JPH0681097A - Method for galvanizing oxidized scale adhered steel worked product - Google Patents

Abstract

PURPOSE:To improve the operating environment by heating a worked product in an oxidizing atmosphere to burn adhered material and thereafter subjecting it to pretreatment in which reduction and temp. control are executed under specified conditions. CONSTITUTION:In the method for galvanizing in which a hot rolled oxide scale adhered steel worked product is subjected to pretreatment, is thereafter immersed in a galvanizing bath of 430 to 530 deg.C, is plated, is subsequently discharged from the plating bath and is freed from surplus adhered zinc, pretreatment is executed in such a manner that the worked product is heated in an oxidizing atmosphere to burn the adhered material, and after that, it is reduced at 400 to 800 deg.C in an atmosphere of a reducing gas and is thereafter subjected to temp. control to <=560 deg.C in an atmosphere of a nonoxidizing gas. In this way, the environment of the galvanizing operation for the oxidized scale adhered steel worked product can be improved.

Description

Detailed Description of the Invention

[001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to hot dip galvanizing of hot-rolled oxide scale-adhered steel products using a method in which pre-treatment is carried out by directly reducing the oxide scale with a reducing gas without descaling. Regarding the method.

[002]

2. Description of the Related Art In many cases, steel products manufactured by subjecting hot-rolled black skin hot-rolled steel sheet to forming and welding
It is used after being coated with rust-preventive paint, but when it is used for applications requiring appearance and corrosion resistance such as bridges, subway stations, tunnels, etc., it has been hot-dip galvanized.

By the way, since a processed steel product (hereinafter simply referred to as a processed product) uses a molding machine in manufacturing,
Machine oil may be attached or the part number may be marked with paint. In addition, because hot rolled steel sheets left outdoors during manufacturing are used and processed products are also left outdoors, black rust in the hot rolled scale partially changes to red rust, which causes oxidation scale. Le is a mixture of black rust and red rust.
For this reason, machine oil, black rust, and red rust were removed by pretreatment before hot-dip galvanizing.

In this pretreatment, the mechanical oil is first removed by degreasing treatment with an organic solvent or alkali, followed by washing with water, and then pickling treatment with hydrochloric acid or a mixed acid of hydrochloric acid and sulfuric acid for 10 minutes or more.
However, in this pretreatment, fumes of organic solvent and alkali are constantly generated from the degreasing treatment equipment, and from the pickling treatment equipment each time treatment is performed. A large amount of acid and reaction gas are generated.

[0095]

However, since the processed product has a non-uniform shape and size, each process cannot be carried out by the sealing device and must be carried out by the releasing device. Further, the movement of the processed product cannot be automated due to the shape and the size, and it must be done by the operator. For this reason, the working environment and working conditions in the pretreatment area were extremely poor, but an effective means for preventing or suppressing fumes from the degreasing treatment equipment and acids and reaction gases from the pickling treatment equipment. The reality was that there was no. Further, when pretreatment is performed, a large amount of waste liquid is generated, but since the waste liquid must be subjected to detoxification treatment, there is a problem that the treatment requires a large amount of money.

Further, in the hot dip galvanizing, depending on the processed product, 3 in a plating bath having a bath temperature of 430 to 530 ° C.
Since the processed product must be soaked for about 30 minutes, white smoke with an irritating odor is generated due to flux decomposition during the soaking. However, since the plating bath also has to be an open type, white smoke deteriorates the working environment in the plating bath area.

[0097]

SUMMARY OF THE INVENTION The present invention provides a hot dip galvanizing method for processed products which solves these problems. That is, in the present invention, in the pretreatment, the processed product is heated in an oxidizing atmosphere to burn the deposits, and then reduced at 400 to 800 ° C. in a reducing gas atmosphere, and then the non-oxidizing property is applied. It was decided to perform the method by adjusting the temperature so that the temperature would be 560 ° C. or lower in a gas atmosphere.

