JPH0427296B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a welding stain-free steel. [Prior art] Tein-free steel (hereinafter referred to as TFS-CT), which has a two-layer coating of a metallic chromium layer and a hydrated chromium oxide on the surface of a steel sheet, was developed about 20 years ago.
It is mainly used in large quantities in food cans, 18 cans, confectionery cans, and beverage cans. The TFS-CT can body is usually joined using an adhesive method (a method in which nylon adhesive is sandwiched between the joints and heat-pressed), but in recent years, tinplate or nickel-plated steel sheets have been used as materials. Many welded cans have come into practical use, and attempts have been made to weld TFS-CT. However, it has become clear that it is difficult to weld using electric resistance with ordinary TFS-CT, and that it is particularly difficult to obtain stable weld strength and weld appearance during high-speed welding. Therefore, as a method to improve the weldability of TFS-CT, for example, (1) welding using chromic acid, dichromic acid, etc. as the main component without intentionally adding anions such as sulfate radicals, nitrate radicals, and chloride ions; 0.5~ per side in an aqueous solution
30 mg/m ² of metallic chromium, 2 to 2 in terms of metallic chromium
Produced 50mg/ ^m2 of chromium hydrated oxide
TFS−CT. (Japanese Unexamined Patent Publication No. 55-18542), (2) A metallic chromium layer of 3 to 40 mg/m ² on the surface of the steel sheet, and on top of that a non-metallic chromium layer mainly composed of chromium oxides of 2 to 15 mg/m ² in terms of metallic chromium. A chrome-plated steel sheet consisting of two layers, characterized by a porous metal chromium layer. (Japanese Unexamined Patent Publication No. 55-31124), (3) A chrome-plated steel sheet characterized by subjecting the chrome-plated steel sheet to temper rolling of 20% or less.
55-48406) have been proposed, and the current situation is that efforts are being made to improve the weldability of TFS-CT. The technical concept for achieving improved weldability in these TFS-CTs is explained as follows. That is, in the above-mentioned reference (1), it is explained that the qualitative improvement of the hydrated chromium oxide makes it possible to reduce the metallic chromium weight, resulting in improved weldability. In references (2) and (3), the metallic chromium layer itself obstructs the passage of welding current immediately after welding starts, so the amount of metallic chromium is reduced in order to increase the exposed area of the base steel on the steel plate surface. Even when the weight of chromium metal is high, the weldability is improved by applying cracks to the steel plate due to slight elongation through temper rolling. [Problems to be Solved by the Invention] However, from the viewpoint of the corrosion resistance required for can materials, all of the above-mentioned methods result in a decrease in the amount of metal chromium, or an increase in the exposed steel area due to skin pass rolling. The disadvantage of corrosion resistance was an unavoidable problem. [Means for Solving the Problems] The present invention was discovered as a result of studies from a completely different angle from the above-mentioned technical idea. In other words, the inventors discovered that by forming the metallic chromium layer in TFS-CT into a precipitation form in which a large number of protruding chromium particles coexist, the electrical contact resistance of the joint can be greatly improved, leading to the completion of the present invention. . The greatest feature of the present invention is that in TFS-CT, in order to improve weldability without reducing any properties other than weldability, such as corrosion resistance when unpainted and corrosion resistance after painting, it is necessary to use a metallic chromium layer. It has been found that it is possible to form a precipitation form in which a large number of protruding chromium particles coexist. As shown in Figure 3, the precipitation form of the metallic chromium layer in normal TFS-CT is such that protruding chromium is mainly seen on the {100} plane of the base steel surface, but it can be deposited under specific electrolytic conditions. In the metallic chromium layer, protrusive chromium precipitation occurs not only on the {100} plane but also over the entire surface. (Figure 4)
The number of protruding chromium in this metallic chromium layer,
After dissolving chromium hydrated oxide with hot alkali, JIS
According to Z 8741, the second study looked at the relationship between the difference in specular gloss before and after metal chrome plating at 20 degrees.
