Steel sheet for a can and method of manufacturing the same

Abstract

The present invention provides a steel sheet for a can having excellent weldability and slidability and a method for manufacturing the same. The steel sheet for a can has, in order from the steel sheet side, a metallic chromium layer and a chromium hydrate oxide layer on the surface of the steel sheet, the adhesion amount of the metallic chromium layer is 50 to 150 mg / m 2 , the adhesion amount of the chromium hydrate oxide layer in terms of chromium is 3 to 15 mg / m 2 , the metallic chromium layer includes flat plate-shaped bases and granular projections provided on the bases, the average particle diameter D1 of the granular projections is 20 to 200 nm, and the number density of the granular projections is 10 / μm 2 , and the chromium hydrate oxide layer contains silicon dioxide, the content of the silicon dioxide in the chromium hydrate oxide layer is 0.1 to 45 mg / m 2 in terms of SiO2.

Description

Technical Field

[0001] The present invention relates to a steel plate for a can and a method for manufacturing the same. Background Art

[0002] Patent Documents 1 and 2 disclose a steel sheet for a can having "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", and the metal chromium layer has "granular protrusions".

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: International Publication No. 2017 / 098991

[0006] Patent Document 2: International Publication No. 2017 / 098994 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Conventional can steel sheets disclosed in Patent Documents 1 and 2 have good weldability, for example.

[0009] However, unlike tin, which is relatively soft, chromium is hard and has a high coefficient of friction.

[0010] Therefore, when conventional steel sheets for cans are used in a state where their surfaces are not coated or laminated (so-called bare material state), defects are likely to occur, for example, in a canning process.

[0011] Specifically, when the surface of a can steel sheet contacts an object (the surface of another can steel sheet, a roller on a production line, a tool during processing, etc.), the two may not slide against each other or may get stuck. In other words, the sliding properties may be insufficient.

[0012] Therefore, an object of the present invention is to provide a steel plate for a can having excellent weldability and sliding properties, and a method for producing the same.

[0013] Methods used to solve problems

[0014] The present inventors have conducted intensive studies and have found that the above-mentioned object can be achieved by making the chromium hydrous oxide layer contain a specific amount of silicon dioxide, thereby completing the present invention.

[0015] That is, the present invention provides the following [1] to [9].

[0016] [1] A steel sheet for cans having a metal chromium layer and a chromium hydrated oxide layer on the surface of the steel sheet in this order from the steel sheet side, wherein the amount of the metal chromium layer deposited is 50 to 150 mg / m 2The chromium conversion adhesion amount of the above chromium hydrated oxide layer is 3 to 15 mg / m 2 The metal chromium layer comprises a flat base and granular protrusions arranged on the base, the average particle size D1 of the granular protrusions is 20 to 200 nm, and the number density of the granular protrusions is 10 / μm 2 The above-mentioned chromium hydrated oxide layer contains silicon dioxide, and the content of the silicon dioxide in the above-mentioned chromium hydrated oxide layer is 0.1 to 45 mg / m2 in terms of SiO2. 2 .

[0017] [2] The steel sheet for cans according to [1] above, wherein the average particle size D2 of the silica is 5 to 200 nm.

[0018] [3] The steel sheet for a can according to [1] or [2] above, wherein the ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 0.2 or more.

[0019] [4] The steel sheet for a can according to [1] or [2] above, wherein the ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 0.6 or more.

[0020] [5] The steel sheet for a can according to any one of [1] to [4] above, wherein the ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 4.5 or less.

[0021] [6] The steel sheet for a can according to any one of [1] to [4] above, wherein the ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 3.0 or less.

[0022] [7] A method for manufacturing a steel sheet for a can, which is a method for manufacturing the steel sheet for a can according to any one of [1] to [6] above, wherein the steel sheet is subjected to cathodic electrolysis treatment C1, anodic electrolysis treatment A1 and cathodic electrolysis treatment C2 in sequence using a first aqueous solution containing a hexavalent chromium compound and a fluorine-containing compound, and then an immersion treatment or cathodic electrolysis treatment C3 is performed using a second aqueous solution, the second aqueous solution containing colloidal silica, and the content of the colloidal silica in the second aqueous solution is 0.10 g / L or more in terms of SiO2.

[0023] [8] The method for manufacturing a can steel sheet according to [7] above, wherein the amount of Cr in the second aqueous solution is less than 0.50 mol / L.

[0024] [9] The method for manufacturing a can steel sheet according to [8] above, wherein the amount of Cr in the first aqueous solution is 0.50 mol / L or more.

[0025] Effects of the Invention

[0026] According to the present invention, it is possible to provide a steel sheet for a can having excellent weldability and sliding properties, and a method for producing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a cross-sectional view schematically showing an example of a steel plate for a can. DETAILED DESCRIPTION

[0028] [Steel Plate for Tanks]

[0029] Figure 1 This is a cross-sectional view schematically showing an example of a steel plate for a can.

[0030] like Figure 1 As shown, it has a steel plate 2. The can steel plate 1 further has a metal chromium layer 3 and a chromium hydrated oxide layer 4 on the surface of the steel plate 2 in this order from the steel plate 2 side.

[0031] The metallic chromium layer 3 includes a flat base portion 3a covering the steel plate 2 and granular projections 3b provided on the base portion 3a. The chromium hydrated oxide layer 4 is arranged on the metallic chromium layer 3 so as to follow the shape of the granular projections 3b.

[0032] Hereinafter, each structure of the steel plate for a can will be described in more detail.

