JP2017008387A - Plated steel, flux, and manufacturing method of plated steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide plated steel that includes a hot-dip Zn-Al plating layer of an Al concentration of 15% or less and is excellent in appearance, corrosion resistance, and machinability.SOLUTION: Plated steel includes a hot-dip plating layer composed of Al of 2-15 mass%, Si of 0.01-1.0 mass%, and the balance of Zn and impurities on the surface and an alloy layer containing main components of Al, Si, and Fe and a minor component of Sn of 2 mass% or less and having a thickness of 2 μm or less at the interface between the hot-dip plating layer and the surface of the steel. The plated steel has a Sn coating amount of 0.12-240 mg/mon the interface.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing a plated steel material, a flux, and a plated steel material that has excellent corrosion resistance and is mainly used for civil engineering and building materials.

  As an immersion hot dipped galvanized steel material that is known to have excellent corrosion resistance, there is a zinc-based plated steel material. This zinc-based plated steel material is used in a wide range of applications, and pure zinc plating is most frequently used among them. However, the demand for corrosion resistance tends to increase, and it is difficult to satisfy the demand with conventional pure galvanized steel materials.

  For this reason, alloy plating of various compositions based on a Zn—Al-based alloy has been developed. This Zn—Al alloy-plated steel material is excellent in corrosion resistance, and is produced in large quantities as a steel plate by continuously hot-plating a steel strip.

Zn-Al alloy plating can be easily performed continuously using the hydrogen reduction method, but continuous plating such as bolts / nuts, H-shaped steel, welded structures, etc. is not possible. Plating on a possible steel material is difficult because it is difficult to control the plating reaction. One reason for this is that if the immersion time in the plating bath is prolonged, the effect of the flux is reduced. For example, consider a case where a plating bath having an Al concentration of 10% and a bath temperature of 470 ° C. is used. When a steel material is immersed in a plating bath for 100 seconds or more when the Al concentration is 10%, the reaction between the steel and Al is good, so that a flux containing NaF, SnCl _2, etc. as reported in Patent Document 1 is used. Even if there is, there is no particular problem in the initial stage of plating. However, since the reaction between steel and Al at a high temperature is too intense, an immersion of 100 seconds or more produces a large amount of FeAl alloy, the plated surface is not smooth, and the FeAl alloy is exposed on the surface and becomes gray. Appearance deteriorates, such as presenting. Furthermore, since a large amount of Fe is eluted in the plating bath, problems such as so-called dross are generated.

  In addition, a large object having a length of several meters and a weight of several tons is suspended by a hoist and immersed and pulled up in a plating bath, but it is practically impossible to control the immersion time in seconds. .

  Further, in order to suppress the reaction between Fe in steel and Al in the plating bath, it is effective to add a small amount of Si to the plating bath. However, since the reactivity of FeAl decreases due to the addition of Si, there is a problem that the initial plating reaction is less likely to occur and non-plating is likely to occur.

  Similarly, Mg, which has a significant effect on improving the corrosion resistance, similarly inhibits plating and easily causes non-plating.

In Patent Document 2, when the base material is treated with a flux and immersed in a plating bath, ZnAl alloy immersion plating is plated in one step by setting the preheating temperature of the steel material before plating immersion as high as 300 to 700 ° C. It is written.
Moreover, as a molten Zn-Al alloy plating method in one step, a method using a molten salt flux is disclosed in Patent Document 3, which is applied only to a bath having a high Al concentration of 40 to 80%.

  Moreover, when performing Zn-Al type alloy plating whose Al content rate is about 4-20 mass%, the method generally called the two-step plating shown by patent document 4, for example is put into practical use. . In the two-step plating, the first-stage pure Zn plating is usually performed on the steel material, and the steel material is immersed in the second-stage ZnAl alloy bath after the cooling of the Zn plating or immediately after the Zn plating. The FeZn alloy produced by the first-stage Zn plating is modified to the FeZnAl alloy by the second-stage plating. This improves the corrosion resistance of the alloy layer. Further, the pure Zn plating layer present on the FeZn alloy in the first stage plating is replaced with a ZnAl alloy having excellent corrosion resistance, which is a bath composition of the second stage plating. In this way, the entire plating layer is converted to an alloy containing Al by the second-stage plating, and the corrosion resistance of the plating layer is improved.

  Patent Documents 5 and 6 disclose a technique for manufacturing an Al—Zn-based plated steel material containing Si in a plating layer by a two-step plating method. Patent Documents 5 and 6 disclose the average composition of steel plating. However, there is no mention of the presence or absence of an alloy layer at the interface between the steel plate and the plating. In Patent Documents 5 and 6, since the first plating is plating that does not contain Si, it is predicted that an interface alloy layer that does not contain Si is generated between the steel material and the plating layer.

  Patent Document 7 describes a plated steel material having high corrosion resistance and excellent workability manufactured by a two-step plating method. Patent Document 7 describes the average composition of steel plating and the composition of the interface alloy layer. The interfacial alloy layer of Patent Document 7 has a two-layer structure, and each has a thickness of 5 μm or less and 30 μm or less.

  As described in Patent Documents 4 to 7, the currently popular two-stage plating method is a manufacturing method in which one plating product is made using two types of hot dipping bath equipment, and the equipment efficiency is very poor. It has become. Needless to say, one-step plating is desirable from the viewpoint of efficiency and cost.

