JP6863404B2 - Manufacturing method of high-strength galvanized steel sheet - Google Patents

Description

The present invention relates to a method for manufacturing a high-strength galvanized steel sheet, including a high-strength hot-dip galvanized steel sheet, which is particularly suitable for automobile member applications.

In recent years, there has been a strong demand for improving the fuel efficiency of automobiles in order to reduce _{CO 2 emissions.} Along with this, the movement to reduce the weight of the vehicle body by thinning the thickness of the vehicle body parts has become active, and the need for increasing the strength of the steel plate, which is the material for the vehicle body parts, is increasing.
Addition of solid solution strengthening elements such as Si and Mn is effective for increasing the strength of the steel sheet. However, since these elements are more easily oxidized than Fe, in the production of hot-dip galvanized steel sheets (including alloyed hot-dip galvanized steel sheets) using a high-strength steel sheet containing a large amount of them as a base material, the following Problems arise.

Usually, when a hot-dip galvanized steel sheet is manufactured, the hot-dip galvanized steel sheet is subjected to hot-dip galvanizing treatment after being heat-annealed at a temperature of about 600 to 900 ° C. in a non-oxidizing atmosphere or a reducing atmosphere. In the heat annealing before the plating treatment, the easily oxidizing element in the steel is selectively oxidized even in a generally used non-oxidizing atmosphere or reducing atmosphere, and is concentrated on the surface of the steel sheet to form an oxide. Since this oxide lowers the wettability of hot-dip galvanized during the hot-dip galvanizing treatment, the wettability of the hot-dip galvanized sharply decreases as the concentration of easily oxidizable elements in the steel increases, causing frequent non-plating. Further, even when non-plating does not occur, the plating adhesion deteriorates because the oxide exists between the steel sheet and the plating layer. In particular, since Si significantly reduces the wettability of hot-dip zinc even when added in a small amount, Mn, which has a smaller effect on wettability, is often added to hot-dip galvanized steel sheets. However, since Mn oxide also reduces the wettability of hot-dip zinc, the above-mentioned non-plating problem becomes remarkable when a large amount is added.

In response to the above problems, Patent Document 1 describes a method in which a steel sheet is annealed and then pickled to dissolve and remove oxides formed on the surface, and then annealed again to perform hot-dip galvanizing. Has been proposed.
Further, in Patent Document 2, first, the steel sheet is heated in an Fe-oxidizing atmosphere to rapidly generate Fe oxide on the surface at an oxidation rate equal to or higher than a predetermined value, thereby performing surface selective oxidation of additive elements on the surface of the steel sheet. A method has been proposed in which the wettability of the surface of a steel sheet with molten iron is improved by suppressing it and subsequently heating it in a Fe-reducing atmosphere to reduce the Fe oxide.
Further, Patent Documents 3 to 5 disclose a technique for improving the surface appearance and plating adhesion by subjecting a steel sheet to a pre-Ni plating treatment by electroplating and then a hot-dip galvanizing treatment.

Japanese Patent No. 39565550 Japanese Patent No. 2587724 Special Publication No. 46-19282 Japanese Unexamined Patent Publication No. 4-147954 Japanese Unexamined Patent Publication No. 4-333551

However, each of the above-mentioned conventional techniques has the following problems.
In the method of Patent Document 1, when the amount of the alloying element added is large, the oxide is formed again on the surface at the time of reannealing, and the plating adhesion may be deteriorated even if appearance defects such as non-plating do not occur. Further, in the case of high Si-containing steel, since the formed oxide after annealing is inactive to acid, it may not be sufficiently removed, and the upper limit of the applicable Si amount is about 0.80% by mass, which is relatively high. Low. Further, there is a problem that the productivity is low because the annealing step is required twice.
Further, the method of Patent Document 2 cannot be applied to a CGL that does not have equipment capable of heating in a Fe-oxidizing atmosphere, and a great cost is required for new installation.
Further, in the methods of Patent Documents 3 to 5, since the Ni plating process is performed by electroplating before the annealing process, there is a cost disadvantage in terms of equipment and process.
Further, the decrease in plating adhesion due to the oxide on the surface of the high-strength steel sheet may occur in plating other than hot-dip galvanizing.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to produce a plated steel plate using a high-strength steel plate to which Si and Mn are added as solid solution reinforcing elements as a base material. It is possible to effectively suppress selective oxidation of Si and Mn in heat annealing before plating treatment such as hot-dip galvanizing without performing pre-plating treatment such as, and to improve the surface appearance and plating adhesion of the plated steel plate. The purpose is to provide a manufacturing method. Another object of the present invention is to provide a treatment agent for solution treatment capable of effectively suppressing selective oxidation of Si and Mn in heat annealing before plating.

As a result of diligent studies and studies in order to solve the above-mentioned problems of the prior art, the present inventors have conducted a metal alkoxide of a metal having a higher standard oxidation-reduction potential than Fe or Fe in advance with respect to the steel sheet. By heat-annealing in a Fe-reducing atmosphere after performing a solution treatment to attach a solution containing the above, selective oxidation of Si and Mn in this heat-annealing is effectively suppressed, and the surface appearance and plating of the plated steel sheet are plated. It was found that the adhesion was improved.

The present invention has been made based on such findings, and the gist of the present invention is as follows.
[1] A method for producing a high-strength plated steel sheet using a steel sheet containing Si or / and Mn as a base material.
A solution treatment step of adhering a solution (y) containing a metal alkoxide of one or more metals (x) selected from metals having a standard oxidation-reduction potential higher than Fe and Fe to the surface of a steel plate, and a solution treatment step.
The steel sheet after the solution treatment step, H ₂ concentration is 0.05 vol% or more, and annealing steps which dew point is heated at 700 ° C. or higher at 10 ° C. in the reducing atmosphere,
A method for producing a high-strength plated steel sheet, which comprises a plating process for plating a steel sheet that has undergone the annealing step.

[2] In the production method of the above [1], in the solution treatment step, the solution (y) is applied to the surface of the steel sheet so that the ^{amount of adhesion is 0.01 to 3.0 g / m 2 in terms of metal (x).} A method for manufacturing a high-strength plated steel sheet, which is characterized by being adhered.
[3] In the production method of the above [1] or [2], the metal alkoxide contained in the solution (y) is one or more selected from Ni alkoxide, Cu alkoxide, and Fe alkoxide. A method for manufacturing high-strength galvanized steel sheets.
[4] In the production method of the above [3], the metal alkoxide is one or more selected from Ni ethylene glycol, Cu ethylene glycol, and Fe ethylene glycol. Manufacturing method.

