JP2007238997A - Hot dip plated steel sheet, its production method, surface treatment control method, and surface treatment controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a hot dip galvanized steel sheet also having plating quality on high standards which has no surface defects such as unplating and pressing flaws, and can sufficiently withstand even as a steel sheet for an automobile requiring particularly severe plating properties. <P>SOLUTION: When a hot dip galvanized steel sheet is produced, while continuously conveying a steel sheet, at first, a compound comprising at least one kind of specified element selected from the group of specified elements composed of P, Na, K, Cl, S, F, B, C and N is stuck to the surface of the steel sheet, the amount of the specified element stuck to the steel sheet is measured, and the amount of the specified element upon the sticking of the compound is operated in such a manner that the measured value is made coincident with the objective value. Next, the steel sheet to which the compound is stuck is subjected to oxidation treatment, and, after the oxidation treatment, the amount of iron oxide formed on the surface of the steel sheet is measured, and the oxidation treatment conditions are operated in such a manner that the measured value is made coincident with the objective value. Further, reduction treatment and plating treatment are performed so as to obtain a plated steel sheet. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to the manufacture of hot dip galvanized steel sheet, and more particularly to the hot dip galvanized steel sheet, the manufacturing apparatus thereof, and the surface treatment control method in manufacturing hot dip galvanized or alloyed hot dip galvanized steel by continuously conveying the steel sheet. The present invention relates to a surface treatment control device.

  In recent years, in the fields of automobiles, home appliances, building materials, etc., surface-treated steel sheets that have been given rust resistance to steel sheets, especially hot-dip galvanized steel sheets and galvanized layers that can be manufactured at low cost and have excellent rust prevention properties are alloyed. Alloyed hot-dip galvanized steel sheets are used.

  In general, a hot dip galvanized steel sheet is prepared by using a thin steel sheet that has been hot-rolled as a slab or subsequently cold-rolled or heat-treated as a base, and the surface of the base steel sheet is degreased and / or acidized in a pretreatment step. Or after removing the oil on the surface of the base steel plate in the preheating furnace by omitting the pretreatment step, and then performing recrystallization annealing in a non-oxidizing atmosphere or reducing atmosphere, By cooling the steel sheet to a temperature suitable for plating in an oxidizing atmosphere or reducing atmosphere, and then immersing it in a molten zinc bath to which a small amount of Al (about 0.1 to 0.2 mass%) is added without exposure to the air Manufactured. The alloyed hot-dip galvanized steel sheet is manufactured by subsequently heat-treating the hot-dip galvanized steel sheet in an alloying furnace.

  By the way, in recent years, in order to promote the reduction in performance and weight of the steel sheet used as the base, it has been required to increase the strength of the base steel sheet. The amount of high-strength hot-dip galvanized steel sheet used is increasing.

  Addition of solid solution strengthening elements such as Si, Mn, and P is performed as means for increasing the strength of the steel sheet without deteriorating the mechanical properties of the steel sheet.

  However, hot-dip galvanized steel sheets and alloyed hot-dip galvanized steel sheets based on high-strength steel sheets containing Si, Mn, and P have the following problems.

  As described above, the hot dip galvanized steel sheet is subjected to hot dip galvanizing treatment after annealing at a temperature of about 600 to 900 ° C. in a reducing atmosphere. However, since Si and Mn in steel are easily oxidizable elements, Si and Mn are selectively oxidized and concentrated on the surface even in a reducing atmosphere generally used in annealing of steel sheets prior to hot dip galvanizing. And forms an oxide on the surface. Such Si and Mn oxides reduce the wettability with molten zinc during plating and cause non-plating. Therefore, increasing the Si and Mn concentrations in steel increases the relationship between the base steel plate and molten zinc. The wettability decreases rapidly and non-plating occurs frequently. Further, even when non-plating does not occur, there is a problem that the plating adhesion is poor when a steel plate having a high Si and Mn concentration is used as a base.

  Furthermore, when Si and Mn in the steel are selectively oxidized and concentrated on the surface, the oxides of Si and Mn inhibit the Zn-Fe alloying reaction, so alloying is performed in the alloying process after galvanizing. Is significantly delayed. As a result, productivity is significantly inhibited. Further, when alloying is performed at a higher temperature in order to ensure productivity, there is a problem of deterioration of powdering resistance, and it is difficult to achieve both high productivity and good powdering resistance.

  Further, P in the steel segregates at the grain boundaries during annealing and inhibits the Zn-Fe alloying reaction, so that alloying is significantly delayed in the alloying process after hot dip galvanizing. As a result, productivity is significantly inhibited. Further, when alloying is performed at a higher temperature in order to ensure productivity, there is a problem of deterioration of powdering resistance, and it is difficult to achieve both high productivity and good powdering resistance.

  Furthermore, frequently changing alloying treatment conditions such as alloying temperature and alloying time (line speed) due to differences in the steel type takes time to change the treatment conditions, resulting in lower productivity and yield. In order to stabilize the steel in a short time, considerable skill is required, and maintaining a stable alloying treatment is not easy with many operational difficulties.

Several proposals have been made to solve such problems.
For example, it has been proposed to improve wettability with molten zinc by heating steel sheets in an oxidizing atmosphere in advance to form iron oxide on the surface and then performing reduction annealing (for example, Patent Document 1). ).
In addition, there is a method in which sulfur or a sulfur compound is deposited in an amount of 0.1 to 1000 mg / m ² prior to hot dipping, followed by a preheating step in a weakly oxidizing atmosphere and then annealing in a non-oxidizing atmosphere containing hydrogen. It is disclosed (for example, Patent Document 2).
Japanese Patent No. 2587724 Japanese Patent Laid-Open No. 11-50223

  The technique described in Patent Document 1 intends to suppress surface concentration of Si during reduction annealing by heating in an oxidizing atmosphere to form iron oxide in advance. However, as is generally known, since the oxidation rate on the steel sheet surface greatly decreases as the Si concentration in the steel increases, the steel sheet having a high Si concentration in the steel can be obtained only by the oxidation means disclosed in Patent Document 1. Oxidation does not proceed, and it is difficult to obtain an amount of iron oxide necessary to suppress Si surface concentration.

  As a result, the occurrence of non-plating during hot dipping cannot be sufficiently suppressed, and when alloying, the problem of significant delay in alloying, which is a concern in the alloying process, cannot be sufficiently solved.

  In addition, because the oxidation rate varies depending on the Si concentration in the steel, if the oxidation proceeds excessively, the iron oxide peels off during conveyance of the steel sheet, adheres to the conveyance roll, etc., and causes an appearance defect such as pushing down on the steel sheet There is also a problem.

