Abstract
In this study, we focus on the eddy current testing (ECT) as a method to investigate the hydrogen embrittlement mechanism of austenitic stainless steels which are widely used in hydrogen components. ECT is applied to hydrogen-charged austenitic stainless steel AISI 304 specimens with different amounts of residual strain by tensile test and fatigue test. For tensile specimens, permeability values of the specimens are estimated by comparing the signals obtained by the ECT experiment and the results of the electromagnetic field analysis, and the phase transformation is evaluated from the change of the permeability. For fatigue specimens, the change of ECT signal obtained by scanning around fatigue cracks of hydrogen-charged and uncharged specimens was discussed by comparing experimental and numerical results. As a result, it is confirmed that the relative permeability increases with increasing the applied strain to tensile specimens, and the increments of relative permeability of hydrogen charged specimens are larger than these of uncharged specimens. Concerning fatigue specimens, the difference in obtained ECT signal around fatigue cracks appears to be came from the contact of crack quasi-cleavage surfaces, but also because of the change of the bulk electromagnetic properties by hydrogen charging. From these results by tensile and fatigue tests, it is indicated that α’ phase increases by both charging hydrogen and applying strain. Therefore, the possibility of ECT as an in-situ evaluation method of the phase transformation of austenitic stainless steel by hydrogen charge is suggested.
