TW201211271A - Cold rolled steel sheet and method for manufacturing the same - Google Patents

Abstract

To provide a cold-rolled steel sheet capable of obtaining uniform appearance and shape uniformity after press working without performing special treatment, in a Ti-containing IF steel sheet having excellent deep drawability, and to provide a method for producing the same. The cold-rolled steel sheet to be a Ti-adding IF steel sheet contains 0.02 to 0.1% Ti, ≤ 0.03% Sb and > 0.005% and ≤ 0.03% Cu, contains Ti* defined by Ti*=(Ti%)-3.4*(N%)-1.5*(S%)-4*(C%) in the range satisfying 0< Ti*< 0.02 and further in the range satisfying (Sb%)≥ (Cu%)/5. A Ti element content (mass%) contained in a deposition product having < 20 nm size in a surface layer part of a plate thickness to 10 m μ m from respective surfaces of steel sheet both surfaces is ≤ 9% of the total Ti content of the steel sheet.

Description

[Technical Field] The present invention relates to a cold-rolled steel sheet which is excellent in shape consistency after being used for softness of an exterior decorative steel sheet or the like of an automobile, and a method for producing the same. [Prior Art] Conventionally, a cold-rolled steel sheet or an alloyed hot-dip galvanized steel sheet having a soft tensile strength of less than 35 VMPa and excellent workability has been used for automobile exterior steel sheets. For example, a known cold-rolled steel sheet which is excellent in softness and workability is obtained by hot rolling an ultra-low carbon steel containing a carbonitride-forming element, and carbonitride is formed at the stage of hot-rolled steel sheet to lower the steel. After the solid solution C and the solid solution N, the cold-rolled steel sheet produced by cold rolling and recrystallization annealing treatment, that is, the so-called IF (Interstitial Free) steel sheet, contains Ti as carbon nitrogen. The IF steel sheet of the compound forming element is characterized in that the workability in deep drawability is particularly excellent. However, Ti not only forms carbonitrides but also forms fine sulfides and carbon sulfides because of these fine crystals. Since the precipitates hinder the crystal growth after recrystallization and recrystallization, there is a problem that the unrecrystallized grains remain locally. If the non-recrystallized grains remain locally, they will become areas with a high degree of localized drop in strength, and the shape will become inconsistent after the punching process. Therefore, it is not a good thing. In addition, when alloying molten galvanizing is carried out, if there is a residual portion of the non-recrystallized grains in the surface layer portion of the steel sheet, the alloying speed will be inconsistent, which may cause the inconsistency in the appearance color. -5- 201211271 As one of the solutions to these problems, for example, the method disclosed in Patent Document 1 is to attach a carbide, a nitride, and a boride to the surface of the steel sheet during the hot-dip galvanizing treatment. One or more selected ones, the content of which is 0.1 to lGGG mg/m2 calculated as c, N, and B contents, and sulfur or sulfide is attached thereto, and the content thereof is 0·1 to 1 by the S content. After 〇〇〇mg/rn2, the method of annealing at a temperature of 680 t or more in a non-oxidizing gas phase containing hydrogen gas. Further, in the method disclosed in Patent Document 2, in order to solve the phenomenon in which the surface appearance of the "stripe" is uneven, the steel preform immediately after the continuous casting is kept at a surface temperature of 1 〇〇〇 t: or more In the state of being introduced into the final refining rolling step, the method of refining processing is performed at a temperature of Ar3 or higher. Further, in the method disclosed in Patent Document 3, in order to solve the phenomenon in which the surface appearance is uneven, 'the steel is continuously cast and becomes a steel preform, and then heated, and the oxidizing gas containing oxygen is blown to a surface temperature of 1000 ° C or higher. After the steel embryo, the method of hot rolling, pickling, cold rolling, and annealing is performed. [PATENT DOCUMENT] [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei 9-296222 (Patent Document 3) Japanese Patent Publication No. 9-296222 (Patent Document 3) 201211271 [Disclosure of the Invention] [Problems to be Solved by the Invention] However, in the method disclosed in Patent Document 1, it is necessary to perform a process of attaching sulfur or a sulfide to a content of S to 1000 mg/m 2 , so that there is a case Low productivity and increased costs. The method disclosed in Patent Document 2 cannot perform a so-called "steel germ surface beautification" in which the surface of the steel blank is melted to prevent defects on the surface, particularly for use in a surface that is required to have a beautiful appearance. The appearance of the exterior steel decorative sheet is not appropriate. In addition, in the method disclosed in Patent Document 3, in order to prevent the appearance of unevenness on both sides of the steel sheet, it is necessary to invert the upper and lower surfaces of the high temperature steel preform of 100 ° C or higher, and to spray an oxidizing gas. It is not practical. Further, the techniques of Patent Documents 1 to 3 do not disclose how to solve the problem of a problem in which the shape after punching is different. The present invention is directed to these circumstances, and its object is to provide a Ti-containing IF steel sheet having excellent deep drawability, providing the same appearance and shape uniformity after punching without special treatment. Cold rolled steel sheet and method for producing the same. [Means for Solving the Problems] In order to solve the above-mentioned problems, the inventors of the present invention are directed to the cause of occurrence of defects in surface defects after the punching process, and countermeasures against how to suppress them. Research and investigation. At the end of 201211271, we found a kind of originality, that is, the unrecrystallized grains remained in the extreme surface layer of the steel sheet in which the above problems occurred, and the results of investigation on these non-recrystallized grains were found from the surface of the steel sheet. The crystallization state of the crystallization in the region up to 10 μm is characteristic. Further, the inventors of the present invention have found that the difference in the color of the appearance of the punching process is caused by the influence of the Cu content which is extremely small in the steel. Cu is affected by the global trend of reducing CO2 in recent years, and as a waste material is used in steel sources, the proportion of iron in the water tends to increase, and the element of Cu, once mixed into iron, It cannot be removed, and it is called "tramp element which causes deterioration of metal characteristics", and its influence on metal characteristics is worrying. Cu is sometimes contained in the form of Cu based on the purpose of improving corrosion resistance and strengthening steel properties such as crystallization. However, the IF steel sheet of the present invention is a harmful element from the viewpoint of surface quality. The present invention has been developed based on the above findings, and the gist thereof is as follows. [1] A cold-rolled steel sheet characterized by containing C: 0 · 0 0 0 5 0 0 0 0 %, S i : 0.2 % or less, Μη: 0.1 〜 1.5%, P in mass % : 0.03% or less, S: 0.005 to 0.03%, T i : 0.0 2 〜 0 · 1 %, A1 : 0 · 0 1 ～ 0 · 0 5 %, Ν : 0 · 0 0 5 % or less, Sb: 0.03% Hereinafter, Cu: more than 0.005% and 0.03% or less, and T i * = (T i % ) - 3 · 4 X ( N % ) -1 · 5 X ( S % ) - 4 X ( C% ) The number of Ti* represented by the equation is in the range of 〇&lt; Ti* &lt; 0.02, -8- 8 201211271 and conforms to the range of (Sb%) 2 (Cu%) /5' The rest is Fe and not The component (% by mass) of the Ti element in the crystallization layer having a size of less than 20 nm in the surface layer portion of the thickness of the surface of the steel sheet from the surface to the surface of the steel sheet All of the Ti element content (% by mass) is less than 9%, and the above (Ti%), (N%), (S%), (C%), (

