JPH0576559B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to an alloyed galvanized steel sheet with excellent workability, and in particular to an alloyed galvanized steel sheet suitable for use as an automotive steel sheet from the viewpoint of improving powdering resistance during processing. This relates to steel plates. [Prior art and problems] Performances generally required for automotive steel plates include post-painting corrosion resistance, weldability, workability, etc., but in North America, Canada, and Northern Europe, in particular, as a measure against frozen roads in winter, A large amount of rock salt is sprayed, and in such an environment, corrosion of automobile bodies is accelerated, posing a major problem in terms of anti-corrosion measures.
As a means of solving this problem, the use of rust-proof steel sheets for automobiles is rapidly being carried out. Rust-proof steel plates that meet these purposes include:
For example, alloyed galvanized steel sheets as seen in Japanese Patent Publication No. 57-14752 are known, and such steel sheets have excellent properties such as corrosion resistance and weldability after painting, and can also be made thicker. Therefore, it is used in large quantities as steel sheets for automobiles. Note that the alloy compound galvanized steel sheet referred to here refers to a steel plate or steel strip that is galvanized with a predetermined coating weight on one or both sides, and then subjected to alloy compound heat treatment to form a galvanized layer. It is a Zn-Fe alloy. In this case, the composition of the base steel plate,
Galvanizing method, hot dip galvanizing bath
The Al concentration, zinc basis weight, and alloying treatment method are not particularly limited. However, when alloyed galvanized steel sheets such as those mentioned above are subjected to severe chemical compounding, the plating layer may collapse and flake off into powder, a product defect called powdering, which occurs, making it difficult to process. At the same time, the subsequent corrosion resistance is deteriorated, and at the same time, fragments of the peeled-off coating layer are deposited on the press mold, which may cause problems such as indentation scratches on the molded product. The cause of such powdering in alloyed galvanized steel sheets is not fully understood, but since the plating layer has brittle properties, the plating layer may be affected by plastic deformation of the base steel sheet during processing. This is thought to be caused by the inability to follow the Therefore, various studies have been made to improve the workability of the plated layer. For example, as seen in Japanese Patent Publication No. 49-4134, by appropriately selecting the heating conditions when alloying a galvanized layer, the outermost surface of the alloyed galvanized layer becomes a (η+ζ) mixed phase. There are means to improve the workability of the plated layer. Through these measures, the powdering resistance of alloyed galvanized steel sheets is gradually being improved.
Powdering may still occur,
There is still room for improvement. [Means for Solving the Problem] In view of the above-mentioned actual situation, the present inventors have conducted various experiments and found that an electrolytic zinc coating with an appropriate coating weight is added to the upper layer of the plating layer of an alloyed galvanized steel sheet. It has been found that by forming either a plating layer or an electric Zn-Ni alloy plating layer, it is possible to suppress the occurrence of powdering without deteriorating corrosion resistance, weldability, etc. after painting. The reason for this is not clear, but it is probably because the electrogalvanized layer or electrolytic Zn-Ni alloy plated layer formed on the upper layer of the galvanized steel sheet has good adhesion to the lower layer. This seems to be because it has appropriate ductility. That is, the lower layer Zn−
Even under processing conditions that cause powdering, the Fe alloy plating layer is
The -Ni alloy plating layer can fairly follow the plastic deformation of the underlying steel sheet, so it is thought to suppress the peeling and falling off of the underlying layer. [Structure and operation of the invention] The present invention has been made based on the above-mentioned findings, and the gist thereof is to provide an upper layer of a plating layer of a single-sided or double-sided alloyed galvanized steel sheet with a coating weight per one side. Electrogalvanized layer of 3 to 25 g/m ² or Ni content with area weight of 3 to 15 g/m ²
This invention provides an alloyed galvanized steel sheet with excellent workability, characterized by having one of the electrolytic Zn-Ni alloy plating layers of 30 wt% or less. The present invention will be explained in detail below. First, we will discuss the reason why the upper layer plating was limited to zinc or Zn-Ni alloy. In other words, as mentioned above, in order to improve the powder link resistance of an alloyed galvanized steel sheet, it is necessary that the upper layer of the galvanized layer has good adhesion with the lower layer and has appropriate ductility. It is considered to be effective in suppressing peeling and falling off. Therefore, various studies were conducted through the following experiments regarding plated metals that can exhibit such effects. That is, the powder link resistance during processing of alloyed galvanized steel sheets subjected to various types of plating was investigated, and the corrosion resistance and weldability after painting of those for which an improvement effect was observed was investigated. The results are shown in Table 1.

〔Example〕

Table 2 summarizes the upper plating layer composition, area weight, and workability test, corrosion resistance test, and weldability test results of the test steel sheets. The basis weight of the alloyed galvanized steel sheet used was 40 g/m ² per side. Samples Nos. 4 to 9, 11 to 18, and 23 to 26 are steel plates of the present invention, and the others are comparative materials. Note that No. 29 is an alloyed galvanized steel sheet without upper layer plating. The composition of the plating layer was investigated by chemical analysis. Powdering resistance was examined by a tape test after cylindrical drawing. The evaluation criteria for the test are as follows. ◎ Excellent ○ Excellent △ Average × Poor In addition, the same corrosion resistance test and weldability test as described above were conducted, but no difference was found between the inventive material and the comparative material. It can be seen that the powdering resistance of the present invention material is better than that of the comparative material, and that the powdering resistance is improved if the basis weight and Ni content are within the range of the present invention.

【table】

【table】

[Table] * Comparative material [Effect of the invention] As stated above, the alloyed galvanized steel sheet of the present invention has good workability and does not deteriorate in corrosion resistance and weldability after painting, and its practical The value is truly great.

Claims (1)

[Claims] 1 As the upper layer of the plating layer of single-sided or double-sided alloyed galvanized steel sheet, the basis weight is 3 to 25 per side.
It is characterized by having either an electrogalvanized layer of g/m ² or an electrogalvanized Zn-Ni alloy layer with a basis weight of 3 to 15 g/m ² per side and a Ni content of 30 wt% or less. , alloyed galvanized steel sheet with excellent workability.