Abstract: There is provided a production method of an internally ribbed steel tube, capable of forming spiral ribs stably so as to reduce troubles at the time of cold drawing for forming the spiral ribs of the steel tube. In this production method, the spiral ribs can be formed stably so as to reduce troubles at the time of cold drawing for forming the spiral ribs by straightening bends of a blank tube before the cold drawing for forming the spiral ribs, by optimizing the direction of the spiral rib formation after the bend straightening, and by correcting the drawing schedule depending on the blank tube. The obtained internally ribbed steel tube is well applicable to an increased capacity and a higher temperature/higher pressure operation of a boiler because the steel tube is provided with high formability and excellent quality as a boiler steel tube.

Abstract: There is provided a production method capable of forming spiral ribs stably by reducing troubles at the time of cold drawing for forming the spiral ribs on an internally ribbed steel tube. When the internally ribbed steel tube on which a plurality of stripes of spiral ribs are formed in the tube axis direction is manufactured by inserting a plug on which a plurality of stripes of spiral grooves are formed on the outer peripheral surface thereof into the tube to be worked subjected to chemical treatment and then performing cold drawing, drawing is performed with the plug preheated to 50 to 200° C., thus forming the spiral ribs on the internal surface of a blank tube. The chemical treatment preferably includes a pickling step of removing oxided scale and rust on the tube surface, a step of forming a zinc phosphate coat on the neutralized tube surface, and a step of forming a lubricating layer on the zinc phosphate coat.

Abstract: A process for manufacturing a seamless tube which can effectively suppress thickness deviations which are apt to occur in thin-walled seamless tubes is provided. A billet which has been soaked in a heating furnace at a given temperature for a given length of time is subjected to piercing and elongation rolling to form a mother tube, which is then soaked in a reheating furnace at a given temperature for a given length of time and then subjected to sizing to produce a seamless tube with a wall thickness of at most 4 mm. The wall thickness of the tube after sizing is at most 4 mm, the soaking time at the given temperature in the heating furnace is in the range of [billet diameter (mm)×(from 0.14-0.35 )] minutes, and the soaking time at the given temperature in the reheating furnace is in the range of [mother tube wall thickness (mm)×(from 3.0-10.0)] minutes.

Abstract: There is provided a production method capable of forming spiral ribs stably by reducing troubles at the time of cold drawing for forming the spiral ribs on an internally ribbed steel tube. When the internally ribbed steel tube on which a plurality of stripes of spiral ribs are formed in the tube axis direction is manufactured by inserting a plug on which a plurality of stripes of spiral grooves are formed on the outer peripheral surface thereof into the tube to be worked subjected to chemical treatment and then performing cold drawing, drawing is performed with the plug preheated to 50 to 200° C., thus forming the spiral ribs on the internal surface of a blank tube. The chemical treatment preferably includes a pickling step of removing oxided scale and rust on the tube surface, a step of forming a zinc phosphate coat on the neutralized tube surface, and a step of forming a lubricating layer on the zinc phosphate coat.

Abstract: In order to manufacture a steel pipe for an air bag which can cope with increase in the pressure of gas blown into an air bag and decreases in the wall thickness of an accumulator, a steel having a composition, mass %, of: C: 0.05-0.20%, Si: 0.1-1.0%, Mn: 0.20-2.0%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-1.0%, Al: at most 0.10%, if necessary at least one of Mo: at most 0.50%, Ni: at most 1.5%, Cu: at most 0.5%, V: at most 0.2%, Ti: at most 0.1%, Nb: at most 0.1%, and B: at most 0.005%, and also if necessary, at least one of Ca: at most 0.01%, Mg: at most 0.01%, and REM (rare earth elements): at most 0.01%, and a remainder of Fe and impurities is used to produce a steel pipe, and the pipe is then subjected to cold working to predetermined dimensions, then to heating to a temperature of at least the Ac1 transformation temperature followed by quenching, and then to tempering at a temperature no higher than the Ac1 transformation temperature.

Abstract: There is provided a production method of an internally ribbed steel tube, capable of forming spiral ribs stably so as to reduce troubles at the time of cold drawing for forming the spiral ribs of the steel tube. In this production method, the spiral ribs can be formed stably so as to reduce troubles at the time of cold drawing for forming the spiral ribs by straightening bends of a blank tube before the cold drawing for forming the spiral ribs, by optimizing the direction of the spiral rib formation after the bend straightening, and by correcting the drawing schedule depending on the blank tube. The obtained internally ribbed steel tube is well applicable to an increased capacity and a higher temperature/higher pressure operation of a boiler because the steel tube is provided with high formability and excellent quality as a boiler steel tube.