  When performing molten salt flux treatment in one-stage hot dipping, since the plating composition is limited to high Al concentration plating, the melting point of the plating bath is increased, and the steel and structure are deformed and the material is affected. There is a problem to do. A ZnAl alloy having a high Al concentration is excellent in the corrosion resistance of the plating layer itself, but red rust is likely to occur because the sacrificial anticorrosion performance of the plating is low. For this reason, it is plating which selects a corrosive environment, and its application is limited.

  Moreover, it is thought that the method of raising preheating temperature before plating immersion does not choose the composition of plating. However, since immersion plating targets various forms of steel structures, uniform preheating is difficult and thermal efficiency is poor when increasing the preheating temperature of long materials to be plated or materials with complicated shapes. There is a problem that preheating is necessary for a long time. In addition, when heated at an extremely high temperature for a long time, an oxide may be generated on the surface of the steel material, which may affect the plating. In order to solve this problem, heating in a non-oxidizing atmosphere can be considered, but heat treatment equipment is required, and equipment efficiency is reduced. Furthermore, the non-uniformity of the steel material temperature may cause the plating reaction between the high temperature portion and the low temperature portion to be different, resulting in a partial deterioration in appearance and corrosion resistance. For this reason, the method described in Patent Document 3 is effective when the non-plated object is small and the shape is simple, but is difficult to apply when the object to be plated is long or the shape is complicated, There is a problem of selecting the object of plating.

Japanese Patent No. 3588452 JP 2012-241277 A JP-A-4-323356 JP 2010-70810 A JP 2002-47548 A JP 2002-47521 A JP 2002-47549 A

  This invention is made | formed in view of the said situation, and makes it a subject to provide the plating steel material which was provided with the fusion | melting Zn-Al type plating layer whose Al concentration is 15% or less, and was excellent in the external appearance and corrosion resistance. In addition, the present invention provides a method for manufacturing a plated steel material to which a one-step immersion plating method can be applied when obtaining a molten Zn-Al-based plating layer having an Al concentration of 15% or less, and a flux used in this manufacturing method. This is the issue.

In order to solve the above problems, the inventors have studied the conditions of the flux and the conditions of the plating bath. As a result, 0.01 to 1.0 mass% of Si was added to the plating bath, and SnCl ₄ or SnO ₂ was added to the flux. It was found that the plating reaction can be stabilized and plating with a good appearance can be obtained by adding, and a one-step immersion plating method of molten Zn—Al-based alloy plating with an Al concentration of 15% or less was completed. In addition, when plating is performed by this method, since the reactivity when immersed in the plating bath is good, the plating can be performed in a plating bath containing up to 3% of Mg, which is an element inhibiting the plating reaction.

That is, the gist of the present invention is as follows.
(1) On the surface of the steel material,
Al: 2 to 15% by mass,
Si: 0.01-1.0 mass%
A hot-dip plated layer with the balance being Zn and impurities,
An alloy layer containing 2% by mass or less of Sn as a trace component and having a thickness of 2 μm or less containing Al, Si, and Fe as main components at the interface between the hot-dip plated layer and the surface of the steel material;
The plated steel material, wherein the Sn adhesion amount at the interface is in the range of 0.12 to 240 mg / m ² .
(2) The plated steel material according to (1), wherein the hot-dip plated layer contains Al, Si, and Fe, and a needle-like or massive compound is dispersed in a cross-sectional view.
(3) The plated steel material according to (1) or (2), wherein the hot-dip plated layer further contains Mg in a range of 0.01 to 3% by mass.
(4) NaCl is 5 to 14% by mass, SnCl ₂ is 1.2 to 5% by mass, either one or both of SnCl _{4 and} SnO ₂ is 0.1 to 1.5% by mass in total, and the balance is ZnCl ₂ The flux component which consists of this composition is melt | dissolved in water by the density | concentration of 150-300 g / L, and the pH is adjusted to 2.0 or less.
(5) The flux according to (4), wherein the flux component further contains one or both of NaF and KF in a ratio of more than 0% by mass and 2.0% by mass or less.
(6) The flux according to (4) or (5), wherein the flux component further contains a surfactant in a proportion of more than 0% by mass and 1.0% by mass or less.
(7) The flux according to any one of (4) to (6) is applied to a steel material and dried.
Next, the steel material includes Al: 2 to 15% by mass, Si: 0.01 to 1.0% by mass, and the remainder is dipped in a hot dipping bath made of Zn and pulled up. Production method.
(8) The method for producing a plated steel material according to (7), wherein Mg is further contained in the hot dipping bath in a range of 0.01 to 3% by mass.

According to the present invention, it is possible to provide a plated steel material having a hot-dip plated layer having an Al concentration of 15% or less and excellent in appearance and corrosion resistance.
Moreover, according to this invention, when obtaining the hot dip plating layer whose Al density | concentration is 15% or less, the manufacturing method of the plating steel materials which can apply the one-step immersion plating method, and the flux used for this manufacturing method can be provided.

The cross-sectional SEM photograph which shows an example of the plating layer of the plated steel material of this invention. Sectional SEM photograph which shows another example of the plating layer of the plating steel materials of this invention. The graph which shows an example of the result of the depth direction analysis of the plating layer of the plating steel materials of this invention. The graph which shows another example of the result of the depth direction analysis of the plating layer of the plating steel materials of this invention.

