JP3124233B2 - Surface-treated steel sheet for welded cans having excellent rust resistance and corrosion resistance under coating film, and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet for a welding can and a method for producing the same. More specifically, the surface of the steel sheet is nickel-plated or iron-nickel alloy-plated, heat-treated in a non-oxidizing atmosphere, further iron-nickel alloy-plated, and reflowed to melt the plated tin and melt the island. Disperse the thick portion of metallic tin discontinuously in a shape or grain, and form a dense iron-nickel-tin alloy layer mainly composed of iron-tin alloy to improve the rust resistance and corrosion resistance under the coating film. The present invention relates to an excellent surface-treated steel sheet for a welding can and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, a large number of cans obtained by seam welding can bodies have been used for food and beverage cans. Conventionally, tin-plated steel sheets called tinplates have been used for these welding cans, but recently, from the viewpoint of reducing the cost of cans, various types of ultra-thin tin-plated steel sheets (Lightly TinCoated Steel Sheet; Abbreviated) has been used. As a typical LTS, after a small amount of nickel plating, the plated nickel is diffused to the surface of the steel sheet by a heat treatment in an annealing step, and then tin-plated, and reflow-treated (heated at a temperature equal to or higher than the melting point of tin to be plated. LTS in which tin has been melted and plated tin has been formed into islands or grains, LTS in which a small amount of nickel plating has been performed before tin plating, reflow treatment has been performed after tin plating, and plated tin has been formed in islands or grains. LTS, etc., in which tin plating is performed under specific plating conditions and reflow processing is performed. In addition, many patents have been published, such as LTS, which has been subjected to nickel-tin alloy plating, iron-nickel alloy plating, nickel-phosphorus alloy plating, etc. instead of nickel plating before tin plating.
These LTSs are excellent in spite of a small amount of tin plating by applying the surface treatment as described above before tin plating, and then granulating or islanding the tin plating to be plated. It is intended to ensure weldability. Although excellent weldability can be surely ensured by these surface treatments, corrosion resistance after painting, for example, corrosion resistance under a coating film, rust resistance, and the like, are not always satisfactory. As a method of performing iron-nickel alloy plating before tin plating, for example, the following method is disclosed. (1) A method of forming an iron-nickel alloy layer having a composition of Ni / (Fe + Ni) of 0.02 to 0.50 by weight and having a thickness of 10 to 5000 angstroms on a steel plate before tin plating (Japanese Patent Application Laid-open No. -1
No. 7099 and JP-A-60-114596), (2) An iron-nickel alloy layer having a Fe content of 10 to 80% by weight and a coating amount of 10 to 500 mg / m ^{2 on} a steel plate before tin plating. (JP-A-60-29484),
(3) A method of applying an iron-nickel alloy plating having a composition of Ni / (Fe + Ni) of 0.60 to 0.95 by weight and having a thickness of 0.01 to 0.2 μm on a steel sheet before tin plating (Japanese Patent Application Laid-Open No. 60-1985). 110881
(4) A method of forming an iron-nickel alloy layer having a nickel concentration of 0.5% or more and less than 20% on the surface of a steel sheet before tin plating (Japanese Patent Publication No. 61-104088), (5)
A method in which tin plating of 50 to 250 mg / m ² is applied to a steel sheet, and then an iron-nickel alloy plating having a nickel content of 2 to 95% is applied before tin plating (JP-A-63-125694). All of these disclosed methods are intended to improve the properties required for surface-treated steel sheets for welding cans. Further improvement in the performance of yarn rust and corrosion under the coating film is required, and it is difficult to say that the surface-treated steel sheet for a welding can obtained by the conventional method is sufficient.

[0003]

The LTS used as a conventional material for a welding can as described above is provided with a surface treatment by pre-plating with nickel or the like to prevent a decrease in weldability due to a decrease in the amount of tin plating. The purpose is to prevent the deterioration of weldability by dispersing a small amount of plated tin in the form of particles or islands, but the corrosion resistance after coating required for can materials, especially corrosion under the coating film If it is intended to simultaneously satisfy the properties and the yarn rust resistance, these are not necessarily sufficient because of the conflicting properties. It is an object of the present invention to provide a surface-treated steel sheet for a welding can which is excellent in weldability and corrosion resistance after coating, that is, excellent in rust resistance and corrosion resistance under a coating film, and a method for producing the same.

[0004]

