JPH0637714B2 - Electrolytic chromic acid treated steel plate for welding can - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to food cans such as beverage cans and food cans, or
The present invention relates to an electrolytic chromic acid-treated steel plate for welding cans used in fields related to miscellaneous cans such as 18 cans and art cans.

[Conventional technology]

2 layers of metallic chromium layer and chromium hydrate oxide layer on the surface of steel sheet
Electrolytic chromic acid treated steel sheet having a layer coating (hereinafter TFS-C
T) has been increasingly used in recent years as an alternative to tin in fields such as beverage cans, food cans, art cans, and 18 cans. This is because TFS-CT is less expensive than tinplate and has an excellent function as a steel plate for coating base. However, when this TFS-CT is used as a material for a welding can, it is necessary to mechanically remove the coating made of chromium metal and chromium hydrate oxide just before welding by means such as grinding. Removing the coating before welding has problems in can manufacturing cost, quality, and hygiene. Various methods have been proposed for a TFS-CT that can be welded without grinding and removing the hydrated chromium oxide film and a manufacturing method thereof. For example, Japanese Patent Publication No. 57-1975
2, JP-B-57-36986, JP-A-61-21339
8, JP-A-63-186894 and the like are already known.

Japanese Examined Patent Publication No. 57-19752 has 3-40 mg / m ^{2 on the} steel plate surface.
2 to 15 mg / m of chromium on top of the metal chrome layer
It is characterized in that it is composed of a non-metallic chromium layer composed mainly of chromium oxide of ² and that the metallic chromium layer is made porous. However, if the amount of metallic chromium is simply reduced in this way and the metallic chromium layer is made porous, the corrosion resistance is lowered. Further, the heating applied for curing the paint applied to the surface oxidizes the steel plate surface exposed from the pores of the metal chromium layer, so that the intentionally exposed steel plate surface does not contribute to the improvement of weldability. There are drawbacks.

JP-B-57-36986 is a sulfate ion, a nitrate ion,
In an aqueous solution containing chromic acid, dichromic acid, etc., which does not intentionally add anions such as chlorine ions, 0.5 to 30 mg / m ² of metallic chromium on the surface of the steel sheet and ² to 50 mg of chromium as chromium. TMS-C with excellent paintability, weldability and workability, characterized by producing hydrated chromium oxide of 1 / m ²
The present invention relates to a method of manufacturing T. This is to reduce the amount of metallic chromium in order to improve the weldability and workability, and to compensate the decrease in corrosion resistance due to the modification by modifying the non-metallic chromium layer mainly containing hydrated chromium oxide. However, from the viewpoint of weldability, the aforementioned Japanese Patent Publication No. 57-19
Similar to 572, the metal chromium layer has many pores, and the exposed surface of the steel sheet is oxidized by heating for curing the paint, which may reduce the weldability.

Japanese Patent Laid-Open No. 61-213398 discloses 10-40 mg on the surface of a steel sheet.
relates / m ² of smooth metallic chromium layer and 3 to 30 mg / m superior welded cans for TFS-CT painting corrosion resistance were formed hydrated chromium oxide layer having a uniform thickness of ^2. The manufacturing method is characterized in that a part of the deposited metal chromium layer is dissolved by anodizing. However,
Using a known chromic acid bath, it is very difficult to continuously coat the surface of the steel sheet by deposition of 10-40 mg / m ² of metallic chromium, not porous, and once deposited metallic chromium is dissolved by anodizing. This method rather increases the pores of the metallic chromium layer, resulting in an increase in the exposure rate of the steel plate surface.

