JPH11302816A - Manufacture of hot dipped steel strip having excellent surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a hot dipped steel strip having excellent surface where a spangle pattern is perfectly eliminated. SOLUTION: At the time of applying temper rolling to a hot dipped steel strip after cooling, the hot dipped steel strip is temper rolled by means of a work roll 10 to which matt finish treatment is applied by allowing many craters 15 formed by electron beam machining to overlap each other. At the time of electron beam machining, it is desirable to form the crators in the peripheral surface of the roll under the condition of density distribution where the inside dismeter D and the length L between adjacent craters are 0.07 to 0.20 mm and 0.06 to 0.18 mm, respectively, and D>L is satisfied. Unlike those in the case of shot blasting, the size, pattern, and density distribution of the crators can be easily controlled by means of output and position adjustment at the time of electron beam machining.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-dip coated steel strip having a uniform surface without spangles.

[0002]

2. Description of the Related Art In a continuous hot-dip galvanizing line, as schematically shown in FIG. 1, a steel strip 2 unwound from an unwinding reel 1 is reduced in a reduction annealing furnace 3 to activate the surface, and then a snout 4 And then introduced into the hot-dip plating bath 5. Hot-dip plating bath 5
After adjusting the adhesion amount of the hot-dip plating metal pulled up from the wiping device 6, it is sent to a cooling zone 7 such as an alloying furnace,
Let cool under predetermined conditions. Hot-dip galvanized steel strip 2 after cooling
Is temper-rolled by a skin pass roll 8 and wound on a take-up reel 9. Since crystal growth proceeds during the process of solidification of the hot-dip metal from the molten state, spangles are liable to occur in the hot-dip coating layer formed on the surface of the steel strip 1. In particular, spangles are remarkably generated in a hot-dip Al plating layer cooled from a high temperature.

The spangle pattern does not adversely affect the plating quality such as corrosion resistance and workability, but deteriorates the surface appearance and reduces the commercial value. Further, in applications as a heat reflection plate for heating equipment, cooking equipment, etc., diffuse reflection is promoted and reflection efficiency is reduced. For this reason, a hot-dip steel strip having a uniform surface without spangles is desired. The spangle pattern is eliminated by temper rolling with a temper rolling roll 8 using a dull roll as a work roll. In this method, the matte surface of the dull roll is transferred to the surface of the hot-dip coating layer, and fine irregularities are formed on the surface of the spangle, and the spangle pattern is finely divided to eliminate the spangle pattern.

[0004]

In temper rolling using dull rolls, the spangle pattern disappears as the load is increased. However, a high load increases the elongation of the steel strip 1,
Decreases workability such as press formability and deep drawability. In order to ensure workability, the additional load during temper rolling is limited, and as a result, the skin pass rolling skin pass with the reduced rolling load must be repeated a plurality of times. As a countermeasure, Japanese Patent Publication No. 3-18961 discloses that a spangle pattern can be eliminated without excessively increasing the rolling load by using a work roll having a regulated surface roughness. Here the work rolls to be used is in the satin skin with the maximum height R _max 10 to 30 [mu] m, per unit length of the elevated portions 100 to 250 pieces / surface roughness inches. This matte skin is usually finished by shot blasting. However, even in temper rolling using a work roll having a matte surface with regulated surface roughness, according to subsequent studies by the present inventors, in order to completely eliminate the spangle pattern, the temper rolling of It was found that multiple repetitions were necessary. In this regard, if the spangle pattern can be eliminated by one pass-pass rolling, the equipment load, production cost, delivery date, etc. are greatly reduced, and maintenance becomes easy.

[0005]

DISCLOSURE OF THE INVENTION The present invention has been devised in order to meet such a demand, and a spangle pattern can be effectively formed by using a work roll subjected to satin finish by electron beam processing. An object of the present invention is to eliminate quenching and to reduce the addition of temper rolling to obtain a hot-dip galvanized steel strip having a good surface texture. The production method of the present invention, in order to achieve the object, when tempering rolling after cooling the hot-dip coated steel strip, a plurality of craters formed by electron beam processing are superimposed on each other with a satin-finished work roll. It is characterized by temper rolling of a hot-dip coated steel strip. In electron beam processing, it is desirable to form a crater on the roll peripheral surface with an inner diameter D = 0.07 to 0.20 mm, an adjacent distance L = 0.06 to 0.18 mm, and a density distribution where D> L. Unlike the shot blast, the size, pattern and density distribution of the crater can be easily controlled by adjusting the output and position during electron beam processing.

