WO2016035261A1 - 冷延鋼板、冷延鋼板の製造方法、自動車部材および冷延鋼板の製造設備 - Google Patents
冷延鋼板、冷延鋼板の製造方法、自動車部材および冷延鋼板の製造設備 Download PDFInfo
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- 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
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- C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
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- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
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- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
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- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/081—Iron or steel solutions containing H2SO4
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/085—Iron or steel solutions containing HNO3
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- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/02—Cleaning or pickling metallic material with solutions or molten salts with acid solutions
- C23G1/08—Iron or steel
- C23G1/086—Iron or steel solutions containing HF
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G1/00—Cleaning or pickling metallic material with solutions or molten salts
- C23G1/14—Cleaning or pickling metallic material with solutions or molten salts with alkaline solutions
- C23G1/19—Iron or steel
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- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
- C23G3/00—Apparatus for cleaning or pickling metallic material
- C23G3/02—Apparatus for cleaning or pickling metallic material for cleaning wires, strips, filaments continuously
Definitions
- the present invention relates to a cold-rolled steel sheet and a manufacturing method thereof. Moreover, it is related with the manufacturing equipment of this cold-rolled steel plate.
- the present invention relates to a cold-rolled steel sheet having excellent chemical conversion properties and excellent post-coating corrosion resistance evaluated by a salt warm water immersion test or a combined cycle corrosion test, a manufacturing method thereof, and an automobile member.
- the cold-rolled steel sheet of the present invention can be suitably used as a high-strength cold-rolled steel sheet having a Si-containing tensile strength TS of 590 MPa or more.
- SiO 2 or SiO 2 is present at the interface between the steel sheet surface and the oxide scale during slab heating, hot rolling, or subsequent annealing. It is known that Si-containing oxides such as Si—Mn complex oxides are formed in large quantities. This Si-containing oxide significantly reduces the chemical conversion processability.
- Patent Document 1 discloses that the slab is heated at a temperature of 1200 ° C. or higher during hot rolling, descaled at a high pressure, and the surface of the hot rolled steel plate before pickling.
- Patent Document 2 proposes a high-strength cold-rolled steel sheet in which the corrosion resistance is improved by setting the line width of a linear oxide containing Si observed at 1 to 10 ⁇ m from the steel sheet surface to 300 nm or less. .
- Patent Document 3 proposes a technique for improving the oxide removal ability by setting the iron ion concentration (divalent) in hydrochloric acid to 0.5 to 18%.
- the corrosion resistance does not become a problem in a corrosive environment such as the salt spray test specified in JIS Z2371, but unlike the salt warm water immersion test and the combined cycle corrosion test. In a severe corrosive environment, sufficient post-coating corrosion resistance cannot be obtained.
- a high-strength cold-rolled steel sheet excellent in corrosion resistance after coating cannot be obtained simply by reducing the Si concentration on the surface of the steel sheet after hot rolling or reducing the linear oxide containing Si.
- Patent Document 4 discloses that the Si-containing oxide concentrated on the surface of the steel sheet in an annealing process or the like is removed by pickling and further an S-based compound is added to the surface.
- a technique for improving the chemical conversion treatment performance by increasing the reactivity with the chemical conversion treatment liquid is disclosed.
- Patent Document 5 discloses a technique for providing a P-based compound instead of the S-based compound in Patent Document 4.
- Patent Document 6 as a technique for solving the above problems, pickling with an oxidizing acid is performed at the first stage to remove SiO 2, and pickling with a non-oxidizing acid is performed at the second stage.
- a technique for improving the chemical conversion treatment performance by increasing the reactivity with the chemical conversion treatment liquid by removing the Fe-based oxide formed by the first stage pickling is disclosed.
- Patent Documents 4 and 5 are effective for conventional plain steel sheets, but for high-strength cold-rolled steel sheets containing a large amount of Si, the low temperature of the chemical conversion treatment liquid It is not possible to expect a sufficient improvement effect that can cope with the development.
- Patent Document 6 it is known that the high-temperature cold-rolled steel sheet containing a large amount of Si can cope with the temperature reduction of the chemical conversion treatment liquid. .
- the present invention has been made in view of such circumstances, and an object of the present invention is to provide a cold-rolled steel sheet having excellent chemical conversion properties and excellent corrosion resistance after coating, a manufacturing method thereof, and an automobile member. Furthermore, it aims at providing the manufacturing equipment of this cold-rolled steel plate.
- the inventors conducted a detailed analysis on the steel sheet surface characteristics after annealing, and conducted extensive studies on a method for increasing the reactivity between the steel sheet surface and the chemical conversion treatment liquid.
- the steel sheet surface that has been continuously annealed is strongly pickled, the Si-containing oxide layer formed on the steel sheet surface layer is removed during annealing, and the iron-based oxide that is generated on the steel sheet surface by the strong pickling.
- the present invention has been made based on the above findings, and the gist thereof is as follows.
- a method for producing a cold-rolled steel sheet in which a steel sheet that has been continuously annealed after cold rolling is subjected to a first pickling, then a second pickling, and further a neutralization treatment using an alkaline solution.
- the alkaline solution is an alkaline solution having a pH of 9.5 or more, in which one or any of sodium hydroxide, sodium carbonate, sodium bicarbonate, orthophosphate, and condensed phosphate is mixed.
- the method for producing a cold-rolled steel sheet according to 1].
- [3] The method for producing a cold-rolled steel sheet according to [1] or [2], wherein the neutralization treatment is performed at a temperature of the alkaline solution of 20 to 70 ° C. and a treatment time of 1 to 30 seconds.
- [4] The cold picking according to any one of [1] to [3], wherein the first pickling is performed using any one of nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid and an acid obtained by mixing two or more thereof.
- a method of manufacturing a steel sheet A method of manufacturing a steel sheet.
- [5] The method for producing a cold-rolled steel sheet according to any one of [1] to [4], wherein the first pickling is the acid solution of any one of a) and b) below.
- the non-oxidizing acid is any one of hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, formic acid, acetic acid, citric acid, hydrofluoric acid, oxalic acid, and an acid obtained by mixing two or more of these [6] ]
- the non-oxidizing acid includes hydrochloric acid having a concentration of 0.1 to 50 g / L, 0.1 to 150 g / L sulfuric acid, 0.1 to 20 g / L hydrochloric acid and 0.1 to 60 g / L.
- the steel sheet further includes, as a component composition, C: 0.01 to 0.30 mass%, Mn: 1.0 to 7.5 mass%, P: 0.05 mass% or less, S: 0.01 mass% or less, and The method for producing a cold-rolled steel sheet according to [10], containing Al: 0.06 mass% or less, with the balance being Fe and inevitable impurities.
- the steel sheet further has a component composition of Nb: 0.3 mass% or less, Ti: 0.3 mass% or less, V: 0.3 mass% or less, Mo: 1.0 mass% or less, Cr: 1.0 mass%
- the manufacturing method of the cold rolled steel sheet as described in [11] containing 1 type (s) or 2 or more types chosen from below B: 0.006mass% or less and N: 0.008mass% or less.
- the steel plate is further selected as one of components selected from Ni: 2.0 mass% or less, Cu: 2.0 mass% or less, Ca: 0.1 mass% or less, and REM: 0.1 mass% or less.
