JPH0321632B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an Fe-based electroplating method for forming an Fe-based electroplated film with excellent workability. In this specification, Fe-based electroplating refers to Fe plating, Fe-Zn plating, Fe-Sn plating, Fe-Mn plating, Fe-Ni plating, Fe-Zn-Sn plating, Fe
- Fe-based alloy plating such as Zn-Mn plating and Fe-Zn-Ni plating, and small amounts of one or two types of Cr, Co, Al, Cu, Ti, V, Cd, Mo, etc. in these Fe-based plating films. This is a general term for alloy plating containing the above. The most common steel plate known as a corrosion-resistant material is Zn-plated steel plate. However, recently,
Particularly in the field of automobile bodies, cationic electrodeposition coating has become widely adopted as a secondary coating after chemical conversion treatments such as phosphate treatment are applied to the base material, as it is suitable for harsh corrosive environments. However, Zn-based plated steel sheets have a drawback in that they have poor corrosion resistance after being coated with this cationic electrodeposition coating. Various alloys or composite plated steel sheets have been developed that overcome this drawback and are effective against corrosion under the coating film of cationic electrodeposition coatings.
Examples include Fe-based electroplated films. However, this Fe-based electroplated film also has the following problems. In other words, Fe-based electroplated coatings generally have a 1.0
It has an extremely high internal stress of ~100Kg/ ^mm2 . For this reason, when this film is processed, it has the property of generating many microcracks. On the other hand, when using galvanized steel sheet as a material for automobiles,
It is customary for automobile manufacturers to first perform molding using various types of presses, etc. in the molding process, and then go through a processing process of chemical conversion treatment and cationic electrodeposition painting, but this is especially possible in the molding process for car bodies. It is often accompanied by strong machining. Therefore, when Fe-based electroplated steel sheets are used for automobile bodies, microcracks are likely to occur in the plating film due to processing as described above, so if microcracks occur during initial processing, these will become the starting point for At the stage of intense processing, the steel plate develops into powder and flakes, and the plating film easily peels off from the steel sheet, resulting in so-called significant powdering. The powdering of the plating film does not disturb the smooth operation of the molding process, and is a fatal defect that leads to the occurrence of many surface defects (commonly known as spots and star defects) during the press molding process, which impairs the appearance of the product. Become. The present invention has been made in order to eliminate the above-mentioned drawbacks, and it is possible to suppress the powdering of the plating film during press molding, etc., and to improve the processability of Fe.
The present invention aims to provide a Fe-based electroplating method that enables the formation of an Fe-based electroplated film. The present inventors have conducted various experimental studies with the intention of developing an Fe-based electroplating method that can obtain a plating film that does not cause powdering even during heavy processing such as the molding process of automobile bodies. . As a result, in Fe-based electroplating of steel strips using a plating bath containing sulfate ions,
By adding one or more of Sr, Ba, and Ra compounds in appropriate amounts, Fe-based products that do not cause powdering even during heavy processing such as press molding for automobile bodies can be produced. We succeeded in forming an electroplated film. That is, the present invention provides Fe-based electroplating of steel strips using a plating bath containing sulfate ions, in which 0.3 to 50 mol/m ³ of one or more of Sr, Ba, and Ra compounds are added to the plating bath. This article focuses on an Fe-based electroplating method that is characterized by electrolytic treatment. Sr, Ba, to Fe-based plating bath containing sulfate ions
Academic research on the effect of improving powdering resistance by adding Ra compounds is still insufficient, and various theories have been proposed, but the definitive theory has not yet been elucidated, and further research is required. However, according to the experimental research conducted by the present inventors, the reason why the addition of Sr, Ba, and Ra compounds improves powdering resistance is considered as shown in the following ~. Sr, Ba, and Ra compounds form microcolloids of sulfate with sulfate ions in the bath, and the particles
