[0001]The present invention relates to a steel sheet excellent chemical conversion treatability is obtained.
Background technique
[0002]
　Recently, low fuel consumption and CO 2 for the purpose of improving the weight and collision safety of the vehicle body for the purpose of reducing emissions in the automotive field, increasing demand to use the high-strength cold-rolled steel sheet to a vehicle body or parts ing.
[0003]
　High-strength cold-rolled steel sheet, like the mild steel plate is molded in large quantities and at low cost by press working, is subjected as various members. Therefore, the high-strength cold-rolled steel sheet, obtained also high ductility and good processability. Furthermore, in general, a high-strength cold-rolled steel sheet, in order to improve the corrosion resistance and coating adhesion, is subjected chemical conversion treatment such as zinc phosphate treatment. In the chemical conversion treatment, for example 2 g / m 2 ~ 3 g / m 2 about zinc phosphate coating is formed. Sometimes Zr-based coating is formed by chemical conversion treatment. Also, often a cationic electrodeposition coating is applied over these coatings (chemical conversion layer). If cationic electrodeposition coating is performed, the surface of the chemical conversion layer is exposed to strong alkaline. Accordingly, chemical conversion layer is desired to have alkali resistance. As an index representing the alkali resistance, the parameter called P ratio is utilized. The phosphate contained in the chemical conversion treatment layer, phosphophyllite the like consisting of hopeite and Zn-Fe-P-O made of Zn-P-O. Phosphophyllite is the reaction product of Fe and zinc phosphate in the steel sheet. P ratio is determined from the peak intensity of X-ray diffraction apparatus. Peak intensity of hopeite appear in a diffraction angle 2θ = 14.55 °, peak intensity of phosphophyllite appears at a diffraction angle 2θ = 14.88 °. The X-ray peak intensity at 14.55 ° H, when the X-ray peak intensity at 14.88 ° and P, P ratio is represented by "P / (P + H)". Phosphophyllite exhibits excellent alkali resistance than hopeite. Therefore, high alkali resistance higher P ratio.
[0004]
　In general, the higher the content of Si and Mn, easily obtained high ductility and good processability. However, Si and Mn contained in the steel is easily oxidized. Therefore, the attempt to produce a high strength cold rolled steel sheet using a steel containing a large amount of Si and Mn, Si and Mn are oxidized during the annealing of the process, oxide is formed on the surface of the high strength cold rolled steel sheet that. Oxide formed on the surface reduces the chemical conversion treatability and corrosion resistance.
[0005]
　Therefore, increasing the content of high ductility and good Si order to obtain a workability and Mn, it is difficult to obtain a good chemical conversion treatability and corrosion resistance. For example, although zinc film phosphoric acid is formed by crystallization of zinc phosphate, when a low chemical conversion treatment resistance, less likely to adhere to the surface of the zinc phosphate steel plate, that the portion chemical conversion layer is not formed resulting is there. Further, the reaction of Fe with zinc phosphate in the steel sheet is inhibited hardly generated phosphophyllite by oxides, may not sufficiently alkali resistance can not be obtained. These results can not be properly performed cationic electrodeposition coating after the chemical conversion treatment, not good corrosion resistance can be obtained.
[0006]
　Conventionally been various proposals for the purpose of chemical conversion treatability or corrosion resistance or the improvement of both of these (Patent Documents 1-9). However, in the prior art, or it is difficult to sufficiently improve the chemical conversion treatability, even improved chemical convertibility, concomitantly therewith, the corrosion resistance is lowered or, tensile strength and fatigue strength is lowered or.
CITATION
Patent Literature
[0007]
Patent Document 1: JP 2004-323969 Patent Publication
Patent Document 2: JP 2009-221586 Patent Publication
Patent Document 3: JP 2010-47808 JP
Patent Document 4: JP 2010-53371 JP
Patent Document 5: JP 2012-122086 JP
Patent Document 6: JP 2008-121045 Patent Publication
Patent Document 7: JP 2005-307283 JP
Patent Document 8: JP 2010-90441 JP
Patent Document 9: JP-A 4-247849 JP
Summary of the Invention
Problems that the Invention is to Solve
[0008]
　The present invention, while avoiding the decrease in the reduction and strength of the corrosion resistance, and to provide a steel sheet which can provide excellent chemical conversion treatability.
Means for Solving the Problems
[0009]
　The present inventors have conducted extensive studies to solve the above problems. As a result, the following items were found.
　(A) oxides present on the surface of the steel sheet containing a large amount of Si and Mn is silica and manganese silicate.
　(B) Although manganese silicate can be easily removed with acid as not pitting occurs in the steel sheet, the silica can not be removed with an acid that will not pitting occurs in the steel sheet.
　Silica remaining after (c) pickling can broadly classified into dense ones and porous ones.
　(D) dense silica have excellent chemical conversion treatability than manganese silicates and porous silica.
　Even (e) porous silica remained, porous silica by performing electrolytic plating of Ni is improved chemical convertibility covered with at Ni.
[0010]
　The present inventors, as a result of further intensive studies based on these findings, and conceived to aspects of the invention described below.