Japanese Unexamined Patent Publication No. 63-186894 discloses that the surface of a steel sheet is 50-150.
and mg / m ² of metallic chromium layer has a chromium oxide film of 5 to 20 mg / m ² as chromium, and relates welded cans for TFS-CT which is characterized by having a protruding portion on a part of the metallic chromium Is. It was discovered that the contact electric resistance value (hereinafter referred to as the Rc value) is reduced by providing the metal chrome layer with a protrusion, and as a result, the weldability is improved. It cannot be said that there is a correlation between the Rc value and the weldability, including the case where the precipitation morphology such as the smooth shape or the projection shape is different. Further, since the metal chrome layer is extremely thick in the protruding portion and the portion without the protrusion is extremely thin, the iron exposure rate becomes high in the thin portion of the metal chrome.

The fact that a method for producing TFS-CT for a welding can is disclosed but has not yet been put into practical use suggests that there are various problems as a material for a welding can.

The conventional technology was a technical idea of improving the weldability by reducing the amount of metallic chromium or the form of the metallic chromium layer, and at the same time imparting corrosion resistance, coating corrosion resistance, and coating adhesion by modifying chromium hydrated oxide. However, it is considered that the detailed examination of the factors affecting the weldability from the viewpoint of the oxidation of the steel sheet surface during heating has not been carried out sufficiently.

In addition, as described above, all of the conventional techniques are TFS-C.
The weldability was improved by improving the coating composition and coating morphology of T, and no attention was paid to the carbon content in the steel, which has a large effect on the weldability. However, the effect of the carbon content in the steel was not so remarkable in the case of the surface-treated steel sheet having excellent weldability such as tinplate, but it was not found in the conventional TFS-CT for welding cans disclosed in the prior art. It has been found that such a surface-treated steel sheet having poor weldability is extremely large. Conventionally, the amount of carbon of a usual continuous casting agent used for can materials is in the range of 0.03 to 0.10%, and when the amount of carbon in steel exceeds the range in which good weldability is obtained. there were.

[Problems to be Solved by the Present Invention]

Although various efforts have been made to make the TFS-CT for welding cans practical, as described above, those having a wide weldable current range that can be practically used as a material for welding cans have been obtained. Absent.

The present invention provides an electrolytic chromium oxidation-treated steel sheet excellent in high-speed weldability by determining the carbon content in steel for obtaining a sufficiently wide weldable current range and the optimum film composition of TFS-CT. Is intended.

[Means for Solving the Problems]

In order to achieve the above-mentioned object, the present invention uses a cold-rolled steel sheet in which the carbon content in the steel is specified in the range of 0.001 to 0.02%, and the steel sheet is smooth and has a high coverage of 45 to 90 mg / m
By forming a metallic chromium layer of No. ² and subsequently dissolving the easily soluble chromium hydrated oxide of the outermost layer, a uniform hardly soluble chromium hydrated oxide layer of 1 to 10 mg / m ² as chromium is formed. It is a thing.

Hereinafter, the present invention will be described in detail.

TFS-CT is produced by using a high-concentration chromic acid bath containing fluoric acid, sulfuric acid, and other auxiliaries, and using a high-concentration chromic acid bath containing 100 g / mol or more of chromic acid. Cathodic electrolysis in an acid bath to mainly form a chromium hydrate oxide film, and cathodic electrolysis in a chromic acid bath containing 100 g / or less of chromic acid to which an auxiliary agent such as a fluorine compound or sulfuric acid is added. Two methods are known, a one-liquid method for forming a chromium layer of the gold layer and a hydrated chromium oxide layer. Regarding the metal chromium layer obtained by dissolving and removing the hydrated chromium oxide in a hot alkaline solution, the relationship between the amount of metal chromium and the exposure rate of the steel plate surface from the pores of the metal chromium group is as shown in FIG. (A) CrO ₃ − Fluoride bath (B) Cr
O ₃ -fluoride-sulfuric acid bath (C) CrO ₃ -sulfuric acid bath gives a metallic chromium layer with less pores in that order. Therefore, in the present invention, in order to deposit a metal chromium layer having a high coverage on the steel sheet, a chromic acid bath containing a fluorine compound and sulfuric acid is added,
It is more preferable to use a chromic acid bath to which only a fluorine compound is added. A chromic acid bath containing a fluorine compound and sulfuric acid has a slightly inferior coverage, but is excellent in operability because it is hardly affected by impurity ions in the bath.