[5] In any of the above-mentioned production methods [1] to [4], the steel sheet is characterized by containing Si: 0.10% or more and / and Mn: 0.50% or more in mass%. A method for manufacturing high-strength galvanized steel sheets.
[6] In any of the above-mentioned production methods [1] to [5], high-strength plating is characterized in that a steel sheet having a solution (y) adhered to its surface through a solution treatment step is directly introduced into an annealing step. Steel sheet manufacturing method.
[7] The production method according to any one of [1] to [5] above is characterized in that a steel sheet having a solution (y) adhered to its surface is heat-treated through a solution treatment step and then introduced into an annealing step. Manufacturing method of high-strength galvanized steel sheet.

[8] In any of the above-mentioned production methods [1] to [7], the plating treatment step includes a step of hot-dip galvanizing a steel sheet that has undergone an annealing step (provided that it is alloyed after hot-dip galvanizing). .) A method for manufacturing a high-strength plated steel sheet.
[9] In the production method of the above [8], a method for producing a high-strength plated steel sheet, characterized in that a solution treatment step, an annealing step, and a plating treatment step are continuously performed in a continuous hot-dip galvanizing line.
[10] In any of the above-mentioned production methods [1] to [9], the steel sheet is in mass%, C: 0.040 to 0.500%, Si: 0.10 to 3.00%, Mn: Contains 0.50 to 5.00%, P: 0.100% or less, S: 0.0100% or less, Al: 0.100% or less, N: 0.0100% or less, and the balance is Fe and unavoidable. A method for producing a high-strength galvanized steel sheet, which comprises a component composition composed of impurities.

[11] In the production method of the above [10], the steel sheet is further made of Ti: 0.010 to 0.100%, Nb: 0.010 to 0.100%, and B: 0.0001 to% by mass. A method for producing a high-strength plated steel sheet, which comprises one or more selected from 0.0050%.
[12] In the production method of the above [10] or [11], the steel sheet is further increased in mass% by Mo: 0.01 to 0.50%, Cr: 1.00% or less, Ni: 0.50%. Below, Cu: 1.00% or less, V: 0.500% or less, Sb: 0.10% or less, Sn: 0.10% or less, Ca: 0.0100% or less, and REM: 0.010% or less. A method for producing a high-strength plated steel sheet, which comprises one or more selected from the above.

[13] A treatment agent for solution treatment for suppressing selective oxidation of easily oxidizing elements during annealing of steel sheets for plating.
A treatment agent for solution treatment, which comprises a solution (y) containing a metal alkoxide of one or more metals (x) selected from Fe and a metal having a standard oxidation-reduction potential higher than that of Fe.
[14] The treatment agent for solution treatment according to the above [13], wherein the metal alkoxide is one or more selected from Ni alkoxide, Cu alkoxide, and Fe alkoxide.
[15] In the treatment agent of the above [14], the metal alkoxide is one or more selected from Ni ethylene glycol, Cu ethylene glycol, and Fe ethylene glycol, for solution treatment. Processing agent.

According to the present invention, in the production of a plated steel sheet using a high-strength steel sheet containing Si and Mn, which are easily oxidizing elements, as a base material, selective oxidation of Si and Mn in heat annealing before plating is effectively suppressed. It is possible to produce a plated steel sheet having a good surface appearance and excellent plating adhesion. Moreover, as a pretreatment, it is only necessary to perform a solution treatment of adhering a specific solution to the surface of the steel sheet, and it is not necessary to perform a pre-plating treatment such as nickel plating, so that both the equipment cost and the treatment cost can be kept low. By applying a high-strength plated steel sheet such as a high-strength hot-dip galvanized steel sheet manufactured by the present invention to, for example, an automobile structural member, it is possible to improve fuel efficiency by reducing the weight of the vehicle body.

Enlarged photograph of the surface appearance of the steel plates of Test Examples a to c shown in Table 2. XRD chart showing the results of identifying the constituent components of the steel sheet surface layer by XRD for the steel sheets of Test Examples a to c shown in Table 2.

The present invention is a method for producing a high-strength plated steel sheet using a steel sheet containing Si and / and Mn, which are easily oxidizing elements, as a base material, and has a standard oxidation-reduction potential on the surface of the steel sheet rather than Fe and Fe. A solution treatment step (A) for adhering a solution (y) containing a metal alkoxide of one or more metals (x) selected from high metals, and a reducing atmosphere for the steel plate that has undergone this solution treatment step (A). It has an annealing step (B) in which heat treatment is performed, and a plating treatment step (C) in which the steel plate that has undergone this annealing step (B) is plated.
The preferable conditions of the steel sheet (high-strength steel sheet) used as the base material of the high-strength plated steel sheet produced by the present invention will be described in detail later.

・ Solution treatment step (A)
This solution treatment step (A) is carried out after degreasing and cleaning the surface of the steel sheet by a known method, if necessary. The solution (y) to be adhered to the surface of the steel plate in this solution treatment step (A) contains a metal alkoxide of one or more metals (x) selected from metals having a standard oxidation-reduction potential higher than Fe and Fe. The metal (x) contained in the solution (y) which is the solution (y) and adheres to the surface of the steel plate is a metal oxide layer (for example, metal alkoxide) formed on the surface of the steel plate in the initial heating stage of the subsequent annealing step (B). Is the main metal source of the Ni oxide layer when the metal alkoxide is Ni alkoxide, the Cu oxide layer when the metal alkoxide is Cu alkoxide, and the Fe oxide layer when the metal alkoxide is Fe alkoxide). Further, this metal oxide layer is a metal layer (for example, a metal Ni layer in the case of a Ni oxide layer and a metal Ni layer in the case of a Cu oxide layer) formed on the surface of a steel plate after the heat treatment in the subsequent annealing step (B). It is a raw material film for the metal Cu layer and the metal Fe layer in the case of the Fe oxide layer).

