Effects of sensitization treatment on the evolution of Cr carbides in rapidly solidified Ni-base Alloy 600 by a CO2 laser beam

The effects of heat treatment on the precipitation of Cr carbides in Ni-base Alloy 600 laser surface melted by a CO2 laser beam were investigated with microscopic equipment. Aging treatment at 600°C for 24 h induced precipitation of Cr-rich M23C6 and Cr7C3 carbides on some high angle grain boundaries, and the minimum Cr concentration along the grain boundary was measured to be about 12 wt%. In particular, the Cr-rich M23C6 was precipitated on TiN and MgS type particles surrounded by tangled dislocations along the cell boundaries in the laser melted zone. The precipitation behaviors of Cr carbides in the laser surface melted and subsequently sensitized Alloy 600 were analyzed and then compared with those of the conventionally processed, solution annealed and then identically sensitized Alloy 600 from the viewpoint of different microstructural features.