[0011]
　(1)
　in
　mass%,
　C: 0.050% ~
　0.400%, Si: 0.10% ~ 2.50%, Mn: 1.20%
　~ 3.50%, P: 0.100% or less ,
　Al: 1.200% or
　less, N: 0.0100% or
　less, Cr, Mo, Ni and Cu:
　total,0.00% Nb, Ti and V: 0.000% in total ~
　% 0.200,
　B: 0.0000% ~ 0.0075%, Ca, Mg, Ce, Hf, La, Zr, Sb and REM: 0.0000% ~ 0.1000% in total, and
　balance: Fe and impurities,
in having a chemical composition expressed,
　surface, 1200 cm
　　by Fourier transform infrared spectroscopy analysis by high sensitivity reflection method -1 ~ 1300 cm -1 85% or less reflectivity in the range of wave numbers of not less than 50% an absorption peak of, 　　and, 1000 cm -1 ~ 1100 cm - If no absorption peak in the range of wave numbers, or 1000 cm -1 ~ 1100 cm -1 reflectance in the range of wave number of an absorption peak of 85% or more, 　the surface 3 mg / m 2 ~ 100 mg / m

2 steel plates of Ni is equal to or adhering.
[0012]
　(2)
　said surface, Fourier transform infrared spectroscopy 1200cm Analysis by high sensitivity reflection method -1 ~ 1300 cm -1 , characterized in that shows an absorption peak reflectance less 85% 60% or more within the range of wave numbers steel sheet according to (1) and.
Effect of the invention
[0013]
　According to the present invention, without performing processing such as reduction in the reduction and strength of the corrosion resistance occurs, it is possible to obtain an excellent chemical conversion treatability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014]
[1] Figure 1 is a diagram showing a particularly good samples degree of adhesion of the crystalline zinc phosphate.
FIG. 2 is a diagram showing a good sample degree of adhesion of zinc phosphate crystals.
FIG. 3 is a diagram adhesion degree indicates a sample of the defective crystalline zinc phosphate.
DESCRIPTION OF THE INVENTION
[0015]
　Hereinafter, embodiments of the present invention will be described.
[0016]
　First, a description will be given chemical composition of the steel used for the steel and the manufacturing according to an embodiment of the present invention. Details will be described later, the steel sheet according to the embodiment of the present invention, steel hot rolled, hot rolled after pickling, cold rolling, annealing, is produced through the annealing after pickling and plating. Therefore, the chemical composition of the steel sheet and, not only characteristics of the steel sheet, is taken into consideration these processes. In the following description, a unit of content of each element contained in the steel sheet "%" is especially meant to "mass%" unless otherwise specified. Steel sheet according to the present embodiment, C: 0.050% ~ 0.400%, Si: 0.10% ~ 2.50%, Mn: 1.20% ~ 3.50%, P: 0.100% hereinafter, Al: 1.200% or less, N: 0.0100% or less, Cr, Mo, Ni and Cu: 0.00% ~ 1.20% in total, Nb, Ti and V: 0.000% in total ~ 0.200%, B: 0.0000% ~ 0.0075%, Ca, Mg, Ce, Hf, La, Zr, Sb and rare earth metal (rare earth metal: REM): 0.0000% in total 0 .1000%, the balance has a chemical composition represented by Fe and impurities. As the impurity, those included in raw materials such as ores and scrap, intended to be included in the manufacturing process, is exemplified.
[0017]
　(C: 0.050% ~ 0.400%)
　C is martensite, tempered martensite, to form a hard tissue, such as bainite and residual austenite, is an element that improves the strength of the steel sheet. The C content is less than 0.050%, the effect can not be sufficiently obtained by this action. Therefore, C content is 0.050% or more. In order to obtain higher strength, C content is preferably 0.075% or more. On the other hand, C content is 0.400% greater, sufficient weldability can not be obtained. Therefore, C content is less 0.400%.
[0018]
　(Si: 0.10% ~
　2.50%) Si is an element for improving the strength while maintaining good processability. The Si content is less than 0.10%, the effect can not be sufficiently obtained by this action. Therefore, Si content is 0.10% or more. In order to obtain higher strength while ensuring good processability, Si content is preferably 0.45% or more, more preferably 0.86% or more. On the other hand, the Si content is 2.50% greater than the toughness is lowered, rather workability is deteriorated. Therefore, Si content is less 2.50%.
[0019]
　(Mn: 1.20% ~
　3.50%) Mn, like Si, is an element improving the strength while maintaining good processability. The Mn content is less than 1.20%, the effect can not be sufficiently obtained by this action. Therefore, Mn content is 1.20% or more. In order to obtain higher strength while ensuring good workability, Mn content is preferably 1.50% or more. On the other hand, Mn content is 3.50 percent, sufficient weldability without Tokurae. Therefore, Mn content is less 3.50%.
[0020]
　(P: 0.100% or less)
　P is not an essential element, is contained as an impurity, for example, in the steel. Processability, in terms of weldability and fatigue properties, P content is better as low as possible. Especially in the P content 0.100%, the workability and significant reduction in weldability and fatigue properties. Accordingly, P content is 0.100% or less.
