Steel sheet for cans and method for producing the same

Abstract

Provided is a steel sheet for cans that is excellent in adhesion, weldability, and corrosion resistance. The steel sheet for cans has, on the surface of the steel sheet, in order from the steel sheet side, a metallic chromium layer and a chromium hydrous oxide layer. The chromium hydrous oxide layer contains chromium element Cr and at least one element M selected from the group consisting of sodium, magnesium, potassium, and calcium. The molar ratio M / Cr of the element M to the chromium element Cr is 0.010 or more and 0.100 or less. The chromium hydrous oxide layer contains chromium hydroxide X, and the molar ratio X / Cr of the chromium hydroxide X to the chromium element Cr is 0.400 or more and 0.800 or less.

Description

Technical Field

[0001] The present invention relates to a steel sheet for cans and a method for manufacturing the same.

Background Art

[0002] Conventionally, a steel sheet for cans having a "metal chromium layer" and a "chromium hydrated oxide layer" on the surface of the steel sheet has been known (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] For a steel sheet for cans, in addition to good corrosion resistance, good weldability is also required. Furthermore, the steel sheet for cans may also be required to have excellent adhesion to paints and films (hereinafter, simply referred to as "adhesion"). Therefore, an object of the present invention is to provide a steel sheet for cans and a method for manufacturing the same, both of which have excellent adhesion, weldability, and corrosion resistance.

Means for Solving the Problems

[0005] As a result of intensive studies, the present inventors have found that the above object can be achieved by adopting the following configuration, and have completed the present invention. That is, the present invention provides the following [1] to [5]. [1]The steel sheet for cans has a metal chromium layer and a chromium hydrated oxide layer in this order from the steel sheet side on the surface of the steel sheet. The chromium hydrated oxide layer contains chromium element Cr and at least one element M selected from the group consisting of sodium, magnesium, potassium, and calcium, and the molar ratio M / Cr of the element M to the chromium element Cr is 0.010 or more and 0.100 or less. The chromium hydrated oxide layer contains chromium hydroxide X, and the molar ratio X / Cr of the chromium hydroxide X to the chromium element Cr is 0.400 or more and 0.800 or less. [2]The adhesion amount of the metal chromium layer is 50 mg / m 2 or more and 200 mg / m 2 or less. The steel sheet for cans according to [1] above. [3]The adhesion amount in terms of chromium of the chromium hydrated oxide layer is 3 mg / m 2 or more and 20 mg / m 2 or less. The steel sheet for cans according to [1] or [2] above. [4]A method for manufacturing the steel sheet for cans according to any one of [1] to [3] above, wherein the steel sheet is subjected to a cathodic electrolysis treatment C1 using an aqueous solution 1 containing a hexavalent chromium compound, a fluorine-containing compound, and sulfuric acid, and then, using an aqueous solution 2 having a content of the element M of 0.10 to 1.00 mmol / L, a cathodic electrolysis treatment C2 is performed at an electric quantity density of 0.30 to 3.00 C / dm 2 . A method for manufacturing a steel sheet for cans. [5]The pH of the aqueous solution 2 is 9.0 or more and 11.5 or less. The method for manufacturing a steel sheet for cans according to [4] above. [Advantages of the Invention]

[0006] According to the present invention, it is possible to provide a steel sheet for cans and a method for manufacturing the same, both of which have excellent adhesion, weldability, and corrosion resistance. [Embodiments for Carrying Out the Invention]

[0007] [Steel Sheet for Cans] The steel sheet for cans of the present embodiment has a metal chromium layer and a chromium hydrated oxide layer in this order from the steel sheet side on the surface of the steel sheet. In this embodiment, the chromium hydroxide layer contains chromium element Cr and at least one element M selected from the group consisting of sodium, magnesium, potassium, and calcium, and the molar ratio (M / Cr) of element M to chromium element Cr is 0.010 or more and 0.100 or less. Also, in this embodiment, the chromium hydroxide layer contains chromium hydroxide X, and the molar ratio (X / Cr) of chromium hydroxide X to chromium element Cr is 0.400 or more and 0.800 or less. The steel sheet for cans of this embodiment is excellent in adhesion, weldability, and corrosion resistance. Hereinafter, each component of the steel sheet for cans of this embodiment will be described in more detail.

