JP3048388B2 - Manufacturing method and cooling equipment for galvannealed steel sheet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet and a cooling system for improving the surface properties of the hot-dip galvanized steel sheet while simultaneously cooling the same.

[0002]

2. Description of the Related Art Due to its excellent corrosion resistance, alloyed hot-dip galvanized steel sheets have been widely used in various applications, including automobile outer panels. In addition, there is an increasing need for steel sheets with added value by subjecting alloyed hot-dip coated steel sheets to electroplating treatment, chemical conversion treatment, and the like.

However, when electrodeposition coating is performed on such a plated steel sheet, defects such as craters occur.

[0004] In recent years, alloyed hot-dip galvanized steel sheets have been widely used in applications such as the above-mentioned automobile outer panels which are subjected to complicated press working. It is a problem.

On the other hand, in order to improve the above-mentioned disadvantages of the galvannealed steel sheet, iron-based plating is further performed on the galvannealed layer.

For example, Japanese Unexamined Patent Publication (Kokai) No. 55-133488 discloses that a zinc-based plating is applied as a lower layer plating,
Applying Zn-based upper layer plating, Japanese Patent Publication No. 01-16919
Japanese Patent Application Publication No. JP-A-61-1986 discloses that a zinc-based plating is applied as a lower layer plating and then an Fe-P type upper layer plating is applied.
Japanese Patent No. 253397 discloses an invention in which Fe--P-based upper layer plating is applied as a lower layer plating on an alloyed hot-dip galvanized layer to provide corrosion resistance in the lower layer plating and improve chemical conversion treatment and crater resistance in the upper layer plating. Is disclosed.

[0007] In these techniques, when the lower layer plating is electroplating, a two-layer plated steel sheet having the expected performance can be obtained stably, but when the lower layer plating is alloyed hot-dip galvanizing, it is not always sufficient. There was a problem that a two-layer plated steel sheet with high performance could not be obtained.

In order to solve the above-mentioned powdering, the alloying after hot-dip galvanizing is made low, and the average Fe content of the hot-dip galvanized layer is reduced from 10 to 13% by weight to 7 to 10% by weight. %, But as a result, when the above-mentioned upper plating is applied, the coverage of the upper iron-based electroplating is uneven, so that the crater resistance and the chemical conversion treatment are more remarkable. A new instability problem has arisen.

On the other hand, as an emergency measure, the chemical conversion property can be improved by increasing the amount of iron-based electroplating deposited, but it is not practical because the corrosion resistance deteriorates.

[0010]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the galvannealed steel sheet and provides an alloyed hot-dip galvanized steel sheet which can provide excellent surface properties while cooling in a short time. It is an object of the present invention to provide a method for manufacturing a steel sheet and a cooling facility.

[0011]

Means for Solving the Problems The present inventors have found that an oxide film is formed on the surface of the alloyed hot-dip galvanized layer during the heating alloying step, and becomes extremely inactive. .

It has been considered that activating such an inactive surface state is effective for solving the above-mentioned problem. Although various methods can be considered, activation by pickling using hydrochloric acid or sulfuric acid, which is used in a general electroplating line, has an effect because the alloyed hot-dip galvanizing is remarkably dissolved. In addition, powdering is significantly deteriorated. On the other hand, it has been found that it is particularly effective to remove the oxide film by subjecting the surface of the alloyed hot-dip galvanized steel sheet to a contact with an aqueous alkali solution in a predetermined steel sheet temperature range, and has reached the present invention. .

That is, according to the present invention, in order to attain the above object, in producing an alloyed hot-dip galvanized steel sheet, after the steel sheet subjected to hot-dip galvanizing is subjected to alloying treatment, the steel sheet temperature is 100 to 300 ° C. A method for producing an alloyed hot-dip galvanized steel sheet is provided, wherein the steel sheet is immersed in an aqueous alkali solution and cooled. In the above, the temperature of the aqueous alkali solution may be 25 to 85 ° C. In addition, steel sheets immersed in an alkaline aqueous solution are usually
Then, it is washed and dried.