- [14] A cold-rolled steel sheet produced by the production method according to any one of [1] to [13], wherein the Si-containing oxide layer on the steel sheet surface layer is removed, and the iron-based steel existing on the steel sheet surface A cold-rolled steel sheet having an oxide surface coverage of 40% or less.
- [17] A cold rolled steel sheet manufacturing facility in which a first pickling device, a second pickling device, an acid neutralization processing device, and a drying device are installed in this order after the continuous annealing device.
- a cold-rolled steel sheet having excellent chemical conversion properties and excellent corrosion resistance after coating can be obtained.
- a cold-rolled steel sheet having good chemical conversion property and good corrosion resistance after coating can be easily obtained through ordinary cold rolling and pickling processes only by adjusting the pickling conditions. And it can manufacture stably.
- FIG. 1 shows a cold rolled steel sheet standard sample No. 1 for determining the surface coverage of the iron-based oxide.
- the reflected-electron image of the steel plate surface of a and b is shown.
- 2 shows a cold rolled steel sheet standard sample No.
- Fig. 5 shows a histogram of the number of pixels against the gray values of the reflected electron image photographs of a and b.
- FIG. 3 is a drawing showing the result of observing a cross section of a steel sheet surface coating after pickling with a non-oxidizing acid with a transmission electron microscope.
- FIG. 4 is a graph showing the result of energy dispersive X-ray (EDX) analysis of the iron-based oxide observed in FIG.
- FIG. 5 is a graph obtained by measuring the depth direction distribution of O, Si, Mn, and Fe on the surface of the test piece in Table 2 by GDS.
- EDX energy dispersive X-ray
- a non-oxidizing or reducing gas is usually used as an atmospheric gas.
- the dew point is strictly controlled. Therefore, the oxidation of the steel plate surface is suppressed in a general cold-rolled steel plate with a small alloy addition amount.
- steel sheets containing 0.5% or more of Si and Mn, Si and Mn, etc. which are more easily oxidized than Fe, even if the atmosphere gas components and dew point during annealing are strictly controlled.
- Si-containing oxides such as Si oxide (SiO 2 ) and Si—Mn based complex oxide on the steel sheet surface.
- the structure of these oxides varies depending on the steel plate component and the annealing atmosphere, but generally the steel plate component and the annealing atmosphere often change together.
- the Si-containing oxide is formed not only on the steel sheet surface but also inside the base iron, it inhibits the etching property of the steel sheet surface in the chemical conversion treatment (zinc phosphate treatment) that is performed as a base treatment for electrodeposition coating.
- the chemical conversion treatment zinc phosphate treatment
- the cold-rolled steel sheet surface after continuous annealing is strongly pickled using nitric acid or the like as the pickling solution, and the Si-containing oxide layer on the steel sheet surface layer formed by continuous annealing after cold rolling is removed.
- the Si-containing oxide is a SiO 2 or Si—Mn based composite oxide formed along the grain boundaries inside the steel sheet surface or inside the steel sheet during annealing after slab heating, hot rolling, or cold rolling.
- the thickness of the layer in which these Si-containing oxides are present varies depending on the steel plate components and annealing conditions (temperature, time, atmosphere), but is usually about 1 ⁇ m from the steel plate surface.
- the removal of the Si-containing oxide layer in the present invention means that pickling is performed to a level at which Si and O peaks do not appear when the steel sheet surface is analyzed in the depth direction by GDS (glow discharge emission spectroscopy). Removing the Si-containing oxide layer.
- strong pickling is performed as the first pickling to suppress the formation of iron-based oxides on the steel sheet surface and to remove the Si-containing oxide layer present on the steel sheet surface.
- pickling is performed using a non-oxidizing acid as the second pickling so that the surface coverage of the iron-based oxide existing on the steel sheet surface is 40% or less.
- neutralization treatment is performed with an alkaline solution.
- the inventors set the coverage of the iron-based oxide formed on the steel plate surface by pickling to 40% or less, and when the maximum thickness of the iron-based oxide is 150 nm or less, The processability is further improved and the corrosion resistance is further improved.
- pickling conditions concentration, temperature, time
- non-oxidizing pickling conditions acid concentration, temperature, time
- the iron-based oxide in the present invention refers to an iron-based oxide having an atomic concentration ratio of iron of 30% or more among elements other than oxygen constituting the oxide.
- This iron-based oxide is present in a non-uniform thickness on the surface of the steel sheet, and is an oxide different from a natural oxide film that is uniform and layered with a thickness of several nm.
- the iron-based oxides formed on the surface of this cold-rolled steel sheet are found to be amorphous from observations with a transmission electron microscope (TEM) and analysis of diffraction patterns (diffraction patterns) by electron beam diffraction. ing.
- TEM transmission electron microscope
- a steel material (slab) containing 0.5 to 3.0% of Si is heated, hot-rolled, cold-rolled and continuously annealed, and the first pickling is performed.
- the first pickling is performed.
- a second pickling and further neutralization using an alkaline solution.
- the first pickling it is preferable to strongly pickle the cold-rolled steel sheet after annealing using an acid solution containing nitric acid and hydrochloric acid or an acid solution containing nitric acid and hydrofluoric acid. .
- the Si-containing oxide layer on the steel sheet surface is removed together with the base iron.
- Si-containing oxides Si—Mn-based composite oxides are easily dissolved in acid, but SiO 2 is hardly soluble in acid. Therefore, in order to remove the Si-containing oxide including SiO 2 , it is necessary to remove the oxide layer together with the base iron of the steel plate by strong pickling. Therefore, in the present invention, nitric acid, which is a strong oxidizing acid, can be suitably used as the acid that can be used for the acid solution, and if the Si-containing oxide layer can be removed, hydrofluoric acid, hydrochloric acid, Sulfuric acid or the like may be used, and the type of acid is not particularly limited. Furthermore, you may use the acid which mixed these 2 or more types. It is also effective to promote the dissolution of the base iron by adding a pickling accelerator to the acid solution or using an electrolytic treatment in combination.
- Fe dissolved from the steel sheet surface by pickling may produce iron-based oxides, which may precipitate on the steel sheet surface and cover the steel sheet surface, thereby reducing chemical conversion properties.
- the nitric acid concentration is in the range of 50 g / L to 200 g / L, and further, hydrochloric acid having an oxide film destruction effect is added. It contains nitric acid and hydrochloric acid so that the ratio of hydrochloric acid concentration to nitric acid concentration R1 (hydrochloric acid / nitric acid) is in the range of 0.01 to 0.25, and the Fe ion concentration (sum of divalent and trivalent) is 3 to 50 g. / L is preferable.
- the nitric acid concentration is 100 g / L or more and 200 g / L or less. More preferably, R1 is 0.02 to 0.15. More preferably, the Fe ion concentration is 3 to 25 g / L.
- the nitric acid concentration is set in the range of 50 g / L to 200 g / L, and the hydrofluoric acid having an effect of destroying the oxide film is converted into a ratio R2 ( Nitric acid and hydrofluoric acid are contained so that the hydrofluoric acid / nitric acid ratio is in the range of 0.01 to 0.25, and the Fe ion concentration (the sum of divalent and trivalent) is in the range of 3 to 50 g / L.
- the nitric acid concentration is 100 g / L or more and 200 g / L or less. More preferably, R2 is 0.02 to 0.15. More preferably, the Fe ion concentration is 3 to 25 g / L.
