MANUFACTURING METHOD OF COLD-LAMINATED STEEL SHEET

专利摘要:
cold-rolled steel sheet, cold-rolled steel sheet manufacturing method, automobile member and cold-rolled steel sheet manufacturing facility. it is a cold-rolled steel sheet that has excellent chemical convertibility and excellent corrosion resistance after coating, a method of manufacturing a cold-rolled steel sheet and an automobile member. in the method of manufacturing a cold-rolled steel sheet, the first pickling is applied to a steel sheet which is continuously annealed after cold rolling, the second pickling is applied to the steel sheet subsequently and thereafter , the neutralization treatment is applied to the steel sheet using an alkaline solution.
公开号:BR112017004145B1
申请号:R112017004145-6
申请日:2015-08-12
公开日:2022-01-18
发明作者:Hiroyuki Masuoka；Shoichiro Taira；Shinichi Furuya
申请人:Jfe Steel Corporation；
IPC主号:

专利说明:

FIELD OF TECHNIQUE
[0001] The present invention relates to a cold-rolled steel sheet and a method of manufacturing a cold-rolled steel sheet. The present invention also relates to a plant for manufacturing cold-rolled steel sheet. Particularly, the present invention relates to a cold-rolled steel sheet that has excellent chemical convertibility and, at the same time, corrosion resistance after coating that is evaluated by a hot brine immersion test and a composite cycle corrosion test, a cold-rolled steel sheet manufacturing method and an automobile member. The cold rolled steel sheet of the present invention can preferably be used as a Si-containing high strength cold rolled steel sheet which has a tensile strength TS of 590MPa or more. BACKGROUND TECHNIQUE
[0002] Recently, from a point of view of protecting a global environment, there has been a strong demand to improve the fuel economy of automobiles. Additionally, from a point of view of ensuring the safety of an occupant at the time of collision, there was also a strong demand for the acquisition of high strength in a vehicle body of an automobile. In order to meet these demands, efforts have been positively made to impart high strength to a cold-rolled steel sheet that becomes a raw material for an automobile member and to reduce a thickness of the cold-rolled steel sheet. , which thus simultaneously achieves weight reduction and the acquisition of high strength in a vehicle body of an automobile. Also, many automobile members are manufactured by applying forming to a steel sheet, and therefore the steel sheet which becomes a raw material in such forming is required to have excellent formability in addition to high strength.
[0003] Several methods have been proposed to increase the strength of a cold-rolled steel sheet. As an effective means to acquire high strength without largely imparting formability, a method of solid solution reinforcement with Si addition is named. However, a case is known where when a large amount of Si, particularly 0.5% by mass or more of Si, is added to a cold rolled steel sheet, a large amount of oxide containing Si such as SiO2 or an oxide compound based on Si-Mn is formed at an interface between a steel sheet surface and an oxide scale at the time of heating a slab, at the time of hot rolling or during post annealing. This Si-containing oxide considerably decreases the chemical convertibility. Additionally, when cold rolled steel sheet is exposed to a severe corrosion environment such as a salt water spray test or a composite cycle corrosion test in which wetting and drying are repeated after electroplating coating, the exfoliation of a coated film is likely to occur, thereby causing the disadvantage to arise that a cold-rolled steel sheet exhibits inferior corrosion resistance after coating.
[0004] To deal with the disadvantage that Si-containing steel sheet has, for example, patent literature 1 proposes a high strength cold-rolled steel sheet in which a sheet is heated to a temperature of 1200°C or more at the time of hot rolling, stripping is carried out at a high pressure, a surface of the hot rolled steel sheet is earthed by nylon brush which contains abrasive grains before pickling, the sheet is immersed in a tank of 9% hydrochloric acid twice to carry out pickling in order to reduce the concentration of Si on a steel sheet surface.
[0005] Patent 2 literature proposes a high strength cold rolled steel sheet in which corrosion resistance is increased by defining a line width of a filamentous oxide containing Si that is observed at a depth of 1 to 10μm from a sheet steel surface at 300 nm or less.
[0006] Patent literature 3 proposes a technique to improve an oxide removal capacity of a steel sheet by setting an iron ion concentration (bivalent) in a hydrochloric acid to a value that falls within a range of 0 .5 to 18%.
[0007] However, in the high strength cold rolled steel sheet described in patent 1 literature, even when the concentration of Si on the surface of the steel sheet is reduced before cold rolling, an oxide containing Si is formed on the surface. of the steel sheet by annealing performed after cold rolling, and therefore the improvement in corrosion resistance after coating cannot be expected.
[0008] In the high strength cold rolled steel sheet described in patent 2 literature, no problem arises regarding corrosion resistance in a corrosive environment such as a salt water spray test stipulated in JIS Z2371. However, cold rolled steel sheet cannot acquire sufficient corrosion resistance after coating in a severe corrosion environment such as a hot brine immersion test and a composite cycle corrosion test.
[0009] That is, with the mere reduction of the concentration of Si on a surface of a steel sheet after hot rolling or the mere reduction of an amount of filamentous oxide that contains Si, a cold rolled steel sheet with high strength which has excellent corrosion resistance after coating cannot be acquired.
[00010] In the technique described in the patent literature 3, SiO2 is insoluble in a hydrochloric acid and therefore even when the iron ion concentration is set to a value that is within a range of 0.5 to 18% , SiO2 cannot be removed.
[00011] In view of the above, as a technique that overcomes the above mentioned disadvantages, patent literature 4 discloses a technique that can improve chemical convertibility by increasing the reactivity of a steel sheet with a chemical conversion treatment solution removing an oxide containing Si concentrated on a surface of the steel sheet in an annealing step or the like by pickling and additionally imparting an S-based compound to that surface.
[00012] Patent literature 5 discloses a technique in which a P-based compound is conferred in place of an S-based compound described in patent literature 4.
[00013] Patent literature 6 discloses, as a technique that can overcome the above mentioned disadvantages, a technique that improves chemical convertibility by increasing reactivity with the chemical conversion treatment solution. In this technique, SiO2 is removed by carrying out pickling with the use of an oxidizing acid in a first stage and an Fe-based oxide formed in the first stage pickling is removed by carrying out pickling with the use of a non-oxidizing acid in a subsequent second stage. LIST OF QUOTATIONS OF PATENT LITERATURE
[00014] PTL 1: Japanese Unexamined Patent Application Publication No. 2004-204350
[00015] PTL 2: Japanese Unexamined Patent Application Publication No. 2004-244698
[00016] PTL 3: Japanese Unexamined Patent Application Publication No. 64-62485
[00017] PTL 4: Japanese Unexamined Patent Application Publication No. 2007-217743
[00018] PTL 5: Japanese Unexamined Patent Application Publication No. 2007-246951
[00019] PTL 6: Japanese Unexamined Patent Application Publication No. 2012-132092 SUMMARY OF THE INVENTION TECHNIQUE PROBLEM
[00020] Recently, with the aim of reducing industrial waste (sludge generation suppression) and reducing running cost, the reduction of a chemical conversion treatment solution temperature has been in progress. As a result, compared to a conventional chemical conversion treatment condition, the reactivity of the steel sheet with a chemical conversion treatment solution applied to a steel plate was greatly reduced. Reducing a temperature of a chemical conversion treatment solution does not cause any problem because of the improvement in a surface adjusting technique performed before the chemical conversion treatment in relation to a common steel sheet that was used in a conventional way and contains a small amount of alloy. However, in relation to a high strength cold rolled steel sheet to which a large amount of Si is added, the reactivity of the steel sheet with a chemical conversion treatment solution is reduced considerably due to the influence of the oxide that contains Si formed on a surface layer of the sheet steel during an annealing step and therefore it is necessary to increase the reactivity from one side of the sheet steel using any means. However, with the techniques disclosed in the patent literatures 4 and 5, even when a chemical conversion treatment solution is effective against a conventional common steel sheet, a sufficient enhancement effect capable of handling the reduction of a temperature of a chemical conversion treatment solution cannot be expected in relation to a high strength cold rolled steel sheet that contains a large amount of Si. On the other hand, it is known that with the use of the technique disclosed in the Patent 6, the technique can deal with lowering a temperature of a chemical conversion treatment solution even with respect to a high strength cold rolled steel sheet that contains a large amount of Si. However, with the technique disclosed in patent literature 6, when the Fe concentration is low, a pickling rate is slow so that a removal capacity of an oxide containing Si becomes insufficient, and when When the Fe concentration is high, an iron-based oxide is formed so that chemical convertibility and eventually corrosion resistance after coating is also deteriorated. Additionally, with the technique disclosed in the patent 6 literature, the reactivity between a chemical conversion treatment solution and a surface of a steel sheet is high to consider that a spot rust occurrence rate is increased during storage. of a cold-rolled steel sheet for a long time.
[00021] The present invention was made in view of such circumstances, and it is an object of the present invention to provide a cold-rolled steel sheet that is excellent not only in chemical convertibility, but also in corrosion resistance after coating, a method cold-rolled steel sheet manufacturing plant, and an automobile member. It is yet another object of the present invention to provide a facility for manufacturing such a cold rolled steel sheet. SOLUTION TO THE PROBLEM
[00022] To overcome the above mentioned disadvantages, the inventors of the present invention conducted a detailed analysis of a surface characteristic of steel sheet after annealing, and made extensive studies regarding a method of increasing reactivity between a surface of a steel sheet. steel and a chemical conversion treatment solution. As a result, the inventors of the present invention have found that it is extremely important to apply strong pickling to a surface of a steel sheet that is continuously annealed after cold rolling, to remove an oxide layer containing Si formed on a surface layer. of the steel sheet during annealing, to reduce a sheet steel sheet surface covering of an iron-based oxide formed on the surface of the steel sheet by the above mentioned hard pickling and to subsequently neutralize a residue of a solution acid by an alkaline solution after strong pickling to improve corrosion resistance after coating by preventing spot rusting during storage of a cold rolled steel sheet, and the inventors have completed the present invention.
[00023] The present invention was made on the basis of the above-mentioned conclusions, and the main point of the present invention is as follows.
[00024] [1] A method of manufacturing a cold rolled steel sheet in which the first pickling is applied to a steel sheet which is continuously annealed after cold rolling, the second pickling is applied to the steel sheet subsequently, and subsequently, the neutralization treatment is applied to the steel sheet using an alkaline solution.
[00025] [2] The method of manufacturing a cold-rolled steel sheet described in [1] wherein the alkaline solution has a pH of 9.5 or more, and one or two or more selected from a group consisting of in sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, orthophosphate and condensed phosphate are mixed in the alkaline solution.
[00026] [3] The method of manufacturing a cold-rolled steel sheet described in [1] or [2], wherein the neutralization treatment is carried out in a state where an alkaline solution temperature is set to a value that is within a range of 20 to 70°C, and a treatment time is set to a value that is within a range of 1 to 30 seconds.
[00027] [4] The method of manufacturing a cold-rolled steel sheet described in any one of [1] to [3], wherein the first pickling is carried out using any of a nitric acid, a hydrochloric acid, a hydrofluoric acid, a sulfuric acid and a mixture of two or more of these acids.
[00028] [5] The method of fabricating a cold-rolled steel sheet described in any one of [1] to [4], wherein the first pickling is carried out using any of the following acidic solutions (the ) and (b).
[00029] (a) The acidic solution containing a nitric acid and a hydrochloric acid, wherein the concentration of the nitric acid is greater than 50 g/l and 200 g/l or less, a ratio R1 between the concentration of the hydrochloric acid and the nitric acid (hydrochloric acid/nitric acid) concentration is set to a value that is within a range of 0.10 to 0.25, and the Fe ion concentration is set to a value that is within a range of 3 to 50 g/l.
[00030] (b) The acidic solution containing a nitric acid and a hydrofluoric acid, wherein the concentration of nitric acid is greater than 50 g/l and 200 g/l or less, a ratio R2 between the concentration of hydrofluoric acid and the nitric acid (hydrofluoric acid/nitric acid) concentration is set to a value that is within a range of 0.10 to 0.25, and the Fe ion concentration is set to a value that is within a range from 3 to 50 g/l.