  In the hot dip plating bath for obtaining the hot dip plating layer according to the present invention, the amount of Al that can react with Fe of the steel material is as low as 15% by mass or less. Moreover, the temperature of the hot dipping bath itself becomes a relatively low temperature of 500 ° C. or less. Further, Si that suppresses the growth of the FeAl alloy is included in the plating bath. Accordingly, the reactivity between the steel material and the plating bath becomes relatively gentle, and the alloy layer on the steel material surface is relatively difficult to be formed. Therefore, non-plating is likely to occur. Therefore, the present inventor diligently studied and found that when a tetravalent tin compound was added as a flux component, non-plating was less likely to occur.

  Further, when forming a hot-dip plating layer containing 15% by mass or less of Al and 1.0% by mass or less of Si, the present invention is a so-called immersion plating method in which the steel material after flux treatment is dipped in a hot dipping bath and pulled up. Form. Thereby, in this invention, the alloy layer containing Sn derived from a flux is formed in the steel material surface at the time of immersion in a hot dipping bath. By forming such an alloy layer, non-plating hardly occurs. Further, in the present invention, since the immersion time in the hot dipping bath is relatively longer than that in the continuous plating method, the formed alloy layer is partially broken in the plating bath to expose the base iron. It is believed that a reaction occurs between iron and Al in the hot dipping bath. As a result, a needle-like or massive compound phase containing Al, Si, and Fe may be formed in the hot-dip plating layer. The shape of the compound phase is a shape that appears when the plated layer is viewed in cross section. The presence of these compound phases dispersed in the plating layer during the growth of the hot-dip plating layer is presumed to increase the thickness of the plating layer. As described above, the corrosion resistance of the plated steel material is improved. Moreover, a thin alloy layer is uniformly formed on the steel material surface by treating the steel material surface with a flux containing a tetravalent tin compound in advance. For this reason, the comparatively brittle alloy layer does not become excessively thick, the peeling of the plating layer is difficult to occur, and the workability of the plated steel material is improved.

Incidentally, in the continuous plating method, instead of flux treatment, the steel material surface is subjected to hydrogen reduction treatment, and further, the immersion time in the plating bath is short, so that the growth of highly brittle FeAl alloy is suppressed. For this reason, an alloy layer structure containing Sn as in the present invention cannot be obtained by the continuous plating method. Further, in the normal immersion plating, the alloy layer grows thick, and a part of the alloy containing Sn that is generated at an early stage is dissolved in the plating bath. Therefore, even if a flux containing SnCl ₂ is used, An alloy layer structure containing Sn is not observed.

Hereinafter, embodiments of the present invention will be described.
The plated steel material of the present embodiment includes a steel material, a hot-dip plating layer formed on the surface of the steel material, and an alloy layer formed at the interface between the hot-dip plating layer and the steel material.

  The steel material that is the object of plating of this embodiment is not particularly limited in shape, such as a wire shape such as a steel wire, a plate shape such as a steel plate, a net shape, a cylindrical shape such as a steel pipe, a three-dimensional shape such as a rod shape, etc. Various shapes can be used. For example, from small base materials such as bolts, nuts and power transmission brackets to large base materials such as railings, main pillars, guard fences for bridges, road signs, road card fences, river fences, rockfall prevention nets, steel pipes, etc. Can be used. The material of the steel material is not particularly limited as long as it is plain steel.

  The hot dip plating layer contains Al: 2 to 15% by mass, Si: 0.01 to 1.0% by mass, and the balance is made of Zn and impurities. The hot dipping layer may contain Mg in a range of 0.01 to 3% by mass. In this embodiment, a bath having the same composition as that described above is used as a hot dipping bath for forming the hot dipping layer.

  The reason why the content of Al in the hot dip plating layer and hot dip plating bath is limited to 2 to 15% by mass is that if it is less than 2% by mass, the effect of improving the corrosion resistance of the hot dip plating layer becomes insufficient, and 15% by mass. It is because the effect which improves corrosion resistance will be saturated when it exceeds%. Further, Al must be added in an amount of 2% by mass or more in order to prevent oxidation of Mg in the plating bath.

  As will be described later, since it is desirable that the plating bath be at most about 500 ° C., the Al concentration in the hot dipping bath is limited to 15% by mass or less at the maximum. In reality, considering the decrease in bath temperature when dipping the steel material, it is not desirable to set the bath temperature directly above the melting point, so the Al concentration is preferably 13% by mass or less. The lower limit is desirably 3% by mass or more in order to improve the corrosion resistance more clearly than hot-dip Zn plating. In consideration of keeping the concentration constant in the immersion plating, 4% by mass or more is more preferable.

  The reason for limiting the Si content in the hot-dip plating layer and hot-dip plating bath to 0.01 to 1.0% by mass is that if the content is less than 0.01% by mass, the reaction between the base iron and Al becomes insufficient. In addition, it is difficult to manage the Si concentration in the plating bath. When Si exceeds 1.0 mass%, it will become easy to produce plating defects, such as non-plating. The amount of Si is desirably 0.05 to 0.5% by mass.

