Studies on Microstructure and Mechanical Properties of Weldments Produced in 12 mm Thick Naval Grade High Strength Low Alloy Steel for Sub-Zero Application by Single and Double Pass Hybrid Laser Arc Welding

The present study deals with studies on HLAW joints produced in a naval grade HSLA steel using both single-pass (HLAW-1) and two-pass (HLAW-2) approach. The weld joints were subjected to different methods of characterization—optical microscopy, EBSD analysis, residual stress analysis, and mechanical testing. Microhardness testing, tensile testing and impact testing constituted the mechanical testing. Impact testing was carried out at both room temperature and − 60 °C. For both HLAW-1 and HLAW-2, the fusion zone and heat-affected zone (HAZ) showed higher hardness than the base metal and tensile fracture location was in the base metal. The HLAW-2 joint was characterized by a higher volume fraction of acicular ferrite, a higher fraction of high angle grain boundaries, and a finer grain size compared to the HLAW-1 joint. It is believed that these factors contributed to the observed higher impact toughness of the HLAW-2 joint at − 60 °C.