低炭素鋼の高温クリープ変形における内部応力と微視組織

抄録

The creep strain rate of metals under varying load and temperature depends not only on the instantaneous load and temperature but also on the history of load and temperature conditions, because the microstructure of the metal changes according to the history of these conditions, and affects the degree of resistant stress, or so-called internal stress, which lowers the effect of applied stress upon the movement of mobile dislocations.
As the first step in deriving a general deformation law, the authors examined the change of internal stress and microstructure during transient creep by the stress dip testing and the X-ray diffraction technique.
Results obtained are summarized as follows:
(1) The internal stress increases during transient creep but remains constant during steady state creep. As the applied stress becomes larger, the magnitude of the internal stress becomes larger. The ratio of internal stress during steady state creep σ_i^ss to applied stress σ, that is σ_i^ss/σ, does not remain constant but decreases with increasing applied stress.
(2) The creep strain rate is related to the effective stress (σ_e=σ-σ_i) independently of applied stress and strain.
(3) The dislocation density measured by the X-ray diffraction technique is related to the internal stress as
σ_i=7.8+1.50×10^-4√ρ
(4) Vickers hardness H_V is related to the internal stress as σ_i=0.214H_V-12.4