Abstract: An electric resistance welded steel pipe for a torsion beam, in which a chemical composition of a base metal portion contains, in terms of % by mass, 0.05 to 0.30% of C, 0.03 to 1.20% of Si, 0.30 to 2.50% of Mn, 0.010 to 0.200% of Ti, 0.005 to 0.500% of Al, 0.010 to 0.040% of Nb, and 0.0005 to 0.0050 % of B, the balance containing Fe and impurities, wherein: Vc90, defined by the following Formula (i), is from 2 to 150, a mass ratio Ti/N is 3.4 or more, a microstructure of a wall thickness central portion in an L cross section at a base metal 1800 position is a tempered martensite, an average aspect ratio of prior ? grains in the tempered martensite is 2.0 or less, and a tensile strength in the pipe axis direction is from 750 to 980 MPa: log Vc90=2.94?0.75?a??Formula (i) ?a=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo??Formula (ii).

Abstract: An electric resistance welded steel pipe for a torsion beam, in which a chemical composition of a base metal portion contains, in terms of % by mass, 0.05 to 0.30% of C, 0.03 to 1.20% of Si, 0.30 to 2.50% of Mn, 0.010 to 0.200% of Ti, 0.005 to 0.500% of Al, 0.010 to 0.040% of Nb, and 0.0005 to 0.005(W % of B, the balance containing Fe and impurities, wherein: Vc90, defined by the following Formula (i), is from 2 to 150, a mass ratio Ti/N is 3.4 or more, a microstructure of a wall thickness central portion in an L cross section at a base metal 1800 position is a tempered martensite, an average aspect ratio of prior ? grains in the tempered martensite is 2.0 or less, and a tensile strength in the pipe axis direction is from 750 to 980 MPa: log Vc90=2.94?0.75?a??Formula (i) ?a=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+2Mo??Formula (ii).

Abstract: An electric resistance welded steel pipe for a torsion beam, in which a base metal portion includes, in terms of % by mass, 0.04 to 0.12% of C, 0.03 to 1.20% of Si, 0.30 to 2.50% of Mn, 0.08 to 0.24% of Ti, 0.005 to 0.500% of Al, 0.01 to 0.06% of Nb, and 0.0005 to 0.0100% of N, a balance including Fe and impurities, wherein Vc90, defined by the following Formulae (i) and (ii), is 200 or more, a mass ratio of Ti content to C content is from 0.85 to 5.00, an areal ratio of ferrite is 80% or more, an average crystal grain size of ferrite crystal grains is 10 ?m or less, and an average aspect ratio of ferrite crystal grains is 2.0 or less, in a metallographic microstructure of a central portion in a wall thickness direction of the base metal portion; log Vc90=2.94?0.75(?a?1)??Formula (i); ?a=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+Mo??Formula (ii).

Abstract: The present invention provides electric-resistance welded steel pipe optimal for applications such as production of shale gas which is comprised of steel having a chemical composition which contains, by mass %, respectively, C: 0.08 to 0.18%, Si: 0.01% to 0.50%, Mn: 1.30 to 2.1%, Al: 0.001 to 0.10%, Nb: 0.005 to 0.08%, and Ti: 0.005 to 0.03%, is limited to N 0.008% or less, P: 0.020% or less, and S: 0.010% or less, and has a balance of Fe and unavoidable impurities, wherein a structure at a center part of thickness is 40% to 70% by area of ferrite phase having a circle-equivalent diameter of 1.0 ?m to 10.0 ?m and a balance of a low temperature transformation phase comprising a bainite phase, and Ceq satisfies 0.32?Ceq?0.60.

Abstract: An electric resistance welded steel pipe for a torsion beam, in which a base metal portion includes, in terms of % by mass, 0.04 to 0.12% of C, 0.03 to 1.20% of Si, 0.30 to 2.50% of Mn, 0.08 to 0.24% of Ti, 0.005 to 0.500% of Al, 0.01 to 0.06% of Nb, and 0.0005 to 0.0100% of N, a balance including Fe and impurities, wherein Vc90, defined by the following Formulae (i) and (ii), is 200 or more, a mass ratio of Ti content to C content is from 0.85 to 5.00, an areal ratio of ferrite is 80% or more, an average crystal grain size of ferrite crystal grains is 10 ?m or less, and an average aspect ratio of ferrite crystal grains is 2.0 or less, in a metallographic microstructure of a central portion in a wall thickness direction of the base metal portion; log Vc90=2.94?0.75(?a?1)??Formula (i); ?a=2.7C+0.4Si+Mn+0.45Ni+0.8Cr+Mo??Formula (ii).

