Abstract: A piercing plug includes a plug main body, and a sprayed coating which is formed on a surface of the plug main body and includes iron and iron oxide. A chemical composition of the sprayed coating includes, in addition to the iron and the iron oxide, by mass %, C: 0.015% to 0.6%, Si: 0.05% to 0.5%, Mn: 0.1% to 1.0%, and Cu: 0 to 0.3%.

Abstract: A piercing plug includes a plug main body, and a sprayed coating which is formed on a surface of the plug main body and includes iron and iron oxide. A chemical composition of the sprayed coating includes, in addition to the iron and the iron oxide, by mass %, C: 0.015% to 0.6%, Si: 0.05% to 0.5%, Mn: 0.1% to 1.0%, and Cu: 0 to 0.3%.

Abstract: A piercing and rolling plug has a film composed of oxides such as Fe3O4 and FeO and Fe (metal) as being formed on the surface of the base metal by electric arc spraying using an iron wire whose main component is Fe and, owing to this film, a plug excellent in heat-shielding and seizure-preventing effects can be realized and the lifetime of the plug can be prolonged. Further, in regenerating this plug, a film can be re-formed via the steps of shot blasting of the as-used plug in piercing and rolling and electric arc spraying in that order; thus, it is possible to regenerate the plug at low cost and in a short period of time.

Abstract: Disclosed is a method for producing a seamless pipe by using a piercing mill which pierces and rolls a round billet heated to 1300° C. or lower, wherein the piercing mill is composed of a pair of skew rolls disposed to face each other around a pass line, a pair of guide devices disposed to face each other around the pass line, and a plug disposed along the pass line, between the pair of the skew rolls and also between the pair of the guide devices, wherein the piercing-rolling is performed under the conditions satisfying the following formulas (1) to (3) to prevent wrinkle flaws of the seamless pipe: ?1.0<????(1) ??=?p??r??(2) ?0.37×??+1.47?Rn?0.37×??+2.

Abstract: A piercing and rolling plug has a film composed of oxides such as Fe3O4 and FeO and Fe (metal) as being formed on the surface of the base metal by electric arc spraying using an iron wire whose main component is Fe and, owing to this film, a plug excellent in heat-shielding and seizure-preventing effects can be realized and the lifetime of the plug can be prolonged. Further, in regenerating this plug, a film can be re-formed via the steps of shot blasting of the as-used plug in piercing and rolling and electric arc spraying in that order; thus, it is possible to regenerate the plug at low cost and in a short period of time.

Abstract: Martensitic stainless steel tubes are produced by optimizing the chemical composition of steel for billets (C: 0.15-0.22%, Si: 0.1-1.0%, Mn: 0.10-1.00%, Cr: 12.00-14.00%, N: 0.01-0.05%, P: not more than 0.020% and S: not more than 0.010%) and the relation between the soaking temperature for pierced-and-rolled tubing material and the section area reduction rate in final rolling. By this method, delayed fracture cracking in impact-receiving portions of tubes in martensitic stainless steel s such as 13% Cr tubes can be inhibited and the generation of inner-surface flaws can be prevented.