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.