JP2010043332A - Glare-proof hot dip galvanized steel sheet and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hot dip galvanized steel sheet in which the glossiness is reduced by controlling the surface configuration over the whole length and width of a coil and which has sufficiently practical glare-proofness, and to provide a method for manufacturing the same relatively easily and stably. <P>SOLUTION: The hot dip galvanized steel sheet having excellent glare-proofness is characterized in that, in a roughness curve on an optional surface of the steel sheet, the arithmetical average roughness Ra is 0.3-2.0 μm, the average length RSm of contour curve elements in the roughness curve is >100 μm and ≤300 μm, and Al-based oxide having circle-equivalent diameters of 0.05-1.0 μm exists in an amount of at least 5 pieces or more per 10×10 μm<SP>2</SP>of an optional surface of the steel sheet. The hot dip galvanized steel sheet is obtained by controlling the cooling conditions after hot dip galvanizing and the roughness of work rolls for temper-rolling. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hot dip galvanized steel sheet having excellent antiglare properties and a method for producing the same, and more particularly to a hot dip galvanized steel sheet having excellent antiglare properties used for automobiles, home appliances, building materials and the like.

  Hot-dip galvanized steel sheets used for automobiles, home appliances, building materials, etc. are generally lifted after immersion in a molten zinc bath after removing the surface oil and oxide film, etc. The amount is controlled by air cooling, water cooling, or air / water cooling. The hot-dip galvanized steel sheet produced in this way is rich in surface gloss and may be unsuitable depending on the application. For example, when hot-dip galvanized steel sheets are used uncoated on back rails and building materials in home appliances, such as guardrails, roofs, and wall materials, glare due to the reflection of light such as sunlight and lighting is uncomfortable and safe. It becomes a problem from the viewpoint of sex. For this reason, surface-treated steel sheets with reduced glare have been developed so far.

  For example, in Patent Document 1, a melt having excellent antiglare properties, characterized in that the surface grain size of the hot dip galvanized layer is 50 μm or less and the average roughness Ra of the surface is 0.4 to 1.0 μm. Galvanized steel sheets have been proposed. Although it is possible to reduce the glossiness of the hot-dip galvanized steel sheet by this method, it is effective in the case of a plating bath containing Al at a relatively high concentration such that the effective Al concentration in the plating bath is about 0.25%. This method is not clear for plating baths having an Al concentration of 0.20% or less, but wrinkles are not sufficiently formed and it may be difficult to impart a gloss of 100 or less. Furthermore, in the case of a hot dip galvanized steel sheet with a small plate thickness or a hot dip galvanized steel sheet with a small amount of zinc, it is necessary to obtain a surface crystal grain size of 50 μm or less because the temperature drop rate after pulling up from the plating bath is large. It is difficult to ensure a water spray cooling start temperature of 425 ° C. or more uniformly over the entire length and width of the coil.

Patent Document 2 is not intended for anti-glare properties, but the arithmetic average roughness Ra of the galvanized film is 0.50 μm or more and 1.50 μm or less, and the average peak interval Sm is 40 μm or more and 100 μm or less. By doing so, it is said that a hot-dip galvanized steel sheet in which the “glare sensation”, that is, the surface state in which the metallic luster appears to glare unevenly, can be obtained. Since the glossiness of the surface is affected by the surface morphology, it is possible to reduce the glossiness by controlling the surface roughness of the hot dip galvanized steel sheet within the range of this method. However, this method is effective for anti-glare against general indoor light, but is insufficient for anti-glare against strong light such as direct sunlight.
Japanese Patent No. 3148542 JP 2004-27263 A

  As described above, although various hot-dip galvanized steel sheets with controlled surface morphology and reduced gloss have been proposed, the manufacturing condition range is narrow or the antiglare effect is insufficient for practical use. For this reason, there has been a demand for a hot-dip galvanized steel sheet having an antiglare property sufficient for practical use over the entire length and width of the coil, and a relatively simple method and a method capable of stably producing it.

