KR101004926B1 - Surface treatment method of Steel - Google Patents

Abstract

The present invention relates to a method for treating a surface of steel having excellent corrosion resistance, and the method includes an oxynitriding treatment step of charging a steel material, which has been subjected to a pre-cleaning process, into a furnace and nitriding it, followed by air extraction to take it out of the furnace. Alkali degreasing of the oxynitrided to-be-processed object, followed by a pickling process to release the oxide layer formed in the air-cooling process, and a zinc plating step of trivalent galvanizing the to-be-treated to-be-processed object, and the The galvanized workpiece is characterized by consisting of a chromate step of trivalent chromate post-treatment.

According to the present invention, the nitride layer, the zinc plating, and the chromate layer are formed on the surface of the steel material, and the adhesion of the zinc plating is increased, so that the corrosion resistance is very excellent. Therefore, stainless steel or aluminum, which is an expensive material, is excellent. By replacing steel, the cost of various home appliances can be greatly reduced.

Corrosion Resistance, Steel, Surface Treatment

Description

Surface treatment method of steel with excellent corrosion resistance {Surface treatment method of Steel}

The present invention relates to a method for surface treatment of steel having excellent corrosion resistance, and more particularly, trivalent zinc plating treatment and chromate treatment are sequentially performed after oxynitriding, so that the surface of steel having excellent corrosion resistance can greatly improve the corrosion resistance of steel. It relates to a treatment method.

Generally, stainless steel is mainly used as a material for home appliances such as refrigerators requiring high corrosion resistance and wear resistance, but since stainless steel is excellent in corrosion resistance and expensive, it is necessary to replace it with steel material, which is cheaper in terms of cost reduction. There is this.

Meanwhile, in order to improve corrosion resistance, a surface treatment method of a steel material subjected to chromate treatment in order to further increase corrosion resistance after galvanizing the surface of the steel material has been widely used in various fields.

However, the surface treatment method of the conventional steel plated with zinc plating and chromate treatment improves the corrosion resistance, but the corrosion resistance is significantly lower than that of the stainless steel as a result of the experiment. It is not practical.

Therefore, it is urgently required to develop a method for surface treatment of steel materials having low cost and excellent corrosion resistance so as to replace the stainless steels widely used as materials for home appliances.

The present invention has been made to solve the above-mentioned conventional problems, the object of the present invention is to carry out the nitriding treatment and pickling treatment step in the pre-galvanization step to replace the stainless steel by greatly improving the corrosion resistance through the adhesion of zinc plating It is to provide a method for surface treatment of steel that can be excellent in corrosion resistance.

The present invention for achieving the above object,

An oxynitriding step of charging a steel material, which has been subjected to a pre-cleaning process, into a furnace, followed by nitriding, and taking out of the furnace and air-cooling, and alkali degreasing the oxynitrided to-be-processed object, followed by pickling. A plating pretreatment step of exfoliating the oxide layer formed in the process, a zinc plating step of trivalent galvanizing the pretreated plating object, and a chromate step of trivalent chromate post-treatment of the galvanized workpiece. It is characterized by.

Here, the oxynitriding step is the step of charging the object to the furnace, the step of raising the temperature for 80 to 90 minutes so that the internal temperature is 570 ~ 580 ℃ while injecting the ammonium (NH ₃ ) gas, and Nitriding treatment for 90 to 150 minutes by injecting ammonia (NH ₃ ), nitrogen (N ₂ ) and carbon dioxide (CO ₂ ) gas while maintaining the final temperature of the step of raising the temperature, and 20 to 20 while maintaining the temperature in the furnace. Purging the residual gas for 30 minutes, and the oxidation treatment by taking the nitrified to-be-processed object out of the furnace and air-cooled.

In addition, the pickling treatment in the pre-plating step is 5 to 15 minutes at 40 ~ 60 ℃ using a mixed solution of sulfuric acid 75 ~ 85 ㎖ / L, hydrochloric acid 38 ~ 43 ㎖ / L, degreasing agent 10 ~ 15 ㎖ / ℓ Is preferred.

According to the surface treatment method of the steel material excellent in corrosion resistance according to the present invention,

The nitride layer, zinc plating and chromate layer are formed in multiple layers on the surface of the steel material, and the adhesion of zinc plating is increased, and the corrosion resistance is very excellent. Therefore, by replacing expensive materials such as stainless steel or aluminum steel, There is an effect that can significantly reduce the manufacturing cost of various home appliances.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, if it is determined that the technical features of the present invention may be unnecessarily obscured, as a matter already known to those skilled in the art, such as known functions or known configurations, Detailed description will be omitted.