The TFS-CT of the present invention is provided as a material for welding cans, and is always used by painting. If it is not heated in the baking process of coating, as shown in FIG. 2, the Rc value, which is an index of the weldability, becomes lower as the amount of metallic chromium decreases. However, assuming coating baking, 210 ℃
When heated for 20 minutes, the amount of metallic chromium is 45 to 90 mg.
In the range of / m ² , the Rc value becomes small, and it is estimated that there is an optimum range for weldability. The reason for this is that when the amount of metallic chromium is 45 mg / m ² or less, as shown in FIG.
It is considered that the iron exposure rate remarkably increases with the decrease of metallic chromium, and iron oxide having poor conductivity is generated on the surface of the steel sheet by heating. Also, when the amount of metallic chromium is 90 mg / m ² or more, the exposed area of the steel sheet decreases, but it is considered that the Rc value increases because it is difficult for fine cracks to occur in the thick metallic chromium layer when pressed by the electrode roll. To be

FIG. 3 shows the amount of metallic chromium and T after heating at 210 ° C. for 20 minutes under a constant amount of the poorly soluble chromium hydrate oxide film.
This figure shows the relationship of the weldable current range during FS-CT welding, and this range was determined as the welding upper limit, the current at which splashing begins to occur during welding, and the welding lower limit as the current at which sufficient joint strength begins to be obtained. It is a thing. It shows that the wider the welding range, the better the weldability. The relationship between the width of the weldable current range and the Rc value has a correlation as can be seen from FIGS. 2 and 3.

Therefore, in general, by a simple method by Rc measurement,
Weldable current range is evaluated. In the case of TFS-CT having a smooth metallic chromium layer, a very good correlation is recognized between the Rc value and the weldable current range. However, when the deposition form of the metal chromium layer is changed, for example, TFS-CT having a protrusion on a part of the metal chromium layer obtained by the method disclosed in JP-A-63-186894.
In the case of, this relationship is not clear. The thickness of the protrusion of the metal chromium layer having a protrusion on a part of the metal chromium layer is 3 to 10 times the thickness of the smooth portion. Therefore, in the protruding portion, the forgeability of steel is impeded, and in the smooth portion, the iron exposure rate is high, so that iron oxide is easily generated on the surface of the steel sheet by heating. For this reason, TFS-CT having a protrusion on a part of the metal chromium layer has a relatively small Rc value,
It is considered that the current range for welding is narrow.

As described above, the TFS- which has excellent weldability according to the present invention.
The metal chrome layer of CT prevents the steel sheet from being directly exposed to the air during heating and is oxidized, and is smooth, thin, and has a high coverage so that it is easily broken by the pressure of the electrode roll during welding. I need.

