The influence of temperature on pre-yield plastic and anelastic microstrain in low-carbon steel

Abstract

Pre-yield plastic and anelastic microstrains in an annealed low-carbon steel have been measured as a function of time under rapidly applied constant tensile stress at temperatures of −23°F (−31°C), + 76°F (+ 24°C), and + 150°F (+ 66°C). The rates of pre-yield microstrain when stress is first applied are compared with the theoretical rates for the thermally activated release of dislocations from atmospheres of interstitial solute atoms. This comparison indicates limited agreement with theory in that the apparent activation energy for dislocation release is inversely proportional to the applied stress, as predicted by Fisher. However, the results obtained at +150°F (+ 66°C) do not correlate with those obtained at the two lower temperatures in the manner predicted. Also, the magnitudes of the activation energies required to fit the experimental measurements are almost two orders of magnitude lower than those predicted by previous dislocation theory. A modification of existing theory which might account for these discrepancies is discussed qualitatively. The total amounts of pre-yield microstrain observed at + 150°F (+ 66°C) are found to be several times larger than those at the two lower temperatures. This result also indicates that some modification of existing theories is required.