MX2008007350A - High strength cold rolled steel sheet and hot dip galvanized steel sheet having excellent formability and coating property, and the method for manufacturing thereof - Google Patents

Abstract

PURPOSE:A cold rolled steel sheet and a hot dip galvanized steel sheet having a tensile strength of 490 MPa or more which are excellent in formability, bake hardenability and plating characteristics by adding Sb and properly controlling N, and a method for manufacturing the same are provided. CONSTITUTION:A method for manufacturing a high strength cold rolled steel sheet having excellent formability, bake hardenability and plating characteristics comprises:reheating a steel slab having a composition comprising, by weight percent, 0.02 to 0.2%of C, 0.01 to 1.0%of Si, 0.5 to 4.0%of Mn, 0.1%or less of P, 0.03%or less of 5, 0.2%or less of soluble Al, 0.01 to 0. 1%of N, more than 0.01 to 1.0%of Sb and the balance ofFe and other inevitable impurities in a temperature range from 1100 to 1300 deg. C;finishing hot finish rolling of the reheated steel slab in a temperature range from Ar3 transformation temperature to 1000 deg. C;coiling the hot finish rolled steel sheet in a temperature range from 450 to 750 deg.C;pickling and cold-rolling the coiled steel sheet;continuously annealing the cold rolled steel sheet in a temperature range from 750 to 900 deg.C for 10 to 1000 seconds;primarily cooling the continuously annealed steel sheet to a temperature range from 650 to 720 deg.C at a cooling rate of 1 to 10 deg.C/sec;and secondly cooling the primarily cooled steel sheet to a temperature range from 100 to 400 deg.C at a cooling rate of 1 to 100 deg.C/sec.

Description

LAMINATED STEEL SHEET IN FRIÓ OF HIGH RESISTANCE THAT IT HAS EXCELLENT PROPERTY OF FORMABILITY AND COATING, STEEL SHEET ELECTRODEPOSITATED WITH METAL BASED ON ZINC DATE OF THIS AND THE MANUFACTURING METHOD Technical Field The present invention relates to a steel sheet that is used mainly as structural and body-reinforcing members, an electroplated steel sheet with zinc-based meta (steel sheet zinc coated) made of this and a method to manufacture it. More specifically, the present invention relates to a cold-rolled, high-strength steel sheet having tensile strength of more than 490 MPa and excellent coating properties, a steel sheet electroplated with meta] based on zinc ( Zinc coated steel sheet) made of this and a method to manufacture it. Background Technique Recently, with the reinforcement and expansion of the regulations for the safety of passengers of motorized vehicles, many investigations and studies have been actively undertaken to achieve weight reduction and body reinforcement, in order to improve the impact resistance of the body To face such a trend, steel sheets with high tensile strength which have tensile strength of more than 490 MPa are actively used to simultaneously achieve weight reduction and body reinforcement. In addition, since most automotive steel sheets are formed by press finishing, they are required to have excellent press formability. High ductility is also essentially required to ensure formability with excellent press. That is, automotive steel sheets are steel sheets with high tensile strength, and the most important issue that should be considered in automotive steel sheets is the high ductility. The reinforcement of the automotive steel sheet results in significant deterioration of the formability and coating properties of the steel sheet, thus suffering from various difficulties in the practical applications thereof. In addition, automotive steel sheet also requires high corrosion resistance, and therefore hot dipped galvanized steel sheets having excellent corrosion resistance have conventionally been used as automotive steel sheet. That is, such steel amines can be manufactured with excellent corrosion resistance at low production costs, since they are manufactured through a line of Continuous hot dip galvanization where the annealing and reclosing coating is carried out in the same line. In addition, alloy hot dip galvanized steel sheets, which were again subjected to heat treatment after hot dip galvanization, are widely used in terms of excellent solubility and formability, as well as excellent corrosion resistance. That is, in order to achieve weight reduction and additional body reinforcement, there is a need in the art for the development of cold-rolled steel sheets with high corrosion resistance having excellent formability, and galvanized steel sheets for hot dip with high tensile strength that have excellent resistance to corrosion through the galvanization line by continuous hot immersion. As a representative conventional technique relating to high dip resistance galvanized steel sheets having excellent formability, mention may be made of Korean Patent Laid-open Publication No. 2002-0073564. This patent relates to a steel sheet having a structure composed of soft ferrite and martensite hard and discloses a method for manufacturing a hot-dip galvanized steel sheet having a ratio and r value (Lan ford value) of improved elongation. However, the conventional technique mentioned in the above suffers from a difficulty in ensuring the excellent quality of coating due to the addition of large amounts of silicon (S), and problems associated with increased production costs due to the addition of large quantities of titanium (Ti) and molybdenum (Mo). In addition, the non-examined patent publication Japanese No. 2004-292891 suggests a method for manufacturing a steel sheet with high tensile strength. This conventional technique is directed to a steel sheet composed of a composite structure containing ferrite as a primary phase, the austem ta retained as a secondary phase, and bainite and martensite as transformation phases at ba at temperature, and suggests a method for manufacture a sheet of steel having improved ductility and ability to form lash straightening. However, this conventional technique suffers from a difficulty in achieving the desired coating capacity due to large amounts of silicon (Si) and aluminum (Al), and a difficulty in ensuring the desired surface quality in steelmaking and casting. continuous.

