Tensile properties of a high-purity iron from -196°C to 200°C at two rates of strain

Abstract

Abstract Results are given of tensile tests at two rates of strain, 10−4 and 0•37 per second on a polycrystalline high-purity iron at temperatures in the range 200°C to -196°c. No definite effect of rate of strain on cleavage strength at -196°C was detected. At the low rate of strain, the upper and lower yield stresses were approximately constant in the range 20°C to 200°C, but rose sharply below 20°c. At the high rate of strain these stresses increased as the temperature was lowered below 200°C. Within the lower temperature range the lower yield stress at each rate of strain could be represented by a linear function of temperature, which extrapolated to a common value, viz. 91 000 lb/in.2 at 0°k. Comparing these results with Seeger's theory, an activation energy for slip of 0•64 ev was obtained. The results were also compared with Petch's relations between lower yield stress and grain size. Reasonable agreement was obtained between the average value of k y over the whole temperature range, with that give...