Next, in the TFS-CT of the present invention, the chromium hydrated oxide formed on the smooth and high coverage 45-90 mg / m ² metallic chromium layer is uniformly soluble in the electrolyte solution. It has excellent weldability and requires dipping after electrolysis. The chromium hydrated oxide layer immediately after electrolysis is composed of one that is easily soluble in the electrolyte solution containing a large amount of the auxiliary agent on the outermost surface and one that is poorly soluble in the electrolyte solution below that containing a small amount of the auxiliary agent. Has been done. The amount of easily soluble chromium hydrate oxide in the outermost layer is likely to vary depending on the electrolytic conditions such as bath composition, bath temperature and current density, and the stirring state of the liquid, so it is not uniform across the width and length of the steel sheet. Easy to cause precipitation. On the contrary,
The amount of poorly soluble chromium hydrate oxide thereunder is almost constant regardless of the electrolysis conditions and the stirring state, and more conveniently, even if the amount of electricity is increased, it is above a certain thickness. Since it is not generated, it has excellent uniformity in the width direction and the longitudinal direction. Also, in more detail, the difference in the thickness of the refractory chromium hydrate oxide for each crystal orientation of the steel observed by an electron microscope is the difference in the thickness for each crystal orientation of the chromium hydrate oxide immediately after electrolysis. Excellent in uniformity compared to. As described above, the hydrated chromium hydrate oxide layer immediately after electrolysis forms the easily soluble chromium hydrated oxide layer having a nonuniform thickness on the hardly soluble chromium hydrated oxide layer having a uniform thickness. However, the thickness becomes uneven as a whole, which causes local heat generation during welding, which is not preferable. Therefore, even with the same amount of chromium hydrate oxide, TFS-CT obtained by sufficiently dipping the easily soluble chromium hydrate oxide by electrolysis after electrolysis is more than that of TFS-CT immediately after electrolysis. It was found that the weldability is remarkably excellent, and stable weldability cannot be obtained by simply defining the amount of hydrated chromium oxide as disclosed in the prior art. In order to obtain a sparingly soluble chromium hydrate oxide, it is necessary to immerse it in an electrolytic solution for at least 2 seconds after electrolysis. As shown in FIG. 4, most of the easily soluble chromium hydrate oxide was dissolved within 2 seconds after the electrolysis was completed.
Only the sparingly soluble chromium hydrate oxide. In addition to the electrolyte solution, 25
Chromic acid solutions of g / g or higher can be used. The higher the temperature is, the more easily soluble chromium hydrate oxide can be dissolved at room temperature.

From the viewpoint of weldability, it is preferable that the amount of the sparingly soluble chromium hydrated oxide is small, but even if it is immersed in a high-concentration chromic acid bath for a long time, it cannot be reduced to 1 mg / m ² or less as chromium. On the other hand, when the chromium content exceeds 10 mg / m ² , the poorly soluble chromium hydrated oxide film becomes too thick even if the uniformity is good, and the weldability deteriorates. Therefore, the amount of poorly soluble chromium hydrate oxide is specified as 1 to 10 mg / m ² .

Since the poorly soluble chromium hydrate oxide film thus obtained has excellent uniformity, it is considered that the distribution of the welding current becomes uniform and the weldability is improved.

Based on the optimum film composition of TFS-CT and the above-mentioned findings regarding the film morphology, first, "45-90 mg / m
² smooth deposited metal chrome layer and 1 as chrome
A method for producing an electrolytic chromic acid-treated steel sheet having excellent weldability, which is characterized by forming a poorly soluble chromium hydrated oxide layer of 10 mg / m ² , was filed in Japanese Patent Application No. 63-261440. The cold-rolled steel sheet used in this application was a steel sheet having a normal chemical composition used for can materials, and had a carbon content of 0.05%.

However, as a result of a more detailed examination of the factors on the material side that affect the weldability, it was found that among the trace elements such as C, Si, Mn, P, S, Cu, Al, N contained in the steel. In particular, it became clear that carbon has a great influence on weldability.

It has been conventionally known that the carbon content in steel influences the mechanical properties of the weld heat affected zone, and that if the carbon content in the steel becomes 0.10% or more, the forgeability deteriorates. 10%
Within the range of less than, no detailed study was conducted on the carbon content in steel and weldability. Traditionally, tinplate has been used as a material for welding cans, but materials such as tinplate that retain a large amount of metallic tin even after heating during coating baking have good weldability, and the amount of carbon in steel The relationship of weldability is relatively unlikely to appear. Further, in the case of ordinary TFS-CT, since the coating composition is inappropriate, welding cannot be performed even if the carbon content in the steel is reduced. TFS-C for welding can disclosed in the prior art
In the case of T, when the amount of carbon is reduced, the current range that can be welded tends to be wide, but it does not yet have sufficient weldability. On the other hand, in the case of TFS-CT, which was applied to Japanese Patent Application No. 63-261440 and has excellent weldability, the effect of the amount of carbon in the chain was remarkably exhibited, and the amount of carbon in the conventional range of 0.03 to
It was found that the weldability was further improved by lowering the melting point from the range of 0.10% to the range of 0.001 to 0.02%.