[0006]

[Function] In the conventional satin finish processing by shot blast,
Fine-grained shots are sprayed at high speed on the peripheral surface of the roll, and traces of collision of the shots are formed as recesses. For this reason, the peripheral surface of the work roll 10 that has undergone the satin finish has a satin finish made up of a number of concave portions 11 as illustrated in FIG.
However, since the recess 11 is formed by the impact of the shot, it is difficult to control the size and distribution of the recess 11. Also, the initial surface 12 which is not affected by the shot
Tends to remain after shot blasting. The present inventors presumed that the spangle pattern was not stably and efficiently erased due to such a pear surface caused by shot blasting.

[0007] Therefore, it has been studied to perform a satin finish by electron beam processing instead of shot blasting. Electron beam processing is a method of irradiating a roll peripheral surface with an electron beam having a high energy density to perform surface processing, and is excellent in processing accuracy, uniformity, and reproducibility. At the place where the electron beam collided,
As shown in FIG. 3A, a crater 13 in which the material is excavated by the electron beam is generated. Around the crater 13, there is a rim 14 into which the cut material has moved. Since the crater 13 and the rim 14 are instantaneously heated and cooled by the electron beam, they have a hard martensitic structure.

In the electron beam processing, the irradiation portion can be adjusted with high precision, so that the distribution control of the crater 13 is easy. Therefore, as shown in FIG. 3B, when a crater 13 formed by one electron beam and a crater formed by another electron beam are overlapped, a crater 15 is formed by combining the two. The composite crater 15
The difference is that the rim 14 is sharpened, and the initial surface 12 (FIG. 2) is completely destroyed.
Adjacent craters are easily overlapped by adjusting the relative movement distance of the spot connected to the roll peripheral surface during electron beam processing. That is, the inner diameter of the crater 13 formed by one electron beam is set to be larger than the crater adjacent space. As a result, as shown in FIG. 4, a large number of composite craters 15 form a roll peripheral surface formed on the surface,
Most of the rim 14 around each composite crater 15 is also sharpened.

The crater 13 formed by one electron beam irradiation has an inner diameter of 0.07 to 0.07 due to the output control of the electron gun.
It can be adjusted to the range of 0.20 mm. Therefore, the distance between adjacent portions smaller than the inner diameter (specifically, 0.06 to 0.18
mm) and the adjacent craters 13
０．２0.20 composite crater 15. In consideration of sink marks at the spangle grain boundary, sink marks cannot be eliminated with a crater having an inner diameter of less than 0.07 mm. Conversely, with a large inner diameter exceeding 0.20 mm, the contact area of the steel strip with the roll is reduced, and a spangle pattern is formed. It cannot be erased efficiently. The composite crater 15 is preferably formed with a density such that the area ratio of the convex portion of the work roll in contact with the hot-dip coated steel strip is 30% or more. In other words, if the area ratio of the concave portion of the work roll exceeds 70%, the contact area of the steel strip with the roll becomes small, and the elimination of the spangle pattern becomes insufficient.

[0010] The effects of shot blasting and electron beam processing on the erasure of spangled patterns differ greatly depending on the roll surface that has been matted. When temper rolling is performed using a work roll subjected to satin finish processing by shot blast, the roll peripheral surface (FIG. 2) having the concave portion 11 and the initial surface 12 is transferred to the hot-dip plating layer. That is, in the hot-dip plated layer subjected to the temper rolling, a portion corresponding to the concave portion 11 is raised, and a portion corresponding to the initial surface 12 is a flat portion where the pressure is reduced. There is a large difference in gloss between the raised portion and the flat portion, and as a result, uneven gloss is generated in the hot-dip coated steel strip.
Although the difference in gloss is reduced by the multi-stage temper rolling, this does not improve productivity or equipment burden. On the other hand, when temper rolling is performed using a work roll (FIG. 4) on which the composite crater 15 and the sharp rim 14 are formed, the ridges and grooves corresponding to the composite crater 15 and the sharp rim 14 are hot-dipped. Formed on the layer surface. The raised portion has a shape rising from the reference surface of the hot-dip plating layer, and the groove around the raised portion has an annular and independent shape. Also,
The height of the rim 14 can be controlled over a wide range and there is no portion of the initial surface 12 (FIG. 2) that is reduced. Therefore, even in the case of one-time temper rolling, the hot-dip-coated steel strip after temper rolling has no gloss unevenness and exhibits a high-quality surface skin from which spangle patterns are completely eliminated.