In this embodiment, Mg may be added to the hot dipping layer and the hot dipping bath. The reason why the content of Mg is limited to 0.01 to 3% by mass is that if it is less than 0.01%, the effect of improving the corrosion resistance is insufficient, and if it exceeds 3% by mass, the effect of adding Mg This is because a problem arises in the operation such as saturation of the amount of dross in the plating bath. Mg contributes to improving corrosion resistance by being finely dispersed in the plating layer as the MgZn ₂ phase. Since Mg promotes the formation of ZnCl ₂ · 4Zn (OH) ₂ , the zinc corrosion product during corrosion becomes a protective film by finely dispersing the MgZn ₂ phase in the plating layer. Corrosion resistance can be improved.

  Mg is an alloy element often added in continuous plating in order to improve corrosion resistance. However, in immersion plating, the plating property is clearly reduced and plating defects such as non-plating are likely to occur. In this embodiment, since the plating reaction is suppressed by adding Si, problems are more likely to occur. For this reason, until now, in flux-type immersion plating, Mg could be added only by two-step plating. However, as will be described later, it is possible to add 3% by mass or less of Mg by using the flux according to the present invention having high initial reactivity of plating. From the management of the bath composition, 2.5% by mass or less is desirable.

  There may be a case where needle-like or massive compounds containing Al, Si and Fe are dispersed in the hot-dipped layer. The shape of such a compound phase is a shape observed when the hot-dip plated layer is viewed in cross section. It is estimated that the presence of such a compound phase can increase the thickness of the hot-dip plating layer. Such a compound phase can be obtained by setting the immersion time of the steel material in the plating bath to 100 seconds or more, more preferably 300 seconds or more, although it depends on the amount of Al in the plating bath.

  The compound phase is distributed in a relatively large amount on the alloy layer side in the thickness direction of the hot dipped layer, and is relatively distributed in the surface side of the hot dipped layer. The reason for this distribution is presumed to be that the compound phase grows from the location where the alloy layer was destroyed during the formation of the hot dip plating layer.

  The composition of the compound phase is, for example, Al: 50 to 70% by mass, Si: 10 to 20% by mass, Fe: 10 to 30%, and the balance is Zn. The compound phase distributed on the alloy layer side may contain a small amount of Sn. The chemical composition of the compound phase may be obtained by elemental analysis of the compound phase exposed on the cross section of the plating layer using an analyzer such as an electron beam microanalyzer (EPMA).

  The size of the massive compound phase is not particularly limited, but may be, for example, a circle average equivalent diameter of about 0.5 to 80 μm. The length of the acicular compound phase may be about 10 to 100 μm. If the size of the compound phase is in the above range, the effect of increasing the thickness of the hot dipped layer is sufficient. The size of the compound phase may be determined by observing the cross section of the plating layer with an electron microscope, measuring the equivalent circle diameter or length of 30 or more compounds, and adopting the average value thereof. If a thick plating layer is obtained, the size of the compound phase may be out of the above range.

  Next, an alloy layer is formed between the steel material surface and the hot dipped plating layer. The alloy layer contains Al, Si, and Fe as main components and contains Sn as a minor component. The alloy layer desirably has a uniform thickness and composition, but the thickness and composition may vary depending on the location. As a guide, the Sn concentration in the alloy layer is more than 0% by mass and 2% by mass or less. The thickness of the alloy layer is 2 μm or less. By forming such an alloy layer, the adhesiveness of the hot dipped layer is improved. When the amount of Sn in the alloy layer exceeds 2% by mass, the strength of the alloy layer is lowered and the adhesion of the hot-dip plated layer is lowered, which is not preferable. In this embodiment, since the tetravalent tin compound is contained in the flux applied to the steel material, the alloy layer on the steel material surface contains a small amount of Sn. Therefore, the amount of Sn is more than 0% by mass. On the other hand, when the thickness of the alloy layer exceeds 2 μm, the alloy layer is easily peeled off, and the adhesion of the hot dip plating layer is lowered, which is not preferable.

Moreover, it is preferable that the adhesion amount of Sn in the interface of a steel material surface and a hot dipping layer is the range of 0.12-240 mg / m < ² >. When the adhesion amount of Sn at the interface is in the range of 0.12 to 240 mg / m ² , non-plating is less likely to occur, and defects such as pinholes are less likely to occur. Adhesion amount of Sn is more preferably in the range of 10~240mg / ^{m 2,} more preferably in the range of 30~150mg / ^{m 2.}

  The alloy layer is a concentrated layer of Al, Si, and Sn by analyzing the cross section near the interface between the hot dipped layer and the steel with an analyzer such as an electron beam microanalyzer (EPMA) or glow discharge emission analysis (GDS). By specifying, it is possible to measure the type of element contained in the alloy layer, the concentration and thickness of Sn.

Next, the flux provided for the production of the plated steel material of this embodiment will be described.
In the present embodiment, a flux in which the flux component is dissolved in water at a concentration of 150 to 300 g / L and the pH is adjusted to 2.0 or less is used. The flux component contains ZnCl ₂ , NaCl and SnCl ₂ and either or both of SnCl _{4 and} SnO ₂ . Hereinafter, the flux component will be described.

The main component of the flux of the present invention is a ZnCl _2. ZnCl ₂ is a basic component of a flux that removes an oxide film on the surface of a steel material in a plating bath. The content of ZnCl _{2 in} the flux component is not particularly defined, and is the balance of other additive components. However, relatively little ZnCl ₂ is not preferable because the function of removing the oxide film in the plating bath deteriorates. If the ZnCl ₂ is relatively excessive, the effect is saturated.