FIG. 1 shows the relationship between the electrical contact resistance before dissolving chromium hydrated oxide and the difference in specular gloss before and after metal chrome plating after dissolving chromium hydrated oxide. As shown in Figure 2, there is a good relationship between the number of chromium protrusions per unit area observed in transmission electron micrographs and the difference in specular gloss before and after metal chrome plating, and the number of chromium protrusions decreases. As this progresses, the specular gloss of the chrome plating surface improves. Although it depends on the roughness of the steel plate, when using regular tin plate or TFS plate, metallic chromium has a higher gloss than iron, so chrome plating generally improves the specular gloss of the sample. It is. However, when metallic chromium is made into a precipitation form in which protruding chromium is mixed, and the number of protruding chromium is increased, the gloss of the metallic chromium layer gradually deteriorates, and eventually becomes worse than the specular gloss of the steel sheet before chromium plating. . Therefore, when we accurately measured the precipitation state of the metallic chromium layer using a gloss meter and looked at its relationship with the electrical contact resistance before dissolving the chromium hydrated oxide, we found that the more the gloss deteriorates, the more the gloss deteriorates, as shown in Figure 1. It can be seen that the electrical contact resistance becomes smaller. This shows that a metallic chromium layer with good gloss, ie, a smooth surface, does not have a good effect on welding. On the other hand, a metallic chromium layer with poor gloss, that is, a surface where many protruding chromium particles with a diameter of 1000 angstroms or less coexist, as shown in the micrograph in Figure 4, has a good effect on welding. . In this way, the protruding chromium serves as a starting point for current passage during seam welding, and
This is thought to have the advantage that the electrically insulating surface chromium hydrated oxide film is easily destroyed when pressurized. As shown in Figure 1, Ga (20°) − Gb
(20°) exceeds 8%, weldability expressed in electrical contact resistance value becomes extremely poor. Also, Ga (20°) −
The more negative the value of Gb (20°) is, that is, the worse the gloss of the surface after chrome plating is than that of the steel plate, the better the weldability is, but even if the number of protruding chromium is increased, it still exceeds -6%. Nothing happened. Therefore, for the metallic chromium layer in the present invention, after dissolving the upper layer of chromium hydrated oxide with a hot alkali, the specular gloss before and after metallic chromium plating at 20 degrees was measured according to JIS Z 8741, and the gloss after chromium plating was measured. degree
Ga (20°), when the gloss before chrome plating is Gb (20°), the value of Ga (20°) - Gb (20°) is -6 to +8%
It is defined as falling within the scope of. The reason why we measured the specular gloss of the metallic chromium layer after dissolving the chromium hydrated oxide film was to eliminate the influence of the chromium hydrated oxide film on the specular gloss value. The reason why the precipitation state was evaluated based on the difference in degree was to eliminate the influence of the roughness of the steel plate on the specular gloss. The larger the amount of metallic chromium is, the more advantageous it is to generate protruding chromium, and when the amount of metallic chromium is less than 30 mg/ ^m2 , protruding chromium will not be produced. The amount of metallic chromium is 500mg/ ^m2
There is no inconvenience in terms of performance even if the value is exceeded, but
This value was set as the upper limit from the viewpoint of cost and productivity. Therefore, the amount of metallic chromium in the present invention is defined as 30 to 500 mg/m ² . There are various conditions for producing protruding chromium, such as (1) intermittent electrolysis in a highly concentrated chromic acid solution. (2) A method of performing short-term reverse electrolysis during chrome plating. and so on. Of course, in addition to this method, bath temperature,
If the electrolytic conditions such as current density and pretreatment are carefully selected,
It is also possible to generate protruding chrome by a normal chrome plating method. however,
In method (1) above, it is difficult to generate a sufficient number of protruding chromium, and depending on the electrolysis conditions, protruding chromium may not be generated. Further, in method (2), although a sufficient number of protruding chromium particles can be generated, surface stains are likely to occur. Therefore, we investigated various chrome plating methods that stably produce protruding chromium regardless of electrolysis conditions and are less likely to cause surface stains.We found that it is effective to wash and dry with water during chrome plating and then continue with electrolysis. I discovered something. The reason why protruding chromium is produced by this intermediate drying is considered to be as follows. It is generally believed that when metallic chromium is produced by electrolytic chromic acid treatment, a soluble sol-like chromium hydrated oxide film is first formed on the surface of the steel strip that will serve as the cathode, and that metallic chromium is precipitated through this film. There is. In the case of continuous electrolysis, the surface is almost completely covered by the sol-like hydrated chromium oxide, so the formation of protruding chromium hardly occurs. On the other hand, in intermittent electrolysis, the sol-like chromium hydrated oxide film repeats dissolution during intermittent electrolysis and formation during electrolysis, and protrusive chromium is preferentially formed in defective areas of the film. The reason why granular precipitation is more likely to occur when using higher concentrations of chromic acid is explained by the fact that higher concentrations have a stronger ability to dissolve the sol-like chromium hydrated oxide film, making it easier to form defects in the film. . Therefore, if the electrolysis is temporarily stopped, washed with water, and then dried, the electrolysis is continued again, as the hydrated chromium oxide in the form of a sol shrinks during drying and generates many defects.
