With Working At Or Below 120c Or Unspecified Cold Working Patents (Class 148/603)
  • Patent number: 11421294
    Abstract: A high strength steel sheet including, by weight, C: 0.001% to 0.004%, Si: 0.5% or less (excluding 0%), Mn: 1.2% or less (excluding 0%), P: 0.005% to 0.12%, S: 0.01% or less, N: 0.01% or less, acid soluble Al: 0.1% or less (excluding 0%), Ti: 0.01% to 0.04%, a remainder of Fe, and unavoidable impurities, wherein the contents of Ti, N, and S satisfy the following Relationship 1, a ratio (b/a) of an average random intensity ratio (b) of an orientation group of (111) [1-10] to (111) [?1-12] to an average random intensity ratio (a) of an orientation group of (001) [1-10] to (110) [1-10] at a point t/4 (where t is a thickness of the steel sheet) in a thickness direction of the steel sheet is 2.3 or more, and a bake hardenability (BH) of the steel sheet is 4 MPa or more.
    Type: Grant
    Filed: August 4, 2017
    Date of Patent: August 23, 2022
    Assignee: POSCO
    Inventors: Sang-Ho Han, Je-Woong Lee
  • Patent number: 11261935
    Abstract: Manufacturing a steel sheet for a steel belt includes hot rolling a steel slab containing, in mass %, 0.60 to 0.80% of C, 1.0% or less of Si, 0.10 to 1.0% of Mn, 0.020% or less P, 0.010% or less S, 0.1 to 1.0% of Cr, 0 to 0.5% of V, 0 to 0.1% of Ti, 0 to 0.1% of Nb, and 0 to 0.01% of B, the balance Fe and unavoidable impurities, under a finish hot rolling temperature of 800 to 900° C. An average cooling rate from finish rolling to coiling is 20° C. per second or more. A coiling temperature is 450 to 650° C. The hot-rolled slab is cold rolled with a total rolling reduction ratio of 40% or more and a reduction ratio per one pass of less than 12%, without performing a heat treatment. The cold-rolled slab is aged at 200 to 500° C. for 0.5 to 30 hours.
    Type: Grant
    Filed: January 10, 2019
    Date of Patent: March 1, 2022
    Assignee: NIPPON STEEL NISSHIN CO., LTD.
    Inventors: Satoshi Tagashira, Shoichi Koutani, Koji Omosako
  • Patent number: 11186889
    Abstract: A high-strength steel sheet contains, in mass %, C: 0.07 to 0.14%, Si: 0.65 to 1.65%, Mn: 1.8 to 2.6%, P: 0.05% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.0060% or less, Ti: 0.005 to 0.030%, B: 0.0002 to 0.0030%, and either or both of Cr: 0.01 to 0.40% and Mo: 0.01 to 0.50% and satisfies the expression (1); where: an average grain size of a ferrite phase is 1.5 ?m or less; an area ratio of the ferrite phase is 2% or more and 15% or less; an area ratio of a tempered martensite phase is 75% or more and 96% or less; and a total length per unit area of an interface between an untempered martensite phase and the ferrite phase and an interface between the untempered martensite phase and the tempered martensite phase is 6.3×108 ?m/m2 to 5.0×1011 ?m/m2.
    Type: Grant
    Filed: August 10, 2017
    Date of Patent: November 30, 2021
    Assignee: JFE Steel Corporation
    Inventors: Noriaki Kohsaka, Michitaka Sakurai, Yoshikazu Suzuki, Yoshimasa Himei
  • Patent number: 11136643
    Abstract: A high-strength steel sheet having a specified chemical composition and a method for producing the same. The steel sheet including a multi-phase structure including, by volume fraction, ferrite of 35% to 65%, residual austenite of 7% or less (including 0%), martensite of 20% to 60%, bainite of 20% or less (including 0%), the ferrite having an average crystal grain size of 8 ?m or less and an average aspect ratio of 3.5 or less, the martensite having an average crystal grain size of 3 ?m or less, and the bainite having an average crystal grain size of 3 ?m or less when contained. A standard deviation of Vickers hardness of the steel sheet being 30 or less when measured at 200 ?m intervals from a position of 100 ?m from a surface to a central portion in a thickness direction of the sheet.
    Type: Grant
    Filed: August 10, 2017
    Date of Patent: October 5, 2021
    Assignee: JFE STEEL CORPORATION
    Inventors: Katsutoshi Takashima, Koichi Taniguchi, Takashi Kobayashi, Hiroshi Matsuda, Rinsei Ikeda
  • Patent number: 11136642
    Abstract: A steel sheet, a plated steel sheet, and methods for producing a hot-rolled steel sheet, a cold-rolled full hard steel sheet, and a steel sheet. The steel sheet has a specified composition and a microstructure including 0 to 80% of polygonal ferrite and 20 to 100% of a total of martensite, bainite, and residual austenite in terms of an area ratio within 20 ?m of the steel sheet surface. The content of Mn in martensite present within 20 ?m of the steel sheet surface ([Mn]SM) and the content of Mn in a bulk ([Mn]B) satisfy [Mn]SM/[Mn]B?1.5. At a location 300 ?m from the steel sheet surface, an area ratio of the martensite is in a range of 20 to 50%.
    Type: Grant
    Filed: January 17, 2017
    Date of Patent: October 5, 2021
    Assignee: JFE STEEL CORPORATION
    Inventors: Hiroshi Hasegawa, Yoshimasa Funakawa
  • Patent number: 11059269
    Abstract: Disclosed are a hot dip coated steel and a method for manufacturing the same, the hot dip coated steel comprising a hot rolled steel and a hot dip coated layer formed on the surface of the hot rolled steel, wherein the hot rolled steel comprises: by wt %, 0.05-0.15% of C, 0.5% or less of Si (excluding 0%), 0.5-1.5% of Mn, 0.01-0.05% of Nb, 0.005-0.05% of V, 0.03% or less of P (excluding 0%), 0.015% of S or less (excluding 0%), 0.05% or less of Al (excluding 0%), 0.01% or less of N (excluding 0%), and the balance of Fe and inevitable impurities; 90 area % or more of ferrite as the microstructure thereof; and 5,000-15,000/?m2 of V-based precipitates.
