Abstract: The railway axle according to this disclosure has a pair of fitting portions and which each include a fitting portion hardened layer and a base metal portion, and a center parallel portion which includes a center parallel portion hardened layer and the base metal portion. The base metal portion has the chemical composition described in the description. In a region having the Vickers hardness of 480 HV or more in the center parallel portion hardened layer, a dislocation density p obtained based on a CoK? characteristic X-ray diffraction result is 2.5×1016 m?2 or less, a half-value width B of the (211) diffraction plane is 1.34 degrees or less, and the dislocation density p and the half-value width B of the (211) plane obtained by X-ray diffraction satisfy Formula (1). (?4.8×1016×B+8.5×1016)/??1.

Abstract: A manufacturing method of a seamless metal pipe includes: preparing a plurality of mandrel bars in which lengths of work portions which come into contact with a hollow shell during elongating are different from one another; selecting a mandrel bar including a work portion having a length corresponding to the number of stands used in thickness reduction, among the plurality of mandrel bars; inserting the mandrel bar selected in the selecting into the hollow shell; and performing the elongating on the hollow shell into which the mandrel bar is inserted. Moreover, in the elongating, outer diameter reduction is performed by one of a preceding-stage stand group and a succeeding-stage stand group and the thickness reduction is performed by the other of the preceding-stage stand group and the succeeding-stage stand group, or the thickness reduction is performed by both of the preceding-stage stand group and the succeeding-stage stand group.

Abstract: A manufacturing method of a seamless metal pipe includes determining whether a preceding-stage stand group is used in outer diameter reduction or in thickness reduction of a hollow shell; and performing elongating on the hollow shell, into which a mandrel bar is inserted, based on the determination. In addition, in the elongating, when the preceding-stage stand group is used in the outer diameter reduction, the hollow shell is rolled in a state where an inner surface of the hollow shell does not come into contact with the mandrel bar in the preceding-stage stand group, and the hollow shell is rolled in a state where the inner surface of the hollow shell comes into contact with the mandrel bar in the succeeding-stage stand group.

Abstract: A mandrel mill a method for manufacturing a seamless pipe by using the mandrel mill includes a plurality of roll stands in which three grooved rolls R are disposed in each roll stand such that an angle formed by pressing directions is 120° and the pressing directions of the grooved rolls R are alternately shifted by 60° between adjacent roll stands, wherein a central angle ? defining a circular arc that constitutes a groove bottom profile of the grooved roll R disposed at least in the first and second roll stands is set at less than 60°. The mandrel mill can adequately suppress the problem of the mandrel bar not being able to be pulled out from a pipe after drawing and rolling, without resulting in an increase in facility cost and deterioration of maintainability.

Abstract: A manufacturing method of a seamless metal pipe includes determining whether a preceding-stage stand group is used in outer diameter reduction or in thickness reduction of a hollow shell; and performing elongating on the hollow shell, into which a mandrel bar is inserted, based on the determination. In addition, in the elongating, when the preceding-stage stand group is used in the outer diameter reduction, the hollow shell is rolled in a state where an inner surface of the hollow shell does not come into contact with the mandrel bar in the preceding-stage stand group, and the hollow shell is rolled in a state where the inner surface of the hollow shell comes into contact with the mandrel bar in the succeeding-stage stand group.

Abstract: A rolling stand 100 in accordance with the invention is a rolling stand provided with three grooved rolls for rolling a tubular or bar shaped material to be rolled, in which three grooved rolls R21 to R23 are arranged in such a manner that an angle formed by pressing directions of any two adjacent grooved rolls of the three grooved rolls R21 to R23 comes to 120 degrees. With regard to a cross sectional shape of each of the grooved rolls R21 to R23 formed by cutting each of the grooved rolls in a plane which includes a center line of a rotating axis of each of the grooved rolls R21 to R23 and is orthogonal to a pass line of a material to be rolled, any one grooved roll R21 is provided with a first straight portion L1 extending vertically to the pressing direction in both side flange portions, and the other two grooved rolls R22 and R23 are provided with a second straight portion L2 opposing to the first straight portion L1 and extending in parallel to the first straight portion L1 in the flange portions.

Abstract: A manufacturing method of a seamless metal pipe includes: preparing a plurality of mandrel bars in which lengths of work portions which come into contact with a hollow shell during elongating are different from one another; selecting a mandrel bar including a work portion having a length corresponding to the number of stands used in thickness reduction, among the plurality of mandrel bars; inserting the mandrel bar selected in the selecting into the hollow shell; and performing the elongating on the hollow shell into which the mandrel bar is inserted. Moreover, in the elongating, outer diameter reduction is performed by one of a preceding-stage stand group and a succeeding-stage stand group and the thickness reduction is performed by the other of the preceding-stage stand group and the succeeding-stage stand group, or the thickness reduction is performed by both of the preceding-stage stand group and the succeeding-stage stand group.