The surface-treated steel sheet for a welding can according to the present invention has an iron-nickel alloy layer as the lowermost layer on the surface of the steel sheet, and a portion closer to the iron-nickel alloy layer in the thickness direction as an upper layer. Nickel concentration is low, the iron-nickel-tin alloy layer mainly composed of an iron-tin alloy having a thickness concentration of 0.01 to 0.3 μm having a nickel concentration gradient having a higher nickel concentration as the portion farther from the iron-nickel alloy layer, furthermore, As an upper layer, an iron-nickel-tin alloy layer mainly composed of an iron-tin alloy having a thickness of 0.001 to 0.1 μm having no concentration gradient of nickel in a thickness direction, and an upper layer of a thick metal tin in an island shape or a granular shape Adhesion amount where parts are dispersed discontinuously
100~1500mg / m ² of metallic tin layer, the adhesion amount of 10 to 50 made of metal chromium and hydrated chromium oxide as the top layer further thereon
It is characterized by having a chromate film layer of mg / m ² and having excellent thread rust resistance and corrosion resistance under a coating film. Further, the production method of the present invention is to provide a steel plate surface with nickel plating of nickel amount of ²⁰ to 200 mg / m2 or an iron-nickel alloy plating, and then heat-treating the steel plate surface in a non-oxidizing atmosphere. After forming the nickel alloy layer, temper rolling is performed, and then the nickel content is 10 to 30% and the nickel amount is 5
To 50 mg / m ² of iron - applying nickel alloy plating, it was then subjected to tin plating of tin content 500 to 2000 / m ^2, and then melt the tin plating is subjected to a reflow process of heating to a temperature above the melting point of tin In addition to discontinuously dispersing a thick portion of metal tin in an island shape or a granular shape, a portion closer to the iron-nickel alloy layer between the tin plating layer and the iron-nickel alloy layer has a lower nickel concentration, Forming an iron-nickel-tin alloy layer mainly composed of an iron-tin alloy having a nickel concentration gradient having a higher nickel concentration at a portion farther from the nickel alloy layer, and having a nickel concentration gradient in a thickness direction; After forming an iron-nickel-tin alloy layer having an upper-lower two-layer structure in which an iron-nickel-tin alloy layer mainly composed of an iron-tin alloy is formed on the upper side, electrolytic chromic acid treatment is applied to the metal chromium. And chromium hydrate oxidation Consisting adhered amount 10 to 50 mg / m ²
Which is characterized by having excellent rust resistance and corrosion resistance under the coating film.

[0005]

DETAILED DESCRIPTION OF THE INVENTION At first glance, the present invention provides a method for producing a surface-treated steel sheet for a welding can by applying a nickel or iron-nickel alloy plating before a tin plating, and performing a heat treatment in a non-oxidizing atmosphere. It can be seen that this is a method in which a method of forming an iron-nickel alloy layer and a method of applying an iron-nickel alloy plating before tin plating as described above are used. The state of the alloy layer under the existing tin layer is different from the conventional state by the combination of the two methods, and a dense alloy layer mainly composed of an iron-tin alloy is formed. Since they have distinctly different cross-sectional structures, a surface-treated steel sheet having excellent thread rust resistance and corrosion resistance under the coating film can be obtained.

Here, the cross-sectional steel structures of the conventional LTS and the surface-treated steel sheet for a welding can of the present invention are shown in FIGS. 1 to 3 and the differences will be described. FIG. 1 shows a conventional LT.
It is the schematic which shows the example cross-section structural example of S typically. That is, it is a schematic cross-sectional structure diagram of an LTS that has been subjected to heat treatment in a non-oxidizing atmosphere after nickel plating, temper rolling, tin plating, and then reflow treatment. FIG. 2 is a schematic diagram schematically showing a cross-sectional structure diagram as another example of the conventional LTS. That is, it is a schematic cross-sectional structure diagram of an LTS in which an annealed and temper-rolled steel plate is subjected to an iron-nickel alloy plating, a tin plating, and a reflow treatment. FIG. 3 is a schematic view schematically showing a cross-sectional structure diagram of an example of the surface-treated steel sheet for a welding can of the present invention. That is, after nickel plating, heat-treated in a non-oxidizing atmosphere, after temper rolling, iron-nickel alloy plating, tin plating sequentially,
FIG. 3 is a schematic cross-sectional structure diagram of a surface-treated steel sheet that has been subjected to a reflow treatment. 1, 2 and 3, reference numeral 1 denotes a steel plate, 2 denotes an iron-nickel alloy layer formed by heat treatment in a non-oxidizing atmosphere, and 3 denotes a thickness formed by reflow treatment after tin plating. In the present invention, the iron-nickel-tin alloy layer 4 having a nickel concentration gradient in the direction includes a small amount of nickel formed by reflow treatment after tin plating in the present invention, and has no nickel concentration gradient in the thickness direction. The tin alloy layers 5 and 5 are island-shaped or granular tin layers formed by reflow treatment after tin plating. 1 to 3, the metal chromium layer and the chromium hydroxide layer formed by the electrolytic chromic acid treatment performed after the reflow treatment are omitted.

