High Strength Steel Sheet and Hot Dip Galvanized Steel Sheet Having High Ductility and Excellent Delayed Fracture Resistance and Method for Manufacturing the Same

A cold rolled steel sheet and a hot dip galvanized steel sheet, which have high strength and elongation, such as a tensile strength of 980 MPa or more and an elongation of 28% or more, and excellent delayed fracture resistance, and manufacturing methods thereof. The cold rolled steel sheet has a composition including 0.05 to 0.3 weight percent C, 0.3 to 1.6 weight percent. Si, 4.0 to 7.0 weight percent Mn, 0.5 to 2.0 weight percent Al, 0.01 to 0.1 weight percent Cr, 0.02 to 0.1 weight percent Ni and 0.005 to 0.03 weight percent Ti, 5 to 30 ppm B, 0.01 to 0.03 weight percent Sb, 0.008 weight percent or less S, balance Fe and impurities. The hot dip galvanized steel sheet has a hot dip galvanized layer or a hot dip galvannealed layer on the cold rolled steel sheet.

High strength thin steel sheet for the superior press formability and surface quality and galvanized steel sheet and method for manufacturing the same

A high strength thin steel sheet that is mainly used for structural members and inner and outer panels for a vehicle, a galvanized steel sheet, and methods of manufacturing the same. The high strength thin steel sheet for superior press formability includes, by weight percent, 0.06 to 0.4% C, 1.0 to 5.0% Mn, 0.05 to 2.5% Si, 0.01 to 2.0% Ni, 0.02 to 2% Cu, 0.01 to 0.04% Ti, 0.05 to 2.5% Al, 0.005 to 0.1% Sb, 0.0005 to 0.004% B, 0.007% or less N, and balance Fe and inevitable impurities, and meeting relation of Ni+0.5×Mn+0.3×Cu>0.9, which is defined as Ni*, and Al/Ni*<1.3 at a same time, and relation of Ti≧0.028×Al. This thin steel sheet is galvanized or galvannealed.

High Strength Thin Steel Sheet for the Superior Press Formability and Surface Quality and Galvanized Steel Sheet and Method for Manufacturing the Same

A high strength thin steel sheet that is mainly used for structural members and inner and outer panels for a vehicle, a galvanized steel sheet, and methods of manufacturing the same. The high strength thin steel sheet for superior press formability includes, by weight percent, 0.06 to 0.4% C, 1.0 to 5.0% Mn, 0.05 to 2.5% Si, 0.01 to 2.0% Ni, 0.02 to 2% Cu, 0.01 to 0.04% Ti, 0.05 to 2.5% Al, 0.005 to 0.1% Sb, 0.0005 to 0.004% B, 0.007% or less N, and balance Fe and inevitable impurities, and meeting relation of Ni+0.5×Mn+0.3×Cu>0.9, which is defined as Ni*, and Al/Ni*<1.3 at a same time, and relation of Ti≧0.028×Al. This thin steel sheet is galvanized or galvannealed. 1. A method of manufacturing a high strength thin steel sheet for superior press formability , the method comprising:hot-working a steel slab, which comprises, by weight percent, 0.06 to 0.4% C, 1.0 to 5.0% Mn, 0.05 to 2.5% Si, 0.01 to 2.0% Ni, 0.02 to 2% Cu, 0.01 to 0.04% Ti, 0.05 to 2.5% Al, 0.005 to 0.1% Sb, 0.0005 to 0.004% B, 0.007% or less N, and balance Fe and inevitable impurities, and which meets relation of Ni+0.5×Mn+0.3×Cu≧0.9, which is defined as Ni*, and Al/Ni*≦1.3 at a same time, and relation of Ti≧0.028×Al, at a temperature above Ar3;hot-rolling winding the hot-wrought steel slab at a temperature between 500 C and 700 C;pickling and cold rolling the wound steel slab;annealing the cold-rolled steel slab at a temperature at which a fraction of austenite has at least 30%; andquenching the annealed steel slab from a temperature direct above a martensite forming temperature to a temperature below a bainite forming temperature, and cooling the quenched steel slab after at least 30 seconds.2. The method according to the claim 1 , wherein the steel slab further includes at least one selected from the group consisting of claim 1 , by weight percent claim 1 , 0.01 to 1.0% Cr claim 1 , 0.005 to 0.3% Mo claim 1 , and 0.001 to 0.1% Nb.3. A method of manufacturing a galvanized high strength steel sheet ...