[0033] <Steel Plate>

[0034] The type of steel plate is not particularly limited. Typically, plates used for container materials (e.g., low-carbon steel plates and ultra-low-carbon steel plates) can be used. The steel plate's manufacturing method and material are also not particularly limited. It is manufactured through conventional steel sheet manufacturing processes, including hot rolling, pickling, cold rolling, annealing, and temper rolling.

[0035] <Metallic chromium layer>

[0036] A metallic chromium layer is disposed on the surface of the steel sheet. The metallic chromium prevents the steel sheet from being exposed on the surface, thereby improving corrosion resistance.

[0037] Adhesion

[0038] The adhesion amount of the metal chromium layer is 50 mg / m2 due to the excellent corrosion resistance of the steel sheet for cans. 2 More than 60 mg / m 2 More than 70 mg / m 2 The adhesion amount is the adhesion amount per one side of the steel plate (the same applies hereinafter).

[0039] On the other hand, when the amount of metallic chromium is too much, sometimes the high-melting-point metallic chromium covers the entire surface of the steel sheet, and the reduction in weld strength and the generation of dust become significant, and the weldability deteriorates.

[0040] From the reason that the weldability of the steel sheet for a can is more excellent, the attached amount of the metallic chromium layer is preferably 150 mg / m 2 Hereinafter, 140 mg / m 2 Hereinafter, 130 mg / m 2 Hereinafter.

[0041] (Measurement method of attached amount)

[0042] The attached amount of the metallic chromium layer and the attached amount of chromium conversion of the chromium hydrate oxide layer described later are measured in the following manner.

[0043] First, for the steel sheet for a can on which the metallic chromium layer and the chromium hydrate oxide layer are formed, the amount of chromium (total chromium amount) is measured using a fluorescent X-ray device. Next, the steel sheet for a can is subjected to an alkali treatment of being immersed in 7.5 N-NaOH at 90°C for 10 minutes, and then the amount of chromium is measured again using the fluorescent X-ray device (chromium amount after alkali treatment). The chromium amount after alkali treatment is taken as the attached amount of the metallic chromium layer.

[0044] 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 attached amount of chromium conversion of the chromium hydrate oxide layer.

[0045] Such a metallic chromium layer contains a flat base and a granular protrusion provided on the base. Next, these respective parts contained in the metallic chromium layer are described in detail.

[0046] 《Base》

[0047] The base of the metallic chromium layer mainly covers the surface of the steel sheet, and the corrosion resistance is improved.

[0048] In order to avoid the granular protrusion provided on the surface layer damaging the base and exposing the steel sheet when the steel sheets for a can inevitably come into contact with each other at the time of processing, the base of the metallic chromium layer preferably ensures a sufficient thickness.

[0049] From the reason that the corrosion resistance of the steel sheet for a can is excellent, the attached amount of the base of the metallic chromium layer is preferably 30 mg / m 2 More preferably, 40 mg / m 2 Hereinafter.

[0050] 《Granular protrusion》

[0051] The granular protrusion of the metallic chromium layer is formed on the surface of the above-described base, and the contact resistance of the steel sheet for a can with each other is reduced, and the weldability is improved. The following describes the inferred mechanism of the reduction in contact resistance.

[0052] Because the chromium hydrated oxide layer covering the metallic chromium layer is a non-conductive film, it has a higher electrical resistance than the metallic chromium, hindering welding. However, if granular projections are formed on the surface of the base of the metallic chromium layer, the surface pressure of the can steel sheets in contact during welding causes the granular projections to break through the chromium hydrated oxide layer, acting as points of conduction for the welding current and significantly reducing contact resistance.

[0053] (Average particle size D1)

[0054] Because the weldability of the can steel sheet is excellent, the average particle size D1 of the granular protrusions of the metal chromium layer is 20 nm or more, preferably 40 nm or more, and more preferably 60 nm or more.

[0055] On the other hand, to ensure excellent surface appearance of the can steel sheet, the average particle size D1 of the granular protrusions in the metallic chromium layer is 200 nm or less, preferably 150 nm or less, more preferably 100 nm or less, further preferably 80 nm or less, and particularly preferably 70 nm or less. This is believed to be because reducing the diameter of the granular protrusions suppresses absorption of light with short wavelengths and scattering of reflected light.

[0056] (Number density)

[0057] When the number of granular protrusions in the metal chromium layer is large, the number of energized points increases, thereby improving weldability. Therefore, the number density of granular protrusions in the metal chromium layer is 10 / μm. 2 More than 15 / μm 2 More than 20 / μm 2 More than 30 / μm 2 More than 50 / μm is particularly preferred 2 More than 100 / μm is most preferred 2 above.

[0058] On the other hand, the number density of the granular protrusions in the metal chromium layer is preferably 10,000 / μm because the surface appearance of the steel sheet for cans is excellent. 2 Below, more preferably 5000 pieces / μm 2 Below, more preferably 1000 pieces / μm 2 Below, particularly preferably 800 pieces / μm 2 the following.

[0059] (Method for measuring particle size and number density)

[0060] The particle size and number density of the granular protrusions in the metal chromium layer were determined as follows.

[0061] First, a carbon vapor deposition is performed on the surface of the steel sheet for a tank formed with a metallic chromium layer and a chromium hydrate oxide layer, and an observation sample is produced. Then, a photograph is taken at 20,000 times using a scanning electron microscope (SEM). For the taken photograph, binarization is performed using a software (trade name: ImageJ) and image analysis is performed. The area occupied by the granular projections is inversely calculated, a circle conversion is performed, and a particle diameter and a number density are calculated. The average particle diameter Dl and the number density are set as the average of 5 fields of view.

