WO2011142473A1 - Cold-rolled steel sheet and method for producing same - Google Patents

Cold-rolled steel sheet and method for producing same Download PDF

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Publication number
WO2011142473A1
WO2011142473A1 PCT/JP2011/061131 JP2011061131W WO2011142473A1 WO 2011142473 A1 WO2011142473 A1 WO 2011142473A1 JP 2011061131 W JP2011061131 W JP 2011061131W WO 2011142473 A1 WO2011142473 A1 WO 2011142473A1
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Prior art keywords
steel sheet
less
cold
mass
temperature
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PCT/JP2011/061131
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French (fr)
Japanese (ja)
Inventor
孝子 山下
杉原　玲子
長滝　康伸
俊治 飯塚
恭二 渡邉
妻鹿　哲也
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Ｊｆｅスチール株式会社
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Application filed by Ｊｆｅスチール株式会社 filed Critical Ｊｆｅスチール株式会社
Priority to KR1020127031260A priority Critical patent/KR101461773B1/en
Priority to CN201180023404.7A priority patent/CN102884213B/en
Publication of WO2011142473A1 publication Critical patent/WO2011142473A1/en

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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0405—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • C21D9/48—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals deep-drawing sheets
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/004—Dispersions; Precipitations

Definitions

  • the present invention relates to a cold-rolled steel sheet that is soft and excellent in shape uniformity after processing, and a method for producing the same.
  • cold-rolled steel sheets and galvannealed steel sheets that are soft and have excellent workability have been widely used as exterior panels for automobiles.
  • a cold-rolled steel sheet that is soft and excellent in workability an ultra-low carbon steel containing a carbonitride-forming element is hot-rolled to produce carbonitride at the stage of the hot-rolled steel sheet, thereby A cold-rolled steel sheet, so-called IF (Interstitial Free) steel sheet, which is manufactured through cold rolling and recrystallization annealing after reducing dissolved C and solid solution N is known.
  • IF Interstitial Free
  • IF steel sheets containing Ti as a carbonitride-forming element are particularly characterized by excellent workability such as deep drawability.
  • Ti forms not only carbonitrides but also fine sulfides and carbonitrides, and these fine precipitates may hinder recrystallization and grain growth after recrystallization.
  • recrystallized grains There was a problem that recrystallized grains remained. If the non-recrystallized grains partially remain, a region having a high yield strength exists locally, and shape unevenness may occur after press working, which is not preferable.
  • alloyed hot dip galvanizing is performed, if a remaining portion of non-recrystallized grains is present in the surface layer portion of the steel sheet, unevenness occurs in the alloying speed, which may cause uneven appearance.
  • Patent Document 1 when performing hot dip galvanizing treatment, one or more selected from a carbon compound, a nitrogen compound, and a boron compound are added to the steel sheet surface.
  • C, N, B amount as 0.1 ⁇ 1000mg / m 2 adhered to, and after the sulfur or sulfur compound is 0.1 ⁇ 1000mg / m 2 deposited as S content, 680 ° C. in a non-oxidizing atmosphere containing hydrogen A method of annealing at the above temperature is disclosed.
  • Patent Document 2 in order to solve uneven surface appearance called “straight unevenness”, the slab immediately after continuous casting is held at a surface temperature of 1000 ° C.
  • Patent Document 3 in order to solve the surface appearance non-uniformity, steel is continuously cast into a slab and then heated, and an oxidizing gas containing oxygen is sprayed on a slab having a surface temperature of 1000 ° C. or higher. Thereafter, a method of performing hot rolling, pickling, cold rolling, and annealing is disclosed.
  • Patent Document 1 requires a step of depositing 0.1 to 1000 mg / m 2 of sulfur or a sulfur compound as the amount of S, and there is a problem that the productivity is lowered and the cost is increased.
  • slab care that prevents surface defects by cutting the surface of the slab or the like cannot be performed, and it is used for an automobile exterior plate that requires a particularly beautiful surface appearance.
  • in the method described in Patent Document 3 in order to prevent non-uniform appearance on both sides of the steel sheet, it is necessary to invert an slab having a high temperature of 1000 ° C. or higher and spray an oxidizing gas, which is practical.
  • the techniques of Patent Documents 1 to 3 do not disclose a method for solving the non-uniform shape after press working.
  • the present invention is a cold rolled steel sheet capable of obtaining a uniform appearance and shape uniformity after press processing without performing special treatment in a Ti-containing IF steel sheet excellent in deep drawability, and its An object is to provide a manufacturing method.
  • the inventors have conducted intensive research and investigation on the generation mechanism of the defects that appear as surface defects after press working and the suppression measures.
  • unrecrystallized grains remain in the extreme surface layer, and as a result of investigating these non-recrystallized grains, it is characterized by the precipitate state in the region from the steel sheet surface to 10 ⁇ m. Found that there is.
  • Cu has a tendency to increase the content ratio in hot metal due to the recent utilization of scrap as an iron source by CO 2 reduction. And as a so-called trump element that cannot be removed when mixed in iron, it is also an element that is concerned about the effect on its characteristics.
  • Cu may be contained for the purpose of improving the properties of the steel, such as corrosion resistance improvement and precipitation strengthening, but is an element harmful to the surface quality of the IF steel sheet that is the subject of the present invention. .
  • the steel having the component described in [1] or [2] is made into a slab by continuous casting, and the heating temperature is 1000 ° C. or more and less than 1200 ° C. and a temperature range of 1000 ° C. or more with respect to the slab.
  • the heating temperature is 1000 ° C. or more and less than 1200 ° C. and a temperature range of 1000 ° C. or more with respect to the slab.
  • a method for producing a cold-rolled steel sheet is 1000 ° C. or more and less than 1200 ° C. and
  • the cold-rolled steel sheet to which the present invention is directed includes a steel sheet obtained by subjecting a cold-rolled steel sheet to surface treatment such as electrogalvanizing, hot-dip galvanizing, and alloying hot-dip galvanizing. Further, it includes a steel plate having a film formed thereon by chemical conversion treatment or the like.
  • a cold-rolled steel sheet having a uniform appearance and excellent shape uniformity after press working can be obtained without performing special treatment.
  • the present inventors then examined in detail the cause of the remaining non-recrystallized grains in the vicinity of the surface layer. As a result, it was found that there were many precipitates containing very fine Ti having a size of less than 20 nm in the portion where unrecrystallized grains remained. Such fine precipitates remain undissolved under the general annealing conditions applied to steel plates for automobile exterior plates, and hinder the movement of ⁇ 111 ⁇ recrystallized grain boundaries by the so-called pinning effect. Therefore, it is considered that recrystallization does not proceed easily and unrecrystallized grains mainly oriented in ⁇ 100 ⁇ plane remain.
  • the content of Ti element contained in precipitates having a size of less than 20 nm is calculated, and the total Ti content in the steel sheet As a result, it was found that when the ratio is 9% or less, appearance irregularities and non-uniform shapes after press working can be reduced.
  • the amount of Ti contained in the precipitate having a size of less than 20 nm can be measured by the following method. After the sample is electrolyzed in a predetermined amount in the electrolytic solution, the sample piece is taken out of the electrolytic solution and immersed in a solution having dispersibility. Subsequently, the precipitate contained in this solution is filtered using a filter having a pore diameter of 20 nm. Precipitates that have passed through the filter having a pore diameter of 20 nm together with the filtrate have a size of less than 20 nm.
  • the filtrate after filtration is appropriately selected from inductively coupled plasma (ICP) emission spectroscopy, ICP mass spectrometry, atomic absorption spectrometry, etc., and included in precipitates having a size of less than 20 nm.
  • ICP inductively coupled plasma
  • the Ti content (mass%) to be obtained is determined.
  • the amount (mass%) is 9% or less of the total Ti content (mass%) in the steel sheet.
  • Ti that is replaced and becomes free produces Ti-based carbides.
  • this Ti-based carbide exists in a fine form (less than 20 nm), recrystallization is delayed. As a result, non-recrystallized grains remain in the vicinity of the surface layer, resulting in uneven appearance.
  • C 0.0005 to 0.01%
  • C is a solid solution strengthening element, which contributes to an increase in yield strength and is advantageous for improving in-plane rigidity, but is preferably reduced as much as possible to obtain excellent deep drawability. If it is less than 0.0005%, the crystal grain size becomes extremely coarse and the yield strength is greatly reduced, so that the in-plane rigidity is lowered and defects such as hip breakage tend to occur. Moreover, the decarburization cost increases. Therefore, 0.0005% is set as the lower limit.
  • Si 0.2% or less Si is a useful element for strengthening steel by solid solution strengthening without relatively degrading workability. However, it concentrates on the surface during annealing and significantly inhibits hot dip galvanizing. Therefore, the content is set to 0.2% or less.
  • Mn 0.1 to 1.5% Mn increases the steel strength as a solid solution strengthening element.
  • it is necessary to contain 0.1% or more.
  • strength since excessive inclusion inhibits workability, it shall be 1.5% or less.
  • P 0.03% or less
  • P is a solid solution strengthening element and is effective in strengthening steel and improving yield strength. However, if it is contained excessively, it not only causes hot and cold cracking, but also inhibits the alloying reaction of hot dip galvanizing, so it is made 0.03% or less.
  • S 0.005 to 0.03%
  • S is an important element in the present invention.
  • S is usually present in steel as an unavoidable impurity and should be reduced as much as possible.
  • S is intentionally ensured 0.005% or more.
  • TiS produced after continuous casting becomes fine, and it becomes easy to partially re-solidify during slab reheating in hot rolling.
  • a site that precipitates in a large amount is generated, causing unrecrystallized grains of ⁇ 100 ⁇ orientation to remain locally on the surface layer.
  • the content is made 0.005% or more.
  • it is 0.010% or more.
  • it exceeds 0.03%, hot cracking during the production of the steel sheet is likely to occur, which impedes productivity and deteriorates the surface properties. Therefore, it is 0.03% or less.
  • Ti 0.02 to 0.1% and 0 ⁇ Ti * ⁇ 0.02
  • Ti * (Ti%) ⁇ 3.4 ⁇ (N%) ⁇ 1.5 ⁇ (S%) ⁇ 4 ⁇ (C%)
  • Ti is one of the most important elements in the present invention. Ti has an effect of improving workability by fixing C, N, and S in the steel as precipitates. If it is less than 0.02%, such an effect cannot be obtained. On the other hand, if Ti is contained in excess of 0.1%, not only a further effect cannot be expected, but an abnormal structure is formed inside the plate, and the workability is lowered.
  • Ti in steel forms precipitates with C, N, and S in steel. Therefore, inclusion of an equivalent amount or more of these components can improve workability. it can. For that purpose, it is necessary to make Ti * shown by the following formula (1) larger than zero.
  • solute Ti is excessively present, nitridation may occur in the surface layer portion depending on the atmosphere during annealing, and fine TiN may be generated. This fine TiN is unrecrystallized in the ⁇ 100 ⁇ orientation in the surface layer. This is not preferable because it promotes the remaining of the grains.
  • Ti * In order to reduce the amount of fine precipitates containing Ti of less than 20 nm in the surface thickness part from the surface of both surfaces of the steel plate to 10 ⁇ m, Ti * needs to be less than 0.02.
  • Ti * (Ti%) ⁇ 3.4 ⁇ (N%) ⁇ 1.5 ⁇ (S%) ⁇ 4 ⁇ (C%) (1)
  • (Ti%), (N%), (S%), and (C%) indicate the contents (mass%) of Ti, N, S, and C, respectively.
  • Al 0.01 to 0.05%
  • Al is an element contained as a deoxidizing agent and needs to be 0.01% or more. However, even if contained in a large amount, a further deoxidizing effect cannot be obtained, so the content is made 0.05% or less.
  • N 0.005% or less
  • Sb 0.03% or less
  • Cu more than 0.005% to 0.03% or less
  • Sb is used as an oxidation or nitridation inhibitor on the steel sheet surface.
