PROCESS FOR PRODUCING PLUG FOR USE IN PIERCING/ROLLING RAW METALLIC MATERIAL, PROCESS FOR PRODUCING METALLIC TUBE, AND PLUG FOR USE IN PIERCING/ROLLING RAW METALLIC MATERIAL

摘要

A raw plug material having a given shape is heat-treated at a temperature of 950-1,050°C, excluding 1,050°C, in an atmosphere containing at least 1.0 vol.% oxygen to produce a plug having an oxidized scale layer (30) on the surface. In this production process, pores (PO) extending along the surface (SF) of the raw plug material are formed in a lower part of an outer scale layer (20) of the oxidized scale layer (30). Because of this, cracks readily propagate within the outer scale layer (20). The outer scale layer (20) can hence be more easily removed than in conventional ones.