JPH0483860A - Method for regulating surface roughness of galvannealed steel sheet - Google Patents

Abstract

PURPOSE:To control the development of alloy layer and to change surface roughness by regulating the temp. at which a steel sheet is introduced into a bath in a hot-dip galvanizing bath. CONSTITUTION:A steel sheet is immersed into a hot-dip galvanizing bath to undergo galvanizing, and the resulting plated steel sheet is alloyed, by which a galvannealed steel sheet is produced. At this time, the temp. of the steel sheet to be introduced into the above hot-dip galvanizing bath is regulated. The appropriate temp. of this steel sheet is about 460-500 deg.C, and the adequate content of Al in the bath is about 0.12-0.16wt.%. It is preferable to carry out skin pass rolling at about 0.3-1.5% reduction of area in order to uniformize roughness after alloying. By this method, surface roughness in a wide range can be obtained, and the plated steel sheet with high Ra and high PPI can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for adjusting the surface roughness of an alloyed hot-dip galvanized steel sheet.

[Prior Art 1] It is necessary to adjust the surface roughness of an alloyed hot-dip galvanized steel sheet depending on its intended use.

Conventionally, the surface roughness of alloyed hot-dip galvanized steel sheets has been adjusted by changing the surface roughness of temper rolls in the subsequent skin pass process. That is, when trying to obtain a smooth steel machine surface, a bride roll is used, and when trying to obtain a medium roughness, a 380 dull roll (surface roughness Ra = 1.
5), and if you want to get a rough surface, use a #50 dull roll (
Surface roughness Ra = 2.5), rolling reduction rate 0.3~
It was rolled at 1.5%.

However, even if #50 dull rolls are used, the surface roughness of 11ii1i is only about Ra = 1.4 at most, and the rolling reduction in temper rolling is limited to around 1.5%, so it is not possible to obtain a surface rougher than this. It was difficult.

[Problems to be Solved by the Invention] The inventors have discovered that the temperature of the steel sheet entering the hot-dip galvanizing bath affects the development of the alloy layer, and that the surface roughness of the obtained alloyed hot-dip galvanized steel sheet also has some effect. As a result of repeated experiments, we found that the higher the temperature of the copper plate entering the hot-dip galvanizing tank, the lower the surface roughness R of the steel plate.
It was found that the a or PPI was also thick.

[Means for Solving the Problems 1] The present invention provides a method for manufacturing an alloyed foil galvanized steel sheet by immersing a steel sheet in a hot-dip galvanizing bath for galvanizing, and alloying the plated steel sheet. A method for adjusting the surface roughness of an alloyed hot-dip galvanized steel sheet, the method comprising adjusting the surface roughness of the alloyed foil galvanized steel sheet by adjusting the temperature of the steel sheet entering a crystalline hot-dip galvanized steel sheet. .

[Function] According to the present invention, the A! By controlling the formation of the enriched layer and adjusting the development of the alloy layer, the surface roughness can be varied.

FIGS. 1 and 2 are graphs showing this. If the temperature at which the steel sheet enters the hot-dip galvanizing bath is less than 5460° C., the bath temperature will drop and it will be difficult to control the coating amount by gas restriction. If the temperature at which the steel sheet enters the TI8+ of the hot-dip galvanizing tank is 460°C or higher and 530°C or lower, the AR-enriched layer will be thin and alloying will proceed relatively evenly, so there will be little unevenness on the surface of the plating layer due to alloying. .

On the other hand, if the temperature at which the steel sheet enters the hot-dip galvanizing tank exceeds 530° C., alloying progresses unevenly and rapidly, resulting in a high roughness Ra or PPI.

The temperature at which the steel plate enters /b of the hot dip galvanizing tank is 58
If the temperature exceeds 0°C, the alloy layer will develop too much and the plating will easily peel off. The temperature of the plating bath is 460, considering the flowability of the hot water.
℃ or higher, but if it is 500℃ or higher, the loss due to Zn oxidation and the loss of heat retention energy of the bath will increase, so the temperature should be set at 460 to 500℃.
shall be.

