JPH0318961B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention eliminates the spangle pattern of the plated metal layer without impairing the formability of the steel plate and creates a beautiful surface by temper rolling of a molten aluminum plated steel plate in a molten aluminum plating line. Concerning how to form the skin. [Prior Art] The manufacturing process of galvanized steel sheets using a continuous molten aluminum plating line will be explained with reference to Fig. 1. A steel strip (S) sent out from a steel strip coil (C1) at a predetermined line speed is transferred to a pre-annealing furnace. 1, after undergoing softening and surface cleaning treatment (reduction removal of rolling oil, scale, etc.), it passes through a molten aluminum plating bath 2, and is melted by a jet of gas from a blowing nozzle 3 above the bath. After the surplus amount of aluminum is blown off and adjusted to a predetermined basis weight, it is cooled at a predetermined cooling temperature while passing through the cooling zone 4. The steel sheet whose plated metal layer is cooled and solidified through the cooling zone 4 is used for various purposes.
Depending on the required quality, it is temper rolled in a skin pass mill 7 and then wound into a coil C2 to become a product. The thus obtained molten aluminum plated steel sheet has a mottled pattern called spangle on its surface. Spangles are aluminum crystal grains that are generated and grown during the cooling and solidification process of the plated metal layer, and remain as a mottled pattern on the product surface without being completely removed by temper rolling or the like. The boundaries of the spangles form a groove-like network, and the grain size of the spangles and the depth of the grooves at the grain boundaries (grain boundary depth) are determined by the thickness of the steel sheet, the thickness of the plated layer,
It varies depending on the cooling rate of the plating metal, etc., but usually,
The grain size is approximately 3-10 mm, and the grain boundary depth is 3-7 μm. Spangle patterns do not have a negative effect on the plating quality (corrosion resistance, workability, etc.), but they impair the beauty of the product and reduce its value. , which causes diffused reflection and a decrease in reflection efficiency, is required to have a uniform and beautiful surface texture without spangle patterns. As a method for eliminating this spangle pattern without impairing the aesthetic appearance of the product and causing no actual damage in use, a method is known in which the die roll is used as a work roll of a skin pass mill and the rolling load is increased to perform temper rolling. This transfers the matte surface of the die roll to the surface of the plated metal layer, forming fine irregularities on the surface of the spangle, and finely dividing the spangle grain boundaries, thereby erasing the spangle pattern. The work roll diameter differs depending on the type of skin pass mill, but that of a multiple skin pass mill in a melt plating line is approximately
It is 300-350mm. [Problems to be Solved by the Invention] Temper rolling is cold rolling that gives a steel strip an elongation rate of about 0.5 to 1.5% for the purpose of eliminating elongation at yield point and correcting the shape. The rolling load per unit width during temper rolling is approximately 100 to 150 kgf/mm.
That's about it. However, under these temper rolling conditions, the effect of transferring the satin texture of the dull roll to the surface of the plated metal layer is small, and it is impossible to sufficiently erase the spangle pattern. As mentioned above, when temper rolling is performed at a high rolling load for the purpose of eliminating the spangle pattern, the elongation rate of the steel sheet becomes unreasonably large even though the spangle pattern can be eliminated, resulting in a decrease in the workability of the steel sheet.
Subsequent molding processes, such as press molding and drawing, become difficult. When temper rolling is performed in a hot-dip galvanizing line, the elongation rate of the steel sheet increases significantly.
