OXIDATION BEHAVIOR OF MICROSTRUCTURALLY-DIFFERENT REGIONS IN THE WELDMENT OF 9CR-1MO STEEL

Regions with different microstructures have been identified in the wel dments of 9Cr-1Mo steel. Weldments comprising the three legions, i.e., weld metal, heat-affected zone (HAZ), and base metal, were oxidized i n air at 923 K for different durations up to 500 hr. The crown area of the weld metal was found to form a thicker oxide scale than the other regions of the weldment. When the oxidation kinetics of different reg ions were compared (by separating out the coupons of the HAZ and the c rown and root portions of the weld metal and then oxidizing them), the crown area of the weld was found to oxidize at a much higher rate tha n the others. Scanning election microscopy (SEM) was carried out to as sess the morphological variations in the different regions of the weld ment. The compositional variations in the scales over the different re gions have been characterized by the energy-dispersive analyses of X-r ays (EDX), and the results thereof have also been corroborated by seco ndary ion mass spectrometry (SIMS).