In the present invention, the solution (y) as described above is used in order to form a metal oxide layer having a uniform and uniform thickness by forming a film by a method called a sol-gel method. That is, the solvent of the liquid film (sol) of the solution (y) adhering to the surface of the steel plate evaporates and decomposes with the passage of time and the temperature rise, but at that time, the solvent in the liquid film simply evaporates and the solute. It is considered that the whole liquid film gradually loses its fluidity due to the aggregation and polymerization of the components in the liquid film, and becomes a film (gel) containing a metal compound. Then, since the film (metal oxide layer) is formed through the process of forming such a gel-like film, a homogeneous and uniform thickness metal oxide layer can be formed. This metal oxide layer is finally reduced in the annealing step to become a metal layer, and this metal layer serves as a diffusion barrier for easily oxidizing elements such as Si and Mn during annealing, so that the selective oxide on the surface of the steel sheet is used. It is considered that the formation of

Here, in order to form the metal oxide layer through the process of forming a gel-like film from the liquid film of the solution (y) as described above, the temperature at the initial stage of heating in the annealing step (B) can be used. However, a part or all of the film formation may be performed by the heat treatment performed before the annealing step (B).
When the above-mentioned series of film formation is performed in the annealing step (B), first, the liquid film (sol) of the solution (y) becomes a gel-like film in the initial heating of the annealing step (B). Further, the decomposition of the gel-like film causes a metal oxide layer having a uniform and uniform thickness to be formed over the entire surface of the steel sheet. Then, in the subsequent annealing process, the metal oxide layer is reduced to form a metal layer.

Here, the components of the solution (y) for solution treatment will be described. Of Fe and one or more metals (x) selected from the metals having a higher standard oxidation-reduction potential than Fe contained in the solution (y). The metal alkoxide serves as a metal and oxygen source for the metal oxide produced in the heating step (such as the annealing step (B)) after the solution treatment step. The metal alkoxide has a structure in which the O atom of the alcohol, which is a solvent, is coordinated to the metal atom. Therefore, for example, considering the case where an oxide film of a metal (M) is formed in the annealing step (B), the hydrocarbon portion in the gel-like film is decomposed, but the MO bond portion remains. It is considered that an oxide film of metal (M) is formed even in a Fe-reducing atmosphere.

The metal alkoxide is a compound in which the hydrogen of the hydroxy group of the alcohol is replaced with a metal atom, and the metal atom bonded to the oxygen atom in the alcohol molecule is in an ionized state, that is, in an oxidized state.
In the present invention, the metal alkoxide contained in the solution (y) is a metal alkoxide of one or more metals (x) selected from metals having a standard oxidation-reduction potential higher than that of Fe and Fe. Here, there is no particular limitation on the type of metal having a standard oxidation-reduction potential higher than that of Fe, and examples thereof include Ni, Cu, Co, Sn, and Pb. Ni and Cu are particularly preferable from the viewpoint of low toxicity and the like.

Therefore, as the metal alkoxide contained in the solution (y), one or more selected from Ni alkoxide, Cu alkoxide, and Fe alkoxide is particularly preferable. Further, as described later, ethylene glycol is particularly preferable as the alcohol used as a raw material for the metal alkoxide. Therefore, as the metal alkoxide contained in the solution (y), Ni ethylene glycol, Cu ethylene glycol, and Most preferably, one or more selected from Fe ethylene glycolides.
The metal alkoxide adhering to the surface of the steel plate as a solution component becomes a metal oxide in the heating step after the solution treatment step, and this metal oxide layer is further reduced in the annealing step (B) in a Fe-reducing atmosphere to form a metal layer. However, since a metal having a standard oxidation-reduction potential higher than Fe and Fe constituting the metal alkoxide (for example, Ni and Cu described above) is a metal that is easily reduced, it is easily reduced in the annealing step (B). , A metal layer (for example, a metal Ni layer, a metal Cu layer, a metal Fe layer, etc.) is formed.

The metal alkoxide may be added to the solution as an isolated compound, but it is preferable to dissolve the inorganic salt in the alcohol as the alkoxide raw material from the viewpoint of easy handling. The type of the inorganic salt is not particularly limited, but examples of the nickel salt for producing Nialkoxide include nickel nitrate (II), nickel chloride (II), nickel sulfate (II), and nickel bromide (II). ), Nickel iodide (II), nickel tetrafluoroborate (II) and the like, and examples of the copper salt for producing Cu alkoxide include copper (II) nitrate, copper (II) chloride, and the like. Examples thereof include copper (II) sulfate, copper (II) bromide, copper (II) iodide, copper (II) tetrafluoroborate, and examples of the cobalt salt for producing Coalkoxide include nitrate. Cobalt (II), cobalt chloride (II), cobalt bromide (II) and the like can be mentioned, and examples of the tin salt for producing Sn alkoxide include tin sulfate (II) and ferric chloride (II). ), Etc., and examples of the lead salt for producing Pb alkoxide include lead acetate (II), lead nitrate (II), lead chloride (II), and the like, and Fe alkoxide is produced. Examples of iron salts for this purpose include iron nitrate (III), iron chloride (III), iron chloride (II), iron sulfate (II), ammonium iron sulfate (II), iron bromide (III), and iron bromide. (II), iron iodide (II), iron tetrafluoroborate (II) and the like can be mentioned, and one or more selected from these can be used respectively.

The type of alcohol as a solvent is also not particularly limited, and for example, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, One or more of ethylene glycol, diethylene glycol, triethylene glycol and the like can be used. Among these, ethylene glycol, which is a relatively inexpensive alcohol that does not easily evaporate due to its relatively high boiling point, is particularly preferable. That is, it is preferable to dissolve one or more of the above-mentioned inorganic salts in this ethylene glycol to generate metal ethylene glycolide in the solution. The generated metal ethylene glycolide is bonded in the form of capping a metal atom at two oxygen atom sites in the molecule, and the formed metal complex has a low-reactivity carbon skeleton on the outside, so that an intermolecular polymerization reaction occurs. Therefore, bath management is relatively easy from the viewpoint of sludge generation and the like.
In order to generate a metal alkoxide from an inorganic salt and an alcohol, it is only necessary to add the inorganic salt to the alcohol and dissolve it as described above.

