Experimental determination of J-integral at elevated temperatures

Abstract

In past two decades, the development of 9-12% Cr creep-resistant steel for critical components in coal-fired power stations that can withstand higher temperatures and pressures has been intensified in order to increase efficiency of supercritical plants. As the systems that can withstand ultra supercritical steam conditions are of an absolute necessity, it is an imperative to use the materials of adequate strength, physical properties and metallurgical stability at operating temperature. The aim is to prevent catastrophic failures arising based on a few mechanisms: leakage due to variation of the dimensions caused by creep, breakage-explosion due to fracture caused by stress and thermal fatigue due to cyclic stresses caused by heat. Welding is the most important process of joining the components in such plants, and the heataffected zone (HAZ) is often the weakest part of these structures. The variations of microstructures in HAZ affected by welding thermal cycle lead to inferior mechanical properties of this zone in comparison with base metal. In present paper, the effect of post weld heat treatment (PWHT) on behaviour of welded structure made of material P91 at an operating temperature of 600°C has been presented. Research was conducted on the specimens with simulated HAZ, namely in critical zone in which the cracks of type IV might occur. The R curve for J-R curve testing was generated using the single specimen technique on the single edge side grooved test specimens. The tool for tensile testing used for putting the specimens into furnace was of special design.