The cross-sectional structure of the surface-treated steel sheet for a welding can of the present invention shown in FIG. 3 is clearly different from the cross-sectional structure of the conventional LTS shown in FIGS. 1 and 2.
It can be seen that the concentration distribution of tin, iron and nickel in the depth direction from the surface measured by glow discharge emission spectroscopy (GDS) shown in FIG. FIG. 4 shows the results of measuring the concentration distribution of tin, iron, and nickel from the surface in the depth direction by GDS after detinning the surface-treated steel sheet of the present invention shown in FIG. FIG. 5 shows the result of measuring the concentration distribution of tin, iron, and nickel from the surface in the depth direction by GDS after detinning the conventional LTS shown in FIG. FIG. 6 shows FIG.
3 is a photograph obtained by observing the surface of an alloy layer with a scanning electron microscope after detinning the surface-treated steel sheet of the present invention shown in FIG. FIG. 7 is a photograph in which the surface of the alloy layer is observed with a scanning electron microscope after detinning the conventional LTS shown in FIG. Except for the unsteady portion immediately after the start of the etching, in FIG. 5, the nickel concentration gradually decreases after passing through the maximum value in the depth direction. On the other hand, in FIG. 4, after passing through the layer having a relatively uniform nickel concentration, the nickel concentration gradually decreases after passing through the maximum value in the depth direction as in FIG. From these results, as shown in FIG. 1, one example of a conventional LTS is an iron-nickel alloy layer having a nickel concentration gradient in the thickness direction on a steel sheet, and an iron-nickel-tin alloy layer having a nickel concentration gradient in a thickness direction. Another example of the conventional LTS is an iron-nickel-tin alloy layer having no nickel concentration gradient in the thickness direction, as shown in FIG. In addition, the upper layer is composed of a tin layer dispersed and present in the form of islands or grains, and as shown in FIG. 3, the surface-treated steel sheet for a welding can of the present invention has an iron-nickel alloy layer, An iron-nickel-tin alloy layer having a nickel concentration gradient in the thickness direction in the upper layer, an iron-nickel-tin alloy layer having no nickel concentration gradient in the thickness direction in the upper layer, and an island-like or granular dispersion in the upper layer, Consists of an existing tin layer It can be seen.

The difference in the cross-sectional structure of the surface-treated steel sheet obtained as described above is due to the difference in the manufacturing method. As an example, the conventional LTS shown in FIG. 1 is subjected to heat treatment in a non-oxidizing atmosphere after nickel plating, temper rolling, tin plating,
It is manufactured by performing reflow treatment, but when subjected to heat treatment in a non-oxidizing atmosphere after nickel plating on a steel sheet, an iron-nickel alloy having a high nickel content on the surface layer of the steel sheet due to mutual diffusion of iron and nickel. A layer is created.
Therefore, the closer the iron-nickel alloy layer formed by thermal diffusion is to the steel sheet surface, the higher the nickel content is in the structure. After that, temper rolling is performed, and then tin plating and reflow processing are performed. When the molten tin diffuses into the iron-nickel alloy to form an iron-nickel-tin alloy, the closer to the steel sheet surface, the more nickel-containing An iron-nickel-tin alloy having a high ratio is formed, and an iron-nickel-tin alloy having a low nickel content is formed toward the inside. Iron of this heat diffusion material
The disadvantage of the method of forming a nickel-tin alloy layer is that a sufficient amount of iron-
In order to electrochemically reduce the corrosion of the steel sheet by the nickel alloy layer, it is necessary to increase the amount of nickel before annealing, but if the amount of nickel is increased, the annealing temperature and the annealing time are lengthened to completely diffuse nickel. It is not only uneconomical, but also does not provide the desired mechanical properties of the material. In addition, if the nickel concentration in the surface layer of the diffusing material is too high, the island-like or granular dispersion of tin becomes difficult due to the reflow treatment, and a desired dispersion state cannot be obtained.
Another disadvantage of the heat diffusion material is that since the nickel content in the thickness direction of the iron-nickel-tin alloy layer is different, an alloy having a high nickel content near the surface layer has a dense form. On the other hand, an alloy having a low nickel content in the lower layer has a coarse form, and the alloy layer lacks in the overall density. On the other hand, in the present invention, a dense alloy layer containing a certain amount of nickel and a dense alloy layer containing a large amount of nickel are formed under the dense alloy layer. That is, a coarse alloy having a low nickel content such as the heat diffusion material is not formed, and the nickel content in the iron-nickel alloy layer remaining without being alloyed is also higher than that of the heat diffusion material. High electrochemical effect. 6 and 7
Next, an alloy layer formed by the surface-treated steel sheet of the present invention (FIG. 6)
And a microscopic photograph showing a difference between an alloy layer (FIG. 7) formed by a conventional surface-treated steel sheet (the one shown in FIG. 1). On the other hand, the conventional LTS shown in FIG. 2 is manufactured by performing a nickel-iron alloy plating, a tin plating, and a reflow treatment. However, there is no heat treatment step in a non-oxidizing atmosphere after the nickel plating as a pre-process. There is no iron-nickel alloy layer on the steel sheet, and an iron-nickel-tin alloy layer is formed on the steel sheet. The nickel content in the iron-nickel-tin alloy layer can be set to a desired value depending on the conditions of the iron-nickel alloy plating performed before tin plating. On the other hand, the surface-treated steel sheet for a welding can of the present invention is subjected to a heat treatment in a non-oxidizing atmosphere after nickel plating, similarly to the conventional LTS shown in FIG. A nickel alloy layer is formed. Thereafter, temper rolling is performed, and further, iron-nickel alloy plating having a lower nickel content than the alloy layer is performed, and then tin plating and reflow treatment are performed, so that two layers of iron-nickel having different nickel contents are provided. -A tin alloy layer is formed by reflow after tin plating. That is, the surface-treated steel sheet for a welding can of the present invention is characterized by forming an iron-nickel alloy layer by heat treatment in a non-oxidizing atmosphere after nickel plating, which is an advantage of the conventional LTS shown in FIG. At the same time as reducing the corrosion of the steel sheet, the surface layer having a high nickel content, which is a defect of the formed iron-nickel alloy layer, is further subjected to iron-nickel alloy plating having a lower nickel content than the alloy layer. Accordingly, a reflow process after tin plating facilitates formation of a dense alloy layer made of an iron-nickel-tin alloy and easy dispersion of tin islands or particles. Therefore, although it seems that the conventional methods of manufacturing the LTS shown in FIGS. 1 and 2 are simply combined, the combination of the two methods makes it impossible to predict an unexpectedly dense alloy layer of iron-nickel-tin, especially an island. It can be dispersed in a shape or a granular form, and a dense iron-nickel-tin alloy layer can be formed under the existing tin layer. The rust resistance and the corrosion resistance under the coating film are higher than those of the conventional LTS. It has become possible to provide even better surface-treated steel sheets for welding cans.

