EFFECT OF GRAIN SIZE AND STRAIN RATE ON LOWER YIELD STRESS OF PURE IRON AT 288 DEGREES K

The results of previous investigations into the effect of grain size, strain rate and temperature on the lower yield stress of α-iron are briefly discussed in terms of the theory of thermally activated flow. Lower yield stress measurements from room temperature tensile tests on high-purity iron specimens at strain rates throughout the range from 10-4 s-1 to 2350 s-1 are presented. The results are plotted to show the effect of grain size and are analysed in terms of the equations of thermal activation. Estimates of activation volume and activation energy from the present results agree well with those obtained by other workers at conventional rates of strain. © 1969.