Influence of microstructural variations in the weldment on the high-temperature corrosion of 2.25Cr-1Mo steel

In order to study the influence of microstructural variation on the oxidation of the weldment of 2.25Cr-1Mo steel, regions with different microstructures were identified by optical microscopy. The weld metal, the base metal, and the heat-affected zone (HAZ), as well as the subzones within the HAZ regions were separated from the weldment by precise steps of metallography. In order to understand the influence of these microstructural variations on the oxidation behavior, various regions and subzones were oxidized at 773 and 873 K. Results of the SEM/EDX, SIMS, and XRD investigation suggest formation of inner scales with less Cr (i.e., less protective) over the HAZ than over the weld-metal and base-metal regions. Variation in the CR contents of the scales formed over the various regions is proposed to arise from the difference in microstructural features in different regions of the weldments.