| 摘要 |
PURPOSE:To prevent the fracture of a hot metallic billet as a product without spoiling the quality thereof by subjecting the surface in the body part of a roll to hardening to a prescribed pattern by laser light thereby forming a brittle layer. CONSTITUTION:The body part 11a of a roll 11 for transferring a hot billet is hardened to a prescribed pattern by laser light to form an axially extending hardened part at a prescribed interval in the circumferential direction. The part 12 consists of an embrittle layer 12a on the surface having the structure consisting mainly of martensite, a heat affected zone 12b and an unaffected zone 12c. The layer 12a is formed to a prescribed depth, for example, about 0.5mm.. Fine dispersion type cracks are then generated in the layer 12a and propagate axially at prescribed intervals along the hardening pattern. The thermal stress generated on the surface of the roll 11 is thus decreased and the propagation of the cracks C are stopped by the dispersion type cracks in the part 12, by which the fracture of the roll 11 is prevented. |
