JPS6039195A - Iron-zinc alloy plated steel sheet and its manufacture - Google Patents

Abstract

PURPOSE:To munufacture an Fe-Zn alloy plated steel sheet while preventing the reduction of the press workability by forming an Fe-Zn alloy layer consisting essentially of delta1- and GAMMA-phases on the surface of a steel sheet by removing eta- and xsi-phases. CONSTITUTION:An Fe-Zn alloy layer is formed on the surface of a steel sheet by electroplating, and eta- and xsi-phases are selectively removed from the alloy layer by electrolysis to form an Fe-Zn alloy layer consisting essentially of delta- and GAMMA-phases. Since the plating and electrolysis are not carried out at a high temp., the steel sheet is not heated to >= about 100 deg.C after a cold rolling stage, so the deterioration of the quality and the reduction of the press workability are not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to iron-zinc alloy plated steel sheets for rust prevention, used in automobiles and the like.

(Prior Art) Conventionally, various types of surface-treated steel sheets for industrial use such as automobiles have been used depending on the purpose and use. Among these,
The most excellent method for welding, workability, and corrosion resistance after painting is that when zinc plating is performed on a plate, iron in the base steel plate is thermally diffused into the core layer and δ1 One example is iron-zinc alloy plated steel sheet, which is manufactured by forming an alloy layer called a phase into a half-layer.

However, in order to manufacture such iron-zinc alloy coated steel sheets using conventional methods, for example, when manufacturing using hot-dip plating, high temperatures (
Plating must be carried out at a temperature of 460°C), and the alloying heat treatment performed after galvanizing also requires a high temperature change (around 550°C).
Therefore, the material of the obtained steel sheet changes, and the workability such as press formability decreases. Furthermore, with the hot-dip plating method, it is unfortunate that only one side is plated. On the other hand, if the W side plating method is used, it is relatively easy to plate only on one side, and even in this case, heat treatment after plating, that is, post-annealing, is required to obtain an alloy mainly composed of the δl phase. Due to this, the material properties of the steel sheet change, and the press formability decreases (6). There has been a desire for an iron-zinc alloy plated steel sheet mainly consisting of the δ1 phase, which does not require heat treatment by post-annealing.

However, in the iron-zinc plated Φ sheet obtained by the conventional electroplating method, the iron-zinc alloy layer formed on the steel sheet is η
, ζ, δ1 and F phase, resulting in a δ phase with excellent physical properties.
An iron-zinc alloy plated steel sheet having a plating layer consisting mainly of one phase was not known, nor was an electroplating method for producing such a plated steel sheet.

(Object of the invention) The present invention is intended to solve the problems in the above-mentioned prior art, and its purpose is to improve corrosion resistance after painting (l).
The powdering property, which indicates the ease of welding and peeling of the plating, is the same as the conventional δ! To provide an iron-zinc alloy plated steel sheet and its manufacturing method, which is equivalent to or better than the 2016 version of iron-zinc alloy plating, which mainly consists of phases, and whose pressing process is comparable to that of cold-rolled steel sheet, and whose manufacturing method is simplified. It's there.

(Structural strength of the invention) That is, the iron-zinc alloy steel plate of the present invention has δ! on the surface of the steel plate. In order to produce the iron-zinc alloy coated steel sheet of the present invention, the steel sheet surface is coated with electroplating. After shaping an iron-zinc alloy layer, the η layer and the ζ layer are selectively removed from the alloy layer by electrolysis, thereby forming an iron-zinc alloy layer mainly composed of the δ1 phase and the p phase. Features.

Alloys of iron and zinc are divided into several layers on the phase diagram depending on their composition. The phase consisting essentially only of zinc is the η phase belonging to the macrogonal system, and the iron-zinc binary system also contains ζ (zeta) phase as an intermetallic compound.
), δl (del ta ), P (capital g
There are three phases: amma ).

The ζ phase has a crystal structure that resembles a clinic system, and has a crystal structure of 5.75 to 6
．． FeZn1g (61
It is expressed as 6th grade Fe).

δ! The phase has a complex hexagonal crystal structure, with 7 to 114
It exists in the range of Fe and is expressed as FeZn7 (10.1% Fe).

The F phase ranges from 21 to 284 Fe and belongs to the body-centered steric crystal, Fe1iZn21 (1 & 8% F
It is expressed as e).

Among the phases with the above composition, the η phase and the ζ phase are
Since it is more base than the phase, it dissolves easily, so if heavy pressure is applied after plating and electrolysis is performed, it will be selectively eluted. For this reason, the iron-galvanized steel sheet of the present invention has holes in which the η phase and ζ phase have leached out on the surface. These holes do not reduce the physical properties of the plated steel sheet; on the contrary, the holes on the surface improve the quality by increasing the adhesion of paint.

In addition, various physical properties such as corrosion resistance are improved by removing the electrochemically more unstable η and ζ phases.

