MX2007013676A

MX2007013676A - Cold rolled steel sheet having superior formability and high yield ratio, process for producing the same.

Info

Publication number: MX2007013676A
Application number: MX2007013676A
Authority: MX
Inventors: Man-Young Park; Jeong-Bong Yoon; Sang-Ho Han; Sung-Il Kim; Kwang-Geun Chin; Ho-Seok Kim; Jin-Hee Chung; Noi-Ha Cho
Original assignee: Posco
Priority date: 2005-05-03
Filing date: 2006-05-03
Publication date: 2008-01-28
Also published as: KR100742954B1; CN100557058C; KR20060115636A; KR100742951B1; TWI346141B; KR20060115629A; KR100723160B1; JP2008540826A; KR20060115643A; JP2008540827A; KR20060115625A; KR100742934B1; KR20060115638A; KR100742940B1; KR100742819B1; KR100742919B1; KR20060115614A; KR20060115312A; KR20060115639A; KR20060115318A

Abstract

Disclosed herein is a Nb-Ti composite IF steel in which fine precipitates, such as CuS precipitates, having a size of 0.2 ??mum or less are distributed. The distribution of fine precipitates in the Nb-Ti composite IF steel enhances the yield strength and lowers the in-plane anisotropy index. The nanometer-sized precipitates allow the formation of minute crystal grains. As a result, dissolved carbon is present in a larger amount in the crystal grain boundaries than within the crystal grains, which is advantageous in terms of room-temperature non-aging properties and bake handenability.

Description

LAMINATED STEEL SHEET IN FRIÓ HAVING SUPERIOR FORMABILITY AND HIGH RELATION OF DEFORMATION, PROCESS TO PRODUCE [Field Peen i co] s the present invention relates to steel sheets Jammadas cn cold Jibres itersti cal (IF) added with niobium ( Nb) and titanium (Ti) which are used as materials for automobiles, household electronic devices, etc. More specifically, the present invention relates to highly formable foil laminates or IF foils whose deformation resistance is increased due to the dispersion of fine precipitates, and a process for producing cold rolled sheets. ^ [Background Art] In general, cold-rolled steel sheets for use in automobiles and household electronic appliances are required because they have resistance to aging at excellent room temperature and endu in the oven, or together with high resistance and it formed a superior one. 11 aging is a phenomenon of aging by deformation that arises from I hardening caused by loose elements, such as C and N, fixed to dislocations. Since aging causes a defect called "super fi cial deformation", it is important to ensure resistance to aging at excellent room temperature. The oven hardening means increases in strength due to the presence of dissolving charcoal or after press forming, followed by painting and drying, by leaving a slight amount of carbon in a state of solid solution. The steel sheets with excellent oven resistance can overcome the difficulties of form in the press resulting from the high resistance. Resistance to aging at room temperature and oven resistance can be imparted to the steels quenched with aluminum (? L) by batching of the steels quenched with Al. However, the extended time of recoating Lots cause low productivity of the calmed pools with severe variations in steel materials at different sites. In addition, the steels soothed with it have an oven setting value (Bll) (a difference in deformation resistance before and after painting) of 10-20 MPa, which shows that an increase in the forming resistance is low. Under these circumstances, interstitial free steels (11) with resistance to aging at ambient temperature and excellent oven resistance have been developed by adding carbide and nitride-forming elements, such as 1 i and Nb, followed by continuous annealing For example, Japanese Unexamined Patent Publication No. Sho 5 / -041349 describes an increase in the strength of a steel 11 based on J i by adding 0.4-0.8% manganese (Mn) and 0.04-0.1%. phosphorus (P). With very low carbon IF steels, however, P causes the problem of secondary work fragmentation due to segregation at grain boundaries. Japanese Unexamined Patent Publication No.