It specifically adsorbs to the surface of the cathode undergoing Fe-based electroplating, suppressing the hydrogen discharge competitive reaction that is often a problem in Fe-based electroplating. Therefore, the amount of hydrogen occluded in the plating film is reduced, the internal stress of the plating film is relaxed, and the powdering resistance is improved. In general, in Fe-based electroplating from an acidic bath, alkali metal sulfates have high solubility and do not deposit in the plating film. However, sulfates of Sr, Ba, and Ra, which belong to alkaline earth metals, are poorly soluble. These sulfates form extremely fine colloids, and are thought to be physically dispersed and contained in the plating film in the form of colloidal particles. Therefore, when these fine particles are present in the plating film, it can be expected that the fine particles will prevent the propagation of microcracks introduced during processing of the plating film. Fe-based plating baths contain trace impurities such as Bi, Cd, Pb, Tl, Sb, and As that are unavoidably mixed in from industrial raw materials, and when these impurities eutectoid in the plating film, It is expected that many crystal defects such as dislocations will be introduced by intervening into the deposited crystal lattice. Such defects tend to increase the internal stress of the plating film, and can cause powdering during processing as described above. And Sr, Ba,
Sr suspended in the plating bath by the addition of Ra,
It can be assumed that the colloidal sulfates of Ba and Ra and the above impurity ions form a solid solution, which reduces the amount of these impurities eutectoided into the plating film, thereby relaxing the internal stress of the plating film. The powdering resistance is improved. FIG. 1 is a diagram showing the relationship between the amount of [Sr]+[Ba]+[Ra] added to the plating bath (mol/m ³ ) and the amount of powdering in the plating film, using a characteristic curve P. This result shows that using an insoluble electrode of Pb-10%Sb as the anode and a cold-rolled steel plate as the cathode, a plating bath consisting of an acidic bath containing sulfate ions was applied to [Sr] + [Ba] +
By varying the amount of [Ra] added, Fe-based electroplating was performed with a plating precipitation amount of 30 g/cm ² and a plating film composition of 20% Fe-80% Zn, and test pieces for cylindrical deep drawing were made from the resulting plated steel sheets. This is based on the results of punching out 10 test pieces and investigating the powdering amount of the plating film using the cylindrical deep drawing test method described below for each test piece. Test method Weight of test piece before degreasing → pressing (W ₁ )
Measurement → Apply kerosene as a lubricant → Cylindrical deep drawing test (conditions: punch diameter 40mmφ, die diameter 43mmφ, holder pressure 500Kg) → Removal of lubricant Degreasing → Measurement of weight (W ₂ ) after pressing → Weight difference before and after test △ W=W ₁
−W ₂ calculation process, [Sr] + [Ba] + [Ra]
The powdering amount is defined as the average value of ΔW for each test piece plated with various amounts added. In Figure 1, those with a powdering amount of 10 mg or less have good powdering resistance and do not cause powdering during heavy processing such as molding of automobile bodies, and those with a powdering amount of more than 10 mg have good powdering resistance. This is judged to be insufficient. The range of addition amounts of [Sr] + [Ba] + [Ra] in the present invention is shown in the figure. Based on the above test data, [Sr] + [Ba] of the present invention
The reason for limiting the amount of + [Ra] added will be explained. [Sr]＋
If the amount of [Ba] + [Ra] added is less than 0.3 mol/ ^m3 ,
As shown in the figure, the amount of powdering increases rapidly when it exceeds 10 mg, and the effect of suppressing powdering resistance becomes insufficient. Also, if the concentration exceeds 50 mol/m ³ ,
Fine colloids formed by Sr, Ba, Ra, and sulfate ions aggregate, and the aggregates adhere to the energized roll and ringer roll of the plating tank, as well as the material to be plated, resulting in indentation defects in the product steel sheet, etc. Trouble is more likely to occur. There is also the problem that the aggregates settle and stick inside the plating piping, causing blockage of the liquid flow. In some cases, the plating bath is used to filter out the precipitate using, for example, a cloth-type ultra filter (capture particle limit ~ 1μ) using diatomaceous earth as a super-assistant, but when using this type of filter,
If it exceeds mol/ ^m3 , the filter may become clogged frequently, which may interfere with plating production.
The amount is preferably 5 mol/m ³ or less. In the present invention, the plating bath containing sulfate ions may be an acidic bath containing sulfate ions or a mixed bath containing halogen ions, which contain excess sulfate ions, but the same effect can be obtained. Next, examples of the present invention will be described. Example 1 A cold-rolled steel strip with a thickness of 0.7 mm and a width of 1220 mm was coated with a continuous electric plating line under the following conditions according to the method of the present invention.
