実用機械材料の結晶粒径と加工硬化指数について

概要

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The grain-size dependence of the strain-hardening exponent is experimentally investigated and is expressed as a simple power function of the mean-grain size, d_m, as n_<2, 3>=A(d_m)^B, (A, B : const.), where n_<2.3> is the strain-hardening exponent obtained in the plastic strain range larger than about 4% in engineering sheet materials of copper, 6-4 brass, aluminum and a mild steel of SS41. Substituting this relation into the equation of σ_f=Kε_p^<n_<2.3>> (K : a function of d_m), flow stress, σ_f, of these materials can be successfully expressed as a function of plastic strain, ε_p, and the mean-grain diameter. Another equation of σ_f=K'(a+ε_p)^<n'> where n' is the strain-hardening exponent (K', a : functions of d_m) is also applied to experimental data and their correlations with the values obtained in these equations are shown. A theoretical flow-stress equation containing a geometrically-necessary dislocation density, ρ^G, and a statistically-stored one, ρ^S is modified and it predicts the experimental grain-size dependence of strain-hardening exponent, n_<2.3> in copper and 6-4 brass excellently. Is is also shown that the flow-stress dependence on the mean-grain diameter and plastic strain is satisfactorily expressed by these equations with copper.
1986-09-25