High strength thin steel sheet for the superior press formability and surface quality and galvanized steel sheet and method for manufacturing the same

A high strength thin steel sheet that is mainly used for structural members and inner and outer panels for a vehicle, a galvanized steel sheet, and methods of manufacturing the same. The high strength thin steel sheet for superior press formability includes, by weight percent, 0.06 to 0.4% C, 1.0 to 5.0% Mn, 0.05 to 2.5% Si, 0.01 to 2.0% Ni, 0.02 to 2% Cu, 0.01 to 0.04% Ti, 0.05 to 2.5% Al, 0.005 to 0.1% Sb, 0.0005 to 0.004% B, 0.007% or less N, and balance Fe and inevitable impurities, and meeting relation of Ni+0.5×Mn+0.3×Cu>0.9, which is defined as Ni*, and Al/Ni*<1.3 at a same time, and relation of Ti0.028×Al. This thin steel sheet is galvanized or galvannealed.

HIGH STRENGTH THIN STEEL SHEET FOR THE SUPERIOR PRESS FORMABILITY AND SURFACE QUALITY AND GALVANIZED STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME

A high strength thin steel sheet that is mainly used for structural members and inner and outer panels for a vehicle, a galvanized steel sheet, and methods of manufacturing the same. The high strength thin steel sheet for superior press formability includes, by weight percent, 0.06 to 0.4% C, 1.0 to 5.0% Mn, 0.05 to 2.5% Si, 0.01 to 2.0% Ni, 0.02 to 2% Cu, 0.01 to 0.04% Ti, 0.05 to 2.5% Al, 0.005 to 0.1% Sb, 0.0005 to 0.004% B, 0.007% or less N, and balance Fe and inevitable impurities, and meeting relation of Ni+0.5×Mn+0.3×Cu>0.9, which is defined as Ni*, and Al/Ni*<1.3 at a same time, and relation of Ti≧0.028×Al. This thin steel sheet is galvanized or galvannealed.

LOW SPECIFIC GRAVITY AND HIGH STRENGTH STEEL SHEETS WITH EXCELLENT RIDGING RESISTIBILITY AND MANUFACTURING METHODS THEREOF

A low specific gravity and high strength steel sheet includes C of 0.2% to 0.8%, Mn of 2% to 10%, P of 0.02% or less, S of 0.015% or less, Al of 3% to 15%, and N of 0.01% or less. A ratio of Mn/Al is 0.4 to 1.0. Retained austenite in a structure is included in the range of 1% or more. The steel sheet further includes one or two or more elements selected from the group consisting of Si of 0.1% to 2.0%, Cr of 0.1% to 0.3%, Mo of 0.05% to 0.5%, Ni of 0.1% to 2.0%, Cu of 0.1% to 1.0%, B of 0.0005% to 0.003%, Ti of 0.01% to 0.2%, Zr of 0.005% to 0.2%, Nb of 0.005% to 0.2%, W of 0.1% to 1.0%, Sb of 0.005% to 0.2%, and Ca of 0.001% to 0.2%.

High strength steel sheet and hot dip galvanized steel sheet having high ductility and excellent delayed fracture resistance and method for manufacturing the same

A cold rolled steel sheet and a hot dip galvanized steel sheet, which have high strength and elongation, such as a tensile strength of 980 MPa or more and an elongation of 28% or more, and excellent delayed fracture resistance, and manufacturing methods thereof. The cold rolled steel sheet has a composition including 0.05 to 0.3 weight percent C, 0.3 to 1.6 weight percent Si, 4.0 to 7.0 weight percent Mn, 0.5 to 2.0 weight percent Al, 0.01 to 0.1 weight percent Cr, 0.02 to 0.1 weight percent Ni and 0.005 to 0.03 weight percent Ti, 5 to 30 ppm B, 0.01 to 0.03 weight percent Sb, 0.008 weight percent or less S, balance Fe and impurities. The hot dip galvanized steel sheet has a hot dip galvanized layer or a hot dip galvannealed layer on the cold rolled steel sheet.

