Deformation Behavior at Upper Yield Point of Iron Single Crystals

Abstract

The plastic deformation behavior at upper yield point of iron single crystals was studied by the successive stress relaxation method. The specimens used have the same tensile axis [110], but the three specimen groups, of which the upper yield strengths were different from one another, were prepared by controlling carbon content and condition of heat-treatment.
From the results obtained at −61°C, was shown that the true plastic strain rate near the upper yield point can be expressed in terms of the product of two functions: \dotε=f(ε)g(σ), where ε is the plastic strain, and σ the applied tensile stress, the function being the forms of f(ε)∝ε, g(σ)∝σ^m or g(σ)∝exp(−D⁄σ), where m and D are the constants particular to every specimen group.
On the basis of Johnston-Gilman concept, the contribution of the mobile dislocations to yielding characteristics was examined in terms of the mobility and the density separatedly, and compared in the three specimen groups.