Patent application number | Description | Published |
20100061878 | FERRITIC STAINLESS STEEL SHEET FOR WATER HEATER EXCELLENT IN CORROSION RESISTANCE AT WELDED PART AND STEEL SHEET TOUGHNESS - A ferritic stainless steel sheet for a water heater with excellent corrosion resistance of welds and toughness includes, in terms of mass %, 0.020% or less of C, 0.30 to 1.00% of Si, 1.00% or less of Mn, 0.040% or less of P, 0.010% or less of S, 20.0 to 28.0% of Cr, 0.6% or less of Ni, 0.03 to 0.15% of Al, 0.020% or less of N, 0.0020 to 0.0150% of 0, 0.3 to 1.5% of Mo, 0.25 to 0.60% of Nb, and 0.05% or less of Ti, the remainder being composed of Fe and unavoidable impurities, and the ferritic stainless steel sheet satisfying the following formulae (1) and (2): | 03-11-2010 |
20100139818 | FERRITIC STAINLESS STEEL SHEET HAVING SUPERIOR SULFURIC ACID CORROSION RESISTANCE AND METHOD FOR MANUFACTURING THE SAME - Disclosed is a ferritic stainless steel sheet which has excellent corrosion resistance against sulfuric acid in the high-temperature environment and shows less surface roughness at a bent part which is bent at 90° or more. Specifically disclosed is a ferritic stainless steel sheet which has the following chemical composition: C: 0.02 mass % or less, Si: 0.05 to 0.8 mass %, Mn: 0.5 mass % or less, P: 0.04 mass % or less, S: 0.010 mass % or less, Al: 0.10 mass % or less, Cr: 20 to 24 mass % Cu: 0.3 to 0.8 mass %, Ni: 0.5 mass % or less, Nb: 0.20 to 0.55 mass %, and N: 0.02 mass % or less, with the remainder being Fe and unavoidable impurities; and which has such a structure that the maximum particle diameter of an S-containing precipitate is 5 μm or smaller. | 06-10-2010 |
20110030854 | HIGH-STRENGTH STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A high strength steel sheet has a tensile strength of 900 MPa or higher that can achieve both high strength and good formability and a composition including, on a mass basis, C: 0.1% or more and 0.3% or less; Si: 2.0% or less; Mn: 0.5% or more and 3.0% or less; P: 0.1% or less; S: 0.07% or less; Al: 1.0% or less; and N: 0.008% or less, with the balance Fe and incidental impurities. The steel sheet microstructure includes, on an area ratio basis, 5% or more and 80% or less of ferrite, 15% or more of autotempered martensite, 10% or less of bainite, 5% or less of retained austenite, and 40% or less of as-quenched martensite; the mean hardness of the autotempered martensite is HV≦700; and the mean number of precipitated iron-based carbide grains each having a size of 5 nm or more and 0.5 μm or less and included in the autotempered martensite is 5×10 | 02-10-2011 |
20110048589 | HIGH-STRENGTH STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - An ultra-high strength steel sheet has a tensile strength of 1400 MPa or higher that can achieve both high strength and good formability and an advantageous method for manufacturing the steel sheet and includes a composition including, on a mass basis C: 0.12% or more and 0.50% or less; Si: 2.0% or less; Mn: 1.0% or more and 5.0% or less; P: 0.1% or less; S: 0.07% or less; Al: 1.0% or less; and N: 0.008% or less, with the balance Fe and incidental impurities. The steel microstructure includes, on an area ratio basis, 80% or more of autotempered martensite, less than 5% of ferrite, 10% or less of bainite, and 5% or less of retained austenite; and the mean number of precipitated iron-based carbide grains each having a size of 5 nm or more and 0.5 μm or less and included in the autotempered martensite is 5×10 | 03-03-2011 |
20110061777 | FERRITIC STAINLESS STEEL SHEET HAVING SUPERIOR PUNCHING WORKABILITY AND METHOD FOR MANUFACTURING THE SAME - A ferritic stainless steel sheet and a method for manufacturing the ferritic stainless steel sheet include a composition which contains 0.0030 to 0.012 mass percent of C, 0.13 mass percent or less of Si, 0.25 mass percent or less of Mn, 0.04 mass percent or less of P, 0.005 mass percent or less of S, 0.06 mass percent or less of Al, 0.0030 to 0.012 mass percent of N, 20.5 to 23.5 mass percent of Cr, 0.3 to 0.6 mass percent of Cu, 0.5 mass percent or less of Ni, 0.3 to 0.5 mass percent of Nb, 0.05 to 0.15 mass percent of Ti, and the balance being Fe and inevitable impurities is hot-rolled at a finishing temperature of 900° C. or more and at a coiling temperature of 400 to 550° C., softening annealing is performed on an obtained hot-rolled steel sheet, picking is further performed, and cold rolling is subsequently performed. | 03-17-2011 |
