Kinetics of strain aging in drawn pearlitic steels

The kinetics of strain aging in a drawn pearlitic steel wire were analyzed based on measurements from three different experimental techniques: tensile testing, electrical resistivity, and internal friction. The progress of aging after a total reduction in area of 86 pct by drawing and heating between 60 °C and 200 °C was evaluated in terms of the changes in yield strength, electrical resistivity, and temperature-dependent background damping. The kinetic law and the apparent activation energies of the processes occurring in this temperature range were determined by the isothermal variation of the transformed fraction, obtained from the changes in properties with aging time. Under the conditions considered, static strain aging of drawn pearlitic steels seems to occur in two distinct stages, each associated with different atomic mechanisms. The first stage takes place between 60 °C and 100 °C and is characterized by a small increase in yield strength and a decrease in electrical resistivity and background damping. The second stage of aging occurs at higher temperatures or longer aging times and is marked by a sharp increase in yield strength and an increase in electrical resistivity, while the background damping reaches very small values. The probable mechanisms related to this behavior are discussed in terms of the empirical law and the apparent activation energy found.