Showing papers by "Nobuhiro Fujita published in 2012"

Hot-rolled steel sheet and method for producing same

Abstract: A hot-rolled steel sheet according to the present invention is a steel sheet containing a predetermined components, and satisfying O < S/Ca < 0.8, N - 14/ 48 x Ti ≧ "0" (zero)%. It is a high-strength hot-rolled steel sheet for a spiral pipe excellent in low-temperature toughness in which a pro-eutectoid ferrite fraction is 3% or more and 20% or less, and the other is a low-temperature transformation phase in a microstructure at a depth of a half thickness of a sheet thickness from a steel sheet surface, a number average crystal grain size of a whole of the microstructure is 2.5 µm or less, an area average grain size is 9 µm or less, a standard deviation of the area average grain size is 2.3 µm or less, and a reflected X-ray intensity ratio {211}/ {111} in a {211} direction and in a {111} direction relative to a plane in parallel to the steel sheet surface at the depth of the half thickness of the sheet thickness from the steel sheet surface is 1.1 or more. The steel sheet has both high-toughness and strength of API5L-X80 standard or more.

Hot-rolled steel sheet and manufacturing method thereof

Abstract: There are provided a high-strength hot-rolled steel sheet securing low-temperature toughness and having excellent stretch flangeability by controlling a structural fraction and a hardness difference among structures, and a manufacturing method thereof. A hot-rolled steel sheet contains: C: 0.01 to 0.2%; Si: 0.001 to 2.5% or less; Mn: 0.10 to 4.0% or less; P: 0.10% or less; S: less than 0.03%; Al: 0.001 to 2.0%; N: less than 0.01%; Ti: (0.005+48/14[N]+48/32[S]) % or more and 0.3% or less; Nb: 0 to 0.06%; Cu: 0 to 1.2%; Ni: 0 to 0.6%; Mo: 0 to 1%; V: 0 to 0.2%; Cr: 0 to 2%; Mg: 0 to 0.01%; Ca: 0 to 0.01%; REM: 0 to 0.1%; and B: 0 to 0.002%, and has: an texture in which, at a central portion of a sheet thickness located between ⅜ to ⅝ thickness positions of the sheet thickness from a surface of the steel sheet, an average value of X-ray random intensity ratios of a group of {100} to {223} orientations of a sheet plane is 6.5 or less and an X-ray random intensity ratio of a {332} crystal orientation is 5.0 or less; and a microstructure in which a total area ratio of tempered martensite, martensite and lower bainite is more than 85%, and an average crystal grain diameter is 12.0 m or less.

Cold-rolled steel sheet and production method thereof

Abstract: This is a cold-rolled steel sheet includes, by mass %, C: 0.02% to 0.4%, Si: 0.001% to 2.5%, Mn: 0.001% to 4.0%, and Al: 0.001% to 2.0%. The sum of the Si content and the Al content is 1.0% to 4.5%. An average pole density of an orientation group from {100} to {223} is 1.0 to 6.5, and a pole density of a crystal orientation {332} is 1.0 to 5.0. A microstructure includes, by an area ratio %, 5% to 80% of ferrite, 5% to 80% of bainite, and 2% to 30% of retained austenite. In the microstructure, by an area ratio %, martensite is limited to 20% or less, pearlite is limited to 10% or less, and tempered martensite is limited to 60% or less.

Hot-rolled steel sheet and process for producing same

Abstract: This hot-rolled steel sheet has an average pole density for {100} to {223} orientations of 1.0-5.0, has a pole density for the crystal orientation {332} of 1.0-4.0, and has a metallographic structure which comprises, in terms of areal proportion, 30-99% ferrite and bainite and 1-70% martensite and which satisfies the following relationships (1) and (2) wherein fM is the areal proportion of the martensite in % by area, dia is the average size of the martensite in µm, dis is the average distance between martensite grains in µm, and TS is the tensile strength of the steel sheet in MPa. dia≤13 µm (relationship 1) TS/fM×dis/dia≥500 (relationship 2)

High-strength cold-rolled steel sheet with excellent stretch flangeability and precision punchability, and process for producing same

Abstract: A high-strength cold-rolled steel sheet having excellent stretch flangeability and precision punchability which contains given components, with the remainder comprising iron and incidental impurities. In the range of from a depth from a surface of the steel sheet which corresponds to 5/8 the sheet thickness to a depth therefrom which corresponds to 3/8 the sheet thickness, the average pole density for {100} to {223} orientations which are represented by the crystal orientations {100} , {116} , {114} , {113} , {112} , {335} , and {223} is 6.5 or less and the pole density for the crystal orientation {332} is 5.0 or less. The steel sheet has a metallographic structure that contains pearlite in an amount exceeding 5% in terms of areal proportion and has a total content of bainite and martensite limited to below 5% in terms of areal proportion, with the remainder comprising ferrite.