  • Cu is an element added to improve strength and corrosion resistance, but is not actively added when producing a soft steel sheet. However, it is unavoidably present in the iron source even if not added, and it is mixed into the steel by increasing the amount of scrap used from the viewpoint of recycling.
  • the minimum amount of Cu inevitably mixed when scrap is used is approximately 0.005%. If it is 0.005% or less, appearance unevenness due to an increase in the amount of Cu mixed does not become a problem.
  • the present invention performs detoxification by containing Sb. However, when the Cu amount exceeds 0.03%, surface defects are improved, but mechanical Characteristics deteriorate and hot brittleness worsens. From the above, Cu is more than 0.005% and 0.03% or less.
  • (Sb%) and (Cu%) indicate the contents (mass%) of Sb and Cu, respectively.
  • Sb appearance unevenness due to Ti-based carbides, which are fine precipitates due to Cu, is avoided, and a cold-rolled steel sheet having excellent surface properties is obtained. Such an effect is achieved by containing in a range satisfying (Sb%) ⁇ (Cu%) / 5.
  • the balance is Fe and inevitable impurities.
  • Nb 0.001 to 0.01% and B: 0.0002 to 0.0015% are further contained as needed.
  • Nb 0.001 to 0.01%
  • Nb is an element that is advantageous for forming a carbonitride to improve workability.
  • Ti * of the above-described formula (1) is less than 0.005
  • the content exceeds 0.01%, the crystal grains are refined, and workability such as deep drawability may be deteriorated. Therefore, when it contains, it is set as 0.001% or more and 0.01% or less.
  • B 0.0002 to 0.0015%
  • B is an element effective for strengthening the grain boundary of the soft IF steel sheet, and it is effective to contain 0.0002% or more when secondary work brittleness resistance is required.
  • B is 0.0002% or more and 0.0015% or less.
  • the cold-rolled steel sheet of the present invention uses a steel having the above component composition as a slab by continuous casting, and the heating temperature is 1000 ° C. or more and less than 1200 ° C. and a temperature range of 1000 ° C. or more. Heating is performed under conditions of heating time of 3.0 hours or less, scale removal and rough rolling are performed, and then cooling is performed so that the steel sheet surface temperature is in the range of (Ar3 transformation point ⁇ 300 ° C.) to Ar3 transformation point. It is obtained by finish rolling so that the surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point, cooling, winding at a temperature of 650 ° C.
  • the heating temperature is 1000 ° C or higher and lower than 1200 ° C.
  • the heating time in the temperature range of 1000 ° C. or higher is set to 3.0 hours or shorter. It is necessary to satisfy the above conditions throughout the slab heating process and the hot rolling process.
  • heating temperature is less than 1000 degreeC, rolling temperature falls and it is difficult to make the steel plate surface temperature after finish rolling more than an Ar3 transformation point.
  • the heating temperature is 1200 ° C. or higher, a large amount of Ti-containing sulfides such as TiMnS generated during continuous casting are dissolved in a short time, and many fine precipitates having a size of less than 20 nm are generated in the subsequent process. Is not preferable.
  • the heating time in the temperature range of 1000 ° C. or higher is set to 3.0 hours or shorter.
  • the surface temperature of the slab cooled and heated so that the steel sheet surface temperature is in the range of (Ar3 transformation point ⁇ 300 ° C.) or more and below the Ar3 transformation point is subjected to scale removal and rough rolling and before finish rolling. It cools so that it may become the range below (Ar3 transformation point -300 degreeC) more than Ar3 transformation point.
  • the ferrite transformation starts by cooling after finish rolling in the hot rolling process.
  • the surface of the steel sheet is cooled to the Ar3 transformation point or less once before the finish rolling.
  • the surface layer portion starts ferrite transformation and precipitates containing Ti start to be formed, and it becomes easy to grow to a size of 20 nm or more.
  • the amount of precipitates of less than 20 nm is reduced, a large amount of non-recrystallized grains on the ⁇ 100 ⁇ plane does not remain, a cold rolled steel sheet having a uniform appearance and excellent shape uniformity after pressing. Will be obtained.
  • the temperature of the surface layer rises due to recuperation from the center of the plate thickness and processing heat generation during finish rolling.
  • the surface temperature before finish rolling is too low, the surface temperature at the end of finish rolling is below the Ar3 transformation point, and a ferrite structure in which strain remains in the surface layer portion is generated and the uniformity is impaired. It is necessary to set it to (Ar3 transformation point -300 degreeC) or more. Thus, it is a particularly important requirement and a feature in the manufacturing method of the present invention to control the surface temperature by once cooling the surface before finish rolling.
  • a high-pressure water injection device usually used for scale removal can be used to cool the surface so as to be in an appropriate temperature range.
  • the Ar3 transformation point can be obtained as follows. By heating the steel of each composition to a temperature of 100 to 1200 ° C. and then measuring the temperature and volume change while cooling, it is possible to know the temperature (Ar3 transformation point) at which volume expansion occurs due to transformation from austenite to ferrite. .
  • the steel sheet surface temperature is equal to or higher than the Ar3 transformation point, and after finishing rolling is finished, the steel sheet is immediately cooled to promote the ferrite transformation.
  • the allowable time until the start of cooling is preferably within 1 second.
  • the coiling temperature is lower than 650 ° C., the growth rate of precipitates is reduced, and the amount of fine precipitates of less than 20 nm is increased.
  • the upper limit of the coiling temperature is not particularly defined, but if it is too high, the scale of the surface layer tends to grow and cause surface defects.
  • Pickling, cold rolling, and annealing conditions are not particularly limited, and may be performed in accordance with ordinary methods.
  • the steel sheet after winding is pickled to remove scale formed on the surface, and then cold-rolled.
  • the cold rolling rate (cold rolling reduction rate) may be about 50% to 90%, which is usually performed when manufacturing an automobile outer sheet.
  • the cold rolling rate is desirably 70% or more from the viewpoint of improving workability (r value).
  • the cold-rolled steel sheet is washed to remove the degreasing oil and dirt from the rolling oil, and then recrystallized and annealed.
  • the annealing temperature is preferably set to be equal to or lower than the Ac3 transformation point.
  • the lower limit temperature is preferably about 700 ° C. in performing recrystallization annealing.
  • the rolling rate (elongation rate) of temper rolling is preferably about 0.5% to 1.5%.
  • hot dip galvanized steel sheet or an alloyed hot dip galvanized steel sheet When forming a hot dip galvanized steel sheet or an alloyed hot dip galvanized steel sheet, it is performed in the same manner as in the case of the cold-rolled steel sheet until annealing, followed by hot dip galvanizing treatment or alloying hot dip galvanizing treatment. In addition, you may perform light pickling before annealing.
  • the hot dip galvanizing treatment conditions and alloying hot dip galvanizing treatment conditions need not be particularly limited, and may be in accordance with ordinary methods. It is preferable to perform temper rolling for adjusting the surface roughness after the hot dip galvanizing treatment or after the alloying hot dip galvanizing treatment. As described above, a hot-dip galvanized cold-rolled steel sheet or an alloyed hot-dip galvanized cold-rolled steel sheet having excellent shape uniformity after processing can be obtained.
  • molten steel having the composition shown in Table 1 was made into a slab by continuous casting after vacuum degassing treatment.
  • the slab was heated, scale-removed, and then roughly rolled to a plate thickness of 40 mm.
  • the steel sheet surface layer was cooled with a scale removing device, and then finish-rolled to a thickness of 3.5 mm and wound on a coil at a winding temperature of 700 ° C.
  • Table 2 shows the heating conditions of the slab at this time, the steel sheet surface temperature after cooling before finish rolling, and the finish rolling temperature.
  • the atmosphere at the time of the annealing was a non-oxidizing gas containing hydrogen, and the annealing temperature of each test material was 840 ° C. which is lower than the Ac3 transformation point.
  • the hot dip galvanizing treatment was performed using a 460 ° C. zinc plating bath containing 0.12% of Al at an intrusion plate temperature of 460 ° C. and an immersion time of 3 seconds.
  • the alloying treatment was carried out at 510 ° C. for 20 seconds after plating, adjusting the zinc adhesion amount to 60 g / m 2 per side using an N 2 gas wiper.
  • the hot-dip galvanized steel sheet is a plating layer
  • the sample was cut to a size of 3 cm ⁇ 4 cm, and the current density was 20 mA / cm 2 in 10% AA electrolyte (10 vol% acetylacetone-1 mass% tetramethylammonium chloride-methanol).
  • AA electrolyte (10 vol% acetylacetone-1 mass% tetramethylammonium chloride-methanol).
  • constant current electrolysis Electrolysis was performed simultaneously on both sides of the steel sheet, and the electrolytic thickness was from the surface layer to 10 ⁇ m per side.
  • the sample piece with the deposit attached on the surface is taken out from the electrolytic solution and immersed in an aqueous solution of sodium hexametaphosphate (500 mg / l) (hereinafter referred to as an SHMP aqueous solution) to give ultrasonic vibration.
  • the precipitate was peeled from the sample piece and extracted into an aqueous SHMP solution.
  • the SHMP aqueous solution containing the precipitate was filtered using a filter having a pore diameter of 20 nm, and the filtrate after filtration was analyzed using an ICP emission spectroscopic analyzer, and the absolute amount of Ti in the filtrate was measured.
  • the absolute amount of Ti was divided by the electrolytic weight to obtain the Ti content (mass%) contained in the precipitate having a size of less than 20 nm.
  • the electrolysis weight was calculated
  • content shown in Table 3 is the value which averaged content of both surfaces calculated
  • Post-working shape uniformity evaluation is performed by applying a grinding stone after applying a strain of 5% elongation in the direction perpendicular to the rolling, visualizing the shape non-uniformity, Items that were not recognized were marked as ⁇ .
  • the content of the Ti element contained in the precipitate having a component composition within the scope of the present invention and less than 20 nm in the surface layer portion from the surface to 10 ⁇ m is 9% of the total amount of Ti contained in the steel sheet.
  • the average r value which is an index of deep drawability, is 1.5 or more, excellent shape uniformity after processing, uniform in appearance, and suitable for automotive exterior board use. Had performance.
  • the shape uniformity after processing and the appearance were inferior, and the performance suitable for the automobile exterior plate application was not satisfied.
  • the amount of Cu in the steel exceeds 0.005%
  • the comparative example codes A2 and B2 that do not contain Sb increase the amount of Ti contained in precipitates having a size of less than 20 nm, that is, It can be seen that fine precipitates increase and appearance unevenness occurs.
  • Comparative Example Code J2 since the Sb content is not appropriate, the amount of Ti contained in the precipitate having a size of less than 20 nm also increases, resulting in appearance irregularities.
  • the steel sheet of the present invention can be suitably used for various parts such as automobiles and various electrical equipments that require excellent post-molding surface quality, centering on automobile outer plates.

Abstract

Disclosed is a cold-rolled steel sheet that is an IF steel sheet containing Ti and has superior deep drawing characteristics in which a uniform appearance and shape uniformity after pressing can be obtained without carrying out special processing, and a method for producing the same. The IF steel sheet has Ti added. The steel sheet contains 0.02 - 0.1% Ti, 0.03% or less Sb, more than 0.005% and not more than 0.03% Cu, and Ti*, such that Ti* = (Ti%)-3.4 × (N%)-1.5 × (S%)-4 × (C%), in a range that satisfies 0 < Ti* 0.02. The steel sheet content is also in a range that satisfies (Sb%) ≥ (Cu%)/5. Furthermore the elemental Ti content (mass%) contained in deposits sized less than 20 nm in a sheet thickness surface layer part from each of the surfaces on both sides of the steel sheet to 10 µm is 9% or less of the total Ti content (mass%) in the steel sheet.