  Furthermore, as described above, since the oxidation rate varies depending on the Si concentration in the steel, it is necessary to control the oxidation treatment conditions according to the Si concentration in the steel in order to obtain a desired amount of iron oxide. However, in the technique described in Patent Document 1, since there is no means for controlling the oxidation treatment conditions, for example, the amount of iron oxide is estimated after visually confirming the occurrence of non-plating after the plating treatment or the pressing iron of the steel plate. Thus, there is no choice but to change the oxidation treatment conditions. Therefore, when continuously hot galvanizing steel sheets having different Si concentrations in steel, there is a problem that the responsiveness is poor and a remarkable yield reduction is unavoidable.

  The technique described in Patent Document 2 attempts to improve wettability with molten zinc by a sulfide layer formed on the surface of a steel plate. However, when applied to a steel plate having a high Si concentration in steel, the surface concentration of Si cannot be suppressed only by the effect of the sulfide layer. The problem cannot be solved. Further, even if the preheating step is performed in a weakly oxidizing atmosphere, when applied to a steel sheet having a high Si concentration in steel, the surface concentration of Si cannot be sufficiently suppressed. The problems of performance and alloying delay cannot be solved.

  Furthermore, since the technique disclosed in Patent Document 2 attaches sulfur or a sulfur compound to the steel plate surface prior to the preheating step of the weak oxidizing atmosphere, the sulfur component is oxidized in the heating furnace in the subsequent annealing treatment step. A large amount of corrosive gas such as sulfur and hydrogen sulfide is released, which causes severe damage to the heating furnace and the equipment in the furnace, requiring frequent repairs and deterioration updates. Further, when releasing the in-furnace gas into the atmosphere, it is necessary to provide a desulfurization device from the viewpoint of preventing air pollution, and further improvement is necessary to realize the process production.

  The present invention has been made in view of such circumstances, has no surface defects such as non-plating or pressing iron, and has a high level of plating quality that can sufficiently withstand even steel plates for automobiles that require particularly severe plating characteristics. An object of the present invention is to provide a hot-dip galvanized steel sheet, a manufacturing apparatus thereof, a surface treatment control method, and a surface treatment control apparatus.

  As described above, in the case of a steel sheet having a high Si concentration in the steel, the oxidation does not proceed only with the oxidation means according to the prior art, and it is difficult to obtain the iron oxide necessary for improving the non-plating. Therefore, in the case of a steel plate having a high Si concentration in steel, it is necessary to promote oxidation by some method.

Therefore, the inventors conducted extensive studies on means for suppressing non-plating of steel sheets having a high Si concentration in the steel and, at the same time, promoting the alloying of the plating layer. As a result, it has been found that the above-mentioned problems can be solved by adhering specific components to the steel sheet surface prior to the oxidation treatment and employing appropriate oxidation treatment conditions.
That is, in the steel by attaching a compound containing at least one specific element selected from a specific element group consisting of P, Na, K, Cl, S, F, B, C, and N to the surface of the steel sheet. It was found that oxidation can be easily promoted even for steel sheets with high Si concentration.
In addition, it is obvious that the amount of iron oxide varies depending on the oxidation treatment conditions, but the inventors have found that the amount of iron oxide varies depending on the amount of the specific element attached to the steel sheet.
Furthermore, by measuring and feeding back the amount of compound adhering to the steel sheet and the amount of iron oxide formed on the steel sheet surface, a more appropriate amount of compound adheres to the steel sheet surface, and a more appropriate amount of iron oxide is produced. It is formed on the steel plate surface. As a result, a hot-dip galvanized steel sheet having a high level of quality can be obtained.
And by adopting appropriate oxidation treatment conditions, the specific components attached to the steel plate surface prior to the oxidation treatment are taken into the steel plate, and in the oxidation treatment atmosphere in the heating furnace and the subsequent reduction treatment atmosphere The release at is suppressed. Therefore, even when elements that are components of corrosive gases such as S and Cl and environmental pollutant gases are used as specific components that adhere to the steel sheet surface, heating furnace damage problems and installation of pollutant gas recovery equipment It is very advantageous for practical use without causing problems.

The present invention has been made based on the above findings, and the gist thereof is as follows.
[1] A compound attachment step of attaching a compound containing at least one specific element selected from the specific element group consisting of P, Na, K, Cl, S, F, B, C, and N to the steel sheet surface; An oxidation treatment step for forming iron oxide on the surface of the steel sheet to which the compound is attached by performing an oxidation treatment, and an iron oxide amount measurement step for measuring the amount of iron oxide formed on the steel plate surface in the oxidation treatment step, An apparatus for producing a hot dip galvanized steel sheet, comprising: a reduction treatment process for performing reduction treatment on a steel sheet having iron oxide formed on a surface thereof; and a plating treatment process for performing plating treatment.
[2] The apparatus for producing a hot dip galvanized steel sheet according to [1], further including an adhesion amount measurement step of measuring an adhesion amount adhered to the steel sheet surface in the compound adhesion step.
[3] The apparatus for producing a hot dip galvanized steel sheet according to [1] or [2], wherein the amount of the compound attached to the steel sheet surface is 0.1 to 1000 mg / m ² in terms of each specific element. .
[4] The apparatus for producing a hot dip galvanized steel sheet according to any one of [1] to [3], wherein a maximum temperature of the oxidation treatment in the oxidation treatment step is over 500 ° C.
[5] The apparatus for producing a hot dip galvanized steel sheet according to any one of [1] to [4], wherein the compound attaching step includes a drying step.
[6] The apparatus for producing a hot dip galvanized steel sheet according to any one of [1] to [5], wherein an alloying treatment is further performed after the plating treatment step.
[7] A steel plate containing a compound containing at least one specific element selected from a specific element group consisting of P, Na, K, Cl, S, F, B, C, and N while continuously conveying the steel plate In the manufacturing process of hot-dip galvanized steel sheet, which is attached to the surface and subjected to oxidation treatment, reduction treatment, and plating treatment, after the oxidation treatment, the amount of iron oxide formed on the steel plate surface is measured, and the measured value matches the target value. A method for controlling the surface treatment of a hot dip galvanized steel sheet, wherein the oxidation treatment conditions are manipulated so that
[8] In the above [7], after attaching the compound to the steel plate surface, the amount of adhesion attached to the steel plate is measured, and the specific element amount at the time of compound attachment is adjusted so that the measured value matches the target value. A surface treatment control method for a hot-dip galvanized steel sheet.
[9] A surface treatment control method for a hot-dip galvanized steel sheet according to [7] or [8], wherein the compound is attached to the surface of the steel sheet, dried, and then oxidized.
[10] The surface treatment control method for a hot dip galvanized steel sheet according to any one of the above [7] to [9], wherein an alloying treatment is further performed after the plating treatment.
[11] A compound attachment device for attaching a compound containing at least one specific element selected from the specific element group consisting of P, Na, K, Cl, S, F, B, C, and N to the steel sheet surface; An oxidation treatment apparatus that forms an iron oxide on the surface of the steel sheet to which the compound is attached by performing an oxidation treatment, and an iron oxide amount measurement that is provided after the oxidation treatment apparatus and measures the amount of iron oxide formed on the steel sheet surface An iron oxide amount adjusting device for operating the conditions of the oxidation treatment device so as to match the measured iron oxide amount with a target value, and a reduction treatment for performing a reduction treatment on a steel plate having iron oxide formed on the surface A surface treatment control apparatus for a hot dip galvanized steel sheet, comprising: an apparatus; and a plating apparatus for performing plating.
[12] In the above [11], the compound adhesion amount measuring device that is provided after the compound adhesion device and measures the adhesion amount adhered to the surface of the steel sheet, and the measured adhesion amount is made to coincide with the target value. An apparatus for controlling the surface treatment of a hot-dip galvanized steel sheet, further comprising: an adhesion amount adjusting device for operating conditions of the compound attaching device.
[13] The surface treatment control apparatus for hot-dip galvanized steel sheets according to [11] or [12], wherein the compound adhesion apparatus includes a drying apparatus.
[14] The hot dip galvanized steel sheet according to any one of [7] to [10], wherein the amount of iron oxide on the steel sheet surface is adjusted by the surface treatment control method for a hot dip galvanized steel sheet according to any one of claims 7 to 10.