High-strength hot-dipped galvanized steel sheet and high-strength alloyed hot-dipped galvanized steel sheet, each having tensile strength of 980 mpa or more, excellent plating adhesion, excellent formability and excellent bore expanding properties, and method for producing same

Abstract: Provided is a high-strength hot-dip galvanized steel sheet having excellent plating adhesion, formability, and hole expandability with an ultimate tensile strength of 980 MPa or more, the hot-dip galvanized steel sheet comprising a hot-dip galvanized layer formed on a surface of a base steel sheet. The base steel sheet contains, by mass%, C: 0.05% to 0.4%; Si: 0.01% to 3.0%; Mn: 0.1% to 3.0%; Al: 0.01 to 2.0%; in which Si + Al > 0.5%, P: limited to 0.04% or less; S: limited to 0.05% or less; N: limited to 0.01% or less; and a balance including Fe and inevitable impurities, a microstructure of the base steel sheet contains 40% or more by total volume fraction of martensite and bainite, 8% or more by volume fraction of residual austenite, and a balance of the microstructure being ferrite or ferrite and 10% or less by volume fraction of pearlite. The martensite contains 10% or more by total volume fraction of two or more kinds of three kinds of martensites (1), (2), and (3), and the hot-dip galvanized layer contains less than 7 mass% of Fe.

Galvanized steel sheet and method of manufacturing same

Abstract: This galvanized steel sheet is provided with a steel plate and a plating layer on the surface of the steel plate. The steel plate has a steel chemical composition including, in mass%, C:0.05-0.40%, Si:0.5-3.0% and Mn:1.5-3.0%, has a microstructure containing ferrite, bainite, a 30% or higher volume fraction of tempered martensite, and an 8% or higher volume fraction of austenite, and has a 980MPa or greater tensile strength; the plating layer contains an oxide containing at least one chemical element selected from Si, Mn and Al, and has a 10% or greater projected area ratio of the aforementioned oxide when seen in a plate thickness direction cross-section that includes the steel plate and the plating layer.

Hot-rolled steel sheet and production method therefor

Abstract: Disclosed is a hot-rolled steel sheet including, by mass%, C:0.02% to 0.5% of C, and the sum of the content of Si and the content ofAl is 1.0% to 4.0%. An average pole density of an orientation group from {100} to {223} is 1.0 to 6.5, and a pole density of a crystal orientation {332} is 1.0 to 5.0. A microstructure includes, by of an area ratio, 2% to 30% of retained austenite, 20% to 50% of ferrite, and 10% to 60% of bainite. rC that is a Lankford value in a direction orthogonal to a rolling direction is 0.70 to 1.10, and r30 that is a Lankford value in a direction forming an angle of 30° with the rolling direction is 0.70 to 1.10.

High-strength cold-rolled steel sheet with highly even stretchabilty and excellent hole expansibility, and process for producing same

Abstract: This high-strength cold-rolled steel sheet having excellent uniform elongation and hole expandability contains, C: 0.01 to 0.4%; Si: 0.001 to 2.5%; Mn: 0.001 to 4.0%; P: 0.001 to 0.15%; S: 0.0005 to 0.03%; Al: 0.001 to 2.0%; N: 0.0005 to 0.01%; and O: 0.0005 to 0.01%; in which Si + Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which at a sheet thickness center portion, an average value of pole densities of the {100} to {223} orientation group is 5.0 or less, and a pole density of the {332} crystal orientation is 4.0 or less, a metal structure contains 5 to 80% of ferrite, 5 to 80% of bainite, and 1% or less of martensite in terms of an area ratio and the total of martensite, pearlite, and retained austenite is 5% or less, and an r value (rC) in a direction perpendicular to a rolling direction is 0.70 or more and an r value (r30) in a direction 30° from the rolling direction is 1.10 or less.