The reason for this is that the steel plate transfer speed (line speed) in a hot-dip galvanizing line is usually 30 to 200 m/min due to the hot-dipping technology and annealing process, and the line speed in a cold rolling line (about 500 to 200 m/min). 1000m/min)
Unlike temper rolling in a cold rolling line, the strain rate (ε) of the steel plate is lower, and the deformation resistance (σk・μ) of the steel plate is accordingly lower. Therefore, the same rolling load Even so, the elongation rate of the steel sheet becomes unreasonably large. As a countermeasure, it is possible to reduce the rolling load and increase the number of skin pass mills, but to do so, it is necessary to install multiple stages of skin pass mills,
It is not an effective countermeasure because it requires multiple passes, and as the number of passes increases, the elongation rate of the steel plate increases. The present invention has been made in view of the above,
During temper rolling in a continuous molten aluminum plating line, the original purpose of temper rolling is achieved without impairing the workability of the steel plate, and at the same time, the spangle pattern on the surface of the plated metal layer is eliminated, resulting in a beautiful surface texture. Provided is a method for improving the surface texture of a hot-dip aluminum plated steel sheet. [Means and effects for solving the problem] The first method for improving surface texture according to the present invention provides a continuous molten aluminum plating line with a maximum height (μRmax) of 10 to 30 and a number of peaks (PPI) of 100 to 30. Rolling load per unit width of 250 to 400 kgf/
The feature is that the hot-dip galvanized steel plate is temper-rolled in mm. The second method for improving surface texture of the present invention is to subject a hot-dip galvanized steel plate to temper rolling using the dull roll described above in a continuous hot-dip aluminum plating line, and then to use a bright roll with a roll diameter of 400 mm or more as a work roll. It is characterized in that skin pass rolling is carried out at a rolling load of 300 to 350 Kgf/mm per unit width using a multiple skin pass mill. According to the first method of the present invention, in a skin pass mill in which a dull roll in a continuous molten aluminum plating line is used as a work roll, the aluminum-plated steel plate has a relatively high temperature so as to sufficiently transfer the matte surface of the dull roll. Despite being rolled down by the rolling load, the elongation rate of the steel plate does not become unreasonably high as in conventional methods, and it is possible to perform skin pass rolling on a normal cold rolling line (threading speed: approx. 500~
1000m/min), the desired temper rolling is achieved without impairing the workability of the steel plate, and at the same time, the spangle pattern is erased by the transfer effect of the matte surface of the dull roll, covering the entire surface of the plated steel plate.
A uniform and beautiful satin skin is formed. According to the second method of the present invention, the surface of the galvanized steel sheet having a matte surface formed by the temper rolling is subjected to temper rolling using a bright roll,
By transferring the glossy surface of the bright roll, the surface of the plated metal layer is finished as a glossy and smooth surface. Next, the reasons for limiting the temper rolling conditions in the present invention will be explained. The reason why temper rolling is performed using a multiple skin pass mill using dull rolls as work rolls is to apply a uniform rolling force over the entire surface of the steel sheet. A multi-skin pass mill is a 4-skin pass mill consisting of a pair of work rolls and a back-up roll that contacts the back surface of the rolls to apply the rolling load, or a 4-skin pass mill that consists of a pair of work rolls and a back-up roll that applies a rolling load to the back surface of each work roll, or a back-up roll that applies a rolling load to the back surface of each of the pair of work rolls. Examples include a 6-high-skin pass mill in which an uproll comes into contact. Unlike skin pass mills that do not have intermediate rolls or back-up rolls, these multiple skin pass mills have extremely little axial deflection of the work rolls and apply uniform rolling force across the entire width of the plated steel plate. Therefore, a predetermined skin pass rolling effect and surface texture improvement effect can be obtained over the entire surface of the steel plate. The roll diameter of the dull roll should be 450mm or more.
This is to perform temper rolling at a high rolling load (250 Kgf/mm or more per unit width) necessary to eliminate the spangle pattern without excessively increasing the elongation rate of the steel sheet. The larger the roll diameter, the lower the elongation rate of the steel plate under the same rolling load.When rolling with the same elongation rate, a larger rolling load is permissible. The transfer rate of satin texture to the surface is increased. Therefore, the larger the diameter of the dull roll is, the more advantageous it is in terms of suppressing an unreasonable increase in the elongation rate of the steel sheet and enhancing the effect of transferring the satin texture of the dull roll. However, as the roll diameter increases, the equipment becomes larger and the cost increases, so it goes without saying that these points should be taken into consideration when determining the actual roll diameter. In practice, the roll diameter may be up to about 650 mm, and there is no need to increase the roll diameter even though the disadvantages described above may be incurred. The reason for setting the rolling load per unit width of temper rolling using dull rolls to be 250 Kgf/mm or more is because if it is lower than that, the effect of transferring the matte texture of the dull rolls to the surface of the plated metal layer will be insufficient, and the erasure of the spangle pattern will be insufficient. Because it will be. As the rolling load increases, the transfer rate of the dull roll matte surface [ratio between μRmax (A) of the roll surface and μRmax (B) of the matte surface transferred to the mated metal layer, B/A × 100 (%)]