Sb%) and (Cu%) are the contents (% by mass) of Ti, N, S, C, Sb, and Cu, respectively. [2] The cold-rolled steel sheet according to the above [1], wherein, in mass%, further contains: one or two selected from Nb, B, and the content of the above Nb, B, by mass The cold-rolled steel sheet according to the above-mentioned [1] or [2], which has a zinc-based plating layer on the surface of the steel sheet, is 0.001 to 0.01%, and B: 0.0002 to 0.0015%. [4] A method for producing a cold-rolled steel sheet, characterized in that a steel having a component according to the above [1] or [2] is produced into a steel preform by continuous casting, and for the steel embryo, heating is performed: The temperature is 1 000 ° C or more and less than 1 200 ° C, and the heating time in the temperature range of 1 000 ° C or higher is 3 hours or less, and the removal of the scale and the rough rolling are performed. , after the surface temperature of the steel sheet is at least (Ar3 metamorphic point - 00 ° C) and is below the range of the Ar3 transformation point, 201211271 is used so that the surface temperature of the steel sheet at the end of the final rolling is at a temperature higher than the Ar3 transformation point. After the final rolling, the film was cooled, and wound up at a temperature of 650 ° C or higher. Next, after pickling and cold rolling, annealing treatment was performed. [5] The method for producing a cold-rolled steel sheet according to the above [4], wherein, after the annealing treatment, a hot-dip galvanizing treatment or an alloying melting ruthenium treatment is performed. Further, the % used to indicate the composition of steel in the present specification is all % by mass. Further, the cold-rolled steel sheet which is the object of the present invention also includes a steel sheet which has been subjected to surface treatment such as electro-galvanizing, hot-dip galvanizing or alloying hot-dip galvanizing on the cold-rolled steel sheet. Further, it is also included in these steel sheets, which are subjected to chemical conversion treatment or the like, and a steel sheet to which a film is attached. [Effects of the Invention] According to the present invention, it is possible to obtain a cold-rolled steel sheet having a uniform appearance and excellent shape uniformity after punching, without performing special treatment. [Embodiment] Hereinafter, the present invention will be described in detail. Conventionally, the aggregate structure of the titanium-containing IF steel sheet for automobile exterior steel sheets is known to have a plurality of { 1 1 1 } crystal faces formed in a direction parallel to the plate surface. However, as mentioned above, the alloyed hot-dip galvanized steel sheet having such a collective structure sometimes has an inconsistent color depth, and the cold-rolled steel sheet and the alloyed hot-dip galvanized steel sheet are sometimes subjected to a punching process, and sometimes Produces inconsistencies in shape 8-10-201211271. Therefore, it is a detailed investigation of the inconsistency in the color depth of the appearance and the inconsistency in the shape after the punching process. As a result, it has been found that the surface layer portion of the steel sheet body which causes the above-mentioned problem, specifically, the surface layer portion from the surface of the steel sheet to the surface of the steel sheet, has a phenomenon in which non-recrystallized grains remain locally. And the orientation of these non-recrystallized grains is mainly composed of {1 00 } crystal faces. Further, it has been further found that when these non-recrystallized grains mainly composed of the {100} crystal face remain in the vicinity of the surface layer, not only the shape inconsistency but also the alloying treatment is performed after the punching process. At the time, the color depth is inconsistent due to the locality of the alloying speed. Based on the findings and the above findings, the inventors of the present invention have further examined in detail the reasons why unrecrystallized grains remain in the vicinity of the surface layer. As a result, it was found that a portion containing no recrystallized grains remained, and many fine titanium-containing crystal granules having a size of less than 2 Å were present. Such a fine crystallization product, if it is applied under the general annealing conditions of a steel sheet for automotive exterior plating, does not solidify and remains, because it is considered to be: a so-called "nail The effect of the "stop effect" causes the grain boundary movement of the recrystallized grains on the {111} plane to be hindered, and recrystallization is difficult to proceed, and the non-recrystallized grains having the {10 0 } crystal plane as the main orientation remain. Therefore, in order to solve such a problem, various steel sheets were obtained after repeated experiments under various manufacturing conditions, and then the state near the surface layer was investigated for the obtained steel sheets. In this process, it was found that -11 - 201211271. If the steel is based on a specific composition, there will not be many {1 00 } crystallized unrecrystallized grains remaining near the surface layer, and will not be alloyed by hot-dip plating. The appearance of the color of the zinc steel plate is inconsistent, and the shape of the cold-rolled steel sheet and the alloyed hot-dip galvanized steel sheet will not be produced. In the vicinity of the outermost layer of the steel sheet, specifically, in the region from the surface of both sides of the steel sheet to the surface of the steel sheet, the amount of crystallization of less than 20 nm is largely lowered. Therefore, in order to quantify the favorable conditions that do not cause the appearance of the color shade and the shape inconsistency after the punching process, it is calculated that the crystal crystallization is contained in a size of less than 20 nm. The content of the Ti element in the middle, and the ratio of the total Ti content in the steel sheet is determined, and it is found that if the ratio is less than 9%, the color depth difference of the appearance can be lowered, and the processing can be reduced after the punching process. The resulting shape is inconsistent. Further, the Ti content contained in the crystallization solution having a size of less than 20 nm can be measured by the following method. After the sample was subjected to a predetermined amount of electrolysis in the electrolytic solution, the sample piece was taken out from the electrolytic solution and immersed in a dispersible solution. Next, the crystallization product contained in this solution was filtered through a filter paper having a pore size of 20 nm. The size of the crystallization after passing through the 20 nm filter paper with the filtrate was less than 20 nm. Next, for the filtered filtrate, a method is appropriately selected from among various analysis methods such as inductively coupled plasma (ICP) luminescence spectrometry, ICP mass spectrometry, and atomic absorption spectrometry. The Ti content (% by mass) contained in the crystallization solution having a size of less than 20 nm was determined. 8 -12- 201211271 According to the above description, in order to obtain the same appearance and uniformity in shape after punching, the present invention is included in the area up to 10 μm from each surface of both sides of the steel sheet. The content (% by mass) of the Ti element in the crystallization of less than 20 nm is selected to be 9% or less of the total content (% by mass) of Ti in the steel sheet. Further, after further review, it was found that the appearance of the marks during the punching process varies depending on the amount of Cu contained in the steel in a very small amount. The inventors believe that the reason is mainly due to the change in the shape of the sulfide. That is, in the case of an IF steel composed of a conventional component which is not mixed with Cu, it is known that a relatively coarse crystallization such as a Ti-based sulfide (for example, Ti4C2S2) is generated during hot-rolling coiling. Things. However, in the case of an IF steel composed of a component containing a certain amount or more of Cu, Cu is replaced with a part of Ti in the Ti-based sulfide to form a TiCu-based sulfide. Further, Ti which is freed by substitution is a Ti-based carbide. When such a Ti-based carbide exists in a fine state (less than 20 nm in size), recrystallization is slowed down. As a result, the non-recrystallized grains remain in the vicinity of the surface layer, and thus the appearance color depth is inconsistent. As a result of further review, a finding is found that the color of the above-mentioned appearance is caused by an increase in the amount of Cu mixed. Inconsistent occurrences, the practice of containing Sb is very effective. If the steel containing an increased amount of Cu is melted, if it contains Sb, the formation of TiCu-based sulfide can be suppressed. As a result, formation of a fine Ti-based carbide (less than 20 nm in size) can be avoided, and a cold-rolled steel sheet excellent in surface properties can be obtained. -13- 201211271 Next, the reason for the composition of the limited components of the present invention will be explained. C: 0.0005 ~0.01〇/〇C is a solid-melt strengthening element, which helps to increase the strength of the fall, which is helpful for improving the in-plane rigidity. However, if you want to obtain excellent deep drawability, it is best to reduce it. . If it is less than 0.0005%, the crystal grain size is remarkably coarsened so that the drop strength is greatly lowered, and the rigidity in the plane is lowered to easily cause defects such as waist breakage. It also leads to an increase in the cost of decarbonization. Therefore, the lower limit is 0.0005%. In addition, if the amount of C is large, the amount of Ti carbide in the steel increases, and the amount of crystallization of the surface layer increases, and the amount of non-recrystallized grains whose main orientation is the {100} crystal plane in the direction parallel to the plate surface. Will increase, so the upper limit is 0.01%. S i : 0.2 % or less

