A process of producing a duplex stainless steel tube comprises the steps of: a) producing an ingot or a continuous casted billet of said duplex stainless steel; b) hot extruding the ingot or the billet obtained from step a) into a tube; and c) cold rolling the tube obtained from step b) to a final dimension thereof.
The outer diameter D and the wall thickness t of the cold rolled tube is 50-250 mm respectively is 5-25 mm, and, for the cold rolling step, R and Q are set such that the following formula is satisfied:
Rp0.2target=416.53+113.26.Math.log Q+4.0479.Math.R+2694.9.Math.C %82.750.Math.(log Q).sup.20.04279.Math.R.sup.22.2601.Math.log Q.Math.R+16.9.Math.Cr %+26.1.Math.Mo %+83.6.Math.N %+Z(1)
wherein Rp0.2target is targeted yield strength and is 800-1100 MPa and 0<Q<3.6.

Steel material for composite pressure vessel liners that, when used as raw material for manufacturing a composite pressure vessel liner, yields a liner having sufficient strength and a high fatigue limit and enables the manufacture of an inexpensive composite pressure vessel is provided. Steel material for composite pressure vessel liners comprises: a chemical composition containing, in mass %, C: 0.10% to 0.60%, Si: 0.01% to 2.0%, Mn: 0.1% to 5.0%, P: 0.0005% to 0.060%, S: 0.0001% to 0.010%, N: 0.0001% to 0.010%, and Al: 0.01% to 0.06%, with a balance being Fe and incidental impurities; and a metallic microstructure in which a mean grain size of prior austenite grains is 20 m or less, and a total area ratio of martensite and lower bainite is 90% or more.

A hot stamping die includes a body having a stamping surface, and cooling channels within the body. The cooling channels are positioned to transfer heat from region(s) of the surface to the channels. The hot stamping die also includes a heating element within the body, separate and apart from the channels. The heating element is positioned to heat region(s) of the body different from the region(s) of the surface at a rate greater than heat transfer from the channels to the region(s) of the surface.

A process for the industrial production of wear-resistant steel pipes having an optimized life. The process includes providing a wear-resistant, hardenable steel sheet in an unhardened or tempered state, shaping the steel sheet into a tubular preform in which two longitudinal edges of the steel sheet are positioned opposite one another with a welding gap extending between the two edges, welding the longitudinal edges by forming a welded seam which closes the welding gap, thereby forming a steel pipe, and heat treating the steel pipe. The heat treatment of the steel pipe includes heating the steel pipe at an average heating rate of 5-400 K/s to a hold temperature which is the Ac3 temperature of the steel and 1100 C., holding the steel pipe at the hold temperature for 1-120 s, and cooling the steel pipe at an average cooling rate of 10-600 K/s to room temperature.

A hardening apparatus comprises a tracing gauge that is a member having the same axis shape as the axis shape of a bent pipe and being held in an attitude identical to the bent pipe, and a tracing device that is a member which can move in the longitudinal direction of the bent pipe and the tracing gauge and can move in the direction perpendicular to the longitudinal direction. A guide part engaged with the tracing gauge in a manner slidable along the tracing gauge is held at one end of the tracing device, and a hardening device is held at the other end. A transportation device moves the hardening device in the longitudinal direction by moving the tracing device.

A pipe system for oil country tubular goods (OCTG) and a method of manufacturing the OCTG pipe system is disclosed. The pipe system includes at least one OCTG pipe having a pipe body, the pipe body having at least one connection end formed in unipartite and materially integral manner with the pipe body for coupling to a second OCTG pipe. The OCTG pipe is formed in seamless fashion from a hardenable steel alloy, and the connection end has a yield strength higher than the yield strength of the pipe body.

Provided is a high-strength seamless stainless steel pipe for oil country tubular goods which possesses a high strength, excellent low-temperature toughness and excellent corrosion resistance even when the steel pipe has a large wall thickness. The high-strength seamless stainless steel pipe has the composition which contains, by mass %, C: 0.05% or less, Si: 1.0% or less, Mn: 0.1 to 0.5%, P: 0.05% or less, S: less than 0.005%, Cr: more than 15.0% to 19.0% or less, Mo: more than 2.0% to 3.0% or less, Cu: 0.3 to 3.5%, Ni: 3.0% or more and less than 5.0%, W: 0.1 to 3.0%, Nb: 0.07 to 0.5%, V: 0.01 to 0.5%, Al: 0.001 to 0.1%, N: 0.010 to 0.100%, O: 0.01% or less, and Fe and unavoidable impurities as a balance. Nb, Ta, C, N and Cu satisfy a specified formula. The steel pipe has a microstructure which is formed of 45% or more of a tempered martensite phase, 20 to 40% of a ferrite phase, and more than 10% and 25% or less of a residual austenite phase in terms of volume ratio.

The steel material according to the present invention contains, in mass %, C: 0.15 to 0.45%, Si: 0.10 to 1.0%, Mn: 0.10 to 0.8%, P: 0.050% or less, S: 0.010% or less, Al: 0.01 to 0.1%, N: 0.010% or less, Cr: 0.1 to 2.5%, Mo: 0.35 to 3.0%, Co: 0.05 to 2.0%, Ti: 0.003 to 0.040%, Nb: 0.003 to 0.050%, Cu: 0.01 to 0.50%, and Ni: 0.01 to 0.50%, and satisfies the following Formulae. A prior-austenite grain diameter of its microstructure is less than 5 m, and a block diameter of its microstructure is less than 2 m. The microstructure contains a total of 90% by volume or more of tempered martensite and tempered bainite.
C+Mn/6+(Cr+Mo+V)/5+(Cu+Ni)/15Co/6+0.70(1)
(3C+Mo+3Co)/(3Mn+Cr)1.0(2).

A method for manufacturing a cold-forged, extruded aluminum alloy tube includes the steps of: providing a primary material having a hollow columnar shape and made of an aluminum alloy material, and a first cold extrusion apparatus; processing the primary material to form a preform; subjecting the preform to a homogeneous annealing by heating to a temperature of about 410 C. to 510 C. and then cooling to a temperature of about 160 C. to 200 C.; testing the hardness of the preform; immersing the preform in a tank containing lubricant having a total acidity concentration of 40 to 50 mg/L at a working temperature of 80 C. to 100 C.; and subjecting the preform to cold extrusion.

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.