[00031] [6] The method of manufacturing a cold-rolled steel sheet described in any one of [1] to [5], wherein a non-oxidizing acid is used in the second pickling.
[00032] [7] The method of manufacturing a cold-rolled steel sheet described in [6], wherein the non-oxidizing acid is any one of hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, a formic acid, a formic acid, an acetic acid, a citric acid, a hydrofluoric acid, an oxalic acid, and an acid that is a mixture of two or more of these acids.
[00033] [8] The method of manufacturing a cold-rolled steel sheet described in [6] or [7], wherein the non-oxidizing acid is any of hydrochloric acid having a concentration of 0.1 to 50 g /l, a sulfuric acid that has a concentration of 0.1 to 150 g/l and an acid that is a mixture of a hydrochloric acid that has a concentration of 0.1 to 20 g/l and a sulfuric acid that has a concentration of 0.1 to 60 g/l.
[00034] [9] The method of manufacturing a cold-rolled steel sheet described in any tooth [1] to [8], wherein the second pickling is carried out in a state where an acidic solution temperature is set to a value that is within a range of 20°C to 7, and a pickling time is set to a value that is within a range of 1 to 30 seconds.
[00035] [10] The method of manufacturing a cold-rolled steel sheet described in any one of [1] to [9], wherein the steel sheet contains, as a component of the composition thereof, 0.5 at 3.0% by mass of Si.
[00036] [11] The method of manufacturing a cold-rolled steel sheet described in [10], in which the steel sheet additionally contains, as components of its composition: from 0.01 to 0.30% by mass of C, from 1.0 to 7.5% by mass of Mn, 0.05% by mass or less of P, 0.01% by mass or less of S, 0.06% by mass or less of Al, and Fe and unavoidable impurities as a balance.
[00037] [12] The method of manufacturing a cold-rolled steel sheet described in [11], in which the steel sheet additionally contains, as components of its composition, one or two or more of the elements selected from the group consisting of 0.3% by mass or less of Nb, 0.3% by mass or less of Ti, 0.3% by mass or less of V, 1.0% by mass or less of Mo, 1, 0% by mass or less of Cr, 0.006% by mass or less of B and 0.008% by mass or less of N.
[00038] [13] The method of manufacturing a cold-rolled steel sheet described in [11] or [12], wherein the steel sheet additionally contains, as the composition components, one or two or more of the selected elements from a group consisting of 2.0% by mass or less of Ni, 2.0% by mass or less of Cu, 0.1% by mass or less of Ca, and 0.1% by mass or less of REM.
[00039] [14] A cold-rolled steel sheet manufactured by the method of manufacturing a cold-rolled steel sheet as described in any one of [1] to [13], wherein an oxide layer containing Si formed in a surface layer of the steel sheet is removed, and a surface coverage of an iron-based oxide existing on a surface of the steel sheet is 40% or less.
[00040] [15] The cold rolled steel sheet described in [14], wherein a maximum thickness of the iron-based oxide existing on the surface of the steel sheet is 150 nm or less.
[00041] [16] An automobile member formed using the cold-rolled steel sheet described in [14] or [15].
[00042] [17] A facility for manufacturing a cold-rolled steel sheet, wherein a first pickling device, a second pickling device, an acid neutralizing treatment device and a drying device are arranged in that order in a later stage of a continuous annealing device.
[00043] [18] The facility for manufacturing a cold-rolled steel sheet described in [17], wherein a water cleaning device is arranged at a later stage of the first pickling device, the second pickling device and the device of acid neutralization treatment.
[00044] [19] The installation for fabricating a cold-rolled steel sheet described in [17] or [18], wherein a water-cleaning sprinkler device is arranged on an inlet side and/or an outlet side of one or more devices selected from a group consisting of the first pickling device, the second pickling device, the acid neutralizing treatment device and the water cleaning device. ADVANTAGEOUS EFFECTS OF THE INVENTION
[00045] According to the present invention, it is possible to obtain a cold rolled steel sheet which is excellent in chemical convertibility as well as corrosion resistance after coating. Additionally, according to the manufacturing method of the present invention, a cold-rolled steel sheet that has favorable chemical convertibility and favorable corrosion resistance after coating can be easily and stably manufactured through a common cold-rolling step. and the pickling step merely by setting a pickling condition.
[00046] It is possible to provide a cold rolled steel sheet which is excellent in chemical convertibility even in a case where chemical conversion treatment solution which has a low temperature is used and which is also excellent in corrosion resistance after coating even in a severe corrosion environment such as a hot brine immersion test or a composite cycle corrosion test even when the cold rolled steel sheet contains 0.5 to 3.0 wt% Si. Thus, according to the present invention, the chemical convertibility and corrosion resistance after coating a high strength cold-rolled steel sheet that contains a large amount of Si, thereby having a tensile strength TS of 590 MPa or more can be greatly improved and therefore the high strength cold rolled steel sheet can preferably be used as a reinforcing member of a vehicle body of an automobile or the like. BRIEF DESCRIPTION OF THE DRAWINGS
[00047] Figure 1 is a view showing electron deflection images of the surfaces of steel sheets that are standard samples of cold rolled steel sheets No. a and No. b prepared to obtain a surface coating of an oxide. iron based.
[00048] Figure 2 is a histogram of pixel count against gray values of reflection electron image photographs of standard samples of cold-rolled steel sheet No. a and No. b.
[00049] Figure 3 is a view showing a result of observing a cross-section of a sheet steel surface covering material after a steel sheet surface has been pickled using a non-oxidizing acid by a transmission type electron microscope.
[00050] Figure 4 is a graph showing a result of an energy distribution type X-ray analysis (EDX) of an iron-based oxide observed in Figure 3.
[00051] Figure 5 is a graph showing a result obtained by measuring the distribution of O, Si, Mn and Fe in the depth direction on a surface of a specimen shown in Table 2 by GDS. DESCRIPTION OF MODALITIES
[00052] The details of the present invention are described from this point in the present document. In the description given hereafter, a unit of content of the respective elements of the steel composition is defined as "% by mass", and "% by mass" is expressed simply as "%" unless otherwise specified. another way.
[00053] In an annealing step with the use of a continuous annealing furnace that is carried out to give the desired structure, the desired strength and the desired formability to the cold-rolled steel sheet obtained through cold rolling by recrystallizing the Cold rolled steel sheet, a non-oxidizing gas or a reducing gas is normally used as an atmospheric gas, and a dew point is strictly controlled. Consequently, in a common general purpose cold rolled steel sheet that has a low alloy content, oxidation of a steel sheet surface is suppressed. However, in a steel sheet that contains 0.5% or more of Si or Mn, even when the component or dew point of an atmospheric gas is strictly controlled during annealing, Si, Mn or the like that is easily oxidized to compared to Fe is oxidized so that the formation of an oxide containing Si such as an oxide of Si (SiO2) or a composite oxide based on Si-Mn on a surface of a steel sheet cannot be avoided. Although the structures of these oxides change depending on the components of a sheet steel, an annealing atmosphere or similar in general is often the case where the structures of these oxides change depending on a mixture of components of a sheet of steel and a annealing atmosphere. Additionally, it is known that the Si-containing oxide is formed not only on a surface of a steel sheet, but also inside a base steel, and therefore an etching property of the surface of the steel sheet in chemical conversion treatment. (zinc atmosphere treatment) that is performed as a surface treatment for electrodeposition coating is imparted, thereby adversely affecting the formation of a safe chemical conversion treatment film.
[00054] On the other hand, recently, with the aim of reducing the amount of sludge generated at the time of chemical conversion treatment and an execution cost, the reduction of a temperature of a chemical conversion treatment solution has been in progress. As a result, compared to a conventional technique, the chemical conversion treatment can be carried out in a state where the reactivity of a chemical conversion treatment solution with a steel sheet is extremely low. Such a change in the chemical conversion treatment condition does not cause any particular problem due to the improvement of a surface fit technique or the like over a common steel sheet that has been used in a conventional manner and contains a small amount of alloy. However, in relation to a steel sheet that contains a large amount of alloying component, particularly in relation to a cold-rolled steel sheet with high strength, which aims at higher strength because it contains a large amount of Si, the influence exerted by the above-mentioned change in the chemical conversion treatment condition, i.e. the reduction of a temperature of a chemical conversion treatment solution is extremely large. To deal with this situation, in relation to a cold-rolled steel sheet that contains a large amount of Si, it is considered necessary to increase the reactivity of the steel sheet with a chemical conversion treatment solution by activating a surface of the steel sheet. steel which, by itself, corresponds to the worsening of a chemical conversion treatment condition.
[00055] To deal with the above-mentioned worsening of the chemical conversion treatment condition, the inventors of the present invention have made studies regarding a method of improving the chemical convertibility of a steel sheet. As a result, the inventors have concluded that a method is effective when a surface of a cold-rolled steel sheet after continuous annealing is subjected to strong pickling with the use of nitric acid or the like as a pickling solution, which thus removes an oxide layer containing Si on a surface layer of steel sheet formed by continuous annealing or similar after cold rolling. In the present context, "Si-containing oxide" means SiO2 or a Si-Mn-based composite oxide formed along a surface of the steel sheet or a grain boundary on the inside of the steel sheet on heating a plate, after hot rolling or in annealing after cold rolling. Although the thickness of a layer in which the Si-containing oxide is present changes depending on the composition of the steel sheet or an annealing condition (temperature, time, atmosphere), the thickness is normally approximately 1μm from a sheet metal surface. steel. Additionally, in the present invention, "removing a Si-containing oxide layer" means that the Si-containing oxide layer is removed by pickling to such a degree that a Si peak and an O peak do not appear when the surface of the steel plate steel is analyzed in a depth direction by GDS (Glow Discharge Atomic Emission Spectrochemical Analysis).
[00056] The reason why a strong acid such as a nitric acid is used as a pickling solution mentioned above is that although a Si-Mn based composite oxide is easily dissolved by an acid between Si-containing oxides, the SiO2 exhibits insolubility and therefore to remove SiO2 it is necessary to remove an oxide containing Si formed on a surface of a steel sheet along with a base steel.
[00057] However, according to the studies carried out by the inventors, although chemical convertibility is greatly improved by removing an oxide layer containing Si present on a surface of a steel sheet by carrying out strong pickling with the use of a nitric acid or the like after continuous annealing, it is revealed that there are some cases in which a steel sheet exhibits lower chemical convertibility. When the inventors investigated a cause of the occurrence of such cases, the inventors made new discoveries that although a layer of Si-based oxide was removed by the above mentioned strong pickling with the use of a nitric acid or similar, the Fe which is dissolved from a surface of a steel sheet by pickling it forms an iron-based oxide, and this iron-based oxide is deposited and precipitates on the surface of the steel sheet and covers the surface of the steel sheet, which thus , reduces chemical convertibility, and when a residue of a pickling solution remains, a rate of occurrence of spot rust during storage of a cold-rolled steel sheet is increased so that the cold-rolled steel sheet exhibits strength to bottom corrosion after coating.
[00058] The inventors did further studies and, as a result of the studies, concluded that in order to reduce an adverse effect that affects chemical convertibility, it is important to suppress the formation of an iron-based oxide on a surface of a steel sheet of so as to define a surface coverage of the iron-based oxide present on the surface of the steel sheet at 40% or less. The inventors also found that an iron-based oxide present on the surface of the steel sheet can be dissolved and removed by carrying out pickling using a non-oxidizing acid after carrying out strong pickling. The inventors have also concluded that it is important to remove a residue from an acid solution that remains after pickling performed twice by carrying out neutralization treatment with the use of an alkaline solution after carrying out pickling with the use of a non-oxidizing acid.
[00059] Based on such findings, in the present invention, strong pickling is performed as the first pickling in order to suppress the formation of an iron-based oxide on a surface of a steel sheet and remove an oxide layer that contains Si present on a surface of the steel sheet. The pickling is then carried out using a non-oxidizing acid as the second pickling in order to define a surface coverage of the iron based oxide present on the surface of the steel sheet at 40% or less. Subsequently, the neutralization treatment is applied to the steel sheet using an alkaline solution.
