JPS5920456A - Manufacture of precoated steel plate - Google Patents

Abstract

PURPOSE:To prevent the stripping of a film formed by galvanizing and to obtain a precoated steel plate with resistance to shearing, deformation due to an impact etc., by restricting the composition of a steel plate contg. C, Si, Mn, P, etc. and by galvanizing the steel plate to form a proper amount of a zinc layer. CONSTITUTION:A steel plate having a composition consisting of <=0.1% C, <=0.1% Si, 0.1-0.5% Mn, 0.24XC%+0.005%-0.03% P and the balance Fe with inevitable impurities is galvanized to form a zinc layer by 45-120g/m<2>. The galvanized steel plate is kept at about 900-1,100 deg.C to alloy the zinc layer. The resulting alloyed galvanized steel plate is subjected to a chemical conversion treatment such as phosphating or chromating, and it is coated with paint by means of a roll coater or the like. The paint is cured by heating in a hot stove or the like to obtain a precoated steel plate.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a pre-coated steel sheet (organic coated steel sheet) in which a paint is applied to an alloyed hot-dip galvanized steel sheet.

Alloyed hot-dip galvanized steel sheets (hereinafter referred to as alloyed steel sheets) are made by interdiffusion between the zinc layer and the copper base, and the entire plating layer is made of Fe-Zn alloy. Compared to steel sheets, ■The painted finish is uniform and uniform in appearance, ■The paint film has good adhesion, ■It has excellent corrosion resistance as a base steel sheet for painting, and ■There is less electrode wear due to resistance welding, making it a cold rolled steel sheet. Because of its characteristics, such as having workability close to that of steel sheets, it has a wide range of uses in automobiles, home appliances, instruments, etc., and since most of them are used after being painted, it functions as a coated steel sheet.

In recent years, with regard to painted steel sheets, pre-painted steel sheets are used that are used by applying paint to thin steel sheets such as cold-rolled steel sheets or galvanized steel sheets, and then processing and assembling them as they are, in order to omit the conventional painting process on the user's part. is becoming more popular, and alloyed steel sheets, which have excellent properties as base steel sheets for painting, are also being used as base sheets for prepainted steel sheets.

In other words, new demand for steel sheets pre-painted by steel sheet manufacturers, i.e., pre-coated copper sheets, has arisen due to users' requests to omit chemical conversion treatment and painting processes, the development of paints with good workability, and improvements in coated steel sheet forming technology. It is increasing. However, with the spread of Brecault metering, problems arose that could not have been foreseen at the beginning. This is a phenomenon in which the plating film peels off when a relatively hard paint is applied to an alloyed steel sheet.

Figure 1a shows the coating structure of a pre-coated steel plate, which is a conventional alloyed steel plate coated with a hard paint. (1) is the base material, (2) is the alloyed galvanized coating, and (3) is the coating. The membrane is shown.

In other words, a normal pre-painted steel sheet is heated to a furnace temperature of 900 to 1100° immediately after applying the base material (1) (hot-dip galvanizing).
The pre-coated copper plate is manufactured by guiding the steel plate into a heating furnace held at a temperature of 150°C, alloying it, and applying a paint after cooling.Pre-coated copper plate is a conventional alloyed steel plate coated with a relatively hard paint (lead hardness of 8H or higher). In this case, when shearing is performed using the shear (4), peeling occurs at the boundary between the base material (1) and the alloyed galvanized film (2) near the cut end surface, as shown in Figure 1. The strength during this peeling is 1M or less, which is commonly observed when a hard coating film is coated on a generally hard plating film.

This peeling phenomenon also occurs due to impact bending deformation of the pre-coated steel sheet.

Such peeling of the plating film not only reduces the product value of the pre-coated steel sheet, but also seriously impedes its use by users. Therefore, when using an alloyed steel sheet as a base sheet for a pre-coated steel sheet, peeling of the plating film must be solved as much as possible.

However, the mechanism of this peeling phenomenon is due to the adhesion of the plating film.
It is thought that various factors such as the hardness of the paint film, shear clearance, and base material components are involved, but the details are not fully understood at present, and an appropriate solution has not been found. This is the current situation.

This invention was made for the purpose of preventing the above-mentioned peeling phenomenon of the plating film, and in order that the alloyed steel sheet, which has excellent properties as a base steel sheet for painting, would have a wide range of uses as a material for pre-coated steel sheets. The present invention proposes a method for producing prepainted steel sheets that exhibit excellent resistance to shearing and impact deformation.