Next, an iron-nickel alloy layer formed on the steel sheet, which is a feature of the surface-treated steel sheet for a welding can of the present invention,
The denseness of the iron-nickel-tin alloy layer containing a smaller amount of nickel than the alloy layer formed thereon will be specifically described. Here, the denseness of the alloy layer means that the surface of the steel sheet is uniformly covered with the alloy layer and the exposed area of the steel sheet surface is extremely small. The exposed area ratio of the steel sheet surface is dispersed on the alloy layer, and after the tin layer present is chemically removed, the alloy layer surface is observed with an electron microscope, and the obtained electron micrograph is image-processed. Asked by. In the surface treated steel sheet for a welding can of the present invention, it is preferable that the exposed area of the steel sheet surface is as small as possible, specifically, 10% or less assures excellent yarn rust resistance and excellent under-film corrosion resistance. Needed to do so.
As is well known, the mechanism of occurrence of rust and under-film corrosion is that, under each corrosive environment, as the corrosion progresses, the island-like or granular tin layer dissolves, and then the underlying alloy layer surface The exposed part of the steel surface is corroded.
Therefore, it is important to reduce the exposure of the steel sheet surface by the alloy layer in order to prevent the thread rust and the under-film corrosion.

The surface-treated steel sheet for welded cans of the present invention, which is excellent in thread rust resistance and under-film corrosion resistance, and a method for producing the same will be described in detail. (Steel Sheet) First, as a raw sheet of the surface-treated steel sheet for a welding can of the present invention, a low carbon aluminum killed continuous cast material generally used for cans is cold-rolled to 0.15 to 0.35 mm by a usual method. Is used. Further, a cold-rolled steel sheet manufactured from a non-aging ultra-low carbon steel to which niobium and titanium are added is also applicable.

(Nickel or iron-nickel alloy plating)
Cold-rolled and electrolytically cleaned cold-rolled steel sheets are plated with nickel or an iron-nickel alloy. Any of known baths such as a sulfate bath, a chloride bath, a mixed bath thereof, and a sulfamic acid bath can be applied to the nickel or iron-nickel alloy plating. This nickel plating layer or iron
The nickel alloy plating layer is subjected to a heat treatment in a non-oxidizing atmosphere described below, whereby nickel and iron are mutually diffused on the surface of the steel sheet to form an iron-nickel alloy layer, and the corrosion of the steel sheet is electrochemically reduced. It is applied for the purpose of preventing, it is preferable to apply nickel plating or iron-nickel alloy plating with a high nickel content,
For iron-nickel alloy plating, nickel content is 60%
It is preferable that it is above. If the nickel content is 60% or less, for example, a steel sheet and iron with a nickel content of 60% or less
When a nickel alloy is coupled in a 3% saline solution, the coupling current becomes large, the effect of preventing corrosion of the steel sheet is small, and the rust resistance and the corrosion resistance under the coating film are not improved. The amount of nickel or iron-nickel alloy plating with a high nickel content is preferably in the range of ^{20 to} 200 mg / m ² as the nickel amount. Is less than the amount of nickel to be plated 20 mg / m ^2, iron is formed by the following referred heat treatment - can not sufficiently cover the steel sheet surface with a nickel alloy layer, filiform rust resistance is an object of the present invention and Ineffective in improving corrosion resistance under the coating film. Also,
When the amount of nickel to be plated is more than 200 mg / m ^2, iron is formed by the following referred heat treatment - as well as workability of the nickel alloy layer is reduced, and sometimes there is a risk that metallic nickel remaining after the heat treatment, rather It is not preferable because the rust resistance and the corrosion resistance under the coating film are reduced.

(Heat Treatment in Non-Oxidizing Atmosphere) Next, the steel plate subjected to the nickel plating or the iron-nickel alloy plating is heat-treated in a non-oxidizing atmosphere. This heat treatment softens the steel sheet and simultaneously converts the nickel plating layer or the iron-nickel alloy plating layer into an iron-nickel alloy and changes the hard and brittle plating layer into a tough layer, thereby causing corrosion of the steel sheet as described above. The purpose is to prevent electrochemically. For this heat treatment, any of a box-type annealing method and a continuous annealing method generally used for a steel sheet after cold rolling can be applied. When the box annealing method is used, heating may be performed at a temperature of 450 to 650 ° C. for 4 to 15 hours. When using the continuous annealing method, at a temperature of 600 to 850 ° C., 0.5
Heat for ~ 3 minutes. In general, the higher the temperature of the heat treatment and the longer the soaking time, the less the possibility of nickel metal remaining. And the workability of the resulting surface-treated steel sheet for welding cans,
The heat treatment temperature and the soaking time may be appropriately determined in consideration of the nickel plating amount and the like.