[0062] < Chromium hydrate oxide layer >

[0063] The chromium hydrate oxide is precipitated on the surface of the steel sheet at the same time as the metallic chromium, and the corrosion resistance is improved. The chromium hydrate oxide contains, for example, chromium oxide and chromium hydroxide.

[0064] < Attached amount >

[0065] From the viewpoint of ensuring the corrosion resistance of the steel sheet for a tank, the attached amount of chromium converted from the chromium hydrate oxide layer is 3 mg / m 2 or more, and preferably 4 mg / m 2 or more.

[0066] On the other hand, the chromium hydrate oxide has a lower electrical conductivity than the metallic chromium, and when the amount is too large, it sometimes becomes an excessive resistance at the time of welding, and causes various welding defects such as dust, spatter, and bubbles accompanying excessive melting, and the weldability of the steel sheet for a tank is poor.

[0067] Therefore, from the viewpoint of excellent weldability of the steel sheet for a tank, the attached amount of chromium converted from the chromium hydrate oxide layer is 15 mg / m 2 or less, and preferably 12 mg / m 2 or less, and more preferably 10 mg / m 2 or less.

[0068] The method for measuring the attached amount of chromium converted from the chromium hydrate oxide layer is as described above.

[0069] < Silicon dioxide >

[0070] The chromium hydrate oxide layer contains silicon dioxide (silicon oxide) in the inside or the surface thereof or the like. Due to this, even in a state where the surface of the steel sheet for a tank is in contact with some object (the surface of another steel sheet for a tank, a roll of a production line, a tool at the time of processing, or the like), it is easy to slide with each other and not easy to be caught. That is, the slidability is excellent. Due to the excellent slidability of the steel sheet for a tank, for example, it is not easy to occur so-called seizure or sand sticking or the like in a can-making process.

[0071] The silicon dioxide as the hard fine particles is present in the chromium hydrate oxide layer that is the outermost layer of the steel sheet for a can, and comes into contact with an object, so abrasion of the chromium layer and the chromium hydrate oxide layer is reduced, or the coefficient of friction is reduced. It is presumed that the above effects are thereby obtained.

[0072] (content)

[0073] In order to sufficiently obtain the effect of improved slidability, the content of the silicon dioxide in the chromium hydrate oxide layer is 0.1 mg / m 2 The above is preferably 0.3 mg / m 2 The above is more preferably 1.0 mg / m 2 The above is further preferably 1.5 mg / m 2 The above.

[0074] However, when the content of the silicon dioxide is too much, the effect of improved slidability is saturated. In addition, since the conductivity of the silicon dioxide is low, when the content of the silicon dioxide is too much, the weldability can become insufficient.

[0075] Therefore, the content of the silicon dioxide in the chromium hydrate oxide layer is 45 mg / m 2 The above.

[0076] From the reason of more excellent weldability, the content of the silicon dioxide in the chromium hydrate oxide layer (conversion to SiO2) is preferably 30 mg / m 2 The above is more preferably 25 mg / m 2 The above is further preferably 10 mg / m 2 The above is particularly preferably 1.6 mg / m 2 The above.

[0077] The content of the silicon dioxide in the chromium hydrate oxide layer (conversion to SiO2) is found in the following manner.

[0078] First, a colloidal silicon dioxide of a known concentration is dropped onto a certain amount of filter paper, and then, it is sufficiently dried to produce a standard sample. With respect to a plurality of standard samples produced, the Si intensity is measured using a fluorescent X-ray device, and thereby, a calibration curve showing the relationship of the Si intensity and the SiO2 amount is produced.

[0079] Next, with respect to the chromium hydrate oxide layer, the Si intensity is measured using a fluorescent X-ray device, and with reference to the calibration curve produced, the SiO2 amount is found. The found SiO2 amount is taken as the content of the silicon dioxide in the chromium hydrate oxide layer (conversion to SiO2).

[0080] (average particle diameter D2)

[0081] From the viewpoint of achieving better sliding properties of the can steel sheet, the average particle size D2 of silica is preferably 5 nm or more, more preferably 10 nm or more, and even more preferably 20 nm or more.

[0082] On the other hand, if the average particle size D2 of silica is too large, the effect of improving the slip properties is saturated. Therefore, the average particle size D2 of silica is preferably 200 nm or less, more preferably 180 nm or less, and even more preferably 160 nm or less.

[0083] The average particle size D2 of silicon dioxide contained in the chromium hydrous oxide layer is determined as follows.

[0084] The surface of the chromium hydrous oxide layer was observed using a SEM (scanning electron microscope) at 20,000x magnification to obtain an SEM image. Silicon was analyzed by elemental mapping using an EDX (energy dispersive X-ray analyzer) instrument attached to the SEM, and the silica in the resulting SEM image was identified. The particle size of the identified silica was calculated using a perfect circle conversion method using software (trade name: ImageJ). The average particle size D2 was set as the average of five fields of view.

[0085] As will be described later, colloidal silica is used as a raw material in the production of can steel sheets, and this colloidal silica becomes silica of the chromium hydrous oxide layer.

[0086] When the coincidence is confirmed in advance, the average particle size of the colloidal silica used as the raw material can be regarded as the average particle size D2 of the silica in the chromium hydrous oxide layer.

