MICROSTRUCTURAL CHARACTERIZATION OF INCOLOY 800H WELDED WITH DIFFERENT FILLER MATERIALS

Abstract

Incoloy 800H is a potential core component material for high temperature gas-cooled reactors (HTGRs). However, the mechanical properties of conventional Incoloy 800H welds could be significantly degraded when the environmental temperature is higher than 475 °C. The objective of this work is to understand the strengthening and plastic deformation mechanisms of Incoloy 800H gas tungsten arc welds with different filler materials, including Haynes 230 and Inconel 625 filler materials, by characterizing and analyzing the microstructural and phase evolution. Optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to identify the constituent phases in the welds at fusion zone (FZ) and heat-affected zone (HAZ). Precipitation of secondary phase particles of Ti(C,N) and other compounds from the solid solution-strengthened austenitic -phase matrix were confirmed in the fusion zone (FZ) and heat-affected zone (HAZ). Solid solution strengthening is the dominant effect for the mechanical properties of Incoloy 800H and its welds with filler materials comprised of Haynes 230 and Inconel 625. Welding-induced nano-precipitates in the HAZ and FZ enhance the high-temperature strength of Incoloy 800H welds.