    Type: Grant
    Filed: December 19, 2017
    Date of Patent: July 13, 2021
    Assignee: POSCO
    Inventor: Jin-You Kim
  • Patent number: 10995387
    Abstract: A weathering steel made by preparing a molten melt producing an as-cast carbon alloy steel strip with a corrosion index of at least 6.0 comprising, by weight, 0.02%-0.08% carbon, <0.6% silicon, 0.2%-2.0% manganese, <0.03% phosphorus, <0.01% sulfur, <0.01% nitrogen, 0.2%-0.5% copper, 0.01%-0.2% niobium, 0.01%-0.2% vanadium, 0.1%-0.4% chromium, 0.08%-0.25% nickel, <0.01% aluminum, and the remainder iron and impurities. The molten melt is solidified and cooled into a cast strip 4 mm in thickness in a non-oxidizing atmosphere. The strip is hot rolled in an austenitic temperature range above Ar3 to between 10% and 50% reduction, cooled at above 20° C./s and coiled below 700° C. to form a steel strip with a microstructure comprising bainite and acicular ferrite with more than 70% niobium in solid solution. Then, age hardening the strip resulting in a yield strength of at least 550 MPa and a total elongation of at least 8%.
    Type: Grant
    Filed: November 29, 2018
    Date of Patent: May 4, 2021
    Assignee: Nucor Corporation
    Inventors: James W. Watson, Tao Wang, Eric Young, Chad Baudendistel
  • Patent number: 10858717
    Abstract: A high strength steel sheet having excellent surface quality and formability with a tensile strength of 980 MPa or more and a TS-El balance of 30000 MPa % or more is provided. A high strength steel sheet comprises: a chemical composition containing C: 0.08% to 0.30%, Si: 2.0% or less, Mn: more than 3.0% and 10.0% or less, P: 0.05% or less, S: 0.01% or less, Al: 1.5% or less, Ti: 0.010% to 0.300%, and N: 0.0020% to 0.0100% in a range satisfying 1.1?(Ti+Mn1/2/400)/(0.01+5N)?6.0; and a microstructure including a retained austenite phase and a ferrite phase, wherein a ratio ?Mn/?Mn of an average Mn concentration (?Mn) of the retained austenite phase to an average Mn concentration (?Mn) of the ferrite phase is 1.5 or more.
    Type: Grant
    Filed: August 10, 2016
    Date of Patent: December 8, 2020
    Assignee: JFE STEEL CORPORATION
    Inventors: Kenji Tsuzumi, Yoshiyasu Kawasaki, Yuji Miki
  • Patent number: 10837075
    Abstract: A hot rolled and annealed ferritic stainless steel sheet includes a composition that contains, on a mass percent basis, 0.015% or less of C, 1.00% or less of Si, 1.00% or less of Mn, 0.040% or less of P, 0.010% or less of S, 12.0% or more and 23.0% or less of Cr, 0.20% or more and 1.00% or less of Al, 0.020% or less of N, 1.00% or more and 2.00% or less of Cu, and 0.30% or more and 0.65% or less of Nb, Si and Al being contained so as to satisfy expression (1) described below, the balance being Fe and incidental impurities, and the hot rolled and annealed ferritic stainless steel sheet having a Vickers hardness less than 205, Si?Al (1) (where in expression (1), Si represents the content of Si (% by mass), and Al represents the content of Al (% by mass)).
    Type: Grant
    Filed: February 3, 2015
    Date of Patent: November 17, 2020
    Assignee: JFE Steel Corporation
    Inventors: Tetsuyuki Nakamura, Hiroki Ota, Chikara Kami
  • Patent number: 10808293
    Abstract: To improve the formability of dual phase steels, the martensite phase is tempered. It may form a ferrite-carbide structure. The tempering step occurs after martensite has been formed in the dual phase steel. The tempering step can occur in a box annealing step or it can be performed in a continuous fashion, such as on a continuous annealing, continuous tempering heat treating, or continuous coating line. The tempering step can further comprise a temper rolling on a temper mill after the heating step.
    Type: Grant
    Filed: July 15, 2016
    Date of Patent: October 20, 2020
    Assignee: AK Steel Properties, Inc.
    Inventors: Robert J. Comstock, George A. Paraskos
  • Patent number: 10655201
    Abstract: A high-strength, cold-rolled steel sheet having a tensile strength of 980 MPa or more, the steel sheet having a chemical composition containing, by mass %, C: 0.070% to 0.100%, Si: 0.50% to 0.70%, Mn: 2.40% to 2.80%, P: 0.025% or less, S: 0.0020% or less, Al: 0.020% to 0.060%, N: 0.0050% or less, Nb: 0.010% to 0.060%, Ti: 0.010% to 0.030%, B: 0.0005% to 0.0030%, Sb: 0.005% to 0.015%, Ca: 0.0015% or less, Cr: 0.01% to 2.00%, Mo: 0.01% to 1.00%, Ni: 0.01% to 5.00%, Cu: 0.01% to 5.
    Type: Grant
    Filed: February 16, 2016
    Date of Patent: May 19, 2020
    Assignee: JFE STEEL CORPORATION
    Inventors: Nobusuke Kariya, Yoshihiko Ono, Yoshimasa Funakawa, Kazuma Mori, Reiko Sugihara
  • Patent number: 10563279
    Abstract: A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition including, by mass %, C: 0.060% or more and 0.150% or less, Si: 0.50% or more and 2.20% or less, Mn: 1.00% or more and 3.00% or less, and one or both of Ti: 0.001% or more and 0.200% or less and Nb: 0.001% or more and 0.200% or less, in which the contents of C, N, S, Ti, and Nb satisfy the equation 500?C*?1300. The steel sheet has a microstructure including ferrite in an amount of 20% or more and martensite in an amount of 5% or more, in terms of area ratio, such that the average grain size of the ferrite is 20.0 ?m or less and the inverse intensity ratio of ?-fiber for ?-fiber is 1.00 or more in the ferrite and the martensite.
