The present invention relates to a high strength steel tube. In addition, the invention relates to a method of manufacturing a high strength steel tube. The method is characterized in that a hot rolled pre-tube is subjected to at least two hardening steps with a final tempering step, the pre-tube is heated to a quenching temperature of at least Ac3 temperature for hardening and is heated to a tempering temperature in the range of 400 to 600° C. for tempering.

The present invention relates to a non-magnetic austenitic stainless steel material having a component composition containing, in terms of mass percent, C: <0.10%, Si: <0.3%, Mn: more than 4.5% to less than 10.0%, P: <0.05%, S: <0.0020%, Ni: 9.0% to 15.0%, Cr: 17.0% to 25.0%, Mo: 3.0% to 7.0%, and N: 0.3% to 0.6%, with the balance being Fe and unavoidable impurities; satisfying (40[N]+1.2[Cr]+0.07exp(0.3[Ni]+0.3[Cu]))×1.5[Mo]{circumflex over ( )}(−0.18)≤60, in which [M] represents a content of an element M in terms of mass %; having an austenite single phase structure; having a critical pitting temperature of 50° C. or higher; and having a 0.2% proof stress of 970 MPa or more.

An apparatus line for manufacturing seamless steel pipes and tubes includes: a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; and a rolling apparatus for applying working to the hollow material to form a seamless steel pipe having a predetermined shape. A cooling apparatus is arranged on an exit side of the rolling apparatus. A heated steel raw material is worked by the rolling apparatus after being pierced by the piercing apparatus, and thereafter, using a surface temperature of a hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the hollow piece is cooled to a cooling stop temperature differing by 50° C. or more from the cooling start temperature and being equal to or above 600° C. at an average cooling speed of 1.0° C./s or more in terms of an outer surface temperature.

The invention is intended to provide a method for quenching a steel pipe, equipment for quenching a steel pipe, and a method of manufacturing a steel pipe that enable a steel pipe to be conveyed at high speed. The method for quenching a steel pipe includes the steps of: conveying a steel pipe onto a rotatable supporting member using a walking-arm type revolving conveyance apparatus; and rapidly cooling the steel pipe with first spray nozzles disposed above the pipe while the steel pipe is being rotated about a pipe axis of the steel pipe on the rotatable supporting member in a state where movements of the steel pipe in a direction parallel to and in a direction perpendicular to the pipe axis are stopped.

The steel material according to the present disclosure contains a chemical composition consisting of, in mass %, C: 0.20 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.030% or less, S: less than 0.0050%, Al: 0.005 to 0.050%, Cr: 0.10 to 1.50%, Mo: 0.25 to 1.80%, Ti: 0.002 to 0.050%, Nb: 0.002 to 0.100%, B: 0.0001 to 0.0050%, N: 0.0070% or less and O: less than 0.0050% with the balance being Fe and impurities. A yield strength is within a range of 655 to 1069 MPa, and a yield ratio is 85% or more. A proportion of KAM values of 1° or less is 30 area % or more.

There are provided an electric resistance welded steel pipe for producing a high strength hollow stabilizer excellent in fatigue resistance and a high strength hollow stabilizer. In an electric resistance welded steel pipe (5) for producing a hollow stabilizer, an internal weld bead cut portion (30) has a three-peak shape and a depth (H) of a trough portion (30a) of the three-peak shape is 0.3 mm or less and an angle (θ) formed by a central portion in the circumferential direction of the trough portion (30a) and the top of right and left peak portions (30b, 30c) located on both the right and left sides of the trough portion (30a) is 160° or more and less than 180°.

Embodiments of the present disclosure are directed to coiled steel tubes and methods of manufacturing coiled steel tubes. In some embodiments, the final microstructures of the coiled steel tubes across all base metal regions, weld joints, and heat affected zones can be homogeneous. Further, the final microstructure of the coiled steel tube can be a mixture of tempered martensite and bainite.

A hot-rolled steel sheet for a heavy-wall, high-strength line pipe, the steel sheet having a chemical composition including, in mass %, C: 0.02 to 0.20%, Mn: 0.80 to 2.10%, Si: 0.01 to 0.50%, P: 0.034% or less, S: 0.0050% or less, Nb: 0.01 to 0.15%, Ti: 0.001 to 0.030%, and Al: 0.001 to 0.080%, the balance being Fe and incidental impurities, the steel sheet having a microstructure in which a main phase is a continuous cooling transformation structure and in which {001}.sub.α grains in a plane whose normal direction is the sheet width direction constitute an area fraction of 10% or less and have a combined size of 10 μm or less, wherein the steel sheet has a tensile strength of 520 MPa or greater, and, in a drop weight tear test, a temperature at which a percent ductile fracture reaches 85% is −25° C. or lower.

A high strength stainless steel seamless pipe for oil country tubular goods which is excellent in hot workability, has a high strength, suppresses scattering in the strength, and has excellent carbon dioxide corrosion resistance. The steel pipe has a yield strength of 655 MPa or more, and a chemical composition comprising, by mass %, C: 0.005 to 0.05%, Si: 0.05 to 0.50%, Mn: 0.20 to 1.80%, P: 0.030% or less, S: 0.005% or less, Cr: 12.0 to 17.0%, Ni: 4.0 to 7.0%, Mo: 0.5 to 3.0%, Al: 0.005 to 0.10%, V: 0.005 to 0.20%, Co: 0.01 to 1.0%, N: 0.005 to 0.15%, and O: 0.010% or less with the balance being Fe and inevitable impurities. Cr, Ni, Mo, Cu, and C satisfy a specified expression, and Cr, Mo, Si, C, Mn, Ni, Cu, and N satisfy another specified expression.

Cooling device (1) for cooling a seamless, rolled pipe (R) made of a metal, preferably steel, which has a nozzle assembly (10) comprising one or more nozzles (14), which are configured to apply a cooling medium (K), preferably water or a water mixture, to the outer circumferential surface of the pipe (R) while the pipe (R) is transported along a conveying direction (F) through a cooling section of the cooling device (1), wherein the nozzle assembly (10) has an access (Z), via which the pipe (R) can be removed from the cooling section in the radial direction of the pipe (R), preferably upward.