JPH0637712B2 - Electrolytic chromate treated steel plate for welding can - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electrolytic chromate-treated steel plate for a welding can having excellent weldability, specifically, an electrolytic chromate treatment for a welding can produced by electric resistance seam welding. Regarding steel plates.

[Conventional technology and its problems]

Electrolytic chromate treated steel sheet (TFS-CT), which has a coating of chromium hydrated oxide mainly consisting of metallic chromium and chromium oxide on the surface of the steel sheet, has excellent paintability and corrosion resistance, and is cheaper than tinplate. Therefore, it is used in a wide range of fields such as food cans related to beverages, pail cans, 18 cans, miscellaneous cans such as oil cans, and the like. Conventionally, a can material using this type of steel sheet has been put into practical use mainly as a two-piece can made by drawing and an adhesive can (3 piece can) using an organic resin or special cement, but its usage ratio as a welding can is Very small. This is because the electrolytic chromate treated steel plate is a plated steel plate having extremely poor weldability.

However, in the recent can manufacturing, a bonding method with high bonding strength and high reliability is required, and therefore, welding bonding has become a major weight in can manufacturing welding, and in the electrolytic chromate treated steel sheet currently used. However, its poor weldability makes it difficult to expand its applications. As described above, the main cause of poor weldability is the surface coating of the electrochromic treated steel sheet, and the non-conductivity and non-conductivity of the metal chrome layer that constitutes the plating layer and the chromium hydrated oxide layer that is mainly composed of chromium oxide. This is because, due to the thermal conductivity, the heat generation mode of the heat generated by the welding current becomes non-uniform, the steel locally generates heat, and welding defects such as dust and blowholes are likely to occur.

For this reason, conventionally, in the case of intentionally welding an ordinary electrolytic chromate-treated steel sheet, a complicated method of polishing and removing the chromate-treated film to be the welded portion and then welding is inevitable. In addition to the above, the following proposals have been made in order to secure the weldability of electrolytic chromate treated steel sheets.

(B) Water glass is applied to a portion of a steel sheet requiring welding and dried, and then the surface of the steel sheet is plated with chrome, and the water glass is peeled off and welded (JP-A-57-143492).
issue).

(B) If a chromium-plated steel sheet is subjected to temper rolling of 20% or less and cracks are generated on the surface, welding current flows through the infinite cracks to the base metal part, and good sudronic welding can be performed. It is possible (JP-A-55-48406).

However, these methods are to perform some pretreatment on the chromate-treated steel plate before welding.
There are major problems in terms of process simplification and can manufacturing costs.

[Means for solving problems]

In view of the conventional problems as described above, the present inventors have studied an electrolytic chromate-treated steel plate for a welding can that can obtain excellent weldability (resistive seam weldability) without performing special pretreatment before welding. added. As a result, it was found that the surface of the metal chrome layer has an extremely excellent weldability with an electrolytic chromate coating having a large number of granular or angular protrusions on all crystal orientation planes over the entire surface of the steel sheet,
The present invention has been completed.

That is, the present invention is that the surface area of the steel sheet is 5 to 200 mg / m ²
And a chromium hydrated oxide layer mainly composed of chromium oxide having a basis weight of 3 to 15 mg / m ^{2 in} terms of metallic chromium, and the metallic chromium layer surface covers the entire surface of the steel sheet. The basic feature of the production is that it has a large number of granular or angular protrusions on all crystal orientation planes.

As a method for producing an electrolytic chromate steel sheet having protrusions on the surface of the metal chromium layer, Japanese Patent Laid-Open No. 59-100291
No. has been proposed, but this technology is limited to mentioning electrolytic chromate treated steel sheets for adhesive cans, and
It is not always necessary to form a large number of protrusions on all crystal orientation planes of the steel sheet. The present invention, the relationship between the protrusions and weldability, further forming a large number of the protrusions on all crystal orientation planes over the entire surface of the steel sheet is an essential condition for obtaining excellent weldability. Found,
It is based on this.