Rakuchu's A℃ is essential for suppressing excessive alloying of iron and zinc, and at 0.12% by weight, the suppressing effect is small, and at 0.16% by weight or more, the suppressing effect becomes too large.
Since uniform alloying becomes difficult, it is appropriate to set the weight to 0.12 to 0.16 weight.

The alloying temperature is set at 420 to 550°C in order to plate at an economical plating rate and to obtain a steel plate without peeling.

Skin pass rolling after alloying is necessary to make the roughness uniform since there is a large variation in roughness if alloyed as is. The rolling reduction ratio is set to be high (this will cause the material quality of the steel plate to deteriorate, so the rolling reduction ratio is set to 0.3 to 1.5%.

[Example 1 Fig. 1 shows an example of the present invention, and is a diagram showing the relationship between the temperature at which a steel plate enters a galvanizing bath and the surface roughness Ra. FIG. 2 is a diagram showing the relationship between the temperature at which the steel sheet enters the hot-dip galvanizing bath and the roughness PPI in the same example.

P P I (Peak Par Inchl is SAE
When considering a standard roughness curve as shown in Fig. 5, a count level P-■ of, for example, 50LLm (1.25 μm) is set relative to the center line, and P-■ is set before crossing the center line.
1 inch (25.4 mm).
) is expressed as the number of peaks per area.

The following measuring device was used.

Measuring device name: Surfcom 300B (manufactured by Tokyo Sekiden) Peak counter: E-MD-3O9A (manufactured by Tokyo Seitomi)
Pickup: E-DT-3OIA (manufactured by Tokyo Seitomi) Examples are shown in Table 1. Table 1 shows plating bath temperature 470
℃, AQa degree (7) O in the plating vortex, 14% Te, plate thickness 0
．． The immersion temperature of the 8 mm steel plate into the plating bath was set to 480℃.
The results are shown when the temperature was adjusted to ~570°C.

FIG. 3 shows a comparison of the adjustment range of Ra according to the prior art and the present invention. FIG. 4 shows a comparison of PPI adjustment ranges according to the prior art and the present invention. According to the embodiment, the roughness can be adjusted over a wide range.

A specific method for adjusting the roughness Ra or PPI of the steel plate surface will be explained. Steel plate surface Ra is 1.0 #
Assume that production is performed using 80 dull rolls. If a steel plate surface with an Ra of 1.3 was required, conventionally it was necessary to change the temper rolling roll to a #50 dull roll, but if the roughness adjustment method of the present invention is used, the steel plate surface can be annealed. Production can be continued using #80 Darroll by simply increasing the cooling end temperature and adjusting the temperature of the steel plate immersed in the hot-dip galvanizing bath. Furthermore, it has become possible to produce products with a roughness Ra of 1.4 or more, which was previously difficult to produce. The same applies to PPI.

[Effects of the Invention] According to the present invention, in the production of alloyed store-dip galvanizing, a wide range of surface roughness can be obtained by adjusting the temperature at which the steel sheet enters the plating bath without frequent replacement of skin pass rolls. be able to. The temperature penetrating into the steel plate can be easily controlled during plating operations. In particular, in the present invention, high Ra
, high PPI plated steel sheets can be produced.

The effect of having a high Ra is that in external panel applications, dust, zinc powder, etc. adhering to the surface of the steel sheet are pushed into the steel sheet during pressing, making the stars less noticeable. Dust and zinc powder are easily captured on the surface of the subsequent plate, and continuous occurrence of grain defects can be prevented.

The result of high PPI is improved coating IIN'1 adhesion.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between the temperature of the steel plate entering the plating tank and surface roughness Ra, Fig. 2 is a graph showing the relationship between the temperature of the steel plate entering the plating tank and surface roughness PPI, Fig. 3,
FIG. 4 is a graph showing the effects of the present invention, and FIG. 5 is an explanatory diagram of PPI.

Claims (1)

[Claims] 1. Galvanize the steel plate by immersing it in a hot-dip galvanizing bath,
In alloying the plated steel sheet to produce an alloyed hot-dip galvanized steel sheet, adjusting the temperature of the steel sheet entering the hot-dip galvanizing bath to adjust the surface roughness of the alloyed hot-dip galvanized steel sheet. A method for adjusting the surface roughness of an alloyed hot-dip galvanized steel sheet.