Steel Sheet for Formed Member Having Enhanced Ductility, Formed Member, and Method for Manufacturing the Formed Member

Provided is a steel sheet for a formed member having enhanced ductility, a formed member, and a method for manufacturing the formed member, and more particularly, to a steel sheet for making a formed member having high strength and ductility such as an automotive structural member and a reinforcing member, a formed member, and a method for manufacturing the formed member. The steel sheet for a formed member has enhanced ductility, and includes, by weight %, C: 0.1% to 1.0%, Si+Al: 0.4% to 3.0%, Mn: 0.1% to 5.0%, P: 0.0001% to 0.1%, S: 0.0001% to 0.03%, N: 0.03% or less (but not 0%), and the balance of Fe and inevitable impurities. The formed member having high strength and ductility that can be used for forming an automotive structural member, a reinforcing member, etc. In addition, the formed member can be used for a heat-treatable impact resistant member. 1. A steel sheet for a formed member having enhanced ductility , the steel sheet comprising , by weight% , C: 0.1% to 1.0% , Si+Al: 0.4% to 3.0% , Mn: 0.1% to 5.0% , P: 0.0001% to 0.1% , S: 0.0001% to 0.03% , N: 0.03% or less but not 0% , and the balance of Fe and inevitable impurities.2. The steel sheet of claim 1 , further comprising at least one selected from the group consisting of (a) claim 1 , (b) claim 1 , (c) claim 1 , (d) claim 1 , and (e) claim 1 , wherein:(a) at least one selected from the group consisting of Cr: 0.01% to 2.0%, Mo: 0.01% to 2.0%, and W: 0.01% to 2.0%;(b) at least one selected from the group consisting of Ti: 0.001% to 0.4%, Nb: 0.001% to 0.4%, Zr: 0.001% to 0.4%, and V: 0.001% to 0.4%;(c) at least one of Cu: 0.005% to 2.0% and Ni: 0.005% to 2.0%;(d) B: 0.0001% to 0.01%; and(e) Sb: 0.001% to 0.1%.3. The steel sheet of claim 1 , wherein the steel sheet is one of a hot-rolled steel sheet claim 1 , a cold-rolled steel sheet claim 1 , and a plated steel sheet.4. The steel sheet of claim 3 , wherein the plated steel sheet is a hot-rolled or cold-rolled steel sheet on which a metal or resin ...

Austenitic, Lightweight, High-Strength Steel Sheet Having High Yield Ratio and Ductility, and Method for Producing the Same

Provided is an austenitic, lightweight, high-strength steel sheet having a high yield ratio and ductility and a method for producing the same, and more particularly, to a high-strength steel sheet for automotive interior panels, exterior panels, and structural parts, and a method for producing the steel sheet. The steel sheet may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a plated steel sheet. The steel sheet includes, by weight %, C: 0.6% to 1.0%, Si: 0.1% to 2.5%, Mn: 10% to 15%, P: 0.02% or less, S: 0.015% or less, Al: 5% to 8%, Ti: 0.01% to 0.20%, N: 0.02% or less, and the balance of Fe and inevitable impurities, wherein the steel sheet has a specific gravity of 7.4 g/cmand a Mn/Al ratio of 2 to 3. 1. An austenitic , lightweight , high-strength steel sheet having a high yield ratio and ductility , the steel sheet comprising , by weight % , C: 0.6% to 1.0% , Si: 0.1% to 2.5% , Mn: 10% to 15% , P: 0.02% or less , S: 0.015% or less , Al: 5% to 8% , Ti: 0.01% to 0.20% , N: 0.02% or less , and the balance of Fe and inevitable impurities , wherein the steel sheet has a specific gravity of 7.4 g/cmand a Mn/Al ratio of 2 to 3.2. The steel sheet of claim 1 , wherein the steel sheet is one of a hot-rolled steel sheet claim 1 , a cold-rolled steel sheet claim 1 , and a plated steel sheet.3. The steel sheet of claim 2 , further comprising at least one selected from the group consisting of Cr: 0.1% to 3.0% claim 2 , Ni: 0.05% to 2.0% claim 2 , Cu: 0.1% to 2.0% claim 2 , and Mo: 0.05% to 0.5%.4. The steel sheet of claim 2 , further comprising at least one selected from the group consisting of V: 0.005% to 0.5% claim 2 , Nb: 0.005% to 0.2% claim 2 , Zr: 0.005% to 0.2% claim 2 , and B: 0.0005% to 0.0030%.5. The steel sheet of claim 2 , further comprising one or two selected from the group consisting of Sb: 0.005% to 0.2% and Ca: 0.001% to 0.02%.6. The steel sheet of claim 4 , further comprising one or two selected from the group consisting of Sb: 0.005% to 0.2% ...