When a conventional electrolytic chromate treated steel sheet is subjected to pseudo-resistance type resistance seam welding, the chromium oxide of the outer layer serves as an insulating film and increases the contact resistance in the lap portion of the vertical edge of the can body. Therefore, the welding current is low immediately after the start of welding and starts to show a constant welding current value only after a certain time has elapsed. As a result, the heat generation becomes non-uniform, the steel locally generates heat, and dust is generated, or an inconvenient cavity (blow hole) is generated in the weld nugget portion. A contact resistance value (static resistance value) is known to evaluate whether or not an excessive current locally flows during such welding. That is, in a material having a high contact resistance, the passage of the welding current is narrow, and a local excessive current easily flows. The contact resistance of an ordinary electrolytic chromate-treated steel sheet is on the order of 10 ² to 10 ⁵ , which is extremely large compared to other surface-treated steel sheets for welding cans.

In view of such a point, the present inventors have made various studies in the direction of reducing the contact resistance of the electrolytic chromate-treated steel sheet, and as a result, basically, in the metal chromium layer constituting the electrolytic chromate film, granular or angular It has been found that the contact resistance can be reduced to two orders of magnitude by forming a film structure in which the protrusions (metallic chromium) are uniformly distributed, specifically, a large number are distributed on all crystal orientation planes over the entire surface of the steel sheet. It was As a result, there was almost no decrease in welding current immediately after the start of contact, and a constant welding current value was instantaneously displayed. Local abnormal heat generation was also reduced and it was found that a good seam weld can be stably obtained. did.

FIG. 1 schematically shows a cross section of such a coating structure of the present invention. (1) is a steel plate, (2) is a metal chromium layer, and (3) is a chromium hydrate oxide layer. A large number of protrusions (4) are formed on the surface of the chrome layer (2). And because of this metal chromium protrusion (4), a chromium hydrate oxide layer on it
(3) also has undulations along the protrusion.

The good weldability as described above can be obtained by such a film structure because the contact areas become large because the steel plate surfaces having the film structure as shown in FIG. It is presumed that this is because the weldability has improved and the welding current has become easier to flow. Furthermore, in addition to such an action, the hydrated chromium oxide layer (3) along the metallic chromium layer (2) is uneven, so that cracks are likely to occur due to external pressure, and therefore the coating surfaces are pressed together. It is presumed that, in this case, a turtle row is easily formed in the hydrated chromium oxide layer on the protrusions of metallic chromium, and the welding current easily flows.

Hereinafter, the film structure of the present invention will be specifically described.

The electrolytic chromate treatment film is composed of a chromium metal layer (2) formed on the steel plate surface and a chromium hydrate oxide layer (3) mainly composed of chromium oxide on the metal chromium layer. Chromium layer (2) is 5-200 mg / m ² , chromium hydrate oxide layer
(3) is an adhesion amount of 3 to 15 mg / m ^{2 in} terms of metal chromium.

From the viewpoint of resistance welding, it is desirable that the amount of metallic chromium and chromium oxide is small, and if possible, the minimum basis weight that secures the basis weight necessary to form a large number of protruding metallic chromium and does not hinder the corrosion resistance. It is preferable to control the amount. When the amount of metallic chromium in the metallic chromium (2) exceeds 200 mg / m ² , the effect of the protrusions of metallic chromium is canceled by the decrease in weldability due to excessive metal chromium, and improvement in weldability cannot be expected. If the amount of metallic chromium is less than 5 mg / m ² , sufficient corrosion resistance cannot be expected for the coating. The same applies to the amount of chromium oxide in the hydrated chromium oxide layer (3). If the amount of adhered chromium oxide exceeds 15 mg / m ^{2 in} terms of metallic chromium, it is difficult for the chrome oxide layer to form a turtle row, and especially when using high speed products. Weldability of the can is reduced. Further, if the adhesion amount is less than 3 mg / m ² , there will be a problem in corrosion resistance.

The protrusions (4) formed on the metallic chrome layer (2) are not formed in a wide area in a plate shape, but are granular or angular in a plan view. Such projections (4) cannot be expected to have the intended effect of the present invention even if they are concentrated and formed only on a specific crystal plane under the influence of the crystal orientation of the steel sheet itself. It is necessary to have uniform distribution so that a large number of crystals are formed on all crystal orientation planes.

It should be noted that such metallic chromium projections can be appropriately formed on both surfaces or one surface of the steel plate.