In addition, this technique also suffers from a difficulty in ensuring the safety of the steel sheet due to the risk of partial deformation of the steel sheet in the cooling, since the cooling of the steel sheet must be carried out in a speed of more than 100 ° C / sec in order to obtain high strength. In addition, as a conventional technique for reducing the problems of coating properties suffered by steel sheets with high tensile strength, there is a Japanese Unexamined Patent Publication No. 2002-088447 which relates to a composite steel sheet of a composite structure that includes ferrite as a primary phase, and divides a method to obtain good working and coating properties. However, this patent suffers from difficulties in the practical application of the same, due to the increased production costs resulting from one or more thermal treatment processes prior to coating, in order to obtain good workability. Description of the Invention Technical Problem Therefore, the present invention has been made in view of the above problems, and the present invention provides advantages capable of achieving excellent coating properties and high tensile strength of more than 490 MPa, by adding antimony (Sb) to a steel material. In addition, the present invention provides advantages to ensure the desired shape of a steel sheet. In addition, the present invention provides advantages for securing the bake hardenability after coating of the steel sheet. Technical Solution According to one aspect of the present invention, the foregoing and other objectives can be achieved by the provision of a cold-rolled steel sheet, comprising 0.01-0.2% by weight of carbon (C), 0.01-2.0% by weight of silicon (S), 0.5-4.0% by weight of manganese (Mn), less than 0.1% by weight of phosphorus (P), less than 0.03% by weight of sulfur (S), less than 1.0% by weight of soluble aluminum (Sol. Al), 0.001-0.1% by weight of nitrogen (N), 0.005-1.0% by weight of antimony (Sb), and the remainder of iron (Fe) with mevitabl impurities is. In one embodiment of the present invention, the cold rolled steel sheet can satisfy the following inequality of (Si / 28 t Al / 27) / (N / 14) > 10, for Si, Al and N. In this case, the contents of the soluble aluminum (Sol. Al) and nitrogen (N) in the cold-rolled steel sheet are preferably in a range of 0.01 to 1.0%, and in a range from 0.001 to 0.03%, respectively. In one embodiment of the present invention, the cold-rolled steel sheet can satisfy the following inequality of N * = (N / 14) / (Al / 27 t Ti / 484 Nb / 93-f V / 51 IB /] 1) > 0.2, for N, Al, Ti, Nb, V and B. In this case, the contents of the soluble aluminum (Sol. Al) and nitrogen (N) in the cold-rolled steel sheet are preferably in the range of less than 0.2%, and in a range of 0.01 to 0.1%, respectively. In one embodiment of the present invention, the cold-rolled steel sheet may additionally comprise at least one selected from the group consisting of: a) 0.001-0.1% of at least one of titanium (Ti), niobium ( Nb) and vanadium (V); b) 0.01-2.0% chromium (Cr) and 0.001-1.0% molybdenum (Mo); and c) less than 0.01% boron (B). In one embodiment of the present invention, a steel structure of the cold rolled steel sheet can have ferrite as a primary phase and a martensite fraction of 2 to 70% as a secondary phase. In one embodiment of the present invention, a sheet of steel coated with zinc includes the above cold rolled steel sheet as a base steel sheet and has a zinc coating layer on at least one surface of the top and bottom surfaces. background of the base steel sheet. The zinc-coated steel sheet may have a layer coated with zinc coating and zinc coating by hot immersion of alloy, without being limited thereto. In one embodiment of the present invention, there is provided a method for manufacturing a cold-rolled steel sheet, which comprises reheating a thick steel sheet that satisfies the steel composition of the present invention at a temperature of 1100 ° C to 1300 °. C; submit the thick steel sheet to the hot finish lamination at a temperature that varies from the Ar3 transformation point to 1000 ° C; roll the thick steel sheet at a temperature of 450 ° C to 750 ° C; strip and cold-roll the thick steel sheet; continuously annealing the thick steel sheet at a temperature of 750 ° C to 900 ° C for 10 to 1000 sec; cool the coarse steel sheet at 600 ° C to 720 ° C at a rate of 1 to 10 ° C / sec (primary cooling); and cooling the coarse steel plate at 100 ° C to 400 ° C at a rate of 1 to 100 ° C / sec (secondary cooling). When it is desired to make the steel sheet coated with zinc, the cold rolled steel sheet is subjected to hot dip galvanization at a temperature of 450 ° C to 500 ° C for less than 10 seconds. Advantageous Effects According to the present invention, a steel sheet ensures high tensile strength of more than 490 MPa, in conjunction with the improvement of coating properties. In addition, the excellent formability of the steel sheet is also ensured. In addition, the hardenability in the furnace after the coating of the steel sheet is increased. Therefore, the steel sheet of the present invention can be applied as structural and reinforcement members of automobiles. BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: Ja EIG. 1 is a graph showing a relationship between (Si / 28 l Al / 27) / (N / 14) and TS * E1 in the present invention; the EIG. 2 is a graph showing a relationship between N and TS * E1 and between N * and BH in the present invention; and the F1G. 3 is a photograph showing surface enrichment properties with the addition of Sb in the present invention. BEST MODE FOR CARRYING OUT THE INVENTION Next in the present invention, the present invention will be described in more detail.

