Effect of Multiaxiality on the Stress Rupture Properties of P92 Steel

High thermal conductivity, low coefficient of thermal expansion makes P92 a candidate material for Ultra Super Critical (USC) power plant piping. Microstructural features viz., high dislocation density, lath martensitic microstructure, fine precipitates of M23C6 and MX (X=C, N) contribute towards the high rupture strength. However, most components are typically subjected to multiaxial stress conditions; either metallurgical (weldments), or mechanical (change in the dimension). The present work involves stress rupture testing of circumferential 60° V- notch specimens in the range of 300 – 375 MPa at 650 °C. Notch strengthening effect was observed; with rupture times ranging from 200 – 1300 h. Scanning electron microscopy (SEM) fractography revealed mixed mode of fracture with brittle fracture observed at notch root, while ductile fracture was seen at the centre of the specimen

Influence of normalizing and tempering temperatures on the creep properties of P92 steel

P92 steel is used as a piping material in ultra super critical power plants that can be operated at steam temperatures up to 650°C. The changes in the martensitic microstructure of P92 steel must be evaluated thoroughly before it is put into actual service. In this study, indigenously developed P92 steel was used. The steel was subjected to normalizing and tempering heat treatments in the range of 1,040–1,060°C and 740–780°C. The changes in the microstructure were evaluated and creep-rupture properties were studied at test temperatures of 600 and 650°C. Although normalizing temperatures influenced the microstructure and creep strength marginally, the change in tempering temperatures led to significant changes. The creep rupture strength at 600°C was influenced largely by the changes in the dislocation substructure, while the precipitation of Laves phases was a significant observation made for 650°C test temperature. Proposed mechanisms for the microstructural evolution and its consequences on the rupture life are discussed in this study

Monoclinic to cubic phase transformation in combustion synthesized gadolinium oxide

Gadolinium oxide, cerium oxide, and 10 mol% gadolinia doped ceria ceramic powders have been synthesized using combustion technique. Though the cubic gadolinia phase is stable at room temperature, single phase monoclinic gadolinia was obtained as a result of combustion synthesis using fuel lean and stoichiometric precursor compositions. This powder was subjected to calcination treatment and ceria doping to study the stability of phases and the rate of phase transformation from monoclinic to cubic gadolinia. It was found that monoclinic gadolinia transforms to cubic gadolinia upon calcination at temperatures less than 1200 degrees C. It was also found that rate of phase transformation is more for powder produced using fuel lean compositions; and the rate is enhanced upon ceria doping. (C) 2015 Elsevier Ltd. All rights reserved