Effect of Post-weld Tempering on the Microstructure and Mechanical Properties in the Simulated HAZs of a High-Strength-High-Toughness Combination Marine Engineering Steel

The effects of tempering temperatures on the microstructure and mechanical properties of the simulated coarse-grain heat-affected zone (CGHAZ) and inter-critical heat-affected zone (ICHAZ) were investigated for a high-strength-high-toughness combination marine engineering steel. The results demonstrate that the microstructure of the simulated CGHAZ and ICHAZ after tempering is characterized by tempering sorbites and coarse grain in the simulated CGHAZ. As tempering temperature increases, the tensile strength of the simulated CGHAZ and ICHAZ decreases and the Charpy absorbed energy of the simulated ICHAZ at - 50 degrees C increases remarkably, but the impact toughness of the simulated CGHAZ is not improved. After tempering at 550 degrees C, the coarse flake carbides, which distribute at the prior austenite grain and martensite lath boundaries, deteriorate the impact toughness of the simulated CGHAZ. With the increase in tempering temperature, the morphology and the size of the carbides gradually change from coarse flake to fine granular, which is beneficial to the improvement of impact toughness. However, the coarse-grain size of the simulated CGHAZ and the M23C6-type carbide precipitated along the grain boundaries weakens the enhancing effect of carbides on impact toughness.