The production method of a seamless steel pipe includes a heating step of heating an Nb-containing steel material to 800 to 1030° C., a pipe-making step of producing a hollow shell by performing piercing-rolling or elongation-rolling on the Nb-containing steel material, by using a piercing mill including a plurality of skewed rolls, a plug disposed between the plurality of skewed rolls, and a mandrel bar, and a cooling step immediately after rolling, of carrying out cooling using a cooling liquid on a hollow shell portion that passes between rear ends of the plurality of skewed rolls, in the hollow shell, so as to reduce an outer surface temperature of the hollow shell portion to 700 to 1000° C. within 15.0 seconds after the hollow shell portion passes between the rear ends of the plurality of skewed rolls.

The production method of a seamless steel pipe includes a heating step of heating an Nb-containing steel material to 800 to 1030° C., a pipe-making step of producing a hollow shell by performing piercing-rolling or elongation-rolling on the Nb-containing steel material, by using a piercing mill including a plurality of skewed rolls, a plug disposed between the plurality of skewed rolls, and a mandrel bar, and a cooling step immediately after rolling, of carrying out cooling using a cooling liquid on a hollow shell portion that passes between rear ends of the plurality of skewed rolls, in the hollow shell, so as to reduce an outer surface temperature of the hollow shell portion to 700 to 1000° C. within 15.0 seconds after the hollow shell portion passes between the rear ends of the plurality of skewed rolls.

Provided is an equipment system for producing a piercing-rolling plug to be used for producing a seamless steel tube/pipe, which includes a shotblasting device for applying shotblasting on a surface of the plug, and an arc-spraying device for performing arc-spraying of iron wires on a surface of a base metal of the plug to which the shotblasting is applied, so as to form a film containing oxide and Fe thereon. The arc-spraying device includes plural spraying booths each of which separately forms part of the film in turn in each of sections into which the surface of the base metal of the plug is divided along an axial direction of the plug. The production efficiency of the plug can therefore be maintained at a high level, and steady enhancement of the durability life of the plug can be realized during the piercing-rolling.

Provided is an equipment system for producing a piercing-rolling plug to be used for producing a seamless steel tube/pipe, which includes a shotblasting device for applying shotblasting on a surface of the plug, and an arc-spraying device for performing arc-spraying of iron wires on a surface of a base metal of the plug to which the shotblasting is applied, so as to form a film containing oxide and Fe thereon. The arc-spraying device includes plural spraying booths each of which separately forms part of the film in turn in each of sections into which the surface of the base metal of the plug is divided along an axial direction of the plug. The production efficiency of the plug can therefore be maintained at a high level, and steady enhancement of the durability life of the plug can be realized during the piercing-rolling.

A skew rolling apparatus with which shape defects in non-steady-state portions at the front and back ends of a seamless pipe shell can be prevented. The skew rolling apparatus includes a skew pierce rolling mill configured to pierce roll a steel material into a seamless pipe shell, and a skew outside-diameter mill following the skew piercing mill in a pass direction of the seamless pipe shell in the skew rolling apparatus. The skew rolling apparatus satisfies specified formulae.

A skew rolling apparatus with which shape defects in non-steady-state portions at the front and back ends of a seamless pipe shell can be prevented. The skew rolling apparatus includes a skew pierce rolling mill configured to pierce roll a steel material into a seamless pipe shell, and a skew outside-diameter mill following the skew piercing mill in a pass direction of the seamless pipe shell in the skew rolling apparatus. The skew rolling apparatus satisfies specified formulae.

The invention relates to a method for producing a tube (2) or tubular pre-product from a solid billet in a rolling mill, comprising at least one roll (5a, 5b) acting from the outside on the solid billet or tubular pre-product and a mandrel (4) carrying a piercing head (3) and engaging from the inside in the tube or tubular pre-product, wherein immediately after the solid billet has been completely pierced by the piercing head a fluidized deoxidation agent and/or an inert gas is supplied to the end of the tube or tubular pre-product facing the roll and is guided through the tube or tubular pre-product into the interior of the tube or tubular pre-product when the mandrel is withdrawn. The invention further relates to a rolling mill for performing the method according to the invention, comprising at least one roll acting from the outside onto the solid billet or tubular pre-product and a mandrel carrying a piercing head and engaging from the inside in the tube or tubular pre-product, wherein a device is provided for feeding and introducing a fluidized deoxidation agent and/or an inert gas to the end of the tube or tubular pre-product facing the at least one roll.

The invention relates to a method for producing a tube (2) or tubular pre-product from a solid billet in a rolling mill, comprising at least one roll (5a, 5b) acting from the outside on the solid billet or tubular pre-product and a mandrel (4) carrying a piercing head (3) and engaging from the inside in the tube or tubular pre-product, wherein immediately after the solid billet has been completely pierced by the piercing head a fluidized deoxidation agent and/or an inert gas is supplied to the end of the tube or tubular pre-product facing the roll and is guided through the tube or tubular pre-product into the interior of the tube or tubular pre-product when the mandrel is withdrawn. The invention further relates to a rolling mill for performing the method according to the invention, comprising at least one roll acting from the outside onto the solid billet or tubular pre-product and a mandrel carrying a piercing head and engaging from the inside in the tube or tubular pre-product, wherein a device is provided for feeding and introducing a fluidized deoxidation agent and/or an inert gas to the end of the tube or tubular pre-product facing the at least one roll.

Disclosed is a hot forming tool (1) which consists of a main tool member (2) having an at least partial surface coating (4) and which can be obtained by providing the main tool member with a raised metal relief that is then entirely or partly oxidized and converted into a protective layer.

Disclosed is a hot forming tool (1) which consists of a main tool member (2) having an at least partial surface coating (4) and which can be obtained by providing the main tool member with a raised metal relief that is then entirely or partly oxidized and converted into a protective layer.