It has far more defects than the chromium hydrated oxide film that is simply subjected to intermittent electrolysis.
As a result, more protruding chromium is produced than in intermittent electrolysis. The degree of drying is sufficient to partially gel the sol-like chromium hydrated oxide film, and in the case of normal hot air drying, it is sufficient to maintain the board temperature at 70° or higher for a few seconds in a drying atmosphere. . If heating is desired in a shorter time, it is also effective to use resistance heating or induction heating in combination. In this way, it is thought that the protruding chromium is stably precipitated regardless of the crystal plane. As is well known, there are two types of manufacturing methods for TFS-CT: a one-liquid method and a two-liquid method. In both manufacturing methods, intermittent electrolysis is carried out by arranging several electrolytic tanks vertically.
Generally, washing and drying are not performed between plating tanks. In the one-component method, a relatively low concentration chromic acid bath is used to simultaneously precipitate metallic chromium and hydrated chromium oxide. In the case of the one-component method, in the present invention, approximately 3 to 15 mg/m ² (hereinafter expressed in terms of chromium equivalent value) of chromium hydrated oxide is generated in the tank at the front stage, and then washed with water and dried. The hydrated chromium oxide on the surface is gelled, and then electrolytic chromic acid treatment is performed using the same solution in a subsequent tank to produce metallic chromium and hydrated chromium oxide. On the other hand, in the two-component method, it is common to first precipitate mainly metallic chromium in a high concentration chromic acid bath, and then mainly produce chromium hydrated oxide in a low concentration chromic acid bath. In the case of the two-component method of the present invention, in the chrome plating process, metallic chromium and approximately 3 to 8 mg/ ^m2 of hydrated chromium oxide are generated in the tank at the front stage, and then the surface is washed and dried. The hydrated chromium oxide is gelled, and the same solution is then used for chromium plating in the subsequent tank.
Forms metallic chromium and small amounts of hydrated chromium oxide. In the case of the two-component method, if necessary, this is followed by electrolysis in a bath that mainly produces hydrated chromium oxide.
Precipitate the desired amount of chromium hydrate. When a plurality of plating tanks are used in both the one-liquid method and the two-liquid method, washing and drying may be performed in front of each plating tank, or may be performed only once. If you only need to wash and dry once, it is best to wash and dry after the plating tank in the previous stage. The uniformity of the thickness of the upper layer chromium hydrated oxide film
This is important to ensure the corrosion resistance of TFS-CT.
By making the metallic chromium layer have a precipitation form in which protruding chromium is mixed, corrosion resistance does not deteriorate. The smaller the amount of chromium hydrated oxide, the better the weldability, but if it is less than 5 mg/m ² , the corrosion resistance will deteriorate significantly. On the other hand, the higher the amount of chromium hydrated oxide, the better the corrosion resistance, but if the amount exceeds 20 mg/m ² , weldability deteriorates significantly. Therefore, the amount of hydrated chromium oxide in the present invention is defined as 5 to 20 mg/m ² . [Function] The method of making the metal chromium layer porous or creating cracks in the metal chromium layer by temper rolling in order to improve the weldability of TFS-CT may deteriorate the corrosion resistance of TFS-CT. Although the present invention has a continuous metallic chromium layer, by precipitating a large number of protruding chromium on the surface, the insulating chromium hydrated oxide film on the outermost layer is easily destroyed when pressure is applied during welding. Made it easier for current to flow. A drying process was added in the middle of the metal chrome plating process to ensure stable formation of protruding chrome. By doing so, the weldability of TFS-CT can be significantly improved without impairing corrosion resistance. [Example] Next, Examples of the present invention will be described together with Comparative Examples. [Example 1] Degreasing in the usual way (NaOH 70g/, temperature 80
℃, current density 5A/dm ² , time 2 seconds) and pickling (N ₂ SO ₄ 70g/, temperature 30℃, immersion for 3 seconds).
Cathodic treatment was performed for 1.5 seconds at a current density of 30 A/dm ² in a chromic acid bath containing 200 g of CrO 3 and 3 g of H _{2 SO 4} .
