Temperature dependence of the yield points in iron

Abstract

Between 300° and 90°K the elastic limit arid the anelastic limit were measured in polycrystalline irons with 0.0014 and 0.012 per cent interstitial impurities using a high sensitivity extensometer. The elastic limit was independent of temperature but depended on purity. The anelastic limit depended on temperature and impurity content, but the decrease in temperature dependence with decreasing amount of impurity indicated that an ultra-pure iron should show no temperature dependence of the anelastic limit as measured with a high sensitivity extensometer. These results do not support the existence of a temperature dependent Peierls-Nabarro force in iron. The large temperature dependence ordinarily associated with the macroscopic measurements of the yield point was shown to be associated with the rate of work hardening in the microstrain region i.e. between our anelastic limit and the macroscopic yield point. The rate of work hardening in the microstrain region increases markedly with decreasing temperature. It was concluded that thermally activated cross-slip would determine the temperature dependence of the macroscopic yield point if impurities could be completely eliminated.