| 摘要 |
In the present invention, heating and cooling processing in which the surface of a steel material machined to a desired shape and subjected to carbonitriding processing is heated by stimulation and then is cooled is repeated a desired number of times so that an ultrafine crystal layer is formed directly below the surface of the steel material and at least a prescribed number of cracks are formed below the formed ultrafine crystal layer. As a result of this configuration, viscosity can be produced by raising the toughness of the surface or directly below the surface and the growth of cracks can be suppressed. |