[00060] The inventors also concluded that when a coating of an iron-based oxide formed on a surface of a steel sheet by pickling is set to 40% or less and, in addition, a maximum thickness of the iron-based oxide is set at 150 nm or less, chemical convertibility is further improved and corrosion resistance is also improved, and as a means of achieving such effects, it is effective to properly define a pickling condition (concentration, temperature, time) and a pickling condition non-oxidizing pickling process (acid concentration, temperature, time).
[00061] In the present invention, "iron-based oxide" means an oxide containing iron as a major component in which an atomic percentage of iron among elements other than oxygen constituting oxides is set to 30% or more. Iron-based oxide is an oxide which is present on a surface of a steel sheet with a non-uniform thickness and differs from a natural oxide film which has a uniform thickness of several nm and which is present as a layer. Additionally, it is understood that an iron-based oxide formed on a surface of a cold-rolled steel sheet is amorphous based on observation using a transmission-type electron microscope (TEM) or an analysis result of a diffraction pattern obtained by an electron beam diffraction.
[00062] The present invention was completed by carrying out additional studies based on the above-mentioned innovative findings.
[00063] Next, a method of manufacturing a cold-rolled steel sheet according to the present invention is described.
[00064] The present invention is distinguished by the fact that the first pickling is applied to a steel sheet which is produced by applying heating, hot rolling, cold rolling and continuous annealing to a steel material (plate) that contains 0.5 to 3.0% Si, for example, and the second pickling is applied to the steel sheet subsequently, and then the neutralization treatment is applied to the steel sheet using an alkaline solution. By carrying out such pickling and neutralization treatment, chemical convertibility and corrosion resistance after coating can be improved considerably. FIRST PICKLING CONDITION
[00065] After continuous annealing, a large amount of an oxide containing Si such as SiO2 or a composite oxide based on Si-Mn is formed in a surface layer of a steel sheet. If this state is maintained as it is, chemical convertibility and corrosion resistance after coating are greatly reduced. In view of the foregoing, according to the manufacturing method of the present invention, it is preferable to apply, as the first pickling, strong pickling to a cold-rolled steel sheet after annealing using an acidic solution containing a nitric acid and a hydrochloric acid or an acidic solution containing a nitric acid and a hydrofluoric acid. By carrying out the first pickling, an oxide layer containing Si formed on a surface of the steel sheet is removed along with a base steel.
[00066] Although a Si-Mn-based composite oxide is easily dissolved by an acid between Si-containing oxides, SiO2 exhibits insolubility against an acid. Consequently, to remove an oxide containing Si, including SiO2, it is necessary to remove an oxide layer along with a base steel from a steel sheet by strong pickling. Accordingly, in the present invention, since an acid which can be used as an acidic solution, a nitric acid which is a strong oxidizing acid can be used favorably. Additionally, as long as an acid can remove an oxide layer containing Si, the acid can be hydrofluoric acid, hydrochloric acid, sulfuric acid or the like. That is, a type of acid is not particularly specified. Additionally, an acid prepared by mixing these two or more acids can be used. It is also effective to accelerate the dissolution of a base steel by adding a pickling accelerating agent to an acid solution or by using electrolytic treatment in combination with the use of an acid.
[00067] Additionally, as described above, Fe that is dissolved from a surface of a steel plate by pickling forms an iron-based oxide, and this iron-based oxide is deposited and precipitates on the surface of the plate. of steel and covers the surface of the steel sheet, thus raising a possibility that the chemical convertibility is reduced. To reduce a load from the second pickling while avoiding such a reduction in chemical convertibility, it is preferable to suppress an amount of iron-based oxide formed on a surface of a steel sheet. Due to the reasons described above, it is preferable to define the following pickling condition.
[00068] To remove an oxide that contains Si efficiently, in a case where an acidic solution that contains both a nitric acid and a hydrochloric acid is used, it is preferred that an acidic solution contains both the nitric acid and the hydrochloric acid so that the concentration of nitric acid is set to a value that is within a range of more than 50 g/l to 200 g/l or less, and an R1 ratio (hydrochloric acid/nitric acid) between the concentration of hydrochloric acid that has an oxide film breaking effect and the nitric acid concentration is set to a value that is within a range of 0.01 to 0.25, and the Fe ion concentration (sum of bivalence and trivalence) is set to a value that is within a range of 3 to 50 g/l. It is more preferred that the concentration of nitric acid is set at a value that is within a range of 100 g/l to 200 g/l. It is more preferred that the above-mentioned R1 is set to a value that is within a range of 0.02 to 0.15. It is more preferred that the Fe ion concentration is set to a value that is within a range of 3 to 25 g/l. In a case where an acidic solution that contains both a nitric acid and a hydrofluoric acid is used, it is preferred that an acidic solution contains both nitric acid and hydrofluoric acid so that the concentration of nitric acid is set to a value that is within from a range of more than 50 g/l to 200 g/l or less, and an R2 ratio (hydrofluoric acid/nitric acid) between the concentration of hydrofluoric acid that has an oxide film breaking effect and the concentration of nitric acid is set to a value that is within a range of 0.01 to 0.25, and the Fe ion concentration (sum of bivalence and trivalence) is set to a value that is within a range of 3 to 50 g /l. It is more preferred that the concentration of nitric acid is set at a value that is within a range of 100 g/l to 200 g/l. It is more preferred that the above-mentioned R2 is set to a value that is within a range of 0.02 to 0.15. It is more preferred that the Fe ion concentration is set to a value that is within a range of 3 to 25 g/l. When R1 and R2 are greater than 0.25 or when the Fe ion concentration (the sum of bivalence and trivalence) is less than 3 g/l, a desired pickling rate cannot be achieved and therefore an oxide that contains Si cannot be removed efficiently. On the other hand, when R1 and R2 are less than 0.01 or when the Fe ion concentration is greater than 50 g/l, although a desired pickling rate can be achieved, an amount of Fe ion in an acidic solution is greater, and therefore a large amount of Fe-based oxide is formed on a surface of the steel sheet from which an Fe-based oxide cannot be completely removed by the second pickling. Consequently, chemical convertibility and corrosion resistance cannot be improved.
[00069] Additionally, as a method of maintaining the Fe ion concentration (the sum of bivalence and trivalence) at a value that is within a range of 3 to 50 g/l, methods are considered to include a method that, when the Fe ion concentration exceeds 50 g/l, an acidic solution is diluted, a method in which a nitric acid or a hydrochloric acid is additionally charged, and a method in which an iron component in an acid is reduced by a device of iron removal.
[00070] Additionally, a maximum thickness of an iron-based oxide can be defined at 150 nm or less by appropriately defining a pickling condition (concentration, temperature, time). Carrying out the first pickling in a state where a temperature of an acid solution is set at 20 to 70°C and a pickling time is 3 to 30 seconds, the maximum thickness of the iron-based oxide becomes 150 nm or less and therefore chemical convertibility is further improved and corrosion resistance is also further improved. SECOND PICKING CONDITION
[00071] With mere strong pickling which is performed as the first pickling, it is difficult to control a surface coating of an iron-based oxide formed on a surface of a steel sheet at 40% or less stably. In view of the foregoing, according to the present invention, in order to more assuredly reduce an amount of iron-based oxide formed on a surface of a steel sheet by the above-mentioned first pickling, the second pickling is carried out. In the present invention, the second pickling is preferably carried out using an acidic solution made of a non-oxidizing acid, and an iron-based oxide is dissolved by the second pickling.
[00072] As a non-oxidizing acid, one type or two or more types selected from the group consisting of a hydrochloric acid, a sulfuric acid, a phosphoric acid, a pyrophosphoric acid, a formic acid, an acetic acid, a citric acid , a hydrofluoric acid and an oxalic acid are preferably used. While any acid can be used, a hydrochloric acid and a sulfuric acid that are commonly used in a steel manufacturing industry can be used in preference. Among these acids, a hydrochloric acid can be used in preference, since a hydrochloric acid is a volatile acid so that a residue such as a sulfate group minimally remains on a surface of a steel sheet after cleaning with water as opposed to an acid. sulfuric acid, and an oxide-breaking effect by chloride ion is large and similar. Additionally, a mixed acid prepared by mixing a hydrochloric acid and a sulfuric acid can be used.
[00073] Among these acids, from a point of view of preventing insufficient removal of an iron-based oxide and the degradation of a surface property of a steel sheet due to excessive pickling, it is preferable to use either from a hydrochloric acid having a concentration of 0.1 to 50 g/l, a sulfuric acid having a concentration of 0.1 to 150 g/l and a mixed acid prepared by mixing a hydrochloric acid having a concentration of 0 .1 to 20 g/l and a sulfuric acid having a concentration of 0.1 to 60 g/l.
[00074] It is preferred that the second pickling be carried out in a state where a temperature of an acid solution is set from 20 to 70°C and a pickling time is from 1 to 30 seconds. When the temperature of an acidic solution is set to 20°C or more and a treatment time is 1 second or more, it is sufficient to remove an iron-based oxide that remains on a surface of a steel sheet. On the other hand, when the temperature of an acidic solution is set to 70°C or less and a treatment time is 30 seconds or less, a surface of a steel sheet is not dissolved excessively so that there is no possibility that a new surface oxide film is formed. It is more preferred to set a temperature of an acidic solution to a value that is within a range of 30 to 50°C. Additionally, it is more preferred to set a pickling time to a value that is within a range of 2 to 20 seconds.
[00075] Additionally, in order to acquire a steel sheet that is more excellent in chemical convertibility and corrosion resistance, it is preferable to guarantee to decrease a maximum thickness of an iron-based oxide present on a surface of a steel sheet after the etching mentioned above to 150 nm or less. For this purpose, it is preferred to suitably increase the concentration of an acid solution consisting of a non-oxidizing acid. For example, when a hydrochloric acid is used, the concentration of hydrochloric acid is preferably set at a value that is within a range of 3 to 50 g/l. When a sulfuric acid is used, the concentration of sulfuric acid is preferably set at a value that is within a range of 8 to 150 g/l. Additionally, when a pickling solution prepared by mixing a hydrochloric acid and a sulfuric acid is used, it is preferable to use an acid prepared by mixing a hydrochloric acid which has a concentration of 3 to 20 g/l and a sulfuric acid which has the concentration from 8 to 60 g/l. As long as the concentration of a pickling solution is within the concentration range mentioned above, a thickness of an iron-based oxide can be guaranteed to be reduced to 150 nm or less and hence chemical convertibility and corrosion resistance after coating can be improved. Additionally, as long as the concentration of a pickling solution is within the concentration range mentioned above, a steel sheet surface is not excessively resolved so that there is no possibility that a new surface oxide film will form. NEUTRALIZATION TREATMENT CONDITION
[00076] The present invention is distinguished by the neutralization treatment being carried out additionally with the use of an alkaline solution after the second pickling is carried out.
[00077] When the reactivity of a steel sheet surface is increased by removing an oxide formed during pickling annealing, a residue of pickling solution remains and therefore there is a possibility that spot rust will occur during the storage of a cold-rolled steel sheet. In order to suppress the occurrence of such spot rust, in the neutralization treatment carried out after pickling and redepicking, it is preferable to carry out the neutralization treatment with the use of an alkaline solution that has a pH of 9.5 or more, in which one type or two or more types selected from a group consisting of sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, orthophosphate and condensed phosphate are mixed. Such an alkaline solution is used to remove a residue from the pickling solution by neutralization. Also, when the pH is less than 9.5, a residue from a pickling solution cannot be completely neutralized. As condensed phosphate, for example, sodium pyrophosphate, sodium polyphosphate and the like are named. The pH mentioned above is most preferably set to a value that is within a range of 10.0 to 12.0.
