Secondary ion mass spectroscopy and surface profilometric characterisation of oxide scales developed over weld metal, heat affected zone, and base metal regions of 9Cr-1Mo steel weldments

Abstract

Microstructurally different regions (namely the weld metal, heat affected zone (HAZ), and base metal) were characterised in weldments of 9Cr-1Mo steel, and composite specimens comprising the three regions were oxidised in air at 923 K. As measured by surface profilometry, the weld metal region was found to form a thicker oxide scale than the other regions of the weldment. The difference in thickness between the scales over the weld and adjoining H AZ regions was found to be ~5 μm after 4 h but had increased to ~100, μm in 100 h. Difference in thickness between the scales was also confirmed by a few examinations using scanning electron microscopy (SEM); this method also described the difference in morphology of the scales developed over the three regions. Secondary ion mass spectroscopy (SIMS) depth profiles of iron and chromium in scales developed over the different regions of the weldments have suggested a considerably higher chromium content of the inner scales on the H AZ and base metal than that of the scale over the weld metal; SIMS profiles have also corroborated formation of a thicker scale over the weld metal, as assessed earlier by surface profilometry and SEM.