Effect Of Cold Work Rate On Mechanical Properties At Tip Of SCC In 304 Austenitic Stainless Steel

Austenitic stainless steel,as the one of the essential materials for the primary circuit piping of PWR,is easy to cause stress corrosion cracking(SCC),which is one of the critical factors to restrict the safe operation and service life of nuclear power equipment and structures.Pipe bending and other cold working processes have an important influence on the SCC and crack growth rate of austenitic stainless steels.Based on combining experimental method and numerical simulation method,the mechanical property parameters of 304 austenitic stainless steel under different cold work rates are discussed,and the stress and strain at the crack tip and SCC crack propagation rate in 304 stainless steel under different cold work rates are analyzed by using ABAQUS sub-model technology in this thesis.The primary research work are as follows:(1)Taking the PWR nuclear power plant as the research background,the bending deformation and other cold working processes of the primary pipe elbow simplify to the uniaxial tensile deformation process,and the uniaxial tensile deformation rate is defined as the cold work rate.Uniaxial tensile tests of 304 austenitic stainless steel plate specimens is carried out using the tensile fatigue tester,including cold work rate prefabricated test and mechanical performance test,the engineering stress-strain curve of 304 stainless steel under different cold work rates of 10%,20%and 30%are obtained,and then the curves are corrected.(2)Based on the numerical simulation method,flat plate tensile model that consistent with the test process are constructed by using finite element software ABAQUS,and based on combining experimental method and numerical simulation method,mechanical property parameters of 304 stainless steel under different cold work rates of 10%,20%and 30%are obtained.(3)Taking the standard compact tensile specimen(1T-CT specimen)as the object,the global macro model and sub-model of SCC crack tip are established by finite element software ABAQUS.The research focus on the law of stress and strain at the SCC crack tip and the effect of cold work rates on the stress-strain field at SCC crack tip composed by oxide film and base metal(304 stainless steel)under the conditions of the constant K value.(4)Based on FRI model,the crack tip strain(or strain rate)is selected as the key mechanical parameter affecting the SCC crack growth rate,and the plastic strain rate is used to replace the strain rate of tip,the influence of cold work rates on the plastic strain rate and crack growth rate in SCC crack are analyzed under the conditions of the constant K value.The results and conclusions in this thesis provide a base for the quantitative prediction of SCC crack growth rate in austenitic stainless steel and residual life of the PWR nuclear power plant primary circuit piping in high-temperature and high-pressure corrosion water environments.