KR20100124436A - Hot dip zn-based alloy coating bath, hot dip zn-based alloy coated steel and method for manufacturing the same - Google Patents

Abstract

PURPOSE: A hot dip Zn-based alloy coating bath, a hot dip Zn-based alloy coated steel and a manufacturing method thereof are provided to uniform the glossiness and surface roughness by removing an alloy layer from a plating layer cross section. CONSTITUTION: A steel material is pre-processed. The pre-processed steel material is heat-treated. The heat-treated steel material is through passed in a molten zinc alloy plating bath. The temperature of the molten zinc alloy plating bath is 500-550°C. The bathing temperature of the steel material is 500-600°C. The steel material is low-carbon steel, extra-low-carbon steel or high-carbon steel.

Description

TECHNICAL FIELD [0001] The present invention relates to a hot dip galvanized steel sheet, a hot dip galvanized steel sheet, a hot dip galvanized steel sheet, a hot dip galvanized steel sheet,

The present invention relates to a plated steel used for building materials, home appliances, automobiles, and the like, and more particularly to a plated steel material used for improving corrosion resistance and bending workability, and a hot-dip galvanized steel sheet And a hot-dip galvanized steel produced by the method.

BACKGROUND ART It has hitherto been widely known to improve the corrosion resistance of a steel material by applying zinc plating to the surface of the steel material. To date, zinc-plated steel materials have been mass-produced and used.

However, in order to be used in various applications such as building materials, home appliances, and automobiles, there is a problem in that corrosion resistance is insufficient only by the above-described zinc plating. Therefore, a hot-dip zinc-aluminum alloy plated steel, for example, a hot-dip zinc-aluminum alloy plated steel using 55% aluminum-zinc is used to improve the corrosion resistance of the plated layer. However, since the molten zinc-aluminum alloy plated steel material has a higher aluminum content of the bulk plating layer than zinc, sacrificial corrosion prevention ability is lowered and the underlying metal such as a cross section in the plated material is lowered. There is a problem that corrosion occurs at the exposed portion.

In addition, when the above-mentioned 55% aluminum-zinc plating is performed, the plating bath has to be set at a high temperature as high as about 600 ° C., so that the processability of the plating layer is poor and corrosion occurs in facilities of various structural parts in the plating bath. The life span is shortened and the productivity due to the replacement of the equipment is lowered.

Meanwhile, a conventional technique for zinc-aluminum alloy plated steel will be described as follows.

WO2007 / 146161 discloses high-alloy (10-40%) hot-dip galvanizing for general hot dip galvanizing. The above patent discloses a so-called flux-zinc plating method in which plating is carried out in a zinc-aluminum plating bath containing silicon and then immersed in a zinc-ammonium flux. However, the flux zinc plating method is mainly applied to intermittently plating unit parts such as a structure and a pipe, and the method of continuously plating the steel material is different from the pretreatment step, and it is difficult to apply the method in terms of plating amount control and surface quality management .

On the other hand, the zinc-aluminum-magnesium plated steel material developed mainly in Japan is likely to be discolored when the zinc-magnesium phase (Zn ₁₁ Mg ₂ ) containing the aluminum phase locally exists on the surface of the steel material. And the surface appearance is remarkably lowered. There is a problem that line-shaped stripes extending in the width direction of the product are generated to adjust the cooling rate after plating or add special elements to the plating bath.

Another type of zinc-aluminum-magnesium alloy plated steel which is being developed mainly in Europe, such as the European Patent No. 1621645, is that the total amount of aluminum and magnesium added is higher than that of the zinc-aluminum-magnesium alloy plated steel material developed in Japan There is a problem that sufficient corrosion resistance is not ensured.

Therefore, there is a demand for a plated steel material excellent in corrosion resistance and bending workability so that it can be applied not only to automobiles, but also to various uses such as building materials, home appliances, etc., and a plating bath component and a plating method therefor are required.

According to one aspect of the present invention, there is provided a molten zinc alloy plating bath capable of lowering the temperature of a plating bath at the time of plating in order to provide a plated steel having excellent corrosion resistance and bending workability, a method of producing a molten zinc alloy plated steel using the same, A prepared hot-dip zinc alloy plated steel is provided.