- R1 and R2 are greater than 0.25 or the Fe ion concentration (the sum of divalent and trivalent) is less than 3 g / L, the desired pickling speed cannot be obtained and the Si-containing oxide is efficiently removed. I can't.
- R1 and R2 are less than 0.01 or the Fe ion concentration is greater than 50 g / L, a desired pickling rate can be obtained, but since there are many Fe ions in the pickling solution, Fe on the steel plate surface.
- the maximum thickness of the iron-based oxide can be made 150 nm or less.
- the maximum thickness of the iron-based oxide becomes 150 nm or less, and the chemical conversion treatment property is further improved. Corrosion resistance is also improved.
- Second pickling conditions It is difficult to stably control the surface coverage of the iron-based oxide formed on the steel sheet surface to 40% or less simply by performing strong pickling as the first pickling. Therefore, in the present invention, the second pickling is performed in order to more reliably reduce the iron-based oxide generated on the steel sheet surface by the first pickling.
- pickling is preferably performed using an acid solution made of a non-oxidizing acid, and the iron-based oxide is dissolved and removed by the second pickling.
- hydrochloric acid As the non-oxidizing acid, one or more of hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, formic acid, acetic acid, citric acid, hydrofluoric acid, and oxalic acid are preferable. Any of them may be used, but any hydrochloric acid or sulfuric acid generally used in the steel industry can be preferably used.
- hydrochloric acid is a volatile acid, so that it is difficult for residues such as sulfate radicals to remain on the surface of the steel sheet after washing like sulfuric acid, and because the oxide destruction effect by chloride ions is large, It can be used suitably.
- the concentration is 0.1 to 50 g / L hydrochloric acid, 0.1 to 150 g / L sulfuric acid, 0.1 It is preferable to use any acid obtained by mixing ⁇ 20 g / L hydrochloric acid and 0.1 to 60 g / L sulfuric acid.
- the temperature of the acid solution is 20 to 70 ° C. and the pickling time is 1 to 30 seconds. If the temperature of the pickling solution is 20 ° C. or higher and the treatment time is 1 second or longer, it is sufficient to remove the iron-based oxide remaining on the steel sheet surface. On the other hand, if the temperature of the pickling solution is 70 ° C. or less and the treatment time is 30 seconds or less, the surface of the steel sheet is not excessively dissolved and a new surface oxide film is not generated. More preferably, the temperature of the acid solution is 30 to 50 ° C. More preferably, the pickling time is 2 to 20 seconds.
- the concentration of the acid solution made of an oxidizing acid is increased appropriately.
- the hydrochloric acid concentration is preferably 3 to 50 g / L
- sulfuric acid concentration is preferably 8 to 150 g / L.
- a pickling solution in which hydrochloric acid and sulfuric acid are mixed it is preferable to use an acid in which hydrochloric acid having a concentration of 3 to 20 g / L and sulfuric acid having a concentration of 8 to 60 g / L are mixed. If it is the said density
- Neutralization Treatment Conditions The present invention is characterized in that after the second pickling, neutralization treatment is further performed using an alkaline solution.
- the neutralization treatment performed after pickling and re- pickling was performed by mixing one kind or two or more kinds of sodium hydroxide, sodium carbonate, sodium bicarbonate, orthophosphate, and condensed phosphate.
- the neutralization treatment is preferably performed using an alkaline solution having a pH of 9.5 or higher. The reason for using the alkaline solution is to neutralize and remove the residue of the pickling solution. If the pH is less than 9.5, the pickling solution residue cannot be completely neutralized.
- the condensed phosphate include sodium pyrophosphate and sodium polyphosphate.
- the pH is more preferably pH 10.0 to 12.0.
- the temperature of the alkaline solution is set at 20 to 70 ° C. for 1 to 30 seconds.
- the liquid temperature of the alkaline solution is 20 ° C. or higher and the treatment time is 1 second or longer, the residue of the pickling solution is sufficiently neutralized.
- the temperature of the pickling solution is higher than 70 ° C., alkali fume is generated, and when the treatment time is longer than 30 seconds, the equipment length becomes long and enormous equipment costs are required.
- the temperature of the alkaline solution is 30 to 50 ° C. More preferably, the processing time is 2 to 20 seconds.
- the first pickling and the second pickling are performed, and further neutralization is performed using an alkaline solution, and then the product plate is subjected to normal processing steps such as temper rolling. (Cold rolled steel sheet).
- the pickling method that is, the contact method with the acid solution described in the present invention is not particularly limited.
- a method of spraying an acid solution or a method of immersing in an acid solution can be considered.
- the first pickling and the second pickling are preferable to perform continuously. By performing continuously, it can prevent that a steel plate naturally oxidizes after the first pickling, and can be made into a final product at a time, and can be manufactured at low cost.
- a water washing treatment may be performed after the first pickling, after the second pickling, and after the neutralization treatment. Further, when performing the first pickling, the second pickling, the neutralization treatment, and the water washing treatment, further water washing may be performed by water washing spray on the entry side and / or the exit side of the treatment. Moreover, it is preferable to perform a drying process with a drier etc. after the water washing process.
- a component composition that has high strength that can be used for automobile underbody members and the like, and that also has good chemical conversion treatment properties.
- Si is an effective element for achieving high strength of steel because it has a large effect on enhancing the strength of steel without significantly reducing the workability (solid solution strengthening ability). It is also an element that adversely affects For the above reasons, addition of 0.5% or more is preferable. On the other hand, if the Si content exceeds 3.0%, the hot rollability and the cold rollability are greatly lowered, which may adversely affect the productivity and may cause the ductility of the steel sheet itself to be lowered. . Therefore, when added, Si is preferably in the range of 0.5 to 3.0%. More preferably, it is in the range of 0.8 to 2.5%.
- Components other than the above can be allowed as long as they are in the composition range of a normal cold-rolled steel sheet.
- a suitable component composition other than the above as follows. .
- C 0.01 to 0.30%
- C is an element effective for increasing the strength of steel, and is also an element effective for generating retained austenite, bainite and martensite having a TRIP (Transformation Induced Plasticity) effect. is there. If C is 0.01% or more, the above-described effect can be obtained. On the other hand, if C is 0.30% or less, the weldability does not deteriorate. Therefore, C is preferably added in the range of 0.01 to 0.30%, and more preferably in the range of 0.10 to 0.20%.
- Mn 1.0 to 7.5%
- Mn is an element having an effect of enhancing the hardenability by solid solution strengthening of steel, enhancing hardenability, and promoting the formation of retained austenite, bainite, and martensite. Such an effect is manifested when 1.0% or more is added. On the other hand, if Mn is 7.5% or less, the above effect can be obtained without causing an increase in cost. Therefore, Mn is preferably added in the range of 1.0 to 7.5%, more preferably in the range of 2.0 to 5.0%.
- P 0.05% or less
- P is an element that does not impair the drawability for a large solid solution strengthening ability, and is an element effective for achieving high strength, so 0.005% or more must be contained. Is preferred. However, although P is an element which impairs spot weldability, if it is 0.05% or less, a problem will not arise. Therefore, P is preferably 0.05% or less, and more preferably 0.02% or less.
- S 0.01% or less
- S is an impurity element inevitably mixed in, and is a harmful component that precipitates as MnS in the steel and lowers the stretch flangeability of the steel sheet.