    Type: Grant
    Filed: July 16, 2014
    Date of Patent: February 18, 2020
    Assignee: JFE STEEL CORPORATION
    Inventors: Hidekazu Minami, Takeshi Yokota, Kazuhiro Seto
  • Patent number: 10385431
    Abstract: A high strength steel sheet having a high Young's modulus, the steel sheet having a chemical composition including, by mass %, C: 0.060% or more and 0.150% or less, Si: 0.50% or more and 2.20% or less, Mn: 1.00% or more and 3.00% or less, Nb: 0.001% or more and 0.200% or less, and V: 0.001% or more and 0.200% or less, in which the contents of C, Nb, and V satisfy the equation 500?C*?1300. The steel sheet has a microstructure including ferrite in an amount of 20% or more and martensite in an amount of 5% or more, in terms of area ratio, such that the average grain size of the ferrite is 20.0 ?m or less and the inverse intensity ratio of ?-fiber for ?-fiber is 1.00 or more in each of the ferrite and the martensite.
    Type: Grant
    Filed: July 16, 2014
    Date of Patent: August 20, 2019
    Assignee: JFE STEEL CORPORATION
    Inventors: Hidekazu Minami, Takeshi Yokota, Kazuhiro Seto
  • Patent number: 10351942
    Abstract: In a high strength hot-dip galvannealed hot-rolled steel sheet that has an excellent hole expansibility suitable for a stretch flanging and preferably has a high yield ratio and a tensile strength of at least 650 MPa, a hot-rolled steel sheet used as a base material for plating has a chemical composition comprising: in mass %, C: from at least 0.01 and at most 0.20%; Si: at most 0.50%; Mn: from at least 0.01% to at most 1.30%; P: at most 0.05%; S: at most 0.01%; N: at most 0.01%; Al: at most 0.50%; and Ti: from at least 0.05% to at most 0.50%, and a steel structure consisting of a polygonal ferrite having at least 80 area % and the remainder containing one kind or two or more kinds selected from bainitic ferrite, bainite, pearlite, and cementite.
    Type: Grant
    Filed: September 11, 2012
    Date of Patent: July 16, 2019
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Takafumi Yokoyama, Shigeki Nomura
  • Patent number: 10272513
    Abstract: The ferritic stainless steel sheet contains, in mass%, C: 0.020% or less, Si: 0.6% or less, Mn: 0.5% or less, P: 0.04% or less, S: 0.010% or less, Al: 0.015% or more and 0.20% or less, Cr: 17.0% or more and 24.0% or less, Ni: less than 0.6%, N: 0.020% or less, Ca: 0.0002% or more and 0.0020% or less, and O: 0.0050% or less and further contains one or two selected from Ti: 0.01% or more and 0.45% or less and Nb: 0.01% or more and 0.55% or less, with the balance being Fe and unavoidable impurities. The ferritic stainless steel sheet satisfies (Ti+Nb×48/93)/(C+N)?8.0 (where Ti, Nb, C, and N represent the contents (% by mass) of these elements, respectively).
    Type: Grant
    Filed: May 12, 2015
    Date of Patent: April 30, 2019
    Assignee: JFE Steel Corporation
    Inventors: Junichiro Hirasawa, Shin Ishikawa, Chikara Kami
  • Patent number: 10253390
    Abstract: A method of making a cold-rolled steel plate has a chemical composition containing, on the basis of percent by mass, C from 0.03 to 0.12%, Si from 0 to 1.0%, Mn from 0.2 to 0.8%, P at 0.03% or less, S at 0.03% or less, and Al at 0.05% or less. The chemical composition further contains any one of Nb from 0.03 to 0.4% and V from 0.03 to 0.3%. These elements satisfy 5*C %?Si %+Mn %?1.5*Al %<1 within the aforementioned range of the corresponding content. A residue is formed of Fe and unavoidable impurities. An average diameter of particles of carbides containing any one of Nb, V and Ti as precipitates is from 20 to 100 nm. In this way, the chemical composition is regulated and the precipitates are dispersed finely and uniformly, thereby enhancing heat spot resistance and antiwear performance.
    Type: Grant
    Filed: April 27, 2017
    Date of Patent: April 9, 2019
    Assignee: NISSHIN STEEL CO., LTD.
    Inventors: Satoshi Tagashira, Masahito Suzuki, Tomohiro Imanaka
  • Patent number: 10246764
    Abstract: Manufacturing a cold-rolled steel plate, having a steel slab having the chemical composition containing, on the basis of percent by mass, C from 0.03 to 0.08%, Si from 0 to 1.0%, Mn from 0.2 to 0.8%, P at 0.03% or less, S at 0.01% or less, and Al at 0.05% or less so as to satisfy the following: formula (1) and at least one of Nb from 0.03 to 0.4%, V from 0.01 to 0.3%, and Ti from 0.01 to 0.3% so as to satisfy the following formula (2), with a residue being formed of Fe and unavoidable impurities. The steel slab is heated to 1200° C. or more and hot rolled to form a hot-rolled steel plate, which is wound from 550 to 700° C. to form a hot-rolled coil, and the hot-rolled coil is cold rolled or annealed and cold rolled, obtaining cross-sectional hardness from 200 to 350 HV.
    Type: Grant
    Filed: April 25, 2017
    Date of Patent: April 2, 2019
    Assignee: NISSHIN STEEL CO., LTD.
    Inventors: Satoshi Tagashira, Masahito Suzuki, Tomohiro Imanaka
  • Patent number: 10201953
    Abstract: A steel foil according to an aspect of the present invention includes a rolled steel foil; and a Ni having <111>//RD texture plated on an outermost layer of the rolled steel foil. Regarding the steel foil, a <111> pole density in an inverse pole figure of a rolling direction may be 3.0 or more and 6.0 or less.
    Type: Grant
    Filed: April 18, 2013
    Date of Patent: February 12, 2019
    Assignees: NIPPON STEEL & SUMITOMO METAL CORPORATION, NIPPON STEEL & SUMIKIN MATERIALS CO., LTD.
    Inventors: Kiyokazu Ishizuka, Yuji Kubo, Jun Nakatsuka, Shuji Nagasaki
  • Patent number: 10197109
    Abstract: A separator plate for use as a clutch plate for a multiplate wet clutch is formed of a steel plate. The steel plate has a chemical composition containing, on a basis of percent by mass, C from 0.03 to 0.08%, Si from 0 to 1.0%, Mn from 0.2 to 0.8%, P at 0.03% or less, S at 0.01% or less, and Al at 0.05% or less, so as to satisfy a formula, 5*C %?Si %+Mn %?1.5*Al %<1. In addition, the steel plate has the chemical component containing at least one of Nb from 0.03 to 0.4%, V from 0.01 to 0.3%, and Ti from 0.01 to 0.3%, so as to satisfy a formula, 0.04<(Nb %/1.4)+(V %/1.1)+Ti %<0.3. Then, an average diameter of particles of a carbide as a precipitate is controlled to be from 20 to 100 nm. The plate is formed by heating, hot rolling, winding and forming.