The present invention is characterized by containing 10-30% of aluminum (Al), 0.01-0.5% of silicon (Si), 0.1-3% of magnesium (Mg), and 0.1-0.5% of misch metal, And an inevitable impurity.

The present invention also provides a method of manufacturing a steel sheet,

Heat treating the pretreated steel material; And

And a step of passing the heat treated steel material through the molten zinc alloy plating bath and plating the molten zinc alloy plated steel material.

The present invention also provides a hot-dip galvanized steel material produced by the above-mentioned production method.

In the present invention, silicon and mischmetal are added to an aluminum-zinc plating bath so that the alloy layer is almost removed from the end face of the plating layer, so that the surface roughness becomes smooth and the gloss becomes uniform. As the plating adhesion of the plating layer becomes better, And the corrosion resistance is improved. In addition, magnesium is added to provide a good appearance on the surface of the plating layer, and the plating property is excellent. In particular, the corrosion resistance of the plating layer is further improved. In addition, according to the present invention, since the temperature of the plating process can be lowered when plating the ternary alloy of zinc-aluminum-magnesium, the elution of the plating bath structure portions is suppressed. As a result, The effect of improvement can be obtained.

Hereinafter, the present invention will be described in detail.

First, the composition of the molten zinc alloy plating bath will be described in detail (hereinafter, "wt%")

The molten zinc alloy plating bath, which is one aspect of the present invention, comprises 10 to 30% of aluminum (Al), 0.01 to 0.5% of silicon (Si), 0.1 to 3% of magnesium (Mg) To 0.5%, the balance being zinc and inevitable impurities.

Aluminum (Al) is added to ensure high corrosion resistance. When the amount of aluminum added in the plating bath is increased, the corrosion resistance of the plated steel is increased because the aluminum is present as an aluminum oxide film in the plating layer to suppress the redox reaction, and the zinc elution rate corresponding to the anode reaction is lowered. That is, the corrosion product film formed at the early stage of corrosion covers the surface of the plating to maintain the conductivity of the corrosion product as zinc hydroxide as a role of the alloying element, and the conductivity of the zinc oxide is lowered, thereby suppressing the redox reaction. The reason for limiting the content of Al in the present invention to 10 to 30% is that when the content is less than 10%, corrosion resistance in the alloy plating layer is deteriorated. When the content exceeds 30%, the amount of dross is increased, This is because the appearance is deteriorated.

Silicon (Si) is added to prevent the powdering phenomenon in the surface texture and the alloy layer growth in the cross-section structure. Silicon reduces the amount of iron diffusing from the base iron to the plating layer while reducing the amount of aluminum diffusing from the plating layer to the base iron, while being present mainly at the base iron / plated layer interface. The effect of silicon addition decreases the alloy layer thickness and improves the bending adhesion. When the content is more than 0.01%, the alloy layer suppressing effect begins to appear. When the content is more than 0.5%, the effect becomes remarkable. Nevertheless, the reason for limiting the silicon content to 0.01 to 0.5% is that when the content is less than 0.01%, the effect of inhibiting the formation of the alloy layer is weak and the bending adhesion of the plating layer is deteriorated. On the other hand, No further improvement in the properties is seen.

Mischmetal is an alloy of about 90% rare earth element (REM) and about 10% iron (Fe) and has been used as a raw material for steel additives and ignition alloys. In the present invention, mischmetal precipitates on the plating layer / substrate iron interface to stabilize the interface layer and smooth the plating layer. However, when the plating bath temperature rises, intermetallic compound formation rate and growth rate increase to form a weak iron-aluminum alloy layer. In the present invention, mischmetal is added in the range of 0.1 to 0.5%, and if it is added in an amount of less than 0.1%, the wettability of the steel and the plating bath can not be improved and the surface of the plating layer is easily roughened. The surface appearance of the plating surface tends to deteriorate.

The mischmetal used in the present invention is not limited. An example of a preferred mischmetal is La-rich mischmetal, which comprises 50% by weight of La, 25% by weight of Ce, 8-15% by weight of Nd, 3 to 7% by weight of Pr and the balance of Fe.

