JPH0543780B2 - - Google Patents

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 steel base, and the entire galvanized layer is made of Fe-Zn alloy. Compared to plated steel plate,
Uniform and even paint finish appearance, good paint film adhesion, excellent corrosion resistance as a base steel sheet for painting, low electrode wear during resistance welding, and workability similar to that of cold-rolled steel sheets. Due to its unique characteristics, it has a wide range of uses, including automobiles, home appliances, and meters, and most of them are used after being painted, so it functions as a coated steel sheet. In recent years, with regard to painted steel sheets, pre-painted steel sheets have been developed, which are used by applying paint to thin steel sheets such as cold-rolled steel sheets and galvanized steel sheets, and then processing and assembling them as they are, in order to eliminate the conventional painting process performed by the user. Alloyed steel sheets, which are becoming popular and have excellent properties as base steel sheets for painting, are also being used as base sheets for pre-painted steel sheets. In other words, new demand for steel sheets that have been pre-painted by steel sheet manufacturers, i.e., pre-painted steel sheets, is increasing due to users' requests for chemical conversion treatment and the abbreviation of painting processes, the development of paints with good workability, and improvements in coated steel sheet forming technology. It's coming. However, with the spread of such precoating, problems that could not have been foreseen at the beginning have arisen. This is a phenomenon in which the plating film peels off when a relatively hard paint is applied to an alloyed steel sheet. FIG. 1a shows the film structure of a pre-coated steel sheet in which a hard paint is applied to a conventional alloyed steel sheet, where 1 is the base material, 2 is the alloyed galvanized film, and 3 is the paint film. In other words, for normal pre-coated steel sheets, after hot-dip galvanizing is applied to the base material 1, the furnace temperature is immediately heated to 900~900°C.
It is guided to a heating furnace maintained at 1100℃ and alloyed.
It is manufactured by applying paint after cooling, but in the case of a pre-coated steel sheet, which is a conventional alloyed steel sheet coated with a relatively hard paint (pencil hardness of 3H or more), it is sheared with a shear 4, as shown in Figure 1. As shown in b,
Base material 1 and alloyed galvanized film 2 near the cut end surface
Separation occurs at the boundary. This peeling width is 1 mm or less, and is commonly observed when a hard plating film is coated with a hard coating 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 an alloyed steel sheet is used 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 depends on the adhesion of the plating film, the hardness of the paint film, shear clearance,
It is thought that various factors such as base material components are involved, but the details have not been fully elucidated at present, and an appropriate solution has not yet been found. This invention was made with the aim 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. This invention improves the effect of biting into other layers (generally called the anchor effect) through mutual diffusion between the zinc layer and the steel base by changing the composition of the steel base, thereby suppressing the peeling phenomenon of the plating film. The main feature is to prevent C≦0.1%, Si≦0.1%,
Mn0.10~0.5%, P is 0.03≧P≧0.24×C%+
0.005, with the balance consisting of Fe and unavoidable impurities, a method for producing a pre-painted steel sheet, characterized by applying hot-dip galvanizing of 45 g/m ² to 120 g/m ² per side to a base material satisfying 0.005 and having a composition consisting of Fe and unavoidable impurities. . As a result of intensive investigation of the adhesion between the steel substrate and the plating layer of alloyed steel sheets, 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 such as powdering and flaking during processing. . Therefore, the inventors conducted a shearing process on an alloyed steel sheet without increasing the degree of alloying more than necessary.
As a result of various studies on methods to ensure the adhesion of the plating film against impact deformation, we found that by adjusting the components of the base metal, especially the content of C and P in the steel, we found that it has excellent resistance to shearing and impact deformation. It was found that it shows resistance. That is, in this invention, as the steel base of the pre-painted steel sheet, C≦0.1%, Si≦0.1%, Mn 0.10 to 0.5
%, 0.030≧P≧0.24×C+0.005%, the balance being Fe and inevitable impurities. The reason why the steel composition of the base metal is limited in this way is as follows. The C content affects the impact deformation resistance of the alloyed steel sheet, and if it exceeds 0.1%, it reduces the impact deformation resistance and has an adverse effect on the 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 steel 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. The content of Si should be 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 is set to 0.1% or less. . Mn is added to maintain a specified strength, and its content is about the same as that of ordinary mild steel sheets.
It was set at 0.1 to 0.5%. Like C, P is one of the main components in this invention steel, and the addition of P improves the impact deformation resistance of pre-coated steel sheets, but there is a balance with C, and if the C content is low, the concentration is low. The impact deformation ability is maintained at P of . On the other hand, when P in steel increases,
During alloying treatment, Fe-Zn alloying is suppressed, and conversely, Zn in the plating layer diffuses into the base ferrite and becomes Zn.
The anchor effect improves the adhesion between the base material of the alloyed steel sheet and the plating film. FIG. 4 is a chart showing the results of an investigation by the inventors of the relationship between the C and P contents and the shear peeling width using the materials shown in the table below. The coating film at this time was formed by applying 15μ of hard acrylic paint. In other words, if the P content exceeds 0.03%, the yield strength will increase, leading to a decrease in workability, and an increase in the yield strength will lead to a decrease in impact deformation resistance, so the upper limit of P is 0.03%.
is preferable, and if it is less than 0.24×C%+0.005, the impact deformation resistance cannot be maintained and the adhesion of the plating film cannot be improved, so the lower limit of P is 0.24×
It was set as C%+0.005.

