JP2012241277A - Method of manufacturing galvanized steel material or galvanized steel molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of efficiently and economically manufacturing a hot-dip galvanized steel material and a hot-dip galvanized steel molding with an excellent appearance and excellent corrosion resistance.SOLUTION: The method of manufacturing the galvanized steel material or the galvanized steel molding is characterized in that the temperature of a base material when dipped into a zinc-based plating bath after the base material to be plated is subjected to flux treatment is 300-700°C.

Description

  The present invention relates to a zinc-based plated steel molded product and a zinc-based plated steel material, and more particularly to a zinc-based plated steel material having good corrosion resistance and productivity and a method for producing a zinc-based plated steel molded product.

  There are various methods for rust prevention of steel materials, for example, there are a method of coating a steel substrate with zinc, aluminum or an alloy thereof, or a method of coating by hot dipping or electroplating. Among them, the hot dip galvanizing method is widely used because it is easy to increase the film thickness and has characteristics such as sacrificial corrosion resistance of zinc.

  For the hot dip galvanizing method, a method of plating in a continuous line and a method of manufacturing by immersing in hot dip galvanizing after flux treatment at the previous stage, such as steel pipes and shaped steels (hereinafter referred to as the “dough pickling method”) There is.

  The soaking method has the merit that it can be plated regardless of the shape of the material to be plated, but unlike the case of plating with a continuous line, the immersion time in the plating bath is long, and the alloy layer of iron and zinc grows excessively, etc. There is also a defect.

  In order to prevent this, it is effective to add aluminum to the plating bath as in the case of the continuous line. The addition of aluminum to the zinc plating bath is also effective from the viewpoint of improving corrosion resistance. In addition to aluminum, addition of magnesium or silicon is also effective in improving the corrosion resistance of zinc-based plating.

  In recent years, the need for high corrosion resistance alloy plating such as zinc / aluminum alloy plating, which is superior in corrosion resistance to pure zinc plating, has been increased while the corrosion resistance of steel materials is required. However, particularly in the case of plating containing aluminum, the plating bath temperature becomes high, so that ammonium chloride used for the flux treatment reacts with aluminum to produce aluminum chloride, which does not function as a flux. As a result, there is a problem that non-plating occurs in plating by the soaking method.

  A method for solving this problem and applying an aluminum and zinc alloy plating by a soaking method is disclosed in Patent Document 1, and a flux that can be used when applying an aluminum and zinc alloy plating by a soaking method is disclosed in Patent Document 2. It is disclosed.

  In addition, as a method of performing alloy plating by the soaking method without changing the flux, so-called two-bath plating, or two-time plating, in which after zinc plating is first performed, plating containing an alloy such as aluminum or magnesium that improves corrosion resistance is performed. Is referred to as Patent Document 3.

  Ammonium chloride and the flux of the above-mentioned patent document are water-soluble, and a substrate to be plated is immersed in an aqueous solution of the flux and then dried and plated. On the other hand, Patent Document 4 discloses a method called a molten flux or a wet flux in which a chloride flux is floated on a plating bath to be in a molten state, and the substrate is immersed in the plating bath through the flux layer. It is disclosed.

  With the melt flux method, it is also possible to use a fluoride that is less soluble in water but is less corrosive than chloride and easy to handle. Patent Document 5 discloses the method.

  In the fusion flux method, it is necessary to remove the flux adhering to the surface when the plated steel material is taken out from the plating bath. However, a method aimed at improving productivity by separating the flux bath and the alloy plating bath is patented. It is disclosed in Document 6.

  In addition to the thin plate material, Patent Document 7 discloses a method of preheating and plating in a reducing atmosphere in the same manner as a continuous line without using a flux instead of a general soaking method using flux. Furthermore, Patent Document 8 discloses a method in which a flux component is introduced into a gas at the time of reduction heating, followed by heat treatment and then plating.

  As a method for improving the productivity of the flux method, Patent Document 9 discloses a method in which a fluoride, which is a component of a molten flux, is applied to a material to be plated, dried, heated to a melting temperature, and then plated. .

JP-A-3-162557 JP-A-4-202751 JP2002-47548 JP-A-4-293761 JP2010-133302 Patent 2963091 JP2007-70725A JP2007-332415A JP 2005-272950 A

Kanto Chemical Co., Ltd. AlF3 MSDS

  The method using an alkali metal chloride or an aliphatic nitrogen derivative disclosed in Patent Document 1 and Patent Document 2 has a higher melting point than zinc chloride or ammonium chloride used in pure zinc flux, The peeling from the steel material is not sufficient in the soaking plating, and the appearance may be deteriorated.