  In order to solve the above-mentioned problems, the present inventors have changed the operating conditions in various ways, and have examined the glossiness of the obtained hot dip galvanizing and the surface state thereof in detail, and as a result, have found the following. That is, in order to improve the antiglare property of the hot dip galvanized steel sheet, the arithmetic average roughness Ra defined by JIS B 0601 in the arbitrary roughness curve is increased on the surface of the hot dip galvanized steel sheet, and the contour curve element In addition to reducing the average length RSm, it was found that it is important to disperse fine Al-based oxides on the hot dip galvanized surface. That is, the gist of the present invention is as follows.

(1) In the roughness curve of the plated surface of the hot dip galvanized steel sheet, the arithmetic average roughness Ra is 0.3 μm or more and 2.0 μm or less, and the average length RSm of the contour curve element in the roughness curve is more than 100 μm, 300 μm. And at least 5 Al-based oxides having an equivalent circle diameter of 0.05 μm or more and 1.0 μm or less are present on the 10 μm × 10 μm surface of the hot dip galvanized steel sheet. Hot-dip galvanized steel sheet with excellent antiglare properties.
(2) A hot-rolled steel plate or a cold-rolled steel plate is immersed in a hot dip galvanizing bath having a bath temperature of 450 to 480 ° C., pulled up, and cooled so that the plating surface temperature becomes 400 ° C. or lower within 1 second to 4 seconds. And temper rolling with a work roll having a surface arithmetic average roughness Ra of 1.0 μm or more and 3.0 μm or less and an average length RSm of the contour curve element in the roughness curve of 50 μm or more and 300 μm or less. A method for producing a hot-dip galvanized steel sheet having excellent antiglare properties.
(3) The method for producing a hot-dip galvanized steel sheet having excellent antiglare properties as described in (2), wherein the work roll surface is plated with Cr.

  The hot dip galvanized steel sheet of the present invention has antiglare properties sufficient for practical use over the entire coil length and width. Moreover, the manufacture can be carried out relatively easily and stably. For this reason, it can be used for household appliances, building materials, etc., and its industrial value is extremely high.

  As described above, in addition to increasing the arithmetic average roughness Ra in the roughness curve of the hot dip galvanized steel sheet and reducing the average length RSm of the contour curve element, a fine Al-based oxide is applied to the hot dip galvanized surface. From the knowledge that the antiglare property is improved by dispersing, the present invention will be described in detail below in order.

<Arithmetic mean roughness Ra of plating surface>
The arithmetic average roughness Ra of the plating surface is one of the important factors in the present invention and needs to be 0.3 μm or more and 2.0 μm or less. If Ra is less than 0.3 μm, the surface becomes smooth and gloss cannot be suppressed. On the other hand, when Ra exceeds 2.0 μm, in a thin hot dip galvanized steel sheet with a coating weight of about 20 g / m ² , an extremely thin portion is formed, which is not preferable from the viewpoint of corrosion resistance.

<Average length RSm of contour curve element in roughness curve of plating surface>
The average length RSm of the contour curve element in the roughness curve of the plating surface is also an important factor in the present invention, and needs to be more than 100 μm and 300 μm or less. When RSm exceeds 300 μm, the area where the smooth portion is continuously present becomes large, which is not preferable because gloss is increased. A smaller RSm is preferable, but if it is 100 μm or less, it is not only insufficient from the viewpoint of antiglare properties, but conversely, the degree of unevenness is excessive, which is not preferable because it causes a decrease in corrosion resistance and causes unevenness in post-processing. For this reason, RSm is in a range of more than 100 μm and 300 μm or less.