However, the satin texture transfer rate necessary to completely erase the spangle pattern can be sufficiently secured at a rolling load of 400 Kgf/mm or less. If a sufficient effect of erasing the spang pattern can be obtained, there is no need to further increase the rolling load, and not increasing the rolling load unnecessarily means that the elongation rate of the steel sheet will be lower and the workability of the product will be higher. This is preferable in that it is maintained at . For this reason, the upper limit was set at 400Kgf/mm. Dull roll has a maximum height (μRmax) of 10 to 30
A material having a surface roughness with a number of peaks (PPI) of 100 to 250 is used. Here,
μRmax is an index of surface roughness specified in JIS B 0601, and the number of peaks (PPI) is the number of peaks per inch of length (Peaks per Inch). By using dull rolls with such surface roughness, unevenness with a depth equal to or greater than the grain boundaries of spangles (the grain boundary depth is usually 3 to 7 μm) is uniformly and finely transferred to the surface of the plated metal layer of the steel sheet. This makes it possible to obtain a sufficient spangle elimination effect. Since the surface of the galvanized steel sheet formed by the first method of the present invention exhibits a satin texture, if a glossy surface is required depending on the use of the steel sheet, the surface of the galvanized steel sheet formed by the first method of the present invention may be coated with a dull roll according to the second method of the present invention. After the skin pass rolling, the material is subjected to skin pass rolling using a multi-skin pass mill using bright rolls as work rolls. The reason why this skin pass rolling is performed using a multiple skin pass mill is to apply a uniform rolling force over the entire width of the steel plate, similar to that in skin pass rolling using dull rolls, and to apply a uniform rolling force to the shiny surface of the bright roll. This is to make the transfer uniform. The reason why the roll diameter of the bright roll is set to 400 mm or more is to prevent the elongation rate of the steel sheet from becoming unduly high during temper rolling. As the roll diameter increases, the steel plate elongation rate under the same rolling load decreases, and the rolling load can be increased accordingly to strengthen the transfer effect of the glossy surface of the roll. Therefore, the larger the roll diameter, the more advantageous it is. . However, as in the case of the dull rolls, it goes without saying that when designing the actual roll diameter, it should be decided on an individual basis, taking into consideration the increase in the size of the device accompanying the expansion of the roll diameter. The surface roughness of the roll is similar to that conventionally used (for example,
μRmax: 0.2 to 0.5). The reason why the lower limit of the rolling load per unit width of temper rolling using the bright roll is set to 300 Kgf/mm is to ensure the transfer effect of the bright roll glossy surface to the surface of the plated metal layer. As the rolling load increases, the transfer rate of the glossy surface of the roll increases, but the transfer rate for converting a matte surface into a good glossy smooth surface is sufficiently secured at a rolling load of 350 Kgf/mm or less. If a sufficient glossing effect of the plated metal layer is obtained, there is no need to further increase the rolling load, and as long as the rolling load is not increased unnecessarily, the elongation rate of the steel sheet will be lower and the product will require more advanced processing. 350Kg because it is preferable in terms of maintaining its properties.
The upper limit was f/mm. The temper rolling in the present invention may be performed by either a wet skin pass mill method in which tempering oil is interposed at the contact interface between the work roll and the surface of the steel sheet, or a dry skin pass mill method in which tempering oil is not used. However, the dry skin pass mill system is advantageous over the wet skin pass mill system in that the transfer rate can be increased. [Example] Example 1 On the continuous hot-dip aluminum plating line shown in Fig. 1, a hot-dip aluminum plated steel plate was manufactured,
Next, temper rolling is performed in a multi-skin pass mill 7 where the work roll is a dull roll to form a coil (C2).
A product with satin skin was obtained by winding it up. The spangle grain size of the plated metal layer of the test material before temper rolling is 3 to 10 mm, and the grain boundary depth is 3 to 7 μm. [] Hot-dip plating conditions (1) Original sheet: low carbon rimmed steel. Board thickness 0.8mm, board width 914mm. (2) Line speed: 100m/min (3) Plating bath temperature: 650℃. (4) Weight: 60g/ ^m2 /single side [] Skin-pass rolling conditions and product quality Table 1 [] shows the skin-pass rolling conditions and the elongation rate of the steel plate during skin-pass rolling, and the table [] shows the products. The tensile properties, which are indicators of surface quality and workability, are shown below. Nos. 11 to 15 are invention examples, and Nos. 101 to 104 are comparative examples. In the table, the "Skin texture" column of "Surface quality" is the result of naked eye observation of the spangle pattern on the product surface, "a" means that the spangle pattern is not visible at all, and "b" means that the spangle pattern remains. Each represents a different thing. Regarding the above test results, looking at Comparative Examples No. 101 to 104, No. 101 and No. 102 have a significantly high elongation rate of steel plate after temper rolling, and their products completely eliminate the spangle pattern and eliminate the yield point elongation. Although this has been fully achieved, it is hard and has low ductility, and its Rankford value and work hardening index (n value), which are important indicators of drawability, are also low. No.103 and No.104