[0008] 〈Steel Sheet〉 The type of the steel sheet is not particularly limited. Usually, steel sheets (for example, low-carbon steel sheets, extra-low-carbon steel sheets) used as container materials can be used. The manufacturing method of the steel sheet is also not particularly limited. It is manufactured through processes such as hot rolling, pickling, cold rolling, annealing, and temper rolling from a normal steel slab manufacturing process. Examples of the composition of the steel sheet include, but are not limited to, the composition defined by ASTM standards. The thickness of the steel sheet is also not particularly limited, for example, it is 0.10 mm or more and 0.60 mm or less. Note that "steel sheet" is a concept that includes "steel strip".

[0009] 〈Metal Chromium Layer〉 The metal chromium layer suppresses the surface exposure of the steel sheet and improves the corrosion resistance.

[0010] 《Coating Amount》 From the viewpoint of obtaining good corrosion resistance, the coating amount of the metal chromium layer is preferably 50 mg / m 2 or more, more preferably 70 mg / m 2 or more, and still more preferably 80 mg / m 2 or more. The coating amount is the coating amount per one side of the steel sheet (hereinafter, the same). On the one hand, when the deposition amount of the metallic chromium layer is excessively large, the welding strength may decrease. In addition, a large amount of spatter may occur during welding, which may damage the metallic chromium layer and impair the corrosion resistance. Therefore, the deposition amount of the metallic chromium layer is preferably 200 mg / m 2 or less, more preferably 150 mg / m 2 or less, and even more preferably 130 mg / m 2 or less.

[0011] 《Measurement method of deposition amount》 The deposition amount of the metallic chromium layer and the deposition amount in terms of chromium conversion of the chromium hydrous oxide layer described below are measured as follows. First, for the steel sheet for cans having a metallic chromium layer and a chromium hydrous oxide layer, the chromium amount (total chromium amount) is measured using a fluorescent X-ray apparatus. Next, an alkali treatment is performed by immersing the steel sheet for cans in a 6.5 N aqueous sodium hydroxide solution (liquid temperature: 90 °C) for 10 minutes, and then the chromium amount (chromium amount after alkali treatment) is measured again using the fluorescent X-ray apparatus. The chromium amount after alkali treatment is taken as the deposition amount of the metallic chromium layer. Next, (alkali-soluble chromium amount) = (total chromium amount) - (chromium amount after alkali treatment) is calculated, and the alkali-soluble chromium amount is taken as the deposition amount in terms of chromium conversion of the chromium hydrous oxide layer.

[0012] 〈Chromium hydrous oxide layer〉 Chromium hydrous oxides include chromium compounds containing oxygen such as chromium oxides and chromium hydroxides. By providing a chromium hydrous oxide layer on the metallic chromium layer, the adhesion to paints and the like is improved. The chromium hydroxide in the chromium hydrous oxide layer has a hydroxy group and polarity. Chromium hydroxide exhibits adhesion through hydrogen bonding with paints and the like.

[0013] 《Deposition amount》 From the viewpoint of obtaining good adhesion, the deposition amount in terms of chromium conversion of the chromium hydrous oxide layer is preferably 3 mg / m 2 or more, more preferably 4 mg / m 2 or more. On the one hand, if there is too much chromium hydrated oxide layer, cohesive failure may occur at the adhesion interface with paints or the like, and the adhesion may decrease. Therefore, the chromium-equivalent adhesion amount of the chromium hydrated oxide layer is 20 mg / m 2 The following is preferable, and 15 mg / m 2 The following is more preferable, and 10 mg / m 2 The following is even more preferable.

[0014] 《Mole ratio (M / Cr)》 The chromium hydroxide of the chromium hydrated oxide layer may undergo dehydration due to heating during welding or the like, resulting in an increase in contact resistance and a decrease in weldability. This is presumably because chromium hydroxides having hydroxy groups (-OH) undergo dehydration condensation with each other to form Cr-O-Cr bonds and change into compounds with low conductivity (such as chromium oxides). In the present embodiment, in order to suppress the progress of such dehydration, a trace amount of element M is contained in the chromium hydrated oxide layer. That is, the chromium hydrated oxide layer contains, in addition to chromium element (Cr), at least one element M selected from the group consisting of sodium (Na), magnesium (Mg), potassium (K), and calcium (Ca). Thereby, it is considered that the hydrogen atom at the terminal of the hydroxy group is substituted with the cation of element M, and dehydration hardly proceeds even by heating or the like.