1 is a process chart of a surface treatment method of a steel material according to an embodiment of the present invention, as shown in the drawings, the surface treatment method of a steel material according to an embodiment of the present invention is an oxynitride treatment step (100) The pre-plating step 200, the zinc plating step 300, and the chromate step 400 are sequentially performed to improve the corrosion resistance of the steel material to be processed.

In the oxynitride treatment step 100, a washing step 110, a temperature raising step 120, a nitriding step 130, a purging step 140, and an air cooling step 150 are sequentially performed.

The washing step 110 is a process for removing substances that interfere with the nitriding treatment, such as foreign matter, cutting oil, rust preventive oil, etc. attached to the steel to be treated, in this embodiment, by using trichloroethylene (TCE, trichloroethylene) Deposition and steam degreasing were performed.

In the temperature raising step 120, the steel material, which is treated through the washing step 110, is charged into the furnace, and the internal temperature is 570 to 580 ° C. for 80 to 90 minutes while injecting ammonium (NH ₃ ) gas. Increase the temperature gradually.

In the nitriding step 130, ammonia (NH ₃ ), nitrogen (N ₂ ), and carbon dioxide (CO ₂ ) gas are injected while maintaining the final temperature in the temperature raising step 120 as it is, for 90 to 150 minutes. Nitride is treated, and thus nitrided layers Fe ₂ N and Fe ₃ N are formed on the surface of the steel material to be processed.

Purging step 140 is a step of purging the residual gas for 20 to 30 minutes while maintaining the temperature in the furnace the same as the nitriding step 130.

The air-cooling step 150 is a step of taking out the workpiece through the nitriding step 130 and the purging step 140 to the outside of the furnace and cooling it until it reaches room temperature. Oxidation treatment occurs by contact of the oxide layer, and thus an oxide layer Fe ₃ O ₄ is formed on the nitride layers Fe ₂ N and Fe ₃ N formed in the nitriding step 130 on the surface of the workpiece.

In the pre-plating step 200, the alkali degreasing step 210, the pickling step 220, and the washing step 230 are sequentially performed.

In the alkali degreasing step 210, foreign matter adhered to the surface of the feature while depositing the treated material for 5 to 15 minutes in a mixed solution of caustic soda 5 to 7 g / l and a degreasing agent 45 to 55 g / l for 5 to 15 minutes. It will degrease to make the surface clean. At this time, the pH of the degreasing solution is preferably 10 ~ 14 and the temperature is preferably 45 ~ 55 ℃.

Pickling treatment step 220 is a step of peeling the oxide layer (Fe ₃ O ₄ ) formed on the surface of the workpiece while passing through the air cooling step (150). To this end, a mixed solution of sulfuric acid 75 to 85 ml / l, hydrochloric acid 38 to 43 ml / l, and a degreasing agent 10 to 15 ml / l is preferably used, and pickling is preferably performed at 40 to 60 ° C. for 5 to 15 minutes.

The water washing step 230 is a step of washing the surface of the object to be treated using pure water.

After the oxynitride treatment step 100 and the pre-plating step 200 as described above, the zinc plating step 300 to process the trivalent zinc plating on the object to be processed is carried out, after the zinc plating itself In order to further improve the corrosion resistance of the chromate treatment to perform a chromate step 400 is further proceeded. Zinc plating and chromate treatment are well known, and thus a detailed description of the process will be omitted.

Figure 2 shows the surface layer of the steel material surface treated according to the present invention described above, the surface of the steel material (a) is a diffusion layer (b) and the adsorption of nitric oxide (NO) is adsorbed on the iron surface in the nitriding step and diffused inside A nitride layer (c, Fe ₂ N, Fe ₃ N), which is a porous layer, is formed at the bottom and a zinc plating / chromate layer d is formed at the top. Therefore, since the nitride layer (c) and the zinc plating / chromate layer (d) are sequentially formed, not only the corrosion resistance is improved, but also the zinc plating / chromate layer (d) is formed on the nitride layer (c), which is a porous layer. Adhesion per unit area of zinc plating is increased, resulting in more excellent corrosion resistance.

According to the present invention having the above-described configuration, the surface treatment was performed in detail.

First, the cold rolled steel to be treated was subjected to a washing process by depositing and degreasing using 111-TCE.

Thereafter, the mixture was charged into a furnace and subjected to a temperature raising step for 90 minutes, followed by nitriding at 575 ° C. for 120 minutes, purging for 30 minutes while maintaining 575 ° C., and then taken out of the furnace and cooled in external air. Nitriding process was carried out.