20110146852 | HIGH STRENGTH STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A high-strength steel sheet has good ductility and stretch-flangeability and has a tensile strength (TS) of 980 MPa or more. The steel sheet contains 0.17%-0.73% C, 3.0% or less Si, 0.5%-3.0% Mn, 0.1% or less P, 0.07% or less S, 3.0% or less Al, and 0.010% or less N, in which Si+Al is 0.7% or more. | 06-23-2011 |
20130048161 | HIGH STRENGTH PRESS-FORMED MEMBER AND METHOD FOR MANUFACTURING THE SAME - A high strength press-formed member includes a steel sheet constituting the member including a composition including by mass %, C: 0.12% to 0.69%, Si: 3.0% or less, Mn: 0.5% to 3.0%, P: 0.1% or less, S: 0.07% or less, Al: 3.0% or less, N: 0.010% or less, Si+Al: at least 0.7%, and remainder as Fe and incidental impurities, wherein a microstructure of the steel sheet includes martensite, retained martensite, and bainite containing bainitic ferrite, an area ratio of said martensite with respect to the entire microstructure of the steel sheet is 10% to 85%, at least 25% of said martensite is tempered martensite, content of retained austenite is 5% to 40%, area ratio of said bainitic ferrite in said bainite with respect to the entire microstructure of the steel sheet is at least 5%, total of area ratios of said martensite, said retained austenite, and said bainitic ferrite in said bainite with respect to the entire microstructure of the steel sheet is at least 65%, and average carbon concentration in the retained austenite is at least 0.65 mass %. | 02-28-2013 |
20130061989 | HIGH STRENGTH HOT-ROLLED STEEL SHEET HAVING EXCELLENT STRETCH FLANGEABILITY AND FATIGUE RESISTANCE AND METHOD FOR MANUFACTURING THE SAME - A high strength hot-rolled steel sheet has a tensile strength of not less than 780 MPa and exhibits excellent stretch flangeability and excellent fatigue resistance. A steel has a composition containing C at 0.05 to 0.15%, Si at 0.2 to 1.2%, Mn at 1.0 to 2.0%, P at not more than 0.04%, S at not more than 0.005%, Ti at 0.05 to 0.15%, Al at 0.005 to 0.10% and N at not more than 0.007%. | 03-14-2013 |
20130087252 | HIGH-STRENGTH HOT-ROLLED STEEL SHEET HAVING EXCELLENT FORMABILITY AND METHOD FOR MANUFACTURING THE SAME - A high-strength hot-rolled steel sheet has a composition including C: 0.005% or more and 0.050% or less, Si: 0.2% or less, Mn: 0.8% or less, P: 0.025% or less, S: 0.01% or less, N: 0.01% or less, Al: 0.06% or less, and Ti: 0.05% or more and 0.10% or less, on a mass percent basis, such that S, N, and Ti satisfy Ti≧0.04+(N/14×48+S/32×48), the remainder being Fe and incidental impurities; a matrix in which a ferrite phase constitutes 95% by area or more of the entire structure; and a structure in which Ti-containing fine carbide having an average grain size of less than 10 nm is dispersedly precipitated, and the volume ratio of the fine carbide to the entire structure is 0.0007 or more. | 04-11-2013 |
20130087253 | HIGH STRENGTH STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A high strength steel sheet has tensile strength of at least 1470 MPa and (tensile strength×total elongation) of at least 29000 MPa·% with a composition including, by mass %, C: 0.30% to 0.73%, Si: 3.0% or less, Al: 3.0% or less, Si+Al: at least 0.7%, Cr: 0.2% to 8.0%, Mn: 10.0% or less, Cr+Mn: at least 1.0%, P: 0.1% or less, S: 0.07% or less, N: 0.010% or less, and remainder as Fe and incidental impurities; and processing the steel sheet such that microstructure satisfies area ratio of martensite with respect to the microstructure of 15% to 90%; content of retained austenite of 10% to 50%; at least 50% of the martensite is constituted of tempered martensite and area ratio of the tempered martensite with respect to the microstructure is at least 10%; and area ratio of polygonal ferrite with respect to the microstructure is 10% or less. | 04-11-2013 |
