Eddy Current Testing of Fatigue Degradation of Metastable Austenitic Steel under Gigacycle Contact-Fatigue Loading

During operation, the surfaces of parts made of austenitic chromium-nickel steels are subjected to intense cyclically repeated contact loads, including shock loads. Therefore, an urgent task is to study contact fatigue and develop methods for nondestructive testing of fatigue degradation of such steels. The aim of this work is to study the possibility of conducting eddy current testing of fatigue degradation under contact loading of AISI 321 austenitic steel. Mechanical tests for contact gigacycle fatigue were carried out according to the scheme of a pulsating shock "plane-plane" contact with an ultrasonic loading frequency. It is shown that eddy current monitoring of fatigue degradation under contact loading of AISI 321 steel is possible, but it has certain limitations due to the nonmonotonic change in the readings of the eddy current device alpha vs the number of loading cycles. In this case, the ascending branch can be used to control the degree of destruction of the surface layer by taking into account the ambiguous nature of the dependences of the readings of the eddy current device on the number of loading cycles in the inspection procedure. The inspection can be carried out by taking the readings of the eddy-current device at the eddy-current transducer excitation frequency f = 124 kHz. In this case, the surface layers, where the fatigue degradation processes develop intensively affecting the physical characteristics of the steel, are analyzed to a greater extent. The quantitative ratio of austenite and deformation martensite in the testing zone has the greatest effect on the value of alpha.