Showing papers by "Nobuhiro Fujita published in 2010"

High-strength steel sheet, hot-dipped steel sheet, and alloy hot-dipped steel sheet that have excellent fatigue, elongation, and collision characteristics, and manufacturing method for said steel sheets

Abstract: This high-strength steel sheet includes: in terms of percent by mass, 0.03 to 0.10% of C; 0.01 to 1.5% of Si; 1.0 to 2.5% of Mn; 0.1% or less of P; 0.02% or less of S; 0.01 to 1.2% of Al; 0.06 to 0.15% of Ti; and 0.01% or less of N; and contains as the balance, iron and inevitable impurities, wherein a tensile strength is in a range of 590 MPa or more, and a ratio between the tensile strength anda yield strength is in a range of 0.80 or more, a microstructure includes bainite at an area ratio of 40% or more and the balance being either one or both of ferrite and martensite, a density of Ti(C,N) precipitates having sizes of 10 nm or smaller is in a range of 1010 precipitates/mm3 or more, and a ratio (Hvs/Hvc) of a hardness (Hvs) at a depth of 10 [mu]m from a surface to a hardness (Hvc) ata center of a sheet thickness is in a range of 0.85 or more.

High-strength hot-dip galvanized steel sheet and process for producing same

Abstract: Disclosed is a hot-dip galvanized steel sheet which comprises a steel sheet part and a deposit formed on the surface of the steel sheet part and has a tensile strength of 770 MPa or higher, wherein the deposit is a zinc layer formed by hot-dip plating or an alloyed zinc layer formed by hot-dip plating, the steel sheet part comprises a soft layer, which is in direct contact with the deposit, and an inner layer, which is the part other than the soft layer, and the thickness (D) of the soft layer is 0.001 to 5% of the thickness (t) of the steel sheet part. In a cross-section along the thickness direction of the steel sheet part, when the hardness of the soft layer measured by a nanoindentation method is expressed by H1 and the representative hardness of the steel sheet part measured by the nanoindentation method is expressed by Ha, then H1 is 5-75% of Ha.

Steel sheet for hot press having excellent delayed fracture resistance and collision safety, and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To provide a steel sheet for hot press which can obtain a strength of ≥1,000 MPa after high temperature forming, and also has excellent delayed fracture resistance and collision safety, and a method for producing the sameSOLUTION: The steel sheet for hot press has a composition which comprises 01 to 05% C, 005 to 2% Si, 01 to 3% Mn and 0003 to 2% Al, and in which the content of P is limited to ≤005%, the content of S is limited to ≤003% and the content of N is limited to ≤001%, and which satisfies formula (1) Si+Al≥10% and formula (2): 50≥Vc≥25; wherein Vc=10^(369-075β) [°C/s]; and β=27C+04Si+Mn

Method of specifying breaking strain of plate-like material

Abstract: PROBLEM TO BE SOLVED: To provide a method by which breaking strain generated in the end part of a flange when forming a stretch flange is specified accurately. SOLUTION: A plate-like test-piece 1 in the end part of which a notch 6 is formed is set to a side bend testing machine and, by making it break by imparting in-plane tension and bending, and strain, a strain gradient and strain concentration in the broken part are measured. Data are collected by using two or more kinds of the plate-like test-pieces 1 which are changed in the strain gradient from the end part of a plate to the inside and the strain concentration along the plate end part, which are generated when applying load are changed and the breaking strain is specified as the function of the strain gradient and the strain concentration, or a map of the strain gradient and the strain concentration. COPYRIGHT: (C)2011,JPO&INPIT

High strength thin steel sheet having excellent elongation and press forming stability

