| The duplex stainless steel composed of equal amounts of ferrite(a)and austenite(y)phases has excellent corrosion resistance and mechanical properties.Therefore,duplex stainless steel is widely used in power plants,marine buildings and desalination facilities.However,with the development of modern industry,the corrosion resistance of duplex stainless steel has been unable to meet the extremely harsh high temperature and acidified chlorination service environment requirements.In order to meet the growing demand,Sandvik has developed high alloyed super duplex stainless steel SAF2707 HD with excellent corrosion resistance and mechanical properties.Compared with duplex stainless steel,super duplex stainless steel SAF2707 HD is a high alloy Duplex stainless steel,the equivalent number of pitting resistance is greater than 48,can replace SAF 2507 for seawater and other acid corrosion,chlorine environment,and is very suitable for hot sea and other harsh environments.Therefore,this paper focuses on the experiment and simulation of the fatigue failure of super duplex stainless steel SAF2707 HD as a marine riser material.The scanning electron microscope is used to analyze the fatigue failure mechanism of the material,and the finite element software ABAQUS and fatigue analysis are used.The FE-SAFE software is used to simulate the rotating bending fatigue specimen.The main research work and research results of this topic are as follows:1.In order to study the rotating bending fatigue performance of the super duplex stainless steel SAF2707 HD,a rotating bending fatigue test was carried out on the material under the experimental conditions of stress ratio R=-1 and rotational speed of 3150r/min.The fatigue strength of rotating bending under the air medium is679.5MPa,and the stress-fatigue life(SN)curve of the material is plotted.2.Observe the fatigue fracture of the sample by scanning electron microscope(SEM),and analyze the type of fatigue crack source,fracture mechanism and crack propagation mode of the sample.The fatigue fracture of the sample as a whole is ductile fracture,and the fatigue crack is propagated in a transgranular manner.The ferrite phase as a whole showed ductile fracture,and the austenite phase as a whole tended to brittle fracture.Using EDS analysis,it was found that the inclusions on the fatigue fracture were mainly carbides and oxides.3 Comparative analysis of the fatigue fracture caused by different fracture mechanisms leading to specimen fracture.Statistics show that the fracture of the sample due to the surface crack source basically occurs at or below 10~5 cycles,while the fracture of the internal crack source basically occurs at 10~6 cycles.As the stress gradually increases,the fatigue source changes from one to Multiple.4.The finite element software was used to analyze the fatigue life of the sample,and the corresponding fatigue life cloud was obtained.The error between the experimental life and the simulated life is less than 15%.It is proved that the experimental S-N curve is consistent with the finite element simulation. |
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