JPH01142076A - Zn-fe alloy plated steel sheet having superior workability and corrosion resistance and production thereof - Google Patents

Abstract

PURPOSE:To gradually increase the Fe content in a plating layer toward the lower part and to improve the corrosion resistance by successively depositing Fe and Zn vapors separately evaporated from separate vessels on a base steel sheet travelling in a vacuum chamber at a controlled temp. while overlapping. CONSTITUTION:The temp. of a base steel sheet 1 travelling in a vacuum chamber is controlled to 100-400 deg.C. Fe and Zn vapors separately evaporated from separate vessels 2a, 2b are successively deposited on the surface of the steel sheet 1 while overlapping. The Fe content in a formed plating layer 3 is increased in the thickness direction of the layer 3 and the existence of gamma phase having inferior workability in the layer 3 is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to Zn-
The present invention relates to an Fe alloy plated steel sheet and a method for manufacturing the same.

[Prior Art] Zn-Fe alloy plated steel sheets are known to have excellent corrosion resistance, and have been widely used in automobiles, various home appliances, building materials, and the like.

Such Zn--Fe alloy plated steel sheets are currently manufactured by two methods as shown below. One method is to eutectoid a Zn-Fe alloy onto a base steel plate by electroplating, and the other method is to form a Zn plating layer on a base steel plate by electroplating or hot-dip plating and then heat-treat it. This is a method of forming a Zn--Fe alloy plated layer by alloying a base steel plate with Zn.

In particular, the steel sheets obtained by the latter method, especially the method of applying heat treatment after hot-dip Zn plating, are so-called alloyed hot-dip Zn-plated steel sheets, and are used in a wide range of fields because of their excellent corrosion resistance. It is used.

The superior corrosion resistance of alloyed hot-dip Zn-plated steel sheets is due to
This is thought to be caused by the plating layer structure. In other words, in alloyed hot-dip Zn-plated steel sheets, as shown in Figure 2, the Fe content gradually decreases from the interface between the plating layer and the base steel sheet toward the surface of the plating layer, and for this reason, the potential of the plating layer is The closer you get to the interface, the more the damage becomes. Therefore, in a corrosive environment, the surface of the plating layer exhibits a completely dispersed form of corrosion, which delays the spread of corrosion to the base steel sheet, which is coupled with the fact that the Zn-Fe intermetallic compound has high corrosion resistance. It is thought that it exhibits excellent corrosion resistance.

[Problems to be Solved by the Invention] However, in the above-mentioned alloyed hot-dip Zn-plated steel sheet, since the alloy layer is formed by heating and diffusion, Zn-Fe intermetallic compounds are formed near the interface between the plating layer and the base steel sheet. The generation of one type of r-phase is unavoidable (see FIGS. 2 and 3), and the generation of this r-phase causes the following problems.

In other words, since the r-phase has hard and brittle properties, it cannot be said that the workability of alloyed hot-dip Zn-plated steel sheets is good, and when processing is applied, a so-called powdering phenomenon occurs in which the plating layer peels off. There was a problem.

The present invention was made in order to solve these problems, and the problem is to obtain Zn-Fe, alloy plated steel sheets and such steel sheets that are excellent not only in corrosion resistance but also in workability. The purpose of the present invention is to provide a method for manufacturing.

[Means for Solving the Problems] The Zn-Fe alloy plated steel sheet of the present invention that achieves the above object is one in which a Zn-Fe alloy vapor-deposited plating layer is formed on a base steel sheet, and the plating layer is formed on a base steel sheet. The gist is that the Fe content in the layer gradually increases in the depth direction of the plating layer, and that the r-phase does not exist in the plating layer.

In addition, the manufacturing method for obtaining the above-mentioned plated steel plate is that when producing a plated steel plate in which a Zn-Fe alloy/plating layer is formed on a base steel plate, at least one side of the base steel plate running in a vacuum chamber, Fe vapor and Zn vapor, which are heated and evaporated separately from separate containers, are vapor-deposited while being lapped in sequence according to the stated order, and the temperature of the base steel sheet during vapor deposition is controlled at 100 to 400°C to reduce F in the coating layer.
The gist is that the Zn--Fe alloy vapor-deposited plating layer is formed so that the e content gradually increases in the depth direction of the plating layer.

[Function] The present inventors have developed Z that has both characteristics of corrosion resistance and workability.
For the purpose of obtaining an n-Fe alloy plated steel sheet, a Zn-Fe alloy which has a concentration gradient in the Fe content in the plating layer like the above-mentioned alloyed hot-dip Zn plated steel sheet and does not have an r phase that has poor workability. In order to realize plated steel sheets, various studies were conducted using various plating methods.