[00078] In carrying out the neutralization treatment using the above-mentioned alkaline solution, it is preferable that a temperature of the alkaline solution is set to a value that is within a range of 20 to 70°C, and a treatment time is set to a value that is within a range of 1 to 30 seconds. When a solution temperature of alkaline solution is set to 20°C or more and the treatment time is set to 1 second or more, a residue of pickling solution is neutralized enough. On the other hand, when the temperature of a pickling solution exceeds 70°C, an alkaline smoke is generated. Additionally, when a treatment time exceeds 30 seconds, an installation duration is lengthened so that a huge installation cost becomes necessary. An alkaline solution temperature is most preferably set to a value that is within a range of 30 to 50°C. It is more preferred to set a treatment time to a value that is within a range of 2 to 20 seconds.
[00079] As described above, after continuous annealing, a steel sheet is subjected to a first pickling and a second pickling, and then the steel sheet is subjected to the neutralization treatment using an alkaline solution. From there, the steel sheet is formed into a product sheet (cold rolled steel sheet) through common treatment steps such as temper rolling.
[00080] In the present invention, a method of pickling, that is, a method of contacting a steel sheet with an acid solution described in the present invention is not particularly limited. As such a method, a method in which an acidic solution is sprinkled on a steel sheet, a method in which a steel sheet is immersed in an acidic solution and the like are called.
[00081] Additionally, it is preferred that the first pickling and the second pickling are carried out continuously. By carrying out the first pickling and the second pickling continuously, it is possible to prevent the natural oxidation of a steel sheet after the first pickling, and therefore the steel sheet can be formed into a final product in a course by which the product can be manufactured at low cost.
[00082] Also, in the present invention, the cleaning treatment with water can be carried out after the first pickling, after the second pickling and after the neutralization treatment, respectively. Additionally, in carrying out the first pickling, the second pickling, the neutralization treatment and the cleaning treatment with water, respectively, the additional cleaning with water can be additionally carried out on an inlet side and/or on an outlet side of the respective treatments with the use of a water cleaning sprinkler. It is preferred that the drying treatment is carried out using a dryer or similar after the cleaning treatment with water.
[00083] Next, the composition of the cold rolled steel sheet according to the present invention is described.
[00084] In the present invention, it is preferred that the steel sheet has the composition that allows the steel sheet to have a high strength so that the steel sheet can be used to form an automobile suspension number and also have favorable chemical convertibility.
[00085] In the composition of the cold rolled steel sheet, the Si content is preferably set at a value that is within a range of 0.5 to 3.0%. Si is a highly effective element in increasing steel strength (solid solution reinforcing capacity) without greatly deteriorating the workability of steel, and therefore Si is an effective element in achieving high steel reinforcement. However, Si is also an element that adversely affects chemical convertibility and corrosion resistance after coating. Due to such reasons, although it is preferable to add 0.5% or more of Si, when the Si content exceeds 3.0%, the hot rolling property and the cold rolling property are greatly reduced, which thus , raises a possibility that productivity will be adversely affected or the ductility of a steel sheet, by itself, will be reduced. Consequently, when Si is added as a component of the composition, the Si content is preferably set at a value that is within a range of 0.5 to 3.0%. The Si content is most preferably set to a value that is within a range of 0.8 to 2.5%.
[00086] Cold rolled steel sheet is permitted to contain components other than the above mentioned components within the range of components of common cold rolled steel sheet. However, in applying the cold rolled steel sheet of the present invention to a high strength cold rolled steel sheet which has a tensile strength TS of 590MPa or more which is used to form a vehicle body of an automobile or the like , it is preferable to define the contents of the desired components other than the components mentioned above as follows. C: 0.01 to 0.30%
[00087] C is an element that is effective in increasing the strength of steel. C is also an effective element in the formation of residual austenite which has the effect of TRIP (Transformation Induced Formability), bainite or martensite. When the C content is set to 0.01% or more, the effects mentioned above can be obtained. On the other hand, when the C content is 0.30% or less, weldability reduction does not occur. Accordingly, the C content to be added is preferably set to a value that is within a range of 0.01 to 0.30%, and the C content is more preferably set to a value that is within a range of 0.10 to 0.20%. Mn: 1.0 to 7.5%
[00088] Mn is an element that has a steel strength enhancing function by steel solid solution reinforcement, a hardenability improving function and a function of accelerating the formation of austenite, bainite or residual martensite. Such an effect can be accomplished by adding 1.0% or more of Mn. On the other hand, when the Mn content is 7.5% or less, the above mentioned advantageous effect can be obtained without the cost increase. Consequently, the Mn content to be added is preferably set to a value that is within a range of 1.0 to 7.5%, and the Mn content is more preferably set to a value that is within from a range of 2.0 to 5.0%.P: 0.05% or less
[00089] P is an element that does not deteriorate a printability although P has a great capacity of solid solution reinforcement and is also an effective element to acquire a high strength. Accordingly, the P content is preferably set at 0.005% or more. Although P is an element that deteriorates spot weldability, no problem arises as long as the P content is set to 0.05% or less. Accordingly, the P content is preferably set at 0.05% or less, and the P content is more preferably set at 0.02% or less. S: 0.01% or less
[00090] S is an impurity element that is inevitably mixed in steel. S is a harmful component that precipitates as MnS in steel and reduces the stretch-flange ability of the steel sheet. To prevent the stretch-flange capability from being reduced, the S content is preferably set to 0.01% or less. The S content is more preferably defined at 0.005% or less, and the S content is further preferably defined at 0.003% or less. Al: 0.06% or less
[00091] Al is an element to be added as a deoxidizing agent in a steel forming step. Additionally, Al is an effective non-metallic inclusion separating element that reduces the stretch-flange capability as a slag. Accordingly, the Al content is preferably set at 0.01% or more. When the Al content is 0.06% or less, the effects mentioned above can be obtained without increasing a raw material cost. Accordingly, the Al content is preferably set at 0.06% or less. The Al content is most preferably set at a value that is within a range of 0.02 to 0.06%.
[00092] The cold rolled steel sheet of the present invention may contain one or two or more of the elements selected from a group consisting of 0.3% or less of Nb, 0.3% or less of Ti, 0 .3% or less of V, 1.0% or less of Mo, 1.0% or less of Cr, 0.006% or less of B and 0.008% or less of N in addition to the above mentioned components.
[00093] Nb, Ti and V are elements that form carbide and nitride, form the fine microstructure by suppressing ferrite growth in a heating step during annealing, and improve formability, particularly flanging-stretchability. Additionally, Mo, Cr and B are elements that improve the hardenability of steel and accelerate the formation of bainite or martensite. Consequently, Nb, Ti, V, Mo, Cr and B can be added to steel within the ranges mentioned above. Additionally, N is an element that forms nitride with Nb, Ti, and V or is dissolved in steel in a solid solution state, and therefore N contributes to increased strength of steel. When the N content is set to 0.008% by mass or less, a large amount of nitride is not formed and therefore the breakage due to void formation in press forming is suppressed, whereby the effects mentioned above can be obtained.
[00094] The cold rolled steel sheet of the present invention may also contain one or two or more selected from a group consisting of 2.0% or less of Ni, 2.0% or less of Cu, 0, 1% or less of Ca and 0.1% or less of REM in addition to the above mentioned component composition.
[00095] Ni and Cu are effective elements in accelerating the formation of a low temperature transformation phase and increasing a steel strength. Consequently, Ni and Cu that are within the ranges mentioned above can be added to the steel sheet. Also, Ca and REM are elements that control a sulfide-based inclusion morphology and improve the stretch-flange capability of the steel sheet. Consequently, Ca and REM that are within the ranges mentioned above can be added to the steel sheet.
[00096] In the cold rolled steel sheet according to the present invention, a balance other than the above mentioned components is Fe and unavoidable impurities. However, cases are not denied when the cold rolled steel sheet according to the present invention contains other components unless such components weaken the effects of the present invention.
[00097] Next, a surface feature of a cold rolled steel sheet according to the present invention is described. As described above, a cold-rolled steel sheet in accordance with the present invention has a steel sheet surface from which an oxide layer containing Si such as SiO2 and a Si-Mn-based composite oxide formed on a surface layer of the steel sheet during annealing is removed. To acquire such a cold-rolled steel sheet, it is necessary to carry out neutralization treatment with the use of an alkaline solution after the first pickling and the second pickling.
[00098] Additionally, in purchasing the cold rolled steel sheet according to the present invention, it is necessary to reduce a surface coverage of an iron-based oxide present on a surface of a steel sheet to 40% or less despite the removal of the Si-containing oxide layer. This is due to the fact that when the surface coverage exceeds 40%, an iron dissolution reaction generated by the chemical conversion treatment is obstructed so that a growth of chemical conversion crystals such as zinc phosphate or the like is deleted. However, in a case where a chemical conversion treatment solution that has a low temperature is used, particularly in relation to a cold rolled steel sheet used in an application where extremely severe corrosion resistance after coating is required as in the case of a suspension member of a vehicle that is exposed to severe corrosion, coverage of 40% or less is insufficient, and coverage needs to be further reduced to 35% or less. It is preferred to set coverage to 35% or less.
[00099] In the present invention, the above-mentioned surface coating of an iron-based oxide is obtained as follows. A surface of a steel plate after pickling is observed using a scanning electron microscope (ULV-SEM) of extremely low accelerating voltage that can detect extreme surface layer information in approximately five fields of view with a accelerating voltage of 2kV, an operating distance of 3.0 mm and a magnification of approximately 1,000 times, and a spectroscopic analysis is performed using an energy dispersion type X-ray spectrometer (EDX) which thus obtains , a reflection electron image. Binary coded processing is applied to the image of reflected electrons using image analysis software, for example Image J (Image J) which thus measures an area ratio of a black colored portion, and a surface coverage of an iron-based oxide can be obtained by averaging the measured values of the respective fields of view. Furthermore, as the aforementioned scanning electron microscope (ULV-SEM) of extremely low accelerating voltage, for example, the ULTRA55 available from SEISS Inc. can be named. Additionally, as the energy dispersion type X-ray (EDX) spectrometer, for example, the NSS312E available from Thermo Fisher Inc. may be named.
[000100] In the present context, a threshold value used in the above mentioned binary coded processing is described. A steel plate having a steel symbol G shown in Table 3 of an example described later was subjected to hot rolling, cold rolling and continuous annealing under a condition indicated in No. 93 of Table 4 in the example described later. likewise for the steel plate which has been formed into a cold rolled steel plate which has a plate thickness of 1.8mm. Then, the cold-rolled steel sheet after continuous annealing was subjected to pickling, cleaning with water and drying under a condition shown in Table 1, and afterwards, the cold-rolled steel sheet was subjected to quench rolling with stretching of 0.7%, which thus manufactures the two types of cold-rolled steel sheet No. a and No. b that differ from each other in an amount of an iron-based oxide on a surface of the steel sheet. So while using cold rolled steel sheet No. a as a standard sample that has a large amount of iron-based oxide and cold rolled steel sheet No. b as a standard sample that has a small amount oxide based iron, a reflection electron image was obtained against the respective steel plates under the above mentioned conditions using a scanning electron microscope. Figure 1 shows reflection electron image photographs of No. a and No. b steel sheets, and Figure 2 shows a histogram of the number of pixels in relation to gray values of the reflection electron image photographs of steel sheets No. a and No. b. In the present invention, a gray value (point Y) that corresponds to an intersection (point X) of the histograms No. a and No. b shown in Figure 2 was defined as a threshold value. When the surface coverage of an iron-based oxide was obtained against No. a and No. b steel sheets using the above mentioned threshold value, the surface coverage of No. a steel sheet was 85, 3% and the surface coverage of the No. b steel plate was 25.8%.

