Method for Producing Plug

Abstract

A method for producing a plug includes: a step of preparing a plug base metal having a concave portion along a circumferential direction in an outer peripheral surface; and an arc spraying step of spraying a spraying wire rod material onto the outer peripheral surface of the plug base metal by arc spraying to form films containing Fe and Fe oxides on the outer peripheral surface of the plug base metal. The arc spraying step includes: a separating step of separating the outer peripheral surface of the plug base metal into a plurality of regions along an axial direction; and a step of performing arc spraying separately in each of the regions. In the separating step, a boundary between the regions is set at the concave portion. In this way, peeling of films at a connecting portion is prevented, and the lifetime of the plug can be increased.

1 . A method for producing a plug that is used in a piercing-rolling mill when producing a seamless steel pipe, the method comprising:
 a step of preparing a plug base metal having a concave portion along a circumferential direction in an outer peripheral surface, and   an arc spraying step of spraying a spraying wire rod material onto the outer peripheral surface of the plug base metal by arc spraying to form films containing Fe and Fe oxides on the outer peripheral surface of the plug base metal;   wherein:   the arc spraying step includes:   a separating step of separating the outer peripheral surface of the plug base metal into a plurality of regions along an axial direction, and   a step of performing arc spraying separately in each of the regions; and   in the separating step, a boundary between the regions is set at the concave portion.   
     
     
         2 . The method for producing a plug according to  claim 1 , wherein:
 in the plug base metal, the outer peripheral surface is formed by connecting a plurality of divided faces successively in the axial direction, and has the concave portion at a joint between the divided faces; and   at the joint which is the concave portion, a slope θ 1  (°) of a divided face located on a front-end side of the plug and a slope θ 2  (°) of a divided face located on a rear-end side of the plug satisfy the following Formula (1).
   θ1<θ2  (1)