The liquid concentration of the solution (y) (the metal (x) equivalent concentration of the metal alkoxide) may be set to a concentration that is easy to manage, but if the liquid concentration is too low, the required adhesion amount (metal (x) equivalent) described later will be used. There is a concern that the liquid film thickness required to obtain the liquid film will increase and the liquid film will become non-uniform. On the other hand, if the liquid concentration is too high, solute precipitation will occur due to supersaturation, or the required adhesion amount (metal (x)) described later will occur. There is a concern that the liquid film thickness required to obtain () conversion) becomes excessively small and the surface of the steel plate is exposed. That is, there is a concern that the formation of Si and Mn surface oxides on the surface of the steel sheet after the annealing step is insufficiently suppressed, which may cause a phenomenon that may cause poor plating adhesion and poor appearance of the finally obtained product. Therefore, the liquid concentration of the solution (y) (the metal (x) equivalent concentration of the metal alkoxide) is preferably about 0.1 to 1000 g / L, more preferably about 0.5 to 700 g / L.

The amount of the solution (y) adhering to the surface of the steel sheet in the solution treatment step (A) is preferably 0.01 to 3.0 g / m ^{2 in} terms of metal (x). If the amount of adhesion in terms of metal (x) ^{is less than 0.01 g / m 2} , the amount of adhesion of the metal layer generated in the annealing step (B) is small, so that the effect of suppressing selective oxidation of Si and Mn by this metal layer is effective. There is a concern that it will not be fully obtained. That is, there is a concern that a phenomenon may occur that may cause poor plating adhesion or poor appearance of the finally obtained product. On the other hand, when the adhesion amount in terms of metal (x) ^{exceeds 3.0 g / m 2} , the adhesion amount of the metal oxide film formed at the initial stage of heating in the annealing step (B) becomes excessive, and the annealing step (baking step (B) B) There is a concern that unreduced metal oxides will remain afterwards. That is, there is a concern that a phenomenon may occur that may cause poor plating adhesion or poor appearance of the finally obtained product, and it is also disadvantageous in terms of cost. From the above viewpoint, the more preferable amount of the solution (y) adhered (converted to metal (x)) is 0.05 to 2.0 g / m ² .
The method of adhering the solution (y) to the surface of the steel sheet is not particularly limited, and for example, a method such as a bar coater, a spray, a dip, a spin coat, or a roll coater can be used.

It was investigated by a test that a metal layer was formed on the surface of the steel sheet after the annealing step (B) by carrying out the above-mentioned solution treatment step (A). In this test, the steel sheet having the composition shown in Table 1 was subjected to solution treatment and annealing treatment under the conditions of Test Examples a and b shown in Table 2. Of these, Test Example a is a solution containing Ni alkoxide (Ni ethylene glycol), and Test Example b is a solution containing Cu alkoxide (Cu ethylene glycol). After each solution treatment, annealing treatment is performed. It was. On the other hand, in Test Example c shown in Table 2, similar steel sheets were only annealed without solution treatment. FIG. 1 shows an enlarged photograph of the surface appearance of the steel sheets obtained in Test Examples a to c. The photographs (a), (b), and (c) of FIG. 1 are those of the steel plates obtained in Test Example a, Test Example b, and Test Example c, respectively. Further, the results of identifying the constituent components of the steel sheet surface layer by XRD for the same steel sheet sample are shown in FIGS. 2 (A) and 2 (B). FIG. 2A compares the XRD charts of the steel plates of Test Example a and Test Example c, and FIG. 2B compares the XRD charts of the steel plates of Test Example b and Test Example c.

The surface appearance of the steel sheet of Test Example a (steel sheet subjected to solution treatment with a solution containing Nialkoxide and then annealing treatment) shown in FIG. 1 (a) is white, and FIG. 1 (c) shows. Compared with the surface appearance of the steel sheet of Test Example c (the steel sheet obtained only by annealing) shown in the above, the appearance is clean without temper color due to Si, Mn oxide and the like. Further, looking at the XRD measurement results of FIG. 2 (A), a metal Ni layer (and a Fe-Ni layer in which a part thereof is alloyed with base iron) is formed on the surface of the steel plate of Test Example a. It turns out. Further, the surface appearance of the steel sheet of Test Example b shown in FIG. 1 (b) (the steel sheet which was subjected to solution treatment with a solution containing Cu alkoxide and then annealed) was red. Compared with the surface appearance of the steel sheet of Test Example c (steel sheet subjected to only annealing treatment) shown in c), the appearance is clean without temper color due to Si, Mn oxide and the like. Further, looking at the XRD measurement results of FIG. 2 (B), it can be seen that a metal Cu layer is formed on the surface of the steel plate of Test Example b. As shown in the above test results, by performing the annealing treatment after the solution treatment as in the present invention, Ni, Cu, etc. can be applied to the surface of the annealed steel sheet without performing pre-plating treatment such as electric Ni plating. It is possible to form a metal layer and suppress selective oxidation of Si and Mn.

In the present invention, the liquid film of the solution (y) adhering to the surface of the steel sheet as described above becomes a film (metal oxide film) via a gel-like film. Although such film formation occurs even at room temperature, it is possible to form a film in a short time by heating as necessary. In particular, in the present invention, in the annealing step (B) following the solution treatment step (A). Filming is possible using the temperature at the initial stage of heating. That is, by introducing the steel sheet to which the solution (y) (liquid film) is attached to the surface through the solution treatment step (A) as it is into the annealing step (B), it is relatively early in the heating in the annealing step (B). In a low temperature range (for example, about 200 to 300 ° C.), the liquid film can be formed into a film (metal oxide layer) via a gel-like film. Therefore, it is not essential to perform the heat treatment for promoting the film formation of the liquid film before the annealing step (B), and it may be performed as needed. When such a heat treatment is performed, the film formation may be completed before the annealing step (B), or the film may be heated to a state in the middle of filming (for example, a gel-like film state), and then the annealing step (for example, a gel-like film state) is performed. The film formation may be completed by heating in B). That is, in that case, the steel sheet to which the solution (y) is adhered to the surface through the solution treatment step (A) is heat-treated by an appropriate heating means, and then introduced into the annealing step (B).