[0021]
　(Al: 1.200% or
　less) Al is not an essential element, is contained as an impurity, for example, in the steel. From the viewpoint of workability, Al content is better as low as possible. In particular Al content is 1.200% greater than the significant reduction in workability. Therefore, Al content is at most 1.200%.
[0022]
　(N: 0.0100% or less)
　N is not an essential element, is contained as an impurity, for example, in the steel. From the viewpoint of workability, N content, the better the lower the. In particular N content is 0.0100% greater than the significant reduction in workability. Therefore, N content is 0.0100% or less.
[0023]
　(Cr, Mo, Ni and Cu:
　0.00% ~ 1.20% in total) Cr, Mo, Ni and Cu contributes to further improvement of the strength of the steel sheet. Therefore, Cr, Mo, Ni or Cu, or any combination thereof may be contained. However, Cr, Mo, at 1.20 percent content of Ni and Cu in total, unnecessarily cost increases this effect is saturated. Further, Cr, Mo, at 1.20 percent content of Ni and Cu in total, halves cast during the casting occurs and it may not be produced in the steel sheet. Accordingly, the content of Cr, Mo, Ni and Cu is less than 1.20% in total.
[0024]
　(Nb, Ti and V: total% ~ 0.200
　0.000%) Nb, Ti and V contribute to further improvement of the strength of the steel sheet. Therefore, Nb, Ti or V, or any combination thereof may be contained. However, Nb, In 0.200 percent content of Ti and V is a total, unnecessarily cost increases this effect is saturated. Moreover, Nb, In 0.200 percent at a content of Ti and V in total, may not sufficiently weldability can not be obtained. Therefore, Nb, the content of Ti and V is less than 0.200% in total.
[0025]
　(B: 0.0000% ~ 0.0075%)
　B contributes to further improvement of the strength of the steel sheet. Thus, B may be contained. However, the B content is 0.0075% greater, unnecessarily cost increases this effect is saturated. Further, the B content is 0.0075%, more than halves cast during the casting occurs and it may not be produced in the steel sheet. Therefore, B content is less 0.0075%.
[0026]
　(Ca, Mg, Ce, Hf , La, Zr, Sb and REM:
　0.0000% ~ 0.1000% in total) Ca, Mg, Ce, Hf, La, Zr, Sb and REM are formability of the steel sheet It contributes to the improvement of. Therefore, Ca, Mg, Ce, Hf , La, Zr, Sb or REM, or any combination thereof may be contained. However, Ca, Mg, Ce, Hf , La, Zr, 0.1000 percent at a content of Sb and REM in total is unnecessarily cost increases this effect is saturated. Further, Ca, Mg, Ce, Hf , La, Zr, 0.1000 percent at a content of Sb and REM in total is halves cast during the casting occurs and it may not be produced in the steel sheet. Accordingly, the content of Ca, Mg, Ce, Hf, La, Zr, Sb and REM are less 0.1000% in total.
[0027]
　REM is Sc, refers to a total of 17 kinds of elements of Y and lanthanoids, the content of REM means the total content of these 17 kinds of elements. Lanthanide is industrially, is added, for example, as a misch metal.
[0028]
　Next, a description will be given surface of the steel sheet according to an embodiment of the present invention. Surface of the steel sheet according to the present embodiment, high-sensitivity reflection method Fourier transform infrared spectroscopy at 1200cm by -1 ~ 1300 cm -1 reflectance in the range of wave numbers of 85% to 50%, preferably 60% It shows an absorption peak of 85% or less. Furthermore, the surface of the steel sheet according to the present embodiment, 1000 cm -1 ~ 1100 cm -1 or no absorption peak in the range of wave numbers, or 1000 cm -1 ~ 1100 cm -1 reflectance in the range of wave numbers of 85 % shows the more absorption peak. Further, the surface of the steel sheet according to the present embodiment is 3 mg / m 2 ~ 100 mg / m 2 is adhered Ni of.
[0029]
　As described above, the steel sheet according to the present embodiment, the steel of the hot rolling, hot-rolled after pickling, cold rolling, annealing, is manufactured through the electroplating or the like after annealing pickling and Ni. During annealing, oxide on the surface of the cold-rolled steel sheet obtained by cold rolling is produced, the oxide present on the surface of the annealed steel sheet obtained by annealing. This is because Si and Mn are easily oxidized materials, because the Si and Mn is selectively oxidized near the surface of the cold rolled steel sheet. The oxide is silica and manganese silicate. To manganese silicate readily soluble in acid, but can be easily removed with acid to the extent that pitting does not occur, the silica can not be removed by acid to the extent that no pitting occurred in cold rolled steel sheet. Therefore, when the annealing after pickling using such acids, part of the manganese silicate or the whole is removed, the silica is left. Silica present after the annealing after pickling can be divided into dense ones and porous ones. When depositing a Ni on annealed steel sheets by electroplating in a state of dense silica and porous silica is present, porous silica is covered with Ni. Ni is the portion of silica annealed steel sheet is not present, i.e., adheres to the surface of the base. Therefore, the surface of the steel sheet according to the present embodiment there are silica, Ni on the surface of the silica and base material are attached.