As a result, the following findings were obtained.

(2) The method of heating and diffusion treatment cannot prevent the formation of r-phase.

■Electroplating has the advantage that the appearance of the r-phase can be prevented by setting specific conditions. However, F in the Metsugi layer
If the E content is to have a concentration gradient, it is necessary to strictly control the plating bath composition, electrolytic conditions, etc., which is extremely difficult in practice.

That is, it has been found that it is impossible or extremely difficult to achieve the desired Zn-Fe alloy plated steel sheet using conventional plating methods no matter how the conditions are controlled.

Therefore, the present inventors conducted various studies to form a plating layer with the above-mentioned structure by employing other plating methods, and as a result, we adopted a vacuum evaporation method as detailed below, and also applied the method to the base steel plate during evaporation. The desired Z can be obtained by adjusting the temperature, vapor deposition conditions, etc. as appropriate.
They discovered that an n-Fe alloy plated steel sheet could be obtained and completed the present invention.

The steps for manufacturing the Zn--Fe alloy plated steel sheet according to the present invention are carried out as shown in FIG. 1 (schematic explanatory diagram).

In other words, a steel plate 1 running in the direction of the arrow in a vacuum chamber (not shown)
Two crucibles 2 are installed along the running direction of the steel plate 1 at the lower part of the
a, 2b are arranged, Fe is charged into the crucible 2a on the upstream side in the traveling direction, and Zn is charged into the crucible 2b on the downstream side.
Charge. Then, Zn and Fe are heated and evaporated, respectively, and vapor deposition is performed while the respective vapor atmospheres are wrapped in the longitudinal direction of the steel plate 1 as shown in the figure. Then, a mixed vapor with a high Fe vapor ratio is first deposited on the steel plate 1, and then Z
Mixed vapors with gradually increasing n vapor ratios are deposited in sequence, and mixed vapors with the highest Fe vapor ratio are deposited on the most downstream side in the running direction. As a result, a plating layer with the highest Zn content is formed at the outermost layer, and a Zn--Fe alloy plating layer 3 whose Fe content gradually increases toward the lower layer is formed. and each crucible 2a, 2
The Zn content of the Zn-Fe alloy constituting the plating layer 3 can be freely controlled by adjusting the heating conditions and vacuum degree of b, and the plating thickness can be adjusted by adjusting the running speed of the steel plate 1 and the amount of Zn and Fe. It can be arbitrarily adjusted by changing the amount of evaporation. At this time, the base steel plate temperature during vapor deposition was 10
It is necessary to control the temperature between 0 and 400°C. That is, if the temperature of the base steel sheet during vapor deposition exceeds 400°C, thermal diffusion of Zn and Fe occurs, forming an η phase, which deteriorates workability, and if the temperature is less than 100°C, the adhesion of the plated layers deteriorates. becomes worse. From this point of view, the preferable range of the base steel plate temperature is about 150 to 300°C.

In FIG. 1, the range of vapor formation of Fe and Zn evaporated from each of the crucibles 2a and 2b is shown by a solid line, but this is only for convenience of explanation, and the range of vapor formation is indicated by the solid line shown in the figure. It is not limited to the range of

Therefore, it does not necessarily indicate that the Zn content is 100% by weight at the outermost layer of the plating layer (ie, the most downstream side of the steel sheet 1). The method of heating the crucibles 2a and 2b is not limited in any way, and may include resistance heating, high frequency heating,
Alternatively, high-energy beam heating using an electron beam, laser, or the like can also be employed. Furthermore, in the manufacturing method shown in FIG. 1, one side of the base steel plate is vapor-deposited and plated, but it is of course possible that the remaining surfaces may be vapor-deposited and plated after this.

The Zn--Fe alloy vapor-deposited steel sheet obtained in this manner has the characteristics shown in FIG. 4.5.

That is, FIG. 4 is a composition distribution diagram in the depth direction of the plating layer in the Zn-Fe alloy plated steel sheet according to the present invention, and FIG.
This is a graph showing the X-ray diffraction pattern of the n-Fe alloy plating layer, and as shown in the figure, the Fe content in the plating layer gradually decreases from the plating layer-steel plate interface toward the plating surface.
Moreover, the plating layer consists of η phase (Zn), ζ phase, δ1 phase, α phase (F
e) etc., and there is no η phase. Because of these characteristics, the Zn-Fe alloy plated steel sheet according to the present invention exhibits excellent performance not only in corrosion resistance without coating (bare corrosion resistance) but also in workability. The composition of the entire plating layer is not particularly limited, but from the viewpoint of corrosion resistance, the Fe content in the entire plating layer is preferably 5 to 40% by weight. The preferred amount is about 10 to 30% by weight. However, the Zn content on the plated surface is 100%.
Alternatively, the Fe content in the plating layer near the interface between the plating layer and the steel sheet may be set to 40% from the viewpoint of preventing red rust.
Preferably, it is less than % by weight.