[0015] At this time, if the molar ratio (M / Cr) of element M to chromium element Cr in the chromium hydrated oxide layer is too low, since there is little element M, such an effect is difficult to be exhibited. Therefore, from the viewpoint of obtaining good weldability, the molar ratio (M / Cr) of the chromium hydrated oxide layer is 0.010 or more, preferably 0.015 or more, more preferably 0.020 or more, even more preferably 0.025 or more, and particularly preferably 0.030 or more.

[0016] Note that the molar ratio (M / Cr) of the chromium hydrated oxide layer may exceed 0.050. In this case, the molar ratio (M / Cr) of the chromium hydroxide layer is preferably 0.055 or more, more preferably 0.060 or more, still more preferably 0.065 or more, particularly preferably 0.070 or more, and most preferably 0.075 or more.

[0017] On the other hand, when the chromium hydroxide layer contains an excessive amount of element M, the continuity of the chromium hydroxide layer may be impaired, the bond between the paint or the like and the hydroxy group may be weakened, and the adhesion may decrease. Further, although the chromium hydroxide layer secures corrosion resistance by covering the pinholes (parts where the steel sheet is not completely covered) of the metal chromium layer, if the continuity of the chromium hydroxide layer is impaired, this covering may become insufficient and the corrosion resistance may decrease. Therefore, from the viewpoint of obtaining good adhesion and corrosion resistance, the molar ratio (M / Cr) of the chromium hydroxide layer is 0.100 or less, preferably 0.090 or less, more preferably 0.080 or less, still more preferably 0.070 or less, and particularly preferably 0.065 or less.

[0018] 《Molar ratio (X / Cr)》 As described above, the chromium hydroxide of the chromium hydroxide layer contributes to adhesion. At this time, in the chromium hydroxide layer, if the molar ratio (X / Cr) of the chromium hydroxide X to the chromium element Cr is too low, since there is little chromium hydroxide X, sufficient adhesion may not be obtained. Therefore, from the viewpoint of obtaining good adhesion, the molar ratio (X / Cr) of the chromium hydroxide layer is 0.400 or more, preferably 0.410 or more, more preferably 0.415 or more, still more preferably 0.420 or more, and particularly preferably 0.425 or more.

[0019] On the other hand, since chromium hydroxide has lower strength than chromium oxide, if there is too much of it, the corrosion resistance may be insufficient. Therefore, from the viewpoint of obtaining good corrosion resistance, the molar ratio (X / Cr) of the chromium hydroxide layer is 0.800 or less, more preferably 0.750 or less, still more preferably 0.650 or less, and particularly preferably 0.550 or less.

[0020] "Method for Measuring Molar Ratio" The above-mentioned molar ratios (M / Cr) and (X / Cr) are determined as follows. First, a steel sheet for cans having a metallic chromium layer and a chromium hydrous oxide layer (a so-called as-manufactured steel sheet for cans without heating etc., except for drying by indoor storage) is placed in an ultra-high vacuum, and under the following conditions, the Cr2p spectrum of the outermost surface of the chromium hydrous oxide layer is obtained by X-ray photoelectron spectroscopy. After background-correcting the obtained Cr2p spectrum, it is separated into a peak of metallic chromium appearing at 574.4 ± 0.1 eV, a peak of chromium hydroxide appearing at 577.4 ± 0.4 eV, and a peak of chromium oxide appearing at 578.1 ± 1.7 eV. The separation of the peaks is carried out by a curve fitting method using a non-linear least squares method with a Gaussian-Lorentz composite function. Next, the area of each separated peak is determined.

