With Working Patents (Class 148/593)
  • Patent number: 11078558
    Abstract: The steel material according to the present invention contains a chemical composition consisting of, in mass %, C: 0.25 to 0.50%, Si: 0.05 to 0.50%, Mn: 0.05 to 1.00%, P: 0.025% or less, S: 0.0100% or less, Al: 0.005 to 0.100%, Cr: 0.30 to 1.50%, Mo: 0.25 to 1.50%, Ti: 0.002 to 0.050%, B: 0.0001 to 0.0050%, N: 0.002 to 0.010% and O: 0.0100% or less, with the balance being Fe and impurities. The steel material also contains an amount of dissolved C within a range of 0.010 to 0.050 mass%. The steel material also contains an yield strength is in a range of 862 to less than 965 MPa, and an yield ratio is 90% or more.
    Type: Grant
    Filed: October 6, 2017
    Date of Patent: August 3, 2021
    Assignee: Nippon Steel Corporation
    Inventors: Yuji Arai, Shinji Yoshida, Atsushi Soma, Hiroki Kamitani
  • Patent number: 11001905
    Abstract: Disclosed is, as a high-strength steel plate of API X80 grade or higher with a thickness of 38 mm or more, a steel plate for structural pipes or tubes that exhibits excellent resistance to PWHT and excellent toughness at the heat-affected zone, particularly at the butting faces joined by welding, without addition of large amounts of alloying elements. The steel plate for structural pipes or tubes disclosed herein has a specific chemical composition, in which the steel plate has mechanical properties including: (a) a 0.5% yield strength of 555 MPa or more; (b) a tensile strength of 625 MPa or more; and (c) a Charpy absorption energy vE?10° C. at ?10° C. at its mid-thickness part of 250 J or more, and maintains the mechanical properties (a) to (c) even after subjection to heat treatment at 650° C. for 2 hours.
    Type: Grant
    Filed: March 25, 2016
    Date of Patent: May 11, 2021
    Assignee: JFE STEEL CORPORATION
    Inventors: Shusaku Ota, Yoshiaki Ota, Shinichi Kakihara, Nobuyuki Ishikawa
  • Patent number: 10995382
    Abstract: The invention provides a production method for stabilizers which produces with high productivity in a compact production line, without tempering. The production method for stabilizers of the invention includes: forming a steel bar material containing at least C: 0.15 wt % to 0.39 wt %, Mn, B and Fe into a product shape by bending; and quenching the bent steel bar material in a medium having a heat transfer coefficient higher than or close to that of water.
    Type: Grant
    Filed: December 7, 2015
    Date of Patent: May 4, 2021
    Assignee: NHK SPRING CO., LTD.
    Inventors: Shinichiro Kuwatsuka, Yurika Okudaira, Akira Tange, Hideki Okada, Ken Takahashi
  • Patent number: 10987714
    Abstract: A forming method for a vehicle body member may include a tube making process of forming a steel pipe by welding a steel plate coil; a non-circular tube making process of primary preforming the steel pipe formed in the tube making process so as to have a cross section of a predetermined shape; a bending process of bending and secondarily preforming the steel pipe preformed firstly in the non-circular tube making process; and a hot stamping process of heating the secondarily preformed steel pipe, inserting the heated steel pipe into a mold to form a desired shape, and then, quenching the heated steel pipe to form a vehicle body member, thereby easily forming a vehicle body member having high rigidity.
    Type: Grant
    Filed: August 26, 2019
    Date of Patent: April 27, 2021
    Assignees: HYUNDAI MOTOR COMPANY, KIA MOTORS CORPORATION, HYUNDAI STEEL COMPANY
    Inventors: Kyung Hoon Son, JiHwan Kim, KyoungSu Jin, BaekGu Kang, JeongReal Kim
  • Patent number: 10920297
    Abstract: A seamless steel pipe having a specific chemical composition. A ratio of Ti to N is in a range of 2.0 to 5.0. The steel pipe has a microstructure including tempered martensite having a volume ratio of 95% or more, and prior austenite grains having a grain size number of 8.5 or more. In a cross-section perpendicular to a rolling direction of the steel pipe a number of nitride-based inclusions having a particle size of 4 ?m or more is 100 or less per 100 mm2, a number of nitride-based inclusions having a particle size of less than 4 ?m is 1000 or less per 100 mm2, a number of oxide-based inclusions having a particle size of 4 ?m or more is 40 or less per 100 mm2, and a number of oxide-based inclusions having a particle size of less than 4 ?m is 400 or less per 100 mm2.
    Type: Grant
    Filed: August 20, 2015
    Date of Patent: February 16, 2021
    Assignee: JFE STEEL CORPORATION
    Inventors: Masao Yuga, Yasuhide Ishiguro, Mitsuhiro Okatsu, Seiji Nabeshima, Hiroki Ota
  • Patent number: 10752979
    Abstract: Provided is a low alloy oil-well steel pipe having a yield strength of 793 MPa or more, and an excellent SSC resistance. A low alloy oil-well steel pipe according to the present invention includes a chemical composition consisting of: in mass %, C: 0.25 to 0.35%; Si: 0.05 to 0.50%; Mn: 0.10 to 1.50%; Cr: 0.40 to 1.50%; Mo: 0.40 to 2.00%; V: 0.05 to 0.25%; Nb: 0.010 to 0.040%; Ti: 0.002 to 0.050%; sol. Al: 0.005 to 0.10%; N: 0.007% or less; B: 0.0001 to 0.0035%; and Ca: 0 to 0.005%; and a balance being Fe and impurities. In a microstructure of the low alloy oil-well steel pipe, a number of cementite particles each of which has an equivalent circle diameter of 200 nm or more is 100 particles/100 ?m2 or more. The above low alloy oil-well steel pipe has a yield strength of 793 MPa or more.
    Type: Grant
    Filed: October 2, 2015
    Date of Patent: August 25, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Keiichi Kondo, Yuji Arai
  • Patent number: 10655200
    Abstract: 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)/15?Co/6+??0.70??(1) (3C+Mo+3Co)/(3Mn+Cr)?1.0??(2).
