Manufacturing method of plug used for piercing and rolling of metal material, manufacturing method of metal tube, and plug used for piercing and rolling of metal material

摘要

A plug material having a predetermined shape is prepared, and the prepared plug material is heat-treated at a heat treatment temperature of 950 ° C. or more and less than 1050 ° C. in a heat treatment atmosphere containing 1.0 vol% or more of oxygen, and the oxide scale layer 30 is formed on the surface. A plug having the same is manufactured. According to this manufacturing method, since the pores PO extending along the plug material surface SF are formed below the outer scale 20 in the oxide scale layer 30, cracks are easily propagated in the outer scale 20. Therefore, the outer layer scale 20 is more easily peeled than before.