The liquation cracking temperature range (LCTR) of CM247LC was evaluated, especially in remelted and reheated weld metals produced during multi-pass repair welding. The LCTR of the remelted weld metal was 282 K, and those of the reheated weld metals were 455-805 K depending on the testing position. In the multi-bead within the reheated weld metal, the LCTR increased from 455 K far from the inter-pass boundary to 805 K near this boundary. The mechanism underlying the varying LCTR for the remelted and reheated weld metals was the amount of MC carbide at each weld position. The single-mode fibre laser welding suppressed the carbide within both areas, and lowered the liquation cracking susceptibility.

Under completely suppressed constitutional liquation of MC carbide, unexplored 247LC superalloy single-mode fibre laser welds experience unexpected liquation cracking. These cracks continuously propagate from a solidification crack, particularly at highly misoriented and epitaxially grown solidification grain boundaries, and dominated by pipeline diffusion of impurities. Two novel metallurgical preconditions were identified which, if satisfied, ensure complete suppression of liquation cracking of 247LC superalloy welds. These preconditions are (i) the constitutional liquation of MC carbide at the heat-affected zone and (ii) pipeline diffusion of impurities at the fusion zone. It is also highly recommended that the welding is carried out in a single directionally solidified grain under scanning conditions, avoiding the formation of highly misoriented solidification grain boundaries.