JPH08188861A - Production of galvanizing steel sheet - Google Patents

Abstract

PURPOSE: To rapidly produce a galvanizing steel sheet at a low cost without deteriorating plating adhesion by cleaning the surface of a steel sheet before annealing the steel sheet and coating the surface with a metallic inorganic compound, in which standard formation free energy of oxide is specified, to specific thickness. CONSTITUTION: Annealing is applied to a steel sheet in a reducing or nonoxidizing atmosphere, and this steel sheet is passed through a hot-dip galvanizing bath without contact with the air to undergo plating and then subjected to heating and alloying treatment, by which the galvanizing steel sheet is produced. At this time, before the annealing of the steel sheet, the surface of the steel sheet is cleaned by pickling, etc., and then the surface of the steel sheet is coated, to a thickness of (0.001 to 5)g/m<2> expressed in terms of coating weight of metal, with a metallic inorganic compound in which the standard formation free energy ΔG of oxide at 450 deg.C is regulated to >=-1100kj/mol and also the standard formation free energy ΔG of oxide at 800 deg.C is regulated to <=-300kj/ mol. Moreover, the metal of the inorganic metallic compound is Mn, Mg, Zn, etc., and the shape of the compound is. hydroxide, oxide, sulfide, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a galvannealed steel sheet rapidly and at low cost without lowering the plating adhesion.

[0002]

2. Description of the Related Art In recent years, the use of high-strength hot-dip galvanized steel sheets has been increasing in order to simultaneously satisfy the two problems of corrosion prevention and weight reduction of automobiles. This steel sheet uses a high-strength steel sheet containing Si or P as its base steel sheet, but has a drawback that the alloying rate of zinc is slow. Therefore, as a measure from the operational aspect,
Although a method of reducing the line speed during manufacturing has been adopted, this is not preferable because it lowers the productivity and increases the manufacturing cost. Therefore, there is a strong demand for a method capable of producing a high-strength hot-dip galvanized steel sheet without lowering productivity.

Further, also in the production of alloyed hot-dip galvanized steel sheet using a general steel sheet having a low P or Si content as a base steel sheet, the improvement of the alloying rate is due to the increase in the line speed. There are major advantages such as improvement of fuel efficiency, reduction of equipment cost by shortening the furnace length of the alloying furnace, reduction of fuel gas and electric power consumed in the alloying furnace. In general,
The alloyed hot-dip galvanized steel sheet is often manufactured in the same production line as the non-alloyed hot-dip galvanized steel sheet (hot-dip galvanized steel sheet not subjected to alloying treatment). However, in the production of the non-alloyed hot-dip galvanized steel sheet, the concentration of Al added to the hot-dip galvanized bath is set to 0.18 to 0.3.
It is set to about wt%, and it is manufactured with a considerably higher Al concentration compared with 0.1 to 0.15 wt% when manufacturing an alloyed hot-dip galvanized steel sheet.

The reason for this is that in the production of non-alloyed galvanized steel sheet, Fe-
When the Zn alloy layer is formed, the adhesion of the plating decreases, so the Al concentration in the hot dip zinc bath is adjusted to a higher value, and a thin Fe-Al alloy layer is preferentially formed at the interface between the steel plate and the zinc plating layer. By doing so, the formation of the Fe-Zn alloy layer is suppressed and the plating adhesion is secured. On the other hand, in the production of the galvannealed steel sheet, in order to promote the formation of the Fe—Zn alloy layer and complete the alloying rapidly, it is rather advantageous that the Al concentration in the hot dip zinc bath is low. And is usually adjusted to about 0.1 to 0.15% by weight. For the above reasons, the Al concentration must be changed in order to separately produce the galvannealed steel sheet and the non-galvanized galvanized steel sheet on the same production line.

Generally, in order to increase the Al concentration in the molten zinc bath, it can be adjusted in a relatively short time by adding pure Al or Al-Zn alloy, but in order to lower the Al concentration, the plating layer is required. Waiting for the natural decrease of Al concentration by supplementing pure zinc with taking out Zn from the molten zinc bath, or pumping molten zinc from the molten zinc bath and supplementing pure zinc to reduce the Al concentration. It is extremely inefficient.
To solve the above problems, a method for producing a high-strength galvannealed steel sheet containing P is disclosed in Japanese Patent Laid-Open No. 5-1.
Japanese Patent Laid-Open No. 48603 proposes a method of applying an aqueous solution of a sulfur compound having a concentration of 0.1% or more to the surface of a steel sheet before hot dip galvanizing and then annealing it in a non-oxidizing atmosphere.
This method is effective for a steel plate that has been strengthened by adding only P, but when other alloy elements such as Si are contained in a large amount, the effect is not always sufficient, and However, the effect is unstable because the sulfur compound aqueous solution is simply applied.