HIGH-STRENGTH COLD ROLLED STEEL SHEET HAVING HIGH HOLE EXPANSION RATIO, HIGHSTRENGTH HOT-DIP GALVANIZED STEEL SHEET, AND MANUFACTURING METHODS 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≤0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.) 1. A high-strength cold rolled steel sheet comprising: {'br': None, '[C]+([Si]+[Al])/5≤0.35%\u2003\u2003[Equation (1)]'}, 'by weight percent (wt %), 0.17 to 0.21% of carbon (C), 0.3 to 0.8% of silicon (Si), 2.7 to 3.3% of manganese (Mn), 0.3 to 0.7% of chromium (Cr, 0.01 to 0.3% of aluminum (Al), 0.01 to 0.03% of titanium (Ti), 0.001 to 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), the balance of iron (Fe), and other inevitable impurities, wherein the contents of carbon (C), silicon (Si), and aluminum (Al) satisfy Equation 1 below, a microstructure thereof includes, by area fraction, 3 to 7% of retained austenite, 5 to 15% of fresh martensite, 5% or less (including 0%) of ferrite, and the balance of bainite or tempered martensite, and, by volume fraction, 1 to 3% of a cementite phase, as a second phase, is precipitated and distributed between bainite laths or in the laths or grain boundary of a tempered martensite phase,'}wherein [C], [Si], [Al] refer to weight percents of C, Si, and Al, respectively.2. The high-strength cold rolled steel sheet of claim 1 , wherein the cold rolled ...

HIGH-STRENGTH COLD ROLLED STEEL SHEET AND GALVANNEALED STEEL SHEET HAVING EXCELLENT BURRING PROPERTY, AND MANUFACTURING METHOD THEREFOR

A high strength cold rolled steel sheet having excellent burring properties includes: by weight %, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon (Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al)+chrome (Cr)+molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of nitrogen (N), and the balance of Fe and inevitable impurities; and, by area fraction, 3-25% of ferrite, 20-40% of martensite, 5-20% of residual austenite. The ferrite has an average grain size of 2 μm or less at the reference point of 4/t (wherein t refers to a steel sheet thickness), with the average ratio between lengths in the thickness direction and in the rolling direction being 1.5 or less. 1. A high-strength cold rolled steel sheet having excellent burring properties , comprising:by weight %, 0.13-0.25% of carbon (C), 1.0-2.0% of silicon (Si), 1.5-3.0% of manganese (Mn), 0.08-1.5% of aluminum (Al)+chrome (Cr)+molybdenum (Mo), 0.1% or less of phosphorus (P), 0.01% or less of sulfur (S), 0.01% or less of nitrogen (N), and a balance of Fe, and unavoidable impurities; andby area fraction, 3-25% of ferrite, 20-40% of martensite, and 5-20% of retained austenite, wherein based on a 4/t point (where t is a steel sheet thickness), the ferrite has an average grain size of 2 μm or less, and an average value of a ratio of a ferrite length in a rolling direction of a steel sheet with respect to a length of the ferrite in a thickness direction of the steel sheet is 1.5 or less.2. The high-strength cold rolled steel sheet having excellent burring properties of claim 1 , wherein the cold-rolled steel sheet further comprises 15 to 50% of bainite in an area fraction.3. The high-strength cold rolled steel sheet having excellent burring properties of claim 1 , wherein the martensite is composed of tempered martensite and fresh martensite claim 1 , wherein a proportion of the tempered martensite in the total martensite exceeds 50 area %.4. The high-strength cold rolled ...