Cold-rolled steel sheet and method for producing same

Abstract: A cold-rolled steel sheet satisfies that an average pole density of an orientation group of {100} to {223} is 1.0 to 5.0, a pole density of a crystal orientation {332} is 1.0 to 4.0, a Lankford-value rC in a direction perpendicular to a rolling direction is 0.70 to 1.50, and a Lankford-value r30 in a direction making an angle of 30° with the rolling direction is 0.70 to 1.50. Moreover, the cold-rolled steel sheet includes, as a metallographic structure, by area %, a ferrite and a bainite of 30% to 99% in total and a martensite of 1% to 70%.

Hot-dip galvanized steel sheet and process for producing same

Abstract: This hot-dip galvanized steel sheet comprises a steel sheet and a deposit layer formed on the surface of the steel sheet, wherein the steel sheet has a microstructure that contains 20-99 vol.% martensite and/or bainite, with the remaining structure comprising ferrite and below 8 vol.% retained austenite and/or up to 10 vol.% pearlite, the steel sheet has a tensile strength of 980 MPa or higher, and the deposit layer is a deposit layer formed by hot-dip galvanization which contains an oxide containing one or more of Si, Mn, and Al and further contains up to 15 mass% Fe, with the remainder comprising Zn, Al, and incidental impurities. When a sheet-thickness-direction cross-section which includes the steel sheet and the deposit layer formed by hot-dip galvanization is examined, the proportion of projected area is 10-90%.

High-strength cold-rolled steel sheet, high-strength galvanized steel sheet, and high-strength alloying hot-dip galvanized steel sheet, excellent in bendability, and method for manufacturing the same

Abstract: PROBLEM TO BE SOLVED: To provide a high-strength steel sheet having excellent bendability and 900 MPa or higher tensile maximum strength, and to provide a method for manufacturing the high-strength steel sheet.SOLUTION: A steel sheet is composed of steel containing 0.075-0.300% C, 0.30-2.50% Si, 1.30-3.50% Mn, 0.001-0.050% P, 0.0001-0.0100 S, 0.001-1.500% Al, 0.0001-0.0100% N, 0.0001-0.0100% O, and having the structure containing ≥50% of bainite and 3-30% of retained austenite, and a ratio of the hardness Hvs on the steel sheet surface layer to the hardness Hvb at 1/4 thickness of the steel sheet being 0.35-0.90. The steel sheet is manufactured in such a manner that after cold rolling, an annealing is applied in the temperature range near the Ac3 transformation point under atmosphere of -3.0 to 0.0 log (water partial pressure/hydrogen partial pressure), and retention at 300-500°C for 10-1000 sec is performed on the way of cooling after annealing.

Hot-dip galvanized steel sheet and manufacturing method thereof

Abstract: A hot-dip galvanized steel sheet includes: a steel sheet; and a plated layer on a surface of the steel sheet, a microstructure contains, by volume fraction, equal to or more than 20% and equal to or less than 99% in total of one or two of martensite and bainite, a residual structure contains one or two of ferrite, residual austenite of less than 8% by volume fraction, and pearlite of equal to or less than 10% by volume fraction, tensile strength is equal to or greater than 980 MPa, the plated layer is a hot-dip galvanized layer which contains oxides including one or two or more of Si, Mn, and Al, contains equal to or less than 15 mass % of Fe, and a remainder including Zn, Al, and unavoidable impurities, and when a cross section including the steel sheet and the hot-dip galvanized layer is seen in a sheet thickness direction, a projected area ratio is equal to or more than 10% and equal to or less than 90%.

High-strength hot dip galvanized steel plate having excellent moldability, weak material anisotropy and ultimate tensile strength of 980 mpa or more, high-strength alloyed hot dip galvanized steel plate and manufacturing method therefor

Abstract: [] Provided 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, by mass%, C: 0.1 to less than 0.40%, Si: 0.5 to 3.0%, Mn: 1.5 to 3.0%, O: limited to 0.006% or less, P: limited to 0.04% or less, S: limited to 0.01% or less, Al: limited to 2.0% or less, N: limited to 0.01% or less, and a balance including Fe and inevitable impurities. A microstructure of the base steel sheet contains ferrite of 40% or more, residual austenite of 8 to less than 60%, by volume fraction, and a balance being bainite or martensite. In a sheet thickness range of 5/8 to 3/8 from the surface of the base steel sheet, a pole density of specific crystal orientation is within a predetermined range. The hot-dip galvanized layer contains Fe: less than 7 mass% and a balance including Zn, Al, and inevitable impurities.

