Abstract: Owing to the small thermal conductivity of nickel-based alloys, the residence time of the joint in the welding process became long, which leads to a coarse tendency about the weld grains. In order to control the size of weld grains, the PTIG welding parameters are optimized and performed the bead-on-plate welding of Inocnel690, using PTIG welding method with adjustable parameters has the advantages of high heat input level is relatively small. The microstructure and precipitation phase of the weld are characterized by energy dispersive spectroscopy(EDS) and scanning electron microscope(SEM) after welding. The results show that the effect of PTIG of different process parameters on the weld morphology and grain size is significant. When the parameters is in a reasonable range, weld grain becomes smaller with the increasing of peak current, duty ratio and pulse frequency. The precipitates is M₂₃C₆(Cr₂₃C₆) type carbides distributed in succession on the austenite grain boundary. The precipitated particle in austenite grain is granular MC(NbC, TiC) carbide, dispersed in the dendrite gap. And when the duty cycle is relatively large, the MC type carbide grows into lamellar trend.

Key words: FM-52M, grain boundary carbides, grain refinement, Inconel690, pulse TIG welding