PURPOSE: To produce a hollow piece which has a long life and good inside surface quality by providing a rugged shape on the surface of a core material in contact with a surface layer.
CONSTITUTION: The plug is so constituted that the surface layer in contact with a work consists of molybdenum and the internal core material 4 consists of a material having the coefft. of thermal expansion higher than the coefft. of thermal expansion of the molybdenum. Rugged grooves 7 are formed on the surface of the core material 4 in such a manner that the joint boundary has the sufficient joint strength to shearing by the reaction received from the rotating force of the work at the time of piercing. This plug has the extremely high resistance to wear, erosion and seizure and does not be broken, and the life thereof is greatly improved even when the plug is used for piercing and rolling of a high-alloy material. Further, the ideal metal flow of the material to be pierced and the material to be rolled is maintained and the generation of seizure flaws, etc., is obviated; therefore, the hollow piece having the good inside surface quality is stably produced. The working efficiency in the production of the seamless steel pipe is, therefore improved and the cost is drastically reduced.
TAMURA TAKASHI
OIKAWA TSUNEO
MIHARA YUTAKA
HIRAKAWA TOMOYUKI
KUWANO TAKASHI