Hot-rolled steel sheet and method of producing the same

Abstract: In this hot rolled steel sheet, the average value of the pole density of the {100} to {223} orientation group, which is an orientation group represented by the arithmetic average of the orientations {100} , {116} , {114} , {112} and {223} in the central part in the sheet thickness direction, which is 5/8 to 3/8 of the sheet thickness from the surface of the steel sheet, is not lower than 1.0 and not higher than 6.5, the pole density of the {332} crystal orientation is not lower than 1.0 and not higher than 5.0, the Lankford value (rC) in a direction perpendicular to the rolling direction is not lower than 0.70 and not higher than 1.10, and the Lankford value (r30) in a direction at an angle of 30° to the aforementioned rolling direction is not lower than 0.70 and not higher than 1.10.

High-strength cold-rolled steel sheet with excellent local formability, and manufacturing method therefor

Abstract: This high-strength cold-rolled steel sheet with excellent local formability contains, in mass%, 0.02% to 0.20% C, 0.001% to 2.5% Si, 0.01% to 4.0% Mn, 0.001% to 0.15% P, 0.0005% to 0.03% S, 0.001% to 2.0% Al, 0.0005% to 0.01% N, and 0.0005% to 0.01% O, where Si + Al is restricted to less than 1.0%, and the remainder comprises iron and unavoidable impurities; the area ratio of bainite in the metal structure is at least 95%; the average value of the polarization density of {100} to {223} orientation groups in a sheet thickness central area, which has a sheet thickness ranging from 5/8 to 3/8 from the surface of the steel sheet, is not more than 4.0, and the polarization density of the {332} crystal orientation is not more than 5.0; and the volume mean diameter of the crystal particles of the metal structure is not more than 7 μm.

Bainite-containing high-strength hot-rolled steel plate with excellent isotropic workability and process for producing same

Abstract: The present invention provides a bainite-containing high-strength hot-rolled steel plate having excellent isotropic workability. This bainite-containing high-strength hot-rolled steel plate contains, in terms of mass%, 0.07-0.2%, excluding 0.07%, C, 0.001-2.5% Si, 0.01-4% Mn, up to 0.15% P (excluding 0%), up to 0.03% S (excluding 0%), up to 0.01% N (excluding 0%), and 0.001-2% Al, with the remainder comprising Fe and incidental impurities. In the thickness-direction middle part which ranges from 5/8 to 3/8 the plate thickness in terms of depth from a surface of the steel plate, the average of the values of pole density of the orientations {100} to {223} is 4.0 or less and the pole density of the crystal orientation {332} is 4.8 or less. The steel plate has an average crystal-grain diameter of 10 µm or less and a Charpy fracture appearance transition temperature (vTrs) of -20oC or lower. The steel plate has a microstructure which comprises 35% or less pro-eutectoid ferrite and a phase generated by low-temperature transformation as the remainder.

Cold rolled steel sheet and production method therefor

Abstract: This is a cold-rolled steel sheet includes, by mass%, C: 0.02% to 0.4%, Si: 0.001% to 2.5%, Mn: 0.001% to 4.0%, and Al: 0.001% to 2.0%. The sum of the Si content and the Al content is 1.0% to 4.5%. An average pole density of an orientation group from {100} to {223} is 1.0 to 6.5, and a pole density of a crystal orientation {332} is 1.0 to 5.0. A microstructure includes, by an area ratio%, 5% to 80% of ferrite, 5% to 80% of bainite, and 2% to 30% of retained austenite. In the microstructure, by an area ratio%, martensite is limited to 20% or less, pearlite is limited to 10% or less, and tempered martensite is limited to 60% or less.

Hot-rolled steel sheet and production method thereof

Abstract: Disclosed is a hot-rolled steel sheet including, by mass %, C:0.02% to 0.5% of C, and the sum of the content of Si and the content of Al is 1.0% to 4.0%. An average pole density of an orientation group from {100} to {223} is 1.0 to 6.5, and a pole density of a crystal orientation {332} is 1.0 to 5.0. A microstructure includes, by of an area ratio, 2% to 30% of retained austenite, 20% to 50% of ferrite, and 10% to 60% of bainite. rC that is a Lankford value in a direction orthogonal to a rolling direction is 0.70 to 1.10, and r30 that is a Lankford value in a direction forming an angle of 30° with the rolling direction is 0.70 to 1.10.