  NaCl lowers the melting point of the flux and improves the reaction uniformity during plating. The content of NaCl in the flux component is 5 to 14% by mass. If the amount is less than 5% by mass, the effect cannot be sufficiently obtained. If the amount exceeds 14% by mass, the effect is saturated.

SnCl ₂ has an effect of greatly improving the plating property in the presence of ZnCl ₂ . The cause is not clear, but it has been confirmed that when steel is immersed in an acidic flux of about 60 to 80 ° C., metal Sn is deposited by substitution plating on the surface of the steel, which improves the plating reaction. I believe. 1.2-5 mass% is suitable for content in a flux component. If it is less than 1.2% by mass, the effect of adding SnCl ₂ is not sufficient, and the effect becomes unstable. Moreover, when it exceeds 5 mass%, not only the effect is saturated but also non-plating may occur.

SnCl ₄ and SnO ₂ have the effect of significantly improving the plating properties in the presence of ZnCl ₂ , as with SnCl ₂ . The total amount of SnCl ₄ and SnO ₂ in the flux component is suitably 0.1 to 1.5% by mass. Addition of 0.1% by mass or more greatly improves plating properties. When the amount exceeds 1.5% by mass, no serious problem necessarily occurs, but the effect may be saturated or lowered, which is disadvantageous in terms of cost. The reason why the plating property is improved by adding one or both of SnCl _{4 and} SnO ₂ is not clear, but the surface of the steel material is easily plated in the presence of SnCl ₄ or SnO ₂ , and 15% by mass. Even when immersed in a relatively mild plating bath containing Al and Si below, it is estimated that no plating occurs.

In addition to SnCl ₄ and SnO ₂ , the improvement effect by adding Sn (IV) compound is expected. For example, a halogenated salt of Sn (IV) other than chloride can be used. However, SnBr ₄ is expensive and has a problem in availability. Therefore, as the agent used in the flux is consumable cost, in terms of availability, effect, is limited to SnCl _4, or SnO _2.

Further, the flux component may contain either one or both of NaF and KF in a proportion of more than 0% by mass and 2.0% by mass or less. In the hot dip plating bath of this embodiment, it is effective to remove the thin oxide Al film formed on the surface of the plating bath. For this purpose, addition of an F compound is effective. For this reason, NaF or KF may be added. Any other compound that forms F ⁻ ions when made into an aqueous solution is considered to be usable, but it is practically limited to these two compounds in terms of cost and availability. NaF is advantageous in terms of cost and low hygroscopicity, but there is no problem with either NaF or KF as an effect.

The content of NaF and KF in the flux component is more than 0% by mass and 2.0% by mass or less as one or a mixture thereof. In order to exhibit the effect of F, 0.5 mass% or more is preferable. Moreover, even if it exceeds 2.0 mass%, the effect will be substantially saturated. However, when the Al concentration in the hot dipping bath is 5% or less, the effect of F is not always clear and may be unnecessary depending on the bath composition. In addition, since the flux is acidic with hydrochloric acid, the flux to which NaF and KF are added becomes a dilute concentration of hydrofluoric acid. Therefore, it is desirable for the operation to set the concentration lower. Further, when the flux contains F ⁻ ions, the corrosiveness of the flux becomes strong, so it is necessary to consider the material of the flux container. In particular, in order to make the flux easy to dry, it is necessary to use a fluororesin or the like when the bath temperature of the flux is set high. For this reason, the amount of NaF and KF added may be 0% in consideration of the fact that it is not always necessary depending on the situation such as when the Al concentration is low.

  Further, by adding a surfactant, even when the pretreatment of the steel material is not complete, the wettability of the flux is improved, and the plating property is slightly improved. For this reason, although it is not essential as a flux from the point of reaction, surfactant can be added in 0 to 1.0% of range as needed from the surface of stable production. The surfactant is preferably a nonionic surfactant because it is not affected by pH.

  The above chemicals are dissolved in water so that the total amount is 150 to 350 g / L and used as a flux. Below 100 g / L, the effect as a flux is not sufficient. More preferably, it is 150 g / L or more. The effect of a flux is stabilized by setting it as 150 g / L or more. Moreover, even if it exceeds 350 g / L, an effect will be saturated. In addition, Sn compounds are expensive, and if the F concentration is further increased, there may be a problem in the environment and equipment, so it is meaningless to increase the concentration more than necessary. The upper limit is more preferably 300 g / L or less. In actual plating work, since the flux concentration tends to gradually decrease due to the water brought in by the object to be plated, the concentration of the flux component should be given a margin of 250 g / L or more and 300 g / L or less. Concentration is desirable.

Since an aqueous solution of flux containing SnCl ₂ or SnCl ₄ becomes cloudy, the pH needs to be about 2.0 or less in order to completely dissolve it. The pH may be adjusted with hydrochloric acid.

Next, the manufacturing method of the plated steel material of this embodiment is demonstrated.
In the method for producing a plated steel material according to the present embodiment, the flux is applied to the steel material and dried, and then the steel material is immersed in a hot dipping bath and pulled up. The manufacturing method of the plated steel material of this embodiment employs a one-step plating method using a flux.

  The surface of the steel material before applying the flux is preferably cleaned by degreasing and pickling. You may combine a shot blast process, a sand blast process, etc. as needed.