HIGH-STRENGTH COLD ROLLED STEEL SHEET HAVING EXCELLENT DUCTILITY, HOT-DIP GALVANIZED STEEL SHEET AND METHOD FOR MANUFACTURING SAME

The present invention relates to: a high-strength steel sheet used for construction materials and transportation means such as vehicles and trains and, more specifically, to a high-strength cold rolled steel sheet having excellent ductility, a hot-dip galvanized steel sheet, and a method for manufacturing the same. 1. A high-strength cold-rolled steel sheet having excellent ductility comprises:by wt %, carbon (C): 0.1% to 0.3%, silicon (Si): 0.1% to 2.0%, aluminum (Al): 0.005% to 1.5%, manganese (Mn): 1.5% to 3.0%, phosphorus (P): 0.04% or less (excluding 0%), sulfur (S): 0.015% or less (excluding 0%), nitrogen (N): 0.02% or less (excluding 0%), and a remainder of iron (Fe) and inevitable impurities,wherein a sum of Si and Al (Si+Al) (wt %) satisfies 1.0% or more, andwherein a microstructure comprises: by area fraction, 5% or less of polygonal ferrite having a minor axis to major axis ratio of 0.4 or greater, 70% or less (excluding 0%) of acicular ferrite having a minor axis to major axis ratio of 0.4 or less, 25% or less (excluding 0%) of acicular retained austenite, and a remainder of martensite.2. The high-strength cold-rolled steel sheet of claim 1 , wherein the martensite is 40% or less (excluding 0%) by area fraction.3. The high-strength cold-rolled steel sheet of claim 1 , further comprising at least one selected from the group consisting of titanium (Ti): 0.005% to 0.1% claim 1 , niobium (Nb): 0.005% to 0.1% claim 1 , vanadium (V): 0.005% to 0.1% claim 1 , zirconium (Zr): 0.005% to 0.1% claim 1 , and tungsten (W): 0.005% to 0.5%.4. The high-strength cold-rolled steel sheet of claim 1 , further comprising at least one selected from the group consisting of molybdenum (Mo): 1% or less (excluding 0%) claim 1 , nickel (Ni): 1% or less (excluding 0%) claim 1 , copper (Cu): 0.5% or less (excluding 0%) claim 1 , and chromium (Cr): 1% or less (excluding 0%).5. The high-strength cold-rolled steel sheet of claim 1 , further comprising at least one selected from the ...

METHOD FOR PREVENTING SPOT WELDING CRACK OF GALVANIZED STEEL PLATE

One aspect of the present invention provides a method for preventing spot welding crack of a galvanized steel plate, which can reduce crack occurring due molten zinc having a low melting point when a galvanized advanced high strength steel (AHSS) plate is spot-welded, and can thus improve welding strength and fatigue life. 1. A method for preventing spot welding cracking of a galvanized steel sheet , comprising:preparing a galvanized steel sheet on which a plating layer is formed on at least one surface of a base steel sheet;molding the galvanized steel sheet;heating a welding spot of the molded galvanized steel sheet; andspot welding the heated welding spot,wherein the heating is performed using a current in the range of 0.4 times an exclusion-occurring current to the exclusion-occurring current.2. The method of claim 1 , wherein the heating is performed an area over 1.2 times a nugget diameter.3. The method of claim 1 , wherein the heating is performed using a tungsten or copper electrode.4. The method of claim 1 , wherein the heated welding spot has a Fe concentration of 65 wt % or more in the plating layer adjacent to an interface between the base steel sheet and the plating layer.5. The method of claim 1 , wherein the heated welding spot has an average Fe concentration of 50 wt % or more in the plating layer.6. The method of claim 1 , wherein claim 1 , when measuring glow discharge spectrometry (GDS) of the plating layer claim 1 , an average Fe concentration claim 1 , represented by Equation (1) below claim 1 , is 0.5 or more:{'br': None, 'Average Fe concentration=Fe (%)/(Fe (%)+Zn (%)).\u2003\u2003Equation (1)'}7. The method of claim 1 , wherein the base steel sheet is an advanced high strength steel (AHSS) having tensile strength of 980 MPa or more. The present invention relates to a method for reducing cracking during spot-welding of a galvanized steel sheet.Steel sheets galvanized with advanced high strength steels (hereinafter, “AHSS”) have recently been ...

