Study On High Temperature Fracture Toughness Of P92 Steel Based On Small Size Specimen

In the aerospace,thermal power and other industries,the components in service not only to withstand a constant working load,but also due to the machine start-stop control caused by a sudden increase in short-term load and so on,therefore,in order to correctly evaluate the reliability of the component,to avoid accidents,it's necessary to obtain fracture toughness or resistance curve of the material.Fracture toughness is usually obtained by standard samples,but if the sampling of the structure is difficult or the material is limited,it will be difficult to meet the required size of the standard,therefore,small size samples will be used to test.In addition,P92 steel has excellent properties and is widely used in ultra-supercritical thermal power units.So,in this paper,the P92 steel of power plant is taken as the research object,the basic mechanical properties under the condition of room temperature and high temperature are obtained first,and then the specimens with different sizes are designed to study the fracture toughness at high temperature.Numerical simulation methods are used to study the effects of sample size and side groove structure on the test.The main contents and results are as follows:(1)Under the condition of 630°C,the fracture toughness resistance curves of P92 steel and the corresponding condition fracture toughness were obtained through the high-temperature fracture toughness test based on various small-size CT specimens.It was found that the small size specimens obtained a more conservative resistance curve and fracture toughness value.(2)The energy release rate(R)was used to study the influence of sample size and side groove,and the resistance curve transformation was studied by R curves.It is found that the energy release rate of steady state of specimen without side-grooved is higher,and the plastic resistance curve of CT15 can be obtained from the plastic resistance curve of CT5.(3)The macroscopic and microscopic observation of the fracture of the specimen under high temperature environment was carried out.Through the scanning analysis of the micro-fracture morphology,it was found that the void of the P92 steel under the high temperature and load was first nucleated on the grain boundary and grew with the load,which would connected and form micro cracks,eventually leading to fracture.(4)Using the numerical analysis method,the models of different specimens were established in ABAQUS,and the stress state and constraint difference were studied.It is found that the effect of the side groove structure on the test is mainly due to the following two points: First,the side groove can improve the specimen constraint level,and the smaller the size of the specimen,the effect is more obvious;Second,the side groove can make the stress distribution in the thickness more uniform,thus leading a more uniform crack front.