The elongation rate of the steel plate in temper rolling is reasonable, but the above
Contrary to No.101 and No.102, it is soft and highly ductile, and the value and n
Although there is no problem with the value, the effect of erasing the spangle pattern is insufficient. In other words, in temper rolling using a dull roll with a normal roll diameter as a work roll, if an attempt is made to sufficiently eliminate the spangle pattern, the elongation rate of the steel sheet becomes unreasonably high, impairing workability (No. 101, 102). Furthermore, if an attempt is made to set the elongation rate of the steel plate to an appropriate value without impairing workability, the effect of erasing the spangle pattern is insufficient and the surface quality cannot be sufficiently improved (No. 103, 104). On the other hand, in Invention Examples Nos. 11 to 15, the elongation rate of the steel plate during skin pass rolling is appropriate, and the products are soft and highly ductile, not to mention that the yield point elongation has been sufficiently eliminated. In addition, the value and n value are at high levels, and the spangle pattern has been completely eliminated, satisfying both requirements for improved surface quality and good workability. Example 2 In the continuous molten aluminum plating line shown in Fig. 1 (however, a 4-high-skin pass mill using a bright roll (not shown) as a work roll is installed at the rear of the skin pass mill 7), a molten aluminum-plated steel plate was produced. A product having a glossy skin was obtained by performing skin pass rolling using a multiple skin pass mill 7 using a dull roll as a work roll and skin pass rolling using a multiple skin pass mill using a bright roll as a work roll. The molten aluminum plating conditions and the spangle grain size and grain boundary depth of the plated metal layer before temper rolling were the same as those in Example 1. The above temper rolling conditions and steel plate elongation rates during temper rolling are shown in Table 2 [], and the tensile properties that are indicators of the surface quality and workability of the obtained products are shown in the same table [].
Nos. 21 to 25 are invention examples, and Nos. 201 to 204 are comparative examples.
In the table, the "Skin Texture" column under "Surface Quality" shows the evaluation of the spangle pattern and gloss by visual observation of the product surface. "A" in the same column indicates that the spangle pattern is not visible at all and the surface has a good gloss, and "B" indicates that the surface is glossy and smooth but the spangle pattern remains. (The degree of gloss of A and B is substantially the same, and the values of their surface roughness μRmax are both close to that of the bright roll). In Table 2, a comparative example (No. 201 ~204), No. 201 and No. 202 have a high elongation rate during temper rolling, and while their products have sufficiently resolved yield point elongation, eliminated spangle patterns, and made them glossy, , hard, low ductility, and low value and n value. On the other hand, the elongation rate of the steel sheets in No. 203 and No. 204 during temper rolling is appropriate, the elongation at yield point has been sufficiently resolved, and they are soft and highly ductile with high value and n value. The spangle pattern remains. That is, it is not possible to simultaneously satisfy the requirements of forming a glossy smooth surface with no spangle pattern and maintaining good workability. On the other hand, in Invention Examples Nos. 21 to 25, temper rolling with an appropriate elongation rate of the steel sheet was performed, and the resulting products were not only sufficiently free of yield point elongation but also soft and
It is highly ductile, has a high value and n value, and has a sufficiently glossy surface without a spang pattern.

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〔Effect of the invention〕

According to the method of the present invention, it is possible to obtain a molten aluminum-plated steel sheet that has a satin finish or glossy surface with good surface texture quality in which the spangle pattern has been eliminated, elongation at yield point has been eliminated, and has good workability. The molten aluminum-plated steel sheet obtained by the present invention has excellent surface quality and workability, so it can be used as a heat reflector 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 interior and exterior panels, structural members of incinerators, chimneys, drying furnace ventilation equipment, and various other uses.

[Brief explanation of drawings]

FIG. 1 is a process diagram showing an example of a continuous melt-melting line. 1: Annealing furnace, 2: Melting bath, 4: Cooling zone, 7: Skin pass mill.

Claims (1)

[Claims] 1. In a continuous hot-dip aluminum plating line, a maximum height (μRmax) of 10
~ 30, with a surface roughness of 100 to 250 peaks (PPI) and a multi-skin pass mill that uses dull rolls with a roll diameter of 450 mm or more as work rolls to perform temper rolling at a unit width rolling load of 250 to 400 Kgf/mm. A method for improving the surface texture of molten aluminum plated steel sheets. 2 In a continuous hot-dip aluminum plating line, the maximum height (μRmax) of 10
~ 30, with a surface roughness of 100 to 250 peaks (PPI) and a dull roll with a roll diameter of 450 mm or more as a work roll. After temper rolling at a unit width rolling load of 250 to 400 Kgf/mm, the roll is rolled. A method for improving the surface texture of a hot-dip aluminum plated steel sheet, which comprises performing temper rolling at a unit width rolling load of 300 to 350 Kgf/mm using a multiple skin pass mill using a bright roll with a diameter of 400 mm or more as a work roll.