The Si system does not cause deterioration in workability, and it is an element which contributes to the strengthening of steel by solid-solution strengthening. However, it is concentrated on the surface during annealing and significantly inhibits the hot-dip galvanizing property. 0.2% or less. Μ η : 0 · 1 〜1 . 5 % Μ 系 can be used as a solid-melting strengthening element to increase steel strength. In order to ensure the rigidity of the steel plate, it must have a content of more than 1%. Although it can be appropriately contained in accordance with the desired strength, excessive inclusion will hinder the workability, so it is selected to be 1.5% or less. Ρ : 0.0 3 % or less The lanthanide solid-melt strengthening element is effective for strengthening steel and increasing the strength of the drop. However, if it is excessively contained, it will not only cause cracks in the hot and cold rooms, but also hinder the alloying reaction of hot-dip galvanizing. Therefore, it is selected to be 0.03% or less. S: 0.005 to 0.03% S is an important element in the present invention. S-like is an element that is inevitable as an impurity in steel and should be reduced as much as possible. However, in the present invention, the amount of the element is selected to be more than 0.005%. That is, if it is less than 0.005%, the TiS generated after continuous casting will tend to be fine. When the steel is reheated by hot rolling, some of it will be easily solidified, so in the subsequent process. In the middle, a fine precipitate of crystallization such as TiS is generated in a relatively large amount, and the unrecrystallized grain of {100} orientation remains locally in the surface layer. In order to reduce the influence of such fine crystallization, it was selected to be 0.005% or more. Preferably, it is selected to be 0 · 0 1 0 % or more. On the other hand, if it is more than 0. 03%, hot cracks are likely to occur during the manufacture of the steel sheet, which not only hinders productivity but also causes deterioration of surface properties. Therefore, it is selected to be 0.03% or less.