[000101] To further improve chemical convertibility and eventually corrosion resistance after coating, it is preferable that, in addition to the condition that a surface coating of an iron oxide on a surface of a steel sheet after the second pickling is 40% or less, a maximum thickness of the iron-based oxide is 150 nm or less. This is due to the fact that when the maximum thickness of the iron-based oxide is 150 nm or less, there is no possibility that an iron dissolution reaction by chemical conversion treatment will be locally impaired, so that the precipitation of chemically converted crystals such as zinc phosphate cannot be locally suppressed. The maximum thickness of an iron-based oxide can preferably be set at 130 nm or less.
[000102] The maximum thickness of an iron-based oxide is obtained as follows.
[000103] First, 10 pieces of extraction replicas, by which a cross-section of a steel plate, which has a length of approximately 8μm in relation to a direction of width of the steel plate can be observed, were prepared by working A focused ion beam (FIB) is generated from a steel sheet surface after pickling. Then, using a transmission electron microscope (TEM) equipped with an energy scattering X-ray spectrometer (EDX) capable of investigating local cross-section information, the 8μm cross-sections of the respective replicas were photographed continuously with an acceleration voltage of 200kV and a magnification of 100,000. As an example, Figure 3 shows a photograph obtained by observing a cross-section of a coating layer formed by the first pickling present on a surface of a steel sheet by a transmission electron microscope (TEM), and Figure 4 shows a result of an EDX analysis of the coating layer. It is understood from Figure 4 that the coating layer is formed by an iron-based oxide and therefore a distance between a line A, which indicates a base steel of the steel sheet, and a line B, which indicates the largest portion of the iron-based oxide layer shown in the cross-sectional photograph in Figure 3 has been measured against all ten replicates, and the maximum thickness between the maximum measured thicknesses is assumed to be the maximum thickness of the oxide-based of iron. Additionally, it goes without saying that the sizes and quantity of replicas mentioned above, TEM measurement conditions and the like are given as an example only, and can be changed as desired.
[000104] The cold rolled steel sheet obtained by the above mentioned method exhibits excellent chemical convertibility and also exhibits excellent corrosion resistance after coating which is evaluated by a hot brine immersion test and a composite cycle corrosion test and therefore, the cold rolled steel sheet can preferably be used to produce the automobile member. EXAMPLE 1
[000105] The present invention is described in more detail with reference to the examples.
[000106] Steel that has a composition that contains 0.125% C, 1.5% Si, 2.6% Mn, 0.019% P, 0.008% S and 0.040% Al and which comprises Fe and impurities unavoidable as a balance was fabricated in such a way that the molten steel was produced by a common refining process including a converting treatment, a degassing treatment and the like and the molten steel was formed into steel materials (plates) by continuous casting. Then the plates were reheated to a temperature of 1150 to 1170°C and subsequently subjected to hot rolling in which a final rolling completion temperature is set to a value that is within a range of 850 to 880 °C, and were wound into coils at a temperature of 500 to 550 °C, thus forming hot-rolled steel sheets that have a thickness of 3 to 4 mm. Then the scales were removed from the steel sheets by applying pickling to these hot rolled steel sheets and later cold rolling was applied to the steel sheets which thus obtains cold rolled steel sheets which have a thickness of 1.8mm. Then, continuous annealing was carried out when these cold rolled steel sheets were heated to a soaking temperature of 750 to 780°C and held for 40 to 50 seconds, and afterwards these steel sheets were cooled to a temperature of 350 to 400°C from the soak temperature at a cooling rate of 20 to 30°C/second and were held for 100 to 120 seconds in a cooling stop temperature range. Thereafter, pickling, water cleaning and drying were applied to the steel sheet surfaces under conditions shown in Table 2-1 to Table 2-2 (from this point in the present document, Table 2-1 and Table 2-2 which are also collectively referred to as Table 2). From this, quench rolling was applied to the steel sheets at an elongation rate of 0.7% which thus obtains the cold rolled steel sheets No. 1 to No. 82 shown in Table 2.
[000107] The specimens were sampled from the respective cold-rolled steel sheets mentioned above. The surfaces of the steel sheets were observed using a scanning electron microscope (ULV-SEM; available from SEISS Inc.; ULTRA55) at an extremely low accelerating voltage in five fields of view with an accelerating voltage of 2kV, an operating distance of 3.0mm and a magnification of 1000 times, and spectroscopic analysis was performed using an energy scattering type X-ray spectrometer (EDX; available from Thermo Fisher Inc.; NSS312E) which thus obtains images of reflected electrons. A binary-coded processing was applied to the reflected electron images using image analysis software (Image J) while defining gray values (Y points) corresponding to intersection points (X points) of the histogram of the above-mentioned standard samples. No. a and No. b as threshold values that thus measure the area ratios of portions colored black, and an average value of the area ratios in five fields of view was obtained and the average value was defined as a surface coverage of an iron-based oxide.
[000108] Additionally, specimens were sampled from the respective cold-rolled steel sheets mentioned above, and the evaluation of spot rust generation of the cold-rolled steel sheets was performed under the following conditions. After a chemical conversion treatment and a coating treatment were applied to the specimens under the following conditions, the specimens were subjected to three types of corrosion tests consisting of a hot brine immersion test, a salt water spray test and a composite cycle corrosion test, and then the corrosion resistance after coating was evaluated. Additionally, the distribution of O, Si, Mn and Fe in the depth direction on surfaces of specimens sampled from the respective cold-rolled steel sheets was measured using a GDS.(1) POINT RUST GENERATION ASSESSMENT DURING THE STORAGE OF COLD-LAMINED STEEL SHEET
[000109] After the anti-rust oil was applied to the respective cold-rolled steel sheets mentioned above, the cold-rolled steel sheets were left in the open air while preventing influences from external factors such as dust. The presence or absence of spot rust generation on the cold-rolled steel sheets was verified approximately one month after the start of the test. An "O" rating is given to cases where the specimens did not have spot rust, and an "X" rating is given to cases where the specimens did have spot rust.(2) CHEMICAL CONVERSION TREATMENT CONDITION
[000110] A chemical conversion treatment was applied to specimens sampled from the respective cold-rolled steel sheets mentioned above with the use of a degreasing agent: FC-E2011, a surface conditioner: PL-X and a treatment agent chemical conversion: palbond PB-L3065 available from Nihon Parkerizing Co., Ltd. so a coating weight of the chemical conversion treatment coating was set at 1.7 to 3.0g/m2 under two conditions, i.e. , the standard condition and the comparison condition under a low temperature by reducing a temperature of a chemical conversion treatment solution. STANDARD CONDITION
[000111] Degreasing step: treatment temperature 40°C, treatment time 120 seconds.
[000112] Spray degreasing and surface adjustment steps: pH 9.5, room temperature, treatment temperature, treatment time 20 seconds.
[000113] Chemical conversion treatment step: chemical conversion treatment solution temperature 35°C, treatment time: 120 seconds. TEMPERATURE REDUCTION CONDITION
[000114] Condition where a temperature of the chemical conversion treatment solution in the standard condition mentioned above has been reduced to 33°C.(3) CORROSION TEST
[000115] Electrodeposition coating was applied to surfaces of specimens to which the above mentioned chemical conversion treatment was applied by electrodeposition paint: V-50 available from NIPPONPAINT Co., Ltd. so that a coating film thickness Electrodeposition is set at 25μm, and the specimens were subjected to the following three types of corrosion tests. HOT BRINE IMMERSION TEST
[000116] A cross-cut fault that has a length of 45mm is formed by a cutter on a surface of the specimen mentioned above (n=1, "n=1" which means the quantity of specimens is 1) to which the treatment of Chemical conversion and electrodeposition coating were applied and, subsequently, the specimen was immersed in 5% by mass of aqueous NaCl solution (60°C) for 360 hours. Then, the specimen was cleaned with water, dried, and an adhesive tape was adhered to the cut failure portion. From this, a tape exfoliation test in which the adhesive tape is exfoliated was performed, and a maximum total exfoliation width including the left and right sides of the shear failure portion was measured. When the maximum total exfoliation width is 6.0 mm or less, the specimen is determined to be non-defective. When the maximum overall width of the exfoliation is 5.0 mm or less, it can be judged that the corrosion resistance of the specimen in the hot brine immersion test is favorable. SALT WATER SPRINKLER TEST (SST)
[000117] A cross-sectional flaw that has a length of 45 mm is formed by a cutter on a surface of the specimen (n=1) mentioned above to which the chemical conversion treatment and electrodeposition coating have been applied, and subsequently the specimen was subjected to a saltwater spray test for 1200 hours in accordance with a neutral saltwater spray test stipulated in JIS Z2371:2000 using 5% by mass aqueous NaCl solution. From this, a tape exfoliation test was performed against the cross-cut fault portion, and a maximum total exfoliation width including the left and right sides of the shear fault portion was measured. When the maximum total exfoliation width is 5.2 mm or less, the specimen is determined to be non-defective. When the maximum total exfoliation width is 4.0 mm or less, it can be judged that the corrosion resistance of the specimen in the salt water spray test is favorable. COMPOSITE CYCLE CORROSION TEST (CCT)
[000118] A cross-sectional flaw that has a length of 45 mm is formed by a cutter on a surface of the specimen (n=1) mentioned above to which the chemical conversion treatment and electrodeposition coating have been applied, and subsequently the specimen was subjected to a corrosion test in which a cycle formed by spraying salt water (5% by mass of aqueous NaCl solution: 35°C, relative humidity: 98%) x 2 hours ^ drying (60°C, relative humidity: 30%) x 2 hours ^ humidification (50°C, relative humidity: 95%) x 2 hours was repeated 120 times, cleaned with water and then dried. Then, a tape exfoliation test was performed against the cut-fault portion, and a maximum total exfoliation width including the left and right sides of the cut-fault portion was measured. When the maximum total exfoliation width is 7.8 mm or less, the specimen is determined not to be defective. When the maximum total exfoliation width is 6.0 mm or less, it can be judged that the corrosion resistance of the specimen in the composite cycle corrosion test is favorable.
[000119] The test result mentioned above is shown in Table 2 along with the condition for the test.












