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 production method of a seamless pipe or tube according to the present invention comprises the steps of applying a lubricant containing carbon to a mandrel bar, producing a material pipe or tube with a mandrel mill using the mandrel bar to which the lubricant is applied, and reheating the material pipe or tube in a reheating furnace, wherein when a temperature of the material pipe or tube is 550° C. or higher and 1000° C. or lower in the reheating step, an oxidizing gas is fed into the material pipe or tube.

Abstract: A process for producing seamless pipes which comprises conducting a piercing rolling step, a elongating rolling step using a mandrel bar, and a sizing rolling step and subsequently conducting a product heat treatment. In the process, when the carbon-equivalent weight, namely the sum of the weight of graphite in the lubricant and the carbon content in the organic binder, per unit area of the lubricant adhering to the mandrel bar surface in the above-mentioned step of elongating rolling is expressed by C (g/m2) or the maximum extent of carburization in the inner surface of the pipe to be heat-treated but prior to the heat treatment is expressed by ?C (% by mass), the heating temperature for the pipe to be heat-treated is expressed by T (° C.

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: A process for stainless-steel pipe production which comprises piercing rolling a raw material stainless steel containing, by mass, Cr: 10-30%, to give a hollow shell, elongating rolling the hollow shell using a mandrel bar, together with a graphite-free lubricant, to give a finishing rolling blank pipe and heating the blank pipe in a reheating furnace and subjecting the same to finishing rolling by sizing rolling to produce a hot-finished pipe, and then subjecting this pipe as a mother pipe to cold working to produce a stainless-steel pipe. In the reheating furnace, the finishing rolling blank pipe is heated to 1000° C. or more and subjected to heating in which an oxidizing gas is blown into the pipe inside, whereby a stainless-steel pipe which is inhibited from forming a carburized layer in the pipe inner surface can be produced. When the finishing rolling by sizing rolling to give a cold working mother pipe is carried out by stretch reducer rolling at 860-1050° C.

Abstract: A production method of a seamless pipe or tube according to the present invention comprises the steps of applying a lubricant containing carbon to a mandrel bar, producing a material pipe or tube with a mandrel mill using the mandrel bar to which the lubricant is applied, and reheating the material pipe or tube in a reheating furnace, wherein when a temperature of the material pipe or tube is 550° C. or higher and 1000° C. or lower in the reheating step, an oxidizing gas is fed into the material pipe or tube.

Abstract: It is an object of the present invention to provide a mandrel bar cleaning facility capable of effectively suppressing carburization generated on the inner surface of a pipe or tube while the pipe or tube is elongated and rolled without hindering an operation. A mandrel bar cleaning facility 15 of the present invention cleans a mandrel bar B which is pulled out of a mandrel bar conveying line after being used for elongating and rolling a pipe or tube in a mandrel mill 8. The mandrel bar cleaning facility 15 is provided with conveying devices 17, 18 that convey the mandrel bar B in the axial direction while revolving the mandrel bar B in the peripheral direction, and cleaning devices 1d that are arranged oppositely to the side of the mandrel bar B conveyed by the conveying devices 17, 18, and jet high-pressure water having a water pressure of 0.2 to 150 MPa (preferably, 20 to 150 MPa) toward the outer surface of the mandrel bar B.

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: A process for producing seamless pipes which comprises conducting a piercing rolling step, a elongating rolling step using a mandrel bar, and a sizing rolling step and subsequently conducting a product heat treatment. In the process, when the carbon-equivalent weight, namely the sum of the weight of graphite in the lubricant and the carbon content in the organic binder, per unit area of the lubricant adhering to the mandrel bar surface in the above-mentioned step of elongating rolling is expressed by C (g/m2) or the maximum extent of carburization in the inner surface of the pipe to be heat-treated but prior to the heat treatment is expressed by ?C (% by mass), the heating temperature for the pipe to be heat-treated is expressed by T (° C.