[Example] A cold-rolled steel plate was used as a base steel plate, and after pretreatment of the cold-rolled steel plate, a Zn-Fe alloy plating layer was formed by the method shown in FIG. Experiments were conducted with various temperatures set on the base steel plate during vapor deposition.

The obtained plated steel sheets were evaluated for the presence or absence of η phase, bare corrosion resistance, and workability. In addition, as a comparison material, a Zn-Fe alloy plated steel sheet (
Similar evaluations were conducted using Sample No. 8) and an alloyed hot-dip Zn-plated steel sheet (Sample No. 9) that had been hot-dipped and then heat-diffused. Each evaluation method is as follows.

Bare corrosion resistance evaluation: Evaluated by corrosion weight loss after salt spray test.

Processability evaluation Evaluated by the amount of plating peeled off after the Nidlow bead test.

These results are summarized in Table 1.

Table 1 ◎...Excellent 0...Good ×...Poor As is clear from the results in Table 1, samples Nos. 1 to 5 that satisfy all the regulatory requirements of the present invention have good bare corrosion resistance and processing It can be seen that it exhibits excellent performance in all aspects. On the other hand, the temperature of the base steel plate during vapor deposition was 40°C.
Sample No. 7, which was heated above 0° C., and sample No. 19, which was subjected to alloyed hot-dip Zn plating, both had r-phase appearance and had poor workability. In addition, in sample No. 016, in which the base steel plate temperature during vapor deposition was less than 100°C, although the r phase did not appear, the adhesion between the plating layer and the base steel plate was insufficient, and the workability was slightly inferior to the examples of the present invention. Furthermore, sample No. 8 of the electroplated Zn-Fe alloy coated steel sheet has satisfactory workability, but as mentioned above, it is difficult to arbitrarily adjust the component distribution of the plating layer, and as a result, the corrosion resistance deteriorates. It is expressed in a simple way.

[Effects of the Invention] As described above, according to the present invention, by forming a Zn-Fe vapor-deposited plating layer using the above-mentioned configuration, a Zn-Fe film that exhibits excellent performance in terms of both corrosion resistance and processability can be obtained. Fe
Alloy plated steel sheet has been realized.

[Brief Description of the Drawings] Figure 1 is a schematic explanatory diagram showing the manufacturing method according to the present invention, Figure 2 is a schematic explanatory diagram showing the manufacturing method according to the present invention;
The figure is a depth direction composition distribution diagram of the plated layer in a conventional Zn-Fe alloy blanked steel sheet, Figure 3 is a graph showing the X-ray diffraction pattern of the conventional Zn-Fe alloy plated layer, and Figure 4 is a graph showing the X-ray diffraction pattern of the conventional Zn-Fe alloy plated layer. Fig. 5 is a graph showing the X-ray diffraction pattern of the plating layer in the Zn-Fe alloy plated steel sheet according to the present invention. 1... Steel plate 2a, 2b... Crucible 3.
・・Zn-Fe alloy plating layer

Claims (2)

[Claims] (1) A Zn-Fe alloy vapor-deposited plating layer is formed on a base steel sheet, and the Fe content in the plating layer gradually increases in the depth direction of the plating layer. A Zn-Fe alloy plated steel sheet with excellent workability and corrosion resistance, characterized in that no Γ phase is present therein. (2) When manufacturing a plated steel sheet in which a Zn-Fe alloy plating layer is formed on a base steel sheet, Fe vapor and Zn, which have been heated and evaporated separately from separate containers, are placed on at least one side of the base steel sheet running in a vacuum chamber. Vapor deposition is performed while lapping the steam sequentially according to the stated order, and the temperature of the base steel plate during vapor deposition is controlled at 100 to 400°C, so that the Fe content in the plating layer gradually increases in the depth direction of the plating layer. Zn-Fe with excellent workability and corrosion resistance, characterized by forming a Zn-Fe alloy vapor-deposited plating layer so as to increase
Method for manufacturing alloy plated steel sheets.