Electroplated with 20% Fe-80% Zn. Plating bath composition: Using an acidic bath containing SO ₄ ions, the ratio of Fe ²⁺ and Zn ²⁺ was adjusted to obtain an alloy plating of 20% Fe to 80% Zn. Sr, Ba,
Ra in the form of a compound of CO ₃ ions [Sr] + [Ba]
+[Ra] was added in amounts of 1 mol/m ³ and 10 mol/m ³ . Plating bath PH: 20 Plating bath temperature: 60℃ Plating current density: 60 A/dm ² Plating coating amount: 30 g/m ² Punching 10 test pieces from each steel strip after plating in the same manner as the deep drawing test method described above. It was collected and used as a test material. For comparison, the same plating bath as above was used except that the amounts of [Sr] + [Ba] + [Ra] were changed to 0.1 mol/m ³ and 0.2 mol/m ³ which were outside the scope of the present invention. An Fe-Zn alloy plating of 20% Fe-80% Zn was applied under the same conditions as above, and a cylindrical deep drawing test piece was similarly taken from the plated steel strip and used as a comparative sample material. A cylindrical deep drawing test was performed on each sample material of the above-mentioned invention examples and comparative examples in the same manner as described above, and the weight difference between the weight of the sample material before the test (W ₁ ) and the weight after the test (W ₂ ) was determined. The average value of (W ₁ −W ₂ ) was determined as the amount of powdering, and the powdering resistance was evaluated from the result. The above results are summarized in Table 1.

[Table] In the table, the ○ mark for powdering resistance evaluation indicates good powdering resistance when the powdering amount is 10 mg or less, and the × mark indicates poor powdering resistance when the powdering amount is more than 10 mg. As shown in Table 1, Comparative Examples 3 and 4 have [Sr]+
The amount of [Ba] + [Ra] added is 0.3 mol/
The amount of powdering is 102mg each because it is below ^m3 .
The amount was extremely high at 77 mg, and powdering resistance was poor in both cases. On the other hand, in Examples 1 and 2 of the present invention, since the amount added was within the range of the present invention, the powdering amount was stably low at 6 mg and 7 mg, respectively, and the powdering resistance was good. Example 2 A cold-rolled steel strip of 0.8 mm thickness x 1220 mm width was coated with a plating bath consisting of an acidic bath containing sulfate ions in the same manner as in Example 1 to adjust Fe ²⁺ and Zn ²⁺ in the bath. Alloy electroplating of 90% Fe-10% Zn was performed under the following conditions. Plating bath PH: 1.5 Plating bath temperature: 65℃ Plating current density: 100 A/dm ² Plating deposition amount: 30 g/m ² Line speed: 150 m/min In the above plating bath, Sr, Ba, and Ra are mixed with CO ₃ ion compounds. The amount of [Sr] + [Ba] + [Ra] added was varied in the range of 0.3 mol/m ³ to 50 mol/m ³ of the present invention, and the plating of the present invention example was performed. The product was obtained and used as a test material. For comparison, the amounts of [Sr] + [Ba] + [Ra] were added in various ways exceeding 50 mol/ ^m3 , which is outside the range of the present invention, and plated on an actual line. Product test materials were obtained. The occurrence of indentation flaws was visually investigated for each of the test materials of the above-mentioned inventive examples and comparative examples. Items with 5 or ^more indentation scratches/m2 that can be felt are judged as defective.
The indentation flaw defect rate was calculated by defining the defect rate as the length of the defective portion relative to the total length of the coil. The results are shown in Figure 2. Figure 2 shows the relationship between the defective rate (%) due to product indentation defects and the amount of [Sr] + [Ba] + [Ra] added (mol/m ³ ) as a characteristic curve Q. The range shown is the result of the example of the present invention. As shown in Figure 2, in the range outside the scope of the present invention where the amount of [Sr] + [Ba] + [Ra] added (mol/m ³ ) exceeds 50 mol/m ³ , it exceeds 50 mol/m ³ . When turning, indentation scratches began to occur frequently, the defective rate rose sharply, and the surface quality deteriorated. In contrast, the amount added is 0.3 to 50 mol/m ³
Within the scope of the present invention, the defective rate due to indentation flaws was extremely low in all cases, and good surface quality was stably obtained. As explained above, the Fe-based electroplating method of the present invention is a simple and low-cost method in which one or more of Sr, Ba, and Ra compounds are added and mixed in a plating bath containing sulfate ions. ,Fe
This makes it possible to improve the workability, especially the powdering resistance, of Fe-based electroplated steel sheets, which greatly contributes to improving the quality and reducing costs of Fe-based electroplated steel sheets used in the automotive body field. It is.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the amount of [Sr] + [Ba] + [Ra] added and the amount of powdering, and Figure 2 shows the relationship between the amount of [Sr] + [Ba] + [Ra] added and the amount of powdering.
FIG. 3 is a diagram showing the relationship between the amount of +[Ba]+[Ra] added and the product indentation defect defect rate.

Claims (1)

[Claims] 1 Steel strip using plating bath containing sulfate ions
In Fe-based electroplating, Sr,
0.3 to 50 of one or more types of Ba and Ra compounds
Characterized by electrolytic treatment with addition of mol/ ^m3
Fe-based electroplating method.