Posco Co., Ltd

Posco

Min-Seo Koo

Jai-Hyun Kwak

Jae-Hoon Lee

Tae-Jin Song

Jong-Chan Park

Young-Roc Im

Seong-Woo Kim

Seong-Ho Han

Man-Young Park

Dong-Seoug Sin

Tae-Oh Lee

Eul-Yong Choi

Jong-Kweon Kim

Provided is a method of manufacturing a high-strength cold rolled steel sheet. The method includes: preparing a slab; heating the slab to 1,150° C. to 1,250° C.; finish hot rolling the heated slab within 900° C. to 980° C.; cooling the slab at an average cooling rate of 10° C./sec to 100° C./sec; winding the slab in 500° C. to 700° C.; cold rolling the slab at a cold-rolling reduction ratio of 30% to 60% to obtain a cold rolled steel sheet; continuously annealing the cold rolled steel sheet at Ae3+30° C. to Ae3+80° C.; primarily cooling the continuously annealed steel sheet at an average cooling rate of 10° C./s or less to 560° C. to 700° C. and secondarily cooling the steel sheet at an average cooling rate of 10° C./s or more to 270° C. to 330° C.; and reheating the cooled steel sheet at a temperature increase rate of 5° C./s or lower to a temperature in a range of 380° C. to 460° C.

Method of manufacutring a high-strength cold rolled steel sheet having high hole expansion ratio, and highstrength hot-dip galvanized steel sheet

Provided are a high-strength steel sheet and a method for manufacturing same, the high-strength steel sheet including: an alloy system having C, Si, Mn, Cr, Al, Nb, Ti, B, P, S, N, and the remainder of Fe and other inevitable impurities. The contents of C, Si, and Al satisfy equation (1) below. The microstructure includes, by an area fraction, greater than 50% to 70% or less of tempered martensite, and the remainder of residual austenite, fresh martensite, ferrite, and bainite, in which a cementite phase as a second phase is precipitated and distributed in an area fraction of 1-3% between bainite laths, or at a lath on the tempered martensite or grain boundaries. [Equation (1)][C]+([Si]+[Al])/5; 0.35 wt. % (wherein [C], [Si], and [Al] denote wt % of C, Si, and Al, respectively.)

High-strength steel sheet and manufacturing method thereof

Provided is a steel sheet and a method for manufacturing same, the steel sheet which can be used for automobile parts and the like, having excellent bending workability, and excellent balance of strength and ductility and of strength and hole expansibility.

High strength steel sheet having excellent workability and method for manufacturing same

Provided is a method of manufacturing a clad steel sheet. The method includes: preparing a base material including C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities; preparing a cladding material including C: 0.1 to 0.45%, Mn: 0.1 to 3.0%, and a remainder of Fe and inevitable impurities; disposing the base material between two of the cladding material to obtain a laminate; welding an edge of the laminate; heating the welded laminate between 1050 and 1350° C.; finish-rolling the heated laminate between 750 and 1050° C. with a rolling reduction ratio of 30% or more in a first pass; coiling the hot-rolled steel sheet between 400 and 700° C.; pickling the coiled hot-rolled steel sheet, and applying a cold-reduction ratio of 35 to 90%; and annealing the cold-rolled steel sheet between 550° C. and A3+200° C. of the cladding material.

Method of manufacturing clad steel sheet having excellent formability and fatigue property

Provided is a steel sheet and a method for manufacturing same, the steel sheet, which can be used for automobile parts and the like, having superb bendability, and excellent balance of strength and ductility and of strength and hole expansion ratio. The steel sheet includes: by wt %, C: 0.25 to 0.75%, Si: 4.0% or less, Mn: 0.9 to 5.0%, Al: 5.0% or less, P: 0.15% or less, S: 0.03% or less, N: 0.03% or less, a balance of Fe, and unavoidable impurities; and as microstructures, ferrite which is a soft structure, and tempered martensite, bainite, and retained austenite which are hard structures.

Provided is a density clad steel sheet having excellent strength and plateability, the clad steel sheet including a base metal, and a clad material provided at both sides of the base metal, wherein the base metal is a ferrite-austenitic duplex lightweight steel sheet comprising, by wt %, 0.3-0.7% of C, 2.0-9.0% of Mn, 4.5-8.0% of Al and the balance of Fe and inevitable impurities, and the clad material is a ferrite carbon steel comprising, by wt %, 0.0005-0.2% of C, 0.05-2.5% of Mn and the balance of Fe and inevitable impurities.

Low-density clad steel sheet having excellent strength and plateability, and manufacturing method therefor

Provided is a high-strength cold rolled steel sheet, a high-strength hot-dip galvanized steel sheet manufactured using the cold rolled steel sheet, and manufacturing methods therefor, the high-strength cold rolled steel sheet comprising, by wt %, 0.17-0.21% of carbon (C), 0.3-0.8% of silicon (Si), 2.7-3.3% of manganese (Mn), 0.3-0.7% of chromium (Cr), 0.01-0.3% of aluminum (Al), 0.01-0.03% of titanium (Ti), 0.001-0.003% of boron (B), 0.04% or less of phosphorus (P), 0.02% or less of sulfur (S), 0.01% or less of nitrogen (N) and the balance of iron (Fe) and other inevitable impurities, wherein the amounts of carbon (C), silicon (Si) and aluminum (Al) satisfy the following mathematical relation (1). [Mathematical relation (1)] [C]+([Si]+[Al])/5&#x2264;0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.)

High-strength cold rolled steel sheet having high hole expansion ratio, highstrength hot-dip galvanized steel sheet, and manufacturing methods therefor

Provided is a low-density clad steel sheet having excellent formability and fatigue properties, including a base material; and cladding materials provided on both side surfaces of the base material, wherein the base material is a lightweight steel sheet including, by weight, C: 0.3 to 1.0%, Mn: 4.0 to 16.0%, Al: 4.5 to 9.0%, and a remainder of Fe and inevitable impurities, and each of the cladding materials is martensitic carbon steel including, by weight, C: 0.1 to 0.45%, Mn: 1.0 to 3.0%, and a remainder of Fe and inevitable impurities.

Low-density clad steel sheet having excellent formability and fatigue property

Provided is an ultra-high strength steel sheet used as a material of a vehicle and, more specifically, to an ultra-high strength steel sheet having excellent bendability and a manufacturing method therefor. There is an effect of providing a steel sheet by utilizing a continuous annealing furnace without having water quenching equipment, thereby simultaneously ensuring a tensile strength of 1200 MPa or greater compared with that of conventional super high strength martensite steel and having excellent shape and bending properties.

Ultra-high strength steel sheet having excellent bendability 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

The present invention relates to a lightweight steel sheet and a method of manufacturing the same, wherein high strength and ductility can be achieved in the lightweight steel sheet even when a small amount of carbon and manganese is added, by preventing loss of austenite due to decarburizing through inhibiting decarburization, which occurs during a heat treatment step of a steel sheet containing austenite.

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Gwangyang-si, South Korea

Min-Seo Koo