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.

The influence of isothermal ageing and subsequent hydrogen charging at room temperature on local mechanical properties and fracture characteristics of martensitic-bainitic weldments for power engineering

“…Furthermore, distinct zones of the weldments such as base material (BM), weld metal (WM) and heat-affected zone (HAZ) undergo their own specific degradation in service or laboratory test conditions [6,7]. In the case of transition weldments between different steel grades, the situation is even more complicated due to redistribution effects of alloying elements and grain size characteristics along the weld metal/base metal interfaces [8][9][10][11]. Typical examples represent dissimilar welded joints between 9Cr martensitic and 2.25Cr bainitic steels interconnecting superheater circuit with steam evaporator i.e.…”

“…Some studies e.g. [8,11] focused on high temperature performance of dissimilar welds between the higher and lower chromium steels indicated a formation of carbon-depleted zones ("white bands") at the lower alloyed weld side, resulting in their mechanical properties deterioration. Apart from long-term thermal degradation of boiler steels welded joints, the hydrogen-induced cold cracking phenomena may be of another concern in power plants during their regular or accidental shutdowns.…”

Hydrogen pre-charging effects on the notch tensile properties and fracture behaviour of heat-affected zones of thermally aged welds between T24 and T92 creep-resistant steels

“…The situation becomes even more complex in the case of dissimilar welds, i.e. the welded joints between chemically different steels which are very frequent in power engineering [5][6][7][8]. For instance, the dissimilar welds combined of lower and higher chromium ferritic steels, such as T24/T92 welded joints can be used in a number of steam generator circuits.…”