    Type: Grant
    Filed: August 30, 2017
    Date of Patent: May 19, 2020
    Assignee: Nippon Steel Corporation
    Inventors: Yuji Arai, Kengo Hata
  • Patent number: 10640843
    Abstract: Electric resistance welded steel pipe securing the high strength and high toughness demanded from oil well pipe in recent years. The metal structure in a region having a width of 0.5 mm in both the thickness directions from a reference point, when using a point defined as a point ¼ of the thickness in the thickness direction from the surface in the base material part of the steel as the reference point, consists of polygonal ferrite: 10 area % or less and a balance: bainitic ferrite. The thickness is 15 mm or more.
    Type: Grant
    Filed: February 15, 2016
    Date of Patent: May 5, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Tetsuo Ishitsuka, Shuji Iwamoto, Takashi Tsusue, Shunichi Kobayashi, Osamu Yoshida, Hideto Kawano
  • Patent number: 10640857
    Abstract: A steel contains, by weight: C: 0.2% to 0.5%, Si: 0.1% to 0.5%, Mn: 0.1% to 1%, P: 0.03% or less, S: 0.005% or less, Cr: 0.3% to 1.5%, Mo: 0.3% to 1%, Al: 0.01% to 0.1%, V: 0.1% to 0.5%, Nb: 0.01% to 0.05%, Ti: 0 to 0.01%, W: 0.3% to 1%, N: 0.01% or less, the remainder of the chemical composition of the steel being constituted by Fe and impurities or residuals resulting from or necessary to steel production and casting processes. The steel can be used to produce seamless tubes with a yield strength after heat treatment of 861 MPa or more.
    Type: Grant
    Filed: November 25, 2009
    Date of Patent: May 5, 2020
    Assignee: Vallourec Oil & Gas France
    Inventor: Alfredo De Lima Figueiredo
  • Patent number: 10570487
    Abstract: A rolled steel material for fracture splitting connecting rods consists of, C: 0.30 to 0.40%, Si: 0.60 to 1.00%, Mn: 0.50 to 1.00%, P: 0.04 to 0.07%, S: 0.04 to 0.13%, Cr: 0.10 to 0.30%, V: 0.05 to 0.14%, Ti: more than 0.15% to 0.20% or less, N: 0.002 to 0.020%, and optionally may contain Cu, Ni, Mo, Pb, Te, Ca, and Bi, with the balance being Fe and impurities. fn1, defined by Formula (1), ranges from 0.65 to 0.80. Relative to the V content in the steel material, a V content in coarse precipitates having a particle size of 200 nm or more is 70% or less, and relative to the Ti content in the steel material, a Ti content in the coarse precipitates is 50% or more.
    Type: Grant
    Filed: October 17, 2014
    Date of Patent: February 25, 2020
    Assignees: NIPPON STEEL CORPORATION, HONDA MOTOR CO., LTD.
    Inventors: Motoki Takasuga, Yusuke Miyakoshi, Tatsuya Hasegawa, Hideki Matsuda, Masashi Kawakami, Isamu Saito
  • Patent number: 10563793
    Abstract: Provided is a low alloy oil-well steel pipe having a yield strength of 827 MPa or more, and an excellent SSC resistance. The low alloy oil-well steel pipe according to the present invention consisting of: in mass %, C: more than 0.35 to 0.65%; Si: 0.05 to 0.50%; Mn: 0.10 to 1.00%; Cr: 0.40 to 1.50%; Mo: 0.50 to 2.00%; V: 0.05 to 0.25%; Nb: 0.01 to 0.040%; sol.Al: 0.005 to 0.10%; N: 0.007% or less; Ti: 0 to 0.012%; Ca: 0 to 0.005%; and a balance being Fe and impurities, the impurities including: P: 0.020% or less; S: 0.002% or less; O: 0.006% or less; Ni: 0.10% or less; Cu: 0.03% or less; and B: 0.0005% or less, wherein in a microstructure, a number of cementite particles each of which has an equivalent circle diameter of 200 nm or more is 200 particles/100 ?m2 or more, and a yield strength is 827 MPa or more.
    Type: Grant
    Filed: July 21, 2015
    Date of Patent: February 18, 2020
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Keiichi Kondo, Yuji Arai
  • Patent number: 10544476
    Abstract: 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.
    Type: Grant
    Filed: October 7, 2015
    Date of Patent: January 28, 2020
    Assignee: JFE Steel Corporation
    Inventors: Shunsuke Sasaki, Tatsuro Katsumura, Hiroki Ushida, Yasushi Kato
  • Patent number: 10472690
    Abstract: Provided is a high-strength seamless steel pipe having the composition which contains, by mass %, 0.20 to 0.50% C, 0.05 to 0.40% Si, 0.3 to 0.9% Mn, 0.015% or less P, 0.005% or less S, 0.005 to 0.1% Al, 0.008% or less N, 0.6 to 1.7% Cr, 0.4 to 1.0% Mo, 0.01 to 0.30% V, 0.01 to 0.06% Nb, 0.0003 to 0.0030% B, and 0.0030% or less O (oxygen). The high-strength seamless steel pipe has the microstructure where a volume fraction of a tempered martensitic phase is 95% or more, and prior austenitic grains have a grain size number of 8.5 or more, and a segregation degree index Ps which is defined by a formula Ps=8.1 (XSi+XMn+XMo)+1.2XP relating to XM which is a ratio between a segregated portion content and an average content is set to less than 65.
    Type: Grant
    Filed: August 20, 2015
    Date of Patent: November 12, 2019
    Assignee: JFE Steel Corporation
    Inventors: Masao Yuga, Mitsuhiro Okatsu, Kazuki Fujimura, Yasuhide Ishiguro
  • Patent number: 10407748
    Abstract: A high-carbon steel sheet has a chemical composition represented by, in mass %, C: 0.60% to 0.90%, Mn: 0.30% to 1.50%, and Cr: 0.20% to 1.00%, and others, and has a structure represented by a concentration of Mn contained in cementite: 2% or more and 8% or less, a concentration of Cr contained in cementite: 2% or more and 8% or less, an average grain diameter of ferrite: 10 ?m or more and 50 ?m or less, an average particle diameter of cementite: 0.3 ?m or more and 1.5 ?m or less, and a spheroidized ratio of cementite: 85% or more.