Further, using a steel sheet containing Si as a base material,
As a method of applying hot-dip galvanizing, Japanese Patent Application Laid-Open No. 5-247
No. 614, the elemental sulfur and / or the sulfur compound is previously converted to the amount of S by 0.01 m on the surface of the steel sheet.
A method has been proposed in which, after forming a film containing g / m ² or more, heating is performed in a non-oxidizing atmosphere, and then hot dip galvanizing is performed. This method has the drawbacks that sulfur compounds easily react with the furnace material in the annealing furnace, shortening the life of the furnace material, thus increasing the repair cost of the furnace and increasing the manufacturing cost due to environmental measures. Furthermore, A in the molten zinc bath
As a method of accelerating the alloying reaction when the l concentration is high, JP-A-60-110859 proposes a method of pre-plating a steel sheet surface before hot dip galvanizing with Ni or a Ni alloy. However, this method requires pre-plating equipment, and there is a difficulty in putting it to practical use in terms of equipment installation space and production cost increase.

[0007]

SUMMARY OF THE INVENTION In view of the above situation, it is an object of the present invention to provide a method for performing galvannealing rapidly and at low cost without lowering the plating adhesion.

[0008]

Means for Solving the Problems As a result of a detailed study to solve the above problems, the present inventors formed an initial reaction between a steel sheet and a molten zinc bath to inhibit the Fe--Zn alloying reaction. The formation and decomposition rate of the Fe—Al alloy layer
It has been found that the reaction rate of the entire e-Zn alloying reaction is rate limiting. Furthermore, P that has thickened on the surface of the steel sheet during annealing
It has been found that and / or Si affects the decomposition rate of the Fe-Al alloy layer and significantly reduces the alloying rate. Then, as a result of various studies on means for solving this problem, finally, the present inventors formed a coating film of an inorganic metal compound on the steel sheet surface before or during annealing before hot dip galvanizing, and then reduced Alternatively, if the alloy is annealed in a non-oxidizing atmosphere and further hot-dip galvanized to form a heat alloy, the formation of the Fe-Al alloy layer is suppressed, and as a result, not only ordinary steel but also P and / or Si is contained. It has been found that even in the case of high strength steel, the alloying rate of zinc is greatly increased and the galvannealed steel sheet can be manufactured industrially and at low cost. Furthermore, by using the above method, even under the plating conditions in which the Al concentration in the molten zinc bath is high, the alloying rate is improved without lowering the plating adhesion, and alloying is performed in the same molten zinc bath. It has been found that hot-dip galvanized steel sheets and non-alloyed hot-dip galvanized steel sheets can be manufactured.

The present invention has been made on the basis of these findings. The gist of the first invention of the present invention is that a steel sheet is annealed in a reducing or non-oxidizing atmosphere and then contacted with the atmosphere. Without passing through the hot dip zinc, in the method of manufacturing a galvannealed steel sheet further heat alloying treatment, before annealing the steel sheet, after cleaning the steel sheet surface, on the steel sheet surface, at 450 ℃ Standard free energy of formation ΔG of oxide is −1100 kJ / mol or more,
Standard free energy of formation of oxide ΔG at 800 ℃
Is 0.001 g / m ² or more in terms of the amount of adhered metal of an inorganic compound of a metal having a value of −300 kJ / mol or less 5
A method for producing an alloyed hot-dip galvanized steel sheet, which comprises coating with a thickness of g / m ² or less.

The gist of the second invention of the present invention is that
In the first invention, the inorganic metal compound is Mn, M
Alloying hot-dip galvanizing, which is one or more of g, Zn, Ni, Ti, and Al, and the compound form is any one of hydroxide, oxide, sulfide, nitrate, sulfate, or a mixture. Steel plate manufacturing method. Further, the third invention of the present invention is summarized in the first invention or the second invention, in which the inorganic metal compound is coated, and the inorganic metal compound is changed to an oxide by heating before annealing or by annealing.
After that, after annealing in a reducing or non-oxidizing atmosphere,
A method for producing an alloyed hot-dip galvanized steel sheet, which comprises hot-dip galvanizing and then heat-alloying.