Description

冷延鋼板およびその製造方法Cold rolled steel sheet and method for producing the same
　本発明は、自動車の外板等に使用される、軟質で加工後の形状均一性に優れた冷延鋼板およびその製造方法に関するものである。 [Technical Field] The present invention relates to a cold-rolled steel sheet that is soft and excellent in shape uniformity after processing, and a method for producing the same.
　従来から、自動車の外装板としては、引張り強さが３５０ＭＰａ未満と軟質で、加工性に優れた冷延鋼板や合金化溶融亜鉛めっき鋼板が多く使用されている。例えば、軟質で加工性に優れた冷延鋼板としては、炭窒化物形成元素を含有する極低炭素鋼を熱間圧延し、熱延鋼板の段階で炭窒化物を生成させ、鋼中の固溶Ｃおよび固溶Ｎを低減させた後、冷間圧延および再結晶焼鈍を経て製造される冷延鋼板、いわゆるＩＦ（Ｉｎｔｅｒｓｔｉｔｉａｌ　Ｆｒｅｅ）鋼板が知られている。 Conventionally, cold-rolled steel sheets and galvannealed steel sheets that are soft and have excellent workability have been widely used as exterior panels for automobiles. For example, as a cold-rolled steel sheet that is soft and excellent in workability, an ultra-low carbon steel containing a carbonitride-forming element is hot-rolled to produce carbonitride at the stage of the hot-rolled steel sheet, thereby A cold-rolled steel sheet, so-called IF (Interstitial Free) steel sheet, which is manufactured through cold rolling and recrystallization annealing after reducing dissolved C and solid solution N is known.
　このようなＩＦ鋼板のうち、炭窒化物形成元素としてＴｉを含有したＩＦ鋼板は、特に深絞り性などの加工性に優れるという特徴がある。しかしながら、Ｔｉは炭窒化物のみならず、微細な硫化物や炭硫化物を形成し、これらの微細析出物が再結晶および再結晶後の粒成長を阻害することがあるため、部分的に未再結晶粒が残存するという問題があった。部分的に未再結晶粒が残存すると局部的に降伏強度が高い領域が存在することになり、プレス加工後に形状不均一が生じることがあるため、好ましくない。また、合金化溶融亜鉛めっきを施す際に、鋼板表層部に未再結晶粒の残存部が存在すると、合金化速度にムラが生じ、外観ムラの原因ともなる。 Among such IF steel sheets, IF steel sheets containing Ti as a carbonitride-forming element are particularly characterized by excellent workability such as deep drawability. However, Ti forms not only carbonitrides but also fine sulfides and carbonitrides, and these fine precipitates may hinder recrystallization and grain growth after recrystallization. There was a problem that recrystallized grains remained. If the non-recrystallized grains partially remain, a region having a high yield strength exists locally, and shape unevenness may occur after press working, which is not preferable. In addition, when alloyed hot dip galvanizing is performed, if a remaining portion of non-recrystallized grains is present in the surface layer portion of the steel sheet, unevenness occurs in the alloying speed, which may cause uneven appearance.
　これらの問題を解決する手法として、例えば、特許文献１には、溶融亜鉛めっき処理を行うに際し、鋼板表面に、炭素化合物、窒素化合物およびホウ素化合物の中から選択される１種または２種以上をＣ、Ｎ、Ｂ量として０．１~１０００ｍｇ／ｍ２付着させ、かつ硫黄または硫黄化合物をＳ量として０．１~１０００ｍｇ／ｍ２付着させた後、水素を含む非酸化性雰囲気で６８０℃以上の温度で焼鈍する方法が開示されている。
　また、特許文献２には、スジムラと呼ばれる表面外観不均一を解決するために、連続鋳造直後のスラブをその表面温度が１０００℃以上になるように保持して仕上圧延工程に導き、Ａｒ３点以上の温度で仕上げる方法が開示されている。
　さらに、特許文献３には、表面外観不均一を解決するために、鋼を連続鋳造してスラブとした後加熱し、表面温度が１０００℃以上のスラブに酸素を含む酸化性ガスを吹付けた後、熱間圧延、酸洗、冷間圧延、焼鈍を行う方法が開示されている。 As a technique for solving these problems, for example, in Patent Document 1, when performing hot dip galvanizing treatment, one or more selected from a carbon compound, a nitrogen compound, and a boron compound are added to the steel sheet surface. C, N, B amount as 0.1 ~ 1000mg / m 2 adhered to, and after the sulfur or sulfur compound is 0.1 ~ 1000mg / m 2 deposited as S content, 680 ° C. in a non-oxidizing atmosphere containing hydrogen A method of annealing at the above temperature is disclosed.
Further, in Patent Document 2, in order to solve uneven surface appearance called “straight unevenness”, the slab immediately after continuous casting is held at a surface temperature of 1000 ° C. or higher and led to a finish rolling process, and Ar3 point or higher A method of finishing at the following temperature is disclosed.
Further, in Patent Document 3, in order to solve the surface appearance non-uniformity, steel is continuously cast into a slab and then heated, and an oxidizing gas containing oxygen is sprayed on a slab having a surface temperature of 1000 ° C. or higher. Thereafter, a method of performing hot rolling, pickling, cold rolling, and annealing is disclosed.
特開平１１−５０２２１号公報Japanese Patent Laid-Open No. 11-50221 特開平９−２９６２２２号公報JP-A-9-296222 特開平１０−３３０８４６号公報Japanese Patent Laid-Open No. 10-330846
　しかしながら、特許文献１に記載の方法では、硫黄または硫黄化合物をＳ量として０．１~１０００ｍｇ／ｍ２付着させる工程が必要となり、生産性の低下やコストの増大を招くという問題がある。
　特許文献２に記載の方法では、スラブの表面を溶削するなどして表面欠陥を防止する、いわゆるスラブ手入れを行うことができず、特に美麗な表面外観を要求される自動車外装板用途に用いるには不適当である。
　さらに、特許文献３に記載の方法では、鋼板の両面で外観不均一を防止するためには、１０００℃以上の高温のスラブを表裏反転させて酸化性のガスを吹付ける必要があり、実用的でない。
さらに、特許文献１~３の技術には、プレス加工後の形状不均一を解決する方法については開示されていない。 However, the method described in Patent Document 1 requires a step of depositing 0.1 to 1000 mg / m 2 of sulfur or a sulfur compound as the amount of S, and there is a problem that the productivity is lowered and the cost is increased.
In the method described in Patent Document 2, so-called slab care that prevents surface defects by cutting the surface of the slab or the like cannot be performed, and it is used for an automobile exterior plate that requires a particularly beautiful surface appearance. Inappropriate for
Furthermore, in the method described in Patent Document 3, in order to prevent non-uniform appearance on both sides of the steel sheet, it is necessary to invert an slab having a high temperature of 1000 ° C. or higher and spray an oxidizing gas, which is practical. Not.
Furthermore, the techniques of Patent Documents 1 to 3 do not disclose a method for solving the non-uniform shape after press working.
　本発明は、かかる事情に鑑み、深絞り性に優れたＴｉ含有ＩＦ鋼板において、特殊な処理を施さずに、均一な外観とプレス加工後の形状均一性を得ることのできる冷延鋼板およびその製造方法を提供することを目的とする。 In view of such circumstances, the present invention is a cold rolled steel sheet capable of obtaining a uniform appearance and shape uniformity after press processing without performing special treatment in a Ti-containing IF steel sheet excellent in deep drawability, and its An object is to provide a manufacturing method.
　発明者らは、上記問題点を解決するため、プレス加工後に表面欠陥として現出する欠陥の発生メカニズムと抑制対策について、鋭意研究調査を重ねた。その結果、上記問題が生じる鋼板には、極表層に未再結晶粒が残存すること、そしてこれらの未再結晶粒を調査した結果、鋼板表面から１０μｍまでの領域における析出物の析出状態に特徴があることを見出した。 In order to solve the above-mentioned problems, the inventors have conducted intensive research and investigation on the generation mechanism of the defects that appear as surface defects after press working and the suppression measures. As a result, in the steel plate in which the above problem occurs, unrecrystallized grains remain in the extreme surface layer, and as a result of investigating these non-recrystallized grains, it is characterized by the precipitate state in the region from the steel sheet surface to 10 μm. Found that there is.
　さらに、発明者らは、プレス加工時の外観ムラが、鋼中に極微量存在するＣｕ量によって変動することをつきとめた。Ｃｕは、近年のＣＯ２削減気運による鉄源へのスクラップ活用により、溶銑中の含有割合が増加する傾向にある。そして、鉄中へ混入すると除去ができない、いわゆるトランプエレメントとして、その特性への影響が懸念されている元素でもある。Ｃｕは、耐食性向上や析出強化など、鋼の特性を向上する目的で含有されることもあるが、本発明の対象とするＩＦ鋼板に対しては、表面品質の観点で害になる元素である。 Furthermore, the inventors have found that the appearance irregularity at the time of pressing varies depending on the amount of Cu present in the steel. Cu has a tendency to increase the content ratio in hot metal due to the recent utilization of scrap as an iron source by CO 2 reduction. And as a so-called trump element that cannot be removed when mixed in iron, it is also an element that is concerned about the effect on its characteristics. Cu may be contained for the purpose of improving the properties of the steel, such as corrosion resistance improvement and precipitation strengthening, but is an element harmful to the surface quality of the IF steel sheet that is the subject of the present invention. .
　本発明は、以上の知見に基づいてなされたものであり、その要旨は以下のとおりである。
［１］ｍａｓｓ％で、Ｃ：０．０００５~０．０１％、Ｓｉ：０．２％以下、Ｍｎ：０．１~１．５％、Ｐ：０．０３％以下、Ｓ：０．００５~０．０３％、Ｔｉ：０．０２~０．１％、Ａｌ：０．０１~０．０５％、Ｎ：０．００５％以下、Ｓｂ：０．０３％以下、Ｃｕ：０．００５％超０．０３％以下であり、かつ、Ｔｉ＊＝（Ｔｉ％）−３．４×（Ｎ％）−１．５×（Ｓ％）−４×（Ｃ％）で示されるＴｉ＊を０＜Ｔｉ＊＜０．０２を満たす範囲で、さらに、（Ｓｂ％）≧（Ｃｕ％）／５を満たす範囲で含有し、残部はＦｅおよび不可避的不純物からなる成分組成を有し、鋼板両面において、各表面から１０μｍまでの板厚表層部における大きさ２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量（ｍａｓｓ％）が、鋼板中の全Ｔｉ含有量（ｍａｓｓ％）の９％以下であることを特徴とする冷延鋼板。ただし、（Ｔｉ％）、（Ｎ％）、（Ｓ％）、（Ｃ％）、（Ｓｂ％）、（Ｃｕ％）は、それぞれＴｉ、Ｎ、Ｓ、Ｃ、Ｓｂ、Ｃｕの含有量（ｍａｓｓ％）を示す。 This invention is made | formed based on the above knowledge, The summary is as follows.
[1] Mass%, C: 0.0005 to 0.01%, Si: 0.2% or less, Mn: 0.1 to 1.5%, P: 0.03% or less, S: 0.005 ~ 0.03%, Ti: 0.02 ~ 0.1%, Al: 0.01 ~ 0.05%, N: 0.005% or less, Sb: 0.03% or less, Cu: 0.005% Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%) In a range satisfying <Ti * <0.02, and further in a range satisfying (Sb%) ≧ (Cu%) / 5, and the balance has a component composition composed of Fe and inevitable impurities, In addition, the content of Ti element (mass%) contained in precipitates having a size of less than 20 nm in the surface thickness part from each surface to 10 μm is the total Ti content (ma ss%), which is 9% or less. However, (Ti%), (N%), (S%), (C%), (Sb%), and (Cu%) are the contents (mass) of Ti, N, S, C, Sb, and Cu, respectively. %).