[0085]

[Operation] In the gas reduction type continuous hot dip galvanizing line, a pretreatment method is performed in which the cold-rolled steel sheet is heated in the pretreatment zone to oxidize and remove impurities, and then reduced with a mixed gas of hydrogen gas and nitrogen gas. However, in this case, the oxide scale generated by heating is thin, usually 0.1 μm or less, and not as thick as the hot rolled oxide scale. Therefore, although it reduced with a reducing gas containing hydrogen gas, hot rolling oxide scale - black Le rust (Fe ₃ O ₄₎ is as thick as 5 to 10 [mu] m, a dense, red rust [Fe ₂ O ₃ by oxidation And Fe (OH) ₃ etc.] are thicker, it has been conventionally considered difficult to remove them without pickling.

However, the present inventors examined the reduction of these hot-rolled oxide scales with hydrogen gas or a mixed gas containing them, and as a result of devising the reduction pretreatment, both black rust and red rust were relatively short. I found that I could return it in time.

FIGS. 1 and 2 show a low carbon hot rolled steel sheet having a black rust oxide scale thickness of 5 to 10 μm (sheet thickness 2.2 mm) in a mixed gas of hydrogen gas and nitrogen gas at 500 ° C. and It shows the hot dip galvanizability depending on the hydrogen gas concentration and the reduction time when directly reduced at 600 ° C.
Indicates good plating on both sides, △ indicates unplated on one side, and × indicates unplated on both sides.

According to these results, when the oxide scale is black rust, the reduction temperature is set to 500 to 600 ° C., and the mixture is directly reduced for 30 to 240 seconds with a mixed gas having a hydrogen gas concentration of 2% or more. Good hot-dip galvanizing can be performed. This reduction time is significantly shorter than the conventional pickling time of 10 minutes or longer.

However, even if the surface of the processed product is directly reduced with an organic substance such as machine oil or paint attached, the atmosphere is reductive and the organic substance is only carbonized, leaving carbon and pigments. It turned out not to be reduced. Also, black rust is reduced in a relatively short time, but red rust is less reducible than black rust, and even if it is reduced under the same conditions as black rust, unreduced parts remain and defective plating parts occur. It turned out to do.

Therefore, the present inventors, as a countermeasure,
It was found that the reduction property of red rust can be improved by heating to a temperature at which organic substances can be burned and removed in an oxidizing atmosphere before the reduction treatment. That is, when the processed product is heated to a high temperature in an oxidizing atmosphere, the machine oil and resin are burnt and become smoke to be removed. Further, even if the pigment is an inorganic pigment, the carbon in the matrix is lost, so that it falls off. On the other hand, the reduction property of red rust is improved because it is difficult to reduce F
This is because e (OH) ₃ is dehydrated and changed to Fe ₂ O ₃ which is easily reduced, and at the same time, the surface layer drops due to powdering, the thickness becomes thin, and it is reduced to the inside in the next reduction step. Conceivable.

The above reduction pretreatment has no effect even if it is carried out in an inert gas atmosphere such as a nitrogen gas atmosphere, and it is necessary to carry out it in an oxidizing atmosphere. Air may be used as the oxidizing atmosphere. The heating temperature is determined by the type of deposit, but if the machine oil or paint is common, the heating temperature is 10
The temperature may be 0 ° C or higher, preferably 200 to 800 ° C.

FIG. 3 shows that black skin hot rolled steel sheet was coated with mechanical oil and paint, exposed to fume hydrochloride to change black rust into red rust, and then heated in air at 300 ° C. for 3 minutes. Then, it shows the hot-dip galvanizing property when reduced with the same mixed gas as in the case of the black skin hot-rolled steel sheet, the hot-dip galvanizing property is the same as when the oxide scale is black rust. You can see that it has become.

The hot-dip galvanizing properties of FIGS. 1 and 2 were investigated by an experimental apparatus as shown in FIG. That is, after inserting the vertically movable test piece holding rod 2 into the inside of the closed quartz cylinder 1 extending vertically and attaching the test piece 3 to the lower side of the test piece holding rod 2. The cylinder 1 was filled with the mixed gas, and the cylinder 1 was heated by the infrared furnace 4 arranged on the outer periphery of the cylinder 1. Then, when the test piece 3 reaches a predetermined temperature, heating in the infrared furnace 4 is stopped and 480
The cylinder 1 was cooled to 0 ° C., the lower part of the cylinder 1 was opened, and the test piece 3 was dropped together with the test piece holding rod 2 into the zinc plating bath 5 having a bath temperature of 450 ° C. arranged under the cylinder 1 and immersed for 30 seconds.