He 5-078784 describes an increase in strength by the addition of Mn as a solid solution reinforcing element in an amount that e > I yield 0.9% and does not exceed 3.0%. Korean patent open to the public No. 2003-0052248 describes an improvement in the strength of embrittlement of secondary work as well as strength and work capacity by the addition of 0.5-2.0% Mn instead of P, together with aluminum ( ? l) and boron (B). Japanese Unexamined Patent Application No. 10-158 / 83 discloses an increase in resistance by reducing the P cont count and utilizing Mn and Si as solids refugee elements. According to this publication, Mn is used in an amount of up to 0.5%, Al as a deoxidizing agent is used in an amount of 0.1%, and nitrogen (N) as an impurity is limited to 0.01% or less. If the content of Mn is increased, the characteristics of plating! Slow they get worse. Japanese Unexamined Patent Publication No. Hei 6-057336 discloses an increase in the strength of a TF steel by adding 0.5-2.5% copper (Cu) to form precipitates of the same.; -Cu. The high strength of the IF ~ steel is achieved due to the presence of e-Cu precipitates, but the working capacity of the steel II worsens. Unexamined Japanese patent publications Nos. He i 9-227951 and He i 10-265900 suggest technologies associated with the improvement in working capacity or surface defects due to carbides from the use of Cu as a core for precipitation. of the carbides. According to the first publication, 0.005-0.1% of Cu is added to precipitate the CuS during the tempering by rolling of a steel 11, and the CuS precipitates are used as cores to form Cu-Ti-CS precipitates during the lamination hot In addition, the first publication establishes that the number of nuclei that form a plane. { 111.}. Parallel to the surface of a plate increases in the vicinity of Cu-Ti-C-S precipitates during recirculation 1, which contributes to an improvement in working capacity. According to the latest publication, 0.01-0.05% of Cu is added to an IF steel to obtain CuS precipitates and then the CuS precipitates are used as a core for the precipitation of carbides to reduce the amount of carbon dissolves Lo ( C), leading to an improvement in surface defects. According to the prior art, since the CuS precipitates are used during the production of cold-rolled steel sheets, the carbides remain in the final products. Further, since the emulsifying elements, such as Ti and /, r, are added in an amount greater than the amount of a / re (S) in an atomic weight ratio, a major portion of the a / ufre (S ) reacts with Ti or Zr before Cu. On the other hand, Japanese Unexamined Patent Publications Nos. Hei 6-240365 and Hei 7-216340 disclose the addition of a combination of Cu and P to improve the corrosion resistance of the ir-type steels of oven hardening. According to these publications, Cu is added in an amount of 0.05-1.0% to ensure improved corrosion resistance. However, at present, Cu is added in an excessively large amount of 0.2% or more. The Japanese Unexamined Patent Publications Nos. Hei 10-280048 and 10-287954 suggest the dissolution of carbosul furo (based on Ti-CS) on a carbide at the time of rec 1 and annealing to obtain a solution solid in the limits of the glass grade, thus achieving a value of oven hardening (BH) (a difference in the deformation resistance before and after baking) of 30 MPa or more. According to the publications mentioned in the above, the resistance is increased by hardening the solid solution or using e-Cu precipitates. Cu is used to form e-Cu precipitates and improves corrosion resistance. In addition, Cu is used as a nucleus for the precipitation of carbides. No mention is made in these publications of an increase in the high strain ratio (ie, strain resistance / tensile strength) and a reduction in the anisotropy index in the plane. If the ratio of tensile strength to strain resistance (ie deformation ratio) of an IF steel sheet is high, the thickness of the steel sheet IF can be reduced, which is effective in reducing weight. In addition, if the anisotropy index in the plane of an IF steel sheet is low, few creases and wavy edges occur during processing and after processing, respectively. [Description] [Technical Problem] It is an object of certain embodiments of the present invention to provide IF cold-rolled steel sheets added with Nb and Ti which are capable of achieving a high deformation ratio and a low index of anisotropy in the plane. It is another object of certain embodiments of the present invention to provide a process for producing cold-rolled steel sheets IF. [Technical Solution] According to the present invention, a cold rolled steel sheet having a composition comprising 0.01% or less of C, 0.01-0.2% Cu, 0.005- 0.08% S, 0.1% or less of Al, 0.004% or less of N is provided. , 0.2% or less of P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% of Ti, by weight, and the rest of Fe and other non-avoidable impurities, where the composition satisfies The following relationships: 1 <; (Cu / 63.5) / (S * / 32) < 30 and S * = S -0.8 x (Ti-0.8 x (48/14) x N) x (32/48) and the steel sheet comprises CuS precipitates having an average size of 0.2 μm or less. According to the present invention, there is provided a sheet of cold rolled steel having a composition comprising 0.01% or less of C, 0.01-0.2% Cu, 0.01-0.3% of Mn, 0.005-0.08% of S, 0.1 % or less of Al, 0.004% or less of N, 0.2% or less of P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% of Ti, by weight, and the rest of Fe and other non-avoidable impurities, wherein the composition satisfies the following ratios: 1 < (Mn / 55 + Cu / 63.5) / (S * / 32) < 30 and S + = S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48), and the steel sheet comprises precipitates of (Mn, Cu) S having an average size of 0.2 μm or less. According to the present invention, there is provided a cold rolled steel sheet having a composition comprising 0.01% or less of C, 0.01-0.2% Cu, 0.005- 0.08% S, 0.1% or less of Al, 0.004-0.02% N, 0.2% or less of P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% of Ti, by weight, and the rest of Fe and other non-avoidable impurities, in where the composition satisfies the following relationships: 1 < (Cu / 63.5) / (S * / 32) < 30, 1 < (Al / 27) / (NVl4) < 10, S + = S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48) and N * = N - 0.8 x (Ti - 0.8 x (48/32) x S)) x (14/48), and the steel sheet comprises CuS and A1N precipitates having an average size of 0.2 μm or less. According to the present invention, there is provided a sheet of cold-rolled steel having a composition comprising 0.01% or less of C, 0.01-0.2% Cu, 0.01-0.3% of Mn, 0.005-0.08% of S, 0.1% or less of Al, 0.004-0.02% of N, 0.2% or less of P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% of Ti, by weight, and the rest of Faith and other non-avoidable impurities, wherein the composition satisfies the following relationships: 1 < (Mn / 55 + Cu / 63.5) / (S * / 32) < 30, 1 < (Al / 27) / (N * / 14) < 10, S * = S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48) and N * = N - 0.8 x (Ti -0.8 x (48/32) x S)) x (14/48), and the steel sheet comprises precipitates of (Mn, Cu) S and A1N having an average size of 0.2 μm or less. According to the present invention, there is provided a cold rolled steel sheet having a composition comprising 0.01% or less of C, 0.08% or less of S, 0.1% or less of Al, 0.004% or less of N, 0.2% or less of P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% of Ti, at least one class selected from 0.01-0.2% Cu, 0.01-0.3% of Mn and 0.004 - 0.2% of N, by weight, and the rest of Fe and other non-avoidable impurities, where the composition satisfies the following relationships: 1 < (Mn / 55 + Cu / 63.5) / (S732) < 30, 1 < (Al / 2) / (N7l4) < 10, where the content N is 0.004% or more, S * = S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48) and N * = N - 0.8 x (Ti - 0.8 x (48/32) x S)) x (14/48), the steel sheet comprises at least one selected class of (Mn, Cu) S and A1N precipitates having an average size of 0.2 μm or less. When the cold-rolled steel sheets of the present invention satisfy the following relationships between the contents of C, Ti, N and S: 0.8 < (Ti748) / (C / 12) < 5.0 and Ti * = Ti - 0.8 x ((48/14) x N + (48/32) x S), show non-aging properties at room temperature. Also, when the solute carbon (Cs) [Cs = (C.- Ti * x 12/48) x 10000 in which Ti * = Ti - 0.8 x ((48/14) x N + (48/32) x S), with the proviso that when Ti * is less than 0, Ti * is defined as 0], which is determined by the contents C and Ti, is from 5 to 30, the cold-rolled steel sheets of the present invention shows hardenability in the furnace. Depending on the design of the compositions, the cold-rolled steel sheets of the present invention have characteristics of soft cold-rolled steel sheets in the order of 280 MPa and high-strength cold-rolled steel sheets in the order of 340 MPa or more. . When the content of P in the compositions of the present invention is 0.015% or less, the cold rolled steel sheets are soft in the order of 280 MPa are produced. When the soft cold-rolled steel sheets further contain at least one solid solution reinforcing element selected from Si and Cr, or the P content is in the range of 0.015-0.2%, a high strength of 340 MPa is achieved. or more. The content of P in high strength steels containing P alone are preferable in the range of 0.03% to 0.2%. Si content in high strength steels is preferably in the range of 0.1 to 0.8%. The Cr content in the high strength steels is preferably in the range of 0.2 to 1.2. In the case where the cold-rolled steel sheets of the present invention contain at least one element selected from Si and Cr, the content of P can be freely designated in an amount of 0.2% or less. For better workability, the cold-rolled steel sheets of the present invention may additionally contain 0.01-0.2 wt.% Mo. According to the present invention, there is provided a process for producing the cold rolled steel sheets, the process comprising reheating a slab to satisfy one of the compositions at a temperature of 1,100 ° C or higher, hot rolling the sheet coarse heated at a finished rolling temperature of the transformation point Ar3 or higher to provide a hot-rolled steel sheet, cooling the hot-rolled steel sheet at a rate of 300 ° C / min, winding the steel sheet cooled to 700 ° C or lower, cold rolling the rolled steel sheet, and continuously annealing the cold rolled steel sheet. [Best Mode] The present invention will be described in detail below. Fine precipitates having a size of 0.2 μm or less are distributed in the cold-rolled steel sheets of the present invention. Examples of such precipitates include precipitates of MnS, precipitates of CuS, and precipitates composed of MnS and CuS. These precipitates are simply referred to as "(Mn, Cu) S".