FIG. 1 shows the results of temper rolling of a hot dip galvanized steel sheet with an extremely low carbon steel plating base plate under various conditions, and examining the surface Ra, RSm and surface gloss. In hot dip galvanizing, the steel sheet was immersed in a hot dip galvanizing bath containing 0.13% Al, pulled up, and then cooled. The amount of zinc adhered per side was about 40 g / m ² . The surface Ra and RSm were measured using a roughness meter manufactured by Tokyo Seimitsu Co., Ltd., Handy Surf E-40A, with an evaluation length of 4 mm, a cut-off value of 0.8 mm, and JIS B 0601 2001. In addition, the gloss is measured using a gloss checker IG-320 manufactured by HORIBA, Ltd. at an incident angle of 60 degrees. When the gloss level is 100 or less, the mark is ○ (pass), and when it is more than 100, the mark is X. (Fail), glossiness is 100 or less, but when the corrosion resistance is rejected, it is represented by Δ mark (fail). The corrosion resistance evaluation was made by cutting a hot-dip galvanized steel sheet into a size of 50 mm (width direction) × 100 mm (rolling direction), bending it at a half angle (50 mm) in the rolling direction at an angle of 60 degrees, and then returning to a flat state. Then, a salt spray test in accordance with JIS Z 2371 was performed, and a red rust occurrence rate after 1000 hours was 20% or less, and a case where it was more than that was rejected. From FIG. 1, when the arithmetic mean roughness Ra of the steel sheet surface is 0.3 μm or more and 2.0 μm or less and the average length RSm of the contour curve element in the roughness curve does not satisfy more than 100 μm and 300 μm or less, It turns out that it passes.

  FIG. 2 shows the relationship between Ra on the work roll surface of temper rolling and Ra on the hot dip galvanized steel sheet surface. The Ra on the surface of the hot dip galvanized steel sheet depends on the Ra on the surface of the work roll. To set the Ra on the surface of the hot dip galvanized steel sheet to 0.3 μm or more and 2.0 μm or less, which is the range of the present invention, It can be seen that Ra needs to be 1.0 μm or more and 3.0 μm or less. Similarly, from FIG. 3, the RSm on the surface of the hot dip galvanized steel sheet also depends on the RSm on the surface of the work roll for temper rolling, and in order to obtain RSm within the scope of the present invention, the RSm on the surface of the work roll is set to 50 μm or more and 300 μm. It turns out that it is necessary.

<Surface Al-based oxide>
On the surface of the hot dip galvanized steel sheet of the present invention, it is necessary that an Al-based oxide be present finely. Originally, Al has a smaller specific gravity than Zn, so when solidified, it concentrates on the hot dip galvanized surface and forms a smooth surface, which has the effect of increasing gloss. Al exists as an oxide. It is estimated that This can also be seen from the fact that one of the purposes of adding Al to the plating bath in the flux-type hot dip galvanizing performed in the air is to improve the surface gloss of the product. However, when the present inventors investigated in detail, it turned out that gloss is reduced conversely by finely dispersing the Al oxide.

  Accordingly, the inventors considered that the distribution and form of the Al-based oxide on the surface of the hot dip galvanizing may affect the antiglare property, and investigated the influence thereof. Here, the Al-based oxide means that when the surface of an arbitrary 10 μm × 10 μm is observed with a secondary electron image under the conditions of an acceleration voltage of 20 kV and an observation magnification of 5000 times using an SEM (scanning electron microscope). In addition, a portion that appears as a dark portion (black portion) than the surroundings, and a portion in which the Al concentration in the dark portion is 5 times or more of the Al concentration in the normal portion when analyzed by EDS (energy dispersive X-ray spectroscopy) After identifying the Al oxide on the surface under these conditions, the equivalent circle diameter and the number thereof are obtained. The result is shown in FIG. If the equivalent circle diameter of the Al oxide is 0.05 μm or more and 1.0 μm or less on the surface of 10 μm × 10 μm and the number thereof is 5 or more, the glossiness is 100 or less, and the corrosion resistance is also evaluated as described above. There was no problem in passing the standards. If the number of Al oxides is less than 5 on the surface of 10 μm × 10 μm, the antiglare property cannot be sufficiently exhibited. The upper limit of the number of Al oxides is not particularly specified, but if it is too large, the corrosion resistance may be deteriorated, and therefore it is preferably 50 or less.

  Further, the form of the Al-based oxide is insufficient for improving the antiglare property when the equivalent circle diameter is less than 0.05 μm. On the contrary, even if Al oxide exceeding 1.0 μm is present, the antiglare property cannot be ensured because it becomes difficult to form fine intricate irregularities on the plating surface.