As a result of a variety of extensive and intensive studies and experiments to solve the problems associated with the surface defects that result from the addition of large amounts of silicon (Si) and manganese (Mn), the inventors of the present invention discovered that it is possible to inhibit the enrichment and thickening of oxides on a steel sheet surface by the addition of an appropriate amount of antimony (Sb). That is, the proper addition of antimony (Sb) interferes with the migration of the oxides to the grain boundaries, in order to result in a significant reduction of the probability of the surface defects due to Si and Mn. Therefore, it is possible to ensure excellent coating properties even when large amounts of S and Mn are added. Further, when it is desired to additionally improve the formability in conjunction with the coating properties mentioned in the above, according to one embodiment of the present invention, it is preferred to control a nitrogen (N) content to satisfy either or both of the following inequalities: (Yes / 28 IA1 / 27) / (N / 14) >; 10 (1) N? = (N / 14) / (AJ / 27 lT? / 48 lNb / 93f V / 5J i-B / J 1) > 0.2 (2) Further, in one embodiment of the present invention, the oven hardenability is also increased due to the nitrogen (N) solute after the coating of the steel sheet, when the solute nitrogen is secured. Hereinafter, the composition components of the steel sheet according to the present invention will be described. Composition of Carbon Steel (C): 0.01-0.2% Carbon (C) is a very important component to increase the strength of a steel sheet and to ensure a composite structure of ferpta and martensite. Where the carbon content is lower than 0.01%, it is impossible to obtain the steel strength that is desired by the present invention. On the other hand, where the carbon content is higher than 0.2%, the steel can be highly susceptible to deterioration of hardness and weldability. Therefore, the carbon content is preferably limited to the 0.01-0.2% range. Silicon (Si): 0.01-2.0% Silicon (Si) is a useful element that is able to ensure the desired strength of a steel sheet while not causing the deterioration of ductility of the steel sheet. In addition, silicon is an element that promotes the formation of martensite by promoting the formation of ferrite and facilitates the enrichment of carbon in the non-transformed austenit. Where the silicon content is lower than 0. 01%, it is difficult to ensure the effects mentioned in the above. On the other hand, where the silicon content is higher than 2.0%, the surface and soldability properties may deteriorate. Therefore, the silicon content is preferably limited to the range of 0.01 to 2.0%. Manganese (Mn): 0.5-4.0% Manganese (Mn) is an element that has reinforcing effects in signifying solid solution, simultaneously with the promotion of formation of a structure composed of ferrite and martensite. Where the manganese content is lower than 0.5%, it is difficult to ensure the strength of the steel desired by the present invention. On the other hand, where the manganese content is higher than 4.0%, this may result in high susceptibility to problems associated with hot rolling performance and weldability. Therefore, the manganese content is preferably limited to the range of 0.5 to 4. 0% Phosphorus (P): Less than 0.1% Phosphorus (P) serves to reinforce a steel sheet, but an excessive amount of it can result in the degradation of formability with press. Therefore, the phosphorus content is preferably limited to a range of less than 0.1%. Sulfur (S): Less than 0.03% Sulfur (S) is an impurity element present in steel, and is likely to inhibit the ductility and weldability of a steel sheet. Therefore, the sulfur content is preferably limited to a range of less than 0.03%. Soluble aluminum (Sol. Al): Less than 1.0% Soluble aluminum (Sol. Al) is an element that is combined with oxygen in steel to exert deoxidation effects, and, in conjunction with silicon (Si), It is effective to improve the hardening of the martensite by distributing carbon in the ferpta within the austenite. If the Sol content exceeds 1.0%, the effects of deoxidation and improvement of martensite hardening are saturated and production costs are increased. Therefore, the content of Sol. Al is limited to the interval of less than J .0%. The content of Sol. Al is preferably in the range of 0.01 to 1.0%, more preferably less than 0.2%. Nitrogen (N): 0.001-0.1% Nitrogen (N) is an effective component to stabilize austenite. Where the nitrogen content is lower than 0.001%, it is difficult to achieve such stabilizing effects. On the other hand, where the nitrogen content is higher than 0.1%, there is no significant increase in the stabilization of the effects of the austemta, in conjunction with the problems associated with soldabity and the increased production costs. Therefore, the nitrogen content is limited to the range of 0.001 to 0.1%. Preferably, the nitrogen content is in the range of 0.01 to 0.1%. The nitrogen is combined with titanium (Ti), niobium (Nb) and aluminum (Al) to form nitrides, in order to increase the resistance to deformation of the steel. In the present invention, sufficient amounts of nitrogen are added in order to increase the resistance to deformation of the steel after coating. Nitrogen serves as a primary cause for an acute increase in the steel's deformation resistance, in such a way that the nitrogen remains in the form of solute N within the crystal grains prior to coating, and then interferes with the movement of nitrogen. dislocation after the coating in order to raise a deformation point. If the nitrogen content is lower than 0.01%, it is difficult to achieve such effects. On the other hand, the nitrogen content exceeds 0.1%, there is no significant increase in the effects to improve the resistance to deformation, in conjunction with the problems associated with weldability and increased production costs. According to one modality of this invention, when considering the costs of weldability