Next, an example of a method for manufacturing the electrolytic chromate-treated steel sheet as described above will be described.

The electrolytic chromate-treated steel sheet of the present invention can be produced by subjecting the steel sheet to electrolytic chromate treatment (cathodic electrolysis treatment) by intermittent electrolysis by a one-component method, and at least once during the cathodic electrolysis treatment. it can. That is, in the case of so-called vertical processing equipment in which a steel sheet is subjected to electrolytic chromate treatment by a plurality of passes of cathodic electrolysis treatment, for example, it is manufactured by performing anodization treatment in at least one pass in the course of a plurality of passes of cathodic electrolysis treatment. You can

To produce an electrolytic chromate-treated steel sheet, in an electrolytic solution containing at least one of chromic anhydride, chromate and dichromate as main components, and containing F ⁻ and / or SO ₄ ²⁻ in it. Cathode electrolysis (intermittent electrolysis) is performed using the steel sheet as a cathode.

There are generally two types of electrolytic chromate treatments, the one-liquid method and the two-liquid method. In the two-liquid method, the amount of chromium oxide deposited becomes too large, and the amount of chromium oxide deposited is 15 mg / It is difficult to keep it below m ² .

The so-called vertical equipment for electrolytic chromate treatment has a plurality of treatment tanks that are continuously arranged, and a steel sheet that is electrolytically chromate treated in such equipment is inevitable due to contact with the sink roll of each treatment tank. It becomes an intermittent process. The above-mentioned protrusions of the metallic chromium layer tend to be generated by such an interrupting treatment, and are inevitably generated when the interrupting time becomes long to some extent. However, the protrusions generated in this way are extremely uneven. That is, the generation of such protrusions is influenced by the crystal orientation of the steel sheet to be processed and is formed only on a specific crystal plane (for example, the (001) plane). As a result, although the contact resistance is reduced to some extent as compared with the electrolytic chromate-treated steel sheet on which such protruding metallic chromium is hardly formed, no good weldability can be expected.

On the other hand, in the present invention, since the anodic treatment is performed during the cathodic treatment by intermittent electrolysis, the protruding metallic chromium is formed in a uniform and dense state, and the detailed mechanism thereof is not always clear. However, it is considered that the reason is basically as follows. That is, a metal chrome layer and a hydrated chromium oxide layer are formed on the steel sheet by the cathodic electrolysis until the anodization is performed or the cathodic electrolysis is interrupted. Since the chromium hydrate oxide layer is colloidal, when the cathodic electrolysis is interrupted, the surface of the metallic chromium is oxidized by the oxidizing electrolytic solution and changed to chromium oxide. Since chromium oxide and metal chromium have different lattice constants, defects in which the atomic arrangement is disturbed are scattered in the chromium oxide layer, and the chromium oxide film thickness is thinner than other parts in this part, or metal chromium is exposed. Therefore, the electric resistance is low,
It is considered that protrusion-shaped metal chromium is generated because metal chromium is preferentially precipitated during the re-cathode electrolysis. The anodizing process during the interruption of the cathodic electrolysis has the effect of producing more defects in which the atomic arrangement in the chromium oxide layer is disturbed than in the case of only the interruption. It is considered that chromium is generated.

In order to grow the protrusions (4) of metallic chromium, it is necessary to further perform cathodic treatment after anodizing, and the anodizing must be introduced at a position satisfying this. Furthermore, by performing the anodizing treatment in the middle of the treatment of the series of cathodic treatments as early as possible, the growth and distribution of the metallic chromium projections can be made uniform. The above-mentioned anodizing treatment is indispensable in the present invention because it forms a wide range of metal chromium projections, but it also has the effect of improving the chromium electrolysis efficiency.

It is preferable that the current density in the cathodic electrolysis treatment does not fall below 10 A / dm ² . That is, the current density is 1
If it is 0 A / dm ² or less, it is difficult to obtain a uniform distribution of metal chromium projections even if anodizing is performed. The amount of electricity for anodization is 0.01
~ 5 coulomb / dm ² , preferably 0.1-5 coulomb / d
It is preferable to select by m ² . When the amount of electricity used for anodizing is less than 0.1 coulombs / dm ² , especially less than 0.01 coulombs / dm ² , the effect of anodizing is not very noticeable, whereas when it exceeds 5 coulombs / dm ² , metallic chromium elutes. It is not preferable because

The above method can be carried out in a so-called vertical processing facility by performing anodizing in one pass during the anodizing process.However, even in a so-called horizontal processing facility, a supply current is supplied during cathode electrolysis. It can be carried out by a method of temporarily reversing and performing anodization.