    Type: Grant
    Filed: May 3, 2017
    Date of Patent: February 5, 2019
    Assignee: NISSHIN STEEL CO., LTD.
    Inventors: Satoshi Tagashira, Masahito Suzuki, Tomohiro Imanaka
  • Patent number: 10144986
    Abstract: The present invention relates to an ultrahigh-strength steel sheet and a manufacturing method therefor. More specifically, the present invention can provide an ultra-high strength steel sheet which can ensure weldability and a delayed fracture resistance property by controlling the contents of elements affecting platability along with the contents of austenite-stabilizing elements and increasing twin formation through re-rolling, and simultaneously improve impact characteristics and workability by ensuring excellent yield strength and ductility.
    Type: Grant
    Filed: August 14, 2013
    Date of Patent: December 4, 2018
    Assignee: POSCO
    Inventors: Sung-Kyu Kim, Won-Tae Cho, Tai-Ho Kim, Kwang-Geun Chin, Sang-Ho Han
  • Patent number: 10113220
    Abstract: A high strength hot dipped galvanized steel sheet is provided. By controlling the amount of addition of Ti instead of the addition of Nb or B, it is possible to obtain an effect of retarding recrystallization and grain growth even if annealing by a continuous annealing process in a temperature range of the general annealing temperature of 720° C. to a temperature of the lower of 800° C. or Ac3 temperature. By controlling the rolling and heat treatment conditions, it is possible to control the ferrite phase rate, grain size of the low temperature transformed phases, ratio of average values of the nano hardnesses of the ferrite phase and low temperature transformed phases, and fluctuations of hardnesses of the low temperature transformed phases in a composite structure steel of ferrite and low temperature transformed phases and obtain a high strength hot dipped galvanized steel sheet.
    Type: Grant
    Filed: September 17, 2015
    Date of Patent: October 30, 2018
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Kengo Takeda, Kazuhisa Kusumi, Haruhiko Eguchi, Jun Hirowatari, Shintarou Fujii
  • Patent number: 10081854
    Abstract: Manufacturing a cold-rolled steel plate by smelting a steel slab having the chemical composition containing on the basis of percent by mass, C from 0.03 to 0.12%, Si from 0 to 1.0%, Mn from 0.2 to 0.8%, P at 0.03% or less, S at 0.03% or less, Ti from 0.04 to 0.3%, and Al at 0.05% or less, with a residue being formed of Fe and unavoidable impurities, the chemical composition satisfying 5*C %?Si %+Mn %?1.5 *Al %<1, and an average diameter of particles of a Ti-based carbide as a precipitate is from 20 to 100 nm; heating the slab to 1200° C. or more and hot rolling, forming a hot-rolled steel plate; winding the hot-rolled steel plate from 500 to 700° C. to form a hot-rolled coil; and cold rolling or annealing and cold rolling the coil obtaining cross-sectional hardness from 200 to 400 HV.
    Type: Grant
    Filed: June 16, 2017
    Date of Patent: September 25, 2018
    Assignee: Nisshin Steel Co., Ltd.
    Inventors: Tomohiro Imanaka, Kouji Omosako, Masahito Suzuki
  • Patent number: 10023947
    Abstract: High strength steel plate with an ultimate tensile strength of 900 MPa or more which is excellent in hydrogen embrittlement resistance characterized in that, in the structure of the steel plate, (a) by volume fraction, ferrite is present in 10 to 50%, bainitic ferrite and/or bainite in 10 to 60%, and tempered martensite in 10 to 50%, and (b) iron-based carbides which contain Si or Si and Al in 0.1% or more are present in 4×108 (particles/mm3) or more.
    Type: Grant
    Filed: November 30, 2010
    Date of Patent: July 17, 2018
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Masafumi Azuma, Noriyuki Suzuki, Naoki Maruyama, Akinobu Murasato, Yasuharu Sakuma, Hiroyuki Kawata, Chisato Wakabayashi
  • Patent number: 9938597
    Abstract: In the present invention, a press-formed product is manufactured by heating a steel sheet for hot pressing use to a temperature of 900° C. or above and 1,100° C. or below, the steel sheet for hot pressing use having a predetermined chemical component composition, some of Ti-containing precipitates contained in the steel sheet, each of which having an equivalent circle diameter of 30 nm or less, having an average equivalent circle diameter of 6 nm or less, and the precipitated Ti amount and the total Ti amount in the steel fulfilling the relationship represented by formula (1) shown below, thereafter starting press-forming, and holding at the bottom dead point and cooling to a temperature lower than the martensite transformation starting temperature Ms while securing the average cooling rate of 20° C./s or more within a tool. Precipitated Ti amount(mass %)?3.4[N]<0.5×[total Ti amount (mass %)?3.4[N]]??(1) (In the formula (1), [N] represents the content (mass %) of N in the steel.).
    Type: Grant
    Filed: February 28, 2013
    Date of Patent: April 10, 2018
    Assignee: Kobe Steel, Ltd.
    Inventors: Toshio Murakami, Hideo Hata, Junya Naitou, Keisuke Okita, Shushi Ikeda
  • Patent number: 9765413
    Abstract: A high-strength galvanized steel sheet with high yield ratio having excellent ductility and stretch flange formability, the steel sheet having a chemical composition containing, by mass %, C: 0.04% or more and 0.13% or less, Si: 0.9% or more and 2.3% or less, Mn: 0.8% or more and 2.4% or less, P: 0.1% or less, S: 0.01% or less, Al: 0.01% or more and 0.1% or less, N: 0.008% or less, and the balance being Fe and inevitable impurities and a microstructure including, in terms of area ratio, 94% or more of a ferrite phase and 2% or less of a martensite ferrite phase, wherein mean grain size of ferrite is 10 ?m or less, Vickers hardness of ferrite is 140 or more, mean grain size of carbide particles existing at grain boundaries of ferrite is 0.5 ?m or less, and aspect ratio of carbide particles existing at the grain boundaries of ferrite is 2.0 or less.