Abstract: A process for stainless-steel pipe production which comprises piercing rolling a raw material stainless steel containing, by mass, Cr: 10-30%, to give a hollow shell, elongating rolling the hollow shell using a mandrel bar, together with a graphite-free lubricant, to give a finishing rolling blank pipe and heating the blank pipe in a reheating furnace and subjecting the same to finishing rolling by sizing rolling to produce a hot-finished pipe, and then subjecting this pipe as a mother pipe to cold working to produce a stainless-steel pipe. In the reheating furnace, the finishing rolling blank pipe is heated to 1000° C. or more and subjected to heating in which an oxidizing gas is blown into the pipe inside, whereby a stainless-steel pipe which is inhibited from forming a carburized layer in the pipe inner surface can be produced. When the finishing rolling by sizing rolling to give a cold working mother pipe is carried out by stretch reducer rolling at 860-1050° C.

Abstract: A seamless tube is manufactured while effectively suppressing the occurrence of carburization in the seamless tube without interfering with operations. A seamless tube is manufactured by a step of washing at least a portion of a conveyor installed in a conveying step of a mandrel bar B which is situated from a lubricant applying device 7 to the entrance of a mandrel mill 8, a step of washing, on the upstream side of the lubricant applying device 7, a mandrel bar B which was used for elongation rolling, and a step of applying a non-graphite-based lubricant to the mandrel bar B with the lubricant applying device 7, wherein the conveyor and the mandrel bar B are each washed such that the amount of graphite C2 (g/m2) adhering to the surface of the mandrel bar B before it is provided to elongation rolling and the amount of carbon C1 (g/m2) contained in the organic binder of the applied lubricant satisfy Equation 1: 0.08×C1+0.05×C2?3 and Equation 2: 3?C1+C2?50.

Abstract: A seamless tube is manufactured while effectively suppressing the occurrence of carburization in the seamless tube without interfering with operations. A seamless tube is manufactured by a step of washing at least a portion of a conveyor installed in a conveying step of a mandrel bar B which is situated from a lubricant applying device 7 to the entrance of a mandrel mill 8, a step of washing, on the upstream side of the lubricant applying device 7, a mandrel bar B which was used for elongation rolling, and a step of applying a non-graphite-based lubricant to the mandrel bar B with the lubricant applying device 7, wherein the conveyor and the mandrel bar B are each washed such that the amount of graphite C2 (g/m2) adhering to the surface of the mandrel bar B before it is provided to elongation rolling and the amount of carbon C1 (g/m2) contained in the organic binder of the applied lubricant satisfy Equation 1: 0.08×C1+0.05×C2?3 and Equation 2: 3?C1+C2?50.

Abstract: A round billet containing, by mass %, 10.50 to 14.00% of Cr with a value represented by the equation of “Cr+4Si?(22C+0.5Mn+1.5Ni+30N)” of not more than 9.0%, wherein the symbols of the elements represent the contents, by mass %, of the elements in the steel, is heated at a soaking temperature of 1100 to 1250 ° C. so that an in-furnace time (min) is not less than “0.5×Diameter of the round billet (mm)”, and then pierced and rolled with a piercing efficiency by a piercing mill of not less than 50%, a value regulated by the equation: “{(Diameter of the round billet?Roll gap at the foremost end of the plug)/Diameter of the round billet}×100” of not more than 8.0, and a plug shape represented by the equation: “Radius of foremost end of the plug (mm)/Diameter of the round billet (mm)” of 0.06 to 0.17. The thus-manufactured high-Cr seamless steel pipe or tube has excellent internal surface properties with minimized internal surface defects.

Abstract: A round billet containing, by mass %, 10.50 to 14.00% of Cr with a value represented by the equation of “Cr+4Si?(22C+0.5Mn+1.5Ni+30N)” of not more than 9.0%, wherein the symbols of the elements represent the contents, by mass %, of the elements in the steel, is heated at a soaking temperature of 1100 to 1250 ° C. so that an in-furnace time (min) is not less than “0.5×Diameter of the round billet (mm)”, and then pierced and rolled with a piercing efficiency by a piercing mill of not less than 50%, a value regulated by the equation: “{(Diameter of the round billet?Roll gap at the foremost end of the plug)/Diameter of the round billet} ×100” of not more than 8.0, and a plug shape represented by the equation: “Radius of foremost end of the plug (mm)/Diameter of the round billet (mm)” of 0.06 to 0.17. The thus-manufactured high-Cr seamless steel pipe or tube has excellent internal surface properties with minimized internal surface defects.