[0021] Thus, for the outermost surface of the chromium hydrous oxide layer, the ratio (X / Cr) of the peak area X of chromium hydroxide to the total peak area Cr of all chromium peaks (peaks of metallic chromium, chromium hydroxide, and chromium oxide) is calculated, and this is determined as the above-mentioned molar ratio (X / Cr).

[0022] Furthermore, for the outermost surface of the chromium hydrous oxide layer, spectra of Na1s, Mg1s, K2p, and Ca2p (narrow spectra) are obtained. From the integrated intensities of the obtained spectra, each element of Na, Mg, K, and Ca is quantified by the relative sensitivity coefficient method, and the total molar amount M is determined. Similarly, the molar amount Cr of chromium element is determined from the integrated intensity of the Cr2p spectrum. From the molar amount M and the molar amount Cr, the above-mentioned molar ratio (M / Cr) is determined.

[0023] (Conditions for X-ray photoelectron spectroscopy) · Measuring device: X-tool manufactured by Ulvac-PHI · Excitation source: monoAl Kα 25W × 15kV · Analysis size: 100 μmφ · Retrieving angle: 45° · Pass Energy Survey scan: 280.0 eV Narrow scan: 112.0 eV

[0024] [Method for manufacturing steel sheet for can] Next, a method for manufacturing the steel sheet for can of the present embodiment will be described. In the present embodiment, generally, first, in an aqueous solution 1 containing a hexavalent chromium compound, a cathodic electrolysis treatment C1 is performed on the steel sheet. As a result, a reduction reaction occurs on the surface of the steel sheet, chromium metal is deposited, and further, chromium hydrated oxide, which is an intermediate product to chromium metal, is deposited on the surface of the chromium metal. The deposition amount can be arbitrarily controlled depending on the conditions of the cathodic electrolysis treatment C1, for example. In this way, a chromium metal layer and a chromium hydrated oxide layer are formed on the surface of the steel sheet. Furthermore, in the present embodiment, after the cathodic electrolysis treatment C1, a cathodic electrolysis treatment C2 is performed using an aqueous solution 2 containing an element M. Thereby, the element M is introduced into the formed chromium hydrated oxide layer. Hereinafter, the aqueous solutions 1 to 2 and the cathodic electrolysis treatments C1 to C2 will be described in detail.

[0025] 〈Aqueous solution 1〉 The aqueous solution 1 used for the cathodic electrolysis treatment C1 contains at least a hexavalent chromium compound, a fluorine-containing compound, and sulfuric acid.

[0026] Examples of the hexavalent chromium compound include chromium trioxide (CrO3); dichromates such as potassium dichromate (K2Cr2O7); chromates such as potassium chromate (K2CrO4); and the like. The content of the hexavalent chromium compound in the aqueous solution 1 is preferably 0.50 mol / L or more, more preferably 0.80 mol / L or more in terms of Cr amount because chromium metal can be deposited stably and efficiently for a long time. On the other hand, the Cr amount in the aqueous solution 1 is preferably 5.00 mol / L or less, more preferably 3.00 mol / L or less.

[0027] Examples of fluorine-containing compounds include hydrofluoric acid (HF), potassium fluoride (KF), sodium fluoride (NaF), hydrosilicic acid (H2SiF6), and salts of hydrosilicic acid. Examples of salts of hydrosilicic acid include sodium silicic acid (Na2SiF6), potassium silicic acid (K2SiF6), and ammonium silicic acid ((NH4)2SiF6). The content of the fluorine-containing compound in the aqueous solution 1, in terms of the amount of F, is preferably more than 0.100 mol / L, more preferably 0.110 mol / L or more, even more preferably 0.150 mol / L or more, and particularly preferably 0.200 mol / L or more. On the other hand, the amount of F in the aqueous solution 1 is preferably 4.000 mol / L or less, more preferably 3.000 mol / L or less, further preferably 2.000 mol / L or less, and particularly preferably 1.000 mol / L or less.

[0028] The use of sulfuric acid in combination with a fluorine-containing compound improves the deposition efficiency of metallic chromium. The sulfuric acid may be partially or entirely in the form of a sulfate salt such as sodium sulfate, calcium sulfate, or ammonium sulfate. The content of sulfuric acid in solution 1 is SO4 2- The amount is preferably 0.0001 mol / L or more, more preferably 0.0003 mol / L or more, and even more preferably 0.0010 mol / L or more. On the other hand, SO4 in solution 1 2- The amount is preferably 0.1000 mol / L or less, more preferably 0.0500 mol / L or less.

