加熱および冷却による炭素鋼棒の変形について(IV)帯状組織による変形

Abstract

In this report the author made clear the influence of the banded structure of carbon steel bars on their dimensional changes due to heating and cooling and investigated its mechanism. When low carbon steel bars are heated and cooled, the transformations don’t proceed uniformly over the whole of a specimen, the α-phase and γ-phase are banded in parallel to the rolling direction, and the widths of bands of the two phases change relatively, so if the α-band yields, then the dimension decreases in the direction of the length of banded structure and increases in the transverse direction. When a eutectoid steel bar is heated and cooled, the A1 transformation does not proceed uniformly over the whole of a specimen, the pearlite and γ-phase are banded in parallel to the rolling direction. And the widths of the both bands change relatively, so if the γ-band yields, then the dimension increases in the rolling direction and decreases in the transverse direction. Dimensional changes of medium carbon steel bars due to heating and cooling diminish owing to the above contrary tendencies. In the case of hyper-eutectoid steel bars, the tendency of the above mentioned plastic deformation in the A1 transformation of the eutectoid steel bar is decreased by the existence of primary cementite.