Hot-dip galvanized thin steel sheet, thin steel sheet processed by hot-dip galvanized layer, and a method of producing the same

Abstract: The present invention provides: a high-strength high-ductility hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having high fatigue resistance and corrosion resistance; a high-strength hot-dip galvanized steel sheet excellent in ductility, which improves non-plating defects and plating adhesion after severe deformation, and a method of producing the same; a high-strength and high-ductility hot-dip galvanized steel sheet having high fatigue resistance and corrosion resistance; a high-strength hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having superiorappearance and workability, which suppresses the generation of non-plating defects, and a method of producing the same; and a high-strength hot-dip galvannealed steel sheet and a high-strength hot-dip galvanized steel sheet, which suppress non-plating defects and surface defects and have both corrosion resistance, in particular corrosion resistance in an environment containing chlorine ion, and high ductility, and a method of producing the same.

Bainite-containing-type high-strength hot-rolled steel sheet having excellent isotropic workability and manufacturing method thereof

Abstract: The present invention provides a bainite-containing-type high-strength hot-rolled steel sheet. The steel sheet, containing C: greater than 0.07 to 0.2%, Si: 0.001 to 2.5%, Mn: 0.01 to 4%, P: 0.15% or less, S: 0.03% or less, N: 0.01% or less, Al: 0.001 to 2% and a balance being composed of Fe and impurities, has an average value of pole densities of the {100} to {223} orientation group at a sheet thickness center portion being a range of ⅝ to ⅜ in sheet thickness from the surface of the steel sheet is 4.0 or less, and a pole density of the {332} crystal orientation is 4.8 or less, an average crystal grain diameter is 10 μm or less and vTrs is −20° C. or lower, and a microstructure is composed of 35% or less in a structural fraction of pro-eutectoid ferrite and a balance of a low-temperature transformation generating phase.

Hot-rolled steel sheet for gas nitrocarburizing and manufacturing method thereof

Abstract: In a hot-rolled steel sheet, an average pole density of an orientation group of {100} to {223} , which is represented by an arithmetic average of pole density of each orientation of {100} , {116} , {114} , {112} , and {223} in a center portion of a sheet thickness which is a range of the sheet thickness of ⅝ to ⅜ from a surface of the steel sheet, is 1.0 or more and 4.0 or less, the pole density of a crystal orientation of {332} is 1.0 or more and 4.8 or less, an average grain size in a center in the sheet thickness is 10 μm or less, and a microstructure includes, by a structural fraction, pearlite more than 6% and ferrite in the balance.

High-strength cold-rolled steel sheet having excellent local deformability and manufacturing method thereof

Abstract: This high-strength cold-rolled steel sheet contains, in mass %, C: 0.02% to 0.20%; Si: 0.001% to 2.5%; Mn: 0.01% to 4.0%; P: 0.001% to 0.15%; S: 0.0005% to 0.03%; Al: 0.001% to 2.0%; N: 0.0005% to 0.01%; and O: 0.0005% to 0.01%; in which Si+Al is limited to less than 1.0%, and a balance being composed of iron and inevitable impurities, in which an area ratio of bainite in a metal structure is 95% or more, at a sheet thickness center portion being a range of ⅝ to ⅜ in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100} to {223} orientation group is 4.0 or less, and a pole density of the {332} crystal orientation is 5.0 or less, and a mean volume diameter of crystal grains in the metal structure is 7 μm or less.

High-strength hot-dip galvanized steel sheet and high-strength alloyed hot-dip galvanized steel sheet having excellent formability and small material anisotropy with ultimate tensile strength of 980 mpa or more and manufacturing method therefor

Abstract: Provided is a hot dip galvanized steel plate having a hot dip galvanized layer on the surface of a base material steel plate. The base material steel plate contains 0.1 to less than 0.40% C, 0.5 to 3.0% Si, 1.5 to 3.0% Mn by mass, the quantity of O is limited to 0.006% or less, quantity of P to 0.04% or less, quantity of S to 0.01% or less, quantity of Al to 2.0% or less and quantity of N to 0.01% or less by mass, with the remainder consisting of iron and unavoidable impurities. The microstructure of the base material steel plate contains 40% or more ferrite, 8 to less than 60% residual austenite, in volume fraction, with the remainder consisting of bainite or martensite. In a plate thickness range of 5/8 to 3/8 from the surface of the base material steel plate, the polar density of specific crystal orientation is within a predetermined range. The hot dip galvanized layer contains less than 7% by mass Fe with the remainder consisting of Zn, Al and unavoidable impurities. Thus, the high-strength hot dip galvanized steel plate of the invention has excellent moldability, weak material anisotropy and an ultimate tensile strength of 980 MPa or more.

