Posco

Posco Co., Ltd

Seong-Ho Han

Yu-Mi Ha

Jun-Sung Yeom

Il-Ryoung Sohn

Sang-Ho Han

Min-Seo Koo

Shin-Hwan Kang

Chung-Won Kim

Sang-Hyun Kim

Min-Ki Seun

Yong-Hoon Choi

Provided are a high-strength galvanized steel sheet having excellent distinctness of image after painting and a manufacturing method therefor. The steel sheet includes: by mass %, 0.003 to 0.005% of C, 0.05% or less of Si, 0.4 to 1.0% of Mn, 0.04 to 0.06% of P, 0.01% or less of S, 0.005% or less of N, 0.1% or less of S. Al, 0.05 to 0.08% of Mo, 0.005 to 0.03% of Ti, 0.02 to 0.035% of Nb, 0.06 to 0.1% of Cu, 0.0015% or less of B, and a balance of Fe and inevitable impurities. The alloy microstructure has ferrite in an amount of 95% by area fraction or greater, and the ferrite has a grain average size of 15 μm or less, with the ultra-fine grain 5 μm or less having an occupancy ratio to 7 to 10% within 1 mm×1 mm area.

High-strength galvanized steel sheet having excellent distinctness of image after painting and manufacturing method therefor

Provided is a plated, ultra-low carbon steel sheet which has excellent strength, formability, and surface properties to allow for the weight lightness of automobiles and a manufacturing method therefor and, more specifically, to a galvanized steel sheet and a manufacturing method therefor, wherein the galvanized steel sheet has high strength and high formability and as such, can be suitably used as a material for an automobile outer body.

Plated steel sheet having excellent strength, formability and surface property and method for manufacturing same

Provided are a bake-hardened hot-dip galvanized steel sheet with excellent powdering resistance, and a manufacturing method therefor. The bake-hardened hot-dip galvanized steel sheet comprises, by wt %, 0.0001-0.005% of carbon (C), 0.1-1.2% of manganese (Mn), 0.02% or less of silicon (Si) (excluding 0%), 0.01-0.04% of phosphorus (P), 0.01% or less of sulfur (S) (excluding 0%), 0.01% or less of nitrogen (N) (excluding 0%), 0.01-0.06% of aluminum (sol.Al), 0.003-0.015% of niobium (Nb), 0.0005-0.0035% of boron (B), 0.01-0.1% of chromium (Cr), 0.005-0.05% of molybdenum (Mo), 0.003% or less of titanium (Ti) (excluding 0%), and the balance of Fe and inevitable impurities, and satisfies relationships 1 and 2, wherein the microstructure thereof is ferrite single phase and satisfies relationship 3.

Bake-hardened hot-dip galvanized steel sheet with excellent powdering resistance, and manufacturing method therefor

Provided is a cold-rolled steel sheet manufactured by a cold-rolled steel sheet manufacturing method comprising a continuous annealing step, which has a composition comprising, by weight %: C: 0.1-0.15%; Si: 0.2% or less (including 0%); Mn: 2.3-3.0%; P: 0.001-0.10%; S: 0.010% or less (including 0%); Sol.Al: 0.01-0.10%; N: 0.010% or less (excluding 0%); Cr: 0.3-0.9%; B: 0.0010-0.0030%; Ti: 0.01-0.03%; Nb:0.01-0.03%; the balance being Fe and other impurities, and satisfies following relationship 1. [relationship 1] 1650&#x2264;5541.4C+239Mn+169.1Cr+0.74SS-1.36RCS&#x2264;1688, in which microstructure comprises, in area %, at least 90% of martensite and tempered martensite; and 10% or less of ferrite and bainite, in which the fraction of the tempered martensite in the martensite and the tempered martensite is 90% or more, in area %, and the ratio (b/a) of the C+Mn concentration (a) in the martensite to the C+Mn concentration (b) in the ferrite and the bainite is 0.65 or more.

