Microstructural Stability of P23/P91 Dissimilar Welds during Creep at 500°C

Abstract

This paper deals with microstructural stability of P23/P91 dissimilar welds during long-term creep exposure at 500°C. Detailed TEM investigations on minor phase evolution were performed on specimens after long-term creep exposure. Microstructural changes in the decarburized layer of the P23 steel were studied using EBSD and TEM. Experimental data on minor phase evolution were compared to the results of thermodynamic (Thermocalc) and kinetic (Dictra) simulations. Evolution of minor phases in the P23/P91 welds during creep at 500°C was in a good agreement with results of microstructural modelling. Partial decarburization of the P23 occurred at the expense of dissolving M7C3 phase. Microstructure of the partly decarburized zone in the P23 steel remained bainitic in all specimens investigated. In spite of the partial decarburization in the P23 steel during longterm creep exposure at 500°C, creep failures occurred in the ICHAZ of the P23 steel.