Abstract: An electric resistance welded steel pipe for an oil well includes in terms of mass %: 0.02 to 0.14% of C, 0.05 to 0.50% of Si, 1.0 to 2.1% of Mn, 0.020% or less of P, 0.010% or less of S, 0.010 to 0.100% of Nb, 0.010 to 0.050% of Ti, 0.010 to 0.100% of Al, and 0.0100% or less of N. Contents of Cu, Ni, Cr, Mo, V, and B are 0 to 0.50%, 0 to 1.00%, 0 to 0.50%, 0 to 0.30%, 0 to 0.10%, and 0 to 0.0030%, respectively. Remainder consisting of Fe and unavoidable impurities. In a case that a full thickness specimen is subjected to a pipe axis direction tensile test, a tensile strength is 780 MPa or more, 0.2% proof stress/tensile strength is 0.80 or more, and 2% flow stress/tensile strength is from 0.85 to 0.98.

Abstract: A steel pipe, consisting of, in terms of mass %: from 0.06% to 0.25% of C, 0.50% or less of Si, 1.00% to 1.80% of Mn, 0.030% or less of P, 0.020% or less of S, 0.08% or less of Al, 0.008% or less of N, 0.080% or less of Nb, and a remainder consisting of Fe and unavoidable impurities, wherein a compressive residual stress at an outer surface measured by an X-ray method is 250 MPa or more, and a compressive residual stress at a position at a depth of 1 mm from the outer surface measured by the X-ray method is 70% or more of the compressive residual stress at the outer surface measured by the X-ray method.

Abstract: Electric resistance welded steel pipe excellent in weld zone quality suitable for oil country tubular goods and line pipe wherein steel plate forming the base metal of the electric resistance welded steel pipe has a predetermined chemical composition, the contents of Ca, O, S, Ce, La, and Al satisfy XCASO = ( Ca O + Ca S + 0.285 ? Ce + La O + 0.285 ? Ce + La S ) × ( Al Ca ) > 78 the oxide-based inclusions in the weld zone of the electric resistance welded steel pipe contains one or both of Ce and La, and the long axis/short axis of the oxide-based inclusions is 2.5 or less.

Abstract: A quenched steel pipe member is formed of a GI galvanized steel pipe, in a middle section in a longitudinal direction of the GI galvanized steel pipe, a cross-section perpendicular to the longitudinal direction has a substantially V shape including a contact section at which opposite parts of an inner circumferential surface of the GI galvanized steel pipe come into contact with each other, the contact section is bonded using a Fe—Zn alloy phase, and a micro Vickers hardness at a location 50 ?m deep from a base material surface layer is 95% or more of a micro Vickers hardness at a location 200 ?m deep from the base material surface layer.

Abstract: A torsion beam which is used in a suspension system of an automobile which is provided with a pair of arm members which extend in a front-rear direction of the automobile and are designed to be connected to a chassis of the automobile so as to be able to swing and to have wheels attached rotably to them is disclosed. The torsion beam is formed with a recess which extends in the longitudinal direction whereby that torsion beam has first and second leg parts in a plane vertical to the longitudinal direction and exhibits a substantially V-shaped or substantially U-shaped cross-sectional shape. The torsion beam is provided with connection parts which are provided at the two ends of that torsion beam and are connected to the arm members, a fixed shape part which is provided at a center part in the longitudinal direction of that torsion beam, and asymmetric shape parts which are provided between that fixed shape part and the connection parts.

Abstract: The present invention provides a steel pipe, consisting of, in terms of mass %: from 0.06% to 0.25% of C, 0.50% or less of Si, 1.00% to 1.80% of Mn, 0.030% or less of P, 0.020% or less of S, 0.08% or less of Al, 0.008% or less of N, 0.080% or less of Nb, and a remainder consisting of Fe and unavoidable impurities, wherein a compressive residual stress at an outer surface measured by an X-ray method is 250 MPa or more, and a compressive residual stress at a position at a depth of 1 mm from the outer surface measured by the X-ray method is 70% or more of the compressive residual stress at the outer surface measured by the X-ray method.

Abstract: An electric resistance welded steel pipe for an oil well includes in terms of mass %: 0.02 to 0.14% of C, 0.05 to 0.50% of Si, 1.0 to 2.1% of Mn, 0.020% or less of P, 0.010% or less of S, 0.010 to 0.100% of Nb, 0.010 to 0.050% of Ti, 0.010 to 0.100% of Al, and 0.0100% or less of N. Contents of Cu, Ni, Cr, Mo, V, and B are 0 to 0.50%, 0 to 1.00%, 0 to 0.50%, 0 to 0.30%, 0 to 0.10%, and 0 to 0.0030%, respectively. Remainder consisting of Fe and unavoidable impurities. In a case that a full thickness specimen is subjected to a pipe axis direction tensile test, a tensile strength is 780 MPa or more, 0.2% proof stress/tensile strength is 0.80 or more, and 2% flow stress/tensile strength is from 0.85 to 0.98.