  According to the present invention, a hot-dip galvanized steel sheet having a beautiful surface appearance free of surface defects such as non-plating and pressing iron and having excellent plating adhesion, and beautiful without surface defects such as non-plating and pressing iron An alloyed hot-dip galvanized steel sheet having a surface appearance and excellent powdering resistance can be obtained. Further, in manufacturing these steel sheets, it is possible to perform process production at a low cost and stably with high productivity, which has a remarkable industrial effect.

Hereinafter, the present invention will be specifically described.
In this invention, after making the compound containing a specific element adhere to the steel plate surface, an oxidation process, a reduction process, and a plating process are given. First, the structure of the manufacturing apparatus of the hot dip galvanized steel plate suitable for implementation of this invention is demonstrated. FIG. 1 is a diagram showing an apparatus for producing a hot dip galvanized steel sheet, which is one embodiment of the present invention.

  The steel plate 1 is cleaned in a normal pretreatment process (not shown), a compound containing a specific element is attached by the compound attaching device 2, iron oxide is formed on the steel plate surface by the oxidation treatment device 3, and reduction treatment is performed. The iron oxide is reduced by the apparatus 4, the steel sheet is cooled to a temperature suitable for plating by the cooling processing apparatus 5, and hot dip galvanizing is performed by the plating processing apparatus 6. Next, after adjusting to a desired plating thickness by the plating adhesion amount adjusting device 7, an alloying treatment is performed by the alloying processing device 8 as necessary.

First, a compound adhesion process is demonstrated. In FIG. 1, a compound containing at least one specific element selected from a specific element group consisting of P, Na, K, Cl, S, F, B, C, and N is added to the steel sheet in the compound deposition apparatus 2. Adhere to the surface.
Here, the specific element is P, Na, K, Cl, S, F, B, C and N, and a compound containing at least one selected from these specific element groups, or these elements as elements It is attached to the surface of the steel sheet alone (limited to those that can be attached alone). Examples of the compound containing such a specific element include the following.

Phosphoric acid (H ₃ PO ₄ ), potassium phosphate (K ₃ PO ₄ ), ammonium phosphate ((NH ₄ ) ₃ PO ₄ ), sodium phosphate (Na ₃ PO ₄ ), sodium hydrogen phosphate (Na ₂ HPO ₄ ), P-containing compounds such as iron phosphate (FePO ₄ ), phosphonic acid (H ₃ PO ₃ ) and phosphinic acid (H ₃ PO ₂ ),
Sodium hydroxide (NaOH), sodium sulfate (Na ₂ SO ₄ ), sodium sulfide (Na ₂ S), sodium thiosulfate (Na ₂ S ₂ O ₃ ), sodium chloride (NaCl), sodium carbonate (Na ₂ CO ₃ ) , Sodium citrate (Na ₃ C ₆ H ₅ O ₇ ), sodium cyanate (NaCNO), sodium acetate (CH ₃ COONa), sodium hydrogen phosphate (Na ₂ HPO ₄ ), sodium phosphate (Na ₃ PO ₄ ) , sodium fluoride (NaF), sodium bicarbonate (NaHCO _3), sodium nitrate _{(NaNO 3), (2 (} COONa)) sodium oxalate, sodium tetraborate (Na ₂ B ₄ O ₇₎ and sodium oxide (Na ₂ Na-containing compounds such as O)
Potassium hydroxide (KOH), potassium acetate (CH ₃ COOK), potassium borate (K ₂ B ₄ O ₇ ), potassium carbonate (K ₂ CO ₃ ), potassium chloride (KCl), potassium cyanate (KCNO), citric acid Potassium hydrogen (KH ₂ C ₆ H ₅ O ₇ ), potassium fluoride (KF), potassium molybdate (K ₂ MoO ₄ ), potassium nitrate (KNO ₃ ), potassium permanganate (KMnO ₄ ), potassium phosphate (K ₃ PO ₄ ), potassium sulfate (K ₂ SO ₄ ), potassium thiocyanate (KSCN) and potassium oxalate ((COOK) ₂ ) and other K-containing compounds,
Hydrochloric acid (HCl), sodium chloride (NaCl), ammonium chloride (NH ₄ Cl), antimony chloride (SbCl ₃ ), potassium chloride (KCl), iron chloride (FeCl ₂ , FeCl ₃ ), titanium chloride (TiCl ₄ ), chloride Cl-containing compounds such as copper (CuCl), barium chloride (BaCl ₂ ), molybdenum chloride (MoCl ₅ ) and sodium chlorate (NaClO ₃ ),
Sulfuric acid (H ₂ SO ₄ ), sodium sulfate (Na ₂ SO ₄ ), sodium sulfite (Na ₂ SO ₃ ), sodium sulfide (Na ₂ S), ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), ammonium sulfide ((NH _{4) 2} S), sodium thiosulfate _{(Na 2 S 2 O 3)} , sodium bisulfate (NaHSO _4), ammonium hydrogen sulfate (NH ₄ HSO _4), potassium sulfate (K ₂ SO _4), iron sulfate (FeSO ₄ , Fe ₂ (SO ₄ ) ₃ ), ammonium iron sulfate (Fe (NH ₄ ) ₂ (SO ₄ ) ₂ , FeNH ₄ (SO ₄ ) ₂ ), barium sulfate (BaSO ₄ ), antimony sulfide (Sb ₂ S ₃ ), S-containing compounds such as iron sulfide (FeS), thiourea (H ₂ NCSNH ₂ ), thiourea dioxide ((NH ₂ ) ₂ CSO ₂ ), thiophenate of SCH group and thiocyanate having SCN group,
Antimony fluoride (SbF ₃ ), ammonium fluoride (NH ₄ F), potassium fluoride (KF), ammonium hydrogen fluoride (NH ₄ FHF), hydrofluoric acid (HF), sodium fluoride (NaF), fluorine F-containing compounds such as barium fluoride (BaF) and cobalt fluoride (CoF ₃ ),
Boric acid (H ₃ BO ₃ ), potassium borate (K ₂ B ₄ O ₇ ), sodium tetraborate (Na ₂ B ₄ O ₇ ), lead borate (Pb (BO ₂ ) ₂ ) and manganese borate (MnH ₄ (BO _{3 2} ) B-containing compounds such as
C and N-containing compounds, including oxalic acid and oxalates, citric acid and citrates, and nitric acid and nitrates. However, the present invention is not limited to this, and even if a compound containing at least one selected from P, Na, K, Cl, S, F, B, C and N other than the above is used, the effect expected in the present invention can be obtained. It goes without saying that it is obtained.