[0029] The liquid temperature of the aqueous solution 1 is preferably 20° C. or higher, more preferably 30° C. or higher, and even more preferably 40° C. or higher. On the other hand, the liquid temperature of the aqueous solution 1 is preferably 80° C. or lower, and more preferably 60° C. or lower. In the cathodic electrolysis C1, it is preferable to use only one type of aqueous solution 1.

[0030] <Cathodic electrolysis C1> As described above, in the cathode electrolysis treatment C2, metallic chromium and chromium hydrous oxide are deposited. As a result, a metallic chromium layer and a chromium hydrous oxide layer are formed on the surface of the steel sheet.

[0031] The current density of the cathode electrolysis treatment C1 is preferably 5 A / dm 2 or more, more preferably 10 A / dm 2 or more, and still more preferably 20 A / dm 2 or more. On the other hand, the current density of the cathode electrolysis treatment C1 is preferably 60 A / dm 2 or less, more preferably 50 A / dm 2 or less, and still more preferably 40 A / dm 2 or less.

[0032] The charge density of the cathode electrolysis treatment C1 is preferably 70.0 C / dm 2 or less, more preferably 60.0 C / dm 2 or less, and still more preferably 50.0 C / dm 2 or less. On the other hand, the charge density of the cathode electrolysis treatment C1 is preferably 10.0 C / dm 2 or more, more preferably 20.0 C / dm 2 or more, and still more preferably 30.0 C / dm 2 or more. The energization time (unit: s) of the cathode electrolysis treatment C1 is appropriately set from the current density and the charge density.

[0033] The cathode electrolysis treatment C1 does not have to be a continuous electrolysis treatment. That is, the cathode electrolysis treatment C1 may be an intermittent electrolysis treatment in which, due to inevitable non-energized immersion time when electrolyzing by dividing into a plurality of electrodes in industrial production, respectively. In the case of intermittent electrolysis treatment, it is preferable that the total charge density is within a suitable range. This also applies to the cathode electrolysis treatment C2 described later.

[0034] Note that after the cathodic electrolysis treatment C1, the steel sheet may be immersed electrolessly in an aqueous solution containing a hexavalent chromium compound for the purpose of controlling and modifying the adhesion amount of the chromium hydrous oxide layer.

[0035] 〈Aqueous solution 2〉 Aqueous solution 2 contains an element M (at least one selected from the group consisting of Na, Mg, K, and Ca). Aqueous solution 2 is prepared, for example, by adding a compound containing element M (also referred to as "M compound") to water as a solvent. As the M compound, sulfates, nitrates, chlorides, and fluorides are avoided, and hydroxides and carbonates are preferred. Examples of the hydroxide of element M include sodium hydroxide (NaOH), magnesium hydroxide (Mg(OH)2), potassium hydroxide (KOH), and calcium hydroxide (Ca(OH)2). Examples of the carbonate of element M include sodium carbonate (Na2CO3), magnesium carbonate (MgCO3), potassium carbonate (K2CO3), and calcium carbonate (CaCO3).

[0036] From the viewpoint of introducing a sufficient amount of element M into the chromium hydrous oxide layer, the total content of element M in aqueous solution 2 is 0.10 mmol / L or more, preferably 0.20 mmol / L or more, more preferably 0.30 mmol / L or more, and still more preferably 0.40 mmol / L or more. On the other hand, in order to suppress the excessive introduction of element M into the chromium hydrous oxide layer, the total content of element M in aqueous solution 2 is 1.00 mmol / L or less, preferably 0.90 mmol / L or less, more preferably 0.80 mmol / L or less, still more preferably 0.70 mmol / L or less, and particularly preferably 0.60 mmol / L or less.

[0037] The total content of element M in aqueous solution 2 is measured by ICP (Inductively Coupled Plasma) emission spectrometry or ICP mass spectrometry.