Next, the gist of the fourth invention of the present invention is that after the steel sheet is annealed in a reducing or non-oxidizing atmosphere, the steel sheet is passed through molten zinc without contact with the atmosphere. In the method for producing an alloyed hot-dip galvanized steel sheet which is subjected to heat-alloying treatment, the steel sheet surface is cleaned before the steel sheet is annealed, and then the standard free energy of formation of oxides at 450 ° C. at 450 ° C. is produced on the steel sheet surface. Is -110
After attaching an acidic solution containing a metal ion having a standard free energy of formation ΔG of oxide of −300 kJ / mol or less at 0 kJ / mol or more and 800 ° C., the steel sheet surface is brought into contact with an alkaline aqueous solution, and then the steel sheet surface is contacted. A method for producing an alloyed hot-dip galvanized steel sheet, which comprises forming a coating film of the metal hydroxide.

The gist of the fifth invention is that, in the fourth invention, the metal which becomes ions is Mn, Mg, Zn or N.
A method for producing an alloyed hot-dip galvanized steel sheet which is any one of i, Ti and Al, or a mixture thereof. Further, the gist of the sixth invention of the present invention is that a steel sheet is annealed in a reducing or non-oxidizing atmosphere, and then the steel sheet is passed through molten zinc without contact with the atmosphere, and further heated. In the method for producing an alloyed hot-dip galvanized steel sheet for alloying treatment, before the steel sheet is annealed, the steel sheet surface is cleaned, and then the steel sheet surface has a standard free energy of formation of oxide at 450 ° C of -1100 kJ / mol or more, 8
After attaching an acidic solution containing a metal ion having a standard free energy of formation ΔG of an oxide of −300 kJ / mol or less at 00 ° C., the steel sheet surface was contacted with an alkaline aqueous solution containing a sulfide ion, and the steel sheet surface A method for producing an alloyed hot-dip galvanized steel sheet, characterized in that a sulfide coating film of the metal is formed on.

The gist of the seventh invention is that, in the sixth invention, the metal which becomes an ion is Mn, Mg, Zn or N.
The manufacturing method of the alloying hot dip galvanized steel sheet which is 1 type, or 2 or more types of i, Ti, and Al. Further, the gist of the eighth invention is that in the first invention, the second invention, the third invention, the fourth invention, the fifth invention, the sixth invention or the seventh invention, the steel sheet is P0.02% or more, It is a method for producing an alloyed hot-dip galvanized steel sheet which is a high-tensile steel sheet containing one or two kinds of Si 0.1% or more.

[0014]

The present invention will be described in detail below. First, in the present invention, after cleaning the steel plate surface, the steel plate surface is coated with an inorganic metal compound. However, when the inorganic metal compound is less than 0.001 g / m ² in terms of metal amount, the steel plate surface is Since it cannot be coated uniformly and effectively, a part of the surface of the steel sheet is exposed, and the effect of accelerating the heat alloying of zinc is not sufficiently exhibited. In order to make alloying more reliable and quicker, the coating of inorganic metal compound is 0.05 g
/ M ² or more is more preferable. On the other hand, for the purpose of promoting alloying of zinc, there is no upper limit to the thickness of the inorganic metal compound coating, but it takes a long time to apply an excessively thick coating, and the productivity is rather lowered. 5 g / m
^2, and more preferably 1 g / m ² or less in order to process at a higher speed. Furthermore, the purpose of producing high-strength alloyed hot-dip galvanized steel sheet with the productivity of ordinary steel,
For the purpose of improving productivity, including ordinary steel, or for producing alloyed hot-dip galvanized steel sheets and non-alloyed hot-dip galvanized steel sheets without changing the Al concentration in the hot-dip zinc bath,
It is desirable to adjust the thickness of the inorganic metal compound film to an optimum amount according to each purpose. Further, depending on the type of the inorganic metal compound, it may be decomposed by annealing treatment, but at a thickness of 0.001 g / m ² or more in terms of the amount of metal deposited immediately before being immersed in the molten zinc bath. It only needs to remain. For cleaning the surface of the steel sheet, a method which has been conventionally applied can be used, and for example, any one of alkali degreasing, electrolytic degreasing, pickling, or a combination thereof can be applied.