Abstract: PROBLEM TO BE SOLVED: To provide a high strength thin steel sheet which has excellent elongation and press stability in retained austenite steel.SOLUTION: The high strength steel sheet having excellent elongation and press forming stability has a steel composition comprising, by mass, 0.05 to 0.35% C, 0.05 to 2.0% Si, 0.8 to 3.0% Mn, 0.0010 to 0.1% P, 0.0005 to 0.05% S, 0.0010 to 0.010% N and 0.01 to 2.0% Al, and the balance iron with inevitable impurities, and has a microstructure composed of a ferrite phase and a bainite phase of 10 to 93% in total by area ratio, a retained austenite phase of 5 to 30% by area ratio and a martensite phase of 5 to 20% by area ratio, and in the steel sheet, the retained austenite phase has lath and insular form, and the area ratio γi of the insular retained austenite phase and the area ratio γof the whole retained austenite phase satisfy formula (1): 0.7≥γi/γ≥0.3.

High strength cold-rolled steel sheet excellent in formability and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To provide a method for producing a steel sheet excellent in 02% proof stress, strength and ductility by optimizing the composition and the production condition of a TRIP (Transformation-Induced Plasticity) steel and controlling the structure of the steel sheetSOLUTION: The steel sheet excellent in the formability contains 010-05% C, 10-40% Mn, 08-40% Si, 001-04% Ti, ≤0015% P, ≤005% S, ≤0005% N and the balance Fe with inevitable impurities, and contains as the steel sheet micro-structure, by an area ratio, 10-60% tempered-martensite, 5-50% ferrite, 5-30% bainite, 5-30% retained austenite and further, 0-20% total of perlite and martensite

Plated steel sheet for hot press having excellent delayed fracture resistance, and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To provide a plated steel sheet for hot press which has excellent strength, formability, corrosion resistance and delayed fracture resistance, and a method for producing the same.SOLUTION: The steel sheet for hot press has a composition comprising 0.1 to 0.5% C, 0.05 to 2% Si, 0.1 to 3% Mn, and one or more kinds selected from 0.005 to 1% Ti, 0.01 to 1% Nb, 0.01 to 1% V, 0.01 to 1% Mo, 0.005 to 1% W, 0.005 to 0.1% Zr, 0.01 to 3% Cu, 0.005 to 0.5% Y, 0.005 to 1% Mg, 0.005 to 0.1% La and 0.005 to 0.1% Ce, and in the steel sheet, plating essentially composed of aluminum or zinc is applied to its surface, and the content of hydrogen in the steel sheet satisfies the relation of Hmax-Ht≥0.07 ppm. In the formula, Hmax denotes the maximum content of non-diffusible hydrogen in which the steel sheet can be trapped, and Ht denotes the content of non-diffusible hydrogen trapped into the steel sheet after the plating.

High-strength galvanized steel sheet and method of manufacturing the same

Abstract: Provided is a galvanized steel sheet having a tensile strength of 770 MPa or more including a steel sheet portion, and a plated layer formed on the surface of the steel sheet portion, in which the plated layer is a galvanized plated layer or an galvannealed plated layer, the steel sheet portion has a soft layer that directly adjoins the interface with the plated layer and an inside layer that is other than the soft layer, the thickness D of soft layer is 0.001% to 5% of thickness t of the steel sheet portion, and, when the hardness of the soft layer measured by nano-indentation method is indicated by H1, and the representative hardness of the steel sheet portion measured by the nano-indentation method is indicated by Ha in cross section that goes along the thickness direction of the steel sheet portion, H1 is 5% to 75% of Ha.

High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing of high-strength steel sheet

Abstract: The high-strength steel sheet includes, by mass %: C: 0.01% to 0.10%; Si: 0.15% or less; Mn: 0.80% to 1.80%; P: 0.10% or less; S: 0.015% or less; Al: 0.10% to 0.80%; Cr: 0.01% to 1.50%; N: 0.0100% or less; and a balance consisting of iron and inevitable impurities, in which a metallic structure is composed of ferrite and a hard second phase, the area fraction of the ferrite is 80% or more, the area fraction of the hard second phase is 1% to 20%, the fraction of unrecrystallized ferrite in the ferrite is less than 10%, the ferrite grain sizes are 5 μm to 20 μm, and the fraction of the ferrite crystal grains having an aspect ratio of 1.2 or less in the entire ferrite crystal grains is 60% or more.