Hot-rolled steel for gaseous nitrocarburizing and manufacturing method thereof

Abstract: This invention provides a hot-rolled steel for gaseous nitrocarburizing with excellent isotropic workability, and a manufacturing method thereof. In addition to having an appropriate chemical composition, this hot-rolled steel for gaseous nitrocarburizing has, in the plate thickness center 5/8 to 3/8 of the plate thickness from the surface of the steel plate, a 1.0-4.0 average pole density of the orientation group {100} -{223} , expressed by the arithmetic average of the pole densities of each orientation of {100} , {116} , {114} , {112} and {223} , and has a 1.0-4.8 pole density of the crystal orientation {332} . This hot-rolled steel sheet further has a 10μm or smaller average crystal particle diameter in the plate thickness center, and the microstructure comprises perlite (over 6% by component percentage) and ferrite (the remaining portion).

High-strength thin steel sheet excellent in elongation and uniform coating-baking hardenability and method for producing the same

Abstract: PROBLEM TO BE SOLVED: To provide a high-strength thin steel sheet excellent in uniform coating-baking hardenability in a retained austenite steel, and a method for producing the high-strength thin steel sheet.SOLUTION: A high-strength thin steel sheet excellent in elongation and uniform coating-baking hardenability has a specific steel composition, contains one or more of ferrite, bainite and tempered martensite, and contains 3% or more of retained austenite, wherein an average particle diameter of the austenite is 1 μm or more and 8 μm or less, and an austenite particle whose central concentration Cgc and grain boundary Cgb satisfy formula (1) accounts for 50% or more. Cgb/Cgc≥1.1 (1).

Galvanized steel sheet and method of manufacturing the same

Abstract: This galvanized steel sheet is provided with a steel plate and a plating layer on the surface of the steel plate. The steel plate has a steel chemical composition including, in mass%, C:0.05-0.40%, Si:0.5-3.0% and Mn:1.5-3.0%, has a microstructure containing ferrite, bainite, a 30% or higher volume fraction of tempered martensite, and an 8% or higher volume fraction of austenite, and has a 980MPa or greater tensile strength; the plating layer contains an oxide containing at least one chemical element selected from Si, Mn and Al, and has a 10% or greater projected area ratio of the aforementioned oxide when seen in a plate thickness direction cross-section that includes the steel plate and the plating layer.

High-strength cold-rolled steel sheet having excellent uniform elongation and hole expandability and manufacturing method thereof

Abstract: A high-strength cold-rolled steel sheet having highly even stretchability and excellent hole expansibility, which contains 0.01-0.4% C, 0.001-2.5% Si, 0.001-4.0% Mn, 0.001-0.15% P, 0.0005-0.03% S, 0.001-2.0% Al, 0.0005-0.01% N, and 0.0005-0.01% O, Si+Al being less than 1.0% and the remainder comprising iron and incidental impurities. In the steel sheet, a thickness-direction middle part has an average pole density for {100} to {223} orientations of 5.0 or less and a pole density for {332} crystal orientation of 4.0 or less. The steel sheet has a metallographic structure which comprises, in terms of areal proportion, 5-80% ferrite, 5-80% bainite, and up to 1% martensite, the total of martensite, pearlite, and retained austenite being 5% or less. The steel sheet has an r value for the direction perpendicular to the rolling direction (rC) of 0.70 or above and an r value for a direction making an angle of 30o with the rolling direction (r30) of 1.10 or below.

High-strength cold-rolled steel sheet having excellent stretch flangeability and precision punchability and manufacturing method thereof

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 5/8 to 3/8 in sheet thickness from the surface of the steel sheet, an average value of pole densities of the {100 } to {223} orientation group represented by respective crystal orientations of {100} , {116} , {114} , {113} , {112} , {335 } , and {223 } is 6.5 or less, and a pole density of the {332} 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.

Cold-rolled steel sheet

Abstract: A cold-rolled steel sheet satisfies that an average pole density of an orientation group of {100} to {223} is 10 to 50, a pole density of a crystal orientation {332} is 10 to 40, a Lankford-value rC in a direction perpendicular to a rolling direction is 070 to 150, and a Lankford-value r30 in a direction making an angle of 30° with the rolling direction is 070 to 150 Moreover, the cold-rolled steel sheet includes, as a metallographic structure, by area %, a ferrite and a bainite of 30% to 99% in total and a martensite of 1% to 70%