[0087] <Particle size ratio D1 / D2>

[0088] The ratio D1 / D2 of the average particle size D1 of the granular protrusions of metallic chromium to the average particle size D2 of silica (hereinafter also referred to as "particle size ratio D1 / D2") is preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more.

[0089] When the particle size ratio D1 / D2 is within this range, the effect of improving the sliding properties is easily maintained over time, and the sliding properties are further improved. The reason for this is presumably as follows.

[0090] First, because silicon dioxide exists in the chromium hydrated oxide layer, which is the outermost layer of the steel sheet for cans, silicon dioxide is generally easily removed by contact with and friction with an object.

[0091] However, the granular protrusions of the metallic chromium layer form recesses between them. If silicon dioxide enters these recesses, it is unlikely to escape. Furthermore, even if it escapes, it easily reenters the recesses. Therefore, the improved slidability of the silicon dioxide is easily maintained. In other words, silicon dioxide retention is excellent.

[0092] When the particle size ratio D1 / D2 is within the above range, good silica retention can be exhibited, and excellent slidability can be easily maintained.

[0093] However, in order to exhibit the effect of improving the slidability due to silica, it is preferable that the silica in the recesses be in a state in which it is easily brought into contact with (initially brought into contact with) the object. That is, it is preferable that the particle-like projections not be too large relative to the size of the silica.

[0094] Therefore, the particle size ratio D1 / D2 is preferably 4.5 or less, more preferably 4.0 or less, further preferably 3.5 or less, and particularly preferably 3.0 or less. When in this range, the slidability of the steel sheet for a can is more excellent.

[0095] [Method for manufacturing steel sheet for can]

[0096] Next, a method for manufacturing the above steel sheet for a can will be described.

[0097] In outline, a first treatment (cathodic electrolysis treatment Cl, anodic electrolysis treatment Al, and cathodic electrolysis treatment C2) is performed on the steel sheet using a first aqueous solution containing a hexavalent chromium compound and a fluorine-containing compound, and then a second treatment (immersion treatment or cathodic electrolysis treatment C3) is performed using a second aqueous solution. The second aqueous solution is an aqueous solution containing a certain amount of colloidal silica and a small amount of Cr.

[0098] It is thought that, first, a chromium hydrate oxide layer is generated by the first treatment, and then colloidal silica (silica) is dispersed in the interior or on the surface of the chromium hydrate oxide layer or the like by the second treatment. That is, the colloidal silica contained in the second aqueous solution becomes the silica of the chromium hydrate oxide layer.

[0099] Each of the amounts of deposition can be controlled by the conditions of each treatment.

[0100] Hereinafter, each of the treatments will be described in detail.

[0101] <First treatment>

[0102] As the first treatment, the cathodic electrolysis treatment Cl, the anodic electrolysis treatment Al, and the cathodic electrolysis treatment C2 are sequentially performed on the steel sheet using a first aqueous solution.

[0103] <First aqueous solution>

[0104] The first aqueous solution contains at least a hexavalent chromium compound and a fluorine-containing compound.

[0105] As the hexavalent chromium compound, for example, chromium trioxide (CrO3), dichromate salts such as potassium dichromate (K2Cr2O7), chromate salts such as potassium chromate (K2CrO4), and the like can be listed.

[0106] Examples of fluorine-containing compounds include hydrofluoric acid (HF), potassium fluoride (KF), sodium fluoride (NaF), fluorosilicic acid (H2SiF6) and / or salts thereof. Examples of salts of fluorosilicic acid include sodium fluorosilicate (Na2SiF6), potassium fluorosilicate (K2SiF6), and ammonium fluorosilicate ((NH4)2SiF6).

[0107] The amount of Cr in the first aqueous solution is preferably 0.50 mol / L or more, more preferably 0.80 mol / L or more. On the other hand, the amount of Cr in the first aqueous solution is preferably 3.00 mol / L or less, more preferably 2.50 mol / L or less.

[0108] The amount of F in the first aqueous solution is preferably 0.020 mol / L or more, more preferably 0.080 mol / L or more. On the other hand, the amount of F in the first aqueous solution is preferably 0.480 mol / L or less, more preferably 0.400 mol / L or less.

[0109] The first aqueous solution may further contain sulfuric acid. Part or all of the sulfuric acid may be a sulfate such as sodium sulfate, calcium sulfate, or ammonium sulfate.

[0110] The fluorine-containing compound and sulfuric acid in the aqueous solution exist in a dissociated state into fluoride ions, sulfate ions, and hydrogen sulfate ions. These act as catalysts for the reduction and oxidation reactions of hexavalent chromium ions present in the aqueous solution during the cathode electrolysis and anodic electrolysis processes.

[0111] The aqueous solution used in the electrolytic treatment contains a fluorine-containing compound and sulfuric acid, thereby reducing the chromium-equivalent adhesion amount of the chromium hydrous oxide layer of the resulting can steel sheet. This is believed to be because the amount of anions increases, thereby reducing the amount of chromium oxide generated.

[0112] When the first aqueous solution contains sulfuric acid, 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.

[0113] On the other hand, the SO4 2- The amount is preferably 0.1000 mol / L or less, more preferably 0.0500 mol / L or less.

[0114] In the first treatment (cathodic electrolytic treatment C1, anodic electrolytic treatment A1 and cathodic electrolytic treatment C1), it is preferred to use only one aqueous solution.

[0115] The liquid temperature of the first aqueous solution is preferably 20° C. or higher, more preferably 40° C. or higher. On the other hand, the liquid temperature is preferably 80° C. or lower, more preferably 60° C. or lower.