    Type: Grant
    Filed: November 21, 2014
    Date of Patent: September 10, 2019
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Kengo Takeda, Toshimasa Tomokiyo, Yasushi Tsukano, Takashi Aramaki
  • Patent number: 10407758
    Abstract: A steel for oil country tubular goods includes, as a chemical composition, by mass %, C, Si, Mn, Al, Mo, P, S, O, N, and a balance containing Fe and impurities, wherein a full width at half maximum HW of a crystal plane corresponding to a (211) crystal plane of an ? phase and a carbon content expressed in mass % in the chemical composition satisfy HW×C1/2?0.38, the carbon content and a molybdenum content expressed in mass % in the chemical composition satisfy C×Mo?0.6, a number of M2C carbides having a hexagonal crystal structure and having an equivalent circle diameter of 1 nm or more is 5 pieces or more per one square micron, and an yield strength is 758 MPa or more.
    Type: Grant
    Filed: June 17, 2013
    Date of Patent: September 10, 2019
    Assignee: NIPPON STEEL CORPORATION
    Inventors: Tomohiko Omura, Yuji Arai, Kaori Kawano, Akihiro Sakamoto, Kazuo Okamura, Kenji Yamamoto, Keiichi Kondo, Koji Nagahashi, Masanao Seo
  • Patent number: 10370734
    Abstract: A heating step, in which a stainless member is heated to a temperature within or above a heating phase-transformation temperature range (Ar) in which the stainless member is phase-transformed, is executed. A cooling step in which the stainless member heated in the heating step is cooled to a temperature below a cooling phase-transformation temperature range (Mr) in which the stainless member is phase-transformed, is executed. In the cooling step, cooling of the stainless member is suppressed in a control temperature range including the cooling phase-transformation temperature range (Mr).
    Type: Grant
    Filed: September 29, 2014
    Date of Patent: August 6, 2019
    Assignee: MITSUBISHI HITACHI POWER SYSTEMS, LTD.
    Inventors: Kohei Hatano, Hiroharu Oyama, Yasuo Matsunami, Naoyuki Umezu, Shuhei Kuroki, Hidetaka Haraguchi, Takumi Matsumura, Motonari Machida
  • Patent number: 10287645
    Abstract: A steel has a chemical composition consisting of, by mass percent, C: 0.15-0.65%, Si: 0.05-0.5%, Mn: 0.1-1.5%, Cr: 0.2-1.5%, Mo: 0.1-2.5%, Ti: 0.005-0.50%, Al: 0.001-0.50%, and optionally at least one element selected from Nb: ?0.4%, V: ?0.5%, and B: ?0.01%, Ca: ?0.005%, Mg: ?0.005%, and REM: ?0.005%, and the balance of Fe and impurities, wherein Ni, P, S, N and O as impurities are Ni: ?0.1%, P: ?0.04%, S: ?0.01%, N: ?0.01%, and O: ?0.01%. The steel is hot-worked into a shape and then sequentially subjected to heating the steel to a temperature exceeding the Ac1 transformation point and lower than the Ac3 transformation point and cooling. Then, a step of reheating the steel to a temperature not lower than the Ac3 transformation point and quenching the steel by rapid cooling, and a step of tempering the steel at a temperature not higher than the Ac1 transformation point are performed.
    Type: Grant
    Filed: February 26, 2013
    Date of Patent: May 14, 2019
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Keiichi Kondo, Yuji Arai
  • Patent number: 10094008
    Abstract: A seamless steel pipe has a yield strength of 400 MPa or less and excellent HIC resistance. The seamless steel pipe includes: a chemical composition consisting, in mass %, of, C: 0.01 to 0.20%, Si: 0.05 to 0.50%, Mn: 0.3 to 2.0%, P: 0.02% or less, S: 0.01% or less, Cr: 0.02 to 0.2%, sol.Al: 0.001 to 0.100%, O: 0.0050% or less, N: 0.0100% or less, Ca: 0 to 0.0050%, Ti: 0 to 0.012%, and Nb: 0 to 0.012%, the balance being Fe and impurities; and a structure consisting, in area ratio, of 10 to 50% of ferrite and 0 to less than 5% of pearlite, the balance being tempered bainite and/or tempered martensite, and the number of inclusions each having a grain diameter of 50 mm or more is not more than 15 per 100 mm2, and the seamless steel pipe has a yield strength of 400 MPa or less.
    Type: Grant
    Filed: June 23, 2014
    Date of Patent: October 9, 2018
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Keiichi Kondo, Yuji Arai, Kenji Kobayashi
  • Patent number: 10006109
    Abstract: A non-oriented electrical steel sheet having a high magnetic flux density and a low iron loss at not only a commercial frequency but also a high frequency zone, which has a chemical composition including C: not more than 0.0050 mass %, Si: more than 1.5 mass % but not more than 5.0 mass %, Mn: not more than 0.10 mass %, sol. Al: not more than 0.0050 mass, P: more than 0.040 mass % but not more than 0.2 mass %, S: not more than 0.0050 mass %, N: not more than 0.0040 mass % and Ca: 0.001-0.01 mass % and the remainder being Fe and inevitable impurities and a compositional ratio of CaO in oxide-based inclusions existing in a steel sheet of not less than 0.4 and/or a compositional ratio of Al2O3 of not less than 0.3, and a hot rolled steel sheet used as a raw steel material thereof.
    Type: Grant
    Filed: August 11, 2014
    Date of Patent: June 26, 2018
    Assignee: JFE STEEL CORPORATION
    Inventors: Tadashi Nakanishi, Shinji Koseki, Yoshihiko Oda, Hiroaki Toda
  • Patent number: 9651175
    Abstract: There is provided a seamless steel pipe for line pipe, wherein a chemical composition consists, by mass percent, of C: 0.03-0.10%, Si: ?0.50%, Mn: 1.0-2.0%, P: ?0.050%, S: ?0.005%, Cr: 0.05-1.0%, Mo: 0.01-0.30%, Al: 0.001-0.10%, N: ?0.01%, Ni: 0.04-2.0%, Ca: 0.0005-0.0050%, Cu: 0-2.0%, Ti: 0-0.05%, Nb: 0-0.05%, V: 0-0.10%, the balance: Fe and impurities, and satisfies the conditions of Cu+Ni: ?0.10%, and Mo+V: ?0.30%, wherein in a scale formed on the surface of the steel pipe, metal particles consisting mainly of Ni or Cu having an average circle-equivalent diameter of 0.1-5 ?m exist, and a distance from a boundary between the base metal of the steel pipe and the scale to a region in which the metal particles do not exist is 20 ?m or longer.
