Study On Creep-fatigue Test And Evaluation Method Of Notched SS304 Stainless Steel

In the chemical,petroleum,energy and other industries,some holes and slots are formed in some parts of the equipment,in order to meet certain specific functions.These devices are subjected to repeated mechanical loads when operating in high temperature environments.In this situation,it tends to damage the equipment in the open and grooved areas,which can cause serious casualties and property damage,because this occurs without obvious signs.The cause of this damage is mainly the creep in high temperature environment and the fatigue of repeated loads.A lot of work need to be done in this research,due to the complex stress and strain distribution in notch root.SS304 stainless steel is widely used in some harsh environments due to its excellent corrosion resistance and processing performance.There-fore,this paper selects this material as the research object.In this paper,a circular rod specimen with a circumferential notch is selected for experiments and analyzing the microstructure of the broken section,including U-shaped notch and V-shaped one.Firstly,the fatigue test at room temperature was carried out on the specimen with V-notch,and the depth and angle of the notch are the variables.At a stress amplitude of 300 MPa,the fatigue life of the specimen becomes shorter as the depth of the notch increases.At a stress amplitude of 400 MPa,the fatigue life of the specimen gradually increases as the depth of the notch increases.Under these two stress amplitudes,the fatigue life of the specimen decreases as the angle of the notch decreases.Secondly,the creep-fatigue test was carried out on the specimens with U-shaped and V-shaped notches at 600 °C.The effect of notch size and holding time on creep-fatigue was studied.For the V-shaped notch,the life of the specimens shows a V-shaped distribution with the increase of the opening angle without the load-holding;the life of the specimens decreases with the increase of the angle when the load is kept for 1 min.With the increase of the holding time,the life of the specimens is drastically reduced,which shows that the strong creep will weaken the fatigue strength of the specimens.Thirdly,the microscopic morphology of the fractured section of the specimen was observed by scanning electron microscope,and the fracture process of the specimen was studied.As the load-holding time increases,it is observed that there are more hollows growing up,and many dimples appear in the section.Finally,several life prediction equations for a single variable are proposed,as well as a model for predicting the life of a notched specimen based on the average deformation rate in the middle of life.After testing,the model has a relatively small errors in predicting life,which can meet the needs of engineering.