  The steel material after the pickling is washed with hot water having the same temperature as the flux, and then immersed in a flux bath. It has been experimentally confirmed that the temperature of the flux bath needs to be 40 ° C. or higher. This is considered to be necessary for Sn substitution plating. Moreover, since there are problems in equipment such as the material of the container and generation of HCl vapor, about 90 ° C. is the practical upper limit of the temperature of the flux bath. In consideration of heating the steel material in order to dry the flux, about 60 to 80 ° C. is desirable. Although the immersion time is affected by the heat capacity, temperature, etc. of the steel material to be immersed, it is usually from several seconds to a maximum of 60 seconds.

  After the steel material is pulled up from the flux bath, the steel material is heated using a drying furnace, induction heating, or the like as necessary to sufficiently dry the adhered flux. At this time, the heating temperature is desirably about 250 ° C. at the maximum so that the steel material surface is not oxidized.

  The steel material thus flux-treated is immersed in a hot dipping bath. The composition of the hot dipping bath includes Al: 2 to 15% by mass, Si: 0.01 to 1.0% by mass, and the balance is made of Zn and impurities. Mg may be added to the hot dipping bath in the range of 0.01 to 3% by mass. The plating bath temperature, dipping speed, dipping time, pulling speed, and the like are largely determined automatically by the shape of the steel material and equipment restrictions such as a hoist that lifts the steel material.

  For example, when plating a steel material having a thickness of 10 mm or more and having a large heat capacity, it is desirable that the bath temperature is set high and the immersion rate is small. For this reason, depending on the hoist or the like, the steel material is immersed for a long time by being intermittently lowered and immersed in the hot dipping bath. For this reason, there may be a difference in immersion time in units of minutes between the lowermost part and the uppermost part when suspended. Further, depending on the heat capacity of the steel material and the plating bath, the bath temperature is greatly lowered. As described above, since it is practically impossible to set the conditions for immersing in the plating bath strictly from the convenience of reaction, there is no particular limitation.

  However, as long as the temperature of the plating bath is such that the shape and material of the steel material are not affected as described above, the bath temperature is desirably about 500 ° C. at the maximum from the results of immersion Zn plating.

  The immersion time of the steel material in the plating bath is at least 100 seconds or more, more preferably 300 seconds or more. By setting the immersion time to 100 seconds or more, a part of the alloy layer is destroyed and the compound phase grows, and the amount of plating adhesion can be increased. The upper limit of the immersion time is preferably 1500 seconds or less. If the immersion time is too long, the reaction cannot be controlled and it becomes difficult to obtain a desired plating layer.

  If the Si concentration in the plating bath is set appropriately, the alloying reaction is suppressed in the process of cooling to solidification after the end of plating, so that there is no fear of so-called plating burn. For this reason, cooling is not particularly specified. Therefore, from the viewpoint of improving productivity such as handling, the solidification can be accelerated by cooling with mist or the like, or the steel material after plating can be submerged and cooled as long as the surface appearance does not deteriorate.

  In the immersion plating of a ZnAl alloy, since the properties of steel materials are various, it is not easy to control the reaction of Zn and Al by strictly controlling the reaction temperature and time. For this reason, in order to suppress the reaction between Fe and Al, which is generally considered to be intense, and obtain a smooth and glossy plating, it is essential to suppress the reaction by adding Si. The added Si diffuses and penetrates into the FeAl alloy layer formed on the steel sheet surface immediately after plating, and suppresses the progress of the FeAl reaction. As a result, an extremely thin alloy layer of 2 μm or less mainly composed of Fe, Al, and Si is generated at the interface between the surface plating layer and the steel material. However, the addition of Si reduces the reactivity and easily causes truffles such as non-plating, so that it is required to be minimized.

  Furthermore, when the plating treatment of the steel material is performed using the flux of the present embodiment, a small amount of Sn adheres to the steel material surface. Further, when the steel material after the flux treatment is subjected to immersion plating in a plating bath containing Si, unlike a general immersion plating, a thin alloy layer is formed on the surface of the steel material, so that Sn is hardly eluted and Al, Si, It will be in the state confined in the alloy layer which has Fe as a main component. This alloy layer is thin and may be partially destroyed when immersed for a long time. In this case, Fe elutes and reacts with Al and Si in the plating bath to form needle-like or massive Al, Si, Fe The compound phase which has as a main component is produced | generated. By forming this compound phase, the hot-dip plated layer can be made thicker.

  As described above, the plated steel material of the present embodiment is manufactured.

According to the plated steel material of the present embodiment, the surface of the steel material includes Al: 2 to 15% by mass, Si: 0.01 to 1.0% by mass, the balance being a molten plating layer made of Zn and impurities, and a trace amount. An alloy layer containing 2% by mass or less of Sn as a component and having Al, Si, or Fe as a main component and having a thickness of 2 μm or less, and the amount of Sn deposited at the interface is 0.12 to 240 mg / m ² Since it is a range, external appearance property, corrosion resistance, and workability can be improved.
In addition, the hot-dipped layer can be thickened and the corrosion resistance can be further improved by containing Al, Si and Fe in the hot-dipped layer and dispersing needle-like or massive compounds in cross-sectional view.
In addition, according to the flux of the present embodiment, ZnCl ₂ , NaCl, SnCl ₂ is included, and since either or both of SnCl _{4 and} SnO ₂ are included, the surface state of the steel material before plating is optimized. can do.
Furthermore, according to the manufacturing method of the plated steel material of this embodiment, a flux is applied to the steel material and dried, and then the steel material is Al: 2 to 15% by mass, Si: 0.01 to 1.0% by mass. In addition, since the remainder is immersed in a hot dipping bath made of Zn and pulled up, a plated steel material excellent in appearance, corrosion resistance, and workability can be manufactured.