Therefore, for example, when the solution treatment step (A), the annealing step (B), and the plating treatment step (C) are continuously performed in the continuous molten zinc plating line, the solution is applied to the surface through the solution treatment step (A). The steel sheet to which (y) (liquid film) is attached may be directly introduced into the annealing step (B), or the steel sheet to which the solution (y) is attached to the surface through the solution treatment step (A) may be heated by an appropriate heating means. After the heat treatment in, it may be introduced into the annealing step (B).
Here, in the solution treatment step (A) of the present invention, since only the solution adheres and there is no energization, the equipment is compared with the methods such as Patent Documents 3 to 5 in which the pre-plating treatment such as electric Ni plating is performed before the annealing step. It can be said that there is a cost advantage in terms of both processing and process.

・ Annealing process (B)
The annealing step (B) is carried out for the purpose of forming a metal layer on the surface of the steel sheet. In the annealing process (B), the steel sheet after the solution treatment step (A), _{H 2} concentration is 0.05 vol% or more, the dew point is heated at 700 ° C. or higher at 10 ° C. in the reducing atmosphere, then, Cool to a predetermined temperature. In this annealing step (B), as described above, the solvent molecules in the liquid film of the solution (y) are evaporated in a relatively low temperature region (for example, about 200 to 300 ° C.) at the initial stage of heating, and the liquid film is formed into a gel-like film. A metal oxide layer can be formed on the surface of the steel plate by forming a film through the above, but the metal oxide layer is reduced by subsequent heating to the maximum temperature, and the metal layer (for example, metal Ni layer, metal Cu layer, metal). Fe layer, etc.). In the case of a metallic Ni layer, a part of the metal Ni layer diffuses into the base iron to form an Fe—Ni layer in which Ni is solid-solved in Fe. In this annealing step (B), the metal oxide layer formed on the surface of the steel sheet with a uniform and uniform thickness is finally reduced, so that the entire surface of the steel sheet is covered without leaving unreduced metal oxide. It is uniformly covered with a metal layer. Then, this metal layer serves as a diffusion barrier for easily oxidizing elements such as Si and Mn during annealing, and as a result of suppressing the formation of selective oxides on the surface of the steel sheet, the reactivity during the plating treatment is improved, and a good surface appearance and a good surface appearance are obtained. It is considered that plating adhesion can be obtained.

_{When the H 2} concentration in the reducing atmosphere is too low, the metal oxide film formed at the initial stage of heating in the annealing step (B) remains as an unreduced metal oxide even after the annealing step (B). There is a risk of causing poor plating adhesion and poor appearance of the final product. From this, in order to sufficiently reduce the metal oxide layer, it is set to 0.05 vol% or more, preferably 1.0 vol% or more. There is no particular upper limit for the _{H 2 concentration, but if the H 2} concentration is higher than necessary, it will lead to cost increase. Therefore, it is preferable to set the upper limit to about 40.0 vol%, and it is more preferable to set the upper limit to about 35.0 vol%. preferable. The residual gas in the reducing atmosphere is usually N ₂ , H ₂ O and unavoidable impurities.
The dew point of the reducing atmosphere is 10 ° C. or lower, preferably 0 ° C. or lower. If the dew point exceeds 10 ° C., Fe is oxidized, which may cause poor plating adhesion or poor appearance. Although there is no particular lower limit for the dew point, it is industrially difficult to carry out a dew point below -60 ° C, so -60 ° C or higher is preferable.

The annealing temperature (steel plate temperature) is 700 ° C. or higher, preferably 750 ° C. or higher. If the annealing temperature is less than 700 ° C., the reduction of the metal oxide layer becomes slow, and it takes a long time to completely form the metal layer, which impairs productivity. In addition, the reduction of the metal oxide layer becomes insufficient, which tends to cause poor appearance after plating and deterioration of plating adhesion. On the other hand, there is no particular upper limit of the annealing temperature (steel plate temperature), but when the temperature exceeds 950 ° C., the diffusion of easily oxidizing elements such as Si and Mn in the steel sheet becomes remarkable, and more surface oxides are formed. In some cases, the heating cost also increases. Therefore, the annealing temperature is preferably 950 ° C. or lower, more preferably 900 ° C. or lower. When the steel sheet is held at the annealing temperature in the annealing step (B), the steel sheet may be held at a constant temperature, or the temperature of the steel sheet is changed as long as the temperature does not deviate from the above temperature range. You may hold it while letting it. Further, the holding time is not particularly limited as long as the surface of the steel sheet is sufficiently reduced and the desired material can be obtained.
The cooling conditions of the steel sheet after the annealing step (B) are not particularly limited, and the cooling rate and the cooling stop temperature may be determined according to the material design and other needs. For example, hot dip galvanizing in the subsequent plating process (C). From the viewpoint of bath management and stabilization of plating wettability, it is preferable to control the plate temperature immediately before immersion in the plating bath so that it is close to the bath temperature (for example, about 470 to 500 ° C.).
The type of annealing furnace used in this annealing step (B) is not particularly limited.

-Plating process (C)
In this plating treatment step (C), the surface of the steel sheet annealed in the annealing step (B) is plated. As described above, when the steel sheet undergoes the solution treatment step (A) and the annealing step (B), the surface of the steel sheet is uniformly covered with a metal layer, and the metal layer suppresses selective oxidation of Si and Mn on the surface of the steel sheet. Therefore, in this plating treatment step (C), a decrease in plating adhesion due to oxides can be suppressed.
The type of plating method performed in the plating treatment step (C) is not particularly limited, and may be any of hot-dip plating, electroplating, electroless plating, vapor phase plating, etc., and zinc or zinc alloy plating, tin or tin alloy plating. , Aluminum or aluminum alloy plating, etc., regardless of the type of plating component (metal or alloy).

Among the plating treatments, hot-dip galvanizing (including the case of alloying after hot-dip galvanizing) is widely applied to steel sheets for various purposes and is also suitable for steel sheets for automobile parts. , The case where hot-dip galvanizing is performed in the plating treatment step (C) will be described.
After annealing in the annealing step (B), the steel sheet cooled to a predetermined temperature is immersed in a hot-dip galvanizing bath to perform hot-dip galvanizing treatment. As described above, when the steel sheet undergoes the solution treatment step (A) and the annealing step (B), the surface of the steel sheet is uniformly covered with a metal layer, and the metal layer suppresses selective oxidation of Si and Mn on the surface of the steel sheet. Therefore, good wettability of molten zinc can be obtained.
Further, if necessary, alloying treatment may be performed after hot-dip galvanizing.
The hot-dip galvanizing conditions are not particularly limited, but the bath temperature of the hot-dip galvanizing bath is preferably about 440 to 550 ° C. If the bath temperature of the hot-dip galvanizing bath is less than 440 ° C., Zn solidifies in the low temperature portion due to temperature fluctuations in the plating bath, which may make the hot-dip galvanizing bath unsuitable. On the other hand, if the bath temperature exceeds 550 ° C, the bath evaporates violently, vaporized Zn may adhere to the inside of the furnace, making operation difficult, and alloying may proceed during plating to result in overalloying. There is.

