抄録
Commercially produced ferritic spheroidal graphite cast iron was used in this study. The materials tested were prepared in two ways, austempering and hot-rolling. The austempering was done either at 573K or at 673K by quenching into salt bath and holding for 5min or 2hr after austenitization at 1173K for 1hr. Finally the materials were hot rolled at temperatures ranging from 1173 to 1073K.
Charpy impact tests were carried out using a V-notched small test specimen (5mm×5mm×55mm) in the temperature range of 77-430K. The results obtained are summarized as follows;
(1) The austempering at 573K elevated the tensile strength and hardness in comparison with that at 673K, while it lowered the impact value.
(2) Both the tensile strength and absorbed energy were lowered by the rolling, because the cracks coalesced easily as a result of the narrower spacing of graphites.
(3) The transition temperature determined by a mean value of the upper and the lower energy absorbed can be written in this order: ferrite<upper bainite<lower bainite<rolled ferrite
(4) The absorbed energy was correlated with the size of the plastic zone ahead of the notch.
