JP2807156B2 - Method for controlling the degree of alloying of galvanized steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the degree of alloying of a galvanized steel sheet.

[0002]

2. Description of the Related Art Heretofore, as a hot-dip galvanized steel sheet, there has been known a hot-dip galvanized steel sheet which has been subjected to an alloying treatment so that a part or the whole of a coating layer is formed of an Fe—Zn alloy layer. As shown in FIG. 9, the alloying treatment is performed by disposing the alloying furnace 2 immediately above the hot-dip galvanizing tank 4 and immersing the zinc in the plating tank 4 by the sink roll 5 to remove the zinc on the surface of the steel sheet 1. The amount of zinc is adjusted by squeezing with the squeezing device 3, and immediately thereafter, the steel sheet is heated by the heating device 6 in the alloying furnace 2 to diffuse iron into the zinc layer. If the alloying treatment performed here is not appropriate, that is, if the alloying is over-alloyed or insufficiently alloyed, the quality characteristics are impaired, so that it is necessary to control the alloying treatment with high accuracy.

Conventionally, methods for online determination of the degree of alloying in such alloying treatment include a method using X-ray diffraction,
There are a method of projecting light on a steel sheet and using the reflected light, and a method of using the emissivity of the steel sheet. As a method based on X-ray diffraction, a relationship between the X-ray diffraction intensity of each alloy layer and the degree of alloying is determined in advance, and the degree of alloying is determined by a calibration curve method (Kawatetsu Technical Report 18 (1986) “Alloys”). Method of Continuous Measurement of Fe Concentration of Galvannealed Galvanized Layer "and JP-A-1-301
No. 155). Also, the method using reflected light is
As disclosed in Japanese Patent Publication No. 64-655, the intensity distribution of reflected light is measured, and the alloying judgment is performed using the measured value.

A method utilizing the emissivity is disclosed in Japanese Patent Application Laid-Open No. 57-18 / 1982.
As disclosed in Japanese Patent No. 5966, it is focused on the fact that the emissivity of the steel sheet surface changes abruptly according to the progress of alloying, the radiant energy is measured, and the value is used to determine the degree of alloying. The judgment is performed. Japanese Patent Application Laid-Open No. 1-444 discloses a method for controlling the alloying by obtaining the alloying position from the reflection intensity level and controlling the position.
No. 782.

[0005]

The method using X-ray diffraction requires a large-scale apparatus and is expensive.
In addition, the installation position is problematic due to the large size of the device, and the accuracy is poor if the plate temperature is high, so the measurement position must be located on the exit side of the water-cooled cooling device behind the alloying furnace, resulting in poor response. was there.

The method using the reflected light has a problem in cost and maintenance because it is necessary to install a light source and a reflected light sensor. In the method using emissivity, there is the simplicity of using a radiation thermometer, but in the conventional method, the method of calculating the emissivity from radiant energy is complicated,
In addition, control using only radiant energy is affected by the temperature of the steel sheet in addition to the emissivity, so that there is a problem that the degree of alloying cannot be accurately controlled.

It is an object of the present invention to provide a technique for controlling the degree of alloying of a hot-dip galvanized steel sheet that solves the above-mentioned problems.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a steel sheet is immersed in a hot-dip galvanizing bath, and the coated steel sheet is formed by using an alloying furnace for hot-dip galvanizing. During alloying, the radiant temperatures of the steel plates at multiple positions in the plate temperature holding zone in the alloying furnace were measured, and the radiant energy was compared with the representative plate temperature measurement to determine the emissivity of the steel plates at each position. The position where the emissivity is in the range of 0.4 to 0.7 is defined as the alloying position, and the fuel flow rate and / or the passing speed of the alloying furnace are controlled so that the alloying position is a constant position. By controlling the alloying position of the plated steel sheet in the furnace, the degree of alloying is controlled within a target range.

In general, it is known that the emissivity of a steel sheet in an alloying process changes suddenly in accordance with a phase change of a plating layer. This rapid change is caused by the disappearance of the pure zinc phase (η phase) in the plating layer. The present invention aims to grasp the progress of alloying by estimating the η phase vanishing point. This is because the formation state of the 状態 phase that grows after the η phase disappears is known to affect the workability (mainly powdering property) of the steel sheet, and the η phase disappearance point is important for alloying. .

However, the emissivity corresponding to the η phase vanishing point is not clear. Therefore, a test was conducted in an actual furnace, and it was found that the alloying position determined from an arbitrary point having an emissivity in the range of 0.4 to 0.7 has a correlation with the degree of alloying. In the present invention, the representative plate temperature is a plate temperature considered as a true plate temperature when calculating the emissivity, and the measurement is represented by a measurement at an arbitrary position in the plate temperature holding zone of the alloying furnace. Can be. This is possible because there is generally no device for heating and cooling in the sheet temperature holding zone of the alloying furnace and there is almost no change in the sheet temperature in the sheet temperature holding zone.