High-strength steel sheet superior in workability and method for manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To attain a high-strength steel sheet superior in workability on an industrial scale, and to provide a method for manufacturing the same on the industrial scale. SOLUTION: The high-strength steel sheet includes, by mass%, 0.07-0.20% C, 0.005-1.5% Si, 1.0-3.1% Mn, 0.001-0.06% P, 0.001-0.01% S, 0.0005-0.01% N, 0.005-1.2% Al and the balance Fe with unavoidable impurities; further has such mass% of C and Mn and a target strength value (TS) as to satisfy expression (A), wherein [TS target value] is a designed strength value of the steel sheet and the unit is MPa; [Mn] is mass% of Mn; and [C] is mass% of C; and has such a hardness distribution as to satisfy expression (B). The manufacturing method includes an annealing step in which in the first heating zone, such a temperature T1 as to satisfy expression (C) is kept for 30 seconds or longer, wherein T1 is temperature (°C); [Mn] is mass% of Mn; [Si] is mass% of Si; [Ti] is mass% of Ti; [Nb] is mass% of Nb; and [Mo] is mass% of Mo; and in a cooling zone after soaking treatment in the annealing step, a cooling rate V1 in such a period that the temperature of the steel sheet is in a range of 800-400°C and a cooling rate V2 is such a period that the temperature is lower than 400°C satisfy expression (D), wherein V1 is a cooling rate m/s in a former stage; and V2 is a cooling rate m/s in a latter stage. The high-strength steel sheet also has a metallographic structure containing ferrite and martensite. COPYRIGHT: (C)2011,JPO&INPIT

Method for manufacturing hot pressed part and hot pressed part

Abstract: PROBLEM TO BE SOLVED: To provide a method capable of improving a molding property by improvement of a lubrication property of a low-temperature heated or non-heated part and manufacturing a press molding part with a partially different strength in a hot pressed part using a zinc-coated steel plate. SOLUTION: An inorganic amorphous covering layer of 2-1,000 mg/m 2 (as a metal) is formed on a surface of the zinc-coated steel plate, and thereafter the steel plate is pressed while still having a part non-heated or heated at a low temperature below an Ac1 point and a part heated to be equal to or higher than the Ac1 point, so that the press molding part is made to have an inclination of materials. COPYRIGHT: (C)2011,JPO&INPIT

High strength hot rolled steel sheet having excellent low cycle fatigue property and corrosion resistance after coating, and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To provide a high strength hot rolled steel sheet which is excellent in both of low cycle fatigue properties and corrosion resistance after coating. SOLUTION: The high strength hot rolled steel sheet having excellent low cycle fatigue properties and corrosion resistance after coating has a composition containing, by mass, 0.06 to 0.12% C, 0.6 to 1.25% Si, 1.60 to 2.20% Mn and 0.20 to 0.65% Al so as to satisfy [Si]≥[Mn]/4+[Al]/1.2, and in which the contents of P, S and N are limited, and the balance Fe with inevitable impurities, and has a metallic structure composed of the two phases of a ferrite phase and a martensite phase, or the three phases of a ferrite phase, a martensite and a bainite phase, and in which the area ratio of the ferrite phase is 10% and the area ratio of the bainite phase is COPYRIGHT: (C)2010,JPO&INPIT

High-strength cold rolled steel sheet excellent in deep drawability, method of manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To provide a high-strength cold rolled steel sheet excellent in deep drawability, and to provide a method of manufacturing the same.SOLUTION: The high-strength cold rolled steel sheet excellent in deep drawability is characterized in that: it contains, by mass%, 0.03-0.25% C, 0.001-3.0% Si, 0.5-3.0% Mn, 0.001-0.15% P, 0.0005-0.05% S, 0.01-1.0% Al, 0.1-3.0% Cr, 0.0005-0.01% N, and the balance Fe with inevitable impurities; a mother phase is a ferrite phase; other metallographic structure contains one or two or more kinds out of bainite, austenite, martensite, pearlite in volume fraction of 2% or more; X-ray random intensity ratios of sheet faces {111} and {100} at a thickness of 1/2 in the steel sheet are respectively 5.0 or higher, and 3.0 or lower; and an average r value is 1.3 or higher.