[Examples] Next, examples of the present invention will be described.

After air-baking the electrolytic chromate treated steel sheet produced under the following conditions by a vertical treatment facility at 210 ° C. for 10 minutes,
It was subjected to a pseudoronic welder and its weldability was examined. Separately from this, the state of formation of protruding metallic chromium was observed by a transmission electron micrograph of the metallic chromium layer, and the amount of Cr deposited and the contact resistance after air-baking at 205 ° C. for 23 minutes were also measured. The results are shown in Table 1. Further, transmission electron micrographs of the metal chromium layer are shown in FIGS. 2 (a) to (h). Correspondence between each drawing in FIG. 2 and the examples and comparative examples is as follows. Note that the steel plates in these photographs have a diameter of 20.
The density of metal chrome protrusions that are ~ 30 nm or more was counted.
The results are also shown below.

Further, FIG. 3 shows the relationship between the anodizing position and the contact resistance based on the results obtained in Examples and the like.

・ Comparative Examples (1) (2) (3) A 0.22 mm thick cold-rolled steel sheet (equivalent to T4CA) was degreased and acid-washed and water-washed according to a conventional method, and then the current density was 5 A / dm ^{2 in} the following first liquid.
(Comparative Example (1)), 25 A / dm ² (Comparative Example (2)), 30 A / dm ²
Energization time under each electrolysis condition of (Comparative Example (3)): 0.3 seconds,
After non-energizing time: 0.3 seconds and total energizing time: 1.2 seconds, the cathode was electrolyzed, washed with water, and then subjected to cathodic electrolysis in the following second liquid under the following conditions, washed with water and dried.

First liquid _{CrO 3: 1750 / Na 2 SiF} 6: 5g / Na 2 SO 4: 0.9g / bath temperature: 45 ° C. Second solution _{CrO 3: 50g / NH 4 F} : 2g / bath temperature: 40 ° C. Current density : 30A / dm ² Energization time: 0.3 seconds Non-energization time: 0.3 seconds Total energization time: 0.9 seconds ・ Comparative Example (4) Bath conditions similar to Comparative Examples (1) (2) (3) , Depending on the treatment procedure, current density in the first liquid: 25 A / dm ² , energization time: 0.3 seconds,
Only the cathodic electrolysis with the non-energization time: 0.3 seconds and the total energization time: 1.5 seconds was performed, washed with water, and then subjected to the same treatment as described above in the second liquid to produce an electrolytic chromate-treated steel sheet.

-Comparative Example (5) In the first liquid under the same bath conditions and treatment procedures as Comparative Examples (1) to (3),
Current density: 5A / dm ^2, the energizing time: 0.3 seconds, total conduction time: per to do intermittent cathodic electrolysis in 1.2 seconds, 1A / dm ² of current density in the processing time in the second pass: 0. Anodization was performed once for 3 seconds, and cathodic electrolysis was performed in the above-mentioned second liquid to produce an electrolytic chromate-treated steel sheet.

-Examples (1) (2) (3) Current density under the same bath conditions as the first liquid of Comparative Examples (1) to (4):
25 A / dm ² , energizing time: 0.3 seconds, total energizing time: 0.9
When performing intermittent cathodic electrolysis for 2 seconds (Example (1)), 1.2 seconds (Example (2)), and 1.5 seconds (Example (3)), 1 A / dm ² was applied in the second pass. Anodizing was performed once at a current density and a treatment time of 0.3 seconds to produce an electrolytic chromate treated steel sheet.