FIG. 5 shows the relationship between the amount of carbon in steel and the weldable current range. When the amount of refractory chromium hydrate oxide is constant, the weldable current range may narrow as the carbon amount increases. Recognize.

In addition, the TFS for welding cans manufactured by the conventional technology in the figure
Although the weldable current range of -CT is shown, it can be seen that good weldability as in the present invention cannot be obtained by simply reducing the amount of carbon in steel.

From the above results, 45-
90 mg / m ² metallic chromium layer and 1-10 mg / chromium as chromium
TFS-with a poorly soluble chromium hydrate oxide layer of m ² formed
In CT, the carbon content in the steel is 0.001-0.02%
It can be seen that TFS-CT defined in the range of 1 has good weldability. In this way, by combining the optimum film structure of TFS-CT and steel with a limited carbon content,
It is possible to provide an electrolytic chromic acid-treated steel sheet having excellent high-speed weldability.

〔Example〕

Hereinafter, the content of the present invention will be specifically described with reference to Examples and Comparative Examples.

Using hot-rolled steel sheets with different carbon contents in steel, the sheet thickness, 0.
A cold rolled steel sheet of 22 mm and temper T-4 was prepared under the conditions shown in Table 1. After normal degreasing and pickling of this cold-rolled steel sheet, cathodic electrolysis is performed in a chromic acid bath to remove 45
~ 90mg / m ² smooth metallic chrome layer and 1 as chrome
TF with -10 to 10 mg / m ² layer of poorly soluble chromium hydrate oxide
S-CT was manufactured. At the same time, TFS-CT shown in Comparative Examples 1 to 3 was manufactured according to typical examples of the prior art using cold-rolled steel sheets having different carbon contents in the steel.

Table 2 shows the coating amount, weldability, corrosion resistance, etc. of these TFS-CT. As is clear from Table 2, a steel plate having a carbon content in the steel of 0.001 to 0.02% was used as a substrate, and
~ 90mg / m ² smooth metallic chrome layer and 1 as chrome
The TFS-CT of the present invention in which a poorly soluble chromium hydrate oxide layer of 10 mg / m ² is formed has a sufficiently wide weldable current range and is extremely excellent in weldability.

Comparative Example 1 is manufactured according to the manufacturing method disclosed in the Example of JP-A-61-213398. Comparative Example 3 is manufactured according to the manufacturing method of Japanese Patent Application No. 63-261440. All of these used ordinary example rolled steel sheets, and the carbon content in the steel was 0.05%. Comparative Example 2 is manufactured according to the example of JP-A-61-213398, but uses an example rolled steel sheet in which the carbon content in the steel is reduced to 0.01% as a substrate. As can be seen from Comparative Example 2, it is understood that TFS-CT having good weldability cannot be obtained simply by reducing the carbon content in steel. Also, in terms of corrosion resistance, the TFS shown in Examples 1 to 5 was used.
-CT is superior to TFS-CT shown in Comparative Examples 1-2.

Next, the evaluation method of the evaluation items in Table 2 showing Examples and Comparative Examples will be described.

(1) Iron exposure rate from pores of metallic chromium layer TFS-CT is immersed in a 7.5N-NaOH solution at 95 ° C for 5 minutes to completely dissolve and remove chromium hydrate oxide on the outermost layer. Subsequently, the sample was sealed with tape leaving 30 mmφ, and the current immediately before passivation was read when positively polarized in a 1M-NaH ₂ PO ₄ solution at a polarization rate of 125 mV / min.
The exposure rate of iron was calculated from the calibration curve of the exposure rate and passivation current of iron which were separately determined.

