JPS61147905A - Method for improving outer skin of steel sheet coated with molten aluminum - Google Patents

Abstract

PURPOSE:To improve the product value of a titled sheet by performing temper rolling with a dull roll having the satin skin of specific surface-roughness and transferring the satin skin to a steel sheet coated with molten aluminum. CONSTITUTION:A crystalline pattern called a spangle is formed through the whole surface of a steel sheet coated with molten aluminum when left as it is. The steel sheet coated with molten aluminum is temper-rolled by a dull roll having the surface formed into the satin skin of 10-30mu Rmax. surface roughness and 100-250 the number of crests (PPI). At that time, the satin skin of the roll is transferred to the surface of each spangle of the coated metal layer, to form the whole sheet surface into the uniform satin skin as well as to make the 1st spangles faint or to eliminate them. Further, the sheet is temper-rolled at need by a bright roll having the smooth surface of about >=2.0mu Rmax. In this way, the outer skin of sheet is improved and the product value of a coated steel sheet is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for eliminating spangle patterns on the surface of a plated metal layer of a hot-dip aluminized steel plate and forming a uniform and beautiful surface texture over the entire surface.

[Prior art]

To give an example of the manufacturing process of aluminized steel sheets in a continuous hot-dip aluminum plating line, first, the steel strip, which is the original sheet, is continuously fed at a predetermined line speed, and the surface of the strip is first cleaned ( The steel strip is subjected to reduction removal (rolling oil, scale, etc.) and softening, and then passed through a hot-dip aluminum plating bath (bath temperature: approximately 650° C.) to adhere molten aluminum to the surface of the steel strip, and then pulled up onto the bath. Since there is an excessive amount of aluminum attached to the surface of the steel strip that has been lifted above the bath, wiping gas is sprayed onto the surface of the steel strip using a gas wiping nozzle to wipe off the excess aluminum, thereby reducing the area weight to a specified level. After adjusting the temperature, the aluminum plating layer is cooled and solidified by passing through a cooling zone. Next, depending on the application and quality requirements, the product is either passed through temper rolling and wound into a coil, or is wound into a coil without being subjected to temper rolling and then sent to an annealing furnace outside the line. The product is annealed and then temper rolled.

However, the hot-dip aluminized steel sheet obtained in this manner has a mottled pattern called spangle over its entire surface. These spangles are aluminum crystal grains that are generated and grown during the cooling and solidification process of the molten aluminum plating layer that adheres to the surface of the belt, and are not completely erased by subsequent temper rolling, etc., and remain as they are on the product surface. This remains as a patchy pattern.

Spangle boundaries (grain boundaries) form a groove-like network, and the grain size of the spangles and the depth of the grooves at the grain boundaries (hereinafter referred to as "grain boundary depth") are determined by the thickness of the steel sheet and the thickness of the plating layer. Although it varies depending on the layer thickness, the cooling rate of the plated metal, etc., the grain size is usually about 3 to 10 m, and the grain boundary depth is 3 to 7 μm.

〔problem〕

The spangle pattern described above does not have a negative effect on the plating quality (corrosion resistance, processability, etc.), but it impairs the beauty of the product and lowers its value. When used as a board, etc., it is desired to have a uniform and beautiful surface texture without spangle patterns, as this causes diffuse reflection and a decrease in reflection efficiency.

Conventionally, as a method for preventing the formation of spangle splotchy patterns, a method is known in which the basis weight of molten aluminum on the surface of the band is adjusted and then rapidly cooled.

This method focuses on the fact that if the spangles are extremely fine, they are not visible as a mottled pattern, and attempts to prevent the growth of spangles during the solidification process by rapid cooling. It is difficult to keep it to a grain, and it is difficult to expect sufficient effects.

On the other hand, as a method for eliminating the generated spangles, there is known a method of performing temper rolling with a high rolling load and/or with a large number of passes in temper rolling of a plated steel sheet. However, when such temper rolling is performed, the elongation rate of the plated steel sheet becomes unduly large, causing hardening and poor workability. Furthermore, increasing the number of passes means sacrificing production efficiency. Moreover, even if such temper rolling is performed, a sufficient erasing effect cannot actually be obtained.

[Purpose of the invention]

The present invention efficiently dilutes and eliminates spangles in the plating metal layer to a harmless extent without causing any change in the material of the hot-dip aluminized steel sheet or reducing production efficiency, and uniformly spreads over the entire surface. The object of the present invention is to provide a method for improving the surface texture of a hot-dip galvanized steel sheet, which can form a beautiful surface texture.

[Technical means]

The first method for improving the surface texture of a hot-dip aluminized steel plate according to the present invention uses a dull roll having a matte surface roughness with a maximum height of 10 to 30 μRmax and a number of peaks (PPI) of 100 to 250. , temper-rolling a hot-dip aluminized steel plate to coat the surface of the plated metal layer of the steel plate,
It is characterized in that the spangle pattern on the surface of the plated metal layer is erased by transferring the matte surface of the dull roll.

