Effect of Hardening Frictional Treatment on Features of Eddy Current Testing of Fatigue Degradation of Metastable Austenitic Steel under Gigacycle Contact Fatigue Loading

Previous studies have shown the possibility of eddy current monitoring of fatigue degradation during contact loading of austenitic AISI 321 steel. However, AISI 321 steel has insufficiently high contact endurance under cyclic impact loading conditions. Therefore, the application of physical methods for nondestructive testing of fatigue degradation of surface-hardened austenitic AISI 321 steel, which has an increased contact endurance, is of considerable interest. The aim of this work is to investigate the possibility of eddy current testing of fatigue degradation during contact loading of austenitic AISI 321 steel subjected to surface hardening frictional treatment. Mechanical tests for contact gigacycle fatigue were carried out according to the scheme of pulsating impact “plane–plane” contact with ultrasonic loading frequency. It is shown that eddy current monitoring of fatigue degradation during contact loading of surface-hardened AISI 321 steel is possible but has certain limitations due to nonmonotonic changes in the readings α of the eddy current device depending on the number of loading cycles. At the same time, it is possible to control the development of intensive destruction of the surface layer of steel that is observed under these loading conditions in the range of the number of cycles 3 ×10^8 – 5 ×10^8 taking into account the ambiguous nature of the dependences of the eddy current readings on the number of loading cycles in the testing method. The testing can be carried out by measuring the readings of the eddy current device at the eddy-current transducer excitation frequencies f = 96- 124 kHz. In this case, we largely analyze surface layers in which fatigue degradation processes are intensively developing and affecting the physical characteristics of steel. The greatest influence on the value of α is exerted by plastic deformation and destruction of the steel surface.