KR100988490B1 - A Method for Manufacturing a Hot Dip Aluminum-Zinc Coated Stainless Steel - Google Patents

Abstract

The present invention relates to a method for manufacturing an aluminum-zinc plated stainless steel plate used for building panel materials and roofing materials, agricultural equipment, industrial equipment, automobile parts, etc., and a method of manufacturing an aluminum-zinc plated stainless steel sheet having excellent plating adhesion and workability. It is intended to provide a purpose.

In the present invention, after pre-treating the stainless steel sheet, the preheating temperature: 550 ℃ or more, the air partial pressure ratio: 1.3 or more, and hydrogen concentration: 1 to 5% so that the activated Fe, Cr composite oxide layer is produced on the steel sheet Heating temperature: 900 ° C. or lower, hydrogen concentration: 40% or higher, and dew point temperature: 35 to −45 ° C. so as to reduce the Fe and Cr composite oxides, and then maintain the temperature at 20-40% hydrogen. The method of manufacturing a molten aluminum-zinc plated stainless steel sheet comprising the step of cooling to annealing by maintaining the concentration to around 600-700 ℃, then annealing the steel sheet in a molten aluminum-zinc plating bath, and then cooling. That's the point.

According to the present invention, it is possible to provide an aluminum-zinc plated stainless steel sheet having a beautiful surface and excellent plating adhesion and workability.

Hot dip, aluminum, zinc, stainless steel, partial pressure ratio, hydrogen, chromium oxide

Description

A method for manufacturing a hot dip aluminum-zinc coated stainless steel

The present invention relates to a method for manufacturing an aluminum-zinc plated stainless steel sheet used in building panel materials and roofing materials, agricultural equipment, industrial equipment, automobile parts, and the like, and more particularly, aluminum-zinc plated stainless steel sheet having excellent plating adhesion and processability. It relates to a method of manufacturing.

Galvalume coated with hot-dip galvanized steel sheet, for example hot-dip 55% aluminum-galvanized steel sheet, combines the durability, heat resistance and heat reflectivity of galvanized steel with sacrificial anticorrosive effects. It is widely used in building panel materials, roofing materials, agricultural equipment, industrial equipment and automobile parts.

In particular, in the case of roofing materials being constructed in the city, high corrosion resistance materials are required to prevent corrosion of buildings due to environmental factors such as acid rain and acid fog.

Hot-dip aluminum-zinc plating of stainless steel sheets containing chromium requires demanding surface treatment control techniques.

It is easy to generate chromium oxide that inhibits plating adhesion on the surface of stainless steel sheet, and the formed oxide is not easily removed, and it remains on the surface of stainless steel sheet and when it is immersed in the aluminum-zinc plating bath, the stainless steel sheet and molten aluminum- This is because blocking the alloy reaction with the zinc plating layer causes plating defects such as unplated.

As a technique for controlling the chromium oxide film to a surface having excellent plating wettability, a technique of reducing and removing the chromium oxide film in the annealing process, a technique of blocking contact between the chromium oxide film and the plating layer with a leading gold, and annealing furnace as a weak oxidation atmosphere By forming the oxide film on the surface of the stainless steel sheet, it can be divided into a technique for reducing the oxide film through heating and soft annealing in the reduction furnace.

In the annealing process, the technique of reducing and removing the chromium oxide film has a problem in that aging of the related equipment occurs easily due to a high working temperature.

In addition, the technology of blocking the contact between the chromium oxide film and the plating layer with the leading gold has a problem that the leading gold is added to increase the cost.

In addition, an example of a technique of forming an oxide film on the surface of a stainless steel plate and then reducing the oxide film through heating and soft annealing in a reduction furnace is described in Japanese Patent Application No. Hei 4-117534, where 10-25% Cr is used. The preheated stainless steel sheet is preheated to 550-700 ° C. in an oxidizing or weakly oxidizing atmosphere with an air ratio of 0.9-1.5 in an annealing furnace, and then heated to rise to 300 ° C. or lower, and softened annealing is maintained at this temperature. At the same time, only the oxide film is reduced, followed by cooling while performing continuous plating.

However, the Japanese technique is difficult to finely control the thickness of the chromium oxide film and to control the growth of the alloy layer after plating, and thus there is a limitation in improving the plating adhesion and processability.