(Temperature rolling) After the above heat treatment,
Temper rolling is performed. Temper rolling is intended to prevent the occurrence of buckling and strainer strain of the heat-treated steel sheet, to give appropriate hardness, to improve the shape of the steel sheet, and to form appropriate surface roughness. This is an essential step in the present invention. Normally, a work roll finished with a grindstone and finished with a bright finish, or a work roll finished with a dull finish by shot blasting, is subjected to light rolling under an elongation of 1 to 2%, but may be rolled twice if necessary. Good.

(Iron-nickel alloy plating) The temper-rolled steel sheet is degreased and pickled by a known method, and then subjected to iron-nickel alloy plating. This iron-nickel alloy plating suppresses the formation of an iron-nickel-tin alloy or a nickel-tin alloy having a high nickel content formed by tin plating described below and a reflow treatment performed thereafter,
An object of the present invention is to form a dense iron-nickel-tin alloy layer having a low nickel content, to improve the rust resistance and the corrosion resistance under the coating film, and to further secure excellent paint adhesion. Known plating baths such as a sulfuric acid bath, a chloride bath, a mixed bath thereof, and a sulfamic acid bath are used for the iron-nickel alloy plating. In the case of iron-nickel alloy plating, it is necessary to perform iron-nickel alloy plating with a low nickel content, and the nickel content is preferably 30% or less, more preferably 20% or less. When an iron-nickel alloy plating with a nickel content exceeding 30% is applied, a tin-plating described below and a reflow treatment performed thereafter form an iron-tin alloy having a high nickel content, and can easily be plated with tin. In addition to the formation of a nickel-tin alloy, not only the original role of nickel cannot be exhibited, but also the reduction of the residual amount of metallic tin after the reflow treatment may be caused, and the weldability may be reduced. The plating amount of the iron-tin alloy was 50 m as nickel.
g / m ² or less, preferably about 10 to 20 mg / m ² for the same reason as above. In the case of iron-nickel plating, the amount of nickel can be continuously controlled by a fluorescent X-ray method or the like, but it is difficult to continuously control the amount of iron plating in iron-nickel alloy plating.
By grasping in advance the relationship between the plating conditions and the amount of iron plating and managing the plating conditions, continuous production is possible.

(Tin Plating) The steel plate on which the above-described iron-nickel alloy plating or iron plating has been performed is washed with water, and then subjected to tin plating. For the tin plating, any of known tin plating baths such as a ferrostan bath, a sulfuric acid bath, a halogen bath, and a methanesulfonic acid bath can be used. The tin plating conditions are the same as those used for tinplate production, and a soluble anode or an insoluble anode can be used. The plated tin is partly formed of an alloy layer mainly composed of an iron-tin alloy, and the amount of metallic tin is reduced by a reflow treatment to be performed next, but the amount of metallic tin is reduced to 100 mg from the viewpoint of weldability. / m ² or more, more preferably 200 mg / m ² or more. Accordingly, tin plating amount is required 500 mg / m ² or more, and preferably 2000 mg / m ² or less, 300~1000mg / m
² is more preferred. If the tin plating amount is less than 500 mg / m ² , it is difficult to leave 150 mg / m ² or more of metallic tin after the reflow treatment, and the high-speed weldability is reduced. In addition, even if the tin plating amount exceeds 2000 mg / m ² , it is preferable from the viewpoint of weldability, thread rust resistance, and corrosion resistance under the coating film, but the surface treatment for welding cans is excellent in inexpensive properties. Contrary to the present invention for providing a steel sheet, it is not preferable.

(Reflow treatment) After the above-mentioned tin plating, a steel plate is subjected to a reflow treatment for heating it to a temperature equal to or higher than the melting point of tin.
Reflow process, even in small tinned amount that uniformly plated 500 to 2000 / m ^2, good to ensure the weldability, the thick portion of the metal tin-plated tin islands or granular discontinuous The purpose of the present invention is to form an alloy layer mainly composed of a dense iron-tin alloy, while dispersing the alloy layer. For the reflow treatment, a resistance heating method and an induction heating method, which are generally used for producing tinplate, are used alone or in combination. The reason why the plated tin layer becomes island-like or granular is not well understood, but it is considered that the wettability of the molten tin on the iron-nickel-tin alloy layer containing a small amount of nickel is partially different.

(Electrochromic treatment) After reflow treatment,
It is subjected to electrolytic chromic acid treatment, washed with water, and dried to complete the production of the surface-treated steel sheet for a welding can of the present invention. Electrolytic chromic acid treatment improves paint adhesion, yarn rust resistance, and corrosion resistance under coating,
The purpose is to prevent these surface properties from deteriorating during storage. In this electrolytic chromic acid treatment, a method of performing cathodic electrolysis using a known bath containing chromic anhydride as a main component and one or more of sulfuric acid and a fluorine compound added as an auxiliary agent is used. Chromic anhydride concentration is 15 ~ 80g /
The range of l is preferred, and the added auxiliary agent is generally preferably about 1/150 to 1/80 of the chromic anhydride concentration. The chromic acid-treated film formed by this electrolytic chromic acid treatment may be composed of only chromium hydrated oxide, but the chromate film composed of chromium metal and chromium hydrated oxide satisfies the above characteristics. preferable. The amount of chromate film is preferably 10 to 50 mg / m ² as the total amount of chromium, more preferably 8~25mg / m ^2, preferably further about half of the total chromium content is metal chromium. If the total chromium content is less than 5 mg / m ² , the above properties cannot be satisfied, and if the total chromium content exceeds 30 mg / m ² , the high-speed weldability is reduced.