[0030]
　Manganese silicate inhibits chemical conversion treatability, and easily dissolved in an acidic atmosphere. The barrier against corrosive factors manganese silicate is low. Therefore, when the manganese silicate is present in a larger amount on the surface of the steel sheet is not good chemical conversion treatability can not be obtained, also because it can not properly form a chemical conversion treatment layer, not good corrosion resistance can be obtained. Silica can be classified into dense ones and porous ones, dense silica have good chemical conversion treatability has also good barrier properties against corrosion factor. Barrier property against corrosive factors porous silica is lower than that of the dense silica, but by Ni is adhered to porous silica by electrolytic plating, good chemical conversion treatment can be obtained.
[0031]
　High sensitivity reflection: Fourier transform infrared spectroscopy according to (reflection absorption spectrometry RAS) method (Fourier transform-infrared spectroscopy: FT -IR) 1200cm analysis -1 ~ 1300 cm -1 absorption peak appearing in the range of the presence of silica show. As described above, in manufacturing the steel sheet according to the present embodiment, silica and manganese silicate generated in annealing, but to remove some or all of the manganese silicate by annealing after pickling, the occurrence of pitting silica is left to suppress. Therefore, in the present embodiment, silica is present on the surface of the steel sheet, the surface 1200 cm -1 ~ 1300 cm -1 indicating an absorption peak in the range of wave numbers. Reflectance at a wave number which indicates the absorption peak indicates the presence degree silica, as the reflectivity is low, indicating that the infrared absorptivity is high, silica is often present. Then, the reflectivity is less than 50%, the silica is present in excess, not sufficiently covered porous silica by Ni, it is impossible to obtain a good chemical conversion treatability. On the other hand, in order to the reflectance 85 percent, either reduce the production amount of silica in the annealing, it is necessary to increase the removal of the silica in the annealing after pickling. In order to reduce the generation amount of silica in the annealing, it is necessary to increase the dew point in the furnace during annealing, the tensile strength and fatigue strength caused significant decarburization decreases. In order to increase the removal of the silica, it is necessary to perform a strong acid washing, bending property caused significant pitting decreases. In other words, the reflectivity at 85 percent, desired mechanical properties can not be obtained. Thus, the surface of the steel sheet, 1200 cm with FT-IR analysis by RAS method -1~ 1300 cm -1 reflectance in the range of wave numbers of 85% to 50%, preferably denote the absorption peak of 85% or more and 60% or less. Below, the "FT-IR analysis by the RAS method", may be simply referred to as "FT-IR analysis."
[0032]
1000cm　with FT-IR analysis -1 ~ 1100 cm -1 absorption peak appearing in the range of wave numbers indicating the presence of a manganese silicate. Since manganese silicate to reduce the chemical conversion treatability, good The less. Thus, the surface of the steel sheet, 1000 cm with FT-IR analysis -1 ~ 1100 cm -1 it is preferred that no absorption peak in the range of wave numbers. 1000 cm -1 ~ 1100 cm -1 even shows an absorption peak in the range of wave number, the reflectance at a wave number which indicates the absorption peak is acceptable small amount of manganese silicate when 85% or more. On the other hand, 1000 cm -1 ~ 1100 cm -1 in the less than 85% reflectance at a wave number illustrating an absorption peak appearing in the range of wave numbers, manganese silicate is present in excess, not good chemical conversion treatability can be obtained and, It can not be properly formed chemical conversion layer, not good corrosion resistance can be obtained. Thus, the surface of the steel sheet, 1000 cm with FT-IR analysis -1 ~ 1100 cm -1 or no absorption peak in the range of wave numbers, or 1000 cm -1 ~ 1100 cm -1 reflectance in the range of wave numbers of 85 % denote the above absorption peaks.
[0033]
　Ni deposited on the surface of the steel sheet according to the present embodiment, improving the chemical conversion treatability over the porous silica. Adhesion amount is 3 mg / m of Ni 2 by weight, no sufficient chemical conversion treatability can not be obtained. Accordingly, the adhesion amount of Ni is 3 mg / m 2 is at least. In order to obtain more excellent chemical conversion treatability, deposition of Ni is preferably 10 mg / m 2 or more, more preferably 40 mg / m 2 is at least. On the other hand, the adhesion amount of Ni is 100 mg / m 2 in greater than an excessive Ni nobler than Fe which is the main component of the steel sheet, no sufficient corrosion resistance can not be obtained. Accordingly, the adhesion amount of Ni is 100 mg / m 2 or less. In order to obtain more excellent corrosion resistance, adhesion amount of Ni is preferably 50 mg / m 2 or less. Ni is not required to cover the entire porous silica, there is no need to cover the whole of the portion exposed from the silica matrix.
[0034]
　Adhesion amount of Ni can be measured using a fluorescent X-ray analyzer. For example, previously, the X-ray intensity measured adhesion amount of Ni is using known samples, preparing a calibration curve showing the relationship between the adhesion amount and the X-ray intensity of Ni, using the calibration curve, from X-ray intensity in the steel to be measured can be specified coating weight and Ni.