[0116] Cathodic Electrolysis Treatment C1

[0117] Cathodic electrolytic treatment C1 precipitates metallic chromium and chromium hydrated oxide.

[0118] At this time, from the viewpoint of obtaining an appropriate precipitation amount, the electric charge density (product of current density and energization time) of the cathode electrolysis treatment C1 is preferably 15 C / dm 2 More than 20C / dm 2 More than, more preferably 25C / dm 2 On the other hand, the charge density of the cathode electrolysis treatment C1 is preferably 50 C / dm 2 Below, more preferably 45C / dm 2 Below, more preferably 35C / dm 2 the following.

[0119] The current density of cathode electrolysis treatment C1 (unit: A / dm 2 ) and the power-on time (unit: seconds) are appropriately set according to the above-mentioned charge density.

[0120] 《Anodic Electrolytic Treatment A1》

[0121] The anodic electrolytic treatment A1 dissolves the metallic chromium deposited in the cathodic electrolytic treatment C1 and forms sites for generating granular protrusions in the metallic chromium layer in the cathodic electrolytic treatment C2.

[0122] At this time, if the dissolution in the anodic electrolysis treatment A1 is too strong or too weak, the production sites may decrease, the number density of granular protrusions may decrease, the dissolution may proceed unevenly, causing fluctuations in the distribution of granular protrusions, or the thickness of the base of the metal chromium layer may decrease.

[0123] From the above viewpoints, the electric charge density (product of current density and energization time) of the anodic electrolysis treatment A1 is preferably 0.1 C / dm 2 More than 0.3C / dm 2 More than 0.3C / dm 2 On the other hand, the charge density of anodic electrolysis treatment A1 is preferably less than 5.0 C / dm 2 , more preferably 3.0C / dm 2 Below, more preferably 2.0C / dm 2 the following.

[0124] The current density of anodic electrolysis treatment A1 (unit: A / dm 2) and the power-on time (unit: seconds) are appropriately set according to the above-mentioned charge density.

[0125] Cathodic Electrolysis Treatment C2

[0126] As described above, cathodic electrolysis precipitates metallic chromium and chromium hydrated oxide. In particular, during cathodic electrolysis C2, granular protrusions of the metallic chromium layer form starting from the aforementioned generation sites. If the charge density is too high, the granular protrusions of the metallic chromium layer may grow rapidly, resulting in a coarse particle size.

[0127] From the above viewpoints, the current density of the cathode electrolysis treatment C2 is preferably less than 60.0 A / dm 2 , more preferably less than 50.0A / dm 2 , further preferably less than 40.0A / dm 2 On the other hand, the current density of the cathode electrolysis treatment C2 is preferably 10A / dm 2 More than 15.0A / dm 2 .

[0128] For the same reason, the charge density (product of current density and energization time) of the cathode electrolysis treatment C2 is preferably less than 30.0 C / dm 2 , more preferably 25.0C / dm 2 On the other hand, the charge density of the cathode electrolysis treatment C2 is preferably 1.0 C / dm 2 More than 2.0C / dm 2 above.

[0129] The energization time (unit: seconds) of the cathode electrolysis treatment C2 is appropriately set according to the above-mentioned electricity density.

[0130] Cathodic electrolysis treatment C1, anodic electrolysis treatment A1, and cathodic electrolysis treatment C2 do not necessarily need to be continuous electrolysis treatments. That is, in industrial production, intermittent electrolysis treatments can be used, where electrolysis is performed at multiple electrodes, inevitably resulting in periods of immersion without power supply. In the case of intermittent electrolysis treatments, the total charge density is preferably within the above-mentioned range.

[0131] <Second treatment>

[0132] As the second treatment, the steel sheet having undergone the first treatment is subjected to an immersion treatment or a cathodic electrolytic treatment C3 using a second aqueous solution containing colloidal silica.

[0133] Thus, as described above, silicon dioxide adheres to the interior or surface of the chromium hydrous oxide layer generated by the first treatment.

[0134] Second Aqueous Solution

[0135] The second aqueous solution contains colloidal silica.

[0136] The colloidal silica is not particularly limited, but colloidal silica in which the dispersion medium is water is preferred from the viewpoint of stability. Specific examples thereof include the SNOWTEX series manufactured by Nissan Chemical Industries, Ltd.

[0137] As described above, the average particle size of the colloidal silica contained in the second aqueous solution can be regarded as the average particle size D2 of the silica in the chromium hydrous oxide layer.

[0138] When the average particle size of colloidal silica is less than 10 nm, it can be calculated from the specific surface area determined by the BET method. The specific surface area by the BET method is measured using nitrogen gas in accordance with JIS Z 8830:2013.

[0139] When the surface area is 10 to 100 nm, the specific surface area is calculated from the SEARS method, which is described in Analytical Chemistry, Vol. 28, No. 12, December 1956, pp. 1981-1983, and is a method for determining the specific surface area by titration with sodium hydroxide.

[0140] When the particle size exceeds 100 nm, the particle size is determined by laser diffraction. More specifically, the particle size at the cumulative value of 50% in the particle size distribution determined by laser diffraction is defined as the average particle size.

[0141] If the colloidal silica contained in the second aqueous solution is too little, the desired silica content cannot be obtained in the finally obtained chromium hydrous oxide layer.

[0142] Therefore, the content of colloidal silica in the second aqueous solution is 0.10 g / L or more, preferably 0.20 g / L or more, and more preferably 0.30 g / L or more, in terms of SiO 2 .