Further, according to the present invention, there is provided an apparatus for continuously cooling an alloyed hot-dip galvanized steel sheet obtained by subjecting a steel sheet to hot-dip galvanizing and then performing an alloying treatment, wherein the alloyed surface is subjected to an alkali treatment. A cooling facility for an alloyed hot-dip galvanized steel sheet, comprising: an alkali treatment means, a washing means following the alkali treatment means, and a drying means following the washing means.

Here, the alkali treatment means, the washing means and the drying means are arranged below the cooling device on the exit side of the alloying furnace, and the steel sheet exiting the alkali treatment means is turned up once in the upstream direction. After passing through the washing means and the drying means, it is arranged so that it is turned back again and sent downstream below the drying means, the washing means and the alkali treatment means. In the above, the steel sheet that has exited the cooling device on the alloying furnace exit side is drooped and inserted into the alkali treatment tank of the alkali treatment means, and can pass through the alkali treatment tank in a U-shape.

Hereinafter, the present invention will be described in more detail.

Although the steel sheet used in the present invention is not particularly limited, for example, a general cooling steel sheet, a high-tensile steel sheet and the like can be used.

The alloyed hot-dip galvanized steel sheet to which the present invention is directed is a steel sheet obtained by subjecting a steel sheet to hot-dip galvanization and immediately subjecting it to a heat treatment to cause a diffusion alloying of Fe from the base steel sheet into the coating layer. Here, the composition of the molten zinc bath, plating conditions, alloying conditions, and the like may be in accordance with commonly used methods.

In the present invention, the surface of the alloyed hot-dip galvanized steel sheet as described above is subjected to a liquid contact treatment with an alkaline aqueous solution. At this time, the alkaline aqueous solution to be used is not particularly limited, but sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, or a carbonate thereof can be preferably used. In addition, liquid contact time 0.5 to 20
In the short-time treatment of seconds, it is particularly preferable to use an alkali metal hydroxide such as sodium hydroxide or potassium hydroxide.

The degree of the activation treatment is preferably such that the amount of dissolution of the galvannealed layer is 0.05 to ² g / m ^2, more preferably 0.1 g / m ² .
It is preferable to perform the treatment so as to be in the range of 1 to 0.5 g / m ² .
A solubility of poor effect of surface activation is less than 0.05 g / ^2, and the plating layer exceeds 2 g / m ² was dissolved excessively,
This is because the powdering property of the obtained steel sheet is deteriorated.

Such processing conditions are achieved when the temperature of the steel sheet after the alloying processing is 100 to 300 ° C. Also,
The alkali concentration of the aqueous solution is 0.05 to 5 N, and the contact time between the alkaline aqueous solution and the surface of the galvannealed layer is 0.5.
The temperature of the aqueous solution is preferably 25 to 80 ° C. for 5 to 5 seconds.

FIG. 4 shows the relationship between the temperature of the steel sheet when the hot-dip galvanized steel sheet after the alloying treatment is subjected to the liquid contact treatment with the alkaline aqueous solution and the amount of the oxide film on the steel sheet surface after the treatment. .

That is, when the temperature of the steel sheet is lower than 100 ° C., the oxide film remains thicker as the temperature becomes lower. Is done.

The hot-dip galvanized steel sheet after alloying is as follows:
Although the surface is highly uneven, the interface between the steel sheets is strongly evaporated with water during the alkali treatment, so that the oxide film can be completely removed up to the concave portions.

However, if the temperature exceeds 300 ° C., the temperature of the steel sheet after the treatment exceeds 50 ° C., and there is a possibility that the material will deteriorate in the next step.

FIG. 4 shows a galvannealed steel sheet having a basis weight of 45 g / m ² per side and an average iron content of the coating layer of 11% by weight.
g /, a solution temperature of 60 ° C) for 3 seconds, but the steel sheet and the alkali in the range of the present invention have high reactivity with the plating layer at a steel sheet temperature of 100 to 300 ° C. The oxide film can be completely removed by the liquid contact treatment for 0.5 to 5 seconds. Further, since a long processing time is not required, there is no need to provide a long facility.