    Type: Grant
    Filed: June 13, 2014
    Date of Patent: May 16, 2017
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Yuji Arai, Yukimasa Ueda, Kei Murata, Yasuyoshi Hidaka
  • Patent number: 9273383
    Abstract: A steel contains, by weight: C: 0.3% to 0.5%, Si: 0.1% to 0.5%, Mn: 1% or less, P: 0.03% or less, S: 0.005% or less, Cr: 0.3% to 1%, Mo: 1% to 2%, W: 0.3% to 1%, V: 0.03% to 0.25%, Nb: 0.01% to 0.15%, Al: 0.01% to 0.1%, the remainder of the chemical composition of the steel being constituted by Fe and impurities or residuals resulting from or necessary to steel production and casting processes. The steel can be used to produce seamless tubes for hydrocarbon wells with a yield strength after heat treatment of 862 MPa or more or even 965 MPa or more.
    Type: Grant
    Filed: May 19, 2011
    Date of Patent: March 1, 2016
    Assignee: VALLOUREC OIL AND GAS FRANCE
    Inventors: Laurent Delattre, Herve Marchebois, Michel Piette, Christoph Bosch, Michaela Hoerstemeier, Joachim Konrad
  • Patent number: 9175371
    Abstract: The present invention provides a steel which simultaneously satisfies a plurality of characteristics, specifically, a steel for tubes with excellent sulfide stress cracking resistance, including, C: 0.2 to 0.7%; Si: 0.01 to 0.8%; Mn: 0.1 to 1.5%; S: not more than 0.005%; P: not more than 0.03%; Al: 0.0005 to 0.1%; Ti: 0.005 to 0.05%; Ca: 0.0004 to 0.005%; N: not more than 0.007%; Cr: 0.1 to 1.5%; and Mo: 0.2 to 1.0%; the balance being Fe, Mg and impurities, being characterized in that: the content of Mg is not less than 1.0 ppm and not more than 5.0 ppm; and inclusions of not less than 50% of the total number of those in steel have such a morphology that Mg—Al—O-based oxides exist at the central part of the inclusion, Ca—Al-based oxides enclose the Mg—Al—O-based oxides, and Ti-containing-carbonitrides further exist on a periphery of the Ca—Al-based oxides.
    Type: Grant
    Filed: May 25, 2011
    Date of Patent: November 3, 2015
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Mitsuhiro Numata, Tomohiko Omura, Masayuki Morimoto, Toru Takayama, Atsushi Soma
  • Patent number: 9175360
    Abstract: There is provided a method for manufacturing a seamless steel pipe for line pipe, capable of improving the toughness of the seamless steel pipe for line pipe. A round billet having a chemical composition, by mass percent, of C: 0.02 to 0.15%, Si: at most 0.5%, and Mn: 0.5 to 2.5%, the balance being Fe and impurities, is heated. The heated round billet is piercing-rolled to produce a hollow shell. The hollow shell is elongated and rolled and sized to produce a seamless steel pipe. The seamless steel pipe is water cooled, and the water cooling is stopped when the temperature of the seamless steel pipe reaches at most 450° C. The water-cooled seamless steel pipe is quenched, and the quenched seamless steel pipe is tempered.
    Type: Grant
    Filed: July 2, 2012
    Date of Patent: November 3, 2015
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Keisuke Hitoshio, Kunio Kondo, Yuji Arai
  • Patent number: 9017494
    Abstract: A high-strength seamless steel pipe for oil wells excellent in sulfide stress cracking resistance which comprises, on the percent by mass basis, C: 0.1 to 0.20%, Si: 0.05 to 1.0%, Mn: 0.05 to 1.0%, Cr: 0.05 to 1.5%, Mo: 0.05 to 1.0%, Al: 0.10% or less, Ti: 0.002 to 0.05% and B: 0.0003 to 0.005%, with a value of equation “C+(Mn/6)+(Cr/5)+(Mo/3)” of 0.43 or more, with the balance being Fe and impurities, and in the impurities P: 0.025% or less, S: 0.010% or less and N: 0.007% or less. The seamless steel pipe may contain a specified amount of one or more element(s) of V and Nb, and/or a specified amount of one or more element(s) of Ca, Mg and REM. The seamless steel pipe can be produced at a low cost by adapting an in-line tube making and heat treatment process having a high production efficiency since a reheating treatment for refinement of grains is not required.
    Type: Grant
    Filed: August 18, 2011
    Date of Patent: April 28, 2015
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Yuji Arai, Tomohiko Omura, Keiichi Nakamura
  • Patent number: 9005379
    Abstract: The present invention relates to a process for producing a pipe, particularly for supplying fuel to an engine, comprising the steps of: prearranging a pipe made of stainless steel (1), executing a hot-pressing operation at at least one end (3) of the pipe (1); and subjecting the at least one end (3) of the pipe (1) to heat treatment, followed by cooling.
    Type: Grant
    Filed: June 10, 2009
    Date of Patent: April 14, 2015
    Assignee: Chesini Meccanica S.R.L.
    Inventor: Natale Chesini
  • Publication number: 20150083282
    Abstract: There is provided a seamless steel pipe having high strength and high toughness even if having a thick wall. A seamless steel pipe according to the present embodiment consists of: in mass %, C: 0.03 to 0.08%, Si: not more than 0.25%, Mn: 0.3 to 2.0%, P: not more than 0.05%, S: not more than 0.005%, Al: 0.001 to 0.10%, Cr: 0.02 to 1.0%, Ni: 0.02 to 1.0%, Mo: 0.02 to 0.8%, N: 0.002 to 0.008%, Ca: 0.0005 to 0.005%, and Nb: 0.01 to 0.1%, the balance being Fe and impurities, and has a wall thickness of not less than 50 mm.