The method for producing a surface-treated steel sheet for a welding can according to the present invention has been described above in accordance with the production process. In particular, the nickel-containing sheet formed by heat treatment in a non-oxidizing atmosphere after nickel plating or iron-nickel alloy plating. High-efficiency iron-nickel alloy layer is coated with low-nickel iron-nickel alloy plating, then tin-plated on top of it, and then reflowed to form tin-plated tin discontinuities in islands or grains And the formation of an iron-nickel-tin alloy layer mainly composed of a dense iron-tin alloy, as compared with the conventional LTS, provides superior yarn rust resistance and corrosion resistance under the coating film. It is important in the production of the surface-treated steel sheet for a welding can of the present invention, and is also a feature of the present invention.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In each of the following Examples and Comparative Examples, the amount of metal plating deposited in each metal plating step is the amount of chromium metal and chromium water formed by electrolytic chromic acid treatment under the conditions shown in the following (1) to (5). The amount of the oxidized oxide (as chromium) was adjusted by changing the electrolysis time under the conditions shown in (6) below. In the case of iron-nickel alloy plating, it was indicated by the amount of nickel. The heat treatment was performed in a non-oxidizing atmosphere of 6.5% hydrogen gas, the balance being nitrogen gas, and a dew point of -55 ° C under the conditions shown in Table 1 under continuous annealing (indicated as CA in Table 1) or box annealing (in Table 1). BA). Further, the temper rolling was performed using a bright-finished work roll under the condition of an elongation of 1%.

(Examples 1 to 3) A cold-rolled steel sheet having a thickness of 0.22 mm is electrolytically cleaned by a known method, nickel-plated under the conditions shown in (1), washed with water, dried, and then subjected to the above. Annealing and temper rolling were performed under the conditions. Then, degreasing, pickling, and water washing were sequentially performed by a known method, iron-nickel alloy plating was performed under the conditions shown in (3), and after water washing, tin plating was performed under the conditions shown in (5). Thereafter, reflow treatment was performed using a known method, and then electrolytic chromic acid treatment was performed under the conditions shown in (6), followed by washing with water and drying.

(Examples 4 to 6) The same cold-rolled steel sheet as in Example 1 was subjected to electrolytic cleaning by a known method, then subjected to iron-nickel alloy plating under the conditions shown in (2), washed with water, and dried. Annealing and temper rolling were performed under the conditions described above. Then, degreasing, pickling, and water washing were sequentially performed by a known method, and iron-nickel alloy plating was performed under the conditions shown in (3).
The same processing steps were used.

(Comparative Example 1 and Comparative Example 2) The same cold-rolled steel sheet as in Example 1 was subjected to electrolytic cleaning by a known method, nickel-plated under the conditions shown in (1), washed with water, dried, and shown above. Annealing and temper rolling were performed under the conditions. Then, degreasing, pickling, and water washing were sequentially performed by a known method, and tin plating was performed under the conditions shown in (5). Thereafter, reflow treatment was performed using a known method, and then electrolytic chromic acid treatment was performed under the conditions shown in (6), followed by washing with water and drying.

Comparative Example 3 A steel plate having a thickness of 0.22 mm, which was subjected to cold rolling, electrolytic cleaning, continuous annealing, and temper rolling by a known method, was sequentially degreased, pickled, and washed with water by a known method. Alms,
Nickel plating under the conditions shown in (1), washing with water,
Tin plating was performed under the conditions shown in (5). Thereafter, reflow treatment was performed using a known method, and then electrolytic chromic acid treatment was performed under the conditions shown in (6), followed by washing with water and drying.

Comparative Example 4 An iron-nickel alloy plating was applied instead of the nickel plating of Comparative Example 3, except that
The same processing steps were used. In Comparative Example 4, the condition shown in (3) was used as the iron-nickel plating condition.

(Comparative Examples 5, 6 and 7) The same cold-rolled steel sheets as in Example 1 were processed in the same processing steps as in Example 1. However, in Comparative Example 5, the conditions shown in (2) were used for the iron-nickel alloy plating conditions in Comparative Examples 6 and 7, (3). The amount of nickel plating and the amount of nickel in the iron-nickel alloy plating are (1) to
Using the plating bath shown in (3), the current density, electrolysis time and bath temperature were changed and adjusted.