- S is preferably 0.01% or less. More preferably, it is 0.005% or less, More preferably, it is 0.003% or less.
- Al 0.06% or less
- Al is an element added as a deoxidizer in the steelmaking process, and is an element effective for separating non-metallic inclusions that reduce stretch flangeability as slag. It is preferable to contain 0.01% or more. If Al is 0.06% or less, the above effects can be obtained without increasing the raw material cost. Therefore, Al is preferably 0.06% or less. More preferably, it is in the range of 0.02 to 0.06%.
- the cold-rolled steel sheet of the present invention further includes Nb: 0.3% or less, Ti: 0.3% or less, V: 0.3% or less, Mo: 1.0% or less, One or two or more selected from Cr: 1.0% or less, B: 0.006% or less, and N: 0.008% or less can be contained.
- Nb, Ti and V are elements that form carbides and nitrides, suppress the growth of ferrite in the heating stage during annealing, refine the structure, and improve formability, particularly stretch flangeability.
- Mo, Cr and B are elements that improve the hardenability of the steel and promote the formation of bainite and martensite, and therefore can be added in the above range.
- N is an element that forms nitrides with Nb, Ti, and V or contributes to increasing the strength of the steel by forming a solid solution in the steel. If it is 0.008 mass% or less, a large amount of nitride is present. Since it is not formed, breakage due to void formation during press molding is suppressed, and the above effect can be obtained.
- the cold-rolled steel sheet of the present invention further includes Ni: 2.0% or less, Cu: 2.0% or less, Ca: 0.1% or less, and REM: 0.1% or less. One or more selected from among them can be contained.
- Ni and Cu have the effect of promoting the formation of a low temperature transformation phase and increasing the strength of the steel, so they can be added in the above range.
- Ca and REM are elements that control the form of sulfide inclusions and improve the stretch flangeability of the steel sheet, and therefore can be added in the above range.
- the balance other than the above components is Fe and inevitable impurities.
- addition of other components is not rejected as long as the effects of the present invention are not impaired.
- the cold-rolled steel sheet of the present invention has a steel sheet surface from which a Si-containing oxide layer such as SiO 2 or Si—Mn-based composite oxide formed on the steel sheet surface layer during annealing is removed. For that purpose, it is necessary to neutralize with an alkaline solution after the first and second pickling.
- a Si-containing oxide layer such as SiO 2 or Si—Mn-based composite oxide formed on the steel sheet surface layer during annealing is removed.
- the cold-rolled steel sheet according to the present invention needs to reduce the surface coverage of the iron-based oxide existing on the steel sheet surface and reduce it to 40% or less. . If it exceeds 40%, the dissolution reaction of iron in the chemical conversion treatment is inhibited, and the growth of chemical crystals such as zinc phosphate is suppressed.
- a coating of 40% or less is required in the case of using a chemical conversion treatment liquid whose temperature has been lowered. The rate is not sufficient and needs to be reduced to 35% or less, which is even lower. Preferably it is 35% or less.
- the surface coverage of the iron-based oxide is determined as follows. Using a scanning electron microscope (ULV-SEM) with ultra-low acceleration voltage that can detect extremely surface layer information, the steel plate surface after pickling is observed at an acceleration voltage of 2 kV, an operating distance of 3.0 mm, and a magnification of about 1000 times to observe about 5 fields of view. Then, spectral analysis is performed using an energy dispersive X-ray spectrometer (EDX) to obtain a reflected electron image. This reflected electron image is binarized using image analysis software, for example, Image J, the area ratio of the black portion is measured, and the surface coverage of the iron-based oxide is obtained by averaging the measured values of each field of view. Can be obtained.
- image analysis software for example, Image J
- Image J the area ratio of the black portion is measured
- the surface coverage of the iron-based oxide is obtained by averaging the measured values of each field of view. Can be obtained.
- the ultra-low acceleration voltage scanning electron microscope (ULV-SEM) is, for example, manufactured by SEISS; ULTRA 55, and the energy dispersive X-ray spectrometer (EDX) is, for example, manufactured by Thermo Fisher NSS 312E may be mentioned.
- the steel slabs of steel code G shown in Table 3 of Examples described later are the same as No. 1 of Table 4 of Examples described later.
- 93 hot-rolled, cold-rolled, continuously annealed to obtain a cold-rolled steel sheet having a thickness of 1.8 mm, and then the cold-rolled steel sheet after the continuous annealing is shown in Table 1. Then, after pickling, washing with water, and drying, temper rolling with an elongation of 0.7% is performed, and the amount of iron-based oxide on the steel sheet surface is different. Two types of cold-rolled steel sheets a and b were obtained. Then, the above No.
- the cold rolled steel sheet a is a standard sample with a lot of iron-based oxides, No.
- the cold rolled steel sheet b was used as a standard sample with a small amount of iron-based oxides, and a reflected electron image was obtained for each steel sheet using the scanning electron microscope under the conditions described above.
- FIG. The reflection electron image photograph of the steel plates a and b is shown in FIG.
- the histogram of the pixel number with respect to the gray value of the said reflection electron image photograph of the steel plate of a and b is shown.
- the gray value (Y point) corresponding to the intersection (X point) of the histograms a and b was determined as the threshold value.
- No. When the surface coverage of the iron-based oxide of the steel plates a and b was determined, No.
- the steel sheet of a is 85.3%, No.
- the steel sheet for b was 25.8%.
- an iron-based The maximum thickness of the oxide is preferably 150 nm or less. If the maximum thickness of the iron-based oxide is 150 nm or less, the dissolution reaction of iron in the chemical conversion treatment is not locally inhibited, and precipitation of chemical crystals such as zinc phosphate is not locally suppressed. is there. More preferably, it is 130 nm or less.
- the maximum thickness of the iron-based oxide is obtained as follows.
- FIG. 3 shows a photograph of a cross-section of the coating layer generated by the first pickling existing on the steel plate surface
- FIG. 4 shows the EDX analysis result of the coating layer. Show. Since FIG.
- the coating layer is an iron-based oxide
- the line A indicating the steel plate steel shown in the cross-sectional photograph of FIG. 3
- the line B indicating the thickest part of the iron-based oxide layer are shown.
- the interval is measured for all 10 replicas, and the maximum thickness among them is taken as the maximum thickness of the iron-based oxide.
- the size and number of replicas, the measurement conditions by TEM, and the like are merely examples, and it is needless to say that the replicas may be changed as appropriate.
- the cold-rolled steel sheet obtained by the above is excellent in chemical conversion treatment property and excellent in post-painting corrosion resistance evaluated by a salt warm water immersion test or a combined cycle corrosion test, it can be suitably used as an automobile member.
- these hot-rolled steel sheets were pickled, scales were removed, and then cold-rolled to obtain cold-rolled steel sheets having a thickness of 1.8 mm.
- these cold-rolled steel sheets are heated to a soaking temperature of 750 to 780 ° C., held for 40 to 50 seconds, and then from a soaking temperature to a cooling stop temperature of 350 to 400 ° C. at 20 to 30 ° C./sec.
- Table 2-1 to Table 2-2 (hereinafter, Table 2-1 and Table 2-2 are collectively referred to as Table 2)
- Table 2 The steel sheet surface was pickled, washed with water and dried under the conditions shown in Table 2) and subjected to temper rolling with an elongation of 0.7%. 1 to 82 cold-rolled steel sheets were obtained.