  Hereinafter, the present invention will be described in more detail with reference to examples.

(Experimental example 1)
As the steel material, a pickled steel plate having a thickness of 200 mm × 100 mm × 1.6 mm or a steel plate with black skin was used. The surface of the pickled plate was washed with a commercially available alkaline degreasing agent and then dipped in a 10% HCl aqueous solution at 50 ° C. for about 1 minute for pickling. The black-coated steel sheet was cleaned with a commercially available alkaline degreasing agent and then immersed in a 10% HCl aqueous solution at 50 ° C. for about 10 minutes to remove the scale on the surface. After washing these steel plates with hot water at 60 ° C., they were immersed in a flux of 60 ° C. for a total concentration of 250 g / L with the composition shown in Table 1 and dried by heating in an atmosphere at 200 ° C. for 5 minutes. did. The steel sheet was immersed in a plating bath at 480 ° C. based on a Zn—Al bath for 300 seconds, plated, then naturally cooled, and water-cooled after the plating was completely solidified. In this way, various plated steel materials were produced.

  The appearance of the plating layer was visually determined for the presence or absence of plating defects, gloss, unevenness, and pattern. Note that the test pieces having plating defects were not evaluated for corrosion resistance and workability. The thickness and composition of the alloy layer were examined by glow discharge emission analysis. The adhesion amount of Sn was investigated by dissolving the plating layer and the alloy layer with hydrochloric acid and analyzing the solution by plasma spectroscopy.

  The corrosion resistance of the plating layer was determined by a dry and wet repeated corrosion acceleration test (common name: JASO test) defined by M609-61. The test-observation for 6 days (18 cycles) was repeated, and the evaluation was made in the period until the occurrence of red rust.

  The workability of the plating layer was bent 180 degrees with a bending test machine for thin plates, then returned to the original state, and the state of the front and back of the bent portion was observed.

Table 2 shows the results of evaluating the appearance, corrosion resistance, and workability of the prepared plated steel material. Moreover, an example of a compound phase is shown in FIG.1 and FIG.2. In FIG. 1, symbol A is a steel material, symbol B is a hot dipped layer, and symbol C is an interface alloy layer. Although the interface alloy layer is difficult to confirm in the photographs of FIGS. 1 and 2, it can be easily confirmed by GDS analysis as described later. In FIG. 1, an acicular compound phase 1 is observed. In FIG. 1, a massive compound phase can also be confirmed. Moreover, in FIG. 2, the massive compound phase 2 can be confirmed. These compound phases had a composition of Al: 50 to 70% by mass, Si: 10 to 20% by mass, Fe: 10 to 30%, and the balance Zn.
Further, from Table 2, it was confirmed that good plating can be obtained when the composition of the plating bath is within the range of the present invention.

  Next, elemental analysis in the depth direction of the plating layer by GDS was performed on the plated steel material in which Sn was detected in the plating layer by plasma spectroscopic analysis. The results are shown in FIGS. 3-4, the curve which shows Zn intensity | strength respond | corresponds to Zn in a plating layer, and the curve which shows Fe intensity | strength respond | corresponds to Fe which comprises steel materials. It can be seen that the area where the Zn curve and the Fe curve intersect is the interface between the plating layer and the steel material, and the Sn intensity shows a peak in the vicinity of this interface. Therefore, it turns out that Sn is contained in the interface alloy layer. All of the plated steel materials of the present invention examples in which Sn was detected from the plated layer have the same results as in FIGS. The same applies to Experimental Examples 2 and 3.

On the other hand, no. In No. 6, the amount of Si was small, the reaction between Al and Fe could not be suppressed, an AlFe alloy layer was grown, the appearance and workability of the plating were lowered, and the corrosion resistance was also lowered.
No. In No. 7, since the amount of Si was excessive, non-plating occurred and the appearance was clearly deteriorated. Therefore, evaluation of an alloy layer, Sn adhesion amount, and corrosion resistance was not implemented.
No. In No. 8, since the amount of Mg was excessive, non-plating occurred frequently and the appearance of the plating was clearly deteriorated. Therefore, evaluation of an alloy layer, Sn adhesion amount, and corrosion resistance was not implemented.
No. In No. 9, since the amount of Al was small, an FeZn alloy was formed, and the corrosion resistance was lowered. There were also problems in workability and appearance. Therefore, the evaluation of the Sn concentration and the Sn adhesion amount in the alloy layer was not performed.
No. 10 is a conventional immersion galvanizing with a small amount of Al, and both the workability and the corrosion resistance were inferior to those of the examples.