When the alloying treatment is not performed after the plating treatment, the Al concentration in the hot-dip galvanizing bath is preferably about 0.13 to 0.24% by mass. If the Al concentration in the bath is less than 0.13% by mass, Fe-Zn alloying may proceed and the plating adhesion may deteriorate, while if it exceeds 0.24% by mass, defects due to Al oxide may occur. There is.
When the alloying treatment is performed after the plating treatment, the Al concentration in the hot-dip galvanizing bath is preferably about 0.10 to 0.20% by mass. If the Al concentration in the bath is less than 0.10% by mass, a large amount of Γ phase may be generated due to alloying of the plating film, and the plating adhesion may deteriorate. On the other hand, if it exceeds 0.20% by mass, Fe—Zn alloying may not proceed.

When the alloying treatment is performed after hot-dip galvanizing, the alloying treatment conditions are not particularly limited, but the alloying treatment temperature is preferably more than 460 ° C and less than 600 ° C. When the alloying treatment temperature is 460 ° C. or lower, the progress of alloying is slow, and it takes a long time to sufficiently alloy, which is not efficient. On the other hand, at 600 ° C. or higher, alloying proceeds too much, and a hard and brittle Zn—Fe alloy layer may be excessively formed at the base iron interface to deteriorate the plating adhesion.
When the material of the base steel sheet deteriorates during the alloying treatment, the treatment temperature should be lowered as necessary, for example, more than 460 ° C and less than 560 ° C.
In the manufacturing method of the present invention, as described above, all the steps may be carried out in continuous equipment (for example, continuous hot-dip galvanizing line), or each step may be carried out independently in separate and independent equipment. Alternatively, some steps may be carried out independently in an independent facility.

Next, the base steel sheet of the plated steel sheet manufactured by the present invention will be described. In the following description, the unit of the content of each element is "mass%", but it is indicated by "%" for convenience.
The base steel sheet to be plated (for example, hot dip galvanized) in the present invention is a steel sheet containing Si or / and Mn as a solid solution reinforcing element, and is generally a high-strength steel sheet having a tensile strength TS of 340 MPa or more. Among them, steel sheets containing Si: 0.10% or more and / and Mn: 0.50% or more are likely to cause selective oxidation of Si and Mn during annealing. Therefore, steel sheets having such a component composition are targeted. Is preferable.

Further, as a more specific component composition of the base steel sheet, as basic components, C: 0.040 to 0.500%, Si: 0.10 to 3.00%, Mn: 0.50 to 5.00. %, P: 0.100% or less, S: 0.0100% or less, Al: 0.100% or less, N: 0.0100% or less, and if necessary, Ti: 0. One or more selected from 010 to 0.100%, Nb: 0.010 to 0.100%, and B: 0.0001 to 0.0050%, Mo: 0.01 to 0.50%, Cr : 1.00% or less, Ni: 0.50% or less, Cu: 1.00% or less, V: 0.500% or less, Sb: 0.10% or less, Sn: 0.10% or less, Ca: 0 It can contain one or more selected from 0.0100% or less and REM: 0.010% or less. The reasons for these limitations will be described below.

・ C: 0.040 to 0.500%
C is an austenite stabilizing element, which is an effective element for improving strength and ductility. In order to obtain such an effect, the C content is preferably 0.040% or more. On the other hand, if the C content exceeds 0.500%, the weldability is significantly deteriorated, and an excellent strength-elongation balance may not be obtained due to the excessively hardened martensite phase. Therefore, the C content is preferably 0.500% or less.
-Si: 0.10 to 3.00%
Si is a ferrite stabilizing element, which is effective for solid solution strengthening of steel and improves the balance between strength and elongation. In order to obtain such an effect, the Si content is preferably 0.10% or more. On the other hand, when the Si content exceeds 3.00%, even if the present invention is applied, Si forms an oxide on the surface of the steel sheet during annealing, which deteriorates the wettability of hot-dip zinc during plating, resulting in adhesion to plating. There is a risk of deterioration. Therefore, the Si content is preferably 3.00% or less.

-Mn: 0.50 to 5.00%
Mn is an austenite stabilizing element and is an element effective for ensuring the strength of the annealed plate. In order to secure this strength, the Mn content is preferably 0.50% or more. However, if the Mn content exceeds 5.00%, even if the present invention is applied, a large amount of oxide is formed on the surface of the steel sheet during annealing, and the wettability of hot-dip zinc is deteriorated during plating. There is a risk of deterioration. Therefore, the Mn content is preferably 5.00% or less.
-P: 0.100% or less P is an element effective for strengthening steel, but if the content is too large, embrittlement may occur due to grain boundary segregation, which may deteriorate impact resistance, and melt. When the alloying treatment is performed after galvanizing, the alloying reaction may be delayed. Therefore, the P content is preferably 0.100% or less. From the viewpoint of strengthening the steel, the P content is preferably 0.001% or more.

-S: 0.0100% or less S becomes an inclusion such as MnS and causes deterioration of impact resistance and cracking along the metal flow of the welded portion. Therefore, the S content should be as low as possible, preferably 0.0100% or less.
-Al: 0.100% or less Excessive addition of Al causes deterioration of surface properties and moldability due to an increase in oxide-based inclusions, and also leads to high cost. Therefore, the Al content is preferably 0.100% or less, and more preferably 0.050% or less.
-N: 0.0100% or less N is an element that deteriorates the aging resistance of steel. Therefore, the smaller the N content, the more preferably 0.0100% or less.

