Abstract
This article will highlight the investigation of the dissimilar metal weld (DMW) between a Grade 22 pipe (2.25 wt% Cr) welded to a Grade 91 header piece (9 wt% Cr) which was in use for 79,000 h at a service temperature of 570 °C at a UK fossil fueled power plant. Results of the optical investigation are presented and compared to results of computational simulations as well as SEM, EMPA, SIMS, and hardness measurements. Severe microstructural changes in the vicinity of the fusion line have been observed as a result of carbon migration from the lower chromium to the higher chromium-containing steel. This change in microstructure is caused by the breakdown of carbides in the low alloyed material leading to a destabilization of the microstructure. Computational simulations with the software MatCalc (TU Vienna) support these claims and are in general in acceptable agreement with the observations made during metallographic investigations.
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