Study Of Crack Growth Behavior In P92 Steel Under Creep-fatigue Interaction

Many pressure vessels and pressure equipments usually work under high temperature and cyclic loading with the development of the industry in our country.The typical failure models of these vessels and equipment are mainly caused by fatigue,creep or their interaction under high temperature and cyclic loading.The reason to the failure under creep and fatigue interaction is not induced by pure creep or pure fatigue,thus crack propagation of creep-fatigue interaction is paid attention for the aim of ensuring high temperature structure integrity,In this paper,crack growth test of P92 steel under creep-fatigue interaction was investigated.The main work and conclusions are as follows:(1)Creep-fatigue interaction tests of P92 steel at 630℃ under stress-controlled were carried out and the effect of different dwell time,thickness and crack depth on creep-fatigue crack growth was studied.The study shows that with the increasing of dwell time,the ratio of initial and steady crack growth is decreasing;with the increasing of crack depth,the breaking life is decreasing.And the 0.35 of crack depth is the largest;and the tension thickness of 7.5mm and 10 mm have little difference on crack growth,their crack growth rate is bigger than that in 5mm.(2)The fracture morphology of P92 steel under creep-fatigue interaction is mainly creep voids and micro-cracks;the degree of nucleation and aggregation is strengthened by the cycle loading,which caught the deep cavities;the micro cracks are caused by strong nucleation and rapidly development of dimples and cavities.(3)The fracture of P92 steel under creep-fatigue interaction is the creep ductile fracture and the t avg(C)parameter should be employed to demonstrate the crack growth behaviour.The transition point of i fa-lg(N /N)curve corresponds to the turning point of initial crack growth changed into steady crack growth while the transition point of da/dN-N curve exhibits the turning point of steady creep crack growth changed into the accelerated crack growth.(4)Based on Saxena liner superposition model,the prediction formula of P92 steel under creep-fatigue interaction is founded.And the formula has certain validity in a given range of error.