  In the case of plating containing magnesium, non-plating or discoloration may occur due to a reaction product of chlorine and magnesium on the surface of the steel material. In order to prevent this, it is necessary to take troubles such as shaking the object to be plated in the bath or washing the surface with a high temperature aqueous solution of ammonium chloride after plating.

  The two-bath plating disclosed in Patent Document 3 does not have the above-described drawbacks, and is a method that can cope with any plating. However, it is always necessary to prepare two or more types of plating baths, and the capital investment and running cost increase, and the productivity also decreases. Moreover, since the alloying of the first galvanized layer progresses and becomes hard, there is a defect inferior in fatigue characteristics.

  The method of floating and melting chloride on a plating bath described in Patent Document 4 has an advantage that a step of immersing in a flux is not required and a drying step is not required. Moreover, since the method of patent document 5 does not use a chloride, there is no possibility of decomposition | disassembly of an ammonium chloride, reaction of chlorine and magnesium, etc.

  However, a large amount of flux is required to float a chloride or fluoride with a certain thickness on the plating bath, and there are problems of workability and high cost. Further, when the plated steel material is removed from the bath, it is necessary to remove the flux from the bath, which is troublesome and cannot be said to be a method with excellent productivity.

  The trouble described above can be saved by separating the flux bath and the plating bath as in Patent Document 6. However, since a large amount of flux is required, it is practically difficult to implement particularly in the case of a large object to be plated. In addition, when a large amount of chloride or fluoride flux is discarded after use, it takes time to process. Furthermore, fluoride is more expensive than conventional ammonium chloride, which is disadvantageous in terms of cost.

  The method of Patent Document 7 is epoch-making in that no flux is used. However, a large-scale facility that can control the atmosphere is required, and the merit of the soaking method, which allows easy plating of large-sized members and various forms of articles, is lost, and there is no freedom in production.

  This point is the same in Patent Document 8, and controlling the atmosphere during heating leads to a decrease in productivity.

Although the method of Patent Document 9 is an excellent method that overcomes the above-described drawbacks, it takes time and effort to change the flux component depending on the plating bath temperature. Although the amount of fluoride used can be kept low, it is less expensive than chloride. It has been proposed that the coating method is an aqueous solution. However, for example, according to Non-Patent Document 1, AlF ₃ has a low solubility in water, such as a low solubility of 5.59 g in 1 L of water, and many fluorides have low solubility in water. The uniform coating over the amount takes time and is inferior in productivity.

  In view of the above-mentioned problems, the present invention provides a flux plating method for economically producing a plated product having a beautiful appearance and excellent corrosion resistance.

  The inventors of the present invention have made various studies on a method for forming a plating layer having a beautiful appearance and excellent corrosion resistance on a steel product.

  The main factor that deteriorates the plating appearance when chloride flux is used for soaking plating of alloys containing aluminum or magnesium is that the flux itself such as zinc chloride remains without peeling. Conventionally known. In addition to this, the fact that chlorine in the flux component reacts with the metal element in the plating bath and remains on the surface of the plated or plated material is a cause of deteriorating the plating appearance. I found it.

  Magnesium in particular has a low generation enthalpy and tends to generate a reaction product with chlorine in the flux component. This is the same even when fluoride is used, and the deterioration of the plating appearance is observed.

  It was also found that the temperature of the base material during immersion in the plating bath is a very important factor for peeling off the product of chlorine and plating metal in the flux component remaining on the surface of the plating or plating material. . This does not simply mean that peeling is promoted by raising the temperature.

  Since the flux is difficult to peel off when the substrate temperature is low, the product of chlorine and plating metal in the flux component is likely to be generated on the substrate surface. The phenomenon of solidification and sticking occurs. When the product is solidified and fixed on the surface of the base material, even if the immersion in the plating bath is continued and the temperature of the base material rises, the separation becomes difficult.

  That is, in order to form a plating layer with a beautiful appearance and excellent corrosion resistance on a steel product, the flux should be promptly peeled off from the surface of the base material, and the product of chlorine and plating metal in the flux component should be removed. It has been found that it is important not to solidify on the substrate surface.