The present inventors have found that when the fine precipitates are distributed on the Ti-based IF steels, the deformation resistance of the IF steels is increased and the anisotropy index in the plane of the IF steels is decreased, thus leading to an improvement in work capacity. The present invention has been achieved based on this invention. The precipitates used in the present invention have little related stress in conventional ir steels. Particularly, the precipitates have not been used actively from the point of view of deformation resistance and index of anisotropy in the plane. The regulation of the components in Ti-based IF steels is required to obtain precipitates of (Mn, Cu) S and / or precipitates of A1N. If the IF steels contain Ti, Zr and other elements, S and N react preferentially with Ti and Zr. Since the cold-rolled steel sheets of the present invention are IF steels composed of Nb and Ti, the Ti reacts with C, N and S. Therefore, it is necessary to regulate the components so that S and N are precipitated in the forms of (Mn, Cu) S and A1N, respectively. The fine precipitates thus obtained allow the formation of tiny crystal grains. The smallness in the size of the crystal grains relatively increases the proportion of crystal grain boundaries. Accordingly, the dissolved carbon is present in a larger amount within the boundaries of the crystal grain than within the crystal grains, thereby achieving excellent non-aging properties at room temperature. Since the dissolved carbon present within the crystal grains can migrate more freely, it joins the movable dislocations, thus affecting the aging properties at room temperature. In contrast, the dissolved carbon segregated in the stable positions, such as in the boundaries of the crystal bead and in the vicinity of the precipitates, is activated at a high temperature, for example, a temperature for the painting / baking treatment, of this way affecting the hardenability in the oven. The fine precipitates distributed in the steel sheets of the present invention have a positive influence on the increase in the deformation resistance that increases the precipitation, improves the resistance-ductility balance, index of anisotropy in the plane, and anisotropy of plasticity. For this purpose, fine (Mn, Cu) S precipitates and A1N precipitates should be distributed evenly. According to the cold-rolled steel sheets of the present invention, the contents of the components that affect the precipitation, the composition between the components, the production conditions, and particularly the cooling ratio after the hot rolling, have a greater influence on the distribution of fine precipitates. The constituent components of the cold-rolled steel sheets according to the present invention will be explained. The content of carbon (C) is preferably limited to 0.01% or less. The carbon (C) affects the resistance to aging at room temperature and the oven hardenability of cold-rolled steel sheets. When the carbon content exceeds 0.01%, the addition of costly Nb and Ti agents is required to remove the remaining carbon which is economically disadvantageous and undesirable in terms of formability. When it is proposed to achieve resistance to aging at room temperature only, it is preferred to keep the carbon content at a low level, which allows the reduction of the amount of expensive Nb and Ti agents added. When it is proposed to ensure the hardenability of the desired furnace, the carbon is preferably added in an amount of 0.001% or more, and more preferably 0.005% to 0.01%. When the carbon content is less than 0.005%, the resistance to aging at room temperature can be ensured without increasing the amounts of Nb and Ti.

The copper (Cu) content is preferably in the range of 0.01-0.2%. Copper serves to form fine CuS precipitates, which make the fine crystal grains. Copper decreases the anisotropy index in the plane of cold-rolled steel sheets and increases the deformation resistance of cold-rolled steel sheets by promoting precipitation. In order to form fine precipitates, the Cu content must be 0.01% or more. When the content of Cu is more than 0.2%, the coarse precipitates are obtained. The content of Cu is more preferably in the range of 0.03 to 0.2%. The manganese content (Mn) is preferably in the range of 0.01-0.3%. Manganese serves to precipitate sulfur in a solid state solution in steels such as MnS precipitates, thus preventing the occurrence of hot brittleness caused by dissolved sulfur, or is known as a solid solution reinforcing element. From such a technical point of view, manganese is generally added in a large amount. The present inventors have found that when the manganese content is reduced and the sulfur content is optimized, very fine MnS precipitates are obtained. Based on this invention, the manganese content is limited to 0.3% or less. In order to ensure this characteristic, the manganese content must be 0.01% or more. When the manganese content is less than 0.01%, it is said the sulfur content that remains in a solid state solution is high, hot brittleness can occur. When the manganese content is greater than 0.3%, the coarse MnS precipitates are formed, thus making it difficult to achieve the desired strength. A more preferable Mn content is within the range of 0.01 to 0.12%. The sulfur content (S) is preferably limited to 0.08% or less. Sulfur (S) reacts with Cu and / or Mn to form precipitates of CuS and MnS, respectively. When the sulfur content is greater than 0.08%, the proportion of dissolved sulfur is increased. This increase in dissolved sulfur greatly deteriorates the ductility and formability of the steel sheets and increases the risk of hot brittleness. In order to obtain as many CuS and / or MnS precipitates as possible, a sulfur content of 0.005% or more is preferred. The content of aluminum (Al) is preferably limited to 0.1% or less. Aluminum reacts with nitrogen (N) to form fine A1 precipitates, thereby completely preventing aging by dissolved nitrogen. When the nitrogen content is 0.004% or more, the AlN precipitates are formed sufficiently. The distribution of the fine AlN precipitates in the steel sheets allows the formation of tiny crystal grains and increases the deformation resistance of the steel sheets by increasing precipitation. A most preferable Al content is in the range of 0.01 to 0.1%. The nitrogen (N) content is preferably limited to 0.02% or less. When it is proposed to use AlN precipitates, the nitrogen is added in an amount of up to 0.02%. Otherwise, the nitrogen content is controlled at 0.004% or less. When the content of nitrogen is less than 0.004%, the number of AlN precipitates is small, and therefore, the effects of the smallness of the crystal grains and the effects of the increase in precipitation are negligible. In contrast, when the nitrogen content is greater than 0.02%, it is difficult to guarantee aging properties by the use of dissolved nitrogen. The phosphorus content (p) is preferably limited to 0.2% or less. Phosphorus is an element that has excellent solid solution reinforcing effects while allowing a slight reduction in the r value. The phosphor guarantees high strength of the steel sheets of the present invention in which the precipitates are controlled. It is desirable that the phosphorus content in steels requiring a strength of the order of 280 MPa be defined as 0.015% or less.It is desirable that the phosphorus content in high strength steels of L order of 340 MPa be limited to a range exceeding 0.015% and not exceeding 0.2% A phosphorus content exceeding 0.2% can lead to a reduction in ductility in the steel sheets, therefore the phosphorus content is preferably limited to a maximum of 0.2%. When Si and Cr are added in the present invention, the phosphorus content can be appropriately controlled to be 0.2% or less to achieve the desired strength. The boron content (B) is preferably in the range of 0.0001 to 0.002%. Boron is added to prevent the occurrence of secondary work embrittlement. For this purpose, a preferable boron content is 0.0001% or more. When the boron content exceeds 0.002%, the deep drawing capacity of the steel sheets can deteriorate markedly. The content of niobium (Nb) is preferably in the range of 0.002 to 0.04%. The niobium is added for the purpose of ensuring the non-aging properties and improving the formability of the steel sheets. Nb, which is an element that forms potent carbide, is added to steels to form NbC precipitates in steels. In addition, the NbC precipitates allow the steel sheets to be well textured during the annealing, thereby greatly improving the deep stiffness of the steel sheets. When the added Nb content is not greater than 0.002%, the NbC precipitates are obtained in very small amounts. Accordingly, the steel sheets are not well textured and thus there is little improvement in the deep drawing capacity of the steel sheets. In contrast, when the Nb content exceeds 0.04%, the NbC precipitates are obtained in very large amounts. Consequently, the deep stretchability and elongation of the steel sheets are diminished, and thus the formability of the steel sheets can deteriorate markedly. The content of titanium (Ti) is preferably in the range of 0.005 to 0.15%. The titanium is added for the purpose of ensuring the non-aging properties and improving the formability of the steel sheets. Ti, which is an element that forms powerful carbide, is added to steels to form TiC precipitates in steels. TiC precipitates allow the precipitation of dissolved carbon to ensure non-aging properties.

