[en] In weakly killed C-Mn steels, the dynamic strain aging (DSA) phenomenon induces an increase in the ultimate tensile strength associated with a ductility loss, usually measured in the 100-200 C temperature range. This phenomenon, which induces large toughness reductions, is not well characterized in the heat affected zones (HAZ) of the welds, since the sensitivity to DSA cannot be directly determined due to the very abrupt microstructure gradients existing in these zones. In order to study the influence of microstructure on DSA, tensile tests were performed on simulated HAZ, resulting from various quenching conditions of C-Mn steels. These results are interpreted through correlations with internal friction results on the same microstructures. It is concluded that the materials which have been submitted to the more severe quenching conditions appear to be less sensitive to DSA. This trend is attributed to the larger density of dislocations which can trap most of the interstitial atoms in these microstructures. Whatever the microstructure, the intensity of DSA, characterized by the ductility loss, is proportional to the Snoek peak height measured by internal friction. This result allows the evaluation of the sensitivity of C-Mn steels to DSA from a unique internal friction test. (orig.)