Ti: 0.02 to 0.1%, and is 〇 &lt;Ti*&lt;0.02, T i * = (T i % ) - 3.4 X ( N % ) -1 · 5 X ( S 0/〇) - 4 X ( C % )

Ti is one of the most important elements in the present invention. The Ti system can fix C, N, and S in the steel as crystallization, thereby improving the workability. If it is less than 0.02%, this effect cannot be obtained. On the other hand, if the T i is more than 0.1%, not only can the effect of further progress be expected, but an abnormal structure is formed inside the plate, which lowers the workability. -15- 201211271 Further, as described above, Ti in the steel forms a crystallization with C, N, and S in the steel. Therefore, when the content of the element is more than or equal to the elemental composition, the workability can be improved. In order to achieve this, Ti* shown in the following formula (1) must be selected to be greater than zero. On the other hand, if the solid-melting Ti is excessively present, sometimes the surface layer portion is nitrided due to the gas phase environment during annealing to form fine TiN, which will promote the fine TiN in the surface layer. Azimuthal non-recrystallized grains remain and are therefore not popular. In order to reduce the amount of Ti-containing fine crystallization of less than 2 Onm in the thickness of the surface layer from the surface to the surface of both sides of the steel sheet, Ti* must be selected to be less than 0.02. T i * = (T i %) - 3.4 X (N %) -1 . 5 X (S %) - 4 X (C %) · · - (1) However, (Ti%), (N%), (S%) and (C%) indicate the content (% by mass) of 1^, :^, 3, (:: A1 : 0.0 1 to 0. 〇5 % A1 is an element contained as a deoxidizer, although It must be 0.01% or more, but even if it is contained in a large amount, it is impossible to obtain a further deoxidation effect', so it is selected to be 0.05% or less. N : 0.0 0 5 % The less the content of N is, the more favorable the processability is. If the content exceeds 0.005% and is excessively contained, the formability will be remarkably lowered, and the amount of solid solution Ti will also decrease, so the upper limit is selected to be 0.00 5% ° 8 • 16 - 201211271

Sb and Cu are contained in a range of Sb: 0.03% or less, Cu: more than 0.005% to 0.03%, and (Sb%) 2 (Cu%) /5. S b is an element contained in the oxidation or nitridation inhibitor on the surface of the steel sheet. However, in the production process of IF steel, nitriding in continuous annealing can be used to suppress the formation of crystallization, thereby reducing the surface fineness of the steel sheet. . In addition, when Cu is mixed in the steel, the effect can be exerted. When the Cu content is more than 0.005%, by including Sb in a ratio of 1/5 of the amount of Cu, the TiCu-based sulfide can be suppressed. The formation can avoid the inconsistency in the appearance color of the fine crystallization product, that is, the Ti-based carbide, and as a result, a cold-rolled steel sheet excellent in surface properties can be obtained. In order to obtain such an effect, (Sb%) 2 (Cu%) /5 is selected in the manner described later. However, if the content exceeds 0.03%, the workability is sometimes impaired. Therefore, if Sb is contained, it is selected to be 0.03% or less.

Cu is an element added to improve strength and corrosion resistance. However, if a soft steel plate is to be produced, it is not actively added. However, even if it is not added, it is unavoidably present in the steel source. In addition, based on the viewpoint of recycling, since the amount of the metal regrind is increased, it is surely mixed into the steel. The minimum amount of unavoidable mixing of Cu in the case of using a metal regrind is about 0.005%. If it is 0.005% or less, the appearance of the color difference due to the increase in the amount of Cu mixed does not cause a problem. On the other hand, once the Cu system mixed in the steel cannot be removed, in the present invention, the inclusion of Sb is used to promote the detoxification of Cu, but if the Cu content exceeds 0.03%, the surface defects are improved, but the mechanical properties are caused. Deterioration and hot fragility -17- 201211271 Sexual deterioration. Therefore, the Cu system is selected to be more than 0.005% and 0.03% or less. (S b % ) ^ ( C u % ) /5 However, (Sb% ) and (Cu%) indicate the content (% by mass) of Sb and Cu, respectively. » As described above, the present invention contains Sb, In order to avoid the inconsistency in the apparent color depth caused by the fine crystallization of Cu, that is, the Ti-based carbide, a cold-rolled steel sheet excellent in surface properties can be obtained. This effect is achieved by containing Sb in the range of (Sb%) 2 (Cu% ) /5. The rest is Fe and inevitable impurities. Further, in the present invention, it is preferable to further contain one or two of Nb and B, and the content thereof is Nb: 0.001 to 0.01%, and B: 0.0002 to 0.0015%.