[0038] The aqueous solution 2 is preferably weakly alkaline for reasons described later. Specifically, the pH of the aqueous solution 2 is preferably 9.0 or more, more preferably 9.5 or more, and still more preferably 10.0 or more. On the other hand, the pH of the aqueous solution 2 is preferably 11.5 or less, more preferably 11.0 or less, and still more preferably 10.5 or less.

[0039] The liquid temperature of the aqueous solution 2 is, for example, 40°C or higher. However, from the viewpoint of suppressing the excessive introduction of the element M into the chromium hydroxide layer, it is preferably 75°C or lower, more preferably 65°C or lower, and still more preferably 55°C or lower.

[0040] 〈Cathodic electrolysis treatment C2〉 After the cathodic electrolysis treatment C1, the steel sheet on which the metal chromium layer and the chromium hydroxide layer are formed is appropriately washed with water, and then the cathodic electrolysis treatment C2 is carried out using the aqueous solution 2 containing the element M. As a result, as described above, the element M is introduced into the chromium hydroxide layer formed in the cathodic electrolysis treatment C1. As a result, it is considered that the hydrogen atom at the terminal of the hydroxy group of the chromium hydroxide in the chromium hydroxide layer is substituted with the cation of the element M.

[0041] Furthermore, by carrying out the cathodic electrolysis treatment C2, a hydroxy group is also introduced into the chromium hydroxide layer. That is, the chromium hydroxide increases. On the surface of the chromium hydroxide layer after the cathodic electrolysis treatment C1, sulfate (SO4 2- ) or a fluorine-containing compound is adsorbed or incorporated. In this state, by carrying out the cathodic electrolysis treatment C2 using the weakly alkaline aqueous solution 2, sulfate and the like are removed, and instead, a hydroxy group is introduced into the chromium hydroxide layer.

[0042] If the charge density of the cathodic electrolysis treatment C2 is too low, it is difficult to introduce a hydroxy group into the chromium hydroxide layer. From the viewpoint of promoting the introduction of the hydroxy group and increasing the chromium hydroxide, the charge density of the cathodic electrolysis treatment C2 is 0.30 C / dm 2The above, and 0.35 C / dm 2 The above is preferable, and 0.40 C / dm 2 The above is more preferable, and 0.45 C / dm 2 The above is even more preferable, and 0.50 C / dm 2 The above is particularly preferable.

[0043] On the other hand, in order to suppress an excessive increase in chromium hydroxide, the charge density of the cathode electrolysis treatment C2 is 3.00 C / dm 2 or less, and 2.50 C / dm 2 or less is preferable, and 2.00 C / dm 2 or less is more preferable, and 1.50 C / dm 2 or less is even more preferable.

[0044] The current density of the cathode electrolysis treatment C2 is not particularly limited as long as the charge density is within the above range, but 0.5 A / dm 2 or more is preferable, and 1.0 A / dm 2 or more is more preferable, and 1.5 A / dm 2 or more is even more preferable. On the other hand, the current density of the cathode electrolysis treatment C2 is preferably less than 10.0 A / dm 2 and more preferably less than 9.0 A / dm 2 and even more preferably less than 8.0 A / dm 2 and even more preferably less than 8.0 A / dm

[0045] The energization time (unit: s) of the cathode electrolysis treatment C2 is appropriately set from the current density and the charge density, but is preferably 0.10 s or more, and more preferably 0.20 s or more. The upper limit is not particularly limited, but from the viewpoint of efficiency in continuous production, the energization time of the cathode electrolysis treatment C2 is preferably 5.00 s or less, more preferably 3.50 s or less, and even more preferably 2.00 s or less.

[0046] 〈Water washing〉 After the cathode electrolysis treatment C2, the obtained steel sheet for cans may be further washed with general industrial water as washing water. By performing water washing, the electrolytic solution remaining on the surface of the steel sheet for cans can be removed. The water washing time is not particularly limited. However, in the chromium hydroxide layer, in order to suppress the return of the hydroxy group in which the terminal hydrogen atom is replaced by the element M to the original hydroxy group, the liquid temperature of the washing water is preferably 40°C or lower, more preferably 30°C or lower. The method of water washing is not particularly limited, and a conventionally known method can be adopted. For example, a water washing tank may be provided on the downstream side of the electrolytic cell used for the cathode electrolysis treatment C1 to C2, and the steel sheet for cans after the cathode electrolysis treatment C2 may be continuously immersed in the washing water. Alternatively, the washing water may be sprayed onto the steel sheet for cans after the cathode electrolysis treatment C2 using a spray. The number of times of water washing is not particularly limited. Each water washing may be carried out in the same method or in different methods.

