Abstract: A hollow stabilizer having an excellent fatigue property and higher strength compared to the conventional ones has a chemical composition containing 0.26% to 0.30% of C, 0.05% to 0.35% of Si, 0.5% to 1.0% of Mn, 0.05% to 1.0% of Cr, 0.005% to 0.05% of Ti, 0.0005% to 0.005% of B, and 0.0005% to 0.005% of Ca, wherein; Al, P, S, N, and O are limited to 0.08% or less, 0.05% or less, less than 0.0030%, 0.006% or less, and 0.004% or less, respectively, a remainder of the chemical composition consists of Fe and unavoidable impurities, a value of a product of the Mn content and the S content is 0.0025 or less, and a critical cooling rate Vc90 represented by a predetermined equation is 40° C./s or less; and wherein a metallic structure comprises a tempered martensite, a length of elongated MnS present at a center part in a thickness direction of the hollow stabilizer is 150 ?m or less, a HRC is from 40 to 50, a thickness to outer diameter ratio is 0.

Abstract: The invention provides a steel pipe excellent in deformation characteristics, most notably a steel pipe for expandable-pipe oil well and a low-yield-ratio line pipe, and a method of producing the same without conducting water cooling requiring large-scale heat treatment equipment, namely a method of producing a steel pipe excellent in deformation characteristics whose microstructure is a two-phase structure including a martensite-austenite constituent at an area fraction of 2 to 10% and a soft phase, which method comprises: heating at Ac1+10° C. to Ac1+60° C. and thereafter cooling a precursor steel pipe which contains, in mass %, C: 0.04 to 0.10% and Mn: 1.00 to 2.50%, is limited to Si: 0.80% or less, P: 0.03% or less, S: 0.01% or less, Al: 0.10% or less and N: 0.01% or less, further contains one or more of Ni: 1.00% or less, Mo: 0.60% or less, Cr: 1.00% or less and Cu: 1.00% or less, where content of Mn and content of one or more of Cr, Ni, Mo and Cu satisfy Mn+Cr+Ni+2Mo+Cu?2.

Abstract: The invention provides a steel pipe excellent in deformation characteristics, most notably a steel pipe for expandable-pipe oil well and a low-yield-ratio line pipe, and a method of producing the same without conducting water cooling requiring large-scale heat treatment equipment, namely a method of producing a steel pipe excellent in deformation characteristics whose microstructure is a two-phase structure including a martensite-austenite constituent at an area fraction of 2 to 10% and a soft phase, which method comprises: heating at Ac1+10° C. to Ac1+60° C. and thereafter cooling a precursor steel pipe which contains, in mass %, C: 0.04 to 0.10% and Mn: 1.00 to 2.50%, is limited to Si: 0.80% or less, P: 0.03% or less, S: 0.01% or less, Al: 0.10% or less and N: 0.01% or less, further contains one or more of Ni: 1.00% or less, Mo: 0.60% or less, Cr: 1.00% or less and Cu: 1.00% or less, where content of Mn and content of one or more of Cr, Ni, Mo and Cu satisfy Mn+Cr+Ni+2Mo+Cu?2.

Abstract: An automobile strength member, having a cross-sectional shape giving a high bending repulsion at the beginning of impact and able to reduce the production cost and lighten the weight and achieve a greater improvement in safety and a reduction of cost of an automobile, that is, an automobile strength member comprised of a rectangular steel tube with a square cross-section, simultaneously satisfying the following relations (1) to (3), and having a strength of at least 690 MPa in terms of tensile strength: R1?1.5t??(1) tR?1.1t??(2) R1?R2??(3) where, t: thickness of side (mm) tR: thickness of corner (mm) R1: outside corner R (mm) R2: inside corner R (mm) where both a maximum value and minimum value of hardness at a cross-section of the rectangular steel tube are in the range of within ±30% of the average value of the entire cross-section.

Abstract: The present invention provides high strength thick-gauge electric-resistance welded steel pipe excellent in hardenability, hot workability, and fatigue strength and a method of production of the same, that is, thick-gauge electric-resistance welded steel pipe containing, by mass %, C: 0.25 to 0.4%, Si: 0.01 to 0.50%, Mn: 0.8 to 1.5%, P: 0.05% or less, S: 0.05% or less, Al: 0.05% or less, Ti: 0.005 to 0.05%, B: 0.0005 to 0.01%, N: 0.001 to 0.05%, and a balance of Fe and unavoidable impurities, having a critical cooling rate Vc expressed by equation <1> of less than 30° C./s, and having a ratio of thickness t and outside diameter D, t/D, of over 0.15 to 0.30 in range: log Vc=2.94?0.75???<1> where, ?=2.7C+0.

Abstract: An automobile strength member, having a cross-sectional shape giving a high bending repulsion at the beginning of impact and able to reduce the production cost and lighten the weight and achieve a greater improvement in safety and a reduction of cost of an automobile, that is, an automobile strength member comprised of a rectangular steel tube with a square cross-section, simultaneously satisfying the following relations (1) to (3), and having a strength of at least 690 MPa in terms of tensile strength: R1?5t ??(1) tR?1.1t ??(2) R1?R2 ??(3) where, t: thickness of side (mm) tR: thickness of corner (mm) R1: outside corner R (mm) R2: inside corner R (mm) where both a maximum value and minimum value of hardness at a cross-section of the rectangular steel tube are in the range of within ±30% of the average value of the entire cross-section.

Abstract: Welded steel pipe having wear resistance properties, corrosion resistance and low-temperature toughness is provided by preparing welded steel pipe formed of composite steel material comprised of an outer layer of high-carbon, low-alloy steel and an inner layer having a relatively low carbon content, heating the pipe to a temperature that is not less than 800.degree. C. and not more than 900.degree. C. and then quenching the pipe so as to harden just the high-carbon outer layer, and if necessary this can be followed by reheating at a temperature of not less than 200.degree. C. and not more than 600.degree. C. to thereby produce a pipe with an inner layer having high corrosion resistance and low temperature toughness and an outer layer having high hardness.

Abstract: Line pipe having good corrosion-resistance and weldability, in which at least the inner surface of the pipe that is in direct contact with the fluid moved through the pipe is formed of high chromium steel that contains, by weight percent, 7.5 to 16 percent chromium, a carbon content reduced to no more than 0.03 percent and a nitrogen content reduced to no more than 0.02 percent, and a substrate that is not in direct contact with the fluid and is formed of steel that contains 0.02 to 0.25 percent carbon, 0.1 to 1.0 percent silicon, 0.05 to 2.0 percent manganese and 0.005 to 0.1 percent aluminum, a phosphorus impurity content reduced to no more than 0.015 percent and a sulfur impurity content reduced to no more than 0.005 percent, and in which the thickness of the high chromium steel portion does not exceed 25 percent of the total thickness of the pipe.

Abstract: A method for the production of an electric seam welded steel pipe for oil-well use which has good resistance to collapse pressure and souring, by providing a steel containing 0.08-0.26% C by weight, 0.8-1.9% Mn by weight, 0.5% or less Si by weight, the remainder being Fe and unavoidable impurities, subjecting the steel to hot rolling, and hardening, and coiling the treated steel at a temperature not exceeding 250.degree. C., after which the steel is then formed into tubular form and welded by electric resistance welding to produce an electric seam welded pipe, and the weld heat affected zones of the pipe are subjected to heating to a temperature of 900.degree. C. or more to effect hardening, and then the whole pipe is tempered.