The present disclosure provides a bainite geological drilling pipe, comprising the following chemical elements in percentage by mass: 0.14-0.22% of C, 0.2-0.55% of Si, 2.1-2.9% of Mn, 0.01-0.04% of Nb, 0.015-0.04% of Al, 0.001-0.005% of B, 0<N?0.007%, with the balance being Fe and inevitable impurities, wherein a content ratio of Al to N is Al/N?3. In addition, the present disclosure further provides a manufacturing method for the bainite geological drilling pipe, comprising the following steps: (1) performing smelting and casting on molten steel to obtain a pipe blank; (2) performing heating, piercing, continuous rolling and sizing on the pipe blank to obtain a pipe body; and (3) performing two-stage air cooling on the pipe body; in first-stage air cooling, performing air circular blowing cooling on the outer surface of the pipe body, the temperature before cooling is greater than or equal to Ar/3+50? C., the cooling rate is 5-15? C./s, and cooling to a temperature range from Bs-100? C. to Bs-50? C.; in second-stage air cooling, performing natural air cooling on the pipe body, the cooling rate is 0.5-4? C./s.

The seamless steel pipe according to the present disclosure includes a chemical composition consisting of, in mass %, C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.030% or less, S: 0.0050% or less, Al: 0.001 to 0.100%, N: 0.0500% or less, O: 0.050% or less, Ni: 3.00 to 6.50%, Cr: more than 10.00 to 13.40%, Mo: 0.50 to 4.00%, V: 0.01 to 1.00%, Ti: 0.010 to 0.300%, and Co: 0.010 to 0.300%, with the balance being Fe and impurities, and satisfying Formula (1), and a microstructure containing, in volume ratio, 80.0% or more of martensite, wherein a depassivation pH of an inner surface is 3.50 or less.
Cr+2.0Mo+0.5Ni+0.5Co?16.0(1)

A high-strength stainless steel seamless pipe for oil country tubular goods has a composition that contains, in mass %, C: 0.012 to 0.05%, Si: 0.05 to 0.50%, Mn: 0.04 to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 11.0 to 14.0%, Ni: 0.5 to 6.5%, Mo: 0.5 to 3.0%, Al: 0.005 to 0.10%, V: 0.005 to 0.20%, Co: 0.01 to 0.3%, N: 0.002 to 0.15%, O: 0.010% or less, and Ti: 0.001 to 0.20%, and in which Cr, Ni, Mo, Cu, C, Si, Mn, N, and Ti satisfy predetermined relations, and the balance is Fe and incidental impurities, the high-strength stainless steel seamless pipe having a steel microstructure with 6 to 20% retained austenite in terms of a volume percentage, a yield strength of 758 MPa or more, and an absorption energy vE.sub.?60 at ?60? C. of 70 J or more.

Described herein are coiled tubes with improved and varying properties along the length that are produced by using a continuous and dynamic heat treatment process (CDHT). Coiled tubes can be uncoiled from a spool, subjected to a CDHT process, and coiled onto a spool. A CDHT process can produce a composite tube such that properties of the tube along the length of the tube are selectively varied. For example, the properties of the tube can be selectively tailored along the length of the tube for particular application for which the tube will be used.

The invention deals with Steel for seamless pipes comprising the following chemical composition elements in weight percent: 0.04Cto 0.18, 0.10Si0.60, 0.80Mn1.90, P0.020, S0.01, 0.01Al0.06, 0.50Cu1.20, 0.10Cr0.60, 0.60Ni1.20, 0.25Mo0.60, B0.005, V0.060, Ti0.050, 0.010Nb0.050, 0.10W0.50, N0.012, where the balance is Fe and inevitable impurities. The steel of the invention can be used in offshore applications, line process pipes, structural and mechanical applications, especially where harsh environmental conditions and service temperatures down to 80 C. occur.

A hollow stabilizer has a tubular shape and is provided with a torsion section that is provided to a vehicle and that extends in the vehicle width direction; an arm section that extends in the front-back direction of the vehicle; and bent sections that connect the torsion section and the arm section. The hardness of the outer surface of the bent inner sides of the bent sections of the hollow stabilizer is 70% or more with respect to the hardness of the outer surface of the arm section.

An oil well pipe for expandable tubular, containing, in terms of % by mass: 0.020 to 0.080% of C, 0.50% or less of Si, 0.30 to 1.60% of Mn, 0.030% or less of P, 0.010% or less of S, 0.005 to 0.050% of Ti, and 0.010 to 0.500% of Al, and the balance being Fe and impurities, wherein, in a metallographic microstructure, an area fraction of a first phase composed of ferrite is from 90.0% to 98.0% and an area fraction of a second phase composed of one or more selected from the group consisting of tempered martensite, tempered bainite, and pearlite is from 2.0% to 10.0%.

A thick-wall oil-well steel pipe has a wall thickness of 40 mm or more, excellent SSC resistance and high strength. The thick-wall oil-well steel pipe has a composition containing, in mass %, C: 0.40 to 0.65%, Si: 0.05 to 0.50%, Mn: 0.10 to 1.0%, P: 0.020% or less, S: 0.0020% or less, sol. Al: 0.005 to 0.10%, Cr more than 0.40 to 2.0%, Mo: more than 1.15 to 5.0%, Cu: 0.50% or less, Ni: 0.50% or less, N: 0.007% or less, and O: 0.005% or less. The number of carbide which has a circle equivalent diameter of 100 nm or more and contains 20 mass % or more of Mo is 2 or less per 100 mm.sup.2. The thick-wall oil-well steel pipe has yield strength of 827 MPa or more. A difference between a maximum value and a minimum value of the yield strength in the wall-thickness direction is 45 MPa or less.

A system for air quenching a heat treated element comprises a tubular component, an internal air quench device moveably disposed within the interior of the tubular component, and an external air quench device moveably disposed about the tubular component. The internal air quench device comprises a nozzle configured to induce an airflow within the tubular component. The external air quenching device can comprise an annular ring disposed about the tubular component that is configured to generate a cone of air about the tubular component.

An induction heating coil for stably heating a steel tube which is being fed in its axial direction without rotating, the heating being uniform in the circumferential direction and in a narrow range in the axial direction has at least two 1-turn coils in the form of a first turn coil body and a second turn coil body. The inner peripheral length Ln (the non-effective coil length) where the effective number of coil turns is less than the total number of coil turns when the coil is projected in the axial direction and the inner peripheral length L0 of the projected coil bodies (the inner coil length) satisfy Ln/L0<0.05. First and second coil bodies have insulating portions on their connecting portions, and the insulating portions are present in locations separated by a central angle of 5-45 measured from the center of the coil bodies.