Nb: 0.001 ~ 0.01%

In the same manner as Ti, Nb forms a carbonitride and is an element which is advantageous for improving workability. In particular, it is preferable that the Ti* in the above formula (1) is less than 0.005, and the effect of improving the workability 'must contain 0.001% or more." However, if the content exceeds 0·0 1%, The crystal grains tend to be fine, sometimes causing deterioration in workability such as deep drawability. Therefore, if you want to contain it, it is selected as 〇.001% or more 〇.〇1% or less 0 B: 0.0002 ～0.0015% B is an effective element for strengthening the grain boundary in soft IF steel plate. In the case of 0.0002% or more, it is very effective. However, if it is excessively contained, there is a concern that the surface properties may deteriorate during the manufacture of the steel sheet. Therefore, if you want to include it, it is selected to be 0 · 0 0 0 2 % or more 0 · ο 〇 1 5 % or less. Next, a method of producing the cold rolled steel sheet of the present invention will be described. The cold-rolled steel sheet according to the present invention is obtained by continuously casting a steel having the above-described composition into a steel preform, and the steel preform has a heating temperature of 100 (TC or more and less than 1 200 ° C, and at 1 000 °). The heating time in the temperature range of c or more is 3.0 hours or less, heating is performed, the scale is removed, and the rough rolling is performed, and then, the surface temperature of the steel sheet is maintained at (Ar3 metamorphosis point - 3 〇〇 ° C) After the cooling is performed in the range below the Ar3 transformation point, the final rolling is performed so that the surface temperature of the steel sheet at the end of the final rolling is at a temperature equal to or higher than the Ar3 transformation point, and then cooled to 650 ° C or higher. The temperature is coiled, and then, after pickling and cold rolling, annealing treatment is performed to obtain the cold-rolled steel sheet of the present invention. Further, if it is desired to obtain a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet, After the annealing process is performed in the same process, the hot-dip galvanizing treatment or the alloying hot-dip galvanizing treatment is performed. The heating temperature is selected to be 1 000 ° C or more and less than 1 200 ° C. The heating time in the temperature range of 100 ° C or higher is selected to be 3.0 hours or less. The above conditions must be met in both the steel billet heating step and the entire hot rolling step. When the heating temperature is less than 1 000 ° C, the rolling temperature is It is difficult to reduce the surface temperature of the steel sheet after the final rolling to be above the Ar3 transformation point. On the other hand, if the heating temperature is 1200 ° C or higher, the titanium-containing sulfide such as TiMnS formed during continuous casting will A large amount of solid solution in a short time, and in the subsequent process, there will be a large amount of fine crystallization of less than 2 Onm, which is not suitable. Even if the heating temperature is less than 1 200 °C If it is maintained for a long period of time, it is not appropriate for the solid solution of titanium-containing sulfide to continue to progress. Therefore, the heating time in the temperature range of 1000 ° C or higher is selected to be 3.0 hours or less. The steel embryo after cooling and heating is held in a range of (Ar3 metamorphic point - 3 00 °c) or more and below the Ar3 transformation point, and after removing the scale and performing rough rolling, the final rolling is performed. The surface temperature is maintained in a range of (Ar3 metamorphic point - 00 ° C) or more in the range of not less than the Ar3 transformation point. In the usual production method, cooling is started after the final rolling in the hot rolling step, and the fat is started. Granular iron metamorphosis. However, in the present invention, the surface of the steel sheet is cooled before the final rolling, so that the surface temperature first becomes below the Ar3 transformation point. In this way, the surface is cooled to a predetermined state before the final rolling. As a result of the temperature, only the surface layer portion starts to undergo the ferrite-grain transformation, and the titanium-containing crystallization product starts to be formed, and it is easy to grow to a size of 20 nm or more. As a result, the amount of crystallization of less than 20 nm can be reduced, and the {100} surface can be reduced. The non-recrystallized grains do not remain in a large amount, and a cold-rolled steel sheet having a uniform appearance and excellent shape uniformity after punching can be obtained. In addition, the temperature of the surface portion will rise due to reheating from the center of the sheet thickness and heat generation during the final rolling. If the surface temperature before the final rolling is too low, the surface temperature at the end of the final rolling will fall below the Ar3 metamorphic point, and the deformed ferrite iron structure will be formed in the surface layer, which will hinder the consistency. The surface temperature before the final rolling must be selected as (Ar3 metamorphic point - 3 00 °C) 201211271 or more. This practice of cooling the surface to control the surface temperature prior to final rolling is a particularly important requirement and feature in the manufacturing method of the present invention. The method of cooling the surface before final rolling, for example, a high-pressure water jet device or the like which is used in general removal of scale can be used to cool the surface to an appropriate temperature range. In addition, it can be confirmed by the method described below whether or not the Ar3 metamorphosis point has been reached. First, the steel of each component is heated to a temperature of 100 to 1200 ° C, and then the temperature and volume change are measured while cooling, thereby obtaining the volume expansion caused by the transformation of the Worth iron into the ferrite iron. Temperature (Ar3 metamorphic point). The final rolling is performed so that the surface temperature of the steel sheet at the end of the final rolling becomes a temperature higher than the Ar3 transformation point, and if the surface temperature of the steel sheet at the end of the final rolling is lower than the Ar3 transformation point, the surface layer of the steel sheet is Will produce residual fermented iron structure that will destroy its consistency. Therefore, the surface temperature of the steel sheet at the end of the final rolling must be controlled to a temperature higher than the Ar3 transformation point. On the other hand, if the surface temperature of the steel sheet remains above the Ar3 metamorphic point for a long time after the final rolling, the relatively coarse crystallization after the growth will be re-solidified so that the fine crystallization is less than 20 nm. The increase in volume is therefore not appropriate. Therefore, after the surface temperature of the steel sheet is maintained at a temperature higher than the Ar3 transformation point and the final rolling is completed, it is preferable to perform cooling immediately to promote the deformation of the ferrite. The allowable time until the start of cooling is preferably within 1 second. The coiling is performed at a temperature of 65 ° C or higher. -21 - 201211271 After cooling, it is coiled at a temperature of 65 (TC or higher. If the temperature at the time of coiling is lower than 650 °C, the growth rate of crystallization is small, and fine crystallization is less than 20 nm. The amount of the material will increase. Although the upper limit of the temperature at the time of coiling is not particularly specified, if it is too high, the scale of the surface layer will grow to cause surface defects, so it is selected to be less than 80 ° C. After picking up, pickling and cold rolling are carried out, sometimes after washing, and then annealing, or after annealing, hot-dip galvanizing or alloying hot-dip galvanizing. Pickling, cold rolling The conditions for annealing are not particularly limited as long as the generally used method is followed. The steel sheet after the coiling is subjected to pickling in order to remove the scale formed on the surface, and then cold rolling is performed. (the rolling rate of the cold rolling) may be about 50% to 90% which is generally carried out for the production of an exterior decorative steel sheet for automobiles. Further, cold rolling is performed from the viewpoint of improving workability (r値). rate It is preferable that it is 70% or more. Next, the steel sheet after cold rolling is subjected to recrystallization annealing treatment in order to remove oil stains during rolling, and further, if the annealing temperature exceeds the Ac3 transformation point, workability ( r値) is easy to reduce, so it is preferable to select the Ac3 metamorphic point or less. In addition, the lower limit temperature is selected to be 7〇〇°C, which is advantageous for recrystallization annealing. After annealing, 'for surface roughness adjustment The reason for the class is to carry out the temper rolling. Preferably, the rolling rate (elongation) of the temper rolling is preferably 0. 5 % to 1.5%. A cold-rolled steel sheet excellent in shape uniformity after processing can be obtained. -22- 8 201211271 When making a molten tantalum-zinc steel sheet or an alloyed hot-dip galvanized steel sheet, the cold rolling is performed before the annealing treatment. In the same step as in the case of the steel sheet, the hot-dip galvanizing treatment or the alloying hot-dip ruthenium plating treatment is carried out. Further, before the annealing, mild pickling may be performed. The processing conditions of the hot-dip galvanizing, The processing conditions of the alloyed hot-dip galvanizing are not particularly limited as long as the usual methods are followed. After the hot-dip galvanizing treatment or after the alloying hot-dip galvanizing treatment, in order to adjust the surface roughness, the most According to the above, a hot-dip galvanized cold-rolled steel sheet or an alloyed molten ore cold-rolled steel sheet excellent in shape consistency after processing can be obtained. [Example 1] Hereinafter, it will be specifically shown. The effect of the present invention is as follows: first, the molten steel liquid having the composition shown in Table 1 is subjected to vacuum degassing treatment, and then cast into a steel preform by continuous casting. Next, the steel embryo is heated to remove the scale. The rough rolling was performed until the thickness of the sheet was 40 mm. Next, the surface layer of the steel sheet was cooled by a scale removing device, and finally rolled until it became a thickness of 3.5 mm, and then rolled at a coiling temperature of 700 °C. Take it into a steel strip roll. Further, the heating conditions of the steel preform at this time, the surface temperature of the steel sheet after cooling after final rolling, and the final rolling temperature are shown in Table 2 [Table 1] -23-201211271 1