Further, the steel sheet subjected to the liquid contact treatment with the aqueous alkali solution according to the present invention can be conveyed to the next step without further cooling.

When an iron-based electroplating apparatus is installed in an alloyed hot-dip galvanizing production line to produce in-line two-layer plated steel sheets, simple and short processing is desirable due to space constraints. In such a case, the alkali concentration is 0.1 to 2 N, the liquid contact time is 0.5 to 5 seconds, and the aqueous solution temperature is 40
It is preferable that the temperature be set to 70C.

As the iron-based plating applied to the upper layer of the alkali solution-treated galvannealed steel sheet obtained in this way, Fe-Zn-based electroplating and Fe-P-based electroplating are suitable, and the composition and plating conditions A known range can be applied.

Next, the cooling equipment for the galvannealed steel sheet of the present invention will be described with reference to the accompanying drawings.

The cooling equipment 1 of the present invention is provided immediately after the alloying treatment equipment 3 following the zinc pot 2 of the hot dip galvanizing equipment as shown in FIG.

The alloying equipment 3 generally has an alloying furnace 4 and a cooling device 5 provided on the outlet side thereof.

The cooling device 5 shown in FIG.
Although a set is provided, it is not limited to this.

That is, the cooling equipment 1 of the present invention is an apparatus for treating the steel sheet 6 which has been processed in the alloying furnace 4 and then exits the cooling device 5 with alkali.

The cooling equipment 1 includes an alkali treatment means 7 for alkali-treating the alloyed surface of the steel sheet 6 treated in the alloying furnace 4 and a cleaning means 8 following the alkali treatment means.
And a drying means 9 following the cleaning means.

The alkali treatment means 7 may be any one which can contact a steel sheet with an aqueous sodium hydroxide solution having an aqueous solution temperature of 25 to 80 ° C. and an alkali concentration of 0.05 to 5 N, for example. Known liquid contacting directions such as immersion and spraying can be used. FIG. 1 shows the one obtained by immersion.

In the above, the steel sheet that has exited the cooling device on the exit side of the alloying furnace is dripped and inserted into the alkali treatment tank of the alkali treatment means 7 and can pass through the alkali treatment tank in a U-shape. FIG. 2 shows one embodiment of the cooling equipment of the present invention by immersion.

In FIG. 2, the alkali treatment means 71 comprises:
A immersion tank 10, a cooling header 11 and a sink roll 12 provided in the immersion tank 10, and a pump 14 for circulating and cooling the alkaline aqueous solution 13 in the immersion tank 10.
And a heat exchanger 15. Immersion tank 10, pump 14, heat exchanger 15, and cooling header 1
1 are connected by a pipe 23.

The cleaning means 8 comprises a rinsing tank 16, a rinsing nozzle 17 and a guide roll 18 provided in the rinsing tank 16.

Between the alkali treatment means 7 and the washing means 8,
A brush roll 19 may be provided as shown in FIG.

The drying means 9 is for removing moisture adhering to the steel sheet 6 treated by the washing means 8, and a known dryer can be used.

Here, as shown in FIG. 1, the alkali treatment means 7, the washing means 8, and the drying means 9 are provided below the cooling device 5b of the alloying treatment equipment 5 and in the next step equipment (in FIG. 1, temper rolling). The drying means 9
Is preferably provided at a position closer to the alloying furnace than any of the alkali treatment means 7 and the cleaning means 8. That is, the steel sheet 6 that has exited the alloying furnace 4 is passed through and cooled so as to form a figure of five. Specifically, the steel sheet that has exited the alkali treatment means 7 is once turned back to the upstream side, passes through the washing means 8 and the drying means 9, and then is turned back again and is turned back to the drying means 9, the washing means 8 and the alkali treatment means 7 It is sent downstream through the lower part.