20130087254 | HIGH STRENGTH HOT-ROLLED STEEL SHEET HAVING EXCELLENT STRETCH-FLANGE FORMABILITY AND METHOD FOR MANUFACTURING THE SAME - A high strength hot-rolled steel sheet has a composition containing more than 0.035% to 0.055% C, 0.2% or less Si, 0.35% or less Mn, 0.03% or less P, 0.03% or less S, 0.1% or less Al, 0.01% or less N, 0.08% to 0.25% Ti, and 0.0005% to 0.0035% B on a mass basis, solute B being 0.0005% or more, the remainder being Fe and unavoidable impurities; a matrix containing a ferrite phase having an area fraction of more than 95%; a microstructure in which Ti carbides having an average grain size of less than 10 nm are finely precipitated in grains of the ferrite phase and the volume fraction of the Ti carbides is 0.0015 to 0.007; and a tensile strength of 780 MPa or more. | 04-11-2013 |
20130133786 | METHOD FOR MANUFACTURING HIGH STRENGTH STEEL SHEET - A method for manufacturing a high strength steel sheet includes heating a steel sheet containing at least 0.10 mass % of carbon to either a temperature in an austenite single phase region or a temperature in an (austenite+ferrite) two-phase region; cooling the steel sheet to a cooling stop temperature as a target temperature set within a cooling temperature region ranging from Ms to (Ms−150° C.) to allow a portion of non-transformed austenite to proceed to martensitic transformation; retaining a coldest part in a sheet widthwise direction of the steel sheet at a temperature in a temperature range from the cooling stop temperature as the target temperature to (the cooling stop temperature+15° C.) for 15 seconds to 100 seconds; and heating the sheet to a temperature to temper said martensite, wherein “Ms” represents martensitic transformation start temperature and said cooling temperature region is exclusive of Ms and inclusive of (Ms−150° C.). | 05-30-2013 |
20140096876 | HIGH STRENGTH PRESS-FORMED MEMEBER AND METHOD FOR MANUFACTURING THE SAME - A method for manufacturing a high strength press-formed member includes preparing a steel sheet having the composition including by mass %: C: 0.12% to 0.69%, Si: 3.0% or less, Mn: 0.5% to 3.0%, P: 0.1% or less, S: 0.07% or less, Al: 3.0% or less, N: 0.010% or less, Si+Al: at least 0.7%, and remainder as Fe and incidental impurities, heating the steel sheet to a temperature of 750° C. to 1000° C. and retaining the steel sheet in that state for 5 seconds to 1000 seconds; subjecting the steel sheet to hot press-forming at a temperature of 350° C. to 900° C.; cooling the steel sheet to a temperature of 50° C. to 350° C.; heating the steel sheet to a temperature in a temperature region of 350° C. to 490° C.; and retaining the steel sheet at temperature in the temperature region for 5 seconds to 1000 seconds. | 04-10-2014 |
20140238555 | HIGH STRENGTH HOT ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A high strength hot rolled steel sheet having a tensile strength of 780 MPa or more is produced by specifying the composition to contain C: more than 0.035% and 0.07% or less, Si: 0.3% or less, Mn: more than 0.35% and 0.7% or less, P: 0.03% or less, S: 0.03% or less, Al: 0.1% or less, N: 0.01% or less, Ti: 0.135% or more and 0.235% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, in such a way that C, S, N, and Ti satisfy ((Ti−(48/14)N−(48/32)S)/48)/(C/12)<1.0 (C, S, N, and Ti: content of the respective elements (percent by mass)) and specifying the microstructure in such a way that a matrix includes more than 95% of ferritic phase on an area fraction basis and fine Ti carbides having an average grain size of less than 10 nm are precipitated in the grains of the above-described ferritic phase. | 08-28-2014 |
20140242416 | HIGH-STRENGTH STEEL SHEET AND METHOD FOR MANUFACTURING SAME - 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 μm or less, average diameter of a group of polygonal ferrite grains is 15 μm 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. | 08-28-2014 |
20140295210 | HIGH STRENGTH HOT ROLLED STEEL SHEET AND METHOD FOR PRODUCING THE SAME - A hot rolled steel sheet includes a composition including: C: 0.03% to less than 0.07%; Si: 0.3% or less; Mn: 0.5% to 2.0%; P: 0.025% or less; S: 0.005% or less; N: 0.0060% or less; Al: 0.1% or less; Ti: 0.07% to 0.11%; and V: 0.08% to less than 0.15% on a mass percent basis, such that Ti and V contents satisfy: | 10-02-2014 |