    Type: Application
    Filed: April 10, 2013
    Publication date: March 26, 2015
    Inventors: Yukimasa Ueda, Yuji Arai
  • Patent number: 8974610
    Abstract: A high-strength welded steel pipe is obtained by welding a seam weld portion of a steel plate that are formed in a pipe shape. In the high-strength welded steel pipe, a base metal of the steel plate includes, by mass %, C: 0.010% to 0.080%, Si: 0.01% to 0.50%, Mn: 0.50% to 2.00%, S: 0.0001% to 0.0050%, Ti: 0.003% to 0.030%, Mo: 0.05% to 1.00%, B: 0.0003% to 0.0100%, O: 0.0001% to 0.0080%, N: 0.006% to 0.0118%, P: limited to 0.050% or less, Al: limited to 0.008% or less, and the balance of Fe and inevitable impurities, Ceq is 0.30 to 0.53, Pcm is 0.10 to 0.20, [N]?[Ti]/3.4 is less than 0.003, the average grain size of the prior ? grains in heat affected zones in the steel plate is 250 ?m or less, and the prior ? grains include bainite and intragranular bainite.
    Type: Grant
    Filed: February 4, 2011
    Date of Patent: March 10, 2015
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Taishi Fujishiro, Takuya Hara, Yoshio Terada, Shinya Sakamoto, Hitoshi Asahi
  • Publication number: 20150050513
    Abstract: The present invention describes a method of manufacturing a near-net shaped hollow shaft useful for high power applications such as gearboxes for wind energy industry. The method involves providing a concast bloom (of a round or rectangular or of any polygonal cross section) or an as-cast round ingot from which a hollow perform is prepared using hollow die punching, followed by process of heat treatment, proof-machining and stress relieving.
    Type: Application
    Filed: December 27, 2012
    Publication date: February 19, 2015
    Inventor: Babasaheb Neelkanth KALYANI
  • Publication number: 20150041030
    Abstract: A steel has a chemical composition consisting of, by mass percent, C: 0.15-0.65%, Si: 0.05-0.5%, Mn: 0.1-1.5%, Cr: 0.2-1.5%, Mo: 0.1-2.5%, Ti: 0.005-0.50%, Al: 0.001-0.50%, and optionally at least one element selected from Nb: ?0.4%, V: ?0.5%, and B: ?0.01%, Ca: ?0.005° A, Mg: ?0.005%, and REM: ?0.005%, and the balance of Fe and impurities, wherein Ni, P, S, N and O as impurities are Ni: ?0.1%, P: ?0.04%, S: ?0.01%, N: ?0.01%, and O: ?0.01%. The steel is hot-worked into a shape and then sequentially subjected to heating the steel to a temperature exceeding the Ac1 transformation point and lower than the Ac3 transformation point and cooling. Then, a step of reheating the steel to a temperature not lower than the Ac3 transformation point and quenching the steel by rapid cooling, and a step of tempering the steel at a temperature not higher than the Ac1 transformation point are performed.
    Type: Application
    Filed: February 26, 2013
    Publication date: February 12, 2015
    Inventors: Keiichi Kondo, Yuji Arai
  • Patent number: 8926771
    Abstract: Process for manufacturing seamless precision steel tubes with improved isotropic toughness at low temperature for hydraulic cylinders comprising the following steps; —(i) providing a steel having a composition comprising 0.06-0.15% by weight of carbon, 0.30-2.5% by weight of Mn, and 0.10-0.
    Type: Grant
    Filed: June 29, 2006
    Date of Patent: January 6, 2015
    Assignee: Tenaris Connections Limited
    Inventors: Gianmario Agazzi, Emanuele Paravicini Bagliani, Andrea Poli
  • Publication number: 20140352836
    Abstract: A seamless steel pipe has a composition containing, by mass %, C: 0.15 to 0.50%, Si: 0.1 to 1.0%, Mn: 0.3 to 1.0%, P: 0.015% or less, S: 0.005% or less, Al: 0.01 to 0.1%, N: 0.01% or less, Cr: 0.1 to 1.7%, Mo: 0.40 to 1.1%, V: 0.01 to 0.12%, Nb: 0.01 to 0.08%, Ti: 0.03% or less, and B: 0.0005 to 0.003%, a structure composed of a tempered martensite phase as a main phase with a prior austenite grain size of 8.5 or more, and a hardness distribution in which in four portions 90° apart from each other in the circumferential direction, hardness is 295 HV10 or less in any one of an inner surface-side region at 2.54 to 3.81 mm from the inner surface of the pipe, an outer surface side-region at the same distance from the outer surface of the pipe, and a center of the thickness.
    Type: Application
    Filed: December 18, 2012
    Publication date: December 4, 2014
    Applicant: JFE STEEL CORPORATION
    Inventors: Kenichiro Eguchi, Yasuhide Ishiguro, Yukio Miyata
  • Patent number: 8871039
    Abstract: The present invention provides a thick welded steel pipe excellent in low temperature toughness in which contents of Mn and Mo satisfy (Expression 1) below, Pcm obtained by (Expression 2) below is 0.16 to 0.19, and a metal structure of a base material steel plate consists of ferrite being 30 to 95% in an area ratio and a low temperature transformation structure, and in a metal structure of a coarse-grained HAZ, an area ratio of grain boundary ferrite is 1.5% or more, the total area ratio of the grain boundary ferrite and intragranular ferrite is not less than 11% nor more than 90%, an area ratio of MA is 10% or less, and its balance is composed of bainite. 1.2325?(0.85×[Mn]?[Mo])?1.5215??(Expression 1) and Pcm=[C]+[Si]/30+([Mn]+[Cu]+[Cr])/20+[Ni]/60+[Mo]/15+[V]/10??(Expression 2).