High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing same

Abstract: Disclosed is a high-strength steel sheet which contains, in mass%, 001-010% of C, 015% or less of Si, 080-180% of Mn, 010% or less of P, 0015% or less of S, 010-080% of Al, 001-150% of Cr and 00100% or less of N with the balance made up of iron and unavoidable impurities The metallic structure thereof is composed of ferrite and a hard second phase The area ratio of the ferrite is not less than 80%, and the area ratio of the hard second phase is 1-20% The unrecrystallized ferrite fraction expressed in terms of area is less than 10% of the above-described ferrite The ferrite particle diameters are 5-20 μm, and ferrite crystal grains having an aspect ratio of 12 or less account for not less than 60% of all the ferrite crystal grains

High strength hot-rolled steel plate exhibiting excellent acid pickling property, chemical conversion processability, fatigue property, stretch flangeability, and resistance to surface deterioration during molding, and having isotropic strength and ductility, and method for producing said high strength hot-rolled steel plate

Abstract: Disclosed is a high strength hot-rolled steel plate containing, in mass%, 0.05 to 0.12% of C, 0.8 to 1.2% of Si, 1.6 to 2.2% of Mn, 0.30 to 0.6% of Al, 0.05% or less of P, 0.005% or less of S, and 0.01% or less of N, the remainder being Fe and unavoidable impurities, wherein: the metal structure is either formed from 60% or more by area of a ferrite phase, more than 10% by area of a martensite phase, and less than 1% by area of a residual austenite phase, or from 60% or more by area of a ferrite phase, more than 10% by area of a martensite phase, less than 5% by area of a bainite phase, and less than 1% by area of a residual austenite phase; and the maximum concentration of Al detected by means of a glow discharge spectrometer is 0.75 mass% or more up to 500nm from the surface of the steel plate after acid pickling was performed.

Method for manufacturing high-strength low-specific gravity steel sheet excellent in ductility

Abstract: PROBLEM TO BE SOLVED: To provide a method for manufacturing a high-strength low-specific gravity steel sheet excellent in ductility. SOLUTION: In the method for manufacturing the high-strength low-specific gravity steel sheet excellent in ductility having a specific gravity of 0.2 to 3.0% Mn, ≤0.02% P, ≤0.02% S, 5.0-10.0% Al, 0.001-0.05% N and satisfied to 20 COPYRIGHT: (C)2010,JPO&INPIT

High-strength steel sheets with excellent resistance to delayed fracture after forming, method for manufacturing the same, and high-strength automotive part manufactured of the same

Abstract: Steel sheets containing residual austenite of not more than 7 vol. %, crystallized and/or precipitated compounds with particle diameters of 0.01 to 5.0 μm of 100 to 100000 particle/mm2 and C of 0.05 to 0.3 mass %, Si of not more than 3.0 mass %, Mn of 0.01 to 3.0 mass %, P of not more than 0.02 mass %, S of not more than 0.02 mass %, Al of 0.01 to 3.0 mass %, N of not more than 0.01 mass % and Mg of 0.0002 to 0.01 mass %, with the remainder comprising iron and unavoidable impurities.

Low specific gravity steel sheet having excellent ductility, fatigue property and toughness

Abstract: PROBLEM TO BE SOLVED: To provide a low specific gravity steel sheet which has excellent ductility, fatigue properties and toughness, and to provide a method for producing the same. SOLUTION: Disclosed is the low specific gravity steel sheet which contains, by mass, 0.9 to 1.8% Mn and 3.0 to 9.0% Al, and is limited to the contents of C of COPYRIGHT: (C)2011,JPO&INPIT