The second method for improving surface texture according to the present invention is to remove the spangle pattern on the surface of the plated metal layer by temper rolling using the dull roll, and then temper rolling with a bright roll having a smooth surface of 2.0μRmax or less. The feature is that rolling is performed. Here 1. uRmax is JIS
It is an index of surface roughness specified in B 0601, and the number of peaks (PPI) is the number of peaks per inch of length (Pe
aks per inch).

[Effect]

In the first method of temper rolling a hot-dip aluminized steel sheet using the dull roll, fine irregularities are created on the surface of each spangle of the plated metal layer by transferring the matte surface of the roll onto the surface of the plated metal layer. is formed, and the grain boundaries, which are continuous groove-like boundaries dividing each spangle, are finely divided. As a result, the surface of the hot-dip aluminum-plated steel sheet becomes a uniform matte surface as a whole. The original spangle pattern is diluted to a harmless extent or completely erased.

Further, according to a second method in which the surface of the plated metal layer is made into a matte surface by temper rolling using dull rolls and the spangle pattern is erased, and then temper rolling is performed using bright rolls.
By flattening the matte surface of the plated metal layer,
Glossy smooth skin without spangle patterns is formed.

The unevenness of the matte surface that is transferred and formed on the surface of the plating metal layer in order to erase the spangle pattern is finer than the grain size of the spangle (usually 3 to 10 mm) (and the grain boundary depth of the spangle is usually 3 to 7 μm). ), and the irregularities must be uniformly formed within the grains and across the grain boundaries of each spangle.

In addition, the transfer rate of the matte texture of the dull roll to the surface of the plated metal layer, that is, the surface roughness of the matte texture of the dull roll (μRmax - r), and the surface roughness of the matte texture of the surface of the plated metal layer transferred and formed by the dull roll. μR
max-m) and the ratio (μRmax°m/μRmax-
Since rx100) (%) cannot actually be 100%, the transfer rate must also be taken into consideration in determining the surface roughness of the dull roll's satin texture.

The above transfer rate varies depending on the roll diameter and rolling load of the dull roll used as a work roll for temper rolling, but
Normal temper rolling conditions (dull roll diameter: approx. 500-600
u, Rolling load per unit width: Approx. 200-400 kg
f/w), approximately 60 to 80% can be expected.

In the present invention, the above-mentioned limitations on the surface roughness of the dull roll are determined by taking into account the transfer rate under the temper rolling conditions, the spangle grain size and grain boundary depth of the plated metal layer, etc. The reason for the limitation is as follows: First, the lower limit of the maximum height is specified as lOμRmax, because if it is smaller than that, the depth of the unevenness will be the depth of the spangle grain boundary, considering the transfer rate. This is because the spangle elimination is insufficient as the upper limit is set to 30μRma.
The reason why x is specified is that if it exceeds this value, the product surface after skin pass rolling will become rough and the aesthetic appearance will be impaired. A more preferable range is 10 to 20 μRmax.

In addition, the lower limit of the number of peaks (PPI) was set at 100 because
If it is less than that, even if μRmax is within the specified range, the fineness of the unevenness formed on the surface of the plating metal layer will be insufficient, and the grain boundaries will remain as relatively long dividing lines, resulting in spangles. This is because the erasing effect will be insufficient. On the other hand, the upper limit of the number of ridges is set at 250 because if it exceeds 250, the height of the surface unevenness of the roll will actually decrease, so even if the transfer rate is adjusted high,
This is because the depth of the irregularities of the matte texture transferred and formed on the surface of the plated metal layer is insufficient, and as a result, the spangle erasing effect becomes insufficient in this case as well. More preferable number of peaks (P
PI) is 100-200.

Surface roughness of dull roll, maximum height above μRma
x) and the number of peaks (PPI), the center line average roughness μRa) must be 1.5μ or more (standard length L
) : 0.8 m) is preferable in that it can further increase the transfer rate to the surface of the plated metal layer.

Temper rolling is performed for the purpose of eliminating the yield point elongation of the steel plate, correcting the shape, etc., and the rolling conditions are usually such that an elongation rate of about 0.5 to 1.5% is given to the steel plate. It is set as follows. The elongation rate is about 0°5% or more because
If it is lower than that, the heat refining effect will be insufficient, and if it exceeds 1.5%, the work hardening of the steel plate will progress, elongation, drawing capacity, etc. will decrease, making subsequent processing difficult. This is because. In the case of temper rolling carried out with dull rolls in the present invention, there is no difference in this respect from normal rolling, but increasing the rolling load within a range that does not involve any disadvantages such as a decrease in workability, This is preferable because it improves the transfer rate and thereby improves the spangle erasing effect.

