Dynamic strain aging and the wire drawing of low carbon steel rods

The dynamic strain aging behaviour of low carbon steel wire rod was examined at room temperature to 450 degrees C using tensile testing at strain rates of 10(-4) to 10(-1) s(-1). The effects of temperature and strain rate on the yield stress, flow stress, UTS, fracture stress, and fracture strain were investigated in detail. In agreement with previous studies, work hardening peaks, minima in ductility, and negative strain rate dependences of the flow stress were observed between 100 and 400 degrees C, the positions of which depended on the strain rate. A model for dynamic strain aging is employed to predict whether or not it will occur al the strain rates and temperatures involved in commercial wire drawing. For a steel containing 32 ppm N, a temperature higher than about 315 degrees C must be attained for dynamic strain aging to occur; this is higher than the temperatures usually encountered in drawing. However, the model also predicts that if the N content is increased to 115 ppm, the minimum temperature for dynamic strain aging decreases to about 250 degrees C, which can be attained if the die and capstan cooling are not adequate. The negative rate dependence of the flow stress attributable to dynamic strain aging is considered to promote flow localization and, therefore, to be a possible cause of wire breaks during drawing.