Abstract: A case hardening steel tube which has a hardness of 72-80 HRB and which gives a carburized layer with a high strength and high wear resistance and adequate resistance to impact fracture when it is formed into a final product by working and subsequent carburizing and quenching under relatively mild conditions is manufactured by forming a tube from a steel having a steel composition comprising, in mass percent, C: 0.1-0.25%, Si: 0.2-0.4%, Mn: 0.3-0.9%, P: at most 0.02%, S: 0.001-0.15%, Cr: 0.5-0.9%, Mo: 0.15-1%, Al: 0.01-0.1%, B: 0.0005-0.009%, N: less than 0.006%, and a remainder essentially of Fe, then subjecting the resulting steel tube to normalizing by soaking at a temperature of 880-980° C. followed by cooling at a cooling rate of at most 70° C. per minute, carrying out cold working of the normalized steel tube, and then annealing the cold worked steel tube at a temperature of 700-820° C.

Abstract: Cold finished seamless steel tubes are made such that the residual stress F to be generated at the stage of the correction process after cold working is controlled to be 30 MPa or more and the scattering thereof is 30 MPa or less, when measured by Crampton method. Further, by adjusting the average grain size of spheroidized carbides, the dimensional change which emerges in lathe turning of the outside and inside diameter of relevant steel tubes due to the residual strain can be suppressed, and the strict roundness as well as the excellent machinability can be secured at the final processing stage of the work pieces for bearing parts. Consequently, steel tubes with high dimensional accuracy and less dimensional change at the final steps such as lathe turning, heat treatment and the like, can be made for use as bearing parts.

Abstract: A process for manufacturing a seamless tube which can effectively suppress thickness deviations which are apt to occur in thin-walled seamless tubes is provided. A billet which has been soaked in a beating furnace at a given temperature for a given length of time is subjected to piercing and elongation rolling to form a mother tube, which is then soaked in a reheating furnace at a given temperature for a given length of time and then subjected to sizing to produce a seamless tube with a wall thickness of at most 4 mm. The wall thickness of the tube after sizing is at most 4 mm, the soaking time at the given temperature in the heating furnace is in the range of [billet diameter (mm)×(from 0.14-0.35)] minutes, and the soaking time at the given temperature in the reheating furnace is in the range of [mother tube wall thickness (mm)×(from 3.0-10.0)] minutes.

Abstract: Cold finished seamless steel tubes are made such that the residual stress F to be generated at the stage of the correction process after cold working is controlled to be 30 MPa or more and the scattering thereof is 30 MPa or less, when measured by Crampton method. Further, by adjusting the average grain size of spheroidized carbides, the dimensional change which emerges in lathe turning of the outside and inside diameter of relevant steel tubes due to the residual strain can be suppressed, and the strict roundness as well as the excellent machinability can be secured at the final processing stage of the work pieces for bearing parts. Consequently, steel tubes with high dimensional accuracy and less dimensional change at the final steps such as lathe turning, heat treatment and the like, can be made for use as bearing parts.

Abstract: In order to manufacture a steel pipe for an air bag which can cope with increase in the pressure of gas blown into an air bag and decreases in the wall thickness of an accumulator, a steel having a composition, mass %, of: C: 0.05-0.20%, Si: 0.1-1.0%, Mn: 0.20-2.0%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-1.0%, Al: at most 0.10%, if necessary at least one of Mo: at most 0.50%, Ni: at most 1.5%, Cu: at most 0.5%, V: at most 0.2%, Ti: at most 0.1%, Nb: at most 0.1%, and B: at most 0.005%, and also if necessary, at least one of Ca: at most 0.01%, Mg: at most 0.01%, and REM (rare earth elements): at most 0.01%, and a remainder of Fe and impurities is used to produce a steel pipe, and the pipe is then subjected to cold working to predetermined dimensions, then to heating to a temperature of at least the Ac1 transformation temperature followed by quenching, and then to tempering at a temperature no higher than the Ac1 transformation temperature.

Abstract: In order to manufacture a steel pipe for an air bag which can cope with increase in the pressure of gas blown into an air bag and decreases in the wall thickness of an accumulator, a steel having a composition, mass %, of: C: 0.05-0.20%, Si: 0.1-1.0%, Mn: 0.20-2.0%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-1.0%, Al: at most 0.10%, if necessary at least one of Mo: at most 0.50%, Ni: at most 1.5%, Cu: at most 0.5%, V: at most 0.2%, Ti: at most 0.1%, Nb: at most 0.1%, and B: at most 0.005%, and also if necessary, at least one of Ca: at most 0.01%, Mg: at most 0.01%, and REM (rare earth elements): at most 0.01%, and a remainder of Fe and impurities is used to produce a steel pipe, and the pipe is then subjected to cold working to predetermined dimensions, then to heating to a temperature of at least the Ac1 transformation temperature followed by quenching, and then to tempering at a temperature no higher than the Ac1 transformation temperature.

Abstract: In order to manufacture a steel pipe for an air bag which can cope with increase in the pressure of gas blown into an air bag and decreases in the wall thickness of an accumulator, a steel having a composition, mass %, of: 1 C: 0.05-0.20%, Si: 0.1-1.0%, Mn: 0.20-2.0%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-1.0%, Al: at most 0.