A solid billet is piercing-rolled using a 4 roll-type inclined rolling mill including larger-diameter cone-type main rolls arranged horizontally or vertically to face each other across a pass line and smaller-diameter auxiliary rolls arranged vertically or horizontally to face each other similarly across the pass line between the facing main rolls, while maintaining a feed angle ? and cross angle ? of the main rolls and a feed angle ? and cross angle ? of the auxiliary rolls to be within the ranges: 5???, ??25?; 3???, ??35?; and 10???+?, ?+??55?.

A solid billet is piercing-rolled using a 4 roll-type inclined rolling mill including larger-diameter cone-type main rolls arranged horizontally or vertically to face each other across a pass line and smaller-diameter auxiliary rolls arranged vertically or horizontally to face each other similarly across the pass line between the facing main rolls, while maintaining a feed angle ? and cross angle ? of the main rolls and a feed angle ? and cross angle ? of the auxiliary rolls to be within the ranges: 5???, ??25?; 3???, ??35?; and 10???+?, ?+??55?.

Disclosed in the present application is a high-strength seamless steel tube resistant to carbon dioxide corrosion. In addition to containing Fe and inevitable impurities, the seamless steel tube comprises the following chemical elements in mass percentage: C: 0.05-0.18%, Si: 0.15-0.40%, Mn: 0.25-0.50%, Cr: 4.0-6.0%, Mo: 0.08-0.35%, Al: 0.020-0.055%, Ca: 0.001-0.004%; and one or more elements selected from Ti, Nb, V, Ce, and La, wherein 0.003%?Ti+Nb+V+Ce+La?0.20%. Also disclosed in the present application is a manufacturing method for the seamless steel tube. The method comprises the following steps: (1) manufacturing a tube billet; (2) subjecting the tube billet to heating, perforating, hot rolling, and sizing to obtain a hot-rolled tube; and (3) subjecting the hot-rolled tube to a quenching and tempering heat treatment: quenching within a temperature range of 860-940? C. for 15-120 min, and then tempering within a temperature range of 520-620? C. for 30-150 min.

A powder lubricant composition according to the present invention includes 65 parts by mass to 95 parts by mass of sodium borate, and 5 parts by mass to 35 parts by mass of cryolite. A method for manufacturing a seamless steel pipe according to the present invention includes adhering the above-described powder lubricant composition to a pipe inner surface of a work piece which is piercing rolled to have a tubular shape, and elongation rolling on the work piece after the adhering of the powder lubricant composition.

A powder lubricant composition according to the present invention includes 65 parts by mass to 95 parts by mass of sodium borate, and 5 parts by mass to 35 parts by mass of cryolite. A method for manufacturing a seamless steel pipe according to the present invention includes adhering the above-described powder lubricant composition to a pipe inner surface of a work piece which is piercing rolled to have a tubular shape, and elongation rolling on the work piece after the adhering of the powder lubricant composition.

An integrated transverse rolling mill for rolling seamless tubes with skewed axes comprising a piercing stand (2) with skewed axis rolling rolls for piercing a first tube (7) having a first length which is shorter than the space which separates it from the subsequent finishing stand (3) in cooperation with the stake (6), which has the first piercing tip (20) at its end and the second finishing tip (21) at the finishing stand (3). The finishing stand (3) is arranged downstream of the piercing stand (2) so that during the rolling operations the front end of the first tube (7) may only be gripped by the finishing stand (3) once the rear end of the first tube (7) is no longer gripped by the rolling stand (2).

An integrated transverse rolling mill for rolling seamless tubes with skewed axes comprising a piercing stand (2) with skewed axis rolling rolls for piercing a first tube (7) having a first length which is shorter than the space which separates it from the subsequent finishing stand (3) in cooperation with the stake (6), which has the first piercing tip (20) at its end and the second finishing tip (21) at the finishing stand (3). The finishing stand (3) is arranged downstream of the piercing stand (2) so that during the rolling operations the front end of the first tube (7) may only be gripped by the finishing stand (3) once the rear end of the first tube (7) is no longer gripped by the rolling stand (2).

A method disclosed herewith is a method for producing a first seamless metal tube with a first wall thickness and a second seamless metal tube with a second wall thickness by using a three-roll-type inclined rolling mill, and the method includes a first inclination rolling step (#5), a setting changing step (#10), and a second inclination rolling step (#15). At the first inclination rolling step, a first workpiece is rolled by the inclined rolling mill. At the setting changing step, a setup condition of the inclined rolling mill is changed in a manner (a) or (b) as described below. At the second inclined rolling step, a second workpiece is rolled by the inclined rolling mill under the changed condition. (a) When the second wall thickness is smaller than the first wall thickness, the cross angle of each of the inclined rolls is made greater than the cross angle set for the first inclination rolling step. (b) When the second wall thickness is larger than the first wall thickness, the cross angle of each of the inclined rolls is made smaller than the cross angle set for the first inclination rolling step.

A method disclosed herewith is a method for producing a first seamless metal tube with a first wall thickness and a second seamless metal tube with a second wall thickness by using a three-roll-type inclined rolling mill, and the method includes a first inclination rolling step (#5), a setting changing step (#10), and a second inclination rolling step (#15). At the first inclination rolling step, a first workpiece is rolled by the inclined rolling mill. At the setting changing step, a setup condition of the inclined rolling mill is changed in a manner (a) or (b) as described below. At the second inclined rolling step, a second workpiece is rolled by the inclined rolling mill under the changed condition. (a) When the second wall thickness is smaller than the first wall thickness, the cross angle of each of the inclined rolls is made greater than the cross angle set for the first inclination rolling step. (b) When the second wall thickness is larger than the first wall thickness, the cross angle of each of the inclined rolls is made smaller than the cross angle set for the first inclination rolling step.

A method of manufacturing a high-strength stainless steel pipe includes forming a steel pipe having a predetermined size, the steel having a composition comprising by mass % 0.005 to 0.05% C, 0.05 to 1.0% Si, 0.2 to 1.8% Mn, 0.03% or less P, 0.005% or less S, 14 to 20% Cr, 1.5 to 10% Ni, 1 to 5% Mo, 0.5% or less V, 0.15% or less N, 0.01% or less O, 0.002 to 0.1% Al, and Fe and unavoidable impurities as a balance; applying a quenching treatment two times or more to the steel pipe where the steel pipe is quenched by reheating to a temperature of 750 C. or above and cooling to a temperature of 100 C. or below at a cooling rate equal to or higher than an air-cooling rate; and applying a tempering treatment where the steel pipe is tempered at a temperature of 700 C. or below.