フェライト系Fe-Cr合金の定常クリープ速度と磁気変態温度との関連性

Abstract

Tensile creep tests have been carried out with ferritic iron-chromium alloys (15, 20 and 25 wt%Cr) at temperatures ranging from 600° to 800°C and stresses up to 5 kg/mm2. The temperature and stress dependences of the steady-state creep rate have been studied with special reference to the magnetic transformation. The results obtained are as follows: (1) The greatest activation energy for steady-state creep is obtained at the magnetic transformation temperature. The activation energy at the higher temperatures does not seem to depend on stress and is higher than the activation energy for self-diffusion. Besides, at the lower temperatures a gradual decrease is found as the stress increases. These values are comparatively higher than the activation energies obtained above the magnetic transformation temperatures. (2) The stress exponent does not seem to depend on the temperatures. Transitional decrease in the activation volume occurred with increasing stress and two activation volumes for steady-state creep are obtained at each testing temperature. Both values are much larger than the atomic volume and increase as the temperature rises. (3) The experimental evidence seems to be governed to some extent by the diffusion-controlled mechanisms, partly by the climbing of edge dislocations and partly by the non-conservative movement of jogged screw dislocations. The models based on the viscous motion of dislocations due to dragging of solute atmosphere and diffusional flow of vacancies without accompanying the motion of dislocations will not be operative.