20140305550 | HIGH STRENGTH HOT ROLLED STEEL SHEET AND METHOD FOR PRODUCING THE SAME - A high strength hot rolled steel sheet has a matrix that has a ferrite phase with an area ratio of 95% or more with respect to an overall structure; and a structure where a fine carbide is dispersedly precipitated, the fine carbide containing Ti and V having an average particle size of less than 10 nm in the matrix, the fine carbide has a volume fraction of 0.0050 or more with respect to the overall structure, a proportion of a number of carbides with a particle size of 30 nm or more containing Ti is less than 10% with respect to a total number of carbides, the high strength hot rolled steel sheet has a tensile strength of 980 MPa or more. | 10-16-2014 |
20150030879 | HOT ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A semi-manufactured steel material has a chemical composition including, by mass %, C: 0.055% to 0.15%, Si: not more than 0.2%, Mn: not more than 1.3%, P: not more than 0.03%, S: not more than 0.007%, Al: not more than 0.1%, N: not more than 0.01%, and Ti: 0.14% to 0.30%, the balance comprising Fe and inevitable impurities. In the composition, 1.0 ([C]/12)/([Ti*]/48) is satisfied ([C], [S], [N] and [Ti]: contents (mass %) of the respective elements, and [Ti*]=[Ti]−3.4×[N]−1.5×[S]), and the contents of niobium and boron as impurities are limited to Nb: less than 0.03% and B: less than 0.0005%. | 01-29-2015 |
Patent application number | Description | Published |
20120216925 | HOT-PRESSED STEEL SHEET MEMBER, STEEL SHEET FOR HOT-PRESS, AND METHOD FOR MANUFACTURING HOT-PRESSED STEEL SHEET MEMBER - A hot-pressed steel sheet member has a composition containing, by mass, C: 0.09% to 0.38%, Si: 0.05% to 2.0%, Mn: 0.5% to 3.0%, P: 0.05% or less, S: 0.05% or less, Al: 0.005% to 0.1%, N: 0.01% or less, Sb: 0.002% to 0.03%, and the balance being Fe and inevitable impurities, and having a tensile strength TS of 980 to 2,130 MPa. | 08-30-2012 |
20130192725 | HIGH STRENGTH STEEL SHEET HAVING EXCELLENT WARM STAMP FORMABILITY AND METHOD FOR MANUFACTURING THE SAME - A high strength steel sheet excellent in warm stamp formability and a method for manufacturing the same. The steel has a composition containing, in terms of % by mass, C: 0.01 to 0.2%, Si: 0.5% or lower, Mn: 2% or lower, P: 0.03% or lower, S: 0.01% or lower, Al: 0.07% or lower, and N: 0.01% or lower and further containing one or two or more elements selected from Ti, Nb, V, Mo, W, and B. | 08-01-2013 |
20130276940 | HIGH STRENGTH HOT ROLLED STEEL SHEET HAVING EXCELLENT FATIGUE RESISTANCE AND METHOD FOR MANUFACTURING THE SAME - A steel having a composition that includes C: 0.05 to 0.15%, Si: 0.2 to 1.2%, Mn: 1.0 to 2.0%, Al: 0.005 to 0.10%, N: 0.006% or less, and at least one selected from Ti: 0.03 to 0.13%, Nb: 0.02 to 0.10%, and V: 0.02 to 0.15% is subjected to rough rolling at a reduction of 80% or more and finish rolling at a finish rolling delivery temperature in the range of 800 to 950° C. The finish rolled sheet is subjected to cooling including cooling the finish rolled sheet from the finish rolling delivery temperature to a cooling end temperature in the range of 550 to 610° C. at an average cooling rate of 25° C./sec. or more and cooling the finish rolled sheet from the cooling end temperature of the previous process to a coiling temperature at an average cooling rate of 100° C./sec. or more. | 10-24-2013 |
20140007993 | HIGH STRENGTH HOT ROLLED STEEL SHEET HAVING EXCELLENT BLANKING WORKABILITY AND METHOD FOR MANUFACTURING THE SAME - A high strength hot rolled steel sheet having excellent blanking workability is provided. The composition contains C: 0.050 to 0.15%, Si: 0.1 to 1.5%, Mn: 1.0 to 2.0%, P: 0.03% or less, S: 0.0030% or less, Al: 0.01 to 0.08%, Ti: 0.05 to 0.15%, N: 0.005% or less, and the balance being Fe and unavoidable impurities. More than 95% of the microstructure is formed of a bainite phase in terms of area fraction. Average grain diameters of the bainite phase in a region having a thickness equal to ¼ of the sheet thickness from the surface in the sheet thickness direction is 5 μm or less in an L-direction cross section and 4 μm or less in a C-direction cross section. The number of crystal grains extended in the rolling direction and having an aspect ratio of 5 or more is 7 or less in a sheet thickness center portion. | 01-09-2014 |