The inorganic metal compound must be a substance that does not inhibit the plating of zinc on the surface of the steel sheet in molten zinc and that suppresses the formation of the Fe-Al alloy layer. According to the study by the present inventors, for that purpose, the inorganic metal compound needs to be reduced by Zn or Al in the molten zinc bath and diffused in the molten zinc bath.
The free energy of formation of the oxide of the metal at 450 ° C., which is the temperature of a general molten zinc bath, is −1100 kJ / m.
It must be ol or more. ΔG is -1100k
If it is less than J / mol, alloying cannot be promoted no matter how thick the film is. Further, since the effect disappears when the inorganic metal film is decomposed and vaporized during annealing,
Standard free energy of formation of oxide ΔG at 800 ℃
Is −300 kJ / mol or less.
The standard free energy of formation is an index showing the reactivity of the compound, and the smaller the value, the more stable it is.
That is, ΔG of the inorganic metal compound is −11 at 450 ° C.
If it is larger than 00 kJ / mol, it easily reacts with Al, and if ΔG is smaller than −300 kJ / mol at 800 ° C., it is not decomposed even in the annealing atmosphere of the hot dip coating line.

The substance of the inorganic metal compound is not particularly limited as long as it is such a substance, but Mn, Mg,
One, two or more of Zn, Ni, Ti and Al are preferable, and the form of the inorganic metal compound is hydroxide, oxide, sulfide, nitrate or sulfate, which is particularly suitable for the above purpose. ing. Further, these compounds may be used alone or as a mixture of two or more kinds. It goes without saying that the amount of the inorganic metal compound converted to the amount of metal must satisfy the above-mentioned value regardless of whether they are present alone or when they are mixed. When the above substances are a mixture, two or more types of substances may be laminated in the plate thickness direction, or a state in which two or more types of substances are mixed with each other, for example, in the form of particles or fine particles. But either is fine. What is important is that the total amount of the inorganic metal compound converted to the amount of metal satisfies the above range.

After coating the surface of the steel sheet with the inorganic metal compound, the steel sheet is annealed in order to obtain the desired material for the steel sheet. At this time, it is necessary to anneal at least the final stage in a reducing or non-oxidizing atmosphere in order not to impair the effect of the inorganic metal compound coating and to effectively carry out the subsequent hot dip galvanizing. Other than this,
It suffices to carry out according to a method that is conventionally applied. For example, after preheating a steel sheet in a reducing atmosphere, a nitrogen or argon gas containing 3 to 25% hydrogen is used to
It can be annealed by heating at 00 to 850 ° C. Alternatively, the steel sheet may be preheated in a weakly oxidizing atmosphere containing a small amount of oxygen, and then annealed by heating at 600 to 850 ° C. in nitrogen or argon gas containing 3 to 25% hydrogen. In any case, the final annealing atmosphere may be reducing or non-oxidizing. The lower the dew point of the atmosphere of the annealing in the final stage, the better.
When the temperature is 30 ° C. or lower, a better result can be obtained. If the steel sheet after being annealed in such an atmosphere is exposed to the air, the surface of the steel sheet may be oxidized or contaminated, and the subsequent galvanization may become defective. Immersion in zinc is necessary.

For the purpose of producing a high-strength alloyed hot-dip galvanized steel sheet containing one or two of P and Si with the same productivity as ordinary steel, or for the purpose of improving productivity including ordinary steel. The hot-dip galvanizing may be performed according to a method that has been conventionally applied in the production of alloyed hot-dip galvanized steel sheets. For example, Al is 0.1 to
Molten zinc bath containing about 0.15% by weight, bath temperature 440
Conditions such as ˜480 ° C. can be used. On the other hand, the alloyed hot-dip galvanized steel sheet and the non-alloyed hot-dip galvanized steel sheet are efficiently changed without changing the Al concentration of the hot-dip zinc bath,
In addition, for the purpose of producing without lowering the plating adhesion, it may be carried out according to the method conventionally applied to the production of non-alloyed galvanized steel sheets. For example, the Al concentration in the molten zinc bath can be adjusted to about 0.18 to 0.3% by weight, and plating can be performed at a bath temperature of about 440 to 480 ° C.