[0011]

According to the present invention, when calculating the emissivity, the representative sheet temperature of the alloying furnace is measured at an arbitrary position in the alloying furnace, and the temperature is used. Is only the following equation (1), and the calculation can be easily performed.

[0012]

(Equation 1)

Here, ε: emissivity ε ₀ : set emissivity of radiation thermometer C: constant T: indicated value of radiation thermometer [K] T ₀ : representative plate temperature of alloying furnace [K] λ: measurement Wavelength.

Further, since only the radiation thermometer is used, the cost can be reduced and the measurement can be performed very easily. In addition, since the emissivity uses the representative temperature T ₀ of the alloying furnace as in equation (1), the influence of the sheet temperature cannot be considered as in the case where only the change in radiant energy is observed. Does not occur.

In the present invention, each emissivity is obtained from a plurality of measured radiant temperatures, and an approximate expression indicating the relationship between the furnace position and the emissivity can be created. A position with a specified emissivity between .4 and 0.7 can be determined.

[0016]

FIG. 1 is an example of an installation drawing in which radiation thermometers 10, 11, and 12 are arranged in a plate temperature holding zone 8 of an alloying furnace 2. FIG.
In FIG. 1, a radiation thermometer 9 for measuring the representative sheet temperature in the alloying furnace is installed on the exit side of the sheet temperature holding zone 8, but this is because the exit side of the sheet temperature holding zone has already progressed alloying. This is because the emissivity has progressed and the emissivity of the steel sheet has little change, so that the temperature of the steel sheet can be measured relatively stably. However, if a radiation thermometer having a function of automatically correcting the emissivity is used, it is possible to measure the temperature of the sheet at a position where the change in the emissivity of the steel sheet is large. It may be installed in a furnace.

FIG. 2 shows an example in which the emissivity is obtained by the arrangement shown in FIG. In the example of FIG. 2, the relationship between the position of the plate temperature holding zone and the emissivity is linearly approximated, and the emissivity at the alloying position is determined as 0.6 to determine the alloying position. FIG. 3 is a block diagram showing a flow for determining an alloying position. The representative plate temperature T ₀ of the alloying furnace and the indicated value T of the radiation thermometer are measured, the emissivity ε is calculated using the above equation (1), and the relationship between the position of the plate temperature holding zone and the emissivity is shown. Create an approximate expression. On the other hand, the emissivity of the alloying position is specified, and the alloying position is determined. Hereinafter, this position is set as an alloying position, and the emissivity at that position is set to 0.
The fuel flow rate and the passing speed are controlled so as to fall within the range of 4 to 0.7. According to the flow of FIG. 3, the alloying position was determined, and the result of sorting by the degree of alloying of the steel sheet manufactured at that time is shown in FIG.
Shown in FIG. 4 shows a threading speed of 80 mpm, a steel type, and an adhesion amount of 60.
The relationship between the alloying position and the degree of alloying was determined while keeping the condition of g / m ² constant. In FIG. 4, the data indicated by black circles is obtained by setting the emissivity at the alloying position to 0.4, and the correlation coefficient r is 0.6. The data indicated by the white squares is obtained by setting the emissivity at the alloying position to 0.6, and the correlation coefficient r at that time is 0.75. The data indicated by the white circles are those where the emissivity at the alloying position is 0.8 and the correlation coefficient r is 0.2.

In FIG. 4, when the emissivity designated as the alloying position is 0.4 or 0.6 which is within the range of the present invention, the correlation coefficient r is as high as 0.6 or 0.75. It turns out that there is a strong correlation. When the designated emissivity is set to 0.8 which is out of the range of the present invention, the correlation coefficient r becomes 0.2, which indicates that the correlation is low. It can be seen that when the alloying position is determined as 0.8, the degree of alloying cannot be accurately controlled. Therefore, the emissivity was set to 0.7 as the upper limit. On the other hand, although not shown, if the emissivity is less than 0.4, the deposited zinc is in a molten state or a state in which alloying has partially started, and the variation in the emissivity is large and unstable. 0.7. More preferably 0.5 to
0.6.

FIG. 5 shows an example of a system configuration for realizing the present invention. Using the signals from the radiation thermometers 9 to 12, the alloying position calculator 15 estimates the alloying position. The alloying position calculator 15 has the function shown in the flow chart of FIG. Also, in advance,
A target alloying position setter 17 is provided for setting a target alloying position determined for each of the threading speed, steel type, destination, etc., and the outputs of the alloying position calculator 15 and the target alloying position setter 17 are used as the alloying position. Input to the control device 16. Then, the amount of operation is calculated by the alloying position controller 16 so that the alloying position matches the target value, and the fuel flow controller 13 and the air flow controller 14 are operated.