    Type: Grant
    Filed: September 13, 2011
    Date of Patent: October 28, 2014
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Yasuhiro Shinohara, Takuya Hara, Naoki Doi, Eiichi Yamashita
  • Patent number: 8852367
    Abstract: A method of production of high-strength hollow bodies from multiphase martensitic steels includes a heating process, a forming process and a cooling process. A heating device heats hollow steel stock to the austenitic temperature of the material from which the stock is made. The stock is then converted by deformation in a forming device into a hollow body having the final shape. A cooling device thereafter cools the hollow body such that the material with the original austenite microstructure refined by deformation during the forming process cools to a temperature at which incomplete transformation of austenite to martensite occurs. The retained austenite stabilization is performed in an annealing device by diffusion-based carbon partitioning within the material from which the hollow body is made. The hollow body is cooled in a cooling device to ambient temperature after stabilization.
    Type: Grant
    Filed: February 1, 2012
    Date of Patent: October 7, 2014
    Assignee: Zapadoceska Univerzita v Plzni
    Inventors: Bohuslav Ma{hacek over (s)}ek, Hana Jirková, Pavel Hronek, Ctibor {hacek over (S)}tádler, Miroslav Urbánek
  • Patent number: 8845830
    Abstract: A steel pipe with a wall thickness over 30 mm is subjected to heat treatment of quenching and tempering using a temperature range of at least not less than 750° C. during the heating stage, makes it possible to obtain a heavy-wall seamless steel pipe having excellent toughness by resulting grain refinement. Quenching is by performing water cooling after heating the steel pipe to a temperature in the range of not less than 900° C. to not more than 1000° C. by using, as a heating means, induction heating at a frequency of not more than 200 Hz. Tempering is performed at a temperature in the range of not less than 500° C. to not more than 750° C. Preferably, after the heating by induction heating, a soaking treatment is performed in the temperature range of not less than 900° C. to not more than 1000° C. for 10 minutes or less followed by water cooling.
    Type: Grant
    Filed: January 20, 2012
    Date of Patent: September 30, 2014
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Kunio Kondo, Yuji Arai
  • Patent number: 8821653
    Abstract: Embodiments of the present disclosure comprise carbon steels and methods of manufacturing thick walled pipes (wall thickness greater than or equal to about 35 mm) there from. In one embodiment, a steel composition is processed that yields an average prior austenite grain size greater than about 15 or 20 ?m and smaller than about 100 ?m. Using this composition, a quenching sequence is provided that yields a microstructure of greater than or equal to about 50% by volume, and less than or equal to about 50% by volume, lower bainite, without substantial ferrite, upper bainite, or granular bainite. After quenching, pipes may be tempered. The quenched and tempered pipes may exhibit yield strengths greater than about 450 MPa (65 ksi) or 485 (70 ksi). Mechanical property measurements find the quenched and tempered pipes suitable for 450 MPa grade and 485 MPa grade, and resistance to sulfide stress corrosion cracking.
    Type: Grant
    Filed: February 6, 2012
    Date of Patent: September 2, 2014
    Assignee: Dalmine S.p.A.
    Inventors: Ettore Anelli, Mariano Armengol, Paolo Novelli, Federico Tintori
  • Patent number: 8758528
    Abstract: The present invention provides a high-strength steel plate having excellent resistance to cutting crack, excellent Charpy absorbed energy, excellent DWTT properties, a low yield ratio, and a tensile strength of 900 MPa or more, a method of producing the steel plate, and a high-strength steel pipe using the steel plate. As solving means, a steel plate contains, by % by mass, 0.03 to 0.12% of C, 0.01 to 0.5% of Si, 1.5 to 3% of Mn, 0.01 to 0.08% of Al, 0.01 to 0.08% of Nb, 0.005 to 0.025% of Ti, 0.001 to 0.01% of N, and at least one component of 0.01 to 2% of Cu, 0.01 to 3% of Ni, 0.01 to 1% of Cr, 0.01 to 1% of Mo, and 0.01 to 0.1% of V; wherein the contents of Ca, O, and S satisfy the equation below; the microstructure includes ferrite and a second hard phase, the area fraction of ferrite being 10 to 50%; cementite in the second phase has an average grin size of 0.5 ?m or less; and the total amount of Nb and the like contained in carbides thereof present in steel is 10% or less of the total content in steel.
    Type: Grant
    Filed: March 30, 2006
    Date of Patent: June 24, 2014
    Assignee: JFE Steel Corporation
    Inventors: Junji Shimamura, Shigeru Endo, Mitsuhiro Okatsu
  • Patent number: 8709174
    Abstract: A seamless steel pipe for line pipe having high strength and high toughness contains, by mass percent, C: 0.02 to 0.10%, Si: at most 0.5%, Mn: 0.5 to 2.0%, Al: 0.01 to 0.1%, P: at most 0.03%, S: at most 0.005%, Ca: at most 0.005%, and N: at most 0.007%, and further contains at least one selected from a group consisting of Ti: at most 0.008%, V: less than 0.06%, and Nb: at most 0.05%, the balance being Fe and impurities. A carbon equivalent Ceq defined by Formula (1) is at least 0.38, a content of Ti, V and Nb satisfies Formula (2), and the size of carbo-nitride containing at least one of Ti, V, Nb and Al is at most 200 nm, Ceq=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15??(1) Ti+V+Nb<0.06??(2).
    Type: Grant
    Filed: September 11, 2012
    Date of Patent: April 29, 2014
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Yuji Arai, Keisuke Hitoshio
  • Patent number: 8696834
    Abstract: A method for suppressing shock and storage cracking when manufacturing seamless steel pipes comprises hot piercing and hot rolling a billet consisting of, by mass percent controlled amounts of C, Si, Mn, Cr, Mo, Ti, and Al, with the balance being Fe and impurities of Ni, P, S, N, and O also in controlled amounts. Further heat treatment is performed, wherein a hot rolled steel pipe is direct quenched from a temperature of not lower than the Ar3 transformation point and the pipe is then subjected to heat treatment at a temperature of not lower than 450° C. and not higher than the Ac1 transformation point in heat treatment equipment for performing direct quenching. The steel pipe subjected to the heat treatment is reheated, quenched from a temperature of not lower than the Ac3 transformation point, and tempered at a temperature of not higher than the Ac1 transformation point.