and production, the nitrogen content is preferably in the range of 0.001 to 0.03%, even though sufficient resistance can not be assured by the solute nitrogen. Antimony (Sb): 0.005-1.0% Antimony (Sb) is a very important element in the present invention, and is an essential component added to ensure excellent coating properties. The Sb, as shown in FIG. 2, reduces surface defects to the surface enrichment of oxides such as MnO, SiO and Al2 03, and exhibits excellent effects on the inhibition of the thickening of the enriched materials of the surface resulting from the elevation of temperatures and changes of the surface. hot rolling process. Where the antimony content is lower than 0.005%, it is difficult to ensure the above effects. On the other hand, a continuous increase in antimony content does not lead to a further significant increase in such effects and may also present problems associated with production costs and work degradation. Therefore, the content of antimony is limited to the range of 0.005 to 1.0%. In addition to the components of the composition mentioned above, one or more elements selected from titanium (Ti), niobium (Nb) and vanadium (V), and chromium (Cr), molybdenum (Mo) and boron (B) can be additionally added to the steel. One or more selected elements of titanium (Ti), niobium (Nb) and vanadium (V): 0.001-0.1% Titanium (Ti), niobium (Nb) and vanadium (V) are effective elements to increase the strength of the sheet steel to achieve the refinement of the grain. Where the content of Ti, Nb and V is lower than 0.001%, it is difficult to achieve desired effects. On the other hand, where the content of Ti, Nb and V exceeds 0.1%, this may result in increased production costs, and decreased ductility of ferrite due to excessive amounts of precipitates. Therefore, the content of Ti, Nb and V is preferably limited to the range of 0.001 to 0.1%. Chromium (Cr): 0.01-2.0% Chromium (Cr) is a component added to improve hardenability of steel and to ensure high strength. Where the chromium content is lower than 0.01%, it is difficult to ensure such effects. On the other hand, where the chromium content exceeds 2.0%, this may result in saturation of such effects and deterioration of the ductility. Therefore, the chromium content is preferably limited in the range of 0.01 to 2.0%. Molybdenum (Mo): 0.001-1.0% MoLibdenum (Mo) is a component added to retard the transformation of the austenit into pearlite and simultaneously to achieve the ferrite refinement and improve the resistance. Where the molybdenum content is lower than 0.001%, it is difficult to obtain such effects. On the other hand, where the molybdenum content exceeds 1.0%, this may result in the saturation of these effects and the deterioration of the ductility. Therefore, the molybdenum content is preferably limited to the range of 0.001 to 1.0%. Boron (B): Less than 0.01% Boron (Bl) is a component that retards the transformation of austenite into pearlite in the cooling of steel during an annealing process, where the boron content exceeds 0.01%, this may result in degradation of the adhesion of the coating, due to the excessive enrichment of boron on the surface of the steel sheet.Therefore, the boron content is preferably limited to the range of less than 0.01% .In one embodiment of the present invention, prefers that the Si, Al and N sat sfagan inequality 1 of (Si / 28 i? l / 27) / (N / 14) > 10. In this case, the contents of the soluble aluminum (Sol. Al) and nitrogen (N) in the steel sheet are preferably in a range of 0.01 to 1.0%, and in a range of 0.001 to 0.03%, respectively.The inequality 1 is a very important equation in terms of the formability of the present invention. As shown in FIG. 1, where the inequality value is smaller than 10, it is difficult to ensure the excellent equilibrium of TS * El. On the other hand, where the inequality value is 10 or higher, it is possible to ensure the TS * balance of more than 15 , 000. That is, the elements that promote the formation of ferrite Si and Al are suitably added to actively induce the formation of ferpta, in order to facilitate carbon enrichment in austenite and improve hardening to promote martensite transformation. you ca The ratio of Al and N is controlled to properly form AlN precipitates, in order to prevent the formation of perlite band during the hot rolling process to induce the refinement and dispersion of the perlite, consequently achieving fine dispersion of the martensite in the final annealing process. As a result, it is possible to ensure the high strength and high ductility of the steel. In one embodiment of the present invention, when one or more components of Al, Ti, Nb, V and B are added, it is preferred to satisfy the following inequality of N * = (N / 14) / (Al / 27 tT? / 48 + Nb / 93 t V / 5J iB / 1 1) >; 0.2. In this case, the contents of the soluble aluminum (Sol. Al) and nitrogen (N) in the steel sheet are preferably in the range of less than 0.2%, and in the range of 0.01 to 0.1%, respectively. N * means a nitrogen content remaining after the formation of nitrides by the combination of nitrogen with Al, Ti and Nb etc., and plays an important role in the present invention. As shown in FIG. 2, where the value of N * is lower than 0.2, it is difficult to ensure the excellent equilibrium of TS * El and a BH value. On the other hand, where the value of N * is 0.2 or higher, it is possible to ensure the TS balance of more than 15,000 and a BH value of more than 80 MPa. That is, N, which refers to the remaining nitrogen after the formation of nitrides, serves as a stabilizer element of austenite, similar to carbon and therefore promotes martensitic transformation during a cooling process. In addition, the enriched nitrogen within the martensite leads to increased strength of the steel. As a result, an improved elongation duration in the same resistance can be obtained. In addition, the hardenability in the furnace is also improved by the solute nitrogen (N) after the coating of the steel sheet. In a