Analysis of microstructure and mechanical properties in alloy 690 weldments using filler metals I-82 and I-52

Abstract

This work investigated the weldability and mechanical properties of weldments made with Inconel filler metals I-52 and I-82 in the welding of Inconel alloy 690. Gas tungsten arc welding was used with different multipass sequences. The microstructures of the fusion and heat affected zones were examined and weldment properties were compared by tensile, hardness, and impact tests. Fracture surfaces were examined by scanning electron microscopy. Experimental results indicate that the subgrain structure near the fusion zone centreline was dominated by equiaxed dendrites in I-82 weldments but by columnar dendrites in I-52 weldments. In addition, the I-82 weldments had a finer subgrain structure near the fusion zone centreline and smaller cellular spacing near the fusion line than I-52 weldments. Mechanical test results demonstrate that the I-82 weldments had higher tensile strength (622–630 MPa) with rupture occurring in the base metal. In comparison, the I-52 weldments had lower tensile strength (568–578 MPa) and rupture occurred in the fusion zone. Filler metal I-52 showed better welding performance and greater impact toughness with only slight sensitivity to the number of passes. However, a gradual increase in the hardness of the weld was observed as the number of passes increased.