Diagnosis of austenitic steel valves with the magneto-optical method

Samples selected from damaged austenitic steel valves of diesel engines have been examined using the magneto-optical (MO) method. The method uses a magnetic excitation normal to the material surface and enables the assessment of two conditions of the originally non-magnetic austenitic steel, namely an integral one, when the coercivity H_c is measured, and a local one that concentrates on the detection and assessment of individual defects. The results have shown that the operational load increases H_c of these materials and a defect of the fatigue crack type has been detected in the position of the valve failure.