    Type: Grant
    Filed: July 12, 2011
    Date of Patent: September 19, 2017
    Assignee: JFE Steel Corporation
    Inventors: Yoshiyasu Kawasaki, Tatsuya Nakagaito, Shinjiro Kaneko, Yasunobu Nagataki, Keisuke Fukushi
  • Patent number: 9617614
    Abstract: A method of manufacturing a high strength steel sheet having excellent formability suitable for the material of an automotive part has a tensile strength (TS) of 980 MPa or more and total elongation (EL) is 25% or more. A steel slab has a chemical composition containing C: 0.03% to 0.35%, Si: 0.5% to 3.0%, Mn: 3.5% to 10.0%, P: 0.100% or less, S: 0.02% or less, and the remainder includes Fe and incidental impurities on a percent by mass basis is hot-rolled, a heat treatment is performed, in which an achieved temperature of Ac1 to Ac1+100° C. is held for 3 minutes or more, subsequently, cold rolling is performed at a rolling reduction of 20% or more and, annealing is performed, in which an achieved temperature of Ac1?30° C. to Ac1+100° C. is held for 1 minute or more.
    Type: Grant
    Filed: October 17, 2012
    Date of Patent: April 11, 2017
    Assignee: JFE Steel Corporation
    Inventors: Hiroshi Hasegawa, Yoshiyasu Kawasaki, Tatsuya Nakagaito, Shinjiro Kaneko, Yasunobu Nagataki
  • Patent number: 9540720
    Abstract: Disclosed is a high-strength hot-dip galvanized steel sheet having small material anisotropy and excellent formability with an ultimate tensile strength of 980 MPa or more. The hot-dip galvanized steel sheet includes a hot-dip galvanized layer formed on a surface of a base steel plate. The base steel plate contains C, Si, Mn, O, P, S, Al and N within predetermined ranges and a balance including Fe and inevitable impurities. The hot-dip galvanized layer contains Fe at less than 7 mass % or 7 to 15 mass % and a balance including Zn, Al, and inevitable impurities.
    Type: Grant
    Filed: September 28, 2012
    Date of Patent: January 10, 2017
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Masafumi Azuma, Chisato Wakabayashi, Takayuki Nozaki, Nobuhiro Fujita, Manabu Takahashi
  • Patent number: 9512508
    Abstract: A high-strength cold-rolled steel sheet having excellent stretch flangeability and precision punchability containing predetermined components and a balance being composed of iron and inevitable impurities, in which in a range of ? to ? in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100}<011> to {223}<110> orientation group represented by respective crystal orientations of {100}<011>, {116}<110>, {114}<110>, {113}<110>, {112}<110>, {335}<110>, and {223}<110> is 6.5 or less, and a pole density of the {332}<113> crystal orientation is 5.0 or less, and a metal structure contains, in terms of an area ratio, greater than 5% of pearlite, the sum of bainite and martensite limited to less than 5%, and a balance composed of ferrite.
    Type: Grant
    Filed: July 27, 2012
    Date of Patent: December 6, 2016
    Assignee: NIPPON STEEL AND SUMITOMO METAL CORPORATION
    Inventors: Hiroshi Shuto, Nobuhiro Fujita, Tatsuo Yokoi, Riki Okamoto, Kazuaki Nakano, Shinichiro Watanabe
  • Patent number: 9315877
    Abstract: A steel sheet for bottom covers of aerosol cans includes, as chemical composition, C: 0.025 to 0.065 mass %, Mn: 0.10 to 0.28 mass %, P: 0.005 to 0.03 mass %, Al: 0.01 to 0.04 mass %, N: 0.0075 to 0.013 mass %, Si: limited to 0.05 mass % or less, S: limited to 0.009 mass % or less, and balance consisting of Fe and unavoidable impurities, wherein yield point YP in rolling direction after aging treatment is in range of 460 to 540 MPa, total elongation in the rolling direction after the aging treatment is 15% or more, yield point elongation ELYP in the rolling direction after the aging treatment is 6% or less, and sheet thickness t in unit of mm, the yield point YP in unit of MPa in the rolling direction after the aging treatment, and the yield point elongation ELYP in unit of % in the rolling direction after the aging treatment satisfy 130?t×YP×(1?ELYP/100).
    Type: Grant
    Filed: December 5, 2011
    Date of Patent: April 19, 2016
    Assignee: NIPPON STEEL & SUMITOMO METAL CORPORATION
    Inventors: Keiichiro Torisu, Seiichi Tanaka, Hirokazu Yokoya, Jyunichi Matsunaga
  • Patent number: 9273382
    Abstract: A stainless steel foil contains, in percent by mass, 0.05% or less of C, 2.0% or less of Si, 1.0% or less of Mn, 0.003% or less of S, 0.05% or less of P, 25.0% to 35.0% of Cr, 0.05% to 0.30% of Ni, 3.0% to 10.0% of Al, 0.10% or less of N, 0.02% or less of Ti, 0.02% or less of Nb, 0.02% or less of Ta, 0.005% to 0.20% of Zr, 0.02% or less of Ce, 0.03% to 0.20% of REM excluding Ce, 0.5% to 6.0% in total of at least one of Mo and W, and the balance being Fe and incidental impurities.
    Type: Grant
    Filed: March 18, 2011
    Date of Patent: March 1, 2016
    Assignee: JFE Steel Corporation
    Inventors: Akito Mizutani, Kunio Fukuda, Shin Ishikawa, Atsutaka Honda, Yasuhiro Yamaguchi, Yasushi Kato, Hiroki Ota, Mitsuyuki Fujisawa, Takumi Ujiro, Hideaki Yamashita
  • Patent number: 9255318
    Abstract: A high-strength galvanized steel sheet has a low YP, good stretch flangeability, and excellent corrosion resistance and contains, on a percent by mass basis, more than 0.015% to less than 0.10% of C, 0.5% or less of Si, 1.0% to 1.9% of Mn, 0.015% to 0.050% of P, 0.03% or less of S, 0.01% to 0.5% of sol. Al, 0.005% or less of N, less than 0.40% of Cr, 0.005% or less of B, less than 0.15% of Mo, 0.4% or less of V, and less than 0.020% of Ti, in which 2.2?[Mneq]?3.1 and [% Mn]+3.3[% Mo]?1.9, and [% Mn]+3.3[% Mo])/(1.3[% Cr]+8[% P]+150B*)<3.5 are satisfied.