preferred embodiment, the steel of the present invention is composed of the components mentioned above and the iron moiety (Ee) with unavoidable impurities. If necessary, other alloying elements are also they can add. Therefore, it should be understood that the steel of the present invention does not exclude steels with addition of other alloying elements, although they are not mentioned in the embodiments of the present invention. In accordance with the present invention, a cold-rolled steel sheet is provided as set forth above. In addition, a sheet of zinc-coated steel having a zinc coating layer on at least one surface of the top and bottom surface of the cold-rolled steel sheet is provided. Then in the present, the final structure of the cold-rolled steel sheet and the zinc-coated steel sheet after the thermal treatment thereof will be described in greater detail. In one embodiment of the present invention, the steel composite as above can be subjected to the heat treatment suitable for the cold rolled steel sheet and the hot dip galvanized steel sheet for controlling a steel structure, for in this way impart desired physical properties. The steel sheet in the present invention is made to have ferpta as a ppmarra phase and a martensite fraction from 2 to 70% as a secondary phase. Where the martensite fraction is lower than 2%, it is difficult to obtain high tensile strength which is desired by the present invention. On the other hand, where the martensite fraction is higher than 70%, this can result in an acute decrease in an elongation ratio. Therefore, the martensite fraction is preferably limited in the range to 2 to 70%. Furthermore, in the present invention, it is also possible to ensure the physical properties that are desired by the present invention, when the bainite as the secondary phase is contained in a content of less than 5%, in addition to the martensite. Hereinafter, a method for manufacturing a cold rolled steel sheet having the composition and steel structure specified in the above will be described in greater detail. Hot Rolling First, a thick sheet of steel, as it is composed in the above, is reheated to a temperature of 1100 ° C to 1300 ° C. Where the reheat temperature is lower than 1100 ° C, the homogeneity and structural re-dissolution of I'i and Nb are not sufficiently achieved. On the other hand, where the ambient temperature is higher than 1300 ° C, this may result in a high susceptibility to swelling of the steel sheet structure and the occurrence of problems associated with manufacturing processes. Therefore, the reheat temperature it is preferably limited to the range of 1100 ° C to 1300 ° C. Then, the thick steel sheet is subjected to hot finish lamination at a temperature ranging from the Ar3 transformation point to 1000 ° C. Where the Hot Finish Lamination temperature is lower than the Ar3 transformation point, this can lead to a high possibility of a noticeable increase in the resistance to the deformation in the heat and problems associated with the manufacturing processes. On the other hand, where the hot finish lamination temperature is more than 1000 ° C, these can probably result in a high risk of excessively thick oxide scale and thickening of the steel sheet structure. Therefore, the hot finish lamination temperature is preferably limited to a temperature that varies from the Ar3 transformation point to 1000 ° C. After the hot-finish lamination was com- posed, the thick sheet thus rolled was rolled at a temperature of 450 ° C to 750 ° C. Where the winding temperature is lower than 450 ° C, the excessive formation of martensite or baimta leads to excessively increased strength of the hot-rolled steel sheet, thus resulting in problems associated with manufacturing processes such as as imperfect shapes due to the heavy load in the cold rolling. On the other hand, where the winding temperature is higher than 750 ° C, this can result in severe surface enrichment by elements such as Si, Mn and B, which decrease the wettability of the hot dip galvanization. Therefore, the winding temperature is preferably limited to a range of 450 ° C to 750 ° C. The lime-rolled steel sheet can be processed into a cold-rolled steel sheet by cold rolling, if necessary. Cold Rolling The rolled cold rolled steel sheet thus subjected to descaling and cold rolling. In one embodiment of the present invention, cold rolling is preferably carried out at a reduction ratio of 30 to 80%. Where the cold rolling reduction ratio is lower than 30%, it is difficult to achieve a desired thickness of the steel sheet and it is also difficult to achieve shape correction of the steel sheet. On the other hand, where the ratio of cold rolling reduction is higher than 80%, this can result in high susceptibility to the occurrence of cracking at the edges of the steel sheet and increased cold rolling load. The steel sheet thus cold nothing can be undergo the annealing treatment, if necessary. Annealing Next, the cold-rolled steel sheet can be subjected to continuous annealing at a temperature of 750 ° C to 900 ° C for 10 to 1000 sec. Continuous annealing is proposed to carry out the reclassification, simultaneously with the formation of ferp and austenite and the distribution of carbon. Where the continuous annealing temperature is lower than 750 ° C, it is difficult to achieve sufficient recrystallization and sufficient austenite formation, and therefore it is difficult to obtain the strength of the steel desired by the present invention. On the other hand, where the continuous annealing temperature exceeds 900 ° C, this can result in decreased productiv- ity and excessive austenite formation, in order to decrease the ductility. Therefore, the continuous annealing temperature is preferably limited to the range of 750 ° C to 900 ° C. In addition, where the continuous annealing time is shorter than 10 sec, it is difficult to form sufficient amounts of austenite. On the other hand, where the continuous annealing time is longer than 1000 sec, this may result