Application of Magnetic and Eddy-Current Methods to Assess the Thickness of the Hardened Layer on the Surface of AISI 321 Metastable Austenitic Steel Subjected to Frictional Treatment

The possibility of assessing the thickness of the hardened layer on the surface of AISI 321 metastable austenitic steel, subjected to frictional treatment with a sliding indenter under various normal loads, using the magnetic Barkhausen noise method and the eddy-current method is investigated. The production of hardened layers of different thicknesses is simulated by stepwise electrolytic etching. The results of the non-destructive methods were compared to those obtained by the microhardness method to determine the thickness of the hardened layer. It is shown that the thickness of the hardened layer can be assessed using the eddy-current method and the magnetic Barkhausen noise method. However, the eddy-current method is preferable. This is because, in addition to sensitivity to the ferromagnetic phase, it is also sensitive to the level of defectiveness of the γ-phase. At the same time, it is necessary to take into account in the test method that the thickness of the hardened layer determined by the non-destructive methods is less than that determined by the microhardness method.