The present invention provides a method of manufacturing a molten aluminum-zinc plated stainless steel sheet having excellent plating adhesion and workability by controlling the air pressure ratio and hydrogen concentration in the annealing furnace to more finely control the thickness of the surface oxide layer and further cooling the plated water. Its purpose is to provide it.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention provides a method for producing a molten aluminum-zinc plated stainless steel sheet by performing molten aluminum-zinc plating on a stainless steel sheet, the method comprising: pretreating the stainless steel sheet;

As described above, the pre-heated stainless steel sheet is preheated to produce an activated Fe, Cr composite oxide layer, preheated at a temperature of at least 550 ° C., an air partial pressure ratio of at least 1.3, and a hydrogen concentration of 1 to 5%. Heating temperature: 900 ° C. or lower, hydrogen concentration: 40% or higher, and dew point temperature: 35 to −45 ° C. to reduce the Cr composite oxide, and maintained at that temperature, followed by 20-40% hydrogen concentration. Annealing by cooling to around 600-700 ° C. in one state;

Plating the steel sheet annealed as described above in a molten aluminum-zinc plating bath; And

It relates to a method of manufacturing a molten aluminum-zinc plated stainless steel sheet comprising the step of cooling after the plating.

As described above, according to the present invention, it is possible to provide an aluminum-zinc plated stainless steel sheet having a beautiful surface and excellent plating adhesion and workability.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The material to which the present invention is applied is a stainless steel sheet, and the plating performed on the steel sheet is molten aluminum-zinc plating, and the composition of the plating bath contains 30 to 78% aluminum and the remaining zinc. 58% aluminum and the remaining zinc.

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The plating bath may further contain less than 3.0% of silicon.

A more preferred plating bath composition is galvalume plating, which is generally known in the industry, containing 55% aluminum, 43.4% zinc and 1.6% silicon.

The present invention includes a pretreatment step, an annealing step, a plating step and a water cooling step, which will be described below.

(Pretreatment step)

In the present invention, in order to further improve the plating efficiency and plating process, it is preferable to pretreat the stainless steel sheet before the stainless steel sheet passes the direct heating step. This is to induce immediate surface reaction in the oxidizing atmosphere of the preheat zone.

The pretreatment is preferably an electrolytic cleaning method, which will be described in detail below.

In the case of using the electrolytic cleaning method, it is possible to completely remove foreign substances on the surface to secure the beautiful surface quality of the steel sheet in the plating process.

The electrolytic cleaning method includes a surface activation step, an electrolytic cleaning step, and a washing step.

In the surface activation step, by dipping in a caustic soda solution having a concentration of 50% or more, preferably 60 to 80 ° C or more and 1% or more and 2 to 5% in a hot dipping tank. The surface is activated by the principle of saponification while performing cleaning and preheating.

In the electrolytic cleaning step, the surface oil activated in the scrubbing unit is forcedly degreased by physical friction, and then the anode [Anode (+)] and the cathode [Cathode] in an electrolytic cleaning tank using the electrolysis principle. (-)] Electrode utilization induces hydrogen and oxygen chemical reaction to further improve the cleansing.

This electrolytic cleaning step aims to completely block unplated by desorption by completely removing the oil surface due to the surface oil pits and bright roughness unique to the stainless steel sheet, which is not found in ordinary carbon steel.

Thereafter, in the washing step, after the final washing process in a hot water rinse tank, the stainless steel sheet is transferred to the direct heating in the annealing furnace.

The annealing step includes a preheating step, a heating and holding step, and a cooling step.

(Warm up)

Preheating temperature: 550 ° C. or higher, preferably 600 to 700 ° C., air partial pressure ratio: 1.3 or higher, preferably 1.3 to 1.6 and hydrogen concentration: 1 to so that Fe and Cr composite oxides are formed on the pretreated stainless steel sheet. Heat to 5% condition.

If the preheating temperature is less than 550 ° C., there is a problem in that the composite oxide due to low heat is not uniformly produced. Therefore, the preheating temperature is limited to 550 ° C. or more. If the preheating temperature is too high, the amount of heat and hydrogen in the heating step is increased. It is preferable to limit the temperature to 600 to 700 ° C. because there is a problem in that the peroxidized surface cannot be reduced completely.

