The oxidation behaviour of the weld metal, heat affected zone and base metal in the weldments of 2.25Cr-1Mo steel

Abstract

Microstructurally different regions of weld metal, heat affected zone (HAZ) and base metal were identified in the weld pads of 2.25Cr-1Mo steel. The specimens from the weld metal, the HAZ and the base metal were separated out of the weld pads and oxidized for different durations from 2 to 500 h in air at 773 K. All three types of specimens followed parabolic kinetics until the weld metal suffered spallation. While the oxidation rates of the base metal and the weld metal were similar, the HAZ had a much higher rate than those in the other regions. The composite weldment, consisting of the three regions, when oxidized at 773 K, was found to have developed a considerably thicker oxide scale over the HAZ as compared to those of the base metal and the weld metal. When measured by a surface profilometer, the difference in thicknesses that was found to be a fraction of a micrometer higher over the HAZ in 2 h of exposure had increased to more than 14 μm in 500 h. Oxide scales formed over the different regions were characterized by X-ray diffraction and scanning electron microscopy (SEM/EDX).