| 摘要 |
PURPOSE:To eliminate the need for reworking with virtually no generation of strains after hardening and to permit sufficient hardening with air cooling by using laser beam irradiation in a hardening treatment for the surface of a valve seat for cylinder heads made of cast iron. CONSTITUTION:A hardening surface treatment using laser beam irradiation is applied on the surface 2 of a valve seat against which the suction and discharge valve of a cylinder head 1 collides, whereby a surface-hardened layer is formed, and a valve seat part 3 is constituted. This hardening is accomplished by using, for example, a CO2 laser device 4, disposing the device 4 with inclination to the central axis of the valve port in such a way that the beam 5 thereof is made incident to the seat surface 2 at an optimum angle and rotating this one turn in an arrow direction. The surface 2 irradiated by the beam 5 is quickly heated and the range of the irradiation can be considerably narrowed; therefore, when the beam 5 passes therethrough, the irradiated part is quickly cooled by the thermal diffusion and has extremely high hardness by causing martensite transformation. |