  The reason why the antiglare property is influenced by the form and distribution of the Al-based oxide is not clear, but the hardness of the Al oxide is higher than that of Zn. In addition to the roughness transfer, it is estimated that non-uniform deformation is introduced into the plating surface and promotes irregular reflection of light. In addition to setting Ra and RSm on the surface of the hot dip galvanized steel sheet within the range of the present invention, the antiglare property is further improved by the synergistic effect by dispersing the Al oxide.

  Next, a method for obtaining such an Al-based oxide form will be described. The inventors have found that the time after the steel sheet is pulled from the hot dip galvanizing bath to reach 400 ° C. and the subsequent temper rolling conditions have a great influence on the conditions after hot dip galvanizing.

  FIG. 5 illustrates the relationship between the cooling time after the hot dip galvanizing and after being pulled up until the surface temperature of the hot dip galvanized steel sheet reaches 400 ° C. or less, and the equivalent circle diameter of the Al oxide. Of the temper rolling conditions for obtaining the predetermined Ra and RSm, under conditions where the grinding effect of the Al oxide is the largest (Ra of the work roll is 3.0 μm, RSm is 60 μm), and the cooling time is 4 seconds, The equivalent circle diameter of the Al oxide is about 1 μm, which is acceptable. When the cooling time exceeds 4 seconds, the Ra of the temper rolling work roll can be increased, or by reducing the RSm, an Al oxide of 1 μm or less can be realized. Or RSm is out of the acceptable range shown in FIG. In addition, when the time from when the steel sheet is pulled up from the hot dip galvanizing bath until it reaches 400 ° C. is less than 1 second, a sufficient amount of Al oxide is not generated, so the cooling time needs to be 1 second or more. There is.

  Next, a method for obtaining the Al-based oxide distribution will be described. FIG. 6 illustrates the relationship between the cooling time after the hot-dip galvanizing and after the hot-dip galvanized steel sheet is pulled up to 400 ° C. or less, and the number of Al oxides. If the cooling time is less than 1 second, the number of Al oxides is less than 5, which is inappropriate. When the cooling time exceeds 4 seconds, depending on the work roll roughness in the subsequent temper rolling, 50 or more Al-based oxides are formed on the surface of 10 μm × 10 μm, and the corrosion resistance deteriorates.

<Plating original plate>
The kind of the original plate of the hot dip galvanized steel sheet of the present invention is not limited. A hot-rolled steel plate or a cold-rolled steel plate may be used. Moreover, although there is no limitation about the component, when considering the use for household appliances and the use of building materials, it is preferable to use an extremely low carbon steel or a low carbon steel as an original plate.

<Plating adhesion amount>
There is no limitation on the plating adhesion. However, preferably, the zinc adhesion amount per one surface of the steel sheet is 20 g / m ² or more and 600 g / m ² or less. If it is less than 20 g / m ² , the corrosion resistance is insufficient, and if it is 600 g / m ² or more, the workability is inferior and is not practical.

<Plating composition>
The amount of the plating composition is not particularly limited as long as it contains Zn and Al. However, preferably, it contains 95% or more of Zn and 0.1% or more and less than 0.2% of Al. Al is an atom essential for improving the antiglare property and also an element useful for improving workability. When Al is less than 0.1%, it is not only an insufficient amount for improving the antiglare property, but also an alloy layer of Zn—Fe grows during plating and is inferior in workability. On the other hand, if it is 0.2% or more, it is more than sufficient for anti-glare property, and if it is added more than that, it will only increase the cost. A particularly preferable range is 0.12% or more and 0.14% or less. If it is this range, it is not only sufficient for the improvement of anti-glare property, but it can also be suppressed that the amount of Al oxide to be produced becomes excessive and the corrosion resistance tends to decrease. In addition, there is no problem even if elements such as Fe, Mg, Si, Mn, Ni, Pb, Cd, and As are included.