On the other hand, in the hot dip galvanizing property of FIG. 3, in the experimental apparatus shown in FIG. 4, the inside of the cylinder 1 was placed in the atmosphere, the test piece 3 was heated, and then the atmosphere was once replaced with nitrogen gas. The method was carried out by introducing a mixed gas, reducing and hot dipping.

The reduction with the mixed gas is carried out by using the processed product at 400 to 8
It is performed by heating to 00 ° C, preferably 450 to 650 ° C.
If it is less than 400 ° C, it becomes difficult to reduce the scale even if the hydrogen gas concentration is increased, and if it exceeds 800 ° C, the processed product may be deformed or the mechanical properties may be impaired. . The hydrogen gas concentration is 2% as shown in FIG.
If it is above, since it can be reduced, it may be 100%. After the reduction, if the temperature of the processed product is high, the alloy layer is remarkably developed during the hot dip plating, and the coating amount becomes excessively thick, so the temperature is cooled to 560 ° C or lower.

One method for hot dip galvanizing a processed product by the method of the present invention is the method shown in FIG. That is, the processed product is heated in the combustion chamber 6 in the air atmosphere, and when the target temperature is reached, the shutter 7 is opened and the conveyors 8 and 9 are opened.
Then, it is transferred to the indirect heating type reduction chamber 11 provided with the reducing gas supply pipe 10, and is reduced there while supplying the reducing gas.

When the reduction is completed, the shutter 12 is opened, the conveyer 9 and 13 are transferred again to the cooling chamber 15 equipped with the inert gas supply pipe 14, and the temperature suitable for plating is adjusted.
Immerse in the galvanizing bath 16. For immersion in the galvanizing bath 16, a cooling chamber 15 is provided with a closed type plating chamber 18 which is partitioned by a shutter 17, and a crane 19 is arranged inside the chamber. Do it while hanging. In addition, the plating chamber 1 using zinc evaporated from the zinc plating bath 16
In order to prevent the contamination of No. 8, Al is preferably added to the zinc plating bath 16 in an amount of 0.05 to 0.2% to prevent the evaporation of zinc.

As another method, instead of a shutter for partitioning each chamber in FIG. 5, an inert gas supply pipe 14 capable of forming an inert gas caten between the chambers as shown in FIG. 6 is used. The replacement chamber 20 provided is arranged to move from the combustion chamber 6 to the plating chamber 1
It is also possible to have a structure in which one conveyor 21 is passed up to 8 and the processed product is put into the galvanizing bath 16 from the plating chamber 18 and the processed product after plating is taken out by the conveyor type pulling machine 22.

[0222]

【Example】

Example 1 In the experimental apparatus shown in FIG. 4, the inside of the cylinder 1 was placed in the atmosphere, and machine oil and white paint were applied to the column made of hot-rolled steel sheet with a thickness of 2.3 mm, a length of 20 cm, and a 5 cm square, and only black rust. (Black rust thickness 7.2 μm) is heated at 420 ° C. for 3 minutes to incinerate the adhered substances, and then the cylinder 1 is purged with nitrogen gas to generate a H ₂ —N ₂ mixed gas having a hydrogen concentration of 24.2%. It was introduced and reduced for 160 seconds while heating to 420 ° C. When the reduction is completed, immediately drop it in the zinc plating bath 5 with a bath temperature of 450 ° C.
It was immersed for 0 seconds. After pulling up this column from the zinc plating bath 5, the surface was observed, but no non-plating was observed.

Example 2 A column similar to that of Example 1 was left outdoors to cause red rust to occur on about 42% of the total surface area, and mechanical oil and white paint were applied to this, and the same procedure as in Example 1 was performed. Then, hot dip galvanizing was performed using the experimental apparatus shown in FIG. The heating in the cylinder 1 was carried out for 5 minutes in the air atmosphere at 250 ° C., and the reduction after the heating was carried out for 120 seconds in the H ₂ —N ₂ mixed gas having a hydrogen concentration of 4.3% at 760 ° C. After the reduction, heating by the infrared furnace 4 was stopped, the temperature was cooled to 443 ° C., and the zinc plating bath 5 having a bath temperature of 450 ° C. was dropped and immersed for 30 seconds. The surface of this column was also lifted from the zinc plating bath 5 and the surface was observed, but no plating was observed. Comparative Example In Example 2, hot-dip galvanizing was performed by omitting column heating in the air atmosphere, but non-plating occurred in the portion where the machine oil and the white paint were applied.