［２］さらに、ｍａｓｓ％で、Ｎｂ：０．００１~０．０１％、Ｂ：０．０００２~０．００１５％のうち、いずれか一種または二種を含有することを特徴とする前記［１］に記載の冷延鋼板。 [2] The above-mentioned [1], further comprising at least one of Nb: 0.001 to 0.01% and B: 0.0002 to 0.0015% in mass% ] The cold-rolled steel sheet as described in any of the above.
［３］鋼板表面に亜鉛系めっき層を有することを特徴とする前記［１］または［２］に記載の冷延鋼板。 [3] The cold-rolled steel sheet according to [1] or [2], wherein the steel sheet surface has a zinc-based plating layer.
［４］前記［１］または［２］に記載の成分を有する鋼を連続鋳造によりスラブとし、該スラブに対して、加熱温度が１０００℃以上１２００℃未満で、かつ１０００℃以上の温度域での加熱時間が３．０時間以下の条件で加熱し、スケール除去および粗圧延を施し、次いで、鋼板表面温度が（Ａｒ３変態点−３００℃）以上Ａｒ３変態点以下の範囲となるよう冷却した後、仕上げ圧延終了時の鋼板表面温度がＡｒ３変態点以上の温度となるように仕上げ圧延し、冷却し、６５０℃以上の温度で巻取り、次いで、酸洗、冷間圧延後、焼鈍を行うことを特徴とする冷延鋼板の製造方法。 [4] The steel having the component described in [1] or [2] is made into a slab by continuous casting, and the heating temperature is 1000 ° C. or more and less than 1200 ° C. and a temperature range of 1000 ° C. or more with respect to the slab. After heating under the condition of heating time of 3.0 hours or less, applying scale removal and rough rolling, and then cooling the steel sheet surface temperature to be in the range of (Ar3 transformation point-300 ° C.) to Ar3 transformation point. Finishing and rolling so that the steel sheet surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point, cooling, winding at a temperature of 650 ° C. or higher, and then performing annealing after pickling and cold rolling. A method for producing a cold-rolled steel sheet.
［５］前記焼鈍後、さらに、溶融亜鉛めっき処理または合金化溶融亜鉛めっき処理を施すことを特徴とする前記［４］に記載の冷延鋼板の製造方法。 [5] The method for producing a cold-rolled steel sheet according to [4], wherein after the annealing, a hot dip galvanizing treatment or an alloying hot dip galvanizing treatment is further performed.
　なお、本明細書において、鋼の成分を示す％は、すべてｍａｓｓ％である。また、本発明が対象とする冷延鋼板には、冷延鋼板に電気亜鉛めっき、溶融亜鉛めっき、合金化溶融亜鉛めっきなどの表面処理を施した鋼板をも含むものである。さらに、その上に化成処理などにより皮膜をつけた鋼板をも含むものである。 In addition, in this specification,% which shows the component of steel is all mass%. The cold-rolled steel sheet to which the present invention is directed includes a steel sheet obtained by subjecting a cold-rolled steel sheet to surface treatment such as electrogalvanizing, hot-dip galvanizing, and alloying hot-dip galvanizing. Further, it includes a steel plate having a film formed thereon by chemical conversion treatment or the like.
　本発明によれば、特殊な処理を施さずに、均一な外観を有し、かつ、プレス加工後の形状均一性に優れた冷延鋼板が得られる。 According to the present invention, a cold-rolled steel sheet having a uniform appearance and excellent shape uniformity after press working can be obtained without performing special treatment.
　以下に、本発明の詳細を説明する。
従来の自動車の外装板用のＴｉ含有ＩＦ鋼板の集合組織は板面に平行な方向に｛１１１｝面が多く形成されることが知られている。しかしながら、前述したように、このような集合組織を有する合金化溶融亜鉛めっき鋼板では外観ムラが生じることがあり、冷延鋼板および合金化溶融亜鉛めっき鋼板ではプレス加工後の形状不均一が生じる場合がある。 Details of the present invention will be described below.
It is known that the texture of a Ti-containing IF steel sheet for a conventional automobile exterior plate has many {111} planes in a direction parallel to the plate surface. However, as described above, appearance irregularities may occur in an alloyed hot-dip galvanized steel sheet having such a texture, and non-uniform shapes after press working may occur in cold-rolled steel sheets and alloyed hot-dip galvanized steel sheets. There is.
　そこで、このような外観ムラやプレス加工後の形状不均一が生じる鋼板について詳細に調査した。その結果、上記問題が生じる鋼板には、板厚表層部、具体的には鋼板表面から１０μｍ程度までの表層部に部分的に未再結晶粒が残存すること、さらには、これらの未再結晶粒は｛１００｝面を主とする方位であることを知見した。また、これらの｛１００｝面を主体とする未再結晶粒が表層付近に残存した場合には、プレス加工後の形状不均一のみならず、合金化処理時には合金化速度が局部的に異なるため外観ムラが生じることもわかった。 Therefore, the steel sheet in which such uneven appearance and non-uniform shape after press working were investigated in detail. As a result, in the steel plate in which the above problem occurs, non-recrystallized grains partially remain in the plate thickness surface layer portion, specifically, the surface layer portion from the steel plate surface to about 10 μm. It has been found that the grains are oriented in the {100} plane. In addition, when these non-recrystallized grains mainly composed of {100} face remain in the vicinity of the surface layer, not only the shape non-uniformity after press working but also the alloying speed is locally different during the alloying process. It was also found that uneven appearance occurred.
　上記知見を受けて、本発明者らは、次に、表層付近に未再結晶粒が残存する原因を詳細に検討した。その結果、未再結晶粒が残存する部分には大きさが２０ｎｍ未満のごく微細なＴｉを含む析出物が多く存在することがわかった。このような微細な析出物は、自動車外装板用鋼板に施される一般的な焼鈍条件では固溶せずに残存し、いわゆるピン止め効果によって｛１１１｝面再結晶粒の粒界移動を妨げるため、再結晶が容易に進まず、｛１００｝面を主とする方位の未再結晶粒が残存するものと考えられる。 Based on the above findings, the present inventors then examined in detail the cause of the remaining non-recrystallized grains in the vicinity of the surface layer. As a result, it was found that there were many precipitates containing very fine Ti having a size of less than 20 nm in the portion where unrecrystallized grains remained. Such fine precipitates remain undissolved under the general annealing conditions applied to steel plates for automobile exterior plates, and hinder the movement of {111} recrystallized grain boundaries by the so-called pinning effect. Therefore, it is considered that recrystallization does not proceed easily and unrecrystallized grains mainly oriented in {100} plane remain.
　そこで、このような問題を解決するために、様々な製造条件での実験を繰返し実施して種々の鋼板を得、得られた鋼板について表層付近の状態を調査した。そうしたところ、特定の組成の鋼では、表層付近に｛１００｝面の未再結晶粒が多く残存せず、合金化溶融亜鉛めっき鋼板における外観ムラや、冷延鋼板および合金化溶融亜鉛めっき鋼板のプレス加工後形状不均一が生じないことを見出した。そして、この鋼板の板厚最表層付近、具体的には鋼板両面の表面から１０μｍまでの領域では、２０ｎｍ未満の析出物量が低減されていた。そこで、外観ムラやプレス加工後形状不均一が生じない好適な条件を定量化するため、大きさが２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量を算出し、鋼板中の全Ｔｉ含有量に対する割合を求めたところ、その割合が９％以下であれば、外観ムラやプレス加工後形状不均一の発生を低減できることが明らかになった。 Therefore, in order to solve such a problem, experiments under various production conditions were repeatedly carried out to obtain various steel plates, and the state of the surface layer of the obtained steel plates was investigated. As a result, in the steel having a specific composition, many unrecrystallized grains of {100} face do not remain in the vicinity of the surface layer, and uneven appearance in the alloyed hot dip galvanized steel sheet, cold rolled steel sheet and alloyed hot dip galvanized steel sheet It was found that non-uniform shape does not occur after pressing. And the amount of precipitates of less than 20 nm was reduced in the vicinity of the outermost layer thickness of the steel plate, specifically, in the region from the surface of both surfaces of the steel plate to 10 μm. Therefore, in order to quantify suitable conditions that do not cause uneven appearance and non-uniform shape after pressing, the content of Ti element contained in precipitates having a size of less than 20 nm is calculated, and the total Ti content in the steel sheet As a result, it was found that when the ratio is 9% or less, appearance irregularities and non-uniform shapes after press working can be reduced.
　なお、大きさ２０ｎｍ未満の析出物に含まれるＴｉの量は、以下の方法により測定することができる。
　試料を電解液中で所定量電解した後、試料片を電解液から取り出して分散性を有する溶液中に浸漬する。次いで、この溶液中に含まれる析出物を、孔径２０ｎｍのフィルタを用いてろ過する。この孔径２０ｎｍのフィルタをろ液と共に通過した析出物が大きさ２０ｎｍ未満である。次いで、ろ過後のろ液に対して、誘導結合プラズマ（ＩＣＰ）発光分光分析法、ＩＣＰ質量分析法、および原子吸光分析法等から適宜選択して分析し、大きさ２０ｎｍ未満の析出物に含まれるＴｉ含有量（ｍａｓｓ％）を求める。 The amount of Ti contained in the precipitate having a size of less than 20 nm can be measured by the following method.
After the sample is electrolyzed in a predetermined amount in the electrolytic solution, the sample piece is taken out of the electrolytic solution and immersed in a solution having dispersibility. Subsequently, the precipitate contained in this solution is filtered using a filter having a pore diameter of 20 nm. Precipitates that have passed through the filter having a pore diameter of 20 nm together with the filtrate have a size of less than 20 nm. Next, the filtrate after filtration is appropriately selected from inductively coupled plasma (ICP) emission spectroscopy, ICP mass spectrometry, atomic absorption spectrometry, etc., and included in precipitates having a size of less than 20 nm. The Ti content (mass%) to be obtained is determined.
　以上より、均一な外観とプレス加工後の形状均一性を得るために、本発明では、鋼板両面の各表面から１０μｍまでの領域での、大きさ２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量（ｍａｓｓ％）は、鋼板中の全Ｔｉ含有量（ｍａｓｓ％）の９％以下とする。 From the above, in order to obtain a uniform appearance and shape uniformity after press working, in the present invention, the inclusion of Ti element contained in precipitates having a size of less than 20 nm in the region from each surface of both surfaces of the steel plate to 10 μm. The amount (mass%) is 9% or less of the total Ti content (mass%) in the steel sheet.
　さらに、検討を進めたところ、プレス加工時の外観ムラは、鋼中に極微量存在するＣｕ量によって変動することがわかった。この原因は、主に硫化物の形態変化によるものと発明者らは考えている。すなわち、Ｃｕが混入しない従来成分からなるＩＦ鋼の場合は、熱延巻取り時にＴｉ系硫化物（例えばＴｉ４Ｃ２Ｓ２）などの比較的粗大な析出物を生成することが知られている。しかし、Ｃｕが一定量以上含まれる成分からなるＩＦ鋼の場合は、ＣｕがＴｉ系硫化物のＴｉと一部置換してＴｉＣｕ系硫化物を生成してしまう。そして、置換されフリーとなったＴｉはＴｉ系炭化物を生成することになる。このＴｉ系炭化物が微細（大きさ２０ｎｍ未満）のまま存在していた場合、再結晶を遅らせる。その結果、未再結晶粒が表層付近に残存し、外観ムラが生じることになる。 Furthermore, as a result of investigations, it was found that the appearance unevenness during press working fluctuates depending on the amount of Cu present in a trace amount in the steel. The inventors consider that this is mainly due to a change in the form of sulfide. That is, in the case of IF steel made of a conventional component not mixed with Cu, it is known that a relatively coarse precipitate such as a Ti-based sulfide (for example, Ti 4 C 2 S 2 ) is generated during hot rolling. Yes. However, in the case of IF steel made of a component containing a certain amount or more of Cu, Cu is partially substituted with Ti of Ti-based sulfide to generate TiCu-based sulfide. Then, Ti that is replaced and becomes free produces Ti-based carbides. When this Ti-based carbide exists in a fine form (less than 20 nm), recrystallization is delayed. As a result, non-recrystallized grains remain in the vicinity of the surface layer, resulting in uneven appearance.
