Development of low transformation temperature alloys for laser additive manufacturing repairing the defects in HSLA-100 plates: focusing on the microstructure, residual stress and performance

In this work, laser metal deposition (LMD) process was used to repair the defects of HSLA-100 plates, and the strategy of low transformation temperature (LTT) alloys was adopted to control the residuals stress distribution during the repairing process. Two types of LTT powders, namely LTT1, and LTT2 were developed, and the microstructure, residual stress, mechanical properties, as well as the corrosion resistance of repaired samples under LTT materials were compared to that under conventional GH3536 materials. The results show that the repairing materials present excellent metallurgical bonding with the substrate without obvious element segregation. Besides, X-ray diffraction (XRD) and electron-backscatter diffraction (EBSD) confirmed that the microstructure of samples repaired by LTT was mainly composed of lath martensite (93%), while the sample repaired by GH3536 exhibited fish-scale-like austenite with a few thermal cracks generated on the surface. Hardness of the repaired zone revealed an obvious increase trend for LTT when compared to that of GH3536 (~360 HV vs. ~225HV). In addition, XRD tests and finite element simulation demonstrated the effectiveness of the developed LTT materials in tensile residual stress regulation. At last, mechanically tensile, fatigue, and corrosion resistance tests revealed the excellent performance of the LTT-based repaired samples for actual application.

本研究采用激光金属沉积（laser metal deposition, LMD）工艺修复HSLA-100钢板的缺陷，并引入低相变温度（low transformation temperature, LTT）合金策略调控修复过程中的残余应力分布。研发了LTT1与LTT2两种LTT合金粉末，并对比了采用LTT材料修复的试样与采用传统GH3536材料修复的试样的显微组织、残余应力、力学性能及耐蚀性能。研究结果表明，修复材料与基体之间实现了优异的冶金结合，无明显元素偏析。此外，X射线衍射（X-ray diffraction, XRD）与电子背散射衍射（electron-backscatter diffraction, EBSD）分析证实，采用LTT材料修复的试样显微组织主要由93%的板条马氏体构成；而采用GH3536修复的试样则呈现鱼鳞状奥氏体组织，且表面产生少量热裂纹。与GH3536修复试样相比，LTT修复区的硬度呈现显著提升趋势（约360 HV vs. 约225 HV）。此外，XRD测试与有限元模拟验证了所研发的LTT材料在拉残余应力调控方面的有效性。最后，拉伸、疲劳及耐蚀性能测试结果显示，基于LTT材料的修复试样具备优异的实际应用性能。