[0035]
　Next, a method for manufacturing a steel sheet according to the embodiment of the present invention. In this way, the hot rolling of steel having the above chemical composition, hot-rolled after pickling, cold rolling, annealing, electrolytic plating annealing after pickling and Ni performed.
[0036]
　Hot rolling, pickling, and cold rolling after hot rolling can be performed in common conditions.
[0037]
　Annealing after cold rolling, silica and manganese silicate formed on the surface of the cold-rolled steel sheet obtained by cold rolling, carried out in difficult conditions occur internal oxidation. As annealing, it is preferable to carry out the continuous annealing. By adjusting the amount of silica produced by annealing at FT-IR analysis of the surface of the steel sheet according to the embodiment 1200 cm -1 ~ 1300 cm -1 the reflectance at a wave number illustrating an absorption peak appearing in the range of wave numbers it is possible to control. The amount of silica produced by annealing can be controlled by adjusting the temperature and atmosphere in the example annealing. As the temperature of the annealing is high, silica is often produced. Atmosphere annealing, N containing oxygen atoms (O) 2 is preferably controlled by adjusting the oxygen potential in the atmosphere. Higher oxygen potential is high, silica is often generated, the reflectance becomes lower infrared absorptivity becomes higher. How to adjust the amount and reflectance of silica is not particularly limited. When manufacturing a steel sheet, the desired amount of silica is produced condition, that is, 1200cm by FT-IR analysis -1 ~ 1300 cm -1 the reflectance at a wave number illustrating an absorption peak appearing in the range of wave numbers of 50% 85% less than, preferably previously investigated conditions comprising 85% 60% or less, it is preferable to employ this condition. For example, O 2 concentration following N 50 ppm 2 in an atmosphere, H 2 at a concentration of 3% and a dew point is -35 ° C. or less than -20 ° C. greater than the reflectance tends to be lower.
[0038]
　If the oxygen potential is too high, the silica does not easily formed on the surface of the cold rolled steel sheet, internal oxidation proceeds, 1200 cm with FT-IR analysis -1 ~ 1300 cm -1 wavenumbers showing the absorption peak appearing in the range of wave numbers reflectance in the increases. When the internal oxidation proceeds decrease in reduction and fatigue strength of the tensile strength due to decarburization becomes remarkable. The extent of decarburization can be confirmed based on the thickness of the decarburized layer. For example, the area fraction of the hard tissue in 1/4 the thickness of the plate thickness of the steel sheet S1, when the area fraction of hard microstructures in the surface layer of the steel sheet was S2, the value of the ratio S2 / S1 of 0.40 or more the maximum depth of a part can be regarded as a thickness of the decarburized layer. To avoid a decrease in degradation and fatigue strength of the tensile strength, it is preferable that the thickness of the decarburized layer is 3μm or less. The here means hard tissues, martensite, tempered martensite, refers to a structure consisting of bainite or retained austenite, or any combination thereof. For example, O 2 concentration following N 50 ppm 2 in an atmosphere, H 2 at a concentration of 3% and decarburization greatly dew point is -10 ° C. greater than the value of the ratio S2 / S1 is less than 0.40 fear there is.
[0039]
　"H 2 O ￩ ￫H 2 Tasu1/2 (O 2 as can be seen from the equilibrium equation of)", O of the annealing furnace 2 the higher the concentration, H 2 higher O concentration, or, H 2 concentration the lower the oxygen potential of the annealing furnace is increased. H 2 O concentration may be represented by the water vapor concentration or dew point.
[0040]
　After annealing, it is removed by annealing after pickling a part or all of the manganese silicate produced by annealing. By adjusting the amount of manganese silicate remaining after the annealing after pickling, 1000 cm with FT-IR analysis of the surface of the steel sheet according to the present embodiment -1 ~ 1100 cm -1It is possible to control the reflectance at a wave number illustrating an absorption peak appearing in the range of wave numbers. The amount of manganese silicate remaining can be controlled by adjusting, for example, annealing after pickling conditions. Higher concentration of the acid is high, as the temperature of the acid is high, the longer the time the annealed steel sheet is in contact with the acid, manganese silicate is reduced. The annealing after pickling, for example, the surface of the annealed steel sheet is a concentration of 3.0 wt% to 6.0 wt%, the temperature is maintained wet with a 50 ° C. - 60 ° C. HCl 3 seconds to 10 seconds. Wet with hydrochloric acid, the annealed steel sheet can be obtained by immersion in hydrochloric acid, it can also be obtained by spraying the hydrochloric acid annealed steel sheets. The concentration of hydrochloric acid is less than 3.0 mass%, manganese silicate is hardly dissolved. Thus, the concentration of hydrochloric acid is preferably 3.0 mass% or more. The concentration of hydrochloric acid is more than 6.0 mass%, there is a possibility that fine pitting generated on the surface of the annealed steel sheet. Thus, the concentration of hydrochloric acid is preferably not more than 6.0 mass%. The temperature of the hydrochloric acid is lower than 50 ° C., manganese silicate is hardly dissolved. Therefore, the temperature of the hydrochloric acid is preferably 50 ° C. or higher. The temperature of the hydrochloric acid is 60 ° C. greater, there