After being immersed in the molten zinc, the thickness of the molten zinc on the surface of the steel sheet is adjusted by a conventional method, and then the steel sheet is heated to alloy the plated zinc with the steel sheet. The heating for alloying is preferably 460 ° C. or higher, and more preferably 480 ° C. or higher for reliable alloying in a short time. The heating method is not particularly limited, and any conventionally used method such as direct heating with a combustion gas flame, induction heating, or direct current heating can be used. Also, a method combining these methods may be used. The step of coating the surface of the steel sheet with the above-mentioned inorganic metal compound may be an online post-treatment step of the rolling step or an online pre-treatment step of hot dip galvanizing. Further, the method of the present invention may be processed not only online but in a single process outside the line.

When a hydroxide, a nitrate, a sulfate or a mixture thereof is coated as the inorganic metal compound, at least the final stage is annealed in a reducing or non-oxidizing atmosphere, When these are changed to zinc oxide, it is particularly effective for plating and alloying of molten zinc. At this time, the atmosphere does not necessarily need to be reducing or non-oxidizing, and it is not necessary that the atmosphere is weakly oxidizing, only for the purpose of changing any one of the hydroxide, the nitrate, the sulfate, or a mixture thereof into an oxide. May be annealed in a reducing or non-oxidizing atmosphere after being pre-heated to have an oxidizing or oxidizing property. What is important is that at least the final step is annealing in a reducing or non-oxidizing atmosphere, and heating for the purpose of converting hydroxide, nitrate, sulfate, or a mixture thereof into oxide. The atmosphere may be any as long as it does not interfere with the final stage annealing. Any of hydroxide, nitrate, sulfate,
Alternatively, in order to change these mixtures into oxides, the temperature of preheating or annealing is preferably 300 ° C. or higher, and when the temperature is 500 ° C. or higher, the treatment is easy in a short time.

As a method for forming either a sulfate film or a nitrate film of the metal or a mixture film of both of them on the surface of the steel sheet, for example, a roll transfer method, that is, a roll of a sulfate film or a nitrate film of the metal is first prepared. Applying an aqueous solution containing either or both of them, rotating the roll and the steel sheet in contact with each other, and continuously applying the aqueous solution to the surface of the steel sheet, or by spraying, spraying, dipping, or the like. After that, it can be dried. The temperature of the aqueous solution may be room temperature, but may be a high temperature up to 95 ° C., and the temperature is not limited.

As a method of forming a coating film of the metal hydroxide on the surface of the steel sheet, there is a method of electrolyzing in a solution containing a nitrate of the metal with a previously cleaned steel sheet as a cathode. As another method for forming a coating film of the metal hydroxide on the surface of the steel sheet, after cleaning the surface of the steel sheet, a coating of an acidic aqueous solution containing ions of the metal is formed and applied on the surface of the steel sheet. At this time, the concentration of the metal ion in the aqueous solution is preferably 0.01 mol / l or more, and the pH (hydrogen ion concentration index) of the aqueous solution is preferably 2 or more and 5 or less. When the ion concentration of the metal is less than 0.01 mol, it is difficult to form a sufficient hydroxide coating on the surface of the steel sheet. On the other hand, if the pH is less than 2, corrosion of the steel sheet will be remarkable and the surface properties of the steel sheet will be deteriorated.
If it exceeds, the hydroxide may be precipitated in the aqueous solution. To form a film of an acidic aqueous solution containing the metal ions on the surface of a steel sheet, for example, a roll transfer method, that is, the aqueous solution is first applied to a roll, and the roll and the steel sheet are brought into rotary contact to make the aqueous solution a steel sheet. A method of continuously applying to the surface or a method such as spraying, spraying, dipping can be applied. The temperature of the aqueous solution may be room temperature, but may be a high temperature up to 95 ° C., and the temperature is not limited.

Next, the steel sheet coated with the acidic solution containing the metal ions is brought into contact with an alkaline aqueous solution,
Although a hydroxide film is formed on the surface of the steel sheet, the pH of the alkaline aqueous solution is more preferably 8 or more and 12 or less. When the pH is less than 8 or more than 12, the hydroxide becomes unstable and it becomes difficult to effectively coat the surface of the steel sheet. As the alkaline aqueous solution, for example, an aqueous solution of sodium hydroxide, potassium hydroxide or the like can be used. The temperature of the alkaline aqueous solution may be room temperature or high temperature up to 55 ° C, but 60 ° C
Above, it is difficult to form zinc hydroxide, so it is not preferable to raise the temperature too high. In addition, as a method of contacting a steel sheet on which a film of an acidic aqueous solution containing ions of the metal is formed with an alkaline aqueous solution, for example, a steel sheet having a shape such as a cold rolled steel strip is continuously immersed in a tank of the alkaline aqueous solution. -A method of passing through a plate or a method of spraying or spraying an alkaline aqueous solution can be applied.