Magnesium (Mg) has the effect of suppressing the formation of zinc oxide by adding magnesium in the plating bath, and the magnesium eluted in the early stage of corrosion penetrates into zinc hydroxide or zinc oxide and changes into basic zinc chloride, thereby suppressing further generation of rust . Magnesium is added in the range of 0.1 to 3.0% for the purpose of improving the corrosion resistance of the plating layer and the cut surface. When it is less than 0.1%, the effect of improving the corrosion resistance is insignificant. When it is added by more than 3.0%, the plating bath is easily oxidized and the amount of dross is increased. It is because it inhibits.

In the present invention, it is preferable that the content of aluminum (Al) and silicon (Si) satisfy the relation of 30? Al / Si? 120.

As described above, aluminum serves to increase the corrosion resistance of the plated steel, and silicon serves to improve the bending adhesion by reducing the diffusion of iron and aluminum in the ferrous and plated layers. At this time, when the silicon is excessively added and the value of Al / Si is less than 30, the corrosion resistance is in the hot state, and when it exceeds 120, there is a problem that the bending adhesion is inferior.

The remainder consists of zinc (Zn) and inevitable impurities.

Hereinafter, a method for manufacturing a molten zinc alloy plated steel material by using the molten zinc alloy plating bath will be described in detail.

The steel material used in the present invention is not limited, but preferably one of low carbon steel, ultra low carbon steel and high carbon steel is used. The steel material to be used in the present invention may be hot rolled steel or cold rolled steel. The hot-rolled steel material preferably has a thickness of 1.0 to 4.0 mm, and the cold-rolled steel material preferably has a thickness of 0.3 to 2.3 mm.

In order to coat the steel material of the present invention with a molten zinc alloy, the surface of the steel material is first cleaned by performing a pre-treatment or a pre-cleaning.

The pretreatment step includes a step of pickling, washing, degreasing and the like. Pretreatment conditions are important for improving the plating performance of hot-rolled steel, and pickling treatment for scale removal is preferably required. The cold-rolled steel is desirably degreased.

A heat treatment process is performed before passing the pre-treated steel through a plating bath. The heat treatment is preferably a reduction heat treatment performed in a reducing atmosphere, and it is sufficient by a usual method. In one preferred embodiment, the reaction is carried out in an atmosphere of 20% hydrogen and 80% nitrogen at a dew point temperature of -40 ° C.

The temperature range varies depending on whether a hot-rolled steel sheet or a cold-rolled steel sheet is used. Hereinafter, the hot-rolled steel sheet and the cold-rolled steel sheet will be described in detail.

The heat treatment process for plating hot-rolled steel will be described in detail.

The hot-rolled steel has different surface characteristics compared to cold-rolled steel, and proper heat treatment conditions are required for securing the material and securing the adhesion of the plating layer to the bend. In continuous plating, it is desirable to heat the hot-rolled steel to a temperature as low as possible in order to maintain the original material, so it is preferable to heat the steel by heating in a manner similar to the plating bath temperature. This is preferable because the low- . The temperature at this time is preferably 500 to 600 ° C.

Hereinafter, the heat treatment process in the case of rolling the cold rolled steel material in a rolled state will be described in detail.

Cold rolled steel is distinguished by a pretreatment process for cleaning the surface of rolled steel and a post-heat treatment plating and post-treatment process. After the pretreatment such as degreasing, heat treatment is performed for recovery of the rolled structure and annealing for recrystallization. In general low carbon steel is subjected to heat treatment at 700 to 800 ° C, ultra low carbon steel and high strength steel at 800 to 850 ° C.

The steel material subjected to the pretreatment process and the heat treatment process as described above is passed through the above-mentioned molten alloy-coupled gold plating bath to perform plating. The plating is preferably performed continuously.

At this time, the bath temperature of the steel is controlled at 500 to 600 ° C, and the temperature of the hot-dip galvanizing bath is controlled at 500 to 550 ° C.

When the temperature of the plating bath is less than 500 ° C., the plating is undeveloped on the surface of the plating, and the adhesion is deteriorated. When the temperature of the plating bath is 550 Lt; 0 > C, cracking of the plating layer is increased and adhesion is deteriorated. Therefore, it is preferable to control the plating bath temperature to 500 to 550 deg.