is a fear that fine pitting generated on the surface of the annealed steel sheet. Therefore, the temperature of the hydrochloric acid is preferably 60 ° C. or less. The time is wet with hydrochloric acid is less than 3 seconds, manganese silicate is hardly dissolved. Therefore, the time is preferably at least 3 seconds. This time is greater than 10 seconds, there is a possibility that fine pitting generated on the surface of the annealed steel sheet. Therefore, this time the time is less than 10 seconds. Annealing pickling can remove manganese silicate generated by annealing is preferably carried out in pitting hardly occurs conditions annealed steel sheets is not limited to the above example. Even pitting occurs, depth number of more pitting 1μm may be at 5 or less in view of any cross-section width of 100 [mu] m. When the depth is more than the pitting 1μm any cross-sectional width is five super present in the field of view of 100 [mu] m, or not sufficient corrosion resistance can not be obtained, because a sufficient fatigue strength can not be obtained. Acid used in the annealing after pickling is not limited to hydrochloric acid. Then, Ma-1 ~ 1100 cm -1 reflectance increases at a wave number illustrating an absorption peak appearing in the range of wave number, if there is no manganese silicate, absorption peak does not appear in this range. How to adjust the amount and reflectance manganese silicate is not particularly limited. When manufacturing a steel sheet, the type of acid, including, pitting hardly occurs in annealed steel sheet, the condition where the amount of manganese silicate is within the desired range, 1000 cm in clogging the FT-IR analysis -1 ~ 1100 cm -1 or absorption peaks in the range of wave number does not appear, even appeared, the conditions under which the reflectance at a wave number which indicates the absorption peak is 85% or more in advance investigation, it is preferable to employ this condition.
[0041]
　After annealing after pickling, depositing a Ni on the surface of the annealed steel sheet by electrolytic plating. As a result, porous silica is covered with Ni. The treatment liquid used in the electrolytic plating, for example nickel sulfate aqueous solution, may be used nickel chloride aqueous solution, a general processing solution such as nickel carbonate solution. Adhesion amount of Ni can be adjusted by changing the current density during concentration and electrolytic plating, for example the treatment liquid. As described above, Ni is not necessary to cover the entire porous silica, there is no need to cover the whole of the portion exposed from the silica matrix.
[0042]
　In this way, it is possible to produce a steel sheet according to the embodiment of the present invention.
[0043]
　Applications of the steel sheet according to an embodiment of the present invention is not particularly limited. For example, preferably, after it formed by pressing or the like, using subjected to chemical conversion treatment of zinc phosphate treatment. More preferably, use is subjected to electrodeposition coating on the chemical conversion layer formed by chemical conversion treatment.
[0044]
　The above embodiments are all merely illustrate concrete examples of implementing the present invention, in which technical scope of the present invention should not be limitedly interpreted. That is, the present invention is its technical idea or without departing from the essential characteristics thereof, can be implemented in various forms.
Example
[0045]
　Next, a description will be given of an embodiment of the present invention. Conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is not limited to this single example of conditions. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0046]
　In this test, the hot rolling of steel having the chemical compositions shown in Table 1, through the pickling and cold rolling after hot rolling, the thickness was obtained cold-rolled steel sheet of 1.2 mm. Blank in Table 1 indicates that the content of the element is less than the detection limit, the balance being Fe and impurities.
[0047]
[Table 1]

[0048]
　Then, to obtain annealed steel sheet was annealed under conditions peak metal temperature is 820 ° C. by continuous annealing apparatus cold-rolled steel sheet. Gas atmosphere of the annealing furnace, H 2 and water vapor (H 2 N containing O) 2 , the atmospheric. H during annealing 2 concentrations shown in Table 2. The amount of water vapor was controlled by the dew point in the furnace shown in Table 2.
[0049]
　Then, it was subjected to annealing after pickling of the annealed steel sheet. The annealing after pickling, employed was a three types of conditions shown in Table 2. In one of the conditions (weak wash) concentration of 5 mass%, blowing 6 seconds of 60 ° C. hydrochloric acid annealed steel sheet temperature, and then water washing. In one other conditions (first strong acid washing), concentration of 10% by weight, temperature is blown for 20 seconds of 90 ° C. hydrochloric acid annealed steel sheets were then washed with water. In another condition (second strong acid washing), the concentration is 2% by mass, the temperature of the annealed steel sheet was immersed for 2 seconds in the 70 ° C. hydrochloric acid and then washed with water.
[0050]
　Then, was deposited Ni on the surface of the annealed steel sheet by electrolytic plating. The plating bath, with nickel sulfate aqueous solution was adjusted to 2 g / L in terms of Ni concentration. Bath temperature was set to 40 ℃. It was adjusted deposition of Ni by changing the voltage. The amount of deposited Ni was measured using a fluorescent X-ray analyzer. Table 2 shows the adhesion amount and Ni.