  It does not specifically limit as a method to adhere the compound containing an above described specific element to the steel plate surface. Since it only has to be physically attached, for example, using a solution in which the compound is dissolved or mixed with water or an organic solvent, a method of immersing a steel plate in this solution, a method of spraying the solution with a spray, etc. The method of apply | coating a solution with a roll coater etc. is employable. In addition, the effects of the present invention can be obtained in the same manner by directly applying the compound. In addition, in FIG. 1, the compound adhesion apparatus 2 is set as the apparatus structure which can achieve the said method.

  Prior to attaching the compound, a pretreatment conventionally used, such as electrolytic degreasing or pickling, may be performed as necessary. Moreover, after making the said compound adhere, pretreatment conventionally used, such as electrolytic degreasing and pickling, can also be given as needed. However, in this case, it is important that the compound remains attached to the steel plate surface even after the treatment. Furthermore, you may use the method of making it adhere at the time of rolling using the rolling oil containing the said compound. In any case, it is important to perform each treatment so that the compound containing the specific element adheres to the steel plate surface when the steel plate is oxidized.

The amount of the compound containing the specific element is preferably in the range of 0.1 to 1000 mg / m ² as the specific element amount. When the adhesion amount of the compound is less than 0.1 mg / m ² , the above-described effects of the present invention may not be obtained. On the other hand, if it exceeds 1000 mg / m ² , the effect of the present invention may be saturated and disadvantageous economically. In addition, it does not specifically limit as a method of controlling the amount of specific elements in the range of 0.1-1000 mg / m < ² >. For example, using a solution in which a predetermined amount of the compound is dissolved or mixed with water or an organic solvent, the amount of the specific element in the solution is measured in advance, and a steel plate is immersed in the solution or the solution is sprayed. The amount of the specific element adhering to the steel sheet can be controlled by adjusting the amount of the steel sheet adhering solution with a ringer roll or the like after spraying. Moreover, when apply | coating the said solution with a roll coater etc., the amount of specific elements adhering to a steel plate can be controlled by adjusting the amount of solutions adhering to a steel plate.

In order to control to the said adhesion amount, in this invention, it is preferable to have the adhesion amount measurement process of measuring the adhesion amount adhering to the steel plate surface in the compound adhesion process. For example, in FIG. 1, the adhesion amount measuring device 9 is provided after the compound adhesion device 2, and the adhesion amount of the compound containing the specific element adhered to the steel sheet surface in the compound adhesion device 2 is measured by the adhesion amount measurement device 9. To do. In the measurement, the amount of the compound is only required to be able to measure at least the amount of the specific element adhering to the steel sheet, and the method for measuring the amount of adhesion is not particularly limited, but examples thereof include the following methods. When the compound is attached as a solid, for example, a method of measuring the specific element intensity by a fluorescent X-ray method is possible. A calibration curve is created in advance for the relationship between the specific element amount and the specific element intensity, and the specific element amount can be obtained from the specific element intensity measured by the online fluorescent X-ray method. When the compound is attached as an aqueous solution, a method for measuring the water absorption peak intensity by, for example, an infrared absorption method is possible. A calibration curve is prepared in advance for the relationship between the amount of aqueous solution and the absorption peak intensity of water, and the amount of aqueous solution can be determined from the peak intensity of water measured by the online infrared absorption method. If the concentration of the specific element in the aqueous solution is measured in advance, the amount of the specific element can be obtained from the absorption peak intensity of water. When measurement in the steel plate width direction is necessary, a method of scanning the measuring device or a method of arranging a plurality of measuring devices in the steel plate width direction is possible.
The above is a representative example, and it goes without saying that the effect of the present invention can be obtained by any method other than the above that can measure the amount of the specific element online.

Furthermore, in the present invention, it is preferable to manipulate the specific element amount at the time of adhesion so that the measured adhesion amount matches the target value. For example, in FIG. 1, the adhesion amount adjusting device 11 is installed so as to feed back the result of the adhesion amount measuring device 9 and reflect it in the compound attaching device 2. The function of operating the conditions of the compound deposition apparatus 2 so as to match the deposition amount with the target value is received. Here, the method for manipulating the specific element amount at the time of adhesion based on the actual measurement value of the specific element amount adhering to the steel plate is not particularly limited. For example, using a solution containing the specific element described above, When adjusting the amount of steel plate adhesion with a ringer roll after dipping the steel plate in the solution or spraying the solution with a spray etc., change the amount of solution adhering to the steel plate by changing the pressing pressure of the ringer roll etc. The specific element amount at the time of attachment can be manipulated with. Alternatively, the amount of the specific element at the time of attachment can be manipulated by changing the concentration of the specific element in the solution.
The above is a representative example, and it goes without saying that the effect of the present invention can be obtained by any method other than the above which can manipulate the specific element amount at the time of adhesion.