-Ti: 0.010 to 0.100%
Ti is an element that contributes to improving the strength of the steel sheet by forming fine carbides and fine nitrides with C and N in the steel sheet. In order to obtain this effect, the Ti content is preferably 0.010% or more. On the other hand, if the Ti content exceeds 0.100%, this effect is saturated, so the Ti content is preferably 0.100% or less.
・ Nb: 0.010 to 0.100%
Nb is an element that contributes to strength improvement by strengthening solid solution and strengthening precipitation. In order to obtain this effect, the Nb content is preferably 0.010% or more. On the other hand, if the Nb content exceeds 0.100%, the ductility of the steel sheet may be lowered and the workability may be deteriorated. Therefore, the Nb content is preferably 0.100% or less.
・ B: 0.0001 to 0.0050%
B is an element that enhances hardenability and contributes to improving the strength of the steel sheet. In order to obtain this effect, the B content is preferably 0.0001% or more. On the other hand, if B is excessively contained, the ductility may be lowered and the workability may be deteriorated. In addition, excessive content of B also causes an increase in cost. Therefore, the B content is preferably 0.0050% or less.

・ Mo: 0.01 to 0.50%
Mo is an austenite-forming element and is an element effective for ensuring the strength of the annealed sheet. From the viewpoint of ensuring strength, the Mo content is preferably 0.01% or more. On the other hand, since Mo has a high alloy cost, a large amount of Mo added causes an increase in cost. Therefore, the Mo content is preferably 0.50% or less.
-Cr: 1.00% or less Cr is an austenite-forming element and is an element effective for ensuring the strength of the annealed sheet. However, if the amount added is too large, an oxide is formed on the surface of the steel sheet during annealing, and the plating appearance. May deteriorate. Therefore, the Cr content is preferably 1.00% or less.

-Ni: 0.50% or less, Cu: 1.00% or less, V: 0.500% or less Ni, Cu, V are effective elements for strengthening steel, but if added excessively, ductility due to a significant increase in strength In addition, excessive addition of these elements also causes an increase in cost. Therefore, when these elements are added, it is preferable that the Ni content is 0.50% or less, the Cu content is 1.00% or less, and the V content is 0.500% or less. In order to reinforce the steel, it is preferable that the Ni content is 0.05% or more, the Cu content is 0.05% or more, and the V content is 0.005% or more.
-Sb: 0.10% or less, Sn: 0.10% or less Sb and Sn have an effect of suppressing nitriding near the surface of the steel sheet, but the effect is saturated even if they are added excessively. Therefore, when these elements are added, the Sb content is preferably 0.10% or less, and the Sn content is preferably 0.10% or less. In order to suppress nitriding, the Sb content is preferably 0.005% or more, and the Sn content is preferably 0.005% or more.

-Ca: 0.0100% or less Ca has the effect of improving ductility by controlling the shape of sulfides such as MnS, but the above effect is saturated even if it is added in excess, so the Ca content is 0.0100%. The following is preferable. In order to obtain the above effect, the Ca content is preferably 0.0010% or more.
-REM: 0.010% or less REM (rare earth metal: rare earth metal) controls the morphology of sulfide-based inclusions and contributes to the improvement of workability, but when added in excess, it causes an increase in inclusions and is processed. The REM content is preferably 0.010% or less because it may deteriorate the properties. In order to obtain the effect of improving workability, the REM content is preferably 0.001% or more.
The rest other than the basic component and the optional additive component described above are Fe and unavoidable impurities.

In addition, there are no special restrictions on the manufacturing conditions of the base steel sheet. Usually, a steel slab having the above composition is rough-rolled and finish-rolled in a hot-rolling step, then the scale of the hot-rolled plate surface layer is removed in a pickling step, and cold-rolled if necessary. Hot rolling conditions, pickling conditions, and cold rolling conditions are not particularly limited. That is, the base steel sheet may be either a hot-rolled steel plate or a cold-rolled steel plate.
The solution (y) used in the solution treatment step (A) of the present invention is a treatment agent for solution treatment for suppressing selective oxidation of easily oxidizable elements at the time of annealing of a steel plate, and is more than Fe and Fe. A treatment agent for solution treatment, which comprises a solution containing a metal alkoxide of one or more metals (x) selected from metals having a high standard oxidation-reduction potential. The preferable composition of this treatment agent and the like are as described above for the solution (y).

A steel having the component composition shown in Table 3 and having the balance of Fe and unavoidable impurities was melted to form a slab. The slab was heated to 1200 ° C., hot-rolled, and wound. This hot-rolled plate was pickled and cold-rolled at a reduction ratio of 50%. The obtained cold-rolled steel sheet was subjected to a solution treatment step, an annealing step, and a plating treatment step in sequence under the conditions shown in Tables 4 to 9. Each step was carried out using an experimental facility in which each was carried out independently.
In the solution treatment step, the solution was applied to the surface of the steel sheet by a roll coater. The amount of adhesion (the amount of metal alkoxide converted to metal (x)) was controlled by adjusting the roll gap and the peripheral peripheral speed of the roll to change the liquid film thickness. The amount of adhesion was quantified by fluorescent X-ray analysis of the dried steel sheet after applying the solution.

The annealing step was carried out in a furnace capable of adjusting the atmosphere, and the steel sheet coated with the solution in the solution treatment step was placed in the furnace as it was with a liquid film and annealed.
In the plating treatment step, the steel sheet was hot-dip galvanized in a hot-dip galvanizing bath having an Al concentration of 0.132% by mass in the bath. In addition, some steel sheets were continuously alloyed. In this alloying treatment, the holding time was set to 20 seconds, and the temperature at which the Fe concentration in the plating film reached 10% by mass was defined as the alloying treatment temperature. The Fe concentration in the plating film was measured by inductively coupled plasma emission spectroscopy.

The surface appearance and plating adhesion (GI adhesion and GA adhesion) of the hot-dip galvanized steel sheet (GI) and the alloyed hot-dip galvanized steel sheet (GA) obtained as described above were evaluated by the following methods. ..
-Surface appearance The presence or absence of appearance defects such as non-plating, unevenness, pinholes, and cracks was visually judged, and evaluation was performed according to the following criteria.
〇: No non-plating, unevenness, pinholes, or cracks are observed.
Δ: No non-plating, pinholes, or cracks were observed, but slight unevenness was observed.
X: One or more of non-plating, clear unevenness, pinholes, and cracks are observed.