- Specimens were taken from each of the above-mentioned cold-rolled steel sheets, and the surface of the steel sheet was accelerated at an acceleration voltage of 2 kV and a working distance of 3.0 mm using an ultra-low acceleration voltage scanning electron microscope (ULV-SEM; manufactured by SEISS; ULTRA55). Then, 5 fields of view were observed at a magnification of 1000 times, and a reflection electron image was obtained by spectroscopic analysis using an energy dispersive X-ray spectrometer (EDX; manufactured by Thermo Fisher Co., Ltd .; NSS312E). This reflected electron image was obtained by using the image analysis software (Image J) and the standard sample No. described above.
- EDX energy dispersive X-ray spectrometer
- the gray value (Y point) corresponding to the intersection (X point) of the histograms a and b is set as a threshold value, binarization processing is performed, the area ratio of the black part is measured, the average value of the five visual fields is obtained, and iron The surface coverage of the system oxide was used.
- test piece was extract
- the steel sheet of the inventive example pickled under conditions suitable for the present invention after continuous annealing is suppressed in the occurrence of spot rust, and is the maximum in any of the salt warm water immersion test, salt spray test and combined cycle corrosion test. It can be seen that the total width of peeling is small, indicating good chemical conversion property and post-coating corrosion resistance. In particular, it can be seen that all of the cold-rolled steel sheets having an iron-based oxide surface coverage of 40% or less are excellent in post-painting corrosion resistance in a harsh corrosive environment.
- FIG. 5 shows the profile in the depth direction of O, Si, Mn, and Fe when surface analysis was performed by GDS for the test piece of No. 7.
- Steels A to O having the composition shown in Table 3 were melted by a normal scouring process through a converter, degassing treatment, etc., and continuously cast into a steel slab. These steel slabs are hot-rolled under the hot rolling conditions shown in Table 4 to form hot-rolled steel sheets with a thickness of 3 to 4 mm, pickled to remove the scale on the steel sheet surface, and then cold-rolled to obtain a plate thickness. A 1.8 mm cold-rolled steel sheet was used. Then, these cold-rolled steel sheets were subjected to the first and second pickling under the conditions shown in Table 5 after continuous annealing under the conditions shown in Table 4, and then washed with water, neutralized, and washed with water. It was dried and subjected to temper rolling with an elongation of 0.7%. 84 to 107 cold-rolled steel sheets were obtained.
- a specimen was collected from each of the cold-rolled steel sheets thus obtained, and after measuring the surface coverage of the iron-based oxide on the steel sheet surface after pickling in the same manner as in Example 1, the following tensile test was performed. And subjected to a corrosion resistance test after painting. Moreover, the depth direction distribution of O, Si, Mn, and Fe on the surface of the test piece extract
- (1) Mechanical properties Using a JIS No. 5 tensile specimen (n 1) specified in JIS Z2201: 1998 taken from the direction perpendicular to the rolling direction (C direction), tension is applied in accordance with the provisions of JIS Z2241: 1998. A test was performed and the tensile strength TS was measured.
- the surface coverage by iron-based oxides on the steel sheet surface containing Si of 0.5% or more and pickling twice under conditions suitable for the present invention and neutralized was made 40% or less. It can be seen that the high-strength cold-rolled steel sheet of the example of the present invention not only has excellent chemical conversion properties and post-coating corrosion resistance, but also has a high strength with a tensile strength TS of 590 MPa or more. In addition, as a result of measuring the depth direction distribution of O, Si, Mn and Fe by GDS, none of the steel plates pickled under conditions suitable for the present invention show Si or O peaks, and Si-containing oxidation It was confirmed that the material layer was sufficiently removed.
- these cold-rolled steel sheets are heated to a soaking temperature of 750 to 780 ° C. and held for 40 to 50 seconds, and then, from the soaking temperature to a cooling stop temperature of 350 to 400 ° C., 20 to 30 ° C./sec. And then subjected to continuous annealing for 100 to 120 seconds within the above-mentioned cooling stop temperature range, and then Table 6-1 to Table 6-2 (hereinafter, Table 6-1 and Table 6-2 are collectively shown in Table 6).
- the surface of the steel sheet is subjected to the first and second pickling under the conditions shown in FIG. 2), then washed with water, neutralized, washed with water, dried, and then subjected to temper rolling with an elongation of 0.7%. No.
- test pieces were collected from each of the cold-rolled steel sheets, and the surface coverage and the maximum thickness of the iron-based oxide produced on the steel sheet surface by pickling were measured using the above-described method.
- Samples were taken from each of the above cold-rolled steel sheets, subjected to spot rust generation evaluation during cold-rolled steel sheet storage under the following conditions, and subjected to a chemical conversion treatment and a coating treatment, followed by a salt warm water immersion test, a salt spray test, and a composite It was subjected to three kinds of corrosion tests of the cycle corrosion test to evaluate the corrosion resistance after painting. Moreover, the depth direction distribution of O, Si, Mn, and Fe on the surface of the test piece extract
- the steel plate surface after annealing was acidified under the conditions that the surface coverage of the iron-based oxide on the steel plate surface after re-acid washing was 40% or less and the maximum thickness of the iron-based oxide was 150 nm or less.
- the washed steel plate of the present invention has a long maximum test width compared to Example 1 and is extremely good in all of the salt warm water immersion test, salt spray test and combined cycle corrosion test conducted under severe conditions. It can be seen that it shows excellent corrosion resistance after painting.
- none of the steel plates pickled under conditions suitable for the present invention show Si or O peaks, and Si-containing oxidation It was confirmed that the material layer was sufficiently removed.
- the cold-rolled steel sheet produced according to the present invention is not only excellent in chemical conversion treatment and post-coating corrosion resistance, but can also have high strength, and is similar in fields such as home appliances and architecture in addition to materials for automobile parts. It can also be suitably used as a material for members that require characteristics.