Plating conditions and electrolytic conditions, such as current density, liquid temperature, reaction time, etc., are optimally selected depending on the layer structure of the plating layer, desired properties, etc.

As for the composition of the plating solution and the electrolytic solution and the continuous production equipment used to obtain the plated steel sheet of the present invention, conventional ones conventionally used in this field or combinations thereof can be used.

(Example) The present invention will be explained in more detail below based on the drawings.

Note that the present invention is not limited to the following examples.

FIG. 1 is a process diagram showing an outline of an embodiment for obtaining an iron-zinc alloy plated steel sheet of the present invention.

In the figure, 1 is an annealed cold-rolled coil of raw steel plate to be plated, 2 is a raw steel plate, 3 guide rolls, 4 is a submerged guide roll, 5 is a degreasing tank, 6 is a drinking tank, 7 is a washing tank, 8 is an electroplating tank for iron-zinc alloy, and 9 is a special phase (η, ζ) of the plating layer.
), 10 represents a winding coil.

Table 1 shows the electrolytic conditions.

Table 1: Technical Conditions Figure 2 shows a partially enlarged sectional view of the iron-zinc alloy plated steel sheet of the present invention produced by the above-mentioned apparatus.

In the figure, 11 is the steel plate base material, 12 is the plating layer, and 13 is also η
Surface elution holes for phase and ζ phase.

Analysis by X-ray diffraction: FIG. 3 shows a part of the chart of the analysis results by X-ray diffraction of the iron-zinc alloy plated steel sheet of the present invention shown in FIG. 2 and the conventional product.

As is clear from the figure, the product of the present invention has a diffraction angle of 43
The peak of the η phase near ° has disappeared, indicating that the η phase has eluted.

Performance comparison test of various surface-treated steel sheets: Table 2 summarizes the results of a performance comparison test between the iron-zinc alloy coated steel sheet manufactured by the method of the present invention and the iron-zinc alloy coated steel sheet manufactured by other conventional methods. .

The salt spray test in the table is an indicator of paint corrosion resistance. After applying cationic electrodeposition paint on a plated steel plate, cross-cut the surface, spray salt water at a predetermined concentration, and leave it at room temperature. Evaluation is based on the time it takes for corrosion to occur.

As is clear from the table, the product of the present invention is superior to conventional electroplating and hot-dip plating methods in terms of corrosion resistance, and is equivalent to or significantly superior in powderability to conventional products. .

(Effects of the Invention) As described above, the iron-zinc alloy coated steel sheet of the present invention has substantially no η phase and ζ phase, which have a large potential difference with iron, so the electrochemical corrosion rate due to battery action is slow (conventional products). It has superior corrosion resistance compared to Even if rust occurs under the paint film after painting, as mentioned above, the corrosion rate is slow, so there is little lifting of the paint film, and the good appearance can be maintained for a long time, resulting in very poor shelf life.

Furthermore, the voids formed after the η and ζ phases are eluted, especially the holes formed on the surface, create an anchor effect on the paint film during painting, resulting in better adhesion to the paint film than conventional products.

Still, the method for manufacturing iron-zinc alloy coated steel sheets of the present invention does not use high temperatures during plating and electrolysis, so there is no step in which heat of 100'CJ'J is applied to the steel sheets after the cold rolling process. There was no deterioration of the material, and there was no deterioration in the press workability of the Ushida@ board.

Furthermore, in the production method of the present invention, the conventional multi-tank plating line can be used as is by modifying the last few tanks, so the cost associated with new equipment investment can be kept to a minimum. , is available separately and can be easily implemented since it does not require any special methods. Furthermore, it goes without saying that the product of the present invention and its manufacturing method have a wide range of applications other than V for automobiles.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is a partially enlarged sectional view of the iron-zinc alloy plated steel sheet of the present invention produced by the above-mentioned apparatus, and Fig. 2 is a chart showing an X-ray diffraction pattern comparing the product of the present invention shown in FIG. 2 with the conventional product. In the figure, 1... cold rolled coil, 2... raw material raw board, 3... guide roll, 4... submerged guide roll, 5... degreasing tank, 6... pickling tank, 7...Washing tank, 8...Sanity plating tank, 9...Snow melting tank, 10...Outer product coil, 1
DESCRIPTION OF SYMBOLS 1... Steel plate base material, 12... Plating layer, 13... Surface elution hole. Patent applicant: Toyota Motor Corporation (61 people)

Claims (2)

[Claims] (1) An iron-zinc alloy plated steel sheet, characterized in that an iron-zinc alloy layer is formed on the surface of the steel sheet, the iron-zinc alloy layer mainly consisting of KJl phase and F phase, with η phase and ζ phase removed. (2) After forming an iron-zinc alloy layer on the surface of the steel sheet by plating, the η layer and 0 layer are thoroughly removed from the alloy layer by snow melting, thereby producing iron mainly composed of the δ1 phase and F phase. A method for producing an iron-zinc alloy plated steel sheet, which comprises forming a zinc alloy layer.