in decreased productivity and excessive austemta formation. Therefore, the continuous annealing time is preferably limited to the range of 10 to 1000 sec. Next, the steel sheet so continuously Annealing is cooled to 600 ° C to 720 ° C at a rate of 1 to 10 ° C / sec (primary cooling). The primary cooling stage is proposed to increase the ductility and strength of the steel sheet by ensuring an equilibrium carbon concentration of ferpta and austenite. Where the primary cooling termination temperature is lower than 600 ° C or higher than 720 ° C, it is difficult to obtain the ductility of the steel and strength desired by the present invention, therefore, the cooling completion temperature primary is preferably limited in the range of 600 ° C to 720 ° C. In addition, where the primary cooling rate is lower than 1 ° C / sec, this may result in a susceptibility to perlite formation during the cooling process. On the other hand, where the primary cooling rate is higher than 10 ° C / sec, it is difficult to achieve equilibrium carbon concentration, in order to make it difficult to obtain the desired ductility and strength of steel sheet. Therefore, the primary cooling rate is preferably limited to the range of 1 to 10 ° C / sec. After primary cooling, the steel sheet is cooled to 100 ° C to 400 ° C at a rate of 1 to 100 ° C / sec (secondary cooling), and then maintained at that temperature for 10 to 1000 seconds to form a structure composed of ferrite and martensite. Where the secondary cooling rate is lower than l ° C / sec, this results in the formation of greatly pearlite or bainite as the secondary phase, so that it is difficult to ensure the desired ductility and strength. On the other hand, where the secondary cooling speed is higher than 100 ° C / sec, there is an excessive installation investment required. Therefore, the secondary cooling rate is preferably limited to the range of 1 to 100 ° C / sec. In addition, where the secondary cooling termination temperature is lower than 100 ° C, it is difficult to stably secure a composite structure of ferpta and martensite. On the other hand, where the secondary cooling termination temperature is higher than 400 ° C, the pearlite and bain are largely formed as the secondary phase, in order to make it difficult to ensure the desired ductility and strength. Therefore, the secondary cooling termination temperature is preferably limited to the range of 100 ° C to 400 ° C. Furthermore, where the holding time after secondary cooling is shorter than 10 ° C, it is difficult to stably secure a composite structure steel. On the other hand, where the maintenance time is longer than 1000 sec, this can result in increased productivity decreased and a difficulty for the resistance of the desired steel. Therefore, the holding time is preferably limited to the range of 10 to 1000 sec. Therefore, the steel sheet is cooled to room temperature to manufacture an annealed steel sheet cold rolled. Coating Where appropriate, the hot rolled steel sheet, the cold rolled steel sheet and the annealed cold rolled steel sheet (hereinafter referred to simply as "steel sheet") can be coated. In one embodiment of the present invention, the zinc coating or the alloyed z nc coating can be applied to the coating of the steel sheet. There is no particular limit to coating methods and for example, the invention can be made from hot dip coating, electrolytic coating, evaporation and plating deposition coating. From a productivity point, hot dip coating is preferred. Although the coating method will be described according to the much more preferred embodiment, the present invention is not limited thereto. Hot Dip Galvanization The hot dip galvanization of a steel sheet is preferably carried out at a coating temperature of 450 ° C to 500 ° C for less than 10 ° C. sec. Where the coating temperature is lower than 450 ° C, the zinc coating is not sufficiently achieved. On the other hand, where the coating temperature is higher than 500 ° C, this can result in excessive zinc coating. Therefore, the coating temperature is preferably limited in the range of 450 ° C to 500 ° C. Furthermore, where the hot dip galvanization time is longer than 10 sec, this may result in excessive zinc coating. Therefore, the coating time is preferably limited to the range of less than 10 sec. After the hot dip galvanization was completed, the steel sheet is cooled to room temperature. After hot-dip galvanizing, the steel sheet can be cooled to room temperature to manufacture a galvanized steel sheet, or else the steel sheet can be subjected to alloy coating treatment to manufacture a sheet of steel. galvanized steel alloy. The alloy galvanized steel sheet can be subjected to alloy heat treatment at a temperature of 440 ° C to 580 ° C for less than 30 sec. Where the alloy heat treatment temperature is lower than 440 ° C or higher than 580 ° C, this may result in an unstable alloy. In addition, where the alloy heat treatment time exceeds 30 sec, this can give resulting excessive alloy. Mode for the Invention EXAMPLES Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only to illustrate the present invention and should not be considered as limiting the scope and spirit of the present invention. EXAMPLE 1 Thick steel sheets having a steel composition as set forth in Table 1 below were subjected to vacuum melting, and heating in a heating furnace at a reheat temperature of 1150 ° C to 1250 ° C for 1 hour. hour, followed by hot rolling and winding. The hot rolling was finished at a temperature of 850 ° C to 950 ° C. The winding temperature was adjusted to 650 ° C. Then, the hot rolled steel sheets were subjected to cold pickling and lamination at a cold rolling reduction ratio of 50 to 70%. The cold-rolled steel sheets were subjected to continuous annealing, and primary and secondary cooling, under conditions given in Table 2. For the stress test, JIS 5 test pieces were taken from the cold-rolled steel sheets with only annealed and examined for the quality of the material.