Hereinafter, the plating bath of the present invention and the hot-dip galvanized steel material produced by the manufacturing method will be described in detail.

The molten zinc alloy plated steel material includes 10-30% aluminum (Al), 0.01-0.5% silicon (Si), 0.1-3% magnesium (Mg), and 0.1-0.5% misch metal And the remainder is made of zinc and inevitable impurities. Preferably, the content of aluminum (Al) and silicon (Si) satisfy a relation of 30? Al / Si? 120.

Further, the plating layer of the hot-dip zinc-plated steel has a structure in which the zinc single phase and the ternary structure of zinc-aluminum-magnesium exist between the binary process structures of zinc-aluminum.

As shown in FIG. 1, the plated layer of the hot-dip zinc-plated steel according to the present invention is distributed in a form in which the Zn-Al binary process structure surrounds the Zn single phase and the Zn-Mg-Al three- An alloy layer having a thinner Zn-Fe-Al-Si quaternary system is locally formed at the interface of the interface layer. On the contrary, the conventional zinc-aluminum plated steel plating layer shown in FIG. 2 has a structure in which the ternary structure of Zn-Al-Fe occupies the majority of the plating layer, and the thick three- An alloy layer is continuously produced.

The hot-dip galvanized steel material of the present invention can provide a hot-dip zinc-alloy-plated steel material excellent in plating adhesion and cut surface corrosion resistance, having uniform luster and roughness, and excellent in bending workability, by satisfying the above composition and structure have.

Hereinafter, the present invention will be described in detail by way of examples.

(Example 1)

Hot-rolled low-carbon hot-rolled steel (thickness: 2.3 mm) and cold-rolled steel (thickness: 0.6 mm) containing 0.025% carbon, 0.2% manganese and 0.01% silicon were subjected to pre- Respectively.

The hot - rolled steel was subjected to heat treatment at 550 ℃ after the pickling treatment and then plated. The cold - rolled steel was degreased and annealed at 750 ℃ and then plated. At this time, the reducing atmosphere was hydrogen 20% - nitrogen 80% and the dew point temperature was -40 ° C. Plating bath plating bath temperature and plating bath temperature of the steel before plating were 510 ° C. to 550 ° C., respectively.

The corrosion resistance, bending adhesion, surface roughness and gloss of the plated steel after the alloy hot-dip coating were measured and are shown in Table 1 below. At this time, the corrosion resistance of the alloy hot-rolled steel was determined by the occurrence time of 5% red rust in the salt spray test of 1,340 hours (2 months), and it is shown in Table 1. In this case, ⊚ indicates that the red color is less than 5%, ∘ indicates that the red color is less than 10%, Δ indicates that the red color is less than 50%, and × when the red color is more than 50%. In the following Table 1, both the hot-rolled steel and the cold-rolled steel were not judged because the inventive and comparative examples were determined by the components of the plating bath and the plating factors.

Also, the bending adhesion was evaluated as a good result when the crack length was short and the number of cracks was small by observing the cross section after 180 degrees bending. In this case,? Indicates no crack,? Indicates that the crack is 10% or less,? Indicates that the crack is 30% or less, and? When the crack is 30% or more.

As shown in the following Table 1, as a result of the alloy hot dip galvanizing, the corrosion resistance was much better than that of the conventional hot dip galvanized steel, and no plating phenomenon was observed. That is, the bending adhesion of the alloy plated material was comparable to that of the hot dip galvanized material, and the surface roughness and gloss were similar to those of the hot dip galvanized material.