By changing the composition of the steel base, this invention has the effect of biting into other layers due to mutual diffusion between the zinc layer and the steel base (
The main feature is to further enhance the anchor effect (generally called the anchor effect) and prevent the peeling of the plating film. C50.1%, St
≦0.1chi, Mn -0,10~0.5%, P is 0.0
8≧P≧0.24XC%+0.005, balance F
A base material having a composition consisting of e and unavoidable impurities,
1) A method for producing a pre-coated steel sheet, characterized in that hot-dip galvanizing is applied to one side at a rate of 45 y/lr1 to 120 y/lr1 or less.

As a result of intensive study of the adhesion between the steel substrate and the plating layer of an alloyed steel sheet, the inventors confirmed that the adhesion of the plating layer can be improved mainly by increasing the degree of alloying in a general concept. However, although the method of increasing the degree of alloying of the plating layer is effective in improving the adhesion of the plating layer, it tends to cause delamination of the plating film, mainly during processing, such as powdering and flaking. invite

Therefore, the inventors investigated various ways to ensure the adhesion of the plating film against shearing and impact deformation of alloyed steel sheets without unnecessarily increasing the degree of alloying. In particular, it has been found that by adjusting the content of C and P in the steel, it exhibits excellent resistance to shearing and impact deformation.

That is, this invention uses C50.1%, Si≦0.1%, Mn 0.10-0 as the steel base of the pre-painted steel sheet.
．． 5%, o, oao≧P≧0.24 X C+ 0.
0.005%, the balance being Fe and unavoidable impurities. The reason why the steel composition of the base metal is limited in this way is as follows.

C content affects the impact deformation capacity of alloyed steel sheets, and
．． If it exceeds 1%, the impact deformation resistance decreases and
Adversely affects strength and workability. On the other hand, if the C content in the steel is low, the ferrite crystal grains will become larger, and Zn will more easily diffuse into the ferrite base metal during alloying, and the so-called anchor effect will reduce the adhesion between the base material of the alloyed steel sheet and the plating film. In order to improve the carbon content, the C content is preferably 0.1% or less, preferably 0.05% or less.

It is sufficient that the St content is about the same as that of ordinary mild steel sheets, but
If it exceeds 0.1%, it will adversely affect the alloying start temperature, alloying speed, and powdering resistance of the galvanized layer, so it was set to 0.1% or less.

Mn is contained in order to maintain a predetermined strength,
Its content is 0.1 to 0.5%, which is the same as that of ordinary mild steel plates.
And so.

Like C, P is one of the main components in this invention steel, and the addition of P improves the impact deformation resistance of the pre-coated steel sheet, but due to the balance with C, if the C content is low, a low concentration of P will Impact deformation ability is maintained. On the other hand, when the P content in the steel increases, Fe-zn alloying is suppressed during the alloying process, and conversely, the Zn in the plating layer diffuses into the base ferrite, and due to the anchoring effect of Zn, the base material of the alloyed steel sheet is This improves the adhesion of the plating film. FIG. 4 is a chart showing the results of an investigation by the inventors of the relationship between the 01P content and shear peeling using the materials shown in the table below.

In addition, the paint film at this time was made of hard acrylic paint.
It was formed by applying μ. That is, the P content is 0.08%
If it exceeds P, the yield strength will increase, leading to a decrease in workability, and the increase in yield strength will also lead to a decrease in impact deformation resistance. Therefore, the upper limit of P is preferably 0.08%, and 0.24%.
If it is less than ×C%+0.005, the impact deformation resistance will not be maintained and the adhesion of the plating film will not be improved.
The lower limit of P was set to 0.24XC%+0.005.

Ingredient Composition of Test Material (H) In addition, in this invention method, the amount of zinc deposited on the alloyed steel sheet is 45y/ff11 or more on one side or 120? The reason why the value is set to below /rd is as follows.

FIG. 5 shows the results of an investigation by the inventors of the correspondence between the amount of zinc deposited on one side and the period during shear peeling using the materials shown in the table above. The coating film at this time was formed by applying 15 μm of hard acrylic paint in the same manner as described above.

In the case of alloyed steel sheets, the amount of zinc deposited is thought to have some influence on the mechanical factors during impact deformation;
If one side is less than 45 f/=td, the impact deformability of the pre-coated steel sheet will be reduced, and if it is more than 120 P/m', the press formability will be significantly reduced. It is preferably less than lri.

Next, an embodiment of this invention method will be described based on the drawings.