[000120] From Table 2, it is understood that steel sheets of the examples of the present invention in which pickling was carried out under conditions conforming to the present invention after continuous annealing exhibit favorable chemical convertibility and favorable corrosion resistance after coating so that the generation of spot rust is suppressed, and the maximum total exfoliation width is small in all of the hot brine dip test, salt water spray test and composite cycle corrosion test. In particular, it is understood that all cold-rolled steel sheets in which a surface coating of an iron-based oxide is 40% or less exhibit excellent corrosion resistance after coating in a severe corrosion environment. It is ascertained from the result obtained by measuring the distribution of O, Si, Mn and Fe in the depth direction on surfaces of the respective steel sheets in Table 2 by a GDS that a peak of Si and a peak of O did not appear in the steel sheets that were subjected to pickling under conditions conforming to the present invention so that an oxide layer containing Si was sufficiently removed. As a reference, the profiles of O, Si, Mn and Fe in the depth direction when a surface analysis was performed by the GDS against the specimens of example #2 of the present invention and example #7 of the present invention in Table 2 are shown in Figure 5. EXAMPLE 2
[000121] Steels A to O containing compositions shown in Table 3 were manufactured so that the molten steel was produced by a common refining process including a conversion treatment, a degassing treatment and the like, and the molten steel was formed into the steel plates by continuous casting. Hot rolling was applied to these steel plates under hot rolling conditions shown in Table 4, and the steel plates are formed on the hot rolled steel sheet which has a thickness of 3 to 4mm, scale was removed from the sheet surfaces of steel by applying pickling to these hot rolled steel sheets, and later cold rolling was applied to the steel sheets, thus obtaining cold rolled steel sheets which have a thickness of 1.8 mm. Then, after the first pickling and the second pickling had been applied to the cold rolled steel sheet under conditions shown in Table 5 after continuous annealing carried out under conditions shown in Table 4 in the same way, the steel sheet was cleaned with water, and the treatment Deneutralization was applied to the steel sheet, water cleaning and drying were applied to the steel sheet. Quench rolling with 0.7% elongation was applied to the steel sheet, thus obtaining cold rolled steel sheets No. 84 to No. 107.
[000122] The specimens were sampled from the above-mentioned respective cold-rolled steel sheets obtained in such a way and, in the same way as in example 1, after the surface coating of the iron-based oxide on the surface of the steel sheet after pickling had been measured, the specimen was subjected to the following tensile test and the corrosion resistance test after coating. Additionally, the distribution of O, Si, Mn and Fe in the depth direction on surfaces in the specimens sampled from the respective cold-rolled steel sheets was measured using a GDS.(1) MECHANICAL CHARACTERISTICS
[000123] A stress test is performed in accordance with the stipulation of JIS Z 2241: 1998 using a JIS #5 stress test specimen (n=1) stipulated in JIS Z 2201: 1998 sampled from a direction orthogonal to the direction (direction C) which thus measures a tensile strength TS.(2) ASSESSMENT OF RUST GENERATION BY POINTS DURING THE STORAGE OF COLD STEEL SHEET
[000124] After the anti-rust oil was applied to the respective cold-rolled steel sheets mentioned above, the cold-rolled steel sheets were left in the open air while preventing influences from external factors such as dust. The presence or absence of rust generation by spots on cold-rolled steel sheets after approximately one month was verified. The "O" rating is given to cases where the specimens did not have spot rust, and the "X" rating is given to cases where the specimens did have spot rust.(3) CORROSION RESISTANCE AFTER COATING
[000125] The specimens were prepared by applying chemical conversion treatment and electrodeposition coating to specimens sampled from the respective cold-rolled steel sheet under the same condition as example 1. As in example 1, the specimens were subjected to three types of corrosion tests which consist of a hot brine immersion test, a salt water spray test (SST) and a composite cycle corrosion test (CCT), and then the corrosion resistance after coating was evaluated.
[000126] The test result mentioned above is shown in Table 5.