Abstract: [Problem to be Solved] A device for adjusting the rolling positions of rolling rolls and restraining poor roll-biting of the front edge part of a pipe material rolled by a three-roll mandrel mill includes pressing-down devices 1 (P1 to P6) for moving rolling rolls R1 to R6 in the rolling direction and a control unit 2 for controlling the pressing-down devices 1. Immediately after the front edge part of a pipe material T has begun to be rolled by the rolling rolls disposed on at least one rolling stand of the rolling rolls R1 to R6, the control unit 2 controls the pressing-down device 1 to move the rolling rolls in the closing direction. Preferably, the rolling rolls disposed on at least one rolling stand of the rolling rolls R1 to R6 in the closing direction are moved at a speed of 16 mm/sec or higher using the pressing-down device 1.

Abstract: A multi-roll mandrel mill comprises a plurality of grooved roll bodies as a roll pass for elongation rolling of a shell and a plurality of roll stands, each having roll shafts and roll chock portions for driving the grooved roll bodies for driving the grooved roll bodies, wherein bearings are internally contained in each grooved roll body. Optimizing the design of roll chock portions for every setup is achieved by a tube-making setup of the mandrel mill, wherein at least one of either or both of the roll shafts and the roll chock portions is replaced with a part(s) having a different shape(s) in addition to changing of the grooved roll bodies. The optimization of the design is effective in preventing underfill and overfill.

Abstract: The present invention provides a mandrel mill and the like that is capable of not only enhancing the elongation ratio of the pipe or tube, but also suppressing a pinhole defect from occurring. The first means of the present invention provides a mandrel mill comprising a plurality of rolling stands in which two grooved rolls R11, R12 are disposed, respectively, the mandrel mill being characterized in that the roll diameter ratio for the first rolling stand and the second rolling stand is set at a value of 4.6 or over. The second means of the present invention provides a mandrel mill comprising a plurality of rolling stands in which three grooved rolls R21, R22 and R23 are disposed, respectively, the mandrel mill being characterized in that the roll diameter ratio for the first rolling stand and the second rolling stand is set at a value of 2.8 or over.

Abstract: A mandrel mill a method for manufacturing a seamless pipe by using the mandrel mill includes a plurality of roll stands in which three grooved rolls R are disposed in each roll stand such that an angle formed by pressing directions is 120° and the pressing directions of the grooved rolls R are alternately shifted by 60° between adjacent roll stands, wherein a central angle ? defining a circular arc that constitutes a groove bottom profile of the grooved roll R disposed at least in the first and second roll stands is set at less than 60°. The mandrel mill can adequately suppress the problem of the mandrel bar not being able to be pulled out from a pipe after drawing and rolling, without resulting in an increase in facility cost and deterioration of maintainability.

Abstract: A retract mandrel mill, comprising a mandrel mill and an extractor, the mandrel mill including a mandrel bar and being configured to roll a tube blank into which the mandrel bar is inserted, the extractor being configured to extract the mandrel bar from the tube blank that has been rolled in the mandrel mill, wherein the distance between the mandrel mill and the extractor is adjustable, and a method for rolling a tube blank by using the retract mandrel mill. As the result of the adjustable distance, even when a tube blank which is shorter than usual is rolled, there is no need to add an extra extension to the length of the tube blank to be elongation-rolled, and the wear of the mandrel bar can be suppressed so that the tube blank can be rolled efficiently and with high yields.

Abstract: [Problem to be Solved] A device for adjusting the rolling positions of rolling rolls and restraining poor roll-biting of the front edge part of a pipe material rolled by a three-roll mandrel mill includes pressing-down devices 1 (P1 to P6) for moving rolling rolls R1 to R6 in the rolling direction and a control unit 2 for controlling the pressing-down devices 1. Immediately after the front edge part of a pipe material T has begun to be rolled by the rolling rolls disposed on at least one rolling stand of the rolling rolls R1 to R6, the control unit 2 controls the pressing-down device 1 to move the rolling rolls in the closing direction. Preferably, the rolling rolls disposed on at least one rolling stand of the rolling rolls R1 to R6 in the closing direction are moved at a speed of 16 mm/sec or higher using the pressing-down device 1.