division Plating bath composition flex
Adhesiveness Corrosion resistance
Surface roughness
(Ra, 占 퐉) Glossiness
(Gs60 ^o ) Al Si MM Mg zinc Al / Si Inventory 1 13 0.4 0.2 0.5 Honey. 32.5 ◎ ◎ 0.9 140 Inventory 2 24 0.2 0.3 1.2 Honey. 120 ◎ ◎ 1.5 135 Inventory 3 20 0.3 0.1 2.0 Honey. 66.7 ◎ ◎ 1.3 130 Honorable 4 15 0.5 0.2 1.0 Honey. 30 ◎ ◎ 0.9 150 Inventory 5 25 0.35 0.5 0.5 Honey. 71.4 ◎ ◎ 1.5 45 Inventory 6 10 0.2 0.2 0.8 Honey. 50 ◎ ◎ 1.8 120 Honorable 7 30 0.5 0.5 0.3 Honey. 60 ◎ ◎ 1.6 25 Honors 8 18 0.25 0.2 1.5 Honey. 72 ◎ ◎ 1.0 110 Proposition 9 23 0.5 0.3 2.5 Honey. 46 ◎ ◎ 0.8 120 Comparative Example 1 15 0.05 0.1 1.0 Honey. 300 X X 1.8 190 Comparative Example 2 5 1.0 0.05 0.1 Honey. 5 △ △ 1.5 60 Comparative Example 3 10 0.6 0.05 3.5 Honey. 16.7 △ △ 1.8 95 Comparative Example 4 3 1.2 1.0 1.0 Honey. 2.5 X △ 2.5 15 Comparative Example 5 25 2 0.8 1.5 Honey. 12.5 △ ○ 1.5 20 Comparative Example 6 15 0.08 0.9 0.05 Honey. 187.5 △ △ 1.9 150 Comparative Example 7 8 1.5 0.07 5.0 Honey. 5.3 △ X 1.1 135 Comparative Example 8 12 0.8 0.3 4.2 Honey. 15 X △ 1.5 110 Comparative Example 9 7 1.2 0.5 3.8 Honey. 5.8 △ ○ 1.6 30

* MM: La-rich Mischmetal

(Example 2)

(1.6 mm in thickness) and cold-rolled steel (0.4 mm in thickness) containing 0.005% of carbon, 0.10% of manganese and 0.005% of silicon were subjected to pretreatment, Respectively.

The hot rolled steel was pickled with hydrochloric acid and plated after heat treatment at 550 ℃. The cold rolled steel was heat treated at 820 ℃ after degreasing. The temperature of the steel before plating and the temperature of the plating bath were plated for alloy plating at 510 ° C to 550 ° C respectively. At this time, the reducing atmosphere was hydrogen 20% - nitrogen 80% and dew point temperature -40 ° C. After the plating as described above, the corrosion resistance, bending workability, surface roughness and gloss of the plated steel were measured, and the results are shown in Table 2. In Table 2, the evaluation of the corrosion resistance and the bending workability was made according to the criteria of Example 1 above.

As shown in the following Table 2, the hot-dip coated steel in the plating bath composition of the present invention had much better corrosion resistance than the conventional hot-dip galvanized steel, and no plating phenomenon was observed, As a result of observing the cross section after bending, the bending adhesion was the same, and the surface roughness and gloss were also good.

division Plating bath composition flex
Adhesiveness Corrosion resistance Surface roughness
(Ra, 占 퐉) Glossiness
(Gs60 ^o ) Al Si MM Mg Zn Al / Si Inventory 1 20 0.5 0.1 1.0 Honey. 40 ◎ ◎ 0.8 90 Inventory 2 15 0.2 0.3 0.5 Honey. 75 ◎ ◎ 0.6 75 Inventory 3 24 0.3 0.5 0.4 Honey. 80 ◎ ◎ 0.6 105 Honorable 4 18 0.2 0.3 1.5 Honey. 90 ◎ ◎ 0.9 80 Inventory 5 25 0.5 0.2 2.6 Honey. 50 ◎ ◎ 1.0 70 Comparative Example 1 5 0.5 0.1 0.04 Honey. 10 △ △ 0.5 85 Comparative Example 2 10 0.05 0.05 3.5 Honey. 125 X △ 0.9 50 Comparative Example 3 18 0.05 0.05 1.0 Honey. 360 X △ 0.7 125 Comparative Example 4 23 1.0 1.0 2.5 Honey. 23 △ ○ 1.9 95 Comparative Example 5 15 2.5 0.5 0.1 Honey. 6 △ ○ 1.3 75

* MM: La-rich Mischmetal

(Example 3)

(Thickness: 2.0 mm) containing 0.025% of carbon, 0.2% of manganese, and 0.01% or less of silicon, and the bending workability and corrosion resistance were measured. Respectively. In Table 3 below, the evaluation of the corrosion resistance and the bending workability was made according to the criteria of Example 1 above.