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Abstract
Description
[1]冷間圧延後連続焼鈍した鋼板に対して、一回目の酸洗を行い、次いで、二回目の酸洗を行い、さらにアルカリ性溶液を用いて中和処理を行う冷延鋼板の製造方法。
[2]前記アルカリ性溶液が、水酸化ナトリウム、炭酸ナトリウム、炭酸水素ナトリウム、オルトリン酸塩、縮合リン酸塩の1種又はいずれか2種以上を混合した、pH9.5以上のアルカリ性溶液である[1]に記載の冷延鋼板の製造方法。
[3]前記中和処理は、前記アルカリ性溶液の温度が20~70℃、処理時間が1~30秒である[1]または[2]に記載の冷延鋼板の製造方法。
[4]前記一回目の酸洗は、硝酸、塩酸、弗酸、硫酸およびそれらを2種以上混合した酸のいずれかを用いて行う[1]~[3]のいずれかに記載の冷延鋼板の製造方法。
[5]前記一回目の酸洗は、下記ア)またはイ)のいずれかの酸液である[1]~[4]のいずれかに記載の冷延鋼板の製造方法。
ア)硝酸と塩酸を含有した酸液であり、前記硝酸濃度が50g/L超え200g/L以下、前記硝酸濃度に対する前記塩酸濃度の比R1(塩酸/硝酸)が0.01~0.25、さらにはFeイオン濃度が3~50g/Lである酸液
イ)硝酸と弗酸を含有した酸液であり、前記硝酸濃度が50g/L超え200g/L以下、前記硝酸濃度に対する前記弗酸濃度の比R2(弗酸/硝酸)が0.01~0.25、さらにはFeイオン濃度が3~50g/Lである酸液
[6]前記二回目の酸洗には、非酸化性の酸を用いる[1]~[5]のいずれかに記載の冷延鋼板の製造方法。
[7]前記非酸化性の酸は、塩酸、硫酸、リン酸、ピロリン酸、ギ酸、酢酸、クエン酸、弗酸、シュウ酸およびこれらの2種以上を混合した酸のいずれかである[6]に記載の冷延鋼板の製造方法。
[8]前記非酸化性の酸は、濃度が0.1~50g/Lの塩酸、0.1~150g/Lの硫酸、0.1~20g/Lの塩酸と0.1~60g/Lの硫酸とを混合した酸のいずれかである[6]または[7]に記載の冷延鋼板の製造方法。
[9]前記二回目の酸洗は、酸液の温度が20~70℃、酸洗時間が1~30秒である[1]~[8]のいずれかに記載の冷延鋼板の製造方法。
[10]前記鋼板は、成分組成として、Siを0.5~3.0mass%含有する[1]~[9]のいずれかに記載の冷延鋼板の製造方法。
[11]前記鋼板は、さらに成分組成として、C:0.01~0.30mass%、Mn:1.0~7.5mass%、P:0.05mass%以下、S:0.01mass%以下およびAl:0.06mass%以下を含有し、残部がFeおよび不可避的不純物からなる[10]に記載の冷延鋼板の製造方法。
[12]前記鋼板は、さらに成分組成として、Nb:0.3mass%以下、Ti:0.3mass%以下、V:0.3mass%以下、Mo:1.0mass%以下、Cr:1.0mass%以下、B:0.006mass%以下およびN:0.008mass%以下のうちから選ばれる1種または2種以上を含有する[11]に記載の冷延鋼板の製造方法。
[13]前記鋼板は、さらに成分組成として、Ni:2.0mass%以下、Cu:2.0mass%以下、Ca:0.1mass%以下およびREM:0.1mass%以下のうちから選ばれる1種または2種以上を含有する[11]または[12]に記載の冷延鋼板の製造方法。
[14][1]~[13]のいずれかに記載の製造方法により製造される冷延鋼板であって、鋼板表層のSi含有酸化物層が除去され、かつ、鋼板表面に存在する鉄系酸化物の表面被覆率が40%以下である冷延鋼板。
[15]前記冷延鋼板は、鋼板表面に存在する鉄系酸化物の最大厚さが150nm以下である[14]に記載の冷延鋼板。
[16][14]または[15]に記載の冷延鋼板を用いる自動車部材。
[17]連続焼鈍装置の後段に、第一の酸洗装置と、第二の酸洗装置と、酸中和処理装置と、乾燥装置とをこの順で設置する冷延鋼板の製造設備。
[18]前記第一の酸洗装置、前記第二の酸洗装置および前記酸中和処理装置の後段に、水洗装置を設置する[17]に記載の冷延鋼板の製造設備。
[19]前記第一の酸洗装置、前記第二の酸洗装置、前記酸中和処理装置、前記水洗装置のいずれか1つ以上の装置の入側および/または出側に、水洗スプレー装置を設置する[17]または[18]に記載の冷延鋼板の製造設備。
連続焼鈍後の鋼板表層には、SiO2やSi-Mn系複合酸化物等のSi含有酸化物が多量に生成されており、このままでは化成処理性や塗装後耐食性が著しく低下する。そこで、本発明の製造方法では、一回目の酸洗として、硝酸と塩酸を含有した酸液もしくは硝酸と弗酸を含有した酸液を用いて焼鈍後の冷延鋼板を強酸洗することが好ましい。一回目の酸洗により、鋼板表面のSi含有酸化物層を地鉄ごと除去する。
Si含有酸化物のうち、Si-Mn系複合酸化物は酸に容易に溶解するが、SiO2は酸に対して難溶性を示す。したがって、SiO2を含めてSi含有酸化物を除去するには、強酸洗して鋼板の地鉄ごと酸化物層を取り除く必要がある。よって、本発明では、酸液に用いることができる酸として、強酸化性の酸である硝酸を好適に用いることができ、また、Si含有酸化物層を除去することができれば弗酸や塩酸、硫酸等でもよく、酸の種類は特に問わない。更には、これらの2種以上を混合した酸を使用しても良い。また、酸液に酸洗促進剤を添加したり、電解処理を併用したりして地鉄の溶解を促進することも有効である。
なお、Feイオン濃度(2価と3価の和)を3~50g/Lに維持する方法としては、50g/Lを超えた場合は希釈し、硝酸及び塩酸を追加で投入する、もしくは、鉄除去装置にて酸中の鉄分を低減する方法などがある。
一回目の酸洗として強酸洗するだけでは、鋼板表面に生成する鉄系酸化物の表面被覆率を安定して40%以下に制御することは難しい。そこで、本発明では、上記一回目の酸洗によって鋼板表面に生成した鉄系酸化物をより確実に低減するために、二回目の酸洗を行う。本発明では、非酸化性の酸からなる酸液を用いて酸洗を行うことが好ましく、二回目の酸洗により、鉄系酸化物を溶解・除去する。
本発明では、二回目の酸洗後、さらにアルカリ性溶液を用いて中和処理を行うことを特徴とする。
Cは、鋼を高強度化するのに有効な元素であり、さらに、TRIP(変態誘起塑性:Transformation Induced Plasticity)効果を有する残留オーステナイトや、ベイナイト、マルテンサイトを生成させるのにも有効な元素である。Cが0.01%以上であれば上記効果が得られ、一方、Cが0.30%以下であれば、溶接性の低下が生じない。よって、Cは0.01~0.30%の範囲で添加するのが好ましく、0.10~0.20%の範囲で添加するのがより好ましい。
Mnは、鋼を固溶強化して高強度化するとともに、焼入性を高め、残留オーステナイトやベイナイト、マルテンサイトの生成を促進する作用を有する元素である。このような効果は、1.0%以上の添加で発現する。一方、Mnが7.5%以下であれば、コストの上昇を招かずに上記効果が得られる。よって、Mnは1.0~7.5%の範囲で添加するのが好ましく、2.0~5.0%の範囲で添加するのがより好ましい。
Pは、固溶強化能の大きい割に絞り性を害さない元素であり、高強度化を達成するのに有効な元素であるため、0.005%以上含有させることが好ましい。ただし、Pは、スポット溶接性を害する元素であるが、0.05%以下であれば問題は生じない。よって、Pは0.05%以下が好ましく、0.02%以下とするのがより好ましい。