In addition, in order to observe the coating properties, the continuously annealed steel sheets manufactured as above were heated to 460 ° C, subjected to hot dip galvanization for 5 sec and alloy treatment at 500 ° C for 10 sec. sec, and cooled to room temperature, followed by observation of whether or not the steel sheets were coated with the naked eye. Mechanical properties and coating properties of inventive and comparative steels are given in Table 3 below. Table 1 Table 2 Table 3 As shown in Tables 1 to 3, the inventive materials (1 to 10), which satisfy the steel composition and manufacturing method specified herein invention, exhibited an inequality value of 1 of more than 10. That is, as shown in FIG. 1, the Inventive Materials could ensure the formability that is desired by the present invention, as evidenced by the TS x El equilibrium of more than 15,000 at an inequality value of 1 of more than 10. In addition, the inventive materials exhibited high strength at the tension of more than 490 MPa, and exhibited, as shown in FIG. 3, excellent coating properties with the addition of antimony (Sb). Thus, the steel materials of the present invention can be used as automotive structural members and reinforcements having high tensile strength of more than 490 MPa, high ductility and excellent coating properties. On the other hand, the comparative materials (11 to 14), manufactured using Comparative Steels (K to N) that do not meet the composition range of the present invention, exhibited an inequality value of 1 of less than 10. This is, as It is shown in the F1G. 1, The Comparative Materials may not ensure the formability that is desired by the present invention, as evidenced by the TS x El equilibrium of less than 15,000. In addition, Comparative steels are steels with no addition of Sb, and Comparative material 12 with a low content of Si and Mn exhibited excellent coating properties, while comparative materials 13 and 14 exhibited properties of Deficient coating due to the addition of large amounts of Si and Mn. Example 2 Thick steel sheets as shown in Table 4 were then subjected to vacuum melting and heating in a heating furnace at a setback temperature of 1150 ° C to 1250 ° C for 1 hour, followed by rolling in hot and curl. The lamination was finished at a temperature of 850 ° C to 950 ° C. The winding temperature was adjusted to 650 ° C. Then, the hot-rolled steel sheet was subjected to cold pickling and laminating at a cold rolling reduction ratio of 50 to 70%. The cold-rolled steel sheet was subjected to continuous annealing and primary and secondary cooling, under conditions given in Table 5. For stress testing, JIS 5 test pieces were taken from the annealed cold-rolled steel sheet and examined for the quality of the same material. In addition, in order to simulate the quality of the material after coating on automotive parts, 2% stretch was applied to the JIS 5 test pieces thus prepared which were then boiled in oil at 170 ° C for 20 minutes, followed by the test tensile. A BH value was calculated from the following equation: BH = YS (after coating) - strength (after the application of 2% stretch) In addition, in order to observe the coating properties, the continuously annealed steel sheets manufactured as above, were heated to 460 ° C, subjected to hot dip galvanization for 5 sec. and the alloy treatment at 500 ° C for 10 sec, and cooled to room temperature, followed by observation of whether the steel sheet was coated not with the naked eye. Mechanical properties and coating properties of the inventive and comparative steels are given in Table 6 below. Table 4 Table 5 Table 6 As shown in Tables 4 to 6, the Inventive materials (1 to 8), manufactured according to the manufacturing method of the present invention using inventive steels (A to H) that satisfy the steel composition specified in the present invention, exhibited a symbol value of more than 0.2 . This is, as shown in the EIG. 2, The inventive materials could ensure the formability and hardenability of furnace desired by the present invention as evidenced by the TS x The balance of more than 15,000 and a BH value of more than 80 MPa, at an N * value of more of 0.2. In addition, the inventive materials exhibited high tensile strength of more than 490 MPa, and could insure, as shown in FIG. 3, automotive steel sheets that have excellent coating properties with the addition of antimony (Sb). Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims (22)

1. CLAIMS 1. A cold-rolled, high-strength steel sheet having excellent formability and coating properties, characterized in that it comprises 0.01-0.2% by weight of carbon (C), 0.01-2.0% by weight of silicon (Si) , 0.5-4.0% by weight of manganese (Mn), less than 0.1% by weight of phosphorus (P), less than 0 03% by weight of sulfur (S), less than 1.0% by weight of soluble alumnium (Sun Al), 0.001-0 1% by weight of nitrogen (N), 0.005-1.0% by weight of antimony (Sb) and the rest of iron (Fe) with unavoidable impurities.