Temper rolling is roughly divided into wet skin pass method, in which tempering oil is interposed at the contact interface between the work roll and the surface of the steel sheet, and dry skin pass method, in which tempering oil is not used. According to , this method is advantageous in that the transfer rate can be increased by about 25% compared to the wet skin pass method.

After the spangle pattern is removed by temper rolling using the dull roll, the surface of the plated metal layer can be changed from a matte surface to a smooth, glossy surface by performing temper rolling using a bright roll. The surface roughness of the bright roll may be 2.0 μRmax or less.

〔Example〕

A hot-dip aluminum-plated steel sheet was produced on a continuous hot-dip aluminum plating line on the Taihoban, and after being wound into a coil, it was temper-rolled in a multiple skin pass mill using dull rolls as work rolls to obtain a product.

The spangle grain size of the plated metal layer of the test material before temper rolling is 3 to 10 m, and the grain boundary depth is 3 to 7 μm.

The hot-dip plating conditions, temper rolling conditions, and test results are as follows.

(1) Hot-dip aluminum plating conditions (1) Original plate: low carbon rimmed steel, plate thickness 0.8 tm, +
Ii width 914■.

(2) Line speed: 100m/min.

(3) Plating bath temperature: 650℃ (4) Area weight: 60g/rd・
Adjust to one side.

(II) Skin pass rolling conditions shown in Table 1. (III) Results Table 1 shows the evaluation of the surface roughness of the dull roll used in skin pass rolling, the rolling load, and the surface texture quality of the obtained product.

Flavoring (-) 1 to 5 are examples of the present invention, and positive numbers 101 to 104 are comparative examples in which the surface roughness of the dull roll deviates from the specifications of the present invention.

In the table, the meaning of each symbol in the "Product surface quality" column is as follows.

A varnish spangle pattern erase B. Spangle pattern remains.

C The spangle pattern has been erased, but the dull skin is too rough.

As shown in Table 1, in Comparative Examples Na101 to 103, even when the rolling load was increased, the spangle pattern clearly remained due to the insufficient effect of erasing the spangle pattern.
In No. 4, the spangle pattern has been eliminated, but the dull surface on the surface of the steel sheet is too rough, resulting in a product defect. In contrast, in the example of the present invention, one bath of UA quality rolling with a normal rolling load results in a defective product. The spangle pattern is sufficiently diluted or erased, and a good surface texture is formed.

In the SnJILL continuous hot-dip aluminum plating line, a hot-dip aluminum-plated steel sheet was manufactured, wound into a coil, and then subjected to temper rolling using dull rolls and temper rolling using bright rolls. The plating conditions are the same as those in Example 1. Table 2 shows the temper rolling conditions and the quality of the plated steel sheets obtained. In Table 0, the incense (-) 1 to 5 are invention examples, and Arashi 101-104 are comparative examples. Furthermore, the meaning of each symbol in the "Product Surface Quality" column is as follows.

A' Varnish spangle pattern removed, glossy skin good B': Shiny skin good, spangle pattern remaining C' Varnish spangle pattern removed, however, glossy skin poor As shown in Table 2, in the comparative example, spangle pattern remains. In contrast, in the examples of the present invention, the spangles were eliminated by one pass of temper rolling, and the sheets had a good glossy surface.

〔Effect of the invention〕

According to the method of the present invention, the spangle pattern that inevitably occurs on hot-dip aluminized steel sheets can be diluted or eliminated to a harmless extent depending on the use and required specifications of the steel sheet, resulting in a uniform and beautiful matte surface or glossy smooth surface. A hot-dip aluminized steel sheet with excellent commercial value can be obtained.

The molten aluminum steel sheet obtained by the present invention has excellent surface quality and mechanical properties, so it can be used as a heat reflecting plate for cooking appliances such as toaster ovens, gas ranges, and gas stoves, and for heating appliances such as kerosene stoves and electric kotatsu. It is useful for layer plates, structural members of incinerators, chimneys, drying furnaces, blowers, etc., and various other uses.

Claims (2)

[Claims] (1) 10-30μRmax and number of peaks (PPI):
By heat-rolling a hot-dip aluminum plated steel plate with a dull roll having a matte surface roughness of 100 to 250 and transferring the matte texture of the dull roll to the surface of the plated metal layer of the steel plate, the aluminum plated metal is produced. A method for improving the surface texture of a hot-dip aluminized steel sheet, characterized by erasing spangle patterns on the surface of the layer. (2) 10-30μRmax and number of peaks (PPI):
The aluminum plating is achieved by heat-rolling a hot-dip aluminum plated steel sheet with a dull roll having a matte surface roughness of 100 to 250 and transferring the matte surface of the dull roll to the surface of the plated metal layer of the steel sheet. A method for improving the surface texture of a hot-dip aluminized steel sheet, which comprises erasing the spangle pattern on the surface of a metal layer and then temper rolling using a bright roll having a smooth surface of 2.0 μRmax or less.