By arranging in this way, the time until the alkali treatment is shortened, the formed oxide film is reduced, and the alkali treatment means 7 and the cleaning means 8
The oxide film can be easily removed. Further, the space below the cooling zone of the alloying furnace can be effectively used, and the building length of the plating processing line can be shortened.

The alloyed hot-dip galvanized steel sheet 6 is introduced into a dipping tank 10 filled with a predetermined alkaline aqueous solution 13 and dipped. At this time, the cooling effect can be enhanced by spraying a cooling alkaline aqueous solution from the cooling header 11 onto the surface of the steel plate 6 as shown in FIG.

The immersion-treated steel sheet 6 is washed in a rinsing tank 16 with washing water sprayed from a rinsing nozzle 17 and then dried by a drier 9.

Since the cooling system of the present invention is configured as described above, for example, alkali treatment at a steel sheet temperature of 100 to 300 ° C. can be easily performed, and the oxide film on the surface of the galvannealed steel sheet is severely affected. It can be removed by reaction. Therefore, the contact time with the aqueous alkali solution can be shortened. In addition, since cooling can be performed simultaneously with the alkali treatment, equipment dedicated to the alkali treatment is not required.

FIG. 3 shows another embodiment of the cooling equipment of the present invention.

In FIG. 3, the alkali treatment means 72 comprises:
The alkali treatment tank 21, the fog header 22 and the sink roll 12 provided in the alkali treatment tank 21, the receiving tank 24 for the alkaline aqueous solution 13 extracted from the alkaline processing tank 21, and the circulating cooling of the alkaline aqueous solution 13 in the receiving tank 24. , And a heat exchanger 15. A pipe 25 is provided between the alkali treatment tank 21 and the receiving tank 24,
The receiving tank 24, the pump 14, the heat exchanger 15, and the fog header 22 are connected to each other by a pipe 23. The washing means 8 and the drying means 9 are the same as in the case of immersion shown in FIG.

In the case of the above-mentioned cooling equipment by spraying, the number of equipment is larger than in the case of immersion, but the alkali treatment efficiency is improved.

In this case, as in the case of immersion, the alkali treatment means 72 is placed below the cooling device 5b of the alloying equipment 5,
In addition, it is preferable that the drying means 9 is provided at a position above the next process equipment 20, and the drying means 9 is provided at a position above any of the alkali treatment means 7 and the washing means 8.

[0051]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to embodiments.

Example 1 Galvannealed steel sheet (weight per unit area: 35 g / m ² , average iron content: 8.5% by weight,
9.5% by weight and 11.5% by weight) with various alkali solution treatments, acid treatments or no treatments as pretreatments, and then 85% by weight Fe-Zn electroplating or Fe-0.2
Weight percent P electroplating was performed, and the uniformity of upper layer plating, chemical conversion treatment, and corrosion resistance after electrocoating were investigated.

In each of the cases where an alkaline solution was used as the pretreatment, the cooling equipment by immersion of the present invention shown in FIGS. 1 and 2 was used.

Tables 1 and 2 show the obtained results.

The evaluation method of each evaluation item is described below. Uniformity of upper plating: Evaluated by EPMA microanalysis results. ：: The peak of the lower layer Zn is not observed. Δ: The peak of the lower layer Zn is partially observed. X: The peak of the lower layer Zn is observed over the entire surface. Chemical conversion treatment: After iron-based electroplating Subjected to phosphate conversion treatment,
The surface was observed and evaluated by SEM. ：: Granular phosphate crystals were obtained. △: Granular and needle-like phosphate crystals were obtained. X: Needle-like phosphate crystals were obtained. By phosphophyll
ite [Zn ₂ Fe (PO ₄ ) ₂ · 4H ₂ O], needle-like crystals
Hopeite [Zn ₃ (PO ₄ ) ・ 4
H ₂ O]. Corrosion resistance after electrodeposition coating: After iron-based electroplating, phosphate conversion treatment and cationic electrodeposition coating (film thickness: 20 μm) are applied by a conventional method, and a cross-cut is made. Was. ：: Small red rust generated △: Red rust generated ×: Red rust generated large

As is clear from the table, the uniformity of the upper layer plating of the steel sheet obtained by the present invention, the chemical conversion property, and the corrosion resistance after the electrodeposition coating were all excellent.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

Since the present invention is configured as described above, according to the method for producing an alloyed hot-dip galvanized steel sheet according to the present invention, an alloyed hot-dip galvanized steel sheet is excellent in a short time while cooling. Surface properties can be provided.

