DYNAMIC STRAIN-AGING SENSITIVITY OF HEAT-AFFECTED ZONES IN C-MN STEELS

In weakly killed C-Mn steels, the dynamic strain aging (DSA) phenomeno n induces an increase in the ultimate tensile strength associated with a ductility loss, usually measured in the 100-200 degrees C temperatu re range. This phenomenon, which induces large toughness reductions, i s not well characterized in the heat affected zones (HAZ) of the welds , since the sensitivity to DSA cannot be directly determined due to th e very abrupt microstructure gradients existing in these zones. In ord er to study the influence of microstructure on DSA, tensile tests were performed on simulated HAZ, resulting from various quenching conditio ns of C-Mn steels. These results are interpreted through correlations with internal friction results on the same microstructures. It is conc luded 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 micro structure, 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. (C) 1998 Elsevier Science B.V.