If the air partial pressure ratio is less than 1.3, there is a problem in that the amount of oxygen capable of sufficiently producing the surface complex oxide is insufficient, even if the oxidation atmosphere temperature is appropriate, and should be 1.3 or more, and if it exceeds 1.6, peroxidation may occur due to excessive oxygen inflow. It is preferable to limit the air partial pressure ratio to 1.3 to 1.6, because it causes problems such as when the temperature is excessively high.

When the hydrogen concentration is less than 1%, H ₂ O formation is suppressed because the reaction with air introduced for the composition of the oxidation atmosphere is less than -10 ° C. Since there is a problem that the O ₂ required for oxidation is insufficient since H ₂ O is reacted with O _{2 in the} air, the hydrogen concentration is preferably limited to 1-5%.

(Heating and cracking stage)

The steel sheet directly heated as described above is heated to reduce the Fe and Cr composite oxides at a heating temperature of 900 ° C. or lower, preferably 800 to 900 ° C., and a hydrogen concentration of 30% or higher, preferably, 30-45% and a dew point temperature: Heat to 35-45 [deg.] C. and hold at that temperature.

If the heating temperature is too high, since the Cr film itself is reduced and Cr is not dropped even after the plating bath is drawn in, there is a problem that surface defects occur. It is preferable to limit the temperature to 800 to 900 ° C. because there is a problem of poor workability due to insufficient annealing.

If the hydrogen concentration is less than 30%, Fe is not completely reduced in the composite oxide film generated in the preheating step, so that there is a problem in that surface defects are generated. It is preferable to limit the amount to 30-45% because there is an economic problem that causes excessive energy consumption due to excessive atmosphere composition.

If the dew point temperature exceeds 35 ℃, the moisture content is high, it may disperse the whole atmosphere in the furnace, and unplating may occur, if the temperature is below -45 ℃, the target is due to lack of oxidation by air under dry conditions Since there is a problem that the generation amount of the composite oxide to be reduced, the dew point temperature is preferably limited to 35 ~ -45 ℃.

(Cooling stage)

The steel sheet heated and cracked as described above is cooled to 600-700 ° C. while maintaining a hydrogen concentration of 20-40%.

If the cooling end temperature is less than 600 ℃, there is a problem that the reactivity of Fe, Al, Zn molten metal in the molten metal is weak to remove the Cr oxide, if the cooling end temperature exceeds 700 ℃ POT Inductor mobility is lowered Since the growth of the alloy layer due to the uneven spangle and latent heat of the strip due to the fluidity drop is prominent and the workability is a problem, it is limited to 600 to 700 ° C.

If the hydrogen concentration is less than 20%, there is an unplating problem that may occur due to the inability to further proceed with the reduction of Fe that is not completely reduced in the heating and cracking stages. Limited to 20-40% because of problems.

By doing so, the steel sheet not only maintains the activated surface until it is introduced into the plating bath, but further reduction of the unreduced iron is made.

(Aluminium-Zinc Plating Step)

The steel sheet annealed as described above is subjected to aluminum-zinc plating.

Through the pretreatment and annealing process as described above, the bonding strength of the Fe and Cr composite oxides, which are chromium oxide films, is weakened, and the weakened bonds are broken at the heating zone during annealing, and Fe reacts with hydrogen to activate the surface of the plating bath. It is preferable to form an atmosphere such that the chromium oxide film is removed using pure nitrogen immediately before.

As described above, after the Fe and Cr composite oxides, which are chromium oxide films, are removed, a stainless steel sheet having sufficient plating wettability is secured, and then 55% aluminum-zinc plating is continuously performed.

The temperature of the plating bath is preferably 520 to 650 ° C., and the composition of the plating bath is 30 to 78% aluminum and the remaining zinc, and the preferred plating bath is 52 to 58% aluminum and the remaining zinc. .

The plating bath may further contain less than 3.0% of silicon.

More preferred plating bath compositions contain 55% aluminum, 43.4% zinc and 1.6% silicon.

In the present invention, the plated layer diffusion force by the reaction between the base iron and the hot-dip galvanizing layer is superior to the bonding force between the surface chromium oxide layer and the base iron, so that the chromium oxide layer is separated into the plating bath to be top dross or remain on the plated layer to Process design is made to complement corrosion resistance by forming (Multi-Layer).