Further, according to the present invention, it is possible to remarkably improve the uniformity of upper layer plating, chemical conversion treatment, and corrosion resistance after electrodeposition coating of a two-layer plated steel sheet which is cooled and then subjected to iron-based upper layer plating.

Further, by using the cooling equipment of the present invention, it is possible to efficiently cool the steel sheet and remove the oxide film without using a long equipment.

[Brief description of the drawings]

FIG. 1 is a layout view of a cooling facility for a galvannealed steel sheet according to the present invention.

FIG. 2 is a configuration diagram showing one embodiment of a cooling facility by immersion of the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a graph showing a relationship between a steel sheet temperature and an oxide film amount in an alkali treatment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cooling equipment 2 Zinc pot 3 Alloying treatment equipment 4 Alloying furnace 5, 5a, 5b Cooling device 6 Steel plate 7, 71, 72 Alkali treatment means 8 Cleaning means 9 Drying means 10 Immersion tank 11 Cooling header 12 Sink roll 13 Alkaline aqueous solution 14 Pump 15 Heat exchanger 16 Rinse tank 17 Rinse nozzle 18 Guide roll 19 Brush roll 20 Temper rolling mill 21 Alkali treatment tank 22 Fog header 23 Piping 24 Receiving tank 25 Piping

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Naoto Fuji 1-chome, Kawasaki-dori, Mizushima, Kurashiki-shi, Okayama Pref. (72) Inside Mizushima Works, Kawasaki Steel Corporation (72) Inventor Kyushu Furukawa Mizushima-Kawasaki, Kurashiki-shi, Okayama 1-chome (without address) Inside the Mizushima Works of Kawasaki Steel Corporation (58) Field surveyed (Int. Cl. ⁷ , DB name) C23C 2/00-2/40

Claims (6)

(57) [Claims] In producing an alloyed hot-dip galvanized steel sheet, after hot-dip galvanized steel sheet is alloyed, the steel sheet is immersed in an alkaline aqueous solution at a steel sheet temperature of 100 to 300 ° C. and cooled. A method for producing an alloyed hot-dip galvanized steel sheet. 2. The water temperature of the aqueous alkaline solution is 25-8.
The method for producing a galvannealed steel sheet according to claim 1, wherein the temperature is 5 ° C. 3. The method according to claim 1, wherein the steel sheet immersed in the alkaline aqueous solution is washed and dried.
3. The method for producing an alloyed hot-dip galvanized steel sheet according to item 1. 4. A cooling system for continuously cooling an alloyed hot-dip galvanized steel sheet obtained by subjecting a steel sheet to hot-dip galvanizing and then performing an alloying treatment, comprising: an alkali treatment means for alkali-treating the alloyed surface. Having a washing means following the alkali treatment means and a drying means following the washing means,
And a cooling device for the galvannealed steel sheet, wherein the alkali treatment means is provided immediately after the alloying treatment equipment. 5. The alloying treatment facility has a cooling device on the exit side of the alloying furnace, and the alkali treatment means, the washing means, and the drying means are provided below the cooling device. 5. The alloy according to claim 4, wherein the alloying member is arranged so as to be turned back once in the upstream direction, pass through the washing unit and the drying unit, and then turn back again and pass downstream below the drying unit, the washing unit and the alkali treatment unit. Cooling equipment for hot-dip galvanized steel sheets. 6. The steel sheet exiting the cooling device on the alloying furnace exit side is dripped and inserted into an alkali treatment tank of an alkali treatment means and passes through the alkali treatment tank in a U-shape. Cooling equipment for the described galvannealed steel sheet.