[0011]

[Example] 5% Cr having a diameter of 660 mm and a body length of 1400 mm
The surrounding surface of the forged steel work roll was matte-finished by electron beam processing. In the electron beam processing according to the present invention, FIG.
As shown in FIG.
The irradiation position was set so as to occupy the vertex and the center of the 1 mm hexagon, and the irradiation conditions were set so that the crater 13 having an inner diameter of 0.13 mm and a depth of 0.011 mm was formed. Under this condition, adjacent craters 13 overlap each other,
The composite crater 15 had an inner diameter of 0.05 mm and a depth of 0.011 mm. Also, with the formation of the composite crater 15, the flat initial surface 12 (FIG. 2) has completely disappeared.
Plate thickness of hot-dip Al plated with a basis weight of 60 g / m ² .
After cooling the steel strip of 8 mm, the elongation rate is 0.8% by the temper rolling roll 8 incorporating the satin-finished work roll.
Temper rolling.

[0012] The surface of the temper-rolled hot-dip Al-coated steel strip was observed to check for the presence of a spangle pattern. The survey results, for the purpose of comparison, R _max 24.0μ in the shot blast
The results are shown in Table 1 together with the case where temper rolling was performed using a work roll that had been subjected to a satin finish treatment to a surface roughness of m, a number of peaks of 60 / cm (comparative example). As shown in Table 1, in the comparative example using the work roll subjected to the satin finish treatment by the shot blast, a spangle pattern was left though slightly. Further, a portion where the glossiness was locally increased by the reduction by the work roll was also detected. In order to completely eliminate the spangle pattern, it was necessary to repeat the temper rolling twice or more.

On the other hand, in Test Nos. 1 and 2, in which a large number of craters having an inner diameter D and an adjacent distance L according to the present invention were temper-rolled using a work roll formed by electron beam processing, one test was performed. The spangle pattern was completely erased by the temper rolling, and no gloss unevenness was detected. The surface skin obtained in this case is almost the same as the surface skin of Test No. 6 in which the temper rolling was repeated twice, and it can be seen that the number of steps is reduced by half. However, when the inner diameter D and the distance L between adjacent portions did not satisfy the conditions specified in the present invention, spangle removal was not sufficient as shown in Test Nos. 3 and 4 even under similar rolling conditions. As is clear from this comparison, the use of a temper rolling roll incorporating a work roll formed by electron beam processing of a large number of craters having a regulated inner diameter D and adjacent distance L results in an effect of the unevenness of the roll peripheral surface. The hot-dip galvanized steel strip is transferred to the hot-dip coating layer, and has a good surface without spangles.

[0014]

[0015]

As described above, in the present invention, the hot-dip coated steel strip is temper-rolled using a work roll that has been subjected to high-accuracy satin finishing by electron beam processing. The peripheral surface of the work roll is an uneven surface where a number of craters are superimposed, and the peripheral surface of the roll is transferred to the hot-dip coating layer, so that spangle patterns are efficiently erased and a uniform and high quality surface skin is obtained. Hot-dip coated steel strip is easily manufactured.

[Brief description of the drawings]

Fig. 1 Schematic of continuous hot-dip plating equipment

Fig. 2 Peripheral surface of a work roll subjected to satin finish treatment by shot blast

FIG. 3 is a schematic diagram showing a crater (a) formed on a roll peripheral surface by electron beam irradiation and a roll peripheral surface (b) on which adjacent craters are superimposed.

FIG. 4 is a schematic view showing a peripheral surface of a work roll subjected to a satin finish according to the present invention;

FIG. 5 is a layout diagram of craters on a peripheral surface of a work roll subjected to a satin finish according to the present invention.

[Explanation of symbols]

1: Unwinding reel 2: Steel strip 3: Reduction annealing furnace
4: Snout 5: Hot-dip plating bath 6: Wiping device 7: Cooling zone 8: Temper rolling roll 9: Winding reel 1
0: Work roll 11: Recess 12: Initial surface
13: Crater 14: Rim 15: Composite crater

Claims (2)

[Claims] When a hot-dip steel strip is cooled and skin-pass-rolled, a large number of craters formed by electron beam processing are superimposed on each other, and the hot-dip coated steel strip is temper-rolled with a work roll subjected to a satin finish treatment. A method for producing a hot-dip galvanized steel strip having an excellent surface texture characterized by the following. 2. A work roll having an inner diameter D = 0.07 to 0.20 mm, an adjacent distance L = 0.06 to 0.18 mm, and a crater formed with a density distribution satisfying D> L. Of hot-dip galvanized steel strip.