Nippon Steel Corporation

Mai Nagano

Akihiro Uenishi

Koutarou Hayashi

Yasuhiro Ito

Kengo Takeda

Hiroyuki Kawata

Shigeru Yonemura

Ryuichi Nishimura

Yasunori Sawa

Hiroshi Kaido

Satoshi Hironaka

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.

Steel sheet

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