When the added Ti content is less than 0.005%, the TiC precipitates are obtained in very small amounts. Consequently, the steel sheets are not well textured and thus there is little improvement in the deep drawing capacity of the steel sheets. In contrast, when titanium is added in an amount exceeding 0.15%, very large T C precipitates are formed. Accordingly, the smallness effects of the crystal grains are reduced, resulting in anisotropy index in the high plane, reduction of the deformation resistance and marked deterioration of the plating characteristics. To obtain the precipitates of (Mn, Cu) S and AlN, the contents of Mn, Cu, S, Nb, Ti, Al, N and C are adjusted within the ranges defined by the following relationships. The respective components indicated in the following ratios are expressed as percentages by weight. 1 < (Cu / 63.5) / (S * / 32) < 30 (1) S * = S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48) (2) In relation 1, S, which is determined by the ratio 2, represents the Sulfur content that does not react with Ti and then reacts with Cu. To obtain precipitates of fine CuS, it is preferred that the value of (Cu / 63.5) / (S / 32) is equal to or greater than 1. If the value of (Cu / 63.5) / (S * / 32) is greater that 30, thick CuS precipitates are distributed, which is undesirable. To stably obtain CuS precipitates having a size of 0.2 μm or less, the value of (Cu / 63.5) / (S * / 32) is preferably in the range of 1 to 20, more preferably 1 to 9, and much more preferably from 1 to 6. 1 < (Mn / 55 t Cu / 63.5) / (S732) < 30 (3) The ratio 3 associated with the formation of precipitates of (Mn, Cu) S, and is obtained by adding a content of Mn to the re Lac ion 1. To obtain precipitates from (Mn, Cu) S effective, the value of (Mn / 55 + Cu / 63.5) / (S * / 32) must be 1 or greater. When the value of ratio 3 is greater than 30, coarse (Mn, Cu) S precipitates are obtained. To stably obtain precipitates of (Mn, Cu) having a size of 0.2 μm or less, a more preferable value of (Cu / 63.5) / (S * / 32) is preferably in the range of 1 to 20, more preferably 1 to 9, and most preferably from 1 to 6. When Mn and Cu are added together, the sum of Mn and Cu is more preferably 0.05-0.4%. The reason for this limitation to the sum of Mn and Cu is to obtain precipitates of fine (Mn, Cu) S. 1 < (Al / 27) / (N7l4) < 10 (4) N * = N - 0.8 x (Ti - 0.8 x (48/32) x S)) x (14/48) (5) Ratio 4 is associated with the formation of precipitates (Mn, Cu) S thin. In the ratio 4, N, which is determined by ratio 5, represents the nitrogen content that does not react with Ti and then reacts with Al. To obtain fine AlN precipitates, it is preferred that the value of (Al / 27) / (N7l 4) is in the range of 1-10. To obtain the effective AlN precipitates, the value of (Al / 27) / (N7l4) must be 1 or greater. If the value of (Al / 27) / (N / 14) is greater than 10, coarse AlN precipitates are obtained and thus poor working capacity and low forming resistance are caused. It is preferred that the value of (Al / 27) / (N7l4) is in the range of 1 to 6. The components of the cold-rolled steel sheets according to the present invention can be combined in various ways according to the class of precipitates to be obtained. For example, the present invention provides a foil laminated steel sheet having a composition comprising 0.01% or less of C, 0.08% or less of S, 0.1% or less of Al, 0.004% or less of N, 0.2. % or less than P, 0.0001-0.002% of B, 0.002-0.04% of Nb, 0.005-0.15% of Ti, at least one class selected from 0.01-0.2% of Cu, 0.01-0.3% of Mn and 0.004- 0.2% N, by weight, and the rest of FE and other non-avoidable impurities where the composition satisfies the following relationships: 1 < (Mn / 55 i Cu / 63.5) / (S732) < 30, 1 < (Al / 27) / (N7l4) <; 10 (with the proviso that the content of N is 0.004% or more), S "= S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48) and N * = N - 0.8 x (Ti-0.8 x (48/32) x S)) x (14/48), and the steel sheet comprises at least one selected class of MnS, CuS, MnS and AlN precipitates having an average size of 0.2 μm or less.That is, one or more classes selected from the group consisting of 0.01-0.2% Cu, 0.01-0.3% Mn and 0.004-0.2% N lead to various combinations of precipitates of (Mn, Cu) S and AlN having a size no greater than 0.2 μm In the steel sheets of the present invention, the carbon is precipitated in the NbC and TiC forms.Therefore, the resistance to aging at room temperature and the harden In the oven the steel sheets are affected depending on the conditions of the dissolved carbon under which the NbC and TiC precipitates are not obtained, taking into account these requirements, it is much preferred that the two of Ti and C satisfy the following relationships. 0.8 < (Ti 748) / (C / 12) < 5.0 (6) Ti '= T - 0.8 x ((48/14) x N i (48/32) x S) (7) Ratio 6 is associated with the formation of TiC precipitates to remove carbon in a solution of solid state, in this way achieving non-aging properties at room temperature. In relation 6, the T *, which is determined by the ratio 7 represents the content of titanium that reacts with N and S and then reacts with C. When the value of (Ti / 48) / (C / 12) is lower than 0.8, it is difficult to ensure the non-aging properties at room temperature. In contrast, when the value of (Ti / 48) / (C / 12) is greater than 5, the amount is of Ti that remain in a solution of solid state in the steels are large, which deteriorates the durability of the steels . When it is proposed to achieve non-aging properties at room temperature without ensuring oven hardenability, it is preferred to remove the carbon content to 0.005% or less. Although the carbon content is more than 0.005%, the properties of non-aging at room temperature can be achieved when the ratio 6 is satisfied is satisfied by the amounts of TiC precipitates are increased, thus deteriorating the work capacity of the steel sheets. Cs = (C - Ti * x 12/48) x 10000 (8) (with the proviso that when Ti "is less than 0, Ti * is defined as 0.) The relation 8 is associated with the achievement of the hardening The Cs, which is expressed in ppm by the ratio 8, represents the dissolved carbon content that does not precipitate in the TiC forms.In order to achieve a high oven setting value, the value of Cs must If the value of Cs exceeds 30 ppm, the content of the dissolved carbon increases, making it difficult to achieve non-aging properties at room temperature It is advantageous that the fine precipitates are evenly distributed in the compositions of the present invention. It is preferable that the precipitates have an average size of 0.2 μm or less According to a study conducted by the present inventors, when the precipitates have an average size greater than 0.2 μm, the steel sheets have poor strength and index of anisotropy in the In addition, large amounts of precipitates having a size of 0.2 μm or less are distributed to the compositions of the present invention. While the number of distributed precipitates is not particularly limited, it is more advantageous with the higher number of precipitates. The number of precipitates distributed is preferably 1 x l? mm ^ or more, more preferably 1 x 10 ° / mrtr or more, and much more preferably 1 x 10 / mm "" or more. The anisotropy index of plasticity increases and the onset of amsotropy in the plane decreases with the increase in the number of precipitates, and as a result, the capacity for work is greatly improved. It is commonly known that there is a limitation in the increase in working capacity because the anisotropy index in the plane increases with the anisotropy index of plasticity. It does not help that the number of precipitates distributed in the steel sheets of the present invention increases, the anisotropy index of plasticity of the steel sheets increases and the amyotropy index in the plane of the steel sheets decreases. The steel sheets of the present invention in which the fine precipitates are formed satisfy a deformation ratio (strain resistance / tensile strength) of 0.58 or higher. When the steel sheets of the present invention are applied to the high strength steel sheets, they may contain at least one solution reinforcing element selected from P, Si and Cr. The effects of the addition of P are they have previously described, and so their explanation is omitted. The content of silicon (Si) is preferably in the range of 0.1 to 0.8%. If it is an element that has solid solution strengthening effects and shows a slight reduction in elongation. If it guarantees high resistance of the steel sheets of the present invention in which the precipitates are controlled. Only when the Si content is 0.1% or more can the high strength be assured. However, when Si content is more than 0.8%, the ductility of steel sheets deteriorates.