Abstract: The present invention provides electric-resistance welded steel pipe optimal for applications such as production of shale gas which is comprised of steel having a chemical composition which contains, by mass %, respectively, C: 0.08 to 0.18%, Si: 0.01% to 0.50%, Mn: 1.30 to 2.1%, Al: 0.001 to 0.10%, Nb: 0.005 to 0.08%, and Ti: 0.005 to 0.03%, is limited to N 0.008% or less, P: 0.020% or less, and S: 0.010% or less, and has a balance of Fe and unavoidable impurities, wherein a structure at a center part of thickness is 40% to 70% by area of ferrite phase having a circle-equivalent diameter of 1.0 ?m to 10.0 ?m and a balance of a low temperature transformation phase comprising a bainite phase, and Ceq satisfies 0.32?Ceq?0.60.

Abstract: Electric resistance welded steel pipe excellent in weld zone quality suitable for oil country tubular goods and line pipe wherein steel plate forming the base metal of the electric resistance welded steel pipe has a predetermined chemical composition, the contents of Ca, O, S, Ce, La, and Al satisfy XCASO = ( Ca O + Ca S + 0.285 ? Ce + La O + 0.285 ? Ce + La S ) × ( Al Ca ) > 78 the oxide-based inclusions in the weld zone of the electric resistance welded steel pipe contains one or both of Ce and La, and the long axis/short axis of the oxide-based inclusions is 2.5 or less.

Abstract: A torsion beam which is used in a suspension system of an automobile which is provided with a pair of arm members which extend in a front-rear direction of the automobile and are designed to be connected to a chassis of the automobile so as to be able to swing and to have wheels attached rotably to them is disclosed. The torsion beam is formed with a recess which extends in the longitudinal direction whereby that torsion beam has first and second leg parts in a plane vertical to the longitudinal direction and exhibits a substantially V-shaped or substantially U-shaped cross-sectional shape. The torsion beam is provided with connection parts which are provided at the two ends of that torsion beam and are connected to the arm members, a fixed shape part which is provided at a center part in the longitudinal direction of that torsion beam, and asymmetric shape parts which are provided between that fixed shape part and the connection parts.

Abstract: An automobile chassis part which is excellent in low cycle fatigue characteristics, characterized by being formed by steel which contains, by mass %, C: 0.02 to 0.10%, Si: 0.05 to 1.0%, Mn: 0.3 to 2.5%, P: 0.03% or less, S: 0.01% or less, Ti: 0.005 to 0.1%, Al: 0.005 to 0.1%, N: 0.0005 to 0.006%, and B: 0.0001 to 0.01 and has a balance of Fe and unavoidable impurities, in which 80% or more of the part structure comprises a bainite structure and in which a portion where a ratio R/t of the thickness “t” and external surface curvature radius R is 5 or less has an X-ray half width of an (211) plane of 5 (deg) or less.

Abstract: A quenched steel pipe member is formed of a GI galvanized steel pipe, in a middle section in a longitudinal direction of the GI galvanized steel pipe, a cross-section perpendicular to the longitudinal direction has a substantially V shape including a contact section at which opposite parts of an inner circumferential surface of the GI galvanized steel pipe come into contact with each other, the contact section is bonded using a Fe—Zn alloy phase, and a micro Vickers hardness at a location 50 ?m deep from a base material surface layer is 95% or more of a micro Vickers hardness at a location 200 ?m deep from the base material surface layer.

Abstract: A method of press-forming a tubular part having a cross section of an irregular shape crushes a steel tube between an upper die and a lower die in order to form a V-shaped cross section. When the curvature radius of a tip of the upper die is defined as R1, the curvature radius of a bottom portion of the lower die corresponding to the tip of the upper die is defined as R2, and the wall thickness of the steel tube is defined as t; R1, R2, and t satisfy R1+2t=R2 and 1.5t?R1?3t.

Abstract: The present invention provides a steel material for automobile chassis parts which has high fatigue characteristics, does not require much cost for heat treatment, and further is superior in shapeability and a method of production of automobile chassis parts using this steel material, that is, one being a steel material to which Nb and Mo have been compositely added and having a difference 50 to 150 points between a Vicker's hardness of the center of plate thickness and a maximum value of Vicker's hardness within 0.5 mm from the surface after bending by a bending R of the plate outer surface of 2 to 5 times the plate thickness. The surface is high in hardness and the center part is low in hardness, so the fatigue characteristics and shapeability are superior. Note that if annealing under conditions giving a tempering parameter ? defined by ?=T(20+log(t)) of 14000 to 19000 (where T is the absolute temperature, t is the time (h), and the temperature rise is 660° C.

Abstract: The present invention provides a steel material for automobile chassis parts, having high fatigue characteristics, without a heat treatment, and superior shapeability, and a method of production of such automobile chassis parts. The surface of the steel has a high hardness and the center has a low hardness, providing the superior characteristics. With an annealing step of the invention, it is possible to relieve internal stress and further improve fatigue characteristics.