Nippon Steel Corporation

Mai Nagano

Akihiro Uenishi

Koutarou Hayashi

Yasuhiro Ito

Satoshi Hironaka

Hiroyuki Kawata

Kengo Takeda

Shigeru Yonemura

Ryuichi Nishimura

Yasunori Sawa

Hiroshi Kaido

Takuya Takayama

An objective of the present invention is to provide a steel sheet having a high strength which can provide excellent appearance quality. The steel sheet has a chemical composition including, in mass %, C: more than 0.030% to 0.145%, Si: 0% to 0.500%, Mn: 0.50% to 2.50%, P: 0% to 0.100%, S: 0% to 0.020%, Al: 0% to 1.000% or less, N: 0% to 0.0100%, and the like, wherein a metal micro-structures consisting of 70 to 95% of ferrite in volume fraction and 5 to 30% of hard phases in volume fraction, and a value X1 obtained by dividing a standard deviation of average Mn concentrations in a rolling direction at ¼ sheet-thickness positions in a sheet thickness direction by an average Mn concentration at the ¼ sheet-thickness positions is 0.025 or less.

Steel sheet

There is provided a steel sheet that delivers an excellent appearance quality in its formed product. The steel sheet has a chemical composition including, in mass %, C: 0.030% to 0.145%, Si: 0% to 0.500% or less, Mn: 0.50% to 2.50%, P: 0% to 0.100%, S: 0% to 0.020%, Al: 0% to 1.000%, N: 0% to 0.0100%, and the like, wherein a metal micro-structure consists of 70 to 95% ferrite in volume fraction and 5 to 30% hard phases in volume fraction, and a value X1 obtained by dividing a standard deviation of Vickers hardnesses Hat ¼ sheet-thickness positions by an average value of the Vickers hardnesses His 0.025 or less, and a value X2 obtained by dividing a standard deviation of Vickers hardnesses Hat a ½ sheet-thickness position by an average Value of the Vickers hardnesses His 0.030 or less.

A shock absorbing member which can increase impact absorption energy and also enables thinning of a steel sheet that is a starting material, a method for producing the shock absorbing member, and a method for producing a steel sheet for cold plastic working are provided. The shock absorbing member includes a ridge portion formed in a curved shape as viewed from a longitudinal direction, and a wall portion extending from the ridge portion. In the wall portion, a ratio σ/τbetween a tensile stress σwhen an elongation in a tensile test is 5% and a shear stress τwhen a shear strain in a shear test is 5√3% is 1.70 or less, or a ratio σ/τbetween a tensile stress σwhen an elongation in a tensile test is 10% and a shear stress τwhen a shear strain in a shear test is 10√3% is 1.70 or less.

Shock absorbing member, method for producing shock absorbing member, and method for producing steel sheet for cold plastic working

A galvannealed steel sheet according to one aspect of the present invention has a hot-dip galvannealed layer on at least one surface of the steel sheet, and the steel sheet has a predetermined chemical composition, in which the steel sheet contains 10% or more and 90% or less of ferrite, and 10% or more of tempered martensite and tempered bainite in terms of an area ratio, a sum of the ferrite, the tempered martensite, and the tempered bainite is 90% or more, carbides having a major axis of 50 nm or more and 300 nm or less are contained in grains of the ferrite in a number density of 20/μmor more, and a two-dimensional homogeneous dispersion ratio S of Mn is 0.75 or more and 1.30 or less.

Galvannealed steel sheet

There is provided an exterior panel including a steel sheet, the steel sheet including a flat portion, wherein in an outer-layer region of the flat portion, a microstructure contains, in volume fraction, ferrite of 80% or more, an average grain diameter of ferrite is 1.0 to 15.0 μm, an intensity ratio Xof ferrite is 0.30 or more to less than 3.50, when uEldenotes a uniform elongation measured with a tensile test specimen cut from the flat portion, and uEldenotes a theoretical uniform elongation that is derived from volume fractions, hardnesses, and average grain diameters of ferrite and martensite in a microstructure of an inside region of the flat portion, and a sheet thickness of the flat portion, uEl/uElis 0.44 to 0.80.

