Effect And Obtained Approach Of Cold-Work Hardening On Mechanical Property In Local Structure Of Nuclear Power Plants

In the actual manufacturing and processing of nuclear power plants,local mechanical properties of materials will change significantly after affected by cold and hot work process.In view of the structural integrity assessment,accurate local structural material mechanical parameters are very important.In this dissertation,a method for obtaining local mechanical properties of materials based on theoretical analysis,numerical simulation and experiments is proposed and discussed.Taking 304 austenitic stainless steel as an example,the cold processing method involved in the production and manufacturing process of nuclear power plants is simplified to uniaxial stretching and compression process.The effect of cold work hardening on mechanical properties of 304SS is analyzed and a mathematical model for predicting the strength based on hardness is established.The main research work is as follows:(1)The influence of the head load on the results during the Vickers hardness test of 304 SS under different cold work hardening degrees is analyzed by combining the Vickers hardness test theory and uniaxial stretching process.The corresponding indenter load range under the true Vickers hardness of the material is calculated by theoretical model.(2)Using the combination of theoretical analysis and experimental research,the variation of 304SS properties under uniaxial tension and compression is analyzed from the perspective of macromechanics and microstructure.And the sensitivity of mechanical properties to cold work hardening under two stress states is studied.(3)The distribution of stress-strain curves and constitutive relations of 304SS at different room temperature during uniaxial stretching and compression are analyzed.Then the stress and strain constitutive equations and the mathematical model of hardness prediction strength are established and both of them are verified by"indentation method"combined with physical experiment and numerical simulation.(4)Taking the nuclear voltage force vessel to take over the safety end dissimilar metal welded joint as an example,based on the structural analysis,the mechanical properties of the overburden layer and the main pipeline material under different cold work hardening degrees are analyzed by theoretical combined experimental method.Then the prediction model is applied to quantitative prediction on the local mechanical properties of pipeline,and the applicability is verified.