The content of chromium (Cr) is preferably in the range of 0.2 to 1.2%. Cr is an element that has solid solution reinforcement effects, the secondary work embrittlement temperature decreases, and the aging index due to the formation of Cr carbides decreases. Cr guarantees high strength of the steel sheets of the present invention in The precipitates are controlled and serve to decrease the rate of amyotropia in the plane of the steel sheets. Only when the Cr content is 0.2% or more, high resistance can be assured. However, when the Cr content exceeds 1.2%, the ductility of the steel sheets deteriorates. The cold-rolled steel sheets of the present invention may additionally contain molybdenum (Mo). The content of molybdenum (Mo) in the cold-rolled steel sheets of the present invention is preferably in the range of 0.01 to 0.2%. Mo is added as an element that increases the plasticity amsotropy index of the steel sheets. Only when the molybdenum content is not less than 0.01%, the plasticity anisotropy index of the steel sheets increases. However, when the molybdenum content exceeds 0.2%, the anisotropy index of plasticity does not increase adi cially and there is a danger of hot brittleness. Production of cold-rolled steel sheets. Then in The present, a process for producing the cold-rolled steel sheets of the present invention will be explained with reference to the preferred embodiments that follow. Various modifications of the embodiments of the present invention can be made, and such modifications are within the scope of the present invention. The process of the present invention is characterized in that a steel satisfying one of the steel compositions defined above is processed through hot rolling and cold rolling to form precipitates having an average size of 0.2 μm. or smaller in a cold rolled steel sheet. The average size of the precipitates in the cold-rolled plate is affected by the design of the steel composition and the processing conditions, such as preheating temperature and coiling temperature. Particularly, the rate of cooling after hot rolling has a direct influence on the average size of the precipitates. Hot Rolling Conditions In the present invention, a steel satisfying one of the compositions defined above is reheated and then subjected to hot rolling. The relapse temperature is preferably 1,100 ° C or higher. When the steel is reheated to a temperature lower than 1,100 ° C, the coarse precipitates formed during continuous pouring do not completely dissolve and remain, the coarse precipitates still remain after the hot lamination. It is preferred that the hot rolling is carried out at a finishing rolling temperature not lower than the transformation point of Ar3. When the finishing lamination temperature is lower than the transformation point of? R3, laminated grains are created which deteriorate the working capacity and cause poor strength. The cooling is preferably carried out in a range of 300 ° C / nm or higher before winding and then hot rolling. Although the composition of the components is controlled to obtain fine precipitates, the precipitates may have an average size greater than 0.2 μm in a cooling ratio of less than 300 ° C / m? N. That is, as the cooling rate increases, many cores are created so the size of the precipitates becomes finer and finer. Since the size of the precipitates decreases with the increase of the cooling rate, it is not necessary to define the upper limit of the cooling ratio. When the cooling rate is higher than 1, 000 ° C / m? N. , however, a significant improvement in the effects of the reduction in size of the precipitates is not shown further. Therefore, the cooling ratio is preferably in the range of 300-1000 ° C / m? N. Winding conditions After hot rolling, winding is carried out at a temperature no higher than 700 ° C. When the winding temperature is higher than 700 ° C, the precipitates develop very thickly, thus making it difficult to ensure high strength. Lamination conditions in river The steel is cold rolled at a reduction rate of 50-90%. Since a cold reduction ratio of less than 50% leads to the creation of a small amount of nuclei in J to recrystallization of annealing, cpstaL grains develop excessively in the annealing, thus thickening recpstal crystal grains. / through the annealing, which results in the reduction of the resistance and ormabilidad. A ratio of cold reduction greater than 90% leads to increased formability, while creating an excessively large number of cores so that the recrystallized crystal grains through the annealing become very thin, thus deteriorating the ductility of steel. Continuous collection The continuous collection temperature plays an important role in determining the mechanical properties of the final product. According to the present invention, the continuous annealing is preferably carried out at a temperature of 700 to 900 ° C. When continuous re-coagulation is carried out at a temperature lower than 700 ° C, the recrystallization is not complete and thus a desired ductility can not be ensured. In contrast, when continuous annealing takes place at a temperature higher than 900 ° C, the recharged grains become thick and thus the strength of the steel deteriorates. Continuous annealing is maintained until the steel is completely recrystallized. Replantation of the steel can be completed for approximately 10 seconds or more. The continuous annealing is preferably carried out for 10 seconds to 30 minutes. [Mode for the Invention] The present invention will now be described in greater detail with reference to the following examples. The mechanical properties of the steel sheets produced in the following examples were valued according to the ASTM C-8 standard test methods. Specifically, each of the steel sheets was machined to obtain standard samples. The deformation resistance, tensile strength, elongation, anisotropy index of plasticity (rm value) and index of amsotropy in the plane (value? r), and the aging index were measured using a tensile strength tester (available from 1 NSTRON Company, Model 6025). The anisotropy index of plasticity rm and the index of anisotropy in the plane (value? R) were calculated by means of the following equations: rm = (r0 t 2 ^ 5 i r90) / 4 and? R = (r0 - 2r45 + r90 ) / 2, respectively. The aging index of the steel sheets is defined as an elongation of the deformation point measured when each sample is annealed, followed by the lamination process of the re-pass and thermal lamination of 1.0% at 100 ° C for 2 hours. The furnace hardness (BH) Lor value of the standard samples was measured by the following procedure. After a deformation of 2% was applied to each of the samples, the deformed sample was annealed at 170 ° C for 20 minutes. The deformation strength of the annealed sample was measured. The value Bll was calculated by subtracting the strain resistance measured before the annealing of the strain resistance value measured after the annealing.