Abstract: A pipe in which polygonization is substantially eliminated is manufactured by a reducer with a grooved roll with a groove having a groove bottom zone including the center of the groove in the roll axial direction and flange zones adjoining both sides of the groove bottom zone. The groove surface has a friction distribution in the roll axial direction such that the frictional force with respect to a material being rolled in the groove bottom zone is larger than the frictional force with respect to a material being rolled in the flange zones. This friction distribution can be achieved by working the groove surface so that the surface roughness of the groove bottom zone becomes greater than the surface roughness of the flange zones or by applying a lubricity modifier which differs with respect to amount and/or type between the groove bottom zone and the flange zones.

Abstract: A retract mandrel mill, comprising a mandrel mill and an extractor, the mandrel mill including a mandrel bar and being configured to roll a tube blank into which the mandrel bar is inserted, the extractor being configured to extract the mandrel bar from the tube blank that has been rolled in the mandrel mill, wherein the distance between the mandrel mill and the extractor is adjustable, and a method for rolling a tube blank by using the retract mandrel mill. As the result of the adjustable distance, even when a tube blank which is shorter than usual is rolled, there is no need to add an extra extension to the length of the tube blank to be elongation-rolled, and the wear of the mandrel bar can be suppressed so that the tube blank can be rolled efficiently and with high yields.

Abstract: A multi-roll mandrel mill for compacting of roll chock portions has a plurality of grooved roll bodies as a roll pass which performs a reduction rolling of a shell, and a plurality of roll stands each having backup rolls for driving the grooved roll bodies, wherein bearings are internally contained in the grooved roll body. A multi-roll mandrel mill for optimizing the design of roll chock portions for every setup has a plurality of grooved roll bodies as a roll pass which performs the reduction rolling of a shell and a plurality of roll stands each having roll shafts and roll chock portions for driving the grooved roll bodies. According to a tube-making setup of the mandrel mill, at least one of either or both of the roll shafts and the roll chock portions is replaced with a part(s) having a different shape(s) in addition to the grooved roll bodies.

Abstract: A device for adjusting the rolling positions of rolling rolls and restraining poor roll-biting of the front edge part of a pipe material rolled by a three-roll mandrel mill includes pressing-down devices 1 (P1 to P6) for moving rolling rolls R1 to R6 in the rolling direction and a control unit 2 for controlling the pressing-down devices 1. Immediately after the front edge part of a pipe material T has begun to be rolled by the rolling rolls disposed on at least one rolling stand of the rolling rolls R1 to R6, the control unit 2 controls the pressing-down device 1 to move the rolling rolls in the closing direction. Preferably, the rolling rolls disposed on at least one rolling stand of the rolling rolls R1 to R6 in the closing direction are moved at a speed of 16 mm/sec or higher using the pressing-down device 1.

Abstract: A mandrel mill is provided which can perform elongation rolling with a markedly increased working ratio and dimensional accuracy on a material which is inherently difficult to roll such as a hollow shell made of stainless steel or a thin-walled material. A mandrel mill for manufacturing a mother tube by performing elongation rolling of a hollow shell comprises a plurality of roll stands, having at least one 4-roll stand for wall thickness reduction of a hollow shell and at least one 2-roll stand including the final stand downstream of the 4-roll stand.

Abstract: The present invention provides a mandrel mill and the like that is capable of not only enhancing the elongation ratio of the pipe or tube, but also suppressing a pinhole defect from occurring. The first means of the present invention provides a mandrel mill comprising a plurality of rolling stands in which two grooved rolls R11, R12 are disposed, respectively, the mandrel mill being characterized in that the roll diameter ratio for the first rolling stand and the second rolling stand is set at a value of 4.6 or over. The second means of the present invention provides a mandrel mill comprising a plurality of rolling stands in which three grooved rolls R21, R22 and R23 are disposed, respectively, the mandrel mill being characterized in that the roll diameter ratio for the first rolling stand and the second rolling stand is set at a value of 2.8 or over.

Abstract: A rolling stand 100 in accordance with the invention is a rolling stand provided with three grooved rolls for rolling a tubular or bar shaped material to be rolled, in which three grooved rolls R21 to R23 are arranged in such a manner that an angle formed by pressing directions of any two adjacent grooved rolls of the three grooved rolls R21 to R23 comes to 120 degrees. With regard to a cross sectional shape of each of the grooved rolls R21 to R23 formed by cutting each of the grooved rolls in a plane which includes a center line of a rotating axis of each of the grooved rolls R21 to R23 and is orthogonal to a pass line of a material to be rolled, any one grooved roll R21 is provided with a first straight portion L1 extending vertically to the pressing direction in both side flange portions, and the other two grooved rolls R22 and R23 are provided with a second straight portion L2 opposing to the first straight portion L1 and extending in parallel to the first straight portion L1 in the flange portions.