    Type: Grant
    Filed: June 25, 2010
    Date of Patent: February 9, 2016
    Assignee: JFE Steel Corporation
    Inventors: Yoshihiko Ono, Kenji Takahashi, Kaneharu Okuda, Shoichiro Taira, Michitaka Sakurai, Yusuke Fushiwaki
  • Publication number: 20150144231
    Abstract: In a steel sheet having a specific chemical composition and having a microstructure including ferrite that is a soft first phase by 20-50% in terms of the area ratio, the remainder being tempered martensite and/or tempered bainite that is a hard second phase, the microstructure of steel of a surface layer section of the steel sheet from the surface to the depth of 100 ?m and a center section of t/4-3t/4 (t is the sheet thickness) is controlled.
    Type: Application
    Filed: May 29, 2013
    Publication date: May 28, 2015
    Applicant: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.)
    Inventors: Tomokazu Masuda, Katsura Kajihara, Toshio Murakami, Masaaki Miura, Muneaki Ikeda
  • Publication number: 20150114524
    Abstract: In a high strength cold-rolled steel plate having a specific chemical composition, a soft first phase (ferrite) has an area ratio of 20-50%, the remainder being a hard second phase (tempered martensite and/or tempered bainite), among all the ferrite grains, ferrite grains that have an average grain diameter of 10-25 ?m account for a total area ratio of 80% or more, the number of the cementite grains that have an equivalent circle diameter of 0.3 ?m or more is more than 0.15 piece and 1.0 piece or less per 1 ?m2 of ferrite, and the tensile strength is 980 MPa or more.
    Type: Application
    Filed: May 24, 2013
    Publication date: April 30, 2015
    Applicant: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.)
    Inventors: Tomokazu Masuda, Katsura Kajihara, Toshio Murakami, Masaaki Miura, Muneaki Ikeda
  • Patent number: 9011614
    Abstract: A high-strength galvanized steel sheet has excellent mechanical properties such as a TS of 1200 MPa or more, an El of 13% or more, and a hole expansion ratio of 50% or more and a method for manufacturing the same. A high-strength galvanized steel sheet excellent in formability contains 0.05% to 0.5% C, 0.01% to 2.5% Si, 0.5% to 3.5% Mn, 0.003% to 0.100% P, 0.02% or less S, and 0.010% to 0.5% Al on a mass basis, the remainder being Fe and unavoidable impurities, and has a microstructure which contains 0% to 10% ferrite, 0% to 10% martensite, and 60% to 95% tempered martensite on an area basis as determined by structure observation and which further contains 5% to 20% retained austenite as determined by X-ray diffractometry.
    Type: Grant
    Filed: January 28, 2009
    Date of Patent: April 21, 2015
    Assignee: JFE Steel Corporation
    Inventors: Tatsuya Nakagaito, Saiji Matsuoka, Yoshitsugu Suzuki, Yuki Toji
  • Patent number: 9005375
    Abstract: A steel sheet for cans containing 0.0060 to 0.01 mass % C and 0.02 to 0.12 mass % Nb and having the following characteristics: (i) an average ferrite grain size in a cross section in the rolling direction in a region from a surface layer of the steel sheet to a position ¼ of a sheet thickness away from the surface layer of the steel sheet is 7 ?m to 10 ?m or less, and (ii) an average ferrite grain size in a cross section in the rolling direction in a region from the position ¼ of a sheet thickness away from the surface layer of the steel sheet to a sheet thickness center portion of the steel sheet is 15 ?m or less, wherein the average ferrite grain size (1) is smaller than the average ferrite grain size (2).
    Type: Grant
    Filed: October 26, 2010
    Date of Patent: April 14, 2015
    Assignee: JFE Steel Corporation
    Inventors: Yusuke Nakagawa, Masaki Tada, Katsumi Kojima, Hiroki Iwasa
  • Patent number: 8999085
    Abstract: A high-ductility, high-strength and high Mn steel strip used for steel strips of automobiles requiring superior formability and high strength, a plated steel strip produced by using the same, and a manufacturing method thereof are disclosed. The high Mn steel strip comprises, by weight %, 0.2˜1.5% of C, 10˜25% of Mn, 0.01˜3.0% of Al, 0.005˜2.0% of Si, 0.03% or less of P, 0.03% or less of S, 0.040% or less of N, and the balance of Fe and other unavoidable impurities. The high-ductility, high-strength and high Mn steel strip, and the plated steel strip produced by using the same have superior surface properties and plating characteristics.
    Type: Grant
    Filed: December 22, 2006
    Date of Patent: April 7, 2015
    Assignee: Posco
    Inventors: Seong-Ju Kim, Kwang-Geun Chin, Hyun-Gyu Hwang, Sung-Kyu Kim, Il-Ryoung Sohn, Young-Kook Lee, Oh-Yeon Lee
  • Publication number: 20150075680
    Abstract: A steel sheet suitable as a starting material for a vehicle impact absorbing member with high absorption of impact energy and resistance to cracking contains, by mass %, C: 0.08-0.30%, Mn: 1.5-3.5%; Si+Al: 0.50-3.0%, P: 0.10% or less, S: at most 0.010%, and N: at most 0.010%, and optionally, one or more types selected from Cr: at most 0.5%, Mo: at most 0.5%, B: at most 0.010%, Ti: less than 0.04%, Nb: less than 0.030%, V: less than 0.5%, Ca: at most 0.010%, Mg: at most 0.010%, REM: at most 0.050%, and Bi: at most 0.050%. The microstructure contains, by area %, bainite: more than 50%, martensite: 3-30%, and retained austenite: 3-15%, the remainder comprising ferrite having an average grain diameter of less than 5 mm. The product of uniform elongation and hole expansion ratio is at least 300%2 and 5% effective flow stress is at least 900 MPa.
    Type: Application
    Filed: April 8, 2013
    Publication date: March 19, 2015
    Inventors: Yasuaki Tanaka, Kaori Kawano, Masahito Tasaka, Yoshiaki Nakazawa, Takuya Nishio, Masayuki Wakita, Jun Haga, Toshiro Tomida
  • Patent number: 8951366
    Abstract: A high-strength cold-rolled steel sheet includes, by mass %, C: 0.10% to 0.40%, Mn: 0.5% to 4.0%, Si: 0.005% to 2.5%, Al: 0.005% to 2.5%, Cr: 0% to 1.0%, and a balance of iron and inevitable impurities, in which an amount of P is limited to 0.05% or less, an amount of S is limited to 0.02% or less, an amount of N is limited to 0.006% or less, the microstructure includes 2% to 30% of retained austenite by area percentage, martensite is limited to 20% or less by area percentage in the microstructure, an average particle size of cementite is 0.01 ?m to 1 ?m, and 30% to 100% of the cementite has an aspect ratio of 1 to 3.