Examples

[0047] Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the examples described below.

[0048] 〈Manufacture of steel sheet for cans〉 A steel sheet (tempering degree: T4CA) having a thickness of 0.22 mm was subjected to normal degreasing and pickling. For this steel sheet, the cathode electrolysis treatment C1 was carried out using the aqueous solution 1, and then the cathode electrolysis treatment C2 was carried out using the aqueous solution 2. The composition of the aqueous solution 1 is shown in Table 1 below, the composition of the aqueous solution 2 is shown in Table 2 below, and the conditions of the cathode electrolysis treatment C1 and the cathode electrolysis treatment C2 are shown in Table 3 below. The pH of the aqueous solution 2 used was in the range of 9.0 or more and 11.5 or less in all cases. When the cathode electrolysis treatment C2 was not carried out, "-" was described in the corresponding column in Table 3 below. In the cathode electrolysis treatments C1 to C2, the aqueous solutions 1 to 2 were circulated by a pump at a rate equivalent to 100 mpm in a flow cell, and a lead electrode was used. In this way, a steel sheet for cans was manufactured. After manufacturing, the steel sheet for cans was washed by immersing it in industrial water (liquid temperature: 25°C) and dried at room temperature using a blower.

[0049] 〈Adhesion amount, etc.〉 Regarding the produced steel sheet for cans, the amount of chromium deposition and the amount of chromium equivalent deposition in the chromium hydroxide layer (simply referred to as "deposition amount" in Table 3 below) were measured. Furthermore, for the produced steel sheet for cans, the molar ratios (M / Cr) and (X / Cr) of the chromium hydroxide layer were measured. All the measurement methods are as described above. The results are shown in Table 3 below.

[0050] 〈Evaluation〉 Regarding the produced steel sheet for cans, the adhesion, corrosion resistance, and weldability were evaluated by conducting the following tests. The results are shown in Table 3 below.

[0051] 《Adhesion》 Two test pieces were cut out from the produced steel sheet for cans, and their surfaces were painted. Specifically, an epoxy phenolic paint was applied to the surface of the test pieces at a coating amount of 50 mg / dm 2 and baked at 210 °C for 10 minutes. A nylon film was sandwiched between the painted surfaces of the two test pieces, preheated at 190 °C for 1 minute, and then pressure-bonded at a pressure of 3 kgf / cm 2 for 30 seconds to prepare a test specimen. After that, the test specimen was sheared to a width of 5 mm and then immersed in a test solution (an aqueous mixed solution of 1.5 mass% citric acid and 1.5 mass% sodium chloride) at 55 °C for 336 hours. After immersion, the test specimen was taken out from the test solution, washed with water, and then dried. Then, the two test pieces of the test specimen were pulled using a tensile testing machine at a tensile speed of 3.33 mm / s, and the tensile strength at the time of peeling was determined as the peel strength (unit: kgf / cm 2 ). In practical terms, if the peel strength is the following "A" or "B", it can be evaluated that the adhesion is excellent. A: 2.5 kgf / cm 2 or more B: 2.0 kgf / cm 2 or more and less than 2.5 kgf / cm 2 C: 1.5 kgf / cm 2 or more and less than 2.0 kgf / cm 2 ​​ D: 1.5 kgf / cm 2 less than