Next, the processing conditions used in each of the examples and comparative examples are specifically shown below. (1) Nickel plating conditions before heat treatment (indicated as Ni in Table 1) Bath composition Nickel sulfate (hexahydrate) 250 g / l Nickel chloride (hexahydrate) 40 g / l Boric acid 30 g / l Bath temperature 55 ° C Current density 10 A / dm ² (2) Iron-nickel alloy (A) plating conditions (indicated as Fe-Ni (A) in Table 1) Bath composition Nickel sulfate (hexahydrate) 110 g / l Nickel chloride ( (6 hydrates) 110 g / l Ferrous sulfate (7 hydrates) 15 g / l Boric acid 30 g / l Bath temperature 50 ° C Current density 15 A / dm ² (3) Iron-nickel alloy plating (B) Conditions (indicated as Fe-Ni (B) in Table 1) Bath composition Nickel sulfate (hexahydrate) 30 g / l Ferrous sulfate (heptahydrate) 150 g / l Boric acid 30 g / l Bath temperature 45 ° C Current density 20 A / dm ² (4) Tin plating conditions (indicated as Sn in Table 1) Bath composition Tin sulfate 60 g / l Phenolsulfonic acid (65% solution) 30 g / l Ethoxylated α-naphthol 5 g / l Bath Temperature 40 ° C Current density 15 A / dm ² (5) Electrolytic chromic acid treatment Processing conditions Bath composition Chromic anhydride 30 g / l Sulfuric acid 0.3 g / l Bath temperature 50 ° C Current density 30 A / dm ²

The properties of the surface-treated steel sheets obtained in the above Examples and Comparative Examples were evaluated by the following methods. (1) Weldability After heating the above sample at 210 ° C for 20 minutes, the welding speed was 70m / min.
Perform seam welding under the conditions of a pressure of 40 kgf and an overlap of 0.4 mm to determine the welding current range (appropriate welding current range) in which nuggets with sufficient strength are formed without generating "splashing". Was evaluated. ：: Proper welding current range of 500A or more △: Proper welding current range of 100A or more and less than 500A ×: Proper welding current range of less than 100A (2) Yarn rust resistance The above sample was coated with an epoxyphenol-based paint at a dry weight of 50 m.
g / dm ^{2 was} applied and baked at 210 ° C. for 12 minutes. It was cut into a size of 100 mm x 100 mm, a razor was used at the center, and a cross cut reaching a base material having a length of 50 mm was made, and the center was overhanged by 5 mm with an Ericksen tester. The test piece was put in a salt water spray tester, sprayed with a 5% saline solution at 35 ° C. for 1 hour, wiped off the saline solution, put in a thermo-hygrostat at a temperature of 45 ° C. and a relative humidity of 85% for 14 days. It was left to stand, and the occurrence of thread rust from the cross cut portion was visually observed and evaluated according to the following criteria. ○: No thread rust generated △: Slightly rusted ×: Slightly rusted (3) Corrosion resistance under coating film A coated sample similar to the above (2) was cut into a size of 70 mm × 70 mm. Using a razor at the center, a cross cut reaching a 50 mm long base was made, and the center was overhanged by 5 mm with an Ericksen tester. 15 g of citric acid and 15 g of common salt were dissolved in 1 liter of water, and the pH was adjusted with NaOH.
The solution was set in a container filled with 200 ml of a 70 ° C solution adjusted to 3.0, and allowed to stand for 24 hours in a state where the solution and the test piece were in contact with each other. Thereafter, the test piece was taken out, dried, and then the coating film floating due to corrosion was peeled off with a cellophane tape, and the peeled area was evaluated according to the following criteria. ○: Peeling area of coating film less than 50 mm ² △: Peeling area of coating film 50 or more and less than 100 mm ² ×: Peeling area of coating film 100 mm ² or more (4) Paint adhesion 70 mm of the coated sample similar to the above (2) It was cut into a size of 70 mm, immersed in 3% saline, and subjected to a retort treatment at 125 ° C. for 60 minutes. Thereafter, the coating film was cut in a grid pattern at intervals of 2 mm with a razor, peeled off with a cellophane tape, and evaluated according to the following criteria. ：: no peeling of the coating film △: slight peeling of the coating film ×: considerable peeling of the coating film After the tin layer was chemically removed, the alloy layer surface was observed with an electron microscope, and the obtained electron micrograph was subjected to image processing to determine the steel sheet exposure rate, which was evaluated according to the following criteria. ○: Exposed area of steel sheet surface less than 10% △: Exposed area of steel sheet surface 10% or more and less than 20% ×: Exposed area of steel sheet surface 20% or more

The results of the above property evaluation tests are shown in Table 1 together with the processing conditions of the steel sheet.

[0029]

[Table 1]

[0030]

The surface-treated steel sheet for a welding can according to the present invention can be used for a conventional welding can by increasing the density of the alloy layer under the island or granular tin layer, which is a disadvantage of the conventional welding can LTS. For welding cans that have improved rust resistance and corrosion resistance under the coating without reducing the weldability of LTS, and that can be continuously manufactured by an easy method and have excellent properties. The surface-treated steel sheet can be stably provided, and the industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic diagram schematically showing a cross-sectional structure diagram of an example of a conventional LTS.

FIG. 2 is a schematic diagram schematically showing a cross-sectional structure diagram as another example of the conventional LTS.

FIG. 3 is a schematic view schematically showing a cross-sectional structural view of an example of the surface-treated steel sheet for a welding can of the present invention.

FIG. 4 is a graph showing the results of measuring the concentration distribution of tin, iron, and nickel in the depth direction from the surface by GDS after removing the surface-treated steel sheet of the present invention from tin.

FIG. 5: After detinning a conventional LTS, in the depth direction from the surface,
It is a graph which shows the result of having measured the density distribution of tin, iron, and nickel by GDS.