　そして、さらなる検討の結果、Ｃｕの混入量増加による上記外観ムラの発生に対しては、Ｓｂの含有が効果があることを見出した。Ｃｕ量が増加した鋼が溶製されても、Ｓｂが含有する場合、ＴｉＣｕ系硫化物の生成が抑止される。その結果、微細な（大きさ２０ｎｍ未満）Ｔｉ系炭化物の生成を回避することができ、表面性状に優れた冷延鋼板を得ることが出来る。 Further, as a result of further studies, it was found that the inclusion of Sb is effective for the occurrence of the above-described uneven appearance due to an increase in the amount of Cu mixed. Even when steel with an increased amount of Cu is melted, the formation of TiCu sulfide is suppressed when Sb is contained. As a result, generation of fine (less than 20 nm in size) Ti-based carbide can be avoided, and a cold-rolled steel sheet having excellent surface properties can be obtained.
　次に、本発明の成分組成の限定理由について説明する。
Ｃ：０．０００５~０．０１％
Ｃは、固溶強化元素であり、降伏強度の上昇に寄与し、面内剛性の向上には有利であるが、優れた深絞り性を得るためには極力低減することが好ましい。０．０００５％未満では、結晶粒径が著しく粗大化して降伏強度が大きく低下するため、面内剛性が低下して腰折れなどの欠陥が発生しやすくなる。また、脱炭コストの増大を招く。よって、０．０００５％を下限とする。一方、Ｃを多量に含有すると鋼中でのＴｉ炭化物量が増加し、表層部での析出物量が増加して、板面に平行な方向の｛１００｝面を主とする方位の未再結晶粒の残存量が増大するため、０．０１％を上限とする。 Next, the reason for limiting the component composition of the present invention will be described.
C: 0.0005 to 0.01%
C is a solid solution strengthening element, which contributes to an increase in yield strength and is advantageous for improving in-plane rigidity, but is preferably reduced as much as possible to obtain excellent deep drawability. If it is less than 0.0005%, the crystal grain size becomes extremely coarse and the yield strength is greatly reduced, so that the in-plane rigidity is lowered and defects such as hip breakage tend to occur. Moreover, the decarburization cost increases. Therefore, 0.0005% is set as the lower limit. On the other hand, when C is contained in a large amount, the amount of Ti carbide in the steel increases, the amount of precipitates in the surface layer increases, and the non-recrystallized orientation mainly of {100} plane parallel to the plate surface. Since the residual amount of grains increases, 0.01% is made the upper limit.
　Ｓｉ：０．２％以下
Ｓｉは、比較的加工性を劣化することなく固溶強化により鋼を強化するのに有用な元素であるが、焼鈍時に表面に濃化して溶融亜鉛めっき性を著しく阻害するため、０．２％以下とする。 Si: 0.2% or less Si is a useful element for strengthening steel by solid solution strengthening without relatively degrading workability. However, it concentrates on the surface during annealing and significantly inhibits hot dip galvanizing. Therefore, the content is set to 0.2% or less.
　Ｍｎ：０．１~１．５％
Ｍｎは、固溶強化元素として鋼強度を増大させる。鋼板剛性確保のため、０．１％以上の含有が必要である。所望の強度を得るために適宜含有することができるが、過剰な含有は加工性を阻害するため、１．５％以下とする。 Mn: 0.1 to 1.5%
Mn increases the steel strength as a solid solution strengthening element. In order to ensure the rigidity of the steel plate, it is necessary to contain 0.1% or more. Although it can contain suitably in order to obtain desired intensity | strength, since excessive inclusion inhibits workability, it shall be 1.5% or less.
　Ｐ：０．０３％以下
Ｐは固溶強化元素であり、鋼の強化と降伏強度向上には有効である。しかし、過度に含有すると、熱間、冷間割れの原因となるばかりでなく、溶融亜鉛めっきの合金化反応を阻害するため、０．０３％以下とする。 P: 0.03% or less P is a solid solution strengthening element and is effective in strengthening steel and improving yield strength. However, if it is contained excessively, it not only causes hot and cold cracking, but also inhibits the alloying reaction of hot dip galvanizing, so it is made 0.03% or less.
　Ｓ：０．００５~０．０３％
Ｓは本発明において重要な元素である。Ｓは通常、不可避的不純物として鋼中に存在し、極力低減すべきものとされるが、本発明では敢えてその存在量を０．００５％以上確保する。すなわち、０．００５％未満では、連続鋳造後に生成するＴｉＳが微細となり、熱延でのスラブ再加熱時に部分的に再固溶しやすくなるため、後工程で微細なＴｉＳなどの析出物を比較的多量に析出する部位が生じ、表層に局部的に｛１００｝方位の未再結晶粒を残存させる原因となる。このような微細析出物の影響を低減するため、０．００５％以上とする。好ましくは０．０１０％以上である。一方０．０３％超えでは、鋼板製造時の熱間割れが生じ易くなり、生産性が阻害されるとともに表面性状を劣化させる。よって、０．０３％以下とする。 S: 0.005 to 0.03%
S is an important element in the present invention. S is usually present in steel as an unavoidable impurity and should be reduced as much as possible. In the present invention, S is intentionally ensured 0.005% or more. In other words, if it is less than 0.005%, TiS produced after continuous casting becomes fine, and it becomes easy to partially re-solidify during slab reheating in hot rolling. A site that precipitates in a large amount is generated, causing unrecrystallized grains of {100} orientation to remain locally on the surface layer. In order to reduce the influence of such fine precipitates, the content is made 0.005% or more. Preferably it is 0.010% or more. On the other hand, if it exceeds 0.03%, hot cracking during the production of the steel sheet is likely to occur, which impedes productivity and deteriorates the surface properties. Therefore, it is 0.03% or less.
　Ｔｉ：０．０２~０．１％、かつ０＜Ｔｉ＊＜０．０２
　ただし、Ｔｉ＊＝（Ｔｉ％）−３．４×（Ｎ％）−１．５×（Ｓ％）−４×（Ｃ％）
Ｔｉは本発明における最も重要な元素のひとつである。Ｔｉは、鋼中のＣ、Ｎ、Ｓを析出物として固定することにより、加工性向上効果を有する。０．０２％未満では、このような効果を得ることができない。一方、Ｔｉを０．１％を超えて含有してもそれ以上の効果が望めないばかりでなく、板内部に異常組織の形成を招き、加工性を低下させる。 Ti: 0.02 to 0.1% and 0 <Ti * <0.02
However, Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%)
Ti is one of the most important elements in the present invention. Ti has an effect of improving workability by fixing C, N, and S in the steel as precipitates. If it is less than 0.02%, such an effect cannot be obtained. On the other hand, if Ti is contained in excess of 0.1%, not only a further effect cannot be expected, but an abnormal structure is formed inside the plate, and the workability is lowered.
　また、前述したように、鋼中のＴｉは、鋼中のＣ、Ｎ、Ｓと析出物を形成するため、これらの成分に対して、当量以上含有することにより、加工性を向上させることができる。そのためには、下記（１）式で示されるＴｉ＊を０より大きくする必要がある。一方、固溶Ｔｉを過剰に存在させると、焼鈍時の雰囲気によっては表層部で窒化が生じ、微細なＴｉＮを生成する場合があり、この微細なＴｉＮは表層において｛１００｝方位の未再結晶粒残存を助長するため好ましくない。鋼板両面の表面から１０μｍまでの板厚表層部での、２０ｎｍ未満のＴｉを含む微細析出物量を低減するには、Ｔｉ＊を０．０２未満とする必要がある。
Ｔｉ＊＝（Ｔｉ％）−３．４×（Ｎ％）−１．５×（Ｓ％）−４×（Ｃ％）・・・（１）
ただし、（Ｔｉ％）、（Ｎ％）、（Ｓ％）、（Ｃ％）は、それぞれＴｉ、Ｎ、Ｓ、Ｃの含有量（ｍａｓｓ％）を示す。 In addition, as described above, Ti in steel forms precipitates with C, N, and S in steel. Therefore, inclusion of an equivalent amount or more of these components can improve workability. it can. For that purpose, it is necessary to make Ti * shown by the following formula (1) larger than zero. On the other hand, if solute Ti is excessively present, nitridation may occur in the surface layer portion depending on the atmosphere during annealing, and fine TiN may be generated. This fine TiN is unrecrystallized in the {100} orientation in the surface layer. This is not preferable because it promotes the remaining of the grains. In order to reduce the amount of fine precipitates containing Ti of less than 20 nm in the surface thickness part from the surface of both surfaces of the steel plate to 10 μm, Ti * needs to be less than 0.02.
Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%) (1)
However, (Ti%), (N%), (S%), and (C%) indicate the contents (mass%) of Ti, N, S, and C, respectively.
　Ａｌ：０．０１~０．０５％
Ａｌは脱酸剤として含有する元素であり、０．０１％以上必要であるが、多量に含有してもより一層の脱酸効果は得られないので、０．０５％以下とする。 Al: 0.01 to 0.05%
Al is an element contained as a deoxidizing agent and needs to be 0.01% or more. However, even if contained in a large amount, a further deoxidizing effect cannot be obtained, so the content is made 0.05% or less.
　Ｎ：０．００５％以下
Ｎは少ないほど加工性には有利であるので、少ないほど望ましい。０．００５％を超えて、過剰に含有すると、成形性の著しい低下と固溶Ｔｉ量の低下につながるので、上限を０．００５％とする。 N: 0.005% or less The smaller the N, the better the workability. If it exceeds 0.005% and excessively contained, it leads to a significant decrease in formability and a decrease in the amount of dissolved Ti, so the upper limit is made 0.005%.
　Ｓｂ：０．０３％以下、Ｃｕ：０．００５％超え~０．０３％以下、さらに（Ｓｂ％）≧（Ｃｕ％）／５を満たす範囲で含有
Ｓｂは鋼板表面の酸化あるいは窒化抑制剤として含有される元素であるが、ＩＦ鋼の製造においては、連続焼鈍中の窒化による析出物生成を抑制することで鋼板表面組織微細化を軽減している。加えて、鋼中にＣｕが混入した場合にも効果を発揮し、Ｃｕの量が０．００５％を超えた場合に、Ｃｕ量の１／５の割合のＳｂを含有することによって、ＴｉＣｕ系硫化物の生成を抑止し、微細な析出物であるＴｉ系炭化物による外観ムラ発生を回避することができ、結果として表面性状に優れた冷延鋼板を得ることが出来る。このような効果を得るために、後述するように、（Ｓｂ％）≧（Ｃｕ％）／５とする。ただし、０．０３％超えで含有すると、加工性を損なう場合がある。よって、含有する場合は、０．０３％以下とする。 Sb: 0.03% or less, Cu: more than 0.005% to 0.03% or less, and further contained in a range satisfying (Sb%) ≧ (Cu%) / 5, Sb is used as an oxidation or nitridation inhibitor on the steel sheet surface. Although it is an element contained, in the production of IF steel, the refinement of the steel sheet surface structure is reduced by suppressing the formation of precipitates due to nitriding during continuous annealing. In addition, when Cu is mixed in the steel, the effect is also exhibited. When the amount of Cu exceeds 0.005%, by containing Sb at a ratio of 1/5 of the Cu amount, the TiCu system Generation of sulfides can be suppressed and occurrence of unevenness in appearance due to Ti-based carbides that are fine precipitates can be avoided, and as a result, a cold-rolled steel sheet having excellent surface properties can be obtained. In order to obtain such an effect, as described later, (Sb%) ≧ (Cu%) / 5. However, if the content exceeds 0.03%, the workability may be impaired. Therefore, when it contains, it is 0.03% or less.
