Abstract: A method for manufacturing an electric resistance welded steel pipe having an identifiable seam portion. The method includes electric resistance welding a steel pipe, cutting an inner surface bead and an outer surface bead of the steel pipe in such a manner so as to cut: (i) a whole the outer surface bead and a part of the inner surface bead to leave an uncut portion in the inner surface bead, or (ii) a whole of the inner surface bead and a part of the outer surface bead to leave an uncut portion in the outer surface bead, coating the steel pipe with zinc phosphate, and cold drawing the steel pipe using a plug and a die to make the seam portion of the steel pipe identifiable.

Abstract: An electric resistance welded steel pipe manufactured by performing electric resistance welding on the steel pipe. The steel pipe having a chemical composition including by mass %, C: 0.20% to 0.40%, Si: 0.1% to 1.0%, Mn: 0.1% to 2.0%, Al: 0.01% to 0.10%, Cr: 0.01% to 0.5%, Ti: 0.01% to 0.05%, B: 0.0005% to 0.005%, Ca: 0.0001% to 0.0050%, N: 0.0050% or less, and Fe and inevitable impurities. Additionally, the steel pipe having a microstructure in which each of amounts of TiS particles, having a particle size of 10 ?m or more, and MnS particles, having a particle size of 10 ?m or more, are decreased to 0.1% or less in terms of cleanliness. The steel pipe having excellent fatigue resistance, exhibiting a high strength, and having an average grain size of prior austenite grains of 50 ?m or less when subjected to cold forming followed by quenching and tempering treatments.

Abstract: A method for manufacturing an electric resistance welded steel pipe having an identifiable seam portion. The method includes electric resistance welding a steel pipe, cutting an inner surface bead and an outer surface bead of the steel pipe in such a manner so as to cut: (i) a whole the outer surface bead and a part of the inner surface bead to leave an uncut portion in the inner surface bead, or (ii) a whole of the inner surface bead and a part of the outer surface bead to leave an uncut portion in the outer surface bead, coating the steel pipe with zinc phosphate, and cold drawing the steel pipe using a plug and a die to make the seam portion of the steel pipe identifiable.

Abstract: An electric resistance welded steel pipe having an identifiable seam portion and a method for manufacturing the same. The electric resistance welded steel pipe includes a steel pipe portion with a seam portion, which is formed by electric resistance welding, and a coating portion of zinc phosphate. The coating portion covers at least an outer surface side of the steel pipe portion. A part of the coating portion that is immediately above the seam portion forms a color difference portion that has a width W along a pipe circumferential direction of greater than or equal to 0.1 times a wall thickness of the pipe and less than or equal to the wall thickness of the pipe. The color difference portion has a visually identifiable color difference from the other parts of the coating portion.

Abstract: Disclosed is a high-strength welded steel pipe for airbag inflators that has high toughness and workability. A base material portion of the steel pipe has a composition containing, in mass %, C: 0.02 to 0.08%, Si: 0.001 to 1.0%, Mn: 0.1 to 2.0%, P: 0.1% or less, Al: 0.01 to 0.1%, N: 0.01% or less, Ti: 0.01 to 0.20%, and V: 0.01 to 0.50%, with the balance being Fe and incidental impurities. The base material portion has a structure that includes a ferrite phase having an average grain size of 10 ?m or less at an area fraction of 90% or more and a Ti, V-based carbide having an average grain size of 10 nm or less and dispersed in the ferrite phase. The welded steel pipe has a high tensile strength TS of 780 MPa or more and a strength-elongation balance TS×El of 15,000 MPa % or more. The difference ?HV in Vickers hardness between the base material portion and the welded portion is 60 points or less.

Abstract: An electric resistance welded steel pipe manufactured by performing electric resistance welding on the steel pipe. The steel pipe having a chemical composition including by mass %, C: 0.20% to 0.40%, Si: 0.1% to 1.0%, Mn: 0.1% to 2.0%, Al: 0.01% to 0.10%, Cr: 0.01% to 0.5%, Ti: 0.01% to 0.05%, B: 0.0005% to 0.005%, Ca: 0.0001% to 0.0050%, N: 0.0050% or less, and Fe and inevitable impurities. Additionally, the steel pipe having a microstructure in which each of amounts of TiS particles, having a particle size of 10 ?m or more, and MnS particles, having a particle size of 10 ?m or more, are decreased to 0.1% or less in terms of cleanliness. The steel pipe having excellent fatigue resistance, exhibiting a high strength, and having an average grain size of prior austenite grains of 50 ?m or less when subjected to cold forming followed by quenching and tempering treatments.