(Cooling stage)

As described above, the plated steel sheet is cooled at a cooling rate of 20 to 40 ° C./sec after hot dip plating, and a preferable cooling rate is 25 to 35 ° C./sec.

Examples of the cooling method include air cooling or air cooling after water cooling.

Here, air cooling means cooling by injecting cold air, and water cooling means cooling by spraying water vapor or water particles.

If the cooling rate is faster and is too slow, the variation of the spangle size on the surface of the plating layer is increased and the workability of the product is degraded due to the growth of the alloy layer.

At this time, the cooling end temperature is preferably 350 ° C or less.

The reason for this is that when the cooling end temperature exceeds 350 ° C, the plated layer is not firm, so that surface defects may occur due to transfer of the pattern by contact with the outer rolls (Touch Roll, Top Roll), and sufficient cooling is achieved. This is because there is a problem in workability due to growth of the alloy layer.

By water-cooling after plating as mentioned above, the outstanding plating adhesiveness, sequin size deviation reduction, sequin refinement, and workability improvement can be ensured.

In other words, it ensures excellent plating adhesion through the water-cooled cooling process and improves workability by suppressing the Fe-Al-Si alloy layer formation between the plating layer and the base iron, and has a beautiful appearance by controlling the sequin size deviation and miniaturizing the sequins. Produce a product.

The temperature section below the cooling end temperature is cooled in air.

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

(Example)

After pretreating the stainless steel sheet under the conditions as shown in Table 1, annealing under the conditions as shown in Table 2, and then performing a plating and cooling under the conditions as shown in Table 3 to produce a molten aluminum-zinc plated steel sheet, plating adhesion, Surface properties and workability were investigated, and the results are shown in Table 4 below.

In the cooling conditions shown in Table 3, the water-cooled + air-cooled type means air-cooled after water cooling, and the average cooling rate was 30 ° C./sec.

In the case of air cooling, the cooling rate was 20 ° C / sec.

In Table 4, the adhesion, surface properties and workability were evaluated as follows.

1) Adhesion

Δ: plating peeling occurs

○: Hair cracks but no plating peeling

◎: No plating peeling

2) Surface characteristics

Δ: Unplated more than 10% with a diameter of 2 mm or more

○: Unplated within 5% of the diameter within 20mm

◎: no plating

3) Machinability

Δ: Cracks occur in several places after LOCK FORMING

    Al layer is little by little when rubbed crack part

○: Partially minimal cracks appear on the surface after performing the lock forming.

◎: No abnormality on the surface after performing the rock forming

Psalm No. Pretreatment conditions Pretreatment Type Pretreatment solution (caustic soda solution) concentration (%) Pretreatment temperature (℃) One Brush cleaning 3 65 2 Electrolytic cleaning 3 65 3 Brush cleaning 3 75 4 Electrolytic cleaning 3 75 5 Brush cleaning 3 65 6 Electrolytic cleaning 3 65 7 Brush cleaning 3 65 8 Electrolytic cleaning 3 65 9 Brush cleaning 3 65 10 Electrolytic cleaning 3 65

Psalm No.

Annealing Condition Preheating condition Heating and maintenance conditions Cooling condition Temperature
(℃) Air partial pressure ratio Hydrogen concentration
(%) Temperature
(℃) Hydrogen concentration
(%) dew point
Temperature (℃) Cooling end
Temperature (℃) Hydrogen concentration
(%)  One 400 1.3 One 820 35 -40 620 30 2 500 1.1 3 900 35 -40 620 40 3 500 1.3 One 800 35 -40 620 30 4 500 1.3 3 900 35 -40 620 40 5 600 1.1 One 800 25 -30 620 30 6 600 1.1 3 920 25 -30 620 40 7 600 1.1 One 800 35 -35 545 35 8 600 1.3 3 900 40 -40 650 40 9 600 1.3 One 800 40 -30 620 30 10 600 1.3 3 900 35 -40 620 40

