Ni;Yang Yuhe;Si Yang;Peipei Hu
研究了30 CrMnSiA钢激光-金属活性气体（MAG）复合焊接接头裂纹的形成及抑制机理。裂纹多发生在焊道端部的焊口处。根据断裂特征，裂纹可视为凝固裂纹。通过扫描电子显微镜（SEM）观察发现了缩孔和晶间膜，证实了凝固裂纹的存在。能谱仪（EDS）显示焊缝金属中杂质元素严重偏析。随后的差热分析（DTA）表明，在1130 °C-1150 °C范围内，差温存在突变，表明诱发凝固裂纹的低熔点共晶最有可能是FeS-MnS共晶。建立了热源的有限元模型。拉伸试验结果表明，焊缝金属的抗拉强度在1100 °C时达到40 MPa，在1150 °C时下降到24 MPa左右，计算得到的最大横向拉应力为430 MPa。因此，焊缝端部的拉伸应力超过拉伸强度约400 MPa。采用双层复合焊接工艺，成功地抑制了焊口裂纹。电子背散射衍射（EBSD）结果表明，双层复合焊接接头组织得到明显细化。焊缝金属的拉应力降低，晶间膜消失。
This paper investigated the crack formation and suppression mechanism in laser-metal active gas (MAG) hybrid welded 30CrMnSiA joints. The cracks were usually found in the weld crater that was located at the end of the weld bead. According to the fracture characteristics, the cracks could be considered as solidification cracks. Shrinkage cavities and intergranular films were found by means of scanning electron microscopy (SEM) observation, confirming the presence of solidification cracks. The energy dispersive spectrometer (EDS) shows severe segregation of impurity elements in the weld metal. The following differential thermal analysis (DTA) shows that there was a sudden change in the differential temperature in the range of 1130 °C–1150 °C, indicating that the low melting point eutectic inducing solidification cracks was most likely to be FeS-MnS eutectic. Finite element models for heat sources were developed. The tensile test results show that the tensile strength of weld metal reached 40 MPa at 1100 °C but dropped to about 24 MPa at 1150 °C, while the calculated highest transverse tensile stress amounted to 430 MPa. Therefore, the tensile stress at the end of the weld seam exceeded the tensile strength by approximately 400 MPa. By adopting double-layer hybrid welding process, crater cracks were successfully suppressed. The electron backscattered diffraction (EBSD) shows that the microstructure of double-layer hybrid welded joints was notably refined. The tensile stress of the weld metal was reduced and intergranular films were absent.