J-integral Analysis of the Simulated Heat-affected Zone of the Elevated-temperature Martensitic Steel

Abstract

Due to its superior strength at high temperatures P/T91 steel is often applied in the chemical, petrochemical and fossil-fired power generation industries. The high strength is achieved by a suitable martensitic microstructure after appropriate heat treatment procedure. Welding is the most important process of joining the components in such plants, and the heat-affected zone is often the weakest part of these structures. Having in mind that the welded joint is the weakest area, it is necessary to know its properties and assess the level of its degradation. It was found that the life-limiting factor in case of P/T91 steel welded structures are the cracks located in the heat affected zones, more precisely in its intercritical region. In present paper the results of the fracture toughness measurement carried out on simulated P91 steel ICHAZ specimens produced using a weld simulator has been presented. The tests were done on two types of simulated specimens, those subjected to the subsequent PWHT and with those left untreated (without PWHT), at room temperature and 600 °C. For the J-integral estimation pin-loaded SEN(T) specimens were tested in plane stress conditions using the unloading compliance method of deriving a single specimen resistance curve and the η-method.