Study on uni-axial tensile strength properties of Ytterbium fiber laser welded Hastelloy C-276 sheet

摘要

Failure of as-welded Hastelloy C-276 specimen in uni-axial tensile test has been reported to occur at the weld joint with around 50% reduction in elongation length relative to that of as-received Hastelloy C-276 specimen. The proposed reason for such an occurrence is due to the micro-segregation of elements during solidification of the weld zone. Micro-segregation causes formation of brittle inter-metallic phases, mainly at the grain boundaries of the weld zone, leading to a change in deformation behavior of the welded specimen. Reduction in the linear heat input required for welding tends to reduce micro-segregation. Ytterbium fiber laser with its higher melting efficiency, requires lower linear heat input for welding, in comparison to other sources of heat. In the present investigation, Ytterbium fiber laser has been used for welding of 3?mm thick Hastelloy C-276 sheet and the tensile strength properties of the as-welded specimens have been studied. It is observed that the fiber laser as-welded specimens fail at the base metal, and the percent elongation is found to be increase twice as compared to that of previous reported literatures. Analysis of the fiber laser as-welded specimen showed (a) Reduction in micro-segregation within the weld zone due to high cooling rate (=1000 °C/s) of the melt pool; (b) Cooling time through the sensitization temperature range at the heat-affected zone was found to be 1.01?s as compared to 360?s required for precipitation of inter-metallic phase; (c) Ductile nature of the weld zone due to presence of inclined cellular dendrites at the weld centerline facilitating plastic deformation; and (d) Significant increase in elongation of heat-affected zone grains as compared to that of the base metal grains.