    Type: Grant
    Filed: September 20, 2011
    Date of Patent: April 15, 2014
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Keiichi Kondo, Toshiharu Abe, Kunio Kondo, Yuichi Yano, Yuji Arai
  • Patent number: 8685182
    Abstract: This high-strength steel pipe includes, by mass %, C: 0.02% to 0.09%, Mn: 0.4% to 2.5%, Cr: 0.1% to 1.0%, Ti: 0.005% to 0.03%, Nb: 0.005% to 0.3%, and a balance consisting of Fe and inevitable impurities, in which Si, Al, P, S, and N are limited to 0.6% or less, 0.1% or less, 0.02% or less, 0.005% or less, 0.008% or less, respectively, the bainite transformation index BT is 650° C. or less, and the microstructure thereof is a single bainite microstructure including first bainite and second bainite, the first bainite being a gathered microstructure of bainitic ferrite including no carbide, and the second bainite being a mixed microstructure of bainitic ferrite including no carbide and cementite between the bainitic ferrites.
    Type: Grant
    Filed: June 10, 2010
    Date of Patent: April 1, 2014
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Kensuke Nagai, Yasuhiro Shinohara, Shinya Sakamoto, Takuya Hara, Hitoshi Asahi
  • Patent number: 8636856
    Abstract: Embodiments of the present disclosure comprise carbon steels and methods of manufacture. In one embodiment, quenching and tempering procedure is performed in which a selected steel composition is formed and heat treated to yield a slightly tempered microstructure having a fine carbide distribution. In another embodiment, a double austenizing procedure is disclosed in which a selected steel composition is formed and subjected to heat treatment to refine the steel microstructure. In one embodiment, the heat treatment may comprise austenizing and quenching the formed steel composition a selected number of times (e.g., 2) prior to tempering. In another embodiment, the heat treatment may comprise subjecting the formed steel composition to austenizing, quenching, and tempering a selected number of times (e.g., 2). Steel products formed from embodiments of the steel composition in this manner (e.g., seamless tubular bars and pipes) will possess high yield strength, e.g.
    Type: Grant
    Filed: February 18, 2011
    Date of Patent: January 28, 2014
    Assignee: Siderca S.A.I.C.
    Inventors: Eduardo Altschuler, Teresa Perez, Edgardo Lopez, Constantino Espinosa, Gonzalo Gomez
  • Patent number: 8613817
    Abstract: The present invention is to provide a method for producing duplex stainless steel seamless pipe in which a duplex stainless steel billet can be inhibited from generating an oxide scale on the surface thereof during heating and the generation of outer surface flaw can also be prevented. The billet is heated in the a heating furnace for 1.5 hours or more and 4.0 hours or less at a heating temperature of 1250° C. or more and 1320° C. or less while regulating the average concentration of sulfur dioxide (SO2) gas in the atmosphere within the furnace to 0.01 volume % or less.
    Type: Grant
    Filed: March 23, 2007
    Date of Patent: December 24, 2013
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Naoya Hirase, Tetsuya Nakanishi, Kazuhiro Shimoda, Hirokazu Okada, Tomio Yamakawa, Yasuyoshi Hidaka
  • Patent number: 8608871
    Abstract: There is provided a high-strength steel tube having excellent chemical conversion treatability and excellent formability and a method for manufacturing the high-strength steel tube. More specifically, in processing a mother steel sheet containing, on the basis of mass percent, 0.05% or more C, more than 0.7% Si, and 0.8% or more Mn into a pipe shape, the sum total of absolute circumferential surface strains each applied in individual process steps of the processing is 5% or more as nominal strain. A welded steel tube thus manufactured using a steel sheet even containing more than 0.7% Si can have excellent chemical conversion treatability without mechanical grinding or chemical pickling treatment.
    Type: Grant
    Filed: October 7, 2009
    Date of Patent: December 17, 2013
    Assignees: JFE Steel Corporation, Honda Motor Co., Ltd.
    Inventors: Yasuhide Ishiguro, Akio Sato, Yasuhisa Shimizu
  • Patent number: 8585835
    Abstract: A high-strength steel machined product giving excellent hardenability has a metal microstructure with excellent balance of strength and toughness and high stability of retained austenite. The product is composed of an ultra-high low-alloy TRIP steel having a metal microstructure which contains an appropriate quantity of two or more of Cr, Mo, and Ni, and an appropriate quantity of one or more of Nb, Ti, and V, and having an appropriate value of carbon equivalent; the metal microstructure has a mother-phase structure composed mainly of lathy bainitic ferrite with a small amount of granular bainitic ferrite and polygonal ferrite, and has a secondary-phase structure composed of fine retained austenite and martensite.
    Type: Grant
    Filed: October 29, 2009
    Date of Patent: November 19, 2013
    Assignees: Usui Kokusai Sangyo Kaisha Limited, Shinshu University
    Inventors: Koh-ichi Sugimoto, Sho-hei Sato, Teruhisa Takahashi, Goro Arai
  • Patent number: 8512487
    Abstract: A seamless expandable oil country tubular article, which has a superior pipe expansion property in a expanding process at an expand ratio of more than about 30% although having a high strength such as a tensile strength (TS) of about 600 MPa or more, and a manufacturing method thereof, the seamless expandable oil country tubular goods being in an as-rolled state or being processed, optionally necessary, by inexpensive nonthermal-refining type heat treatment.
    Type: Grant
    Filed: October 18, 2004
    Date of Patent: August 20, 2013
    Assignee: JFE Steel Corporation
    Inventors: Yoshio Yamazaki, Yukio Miyata, Mitsuo Kimura, Kei Sakata, Masahito Tanaka
  • Patent number: 8496763
    Abstract: A seamless steel tube for an airbag accumulator which can be manufactured by heat treatment of normalizing without quenching and tempering and which has a tensile strength of at least 850 MPa and resistance to bursting at ?20° C. has a stee; composition comprising, in mass %, C: 0.08-0.20%, Si: 0.1-1.0%, Mn: 0.6-2.0%, P: at most 0.025%, S: at most 0.010%, Cr: 0.05-1.0%, Mo: 0.05-1.0%, Al: 0.002-0.10%, at least one of Ca: 0.0003-0.01%, Mg: 0.0003-0.01%, and REM (rare earth metals): 0.0003-0.01%, at least one of Ti: 0.002-0.1% and Nb: 0.002-0.1%, with Ceq which is defined by the following Equation (1) being in the range of 0.45-0.63, with the metallurgical structure being a mixed structure of ferrite+bainite: Ceq=C+Si/24+Mn/6+(Cr+Mo)/5+(Ni+Cu)/15??(1) wherein the symbol for each element in Equation (1) indicates the number expressing the mass percent of the element.
