JP3173354B2 - Alloying treatment method for hot-dip galvanized steel sheet and its alloying control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for alloying a hot-dip galvanized steel sheet and an alloying control apparatus therefor.

[0002]

2. Description of the Related Art Hot-dip galvanized steel sheets have been spotlighted because alloyed hot-dip galvanized steel sheets have the following features.

[0003] The finished paint appearance is uniform and uniform. Good coating film adhesion. Excellent corrosion resistance as a coated steel sheet. Low wear of electrodes due to resistance welding, and has workability similar to cold rolled steel plate.

[0004] Such a method of alloying a hot-dip galvanized steel sheet is performed, for example, in a continuous plating line as shown in FIG.

[0005] In FIG. 5, an alloying furnace 2 is disposed immediately above a hot-dip galvanizing bath 4 (hereinafter referred to as a “plating bath”). The zinc-plated steel sheet 1b is pulled up from the plating bath 4 after being inverted in the plating bath 4, and the excess zinc is squeezed out by the gas wiping 3 provided immediately above the plating bath 4 to adjust the adhesion amount. After that, the hot dip galvanized steel sheet 1b is alloyed in the alloying furnace 2 and is cooled by the cooling device 7 to be sent to the next step through the top roll 8 as the galvannealed steel sheet 1c. 9 is an adhesion amount measuring device.

However, when the alloying treatment is not appropriate, that is, when the Fe% of the plating layer is too high, a press failure called powdering occurs, and when the Fe% of the plating layer is too low, the alloying reaction is completed. Without this, a defect called uneven printing occurs.

[0007] In order to carry out proper alloying so as not to cause the above-mentioned excessive alloying or insufficient alloying, factors that affect alloying are accurately grasped, and alloying control is performed based on the factors. It is necessary to.

[0008] Factors affecting alloying include sheet temperature, zinc deposition amount, plating bath aluminum concentration, soaking time, sheet passing speed, and the like. Is required.

It is known that, among the above factors, the concentration of aluminum in the plating bath affects the alloying speed and fluctuates the alloying composition (the amount of iron in the plating layer).

If the aluminum concentration is too high, Fe-A
(1) The initial alloy layer becomes too thick, and the subsequent alloying treatment becomes difficult.

When the aluminum concentration is extremely low, F
An e-Al initial alloy layer is not generated, and a hard and brittle Fe-Zn alloy layer is generated in a plating bath. In any case, as described above, defects that adversely affect the quality are likely to occur. Become.

As a method for solving the above problem, Japanese Patent Laid-Open No.
Japanese Patent No. 272163 (Prior Art 1) discloses measuring the aluminum concentration in a hot-dip galvanizing bath, and adding aluminum or zinc into the bath based on the measurement result to adjust the aluminum concentration. It is disclosed to adjust and adjust the temperature or plate speed of the alloying furnace.

[0013]

In recent years, galvannealed steel sheets have been required to further improve weldability, paint adhesion, workability, corrosion resistance, etc., particularly as steel sheets for automobiles and steel sheets for household appliances. It is strongly required to precisely adjust the iron concentration of the alloyed layer of the alloyed hot-dip galvanized steel sheet which affects these.

However, the above-mentioned prior art document 1 has the following problems. The alloying control method disclosed in the prior art document 1 measures the aluminum concentration in the plating bath and adjusts the aluminum concentration in the bath from the results, or the temperature and the passing speed of the alloying furnace according to the aluminum concentration in the bath. In the plating bath, there is iron inevitably eluted from the steel plate or the like in the plating bath, and this iron is referred to as dross according to the aluminum concentration and the iron concentration in the bath. Forming an intermetallic compound of Zn or Fe-Al;

[0015] Since aluminum formed with an intermetallic compound of Fe-Al and Fe-Zn in a plating bath does not contribute to the formation of the initial alloy layer of Fe-Al, accurate measurement of the aluminum concentration in the bath alone is sufficient. It is difficult to control the conversion. For this reason, it is difficult to obtain an alloyed hot-dip galvanized steel sheet in which the iron concentration of the alloyed layer suitable for applications such as automotive steel sheets and home appliance steel sheets is precisely adjusted.

The present invention has been made to solve the above problems, and accurately grasps the aluminum concentration that fluctuates due to iron eluted from a steel plate or the like in a plating bath.
An object of the present invention is to provide a method for alloying a hot-dip galvanized steel sheet and an apparatus for controlling the alloying, which can accurately perform the alloying treatment based on the method.

[0017]

Means for Solving the Problems In order to achieve the above object, the present inventors have focused on the fact that the measurement of the concentration of aluminum contained in the plating bath does not show an effective aluminum concentration, and have studied the present invention. The invention has been reached.

In the continuous hot-dip galvanizing line, the invention according to claim 1 continuously analyzes the aluminum and iron contained in the galvanizing bath of the hot-dip galvanized steel sheet when alloying the same. Alloying treatment of a hot-dip galvanized steel sheet, wherein the effective aluminum concentration is calculated according to the following equation (2) or (4) according to the iron analysis value , and alloying is performed based on the effective aluminum concentration. Is the way.

(Equation 4)

In the invention according to claim 2, in a continuous galvanizing line, when alloying a hot-dip galvanized steel sheet, aluminum and iron contained in a plating bath of the line are continuously analyzed and the aluminum and iron are analyzed. The effective aluminum concentration is calculated according to the following equation (2) or (4) according to the iron analysis value , and the component is adjusted so that the aluminum concentration of the plating bath becomes the set aluminum concentration according to the effective aluminum concentration. An alloying treatment method for a galvanized steel sheet, wherein an alloying treatment is performed based on the adjusted aluminum concentration.

(Equation 5)

According to a third aspect of the present invention, there is provided a sensor for continuous analysis of aluminum and iron immersed in a plating bath of a continuous hot-dip galvanizing line, and the following sensor according to the analysis value of aluminum and iron of the sensor. Calculation of effective aluminum concentration by formula (2) or (4), adjustment of plating bath composition by the effective aluminum concentration, alloy of galvannealed steel sheet equipped with a process computer for alloying treatment based on the adjustment of the composition Control device.

(Equation 6)

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is configured as described above, and is implemented by the following procedure. In the present invention, aluminum and iron contained in the plating bath are continuously analyzed. A method for continuously analyzing aluminum and iron is as follows. Immerse the sensor in the plating bath,
The aluminum and iron concentrations are measured continuously. As the analyzer, a laser emission spectrometer or a laser vaporization analyzer is used in view of the stability and analysis accuracy of the device.

The aluminum concentration and the iron concentration measured by the above-mentioned analyzer are the total aluminum [T. Al (% by weight)] and total iron [T. Fe (% by weight)].

Since dross composed of Fe—Al or Fe—Zn intermetallic compound floats in the plating bath according to the aluminum concentration and the iron concentration, the T . Al (% by weight) and T.I. From the analysis values of Fe (% by weight), the effective aluminum [E.
Al (% by weight)].

E. Various methods have been proposed for calculating Al (% by weight ) . As one of them, there is a method of reading the solubility of Al and Fe in zinc by a three-element phase diagram as shown in FIG. FIG. 2 shows a solubility curve at a bath temperature of 460 ° C.

In FIG. 2, the dross form is FeZn.
₇ (δ ₁ phase bottom dross ; Fe-Zn intermetallic compound ) and F
There is a deposition region of e ₂ Al ₅ (top dross ; Fe-Al intermetallic compound ).

Usually, the Fe concentration in the galvanizing bath in the continuous hot-dip galvanizing line rises due to dissolution from the material to be plated and exceeds the saturation solubility.

The required amount of Al is added to the zinc plating bath,
T. Al (weight%) was measured. Due to the relationship with Fe (% by weight), it enters the precipitation region of Fe ₂ Al ₅ (top dross), and part of it contributes to the precipitation of Fe ₂ Al ₅ (indicated by point P).

In the region surrounded by the boundary (indicated by m) and the solubility curve (indicated by n) between FeZn ₇ and Fe ₂ Al ₅ , the aluminum added to the galvanizing bath is Fe ₂ A
It precipitates as l _5.

Therefore, T. Al (% by weight) to Fe ₂ Al
₅ Al that contributed to deposition of minus (weight%) of E.
Calculated as Al (% by weight).

The equations (1), (2), (3) and (4) can be obtained from the three-element phase diagram as shown in FIG. 2 and can be used as a simplified method.

[0031]

(Equation 7)

[0032]

(Equation 8)

In equations (1) and (2), E.D. Al (% by weight)
Is T. It is equivalent to Al (% by weight).

In equations (3) and (4), E.D. Al (% by weight) This is the result of removing Al (% by weight) that contributed to precipitation of Fe ₂ Al ₅ from Al (% by weight).

The above calculations can be performed by a process computer. FIG. 3 shows the results of analyzing the iron and aluminum in the plating bath and calculating the E.C. Al
(% By weight) and the corresponding initial alloy layer (Fe-
It is a figure which shows the relationship of the measured value of thickness of Al). E. FIG. Al
The measured values (indicated by O marks) corresponding to (% by weight) are plotted. As is clear from FIG. 3, the actual measured value of the thickness of the initial alloy layer (Fe—Al) of the steel sheet and the calculated E.E.
It was confirmed that Al (% by weight) had a correlation.

Next, FIG. The conditions of the alloying treatment are adjusted based on Al (% by weight), and the alloying treatment of the hot-dip galvanized steel sheet is thereby performed.

In addition, the obtained E.D. Depending on the value of Al (% by weight), E.I. The components of the plating bath are adjusted so as to be set aluminum (% by weight) based on Al (% by weight).

E. When Al (% by weight) is excessive, a zinc ingot having a low aluminum content is put into the plating bath. E. FIG. When Al (% by weight) is insufficient, a zinc ingot having a high aluminum content is put into the plating bath. The above can be adjusted by preparing a plurality of zinc ingots with adjusted aluminum contents. Usually, about five types are used.

FIG. 1 is a schematic diagram of a hot dip galvanizing line provided with the alloying control device of the present invention. It is suitable for performing the method for alloying a hot-dip galvanized steel sheet.

Parts common to those in FIG. 6 are denoted by the same reference numerals. In FIG. 1, reference numeral 11 denotes a sensor for continuous analysis of aluminum and iron immersed in the plating bath 4, to which an analyzer 14 is connected. The continuous analysis sensor 11 is attached at a position of about 100 mm from the surface of the plating bath 4. Here, a portion where the bottom dross 10a and the top dross 10b are less affected and an average bath composition is obtained is selected.
Reference numeral 12 denotes a process computer, a sensor 11 for continuous analysis.
From the iron concentration [T. Fe (% by weight)] and aluminum concentration [T. Al
(Weight%)] by the input signal of [E. Al (% by weight)] is calculated.

E. When the calculated value of Al (% by weight) exceeds a predetermined value, the set aluminum (% by weight) of the plating bath and E.I. An instruction for component adjustment is issued based on the difference from the calculated value of Al (% by weight).

On the basis of the command, the zinc ingot 13 having an appropriate aluminum content is supplied by switching the switching device 15 manually or automatically.

As described above, E.I. If the Al (weight%) is excessive, a zinc ingot 13 having a low aluminum content is used. When Al (% by weight) is insufficient, a zinc ingot having a high aluminum content is put into the plating bath.

In the continuous plating line, the steel sheet 1a whose surface has been cleaned in the annealing furnace is supplied from the snout 5 to the plating bath 4
The zinc-plated steel sheet 1b is pulled up from the plating bath 4 after being inverted by the sink roll 6, and the excessively adhered molten zinc is squeezed out by the gas wiping 3 provided immediately above the plating bath 4. The amount of adhesion is adjusted, and thereafter, the hot dip galvanized steel sheet 1b is alloyed in the alloying furnace 2 and sent to the next step via the top roll 7 as the galvannealed steel sheet 1c. In the present invention, E.I. Al. (% By weight) or E.I. The aluminum concentration of the plating bath 4 is adjusted to the set aluminum concentration based on Al (% by weight), and the alloying process is properly performed by the process computer 12.

Data necessary for performing the set alloying (Fe% display) is input to the process computer 12.
Based on this, the processing in the alloying furnace 2 is performed.

E. Control for controlling the output of the alloying furnace Al
The necessary data other than (weight%) include, as conventionally proposed, the steel sheet components, the steel sheet size, the annealing conditions before plating, the temperature of the steel sheet in the plating bath, the plating bath temperature, the coating weight, and There is a passing speed and the like.

The method of the alloying furnace is not particularly limited, but the high frequency induction heating method is particularly effective in view of the easiness of the output control and the speed of response.

As a result, a high quality alloyed hot-dip galvanized steel sheet can be stably manufactured.

[0049]

Embodiments of the present invention will be described below in detail. FIG. 4 shows the effective aluminum (% by weight) of the plating bath and the F of the alloyed layer of the alloyed hot-dip galvanized steel sheet when the alloyed hot-dip galvanized steel sheet was continuously manufactured for one month by the method of the present invention.
It is a figure which shows the relationship with e (weight%).

As a comparison, a case of aluminum weight% of a conventional plating bath is shown. As is clear from FIG. 4, in the case of the present invention, the variation is small and the Fe of the predetermined alloyed layer is small.
(% By weight), stable operation could be performed.

In the case of the comparative example, Fe (% by weight) of the alloyed layer
And the operation was unstable. On the other hand, the average alloying layer having an alloying layer out of the range of Fe (% by weight) has a nonuniformity of 0.1% as an alloying failure occurrence rate in the present invention.
5% and the powdering failure were 0.28%, but in the comparative example, the firing unevenness was 0.55% as the alloying failure occurrence rate.
Poor powdering was 0.80%.

When the aluminum concentration in the plating bath was not measured continuously, the occurrence rate of alloying failure was 1.80% for uneven baking and 3.00% for poor pattering.

[0053]

As described above, according to the present invention, it is possible to suppress the occurrence of poor alloying due to fluctuations in the components of the plating bath, and to stably produce a high-quality galvannealed steel sheet. Is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a hot-dip galvanizing line provided with an alloying control device of the present invention.

FIG. 2 is a diagram showing the solubility of Al and Fe in zinc of the present invention.

FIG. 3 is a diagram showing the relationship between the calculated effective aluminum of the present invention and the thickness of an actually measured initial alloying layer (Fe—Al) corresponding thereto.

FIG. 4 is a graph showing the relationship between the effective aluminum content (%) of a plating bath and the Fe% of the alloyed layer of an alloyed hot-dip galvanized steel sheet over time in the method of the present invention.

FIG. 5 is a diagram showing an example of a conventional hot-dip galvanizing line.

[Explanation of symbols]

 Reference Signs List 1a steel sheet 1b galvanized steel sheet 1c alloyed steel sheet 2 alloying furnace 3 gas wiping 4 plating bath 5 snout 6 sink roll 7 cooling device 8 top roll 9 adhesion measuring device 10a bottom dross 10b top dross 11 sensor for continuous analysis 12 Process computer 13 Zinc ingot 14 Analyzer 15 Switching device

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (3)

(57) [Claims] 1. In a continuous galvanizing line,
In alloying the hot-dip galvanized steel sheet, aluminum and iron contained in the plating bath of the line are continuously analyzed, and according to the analysis values of the aluminum and iron,
An alloying treatment method for a hot-dip galvanized steel sheet, comprising calculating an effective aluminum concentration by the formula (2) or (4) and performing an alloying process based on the effective aluminum concentration. (Equation 1) 2. In a continuous galvanizing line,
In alloying the hot-dip galvanized steel sheet, aluminum and iron contained in the plating bath of the line are continuously analyzed, and according to the analysis values of the aluminum and iron,
(2) or (4) to calculate the effective aluminum concentration by formula, its effective aluminum concentration by subjected to component adjustment so as to set the aluminum concentration of aluminum concentration in the plating bath, <aluminum concentrations the component adjustment br / > A method for alloying galvanized steel sheets, wherein the alloying is performed based on: (Equation 2) 3. A sensor for continuous analysis of aluminum and iron immersed in a plating bath of a continuous hot-dip galvanizing line , and according to an analysis value of aluminum and iron of the sensor.
Calculation of the effective aluminum concentration by the following equation (2) or (4), adjustment of the composition of the plating bath by the effective aluminum concentration, and alloying hot-dip galvanized steel sheet equipped with a process computer for alloying based on the adjustment of the composition Alloying control device. (Equation 3)