In the system configuration shown in FIG. 5, three thermometers 10, 11, and 12 for obtaining the emissivity are used, but it goes without saying that the number can be increased or decreased according to required accuracy or the like. In addition, although the fuel flow rate is used as the operation amount, the same effect can be obtained even if the passing speed is selected. Further FIG.
In this case, since the representative plate temperature is measured at one point by one radiation thermometer, an error occurs if there is a plate temperature distribution in the plate temperature holding zone 8. For this purpose, as shown in FIG. 6, radiation thermometers 9 and 18 are arranged on the entrance side and the exit side of the sheet temperature holding zone 8 to measure the sheet temperature, and to obtain the sheet temperature distribution from the measured values. There is also a method in which a plate temperature is provided at each position of the radiation thermometers 10, 11, and 12 and used for emissivity calculation.

The effect of the present invention will be described with reference to FIG. In FIG. 7, the position where the emissivity is 0.6 is set as the alloying position. Before the implementation of the present invention, the line speed was 100m
When changing from pm to 80 mpm, the alloying position is 10
m to 5 m. This is because the time required for the emissivity to reach 0.6 is constant, and if the heating amount (fuel flow rate) is the same, the line speed is reduced and the position is shortened. As a result, the degree of alloying eventually deviates from the target range.

On the other hand, when the present invention is carried out, when the line speed changes from 100 mpm to 80 mpm, the control system shown in FIG. The alloying position is determined and changed to the alloying position (13 m in FIG. 4) at which the target value alloying degree becomes 9%. The lower the line speed, the longer the in-furnace retention time, and the higher the alloying, the higher the alloying position. As a result, the fuel flow rate is controlled to decrease, and the degree of alloying can be controlled to the target range.

FIG. 9 shows the relationship between the alloying position and the Al concentration in the bath of the immersion tank. From this figure, it can be seen that the alloying position for obtaining an alloying degree of 9% is almost constant regardless of the Al concentration in the bath. That is, it can be seen that the Al concentration in the bath, which greatly affects the degree of alloying, is not a control disturbance by controlling the alloying position. An evaluation test was performed on each of the 100 coils when the present invention was used and when it was not used. Table 1 shows the results.

Table 1 shows the usefulness of the present invention.

[0025]

[Table 1]

[0026]

According to the present invention, since the position of an arbitrary emissivity determined in the range of 0.4 to 0.7 is estimated as the alloying position, the alloying position can be accurately estimated. . Further, since the conditions of the alloying furnace are controlled so that the alloying position determined by using this method is constant, the responsiveness is good and the degree of alloying can be accurately controlled.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a radiation thermometer arrangement according to an embodiment.

FIG. 2 is a diagram showing a change in emissivity in a plate temperature holding zone.

FIG. 3 is a flowchart for determining an alloying position.

FIG. 4 is a diagram showing a relationship between an alloying position and a degree of alloying.

FIG. 5 is a system configuration diagram of alloying degree control.

FIG. 6 is a system configuration diagram of alloying degree control.

FIG. 7 is a chart showing an example of the present invention.

FIG. 8 is a graph showing a relationship between an alloying position and an Al concentration in a bath.

FIG. 9 is an explanatory view of an alloying furnace.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Alloying furnace 3 Drawing device 4 Plating tank 5 Sink roll 6 Heating device 7 Alloying furnace heating zone 8 Sheet temperature holding zone 9 Radiation thermometer for representative sheet temperature measurement 10 Radiation thermometer for emissivity calculation 11 Emissivity calculation Radiation thermometer for emissivity 12 Radiation thermometer for emissivity calculation 13 Fuel flow control device 14 Air flow control device 15 Alloying position calculator 16 Alloying position control device 17 Target alloying position setting device 18 Radiation thermometer for representative sheet temperature measurement 19 Sheet temperature distribution calculator

Continuation of the front page (72) Inventor Masakuni Nagai 1 Kawasaki-cho, Chuo-ku, Chiba-shi Kawasaki Steel Corporation Chiba Works (56) References JP-A-4-218654 (JP, A) JP-A-57-185966 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 2/00-2/40

Claims (1)

(57) [Claims] When a steel sheet is immersed in a hot-dip galvanizing tank and the coated steel sheet is alloyed by using a hot-dip galvanizing alloying furnace, radiation of the steel sheet at a plurality of positions of a sheet temperature holding zone in the hot-dip galvanizing furnace is performed. The temperature is measured, the radiant energy is compared with the representative plate temperature measurement value to determine the emissivity of the steel sheet at each position, and the position where the emissivity is in the range of 0.4 to 0.7 is determined as the alloying position. ,
Hot-dip galvanized steel sheet, characterized in that the alloying position is constant, the fuel flow rate of the alloying furnace and / or the passing speed are controlled to control the alloying position of the plated steel sheet in the furnace. Alloying degree control method.