Welding hot cracking characteristics and fracture mechanisms of nickel-based alloy NS1402 under different constraint conditions

The influence of trace elements variation and constraint conditions on welding hot cracking was investigated to reveal the cracking characteristics of nickel-based alloy NS1402. The fishbone tests and full restraint welding tests have been conducted to determine the cracking ratio. The mechanical and metallurgical fracture mechanisms were elaborated simultaneously. And the low-melting point liquid membrane, which was a key metallurgical factor, was found in cracking fracture surface. Numerical simulations were conducted to illustrate the effects of transverse tensile stress/strain during welding processing. Results show that the liquid membranes were composed of FeNi, FeP, Co₃Fe₇, etc., indicating that liquid membranes were developed to higher melting point by Co₃Fe₇ eutectics due to the addition of Co, and it contributes to reducing cracking susceptibility of NS1402. The cracking was ductility-dip cracking (DDC), which propagated in the forms of intergranular or transgranular fracture. Thus, adjusting element content and degrees of constraint could control the cracking tendency.