Exterior panel and automobile including the same

A steel sheet includes a predetermined composition satisfying Expression (1), in which the microstructure at the ¼ thickness position from the surface in the sheet thickness direction includes, by vol %, ferrite: 95% or more and a remainder of the microstructure: 5% or less, has a proportion of unrecrystallized ferrite in the ferrite of 5% or less, and a half width w and an X-ray wavelength λ at a peak of (200) plane of the ferrite satisfy Expression (2).0.80≤{(Ti/48−N/14)+Nb/93}/(C/12)≤5.00  (1)×λ≥0.20  (2)

Steel sheet and method of manufacturing the same

The cold-rolled steel sheet having a high bake hardening amount and excellent bendability after bake hardening according to the present invention has a predetermined composition, and contains 20% or more and 70% or less of ferrite and 30% or more of tempered martensite in terms of area ratio, in which a sum of ferrite and tempered martensite is 90% or more, and in a case where a microstructure image of 30 &#x3bc;m&#xd7;30 &#x3bc;m obtained by photographing a structure at a magnification of 2,000-fold is disposed in an xy coordinate system having a sheet thickness direction as an x-axis and a rolling direction as a y-axis, the microstructure image is divided into 1024 pieces in an x-axis direction and 1024 pieces in a y-axis direction to form 1024&#xd7;1024 divided regions, and a two-dimensional image is created by performing double gradation by assuming a value of '1' in each of the divided regions in one case where the structure is ferrite and assuming a value of '0' in the other cases, a heterogeneity &#x3b1; when two-dimensional discrete Fourier transform is performed on the two-dimensional image is 1.20 or less.

Cold-rolled steel sheet

What is provided is a high-strength steel sheet including, by mass %: C: 0.05% to 0.15%; Si: 1.5% or less; Mn: 2.00% to 5.00%; P: 0.100% or less; S: 0.010% or less; Al: 0.001% to 2.000%; N: 0.010% or less; and a remainder of Fe and impurities, in which Ceq defined by Ceq=C+Si/90+Mn/100+1.5P+3S is less than 0.21, the high-strength steel sheet contains martensite in an area ratio of 98% or more, and a residual structure is in an area ratio of 2% or less, a two-dimensional homogeneous dispersion ratio S defined by S=Sy/Sx(Sxis a dispersion value of Mn concentration profile data in a sheet width direction, and Syis a dispersion value of the Mn concentration profile data in a sheet thickness direction) is 0.85 or more and 1.20 or less, and a tensile strength is 1200 MPa or more.

High-strength steel sheet

What is provided is a high-strength steel sheet having a large bake hardening amount and a uniform bake hardenability is provided according to the present invention, the high-strength steel sheet comprising, by mass %: C: 0.13% to 0.40%; Si: 0.500% to 3.000%; Mn: 2.50% to 5.00%; P: 0.100% or less; S: 0.010% or less; Al: 0.001% to 2.000%; N: 0.010% or less; and a remainder consisting of Fe and impurities, wherein martensite is 95% or more in an area ratio, and residual structure is 5% or less in an area ratio, a ratio C1/C2 of an upper limit C1 (mass %) of Si concentrations to a lower limit C2 (mass %) of the Si concentrations in a cross section in a thickness direction is 1.25 or less, precipitates having a major axis of 0.05 &#x3bc;m or more and 1.00 &#x3bc;m or less and an aspect ratio of 1:3 or more are included in a number density of 30/&#x3bc;mor more, and a tensile strength is 1300 MPa or more.

A steel sheet includes, as a chemical composition, by mass %: C: 0.05-0.30%; Si: 0.2-2.0%; Mn: 2.0-4.0%; Al: 0.001-2.000%; P: 0.100% or less; S: 0.010% or less; N: 0.010% or less; Ti: 0-0.100%; Nb: 0-0.100%; V: 0-0.100%; Cu: 0-1.00%; Ni: 0-1.00%; Mo: 0-1.00%; Cr: 0-1.00%; W: 0-0.005%; Ca: 0-0.005%; Mg: 0-0.005%; a rare earth element (REM): 0-0.010%; B: 0-0.0030%; and a remainder of Fe and impurities, in which a metallographic structure contains, by area ratio, 95% or more of a hard structure and 0-5% of residual austenite, by mass % in a cross section in a thickness direction, C1/C2 which is a ratio of an upper limit C1 of a Mn content to a lower limit C2 of the Mn content is 1.5 or less, and a bake-hardening amount BH is 150 MPa or less.

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Tokyo, Japan

Mai Nagano