[0143] On the other hand, the upper limit is not particularly limited. For example, the colloidal silica content in the second aqueous solution is preferably 40 g / L or less, more preferably 30 g / L or less, and even more preferably 20 g / L or less, calculated as SiO2. However, this is not limiting and can be appropriately adjusted depending on the desired silica content.

[0144] In order to stably disperse the colloidal silica in water, the second aqueous solution is preferably a substance different from the first aqueous solution.

[0145] Therefore, the amount of Cr in the second aqueous solution is preferably less than 0.50 mol / L, more preferably 0.45 mol / L or less, and even more preferably 0.40 mol / L or less.

[0146] However, if the Cr content is within this range, colloidal silica can be intentionally added to the aqueous solution containing the hexavalent chromium compound to prepare a second aqueous solution for the purpose of controlling the amount of chromium hydrous oxide layer adhered or modifying it. In this case, cathodic electrolysis treatment C3 is performed as the second treatment instead of the immersion treatment.

[0147] It should be noted that when the steel sheet that has undergone the first treatment is washed with water, colloidal silica may be added to the water (rinsing liquid) used for the washing to prepare a second aqueous solution. In this case, the second treatment becomes an immersion treatment rather than the cathodic electrolysis treatment C3.

[0148] The higher the temperature of the second aqueous solution, the easier it is for silicon dioxide to adhere to the chromium hydrous oxide layer. Therefore, from the perspective of increasing the silicon dioxide content in the chromium hydrous oxide layer, the temperature of the second aqueous solution is preferably 20°C or higher, more preferably 40°C or higher.

[0149] On the other hand, the upper limit is not particularly limited. For example, the liquid temperature of the second aqueous solution is preferably 80° C. or lower, and more preferably 60° C. or lower. However, this is not limiting and can be appropriately adjusted according to the desired silica content.

[0150] Impregnation treatment

[0151] The steel sheet having undergone the first treatment was immersed in the second aqueous solution in a non-energized state.

[0152] The longer the immersion time, the easier it is for silicon dioxide to adhere to the chromium hydrous oxide layer. Therefore, from the perspective of increasing the silicon dioxide content in the chromium hydrous oxide layer, the immersion time is preferably 0.20 seconds or longer, more preferably 0.80 seconds or longer, and even more preferably 1.20 seconds or longer.

[0153] On the other hand, the upper limit is not particularly limited. For example, the immersion time is preferably 10.00 seconds or less, more preferably 8.00 seconds or less, and further preferably 6.00 seconds or less. However, it is not limited thereto and can be appropriately adjusted according to the desired silica content.

[0154] Cathodic Electrolysis C3

[0155] The first treated steel sheet is used as a cathode and electrolytic treatment is performed in a second aqueous solution containing a hexavalent chromium compound in the same manner as in cathodic electrolytic treatments C1 and C2. This allows silicon dioxide to adhere to the chromium hydrous oxide layer, thereby increasing the chromium hydrous oxide layer.

[0156] The electrolysis conditions (electric quantity density, etc.) of the cathodic electrolysis treatment C3 are not particularly limited from the viewpoint of the content of the silicon dioxide in the chromium hydrate oxide layer, but by adjusting the conditions, the attached amount of the chromium hydrate oxide layer can be controlled.

[0157] For example, the electric quantity density (product of current density and electric current time) of the cathodic electrolysis treatment C3 is preferably 5 C / dm 2 More preferably, it is 10 C / dm 2 or less. On the other hand, the electric quantity density of the cathodic electrolysis treatment C3 is preferably 30 C / dm 2 More preferably, it is 20 C / dm 2 or less.

[0158] The current density (unit: A / dm 2 ) and the electric current time (unit: seconds) of the cathodic electrolysis treatment C3 are appropriately set according to the above electric quantity density.

[0159] Examples

[0160] Hereinafter, the present application will be specifically described by citing examples. However, the present application is not limited to the following examples.

[0161] Preparation of Steel Sheet for Can

[0162] A steel sheet (tempering degree: T5CA, surface roughness Ra: 0.25 μm) manufactured with a sheet thickness of 0.20 mm was subjected to ordinary degreasing and pickling.

[0163] Next, the steel sheet was subjected to the first treatment and the second treatment using the aqueous solution shown in Table 1 below.

[0164] More specifically, first, the aqueous solution A was circulated in a flow cell at a speed corresponding to 100 mpm using a pump, and the first treatment (cathodic electrolysis treatment Cl, anodic electrolysis treatment Al, and cathodic electrolysis treatment C2) was performed under the conditions shown in Table 2 below using a lead electrode. However, in Comparative Example 3, the anodic electrolysis treatment Al and the cathodic electrolysis treatment C2 were not performed (described as "-" in the corresponding column in Table 2 below).

[0165] Then, the second treatment (immersion treatment or cathodic electrolysis treatment C3) was performed under the conditions shown in Table 2 below using any one of the aqueous solutions Bl to G (described as "-" in the column of the treatment not performed in Table 2 below).

[0166] In this way, a steel sheet for can was prepared. The prepared steel sheet for can was washed with water and dried at room temperature using an air blower.

[0167] Attached Amount and Number of Granular Protrusions

[0168] The adhesion amount of the metallic chromium layer and the adhesion amount of the chromium hydrous oxide layer in terms of chromium (abbreviated as "adhesion amount" in Table 2 below) of the produced steel sheets for cans were measured.

[0169] In addition, the number density and average grain size D1 of the granular protrusions were measured for the metallic chromium layer of the produced steel sheet for cans.