As a method of forming a sulfide film on the surface of a steel sheet, after cleaning the surface of the steel sheet, first, a film of an acidic aqueous solution containing ions of the metal is formed on the surface of the steel sheet. At this time, the concentration of zinc ions in the aqueous solution is preferably 0.01 mol / l or more, and the pH (hydrogen ion concentration index) of the aqueous solution is preferably 2 or more and 6 or less. If the lead ion concentration of the metal is less than 0.01 mol, it is difficult to sufficiently form a sulfide coating on the surface of the steel sheet. Also, p
If H is less than 2, corrosion of the steel sheet becomes remarkable and the surface properties of the steel sheet are deteriorated. If the pH exceeds 6, hydroxide may be precipitated in the aqueous solution. To form a film of an acidic aqueous solution containing zinc ions on the surface of a steel sheet, for example, a roll transfer method (first applying the aqueous solution to a roll and rotating the roll and the steel sheet into contact with each other, the aqueous solution is continuously applied to the surface of the steel sheet. Or a method such as spraying, spraying, dipping or the like can be applied. The temperature of the aqueous solution may be room temperature, but may be a high temperature up to 95 ° C., and the temperature is not limited.

Next, the steel sheet on which the film of the acidic aqueous solution containing the ions of the metal has been formed is brought into contact with the alkaline aqueous solution containing the sulfide ion to form a film of zinc sulfide on the surface of the steel sheet. P of alkaline aqueous solution
More preferably, H is 8 or more. If the pH is less than 8, the sulfide becomes unstable and it becomes difficult to effectively coat the surface of the steel sheet. As the alkaline aqueous solution containing sulfide ions, for example, the pH of an aqueous solution of sodium sulfide, potassium sulfide, or the like can be adjusted and used. Here, the concentration of sulfide ions is preferably 0.001 mol / l or more. The temperature of the alkaline aqueous solution may be room temperature.
The temperature may be as high as ℃, and there is no restriction on the temperature. Also,
As a method of contacting a steel sheet coated with an acidic aqueous solution containing ions of the metal with a sulfide ion-containing alkaline aqueous solution, for example, a steel sheet having a shape such as a cold rolled steel strip,
A method of continuously immersing and passing through a bath of an alkaline aqueous solution containing sulfide ions, a method of spraying or spraying an alkaline aqueous solution, and the like can be applied.

According to this method, in the zinc plating bath, A
l, Pb, Sb, Si, Fe, Sn, Mg, M
Even a bath containing one or more of n, Ni, Cr, Co, Ca, Li, Ti, and rare earth elements or a bath mixed as an impurity will not cause any trouble. The steel plates targeted by this method are ordinary steel plates and P
A steel sheet containing and / or Si is the main object, but the same effect can be obtained by applying it to a steel sheet containing an element having a higher oxide forming ability than Zn. As a matter of course, on the alloyed hot-dip galvanized steel sheet obtained by the method of the present invention, for the purpose of improving paintability, weldability, etc., it is of course possible to perform various types of electroplating. It does not deviate. Further, it is of course possible to add various treatments to the alloyed hot-dip galvanized steel sheet obtained by the method of the present invention, and, for example, chromate treatment, phosphate treatment, phosphate treatment Even if a treatment for improving, a lubricity improving treatment, a weldability improving treatment, a resin coating treatment, or the like is performed, it does not depart from the scope of the invention of the present application, and according to the characteristics required to be added, various It can be treated.

[0027]

【Example】

Example 1 A steel sheet whose components are shown in Table 1 was used as a test material. Here, the plate thickness is
The cold-rolled steel sheet has a thickness of 0.6 mm, and the hot-rolled steel sheet has a thickness of 3.2 mm. After coating an inorganic metal compound whose composition and conditions are shown in Tables 2 and 3, hot-dip galvanizing is performed to check the time until alloying is completed. It was At the time of plating, the annealing atmosphere is 5
% Hydrogen + 95% nitrogen mixed gas, annealing temperature is 800
° C., annealing time was 75 seconds, the composition of the molten zinc bath and molten zinc containing 0.12 wt% of Al, was adjusted adhesion amount of the zinc gas wiper 60 g / m ^2. The alloying was performed with induction heating type heating equipment, and the heating temperature was 490 ° C.