(Experimental example 2)
As the steel material, a 200 mm × 100 mm × 1.6 mm hot-rolled steel sheet (black-coated steel sheet) was used. The surface of the hot-rolled steel sheet was washed with a commercially available alkaline degreasing agent and then immersed in a 10% HCl aqueous solution at 50 ° C. for about 10 minutes to remove the scale on the surface. After pickling, the steel sheet was washed with hot water at 60 ° C., immersed in a flux at 60 ° C. adjusted to a predetermined composition for about 1 minute, and dried by heating in a heating furnace at 200 ° C. for 5 minutes in an air atmosphere. This steel plate was immersed in a plating bath of 470 ° C. with a composition of Zn-11% Al-0.3% Si-0.5% Mg for 100 seconds to 600 seconds, then pulled up, allowed to cool naturally, and plated. After completely solidified, it was cooled with water. In this way, various plated steel materials were produced.

  Table 3 shows the results of evaluating the appearance, corrosion resistance, and workability of the plated steel material thus prepared. The evaluation method is the same as in Experimental Example 1. From Table 3, it was confirmed that good plating can be obtained when the composition of the flux and the composition of the plating bath are within the scope of the present invention.

No. In No. 24, since the flux concentration was too low, an alloy layer containing Sn was not formed, many pinholes were generated, and the appearance was greatly deteriorated. For this reason, evaluation of corrosion resistance and workability was not performed.
No. In No. 25, SnCl ₄ and SnO ₂ were not included in the flux, so an alloy layer containing Sn was not formed, a large number of unplating occurred, and the appearance was greatly reduced. For this reason, evaluation of corrosion resistance and workability was not performed.
No. In No. 26, the SnO ₂ amount in the flux was excessive, so the plating appearance deteriorated, and the corrosion resistance and workability also decreased.
No. In No. 27, since the amount of SnCl ₂ in the flux was excessive, Sn adhered excessively to the steel material, the plating appearance deteriorated, and the corrosion resistance and workability also decreased.
No. Since Nos. 28-31 did not contain SnCl ₂ in the flux, the plating appearance was greatly deteriorated. For this reason, evaluation of an alloy layer, Sn adhesion amount, corrosion resistance, and workability was not implemented.
No. In No. 32, the appearance of plating deteriorated because the amount of NaCl was excessive. Further, the amount of Sn attached to the steel material also increased.

(Experimental example 3)
As a steel material, a 200 mm × 100 mm × 4.2 mm hot-rolled steel plate (black-coated steel plate) was used. The surface of the hot-rolled steel sheet was washed with a commercially available alkaline degreasing agent and then immersed in a 10% HCl aqueous solution at 50 ° C. for about 10 minutes to remove the scale on the surface. After pickling, the steel sheet was washed with hot water at 60 ° C., immersed in a flux at 60 ° C. adjusted to a predetermined composition for about 1 minute, and dried by heating in a heating furnace at 200 ° C. for 4 minutes in an air atmosphere. This steel plate was immersed in a plating bath of 450 ° C with a composition of Zn-4.5% Al-0.1% Si-1% Mg for 300 seconds, and then pulled up and allowed to cool naturally. After solidifying, it was cooled with water. A polyoxyethylene nonionic surfactant was used as the flux surfactant. In this way, various plated steel materials were produced.

Table 4 shows the results of evaluating the appearance, corrosion resistance, and workability of the plated steel material thus prepared. The evaluation method is the same as in Experimental Example 1. From Table 4, it can be seen that NaF is an optional additive component under the plating conditions, and that SnCl ₄ or SnO ₂ is essential for improving the plating properties. In the comparative example not containing SnCl ₄ or SnO ₂ , an alloy layer containing Sn was not formed, pinholes or non-plating occurred, and the plating appearance was greatly reduced.

  DESCRIPTION OF SYMBOLS 1 ... Acicular compound phase, 2 ... Massive compound phase, A ... Steel material, B ... Hot-dipped plating layer, C ... Interface alloy layer.

Claims (8)

On the surface of steel
Al: 2 to 15% by mass,
Si: 0.01-1.0 mass%
A hot-dip plated layer with the balance being Zn and impurities,
An alloy layer containing 2% by mass or less of Sn as a trace component and having a thickness of 2 μm or less containing Al, Si, and Fe as main components at the interface between the hot-dip plated layer and the surface of the steel material;
The plated steel material, wherein the Sn adhesion amount at the interface is in the range of 0.12 to 240 mg / m ² .   2. The plated steel material according to claim 1, wherein the hot-dip plated layer contains Al, Si, and Fe and has a needle-like or massive compound dispersed in a cross-sectional view.   The plated steel material according to claim 1 or 2, wherein Mg is further contained in the hot-dip plated layer in a range of 0.01 to 3 mass%. 5 to 14% by mass of NaCl, 1.2 to 5% by mass of SnCl ₂ , one or both of SnCl _{4 and} SnO ₂ in total, 0.1 to 1.5% by mass, and the balance from ZnCl ₂ The flux component is dissolved in water at a concentration of 150 to 300 g / L, and the pH is adjusted to 2.0 or less.   The flux according to claim 4, wherein the flux component further contains one or both of NaF and KF in a ratio of more than 0% by mass and 2.0% by mass or less.   The flux according to claim 4 or 5, wherein the flux component further contains a surfactant in a proportion of more than 0% by mass and 1.0% by mass or less. The flux according to any one of claims 4 to 6 is applied to a steel material and dried.
Next, the steel material includes Al: 2 to 15% by mass, Si: 0.01 to 1.0% by mass, and the remainder is dipped in a hot dipping bath made of Zn and pulled up. Production method.   The method for producing a plated steel material according to claim 7, wherein Mg is further contained in the hot dipping bath in a range of 0.01 to 3 mass%.