Moreover, in this invention, it is preferable to make it dry after making the compound containing a specific element adhere to the steel plate surface. After the compound containing the specific element was dissolved in water or an organic solvent or mixed with the solution, the compound was attached to the steel sheet surface, and then the oxidation treatment process, reduction treatment process, and plating treatment process were performed without drying. In this case, uneven application of the solution may occur, which may cause a problem in surface appearance. Although the details of this reason are unclear, when the steel sheet is introduced into the oxidation treatment process in a state where the solution is not dried, and heated and dried in the oxidation treatment process, the specific element amount on the steel sheet may be reduced depending on the sheet passing conditions. It is estimated that the occurrence of uniformity is a cause of coating unevenness. When non-uniformity of specific element amount occurs on the steel plate, non-uniformity occurs in the iron oxide amount in the oxidation treatment process, or non-uniformity in the initial Zn-Fe alloying reaction or plating adhesion amount in the plating treatment process Sometimes. As a result, since unevenness in appearance due to nonuniformity of the specific element amount occurs, it is preferable to dry the compound containing the specific element after adhering it to the steel sheet. However, since a drying facility is required, an increase in facility costs is caused, and therefore the drying facility may be omitted when the above-described coating unevenness does not occur.
Here, the drying device is not particularly limited, and may be any device that can dry the solution, for example, and conventionally used drying devices such as radiant heating, induction heating, and electric heating can be used.

After the compound is attached to the steel sheet surface, in the present invention, oxidation treatment is performed to form iron oxide on the steel sheet surface. Next, the oxidation treatment process will be described. For example, in FIG. 1, the oxidation treatment device 3 is provided after the adhesion amount measuring device 9, and the oxidation treatment device 3 forms iron oxide on the steel sheet surface to which the compound is adhered. As a means for oxidizing the steel sheet, for example, it can be easily achieved by heating the steel sheet in an oxidizing atmosphere, but the difference in the oxidation means does not hinder the effect of the present invention, and the steel sheet can be oxidized. There is no particular limitation as long as it can be used.
The means for heating the steel plate may be a conventionally used heating method such as burner heating, induction heating, radiant heating, and current heating, and is not particularly limited.

  For example, as the burner heating method, a conventionally used heating furnace such as an oxidation furnace or a non-oxidation furnace can be used. In the case of the burner heating method, for example, the steel sheet can be easily oxidized by setting the air-fuel ratio of the direct fire burner to exceed 1.0.

  In addition, in the case of the induction heating method, the radiant heating method, and the energization heating method, the steel plate can be easily oxidized by setting the atmosphere in the vicinity of the steel plate to be heated to an oxidizing atmosphere. The oxidizing atmosphere is generally one containing one or more oxidizing gases such as oxygen, water vapor and carbon dioxide, but is not particularly limited as long as the steel sheet can be oxidized.

  Further, as a condition for oxidizing the steel sheet, it is important to perform the heat treatment in which the maximum temperature reaches over 500 ° C. in an oxidizing atmosphere. This is because when the heat treatment is 500 ° C. or less, the amount of iron oxide produced is insufficient, for example, suppressing surface enrichment of Si, Mn, etc., suppressing grain boundary segregation such as P, and the like on the steel plate surface prior to oxidation treatment. This is because the effects of the present invention, such as suppression of gas release of the adhered components, may not be sufficiently obtained. On the other hand, the upper limit is not particularly limited, but is preferably less than the steel plate temperature required for the subsequent reduction treatment because it is practically economical.

If the amount of iron oxide formed on the surface of the steel sheet is too small, the amount of iron oxide may be insufficient and it may be difficult to suppress surface concentration of Si or the like. On the other hand, if the amount of iron oxide is excessive, the effect of suppressing the surface enrichment of Si or the like is saturated, but in the subsequent reduction treatment step, the reduction cannot be sufficiently performed and remains as unreduced iron oxide, There is a possibility of causing a significant delay in alloying in the alloying process after plating. Further, if the amount of oxygen iron is excessive, the iron oxide may be peeled off during conveyance of the steel sheet and may cause problems such as poor appearance such as adhesion to a conveyance roll or the like and generation of pressing iron on the steel sheet.

Therefore, in this invention, it has the iron oxide amount measurement process which measures the iron oxide amount formed in the steel plate surface. For example, in FIG. 1, an iron oxide measuring device 10 is provided after the oxidation treatment device 3, and the amount of iron oxide formed by the oxidation treatment device 3 is measured by the iron oxide measurement device 10. The method for measuring the amount of iron oxide is not particularly limited, but there are the following methods. For example, a method of measuring the oxygen intensity by a fluorescent X-ray method is possible. A calibration curve is created in advance for the relationship between the amount of iron oxide and oxygen intensity, and the amount of iron oxide can be determined from the oxygen intensity measured by the on-line fluorescent X-ray method. Further, as an optical measurement method, for example, a method of measuring the emissivity of a steel plate is possible. Prepare a calibration curve for the relationship between the emissivity, steel plate temperature, etc. of the steel plate with iron oxide formed on the surface in advance, and the amount of iron oxide. The amount can be determined. When measurement in the steel plate width direction is necessary, a method of scanning the measuring device or a method of arranging a plurality of measuring devices in the steel plate width direction is possible.
The above shows a typical example, and it goes without saying that the effect of the present invention can be obtained by any method other than the above that can measure the amount of iron oxide online.

  Furthermore, in the present invention, the oxidation treatment conditions are manipulated so that the measured iron oxide amount matches the target value. For example, in FIG. 1, an iron oxide amount adjusting device 12 is provided so that the result of the iron oxide amount measuring device 10 is fed back and reflected in the oxidation processing device 3. The iron oxide amount adjusting device 12 measures the iron oxide amount. In response to the result of the apparatus 10, it has a function of operating the conditions of the oxidation treatment apparatus 3 so that the amount of iron oxide matches the target value. This is because, for example, the oxidation rate varies depending on the Si concentration in the steel as described above, and therefore it is necessary to adjust the oxidation treatment conditions depending on the Si concentration in the steel in order to obtain a desired amount of iron oxide. Here, the method of operating the oxidation treatment condition based on the actual measurement value of the iron oxide amount is not particularly limited. For example, when a heating furnace is used, the steel plate temperature can be changed. In addition, when a direct-fired burner heating method is used as a heating furnace, the air-fuel ratio of the burner is changed, or in the case of an induction heating method, a radiant heating method, and an electric heating method, for example, the concentration of an oxidizing atmosphere such as oxygen or water vapor is changed. Can be changed. However, when changing the concentration of the oxidizing atmosphere, there is a problem that the responsiveness deteriorates if the volume of the heating furnace is large. In such a case, the oxidation treatment conditions can be manipulated by changing the steel plate temperature. That is, it is only necessary to select optimum oxidation treatment conditions for operation in consideration of operational costs, responsiveness, and the like.