First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and laminated to finish lime to provide hot-rolled steel sheets. The laminated steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the hot rolling of the finish was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out by heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 1 TABLE 2 TABLE 3 * Note: YS = deformation resistance, TS = tensile strength, EL = elongation, rra = plasticity anisotropy index,? R = index of sotropy in the plane, AI = index of aging, SWE = fragile inequality of Secondary Work Capacity, IS =? zero Inventive, CS = Comparative Steel Example 2 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide sheets of J.- > hot rolled steel. The hot-rolled steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a 75% reduction rate, followed by continuous annealing to produce laminated steel sheets cold At this time, the hot rolling of the finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out when heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 4 TABLE 5 TABLE 6 * Note: YS = Deformation resistance, TS = Stress Resistance, Cl = Elongation, r, n = Plasticity Anisotropy index,? R = Plane Anisotropy index, AI = Aging index, SWE = Cragí li Secondary Work Capacity Determination, 1S = Inventive Steel, CS = Comparative Steel Example 3 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / m², were rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the hot rolling of the finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out when heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets.

TABLE 7 TABLE 8 TABLE 9 * Note: YS = deformation resistance, TS = tensile strength, el = elongation, rra = plasticity anisotropy index,? R = anisotropy index in the plane, AI = aging index, SWE = fragile work Secondary, TS = Inventive steel, CS = Comparative steel Example 4 First, thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The laminated steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the hot-finish lamination was carried out at 910 ° C, which is above the Ar ting point, and the continuous annealing was carried out by heating the hot-rolled steel sheets in a proportion of 10 ° C. / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 10 TABLE 11 * Note: YS = deformation resistance, TS = tensile strength, el = elongation, rra = plasticity anisotropy index,? R = index of? Msotropia in the plane, AI = index of aging, SWL = fragmentation of Secondary work, JS = Inventive Steel, CS = Comparative Steel Example 5 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the Hot Rolling Finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out at a slow rate with hot-rolled steel sheets in a proportion of 10 °. C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets.

TABLE 13 TABLE 14 TABLE 15 * Note: YS = deformation resistance, TS = resistance to Tension, El = Alamiento, rm = Index of Plasticity Anisotropy,? R = Index of Anisotropy in the Plane, AI = Index of Aging, SWE = Secondary Work Fragilization, IS = Inventive Steel, CS = Comparative Steel Example First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / mm, rolled at 650 ° C, cold rolled at a reduction rate of / 5%, followed by continuous annealing to produce steel sheets cold rolled. At this time, the hot-finish lamination was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out by heating the hot-rolled steel sheets at a rate of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 16 TABLE 1 7 TABLE 1 8 * Note: YS = Deformation resistance, TS - Resistance to Stress, Ll = Elongation, rm = Plasticity Anisotropy index,? R = Index of? Msotropia in the Plane, AI = Index of Aging, SWL = Secondary Work Eragilization, IS = Experimental Steel, CS = Comparative Steel Example / First , the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and laminated in finished material to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / m²., were rolled at 650 ° C, cold rolled at a 75% reduction rate, followed by continuous annealing to produce cold rolled steel sheets. At this time, the hot rolling of the finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out when heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 19 TABLE 20 TABLE 21 * Note: YS = deformation resistance, J'S = Stress Resistance, El = Elongation, r, "= Plasticity Anisotropy IndLce,? R = Index of nisotropy in the Plane, Al = Aging index, SWE = Fragilization of Secondary work, 1S = Inventive steel, CS = Comparative steel Example 8 First, the thick steel sheets were prepared -16 according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the finishing roll was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out at ca.Lent the hot-rolled steel sheets at a ratio of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 22 TABLE 23 TABLE 24 * Note: YS = deformation resistance, TS = tensile strength, el = elongation, ra = plasticity anisotropy index,? R = index of? Msotropia in the plane, AI = index of aging, SWL, = tragisation of Secondary work, IS = Inventive steel, CS = Comparative steel Example 9 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the hot-finish lamination was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out by heating the hot-rolled steel sheets at a rate of 10 ° C / second at 830 ° C for 40 seconds to produce the final Cold Rolled steel sheets. TABLE 25 TABLE 26 TABLE 27 * Note: YS = Deformation resistance, TS = Stress Resistance, El = Alamage, rm = Plasticity Anisotropy index,? R = Anisotropy index in the Plane, AI = Aging index, SWE = Work fragility Secondary, JS = Inventive Steel, CS = Comparative Steel Example 10 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold rolled at a reduction ratio of 75%, followed by continuous annealing to produce sheets of cold rolled steel. During this time, the hot-rolled finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out when heating the hot-rolled steel sheets at a rate of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 28 TABLE 29 TABLE 30 * Note YS = deformation resistance, TS = tensile strength, el = elongation, rra = plasticity anisotropy index, r = anisotropy index in the plane, AI = aging index, SWE = Secondary work fragility, 1S = Inventive Steel, CS = Comparative Steel Example 11 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The laminated steel sheets were cooled at a rate of 400 ° C / min., were rolled at 650 ° C, cold rolled at a 75% reduction rate, followed by continuous annealing to produce cold rolled steel sheets. At this time, the hot-rolled finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out by heating the hot-rolled steel sheets in a proportion of 10 ° C. / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 31 33 TABLE 32 TABLE 33 * Note: YS = Deformation resistance, TS = Stress Resistance, El = Alamage, rm = Index of Plasticity Anisotropy,? R = Index of An i sotropy in the Plane, AI = Index of Aging, SWE = Fragí Secondary Work Lization, IS = Inventive Steel, CS = Comparative Steel Example 12 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide rolled sheets of steel. The hot rolled steel sheets were cooled at a rate of 400 ° C / mm, rolled at 650 ° C, cold rolled at a 75% reduction rate, followed by continuous annealing to produce laminated steel sheets cold At this time, the hot rolling of the finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out when heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 34 ? TABLE 35 TABLE 36 * Note YS = deformation resistance, TS = Stress Resistance, El = Elongation, rm = Plasticity Anisotropy index,? R = index of? Or sotropy in the Plane, AI = index of Aging, SWE = Fragilization of work Secondary, IS = Stainless Steel, CS = Comparative Steel Example 13 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / min., Rolled at 650 ° C, cold-rolled at a 75% reduction ratio, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the hot rolling of finishing was carried out at 910 ° C, which is above the transformation point of? R3, and the continuous annealing was carried out when heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 37 TABLE 38 TABLE 39 * Note: YS = Deformation resistance, TS = Stress Resistance, El = Elongation, rm = Plasticity Anisotropy index,? R = Amsotropy index in the Plane, AI = Aging index, SWE = Fragileness of Secondary work, 1S = Inventive Steel, CS = Comparative Steel Example 14 First, the thick steel sheets were prepared according to the compositions shown in the following tables. The thick steel sheets were reheated and hot-rolled finished to provide hot-rolled steel sheets. The hot-rolled steel sheets were cooled at a rate of 400 ° C / m², rolled at 650 ° C, cold rolled at a 75% reduction rate, followed by continuous annealing to produce sheets of cold rolled steel. At this time, the hot rolling of the finishing was carried out at 910 ° C, which is above the transformation point of Ar3, and the continuous annealing was carried out when heating the hot-rolled steel sheets in a proportion of 10 ° C / second at 830 ° C for 40 seconds to produce the final cold-rolled steel sheets. TABLE 40 TABLE 41 TABLE 42 * Note: YS = deformation resistance, TS = resistance to Stress, El = Elongation, rm = Plasticity Anisotropy index,? R = LndLce of Amsotropia in the Plane, AI - Index of Aging, SWE = Fragile of Secondary work, IS = Inventive Steel, CS = Comparative Steel Preferred modalities illustrated in the present invention do not serve to limit the present invention, but are exposed for illustrative purposes. Any embodiment having substantially the same constitution in the same operative effects thereof as the technical spirit of the present invention as defined in the appended claims is encompassed within the technical scope of the present invention. [Field of Industrial Application] As is evident from the above description, according to the cold rolled steel sheets of the present invention, the distribution of the fine precipitates in the steels composed of Nb and Ti allow the formation of tiny crystal grains, and as a result, the anisotropy index in the plane is decreased and the deformation resistance is increased by increasing precipitation.

