Abstract: A method for removing ferric ions contained in a sulfate-based iron electroplating solution comprises a step of regeneration for reduction of the ferric ions by circulating a ferric ion-containing sulfate-based iron electroplating solution in a solution bath containing ferrous metal charged therein, wherein the ferrous metal is charged in an amount that satisfies the following formula (1): S?0.01 Iconv/Cmax (1). In formula (1), S indicates a total surface (m2) of ferrous metal, Cmax indicates a maximum permissible ion concentration level (g/L) of the ferric ions in the solution, and Iconv indicates, as represented by the following formula (2), converted current (A) obtained by dividing the sum of current (I) applied to an electroplated cell during the plating time (tp, sec) by the regeneration time (tr, sec) for reduction of the ferric ions in an electrolyte.

Abstract: The present invention relates to a solution for electroplating iron, comprising: iron ions comprising first iron ions and second iron ions; a complexing agent; and unavoidable impurities, wherein the amount of second iron ions among the iron ions is 5 to 60 wt %. According to the present invention, electroplating efficiency is high, there is no drop in electroplating efficiency due to a continuous plating operation, and sludge generation is prevented, and, thus, the plating solution is easily managed. Burning can be prevented even in a high current density operation, and, thus, a high-quality iron-plated layer can be achieved. The plating solution does not need to be replaced, as the concentration of second iron ions generated by a plating reaction is maintained to be constant, and, thus, the present invention is appropriate for a continuous plating process.

Abstract: The steel sheet for plating according to an aspect of the present invention has a GDS profile of an Mn element, as observed in the depth direction from the surface, sequentially including a maximum point and a minimum point, wherein a difference of converted concentration of Mn may be 80% or more, and a difference of converged concentration of Si may be 50% or more.

Abstract: In a steel sheet for plating, according to one aspect of the present invention, the CBS profile of an Mn element, which is observed in the direction of surface to depth, sequentially comprises local maximum points and local minimum points, difference of converted concentration of Mn can be 10% or higher, and difference of converted concentration of Si can be 10% or higher.

Abstract: Provided is an ultra-high-strength steel sheet having an excellent hole expandability and yield ratio, including, in terms of wt %: 0.05-0.2% of carbon (C); 2.0% or less of silicon (Si); 4.1-9.0% of manganese (Mn); 0.05% or less (excluding 0%) of phosphorus (P); 0.02% or less (excluding 0%) of sulfur (S); 0.5% or less (excluding 0%) of aluminum (Al); 0.02% or less (excluding 0%) of nitrogen (N); and a balance of iron (Fe) and other inevitable impurities, wherein the following Equation 1 is satisfied, and wherein microstructures includes, in volume percentage, 10-30% or retained austenite, 50% or more of annealed martensite, and 20% or less of other phases including alpha martensite and epsilon martensite, Equation 1: C/12+Ti/48+Nb/93+V/51+Mo/96?0.015.

Abstract: Provided is an ultra-high strength steel plate for automobiles and, more specifically, to an ultra-high strength steel plate having high formability and hole expandability, and a method for manufacturing the ultra-high strength steel plate. The ultra-high strength steel plate includes: by wt %, carbon (C): 0.04% to 0.17%, silicon (Si): 2% or less, manganese (Mn): 4% to 10%, phosphorous (P): 0.05% or less (excluding 0%), sulfur (S): 0.02% or less (excluding 0%), aluminum (Al): 0.5% or less (excluding 0%), nitrogen (N): 0.02% or less (excluding 0%), and a balance of iron (Fe) and inevitable impurities. Carbon (C) and manganese (Mn) satisfy Formula C+(Mn/25)?0.46. The ultra high strength steel plate has a microstructure comprising retained austenite in a volume fraction of 20% or greater and annealed martensite in a volume fraction of 50% or greater.

Abstract: Provided is an ultrahigh-strength steel sheet for a vehicle and, more specifically, to an ultrahigh-strength and high-ductility steel sheet having excellent yield ratio and a manufacturing method therefor. Provided is an ultrahigh-strength and high-ductility steel sheet for cold press forming and a manufacturing method therefor, the steel sheet ensuring ultrahigh strength and high ductility since an alloy component of steel and manufacturing conditions are controlled and, simultaneously, having excellent impact characteristics due to a high yield strength ratio (yield ratio). Provided is the steel sheet capable of satisfying formability and impact stability, which are required for a vehicle steel sheet for cold forming, and replacing a conventional steel sheet for hot press forming, thereby reducing manufacturing costs.