  Note that the above shows a representative example, and the effect of the present invention can be obtained if the method can operate the oxidation treatment conditions so that the actually measured value of the iron oxide amount other than the above is matched with the target value. Needless to say.

  In the present invention, after the oxidation treatment is performed to form iron oxide on the steel sheet surface, the reduction treatment is performed. Next, this reduction process step will be described. For example, in FIG. 1, the reduction treatment device 4 is installed after the iron oxide amount measurement device 10, and the reduction treatment device 4 performs a reduction treatment on a steel plate having iron oxide formed on the surface by the oxidation treatment device 3. The reduction treatment method may be performed according to a conventionally used method, and is not particularly limited. For example, it is common to perform reduction treatment at a temperature of about 600 to 900 ° C. in a reducing atmosphere containing hydrogen in a radiant heating type annealing furnace, but any means can be used if iron oxide on the surface of the steel sheet can be reduced. Absent.

Next, the plating process will be described. For example, in FIG. 1, a steel sheet that has been subjected to reduction treatment by the reduction treatment device 4 is cooled to a temperature suitable for plating in a non-oxidizing or reducing atmosphere by a cooling treatment device 5, and then plated. The treatment apparatus 6 is immersed in a plating bath to perform hot dip galvanization. Further, the plating adhesion amount adjusting device 7 adjusts the thickness of the plating layer according to the purpose. This hot dip galvanizing treatment may be performed in accordance with a conventional method. For example, the plating bath temperature is about 440 to 520 ° C., the plating bath immersion temperature of the steel sheet is substantially equal to the plating bath temperature, and the Al concentration in the galvanizing bath is generally about 0.1 to 0.2%. However, there is no particular limitation.
Depending on the application of the product, the plating conditions such as the plating temperature and the plating bath composition may be changed. However, the difference in the plating conditions does not affect the effect of the present invention and is not particularly limited. . For example, even if elements such as Pb, Sb, Fe, Mg, Mn, Ni, Ca, Ti, V, Cr, Co, and Sn are mixed in the plating bath, the effect of the present invention is not changed. .
Furthermore, the method for adjusting the thickness of the plated layer after plating is not particularly limited, but generally, gas wiping is used, and the gas pressure of gas wiping, the distance between the wiping nozzle and the steel plate, etc. are adjusted. By adjusting, the thickness of the plating layer is adjusted. At this time, the thickness of the plating layer is not particularly limited, but is preferably about 3 to 15 μm. This is because if the thickness is less than 3 μm, sufficient rust resistance cannot be obtained, while if it exceeds 15 μm, not only the rust resistance is saturated, but also workability and economy may be impaired. However, the difference in the thickness of the plating layer does not hinder the effect of the present invention and is not particularly limited.

Moreover, in this invention, it is also possible to give an alloying process after the above hot dip galvanizing. For example, in FIG. 1, after the thickness of the plating layer is adjusted by the plating adhesion amount adjusting device 7, alloying processing is performed by the alloying processing device 8 to obtain an alloyed hot dip plated steel sheet. As described above, according to the present invention, since Si surface concentration and P grain boundary segregation during annealing can be suppressed, the problem in the prior art of significant alloying delay can be solved. As a result, an alloyed hot-dip galvanized steel sheet having excellent powdering resistance can be produced without impairing productivity. As the alloying treatment method, any conventionally used heating method such as gas heating, induction heating, and current heating may be used, and it is not particularly limited. For example, the alloying plate temperature is generally about 460 to 600 ° C., and the alloying holding time is generally about 5 to 60 seconds.
By the above, the hot-dip galvanized steel sheet (including the alloyed hot-dip galvanized steel sheet) of the present invention is obtained.

In addition, in the above, it does not specifically limit about the component composition of a plating original plate (underlying steel plate), A conventionally well-known composition can be utilized. However, in order to suitably carry out the present invention, it is preferable that the base steel plate has the following composition. Hereinafter, in the present specification, “%” indicating the components of steel is all “mass%”.
Si: 0.1-3.0%
The lower limit is defined as 0.1% because, if the concentration is less than this, the Si surface concentration during annealing is not so remarkable, so that non-plating occurs frequently or there is no significant alloying delay. The upper limit is set to 3.0% because Si is an element that can increase the strength while ensuring the ductility of steel, but if it exceeds 3.0%, the steel sheet itself becomes too hard, Less than this is preferable.
Mn: 0.1-5% or less The lower limit is defined as 0.1% because if the concentration is less than this, the Mn surface concentration at the time of annealing is not so remarkable, and therefore non-plating does not occur frequently. . Mn is an element useful for increasing the strength of steel, and is an element normally contained in steel in a range of 5% or less. Even in the present invention, even if Mn is contained in this range in the base steel plate Good. In particular, the effect can be exhibited by containing 0.1% or more, preferably 0.5% or more. Moreover, it is preferable that Mn content shall be 3.0% or less from the point of ensuring weldability and a strength-ductility balance. More preferably, it is 0.5 to 3.0% of range.
P: 0.005-0.5%
The lower limit is defined as 0.005% because the grain boundary segregation at the time of annealing is not so remarkable when the concentration is less than this, and therefore, the alloying is not significantly delayed. P is an element useful for increasing the strength of steel, and is an element that is usually contained in steel in a range of 0.5% or less, and even in the present invention even if P is contained in this range in the base steel plate. Good. In particular, the effect can be exhibited by containing 0.01% or more, preferably 0.015% or more. Further, the P content is preferably 0.2% or less from the viewpoint of weldability. More preferably, it is 0.015 to 0.2% of range.
C: 0.5% or less C is an element contained in steel and is generally contained in the range of 0.0001 to 0.5%. Also in the present invention, C may be contained in this range in the base steel plate. C is not only useful for increasing the strength, but also an element useful for controlling the structure such as generating retained austenite to improve the strength-ductility balance. In order to express these effects, it is preferably contained in an amount of 0.05% or more. However, if the content exceeds 0.25%, weldability deteriorates, so it is preferable to set the upper limit to 0.25%.
Al: 5.0% or less
Al is an element added complementary to Si and is preferably contained in an amount of 0.01% or more. However, if the Al content exceeds 5.0%, it also has an adverse effect on securing weldability and strength-ductility balance. Therefore, Al is preferably 5.0% or less. More preferably, it is 0.01 to 3.0% of range.

