Cyclic deformation behaviour of AISI 321 austenitic steel and its characterization by means of HTC-SQUID

AISI 321 austenitic steel forms martensite due to quasi-static and cyclic loading. This presupposes the exceeding of the threshold value of cumulated plastic strain. The main aim is to determine the fatigue damage of austenitic steel by characterizing the martensitic structure with the help of the SQUID measuring technique. Several specimen batches were evaluated and thereby the load amplitudes and the test temperatures were varied (room temperature and 300°C). The experiments result in characteristic curves of the SQUID signals according to the fatigue damage which could be confirmed with comparative measurements with different methods, such as, e.g. ultrasonic absorption measurements. The extremely sensitive SQUID measuring technique allows also detection of information in specimens fatigued at a temperature of 300°C in which the phase fractions of strain-induced martensite are extraordinarily low.