Patent application number | Description | Published |
20130160904 | HIGH STRENGTH HOT ROLLED STEEL SHEET HAVING EXCELLENT TOUGHNESS AND METHOD FOR MANUFACTURING THE SAME - The steel sheet includes C: 0.04 to 0.12%, Si: 0.5 to 1.2%, Mn: 1.0 to 1.8%, P: not more than 0.03%, S: not more than 0.0030%, Al: 0.005 to 0.20%, N: not more than 0.005% and Ti: 0.03 to 0.13%, the balance being Fe and inevitable impurities, includes a microstructure containing a bainite phase at an area fraction exceeding 95% and having an average grain diameter of not more than 3 μm, has a difference ΔHv1 of not more than 50 between a Vickers hardness value at 50 μm from the surface and a Vickers hardness value at ¼ of a sheet thickness, has a difference ΔHv2 of not more than 40 between the Vickers hardness value at ¼ of the sheet thickness and a Vickers hardness value at ½ of the sheet thickness. | 06-27-2013 |
20130167985 | HIGH STRENGTH HOT ROLLED STEEL SHEET HAVING EXCELLENT BENDABILITY AND METHOD FOR MANUFACTURING THE SAME - A steel sheet including C at 0.05 to 0.15%, Si at 0.2 to 1.2%, Mn at 1.0 to 2.0%, P at not more than 0.04%, S at not more than 0.0030%, Al at 0.005 to 0.10%, N at not more than 0.005% and Ti at 0.03 to 0.13%, the balance being Fe and inevitable impurities, includes surface regions having an area fraction of bainite of less than 80% and an area fraction of a ferrite phase with a grain diameter of 2 to 15 μm of not less than 10%, the surface regions extending from both surfaces of the steel sheet each to a depth of 1.5 to 3.0% relative to a total sheet thickness, as well as an inner region other than the surface regions having an area fraction of a bainite phase of more than 95%, and has a tensile strength of not less than 780 MPa. | 07-04-2013 |
20140069556 | HIGH CARBON THIN STEEL SHEET AND METHOD FOR PRODUCING SAME - A high carbon steel sheet having a chemical composition containing C: 0.20% to 0.50%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.02% or less, sol. Al: 0.08% or less, N: 0.02% or less, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and a microstructure composed of ferrite and cementite, wherein the fraction of pro-eutectoid ferrite, among the ferrite, in the whole steel microstructure is 20% or more and less than 50%, the average grain size dc of the cementite in the region from the position at one-quarter of the sheet thickness of the steel sheet to the sheet thickness center is 0.50 to 1.5 μm, and the average grain size ds of the cementite in the region from the surface of the steel sheet to the position at one-quarter of the sheet thickness satisfies ds/dc≦0.8. | 03-13-2014 |
20140076469 | HIGH CARBON THIN STEEL SHEET AND METHOD FOR PRODUCING SAME - A steel sheet having a composition containing C: 0.20% to 0.50%, Si: 1.0% or less, Mn: 2.0% or less, P: 0.03% or less, S: 0.02% or less, sol.Al: 0.08% or less, N: 0.02% or less, and Fe and incidental impurities, and a microstructure composed of ferrite and cementite, wherein each of the average grain size ds of the ferrite in the region from the surface of the steel sheet to the position at one-quarter of the sheet thickness and the average grain size dc of the ferrite in the region from the position at one-quarter of the sheet thickness of the steel sheet to the sheet thickness center is 20 to 40 μm, 0.80≦ds/dc≦1.20 is satisfied, the average grain size of the cementite is 1.0 μm or more, the spheroidizing ratio is 90% or more, and 90% or more of cementite is present inside ferrite grains. | 03-20-2014 |
20140141280 | HIGH-STRENGTH STEEL SHEET FOR WARM FORMING AND PROCESS FOR PRODUCING SAME - Provided is a high-strength steel sheet having good warm press formability and excellent strength and ductility after warm press forming, and a method for manufacturing such. The high-strength steel sheet has a tensile strength at room temperature not less than 780 MPa, a yield stress at a heating temperature range of 400° C. to 700° C. not more than 80% of the yield stress at room temperature, total elongation at the heating temperature range not less than 1.1 times the total elongation at room temperature, yield stress and total elongation after the steel sheet is heated to the heating temperature range, subjected to a strain of not more than 20%, and cooled from the heating temperature to room temperature, not less than 70% of the yield stress and total elongation, respectively, at room temperature before the heating. | 05-22-2014 |
