Effect of Mo in Ni-30Cr filler metal on the eutectic phases of weld metal

The effects of Mo content on the microstructure and solidification path of gas tungsten arc welding deposited Nb-bearing nickel-based alloy welding wire were studied. The Mo entered the matrix gamma phase as a solid solution and was precipitated in the form of the eutectic phases including Laves, sigma, and MC carbides. In Ni-30Cr weld metal, Mo plays a leading role in the eutectic sigma formation, while a relatively minor role in the eutectic MC carbides and Laves formation compared with Nb. The addition of Mo could reduce the content of Nb in the dendrite arm, interdendritic region, and Laves phase. With the increasing Mo content, the Laves phase changed from a rod-like shape to a blocky shape. When the Mo content exceeded 4%, sigma + Laves + gamma eutectic structure was formed. When the Mo content was about 5.0%, there were microcracks in the sigma and Laves phases, and at the sigma/MC interface. To avoid the formation of the sigma phase due to the segregation of Mo, the Mo content had to be controlled below 4%.