Failure analysis of the impellers of coke plant

(in lingua inglese)

A high carbon content is also a critical point for the occurrence of sensitization. As can be seen in Table 1, the plates used in the construction of the impeller have a carbon content of 0.056%, which is almost twofold higher than the maximum allowable limit of 0.03% for a weld able grade. In this case, the precipitation of chromium carbides occurred by the welding operation when the heat affected zone (HAZ) experiences a particular temperature range (550–850 8C). From the microstructure it is observed that the welding operation was not proper and there is every chance that there is heat generation in around sensitization range leading to precipitation of chromium carbides consumed the alloying element – chromium from a narrow band along the grain boundary and this makes the zone anodic to the unaffected grains.