　Ｃｕは強度向上や耐食性向上のために添加される元素であるが、軟質な鋼板を製造する場合には積極的に添加しない。しかしながら、添加しなくとも鉄源に不可避的に存在するほか、リサイクルの観点からスクラップ使用量を増加することによって、鋼中に混入する。スクラップを使用する場合のＣｕの不可避的に混入する最低量は、ほぼ０．００５％である。０．００５％以下であれば、Ｃｕの混入量増加による外観ムラ発生は問題とならない。一方で、鋼中に混入したＣｕは除去することができないため、本発明ではＳｂ含有による無害化を行うが、Ｃｕ量が０．０３％超えになると、表面欠陥は改善されるものの、機械的特性が劣化し、熱間脆性悪化する。以上より、Ｃｕは０．００５％超え０．０３％以下とする。 Cu is an element added to improve strength and corrosion resistance, but is not actively added when producing a soft steel sheet. However, it is unavoidably present in the iron source even if not added, and it is mixed into the steel by increasing the amount of scrap used from the viewpoint of recycling. The minimum amount of Cu inevitably mixed when scrap is used is approximately 0.005%. If it is 0.005% or less, appearance unevenness due to an increase in the amount of Cu mixed does not become a problem. On the other hand, since Cu mixed in steel cannot be removed, the present invention performs detoxification by containing Sb. However, when the Cu amount exceeds 0.03%, surface defects are improved, but mechanical Characteristics deteriorate and hot brittleness worsens. From the above, Cu is more than 0.005% and 0.03% or less.
（Ｓｂ％）≧（Ｃｕ％）／５　ただし、（Ｓｂ％）、（Ｃｕ％）は、それぞれＳｂ、Ｃｕの含有量（ｍａｓｓ％）を示す。
前述したように、本発明では、Ｓｂを含有することで、Ｃｕによる微細な析出物であるＴｉ系炭化物による外観ムラ発生を回避し、表面性状に優れた冷延鋼板を得る。このような効果は、（Ｓｂ％）≧（Ｃｕ％）／５を満たす範囲で含有することで達成される。 (Sb%) ≧ (Cu%) / 5 However, (Sb%) and (Cu%) indicate the contents (mass%) of Sb and Cu, respectively.
As described above, in the present invention, by containing Sb, appearance unevenness due to Ti-based carbides, which are fine precipitates due to Cu, is avoided, and a cold-rolled steel sheet having excellent surface properties is obtained. Such an effect is achieved by containing in a range satisfying (Sb%) ≧ (Cu%) / 5.
　残部はＦｅおよび不可避的不純物である。なお、必要に応じて、本発明では、さらにＮｂ：０．００１~０．０１％、Ｂ：０．０００２~０．００１５％のうち、いずれか一種または二種を含有することが好ましい。 The balance is Fe and inevitable impurities. In addition, according to the present invention, it is preferable that any one or two of Nb: 0.001 to 0.01% and B: 0.0002 to 0.0015% are further contained as needed.
　Ｎｂ：０．００１~０．０１％
Ｎｂは、Ｔｉと同様に、炭窒化物を形成して加工性を向上させるのに有利な元素である。特に、前述した（１）式のＴｉ＊が０．００５未満の場合には含有することが望ましく、加工性向上効果を得るためには、０．００１％以上含有する必要がある。しかし、０．０１％を超えて含有すると、結晶粒が微細化され、深絞り性などの加工性を劣化させる場合がある。よって、含有する場合は、０．００１％以上０．０１％以下とする。 Nb: 0.001 to 0.01%
Nb, like Ti, is an element that is advantageous for forming a carbonitride to improve workability. In particular, when Ti * of the above-described formula (1) is less than 0.005, it is desirable to contain, and in order to obtain a workability improvement effect, it is necessary to contain 0.001% or more. However, if the content exceeds 0.01%, the crystal grains are refined, and workability such as deep drawability may be deteriorated. Therefore, when it contains, it is set as 0.001% or more and 0.01% or less.
　Ｂ：０．０００２~０．００１５％
Ｂは軟質ＩＦ鋼板の粒界強化に有効な元素であり、耐二次加工脆性が必要とされる場合に０．０００２％以上含有すると効果的である。しかし、過剰に含有すると、鋼板製造時の表面性状を劣化させる恐れがある。よって、含有する場合は、０．０００２％以上０．００１５％以下とする。 B: 0.0002 to 0.0015%
B is an element effective for strengthening the grain boundary of the soft IF steel sheet, and it is effective to contain 0.0002% or more when secondary work brittleness resistance is required. However, when it contains excessively, there exists a possibility of deteriorating the surface property at the time of steel plate manufacture. Therefore, when it contains, it is 0.0002% or more and 0.0015% or less.
　次に、本発明の冷延鋼板の製造方法について説明する。本発明の冷延鋼板は、上記のような成分組成を有する鋼を連続鋳造によりスラブとし、該スラブに対して、加熱温度が１０００℃以上１２００℃未満で、かつ１０００℃以上の温度域での加熱時間が３．０時間以下の条件で加熱し、スケール除去および粗圧延を施し、次いで、鋼板表面温度が（Ａｒ３変態点−３００℃）以上Ａｒ３変態点以下の範囲となるよう冷却した後、仕上げ圧延終了時の表面温度がＡｒ３変態点以上の温度となるように仕上げ圧延し、冷却し、６５０℃以上の温度で巻取り、次いで、酸洗、冷間圧延、焼鈍を行うことにより得られる。また、溶融亜鉛めっき処理鋼板または合金化溶融亜鉛めっき処理鋼板を得る場合は、上記焼鈍まで同様に行った後、溶融亜鉛めっき処理または合金化溶融亜鉛めっき処理を行う。 Next, the manufacturing method of the cold rolled steel sheet of the present invention will be described. The cold-rolled steel sheet of the present invention uses a steel having the above component composition as a slab by continuous casting, and the heating temperature is 1000 ° C. or more and less than 1200 ° C. and a temperature range of 1000 ° C. or more. Heating is performed under conditions of heating time of 3.0 hours or less, scale removal and rough rolling are performed, and then cooling is performed so that the steel sheet surface temperature is in the range of (Ar3 transformation point−300 ° C.) to Ar3 transformation point. It is obtained by finish rolling so that the surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point, cooling, winding at a temperature of 650 ° C. or higher, and then pickling, cold rolling, and annealing. . Moreover, when obtaining a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet, after carrying out similarly to the said annealing, the hot-dip galvanizing process or an alloying hot-dip galvanizing process is performed.
　加熱温度は１０００℃以上１２００℃未満とする。かつ１０００℃以上の温度域での加熱時間は３．０時間以下とする。スラブ加熱工程と熱間圧延工程の全体で上記条件を満たす必要がある。加熱温度が１０００℃未満の場合、圧延温度が低下して仕上げ圧延後の鋼板表面温度をＡｒ３変態点以上とすることが困難である。一方、加熱温度が１２００℃以上では、連続鋳造時に生成したＴｉＭｎＳなどのＴｉを含有する硫化物が短時間に多く固溶し、後に続く工程において大きさ２０ｎｍ未満の微細析出物が多く生成するため、好ましくない。加熱温度が１２００℃未満であっても長時間保持すると、Ｔｉを含有する硫化物の固溶が進むため好ましくない。よって、１０００℃以上の温度域での加熱時間は３．０時間以下とする。 The heating temperature is 1000 ° C or higher and lower than 1200 ° C. The heating time in the temperature range of 1000 ° C. or higher is set to 3.0 hours or shorter. It is necessary to satisfy the above conditions throughout the slab heating process and the hot rolling process. When heating temperature is less than 1000 degreeC, rolling temperature falls and it is difficult to make the steel plate surface temperature after finish rolling more than an Ar3 transformation point. On the other hand, when the heating temperature is 1200 ° C. or higher, a large amount of Ti-containing sulfides such as TiMnS generated during continuous casting are dissolved in a short time, and many fine precipitates having a size of less than 20 nm are generated in the subsequent process. Is not preferable. Even if the heating temperature is less than 1200 ° C., holding for a long time is not preferable because the solid solution of the sulfide containing Ti proceeds. Therefore, the heating time in the temperature range of 1000 ° C. or higher is set to 3.0 hours or shorter.
　鋼板表面温度が（Ａｒ３変態点−３００℃）以上Ａｒ３変態点以下の範囲となるよう冷却加熱されたスラブに対して、スケール除去および粗圧延を施した後、仕上げ圧延を行う前に表面温度が（Ａｒ３変態点−３００℃）以上Ａｒ３変態点以下の範囲となるよう冷却する。 The surface temperature of the slab cooled and heated so that the steel sheet surface temperature is in the range of (Ar3 transformation point−300 ° C.) or more and below the Ar3 transformation point is subjected to scale removal and rough rolling and before finish rolling. It cools so that it may become the range below (Ar3 transformation point -300 degreeC) more than Ar3 transformation point.
　通常の製造方法では、熱間圧延工程における仕上げ圧延後に冷却することでフェライト変態が始まる。しかし、本発明では、仕上げ圧延前に鋼板表面を冷却して表面温度を一旦Ａｒ３変態点以下とする。このように仕上げ圧延前に所定の温度まで表面を冷却することで、表層部のみはフェライト変態を開始してＴｉを含む析出物が生成し始め、２０ｎｍ以上のサイズに成長しやすくなる。その結果、２０ｎｍ未満の析出物量が低減され、｛１００｝面の未再結晶粒が多く残存することなく、均一な外観を有し、かつ、プレス加工後の形状均一性に優れた冷延鋼板が得られることになる。なお、仕上げ圧延中に板厚中央からの復熱および加工発熱によって表層部の温度は上昇する。 In the normal manufacturing method, the ferrite transformation starts by cooling after finish rolling in the hot rolling process. However, in the present invention, the surface of the steel sheet is cooled to the Ar3 transformation point or less once before the finish rolling. Thus, by cooling the surface to a predetermined temperature before finish rolling, only the surface layer portion starts ferrite transformation and precipitates containing Ti start to be formed, and it becomes easy to grow to a size of 20 nm or more. As a result, the amount of precipitates of less than 20 nm is reduced, a large amount of non-recrystallized grains on the {100} plane does not remain, a cold rolled steel sheet having a uniform appearance and excellent shape uniformity after pressing. Will be obtained. Note that the temperature of the surface layer rises due to recuperation from the center of the plate thickness and processing heat generation during finish rolling.
　仕上げ圧延前の表面温度が低すぎると、仕上げ圧延終了時の表面温度がＡｒ３変態点以下となり表層部に歪みが残存したフェライト組織が生成し均一性が損なわれるため、仕上げ圧延前の表面温度は（Ａｒ３変態点−３００℃）以上とする必要がある。このように仕上げ圧延前に表面を一旦冷却して表面温度を制御することは、本発明の製造方法において特に重要な要件であり、特徴である。 If the surface temperature before finish rolling is too low, the surface temperature at the end of finish rolling is below the Ar3 transformation point, and a ferrite structure in which strain remains in the surface layer portion is generated and the uniformity is impaired. It is necessary to set it to (Ar3 transformation point -300 degreeC) or more. Thus, it is a particularly important requirement and a feature in the manufacturing method of the present invention to control the surface temperature by once cooling the surface before finish rolling.
　仕上げ圧延前に表面を冷却する方法としては、例えば、通常スケール除去に用いられる高圧水噴射装置などを用いて、表面が適切な温度域となるよう冷却することができる。なお、Ａｒ３変態点は以下のようにして求めることができる。各組成の鋼を１００~１２００℃の温度に加熱し、その後冷却しながら温度と体積変化を測定することによりオーステナイトからフェライトへの変態による体積膨張が生じる温度（Ａｒ３変態点）を知ることができる。 As a method for cooling the surface before finish rolling, for example, a high-pressure water injection device usually used for scale removal can be used to cool the surface so as to be in an appropriate temperature range. The Ar3 transformation point can be obtained as follows. By heating the steel of each composition to a temperature of 100 to 1200 ° C. and then measuring the temperature and volume change while cooling, it is possible to know the temperature (Ar3 transformation point) at which volume expansion occurs due to transformation from austenite to ferrite. .