[0242]

As described above, since the hot dip galvanizing method of the present invention is not a wet pretreatment but a dry pretreatment,
The working environment and working conditions can be significantly improved.

[Brief description of drawings]

FIG. 1 is a plot diagram showing the hot dip galvanizability depending on the hydrogen gas concentration and the reduction time when a black-skinned low carbon hot-rolled steel sheet is reduced at 500 ° C. in a mixed gas of hydrogen gas and nitrogen gas.

FIG. 2 is a plot diagram showing hot-dip galvanizability according to hydrogen gas concentration and reduction time when a black skin low carbon hot-rolled steel sheet is reduced at 600 ° C. in a mixed gas of hydrogen gas and nitrogen gas.

FIG. 3 shows hot dip galvanizability depending on hydrogen gas concentration and reduction time when a low carbon hot-rolled steel sheet in which red rust caused by oxidation of black rust is reduced in a mixed gas of hydrogen gas and nitrogen gas at 500 ° C. FIG.

FIG. 4 is a schematic diagram of a gas reduction type experimental apparatus used for an experiment of hot-dip galvanizing a hot-rolled steel sheet.

FIG. 5 is a schematic diagram of a plating apparatus for industrially hot-dip galvanizing a processed product by the method of the present invention.

FIG. 6 is a schematic view of another plating apparatus for industrially hot-dip galvanizing a processed product by the method of the present invention.

[Explanation of symbols]

1 ... Cylinder, 2 ... Test piece holding rod, 3 ... Test piece, 4 ... Infrared furnace, 5 ... Zinc plating bath, 6 ... Combustion chamber, 7 ... Shutter,
8, 9 ... Conveyor, 10 ... Reducing gas supply pipe, 11 ... Reduction chamber, 12 ... Shutter, 13 ... Conveyor, 14 ... Inert gas supply pipe, 15 ... Cooling chamber, 16 ... Zinc plating bath, 1
7 ... Shutter, 18 ... Plating chamber, 19 ... Crane, 2
0 ... Substitution chamber, 21 ... Conveyor, 22 ... Conveyor type pulling machine,

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Nakamura 1 at 672 Owada Nitta, Yachiyo-shi, Chiba Shinsei Kogyo Co., Ltd. (72) Inventor Masuhiko Maekita, 672 Owada Nitta, Yachiyo-shi, Chiba 1 Within Nova Steel Industry Co., Ltd. (72) Inventor Shuichi Ito 672 Owada Nitta, Yachiyo City, Chiba Prefecture Within Nova Steel Industry Co., Ltd. (72) Inventor Nobuhiro Abe 7-21 Ninomachi, Mizuho-ku, Nagoya City, Aichi Prefecture No. Incorporated company Estem (72) Inventor Jitsuzo Suto 3-3-44 Kitakagaya, Suminoe-ku, Osaka City, Osaka Prefecture O-M Industrial Co., Ltd. (72) Inventor Takashi Nagao Nino, Mizuho-ku, Aichi Prefecture 7-21 Machi Incorporated company Estem

Claims (3)

[Claims] 1. A hot-rolled oxide scale-adhered steel product is pretreated, then immersed in a hot dip galvanizing bath at 430 to 530 ° C. for plating, and then taken out from the plating bath and excessively adhered. In the hot dip galvanizing method for removing zinc, the pretreatment is performed by heating the processed product in an oxidizing atmosphere to burn the deposits, and then in a reducing gas atmosphere.
A hot dip galvanizing method for a steel product on which an oxide scale is attached, which is carried out by a method of reducing at 00 to 800 ° C. and then adjusting the temperature so as to be 560 ° C. or less in a non-oxidizing gas atmosphere. 2. A hydrogen concentration of 2 to 10 as the reducing gas.
The hot-dip galvanizing method for a steel product with an attached oxide scale according to claim 1, wherein a gas consisting of 0% and the balance being nitrogen gas is used. 3. The hot dip galvanizing method for a steel oxide-fabricated steel workpiece according to claim 1, wherein the workpiece is preheated before being reduced in a reducing gas atmosphere.