Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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?0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.

Abstract: 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.

Abstract: 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.

Abstract: 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.

Abstract: 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?0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.

Abstract: 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.

Abstract: 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.

Abstract: 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?5541.4C+239Mn+169.1Cr+0.74SS-1.36RCS?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.

Abstract: 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.

Abstract: An ultrahigh strength cold-rolled steel sheet and a manufacturing method thereof are provided. An ultrahigh strength cold-rolled steel sheet, according to a preferred aspect of the present invention, comprises, in percentage by weight: C: 0.25 to 0.4%; Si: 0.5% or less (excluding 0); Mn: 3.0 to 4.0%; P: 0.03% or less (excluding 0); S: 0.015% or less (excluding 0); Al: 0.1% or less; Cr: 1% or less (excluding 0); Ti: 48/14*[N] to 0.1% or less; Nb: 0.1% or less (excluding 0); B: 0.005% or less (excluding 0); N: 0.01% or less (excluding 0); and a balance of Fe and unavoidable impurities, and a microstructure includes 90% or more(including 100%) of martensite, and one or two kinds of 10% or less (including 0%) of ferrite and bainite.

Abstract: 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.

Abstract: 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.

Abstract: 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?5541.4C+239Mn+169.1Cr+0.74SS?1.36RCS?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.

Abstract: A ferritic steel sheet according to an exemplary embodiment of the present invention includes C at 0.01 to 0.3 wt %, Mn at 0.5 to 8 wt %, Al at 5 to 12 wt %, and Nb at 0.015 to 0.2 wt % based on an entire composition of 100 wt %, and a remaining part of Fe and an impurity.

Abstract: 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.