鋼の脆性破壊の原因に関する考察
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概要
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Steel in the state of casting and forging is very brittle. Some times the breakage of steel in machining or cold bending is caused by its brittleness. Especially such breakage occurs much more frequently in self hardening low alloy steel than in carbon steel. Causes of such brittle rupture have generally been considered to be impurities, coarseness of grain size and micro crack in the material, but this consideration is not satisfactory, and can not explain some phenomena. The present writer tries fo offer a new considerafion on the causes of such brittle rupture from the view point of metallography, and the new consideration is as follows : - (1) The principal factor controlling such brittle rupture is the relation between local concentrated stress in the crystal grain boundary and breaking stress of structure component. (2) The factors controlling local concentrated stress are the size of crystal grain, the thickness of precipitate, the breaking stress of structure compoment and the micro-crack in grain boundary. (3) Impurities in grain boundary are an additional factor of such brittle rupture, and not an effective one. (4) Steel spcimens annealed at a temperature lower than its critical point are tough. Causes of the toughness are considered to be possibility of plastic deformation owing to the softening of matrix, the uniforming of local stress concentration due to the developement of deformation area and the increase of breaking stress caused by plastic deformation. (5) As causes of the toughness of steel specimens annealed at a temperature higher than its critical point can be enumerated the uniforming of stress concentration due to fine crystal grain, plastic deformation owing to the softening of matrix and the inercase of breaking stress caused by plastic deformation.
- 山形大学の論文
- 1952-11-30