[000127] It is understood from Table 5 that the high strength cold rolled steel sheet of the example of the present invention wherein the steel sheet contains 0.5% or more of Si, and an oxide surface coating at iron base on the surface of steel sheet, whose neutralization treatment is carried out by applying pickling twice under the condition that conforms to the present invention is set at 40% or less, not only is it excellent in chemical convertibility and corrosion resistance after coating, but also has a high strength of 590MPa or more than TS tensile strength. It is ascertained from the result obtained by measuring the distribution of O, Si, Mn and Fe in the depth direction by a GDS that a Si peak and an O peak did not appear on any steel sheets that were subjected to pickling under the conditions conforming to the present invention for a Si-containing oxide layer to be sufficiently removed. EXAMPLE 3
[000128] Steel that has a composition that contains 0.125% C, 1.5% Si, 2.6% Mn, 0.019% P, 0.008% S and 0.040% Al and which comprises Fe and impurities unavoidable as a balance was fabricated in such a way that molten steel was formed into steel materials (plates) by continuous casting. The plates were reheated to a temperature of 1150 to 1170°C and subsequently subjected to hot rolling in which a final rolling completion temperature is set to a value that is within a range of 850 to 880°C, and were rolled at a temperature of 500 to 550°C, thus forming hot-rolled steel sheets having a thickness of 3 to 4 mm. The scales were removed from the steel sheets by applying pickling to these hot rolled steel sheets and later cold rolling was applied to the steel sheets thus obtaining cold rolled steel sheets which have a thickness of 1.8 mm. Then, continuous annealing was carried out when these cold rolled steel sheets were heated to a soaking temperature of 750 to 780°C and held for 40 to 50 seconds and afterwards these steel sheets were cooled to a temperature from the above mentioned soaking temperature at a cooling rate of 20 to 30°C/second and were held for 100 to 120 seconds in a cooling stop temperature range. Thereafter, the first pickling and second pickling were applied to the steel sheet surfaces under conditions shown in Table 6-1 to Table 6-2 (from this point in the present document, Table 6-1 and Table 6-2 which are also collectively referred to as Table 6) and then the steel sheets were washed with water, the neutralization treatment was applied to the steel sheets, and the steel sheets were washed with water and dried. From this, quench rolling was applied to the steel sheets at an elongation rate of 0.7% which thus obtains the cold rolled steel sheets No. 108 to No. 162 shown in Table 6.
[000129] The specimens were sampled from the respective cold-rolled steel sheets mentioned above and, using the above-mentioned method, an iron-based oxide surface coating generated on the surface of the steel sheets by pickling and a maximum thickness were measured.
[000130] Additionally, the specimens were sampled from the respective cold-rolled steel sheets mentioned above, and the evaluation of spot rust generation during storage of the cold-rolled steel sheets was performed under the following conditions and, after A chemical conversion treatment and a coating treatment were applied to the specimens under the following conditions, the specimens were subjected to three types of corrosion tests consisting of a hot brine immersion test, a salt water spray test and a composite cycle corrosion test, and then the corrosion resistance after coating was evaluated. Additionally, the distribution of O, Si, Mn and Fe in the depth direction on surfaces in the specimens sampled from the respective cold-rolled steel sheets was measured using a GDS.(1) POINT RUST GENERATION ASSESSMENT DURING THE STORAGE OF COLD-LAMINED STEEL SHEET
[000131] After the anti-rust oil was applied to the respective cold-rolled steel sheets mentioned above, the cold-rolled steel sheets were left in the open air while preventing influences from external factors such as dust. The presence or absence of rust generation by spots on the cold-rolled steel sheets after approximately one month was verified. An "O" rating is given to cases where the specimens did not have spot rust, and an "X" rating is given to cases where the specimens did have spot rust.(2) CHEMICAL CONVERSION TREATMENT CONDITION
[000132] A chemical conversion treatment was applied to specimens sampled from the respective cold-rolled steel sheets mentioned above with the use of a degreasing agent FC-E2011, a surface conditioner: PL-X and a surface treatment agent: chemical conversion: palbond PB-L3065 available from Nihon Parkerizing Co., Ltd. so a coating weight of chemical conversion treatment film was set at 1.7 to 3.0g/m2 under two conditions, namely, the standard condition and the comparison condition under a low temperature by reducing a temperature of a chemical conversion treatment solution.STANDARD CONDITION
[000133] Degreasing step: treatment temperature 40°C, treatment time 120 seconds.
[000134] Spray degreasing and surface adjustment steps: pH 9.5, room temperature of the treatment temperature, treatment time: 20 seconds.
[000135] Chemical conversion treatment step: chemical conversion treatment solution temperature 35°C, treatment time: 120 seconds. TEMPERATURE REDUCTION CONDITION
[000136] Condition where a temperature of the chemical conversion treatment solution in the standard condition mentioned above has been reduced to 33°C.(3) CORROSION TEST
[000137] Electrodeposition coating was applied to surfaces of specimens to which the above mentioned chemical conversion treatment was applied by electrodeposition paint: V-50 available from NIPPONPAINT Co., Ltd. so that a coating film thickness Electrodeposition is set at 25μm, and the specimens were subjected to the following three types of corrosion tests under more severe condition than example 1. HOT BRINE IMMERSION TEST
[000138] A cross-sectional flaw that has a length of 45 mm is formed by a cutter on a surface of the specimen (n=1) mentioned above to which the chemical conversion treatment and electrodeposition coating have been applied, and subsequently the specimen was immersed in 5% by mass of aqueous NaCl solution (60°C) for 480 hours. Then, the specimen was cleaned with water, dried, and an adhesive tape was adhered to the cut failure portion. From this, a tape exfoliation test in which the adhesive tape is exfoliated was performed, and a maximum total exfoliation width including the left and right sides of the shear failure portion was measured. When the maximum total exfoliation width is 6.0 mm or less, the specimen is determined to be non-defective. When the maximum total exfoliation width is 5.0 mm or less, it can be judged that the corrosion resistance of the specimen in the hot brine immersion test is favorable. SALT WATER SPRINKLER TEST (SST)
[000139] A cross-sectional flaw that has a length of 45 mm is formed by a cutter on a surface of the specimen (n=1) mentioned above to which the chemical conversion treatment and electrodeposition coating have been applied, and subsequently the specimen was subjected to a saltwater spray test for 1400 hours in accordance with a neutral saltwater spray test stipulated in JIS Z2371:2000 using 5% by weight aqueous NaCl solution. From this, a tape exfoliation test was performed against the cross-cut fault portion, and a maximum total exfoliation width including the left and right sides of the shear fault portion was measured. When the maximum total exfoliation width is 5.2 mm or less, the specimen is determined to be non-defective. When the maximum overall exfoliation width is 4.0 mm or less, it can be judged that the corrosion resistance of the specimen in the saltwater spray test is favorable.COMPOSITE CYCLE CORROSION TEST (CCT)
[000140] A cross-sectional flaw that has a length of 45 mm is formed by a cutter on a surface of the specimen (n=1) mentioned above to which the chemical conversion treatment and electrodeposition coating have been applied, and subsequently the specimen was subjected to a corrosion test in which a cycle formed by spraying salt water (5% by mass of aqueous NaCl solution: 35 °C, relative humidity: 98%) x 2 hours ^ drying (60 °C, relative humidity: 30%) x 2 hours ^ humidification (50°C, relative humidity: 95%) x 2 hours was repeated 150 times, cleaned with water and then dried. Then, a tape exfoliation test was performed against the cut-fault portion, and a maximum total exfoliation width including the left and right sides of the cut-fault portion was measured. When the maximum total exfoliation width is 7.8 mm or less, the specimen is determined not to be defective. When the maximum total exfoliation width is 6.0 mm or less, it can be judged that the corrosion resistance of the specimen in the composite cycle corrosion test is favorable.
[000141] The test result mentioned above is shown in Table 6.