-Example (4) (5) (6) and Comparative Example (6) Current density under the same bath conditions as the first liquid of Comparative Examples (1) to (4):
25 A / dm ² , energizing time: 0.3 seconds, total energizing time: 1.5
In performing the second intermittent cathode electrolysis, the third pass (Example
(4)), 4th pass (Example (5)), 5th pass (Example)
(6)), the sixth pass (after the final cathodic electrolysis) (Comparative Example (6)) was subjected to anodizing treatment once at a current density of 1 A / dm ² for 0.3 seconds each, and was subjected to electrolytic chromate treatment. Was manufactured.

The contact resistance in Table 1 above was measured as follows. That is, the comparative examples (1) to (5) and the electrolytic chromate treatments of Examples (1) to (3) were applied to one surface of the steel sheet to be treated, and the other surface was plated with # 25 tin. Apply plating. The surfaces of the electrolytic chromate coatings after being air-baked at 205 ° C. for 23 minutes are put together to form two laminated plates of the above steel plates, which are sandwiched between the upper and lower copper chips of a contact resistance measuring machine and the resistance is measured. Therefore, the upper and lower copper chips are in contact with the # 25 plated tin layer. The contact resistance was obtained by subtracting the resistance of one steel plate having both sides plated with # 25 tin from the value thus obtained.

The weldability was evaluated by using a pseudoronic welder and was a comprehensive evaluation based on the range of the current range suitable for welding, the weld appearance, and the weld strength. The evaluation is as follows.

◎ …… Remarkably good, △ …… Slightly inferior ○ …… Comparatively good, × …… Remarkably inferior According to Table 1, the comparative examples (1) to (4) have a contact resistance of 1
While the weldability is inferior at 0 ² order or more, the contact resistance is 10 μm in the electrolytically treated steel sheet according to the present invention in which a large number of protruding metallic chromium is formed on all the crystal orientation planes over the entire surface of the steel sheet.
It has fallen to less than Ω and shows favorable weldability. It is apparent that the weldability is remarkably improved in the electrolytic chromated steel sheet on which the uniform protruding chromium metal is formed.

In Comparative Example (1), the contact resistance was extremely high despite the small Cr basis weight, but this was because the cathodic treatment current density of the first liquid was small and almost no protruding metallic chromium was formed. It is presumed that there is no. Comparative example (2),
Even if the Cr basis weight is large as in (3) and (4), the contact resistance is smaller than that in Comparative Example (1) only in a specific orientation, but slightly protruding metallic chromium is formed. It is presumed that this is because From Comparative Example (5), it can be seen that anodizing has no effect when cathodic treating is performed with an excessively low current density.

Further, Comparative Example (6) is an example in which anodic electrolysis was performed after cathodic electrolysis (anodic electrolysis in the final pass), in which case granulation was insufficient and weldability was poor. Further, FIG. 3 shows the relationship between the anodizing position and the contact resistance based on the results obtained in the examples, etc., but the steel sheet obtained by the one-component method is 1 compared to the two-component method. It can be seen that a contact resistance of the order of magnitude is obtained.

〔The invention's effect〕

According to the electrolytic chromate-treated steel sheet of the present invention described above,
Excellent weldability can be obtained without performing special pretreatment, and the application of this type of surface-treated steel sheet can be greatly expanded.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing the coating cross-section structure of the electrolytic chromate-treated steel sheet of the present invention. 2 (a) to (h) are transmission electron micrographs of the metal chromium crystal structure of the electrolytic chromate-treated steel sheets in Examples. FIG. 3 shows the relationship between the anodizing position and contact resistance based on the results of the examples. In the figure, (1) is a steel plate, (2) is metallic chromium, (3) is a chromium hydrate oxide layer, and (4) is a protrusion.

Continuation of the front page (56) Reference JP-A-59-100291 (JP, A) JP-A-61-281899 (JP, A) JP-B-57-19752 (JP, B1)

Claims (1)

[Claims] 1. A metallic chromium layer having a basis weight of 5 to 200 mg / m ^{2 on} the surface of a steel plate, and a basis weight of 3 to 1 in terms of metallic chromium on the upper portion thereof.
A chromium hydrated oxide layer mainly containing 5 mg / m ² of chromium oxide, wherein the surface of the metallic chromium layer is a large number of granular or angular projections on all crystal orientation planes over the entire surface of the steel sheet. An electrolytic chromate-treated steel plate for a welding can, which is characterized by having: