Title of the invention: A hot-dip galvanizing method, a method for manufacturing an alloyed hot-dip galvanized steel sheet using the hot-dip galvanizing method, and a method for manufacturing a hot-dip galvanized steel sheet using the hot-dip galvanizing method.
Technical field
[0001]
The present invention relates to a hot-dip galvanizing method, a method for producing an alloyed hot-dip galvanized steel sheet using the hot-dip galvanizing method, and a method for producing a hot-dip galvanized steel sheet using the hot-dip galvanizing method.
Background technology
[0002]
The hot-dip galvanized steel sheet (hereinafter, also referred to as GI) and the alloyed hot-dip galvanized steel sheet (hereinafter, also referred to as GA) are manufactured by the following manufacturing process. First, a steel sheet (base steel sheet) to be hot-dip galvanized is prepared. The base steel plate may be a hot-rolled steel plate or a cold-rolled steel plate. When the base steel sheet is a hot-rolled steel sheet, for example, a pickled hot-rolled steel sheet is prepared. If necessary, the pickled hot-rolled steel sheet may be subjected to a Ni pre-plating treatment to prepare a hot-rolled steel sheet having a Ni layer formed on its surface. A hot-rolled steel sheet that has been subjected to a treatment other than the above may be prepared. When the base steel sheet is a cold-rolled steel sheet, for example, an annealed cold-rolled steel sheet is prepared. If necessary, the annealed cold-rolled steel sheet may be subjected to a Ni pre-plating treatment to prepare a cold-rolled steel sheet having a Ni layer formed on its surface. Cold-rolled steel sheets that have been subjected to treatments other than those described above may be prepared. The prepared base steel sheet (the above-mentioned hot-rolled steel sheet or cold-rolled steel sheet) is immersed in a hot-dip galvanized bath to perform a hot-dip galvanizing treatment to produce a hot-dip galvanized steel sheet. When the alloyed hot-dip galvanized steel sheet is manufactured, the alloyed hot-dip galvanized steel sheet is further manufactured by heat-treating the hot-dip galvanized steel sheet in an alloying furnace.
[0003]
The details of the hot-dip galvanized treatment during the manufacturing process of the hot-dip galvanized steel sheet and the alloyed hot-dip galvanized steel sheet are as follows. The hot-dip galvanizing facility used for the hot-dip galvanizing treatment includes a hot-dip galvan pot containing a hot-dip galvanizing bath, a sink roll arranged in the hot-dip galvanizing bath, and a gas wiping device.
[0004]
In the hot-dip galvanizing process, the steel sheet (base steel sheet) is immersed in a hot-dip galvanizing bath. Then, the sink roll arranged in the hot-dip galvanizing bath changes the traveling direction of the steel sheet upward, and pulls the steel sheet out of the hot-dip galvanizing bath. Wiping gas is sprayed onto the surface of the steel sheet from the gas wiping device to scrape off the excess molten zinc on the steel sheet that is pulled up and moves upward, and the amount of plating adhered to the surface of the steel sheet is adjusted. The hot-dip galvanizing treatment step is carried out by the above method. In the case of manufacturing an alloyed hot-dip galvanized steel sheet, a steel sheet having an adjusted plating adhesion amount is further charged into an alloying furnace to carry out an alloying treatment.
[0005]
The hot-dip galvanizing bath contains a small amount of Al in order to properly maintain the reaction between the steel sheet (base steel sheet) and the hot-dip zinc. Al in the hot-dip galvanizing bath is consumed when the hot-dip galvanizing treatment is performed. Therefore, it is necessary to supply an appropriate amount of Al to the hot-dip galvanizing bath at any time. It is known that the Al concentration in the hot-dip galvanized bath affects the adhesion of the hot-dip galvanized layer of the hot-dip galvanized steel sheet, the degree of alloying of the alloyed hot-dip galvanized steel sheet, and the like. Therefore, it is preferable that the Al concentration in the hot-dip galvanizing bath is kept constant. In the present specification, the "Al concentration in the hot-dip galvanizing bath" means the Al concentration (so-called Free-Al concentration) melted in the hot-dip galvanizing bath. That is, in the present specification, the "Al concentration in the hot-dip galvanizing bath" is melted in the hot-dip galvanizing bath (that is, liquid) excluding the Al content contained in the dross (top dross and bottom dross). It means the Al concentration (in the phase).
[0006]
A technique for keeping the Al concentration in a hot-dip galvanizing bath constant has been proposed in, for example, Japanese Patent Application Laid-Open No. 2018-184630 (Patent Document 1). In the Zn-Al alloy supply method described in Patent Document 1, Al is uniformly contained in the hot-dip zinc bath when the Zn-Al alloy wire is penetrated into the bath from the bath surface layer and sent out at a predetermined molten zinc bath temperature. It is characterized in that it is fed at a wire feeding speed such that the Zn—Al alloy wire is completely melted at a molten zinc bath depth that can be diffused. As a result, it is described in Patent Document 1 that the operation can be performed with a stable Al concentration as compared with the case where the Al cake is added to adjust the Al concentration.
Prior art literature
Patent documents
[0007]
Patent Document 1: Japanese Unexamined Patent Publication No. 2018-184630
Non-patent literature
[0008]
Non-Patent Document 1: Practical Applications of Phase Diagrams in Continuous Galvanizing, Nai-Yong Tang, Journal of Phase Equilibria and Diffusion. 27 No. 5,2006
Outline of the invention
Problems to be solved by the invention
[0009]
For example, the Al concentration in the hot-dip galvanizing bath can be stabilized by the method described in Patent Document 1. However, it is preferable that the Al concentration in the hot-dip galvanizing bath can be stabilized without necessarily depending on the Al supply method.
[0010]
An object of the present disclosure is a hot-dip galvanizing treatment method capable of stabilizing the Al concentration in a hot-dip galvanizing bath, a method for manufacturing an alloyed hot-dip galvanized steel sheet using the hot-dip galvanizing treatment method, and hot-dip galvanizing thereof. It is an object of the present invention to provide a method for manufacturing a hot-dip galvanized steel sheet using a treatment method.
Means to solve problems
[0011]
The hot-dip galvanizing method according to the present disclosure is a hot-dip galvanizing method used for manufacturing a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet.
A sample collection process in which a sample is collected from a hot-dip galvanizing bath containing Al, and
Using the collected sample, the dross amount determination step for obtaining the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath, and
It is provided with an operating condition adjustment step for adjusting the operating conditions of the hot-dip galvanizing treatment based on the obtained Γ 2-phase dross amount and δ 1-phase dross amount.
[0012]
The method for manufacturing alloyed hot-dip galvanized steel sheets according to this disclosure is
The hot-dip galvanizing treatment step of forming a hot-dip galvanizing layer on the surface of the steel sheet by implementing the above-mentioned hot-dip galvanizing treatment method on the steel sheet,
The steel sheet having a hot-dip galvanized layer formed on its surface is alloyed to produce an alloyed hot-dip galvanized steel sheet.
[0013]
The manufacturing method of the hot-dip galvanized steel sheet according to this disclosure is
A hot-dip galvanizing treatment step is provided in which the above-mentioned hot-dip galvanizing treatment method is carried out on a steel sheet to form a hot-dip galvanizing layer on the surface of the steel sheet.
The invention's effect
[0014]
The hot-dip galvanizing treatment method according to the present disclosure can stabilize the Al concentration in the hot-dip galvanizing bath. Further, the method for producing an alloyed hot-dip galvanized steel sheet according to the present disclosure can stabilize the Al concentration in the hot-dip galvanized bath. The method for producing a hot-dip galvanized steel sheet according to the present disclosure can stabilize the Al concentration in the hot-dip galvanized bath.
A brief description of the drawing
[0015]
FIG. 1 is a functional block diagram showing an example of the overall configuration of a hot-dip galvanized line facility used for manufacturing an alloyed hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet.
FIG. 2 is a side view of the hot dip galvanizing facility in FIG.
FIG. 3 is a side view of a hot-dip galvanizing facility having a configuration different from that of FIG. 2.
FIG. 4 is a side view of a hot-dip galvanizing facility having a configuration different from that of FIGS. 2 and 3.
FIG. 5 is a functional block diagram showing an example of the overall configuration of a hot-dip galvanizing line facility having a configuration different from that of FIG. 1.
FIG. 6 is a side view of a hot dip galvanizing facility in which an Al ingot is immersed.
FIG. 7 is a flow chart showing a process of the hot dip galvanizing treatment method of the present embodiment.
FIG. 8 is a diagram showing an example of a photographic image in a part of the observation field of view of a sample collected in the sample collection step of the hot dip galvanizing treatment method of the present embodiment.
Embodiment for carrying out the invention
[0016]
As described above, Al in the hot-dip galvanizing bath is consumed by the hot-dip galvanizing treatment. Therefore, Al needs to be supplied at any time during the hot-dip galvanizing bath. Al is usually supplied by immersing the Al ingot in a hot dip galvanizing bath. Al elutes and diffuses from the Al ingot immersed in the hot-dip galvanizing bath, thereby increasing the Al concentration (Free-Al concentration) in the hot-dip galvanizing bath. When lowering the Al concentration in the hot-dip galvanizing bath, the immersion of the Al ingot in the hot-dip galvanizing bath is stopped, and the hot-dip galvanizing treatment is performed for a certain period of time.
[0017]
For example, when the shape of the Al ingot is rod-shaped, the Al ingot is gradually immersed in a hot-dip galvanizing solution or an Al pot that dissolves Al with the axial direction of the Al ingot as the vertical direction. The Al pot is connected to the hot-dip zinc pot, and the melted Al is supplied to the hot-dip galvanizing bath. Increasing the immersion rate of the Al ingot increases the supply of Al into the hot-dip galvanizing bath. On the other hand, if the immersion of the Al ingot is stopped, the supply of Al to the hot-dip galvanizing bath is stopped, and the Al concentration in the hot-dip galvanizing bath gradually decreases. Alternatively, Al is supplied into the hot-dip galvanizing bath by directly putting a small Al ingot into the hot-dip galvanizing bath. When the charging of the Al ingot is stopped, the supply of Al to the hot-dip galvanizing bath is stopped, and the Al concentration in the hot-dip galvanizing bath gradually decreases.
[0018]
Conventionally, the Al concentration in the hot-dip galvanizing bath has been adjusted by adjusting the immersion speed of the Al ingot and the stirring speed of the hot-dip galvanizing bath. In this case, it may be difficult to finely adjust the Al concentration in the hot-dip galvanizing bath. For example, the rate of increase in Al concentration in the hot-dip galvanizing bath is controlled by the rate of dissolution of Al from the Al ingot and the rate of diffusion of Al in the hot-dip galvanizing bath. Further, the rate of decrease of the Al concentration in the hot-dip galvanizing bath is controlled by the processing rate of the hot-dip galvanizing process.
[0019]
The present inventor not only adjusts the immersion speed of the Al ingot and the stirring speed of the hot-dip galvanizing bath, but also adjusts the Al concentration in the hot-dip galvanizing bath by other methods in the hot-dip galvanizing bath. It was thought that the Al concentration of the above could be more stabilized.
[0020]
As a result of the inventor's detailed investigation of Al in the hot-dip galvanizing bath, the following findings were obtained. In the hot-dip galvanizing bath, it was found that Al can exist in four forms: Free-Al, top dross, gamma 2-phase (Γ 2-phase) dross and delta 1-phase (δ 1-phase) dross. Free-Al is Al dissolved in the hot-dip galvanizing bath as described above. More specifically, Free-Al means the concentration of Al melted (in the liquid phase) in the hot-dip galvanizing bath, excluding the Al content contained in the dross (top dross and bottom dross). .. Top dross is an intermetallic compound having a lighter specific gravity than that of a hot-dip galvanizing bath, and is a dross that floats on the liquid surface of the hot-dip galvanizing bath. Γ 2-phase dross and δ 1-phase dross are called bottom dross.
[0021]
The Γ 2-phase dross has a chemical composition of 2% Al, 8% Fe, and 90% Zn in mass%, and the crystal structure is a face-centered cubic dross. On the other hand, the δ 1-phase dross has a chemical composition of 1% or less of Al, 9% or more of Fe, and 90% or more of Zn in mass%, and has a hexagonal crystal structure. The present inventor has found that the Γ 2-phase dross and the δ 1-phase dross undergo phase transformation with each other in a hot-dip galvanizing bath. The Al content of the Γ 2-phase dross is different from the Al content of the δ 1-phase dross. Therefore, when the Γ 2-phase dross and the δ 1-phase dross undergo a phase transformation, the absorption and release of Al occur.
[0022]
The present inventor conducted further studies and obtained the following findings. The dross in the hot-dip galvanizing bath depends on the temperature of the hot-dip galvanizing bath and the Al concentration in the hot-dip galvanizing bath. Accordingly, it mainly undergoes phase transformation into top dross, Γ 2-phase dross and δ 1-phase dross. In addition, top dross, Γ 2-phase dross and δ 1-phase dross undergo phase transformation with each other. Whether Γ 2-phase dross or δ 1-phase dross is more likely to occur in a hot-dip galvanizing bath affects the temperature of the hot-dip galvanizing bath and the Al concentration (that is, Free-Al concentration) in the hot-dip galvanizing bath. Receive. Further, on the equilibrium state diagram in which the temperature of the hot-dip galvanizing bath and the Al concentration in the hot-dip galvanizing bath are taken on the horizontal axis and the vertical axis, respectively, there is a region where both Γ 2-phase dross and δ 1-phase dross exist. .. In this region, depending on the temperature of the hot-dip galvanizing bath and the Al concentration in the hot-dip galvanizing bath, the Γ 2-phase dross undergoes a phase transformation to δ 1-phase dross, and the δ 1-phase dross becomes Γ 2-phase dross. It transforms. The present inventor stabilizes the Al concentration in the hot-dip galvanizing bath by adjusting the operating conditions so that both the Γ 2-phase dross and the δ 1-phase dross are present in the hot-dip galvanizing bath at an appropriate content ratio. I thought it could be done.
[0023]
Specifically, when the Al concentration in the hot-dip galvanizing bath is high, the equilibrium tilts in the direction in which the Γ 2-phase dross, which has a higher Al content than the δ 1-phase dross, is generated. Therefore, the δ 1-phase dross in the hot-dip galvanizing bath is likely to undergo a phase transformation into a Γ 2-phase dross. When the δ 1-phase dross undergoes a phase transformation to the Γ 2-phase dross, Al is absorbed from the hot-dip galvanizing bath. As a result, the Al concentration in the hot-dip galvanizing bath decreases. On the contrary, when the Al concentration in the hot-dip galvanizing bath is low, the equilibrium is inclined in the direction in which the δ 1-phase dross having a lower Al content than the Γ 2-phase dross is generated. Therefore, the Γ 2-phase dross in the hot-dip galvanizing bath is likely to undergo a phase transformation into a δ 1-phase dross. When the Γ 2-phase dross undergoes a phase transformation to the δ 1-phase dross, Al is released into the hot-dip galvanizing bath. As a result, the Al concentration in the hot-dip galvanizing bath increases.
[0024]
That is, the present inventor uses a method different from the conventional method of stabilizing the Al concentration (that is, the Free-Al concentration) in the hot-dip galvanizing bath by utilizing the absorption and release of Al accompanying the phase transformation of the bottom dross. I found it. Then, in the hot-dip galvanizing treatment method, it was considered that the above-mentioned operation can be carried out by controlling the amount of Γ 2-phase dross and the amount of δ 1-phase dross in the hot-dip galvanizing bath.
[0025]
As described above, the hot-dip galvanizing treatment method of the present embodiment has been completed based on an idea different from the conventional technical idea, and specifically, it is as follows.
[0026]
The hot-dip galvanizing method of [1] is
A hot-dip galvanized treatment method used in the manufacture of hot-dip galvanized steel sheets or alloyed hot-dip galvanized steel sheets.
A sample collection process in which a sample is collected from a hot-dip galvanizing bath containing Al, and
Using the collected sample, a dross amount determination step for obtaining the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath, and
It is provided with an operating condition adjusting step for adjusting the operating conditions of the hot-dip galvanizing treatment based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount.
[0027]
Here, "adjusting the operating conditions of the hot-dip galvanizing treatment" means adjusting the operating conditions of the hot-dip galvanizing treatment in which the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath can be adjusted. Means that. Further, "adjusting the operating conditions of the hot-dip galvanizing treatment" includes not only the act of changing the operating conditions of the hot-dip galvanizing treatment but also the act of maintaining the operating conditions as they are.
[0028]
According to the hot-dip galvanizing treatment method having the above configuration, Γ 2-phase dross and δ 1-phase are based on the amount of Γ 2-phase dross and δ 1-phase dross in the hot-dip galvanizing bath obtained using the sample. Adjust the operating conditions of the hot-dip galvanizing method so that the dross is sufficient and the Γ 2-phase dross and the δ 1-phase dross are present in an appropriate content ratio. As described above, in the hot-dip galvanizing bath, the amount of Γ 2-phase dross and the amount of δ 1-phase dross undergo phase transformation with each other. With the phase transformation of the Γ 2-phase dross amount and the δ 1-phase dross amount, absorption and release of Al occur. As a result, the Al concentration in the hot-dip galvanizing bath is stable.
[0029]
The hot-dip galvanizing treatment method of [2] is the hot-dip galvanizing treatment method according to [1].
In the dross amount determination process,
Using the collected sample, the number of Γ 2-phase dross per predetermined area is determined as the Γ 2-phase dross amount, and the number of δ 1-phase dross per predetermined area is determined as the δ 1-phase dross amount.
[0030]
Here, the predetermined area is not particularly limited. The predetermined area may be, for example, the entire area of ​​the observation field of view when Γ 2-phase dross and δ 1-phase dross are observed in a predetermined observation field of view using a sample, or may be a unit area (cm 2). May be good.
[0031]
The hot-dip galvanizing treatment method of [3] is the hot-dip galvanizing treatment method according to [1] or [2].
In the operating condition adjustment process,
Based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount, the bath temperature of the hot-dip galvanizing bath is adjusted to adjust the Γ 2-phase dross amount and the δ 1-phase dross amount.
[0032]
The bath temperature of the hot-dip galvanizing bath is an effective operating condition for switching between the phase transformation from Γ 2-phase dross to δ 1-phase dross and the phase transformation from δ 1-phase dross to Γ 2-phase dross. Therefore, the hot-dip galvanizing bath is adjusted by adjusting the bath temperature of the hot-dip galvanizing bath based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount to adjust the Γ 2-phase dross amount and the δ 1-phase dross amount. The Al concentration inside can be more stabilized.
[0033]
The hot-dip galvanizing treatment method of [4] is the hot-dip galvanizing treatment method according to any one of [1] to [3].
In the operating condition adjustment process,
Based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount, the transport speed of the steel plate in the hot-dip galvanizing facility for performing the hot-dip galvanizing treatment is adjusted to adjust the Γ 2-phase dross amount and the above. δ 1 Adjust the amount of dross.
[0034]
The transfer speed of the steel sheet is an effective operating condition for increasing or decreasing the amount of dross generated, including Γ 2-phase dross and δ 1-phase dross. Therefore, by adjusting the transport speed of the steel plate based on the obtained Γ 2-phase dross amount and δ 1-phase dross amount and increasing the Γ 2-phase dross amount and δ 1-phase dross amount, a sufficient amount of Al is absorbed. Will be released. As a result, the Al concentration in the hot-dip galvanizing bath can be further stabilized.
[0035]
The hot-dip galvanizing treatment method of [5] is the hot-dip galvanizing treatment method according to any one of [1] to [4].
In the dross amount determination process,
Using the collected sample, the number of Γ 2-phase dross per unit area (1 cm 2) was determined as the amount of Γ 2-phase dross (pieces / cm 2), and δ 1 phase per unit area (1 cm 2). The number of dross is determined as the δ 1-phase dross amount (pieces / cm 2).
In the operating condition adjustment process,
Adjust so that the Γ 2-phase dross amount and the δ 1-phase dross amount satisfy the equations (1) and (2).
15 ≤ Γ 2-phase dross amount + δ 1-phase dross amount (1)
0.05 ≤ Γ 2-phase dross amount / δ 1-phase dross amount ≤ 20.00 (2)
[0036]
If the total amount of Γ 2-phase dross and δ 1-phase dross is 15 pieces / cm 2 or more, a sufficient amount of Al to stabilize the Al concentration in the hot-dip galvanizing bath is more stably absorbed. It is released. Further, if the ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount satisfies the equation (2), both the increase and decrease of the Al concentration in the hot-dip galvanizing bath are suppressed more stably. Therefore, in this case, the Al concentration in the hot-dip galvanizing bath can be further stabilized.
[0037]
The hot-dip galvanizing treatment method of [6] is the hot-dip galvanizing treatment method according to any one of [1] to [5].
In the hot-dip galvanized pot in which the hot-dip galvanizing bath is stored, a sink roll for contacting the steel strip immersed in the hot-dip galvanizing bath and changing the traveling direction of the steel strip up and down is arranged. And
In the sample collection process,
The sample is collected from the depth range from the upper end to the lower end of the sink roll in the hot dip galvanizing bath in the hot dip galvan pot.
[0038]
In this case, the sample is taken from the area with the same depth as the sink roll. Therefore, the performance such as the adhesion of the alloyed hot-dip galvanized layer of the alloyed hot-dip galvanized steel sheet, the degree of alloying of the hot-dip galvanized layer of the hot-dip galvanized steel sheet, and the Γ 2-phase dross amount and the δ 1-phase dross amount. Correlation can be increased.
[0039]
The method for manufacturing the alloyed hot-dip galvanized steel sheet in [7] is
A hot-dip galvanizing treatment step of forming a hot-dip galvanizing layer on the surface of the steel sheet by carrying out the hot-dip galvanizing treatment method according to any one of [1] to [6] on the steel sheet.
The steel sheet having the hot-dip galvanized layer formed on the surface thereof is subjected to an alloying treatment to produce the alloyed hot-dip galvanized steel sheet.
[0040]
As the method for manufacturing the alloyed hot-dip galvanized steel sheet of the present embodiment, the above-mentioned hot-dip galvanized treatment method of the present embodiment is applied. Therefore, the Al concentration in the hot-dip galvanizing bath can be stabilized.
[0041]
The manufacturing method of the hot-dip galvanized steel sheet in [8] is
A hot-dip galvanizing treatment step is provided for forming a hot-dip galvanizing layer on the surface of the steel sheet by carrying out the hot-dip galvanizing treatment method according to any one of [1] to [6] on the steel sheet.
[0042]
As the method for manufacturing the hot-dip galvanized steel sheet of the present embodiment, the above-mentioned hot-dip galvanized treatment method of the present embodiment is applied. Therefore, the Al concentration in the hot-dip galvanizing bath can be stabilized.
[0043]
Hereinafter, the hot-dip galvanizing treatment method, the alloying hot-dip galvanized steel sheet manufacturing method, and the hot-dip galvanized steel sheet manufacturing method according to the present embodiment will be described with reference to the drawings. In the present specification and the drawings, the configurations having substantially the same functions are designated by the same reference numerals and the description thereof will not be repeated.
[0044]
[About the configuration of hot-dip galvanizing line equipment]
FIG. 1 is a functional block diagram showing an example of the overall configuration of a hot-dip galvanized line facility used for manufacturing an alloyed hot-dip galvanized steel sheet and a hot-dip galvanized steel sheet. With reference to FIG. 1, the hot-dip galvanizing line facility 1 includes an annealing furnace 20, a hot-dip galvanizing facility 10, and a tempering rolling mill (skin pass mill) 30.
[0045]
The annealing furnace 20 includes one or more heating zones (not shown) and one or more cooling zones arranged downstream of the heating zones. In the annealing furnace 20, the steel sheet is supplied to the heating zone of the annealing furnace 20, and the steel sheet is annealed. The annealed steel sheet is cooled in the cooling zone and transported to the hot-dip galvanizing facility 10. The hot-dip galvanizing facility 10 is located downstream of the annealing furnace 20. In the hot-dip galvanizing facility 10, a hot-dip galvanizing treatment is performed on the steel sheet, and an alloyed hot-dip galvanized steel sheet or a hot-dip galvanized steel sheet is manufactured. The tempering rolling mill 30 is arranged downstream of the hot dip galvanizing facility 10. In the tempering rolling mill 30, the alloyed hot-dip galvanized steel sheet or the hot-dip galvanized steel sheet manufactured in the hot-dip galvanized equipment 10 is lightly reduced as necessary to the alloyed hot-dip galvanized steel sheet or the hot-dip galvanized steel sheet or the hot-dip galvanized steel sheet. Adjust the surface of the galvanized steel sheet.
[0046]
[About hot-dip galvanizing equipment 10]
FIG. 2 is a side view of the hot-dip galvanizing facility 10 in FIG. With reference to FIG. 2, the hot-dip galvanizing facility 10 includes a hot-dip galvan pot 101, a sink roll 107, a support roll 113, a gas wiping device 109, and an alloying furnace 111.
[0047]
The annealing furnace 20 located upstream of the hot-dip galvanizing facility 10 is shielded from the atmosphere inside and is maintained in a reducing atmosphere. As described above, the annealing furnace 20 heats the steel sheet S that is continuously conveyed in the heating zone. As a result, the surface of the steel sheet S is activated and the mechanical properties of the steel sheet S are adjusted.[0048]
The downstream end of the annealing furnace 20, which corresponds to the exit side of the annealing furnace 20, has a space in which the turndown roll 201 is arranged. The downstream end of the annealing furnace 20 is connected to the upstream end of the snout 202. The downstream end of the snout 202 is immersed in the hot dip galvanizing bath 103. The inside of the snout 202 is shielded from the atmospheric atmosphere and is maintained in a reducing atmosphere.
[0049]
The steel plate S whose transport direction has been changed downward by the turndown roll 201 passes through the snout 202 and is continuously immersed in the hot-dip galvanizing bath 103 stored in the hot-dip galvanized pot 101. A sink roll 107 is arranged inside the hot-dip zinc pot 101. The sink roll 107 has a rotation axis parallel to the width direction of the steel plate S. The axial width of the sink roll 107 is larger than the width of the steel plate S. The sink roll 107 comes into contact with the steel plate S and changes the traveling direction of the steel plate S to the upper side of the hot-dip galvanizing facility 10.
[0050]
The support roll 113 is in the hot-dip galvanizing bath 103 and is arranged above the sink roll 107. The support roll 113 includes a pair of rolls. The pair of rolls of the support roll 113 has a rotation axis parallel to the width direction of the steel plate S. The support roll 113 supports the steel plate S to be conveyed upward by sandwiching the steel plate S whose traveling direction is changed upward by the sink roll 107.
[0051]
The gas wiping device 109 is arranged above the sink roll 107 and the support roll 113 and above the liquid level of the hot-dip galvanizing bath 103. The gas wiping device 109 includes a pair of gas injection devices. The pair of gas injection devices have gas injection nozzles that oppose each other. During the hot-dip galvanizing process, the steel sheet S passes between the pair of gas injection nozzles of the gas wiping device 109. At this time, the pair of gas injection nozzles face the surface of the steel plate S. The gas wiping device 109 sprays gas on both surfaces of the hot-dip galvanized steel sheet S pulled up from the hot-dip galvanized bath 103 to scrape off a part of the hot-dip galvanized sheet adhering to both surfaces of the hot-dip galvanized steel sheet S. Adjust the amount of hot-dip galvanized on the surface.
[0052]
The alloying furnace 111 is arranged above the gas wiping device 109. The alloying furnace 111 passes the steel plate S conveyed upward through the gas wiping device 109 through the inside, and performs the alloying treatment on the steel plate S. The alloying furnace 111 includes a heating zone, a tropical zone, and a cooling zone in this order from the entry side to the exit side of the steel sheet S. The heating band is heated so that the temperature (plate temperature) of the steel plate S becomes substantially uniform. The tropics maintain the plate temperature of the steel plate S. At this time, the hot-dip galvanized layer formed on the surface of the steel sheet S is alloyed to become an alloyed hot-dip galvanized layer. The cooling zone cools the steel sheet S on which the alloyed hot-dip galvanized layer is formed. As described above, the alloying furnace 111 carries out the alloying treatment using the heating zone, the tropical zone, and the cooling zone. The alloying furnace 111 carries out the above-mentioned alloying treatment when manufacturing an alloyed hot-dip galvanized steel sheet. On the other hand, when the hot-dip galvanized steel sheet is manufactured, the alloying furnace 111 does not carry out the alloying treatment. In this case, the steel plate S passes through the non-operating alloying furnace 111. Here, "not operating" means, for example, a state in which the power supply is stopped (a state in which the alloying furnace 111 is not started) while the alloying furnace 111 is placed online. The steel plate S that has passed through the alloying furnace 111 is conveyed to the next process by the top roll 115.
[0053]
When manufacturing a hot-dip galvanized steel sheet, the alloying furnace 111 may be moved offline as shown in FIG. In this case, the steel plate S is conveyed to the next process by the top roll 115 without passing through the alloying furnace 111.
[0054]
When the hot-dip galvanizing facility 10 is a facility dedicated to the hot-dip galvanized steel sheet, the hot-dip galvanizing facility 10 does not have to be equipped with the alloying furnace 111 as shown in FIG.
[0055]
[About other configuration examples of hot-dip galvanizing line equipment]
The hot-dip galvanizing line equipment 1 is not limited to the configuration shown in FIG. For example, when a Ni pre-plating process is performed on a steel sheet before hot-dip galvanizing to form a Ni layer on the steel sheet, Ni is placed between the quenching furnace 20 and the hot-dip galvanizing facility 10 as shown in FIG. The pre-plating equipment 40 may be arranged. The Ni pre-plating equipment 40 includes a Ni plating cell for storing a Ni plating bath. The Ni plating process is carried out by an electroplating method. The hot-dip galvanizing line equipment 1 of FIGS. 1 and 5 includes an annealing furnace 20 and a temper rolling mill 30. However, the hot dip galvanizing line equipment 1 does not have to be provided with the annealing furnace 20. Further, the hot-dip galvanizing line equipment 1 does not have to be equipped with the tempering rolling mill 30. The hot-dip galvanizing line equipment 1 may be provided with at least the hot-dip galvanizing equipment 10. The annealing furnace 20 and the tempering rolling mill 30 may be arranged as needed. Further, the hot-dip galvanizing line facility 1 may be provided with a pickling facility for pickling a steel plate upstream of the hot-dip galvanizing facility 10, or other facilities other than the annealing furnace 20 and the pickling facility. May be provided. The hot-dip galvanizing line equipment 1 may be further provided with equipment other than the tempering and rolling mill 30 downstream of the hot-dip galvanizing equipment 10.
[0056]
[Adjustment of Al concentration in hot-dip galvanizing bath]
In the hot-dip galvanizing treatment step during the manufacturing process of the alloyed hot-dip galvanized steel sheet or the hot-dip galvanized steel sheet using the hot-dip galvanizing line facility 1 described above, the method for adjusting the Al concentration in the conventional hot-dip galvanizing bath 103 is as follows. It is as follows.
[0057]
FIG. 6 is a side view of the hot-dip galvanizing facility 10 in which the Al ingot is immersed. With reference to FIG. 6, the Al ingot 300 is transported onto the hot-dip zinc pot 101 by a well-known transport means. The Al ingot 300 is lowered by a well-known transport means and immersed in the hot-dip galvanizing bath 103.
[0058]
The method of supplying Al into the hot-dip galvanizing bath 103 is not particularly limited. Al may be supplied by the Al ingot 300 as shown in FIG. 6, or may be another method. For example, Al may be supplied by immersing a wire containing Al in a hot-dip galvanizing bath 103. Further, for example, after melting the Al ingot 300 or the like in a pot different from the hot-dip zinc pot 101, the molten Al may be added to the hot-dip galvanizing bath 103.
[0059]
As described above, conventionally, the Al concentration in the hot-dip galvanizing bath 103 has been adjusted by adjusting the immersion speed of the Al ingot 300 in the hot-dip galvanizing bath 103, stirring the hot-dip galvanizing bath 103, or the like. For example, if the immersion rate of the Al ingot 300 is increased, the amount of Al supplied to the hot-dip galvanizing bath 103 increases, and the Al concentration (that is, the Free-Al concentration) in the hot-dip galvanizing bath 103 increases. If the immersion rate of the Al ingot 300 is slowed down, the amount of Al supplied to the hot-dip galvanizing bath 103 is reduced, and the increase in the Al concentration in the hot-dip galvanizing bath 103 is suppressed. When the immersion of the Al ingot 300 is stopped, the supply of Al to the hot-dip galvanizing bath 103 is stopped, so that the Al concentration in the hot-dip galvanizing bath 103 gradually decreases.
[0060]
As mentioned above, the dross includes Γ 2-phase dross and δ 1-phase dross. The Γ 2-phase dross and the δ 1-phase dross undergo phase transformation with each other according to the temperature of the hot-dip galvanizing bath 103 and the Al concentration in the hot-dip galvanizing bath 103. That is, the Γ 2-phase dross undergoes a phase transformation into a δ 1-phase dross, and the δ 1-phase dross undergoes a phase transformation into a Γ 2-phase dross. The Al content of the Γ 2-phase dross is different from the Al content of the δ 1-phase dross. Therefore, when the Γ 2-phase dross and the δ 1-phase dross undergo a phase transformation with each other, the absorption and release of Al occur in response to the phase-transformed dross. Therefore, the Γ 2-phase dross and the δ 1-phase dross in the hot-dip galvanizing bath 103 are obtained, and the operating conditions are adjusted based on the obtained Γ 2-phase dross and the δ 1-phase dross to obtain the Γ 2-phase dross and the δ 1-phase dross. The Al concentration in the hot-dip galvanizing bath 103 can be stabilized by adjusting so that the δ 1-phase dross is in a sufficient amount and the Γ 2-phase dross and the δ 1-phase dross are present at an appropriate content ratio.
[0061]
Therefore, in the hot-dip galvanizing treatment method of the present embodiment, the Γ 2-phase dross amount and the δ 1-phase dross amount of the dross in the hot-dip galvanizing bath 103 are obtained. Then, the operating conditions of the hot-dip galvanizing treatment are adjusted based on the amount of Γ 2-phase dross and the amount of δ 1-phase dross in the hot-dip galvanizing bath 103. Preferably, the Γ 2-phase dross amount and the δ 1-phase dross amount are sufficient, and the Γ 2-phase dross amount and the δ 1-phase dross amount are based on the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103. δ Adjust the operating conditions of the hot-dip galvanizing treatment so that both the 1-phase dross amounts are present. Due to the phase transformation between the Γ 2-phase dross and the δ 1-phase dross, the Γ 2-phase dross and the δ 1-phase dross absorb and release Al in the hot-dip galvanizing bath 103. As a result, the Al concentration in the hot-dip galvanizing bath 103 can be stabilized. Preferably, based on the amount of Γ2 phase dross and the amount of δ1 phase dross in the hot dip galvanizing bath 103, the amount of Γ2 phase dross and the amount of δ1 phase dross have a constant total amount and relative amount. Adjust the operating conditions of the plating process.
[0062]
The hot-dip galvanized treatment method of the present embodiment can be applied to a method for manufacturing an alloyed hot-dip galvanized steel sheet (GA) and also to a method for manufacturing a hot-dip galvanized steel sheet (GI). Hereinafter, the hot dip galvanizing treatment method of the present disclosure will be described in detail.
[0063]
[About the hot-dip galvanizing treatment method of this embodiment]
[About hot-dip galvanizing equipment to be used]
In the hot-dip galvanizing treatment method of this embodiment, a hot-dip galvanizing line facility is used. The hot-dip galvanizing line equipment has, for example, the configurations shown in FIGS. 1 and 5. However, as described above, the hot-dip galvanizing line equipment used in the hot-dip galvanizing treatment method of the present embodiment may be the equipment shown in FIGS. 1 and 5, and may be further added to the equipment shown in FIGS. 1 and 5. Other configurations may be added. Further, a well-known hot-dip galvanizing line facility having a configuration different from that of FIGS. 1 and 5 may be used.
[0064]
[About steel sheets used for hot-dip galvanizing]
The steel type and size (plate thickness, plate width, etc.) of the steel plate (base steel plate) used for the hot-dip galvanizing treatment of the present embodiment are not particularly limited. The steel sheet is an alloyed hot-dip galvanized steel sheet or a hot-dip galvanized steel sheet according to each mechanical property (for example, tensile strength, workability, etc.) required for the alloyed hot-dip galvanized steel sheet or the hot-dip galvanized steel sheet to be manufactured. A known steel plate applied to the above may be used. The steel sheet used for the outer panel of the automobile may be used as the steel sheet (base steel sheet) used for the hot-dip galvanizing treatment.
[0065]
The steel sheet (base steel sheet) used for the hot-dip galvanizing treatment of the present embodiment may be a hot-rolled steel sheet or a cold-rolled steel sheet. As the base steel plate, for example, the following steel plate is used.
(A) Pickled hot-rolled steel sheet
(B) Hot-rolled steel sheet that has been pickled and then subjected to Ni pre-plating treatment to form a Ni layer on the surface.
(C) Annealed cold-rolled steel sheet
(D) Cold-rolled steel sheet that has been annealed and then subjected to Ni pre-plating to form a Ni layer on the surface.
The above (a) to (d) are examples of the steel sheet used for the hot-dip galvanizing treatment of the present embodiment. The steel sheet used for the hot-dip galvanizing treatment of the present embodiment is not limited to the above (a) to (d). A hot-rolled steel sheet or a cold-rolled steel sheet that has been subjected to a treatment other than the above (a) to (d) may be used as a hot-dip galvanized steel sheet.
[0066]
[About hot-dip galvanizing bath]
The main component of the hot-dip galvanizing bath 103 is Zn. The hot dip galvanizing bath 103 further contains Al in addition to Zn. That is, the hot-dip galvanizing bath 103 used in the hot-dip galvanizing treatment method of the present embodiment contains a specific concentration of Al.The balance is a plating solution consisting of Zn and impurities. If the hot-dip galvanizing bath 103 contains a specific concentration of Al, it is possible to suppress an excessive reaction between Fe and Zn in the bath, and the steel plate immersed in the hot-dip galvanizing bath 103 and Zn are not compatible. The progress of a uniform alloy reaction can be suppressed. Further, the impurity is, for example, Fe as described later.
[0067]
The preferable Al concentration (more specifically, Free-Al concentration) in the hot-dip galvanizing bath 103 is 0.100 to 0.159% by mass. Here, the Al concentration in the hot-dip galvanizing bath 103 means the Al concentration (mass%) dissolved in the hot-dip galvanizing solution, and means the so-called Free-Al concentration. When the Al concentration in the hot-dip galvanizing bath 103 is in the range of 0.100 to 0.159% in mass%, it is possible to suppress the occurrence of other pattern defects different from the dross defects, and further, alloying and melting. It is possible to suppress the generation of unalloy in the alloying process during the manufacturing process of the galvanized steel sheet.
[0068]
As described above, the hot-dip galvanizing bath 103 according to the present disclosure is a plating bath containing Zn as a main component and further containing Al. The hot-dip galvanizing bath 103 may further contain 0.020 to 0.100% by mass of Fe eluted from the equipment in the bath or the steel plate. That is, the Fe concentration (mass%) in the hot-dip galvanizing bath 103 is, for example, 0.020 to 0.100% by mass. However, the Fe concentration in the hot-dip galvanizing bath 103 is not limited to the above numerical range. Here, the Fe concentration in the hot-dip galvanizing bath 103 means a so-called Free-Fe concentration. That is, in the present specification, the "Fe concentration in the hot-dip galvanizing bath" is melted in the hot-dip galvanizing bath (that is, the liquid) excluding the Fe content contained in the dross (top dross and bottom dross). Means Fe concentration (in phase).
[0069]
The Fe concentration (Free-Fe concentration) in the hot-dip galvanizing bath and the Al concentration (Free-Al concentration) in the hot-dip galvanizing bath can be obtained by the following method. In the hot-dip galvanizing bath 103 of FIG. 2, a sample is taken from within a specific depth range in the depth direction D. More specifically, in the hot-dip galvanizing bath 103 of FIG. 2, a section is formed in a specific depth range in the depth direction D, a specific width range in the width direction W, and a specific length range in the length direction L. A sample is collected from within the specific area (hereinafter referred to as the sampling area). When collecting samples sequentially over time, the sampling positions of the samples shall be the same (within the same sampling area). Cool the collected sample to room temperature. An ICP emission spectrophotometer is used to measure the Fe concentration (% by mass) and the Al concentration (% by mass) in the sample after cooling. The balance other than the Fe concentration and the Al concentration can be regarded as Zn.
[0070]
The Fe concentration obtained by the above-mentioned ICP emission spectrophotometer is a so-called Total-Fe concentration including not only the Fe concentration (Free-Fe concentration) in the hot-dip zinc plating bath but also the Fe concentration in the dross. Similarly, the Al concentration obtained by the above-mentioned ICP emission spectrophotometer is a so-called Total-Al concentration including not only the Al concentration (Free-Al concentration) in the hot-dip galvanizing bath but also the Al concentration in the dross. be. Therefore, the Free-Fe concentration and the Free-Al concentration are calculated using the obtained Total-Fe concentration and Total-Al concentration and a well-known Zn-Fe-Al ternary phase diagram. Specifically, a Zn-Fe-Al ternary phase diagram at the bath temperature at the time of collecting the sample is prepared. As described above, the Zn-Fe-Al ternary phase diagram is well known and is also disclosed in FIGS. 2 and 3 in Non-Patent Document 1. Non-Patent Document 1 is a well-known paper among researchers and developers of hot-dip galvanizing baths. On the Zn-Fe-Al ternary phase diagram, the points specified from the Total-Fe concentration and the Total-Al concentration obtained by the ICP emission spectrophotometer are plotted. Then, a tie line (conjugated line) is drawn on the liquid phase line in the Zn-Fe-Al ternary phase diagram from the plotted points. The Fe concentration at the intersection of the liquid phase line and the tie line corresponds to the Free-Fe concentration, and the Al concentration at the intersection of the liquid phase line and the tie line corresponds to the Free-Al concentration. By the above method, the Fe concentration (Free-Fe concentration) in the hot-dip galvanizing bath and the Al concentration (Free-Al concentration) in the hot-dip galvanizing bath can be obtained.
[0071]
[Hot-dip galvanizing method]
The hot-dip galvanizing treatment method of the present embodiment uses a hot-dip galvanizing bath 103 containing Al. FIG. 7 is a flow chart showing a process of the hot dip galvanizing treatment method of the present embodiment. With reference to FIG. 7, the hot-dip galvanizing treatment method of the present embodiment includes a sample sampling step (S1), a dross amount determination step (S2), and an operating condition adjusting step (S3). Hereinafter, each step will be described in detail.
[0072]
[Sample collection process (S1)]
In the sample collection step (S1), a part of the plating solution is collected as a sample from the hot-dip galvanizing bath 103. In the sample collection step (S1), a sample is collected over time. "Taking a sample over time" means taking a sample every time a specific time elapses. The specific time (the period from one sample to the next) may or may not be constant. For example, a sample may be taken hourly. Further, the next sample may be collected 1 hour after the sample is collected, and the next sample may be collected 30 minutes later. The specific time is not particularly limited.
[0073]
The amount of sample collected from the hot-dip galvanizing bath 103 is not particularly limited. In the dross amount determination step (S2) of the next step, the sample collection amount is not particularly limited as long as the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 can be obtained. The sample collection amount is, for example, 100 to 400 g. The collected sample may be brought into contact with a metal at room temperature having a high thermal conductivity, and the sample may be rapidly cooled to room temperature to solidify. A metal at room temperature having high thermal conductivity is, for example, copper.
[0074]
The sampling position in the hot-dip galvanizing bath 103 is not particularly limited. For example, referring to FIGS. 2 to 4, when the hot-dip galvanizing bath 103 is divided into three equal parts D1 to D3 in the depth direction D, a sample is taken in the uppermost region D1 in the hot-dip galvanizing bath 103. A sample may be collected in the central region D2, or a sample may be collected in the lowermost region D3. The amount of Γ 2-phase dross and the amount of δ 1-phase dross in the samples collected in each region D1 to D3 are different. However, it is possible to determine to some extent whether or not the obtained Γ 2-phase dross amount and δ 1-phase dross amount are large depending on the sampling position. Therefore, the sampling position is not particularly limited. As shown in FIGS. 2 to 4, in the hot-dip zinc plating bath 103, the direction parallel to the plate width direction of the steel plate S is defined as the width direction W, and the depth direction of the hot-dip zinc plating bath 103 is defined as the depth direction D. It is defined, and the direction perpendicular to the width direction W and the depth direction D is defined as the length direction L. In this case, it is preferable to sample over time from within a specific region partitioned by a specific width range in the width direction W, a specific depth range in the depth direction D, and a specific length range in the length direction L. To collect. In short, a sample is taken over time from the same position (within a specific region) in the hot-dip galvanizing bath 103.
[0075]
Preferably, take a sample from the area near the sink roll 107 as much as possible. Specifically, as shown in FIGS. 2 to 4, a sample is taken from within a specific depth range D107 from the upper end to the lower end of the sink roll 107 in the depth direction D of the hot-dip galvanizing bath 103. .. That is, the specific depth range is the depth range D107 from the upper end to the lower end of the sink roll 107. The highest correlation with the influence of the Al concentration on the steel sheet S is the Al concentration (Free-Al concentration) in the vicinity of the steel sheet S. Therefore, the amount of Γ 2-phase dross and the amount of δ 1-phase dross in the vicinity of the sink roll 107 are the most effective indicators for stabilizing the Free-Al concentration. Therefore, it is preferable to take a sample from the depth range D107. In this case, in order to obtain the Γ 2-phase dross amount and the δ 1-phase dross amount based on the sample taken from the range closest to the surface of the steel plate S, the Γ 2-phase dross amount and the δ 1-phase dross amount and the alloyed hot-dip galvanized zinc. It is possible to enhance the correlation between the degree of alloying of the alloyed hot-dip galvanized layer of the plated steel sheet and the adhesion of the hot-dip galvanized layer of the hot-dip galvanized steel sheet. Also in the width direction W and the length direction L, it is preferable to collect a sample from a region near the sink roll as much as possible. As described above, the sample is collected over time from the same region in the hot-dip galvanizing bath 103.
[0076]
[Dross amount determination process (S2)]
In the dross amount determination step (S2), the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 are obtained using the collected sample. The method for obtaining the Γ 2-phase dross amount and the δ 1-phase dross amount using a sample is not particularly limited, and various methods can be considered.
[0077]
For example, a test piece for observing Γ2 phase dross and δ1 phase dross is prepared from the sample collected in the sample collection step (S1). As an example of a test piece for Γ 2-phase dross and δ 1-phase dross observation, a rectangular parallelepiped (small plate shape) having a surface (inspection surface) capable of securing an observation field of view of 15 mm × 15 mm and a thickness of 0.5 mm. ). Using an optical microscope or a scanning electron microscope (SEM) with a predetermined magnification, full-field observation is performed in the above observation field (15 mm × 15 mm), and dross in the entire field is specified. The contrast in the visual field can identify the dross, and the contrast can distinguish between the top dross and the bottom dross.
[0078]
FIG. 8 is an example of a photographic image in a part of the observation field of view of the sample collected in the sample collection step (S1). With reference to FIG. 8, in the photographic image, the hot-dip galvanized matrix 200, the top dross 100T, and the bottom dross 100B are observed. The top dross 100T has a lower brightness (darker) than the mother phase 200 and the bottom dross 100B. On the other hand, the bottom dross 100B has a lower brightness (darker) than the mother phase 200 and a higher brightness (brighter) than the top dross 100T. As described above, the top dross and the bottom dross can be distinguished based on the contrast.
[0079]
Of the dross specified in the above observation field (15 mm × 15 mm), composition analysis using EPMA is performed for each bottom dros, and Γ 2-phase dross and δ 1-phase dross are specified. Further, crystal structure analysis using TEM may be carried out for each bottom dross to identify the Γ 2-phase dross and the δ 1-phase dross in the observation field. In addition, without distinguishing between top dross and bottom dross by contrast, composition analysis using EPMA and / or crystal structure analysis using TEM was performed for each dros, and the type of each dros in the visual field (top). Dross, Γ 2-phase dross and δ 1-phase dross) may be specified.
[0080] [0080]
Based on the specified Γ 2-phase dross and δ 1-phase dross, the amount of Γ 2-phase dross and the amount of δ 1-phase dross in the hot-dip galvanizing bath 103 are obtained. The amount of Γ 2-phase dross and the amount of δ 1-phase dross in the hot-dip galvanizing bath 103 can be determined by various indexes. For example, the number of Γ 2-phase dross and δ 1-phase dross per predetermined area may be used as the Γ 2-phase dross amount and the δ 1-phase dross amount. Here, the predetermined area is not particularly limited, and may be, for example, the entire area of ​​the observation field of view or a unit area (1 cm 2). For example, when the observation field of view is 15 mm × 15 mm, the number of Γ 2-phase dross (pieces / 225 mm 2) and the number of δ 1-phase dross (pieces / 225 mm 2) in the observation field of view (15 mm × 15 mm = 225 mm 2) can be determined. , Γ 2-phase dross amount and δ 1-phase dross amount may be used. Also, the unit area (1 cm 2)The number of Γ 2-phase dross (pieces / cm 2) and the number of δ 1-phase dross (pieces / cm 2) per unit may be used as the Γ 2-phase dross amount and the δ 1-phase dross amount. In this case, the number of Γ 2-phase dross and δ 1-phase dross in the observation field is determined by the following method. First, the circle-equivalent diameter (μm) of the specified Γ 2-phase dross and the circle-equivalent diameter (μm) of the δ 1-phase dross are obtained. The diameter when the area of ​​each Γ 2-phase dross and δ 1-phase dross in the above observation field is converted into a circle is defined as the equivalent circle diameter (μm). Using the photographic image of the observation field, the equivalent circle diameter (μm) of the specified Γ 2-phase dross and δ 1-phase dross is obtained by well-known image processing. In the field of view, the number of Γ 2-phase dross with a circle-equivalent diameter of 10 μm or more and the number of δ 1-phase dross with a circle-equivalent diameter of 10 μm or more are the number of Γ 2-phase dross (pieces / 225 mm 2) and δ 1-phase dross. It is defined as the number of pieces (pieces / 225 mm 2). The number of obtained Γ 2-phase dross (pieces / 225 mm 2) and the number of δ 1-phase dross (pieces / 225 mm 2) are the number of Γ 2-phase dross per unit area (pieces / cm 2) and per unit area. Δ Convert to the number of 1-phase dross (pieces / cm 2). In this way, the number of Γ 2-phase dross with a circle-equivalent diameter of 10 μm or more per unit area (1 cm 2) and the number of δ 1-phase dross with a circle-equivalent diameter of 10 μm or more per unit area (1 cm 2) can be determined as Γ 2-phase. It may be defined as the amount of dross and the amount of δ 1-phase dross. The observation field of view is not limited to the above region (15 mm × 15 mm = 225 mm 2). Further, the upper limit of the equivalent circle diameter of the Γ 2-phase dross and the δ 1-phase dross is not particularly limited. The upper limit of the equivalent circle diameter of the Γ 2-phase dross and the δ 1-phase dross is, for example, 300 μm.
[0081]
Alternatively, other indicators may be the amount of Γ 2-phase dross and the amount of δ 1-phase dross in the hot-dip galvanized solution. For example, in the above-mentioned observation field of view, the area of ​​each bottom dross (each Γ 2-phase dross and each δ 1-phase dross) is obtained. Then, the ratio of the total area of ​​the Γ 2-phase dross to the total area of ​​the bottom dross and the ratio of the total area of ​​the δ 1-phase dross may be used as the Γ 2-phase dross amount and the δ 1-phase dross amount. Further, the ratio of the total area of ​​the Γ 2-phase dross and the ratio of the total area of ​​the δ 1-phase dross to the observation field area may be used as the Γ 2-phase dross amount and the δ 1-phase dross amount. Further, the total area of ​​the Γ 2-phase dross (μm 2) and the total area of ​​the δ 1-phase dross (μm 2) in the above-mentioned visual field may be used as the Γ 2-phase dross amount and the δ 1-phase dross amount. In addition, X-ray diffraction measurement is performed on the test surface of the above-mentioned sample to measure the peak intensity of each bottom dross (Γ 2-phase dross and δ 1-phase dross). Then, the ratio of the peak intensity of the Γ2-phase dross and the peak intensity of the δ1-phase dross to the sum of the peak intensities of each bottom dross (that is, the sum of the peak intensities of the Γ2-phase dross and the peak intensity of the δ1-phase dross). The ratio may be Γ 2-phase dross amount and δ 1-phase dross amount. In X-ray diffraction measurement, it is not easy to clearly distinguish between Γ 2-phase dross and Γ 1-phase dross. However, it is considered that the Γ1 phase dross is hardly present in the hot dip galvanizing bath 103. Therefore, all the peak intensities obtained at the diffraction angle 2θ = 43 to 44 ° are regarded as the peak intensities of the Γ2 phase dross. For example, a Co dry ball is used as a target for X-ray diffraction measurement. The Γ 2-phase dross amount and the δ 1-phase dross amount may be obtained by methods other than the above.
[0082]
By the above method, the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 are obtained using the sample collected in the sample collection step (S1). The dross amount determination step (S2) is preferably performed every time a sample is collected in the sample collection step (S1). By taking a sample over time and determining the amount of Γ 2-phase dross and the amount of δ 1-phase dross each time the sample is taken, the amount of Γ 2-phase dross and the amount of δ 1-phase dross in the hot-dip galvanizing bath 103 can be determined. It is also possible to grasp changes over time. Therefore, the amount of Γ2 phase dross and the amount of δ1 phase dross may be determined over time based on the sample collected over time.
[0083]
[Operating condition adjustment process (S3)]
After determining the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 in the dross amount determination step (S2), the operating condition adjustment step (S3) is carried out.
[0084]
In the operating condition adjustment step (S3), the operating conditions of the hot-dip galvanizing treatment are adjusted based on the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103. Specifically, when the obtained Γ 2-phase dross amount and δ 1-phase dross amount are small, the operating conditions are such that the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 are increased. To adjust (change). If either the Γ 2-phase dross amount or the δ 1-phase dross amount is excessively large, the operating conditions are adjusted (changed) so as to reduce the larger dross. If either the Γ 2-phase dross amount or the δ 1-phase dross amount is excessively small, the operating conditions are adjusted (changed) so that the smaller dross is increased. If the obtained Γ 2-phase dross amount and δ 1-phase dross amount are appropriate, the operating conditions may be maintained as they are. The method for adjusting the operating conditions is not particularly limited as long as the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 can be adjusted. Specifically, the method of adjusting the operating conditions is not particularly limited as long as the Γ 2-phase dross amount and / or the δ 1-phase dross amount in the hot-dip galvanizing bath 103 can be adjusted so as to be able to increase or decrease.
[0085]
Preferably, at least one of the following (A) or (B) is carried out as a method for adjusting the operating conditions.
(A) Adjust the bath temperature of the hot-dip galvanizing bath 103.
(B) Adjust the transport speed of the steel sheet in the hot-dip galvanizing equipment 10 that carries out the hot-dip galvanizing treatment.
[0086]
Regarding (A) above, if the temperature of the hot-dip galvanizing bath is raised, there is a high possibility that the Γ 2-phase dross will undergo a phase transformation into a δ 1-phase dross. Therefore, if the temperature of the hot-dip galvanizing bath is increased, the Γ 2-phase dross in the hot-dip galvanizing bath 103 decreases, and instead, the δ 1-phase dross increases. On the contrary, if the temperature of the hot-dip galvanizing bath is lowered, the possibility that the δ 1-phase dross undergoes a phase transformation into the Γ 2-phase dross increases. Therefore, if the temperature of the hot-dip galvanizing bath is lowered, the δ 1-phase dross in the hot-dip galvanizing bath 103 decreases, and instead, the Γ 2-phase dross increases. Of the Γ 2-phase dross amount and the δ 1-phase dross amount determined in the dross amount determination step (S2), if the Γ 2-phase dross amount is excessively large, the temperature of the hot-dip galvanizing bath is increased to Γ 2. Decrease the amount of phase dross and increase the amount of δ1 phase dross. As a result, the absorption effect of Al in the bath (the effect of reducing Al in the bath) associated with the phase transformation from the δ 1-phase dross to the Γ 2-phase dross is maintained. Of the Γ 2-phase dross amount and the δ 1-phase dross amount determined in the dross amount determination step (S2), if the δ 1-phase dross amount is excessively large, the temperature of the hot-dip galvanizing bath is lowered to δ 1. Decrease the amount of phase dross and increase the amount of Γ2-phase dross. As a result, the effect of releasing Al into the bath (the effect of increasing Al in the bath) associated with the phase transformation from the Γ 2-phase dross to the δ 1-phase dross is maintained. If the amount of Γ 2-phase dross is excessively small, the temperature of the hot-dip galvanizing bath is lowered. δ If the amount of 1-phase dross is excessively small, raise the temperature of the hot-dip galvanizing bath. This makes it possible to stabilize the Al concentration in the hot-dip galvanizing bath 103.
[0087]
Regarding (B), if the transport speed of the steel sheet S in the hot-dip galvanizing facility 10 is increased, the amount of Fe dissolved in the hot-dip galvanizing bath 103 from the steel sheet S immersed in the hot-dip galvanizing bath 103 increases. do. More specifically, if the transport speed of the steel plate S in the hot-dip galvanizing facility 10 becomes high, the amount of the steel plate S passing through the hot-dip galvanizing bath 103 per unit time increases. As a result, the amount of Fe dissolved in the hot-dip galvanizing bath 103 from the steel sheet S immersed in the hot-dip galvanizing bath 103 increases. At this time, the amount of dross generated including the Γ 2-phase dross and the δ 1-phase dross increases as a whole. Therefore, when the total amount of Γ 2-phase dross and δ 1-phase dross in the hot-dip galvanizing bath 103 is excessively small, the hot-dip galvanizing equipment 10 is used to increase the transfer speed of the steel sheet to obtain hot-dip zinc. The amount of Γ 2-phase dross and the amount of δ 1-phase dross in the plating bath 103 can be increased. If both the Γ 2-phase dross amount and the δ 1-phase dross amount are present in a sufficient amount in the hot-dip galvanizing bath 103, a sufficient amount of Al is more to stabilize the Al concentration in the hot-dip galvanizing bath 103. Stable absorption and release. Therefore, in the hot-dip galvanizing bath 103, the transfer speed of the steel plate is adjusted based on the obtained Γ 2-phase dross amount and δ 1-phase dross amount to increase the Γ 2-phase dross amount and δ 1-phase dross amount. The Al concentration can be stabilized.
[0088]
Of the above-mentioned operating conditions (A) and (B), only one of the operating conditions may be adjusted based on the obtained Γ 2-phase dross amount and δ 1-phase dross amount, or (A). And (B) both operating conditions may be adjusted. For example, if the total amount of Γ 2-phase dross and δ 1-phase dross is excessively small and the total amount of δ 1-phase dross is excessively smaller than the amount of Γ 2-phase dross, the steel plate in the hot-dip galvanizing facility 10 The transport speed of the hot-dip galvanizing bath may be increased and the temperature of the hot-dip galvanizing bath may be increased. If the ratio of the Γ 2-phase dross amount to the δ 1-phase dross amount is appropriate, the operating conditions of (A) may be maintained as they are. If the total amount of Γ 2-phase dross and δ 1-phase dross is appropriate, the operating conditions of (B) may be maintained as they are.
[0089]
A threshold value may be set as an index for determining whether or not the dross amount obtained in the dross amount determination step (S2) is appropriate. In this case, the operating conditions may be adjusted depending on whether or not the total amount of the obtained Γ 2-phase dross amount and δ 1-phase dross amount is less than the threshold value. Specifically, depending on whether the total amount of the obtained Γ 2-phase dross and δ 1-phase dross is less than the threshold value, the operating conditions may be changed or maintained without change. good. For example, if the total amount of the obtained Γ 2-phase dross and δ 1-phase dross is less than the threshold value, it is determined that the total amount of Γ 2-phase dross and δ 1-phase dross is excessively small. The operating conditions are changed so that the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip zinc plating bath 103 are increased from the present level. Preferably, when the total amount of the obtained Γ 2-phase dross amount and the δ 1-phase dross is less than the threshold value, the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount is equal to or more than the threshold value. To change the operating conditions. On the other hand, when the total amount of the obtained Γ 2-phase dross and δ 1-phase dross is equal to or greater than the threshold value, the Γ 2-phase dross and δ 1-phase dross in the hot-dip galvanizing bath 103 are sufficiently large. Judge and maintain the operating conditions as they are.
[0090]
The number of Γ 2-phase dross and the number of δ 1-phase dross per predetermined area, for example, as described above, the number of Γ 2-phase dross and the number of δ 1-phase dross in the observation field are the Γ 2-phase dross amount and δ 1. In the case of the phase dross amount, the number corresponding to 15 pieces / cm 2 when converted to the number per unit area (1 cm 2) is the threshold value of the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount. And. In this case, if the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount obtained in the dross amount determination step (S2) is less than the threshold value (15 pieces / cm 2), the Γ 2-phase dross Judging that the total amount of the amount and the δ 1-phase dross amount is excessively small, the operating conditions are adjusted so that the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 increases. do. Preferably, when the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount obtained in the dross amount determination step (S2) is less than the above threshold value (15 pieces / cm 2), the Γ 2-phase dross amount and δ Of the amount of 1-phase drossAdjust the operating conditions so that the total amount is equal to or greater than the threshold value (15 pieces / cm 2). For example, when the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount obtained in the dross amount determination step (S2) is less than 15 pieces / cm 2 in terms of unit area, the above-mentioned (B) ) Is implemented to increase the total amount of Γ 2-phase dross and δ 1-phase dross. The larger the number of Γ 2-phase dross and the number of δ 1-phase dross per predetermined area, the more the Al concentration in the hot-dip galvanizing bath 103 can be stabilized, and therefore the upper limit is not specified. However, if the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount is excessively large, dross defects may occur on the surface of the hot-dip galvanized steel sheet or the alloyed hot-dip galvanized steel sheet. Therefore, for example, an upper limit may be set for the number of Γ 2-phase dross and the number of δ 1-phase dross per predetermined area. For example, the upper limit of the total amount of the Γ 2-phase dross amount and the δ 1-phase dross amount may be 100 per unit area (cm 2).
[0091]
Further, a threshold value may be set as an index for determining whether or not the ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount obtained in the dross amount determination step (S2) is appropriate. Here, the ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount is, for example, the ratio of the Γ 2-phase dross amount to the δ 1-phase dross amount (= Γ 2-phase dross amount / δ 1-phase dross amount). .. In this case, the operating conditions may be adjusted depending on whether or not the ratio of the obtained Γ 2-phase dross amount and the δ 1-phase dross amount is within a predetermined range. Specifically, depending on whether the ratio of the obtained Γ 2-phase dross amount and the δ 1-phase dross amount is within a predetermined range, the operating conditions may be changed or maintained without change. good. For example, if the ratio of the obtained Γ 2-phase dross amount to the δ 1-phase dross amount (for example, Γ 2-phase dross amount / δ 1-phase dross amount) is less than a predetermined lower limit, the δ 1-phase dross amount is Γ. Judging that it is excessively large with respect to the amount of 2-phase dross, the operating conditions are changed so that the amount of Γ 2-phase dross in the hot-dip zinc plating bath 103 is higher than the current amount with respect to the amount of δ 1-phase dross. Alternatively, the operating conditions are adjusted so that the amount of δ 1-phase dross is smaller than the current amount of Γ 2-phase dross. On the contrary, when the ratio of the obtained Γ 2-phase dross amount to the δ 1-phase dross amount (for example, Γ 2-phase dross amount / δ 1-phase dross amount) is larger than the predetermined upper limit, the Γ 2-phase dross amount is δ. Judging that it is excessively large with respect to the amount of 1-phase dross, the operating conditions are changed so that the amount of Γ 2-phase dross in the hot-dip zinc plating bath 103 is smaller than the current amount with respect to the amount of δ 1-phase dross. Alternatively, the operating conditions are adjusted so that the amount of δ 1-phase dross increases with respect to the amount of Γ 2-phase dross. On the other hand, when the ratio of the obtained Γ 2-phase dross amount to the δ 1-phase dross amount (for example, Γ 2-phase dross amount / δ 1-phase dross amount) is within a predetermined range, Γ in the hot-dip zinc plating bath 103. Judging that the ratio of the 2-phase dross amount and the δ 1-phase dross amount is appropriate, the operating conditions are maintained as they are.
[0092]
The number of Γ 2-phase dross and the number of δ 1-phase dross per predetermined area, for example, as described above, the number of Γ 2-phase dross and the number of δ 1-phase dross in the observation field are the Γ 2-phase dross amount and δ 1. When the amount of phase dross is used, the ratio of the number of Γ 2-phase dross to the number of δ 1-phase dross when converted to the number per unit area (1 cm 2) (= number of Γ 2-phase dross / δ 1-phase dross) The range in which (the number of) is 0.05 to 20.00 is an appropriate range in which the ratio of the amount of Γ 2-phase dross to the amount of δ 1-phase dross is appropriate. In this case, the ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount (Γ 2-phase dross amount / δ 1-phase dross amount) obtained in the dross amount determination step (S2) is less than the lower limit (0.05). In some cases, it is determined that the amount of δ 1-phase dross is excessively larger than the amount of Γ 2-phase dross, and the amount of δ 1-phase dross in the hot-dip zinc plating bath 103 is reduced with respect to the amount of Γ 2-phase dross. Or, adjust the phase operation conditions so that the amount of Γ 2-phase dross increases with respect to the amount of δ 1-phase dross. Further, when the ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount (Γ 2-phase dross amount / δ 1-phase dross amount) obtained in the dross amount determination step (S2) is larger than the upper limit value (20.00). , Γ 2-phase dross amount is judged to be excessively larger than δ 1-phase dross amount, so that the Γ 2-phase dross amount in the hot-dip zinc plating bath 103 decreases with respect to δ 1-phase dross amount, or , Δ Adjust the operating conditions so that the 1-phase dross amount increases with respect to the Γ 2-phase dross amount.
[0093]
Preferably, the ratio of the number of Γ 2-phase dross (Γ 2-phase dross amount / δ 1-phase dross amount) to the number of δ 1-phase dross determined by the dross amount determination step (S2) is the lower limit (0.05). If it is less than, the operating conditions are adjusted so that the ratio of the number of Γ 2-phase dross to the number of δ 1-phase dross is equal to or more than the above lower limit (0.05). For example, when the ratio of the number of Γ 2-phase dross to the number of δ 1-phase dross obtained in the dross amount determination step (S2) is less than the above lower limit value (0.05), the operation condition of (A) above is adjusted. Then, the ratio of the number of Γ 2-phase dross to the number of δ 1-phase dross is increased. Further, when the ratio of the number of Γ 2-phase dross to the number of δ 1-phase dross determined by the dross amount determination step (S2) is larger than the above upper limit (20.00), the Γ 2-phase to the number of δ 1-phase dross. The operating conditions are adjusted so that the ratio of the number of dross is equal to or less than the above upper limit (20.00). For example, when the ratio of the number of Γ 2-phase dross to the number of δ 1-phase dross obtained in the dross amount determination step (S2) is larger than the above upper limit value (20.00), the operation condition of (A) above is adjusted. To reduce the ratio of the number of δ 1-phase dross to the number of Γ 2-phase dross.
[0094]
[About the more preferable bath temperature of the hot-dip galvanized bath]
The temperature (bath temperature) of the hot-dip galvanizing bath in the above-mentioned hot-dip galvanizing treatment method is preferably 440 to 500 ° C. The dross in the hot-dip galvanizing bath 103 undergoes phase transformation mainly into top dross, Γ 2-phase dross and δ 1-phase dross, depending on the temperature of the hot-dip galvanizing bath and the Al concentration in the hot-dip galvanizing bath 103. Γ Two-phase dross is likely to occur in the region where the bath temperature is low. δ One-phase dross is likely to be formed in the region where the bath temperature is high. If the region is adjusted so that both the Γ 2-phase dross and the δ 1-phase dros are stably generated, the effect of stabilizing the Al concentration of the hot-dip galvanizing bath is enhanced.
[0095]
Further, if the bath temperature of the hot-dip galvanizing bath is 500 ° C. or lower, it is possible to suppress Zn from evaporating to become a fume. When a fume is generated, the fume adheres to the steel sheet and tends to cause a surface defect (fume defect). The preferable lower limit of the bath temperature of the hot-dip galvanizing bath is 460 ° C, more preferably 465 ° C, still more preferably 469 ° C. The preferred upper limit of the bath temperature of the hot-dip galvanizing bath is 490 ° C, more preferably 480 ° C, still more preferably 475 ° C. It should be noted that the top dross is likely to be generated in the region where the Al concentration is higher than the region where the Γ2 phase dross is generated and the region where the δ1 phase dross is generated.
[0096]
As described above, in the hot-dip galvanizing treatment method of the present embodiment, a sample is sampled from the hot-dip galvanizing bath (sample sampling step (S1)), and the amount of Γ 2-phase dross and δ 1-phase in the hot-dip galvanizing bath 103 are taken. The amount of dross is obtained (dross amount determination step (S2)). Then, the operating conditions of the hot-dip galvanizing treatment are adjusted based on the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath 103 (operating condition adjusting step (S3)). By controlling the total amount and ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount, the Al concentration of the hot-dip galvanizing bath can be stabilized.
[0097]
[Manufacturing method of alloyed hot-dip galvanized steel sheet]
The hot-dip galvanizing treatment method of the present embodiment described above can be applied to a method for manufacturing an alloyed hot-dip galvanized steel sheet (GA).
[0098]
The method for manufacturing an alloyed hot-dip galvanized steel sheet according to the present embodiment includes a hot-dip galvanized treatment step and an alloying treatment step. In the hot-dip galvanizing treatment step, the hot-dip galvanizing treatment method described above is carried out on the steel sheet to form a hot-dip galvanizing layer on the surface of the steel sheet. On the other hand, in the alloying treatment step, the alloying treatment is carried out using the alloying furnace 111 shown in FIG. 2 on the steel sheet having the hot-dip galvanized layer formed on the surface by the hot-dip galvanizing treatment step. As the alloying treatment method, it is sufficient to apply a well-known method.
[0099]
The alloyed hot-dip galvanized steel sheet can be manufactured by the above manufacturing process. In the alloyed hot-dip galvanized steel sheet of the present embodiment, the hot-dip galvanized treatment method of the present embodiment described above is adopted. That is, based on the Γ 2-phase dross amount and the δ 1-phase dross amount, the operating conditions of the hot-dip galvanizing treatment are adjusted to adjust the total amount and ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount. Therefore, the Al concentration in the hot-dip galvanizing bath 103 is stable. As a result, the degree of alloying of the alloyed hot-dip galvanized layer of the manufactured hot-dip galvanized steel sheet is stable. If the degree of alloying of the alloyed hot-dip galvanized layer is stable, the appearance of the alloyed hot-dip galvanized layer becomes more beautiful.
[0100]
The method for manufacturing the alloyed hot-dip galvanized steel sheet of the present embodiment may include a hot-dip galvanized treatment step and a manufacturing step other than the alloying treatment step. For example, the method for producing an alloyed hot-dip galvanized steel sheet of the present embodiment may include a tempering rolling step of performing tempering rolling using the tempering rolling mill 30 shown in FIG. 1 after the alloying treatment step. .. In this case, the appearance quality of the surface of the alloyed hot-dip galvanized steel sheet can be further improved. Further, a manufacturing process other than the temper rolling process may be included.
[0101]
[Manufacturing method of hot-dip galvanized steel sheet]
The hot-dip galvanizing treatment method of the present embodiment described above can also be applied to a method for manufacturing a hot-dip galvanized steel sheet (GI).
[0102]
The method for manufacturing a hot-dip galvanized steel sheet according to the present embodiment includes a hot-dip galvanized treatment step. In the hot-dip galvanizing treatment step, the hot-dip galvanizing treatment method described above is carried out on the steel sheet to form a hot-dip galvanizing layer on the surface of the steel sheet. In the method for manufacturing a hot-dip galvanized steel sheet of the present embodiment, the above-mentioned hot-dip galvanized treatment method of the present embodiment is adopted. Based on the Γ 2-phase dross amount and the δ 1-phase dross amount, the operating conditions of the hot-dip galvanizing treatment are adjusted to adjust the total amount and ratio of the Γ 2-phase dross amount and the δ 1-phase dross amount. Therefore, the Al concentration in the hot-dip galvanizing bath 103 is stable. As a result, the adhesion of the produced hot-dip galvanized layer is stable. If the adhesion of the hot-dip galvanized layer is stable, the workability of the hot-dip galvanized steel sheet is improved.
[0103]
The method for manufacturing a hot-dip galvanized steel sheet according to the present embodiment may include a manufacturing step other than the hot-dip galvanizing treatment step. For example, the method for producing a hot-dip galvanized steel sheet of the present embodiment may include a temper rolling step in which temper rolling is performed using the temper rolling machine 30 shown in FIG. 1 after the hot-dip galvanizing treatment step. In this case, the appearance quality of the surface of the hot-dip galvanized steel sheet can be further improved. Further, a manufacturing process other than the temper rolling process may be included.
Example
[0104]
Hereinafter, the effect of one aspect of the hot-dip galvanizing treatment method of the present embodiment will be described more specifically by way of examples. The conditions in the examples are one condition example adopted for confirming the feasibility and the effect of the present embodiment. Therefore, the hot-dip galvanizing treatment method of the present embodiment is not limited to this one condition example.
[0105]
In the above-mentioned operating condition adjustment step, the relationship between the amount of Γ 2-phase dross and δ 1-phase dross and the Al concentration in the hot-dip galvanizing bath was investigated.
[0106]
Specifically, a hot-dip galvanizing treatment method was carried out using a hot-dip galvanizing facility having the same configuration as in FIG. Specifically, the hot-dip galvanizing treatment was carried out under the conditions that the Γ 2-phase dross amount and the δ 1-phase dross amount were different, and the Al concentration in the hot-dip galvanizing bath was investigated. Γ 2-phase dross amount (pieces / cm 2) and δ 1-phase dross amount (pieces / cm 2) for each test number It is shown in Table 1. As the steel plate, a steel plate for automobile outer panels (cold-rolled steel plate) was used. The bath temperature of the hot-dip galvanizing bath is appropriately set in the range of 440 to 500 ° C. so as to have the Γ 2-phase dross amount (pieces / cm 2) and the δ 1-phase dross amount (pieces / cm 2) shown in Table 1. It was adjusted. The transport speed of the steel sheet was appropriately adjusted to be the Γ 2-phase dross amount (pieces / cm 2) and the δ 1-phase dross amount (pieces / cm 2) shown in Table 1. In each test number, the bath temperature of the hot-dip galvanizing bath and the transport speed of the steel sheet were constant.
[0107]
In each test number, a sample was taken from within a specific depth range D107 from the upper end to the lower end of the sink roll 107 in the depth direction D of the hot dip galvanizing bath 103 of FIG. More specifically, in the hot-dip galvanizing bath 103 of FIG. 2, in a specific depth range D107 in the depth direction D, a specific width range in the width direction W, and a specific length range in the length direction L. Samples were collected from within the specific area to be partitioned (hereinafter referred to as the sampling area). In any of the test numbers, about 400 g of a sample was collected from the same sampling area as described above. The collected sample was cooled to room temperature. Using the cooled sample, the chemical composition of the hot-dip galvanized bath of each test number was measured using an ICP emission spectrophotometer. The Fe concentration (mass%) and Al concentration (mass%) obtained by the measurement are Total-Fe concentration (mass%) and Total-Al concentration (mass%). Therefore, the Fe concentration (Free-Fe concentration) in the hot-dip galvanizing bath is calculated using the obtained Total-Fe concentration and Total-Al concentration and a well-known Zn-Fe-Al ternary system state diagram. did. Specifically, a Zn-Fe-Al ternary phase diagram at the bath temperature at the time of collecting the sample was prepared. On a well-known Zn-Fe-Al ternary phase diagram, the points identified from the Total-Fe concentration and the Total-Al concentration obtained by the ICP emission spectrophotometer were plotted. From the plotted points, a tie line (conjugate line) was drawn on the liquid phase line in the Zn-Fe-Al ternary phase diagram to obtain the intersection of the liquid phase line and the tie line. The Fe concentration at the intersection was defined as the Free-Fe concentration (% by mass). By the above method, the Fe concentration (Free-Fe concentration) in the hot-dip galvanizing bath was determined. As a result, the Fe concentration in the hot-dip galvanizing bath was in the range of 0.020 to 0.050% by mass in all the test numbers.
