104. Evaluation of Stress-Rupture Behaviour of Simulated Weld Joint (HAZ) Microstructures of P91 Steel Singh Kulvir, Reddy G. Jaipal, Bose S.C., Reddy K.S., Thyagarajan V. (BHEL Journal, December 2003, pp. 14–31). Abstract P91 steel is used in subcritical and supercritical boilers in welded condition. Welding results in different microstructural features in the heat-affected zone (HAZ), and the performance of the weld joint during service depends on the above microstructural conditions. Failure often takes place in the intercritical region of the HAZ. The study involved simulation of various microstructural conditions encountered during welding through heat-treatment at different temperatures and correlating them with stress-rupture properties. P91 steel samples were heat-treated in the temperature range of 800 to 1300OC, and were subjected to stress-rupture testing at 500, 550, 575, 600 and 625OC at stress range varying from 6 to 30 kg/mm2. Creep-rupture properties are lowest for P91 steel heat-treated at 900 OC which represents intercritical zone, and are very high for the material heat-treated at 1200 or 1300 OC. Creep-rupture properties, room and high temperature tensile strengths are found to be increasing with increasing grain size when austenitised above 900OC, whereas the impact properties exhibited an opposite trend and decreased with increasing grain size. The role of carbides was also studied using Transmission Electron Microscope. It is inferred that the austenitising temperature of P91 steel could be beneficially increased up to 1100OC if higher creeprupture properties are desired, at the cost of marginal reduction in impact strength. Top Keywords P91 steel, Weld joint, Stress rupture behaviour, Impact strength, Heat-affected zone, Intercritical region, Microstructure. Top |