High yield ratio type high-strength cold-rolled steel sheet and manufacturing method thereof

A hot-dip galvanized steel sheet includes a base steel sheet and a hot-dip galvanized layer formed on the base steel sheet, the base steel sheet including, by wt %, C:0.02% to 0.08%, Mn:1.3% to 2.1%, Si:0.3% or less (excluding 0%), Cr:1.0% or less (excluding 0%), P:0.1% or less (excluding 0%), S: 0.01% or less (excluding 0%), N:0.01% or less (excluding 0%), sol.Al: 0.02% to 0.06%, Mo:0.2% or less (excluding 0%), B:0.003% or less (excluding 0%), and a balance of Fe and inevitable impurities, wherein the base steel sheet has a microstructure comprising 90% or more by area of ferrite, 3% or less by area of bainite as described in Formula 1, and martensite as a remainder.

Hot-dip galvanized steel sheet and hot-dip galvannealed steel sheet having improved hole expansion ratio, and manufacturing methods thereof

Provided are a bake hardening steel having a crystalline grain size of ASTM No. 9 or more and a method for preparing the bake hardening steel by controlling the winding, rolling and cooling conditions. The bake hardening steel includes: C:0.0016&#x2dc;0.0025%, Si:0.02% or less, P:0.01&#x2dc;0.05%, S:0.01% or less, sol.Al:0.08&#x2dc;0.12%, N:0.0025% or less, Ti:0.003% or less, Nb:0.003&#x2dc;0.011%, Mo:0.01&#x2dc;0.1%, B:0.0005&#x2dc;0.0015% or less, balance Fe and other inevitable impurities, wherein % is weight %, and Mn and P satisfy the relation of &#x2212;30(&#xb0; C.)&#x2267;803P&#x2212;24.4Mn&#x2212;58.

Bake hardening steel with excellent surface properties and resistance to secondary work embrittlement, and preparation method thereof

It is an object of the present invention to provide a high strength cold-rolled steel sheet, which has superior bake hardenability, aging resistance at room temperature and secondary work embrittlement resistance, and a method for manufacturing the same. The steel sheet has a grain size of ASTM No. of 9 or more after annealing, a BH of 30 MPa or more, an AI of 30 MPa or less, and a tensile strength of 340&#x2dc;390 MPa through appropriate control of solute elements in steel by addition of a small amount of Ti, addition of Al and Mo, and control of manufacturing conditions, and refinement of crystal grains after annealing. The cold-rolled steel sheet and the galvannealed steel sheet produced using the cold-rolled steel sheet have the superior bake hardenability, aging resistance at room temperature, and secondary work embrittlement resistance.

Bake-hardenable cold rolled steel sheet with superior strength, galvannealed steel sheet using the cold rolled steel and method for manufacturing the cold rolled steel sheet

A cold-rolled steel sheet for outer panels and the like of an automobile body, a galvannealed steel sheet using the cold-rolled steel sheet, and a method for manufacturing the same are disclosed. It is an object of the present invention to provide a high strength cold-rolled steel sheet, which has superior bake hardenability, aging resistance at room temperature and secondary work embrittlement resistance, and a method for manufacturing the same. The steel sheet has a grain size of ASTM No. of 9 or more after annealing, a BH of 30 MPa or more, an AI of 30 MPa or less, and a tensile strength of 340&#x2dc;390 MPa through appropriate control of solute elements in steel by addition of a small amount of Ti, addition of Al and Mo, and control of manufacturing conditions, and refinement of crystal grains after annealing. The cold-rolled steel sheet and the galvannealed steel sheet produced using the cold-rolled steel sheet have the superior bake hardenability, aging resistance at room temperature, and secondary work embrittlement resistance.

Bake-hardenable cold rolled steel sheet with superior strength, galvannealed steel sheet using the cold rolled steel sheet and method for manufacturing the cold rolled steel sheet

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Gwangyang-si, South Korea

Seong-Ho Han