Abstract: An electric resistance welded steel pipe having an identifiable seam portion and a method for manufacturing the same. The electric resistance welded steel pipe includes a steel pipe portion with a seam portion, which is formed by electric resistance welding, and a coating portion of zinc phosphate. The coating portion covers at least an outer surface side of the steel pipe portion. A part of the coating portion that is immediately above the seam portion forms a color difference portion that has a width W along a pipe circumferential direction of greater than or equal to 0.1 times a wall thickness of the pipe and less than or equal to the wall thickness of the pipe. The color difference portion has a visually identifiable color difference from the other parts of the coating portion.

Abstract: Disclosed is a high-strength welded steel pipe for airbag inflators that has high toughness and workability. A base material portion of the steel pipe has a composition containing, in mass %, C: 0.02 to 0.08%, Si: 0.001 to 1.0%, Mn: 0.1 to 2.0%, P: 0.1% or less, Al: 0.01 to 0.1%, N: 0.01% or less, Ti: 0.01 to 0.20%, and V: 0.01 to 0.50%, with the balance being Fe and incidental impurities. The base material portion has a structure that includes a ferrite phase having an average grain size of 10 ?m or less at an area fraction of 90% or more and a Ti, V-based carbide having an average grain size of 10 nm or less and dispersed in the ferrite phase. The welded steel pipe has a high tensile strength TS of 780 MPa or more and a strength-elongation balance TS×El of 15,000 MPa % or more. The difference ?HV in Vickers hardness between the base material portion and the welded portion is 60 points or less.

Abstract: A raw steel tube has a composition containing, by mass, 0.25% to 0.60% carbon, 0.01% to 2.0% silicon, 0.2% to 3.0% manganese, 0.001% to 0.1% aluminum, 0.001% to 0.05% phosphorus, 0.02% or less sulfur, 0.0010% to 0.0100% nitrogen, 0.0003% to 0.0050% boron, and 0.0001% to 0.0050% calcium, the balance being iron and incidental impurities. The raw steel tube is heated to and soaked at an Ac3 transformation point or higher and is then subjected to stretch-reducing rolling at a finishing temperature of rolling of 900° C. to (Ac1 transformation point) with a cumulative reduction in diameter of 30% to 70% within the temperature range of 900° C. or lower.

Abstract: A method of manufacturing an electric resistance welding pipe is provided in which a lateral edge shape is made to be an appropriate shape immediately before electric resistance welding is performed, whereby penetrators are securely removed during the electric resistance welding and, consequently, an electric resistance welding pipe having excellent characterization of welded seam can be obtained. A fin shape in finpass forming is printed to lateral edges of a strip, whereby the lateral edges of the strip are shaped with predetermined tapering.

Abstract: A base material portion of an electric resistance welded steel pipe has a composition including C at 0.25 to 0.55%, Si at 0.01 to 1.0%, Mn at 0.2 to 3.0%, Al at not more than 0.1% and N at 0.0010 to 0.0100%, with the balance being represented by Fe and inevitable impurities, and the weld defect area, which is a projected area of a weld defect in an electric resistance weld zone, is less than 40000 ?m2.

Abstract: A method of manufacturing an electric resistance welding pipe is provided in which a lateral edge shape is made to be an appropriate shape immediately before electric resistance welding is performed, whereby penetrators are securely removed during the electric resistance welding and, consequently, an electric resistance welding pipe having excellent characterization of welded seam can be obtained. A fin shape in finpass forming is printed to lateral edges of a strip, whereby the lateral edges of the strip are shaped with predetermined tapering.

Abstract: A laser welded steel pipe having a weld zone containing a steel pipe containing 0.01 to 0.2 weight % C, 1 weight % or less S, 0.05 to 2 weight % Mn and 6 weight % or less Mn. The weld zone has a melted and solidified metal structure containing carbon and oxygen which satisfy the following equations:(carbon weight %)(oxygen weight %).ltoreq.0.006for a steel pipe containing carbon in an amount of less than 0.2 weight %, and(oxygen weight %).gtoreq.0.02.A method for manufacturing a laser-welded steel pipe including producing an open pipe made from a hot-rolled steel strip with opposing edge portions facing each other by employing a formal roll, preheating the two edge portions, pressing the two edge portions to butt against each other by using squeeze rolls and welding the butted edge portions by irradiation with a laser beam to heat and melt the two edge portions.

Abstract: A laser-welded steel pipe includes: a steel pipe consisting essentially of C in an amount of 0.01 to 0.5 wt. %, Si in an amount of 1 wt. % or less, Mn in an amount of 0.05 to 2 wt. % and Cr in an amount of 6 wt. % or less; and a weld zone having a melted and solidified metal structure containing carbon and oxygen. The carbon content, ?C wt. %!, and the oxygen content, ?O wt. %!, in the melted and solidified metal structure satisfies the following equations:?C wt. %!.times.?O wt. %!.ltoreq.0.006, for the steel pipe containing C in an amount of less than 0.2 wt. %,?O wt. %!.ltoreq.0.03, for the steel pipe containing C in an amount of 0.2 wt. % or more.