Effect of boron addition on the GB precipitation and SRC resistance of CGHAZ in advanced bainitic heat-resistant steel

We investigated the influence of boron addition on the high-temperature ductility of the coarse-grain heat-affected zone (CGHAZ) to eliminate the stress-relief cracking (SRC) in T23 steel. First, the CGHAZ was simulated for T23 steel with varying boron content. Then, high-temperature tensile tests were conducted to evaluate the stress release process of the welds, and finally, the fracture modes, precipitation evolutions, and boron distributions were observed. There was a significant improvement in grain boundary (GB) plasticity and SRC resistance with the addition of 0.01 wt.% boron. This is attributed to the segregation of boron at the GB, which delays the rapid precipitation and growth of M 23 C 6 , hinders micro-void formation, and reduces the depletion of alloying elements near the GB. Furthermore, during the tensile test, boron competes with carbon for segregation at the GB, resulting in the initial formation of boron-rich phases ((Fe, Cr) 23 (B, C) 6 ), which subsequently transform into more stable phases ((Fe, Cr, W) 23 C 6 ) over time. This study provides a straightforward method for eliminating SRC in T23 steel and other creep-resistant alloys.