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I Preparation Comparative Example Comparative Example Comparative Example Comparative Example Invention Example Invention Example Invention Example Invention Example Invention Example Invention Example I Comparative Example Comparative Example Invention Example I Invented Example Invented Example I Comparative Example I Comparative Example Final Form Cold Rolled steel plate I alloyed hot-dip galvanized steel sheet I cold-rolled steel plate alloyed hot-dip galvanized steel sheet cold-rolled steel sheet 1 cold-rolled steel sheet alloyed hot-dip galvanized steel sheet I cold-rolled steel sheet I 1 tm 趄m &lt;π I cold-rolled steel sheet I Cold-rolled steel sheet 颉.颉ammonium. collar&lt;π I cold-rolled steel sheet I % m 坻Μ m &lt;π cold-rolled steel sheet containing gold-melting hot-dip galvanized steel sheet cold-rolled steel sheet alloyed molten shovel zinc plated steel plate Alloyed hot-dip galvanized steel sheet Ar3 metamorphic point (°C) σ&gt; I_9UI 913 913 1_?07| σ&gt; 1_914J inch σ&gt; 914 I_9141 914 914 I_9171 917 907 5 Ο) 914 914 i 914 914 Final rolling temperature (t) 〇〇930 930 1 930 1 〇CO σ&gt; 940 ο σ&gt; 940 丨940 I σ&gt; 〇CO ο o CM 03 ο CM σ&gt; 920 〇CM σ&gt; ο CO σ&gt; g Ο) i 940 游游 16 魅幽§ CO I 680 I 680 § &lt;〇1 660 1 s CO 680 g CO 660 [ 6601 660 660 [ 6801 680 680 680 s CO I 660 660 〇 &lt; 〇CO steel embryo reheating conditions retention time above 1000 ° C (hours) ο csi 〇〇0*4 〇csi 〇csi oc\i ο Csi Ο csi ο o ο csi ο csi o ο cvi ο C*i ο CNl o csi ο csi ο csi ο c*i P m si 1110 _m〇J 1120 I 1120 1 1 1120 1 1 1120 1 ! 1100 I 1100 1 1115 I 1115 I 1120 1120 1 1090 1 1090 1100 1100 1120 1120 1110 1110 Sao &lt;&lt; CQ CD ο o QQ LU LU LL u. ϋ ο Work X A symbol &lt; m CVJ m Τ Ο CSI 〇Q CVJ Q τ — LU CSI UJ L: OJ τ α CM α τ— X CM X τ— *r— CM &quot;3 -25- 201211271 Next, the coiled steel sheet is pickled and then cold rolled to make the steel sheet thickness 〇.70mm (cold rolling rate: 80%) is used as a test material. The pretreatment process is degreasing and pickling, and then annealing, hot-dip galvanizing, alloying, and further processing on the hot-dip galvanizing line. The temper rolling was performed at an elongation of 1.0%, and finally, the alloyed hot-dip galvanized steel sheet was obtained. Further, in order to evaluate the characteristics of the cold-rolled steel sheet for a part of the steel sheets, only the temper rolling having an elongation of 1.0% was performed after the annealing, thereby obtaining a cold-rolled steel sheet. Further, the gas phase environment during the annealing described above is a non-oxidizing gas containing hydrogen gas, and the annealing temperature of each test material is selected to be 840 ° C or less at the Ac3 transformation point. The hot-dip galvanizing treatment was carried out by using a galvanizing bath containing 1200 ° C having an A1 of 0.12%, immersed in a sheet temperature of 460 ° C, and an immersion time of 3 seconds. The alloying treatment was carried out by using a nitrogen scraper to adjust the amount of zinc adhered to 60 g/m2 per surface after plating, and at 510 ° C for 20 seconds. The cold-rolled steel sheet and the alloyed molten zinc steel sheet obtained by the above-described production method were measured by the following methods: crystals having a surface thickness of less than 20 nm from the surface of the steel sheet from the surface of 10 μm The content of the Ti element contained in the precipitate, the mechanical properties, and the shape consistency after processing were evaluated. Further, in addition to the above items, the alloyed hot-dip galvanized steel sheet was also evaluated for appearance. The results obtained are shown in Table 3. For the crystallization of the surface layer of the thickness of the surface of the steel sheet up to 10 pm from the surface of the steel sheet up to 10 pm, the content of the Ti element is obtained. The cold-plated steel sheet and the alloyed molten niobium-zinc steel sheet are obtained. The hot-dip galvanized steel sheet is stripped to a size of 3 cm x 4 cm by using hydrochloric acid, and is cut into a sample having a size of 3 cm x 4 cm, and a 10% concentration of AA-based electrolyte (10 vol% acetonitrile acetone - 1 mass% tetrachloromethylene chloride). In -methanol), constant current electrolysis was carried out at a current density of 20 mA/cm2. The electrolysis system was carried out simultaneously on both sides of the steel sheet, and the electrolytic thickness was set to ΙΟμπι from the surface of each surface. A sample piece having crystallization adhered to the surface after electrolysis was taken out from the electrolytic solution, and immersed in an aqueous sodium metaphosphate solution (500 mg/l) (hereinafter referred to as an aqueous SHMP solution) to apply ultrasonic vibration to crystallize the crystallization product. The sample piece was peeled off and extracted into an aqueous SHMP solution. Next, the SHMP aqueous solution containing the crystallization product was filtered using a filter paper having a pore diameter of 20 nm, and the filtered filtrate was analyzed using an ICP emission spectroscopic analyzer to determine the absolute amount of Ti in the filtrate. By dividing the absolute amount of Ti by the weight of the electrolysis, the Ti content (% by mass) contained in the crystallization crystal having a size of less than 20 nm can be obtained. Further, the electrolyzed weight was obtained by measuring the weight of the sample after the crystallization of the crystallization product, and subtracting the measured weight from the weight of the sample before electrolysis. Further, the content shown in Table 3 is the average enthalpy of the content of the two surfaces obtained by the above method. Mechanical properties The formability was evaluated based on the tensile properties and the mechanical properties of r値. The tensile property was processed into a test piece No. 5 described in Japanese Industrial Standard JISZ 220 1 and then subjected to a test method described in Japanese Industrial Standard JIS Z 2241. In addition, the average r値 is firstly imparted to the tensile deformation of -15-201211271, and then measured by the three-point method. For one direction of the steel plate, the direction is 90°, 45°, 0°. The average of the direction r値 = (r(0°) + 2xr(45°) + r(90°))/4 is obtained by the formula of the shape after processing. The consistency of the shape after processing is evaluated. Firstly, after the deformation in the direction perpendicular to the rolling direction is given to the elongation of 5%, the grinding wheel is used for honing, and the inconsistency in the shape is visualized. For the shape that is seen to be inconsistent, it is marked as X, and is not seen. The shapes are inconsistent and are marked as 〇. The appearance after electroplating is applied to the steel plate which has been alloyed by hot-dip galvanizing. It is observed whether the color of the appearance is inconsistent, and the color of the appearance is inconsistent. It is marked as X, does not have the appearance of color inconsistent, and has a good appearance. . [Table 3] -28- 201211271 s