Claims

CLAIMS 1. A cold-rolled steel sheet with superior formability, the cold-rolled steel sheet, characterized in that it has a composition comprising 0.01% or less of C, 0.01-0.2% Cu, 0.005- 0.08% of S, 0.1% or less of DC, 0.004% or less of N, 0.2% or less of P, 0.0001-0.002% of 13, 0.002-0.04% of Nb, 0.005-0.15% of Ti, by weight, and the rest of Fe and other impurities not avoidable. wherein the composition satisfies the following relationships: 1 < (Cu / 63.5) / (S * / 32) < 30 and s' = S-0.8 x (Ti -0.8 x (48/14) x N) x (32/48), and wherein the steel sheet comprises CuS precipitates having an average size of 0.2 μm or less.
2. The cold-rolled steel sheet according to claim 1, characterized in that the composition further comprises 0.01-0.3% of Mn, and satisfies the following ratios: 1 < (Mn / 55 t Cu / 63.5) / (S * / 32) < 30, and the steel sheet comprises precipitates of (Mn, Cu) S of 0.2 μm or less.
3. The cold-rolled steel sheet according to claim 1, characterized in that the content of N is 0.004-0.02%, and the composition satisfies the following ratios: 1 < "(? l / 27) / (NVl4) < 10 &N * = N - 0.8 x (Ti - 0.8 x (48/32) x S)) x (14/48), and the steel sheet comprises precipitates of? 1N having an average size of 0.2 μm or less
4. The cold-rolled steel sheet in accordance with the re LV ind i falls LÓ? 1, acterizada because the composition also comprises 0.01-0.3% of Mn, and 0.004-0.02% of N, and satisfies the following ratios: 1 <(Mn / 55 + Cu / 63.5) / (SV32) <30, 1 <(? 1 /? I) / (N * / l 4) <10 and N * = N - 0.8 x (Ti - 0.8 x (48/32) x S)) x (14/48), and the steel sheet comprises precipitates of (Mn, Cu) S and precipitates of AlN having an average size of 0.2 μm or less
5. The cold-rolled steel sheet with superior formability and high deformation ratio, the cold-rolled steel sheet characterized in that it has a composition comprising 0.01% or less of C, 0.08% or less of S, 0.1% or less of?, 0.004% or less of N, 0.2% or less of P, 0.0001-0.002% of 13, 0.002-0.04% Nb, 0.005-0.15% Ti, at least one class selected from 0.01-0.2% Cu, 0.01-0.3% Mn and 0.004- 0.2% N, by weight, and the rest of Fe and other impurities do not avoid them, where the composition satisfies the following relationships: 1 < (Mn / 55 i Cu / 63.5) / (S732) < 30, 1 < (Al / 27) / (N '/ 14) < 10, where the content of N is 0.004% or more, and S '= S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48) and N * = N - 0.8 x ( Ti - 0.8 x (48/32) x S)) x (14/48), and wherein the steel sheet comprises at least one selected class of (Mn, Cu) S precipitates and AlN precipitates having a average size 0.2 μm or less.
6. The cold-rolled steel sheet according to claim 1 or 5, characterized in that the contents of C, Ti, N and S satisfy the following ratios: 0.8 < (Ti / 48) / (C / 12) < 5.0 and Ti '= Ti - 0.8 x ((48/14) x N i (48/32) x S).
7. The cold rolled steel sheet according to claim 6, characterized in that the content of C is 0.005% or less.
8. The cold rolled steel sheet according to claim 1 or 5, characterized in that the soluble carbon (Cs) [Cs = (C - T i * x 12/48) x 10000 where TT = Ti - 0.8 x ((48/14) x N t (48/32) x S), with the proviso that Ti cs less than 0, T * is defined as 0], which is determined by the contents of C and Ti, is from 5 to 30.
9. The cold-rolled steel sheet according to claim 8, characterized in that the C content is from 0.001 to 0.01%.
10. The cold-rolled steel sheet according to any of claims 1 to 5, characterized in that the cold-rolled steel sheet satisfies a deformation ratio (resistance of forming / resisting tension) of 0.58 or higher
11. The cold rolled steel sheet according to any of claims 1 to 5, characterized in that the number of precipitates is 1 x 10d / mm2 or more.
12. The cold rolled steel sheet according to claim 1 or 5, characterized in that the P content is 0.015% or less.
13. The cold rolled steel sheet according to claim 1 or 5, characterized in that the P content is from 0.03% to 0.2%.
14. The cold-rolled steel sheet according to claim 5, characterized in that the composition further comprises at least one class of 0.1 to 0.8% Si and 0.2 to 1.2% Cr.
15. The laminated steel sheet cold according to claim 1 or 5, characterized in that the composition further comprises 0.01 to 0.2% Mo.
16. The cold rolled steel sheet according to claim 14, characterized in that the composition further comprises 0.01 to 0.2% Mo.
17. The cold-rolled steel sheet according to any of claims 2, 4 and 5, characterized in that the sum of Mn and Cu is from 0.05% to 0.4%.
18. The cold rolled steel sheet according to any of claims 2, 4 and 5, characterized in that the Mn content is 0.01-0.12%.
19. The cold-rolled steel sheet according to claim 2, 4 or 5, characterized in that the value of (Mn / 55 t Cu / 63.5) / (S * / 32) is from 1 to 9.
The sheet of cold-rolled steel according to claim 3, 4 or 5, characterized in that the value of (? l / 2 /) / (N / 14) is from 6.