〔Example〕

Cold-rolled steel sheets with different compositions (thickness 0.49 to 0.71
mm) as the base material, alloyed after continuous hot-dip galvanizing, and processed these alloyed steel sheets into specimens of width 80 mm x length 150 mm, followed by normal degreasing, zinc phosphate treatment, hard acrylic Apply 15μ of the paint, heat cure, shear it with an electric shear, measure the edge peeling width, and conduct the Dupont impact test (ball diameter
12φ, load 1Kg, steel ball falling height 50mm),
The peeling status of plating was evaluated. The test materials in this example were 26 steel types in total, 11 steel types related to the present invention and 15 steel types used as comparative examples. Table 1 shows the chemical composition of these 26 steel types and the evaluation results of plating peeling. As is clear from Table 1, in the case of the pre-coated steel sheet according to the present invention, the shear peeling width is small, almost 0.25 mm or less, compared to the pre-coated steel sheet of the comparative example in which the content of C and P is outside the range of the present invention. Therefore, it was found that the DuPont impact test results were also good, and the impact deformation resistance was high.

【table】

[Table] As explained above, according to the method of the present invention, it is possible to improve the adhesion between the steel substrate of the alloyed steel sheet and the plating film, so even if hard paint is applied, shearing and impact deformation will not occur. It is possible to obtain a pre-coated steel sheet that exhibits excellent resistance to anti-alloyed steel sheets, which 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 film structure of a pre-coated steel plate in which a hard paint is applied to a conventional alloyed steel plate, Fig. 1b is a cross-sectional view showing the peeling of the plating film when the same pre-coated steel plate is subjected to shear processing, Second
The figure is a schematic diagram showing an example of alloying treatment equipment, and Figure 3 is a schematic diagram showing a coil coating method, in which figure a is a natural coater, figure b is a reverse coater, and figures 4 and 5 are in accordance with the present invention. Figure 4 shows the relationship between the content of C and P and the shear peeling width, and Figure 5 shows the relationship between the amount of zinc deposited on one side and the peeling width during shearing. This is a chart showing. 1... Base material, 2... Alloyed zinc plating film, 3
... Paint film, 4 ... Shear, 11 ... Plating tank, 1
2... Adhesion amount control device, 13... Heating furnace, 14...
... Heat retention furnace, 15 ... Cooling device, 16 ... Top roll, 20 ... Paint pan, 21 ... Pick-up roll, 22 ... Coating roll, 23 ...
Backup Prowl, 24...Coil.

Claims (1)

[Claims] 1. A method for producing a pre-coated steel sheet in which a paint is applied to an alloyed hot-dip galvanized steel sheet, C≦0.1%,
Si≦0.1%, Mn0.10-0.5%, P satisfies the following formula, and the balance consists of Fe and unavoidable impurities. Hot-dip galvanizing of 45 g/m ² or more and 120 g/m ² or less on one side A method for producing prepainted steel sheets characterized by applying a layer. Note 0.03≧P≧0.24×C%+0.005