[0170] Furthermore, the SiO 2 -equivalent content of silicon dioxide (abbreviated as "content" in Table 2 below) was measured for the chromium hydrous oxide layer of the produced steel sheet for cans.

[0171] The measurement methods were all as described above. The results are shown in Table 2 below.

[0172] The average particle size D2 and the particle size ratio D1 / D2 of silica are also shown in Table 2 below.

[0173] The average silica particle size D2 (see Table 2 below) of the produced can steel sheet was consistent with the average particle size of the colloidal silica used as a raw material (see Table 1 below).

[0174] <Evaluation>

[0175] The following evaluations were performed on the produced steel sheets for cans. The evaluation results are shown in Table 2 below.

[0176] Sliding 1

[0177] The static friction coefficient of the surface (target surface) of the produced steel sheet for cans was measured by the inclination method in accordance with JIS P 8147:2010.

[0178] More specifically, a sample cut from a can steel plate is placed on a base with its target surface facing the base. A 150g weight is placed on the surface of the sample opposite the target surface, and the base is tilted. The static friction force is calculated based on the base angle at the moment the sample begins to move, and the static friction coefficient is determined. Based on the calculated static friction coefficient, the sliding properties are evaluated according to the following criteria. A value of "◎◎", "◎", or "○" indicates excellent sliding properties.

[0179] ◎◎: Static friction coefficient is less than 0.25

[0180] ◎: Static friction coefficient is 0.25 or more and less than 0.30

[0181] ○: Static friction coefficient is 0.30 or more and less than 0.45

[0182] △: Static friction coefficient is 0.45 or more and less than 0.55

[0183] ×: Static friction coefficient is 0.55 or more

[0184] Sliding 2

[0185] The prepared steel plate for cans was passed 10 times between 40 mmφ nitrile rubber rolls having a Shore hardness Hs of 75 at a rotation speed of 40 mpm and a surface pressure of 0.2 MPa.

[0186] Then, the sliding property was evaluated in the same manner as in the above-mentioned "Sliding Property 1".

[0187] If at least the result for Sliding Property 1 is "◎◎", "◎", or "○", the sliding property can be evaluated as excellent, but the result for Sliding Property 2 is also preferably "◎◎", "◎", or "○". In this case, it can be evaluated that good silica retention is exerted, and the effect of improving the sliding property is maintained over time.

[0188] Sliding 3

[0189] The produced can steel plates were used to perform a pin-on-disc test (if this test was not performed, "-" is indicated in Table 2 below).

[0190] Specifically, a pin was pressed against the surface of a 35 mm diameter circular can steel plate with a load of 1 N. The plate was rotated 10 times at a peripheral speed of 500 rpm. The kinetic friction coefficient was then calculated from the frictional force. The sliding properties were evaluated based on the calculated kinetic friction coefficient according to the following criteria. A value of "◎◎," "◎," or "○" indicated excellent sliding properties.

[0191] ◎◎: Dynamic friction coefficient less than 0.20

[0192] ◎: Dynamic friction coefficient is 0.20 or more and less than 0.25

[0193] ○: Dynamic friction coefficient is 0.25 or more and less than 0.30

[0194] △: Dynamic friction coefficient is 0.30 or more and less than 0.45

[0195] ×: Dynamic friction coefficient is 0.45 or more

[0196] Weldability

[0197] Two samples cut from the produced can steel plates were heat treated at 210°C for 10 minutes and then spot welded. The two samples were sandwiched between DR-type 1 mass% Cr-Cu electrodes (processed with a tip diameter of 2.3 mm and a curvature R of 40 mm) and current was applied under the following conditions. Based on the minimum current required to achieve sufficient strength and the maximum current required to avoid dust generation, the appropriate current range (= maximum current - minimum current) was determined, and weldability was evaluated using the following criteria. A rating of "◎◎," "◎," or "○" indicates excellent weldability.

[0198] • Transistorized power supply: MDA-8000A manufactured by Tenryu Maki Co., Ltd.

[0199] • Welding head: AH-200

[0200] • Pressurization: 40 kgf

[0201] • On-time: 1.6 msec (ramp-up time 0.2 msec)

[0202] • Waveform: rectangular wave

[0203] ◎◎: 2.5 kA or more

[0204] ◎: 2.0 kA or more and less than 2.5 kA

[0205] O: 1.5 kA or more and less than 2.0 kA

[0206] Δ: 1.0 kA or more and less than 1.5 kA

[0207] X: less than 1.0 kA [Table 1]

[0208] Table 1

[0209]

[0210]

[0211] <Summary of Evaluation Results>

[0212] As is apparent from the results shown in Table 2 above, the sliding property and the weldability of Inventive Examples 1 to 22 are all good. In contrast, at least one of the sliding property and the weldability of Comparative Examples 1 to 5 is insufficient.

[0213] Comparative Example 1 is an example in which the aqueous solution B1 not containing colloidal silica is used as the second aqueous solution, but the chromium hydroxide layer does not contain silica and the sliding property is insufficient.

[0214] If Inventive Example 1 is compared with Inventive Example 2, Inventive Example 1 in which the immersion treatment is performed as the second treatment has less amount of the chromium hydrate oxide layer attached and has better weldability than Inventive Example 2 in which the cathode electrolysis treatment C3 is performed as the second treatment.

[0215] If Inventive Example 1 is compared with Inventive Example 3, Inventive Example 1 in which the particle size ratio D1 / D2 is 1.2 has better sliding property than Inventive Example 3 in which the particle size ratio D1 / D2 is 14.0.

