254 / 2019-10-25 14:19:02

Study on Effect of Electromagnetic Characteristics of Deformed 304 Stainless Steel on Eddy Current Testing

304 austenitic stainless steel, deformation, eddy current testing, optimal frequency

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The induced ferrite and other high magnetic microstructures content changes are studied when 304 austenitic stainless steel stripe specimens are tested under different uniaxial tension deformation, namely its deformation less than 50%. Furtherly, the correlation is plotted between the resulting magnetic permeability or coercivity caused by these microstructures and deformation. Meanwhile, the optimal eddy current excitation frequency under different deformation was obtained, which was basically consistent with 3-D finite element analysis (FEA). In addition, other various factors affecting the quality of eddy current testing (ECT), such as temperature and conductivity, are also considered comprehensively during tensile test. The results of experiment and simulation calculation show that when the deformation is within 50% that necking deformation has occurred, the magnetic permeability of specimens increases with deformation, and gradually begin to have the magnetic properties of weak ferromagnetic materials, which also changes the optimal excitation frequency. The electromagnetic response noise will be increasing, and the impedance plane diagrams of defects are simultaneously distorted because of it, which leads to the quantitative evaluation error of defects.