(2) Weldable current range TFS-CT was air-baked at 210 ° C for 20 minutes, and then it was used as a cutting plate welding machine for experiment, frequency 60Hz, lap width 0.4mm, speed 5m /
After the welding was performed under the conditions of a pressure of 50 kg and a pressure of 50 kg, the joint state of the welded portion was evaluated. The welding current is increased in steps of 25 A, the current at which splash starts to be the welding upper limit, the welding current is lowered, and the current immediately before the joint strength of the weld becomes lower than the fracture strength of the base metal is the welding lower limit. As
This difference in current was defined as the welding possible current range.

(3) Contact electric resistance (Rc) After TFS-CT was air-baked at 210 ° C. for 20 minutes, Rc was measured with a hand-made contact electric resistance measuring instrument. The measuring method is as follows: sandwich two sample plates in the contact area of two copper disc electrodes, rotate them at a peripheral speed of 5 m / min while applying a pressure of 50 kg between the electrodes,
While moving the sample plate, a DC current of 5 A was passed between the electrodes to measure the voltage between the electrodes to obtain the Rc value.

(4) Filiform corrosion Approximately 60 mg / d of epoxy phenolic paint on TFS-CT
After applying m ² and baking at 210 ° C. for 10 minutes, a cross cut is put and it is projected by 5 mm with an Erichsen tester. After immersing the sample in 3% NaCl, stand it on the sample table and
After standing in an atmosphere of 5 ° C. and a humidity of 85% for 10 days, the state of rust generation was observed.

(5) Salt Spray Test TFS-CT is heated at 210 ° C. for 10 minutes and then placed in a salt spray tester. The generation state of rust when a 3% NaCl solution at 35 ° C. was sprayed for 1 hour was evaluated.

(6) Corrosion under coating A coated plate obtained by the same method as the filiform corrosion test has a width of 10 μm.
m, depth of 15 μm cross-cut, citric acid 1.
It was immersed in a corrosive liquid consisting of 5% and 1.5% of salt at 38 ° C. for 2 weeks, and the corrosion state of the cut part was evaluated.

〔The invention's effect〕

INDUSTRIAL APPLICABILITY The TFS-CT of the present invention is excellent in the coverage of the metal chromium layer and the uniformity of the hydrated chromium oxide film, and because of the small amount of carbon in the steel, it is excellent in the bondability at low temperatures, Since it has excellent weldability, it can be applied to a wide range of applications as a material for welding cans that is cheaper than tinplate, and has an extremely large industrial effect.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the iron exposure rate from the pores of the metallic chromium layer after the dissolution and removal of the chromium hydrated oxide film on the surface layer of TFS-CT in a heated alkaline solution, and the amount of metallic chromium. The figure shows the relationship between the contact electric resistance (Rc) value before and after heating at 210 ° C for 20 minutes and the amount of metallic chromium, and Fig. 3 shows TFS-CT with the amount of refractory chromium hydrate oxide kept constant at 210 ° C. Showing the relationship between the weldable current range and the amount of metallic chromium after heating for 20 minutes at 40 ° C., FIG. 4 is a diagram showing an example of the dissolution rate of the hydrated chromium oxide film in the electrolytic solution after electrolysis, FIG.
The figure shows TFS- with a constant amount of poorly soluble chromium hydrate oxide.
It is a figure which shows the relationship between the weldable electric current range after heating 20 minutes at 210 degreeC, and the amount of carbon in steel about CT.

Claims (1)

[Claims] 1. A steel plate after degreasing and pickling, followed by cathodic electrolysis in a chromic acid bath containing a fluorine compound or a fluorine compound and a small amount of sulfuric acid, followed by a solution containing 25 g / or more chromic acid for 2 seconds or more. By immersing it in the steel plate and dissolving the easily soluble chromium hydrate oxide, 45 to 9
In the electrolytic chromic acid treated steel sheet in which 0 mg / m ² of the metal chromium layer deposited smoothly and 1-10 mg / m ² of a poorly soluble chromium hydrated oxide layer were formed as chromium, the carbon content in the steel sheet was An electrolytic chromic acid treated steel sheet for welding cans, which has been reduced to a range of 0.001 to 0.02%.