  Examples of elements other than those exemplified above include Ti, Nb, V, Cr, S, Mo, Cu, Ni, B, Ca, N, and Sb. The content of these elements is as follows: Ti: 1% or less, Nb: 1% or less, V: 1% or less, Cr: 3% or less, S: 0.1% or less, Mo: 1% or less, Cu: 3% or less Ni: 3% or less, B: 0.1% or less, Ca: 0.1% or less, N: 0.1% or less, and Sb: 0.5% or less, the present invention can be suitably implemented. The total content of one or more selected from these elements is preferably in the range of 5% or less. The balance is Fe and inevitable impurities.

Using the hot-dip galvanized steel plate manufacturing equipment shown in Fig. 1, the steel plate made of the components shown in Table 1 is passed at a plate passing speed of 80 mpm, and the hot dip galvanized plate is manufactured under the following conditions. did.
First, electrolytic degreasing is carried out with a degreasing liquid whose main component is 5% NaOH, and an aqueous solution of a compound containing a specific element in the compound adhering apparatus 2 composed of an aqueous spraying apparatus, a ringer roll and a radiant heating type drying apparatus. Was applied to the steel plate 1. As a comparison, a radiant heating type drying apparatus was passed through by air. The amount of the specific element adhering to the steel sheet is measured by the X-ray fluorescence method with the adhesion amount measuring device 9, and the amount of the aqueous solution at the time of adhering the steel sheet is adjusted with the adhesion amount adjusting device 11 so that the desired specific element amount is obtained. The specific element amount was manipulated. The oxidation treatment apparatus 3 was heated and heated in a direct-fired burner type heating furnace to change the maximum temperature reached by the steel sheet and the air-fuel ratio of the burner combustion gas. As a comparison, an open fire burner was extinguished and passed through without assuming that oxidation treatment was not performed. The amount of iron oxide on the surface of the steel sheet was measured by an X-ray fluorescence method using an iron oxide amount measuring device 10 and converted to the amount of oxygen in the iron oxide. The reduction treatment was carried out using the reduction treatment device 4 at an annealing temperature of 850 ° C. in a 5 vol% hydrogen + balance nitrogen atmosphere (dew point: −30 ° C.). In addition, the said reduction process condition was made into the condition 1, and the case where reduction annealing was carried out in 1 vol% hydrogen + remainder nitrogen atmosphere (dew point: +10 degreeC) as the comparison was made into the reduction process condition 2. After the reduction treatment, the steel sheet was cooled to 460 ° C. by the cooling treatment device 5 and hot dip galvanized by the plating treatment device 6. As the plating conditions, a 460 ° C. galvanizing bath containing 0.14% Al (Fe saturated) was used.
After plating, the adhesion amount was adjusted to 45 g / m 2 on one side with the plating adhesion amount adjusting device 7, and alloying treatment was performed with the alloying processing device 8.

For the plated steel sheet obtained as described above, the plating appearance and plating adhesion of the plated steel sheet after the plating treatment were investigated by the following methods and evaluation criteria, and the alloyed hot dip galvanized after the alloying treatment. The steel sheet was examined for alloying speed and powdering resistance. We also investigated the yield that could ensure plating quality.
Each evaluation standard of plating quality is as follows.
<Plating appearance>
The appearance was visually observed. The case where there was no unplating was regarded as no plating, and the case where unplating could be observed visually was regarded as unplating. Further, the appearance was visually observed to evaluate the presence or absence of pressing folds.
○: No plating, no pushing bar ×: No plating, pressing bar <Plating adhesion>
A 180 ° bending (0-T bending) test was performed to evaluate the plating peeling state when the convex side was peeled off by tape.
○: Plating crack / peeling ×: No plating peeling <Alloying speed>
The alloying speed was compared according to the alloying temperature at which the Fe content in the plating layer was 10% ± 0.5%.
○: Alloying temperature: Completion of alloying at 520 ° C or less ×: Alloying temperature: Completion of alloying at over 520 ° C <Powdering resistance>
A test piece having a width of 25 mm and a length of 40 mm was cut out from the galvannealed steel sheet in which the Fe content in the plating layer was 10% ± 0.5%, and the cellophane tape (registered trademark) (width: 24 mm) was long. Length: Attached at a position of 20 mm, the tape surface is bent 90 ° inward, then bent back and the cellophane tape (registered trademark) (width: 24 mm) is peeled off to count the amount of Zn attached by fluorescent X-rays. As measured. The measured Zn count number was corrected to the count number per test piece width: unit length (1 m) and evaluated according to the following criteria.
○: Good (Count: 0 to 5000)
X: Defect (count: 5000 or more)
<Yield>
As the yield at which plating quality can be ensured, the ratio of the area of the good plating quality part to the total length and width of the steel sheet was determined and evaluated.
○: Yield 80% or more ×: Yield less than 80% Table 2 shows the results obtained from the above.

  From the results in Table 2, it can be seen that the type and amount of the specific element deposited on the surface of the steel plate before the oxidation treatment, the maximum temperature reached during the oxidation treatment, and the air-fuel ratio affect the plating quality.

Therefore, using the hot dip galvanized steel sheet manufacturing apparatus of the present invention shown in FIG. 1, 20 tons of C and F steel sheets in Table 1 are connected at the entry side of the plated steel sheet manufacturing apparatus and continuously in this order. When passing through the plate, the specific elements to be deposited by the compound deposition apparatus 2 and the amount of deposition were constant (ammonium sulfate, 120 mg / m ² as S) regardless of the type of the steel plate, and were dried before the oxidation treatment. In performing the oxidation treatment, the iron oxide amount was made constant based on the iron oxide film oxygen amount measured by the iron oxide amount measuring apparatus 10. That is, in the iron oxide amount adjusting device 12, 0.9 g / m ² is preset as a target value of the oxygen amount in the oxide film, and the oxygen amount in the oxide film measured by the iron oxide amount measuring device 10 is the target value. If lower, the maximum heating temperature in the oxidation treatment device 3 is increased, and conversely, if the oxygen amount in the oxide film measured by the iron oxide amount measurement device 10 is higher than the target value, the oxidation treatment device 3. Is controlled to lower the maximum heating temperature. The plate passing speed and plating conditions were the same as in the case of obtaining the results shown in Table 2. The reduction treatment condition was the above condition 1. The plating quality of each of the C and F steel plates was also evaluated in the same manner as when the results shown in Table 2 were obtained.

