Analysis Of The Creep Crack Growth Rate In P92 Welded Joint HAZ

Currently, new high-temperature resistant alloy P92 steel has been widely applied in the construction of supercritical and ultra supercritical coal-fired and fuel-fired power station, and it has been applied for the long-term operation under high temperature, low stress conditions in the structures including drum boilers, main steam pipelines and housing of steam turbines, which were prone to Type IV crack of P92 steel welded joints. Both China's and the rest of the world's research on the creep crack growth rate of P92 steel welded joints HAZ was rather limited, therefore, it should be paid much attentions in order to prevent the creep crack and give properly safety evaluation on the welded joints, and also provide evidences for the life evaluation of creep crack growth.In the event that designated welding process and welding consumables were adopted, the welding thermal simulation curves were measured when performing the welding of P92 steel. According to the measured curves, the samples with microstructure characteristics of thermal affected zone were prepared in the way of heat treatment simulation. From the contrastive analysis on the microstructure and hardness of welded joints, it showed that the simulation results were in well agreement with the measured results, and proved that the simulation samples were successful and effective.By performing accelerated creep test on the simulation thermal affected zone under the same temperature but different stress, the strain rate of steady state creep was calculated under different stress. The results indicated that fine crystal zone has the maximum creep rate among all the welding thermal affected zones under low stress, and be more liable to resulting in creep crack than the other zones.According to ASTM E1457 standard, the creep crack growth curve of P92 steel welded joints and base metal and C* parameters of crack tip stress field were measured by performing compact tension test, respectively. On the correlation between crack growth rate and C*, the creep growth rate of P92 creep crack under steady conditions was predicted. We proved that when P92 steel was employed for long-term operation in high-temperature, low-stress circumstances; any defects in heat-affected zone was more dangerous than that in the base metal, once the crack appears it shall grow up rapidly.