    Type: Grant
    Filed: January 26, 2011
    Date of Patent: February 10, 2015
    Assignee: Nippon Steel & Sumitomo Metal Corporation
    Inventors: Kohichi Sano, Chisato Wakabayashi, Hiroyuki Kawata, Riki Okamoto, Naoki Yoshinaga, Kaoru Kawasaki, Natsuko Sugiura, Nobuhiro Fujita
  • Publication number: 20150037610
    Abstract: A high-strength cold-rolled steel sheet includes a composition having controlled amounts of carbon, silicon, manganese, phosphorous, sulfur, titanium, niobium, sol. Aluminum, chromium, molybdenum, vanadium, boron, calcium, REM, and iron. A microstructure thereof has a main phase of ferrite of at least 40 area %, and a second phase of a low-temperature transformation phase consisting either or both of martensite and bainite, which comprises at least 10 area % in total and retained austenite (?) at least comprising 3 area %. An average grain diameter of ferrite has a tilt angle of at least 15° is at most 5.0 mm, an average grain diameter of the low-temperature transformation-produced phase is at most 2.0 mm, an average grain diameter of lump-like retained ? having an aspect ratio of less than 5 is at most 1.5 mm, and an area fraction of the lump-like retained ? relative to the retained ? is at least 50%.
    Type: Application
    Filed: February 13, 2013
    Publication date: February 5, 2015
    Inventors: Kengo Hata, Toshiro Tomida, Norio Imai, Jun Haga, Takuya Nishio
  • Publication number: 20150020933
    Abstract: Provided is a heat-resistant cold rolled ferritic stainless steel sheet containing, in terms of mass %, 0.02% or less of C, 0.1% to 1.0% of Si, greater than 0.6% to 1.5% of Mn, 0.01% to 0.05% of P, 0.0001% to 0.0100% of S, 13.0% to 20.0% of Cr, 0.1% to 3.0% of Mo, 0.005% to 0.20% of Ti, 0.3% to 1.0% of Nb, 0.0002% to 0.0050% of B, 0.005% to 0.50% of Al, and 0.02% or less of N, with the balance being Fe and inevitable impurities, in which {111}-oriented grains are present at an area ratio of 20% or greater in a region from a surface layer to t/4 (t is a sheet thickness), {111}-oriented grains are present at an area ratio of 40% or greater in a region from t/4 to t/2, and {011}-oriented grains are present at an area ratio of 15% or less in the entire region in a thickness direction.
    Type: Application
    Filed: March 26, 2013
    Publication date: January 22, 2015
    Applicant: Nippon Steel & Sumikin Stainless Steel Corporation
    Inventors: Junichi Hamada, Yuji Koyama, Yoshiharu Inoue, Tadashi Komori, Fumio Fudanoki, Toshio Tanoue, Naoto Ono
  • Patent number: 8936687
    Abstract: In a method for manufacturing grain oriented electrical steel sheets from a slab, controlling the steel sheet temperature so as to satisfy T (t)<FDT?(FDT?700)×t/6 (wherein T (t): steel sheet temperature (° C.), FDT: finishing temperature (° C.) and t: time (sec) after the completion of finish rolling) throughout the entire length of a coil during cooling after the completion of finish rolling in hot rolling, and controlling the steel sheet temperature of a tip portion of the coil representing 10% of the length of the coil to be not less than 650° C. at a lapse of 3 seconds from the completion of hot rolling, thus manufacturing a grain oriented electrical steel sheet exhibiting excellent magnetic properties throughout the entire coil length.
    Type: Grant
    Filed: March 9, 2011
    Date of Patent: January 20, 2015
    Assignee: JFE Steel Corporation
    Inventor: Kenichi Sadahiro
  • Patent number: 8926772
    Abstract: The invention relates to a hot rolled sheet which is made from austenitic iron/carbon/manganese steel and which has a resistance of greater than 900 MPa, whereby: resistance (MPa) x elongation at rupture (%) is greater than 45000. The chemical composition of the inventive sheet comprises the following concentrations expressed as weight: 0.5%=C=0.7%, 17%=Mn=24%, Si=3%, Al=0.05%, S=0.03%, P=0.08%, N=0.1% and, optionally, one or more elements such as Cr=1%, Mo=0.4%, Ni=1%, Ti=0.5%, Nb=0.5%, V=0.5%, Cu=5%, Cu=5%, the rest of the composition comprising iron and impurities resulting from production. According to the invention, the recrystallised fraction of the steel is greater than 75% and the surface fraction of precipitated carbides of the steel is less than 1.5%, the average grain size of the steel being less than 18 micrometers.
    Type: Grant
    Filed: July 8, 2004
    Date of Patent: January 6, 2015
    Assignee: Usinor
    Inventors: Mohamed Bouzekri, Michel Faral, Colin Scott
  • Publication number: 20140363694
    Abstract: A low density high strength steel sheet including 0.15% to 0.25% C, 2.5% to 4% Mn, 0.02% or less P, 0.015% or less S, 6% to 9% Al and 0.01% or less N, the balance being iron and inevitable impurities, wherein 1.7·(Mn—Al)+52.7·C is at least 3 and at most 4.5. A method of producing the low density and high strength steel sheet.
    Type: Application
    Filed: February 21, 2012
    Publication date: December 11, 2014
    Applicant: TATA STEEL NEDERLAND TECHNOLOGY BV
    Inventors: Cheng Liu, Radhakanta Rana
  • Patent number: 8876987
    Abstract: A high strength pressed member has excellent ductility and stretch flangeability and tensile strength of 780-1400 MPa, with a predetermined steel composition and steel microstructure relative to the entire microstructure of steel sheet, where area ratio of martensite 5-70%, area ratio of retained austenite 5-40%, area ratio of bainitic ferrite in upper bainite 5% or more, and total thereof is 40% or more, 25% or more of martensite is tempered martensite, polygonal ferrite area ratio is above 10% and below 50% to the entire microstructure of steel sheet, and average grain size is 8 ?m or less, average diameter of a group of polygonal ferrite grains is 15 ?m or less, the group of polygonal ferrite grains represented by a group of ferrite grains of adjacent polygonal ferrite grains, and average carbon content in retained austenite is 0.70 mass % or more and tensile strength is 780 MPa or more.
