Disclosed in the present disclosure is an S32750 austenitic ferrite super duplex stainless steel seamless pipe for a deep sea manifold and a method for preparing the same. The stainless steel seamless pipe includes the following components in percentage by mass: less than or equal to 0.03% of C, less than or equal to 0.80% of Si, less than or equal to 1.20% of Mn, less than or equal to 0.035% of P, less than or equal to 0.01% of S, 24.0-26.0% of Cr, 6.0-8.0% of Ni, 3.0-5.0% of Mo, less than or equal to 0.50% of Cu, 0.24-0.32% of N, 0.012-0.018% of Al, and the balance of Fe and impurities. The ferrite content of the stainless steel seamless pipe is 40-60%, and 41≤PREN<45. The stainless steel seamless pipe is prepared by metal collaborative design, smelting, pouring, forging, hot piercing and cold working.

A lumen stent preform is provided using a plasma nitriding technology, a preparation method thereof, a method for preparing a lumen stent by using the preform, and a lumen stent obtained according to the method. The preform is manufactured by using pure iron or an iron alloy containing no strong nitrogen compound, has a hardness of 160-250HV0.05/10, and has a microstructure that is a deformed structure having a grain size scale greater than or equal to 9 or a deformed structure after cold machining. Alternatively, the preform is an iron alloy containing a strong nitrogen compound, and has a microstructure that is a deformed structure having a grain size scale greater than or equal to 9 or a deformed structure after cold machining. The lumen stent preform meets the requirements of a conventional stent for radial strength and plasticity, so that plasma nitriding is applicable to commercial preparation of a lumen stent.

A stainless steel material having compositions which contain on the basis of percent by mass, C from 0.04 to 0.12%, Ni from 0 (including a case of no addition) to 5.0%, Cr from 12.0 to 17.0%, N from 0.0 to 0.10%, Si from 0.2 to 2.0%, Mn at 2.0% or less, Cu from 0.0 to 2.0%, P at 0.06% or less, S at 0.006% or less, with residue being Fe and unavoidable impurities. Further, a parent phase has any one of a single phase structure of ferrite phase or martensite phase and a diploid phase structure of ferrite phase and martensite phase. An end of the base material is melt-welded as a joint to form a pipe. The parent phase is provided with carbide uniformly separated at grain boundaries and within grains, with a dissolved amount of C being 0.03% by mass or less.

A stainless steel material having compositions which contain on the basis of percent by mass, C from 0.04 to 0.12%, Ni from 0 (including a case of no addition) to 5.0%, Cr from 12.0 to 17.0%, N from 0.0 to 0.10%, Si from 0.2 to 2.0%, Mn at 2.0% or less, Cu from 0.0 to 2.0%, P at 0.06% or less, S at 0.006% or less, with residue being Fe and unavoidable impurities. Further, a parent phase has any one of a single phase structure of ferrite phase or martensite phase and a diploid phase structure of ferrite phase and martensite phase. An end of the base material is melt-welded as a joint to form a pipe. The parent phase is provided with carbide uniformly separated at grain boundaries and within grains, with a dissolved amount of C being 0.03% by mass or less.

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.

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.

There is provided a high-strength steel material for oil well having a chemical composition consisting, by mass percent, of C: 0.70-1.8%, Si: 0.05-1.00%, Mn: 12.0-25.0%, Al: 0.003-0.06%, P: ≦0.03%, S: ≦0.03%, N: ≦0.10%, V: >0.5% and ≦2.0%, Cr: 0-2.0%, Mo: 0-3.0%, Cu: 0-1.5%, Ni: 0-1.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: 0-0.005%, Mg: 0-0.005%, B: 0-0.015%, the balance: Fe and impurities, satisfying [0.6≦C-0.18V-0.06Cr<1.44], wherein a metal micro-structure is consisting essentially of an austenite single phase, V carbides having circle equivalent diameters of 5 to 100 nm exist at a number density of 20 pieces/μm.sup.2 or higher, and a yield strength is 654 MPa or higher.

There is provided a high-strength steel material for oil well having a chemical composition consisting, by mass percent, of C: 0.70-1.8%, Si: 0.05-1.00%, Mn: 12.0-25.0%, Al: 0.003-0.06%, P: ≦0.03%, S: ≦0.03%, N: ≦0.10%, V: >0.5% and ≦2.0%, Cr: 0-2.0%, Mo: 0-3.0%, Cu: 0-1.5%, Ni: 0-1.5%, Nb: 0-0.5%, Ta: 0-0.5%, Ti: 0-0.5%, Zr: 0-0.5%, Ca: 0-0.005%, Mg: 0-0.005%, B: 0-0.015%, the balance: Fe and impurities, satisfying [0.6≦C-0.18V-0.06Cr<1.44], wherein a metal micro-structure is consisting essentially of an austenite single phase, V carbides having circle equivalent diameters of 5 to 100 nm exist at a number density of 20 pieces/μm.sup.2 or higher, and a yield strength is 654 MPa or higher.

According to the present invention, there is provided a cooling apparatus for a steel material in which one portion in a longitudinal direction of an elongated steel material (10) is heated while the steel material is fed in the longitudinal direction in a state where one end portion of the steel material is gripped, and the one end portion is moved in a two-dimensional or three-dimensional direction so as to form the steel material into a predetermined shape including a bent portion and thereafter to cool a heated portion including the bent portion. The cooling apparatus includes a first cooling apparatus (22) that ejects a first cooling medium to the heated portion, and a second cooling apparatus (23) that is disposed on a downstream side from the first cooling apparatus when viewed along a feeding direction of the steel material, and that ejects a second cooling medium to the heated portion. A plurality of the second cooling apparatuses are disposed along the feeding direction, and flow rates of the second cooling media can be controlled independently of each other. According to the configuration, it is possible to reduce the insufficient quenching of the steel material.

A process for manufacturing a bellows, made of austenitic high-grade steel with high compressive strength and fatigue strength, forms a single-layer or multilayer sleeve into a bellows with hydraulic forming. The pressure resistance and fatigue strength are improved by the bellows being cleaned after the forming and by the bellows being exposed to a surrounding area containing carbon and/or nitrogen atoms at temperatures between 100° C. and 400° C., preferably 200° C. to 320° C. With this a hardening of the bellows takes place by means of the diffusing in of carbon and/or nitrogen atoms. A bellows made of austenitic high-grade steel with one or more layers created in this manner has the edge layer hardened by the incorporation of carbon and/or nitrogen atoms up to a hardening depth of at least 5% of the wall thickness.