Abstract: An electric resistance welded steel pipe or tube comprises: a base metal being a steel sheet having a specific chemical composition and an electric resistance weld portion having a bond width of 40×10?6 m or more and 120×10?6 m or less, wherein C0-C1 is 0.05 mass % or less, where C0-C1 is a difference between C1 in mass % which is a minimum C content of the electric resistance weld portion and Co in mass % which is a C content of the steel sheet, and a depth of a total decarburized layer in each of an inner surface layer and an outer surface layer of the electric resistance welded steel pipe or tube is 50×10?6 m or less.

Abstract: Provided is an electric resistance welded steel pipe or tube having excellent fatigue durability after rapid and short-time heating quenching treatment. An electric resistance welded steel pipe or tube comprises: a base metal being a steel sheet having a specific chemical composition and an electric resistance weld portion having a bond width of 40×10?6 m or more and 120×10?6 m or less, wherein C0-C1 is 0.05 mass % or less, where C0-C1 is a difference between C1 in mass % which is a minimum C content of the electric resistance weld portion and C0 in mass % which is a C content of the steel sheet, and a depth of a total decarburized layer in each of an inner surface layer and an outer surface layer of the electric resistance welded steel pipe or tube is 50×10?6 m or less.

Abstract: A method for manufacturing an electric resistance welded steel tube for high-strength thin hollow stabilizers is provided. A steel with a certain chemical composition is heated to a temperature of 1000 to 1300° C., hot rolled under conditions where the rolling finish temperature is 750 to 950° C., cooled, coiled into a coil at 500 to 650° C., and skin pass rolled with a rolling reduction ratio of not less than 0.3%. The resultant hot rolled sheet is electric resistance welded into an electric resistance welded steel tube, which is then reheated to a temperature of 800 to 1100° C. and hot stretch-reducing rolled under conditions where the rolling finish temperature is not more than 850° C. and the cumulative diameter reduction is not more than 75%. Consequently, a thin electric resistance welded steel tube is produced.

Abstract: A method for manufacturing an electric resistance welded steel tube for high-strength thin hollow stabilizers is provided. A steel with a certain chemical composition is heated to a temperature of 1000 to 1300° C., hot rolled under conditions where the rolling finish temperature is 750 to 950° C., cooled, coiled into a coil at 500 to 650° C., and skin pass rolled with a rolling reduction ratio of not less than 0.3%. The resultant hot rolled sheet is electric resistance welded into an electric resistance welded steel tube, which is then reheated to a temperature of 800 to 1100° C. and hot stretch-reducing rolled under conditions where the rolling finish temperature is not more than 850° C. and the cumulative diameter reduction is not more than 75%. Consequently, a thin electric resistance welded steel tube is produced.

Abstract: Provided is an electric resistance welded steel pipe or tube having excellent fatigue durability after rapid and short-time heating quenching treatment. An electric resistance welded steel pipe or tube comprises: a base metal being a steel sheet having a specific chemical composition and an electric resistance weld portion having a bond width of 40×10?6 m or more and 120×10?6 m or less, wherein C0-C1 is 0.05 mass % or less, where C0-C1 is a difference between C1 in mass % which is a minimum C content of the electric resistance weld portion and C0 in mass % which is a C content of the steel sheet, and a depth of a total decarburized layer in each of an inner surface layer and an outer surface layer of the electric resistance welded steel pipe or tube is 50×10?6 m or less.

Abstract: A seamless steel tube has a particular composition and a structure with an average prior ? grain size of 150 ?m or less in an axial cross-section after cold drawing and heat treatment. The structure retards the growth of a fatigue crack. The steel tube has a tensile strength TS of 500 MPa or more and good internal pressure fatigue resistance and is suitable for use as a fuel injection tube under high injection pressures. The composition of the steel tube may further contain at least one of Cu, Ni, Cr, Mo, and B; at least one of Ti, Nb, and V; and/or Ca.

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: 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 method for manufacturing an electric resistance welded steel tube including: forming a steel tube material into an almost cylindrical open pipe, the steel tube material being a steel sheet wherein Ti and N satisfy (N/14)<(Ti/47.9); forming an electric resistance welded steel tube by bonding ends of the open pipe to each other by induction resistance welding with heat input controlled so that the bond width is 30 to 65 ?m; heating the electric resistance welded steel tube to a temperature equal to or higher than the Ac3 transformation temperature; and diameter-reducing rolling the heated electric resistance welded steel tube with rolling reduction expressed by an outer diameter ratio greater than (1?25/the bond width before diameter-reducing rolling (?m))×100% such that the bond width is 25 ?m or less.

