Abstract
The dilatation curves of steel by heating and by cooling cycles by obtained means of a common dilatometer (attached few springs) do not exactly coincide, that is, the cooling curve is usually located below the heating curve. This difference shows always the same degree of contraction in every repetition of heating and cooling under the same conditions provided that the specimens are cooled down to room temperature. Having made an investigation about the reason for such a peculiar phenomenon in steel, the auther has reached the following conclusion. It is a well known fact that during the transformation period of steel, a volume change occurs due to internal molecular movement or atomic rearrangement caused by dissolution of carbides in austenite (or separation of carbides). It is also well-understood that an enormously large internal stress accompanies this transformation, which according to Dr. Honda’s [K. Honda, Proceedings of the Japan Academy, Vol. 25 (1949), No. 1] calculation in tension or compression amounts to a few thousand Atm. pressures. This internal stresses keep equilibrium within, but if an external pressure be applied into one direction, even though the pressure is meager, the equiliblium will be disbalanced, consequently a deformation is liable to take place in the direction of applied force, however, It is, however difficult to continue the deformation after this transformation has once ceased. Judging by the above fact it will be concluded that the plastic deformation results by small applied compression during the transformation period only.