  The inventors of the present invention have intensively studied a method and conditions for satisfying these requirements. As a result, the substrate coated with the flux is heated to a temperature close to that of the plating bath, and immersed in the plating bath while maintaining the temperature, the flux is quickly peeled off from the substrate surface, and the chlorine in the flux component And found that the product of the plated metal cannot be solidified on the substrate surface.

  The present invention has been completed based on these findings, and the gist thereof is as follows.

  (1) A method for producing a zinc-based plated steel material or a zinc-based plated steel molded product, wherein the steel material or steel molded product as a base material is flux-treated, and then the base material is heated to 300 ° C or higher and lower than 700 ° C. A method for producing a zinc-based plated steel material or a zinc-based plated steel molded product characterized by heating and then immersing in a zinc-based plating bath

  (2) The method for producing a zinc-based plated steel material or a zinc-based plated steel molded product according to (1) above, wherein the temperature of the substrate is in the range of the plating bath temperature ± 20 ° C

  (3) The zinc-based plating bath contains at least one of Al: 1 to 75%, Mg: 0.1 to 10%, and Si: 0.1 to 10% by mass%. Method for producing a zinc-based plated steel material or a zinc-based plated steel molded product according to (1) or (2)

  (4) The method for producing a zinc-based plated steel material or a zinc-based plated steel molded product according to any one of (1) to (3), wherein the flux does not contain fluoride.

  (5) The zinc-based plated steel material or the zinc-based plated steel molding according to any one of (1) to (4), wherein the flux comprises a mixture of zinc chloride, an alkali metal chloride, and tin chloride. Manufacturing method

(6) the _{flux, ZnCl 2: 100~200g / L,} 1 kind of NaCl and KCl or two: 20~100g _/ L, SnCl 2: comprises 5 to 30 g / L, adjusted to pH 3 or less A method for producing a zinc-based plated steel material or a molded product made of zinc-based plated steel according to any one of (1) to (5) above,

  According to the present invention, it is possible to efficiently and economically provide a zinc-based hot-dip galvanized steel material and a molded product made of galvanized steel that are excellent in appearance and excellent in corrosion resistance.

  Details of the present invention will be described below. Hereinafter, “%” represents “mass%”.

  The present invention is a method in which a steel material or a steel molded product as a base material before plating is treated with a flux, then heated to a temperature of 300 ° C. or higher and lower than 700 ° C., and dip plated in a predetermined plating bath. The component of the steel material applied here is not particularly limited, and the shape is not limited, but in particular, steel plate, section steel, steel pipe, bar steel, wire, etc. Effective for molded products.

  As described above, the temperature of the substrate during immersion in the plating bath is an important factor in that the flux peels off when immersed in the plating bath and the reaction product of the flux and the plating bath components peels off without solidification. is there.

  As a result of investigations by the present inventors, if the temperature of the substrate during immersion in the plating bath is set to 300 ° C. or higher and lower than 700 ° C., the flux peels when immersed in the plating bath, and the reaction product of the flux and the plating bath components Was found to peel without solidification.

  When the temperature of the base material at the time of immersion in the plating bath is less than 300 ° C., the reaction product of the flux and the components of the plating bath becomes difficult to peel from the base material, and the appearance of plating deteriorates. Further, the temperature of the base material is set to 700 ° C. or higher because the melting point of the plating having the component composition usually used for soaking plating is greatly exceeded, so that the cost is meaningless. In addition, the influence on the material of the base material is increased, and there are no advantages such as deformation of the base material, the original use of the immersion plating, and the creation of the final product.

  The temperature of the base material at the time of preferable plating bath immersion is 400 degreeC or more and less than 650 degreeC, More preferably, it is 450-620 degreeC.

  From the viewpoint of heating cost and handling, and maintaining the plating bath temperature, the temperature of the substrate during immersion in the plating bath is preferably set to a plating bath temperature ± 20 ° C.

  Various methods for applying the flux to the substrate can be selected depending on the flux. In the case of a chloride-based flux, methods such as applying a powder, heating and melting the flux and immersing it in a bath, or immersing it in an aqueous flux solution are conceivable.

  On the other hand, in the case of a fluoride-based flux, since the solubility in water is generally low, a method in which powder is applied, melted by heating, and immersed in the bath can be considered.

  Although the present invention can be applied by any method, it is easy to apply uniformly, it is easy to handle, it is on the extension line of conventional soaking plating, can be used stably, and the cost is low. It can be said that a dipping method is more desirable.