　仕上げ圧延終了時の鋼板の表面温度がＡｒ３変態点以上の温度となるように仕上げ圧延し、冷却仕上げ圧延終了時の鋼板表面温度がＡｒ３変態点を下回ると、鋼板表層部に歪みが残存したフェライト組織が生成し、均一性が損なわれる。このため、仕上げ圧延終了時の鋼板表面温度がＡｒ３変態点以上となるように、制御する必要がある。 Ferrite in which finish rolling is performed so that the surface temperature of the steel plate at the end of finish rolling is equal to or higher than the Ar3 transformation point, and when the surface temperature of the steel plate at the end of cooling finish rolling is lower than the Ar3 transformation point, strain remains in the surface layer portion of the steel plate. Tissue forms and uniformity is compromised. For this reason, it is necessary to control so that the steel plate surface temperature at the end of finish rolling is equal to or higher than the Ar3 transformation point.
　一方、仕上げ圧延終了後に鋼板表面温度がＡｒ３変態点以上に長時間保持されると、成長した比較的粗大な析出物が再固溶して、２０ｎｍ未満の微細析出物量が増加するため好ましくない。そのため、鋼板表面温度がＡｒ３変態点以上の温度で仕上げ圧延が終了した後、ただちに冷却してフェライト変態を促進することが好ましい。冷却開始までの許容時間は、好ましくは１秒以内である。 On the other hand, if the surface temperature of the steel sheet is maintained at a temperature higher than the Ar3 transformation point for a long time after finishing rolling, the grown relatively coarse precipitates are re-dissolved and the amount of fine precipitates of less than 20 nm increases, which is not preferable. For this reason, it is preferable that the steel sheet surface temperature is equal to or higher than the Ar3 transformation point, and after finishing rolling is finished, the steel sheet is immediately cooled to promote the ferrite transformation. The allowable time until the start of cooling is preferably within 1 second.
　６５０℃以上で巻取り
冷却後、６５０℃以上で巻取る。巻取り温度が６５０℃を下回ると、析出物の成長速度が小さくなり、２０ｎｍ未満の微細析出物量が増加する。巻取り温度の上限は特に規定するものではないが、高すぎると表層のスケールが成長して表面欠陥の原因となりやすいため、８００℃未満とすることが望ましい。 It winds up at 650 degreeC or more after winding up and cooling at 650 degreeC or more. When the coiling temperature is lower than 650 ° C., the growth rate of precipitates is reduced, and the amount of fine precipitates of less than 20 nm is increased. The upper limit of the coiling temperature is not particularly defined, but if it is too high, the scale of the surface layer tends to grow and cause surface defects.
　巻取り後、酸洗、冷間圧延、場合によっては洗浄した後、焼鈍を行う。または、焼鈍後、溶融亜鉛めっき処理、合金化溶融亜鉛めっき処理を行う。酸洗、冷間圧延および焼鈍条件は特に限定する必要は無く、常法に従えばよい。巻き取り後の鋼板は、表面に生成したスケールを除去するために酸洗し、次いで冷間圧延を行う。冷間圧延率（冷間圧延圧下率）は自動車用外板を製造する際に通常行われている５０％~９０％程度とすればよい。なお、冷間圧延率は加工性（ｒ値）向上の観点からは７０％以上とするのが望ましい。 後 After winding, pickling, cold rolling, and in some cases, cleaning and then annealing. Alternatively, after annealing, a hot dip galvanizing process or an alloyed hot dip galvanizing process is performed. Pickling, cold rolling, and annealing conditions are not particularly limited, and may be performed in accordance with ordinary methods. The steel sheet after winding is pickled to remove scale formed on the surface, and then cold-rolled. The cold rolling rate (cold rolling reduction rate) may be about 50% to 90%, which is usually performed when manufacturing an automobile outer sheet. The cold rolling rate is desirably 70% or more from the viewpoint of improving workability (r value).
　次いで、冷間圧延後の鋼板は、圧延油の脱脂や汚れを除くため洗浄した後、再結晶焼鈍される。なお、焼鈍温度は、Ａｃ３変態点を超えると加工性（ｒ値）が低下しやすいため、Ａｃ３変態点以下とすることが好ましい。なお、下限温度は、７００℃程度とすることが、再結晶焼鈍を行う上で好ましい。焼鈍後、表面粗度の調整などのため調質圧延を行うことが好ましい。この際、調質圧延の圧延率（伸長率）は、０．５％~１．５％程度とすることが好ましい。以上により、加工後の形状均一性に優れた冷延鋼板が得られる。 Next, the cold-rolled steel sheet is washed to remove the degreasing oil and dirt from the rolling oil, and then recrystallized and annealed. In addition, since the workability (r value) tends to decrease when the annealing temperature exceeds the Ac3 transformation point, the annealing temperature is preferably set to be equal to or lower than the Ac3 transformation point. The lower limit temperature is preferably about 700 ° C. in performing recrystallization annealing. After annealing, it is preferable to perform temper rolling for adjusting the surface roughness. At this time, the rolling rate (elongation rate) of temper rolling is preferably about 0.5% to 1.5%. As described above, a cold-rolled steel sheet having excellent shape uniformity after processing can be obtained.
　溶融亜鉛めっき鋼板または合金化溶融亜鉛めっき鋼板とする際は、焼鈍まで上記冷延鋼板の場合と同様に行い、引き続き溶融亜鉛めっき処理または合金化溶融亜鉛めっき処理を行う。なお、焼鈍前に軽酸洗を行ってもよい。溶融亜鉛めっき処理条件、合金化溶融亜鉛めっき処理条件は特に限定する必要はなく、常法に従えばよい。溶融亜鉛めっき処理後、または合金化溶融亜鉛めっき処理後、表面粗度の調整などのため調質圧延を行うことが好ましい。以上により、加工後の形状均一性に優れた溶融亜鉛めっき冷延鋼板または合金化溶融亜鉛めっき冷延鋼板が得られる。 When forming a hot dip galvanized steel sheet or an alloyed hot dip galvanized steel sheet, it is performed in the same manner as in the case of the cold-rolled steel sheet until annealing, followed by hot dip galvanizing treatment or alloying hot dip galvanizing treatment. In addition, you may perform light pickling before annealing. The hot dip galvanizing treatment conditions and alloying hot dip galvanizing treatment conditions need not be particularly limited, and may be in accordance with ordinary methods. It is preferable to perform temper rolling for adjusting the surface roughness after the hot dip galvanizing treatment or after the alloying hot dip galvanizing treatment. As described above, a hot-dip galvanized cold-rolled steel sheet or an alloyed hot-dip galvanized cold-rolled steel sheet having excellent shape uniformity after processing can be obtained.
　以下に本発明による効果を具体的に示す。まず、表１に示す成分組成からなる溶鋼を、真空脱ガス処理後、連続鋳造によりスラブとした。次いで、上記スラブを加熱し、スケール除去後、板厚４０ｍｍまで粗圧延した。次いで、スケール除去装置で鋼板表層を冷却した後、３．５ｍｍ厚まで仕上げ圧延し、巻取り温度７００℃でコイルに巻き取った。なお、この時のスラブの加熱条件、仕上げ圧延前の冷却後の鋼板表面温度、仕上げ圧延温度を表２に示す。 The effects of the present invention are specifically shown below. First, molten steel having the composition shown in Table 1 was made into a slab by continuous casting after vacuum degassing treatment. Next, the slab was heated, scale-removed, and then roughly rolled to a plate thickness of 40 mm. Next, the steel sheet surface layer was cooled with a scale removing device, and then finish-rolled to a thickness of 3.5 mm and wound on a coil at a winding temperature of 700 ° C. Table 2 shows the heating conditions of the slab at this time, the steel sheet surface temperature after cooling before finish rolling, and the finish rolling temperature.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
　次いで、巻取り後の鋼板を酸洗後、０．７０ｍｍまで冷間圧延（冷間圧延率：８０％）して供試材とし、前処理として脱脂、酸洗した後、溶融亜鉛めっきラインで焼鈍、溶融亜鉛めっき処理、合金化処理、伸長率１．０％の調質圧延を行い、合金化溶融亜鉛めっき鋼板を得た。また、一部の鋼板については、冷延鋼板の特性を評価するため、焼鈍後、伸長率１．０％の調質圧延のみの処理を行い、冷延鋼板を得た。 Next, after pickling the steel sheet after winding, it is cold-rolled to 0.70 mm (cold rolling rate: 80%) as a test material, degreased and pickled as pretreatment, and then hot-dip galvanized line Annealing, hot-dip galvanizing treatment, alloying treatment, and temper rolling with an elongation of 1.0% were performed to obtain an alloyed hot-dip galvanized steel sheet. Moreover, about some steel plates, in order to evaluate the characteristic of a cold-rolled steel plate, after annealing, only the temper rolling process of the elongation rate 1.0% was performed, and the cold-rolled steel plate was obtained.
　なお、前記焼鈍時の雰囲気は水素を含む非酸化性ガスとし、各供試材の焼鈍温度はＡｃ３変態点以下である８４０℃とした。溶融亜鉛めっき処理は、Ａｌを０．１２％含む４６０℃亜鉛めっき浴を用いて、浸入板温４６０℃、浸漬時間３秒にて行った。合金化処理は、めっき後、Ｎ２ガスワイパーを用いて亜鉛付着量を片面当たり６０ｇ／ｍ２に調整し、５１０℃、２０秒にて行った。 In addition, the atmosphere at the time of the annealing was a non-oxidizing gas containing hydrogen, and the annealing temperature of each test material was 840 ° C. which is lower than the Ac3 transformation point. The hot dip galvanizing treatment was performed using a 460 ° C. zinc plating bath containing 0.12% of Al at an intrusion plate temperature of 460 ° C. and an immersion time of 3 seconds. The alloying treatment was carried out at 510 ° C. for 20 seconds after plating, adjusting the zinc adhesion amount to 60 g / m 2 per side using an N 2 gas wiper.
　上記の製造方法により得られた冷延鋼板および合金化溶融亜鉛鋼板に対して、鋼板両面の表面から１０μｍまでの板厚表層部における大きさ２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量、機械的特性および加工後形状均一性を下記の方法により測定、評価した。また、合金化溶融亜鉛めっき鋼板に対しては、上記に加え、さらに外観も評価した。得られた結果を表３に示す。 For the cold-rolled steel sheet and alloyed hot-dip galvanized steel sheet obtained by the above production method, the content of Ti element contained in precipitates having a size of less than 20 nm in the surface thickness part from the surface of both surfaces of the steel sheet to 10 μm, Mechanical properties and post-processing shape uniformity were measured and evaluated by the following methods. In addition to the above, the appearance was further evaluated for the galvannealed steel sheet. The obtained results are shown in Table 3.
　鋼板両面の表面から１０μｍまでの板厚表層部における大きさ２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量得られた冷延鋼板および合金化溶融亜鉛めっき鋼板について、溶融亜鉛めっき鋼板はめっき層を塩酸で剥離した後、試料寸法が３ｃｍ×４ｃｍとなる大きさに切断し、１０％ＡＡ系電解液（１０ｖｏｌ％アセチルアセトン−１ｍａｓｓ％塩化テトラメチルアンモニウム−メタノール）中で、電流密度２０ｍＡ／ｃｍ２で定電流電解した。電解は、鋼板両面同時に行い、電解厚みは片面あたり表層から１０μｍまでとした。 About the cold-rolled steel sheet and the alloyed hot-dip galvanized steel sheet obtained by the content of Ti element contained in the precipitate having a size of less than 20 nm in the surface layer portion of the plate thickness from 10 μm to both surfaces of the steel sheet, the hot-dip galvanized steel sheet is a plating layer After peeling off with hydrochloric acid, the sample was cut to a size of 3 cm × 4 cm, and the current density was 20 mA / cm 2 in 10% AA electrolyte (10 vol% acetylacetone-1 mass% tetramethylammonium chloride-methanol). And constant current electrolysis. Electrolysis was performed simultaneously on both sides of the steel sheet, and the electrolytic thickness was from the surface layer to 10 μm per side.
