2008 Volume 48 Issue 11 Pages 1592-1595
The influence of dynamic strain aging (DSA) on the high temperature strength of a structural steel microalloyed with Mo and Nb was investigated by means of tensile tests performed at temperatures ranging from 25 to 600°C and strain rates of 10−4 to 10−1 s−1. This steel showed a ferrite and pearlite microstructure. DSA manifestations are less intense than those observed for low carbon steels and they take place at higher temperatures. The secondary precipitation behavior of the steel was also investigated. The hardness of samples heat treated at 100 to 600°C displayed a maximum at 400°C. Samples treated at this temperature and tensile tested at 600°C didn't showed a higher yield strength than the untreated specimens, indicating that secondary precipitation does not contribute to its high temperature strength. Results obtained here indicated that DSA in the structural steel might be an important mechanism responsible for its fire resistance. The empirical activation energies related to the appearance of serrations on the stress–strain curves and to the maxima on the variation of tensile strength with temperature or disappearance of serrations suggested that the high temperature strengthening associated with DSA in this steel is the dynamic interaction of interstitial-substitutional solute dipoles and dislocations.