[0051]
　In this manner it was produced 56 kinds of steel plates. And it was subjected to FT-IR analysis of the surface of these steel sheets. The FT-IR analysis using Fourier transform infrared spectroscopic analysis apparatus of the FT-IR6200 type manufactured by JASCO Corporation. The FT-IR analysis, the wave number of the infrared absorption spectrum 1200 cm -1 ~ 1300 cm -1 absorption peak, and 1000cm within the range of -1 ~ 1100 cm -1 identifies the absorption peak in the range of, these absorption It was determined reflectance at a wave number of a peak. The results are shown in Table 2. As described above, 1200 cm -1 ~ 1300 cm -1 reflectance at a wave number indicating an absorption peak in the range of wave numbers of reflecting the amount of silica, 1000 cm -1 ~ 1100 cm -1 absorption in the range of wave numbers reflectance at a wave number of a peak reflects the amount of manganese silicate. Underlined in Table 2 indicates that the value is out of range of the present invention.
[0052]
[Table 2]

[0053]
　To investigate the pitting of each steel plate. In this study, any surface near the cross section of the steel sheet was observed with a scanning electron microscope, the depth be present in any cross-sectional width 100μm field was investigated how many more pitting 1 [mu] m. The results are shown in Table 3.
[0054]
　The decarburized layer of the thickness of each steel sheet were investigated. In this study, the hard tissue of area fraction S1, and the area fraction S2 of the hard tissue in the surface layer was measured at 1/4 the thickness of the plate thickness of the steel sheet, were these ratios S2 / S1 and the thickness of the decarburized layer . In the measurement of the area fraction S1 and the area fraction S2, the observation surface parallel plate thickness cross section in the rolling direction of the steel sheet, subjected to polishing and nital etching of the observation plane, field emission scanning electron microscope (FE- by SEM), it was observed at 500-fold to 3000-fold magnification. In this case, draw a line parallel to the plate surface of the steel sheet, line obtains a total length L that overlaps with the hard tissue, the ratio L / L0 of the length L0 of the line, the area fraction of the hard tissue at the depth position and the. The results are shown in Table 3.
[0055]
　The tensile strength of each steel sheet, chemical conversion treatability and also the evaluation of corrosion resistance after coating was performed.
[0056]
　In the evaluation of tensile strength, cut out JIS5 No. specimen perpendicular to the rolling direction of a steel plate, a tensile test was performed at room temperature. Then, the tensile strength is greater than or equal to 780MPa ○, was evaluated as × if it is less than 780MPa. The results are shown in Table 3.
[0057]
　In the evaluation of the chemical conversion treatability, first, was cut out 70 mm × 150 mm from the steel sheet was subjected to degreasing and chemical treatment of the test piece. In the degreasing, the concentration in the sample was 120 seconds sprayed at 40 ° C. The aqueous solution of the degreasing agent 18 g / L, and then washed with water. The degreasing agent, using a fine cleaner E2083 manufactured by Nippon Parkerizing Co.. The chemical conversion treatment, a test piece concentrations were immersed for 60 seconds at room temperature in an aqueous solution of a surface treatment agent of 0.5 g / L, was immersed for 120 seconds in zinc phosphate treatment agent, washed with water, a chemical conversion coating film by drying the formed. As the surface treatment agent, using a Nippon Parkerizing Co. Prepalene XG, as the zinc phosphate treatment agent, using Nippon Parkerizing Co., Ltd. Palbond L3065.
[0058]
　The chemical conversion as appearance evaluation of treated film, the top of the specimen, observed in the middle and lower portions of the three scanning electron microscope (SEM) the use by 1000-fold magnification, the degree of adhesion of the crystalline zinc phosphate the observed. Then, the ratio of the area which is not film zinc phosphate is formed ○ a of less than 5 area%, those less than 5 area% or more and 20 area% △, it was evaluated as × more than 20 area%. The results are shown in Table 3. The SEM photograph of a sample in which the evaluation of ○ shown in FIG. 1, a SEM photograph of a sample in which the evaluation of △ shown in FIG. 2 shows an SEM photograph of a sample in which the evaluation of × in FIG.
[0059]
　Measurement of adhesion amount of chemical conversion coating film using X-ray fluorescence was also performed. In this measurement relates to P the intensity of the fluorescent X-rays, the adhesion amount of the chemical conversion coating of zinc phosphate was used a calibration curve prepared in advance using a known steel sheet. Chemical conversion coating coating weight of about chemical conversion is low low, 2 g / m 2 if more adhesion amount is, is good chemical conversion treatability. In this evaluation, coating weight of 2 g / m 2 ○ the above things, 1.5 g / m 2 or more 2 g / m 2 less than what the △, 1.5 g / m 2 was × those below. The results are shown in Table 3.
[0060]
　In the evaluation of corrosion resistance after painting, first, similarly to the evaluation of the chemical conversion treatability of the steel sheet to form a chemical conversion coating, it was coated electrodeposition paint thereon. The electrodeposition paint, using a POWERNICS manufactured by Nippon Paint Co., Ltd.. In this coating, applying a voltage in a state in which the specimen temperature was immersed in 30 ° C. of electrodeposition coating, thickness of the coating was adjusted energization time so that 20μm in dry thickness at 150V voltage. Energization time was about 3 minutes. The film thickness was measured using an electromagnetic film thickness meter.