    Type: Grant
    Filed: October 2, 2012
    Date of Patent: November 4, 2014
    Assignee: JFE Steel Corporation
    Inventors: Hiroshi Matsuda, Yoshimasa Funakawa, Kaneharu Okuda, Kazuhiro Seto
  • Publication number: 20140305553
    Abstract: A high-strength cold-rolled steel sheet has a chemical composition including C of 0.05% to 0.30%, Si of greater than 0% to 3.0%, Mn of 0.1% to 5.0%, P of greater than 0% to 0.1%, S of greater than 0% to 0.02%, Al of 0.01% to 1.0%, and N of greater than 0% to 0.01%, in mass percent, with the remainder including iron and inevitable impurities. The steel sheet has a microstructure containing ferrite as a soft primary phase in an area percentage of 20% to 50% with the remainder including tempered martensite and/or tempered bainite as a hard secondary phase. The ferrite grains are adapted to contain cementite particles having an appropriate size in an appropriate number density.
    Type: Application
    Filed: December 11, 2012
    Publication date: October 16, 2014
    Applicant: Kabushiki Kaisha Kobe Seiko Sho (Kobe Steel, Ltd.)
    Inventors: Tomokazu Masuda, Hideo Hata, Katsura Kajihara, Toshio Murakami, Masaaki Miura, Muneaki Ikeda
  • Publication number: 20140290810
    Abstract: A high strength cold rolled steel sheet includes a chemical composition containing, by mass %, C: 0.010% or more and 0.060% or less, Si: more than 0.5% and 1.5% or less, Mn: 1.0% or more and 3.0% or less, P: 0.005% or more and 0.100% or less, S: 0.010% or less, sol.Al: 0.005% or more and 0.500% or less, N: 0.0100% or less, Nb: 0.010% or more and 0.100% or less, Ti: 0.015% or more and 0.150% or less and the balance comprising Fe and inevitable impurities. The microstructure includes, in area fraction, 70% or more of a ferrite phase and 3% or more of a martensite phase. The tensile strength is 440 MPa or more and an average r value is 1.20 or more.
    Type: Application
    Filed: August 23, 2012
    Publication date: October 2, 2014
    Applicant: JFE STEEL CORPORATION
    Inventors: Hideyuki Kimura, Yasunobu Nagataki, Kaneharu Okuda, Kenji Kawamura
  • Publication number: 20140261916
    Abstract: A high strength-high ductility cold rolled steel sheet is provided. The steel sheet has a recovery annealed microstructure, a yield strength greater than 820 megapascals (MPa) and a percent elongation to failure greater than 3.5%. In some instances, the steel alloy sheet has a Rockwell B hardness greater than 100 and may or may not exhibit a yield strength-to-tensile strength ratio between 0.25 and 1.00.
    Type: Application
    Filed: July 18, 2013
    Publication date: September 18, 2014
    Inventors: Chris John Paul Samuel, Marisa Vann, Bertram Wilhelm Ehrhardt, Stanley Wayne Bevans
  • Publication number: 20140261919
    Abstract: A low carbon-high manganese steel sheet and process for manufacturing the sheet is provided. The process includes soaking a steel slab with a desired chemical composition within a temperature range of 1200-1350° C., followed by hot rolling of the slab into hot strip. The cold rolled sheet is continuously annealed within a temperature range of 730-850° C. and temper rolled between 1.0-2.0%. The temper rolled sheet has a yield strength greater than 280 megapascals (MPa), a tensile strength greater than 400 MPa, an elongation to fracture greater than 30%, an n-value greater than 0.15, and a bakehard index between 15-35 MPa.
    Type: Application
    Filed: February 25, 2014
    Publication date: September 18, 2014
    Applicant: THYSSENKRUPP STEEL USA, LLC
    Inventors: Chris John Paul Samuel, Bertram Wilhelm Ehrhardt, Joseph Frimpong, Stanley Wayne Bevans
  • Publication number: 20140261903
    Abstract: A bake hardenable steel and a process for manufacture of a bake hardenable steel. Steel alloy slabs with a predefined chemical composition are hot rolled into hot rolled strip. The hot rolled strip is cold rolled and continuously annealed on a continuous annealing line and then rapidly cooled to at least 600° C. using a cooling rate of between 20-100 K/sec, and optionally cooled to at least 140° C. using a cooling rate of between 3-20 K/sec. As such, the cold rolled and annealed sheet is not subjected to an overageing treatment and yet still exhibits excellent and well defined bake hardening values. For example BH2 values between 25 and 45 MPa are exhibited by the low alloy steel grades. In addition, the bake hardeneable steel sheet has a minimum yield strength of 220 MPa and in some instances has a minimum yield strength as high as 380 MPa.
    Type: Application
    Filed: March 17, 2014
    Publication date: September 18, 2014
    Applicant: AM/NS CALVERT LLC
    Inventors: Joseph Frimpong, Bertram Wilhelm Ehrhardt, Stanley Wayne Bevans, Harald Van Bracht
  • Publication number: 20140242416
    Abstract: A high strength pressed member has excellent ductility and stretch flangeability and tensile strength of 780-1400 MPa, with a predetermined steel composition and steel microstructure relative to the entire microstructure of steel sheet, where area ratio of martensite 5-70%, area ratio of retained austenite 5-40%, area ratio of bainitic ferrite in upper bainite 5% or more, and total thereof is 40% or more, 25% or more of martensite is tempered martensite, polygonal ferrite area ratio is above 10% and below 50% to the entire microstructure of steel sheet, and average grain size is 8 ?m or less, average diameter of a group of polygonal ferrite grains is 15 ?m or less, the group of polygonal ferrite grains represented by a group of ferrite grains of adjacent polygonal ferrite grains, and average carbon content in retained austenite is 0.70 mass % or more and tensile strength is 780 MPa or more.
    Type: Application
    Filed: October 2, 2012
    Publication date: August 28, 2014
    Inventors: Hiroshi Matsuda, Yoshimasa Funakawa, Kaneharu Okuda, Kazuhiro Seto