Preparation for Comparative Example 1 Comparative Example I m 镒jj Comparative Example I Inventive Example I Inventive Example | m Inventive Example 丨 Inventive Example I Inventive Example I 豳镞 Comparative Example I Comparative Example I Helmet m Distillation Invention Example 丨莩m 镒dS JJJ Interest T j〇-m 1 XIXI 〇I 〇I 〇I 〇IXI 〇I 〇IX Shape consistency after processing XXXX 〇〇〇〇〇〇〇〇XX 〇〇〇〇XX Mechanical properties average r値σ&gt; GO oq T o ϊ ~ ~ c c c c c CO CO CO CM CM CM 〇s TS (MPa) 283 286 295 290 CO σ&gt; CM 295__I 292 292 ! 294 l〇σ&gt; CVJ 302 290 CM CO 310 T~ CO τ — w ! 280 I 285 in CO 310 1 10.2 10.5 15.0 15.0 o lO o Vri o IT&gt; o IT&gt; o in 〇id so csi CO σ&gt; 00 σ&gt; qt_ σ&gt; ο σ&gt; ο 00 ο 12.0 12.0 Symbol &lt; CM &lt; 5 CM 0□ 〇CSJ 〇Τ Ο CM a Ύ^ 1 LU CM LU τ — lx δ CM CM CM X CNJ »— CM -29- 201211271 It can be seen from Table 3 that the composition of the composition is within the scope of the invention and from the surface The content of the Ti element contained in the crystallization product having a size of less than 20 nm in the surface layer portion up to 10 μηι is 9% or less of the total amount of Ti contained in the steel sheet, and is an example of deep drawability. That is, the average r値 system is 1.5 or more, the shape consistency after processing is excellent, and there is no inconsistency in the appearance of the color, and the performance is suitable for the use of the automobile exterior panel. In contrast, in the comparative example, the shape consistency and appearance after processing were relatively poor, and it was not able to meet the performance of the automobile exterior decorative steel sheet. Further, it can be seen that the amount of Ti contained in the crystallization granules having a size of less than 20 nm in the comparative example symbols A2 and B2 containing Cu in the steel exceeding 0.005% and not containing Sb is increased, that is, fine crystals. The increase in the amount of the precipitate causes a phenomenon in which the color of the appearance is inconsistent. In the comparative example symbol J2, the content of Ti contained in the crystallization product having a size of less than 20 nm was also increased due to the inappropriate content of Sb, and the appearance color inconsistency was inconsistent. On the other hand, the symbols C2, D2, E2, F2, H2, and 12 of the present invention containing an appropriate amount of Sb contain a small amount of Ti contained in a crystallization of a size of less than 20 nm, and the appearance color can be avoided. Inconsistent phenomenon. [Industrial Applicability] The steel sheet of the present invention is widely used for various electrical equipments and automobiles and the like which require excellent surface quality after molding, centering on the outer decorative steel sheet of an automobile. -30-

