オーステナイト領域における 0.16% 炭素鋼の変形挙動

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High temperature tensile deformation of a 0.16% carbon steel was studied over a wide range of strain rates from 1.43 sec^<-1> to 2.73×10^<-5>sec^<-1> in the austenite (γ) range. The shape of the true stress-true strain (σ-ε) curve showed a sharp maximum or regular oscillation in the low strain region and then reached to a steady state deformation in the higher strain region. With a given initial grain size, D_0, the σ-ε curve is expressed solely in terms of the first maximum flow stress, σ_M, or Z in the following equation. σ_M which is independent of D_0 can be correlated with temperatuer, T, and strain rate, ε^^., approximately by the following deformation equation ; ε^^.=A・σ^n_M・exp(-Q_0/(RT)) or Z(=ε^^.・exp(Q_0/(RT))=A・σ^n_M in which n (=5.4) and Q (=68.5 kcal/mol) are nearly equal to those obtained in creep experiments. The energy value is almost the same as the activation energy for self-diffusion in the γ phase of the 0.16% carbon steel. The austenite grain size (D) in the deformed structure is unchanged in the high strain region. D is a function of σ_M or Z in the above equation and is independent of the actual D_0 and T or ε^^.. From these results and the metallographic observations reported previously, it is considered that the high temperature deformation of the 0.16% carbon steel in the γ range is controlled by the dynamic recrystallization process assisted by the diffusion of atoms. The mono-peak stress type curve is observed when the grain size decreases with deoformation (D_0>D), and the oscillated stress type curve appears when the grain size increases with deformation (D_0>D). It is concluded, therefore, that whether the observed σ-ε curve shows a peak stress type or an oscillated stress type depends on the relative difference between the initial grain size, D_0, and the dynamically recrystallized grain size, D. This suggests that the shape of σ-ε curves is dependent on not only Z but also D_0 and the change in the shape with Z and D_0 is explained qualitatively in terms of the nucleation and growth model applied to the dynamic recrystallization.
社団法人日本鉄鋼協会の論文
1977-02-01

オーステナイト領域における 0.16% 炭素鋼の変形挙動

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