　電解後の、表面に析出物が付着している試料片を電解液から取り出して、ヘキサメタリン酸ナトリウム水溶液（５００ｍｇ／ｌ）（以下、ＳＨＭＰ水溶液と称す）中に浸漬し、超音波振動を付与して、析出物を試料片から剥離しＳＨＭＰ水溶液中に抽出した。次いで、析出物を含むＳＨＭＰ水溶液を孔径２０ｎｍのフィルタを用いてろ過し、ろ過後のろ液に対してＩＣＰ発光分光分析装置を用いて分析し、ろ液中のＴｉの絶対量を測定した。次いで、Ｔｉの絶対量を電解重量で除して、大きさ２０ｎｍ未満の析出物に含まれるＴｉの含有量（ｍａｓｓ％）を得た。なお、電解重量は、析出物剥離後の試料に対して重量を測定し、電解前の試料重量から差し引くことで求めた。なお、表３に示す含有量は、上記にて求めた両面の含有量を平均した値である。 After the electrolysis, the sample piece with the deposit attached on the surface is taken out from the electrolytic solution and immersed in an aqueous solution of sodium hexametaphosphate (500 mg / l) (hereinafter referred to as an SHMP aqueous solution) to give ultrasonic vibration. The precipitate was peeled from the sample piece and extracted into an aqueous SHMP solution. Next, the SHMP aqueous solution containing the precipitate was filtered using a filter having a pore diameter of 20 nm, and the filtrate after filtration was analyzed using an ICP emission spectroscopic analyzer, and the absolute amount of Ti in the filtrate was measured. Next, the absolute amount of Ti was divided by the electrolytic weight to obtain the Ti content (mass%) contained in the precipitate having a size of less than 20 nm. In addition, the electrolysis weight was calculated | required by measuring a weight with respect to the sample after deposit peeling, and subtracting from the sample weight before electrolysis. In addition, content shown in Table 3 is the value which averaged content of both surfaces calculated | required above.
　機械的特性
成形性は、引張特性とｒ値の機械的特性により評価した。引張特性は、ＪＩＳＺ　２２０１記載の５号試験片に加工した後、ＪＩＳＺ　２２４１記載の試験方法に従って行った。また平均ｒ値は、１５％の引張予歪を与えた後、３点法にて測定し、鋼板の１方向に対して、９０°方向、４５°方向、０°方向のｒ値の平均＝（ｒ（０°）＋２×ｒ（４５°）＋ｒ（９０°））／４として求めた。 Mechanical properties Formability was evaluated by tensile properties and r-value mechanical properties. Tensile properties were measured according to the test method described in JISZ 2241 after processing into a No. 5 test piece described in JISZ 2201. The average r value was measured by a three-point method after giving a tensile pre-strain of 15%, and the average r value in the 90 ° direction, 45 ° direction, and 0 ° direction with respect to one direction of the steel sheet = It was determined as (r (0 °) + 2 × r (45 °) + r (90 °)) / 4.
　加工後形状均一性
加工後形状均一性評価は、圧延直角方向に伸び率５％の歪みを付与した後、砥石がけを行い、形状不均一を可視化して、不均一の認められるものを×、認められないものを○とした。 Post-working shape uniformity Post-working shape uniformity evaluation is performed by applying a grinding stone after applying a strain of 5% elongation in the direction perpendicular to the rolling, visualizing the shape non-uniformity, Items that were not recognized were marked as ◯.
　めっき後外観
合金化溶融亜鉛めっきを施したものについては、外観ムラの有無を観察し、ムラの生じたものを×、ムラなく均一な外観であったものを○とした。 Appearance of the alloyed hot-dip galvanized after plating was observed for the presence or absence of unevenness in appearance.
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　表３より、成分組成が本発明範囲内で、かつ表面から１０μｍまでの表層部における、大きさ２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量が鋼板中に含有する全Ｔｉ量の９％以下である本発明例は、深絞り性の指標である平均ｒ値が１．５以上であり、加工後の形状均一性に優れ、かつ外観にムラがなく均一で自動車外装板用途に適した性能を有していた。
一方、比較例では、加工後形状均一性、外観が劣り、自動車外装板用途に適した性能を満足しなかった。 From Table 3, the content of the Ti element contained in the precipitate having a component composition within the scope of the present invention and less than 20 nm in the surface layer portion from the surface to 10 μm is 9% of the total amount of Ti contained in the steel sheet. In the following examples of the present invention, the average r value, which is an index of deep drawability, is 1.5 or more, excellent shape uniformity after processing, uniform in appearance, and suitable for automotive exterior board use. Had performance.
On the other hand, in the comparative example, the shape uniformity after processing and the appearance were inferior, and the performance suitable for the automobile exterior plate application was not satisfied.
　また、鋼中のＣｕ量が０．００５％を超えたもので、Ｓｂが含有されていない比較例符号Ａ２、Ｂ２は、大きさ２０ｎｍ未満の析出物に含まれるＴｉ量が増加し、すなわち、微細な析出物が増加し、外観ムラが発生しているのがわかる。比較例符号Ｊ２はＳｂの含有量が適正でないために大きさ２０ｎｍ未満の析出物に含まれるＴｉ量も増加し、外観ムラが発生したものである。一方、Ｓｂを適正に含有している本発明例符号Ｃ２、Ｄ２、Ｅ２、Ｆ２、Ｈ２、Ｉ２は大きさ２０ｎｍ未満の析出物に含まれるＴｉ量が少なく、外観ムラは回避できている。 Further, the amount of Cu in the steel exceeds 0.005%, and the comparative example codes A2 and B2 that do not contain Sb increase the amount of Ti contained in precipitates having a size of less than 20 nm, that is, It can be seen that fine precipitates increase and appearance unevenness occurs. In Comparative Example Code J2, since the Sb content is not appropriate, the amount of Ti contained in the precipitate having a size of less than 20 nm also increases, resulting in appearance irregularities. On the other hand, the present invention example codes C2, D2, E2, F2, H2, and I2, which contain Sb appropriately, have a small amount of Ti contained in precipitates having a size of less than 20 nm, thereby avoiding uneven appearance.
　本発明の鋼板は、自動車の外板を中心に、優れた成形後表面品質を必要とする各種電気機器、自動車などの部品に対して好適に使用できる。 The steel sheet of the present invention can be suitably used for various parts such as automobiles and various electrical equipments that require excellent post-molding surface quality, centering on automobile outer plates.

Claims (5)

  1. 　ｍａｓｓ％で、Ｃ：０．０００５~０．０１％、Ｓｉ：０．２％以下、Ｍｎ：０．１~１．５％、Ｐ：０．０３％以下、Ｓ：０．００５~０．０３％、Ｔｉ：０．０２~０．１％、Ａｌ：０．０１~０．０５％、Ｎ：０．００５％以下、Ｓｂ：０．０３％以下、Ｃｕ：０．００５％超０．０３％以下であり、かつ、Ｔｉ＊＝（Ｔｉ％）−３．４×（Ｎ％）−１．５×（Ｓ％）−４×（Ｃ％）で示されるＴｉ＊を０＜Ｔｉ＊＜０．０２を満たす範囲で、さらに、（Ｓｂ％）≧（Ｃｕ％）／５を満たす範囲で含有し、残部はＦｅおよび不可避的不純物からなる成分組成を有し、鋼板両面において、各表面から１０μｍまでの板厚表層部における大きさ２０ｎｍ未満の析出物に含まれるＴｉ元素の含有量（ｍａｓｓ％）が、鋼板中の全Ｔｉ含有量（ｍａｓｓ％）の９％以下であることを特徴とする冷延鋼板。
    ただし、（Ｔｉ％）、（Ｎ％）、（Ｓ％）、（Ｃ％）、（Ｓｂ％）、（Ｃｕ％）は、それぞれＴｉ、Ｎ、Ｓ、Ｃ、Ｓｂ、Ｃｕの含有量（ｍａｓｓ％）を示す。     In mass%, C: 0.0005 to 0.01%, Si: 0.2% or less, Mn: 0.1 to 1.5%, P: 0.03% or less, S: 0.005 to 0.00. 03%, Ti: 0.02 to 0.1%, Al: 0.01 to 0.05%, N: 0.005% or less, Sb: 0.03% or less, Cu: more than 0.005% And Ti * = (Ti%) − 3.4 × (N%) − 1.5 × (S%) − 4 × (C%), where Ti * is 0 <Ti * <In a range satisfying 0.02, and further in a range satisfying (Sb%) ≧ (Cu%) / 5, and the balance has a component composition composed of Fe and inevitable impurities. The content (mass%) of Ti element contained in precipitates having a size of less than 20 nm in the surface thickness portion of the plate thickness from 1 to 10 μm is the total Ti content (mass%) in the steel sheet. ) 9% or less of a cold-rolled steel sheet.
    However, (Ti%), (N%), (S%), (C%), (Sb%), and (Cu%) are the contents (mass) of Ti, N, S, C, Sb, and Cu, respectively. %).
  2. 　さらに、ｍａｓｓ％で、Ｎｂ：０．００１~０．０１％、Ｂ：０．０００２~０．００１５％のうち、いずれか一種または二種を含有することを特徴とする請求項１に記載の冷延鋼板。 Further, as a mass%, any one or two of Nb: 0.001 to 0.01% and B: 0.0002 to 0.0015% are contained. Cold rolled steel sheet.
  3. 　鋼板表面に亜鉛系めっき層を有することを特徴とする請求項１または２に記載の冷延鋼板。 The cold-rolled steel sheet according to claim 1 or 2, further comprising a zinc-based plating layer on the surface of the steel sheet.
  4. 　請求項１または２に記載の成分を有する鋼を連続鋳造によりスラブとし、該スラブに対して、加熱温度が１０００℃以上１２００℃未満で、かつ１０００℃以上の温度域での加熱時間が３．０時間以下の条件で加熱し、スケール除去および粗圧延を施し、次いで、鋼板表面温度が（Ａｒ３変態点−３００℃）以上Ａｒ３変態点以下の範囲となるよう冷却した後、仕上げ圧延終了時の鋼板表面温度がＡｒ３変態点以上の温度となるように仕上げ圧延し、冷却し、６５０℃以上の温度で巻取り、次いで、酸洗、冷間圧延後、焼鈍を行うことを特徴とする冷延鋼板の製造方法。 The steel having the component according to claim 1 or 2 is made into a slab by continuous casting, and the heating time is 1000 ° C. or more and less than 1200 ° C. and the heating time is 1000 ° C. or more with respect to the slab. Heating is performed under conditions of 0 hours or less, descaling and rough rolling are performed, and then cooling is performed so that the steel sheet surface temperature is in the range of (Ar3 transformation point-300 ° C.) to Ar3 transformation point, and then the finish rolling is finished. Cold rolling characterized in that the steel sheet surface temperature is finish-rolled so as to be a temperature equal to or higher than the Ar3 transformation point, cooled, wound at a temperature of 650 ° C. or higher, and then annealed after pickling and cold rolling. Manufacturing method of steel sheet.
  5. 　前記焼鈍後、さらに、溶融亜鉛めっき処理または合金化溶融亜鉛めっき処理を施すことを特徴とする請求項４に記載の冷延鋼板の製造方法。 The method for producing a cold-rolled steel sheet according to claim 4, wherein after the annealing, a galvanizing treatment or an alloying galvanizing treatment is further performed.
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