SECONDARY-ION MASS-SPECTROSCOPY AND SURFACE PROFILOMETRIC CHARACTERIZATION OF OXIDE SCALES DEVELOPED OVER WELD METAL, HEAT-AFFECTED ZONE, AND BASE-METAL REGIONS OF 9CR-1MO STEEL WELDMENTS

Microstructurally different regions (namely the weld metal, heat affec ted 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 wel d metal legion was found to form a thicker oxide scale than the other regions of the weldment. The difference in thickness between the scale s over the weld and adjoining HAZ regions was found to be similar to 5 mu m after 4 h but had increased to similar to 100 mu m in 100 h. Dif ference in thickness between the scales was also confirmed by a few ex aminations using scanning electron microscopy (SEM); this method also described the difference in morphology of the scales developed over th e three regions. Secondary ion mass spectroscopy (SIMS) depth profiles of iron and chromium in scales developed over the different regions o f the weldments have suggested a considerably higher chromium content of the inner scales on the HAZ and base metal than that of the scale o ver the weld metal; SIMS profiles have also corroborated formation of a thicker scale over the weld metal, as assessed earlier by surface pr ofilometry and SEM. (C) 1998 The Institute of Materials.