About 50 mg/m ² of metallic chromium and about 6 mg/m ² of chromium hydrated oxide were deposited. After electrolysis, immediately take it out of the bath, wash it with water, and dry it (using a dryer at about 100℃).
Dry thoroughly with hot air) and then continue in the same bath.
Cathodic treatment was performed at 30 A/dm ² for 1.5 seconds to precipitate approximately 50 mg/m ² of metallic chromium and hydrated chromium oxide. [Comparative Example 1] 0.22mm pre-treated with degreasing and pickling using the usual method
A thick cold-rolled steel plate is treated with 200g of CrO ₃ at 55℃,
In a chromic acid bath with 3 g of H ₂ SO ₄ / current density
Cathodic treatment was performed at 30 A/dm ² for 1.5 seconds to precipitate about 50 mg/m ² of metallic chromium and about 6 mg/m ² of hydrated chromium oxide. After electrolysis, the sample was immersed in the same bath for 2 seconds, followed by cathodic treatment at 30 A/dm ² for 1.5 seconds,
Approximately 50 mg/m ² of metallic chromium and chromium hydrated oxide were deposited. [Example 2] The cold-rolled steel sheet of Example 1 was treated with 100 g of CrO ₃ /
, in a chromic acid bath of MaF6g/current density
Cathodic treatment was performed at 40 A/dm ² for 1.0 seconds to precipitate about 50 mg/m ² of metallic chromium and about 5 mg/m ² of hydrated chromium oxide. Immediately after electrolysis, take it out of the bath, wash it with water, dry it, and continue to put it in the same bath at 20A/ ^dm2 .
Cathode treatment was performed for 2.0 seconds, and about 50 mg/m ² of metallic chromium and chromium hydrated oxide were deposited. [Example 3] After washing the TFS-CT of Example 2 with water, it was stored at 30°C.
In a chromic acid bath containing 50 g of CrO ₃ /, 2 g of MaF,
A hydrated chromium oxide was deposited thereon by cathodic treatment at a current density of 10 A/dm ² for 2 seconds. [Comparative Example 2] The cold rolled steel sheet of Example 1 was treated with 100 g of CrO ₃ at 55°C.
, in a chromic acid bath of MaF6g/current density
Cathodic treatment was performed at 40 A/dm ² for 1.0 seconds to precipitate about 50 mg/m ² of metallic chromium and about 5 mg/m ² of hydrated chromium oxide. After electrolysis, immerse in the bath for 2 seconds, then cathode treatment at 20 A/dm ² for 2.0 seconds,
mg/m ² of metallic chromium and chromium hydrated oxide were deposited. After washing with water, add 50g of _CrO3 /NaF2 at 30℃.
g/2 at a current density of 10 A/ ^dm2 in a chromic acid bath.
A cathodic treatment was applied for a second to precipitate chromium hydrated oxide thereon. Table 1 shows the characteristics evaluation results.

〔Effect of the invention〕

TFS-CT manufactured by the method of manufacturing stain-free steel for welding of the present invention has better corrosion resistance after painting, paint adhesion, and resistance to sulfide blackening than conventional TFS-CT.
It is possible to significantly improve weldability without impairing the properties possessed by Therefore, it can be used as a substitute for welding materials plated with Sn or Ni, and can be widely used not only for beverage cans but also for general food cans containing fish, meat, etc., and is extremely useful. It is an expensive material.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the electrical contact resistance value of TFS-CT and the difference in specular gloss before and after metal chrome plating, which was measured after dissolving chromium hydrated oxide.
FIG. 2 is a diagram showing the relationship between the density of protruding chromium formed on metallic chromium as seen in a transmission electron micrograph, and the difference in specular gloss before and after metallic chromium plating, measured after dissolving chromium hydrated oxide. FIG. 3 is a transmission electron micrograph of the metallic chromium layer of a normal TFS-CT, and FIG. 4 is a transmission electron micrograph of the metallic chromium layer with many protruding chromium. { } in the figure indicates the crystal plane of metallic chromium.

Claims (1)

[Claims] 1. A protruding metallic chromium layer of 30 to 500 mg/m ² per side on the surface of a steel plate, and on this metallic chromium layer,
In a method for producing a tain-free steel having a chromium hydrated oxide content of 5 to 20 mg/ ^m2 per side in terms of chromium, once a steel strip is cathodically treated in an electrolytic chromic acid bath containing chromic anhydride as the main component, A method for manufacturing stain-free steel with excellent seam weldability, which is characterized by washing with water, drying, and cathodic treatment again in the same bath.