    Type: Grant
    Filed: April 24, 2009
    Date of Patent: July 30, 2013
    Assignee: Sumitomo Metal Industries, Ltd.
    Inventors: Yuji Arai, Takashi Takano
  • Patent number: 8414715
    Abstract: Embodiments of the present disclosure comprise carbon steels and methods of manufacture. In one embodiment, a double austenizing procedure is disclosed in which a selected steel composition is formed and subjected to heat treatment to refine the steel microstructure. In one embodiment, the heat treatment may comprise austenizing and quenching the formed steel composition a selected number of times (e.g., 2) prior to tempering. In another embodiment, the heat treatment may comprise subjecting the formed steel composition to austenizing, quenching, and tempering a selected number of times (e.g., 2). Steel products formed from embodiments of the steel composition in this manner (e.g., seamless tubular bars and pipes) will possess high yield strength, at least about 175 ksi (about 1200 MPa) while maintaining good toughness.
    Type: Grant
    Filed: February 18, 2011
    Date of Patent: April 9, 2013
    Assignee: Siderca S.A.I.C.
    Inventors: Eduardo Altschuler, Teresa Perez, Edgardo Lopez, Constantino Espinosa, Gonzalo Gomez
  • Patent number: 8404061
    Abstract: A component of an air-hardenable steel composed of (contents in mass %): C<0.20; Al<0.08; Si<1.00; Mn 1.20 to <2.50; P<0.020; S<0.015; N<0.0150; Cr 0.30 to <1.5; Mo 0.10 to <0.80; Ti 0.010 to <0.050; V 0.03 to <0.20; B 0.0015 to <0.0060, with the remainder being iron including the usual elements present in steel, is produced by heating a hot- or cold-rolled steel sheet or steel tube section to a temperature of ?blank=800 to 1050° C. and then forming the sheet or tube into a component in a forming tool. After removal from the tool, the component is cooled down in air while the component still has a temperature above ?removal=200° C. and below 800° C. The component achieves the required mechanical properties during air-cooling.
    Type: Grant
    Filed: June 21, 2010
    Date of Patent: March 26, 2013
    Assignee: Salzgitter Flachstahl GmbH
    Inventors: Michael Braun, Uwe Eggers, Cord Schäffner, Joachim Schöttler, Friedrich Luther, Stefan Mütze, Manuel Otto, Thorsten Reier
  • Publication number: 20130056115
    Abstract: An automobile chassis part which is excellent in low cycle fatigue characteristics, characterized by being formed by steel which contains, by mass %, C: 0.02 to 0.10%, Si: 0.05 to 1.0%, Mn: 0.3 to 2.5%, P: 0.03% or less, S: 0.01% or less, Ti: 0.005 to 0.1%, Al: 0.005 to 0.1%, N: 0.0005 to 0.006%, and B: 0.0001 to 0.01 and has a balance of Fe and unavoidable impurities, in which 80% or more of the part structure comprises a bainite structure and in which a portion where a ratio R/t of the thickness “t” and external surface curvature radius R is 5 or less has an X-ray half width of an (211) plane of 5 (deg) or less.
    Type: Application
    Filed: November 25, 2010
    Publication date: March 7, 2013
    Inventors: Takaaki Fukushi, Hideyuki Nakamura, Isao Anai
  • Patent number: 8366843
    Abstract: A method of manufacturing a 13Cr steel pipe which satisfies a hardness (HRC) of at most 22 with 13Cr grade L80 of American Petroleum Institute (API) standards, which is an indicator of a high strength, high yield ratio, and good corrosion resistance, is provided. A steel billet having a chemical composition comprising, in mass percent, C: 0.15-0.21%, Si: 0.16-1.0%, Mn: 0.35-1.0%, Cr: 10.5-14.0%, P: at most 0.020%, S: at most 0.0050%, Al: 0.025-0.050%, and a remainder of Fe and impurities is subjected to hot working with a finishing temperature of 800-960° C. to form a mother pipe, which is immediately quenched at a cooling rate of at least air cooling and then tempered by heating.
    Type: Grant
    Filed: March 27, 2007
    Date of Patent: February 5, 2013
    Assignee: Sumitomo Metal Industries, Ltd.
    Inventor: Nobuyuki Mori
  • Patent number: 8361256
    Abstract: A seamless steel pipe produced by heating a steel billet, which has a chemical composition C: 0.15 to 0.20%, Si: not less than 0.01% to less than 0.15%, Mn: 0.05 to 1.0%, Cr: 0.05 to 1.5%, Mo: 0.05 to 1.0%, Al?0.10%, V: 0.01 to 0.2%, Ti: 0.002 to 0.03%, B: 0.0003 to 0.005% and N: 0.002 to 0.01%, further optionally one or more of Ca, Mg and REM in a specific amount, under the provision that the conditions “C+(Mn/6)+(Cr/5)+(Mo/3)?0.43” and “Ti×N<0.0002?0.0006×Si” are satisfied, with the balance being Fe and impurities, wherein P?0.025%, S?0.010% and Nb<0.005% among the impurities, to a temperature of 1000 to 1250° C. followed by pipe-making rolling at a final rolling temperature 900 to 1050° C., and then quenching the resulting steel pipe directly from a temperature not lower than the Ar3 transformation point followed by tempering at a temperature range from 600° C.
    Type: Grant
    Filed: January 24, 2008
    Date of Patent: January 29, 2013
    Assignee: Sumitomo Metal Industries, Ltd.
    Inventors: Yuji Arai, Keiichi Nakamura