[0028]

[Table 1]

In Table 2, 1, 6, 11, 16, 21
The hydroxide coatings at 26 and 26 have metal ions of 0.
It was formed by continuously passing an aqueous solution containing 03 mol / l and having a pH adjusted to 2.5 to 3.0, and then spraying an alkaline aqueous solution having a pH adjusted to 9 to 10. 5, 1
The sulphide coatings at 0, 20, 25 and 30 contain 0.5 mol / l metal ions and have a pH of 3.5-4.0.
It was formed by continuously passing the aqueous solution adjusted to No. 1 and then spraying an alkaline aqueous solution containing sulfide ions and adjusted to pH 12 to 13. The oxide films at 2, 7, 10, 17, and 27 have an air ratio (the ratio of the input air to the amount of air required to completely burn the fuel gas) of 1. after forming the hydroxide film. In the combustion gas of No. 05, it was heated to 400 ° C. to change the hydroxide into an oxide and formed. The nitrate and sulfate films were formed by applying a nitrate aqueous solution or a sulfate aqueous solution of each metal to the surface of the steel sheet with a roll coater. The mixture of nitrate and sulfate in 31, 32 and 33 was formed by applying a mixed aqueous solution of zinc sulfate and aluminum sulfate, zinc nitrate and aluminum nitrate, and manganese nitrate and titanium sulfate to the surface of the steel sheet with a roll coater.

[0030]

[Table 2]

Table 3 shows a comparative example. In Table 3, the inorganic metal compound film was formed by the same method as in the example. Tables 2 and 3 also show the results of Examples and Comparative Examples, respectively. In Tables 2 and 3, ⊚ represents that the time to complete alloying was 15 seconds or less, ∘ represents that the time to completion of alloying was 25 seconds or less, and x represents the completion of alloying. Indicates that the time until was over 25 seconds. As is clear from Table 2, No. 1 in which the surface of the steel sheet was coated with an inorganic metal compound according to the method of the present invention. 1-3
In No. 7, a galvannealed steel sheet was easily obtained. Moreover, no plating occurred and the surface quality was excellent.
On the other hand, the unprocessed No. In 1A to 1E and 2 to 7 in which the conditions were insufficient, it took a long time to complete the alloying, and non-plating was partially observed.

[0032]

[Table 3]

Example 2 Steel plates having the components shown in Table 1 were used as test materials. Here, the plate thickness is
The cold-rolled steel sheet had a thickness of 0.6 mm and the hot-rolled steel sheet had a thickness of 3.2 mm. After coating an inorganic metal compound having the composition and conditions shown in Table 4, hot dip galvanizing was performed, and the time until alloying was completed was examined. At the time of plating, the annealing atmosphere is 7% hydrogen + 9
A 3% nitrogen mixed gas was used, the annealing temperature was 810 ° C., the annealing time was 90 seconds, the composition of the molten zinc bath was molten zinc containing 0.23% by weight of Al, and the amount of zinc deposited was 60 g / m 2 with a gas wiper. Adjusted to ² . The alloying was performed with induction heating type heating equipment, and the heating temperature was 500 ° C. Each inorganic metal compound film was formed in the same manner as in Example 1. Table 5 shows a comparative example. In Table 5, the inorganic metal compound film was formed by the same method as in Example 1. Table 4 and Table 5
The results of Examples and Comparative Examples are also shown in FIG. In Tables 4 and 5, the evaluation of alloying time is ◎
Indicates that the time until the alloying was completed was 15 seconds or less, ◯ indicates that the time until the alloying was completed was 25 seconds or less, and x indicates the time until the alloying was completed was 45 seconds or less. Representing what was there, XX is the time to complete alloying 4
Indicates that it was over 5 seconds. As is apparent from Table 4, No. 1 in which the surface of the steel sheet was coated with the inorganic zinc compound according to the method of the present invention. The alloyed hot-dip galvanized steel sheets of 1 to 36 were easily obtained. Moreover, no plating occurred and the surface quality was excellent. On the other hand, the unprocessed No. In 1A to 1E and 2 to 7 in which the conditions were insufficient, it took a long time to complete alloying, and non-plating was observed on a part of the steel sheet.