FIG. 6 is a photograph obtained by observing the surface of an alloy layer with a scanning electron microscope after detinning the surface-treated steel sheet of the present invention.

FIG. 7 is a photograph obtained by observing the surface of an alloy layer with a scanning electron microscope after detinning a conventional LTS.

[Explanation of symbols]

1: steel sheet 2: iron-nickel alloy layer 3: iron-nickel-tin alloy layer having a nickel concentration gradient in the thickness direction 4: iron-nickel-tin alloy layer having no nickel concentration gradient in the thickness direction 5: Tin layer with thick metallic tin dispersed in islands or grains

Continuation of the front page (72) Inventor Masanori Ishida 1296 Higashi Toyoi, Kudamatsu City, Yamaguchi Prefecture Toyo Kohan Co., Ltd. Technical Research Institute (56) References JP-A-64-65296 (JP, A) JP-A-62- 40697 (JP, A) JP-A-62-205297 (JP, A) JP-A-61-104088 (JP, A) JP-A-3-197694 (JP, A) JP-A-7-238386 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C25D 11/38 C25D 5/00-7/12

Claims (4)

(57) [Claims] An iron-nickel alloy layer is formed as a lowermost layer on the surface of a steel sheet, and an iron-nickel-tin alloy layer having a thickness of 0.01 to 0.3 μm having a nickel concentration gradient in a thickness direction is formed thereon. An iron-nickel-tin alloy layer having a thickness of 0.001 to 0.1 μm having no nickel concentration gradient in the thickness direction on the upper layer, and a thick portion of metal tin in the form of islands or grains dispersed discontinuously in the upper layer. Existing adhesion amount 10
0~1500mg / m ² of metallic tin layer further has a chromate film layer of coating weight 10 to 50 mg / m ² consisting of metallic chromium and hydrated chromium oxide in its upper layer, filiform rust resistance and耐塗subintimal corrosion Surface treated steel sheet for welded cans with excellent resistance. 2. An iron-nickel alloy layer as a lowermost layer on the surface of a steel sheet, and a nickel concentration is lower in a portion closer to the iron-nickel alloy layer in a thickness direction as an upper layer, and in a portion farther from the iron-nickel alloy layer in a thickness direction. An iron-nickel-tin alloy layer mainly composed of an iron-tin alloy having a nickel concentration gradient having a high nickel concentration and having a thickness of 0.01 to 0.3 μm, and further having a thickness not having a nickel concentration gradient in a thickness direction as an upper layer. 0.001-0.1 μm iron-iron mainly composed of tin-
Nickel - tin alloy layer, further adhesion amount 100~1500mg / m ² of metallic tin layer islands or thick portion of metallic tin in particulate as the upper layer is present discontinuously dispersed metal as further top layer thereon Adhesion amount of chromium and chromium hydrated oxide 10
A surface-treated steel sheet for welded cans having a chromate film layer of up to 50 mg / m ² and excellent in thread rust resistance and corrosion resistance under the coating film. 3. The steel sheet surface is subjected to nickel plating or nickel-iron alloy plating with a nickel amount of ^{20 to} 200 mg / m ² , and then heat-treated in a non-oxidizing atmosphere to form an iron-nickel alloy on the steel sheet surface. After forming the layer, temper rolling is performed,
Then nickel content is 10-30%, nickel content is 5-50m
g / m ² iron-nickel alloy plating, then tin amount 500
Subjected to tin plating of 2000 mg / m ^2, then after discontinuously dispersing the thick portion of the metal tin in an island-like or granular melt the plated tin by subjecting the reflow process of heating to a temperature above the melting point of tin, further subjected to electrolytic chromate treatment to form a chromate film of coating weight 10 to 50 mg / m ² consisting of metallic chromium and hydrated chromium oxides, welded can having excellent filiform rust resistance and耐塗subintimal corrosive Production method of surface-treated steel sheet. 4. The steel sheet surface is subjected to nickel plating or nickel-nickel alloy plating with a nickel amount of ^{20 to} 200 mg / m ² , and then subjected to a heat treatment in a non-oxidizing atmosphere to form an iron-nickel alloy on the steel sheet surface. After forming the layer, temper rolling is performed,
Then nickel content is 10-30%, nickel content is 5-50m
g / m ² iron-nickel alloy plating, then tin amount 500
Subjected to tin plating of 2000 mg / m ^2, then the thick portion of the metallic tin causes discontinuously dispersed in an island-like or granular melt the plated tin by subjecting the reflow process of heating to a temperature above the melting point of tin, Between the tin plating layer and the iron-nickel alloy layer, a portion closer to the iron-nickel alloy layer has a lower nickel concentration, and a portion farther from the iron-nickel alloy layer has a higher nickel concentration gradient. A uniform iron-nickel-tin alloy mainly composed of an iron-tin alloy in which an iron-nickel-tin alloy layer mainly composed of an iron-tin alloy is formed on the lower side and has no nickel concentration gradient in a thickness direction. the after formed above, further subjected to electrolytic chromate treatment to form a chromate film of coating weight 10 to 50 mg / m ² consisting of metallic chromium and hydrated chromium oxides, filiform rust resistance and耐塗film Excellent under-corrosion Method for producing welded cans for surface treated steel sheet was.