HIGH STRENGTH COLD-ROLLED STEEL SHEET HAVING EXCELLENT YIELD STRENGTH, DUCTILITY, AND HOLE EXPANDABILITY, HOT-DIP GALVANIZED STEEL SHEET, AND METHOD FOR PRODUCING SAME

Provided are a high strength cold rolled steel plate having excellent yield strength, ductility, and hole expandability, a hot dip galvanized steel plate, and a method for producing the same. The cold rolled steel plate of the present invention comprises 0.06-0.2 wt % of carbon (C), 1.5-3.0 wt % of manganese (Mn), 0.3-2.5 wt % of silicon (Si), 0.01-0.2 wt % of aluminum (Al), 0.01-3.0 wt % of nickel (Ni), 0.2 wt % or less of molybdenum (Mo), 0.01-0.05 wt % of titanium (Ti), 0.02-0.05 wt % of antimony (Sb), 0.0005-0.003 wt % of boron (B), 0.01 wt % or less (but not 0%) of nitrogen (N), with the remainder comprising Fe and unavoidable impurities, and the microstructure thereof comprises, in terms of area fraction, 50% or more of bainite, 10% or more of tempered martensite (TM), 10% or less of fresh martensite (FM), 20% or less of residual austenite, and 5% or less of ferrite. 1. A high strength cold-rolled steel sheet having excellent yield strength , ductility , and hole expandability , comprising:by wt %, 0.06 to 0.2% of carbon (C), 1.5 to 3.0% of manganese (Mn), 0.3 to 2.5% of silicon (Si), 0.01 to 0.2% of aluminum (Al), 0.01 to 3.0% of nickel (Ni), 0.2% or less of molybdenum (Mo), 0.01 to 0.05% of titanium (Ti), 0.02 to 0.05% of antimony (Sb), 0.0005 to 0.003% of boron (B), 0.01% or less of nitrogen (N), excluding 0, and a balance of Fe and inevitable impurities,wherein a microstructure thereof comprises, by area fraction, bainite of 50% or higher, tempered martensite (TM) of 10% or higher, fresh martensite (FM) of 10% or less, residual austenite of 20% or less, and ferrite of 5% or less.2. The high strength cold-rolled steel sheet of claim 1 , wherein a TM/FM ratio exceeds 2.3. A hot-dip galvanized steel sheet claim 1 , manufactured by hot-dip zinc plating a surface of the cold-rolled steel sheet of .4. An alloyed hot-dip galvanized steel sheet claim 1 , manufactured by alloy hot-dip zinc plating a surface of the cold-rolled steel sheet of .5. A method of ...

Ferritic Lightweight High-Strength Steel Sheet Having Excellent Stiffness and Ductility, and Method of Manufacturing the Same

Provided is a ferritic lightweight high-strength steel sheet having excellent stiffness and ductility and a method of manufacturing the same. The steel sheet including 0.02 wt % to 0.1 wt % of carbon (C), 4 wt % to 15 wt % of manganese (Mn), 4 wt % to 10 wt % of aluminum (Al), 2.0 wt % or less (excluding 0) of silicon (Si), 0.01 wt % to 0.3 wt % of titanium (Ti), 0.005 wt % to 0.2 wt % of antimony (Sb), and iron (Fe) as well as unavoidable impurities as a remainder, and having a value of 0.25×Ti/C ranging from 0.17 to 1.0 and a value of Mn/Al×Log(C×Ti×10000) ranging from 1.0 to 10. 1. A ferritic lightweight high-strength steel sheet comprising:0.02 wt % to 0.1 wt % of carbon (C);4 wt % to 15 wt % of manganese (Mn);4 wt % to 10 wt % of aluminum (Al);2.0 wt % or less (excluding 0) of silicon (Si);0.01 wt % to 0.3 wt % of titanium (Ti);0.005 wt % to 0.2 wt % of antimony (Sb); andiron (Fe) as well as unavoidable impurities as a remainder,wherein a value of 0.25×Ti/C is in a range of 0.17 to 1.0 and a value of Mn/Al×Log(C×Ti×10000) is in a range of 1.0 to 10.2. The ferritic lightweight high-strength steel sheet of claim 1 , wherein the steel sheet comprises one or more precipitates selected from the group consisting of TiC claim 1 , (Fe claim 1 ,Mn)AlC claim 1 , (Fe claim 1 ,Al)C claim 1 , and (Fe claim 1 ,Mn)C.3. The ferritic lightweight high-strength steel sheet of claim 1 , wherein an average diameter of grains in the steel sheet is 10 μm or less.4. The ferritic lightweight high-strength steel sheet of claim 1 , wherein the steel sheet has a specific gravity of 7.2 g/cc or less claim 1 , a tensile strength of 540 MPa or more claim 1 , a yield ratio of 0.8 or more claim 1 , a value of tensile strength×elongation (TS×El)of 17 claim 1 ,000 MPa % or more claim 1 , and an planar anisotropy of 0.3 or less.5. The ferritic lightweight high-strength steel sheet of claim 1 , wherein the steel sheet is any one of a hot-rolled steel sheet claim 1 , a cold-rolled steel sheet claim ...