-Plating adhesion of hot-dip galvanized steel sheet (GI) (GI adhesion)
To evaluate the plating adhesion of hot-dip galvanized steel sheet (GI), a ball impact test was used, and after peeling the cellophane tape on the processed part, the presence or absence of peeling of the plating layer was visually judged to evaluate according to the following criteria. Was passed. In this test, the ball mass was 1.8 kg and the drop height was 100 cm.
◯: No peeling of the plating layer Δ: Slight peeling of the plating layer ×: Non-slight peeling of the plating layer

・ Plating adhesion of alloyed hot-dip galvanized steel sheet (GA) (GA plating adhesion)
The plating adhesion of the alloyed hot-dip galvanized steel sheet (GA) was evaluated by the powdering resistance. Specifically, cellophane tape is attached to the alloyed hot-dip zinc-plated steel plate, the tape surface is bent and bent back 90 degrees, and the cellophane with a width of 24 mm is placed inside the processed portion (compression processed side) in parallel with the bent portion. The tape is pressed and pulled apart, the amount of zinc adhering to the 40 mm long part of the cellophane tape is measured as the Zn count number by fluorescent X-ray, and the amount obtained by converting the Zn count number per unit length (1 m) is as follows. Ranked according to the criteria. Ranks 1 and 2 were good (◯), rank 3 was generally good (Δ), rank 4 and above were bad (x), and ○ and Δ were passed.
Rank 1: Fluorescent X-ray count is 0 or more and less than 2000 Rank 2: Fluorescent X-ray count is 2000 or more and less than 5000 Rank 3: Fluorescent X-ray count is 5000 or more and less than 8000 Rank 4: Fluorescent X-ray count Is 8000 or more and less than 10000 Rank 5: Fluorescent X-ray count is 10000 or more

The above results are shown in Tables 4 to 10 together with the manufacturing conditions.
According to Tables 4 to 10, it can be seen that the high-strength hot-dip galvanized steel sheets of the examples of the present invention are all excellent in surface appearance and plating adhesion. On the other hand, the high-strength hot-dip galvanized steel sheet of the comparative example is inferior in surface appearance, plating adhesion, or both.

Claims (15)

A method for producing a high-strength plated steel sheet using a steel sheet containing Si or / and Mn as a base material.
A solution treatment step of adhering a solution (y) containing a metal alkoxide of one or more metals (x) selected from metals having a standard oxidation-reduction potential higher than Fe and Fe to the surface of a steel plate, and a solution treatment step.
The steel sheet after the solution treatment step, H ₂ concentration is 0.05 vol% or more, and annealing steps which dew point is heated at 700 ° C. or higher at 10 ° C. in the reducing atmosphere,
A method for producing a high-strength plated steel sheet, which comprises a plating process for plating a steel sheet that has undergone the annealing step. The first aspect of claim 1, wherein in the solution treatment step, the solution (y) is adhered to the surface of the steel sheet so that the adhesion amount is 0.01 to 3.0 g / m ^{2 in terms of metal (x).} How to manufacture high-strength galvanized steel sheet. The method for producing a high-strength galvanized steel sheet according to claim 1 or 2, wherein the metal alkoxide contained in the solution (y) is at least one selected from Ni alkoxide, Cu alkoxide, and Fe alkoxide. .. The method for producing a high-strength plated steel sheet according to claim 3, wherein the metal alkoxide is at least one selected from Ni ethylene glycol, Cu ethylene glycol, and Fe ethylene glycol. The method for producing a high-strength plated steel sheet according to any one of claims 1 to 4, wherein the steel sheet contains Si: 0.10% or more and / and Mn: 0.50% or more in mass%. .. The method for producing a high-strength plated steel sheet according to any one of claims 1 to 5, wherein the steel sheet to which the solution (y) is adhered to the surface through the solution treatment step is directly introduced into the annealing step. The method for producing a high-strength plated steel sheet according to any one of claims 1 to 5, wherein the steel sheet to which the solution (y) is adhered to the surface is heat-treated through the solution treatment step and then introduced into the annealing step. The method according to any one of claims 1 to 7, wherein the plating treatment step is a step of hot-dip galvanizing a steel sheet that has undergone an annealing step (provided that the alloying treatment is performed after hot-dip galvanizing). High-strength plated steel sheet manufacturing method. The method for producing a high-strength plated steel sheet according to claim 8, wherein the solution treatment step, the annealing step, and the plating treatment step are continuously performed in the continuous hot-dip galvanizing line. The weight of the steel sheet is C: 0.040 to 0.500%, Si: 0.10 to 3.00%, Mn: 0.50 to 5.00%, P: 0.100% or less, S: Any of claims 1 to 9, which contains 0.0100% or less, Al: 0.100% or less, N: 0.0100% or less, and has a component composition in which the balance is composed of Fe and unavoidable impurities. A method for manufacturing a high-strength galvanized steel sheet described in Crab. The steel sheet is further selected from Ti: 0.010 to 0.100%, Nb: 0.010 to 0.100%, and B: 0.0001 to 0.0050% in mass%. The method for producing a high-strength plated steel sheet according to claim 10, wherein the high-strength plated steel sheet contains. Further, the steel sheet is, in terms of mass%, Mo: 0.01 to 0.50%, Cr: 1.00% or less, Ni: 0.50% or less, Cu: 1.00% or less, V: 0.500%. Hereinafter, it is characterized by containing one or more selected from Sb: 0.10% or less, Sn: 0.10% or less, Ca: 0.0100% or less, and REM: 0.010% or less. The method for producing a high-strength galvanized steel sheet according to claim 10 or 11. A treatment agent for solution treatment for suppressing selective oxidation of easily oxidizing elements during annealing of steel sheets for plating.
A treatment agent for solution treatment, which comprises a solution (y) containing a metal alkoxide of one or more metals (x) selected from Fe and a metal having a standard oxidation-reduction potential higher than that of Fe. The treatment agent for solution treatment according to claim 13, wherein the metal alkoxide is at least one selected from Ni alkoxide, Cu alkoxide, and Fe alkoxide. The treatment agent for solution treatment according to claim 14, wherein the metal alkoxide is at least one selected from Ni ethylene glycol, Cu ethylene glycol, and Fe ethylene glycol.

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