Abstract: An apparatus for detecting the surface flaws of a red-hot metal part includes a light source for illuminating a predetermined area on the surface of a moving red-hot metal part, an image pick-up device for picking-up the image on the metal part surface formed by the light rays from the light source, and a shutter disposed on the optical path between the light receiving surface of the pick-up device and the light source. The reflection energy from the metal part surface corresponding to the incident light rays from the light source is set up to be much larger than the radiation energy of the metal part per se. This relation of energy is set up by adjusting the illumination of the light source. The surface flaws are detected in such a manner that at least one of a series of video signals fed from the image pick-up device after the shutter release is selected as the optimum video signal for flaw detection, and properly selected.

Abstract: When a concavity-shape part is formed in the center of skid material and cooling mechanism is arranging in the concavity-shaped hole, a steel material, e.g. slab, bloom or the like, can be cooled without any of deformation of said material.

Abstract: Heated steel material which is to be cooled is multi-sectioned in the longitudinal direction of said material into n zones. Spaced apart zones of the n zones are individually cooled, and then the material is finally cooled as a whole.