Abstract: A seamless steel tube has a particular composition and a structure with an average prior ? grain size of 150 ?m or less in an axial cross-section after cold drawing and heat treatment. The structure retards the growth of a fatigue crack. The steel tube has a tensile strength TS of 500 MPa or more and good internal pressure fatigue resistance and is suitable for use as a fuel injection tube under high injection pressures. The composition of the steel tube may further contain at least one of Cu, Ni, Cr, Mo, and B; at least one of Ti, Nb, and V; and/or Ca.

Abstract: An electric resistance welded steel pipe excellent in terms of fatigue strength. The steel pipe including a chemical composition containing, by mass %, C: 0.35% or more and 0.55% or less, Si: 0.01% or more and 1.0% or less, Mn: 1.0% or more and 3.0% or less, P: 0.02% or less, S: 0.01% or less, Al: 0.005% or less, N: 0.0050% or less, Cr: 0.1% or more and 0.5% or less, and the balance being Fe and inevitable impurities and a metallic microstructure including pearlite, ferrite, and bainite, in which the area ratio of the pearlite is 85% or more, the total of the area ratios (including 0) of the ferrite and the bainite is 15% or less, and in which a prior austenite grain size is 25 ?m or more.

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 enhances fatigue strength of ear portions which are high fatigue risk parts in a torsion beam almost without bringing about disadvantages in terms of productivity and cost. A torsion beam is formed with a portion of the tubular body into an approximately U-shape in cross section by crushing the portion of the tubular body in the radial direction and, thereafter, due to bending with a bottom line set as a belly side of bending, a bending strain of 2 to 6% in the tube longitudinal direction on a tensile side is imparted to the ear portions.

Abstract: A high-strength electric resistance welded steel tube has a composition including, in terms of percent by mass, C: 0.05 to 0.20%, Si: 0.5 to 2.0%, Mn: 1.0 to 3.0%, P: 0.1% or less, S: 0.01% or less, Al: 0.01 to 0.1%, N: 0.005% or less, and the balance being Fe and unavoidable impurities; and a structure which is a dual phase structure including a ferrite phase and a martensite phase, with a volume ratio of the martensite phase being 20 to 60%, wherein a tensile strength TS is 1180 MPa or more, an elongation El in a tube axis direction is 10% or more, and a yield ratio is less than 90%; and after application of a 2% prestrain and baking finishing that includes a heat treatment of 170° C.×10 min, a strength increase (BH value) is 100 MPa or more and a yield ratio is 90% or more.

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 enhances fatigue strength of ear portions which are high fatigue risk parts in a torsion beam almost without bringing about disadvantages in terms of productivity and cost. A torsion beam is formed with a portion of the tubular body into an approximately U-shape in cross section by crushing the portion of the tubular body in the radial direction and, thereafter, due to bending with a bottom line set as a belly side of bending, a bending strain of 2 to 6% in the tube longitudinal direction on a tensile side is imparted to the ear portions.

Abstract: A frictionally press-bonded member includes a steel pipe, and a stab. The steel pipe has opposite ends. The stab is frictionally press-bonded to at least one of the opposite ends of the steel pipe. The steel pipe is subjected to a normalizing treatment before being frictionally press-bonded to the stab.

Abstract: A steel pipe blank having a composition containing 0.5% or less C and 85% or more Fe in terms of mass percent is heated, and stretch-reducing is then performed so that the diameter decrease ratio is 15% or more and the rolling finishing temperature is (the Ar3 transformation point?10)° C. or lower. Consequently, a structure in which the ratio of X-ray diffraction intensity obtained from the plane in which the <100> direction of crystal grains is preferentially oriented parallel to the circumference direction and the <011> direction of crystal grains is preferentially oriented parallel to the rolling direction of the steel pipe to that obtained for a three-dimensionally randomly oriented sample is 3.0 or more is formed, and the r-value is increased, thereby improving the magnetic properties of the steel pipe.

Abstract: A high-tensile strength welded steel tube has excellent formability and torsional fatigue endurance after being formed into cross-sectional shape and then stress-relief annealed. A steel material used has a composition which contains C, Si, Al, 1.01% to 1.99% Mn, 0.041% to 0.150% Ti, 0.017% to 0.150% Nb, P, S, N, and O such that the sum of the content of Ti and that of Nb is 0.08% or more, the content of each of C, Si, and Al being within an appropriate range, the content of each of P, S, N, and O being adjusted to a predetermined value or less.

Abstract: A frictionally press-bonded member includes a steel pipe, and a stab. The steel pipe has opposite ends. The stab is frictionally press-bonded to at least one of the opposite ends of the steel pipe. The steel pipe is subjected to a normalizing treatment before being frictionally press-bonded to the stab.