Sensitivity to dynamic strain aging of carbon–manganese steels measured by ultrasonic fatigue testing

Some carbon–manganese (C–Mn) structural steels are known to be sensitive to aging under deformation between 100 and 350°C, phenomenon called dynamic strain aging (DSA). This paper is aimed at studying the DSA sensitivity through the thermal response of C–Mn steels during ultrasonic fatigue tests. For this purpose, self‐heating tests are conducted on two C–Mn steel grades, extensively used in the nuclear industry. Tests are monitored by infrared thermography. DSA effect clearly appears on self‐heating curves by a singular temperature rise. The DSA occurrence is correlated with results from internal friction tests, in particular with the presence of the cold work peak. The temperature of 100°C related to the start of the thermally activated DSA phenomenon is retrieved by self‐heating tests. Based on a further intrinsic dissipation computation, DSA distinctly differs from the classical dislocation glide mechanism. Furthermore, a stress threshold of irreversibility is shown to emerge. Highlights Dynamic strain aging (DSA) is investigated by thermography in ultrasonic fatigue. C–Mn steels with different solute atoms contents and thermal treatments are studied. Self‐heating tests in ultrasonic fatigue allow to evaluate the DSA sensitivity. Existence of an irreversibility stress threshold in fatigue without damage is highlighted.