  The heating method before plating is not particularly limited. Various methods such as high-frequency heating inserted into an electric furnace are conceivable. Heating before plating can be sufficiently performed by heating in a normal air atmosphere, and it is not necessary to dare to use an inert gas, a reducing gas, or the like.

  The present invention is widely applicable to zinc-based plating. Although the present invention can also be applied to pure zinc plating, in the case of pure zinc plating, since immersion plating is easy in the prior art, the merit of applying the present invention is small.

  The present invention is significant for application to alloy-based plating, which is difficult to plate by dipping plating with the prior art, and in particular, Al: 1 to 75%, Mg: 0.1 to 10%, Si: 0.00. Application to zinc-based alloy plating containing at least one of 1 to 10% is effective.

  Next, the role of elements added to the zinc-based plating bath and the concentration range will be described.

  Al is an element that enhances corrosion resistance. If the addition amount of Al is less than 1%, the effect is insufficient and there is no point in adding. When the addition amount of Al exceeds 75%, the effect of addition is saturated, and furthermore, the Zn amount is reduced, and accordingly, sacrificial anticorrosion performance is lowered. In addition, the plating bath temperature becomes high, causing problems such as difficulty in operation.

  Mg is also an element that enhances corrosion resistance. If the addition amount of Mg is less than 0.1%, the effect of addition is hardly obtained. When the added amount of Mg exceeds 10%, the effect of the addition is saturated, and further, a problem occurs in operation such as an increase in the dross amount.

Si is also an element that enhances corrosion resistance. Furthermore, the combined use with Al is effective for suppressing the formation of an alloy layer of Al and Fe during plating and maintaining an appropriate interface. Moreover, when used together with Mg, Mg ₂ Si is generated, and the corrosion resistance can be drastically improved. These effects do not appear when the added amount of Si is less than 0.1%, and saturate when the amount exceeds 10%.

  The flux used in the present invention is not particularly limited. However, since it is necessary to be stable with respect to the heating temperature of the base material, it is necessary to select according to the processing temperature. Specifically, chlorides, fluorides, or mixtures thereof can be used.

As the chloride, it is preferable to use a mixture of two or more of alkali metal chlorides such as zinc chloride (ZnCl ₂ ), NH ₄ Cl, NaCl and KCl, and tin chloride (SnCl ₂ ). This is effective in removing oxides on the surface of steel materials and oxides of plating elements. ZnCl ₂ and NH ₄ Cl, which exhibit basic functions as flux, have a high melting point, are chemically more stable, and are secondary to plating metal. This is because a combined effect can be obtained by mixing NaCl, KCl with little reaction, and SnCl ₂ that produces a cleaning effect by substitutional precipitation of Sn on the steel surface. Due to this combined effect, it is possible to expect an effect of improving the surface appearance and preventing non-plating of an alloy plating containing aluminum or magnesium, which is particularly problematic.

As the fluoride, NaAlF ₄ , KAlF ₄ , NaF, KF, AlF ₃ or the like can be applied.

  A flux containing only chloride or a small amount of fluoride can be applied with an aqueous solution, which is preferable from the uniformity of application and ease of handling. A fluoride-only flux can be applied by suspending in water, but the uniformity is somewhat inferior.

  If the amount of fluoride is small, it is possible to immerse the object to be plated in an aqueous flux solution containing fluoride. However, when a large amount of fluoride is dissolved in water, hydrogen fluoride is generated depending on the handling. Since there is a fear and attention is required, a flux containing no fluoride is more preferably used.

In the temperature range of the plating bath of the present invention, ZnCl ₂ contains 100 to 200 g / L, NaCl and KCl, or a total of ₂₀ to 100 g / L, SnCl ₂ contains 5 to 30 g / L, and the pH is 3 A flux which is an aqueous solution prepared as described below is desirable because it exhibits excellent functions.

  The pH adjustment is not particularly limited, but it is preferable to use HCl so as not to increase the types of ions in the aqueous solution.

  More preferably, the substrate is immersed in the plating bath in a state where the flux is uniformly applied. The temperature of the aqueous solution to be applied as a flux is not particularly specified, but is preferably 40 ° C. or higher from the viewpoint of uniform dissolution of the flux component and ease of application of the liquid.