[0216] If Inventive Example 1 is compared with Inventive Example 4, Inventive Example 1 in which the average particle diameter D1 of the granular projections is 70 nm has better weldability than Inventive Example 4 in which the average particle diameter D1 is 40 nm.

[0217] Inventive Example 1 and Inventive Example 5 had equally good sliding properties and weldability.

[0218] When Invention Example 1 is compared with Invention Example 6, Invention Example 1 having a particle size ratio D1 / D2 of 1.2 has better sliding properties than Invention Example 6 having a particle size ratio D1 / D2 of 5.0.

[0219] Comparative Example 2 is an example in which the aqueous solution E1 having a low content of colloidal silica was used as the second aqueous solution. However, the content of silica in the chromium hydroxide layer was as low as less than 0.1 mg / m 2 , the sliding property is not sufficient.

[0220] Inventive Example 1 and Inventive Example 7 had similarly good sliding properties and weldability.

[0221] When comparing Invention Example 1 with Invention Example 8, the content of silicon dioxide in the chromium hydroxide layer is 1.5 mg / m 2 Example 8 of the invention has a content of 1.4 mg / m 2 Compared with Invention Example 1, the sliding property is better.

[0222] In Comparative Example 3, the metal chromium layer did not have granular protrusions, and the weldability was insufficient. In addition, the sliding property was also insufficient.

[0223] The silicon dioxide contents in the chromium hydroxide layers of Inventive Example 8, Inventive Example 9, Inventive Example 10, Inventive Example 11, and Comparative Example 4 increased in this order.

[0224] The content is as high as 62.8mg / m 2 The weldability of Comparative Example 4 was insufficient.

[0225] Among them, a tendency was found that the weldability became better as the content of silicon dioxide in the chromium hydroxide layer decreased.

[0226] The average particle size D1 of the granular protrusions of the metal chromium layers of Invention Example 12, Invention Example 13, and Invention Example 14 becomes smaller in sequence, and the particle size ratio D1 / D2 also becomes smaller in sequence.

[0227] Among them, a tendency was found that the weldability improved as the average particle size D1 of the granular protrusions increased.

[0228] In addition, the evaluation results of the sliding property 2 of Inventive Examples 12 and 13 were good compared with Inventive Example 14 in which the particle size ratio D1 / D2 was 0.1.

[0229] In Comparative Example 5, the average particle size D2 of silicon dioxide is as large as 220 nm, and the content of silicon dioxide is as high as 45.6 mg / m 2 Therefore, weldability is insufficient.

[0230] The sliding properties and weldability of Inventive Examples 15 and 16 were as good as those of Inventive Examples 9 and 10.

[0231] The particle size ratio D1 / D2 of Invention Examples 17 to 22 increases in this order.

[0232] Among them, Invention Examples 18 to 20, in which the particle size ratio D1 / D2 was within the range of 0.6 to 3.0, showed good evaluation results of Sliding Property 3 compared to Invention Examples 17, 21, and 22, which did not meet the above range.

[0233] Explanation of symbols

[0234] 1: Steel plate for tanks

[0235] 2: Steel plate

[0236] 3: Metal chromium layer

[0237] 3a: Base

[0238] 3b: Granular protrusions

[0239] 4: Chromium hydrated oxide layer

Claims

1. A steel sheet for cans, comprising a metallic chromium layer and a chromium hydrated oxide layer on a surface of the steel sheet in this order from the steel sheet side, The adhesion amount of the metal chromium layer is 50 to 150 mg / m 2 , The chromium conversion adhesion amount of the chromium hydrated oxide layer is 3 to 15 mg / m 2 , The metal chromium layer includes a flat plate-shaped base and granular protrusions provided on the base. The average particle size D1 of the granular protrusions is 20 to 200 nm. The number density of the granular protrusions is 10 / μm 2 above, The chromium hydrous oxide layer contains silicon dioxide, The content of silicon dioxide in the chromium hydrated oxide layer is 0.1 to 45 mg / m2 in terms of SiO2. 2 , A ratio D1 / D2 of an average particle size D1 of the granular protrusions to an average particle size D2 of the silica is 0.2 or more and 14.0 or less.

2. The can steel plate according to claim 1, wherein The average particle size D2 of the silicon dioxide is 5 to 200 nm.

3. The steel plate for cans according to claim 1 or 2, wherein: The ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 0.6 or more.

4. The steel plate for cans according to claim 1 or 2, wherein: The ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 4.5 or less.

5. The steel plate for cans according to claim 1 or 2, wherein: The ratio D1 / D2 of the average particle size D1 of the granular protrusions to the average particle size D2 of the silica is 3.0 or less.

6. A method for producing a can steel sheet, the method comprising: The steel sheet is subjected to cathodic electrolysis treatment C1, anodic electrolysis treatment A1, and cathodic electrolysis treatment C2 in sequence using a first aqueous solution containing a hexavalent chromium compound and a fluorine-containing compound, and then subjected to immersion treatment or cathodic electrolysis treatment C3 using a second aqueous solution. The second aqueous solution contains colloidal silica, The content of the colloidal silica in the second aqueous solution is 0.10 g / L or more in terms of SiO 2 .

7. The method for manufacturing a can steel sheet according to claim 6, wherein: The amount of Cr in the second aqueous solution is less than 0.50 mol / L.

8. The method for manufacturing a steel plate for a can according to claim 7, wherein: The amount of Cr in the first aqueous solution is 0.50 mol / L or more.

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