Sは、不可避的に混入してくる不純物元素であり、鋼中にMnSとして析出し、鋼板の伸びフランジ性を低下させる有害な成分である。伸びフランジ性を低下させないためには、Sは0.01%以下が好ましい。より好ましくは0.005%以下、さらに好ましくは0.003%以下である。
Alは、製鋼工程で脱酸剤として添加される元素であり、また、伸びフランジ性を低下させる非金属介在物をスラグとして分離するのに有効な元素であるので、0.01%以上含有させるのが好ましい。Alが0.06%以下であれば、原料コストの上昇を招かず、上記効果を得ることができる。よって、Alは0.06%以下とするのが好ましい。より好ましくは0.02~0.06%の範囲である。
前述したように、本発明の冷延鋼板は、焼鈍時に鋼板表層に形成されるSiO2やSi-Mn系複合酸化物等のSi含有酸化物層を除去した鋼板表面を有するものである。そのためには、一回目および二回目の酸洗後、アルカリ性溶液を用いて中和処理することが必要である。
極表層情報を検出できる極低加速電圧の走査型電子顕微鏡(ULV-SEM)を用いて酸洗後の鋼板表面を加速電圧2kV、作動距離3.0mm、倍率1000倍程度で5視野程度を観察し、エネルギー分散型X線分光器(EDX)を用いて分光分析し、反射電子像を得る。この反射電子像を画像解析ソフト、例えば、Image Jを用いて2値化処理して黒色部の面積率を測定し、各視野の測定値を平均化することで鉄系酸化物の表面被覆率を得ることができる。なお、上記極低加速電圧の走査型電子顕微鏡(ULV-SEM)としては、例えば、SEISS社製;ULTRA55を、また、エネルギー分散型X線分光器(EDX)としては、例えば、Thermo Fisher社製;NSS312Eを挙げることができる。
(1)冷延鋼板保管時の点錆発生評価
上記各冷延鋼板に防錆油を塗布した後、ほこりなど外部要因の影響がないように屋外に放置し約1ヶ月後の点錆発生の有無を調査し、点錆なしを「○」、点錆ありを「×」とした。
(2)化成処理条件
上記各冷延鋼板から採取した試験片に、日本パーカライジング(株)製の脱脂剤:FC-E2011、表面調整剤:PL-Xおよび化成処理剤:パルボンドPB-L3065を用いて、下記の標準条件および化成処理液の温度を下げて低温度化した比較条件の2条件で、化成処理皮膜付着量が1.7~3.0g/m2となるよう化成処理を施した。
<標準条件>
・脱脂工程:処理温度 40°C、処理時間 120秒
・スプレー脱脂、表面調整工程:pH 9.5、処理温度 室温、処理時間 20秒
・化成処理工程:化成処理液の温度 35℃、処理時間 120秒
<低温度化条件>
上記標準条件における化成処理液の温度を33℃に低下した条件
(3)腐食試験
上記化成処理を施した試験片の表面に、日本ペイント(株)製の電着塗料:V-50を用いて、膜厚が25μmとなるように電着塗装を施し、下記3種類の腐食試験に供した。
<塩温水浸漬試験>
化成処理および電着塗装を施した上記試験片(n=1、「n=1」とは試験片の本数が1本ということを意味する。)の表面に、カッターで長さ45mmのクロスカット疵を付与した後、この試験片を、5mass%NaCl溶液(60℃)に360時間浸漬し、その後、水洗し、乾燥し、カット疵部に粘着テープを貼り付けた後、引き剥がすテープ剥離試験を行い、カット疵部左右を合わせた最大剥離全幅を測定した。この最大剥離全幅が6.0mm以下の場合を合格とした。この最大剥離全幅が5.0mm以下であれば、耐塩温水浸漬試験における耐食性は良好と評価することができる。
<塩水噴霧試験(SST)>
化成処理、電着塗装を施した上記試験片(n=1)の表面に、カッターで長さ45mmのクロスカット疵を付与した後、この試験片を、5mass%NaCl水溶液を使用して、JIS Z2371:2000に規定される中性塩水噴霧試験に準拠して1200時間の塩水噴霧試験を行った後、クロスカット疵部についてテープ剥離試験し、カット疵部左右を合わせた最大剥離全幅を測定した。この最大剥離全幅が5.2mm以下の場合を合格とした。この最大剥離全幅が4.0mm以下であれば、塩水噴霧試験における耐食性は良好と評価することができる。
<複合サイクル腐食試験(CCT)>
化成処理、電着塗装を施した上記試験片(n=1)の表面に、カッターで長さ45mmのクロスカット疵を付与した後、この試験片を、塩水噴霧(5mass%NaCl水溶液:35℃、相対湿度:98%)×2時間→乾燥(60℃、相対湿度:30%)×2時間→湿潤(50℃、相対湿度:95%)×2時間、を1サイクルとして、これを120サイクル繰り返す腐食試験後、水洗し、乾燥した後、カット疵部についてテープ剥離試験し、カット疵部左右を合わせた最大剥離全幅を測定した。この最大剥離全幅が7.8mm以下の場合を合格とした。この最大剥離全幅が6.0mm以下であれば、複合サイクル腐食試験での耐食性は良好と評価できる。
(1)機械的特性
圧延方向に直角方向(C方向)から採取したJIS Z2201:1998に規定のJIS5号引張試験片(n=1)を用いて、JIS Z2241:1998の規定に準拠して引張試験を行い、引張強さTSを測定した。
(2)冷延鋼板保管時の点錆発生評価
上記各冷延鋼板に防錆油を塗布した後、ほこりなど外部要因の影響がないように屋外に放置し約1ヶ月後の点錆発生の有無を調査し、点錆なしを「○」、点錆ありを「×」とした。
(3)塗装後耐食性
各冷延鋼板から採取した試験片に、実施例1と同じ条件で、化成処理し、電着塗装を施した試験片を作製し、実施例1と同様にして、塩温水浸漬試験、塩水噴霧試験(SST)および複合サイクル腐食試験(CCT)の3種類の腐食試験に供して、塗装後耐食性を評価した。
上記の各冷延鋼板から試験片を採取し、前述した手法を用いて、酸洗により鋼板表面に生成した鉄系酸化物の表面被覆率および最大厚さを測定した。
(1)冷延鋼板保管時の点錆発生評価
上記各冷延鋼板に防錆油を塗布した後、ほこりなど外部要因の影響がないように屋外に放置し約1ヶ月後の点錆発生の有無を調査し、点錆なしを「○」、点錆ありを「×」とした。
(2)化成処理条件
上記各冷延鋼板から採取した試験片に、日本パーカライジング(株)製の脱脂剤:FC-E2011、表面調整剤:PL-Xおよび化成処理剤:パルボンドPB-L3065を用いて、下記の標準条件および化成処理液の温度を下げて低温度化した比較条件の2条件で、化成処理皮膜付着量が1.7~3.0g/m2となるよう化成処理を施した。
<標準条件>
・脱脂工程:処理温度 40°C、処理時間 120秒
・スプレー脱脂、表面調整工程:pH 9.5、処理温度 室温、処理時間 20秒
・化成処理工程:化成処理液の温度 35℃、処理時間 120秒
<低温度化条件>
上記標準条件における化成処理液の温度を33℃に低下した条件
(3)腐食試験
上記化成処理を施した試験片の表面に、日本ペイント(株)製の電着塗料:V-50を用いて、膜厚が25μmとなるように電着塗装を施し、実施例1と比較してより厳しい条件の下記3種類の腐食試験に供した。
<塩温水浸漬試験>