  Next, a method for realizing a hot-dip galvanized steel sheet having excellent antiglare properties according to the present invention will be described. The hot dip galvanized steel sheet of the present invention is obtained by immersing a hot-rolled steel sheet or a cold-rolled steel sheet in a hot dip galvanizing bath at a bath temperature of 450 to 480 ° C. Cool so that the temperature is 400 ° C. or lower. As long as a predetermined cooling rate can be ensured, the cooling method is not limited at all. For example, water spray, air-water spray, gas cooling, etc., spraying of a solution containing fine particles such as metal and oxide can be mentioned. By cooling under such conditions, generation of coarse Al oxide is suppressed. The obtained hot-dip galvanized steel sheet has a work roll whose surface has an arithmetic average roughness Ra of 1.0 μm or more and 3.0 μm or less and an average length RSm of contour curve elements in the roughness curve of 50 μm or more and 300 μm or less. Temper rolling with a rolling reduction of 3% or less.

  By rolling under such conditions, the Al oxide concentrated on the surface is crushed to a particle size of 0.05 μm or more and 1.0 μm or less, effectively diffuses light, and roughens the surface of the work roll. Combined with the degree transfer, a hot-dip galvanized steel sheet with excellent antiglare properties can be realized. When cooling cannot be performed at the above cooling rate, a coarse Al oxide is formed, and even when rolled under the temper rolling conditions, the Al oxide is not sufficiently divided, so that the glossiness cannot be reduced. On the other hand, when the temper rolling condition is outside the above range, the Al oxide cannot be effectively divided, or the arithmetic average roughness Ra of the hot dip galvanized surface, or the average length of the contour curve element in the roughness curve RSm is not suitable because it falls outside the scope of the present invention.

  In addition, it is preferable to use the work roll which provided the predetermined roughness and gave the hard surface treatment to the work roll of temper rolling. By applying the hard surface treatment, the wear of the roll is reduced and the antiglare property is improved. This is presumed to be due to the fact that the crushing of the Al-based oxide on the hot-dip galvanized surface layer by the work roll works favorably on the antiglare property by the hard surface treatment layer. Examples of the hard surface treatment include Cr plating, Ni-W plating, and W thermal spraying. FIG. 7 shows the relationship between the rolling length and the equivalent circle diameter of the Al oxide when a solid work roll is used as the temper rolling work roll and a work roll whose surface is plated with Cr is used. The work roll roughness before rolling is the same for both Ra 2.5 μm and RSm 160 μm, but the equivalent circle diameter of the Al oxide is smaller when Cr plating is used.

  An ultra-low carbon steel cold-rolled steel sheet is annealed at 800 ° C. for a predetermined time, dipped in a hot dip galvanizing bath containing 0.13% Al and having a bath temperature of 450 ° C., and is pulled in 0.5 to 5 seconds. It cooled so that the plating surface temperature might be 400 degrees C or less. Then, temper rolling with a reduction rate of 2% is performed with a solid work roll having an arithmetic average roughness Ra of 0.6 μm to 4.0 μm and an average length RSm of the contour curve element in the roughness curve of 40 μm to 340 μm. did. Ra and RSm of the surface of the obtained hot-dip galvanized steel sheet were measured by the above-mentioned roughness measurement method, and the Al oxide was identified by the above-described analysis method on the plating surface, and the equivalent circle diameter and number were measured. .

  The gloss measurement was also evaluated by the above-described method, and the corrosion resistance test was also performed in the same manner as described above. The red rust occurrence rate after 1000 hours was 20% or less, and the case where it was more than that was × Expressed with a mark. The results are shown in Table 1. From these results, the Ra, RSm on the steel sheet surface that satisfies the scope of the present invention and the equivalent circle diameter and number of Al oxides are excellent in anti-glare properties after plating, and there is also a problem in corrosion resistance. I understand that there is no.