[0061]
　Then, the × shaped cut flaw to reach from the coating to the material of the test piece (steel plate) formed with a cutter knife in the center of the test piece, next to the end face (side face) by sealing at the tape, to prepare a sample for the corrosion resistance test. This was salt spray test by a method described in JIS Z 2371. The test time is 1000 hours, if it is within 2mm maximum blister width on one side from the cut flaw ○, if it is within 2mm ultra-3mm △, was evaluated as × if 3mm greater. The results are shown in Table 3. Underlined in Table 3 indicates that the numerical value is outside the desired range.
[0062]
[table 3]

[0063]
　In Test No. 1, 3, 6 ~ 8, 10 ~ 14, 16 ~ 18,21,23,27 ~ 29,32,34,38 ~ 40, 43 ~ 45 and 49-51, are within the scope of the present invention Therefore, it obtained excellent chemical convertibility and corrosion resistance after coating. FT-IR analysis at 1200 cm -1 - 1300 cm -1 Test Nos 1,6-reflectance below 85% 60% at a wave number illustrating an absorption peak appearing in the range of wave numbers of 8, 11 ~ 14, 16 ~ in 18,21,27 ~ 29,32,38 ~ 40, 43 ~ 45 and 49-51, is particularly excellent chemical conversion treatability and corrosion resistance after coating was obtained.
[0064]
　In Test No. 2,9,22 and 33, 1000 cm with FT-IR analysis -1 ~ 1100 cm -1 for reflectance at a wave number illustrating an absorption peak appearing in the range of wave number of less than 85%, chemical conversion treatability It is low, after painting corrosion resistance was also low accordingly. Manganese silicate is considered to be because that was a large amount of residual.
[0065]
　In Test No. 15,26,37 and 48, the amount of deposition of Ni is 3 mg / m 2 total for chemical conversion treatment is low, after painting corrosion resistance was also low accordingly. In Test No. 19,30,41 and 52, the amount of deposition of Ni is 100 g / m 2 because it is greater, excellent chemical conversion treatability is that obtained, corrosion resistance after painting was low.
[0066]
　In Test No. 4,5,24,25,35,36,46 and 47, due to performing annealing under conditions such dare decarburization occurs, i.e. the dew point is high, the oxygen potential was annealed at a high atmosphere, thick decarburized layer is formed. For this reason, the fatigue strength is lowered. Further, 1200 cm in FT-IR analysis -1 ~ 1300 cm -1 reflectance at a wave number illustrating an absorption peak appearing in the range of wave number has been a 85%.
[0067]
　In Test No. 20,31,42 and 53, since the dare pitting was annealed after pickling prone conditions, i.e. for performing the first strong acid washing, many pitting occurred. Therefore, bending workability deteriorates. Further, 1200 cm in FT-IR analysis -1 ~ 1300 cm -1 reflectance at a wave number illustrating an absorption peak appearing in the range of wave number has been a 85%.
[0068]
　In Test No. 54-56, since the composition of the steel is out of the range of the present invention, the tensile strength was low.
[0069]
　Any test numbers 57-60, for dare pitting was annealed after pickling prone conditions, i.e. for performing the second strong acid washing, many pitting occurred. Therefore, bending workability deteriorates. Further, 1200 cm in FT-IR analysis -1 ~ 1300 cm -1 reflectance at a wave number illustrating an absorption peak appearing in the range of wave number has been a 85%.
Industrial Applicability
[0070]
　The present invention is, for example, can be used in industry in which a suitable steel plate to the body or parts of an automobile.

claims

[Claim 1] By mass%,C: 0.050% ~
　0.400%, Si: 0.10% ~ 2.50%, Mn: 1.20%
　~ 3.50%, P: 0.100% or
　less, Al: 1.200% or
　less, N: 0.0100% or
　less, Cr, Mo, Ni and Cu:
　total,0.00% Nb, Ti and V: 0.000% in total ~ 0.200
　%,
　B: 0.0000% ~ 0.0075%, Ca, Mg, Ce, Hf, La, Zr, Sb and REM: 0.0000% ~ 0.1000% in total, and
　balance: Fe and impurities,
in has a chemical composition expressed,
　surface,
　　highly sensitive reflection method Fourier transform infrared spectroscopy at 1200cm by -1 ~ 1300 cm -1 wavenumber absorption peak reflectivity in the range below 85% 50% of are shown,
　　and, 1000 cm -1 ~ 1100 cm -1 wave Or no absorption peak in the range of, or 1000 cm -1 ~ 1100 cm -1 reflectance in the range of wave number of an absorption peak of more than 85%, 3 mg / m
　on the surface 2 ~ 100 mg / m 2Steel sheet of Ni is equal to or adhering.
[Claim 2]
　It said surface, Fourier transform infrared spectroscopy at 1200cm according sensitive reflection method -1 ~ 1300 cm -1 claims reflectance in the range of wave number, characterized in that it presents the following absorption peaks 85% 60% steel sheet according to claim 1.