For comparison, similarly, when connecting 20 tons of each of the C and F steel plates in Table 1 on the entry side of the plated steel plate manufacturing apparatus and continuously passing them in this order, the iron oxide amount measuring device 10 is A plated steel sheet was produced without using it. At this time, in the oxidation processing apparatus, conditions of a maximum temperature of 700 ° C. and an air-fuel ratio of 1.25 were adopted. The plate passing speed and the plating conditions were the same as in the case of obtaining the results shown in Table 2, and the reduction treatment conditions were the above-mentioned condition 1. The plating quality of each of the C and F steel plates was also evaluated in the same manner as when the results shown in Table 2 were obtained.
Table 3 shows the results obtained.

From Table 3, in the example of the present invention, the iron oxide amount formed by the oxidation treatment device 3 by the iron oxide amount adjusting device 12 is 0.9 g / m ² in terms of the oxygen amount in the oxide film, regardless of the steel type. Since the amount of iron oxide formed in the oxidation treatment apparatus 3 is within the proper range, the appearance of plating, plating adhesion, alloying speed, powdering resistance, and yield can be obtained for all C and F steel types. All of these were good.
On the other hand, in Comparative Example, the necessary amount of oxygen in the oxide film could not be sufficiently secured for steel type C, and satisfactory results were not obtained in any evaluation of plating quality. Further, with respect to steel type F, the amount of oxygen in the oxide film was too large, so that iron oxide was peeled off during transportation and adhered to transportation rolls and the like, resulting in poor plating appearance. Furthermore, for steel type F, since the amount of oxygen in the oxide film was too large, the reduction of iron oxide in the subsequent reduction treatment apparatus 4 was insufficient, and a delay in the alloying rate was observed.

  In this way, a compound containing a specific element is attached to the surface of the steel sheet, and then oxidized to form iron oxide. Further, by adjusting the specific element adhesion amount and the iron oxide amount, non-plating and pressing It can be seen that there is no surface defect such as excellent plating adhesion, no significant alloying delay, and excellent powdering resistance. Further, according to the present invention, it can be seen that the practicality is high since a good yield can be secured.

  The plated steel sheet of the present invention is excellent in surface properties, exhibits excellent plating adhesion, has no significant alloying delay, and exhibits excellent powdering resistance, so that it is mainly used in the fields of automobiles, home appliances, and building materials. Expected to be used in a wide range of applications.

It is a figure which shows the manufacturing apparatus of the hot dip galvanized steel plate which is one of embodiment of this invention.

Explanation of symbols

1: Steel plate 2: Compound adhesion device 3: Oxidation treatment device 4: Reduction treatment device 5: Cooling treatment device 6: Plating treatment device 7: Plating adhesion amount adjustment device 8: Alloying treatment device 9: Adhesion amount measurement device 10: Oxidation Iron amount measuring device 11: adhesion amount adjusting device 12: iron oxide amount adjusting device

Claims (14)

A compound adhering step for adhering a compound containing at least one specific element selected from the specific element group consisting of P, Na, K, Cl, S, F, B, C, and N to the steel sheet surface;
An oxidation treatment step of forming iron oxide on the surface of the steel plate, to which the compound is attached by performing an oxidation treatment;
An iron oxide amount measuring step for measuring the amount of iron oxide formed on the steel sheet surface in the oxidation treatment step;
A reduction treatment step for carrying out reduction treatment on a steel plate having iron oxide formed on the surface;
An apparatus for producing a hot dip galvanized steel sheet, comprising: a plating treatment step for performing a plating treatment.   The apparatus for producing a hot dip galvanized steel sheet according to claim 1, further comprising an adhesion amount measuring step for measuring an adhesion amount adhering to the steel sheet surface in the compound adhesion step. The apparatus for producing a hot-dip galvanized steel sheet according to claim 1 or 2, wherein the amount of the compound adhered to the steel sheet surface is 0.1 to 1000 mg / m ² in terms of each specific element.   The apparatus for producing a hot-dip galvanized steel sheet according to any one of claims 1 to 3, wherein a maximum temperature of the oxidation treatment in the oxidation treatment step is over 500 ° C.   The apparatus for producing a hot dip galvanized steel sheet according to any one of claims 1 to 4, wherein the compound attaching step includes a drying step.   The apparatus for producing a hot dip galvanized steel sheet according to any one of claims 1 to 5, further comprising an alloying treatment after the plating treatment step. While continuously conveying the steel sheet, a compound containing at least one specific element selected from the specific element group consisting of P, Na, K, Cl, S, F, B, C, and N is adhered to the steel sheet surface. In the manufacturing process of the hot dip galvanized steel sheet that performs oxidation treatment, reduction treatment, and plating treatment,
A surface treatment control method for a hot dip galvanized steel sheet, characterized in that after the oxidation treatment, the amount of iron oxide formed on the steel sheet surface is measured, and the oxidation treatment conditions are manipulated so that the actual measurement value matches the target value.   The amount of the specific element at the time of compound adhesion is operated so that the amount of adhesion adhering to a steel plate may be measured after attaching a compound to the steel plate surface, and the actual measurement may be made to correspond with a target value. Surface treatment control method for hot-dip galvanized steel sheet.   The method for controlling the surface treatment of a hot dip galvanized steel sheet according to claim 7 or 8, wherein the compound is attached to the surface of the steel sheet and then dried and then oxidized.   The method for controlling the surface treatment of a hot dip galvanized steel sheet according to any one of claims 7 to 9, wherein an alloying treatment is further performed after the plating treatment. A compound adhering apparatus for adhering a compound containing at least one specific element selected from a specific element group consisting of P, Na, K, Cl, S, F, B, C, and N to the steel sheet surface;
An oxidation treatment apparatus that forms an iron oxide on the surface of the steel sheet, to which an oxidation treatment is applied and the compound adheres;
Operate the conditions of the oxidation treatment apparatus so that the iron oxide amount measurement device provided after the oxidation treatment device and measures the amount of iron oxide formed on the surface of the steel plate matches the target value. An iron oxide amount control device,
A reduction treatment device for carrying out reduction treatment on a steel plate having iron oxide formed on the surface;
A surface treatment control apparatus for a hot dip galvanized steel sheet, comprising: a plating apparatus for performing a plating process. A compound adhesion amount measuring device that is provided after the compound adhesion device and measures the adhesion amount adhered to the steel sheet surface;
12. The apparatus for controlling the surface treatment of a hot dip galvanized steel sheet according to claim 11, further comprising an adhesion amount adjusting device for operating conditions of the compound adhesion device so that the measured adhesion amount matches a target value. .   The surface treatment control apparatus for hot-dip galvanized steel sheets according to claim 11 or 12, wherein the compound adhesion apparatus includes a drying apparatus.   A hot-dip galvanized steel sheet in which the amount of iron oxide on the steel sheet surface is adjusted by the surface treatment control method for a hot-dip galvanized steel sheet according to any one of claims 7 to 10.

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