化成処理および電着塗装を施した上記試験片(n=1)の表面に、カッターで長さ45mmのクロスカット疵を付与した後、この試験片を、5mass%NaCl溶液(60℃)に480時間浸漬し、その後、水洗し、乾燥し、カット疵部に粘着テープを貼り付けた後、引き剥がすテープ剥離試験を行い、カット疵部左右を合わせた最大剥離全幅を測定した。この最大剥離全幅が6.0mm以下の場合を合格とした。この最大剥離全幅が5.0mm以下であれば、耐塩温水浸漬試験における耐食性は良好と評価することができる。
<塩水噴霧試験(SST)>
化成処理、電着塗装を施した上記試験片(n=1)の表面に、カッターで長さ45mmのクロスカット疵を付与した後、この試験片を、5mass%NaCl水溶液を使用して、JIS Z2371:2000に規定される中性塩水噴霧試験に準拠して1400時間の塩水噴霧試験を行った後、クロスカット疵部についてテープ剥離試験し、カット疵部左右を合わせた最大剥離全幅を測定した。この最大剥離全幅が5.2mm以下の場合を合格とした。この最大剥離全幅が4.0mm以下であれば、塩水噴霧試験における耐食性は良好と評価することができる。
<複合サイクル腐食試験(CCT)>
化成処理、電着塗装を施した上記試験片(n=1)の表面に、カッターで長さ45mmのクロスカット疵を付与した後、この試験片を、塩水噴霧(5mass%NaCl水溶液:35℃、相対湿度:98%)×2時間→乾燥(60℃、相対湿度:30%)×2時間→湿潤(50℃、相対湿度:95%)×2時間、を1サイクルとして、これを150サイクル繰り返す腐食試験後、水洗し、乾燥した後、カット疵部についてテープ剥離試験し、カット疵部左右を合わせた最大剥離全幅を測定した。この最大剥離全幅が7.8mm以下の場合を合格とした。この最大剥離全幅が6.0mm以下であれば、複合サイクル腐食試験での耐食性は良好と評価できる。
Claims (19)
- 冷間圧延後連続焼鈍した鋼板に対して、一回目の酸洗を行い、次いで、二回目の酸洗を行い、さらにアルカリ性溶液を用いて中和処理を行う冷延鋼板の製造方法。
- 前記アルカリ性溶液が、水酸化ナトリウム、炭酸ナトリウム、炭酸水素ナトリウム、オルトリン酸塩、縮合リン酸塩の1種又はいずれか2種以上を混合した、pH9.5以上のアルカリ性溶液である請求項1に記載の冷延鋼板の製造方法。
- 前記中和処理は、前記アルカリ性溶液の温度が20~70℃、処理時間が1~30秒である請求項1または2に記載の冷延鋼板の製造方法。
- 前記一回目の酸洗は、硝酸、塩酸、弗酸、硫酸およびそれらを2種以上混合した酸のいずれかを用いて行う請求項1~3のいずれか1項に記載の冷延鋼板の製造方法。
- 前記一回目の酸洗は、下記ア)またはイ)のいずれかの酸液である請求項1~4のいずれか1項に記載の冷延鋼板の製造方法。
ア)硝酸と塩酸を含有した酸液であり、前記硝酸濃度が50g/L超え200g/L以下、前記硝酸濃度に対する前記塩酸濃度の比R1(塩酸/硝酸)が0.01~0.25、さらにはFeイオン濃度が3~50g/Lである酸液
イ)硝酸と弗酸を含有した酸液であり、前記硝酸濃度が50g/L超え200g/L以下、前記硝酸濃度に対する前記弗酸濃度の比R2(弗酸/硝酸)が0.01~0.25、さらにはFeイオン濃度が3~50g/Lである酸液 - 前記二回目の酸洗には、非酸化性の酸を用いる請求項1~5のいずれか1項に記載の冷延鋼板の製造方法。
- 前記非酸化性の酸は、塩酸、硫酸、リン酸、ピロリン酸、ギ酸、酢酸、クエン酸、弗酸、シュウ酸およびこれらの2種以上を混合した酸のいずれかである請求項6に記載の冷延鋼板の製造方法。
- 前記非酸化性の酸は、濃度が0.1~50g/Lの塩酸、0.1~150g/Lの硫酸、0.1~20g/Lの塩酸と0.1~60g/Lの硫酸とを混合した酸のいずれかである請求項6または7に記載の冷延鋼板の製造方法。
- 前記二回目の酸洗は、酸液の温度が20~70℃、酸洗時間が1~30秒である請求項1~8のいずれか1項に記載の冷延鋼板の製造方法。
- 前記鋼板は、成分組成として、Siを0.5~3.0mass%含有する請求項1~9のいずれか1項に記載の冷延鋼板の製造方法。
- 前記鋼板は、さらに成分組成として、C:0.01~0.30mass%、Mn:1.0~7.5mass%、P:0.05mass%以下、S:0.01mass%以下およびAl:0.06mass%以下を含有し、残部がFeおよび不可避的不純物からなる請求項10に記載の冷延鋼板の製造方法。
- 前記鋼板は、さらに成分組成として、Nb:0.3mass%以下、Ti:0.3mass%以下、V:0.3mass%以下、Mo:1.0mass%以下、Cr:1.0mass%以下、B:0.006mass%以下およびN:0.008mass%以下のうちから選ばれる1種または2種以上を含有する請求項11に記載の冷延鋼板の製造方法。
- 前記鋼板は、さらに成分組成として、Ni:2.0mass%以下、Cu:2.0mass%以下、Ca:0.1mass%以下およびREM:0.1mass%以下のうちから選ばれる1種または2種以上を含有する請求項11または12に記載の冷延鋼板の製造方法。
- 請求項1~13のいずれか1項に記載の製造方法により製造される冷延鋼板であって、鋼板表層のSi含有酸化物層が除去され、かつ、鋼板表面に存在する鉄系酸化物の表面被覆率が40%以下である冷延鋼板。
- 前記冷延鋼板は、鋼板表面に存在する鉄系酸化物の最大厚さが150nm以下である請求項14に記載の冷延鋼板。
- 請求項14または15に記載の冷延鋼板を用いる自動車部材。
- 連続焼鈍装置の後段に、第一の酸洗装置と、第二の酸洗装置と、酸中和処理装置と、乾燥装置とをこの順で設置する冷延鋼板の製造設備。
- 前記第一の酸洗装置、前記第二の酸洗装置および前記酸中和処理装置の後段に、水洗装置を設置する請求項17に記載の冷延鋼板の製造設備。
- 前記第一の酸洗装置、前記第二の酸洗装置、前記酸中和処理装置、前記水洗装置のいずれか1つ以上の装置の入側および/または出側に、水洗スプレー装置を設置する請求項17または18に記載の冷延鋼板の製造設備。
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Also Published As
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BR112017004145B1 (pt) | 2022-01-18 |
MX2017002726A (es) | 2017-05-09 |
TWI586840B (zh) | 2017-06-11 |
AR101727A1 (es) | 2017-01-11 |
BR112017004145A2 (pt) | 2017-12-05 |
KR20170032469A (ko) | 2017-03-22 |
JP6137089B2 (ja) | 2017-05-31 |
US20170306507A1 (en) | 2017-10-26 |
CN106605010A (zh) | 2017-04-26 |
JP2016050354A (ja) | 2016-04-11 |
EP3190211B1 (en) | 2021-11-10 |
EP3190211A4 (en) | 2017-10-11 |
EP3190211A1 (en) | 2017-07-12 |
TW201610235A (zh) | 2016-03-16 |
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