Figure 2 shows an example of alloying treatment equipment, where Ql) is a plating tank, (2) is a coating amount control device, (to) is a heating furnace,
α◆ represents a heat retention furnace, (to) represents a cooling device, and αQ represents a top roll. In other words, the alloyed steel sheet is heated to a temperature of 900 to 1100°CK with molten salt ψ after controlling the amount of zinc deposited on the outlet side of the plating bath in a continuous hot-dip galvanizing line.
It is produced by guiding it to α1. The manufactured alloyed steel sheet is subjected to chemical conversion treatments such as phosphate treatment using a reaction cell and chromate treatment using a roll coater, and then coated with a paint. As for the coating method, a roll coater is used in the case of coil coating. There are two types of roll coaters: one in which the rotating direction of the coating opening is the same as the coil advancing direction as shown in Figure 8a, and the other in the opposite direction as shown in Figure 3.They are called natural coaters and reverse coaters, respectively. There is.

In the figure (1) is the paint pan, QD is the pickup roll, (
A) is a coating roll, B) is a backup roll, and (C) is a coil. After coating with a roll coater, most coatings are thermally cured in a hot air oven, except in special cases.

As described in Kitagi, pre-coated steel sheets that use alloyed steel sheets as the base material are hot-dip galvanized in a continuous hot-dip galvanizing line, then led to a heating furnace for alloying treatment, and this alloyed steel sheet is chemically treated. It is then manufactured by applying paint and curing it with heat.

Examples of the present invention will be described below.

〔Example〕

Cold-rolled steel sheets (thickness 0.49 to 0.71 mm) with different compositions were used as base materials, and alloyed after continuous hot-dip galvanizing. After processing the pieces, they were subjected to the usual degreasing and zinc phosphate treatment, coated with 15μ of hard acrylic paint, sheared with a thermosetting electric shear, measured the peeling width of the end face, and tested with DuPont impact (ball diameter 12φ). , Load 1 and 9. Steel ball falling height 50 degrees) were applied to evaluate the state of plating peeling.

The test materials in this example were those according to the present invention 1
1 steel type and 15 steel types used as comparative examples, totaling 26 steel types.
It was a steel type. Table 1 shows the component compositions of these 265 types and the evaluation results of the plating peeling condition.

As is clear from Table 1, in the case of the pre-coated steel sheet according to the present invention, the C1P content during shear peeling is almost 0.25 wtys or less compared to the pre-coated steel sheet of the comparative example in which the C1P content is outside the range of the present invention. , therefore DuPont ft.
It was found that the i-impact test results were also good, and the impact deformation resistance was high.

As explained above in the margins below, according to this invention method, it is possible to improve the adhesion between the steel substrate of the alloyed steel sheet and the plating film, so even if a hard paint is applied, it will resist shearing and impact deformation. It is possible to obtain a pre-coated steel sheet that exhibits excellent resistance and has a great effect on the spread of pull-coating of alloyed steel sheets.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the coating structure of a pre-coated steel plate in which a hard paint is applied to a conventional alloyed steel plate; Figure 2 is a schematic diagram showing an example of alloying treatment equipment, Figure 8 is a schematic diagram showing a coil coating method, where a is a natural coater, a is a reverse coater, and Figures 4 and 5 are The results of experiments conducted by the present inventors are shown in Figure 4, which shows the relationship between the acid content of C%P and shear removal, and Figure 5, which shows the relationship between the amount of zinc deposited on one side and the shear removal width. This is a chart showing the following. 1... Base material, 2... Alloyed galvanized film, 8...
・Coating film, 4... Shear, 11... Plating tank, 12.
... Adhesive control device, 18... Heating furnace, 14... Heat retention furnace, 15... Cooling device, 16... Top roll,
20...Paint pan, 21...Pickup roll, 22...Coating roll, 2B...Backup roll, 24...Coil. Applicant: Sumitomo Metal Industries, Ltd. Figure 1 Figure 2 α b Figure 4 C (%) Figure 5 Amount of zinc on one side (9/w2)

Claims (1)

[Claims] A method for producing a pre-coated steel sheet in which a paint is applied to an alloyed hot-dip galvanized steel sheet, C50.1%, Si≦0.1.
%, MnO, 10-0.5%, P satisfies the following formula,
A method for producing a pre-coated steel sheet, comprising applying a hot-dip galvanizing layer of 452/- to t20y/m' on one side to a base material having a composition consisting of Fe and unavoidable impurities. 0.03≧P≧0.24XC%+0.005