21. A method for producing a laminated steel sheet in cold with superior shape and high deformation ratio, the method characterized in that it comprises the steps of: reheating a thick sheet at a temperature of 100 ° C or higher, the thick sheet having a composition comprising 0.01% or less of C, 0.01-0.2% Cu, 0.005-0.08% S, 0.1% or less of Al, 0.004% or less of N, 0.2% or less of P, 0.0001- 0.002% of B, 0.002-0.04 of Nb, 0.005-0.15% Ti, by weight, and the remainder of I e and other non-avoidable impurities, the composition satisfying the following ratios: J = (Cu / 63.5) / (S / 32) < 30 and S = S - 0.8 x (Ti - 0.8 x (48/14) x N) x (32/48); hot rolling the hot sheet heated to a finishing lamination temperature of the transformation point? r3 or higher to provide a hot rolled steel sheet; cooling the hot rolled steel sheet in a proportion of 300 ° C / m or higher; roll the steel sheet cooled to 700 ° C or lower; cold rolling the rolled steel sheet; and continuously reheating the cold rolled steel sheet, the cold rolled steel sheet comprising CuS precipitates having an average size of 0.2 μm or less.
22. The method according to claim 21, characterized in that the composition also comprises 0.01 to 0.3% of Mn, and satisfies the following ratios: 1 = (Mn / 55 i Cu / 63.5) / (SV32) < 30, and the steel sheet comprises precipitates of (Mn, Cu) S having an average size of 0.2 μm or less.
23. LJ method in accordance with the claim 21, characterized because the content of N is 0.004-0.02%, and the composition satisfies the following relationships: 1 < (? l / 27) / (N7l4) < 10 and N = N-0.8 x (Ti-0.8 x (48/32) x S)) x (14/48), and the steel sheet comprises precipitates of AlN having an average size of 0.2 μm or less.
24. The method according to the rei indication 21, acterizado because the composition also comprises 0.01 to 0.3% of Mn and 0.004 to 0.02% of N, and satisfies the following relationships: 1 < (Mn / 55 i Cu / 63.5) / (S * / 32) < 30, 1 < (Al / 27) / (N '/ 14) < 10 and N = N - 0.8 x (I'i - 0.8 x (48/32) x S)) x (14/48), and the metal sheet comprises precipitates of (Mn, Cu) S and AlN precipitates they have an average size of 0.2 μm or less.
25. A method for producing a cold rolled steel sheet with superior formability and high deformation ratio, the method characterized in that it comprises the steps of; reheating a thick sheet at a temperature of J, 100 ° C or higher, the thick sheet having a composition comprising 0.01% or less of C, 0.08% or less of S, 0.1% or less of it, 0.004% or less than N, 0.2% or less of P, 0.0001-0.002% of 13, 0.002-0.04% of Nb, 0.005-0.15% of Ti, at least one selected class of 0.01-0.2% Cu, 0.01-0.3 % of Mn and 0.004-0.2% of N, by weight, and the rest of Fe and other non-avoidable impurities, the composition satisfying a ratio: 1 < (Mn / 55 t Cu / 63.5) / (S732) < 30, 1 < (? l / 27) / (N7l4) < 10, where the content of N is 0.004% or more, S * = S - 0.8? (Ti - 0.8 x (48/14) x N) x (32/48) and N * = N - 0.8 x (Ti - 0.8 x (48/32) x S)) x (14/48); hot laminating the hot sheet heated at a finishing lamination temperature of the transformation point? r3 or higher to provide a laminated steel sheet with heating; cooling the hot-rolled steel sheet in a proportion of 300 ° C / m or higher; roll the steel sheet cooled to 700 ° C or ba; cold rolling the rolled steel sheet; and continuously annealing cold-rolled steel sheet, the cold-rolled steel sheet comprising at least one class selected from (Mn, Cu) S precipitates and Al N precipitates having an average size of 0.2 μm or less.
26. The method according to claim 21 or 25, characterized in that the contents of C, Ti, N and S satisfy the following re- lations: 0.8 <; (T? 748) / (C / 12) = 5.0 and Ti '= Ti - 0.8 x ((48/14) x N t (48/32) x S).
27. The method according to claim 26, characterized in that the content of C is 0.005% or less.
28. The cold-rolled steel sheet according to claim 21 or 25, characterized by the solute carbon (Cs) [Cs- (C-Ti * x 12/48) x 10000 in which Ti '= Ti - 0.8 x ((48/14) x N i (48/32) x S), with the proviso that when Ti is less than 0, Ti is defined as 0], which is determined by the contents of C and Ti is 5 to 30.
29. The method according to claim 28, characterized in that the content of C is from 0.001 to 0.01%.
The method according to any of claims 21 to 25, characterized in that the cold rolled steel sheet satisfies a deformation ratio (deformation resistance / tensile strength) of 0.58 or higher.
31. The method according to any of claims 21 to 25, characterized in that the number of precipitates cs of 1? 10 / mm or more.
32. The method according to claim 21 or 25, characterized in that the P content is 0.015% or less.
33. The method according to claim 21 or 25, characterized in that the content of P is 0.03% to 0.2%.
34. The method according to claim 21 or 25, characterized in that the composition further comprises at least one class or 0.1 to 0.8% Si and 0.2 to 1.2% Cr.
35. I 1 method according to claim 21 or 25, characterized in that the composition further comprises 0.01 to 0.2% Mo.
36. I 1 method in accordance with the claim 34, characterized in that the composition further comprises 0.01-0.2% Mo.
37. The method according to claim 22, 24 or 25, characterized in that the sum of MN and Cu is 0.08% to 0.4%.
38. The method according to claim 22, 22 or 25, characterized in that the content of Mn is 0.01-0.12%.
39. The method of compliance with the claim 22, 24 or 25, characterized because the value of (Mn / 55 + Cu / 63.5) / (S / 32) is in the range of 1 to 9.
40. The method of compliance with the claim 23, 24 or 25, characterized in that the value of (? L / 27) / (N * / 1) is in the range of 1 to 6.