Patent application number | Description | Published |
20140332122 | HIGH CARBON HOT ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME (AS AMENDED) - A high carbon hot rolled steel sheet having a chemical composition containing by mass %, C: 0.20% to 0.48%, Si: 0.1% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.01% or less, Al: 0.1% to 0.6%, Cr: 0.05% to 0.5%, B: 0.0005% to 0.0050%, Ca: 0.0010% to 0.0050%, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, where the average amount of N in a surface layer portion from the surface to the position at a depth of 0.1 mm in thickness direction is 0.1% or more and the average amount of N in the central portion in thickness is 0.01% or less, and a microstructure composed of ferrite and carbides, wherein the average grain size of the ferrite is 10 to 20 and the spheroidization ratio of the carbides is 90% or more. | 11-13-2014 |
20140338801 | HIGH-STRENGTH HOT-ROLLED STEEL SHEET AND METHOD FOR PRODUCING SAME - A high-strength hot-rolled steel sheet including a chemical composition containing, in percent by mass, 0.05% to 0.12% of C, 0.05% to 1.0% of Si, 0.5% to 1.8% of Mn, 0.04% or less of P, 0.0030% or less of S, 0.005% to 0.07% of Al, 0.006% or less of N, 0.05% to 0.15% of Ti, and the balance being Fe and incidental impurities, in which, in a region in the range of ⅛ to ⅜ of the sheet thickness, the content of Ti*, which is Ti existing as precipitates, is 0.3×[Ti] to 0.6×[Ti], where [Ti] is the Ti content, and the steel sheet has a microstructure in which the area fraction of the bainite phase in the entire structure is more than 95%. | 11-20-2014 |
20140363696 | HIGH-STRENGTH HOT ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A high-strength hot rolled steel sheets with excellent stretch flangeability has small variations in mechanical properties in individual coils. Variations in strength from place to place in a coil are decreased by minimally reducing the Si and Mn contents to suppress the occurrence of problems such as segregation. Further, the microstructure of the steel sheets is configured such that a ferrite phase represents an area ratio of not less than 95%, the ferrite crystal grains have an average grain size of not less than 1 μm, and the ferrite crystal grains contain TiC with an average particle size of not more than 7 nm dispersed in the crystal grains. | 12-11-2014 |
20150056468 | HIGH STRENGTH STEEL SHEET AND METHOD OF MANUFACTURING THE SAME - The high strength steel sheet has a chemical composition including 0.08% to 0.20% of C, 0.3% or less of Si, 0.1% to 3.0% of Mn, 0.10% or less of P, 0.030% or less of S, 0.10% or less of Al, 0.010% or less of N, 0.20% to 0.80% of V, and the remainder composed of Fe and incidental impurities on a percent by mass basis, and a microstructure which includes 95% or more of ferrite phase on an area percentage basis, in which fine precipitates are dispersed having a distribution in such a way that the number density of precipitates having a particle size of less than 10 nm is 1.0×10 | 02-26-2015 |
20150090376 | HIGH CARBON HOT-ROLLED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME - A high carbon hot rolled steel sheet and a method for manufacturing the same are provided, wherein excellent cold workability and excellent hardenability are obtained stably. The high carbon hot rolled steel sheet has a composition containing C: 0.20% to 0.48%, Si: 0.1% or less, Mn: 0.5% or less, P: 0.03% or less, S: 0.01% or less, sol. Al: more than 0.10% and 1.0% or less, N: 0.005% or less, B: 0.0005% to 0.0050%, and the remainder composed of Fe and incidental impurities, on a percent by mass basis, and a microstructure composed of ferrite and cementite, wherein the average grain size of the above-described ferrite is 10 to 20 μm and the spheroidization ratio of the above-described cementite is 90% or more. | 04-02-2015 |