  An ultra-low carbon steel cold-rolled steel sheet is annealed at 800 ° C. for a predetermined time, immersed in a hot dip galvanizing bath containing 0.13% Al and having a bath temperature of 450 ° C., and plated in 0.5 to 6 seconds. It cooled so that surface temperature might be 400 degrees C or less. Then, temper rolling with a reduction rate of 2% is performed with a solid work roll having an arithmetic average roughness Ra of 0.6 μm to 4.0 μm and an average length RSm of the contour curve element in the roughness curve of 40 μm to 340 μm. did. The obtained hot-dip galvanized steel sheet was evaluated for Ra, RSm, equivalent circle diameter and number of Al oxides, glossiness, and corrosion resistance by the same methods as in Example 1. The results are shown in Table 2.

  From these results, the Ra, RSm on the steel sheet surface that satisfies the scope of the present invention and the equivalent circle diameter and number of Al oxides are excellent in anti-glare properties after plating, and there is also a problem in corrosion resistance. I understand that there is no.

  An ultra-low carbon steel cold-rolled steel sheet is annealed at 800 ° C. for a predetermined time, dipped in a hot dip galvanizing bath containing 0.13% Al and having a bath temperature of 450 ° C., and the plating surface temperature is about 2 seconds. It cooled so that it might become 400 degrees C or less. Then, using a solid steel work roll having an arithmetic mean roughness Ra of 2.5 μm on the surface and an average length RSm of the contour curve element in the roughness curve of 160 μm, or a work roll having Cr plated on the surface, Temper rolling was performed at a rate of 2%. Ra and RSm of the obtained hot-dip galvanized steel sheet and the equivalent circle diameter and number of Al oxides were examined by the same method as in Example 1. The results are shown in Table 3. When compared with a solid roll having the same Ra and RSm, and a Cr plated roll, the equivalent circle diameter of the Al oxide is smaller and the number is larger and the antiglare property is better when using the Cr plated roll than the solid roll. On the other hand, more favorable results were obtained.

It is the figure which investigated Ra, RSm, and surface glossiness of the hot dip galvanized steel plate surface. It is a figure which shows the range of the glare-proof pass by the relationship between Ra of the work roll surface of temper rolling for every RSm, and Ra of the hot dip galvanized steel plate surface. It is a figure which shows the range of the glare-proof pass by the relationship between RSm of the work roll surface of temper rolling for every Ra, and RSm of the hot dip galvanized steel sheet surface. It is a figure which shows the range of the glare-proof pass by the relationship between the circle equivalent diameter and number of Al oxides of the hot dip galvanized steel sheet surface. It is a figure showing the relationship between the cooling time after hot-dip galvanization and pulling up until the surface temperature of a hot-dip galvanized steel plate becomes 400 degrees C or less, and the equivalent circle diameter of Al oxide. It is a figure showing the relationship between the cooling time until the surface temperature of a hot dip galvanized steel plate becomes 400 degrees C or less, and the number of Al oxides. It is a figure showing the relationship between the rolling length and the equivalent circle diameter of the Al oxide when a solid work roll or a Cr plating work roll is used as a temper rolling work roll.

Claims (3)

  In the roughness curve of the plated surface of the hot dip galvanized steel sheet, the arithmetic average roughness Ra is 0.3 μm or more and 2.0 μm or less, and the average length RSm of the contour curve element in the roughness curve is more than 100 μm and 300 μm or less. Further, at least 5 Al-based oxides having an equivalent circle diameter of 0.05 μm or more and 1.0 μm or less are present on the surface of 10 μm × 10 μm of the hot dip galvanized steel sheet. Hot-dip galvanized steel sheet with excellent resistance.   A hot-rolled steel sheet or a cold-rolled steel sheet is immersed in a hot dip galvanizing bath with a bath temperature of 450 to 480 ° C., pulled up, cooled so that the plating surface temperature becomes 400 ° C. or less within 1 second to 4 seconds, and the surface Antiglare, characterized by performing temper rolling with a work roll having an arithmetic average roughness Ra of 1.0 μm or more and 3.0 μm or less and an average length RSm of contour curve elements in the roughness curve of 50 μm or more and 300 μm or less A method for producing hot-dip galvanized steel sheets with excellent properties.   The method for producing a hot-dip galvanized steel sheet having excellent antiglare properties according to claim 2, wherein Cr plating is applied to the work roll surface.

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