Method of continuously annealing a strip

Provided is a method of continuously annealing a strip. The method includes: firstly heating a strip in a first heating zone; firstly cooling the firstly heated strip or maintaining the firstly heated strip at a constant temperature in a first cooling or constant temperature maintaining zone; secondarily heating and soaking the strip, firstly cooled or remaining at the constant temperature, in a second heating and soaking zone; and secondarily cooling the strip, secondarily heated and soaked, in a second cooling zone.

LIGHTWEIGHT STEEL SHEET HAVING EXCELLENT STRENGTH AND DUCTILITY AND METHOD FOR MANUFACTURING SAME

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. 1. A lightweight steel sheet having improved strength and ductility comprising:carbon (C) of 0.1 to 1.2 wt %, manganese (Mn) of 2 to 10 wt %, aluminum (Al) of 3 to 10 wt %, phosphorus (P) of 0.1 wt % or less, and sulfur (S) of 0.01 wt % or less,wherein the composition of the lightweight steel sheet comprises at least one selected from the group consisting of nickel (Ni) of 5.0% or less, copper (Cu) of 5.0 wt % or less, antimony (Sb) of 0.01 to 0.05 wt %, and boron (B) of 0.01 wt % or less,wherein the remainder of the composition comprises iron (Fe) and impurities, and {'br': None, 'B*=Ni+0.5Cu+100Sb+500B (a value of each component corresponds to wt %)'}, 'wherein a value of the following formula B* satisfies from 2 to 10.'}2. The lightweight steel sheet having improved strength and ductility of claim 1 , wherein a microstructure of the lightweight steel sheet comprises a remaining austenite added to a ferritic base material at a surface integral ratio of 10 to 50%.3. The lightweight steel sheet having improved strength and ductility of claim 1 , wherein tensile strength of the lightweight steel sheet is 700 MPa or more claim 1 , and an elongation percentage of the lightweight steel sheet is 30% or more.4. A method of manufacturing a lightweight steel sheet having improved strength and ductility comprising:re-heating a steel slab at a temperature of 1,000 to 1,200° C., the steel slab comprising carbon (C) of 0.1 to 1.2 wt %, manganese (Mn) of 2 to 10 wt %, aluminum (Al) of 3 to 10 wt %, phosphorus (P) of 0.1 wt % or less, and sulfur (S) of 0.01 wt % or less, ...

Apparatus for continuous annealing of strip and method for continuous annealing of same

An apparatus for continuous annealing of a strip comprises: a first heating zone configured to firstly heat a strip; a first cooling or constant temperature maintaining zone configured to cool the strip firstly heated in the first heating zone or to maintain the strip at a constant temperature; a second heating and soaking zone configured to secondarily heat and soak the strip cooled or remaining at the constant temperature in the first cooling or constant temperature maintaining zone; and a second cooling zone configured to cool the strip heated and soaked in the second heating and soaking zone.