2. 2. The steel sheet according to claim 1, characterized in that Si, Al and N satisfy an inequality of (Si / 28 t Al / 27) / (N / l) > 10. The steel sheet according to claim 2, wherein the content of soluble aluminum (Sol. Al) is in the range of 0.01 to 1.0% and the nitrogen content (N) is in the range of 0.001 to 0.03%. 4. The steel sheet according to claim 1, characterized in that N, Al, Ti, Nb, V and B satisfy an inequality of N * = (N / 14) / (Al / 27 + T? / 48 Nb / 93lV / 5HB / ll) > 0.2. 5. The steel sheet according to claim 4, characterized in that the content of the soluble aluminum (sol. Al) is in the range of less than

   0. 2% and the nitrogen content (N) is in the range of 0.01 to 0.1%. The steel sheet according to any of claims 1 to 5, characterized in that it also comprises at least one selected from the group consisting of: a) 0.001-0.1% of at least one of titanium (Ti), niobium (Nb) and vanadium (V); b) 0.01-2.0% chromium (Cr) and 0.001-1.0% molybdenum (Mo); and c) less than 0.01% boron (B). The steel sheet according to any of claims 1 to 5, characterized in that a steel structure of the steel sheet has ferrite as a primary phase and a martensite fraction of 2 to 70% as a secondary phase. 8. A sheet of steel coated with zinc, of high strength, characterized in that it comprises the steel sheet of any of claims 1 to 5 as a sheet of base steel and having a layer of zinc coating on at least one surface of the top and bottom surfaces of the base steel sheet. 9. A method for manufacturing a cold-rolled, high-strength steel sheet that has excellent formability and coating properties, characterized because it comprises reheating a thick steel sheet composed of 0.01-0.2% by weight of carbon (C), 0.01-2.0% by weight of silicon (Si), 0.5-4.0% by weight of manganese (Mn), less than 0.1% by weight of phosphorus (P), less than 0.03% by weight of sulfur (S), less than 1.0% by weight of soluble aluminum (Sol. AL), 0.001-0.1% by weight of nitrogen (N), 0.005 -1.0% by weight of antimony (Sb), and the rest of iron (Fe) with unavoidable impurities at a temperature of 1100 ° C to 1300 ° C; subjecting the thick steel plate to the hot-finish lamination at a temperature ranging from the Ar3 transformation point to 1000 ° C: coiling the thick steel sheet at a temperature of 450 ° C to 750 ° C; descale and cold laminate the thick sheet of steel; coarsely annealing the thick steel sheet at a temperature of 750 ° C to 900 ° C for 10 to 1000 sec; cool the coarse steel sheet at 600 ° C to 720 ° C at a rate of 1 to 10 ° C / sec (primary cooling); and cooling the coarse steel plate at 100 ° C to 400 ° C at a rate of 1 to 100 ° C / sec (secondary cooling). 10. EJ method in accordance with the claim 9, characterized because Yes, Al and N satisfy an inequality of (S? / 28 + Al / 27) / (N / 14) > 10. 11. The method of compliance with the claim 10, characterized in that the soluble aluminum content (Sol. Al) is in the range of 0.0J to 1.0% and the content of nitrogen (N) is in the range of 0.001 to 0.03%. The method according to claim 9, characterized in that N, Al, Ti, Nb, V and B satisfy an inequality of N * = (N / 14) / (Al / 274 Ti / 48 i Nb / 93 V / 51 + B / 11) > 0.2. 13. The method according to the claim 12, characterized in that the content of the soluble aluminum (Sol. Al) in the range of less than 0.2% and the content of nitrogen (N) is in the range of 0.01 to 0.1%. 14. The method according to any of claims 9 to 13, characterized poique also comprises at least one selected from the group consisting of: a) 0.001-0.1% of at least one of titanium (Ti), niobium ( Nb) and vanadium (V); b) 0.01-2.0% chromium (Cr) and 0.001-1.0% molybdenum (Mo); and c) less than 0.01% boron (B). 15. The method according to any of claims 9 to 13, characterized in that a steel structure of the steel sheet has ferp as a primary phase and a martensite fraction of 2 to 70% as a secondary phase. 16. A method to manufacture a steel sheet coated with .me, high strength that has excellent formability and coating properties, characterized in that it comprises subjecting the cold-rolled steel sheet prepared by the method of any of claims 9 to 13 to hot dip galvanization at a temperature of 450 ° C to 500 ° C for less than 10 sec. 17. A method according to claim 16, characterized in that Si, Al and N satisfy an inequality of (S? / 28 + Al / 27) / (N / 14) > 10. The method according to claim 17, characterized in that the content of soluble aluminum (Sol. Al) is in the range of 0.01 a] .0% and the nitrogen content (N) is in the range of 0.001 to 0.03%. 19. The method according to claim 16, characterized in that N, Al, Ti, Nb, V and B satisfy an inequality of N * = (N / 14) / (Al / 27 tT? / 48? -Nb / 93 tv / 51 tB / 11) > 0.2. The method according to claim 19, characterized in that the content of the soluble aluminum (Sol. Al) is in the range of less than 0.2% and the content of nitrogen (N) is in the range of 0.01 to 0.1%. 21. The method according to any of claims 16 to 20, characterized in that it also comprises at least one selected from the group consisting of: a) 0.001-0.1% of at least one of titanium (Ti), niobium (Nb) and vanadium (V); b) 0.01-2.0% chromium (Cr) and 0.001-1.0% molybdenum (Mo); and c) less than 0.01% boron (B). The method according to any of claims 16 to 20, characterized in that a steel structure of the steel sheet has ferpta as a primary phase and a martensite fraction of 2 to 70% as a secondary phase.