Fe-Mn-Al-Si系TRIP/TWIP钢激光焊接接头的微观组织研究

Microstructure of laser-welded joints of Fe-Mn-Al-Si TRIP/TWIP steels

采用光纤激光器对两种锰含量分别为20wt.%和29wt.%的Fe-Mn-Al-Si系TRIP/TWIP钢进行激光焊接。利用扫描电子显微镜(SEM)、能谱仪(EDS)、电子背散射衍射仪(EBSD)和透射电子显微镜(TEM)对接头的显微组织进行研究。结果表明:靠近熔合线的焊缝组织以柱状晶为主,而焊缝心部为细小的等轴晶且出现大量AlN纳米颗粒;焊缝组织的孪晶界比例比母材的大幅度降低,但仍然达到了15.8%;熔合线宽1μm,富Fe、Mn而贫Al、Si;焊缝在凝固过程中,先形成γ-奥氏体,当遇到应力集中时发生局部ε-马氏体的相变来缓解应力,避免裂纹形成。

Two types of Fe-Mn-Al-Si TRIP/TWIP steels with different Mn concentrations, which are respectively 20 wt% and 29 wt% , were welded by fiber laser welding technique. The microstructures of the weld joints were investigated using scanning electron microscope （SEM） , X-ray energy disperse spectroscopy （EDS） , electron backscatter diffraction technology （EBSD） and transmission electron microscopy （TEM）. The results show that the fusion zone （FZ） adjacent to the fusion lines was made up of columnar grains while the centre of the FZ consisted of equiaxed grains, in which a great deal of AIN nano-particles were formed. The fraction of twin boundaries of FZ is about 15.8% although the twin boundaries have decreased greatly compared with that of the base materials. The fusion lines are rich in Fe and Mn but lack of Al and St. In the process of solidification of the FZ, the austenite first formed and some austenite transformed into ε-martensite at the stress concentration regions, which can relieve some stress and prevent formation cracks.