The hot-rolled steel was pickled with hydrochloric acid and then plated at a plating bath temperature of 500 to 580 ° C, and the bath temperature of the pre-plated steel was 475 to 550 ° C. At this time, the reducing atmosphere was hydrogen 20% - nitrogen 80% and dew point temperature -40 ° C.

As shown in Table 3 below. It can be seen that the comparative example in which the composition of the plating bath, the plating bath temperature of the steel material, and the temperature of the plating bath deviate from the range of the present invention, shows that the bending workability and corrosion resistance are not excellent.

division Plating bath composition Plating bath
Temperature Plating bathing
Temperature flex
Adhesiveness Corrosion resistance Al Si MM Mg Zn Al / Si Inventory 1 20 0.5 0.1 1.0 Honey. 40 510 500 ◎ ◎ Inventory 2 15 0.2 0.3 0.5 Honey. 75 530 540 ◎ ◎ Inventory 3 24 0.3 0.5 0.4 Honey. 80 550 520 ◎ ◎ Honorable 4 18 0.2 0.3 1.5 Honey. 90 520 530 ◎ ◎ Inventory 5 25 0.5 0.2 2.6 Honey. 50 550 525 ◎ ◎ Comparative Example 1 5 0.5 0.1 0.04 Honey. 10 500 550 ○ △ Comparative Example 2 10 0.08 0.5 1.5 Honey. 125 520 480 △ ○ Comparative Example 3 18 0.05 0.05 1.0 Honey. 360 580 500 X △ Comparative Example 4 23 1.0 1.0 2.5 Honey. 23 530 490 △ ◎ Comparative Example 5 15 2.5 0.5 0.1 Honey. 6 540 475 X ○

* MM: La-rich Mischmetal

1 is a photograph showing a plating layer of a hot-dip galvanized steel material according to the present invention.

2 is a photograph showing a plating layer of a conventional zinc-aluminum alloy plated steel material.

Claims (11)

And the balance includes zinc and inevitable impurities (in terms of weight%), aluminum (Al) 10-30%, silicon (Si) 0.01-0.5%, magnesium (Mg) 0.1-3%, misch metal 0.1-0.5% Wherein the molten zinc alloy plating bath comprises: The hot-dip zinc-alloy plating bath according to claim 1, wherein the content of aluminum (Al) and silicon (Si) satisfy a relation of 30? Al / Si? Pretreating the steel material; Heat treating the pretreated steel material; And A step of passing the heat-treated steel through the hot-dip zinc-alloy plating bath of claim 1 or 2 to perform plating Wherein the molten zinc alloy plated steel material is a mixture of molten zinc and platinum. The method of manufacturing a hot-dip galvanized steel material according to claim 3, wherein the temperature of the hot-dip galvanizing bath is controlled at 500 to 550 ° C and the bath temperature of the steel is controlled at 500 to 600 ° C. 4. The method of claim 3, wherein the steel material is one of low carbon steel, ultra low carbon steel and high strength steel. 4. The method of manufacturing a molten zinc alloy plated steel material according to claim 3, wherein the plating is performed continuously. The method according to any one of claims 3 to 6, wherein, when the steel material is a hot-rolled steel material, the heat treatment is performed at 500 to 600 占 폚. The method according to any one of claims 3 to 6, wherein, when the steel material is a cold-rolled steel material, the heat treatment is performed at a temperature of 700 to 800 ° C in the case of using low-carbon steel and 800 ° C to 850 ° C in the case of using ultra- Wherein the molten zinc alloy plated steel material is a molten zinc alloy plated steel material. (Si): 0.1 to 0.5%, magnesium (Mg): 0.1 to 3%, misch metal: 0.1 to 0.5%, and the balance of zinc and unavoidable impurities Wherein the hot-dip galvanized steel sheet comprises a plated layer. The hot-dip zinc-alloy-plated steel material according to claim 9, wherein the content of aluminum (Al) and silicon (Si) is in the range of 30? Al / Si? 10. The hot-dip zinc-alloy-plated steel material according to claim 9 or 10, wherein the zinc-single phase and the ternary structure of zinc-aluminum-magnesium exist between the binary structure of zinc-aluminum.

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