冷間圧延した炭素鋼中セメンタイトの内部欠陥組織

抄録

In order to clarify the deformation behaviour of cementite in steels, observations by a transmission electron microscope were made on the dislocation structures of cementite in cold-rolled carbon steels.
The results obtained are summarized as follows:
(1) A plastic deformation of cementite due to dislocation gliding was demonstrated to occur in the carbon steels. The gliding was also found to take place very heterogeneously; it was concentrated only on several slip planes being in parallel and 0.2∼0.3 μ apart from each other.
(2) Many straight dislocations were observed on slip planes, and the density of such dislocations was greatly increased in proportion to the increase in the deformation of steels. In addition to the dislocation, moiré pattern, cell wall, and stacking fault were also observed in the deformed cementite.
(3) Slip planes of cementite crystals at room temperature were determined to be (100)_θ, (010)_θ and (001)_θ. The possibility of two slip directions, [001]_θ on (010)_θ and [010]_θ on (001)_θ, was suggested from a detailed observation of the image of pile-up dislocations on the slip planes. A slip direction, [010]_θ on (100)_θ, was also presumed to be a probable one. However, it must be noted that the slip direction [001]_θ on (010)_θ is not consistent with the one expected from the crystalline structure of cementite. It was confirmed from these experimental results that the major part of dislocations on their slip planes had a screw nature.
(4) The fracture of lamellar cementite proceeded by the following way; the gliding of cementite crystals in the heterogeneous manner results in division of the original cementite crystal into several undeformed blocks. The mutual gliding displacement between two adjacent blocks (height of slip steps) increases with a successive deformation of the cementite. Finally, the cementite is perfectly broken away along the boundaries of the blocks probably due to the stress concentration at the slip steps.