[000142] It is understood from Table 6 that the steel sheet of the example of the present invention, wherein pickling is applied to the surface of the steel sheet after annealing under a condition that an iron-based oxide surface coating on the steel plate surface after redeblasting is set to 40% or less and a maximum thickness of the iron based oxide is 150 nm or less, had a small maximum total exfoliation width in any of the hot brine immersion test, the saltwater spray test and composite cycle corrosion test which were performed under conditions where test times were long and test environments were harsh compared to example 1 and therefore steel sheets exhibited Extremely favorable corrosion resistance after coating. Additionally, it is verified from the result obtained by measuring the distribution of O, Si, Mn and Fe in the depth direction by a GDS that a Si peak and an O peak did not appear in the steel sheets that were subjected to pickling. under conditions conforming to the present invention so that an oxide layer containing Si was sufficiently removed. INDUSTRIAL APPLICABILITY
[000143] A cold-rolled steel sheet manufactured by the present invention can have not only excellent chemical convertibility and corrosion resistance after coating, but also high strength, and therefore, cold-rolled steel sheet can be used, in preferably, as a raw material for forming automobile members and also as a raw material for forming members which are required to have substantially similar property to that of the automobile member in other fields such as household electrical appliances and architecture.

权利要求:
Claims (11)
[0001]
1. Method of manufacturing a cold rolled steel sheet, characterized in that the first pickling is applied to a steel sheet which is continuously annealed after cold rolling, the first pickling is carried out using any one of the following acidic solutions (a) and (b): (a) the acidic solution containing a nitric acid and a hydrochloric acid, in which the concentration of nitric acid is greater than 50 g/L and 200 g/L, or lower, an R1 ratio between the concentration of hydrochloric acid and the concentration of nitric acid (hydrochloric acid/nitric acid) is set to a value that is within a range of 0.01 to 0.25, and the ion concentration of Fe is defined at a value that is within a range of 3 to 50 g/L,(b) the acidic solution containing a nitric acid and a hydrofluoric acid, in which the concentration of nitric acid is greater than 50 g/L and 200 g/L or less, an R2 ratio between the hydrofluoric acid concentration and the nitric acid concentration (hydrofluoric acid/nitric acid ) is set to a value that is within a range of 0.01 to 0.25, and the Fe ion concentration is set to a value that is within a range of 3 to 50 g/L, the second pickling is applied to the steel sheet subsequently, and then the neutralization treatment is applied to the steel sheet using an alkaline solution.
[0002]
2. Method of manufacturing a cold-rolled steel sheet, according to claim 1, characterized in that the alkaline solution has a pH of 9.5 or more, and one or two or more selected from a group consisting of sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, orthophosphate and condensed phosphate are mixed in the alkaline solution.
[0003]
3. Method of manufacturing a cold-rolled steel sheet, according to claim 1 or 2, characterized in that the neutralization treatment is carried out in a state in which an alkaline solution temperature is set at a value that is within a range of 20 to 70°C, and a treatment time is set to a value that is within a range of 1 to 30 seconds.
[0004]
4. Method of manufacturing a cold-rolled steel sheet, according to any one of claims 1 to 3, characterized in that a non-oxidizing acid is used in the second pickling.
[0005]
5. Method of manufacturing a cold-rolled steel sheet, according to claim 4, characterized in that the non-oxidizing acid is any one of hydrochloric acid, sulfuric acid, phosphoric acid, pyrophosphoric acid, a formic acid, an acetic acid, a citric acid, a hydrofluoric acid, an oxalic acid, and an acid that is a mixture of two or more of these acids
[0006]
6. Method of manufacturing a cold-rolled steel sheet, according to claim 4 or 5, characterized in that the non-oxidizing acid is any one of hydrochloric acid that has a concentration of 0.1 to 50 g/ L, a sulfuric acid that has a concentration of 0.1 to 150 g/L and an acid that is a mixture of a hydrochloric acid that has a concentration of 0.1 to 20 g/L and a sulfuric acid that has a concentration from 0.1 to 60 g/L.
[0007]
7. Method of manufacturing a cold-rolled steel sheet, according to any one of claims 1 to 6, characterized in that the second pickling is carried out in a state where a temperature of the acid solution is set to a value that is within a range of 20°C to 70°C, and a pickling time is set to a value that is within a range of 1 to 30 seconds.
[0008]
8. Method of manufacturing a cold-rolled steel sheet, according to any one of claims 1 to 7, characterized in that the steel sheet contains, as a component of its composition, from 0.5 to 3 .0% by mass of Si.
[0009]
9. Method of manufacturing a cold-rolled steel sheet, according to claim 8, characterized in that the steel sheet additionally contains, as components of its composition: from 0.01 to 0.30% in mass of C, from 1.0 to 7.5% by mass of Mn, 0.05% by mass or less of P, 0.01% by mass or less of S, 0.06% by mass or less of Al , and Fe and unavoidable impurities as a balance.
[0010]
10. Method of manufacturing a cold-rolled steel sheet, according to claim 9, characterized in that the steel sheet additionally contains, as components of its composition, one or two or more of the elements selected from from the group consisting of 0.3% by mass or less of Nb, 0.3% by mass or less of Ti, 0.3% by mass or less of V, 1.0% by mass or less of Mo, 1 0.0% by mass or less of Cr, 0.006% by mass or less of B, and 0.008% by mass or less of N.
[0011]
11. Method of manufacturing a cold-rolled steel sheet, according to claim 9 or 10, characterized in that the steel sheet additionally contains, as components of its composition, one or two or more of the selected elements from a group consisting of 2.0% by mass or less of Ni, 2.0% by mass or less of Cu, 0.1% by mass or less of Ca, and 0.1% by mass or less of REM.

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法律状态:
2020-01-21| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|

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2021-09-14| B06A| Patent application procedure suspended [chapter 6.1 patent gazette]|

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2021-11-16| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|

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2022-01-18| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 12/08/2015, OBSERVADAS AS CONDICOES LEGAIS. |

优先权:

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申请号 | 申请日 | 专利标题

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JP2014-177913|2014-09-02|

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JP2014177913A|JP6137089B2|2014-09-02|2014-09-02|Cold rolled steel sheet manufacturing method and cold rolled steel sheet manufacturing equipment|

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PCT/JP2015/004043|WO2016035261A1|2014-09-02|2015-08-12|Cold-rolled steel sheet, method for producing cold-rolled steel sheet, automobile member, and equipment for producing cold-rolled steel sheet|

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