[0034]

[Table 4]

[0035]

[Table 5]

[0036]

As described above, the present invention makes it possible to produce alloyed hot-dip galvanized steel sheets with high productivity and at low cost, and remarkably limits the composition of the steel sheet. It makes it possible to manufacture various high-strength hot-dip galvanized steel sheets, and also to manufacture alloyed hot-dip galvanized steel sheets and non-alloyed hot-dip galvanized steel sheets in the hot-dip zinc bath with the same Al concentration. Therefore, the area that contributes to the development of the industry is extremely large.

Claims (8)

[Claims] 1. An alloyed hot-dip galvanized steel sheet which is obtained by annealing a steel sheet in a reducing or non-oxidizing atmosphere, then passing the steel sheet through hot-dip zinc without contact with the atmosphere, and further heat-alloying it. In the manufacturing method of 1., after the steel plate surface is cleaned before the steel plate is annealed, 4
The standard free energy of formation ΔG of oxide at 50 ° C. is −1100 kJ / mol or more, and the standard free energy of formation ΔG of oxide at 800 ° C. is −300 kJ / mol.
A method for producing an alloyed hot-dip galvanized steel sheet, which comprises coating the following inorganic compound of a metal with a thickness of 0.001 g / m ² or more and 5 g / m ² or less in terms of the amount of metal deposited. 2. The inorganic metal compound, wherein the metal is Mn, Mg,
One or more of Zn, Ni, Ti, and Al,
The method for producing an alloyed hot-dip galvanized steel sheet according to claim 1, wherein the form of the compound is any one of hydroxide, oxide, sulfide, nitrate and sulfate, or a mixture thereof. 3. An inorganic metal compound is coated, and the inorganic metal compound is converted to an oxide by heating before or during annealing, and then annealed in a reducing or non-oxidizing atmosphere, followed by hot dip galvanizing, The method for producing an alloyed hot-dip galvanized steel sheet according to claim 1 or 2, wherein heat-alloying treatment is performed thereafter. 4. A method for producing an alloyed hot dip galvanized steel sheet, which comprises annealing a steel sheet in a reducing or non-oxidizing atmosphere, passing it through hot-dip zinc without contacting it with the atmosphere, and then heat-alloying it. In the above, before annealing the steel sheet, after cleaning the steel sheet surface, the steel sheet surface, 450 ℃
Standard free energy of formation ΔG of the oxide at −11
After depositing an acidic solution containing metal ions having a standard free energy of formation ΔG of an oxide of −300 kJ / mol or less at 800 kJ / mol or more and 800 ° C., the steel sheet surface is brought into contact with an alkaline aqueous solution to form a steel sheet surface. The metal hydroxide film is converted into the amount of metal adhered, which is 0.0
Method for manufacturing a galvannealed steel sheet, characterized in that allowed to produce at 01G / m ² or more 5 g / m ² or less in thickness. 5. The metal which becomes an ion is Mn, Mg or Z.
The method for producing an alloyed hot-dip galvanized steel sheet according to claim 4, which is one or more of n, Ni, Ti, and Al. 6. An alloyed hot-dip galvanized steel sheet which is obtained by annealing a steel sheet in a reducing or non-oxidizing atmosphere, then passing the steel sheet through hot-dip zinc without contacting it with the atmosphere, and further heat-alloying it. In the manufacturing method of, before annealing the steel sheet, after cleaning the steel sheet surface, on the steel sheet surface, 45
The standard free energy of formation ΔG of the oxide at 0 ° C is −
After adhering an acidic solution containing metal ions having a standard free energy of formation ΔG of the oxide at −100 kJ / mol or more and 800 ° C. of −300 kJ / mol or less, the steel plate surface is contacted with an alkaline aqueous solution containing sulfide ions. At least, the alloyed hot dip galvanizing method is characterized in that a sulfide film of the metal is formed on the surface of the steel sheet in a thickness of 0.001 g / m ² or more and 5 g / m ² or less in terms of the amount of the metal deposited. Steel plate manufacturing method. 7. The metal which becomes an ion is Mn, Mg or Z.
The method for producing an alloyed hot-dip galvanized steel sheet according to claim 6, which is one or more of n, Ni, Ti, and Al. 8. The method for producing a galvannealed steel sheet according to claim 1, wherein the steel sheet is a high-strength steel sheet containing P0.02% or more and / or Si0.1% or more. .