Abstract: Provided is an ultra-high strength steel plate for automobiles and, more specifically, to an ultra-high strength steel plate having high formability and hole expandability, and a method for manufacturing the ultra-high strength steel plate. The ultra-high strength steel plate includes: by wt %, carbon (C): 0.04% to 0.17%, silicon (Si): 2% or less, manganese (Mn): 4% to 10%, phosphorous (P): 0.05% or less (excluding 0%), sulfur (S): 0.02% or less (excluding 0%), aluminum (Al): 0.5% or less (excluding 0%), nitrogen (N): 0.02% or less (excluding 0%), and a balance of iron (Fe) and inevitable impurities. Carbon (C) and manganese (Mn) satisfy Formula C+(Mn/25)?0.46. The ultra high strength steel plate has a microstructure comprising retained austenite in a volume fraction of 20% or greater and annealed martensite in a volume fraction of 50% or greater.

Abstract: One aspect of the present invention relates to an ultrahigh-strength steel sheet having an excellent yield ratio, comprising, by wt %, 0.3-0.5% of C, 2.0% (excluding 0%) of Si, 3.0-6.5% of Mn, 0.02% or less of P, 0.01% or less of S, 0.01-3.0% of Al, 0.02% or less (excluding 0%) of N, and the balance of Fe and other inevitable impurities, and a microstructure comprises 5-30% of remaining austenite by area fraction and comprises 5% or less of secondary martensite.

Abstract: Provided is an ultra-high-strength steel sheet having an excellent hole expandability and yield ratio, including, in terms of wt %: 0.05-0.2% of carbon (C); 2.0% or less of silicon (Si); 4.1-9.0% of manganese (Mn); 0.05% or less (excluding 0%) of phosphorus (P); 0.02% or less (excluding 0%) of sulfur (S); 0.5% or less (excluding 0%) of aluminum (Al); 0.02% or less (excluding 0%) of nitrogen (N); and a balance of iron (Fe) and other inevitable impurities, wherein the following Equation 1 is satisfied, and wherein microstructures includes, in volume percentage, 10-30% or retained austenite, 50% or more of annealed martensite, and 20% or less of other phases including alpha martensite and epsilon martensite, Equation 1: C/12+Ti/48+Nb/93+V/51+Mo/96?0.015.

Abstract: Provided is an ultrahigh-strength steel sheet for a vehicle and, more specifically, to an ultrahigh-strength and high-ductility steel sheet having excellent yield ratio and a manufacturing method therefor. Provided is an ultrahigh-strength and high-ductility steel sheet for cold press forming and a manufacturing method therefor, the steel sheet ensuring ultrahigh strength and high ductility since an alloy component of steel and manufacturing conditions are controlled and, simultaneously, having excellent impact characteristics due to a high yield strength ratio (yield ratio). Provided is the steel sheet capable of satisfying formability and impact stability, which are required for a vehicle steel sheet for cold forming, and replacing a conventional steel sheet for hot press forming, thereby reducing manufacturing costs.

Abstract: Provided is a high-strength steel sheet for use in lightening materials for electronic products and materials for vehicles including automobiles, trains and ships and, more particularly, to a high-strength cold rolled steel sheet, a coated steel plate, and a method for manufacturing the same, wherein yield strength and ductility are improved by controlling the internal oxidation depth and the amount of residual austenite after first annealing operation, and the high-strength cold rolled steel sheet and the coated steel plate is stably manufactured and provided without any dent defects during the manufacturing thereof.

Abstract: Provided is an ultra high-strength steel sheet having excellent hole expandability. The ultra high-strength steel sheet includes: 0.15 to 0.30% of C, 1.0 to 3.0% of Si, 3.0 to 5.0% of Mn, 0.020% or less of P, 0.010% or less of S, 0.01 to 3.0% of Al, and 0.020% or less of N (excluding 0%) by weight, with the remainder consisting of Fe and other inevitable impurities, wherein a microstructure contains 5% to 20% by area fraction of retained austenite with the remainder including ferrite, bainite and fresh martensite.