The function of ZnCl ₂ is to remove oxides such as Fe and Zn on the surface of the steel, which is considered to be a basic function of the flux, and facilitate the adhesion of plating. If the amount of ZnCl ₂ is less than 100 g / L, this effect is weak, and if it exceeds 200 g / L, the effect is saturated. Therefore, 100 to 200 g / L is a preferable range of the amount of ZnCl ₂ .

Features of NaCl and KCl, by used in admixture with ZnCl _2, by ZnCl ₂ is an element in the plating, it reacts like aluminum prevents decomposing prior to exert the function as a flux is there. When the amount of NaCl and / or KCl is one or less than 20 g / L in total, the effect is weak, and when it exceeds 100 g / L, the effect is saturated, so 20 to 100 g / L is a preferable range.

SnCl ₂ has an effect of improving the plating property by substitutional precipitation of Sn on the steel material surface. The effect is weak when the amount of SnCl ₂ is 5 g / L or less. Moreover, since Sn hydroxide precipitates when dissolved in a large amount, it is preferably 30 g / L or less.

  Further, when the pH is increased, Sn hydroxide that is hardly soluble in water is generated, and the amount of Sn ions in the aqueous solution is decreased. Therefore, in order to maximize the effects of these fluxes, the pH is set to 3 It is preferable to keep it below.

  When a fluoride-based flux is used, it is more preferable that the temperature of the substrate when immersed in the plating bath is equal to or higher than the melting temperature of the flux so that the flux spreads uniformly on the surface of the substrate. Therefore, it is preferable to use a flux having a melting point of 700 ° C. or lower, or a flux that mixes a plurality of fluorides to lower the melting point and dissolves at 700 ° C. or lower.

  When immersed in an aqueous solution of chloride flux, the flux is already uniformly attached to the surface of the substrate, so it is not necessary to worry about whether or not to melt the flux.

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

  The SS400 (JIS G3141) having a thickness of 3.2 mm was degreased and pickled with 10% hydrochloric acid containing an inhibitor, and then subjected to flux treatment using the flux of the components shown in Table 1.

  The conditions for the flux treatment were either two shown in Table 2.

  The plating bath intrusion temperature when the flux treatment condition is A was one of the two shown in Table 3.

  The plating bath was any one of those shown in Table 4, and was immersed in the plating bath for 10 seconds, then taken out and air-cooled.

  About the manufactured galvanized steel material, the external appearance, corrosion resistance, and workability were evaluated according to the criteria shown in Tables 5-7.

  The test was performed at n = 5 per condition, appearance evaluation and workability evaluation were all summed, and corrosion resistance was evaluated on average. Tables 8 and 9 show the results.

  From the results shown in Tables 8 and 9, it can be seen that the present invention is a plating method excellent in both appearance and corrosion resistance.

  According to the method for producing a zinc-based plated steel material and a zinc-based plated steel molded product according to the present invention, it is possible to efficiently, economically and stably produce a product excellent in appearance and corrosion resistance. The availability of is great.

Claims (6)

A method for producing a zinc-based plated steel material or a molded product made of zinc-based plated steel,
Treat the steel material or steel molding as the base material with flux,
The substrate is heated to 300 ° C or higher and lower than 700 ° C, and then
A method for producing a zinc-based plated steel material or a molded product made of zinc-based plated steel, characterized by being immersed in a zinc-based plating bath.   2. The method for producing a zinc-based plated steel material or a zinc-based plated steel molded product according to claim 1, wherein the temperature of the substrate is in the range of the plating bath temperature ± 20 ° C. 3.   The zinc-based plating bath includes at least one of Al: 1 to 75%, Mg: 0.1 to 10%, and Si: 0.1 to 10% by mass. Or the manufacturing method of the zinc-based plated steel material of 2 or a zinc-based plated steel molded article.   The method for producing a zinc-based plated steel material or a zinc-based plated steel molded product according to any one of claims 1 to 3, wherein the flux does not contain fluoride.   The zinc-based plated steel material or zinc according to any one of claims 1 to 4, wherein the flux comprises a mixture of two or more selected from zinc chloride, alkali metal chloride, and tin chloride. Of manufacturing a molded product made of galvanized steel. The flux is
ZnCl _2: 100~200g / L,
One or two of NaCl and KCl: 20 to 100 g / L,
SnCl _2: 5~30g / L
The method for producing a zinc-based plated steel material or a zinc-based plated steel molded article according to any one of claims 1 to 5, wherein the aqueous solution is adjusted to a pH of 3 or less.