Psalm No.
Plating condition Cooling condition Plating bath temperature (℃) Plating bath composition Cooling method Cooling end temperature (℃) One 600 55% Al, 43.4% Zn, 1.6% Si Air cooling 350 2 600 55% Al, 43.4% Zn, 1.6% Si Air cooling 355 3 600 55% Al, 43.4% Zn, 1.6% Si Air cooling 350 4 600 55% Al, 43.4% Zn, 1.6% Si Water cooled + air cooled 315 5 600 55% Al, 43.4% Zn, 1.6% Si Air cooling 355 6 600 55% Al, 43.4% Zn, 1.6% Si Water cooled + air cooled 310 7 534     35% Al, 65% Zn Water cooled + air cooled 270 8 635     70% Al, 30% Zn Water cooled + air cooled 320 9 600 55% Al, 43.4% Zn, 1.6% Si Air cooling 350 10 600 55% Al, 43.4% Zn, 1.6% Si Water cooled + air cooled 315

Psalm No. Adhesion Surface characteristics Machinability One Δ Δ Δ 2 Δ Δ ○ 3 Δ ○ Δ 4 Δ ○ ◎ 5 Δ Δ Δ 6 Δ Δ ◎ 7 ○ Δ ○ 8 ○ ○ ◎ 9 ◎ ◎ ○ 10 ◎ ◎ ◎

As shown in Table 4, in the case of manufacturing a molten aluminum-zinc plated steel sheet by pretreating, annealing, plating and cooling according to the present invention (Sample No. 8-10), excellent plating adhesion, It can be seen that surface characteristics and workability can be obtained.

Claims (14)

A method of manufacturing a molten aluminum-zinc plated stainless steel sheet by performing molten aluminum-zinc plating on a stainless steel sheet, the method comprising: pretreating the stainless steel sheet; After preheating to a preheating temperature of 600 to 700 ° C., an air partial pressure ratio of 1.3 to 1.6, and a hydrogen concentration of 1 to 5% to generate an activated Fe and Cr composite oxide layer on the pretreated stainless steel sheet as described above. Heating temperature: 800-900 ° C., hydrogen concentration: 30-45%, and dew point temperature: 35-45 ° C. so as to reduce the Fe and Cr composite oxides, and maintained at that temperature, followed by 20-40% hydrogen. Annealing by cooling to 600-700 ° C. while maintaining the concentration; Plating the steel sheet annealed as described above in a molten aluminum-zinc plating bath having a bath temperature of 550 to 650 ° C .; And Cooling the plated molten aluminum-zinc plated steel sheet to a temperature section of 350 ° C. or less at a cooling rate of 20 to 40 ° C./sec, The plated molten aluminum-zinc plated steel sheet is cooled by spraying water vapor or water particles, and then cooled by spraying cold air to cool the molten aluminum-zinc plated stainless steel sheet. The method of claim 1, wherein the plating bath comprises 30 to 78% aluminum and the remaining zinc. The method of claim 2, wherein the plating bath comprises 52 to 58% aluminum and the remaining zinc. The method for producing a hot-dip aluminum-galvanized stainless steel sheet according to any one of claims 1 to 3, wherein the plating bath further contains 3.0% or less of silicon (excluding 0%). The method of claim 4, wherein the plating bath is made of 55% aluminum, 43.4% zinc and 1.6% silicon. delete delete delete The steel sheet according to any one of claims 1 to 3, wherein the pretreatment of the steel sheet is performed by an electrolytic cleaning method including a surface activation step, an electrolytic cleaning step and a washing step; And the solution used in the surface activation step is a method of manufacturing a molten aluminum-zinc plated stainless steel sheet, characterized in that the caustic soda solution of 60 ~ 80 ℃ having a concentration of 2 to 5% as a steel sheet surface activation solution. The method of claim 4, wherein the pretreatment of the steel sheet is performed by an electrolytic cleaning method including a surface activation step, an electrolytic cleaning step, and a washing step; And the solution used in the surface activation step is a method of manufacturing a molten aluminum-zinc plated stainless steel sheet, characterized in that the caustic soda solution of 60 ~ 80 ℃ having a concentration of 2 to 5% as a steel sheet surface activation solution. The method according to claim 5, wherein the pretreatment of the steel sheet is performed by an electrolytic cleaning method including a surface activation step, an electrolytic cleaning step and a washing step; And the solution used in the surface activation step is a method of manufacturing a molten aluminum-zinc plated stainless steel sheet, characterized in that the caustic soda solution of 60 ~ 80 ℃ having a concentration of 2 to 5% as a steel sheet surface activation solution. delete delete delete