High strength cold-rolled steel sheet and hot- dip galvanized steel sheet having excellent hole expansion, ductility and surface treatment properties, and method for manufacturing same

Provided are a high-strength cold-rolled steel sheet and a hot-dip galvanized steel sheet comprising in % by weight: 0.05 to 0.3% of carbon (C); 0.6 to 2.5% of silicon (Si); 0.01 to 0.5% of aluminum (Al); 1.5 to 3.0% of manganese (Mn); and the remainder being Fe and unavoidable impurities, the steel sheet has a microstructure comprised of, in an area fraction, ferrite in an amount of 60% or less, lath-type bainite of 25% or more, martensite of 5% or more, and lath-type retained austenite in an amount of 5%, wherein the ferrite has an average grain diameter of 2 μm or less and the ferrite satisfies Fn2, defined by relational expression 1, is 89% or more and Fa5, defined by relational expression 2, is 70% or less.

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

High strength cold-rolled steel sheet and hot dip galvanized steel sheet having excellent hole expansion, ductility and surface treatment properties, and method for manufacturing same

Ferritic lightweight high-strength steel sheet having excelent stiffness and ductility, and method of manufacturing the same

The present invention relates to a ferritic lightweight high-strength steel sheet having excellent stiffness and ductility and a method of manufacturing the same. An embodiment of the present invention provides a steel sheet including 0.02 wt% to 0.1 wt% of carbon (C), 4 wt% to 15 wt% of manganese (Mn), 4 wt% to 10 wt% of aluminum (Al), 2.0 wt% or less (excluding 0) of silicon (Si), 0.01 wt% to 0.3 wt% of titanium (Ti), 0.005 wt% to 0.2 wt% of antimony (Sb), and iron (Fe) as well as unavoidable impurities as a remainder, and having a value of 0.25×Ti/C ranging from 0.17 to 1.0 and a value of Mn/Al×Log(C×Ti×10000) ranging from 1.0 to 10, and a method of manufacturing the same.

High-strength cold rolled steel sheet having excellent ductility, hot-dip galvanized steel sheet and method for manufacturing same

The present invention relates to: a high-strength steel sheet used for construction materials and transportation means such as vehicles and trains and, more specifically, to a high-strength cold rolled steel sheet having excellent ductility, a hot-dip galvanized steel sheet, and a method for manufacturing the same.

Austenitic, lightweight, high-strength steel sheet having high yield ratio and ductility, and method for producing the same

Provided is an austenitic, lightweight, high-strength steel sheet having a high yield ratio and ductility and a method for producing the same, and more particularly, to a high-strength steel sheet for automotive interior panels, exterior panels, and structural parts, and a method for producing the steel sheet. The steel sheet may be a hot-rolled steel sheet, a cold-rolled steel sheet, or a plated steel sheet. The steel sheet includes, by weight %, C: 0.6% to 1.0%, Si: 0.1% to 2.5%, Mn: 10% to 15%, P: 0.02% or less, S: 0.015% or less, Al: 5% to 8%, Ti: 0.01% to 0.20%, N: 0.02% or less, and the balance of Fe and inevitable impurities, wherein the steel sheet has a specific gravity of 7.4 g/cm 3 and a Mn/Al ratio of 2 to 3.

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

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.

High strength cold rolled steel sheet and galvannealed steel sheet having excellent burring property, and manufacturing method therefor

High-strength cold rolled steel sheet having high hole expansion ratio, highstrength hot-dip galvanized steel sheet, and manufacturing methods 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≤0.35% (wherein [C], [Si] and [Al] respectively mean the wt % of C, Si and Al.)

Ferritic lightweight high-strength steel sheet having excellent stiffness and ductility, and method of manufacturing the same

Provided is a ferritic lightweight high-strength steel sheet having excellent stiffness and ductility and a method of manufacturing the same. The steel sheet including 0.02 wt % to 0.1 wt % of carbon (C), 4 wt % to 15 wt % of manganese (Mn), 4 wt % to 10 wt % of aluminum (Al), 2.0 wt % or less (excluding 0) of silicon (Si), 0.01 wt % to 0.3 wt % of titanium (Ti), 0.005 wt % to 0.2 wt % of antimony (Sb), and iron (Fe) as well as unavoidable impurities as a remainder, and having a value of 0.25×Ti/C ranging from 0.17 to 1.0 and a value of Mn/Al×Log(C×Ti×10000) ranging from 1.0 to 10.