[0052] "Weldability" Two test pieces were cut out from the fabricated steel sheet for cans and heated in a batch furnace. Specifically, heating was carried out twice with the temperature held at 210 °C for 10 minutes. The two heated test pieces were overlapped. Next, using a DR type 1 mass% Cr-Cu electrode (an electrode processed with a tip diameter of 2.3 mm and a curvature radius of 40 mm), the two overlapped test pieces were sandwiched, and a rectangular wave was applied for 1 ms (millisecond) using a DC power supply at a pressing force of 40 kgf / cm. 2 The current value at which the test pieces were joined was determined as the lower limit current (unit: kA), and the current value at which the surface of the test piece was overheated and sputtering occurred was determined as the upper limit current (unit: kA). Furthermore, the current range (= upper limit current - lower limit current) was obtained from both. Practically, if the current range is the following "A" or "B", it can be evaluated that the weldability is excellent. A: 1.0 kA or more B: less than 1.0 kA and 0.6 kA or more C: less than 0.6 kA and 0.2 kA or more D: less than 0.2 kA

[0053] "Corrosion resistance" Two test pieces were cut out from the fabricated steel sheet for cans. The surface on which the coating layer and the chromium-containing layer were formed was taken as the evaluation surface. The two test pieces were passed between metal rolls in a state where the evaluation surfaces (the surfaces on which the metal chromium layer and the chromium hydrate oxide layer were formed) faced each other, and a surface pressure of 40 MPa was applied. After that, an epoxy phenolic resin was applied to the evaluation surface of one of the two test pieces, and a treatment of heating at 210 °C for 10 minutes was carried out twice to form a coating film. Next, after making cross-cuts to a depth reaching the steel sheet in the coating film, the test piece was immersed in a test solution (a mixed aqueous solution of 1.5 mass% citric acid and 1.5 mass% sodium chloride) at 45 °C for 168 hours. After immersion, the test piece was taken out from the test solution, washed with water, and then dried. After that, a test of peeling the coating film was carried out using tape. Four peel widths (total width to the left and right spreading from the intersection) within 10 mm from the intersection of the cross cut were measured, and the average value of the four peel widths was determined as the corrosion width. In practical use, if the corrosion width is "A" or "B", it can be evaluated that the corrosion resistance is excellent. A: 1.0 mm or less B: More than 1.0 mm and 2.0 mm or less C: More than 2.0 mm and 3.0 mm or less D: More than 3.0 mm

[0054]

Table 1

[0055]

Table 2

[0056]

Table 3

[0057] 〈Summary of Evaluation Results〉 As shown in Table 3 above, the steel sheets for cans of Examples 1 to 20 all had good adhesion, weldability, and corrosion resistance. On the other hand, the steel sheets for cans of Comparative Examples 1 to 5 were insufficient in at least one of adhesion, weldability, and corrosion resistance.

Claims

1. The surface of the steel sheet has, in order from the steel sheet side, a metallic chromium layer and a chromium hydrate oxide layer, the chromium hydrated oxide layer contains chromium element Cr and at least one element M selected from the group consisting of sodium, magnesium, potassium and calcium, and a molar ratio M / Cr of the element M to the chromium element Cr is 0.010 or more and 0.100 or less; The chromium hydrated oxide layer contains a chromium hydroxide X, and a molar ratio X / Cr of the chromium hydroxide X to the chromium element Cr is 0.400 or more and 0.800 or less.

2. The deposition amount of the metal chromium layer is 50 mg / m ２ 200mg / m or more ２ 2. The steel sheet for cans according to claim 1, wherein:

3. The chromium-equivalent coating amount of the chromium hydrate oxide layer is 3 mg / m ２ 20mg / m or more ２ 2. The steel sheet for cans according to claim 1, wherein:

4. The steel sheet for cans according to claim 2, wherein the chromium-equivalent deposition amount of the chromium hydrated oxide layer is 3 mg / m 2 or more and 20 mg / m 2 or less.

5. A method for producing a steel sheet for cans according to any one of claims 1 to 4, comprising the steps of: The steel sheet is subjected to cathodic electrolysis C1 using an aqueous solution 1 containing a hexavalent chromium compound, a fluorine-containing compound and sulfuric acid, and then subjected to electrolysis at 0.30 to 3.00 C / dm using an aqueous solution 2 having a content of the element M of 0.10 to 1.00 mmol / L. ２ The method for manufacturing a steel sheet for cans comprises carrying out cathodic electrolysis C2 at a charge density of

6. The method for producing a steel sheet for cans according to claim 5, wherein the pH of the aqueous solution 2 is 9.0 or more and 11.5 or less.

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