微細結晶粒を有するFe-Ni, Fe-Cr合金の超塑性について

Abstract

Tensile tests of grain refined Fe-Ni and Fe-Cr alloys were carried out in the strain rate range 10−4 min−1∼10−1 min−1 in order to measure the strain rate sensitivity, m, in the α single phase, (α+γ) two-phase and γ single phase regions. The effect of the two-phase structure on the superplasticity was discussed.The largest value of m was obtained at a strain rate lower than \dotε=10−3 min−1 and in the (α+γ) two-phase region. In the (α+γ) two-phase region m depends strongly on strain rate, grain size and in particular the volume fraction of the γ phase, Vγ. The m value reached its maximum at the temperature corresponding to Vγ=0.5. Them value was also found to have a strong dependence on the metallographical characteristics of grain boundary.