[0108]
[table 1]

[0109]
For each test number, samples were taken from the hot-dip galvanized bath under the operating conditions shown in Table 1. Specifically, about 400 g of a sample was collected from the above-mentioned sampling area. Γ 2-phase dross and δ 1-phase dross observation test pieces were prepared from the collected samples. The surface to be inspected of the Γ 2-phase dross and δ 1-phase dross observation test pieces was 15 mm × 15 mm, and the thickness was 0.5 mm. Using a 100-fold SEM, full-field observation was performed in the field of view (15 mm × 15 mm) of the surface to be inspected, and dross (top dross, bottom dross) was specified based on the contrast. Furthermore, composition analysis using EPMA was performed to classify bottom dross into Γ 2-phase dross and δ 1-phase dross. Furthermore, the equivalent circle diameters of the specified Γ 2-phase dross and δ 1-phase dross were determined. Among the above-mentioned Γ 2-phase dross and δ 1-phase dross in a field of view of 15 mm × 15 mm, the number of Γ 2-phase dross having a circle equivalent diameter of 10 μm or more and the number of δ 1-phase dross were determined. The number of Γ 2-phase dross with a diameter equivalent to a circle of 10 μm or more (pieces / 225 mm 2) in the observation field of view is converted into the number of Γ 2-phase dross per unit area (pieces / cm 2), and the amount of Γ 2-phase dross is calculated. did. The number of δ 1-phase dross with a diameter equivalent to a circle of 10 μm or more (pieces / 225 mm 2) in the observation field of view is converted into the number of δ 1-phase dross per unit area (pieces / cm 2), and the amount of δ 1-phase dross is calculated. did. The results are shown in Table 1.
[0110]
[Evaluation test for suppressing increase in Al concentration in bath]
The Al concentration in the hot-dip galvanizing bath during the hot-dip galvanizing treatment under the operating conditions of each test number was measured. The Al concentration in the hot-dip galvanized bath was measured by the following method. The chemical composition of the hot dip galvanized bath was measured using an ICP emission spectrophotometer. The Fe concentration (mass%) and Al concentration (mass%) obtained by the measurement are Total-Fe concentration (mass%) and Total-Al concentration (mass%). Therefore, the Al concentration (Free-Al concentration) in the hot-dip galvanizing bath is calculated using the obtained Total-Fe concentration and Total-Al concentration and a well-known Zn-Fe-Al ternary system state diagram. did. Specifically, a Zn-Fe-Al ternary phase diagram at the bath temperature at the time of collecting the sample was prepared. On a well-known Zn-Fe-Al ternary phase diagram, the points identified from the Total-Fe concentration and the Total-Al concentration obtained by the ICP emission spectrophotometer were plotted. From the plotted points, a tie line (conjugate line) was drawn on the liquid phase line in the Zn-Fe-Al ternary phase diagram to obtain the intersection of the liquid phase line and the tie line. The Al concentration at the intersection was defined as the Free-Al concentration (% by mass). By the above method, the Al concentration (Free-Al concentration) in the hot-dip galvanizing bath was determined.
[0111]
The Al ingot was immersed at a constant speed during the hot-dip galvanizing treatment under the operating conditions of each test number. The amount of increase in the Al concentration in the hot-dip galvanizing bath calculated from the total amount of immersed Al was determined and used as the Al increase amount (ingot) (Al concentration (mass%) / unit time). The Al concentration in the hot-dip galvanizing bath during the hot-dip galvanizing treatment under the operating conditions of each test number is measured over time by the above method, and the amount of increase in the Al concentration per unit time is determined, and the amount of increase in Al is obtained. (In the bath) (Al concentration (% by mass) / unit time). The ratio of the Al increase amount (in the bath) to the Al increase amount (ingot) was calculated, and the suppression of the increase in the Al concentration in the hot-dip galvanizing bath was evaluated. The evaluation criteria were as follows. The results are shown in Table 1.
A: The ratio of Al increase (in bath) to Al increase (ingot) is 30% or less.
B: The ratio of the Al increase (in the bath) to the Al increase (ingot) is over 30%.
[0112]
[Evaluation test for suppressing reduction of Al concentration in bath]
The Al concentration in the hot-dip galvanizing bath during the hot-dip galvanizing treatment under the operating conditions of each test number was measured. The Al concentration in the hot-dip galvanizing bath was measured by ICP (radio frequency inductively coupled plasma emission spectroscopy). During the hot-dip galvanizing treatment under the operating conditions of each test number, the immersion of the Al ingot was stopped for a certain period of time to perform the hot-dip galvanizing treatment. The Al concentration in the hot-dip galvanized layer formed on the obtained hot-dip galvanized steel sheet was measured. From the Al concentration in the hot-dip galvanized layer and the transport speed of the steel sheet, the amount of decrease in the Al concentration in the hot-dip galvanized bath per unit time is calculated, and the amount of Al decrease (the amount of Al taken out of the steel sheet) (Al concentration (Al concentration ( Weight%) / unit time). Here, the amount of Al taken out of the steel sheet corresponds to the amount of Al reduced from the hot-dip galvanizing bath in the form of being contained in the hot-dip galvanizing layer as the hot-dip galvanizing treatment progresses. The Al concentration in the hot-dip galvanizing bath during the hot-dip galvanizing treatment under the operating conditions of each test number was measured over time, and the amount of decrease in the Al concentration per unit time was determined, and the amount of Al decrease (in the bath). (Al concentration (mass%) / unit time). The ratio of the Al reduction amount (in the bath) to the Al reduction amount (the amount of Al taken out of the steel sheet) was calculated, and the suppression of the decrease in the Al concentration in the hot-dip galvanizing bath was evaluated. The evaluation criteria were as follows. The results are shown in Table 1.
A: The ratio of the Al reduction amount (in the bath) to the Al reduction amount (Al amount brought out of the steel sheet) is 30% or less.
B: The ratio of the Al reduction amount (in the bath) to the Al reduction amount (Al amount brought out of the steel sheet) exceeds 30%.
[0113]
In Table 1, the column for stabilizing the Al concentration was judged as A in the above-mentioned evaluation test for suppressing the increase in Al concentration in the bath, and was judged as A in the above-mentioned evaluation test for suppressing the decrease in Al concentration in the bath. The test number is described as A. The test number that was judged as B in the above-mentioned evaluation test for suppressing the increase in Al concentration in the bath and / or the above-mentioned evaluation test for suppressing the decrease in Al concentration in the bath is described as B.
[0114]
[Evaluation results]
With reference to Table 1, in test numbers 5 to 7 and 9 to 11, the total amount of Γ 2-phase dross and δ 1-phase dross is 15 pieces / cm 2 or more, and with respect to δ 1-phase dross. The ratio of Γ two-phase dross was controlled to 0.05-20.00. Therefore, in test numbers 5 to 7 and 9 to 11, both the increase in the Al concentration in the hot-dip galvanizing bath and the decrease in the Al concentration in the hot-dip galvanizing bath are suppressed, and the Al concentration in the hot-dip galvanizing bath is suppressed. Stabilized.
[0115]
From the above results, it was found that the Al concentration in the hot-dip galvanizing bath can be stabilized by adjusting the operating conditions based on the Γ 2-phase dross amount and the δ 1-phase dross amount. Then, preferably, the threshold value of the total amount of the Γ 2-phase dross amount and the δ 1-phase dross is 15 pieces / cm 2, and the ratio of the Γ 2-phase dross amount to the δ 1-phase dross amount is 0.05. With an appropriate content ratio in the range of ~ 20.00, the total amount of Γ 2-phase dross and δ 1-phase dross is 15 pieces / cm 2 or more, and Γ 2-phase dross with respect to δ 1-phase dross. It was found that the Al concentration in the hot-dip zinc plating bath can be stabilized by adjusting the operating conditions in the hot-dip zinc plating treatment so that the ratio of the above is in the range of 0.05 to 20.00.
[0116]
The embodiment of the present invention has been described above. However, the embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiment, and the above-mentioned embodiment can be appropriately modified and carried out within a range not deviating from the gist thereof.
Code description
[0117]
10 Hot-dip galvanizing equipment
101 Hot-dip galvanized pot
103 Hot-dip galvanized bath
107 sink roll
109 gas wiping device
111 alloying furnace
202 Snout
The scope of the claims
[Claim 1]
A hot-dip galvanized treatment method used in the manufacture of hot-dip galvanized steel sheets or alloyed hot-dip galvanized steel sheets.
A sample collection process in which a sample is collected from a hot-dip galvanizing bath containing Al, and
Using the collected sample, a dross amount determination step for obtaining the Γ 2-phase dross amount and the δ 1-phase dross amount in the hot-dip galvanizing bath, and
It is provided with an operating condition adjusting step for adjusting the operating conditions of the hot-dip galvanizing treatment based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount.
Hot-dip galvanizing method.
[Claim 2]
The hot-dip galvanizing treatment method according to claim 1.
In the dross amount determination process,
Using the collected sample, the number of Γ 2-phase dross per predetermined area is obtained as the Γ 2-phase dross amount, and the number of δ 1-phase dross per predetermined area is obtained as the δ 1-phase dross amount.
Hot-dip galvanizing method.
[Claim 3]
The hot-dip galvanizing treatment method according to claim 1 or 2.
In the operating condition adjustment process,
Based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount, the bath temperature of the hot-dip galvanizing bath is adjusted to adjust the Γ 2-phase dross amount and the δ 1-phase dross amount.
Hot-dip galvanizing method.
[Claim 4]
The hot-dip galvanizing treatment method according to any one of claims 1 to 3.
In the operating condition adjustment process,
Based on the obtained Γ 2-phase dross amount and the δ 1-phase dross amount, the transport speed of the steel plate in the hot-dip galvanizing facility for performing the hot-dip galvanizing treatment is adjusted to adjust the Γ 2-phase dross amount and the above. δ 1 Adjust the amount of dross,
Hot-dip galvanizing method.
[Claim 5]
The hot-dip galvanizing treatment method according to any one of claims 1 to 4.
In the dross amount determination process,
Using the collected sample, the number of Γ 2-phase dross per unit area (1 cm 2) was calculated as the Γ 2-phase dross amount (pieces / cm 2), and δ per unit area (1 cm 2).The number of 1-phase dross is determined as the δ 1-phase dross amount (pieces / cm 2).
In the operating condition adjustment process,
A hot-dip galvanizing treatment method in which the Γ 2-phase dross amount and the δ 1-phase dross amount are adjusted so as to satisfy the formulas (1) and (2).
15 ≤ Γ 2-phase dross amount + δ 1-phase dross amount (1)
0.05 ≤ Γ 2-phase dross amount / δ 1-phase dross amount ≤ 20.00 (2)
[Claim 6]
The hot-dip galvanizing treatment method according to any one of claims 1 to 5.
In the hot-dip galvanized pot in which the hot-dip galvanizing bath is stored, a sink roll for contacting the steel strip immersed in the hot-dip galvanizing bath and changing the traveling direction of the steel strip up and down is arranged. And
In the sample collection process,
The sample is collected from the depth range from the upper end to the lower end of the sink roll in the hot dip galvanizing bath in the hot dip galvan pot.
Hot-dip galvanizing method.
[Claim 7]
A hot-dip galvanizing treatment step of forming a hot-dip galvanizing layer on the surface of the steel sheet by carrying out the hot-dip galvanizing treatment method according to any one of claims 1 to 6 on the steel sheet.
The steel sheet having the hot-dip galvanized layer formed on the surface thereof is subjected to an alloying treatment to produce the alloyed hot-dip galvanized steel sheet.
Manufacturing method of alloyed hot-dip galvanized steel sheet.
[Claim 8]
A hot-dip galvanizing treatment step for forming a hot-dip galvanizing layer on the surface of the steel sheet by carrying out the hot-dip galvanizing treatment method according to any one of claims 1 to 6 on the steel sheet is provided.
Manufacturing method of hot-dip galvanized steel sheet.