Claims (1)

201211271 VII. Patent application scope: 1 · A cold-rolled steel sheet characterized by: C: 0.0005~0.01%, Si: 〇2% to T, Mn: 0.1~i.5%, P : 0.03% WT, S: 〇.〇05~〇〇3〇/. Ti: 0.02 〇 1·1%, A1: 0.01 〇·〇 5%, N: 0.005% or less, %: 0·03% or less, Cu: more than 0.005% and 0.03% or less, and Ti*= (Ti%) - 3.4x (N%) - 1.5x (s%) -4^(C%) The number of Ti* represented by the equation is 〇 &lt; Ti* &lt; 0.02, and It conforms to the range of (Sb%) 2 (Cu%) /5, and the rest is composed of Fe and unavoidable impurities. On both sides of the steel sheet, from the surface to the surface of the surface of the sheet from 1 to μηη The content (% by mass) of the Ti element in the crystallization crystal having a size of less than 20 nm is 9% or less of the content (% by mass) of all the Ti elements in the steel sheet, and the above (T i % ), (N % ), (S % ), (C % ), (Sb%), and (Cu%) are the contents (% by mass) of Ti, N, S, C, Sb, and Cu, respectively. 2. The cold-rolled steel sheet according to claim 1, wherein, in mass%, further comprising: one or two selected from the group consisting of Nb and B, and the content of the above Nb, B, Nb : 0.001 to 0.01%, B: 0.0002 to 0.0 0 1 5 %. 3. The cold-rolled steel sheet according to claim 1 or 2, wherein the surface of the steel sheet has a zinc-based plating layer. -31 - 201211271 4. A method for producing a cold-rolled steel sheet, characterized in that a steel having a composition as described in claim 1 or 2 is continuously cast into a steel preform for the steel embryo The heating temperature is 1000 ° C or higher and less than 1200 ° C, and the heating time in the temperature range of 1 000 ° C or higher is 3 hours or less, and the scale removal and rough rolling are performed. Next, after the surface temperature of the steel sheet is at least (Ar3 transformation point - 300 °C) and is below the Ar3 transformation point, the surface temperature of the steel sheet at the end of the final rolling is at or above the Ar3 transformation point. After the final rolling, the temperature is finally cooled, and the coiling is performed at a temperature of 65 CTC or more. Next, after pickling and cold rolling, annealing treatment is performed. 5. The method for producing a cold-rolled steel sheet according to claim 4, wherein after the annealing treatment, a hot-dip galvanizing treatment or an alloying hot-dip galvanizing treatment is performed. 8 -32- 201211271 Four designated representatives: (1) The representative representative of the case is: No (2) The symbol of the representative figure is simple: No 201211271 5. If there is a chemical formula in this case, please reveal the best indication of the characteristics of the invention. Chemical formula: none