Thereafter, an alkaline degreasing process was performed at 53 ° C. for 10 minutes at a concentration of PH12.9, and a pickling treatment process was performed at 54 ° C. for 10 minutes.

Thereafter, after washing with water twice in the first and second times, the zinc plating process and the chromate process were sequentially performed.

The results of the corrosion resistance test of the cold rolled steel surface treated through the above process are compared with the conventional galvanized and chromate treated cold rolled steel as shown in Table 1 below.

And the surface state when the 96 hours of the actual treatment by the conventional surface treatment method according to the test result is shown in Figure 3a, the surface state of 456 hours after the actual treatment by the surface treatment method according to the present invention is shown in Figure 3b Each is shown for comparison.

Surface treatment method

Corrosion Resistance Test Conditions
Test result
Galvanized + Chromate
(Comparative Example)


Salt Spray Test
(5% brine, 35 ° C,
8Hr spray, 16Hr pause)


White blue at 96Hr.
Oxidation + Zinc Plating + Chromate
(Example)


White blue at 456 Hr.

As can be seen from the test results shown in Table 1 and FIG. 3A / B, the surface treatment method according to the present invention is 4.8 times better in corrosion resistance than the conventional surface treatment method using zinc plating and chromate treatment.

Table 2 below compares the surface treatment method according to the present invention with other metal materials. The corrosion resistance test results are the same under the same conditions as the corrosion resistance test conditions of Table 1.

division
Symbol
Surface treatment method
Corrosion resistance
Test result
Cost (KRW / ㎏)
Example

Iron
Cr (cold rolled steel)
Oxidation + Zinc Plating
+ Chromate
456
1600
Comparative Example 1

Iron
Cr (cold rolled steel)
Galvanized + Chromate
96
1400
Comparative Example 2
Stainless steel
STS304

-
264
5200
Comparative Example 3
Stainless steel
STS430

-
240
2400
Comparative Example 4
Aluminum
ALDC12

Anodizing
(Anodizing)
100
2900
Comparative Example 6
Zinc-based
ZNDC8
-
124

3100

As shown in Table 2, according to the surface treatment method of the steel according to the present invention, the corrosion resistance is much better than that of stainless steel, aluminum metal and zinc metal, and the cost is relatively very low. When the surface treatment method of the steel material according to the present invention is replaced by replacing the metal or aluminum metal, the cost can be greatly reduced while further increasing the corrosion resistance.

The surface treatment method of the steel material excellent in corrosion resistance according to the present invention has been described above, but the technical scope of the present invention is not limited to the contents described in the above-described embodiments, and should be understood by those skilled in the art. It will be understood that modifications or equivalent equivalent constructions do not depart from the spirit of the present invention.

1 is a process chart of the surface treatment method of the excellent corrosion resistance steel according to an embodiment of the present invention,

2 is a view showing a surface layer of a steel material surface-treated according to the present invention,

Figure 3a is a view showing the surface state after 96 hours of the test object to be treated by the conventional surface treatment,

Figure 3b is a view showing the surface state after 456 hours to test the treated material in accordance with the present invention.

Claims (3)

An oxynitride treatment step of charging the steel material, which has been subjected to a pre-cleaning process, into a furnace and nitriding the same, and then taking it out of the furnace to air-cool it; An alkali degreasing treatment of the oxynitriding target to be treated, followed by a pickling treatment to exfoliate the oxide layer formed in the air cooling process; A zinc plating step of trivalent galvanizing the treated material to be plated; And And a chromate step of subjecting the galvanized workpiece to trivalent chromate post-treatment. The method of claim 1, The oxynitride treatment step, Charging the object to a furnace, and then raising the temperature for 80 to 90 minutes while injecting ammonium (NH ₃ ) gas such that the internal temperature becomes 570 to 580 ° C; Nitriding for 90 to 150 minutes by injecting ammonia (NH ₃ ), nitrogen (N ₂ ) and carbon dioxide (CO ₂ ) gas while maintaining the final temperature of the step of raising the temperature; Purging the residual gas for 20 to 30 minutes while maintaining the temperature in the furnace; And oxidation treatment by taking the nitrified object to be processed out of the furnace and air cooling it. The method according to claim 1 or 2, Pickling treatment in the pre-plating step, Using a mixed solution of sulfuric acid 75 ~ 85 ㎖ / L, hydrochloric acid 38 ~ 43 ㎖ / L, degreasing agent 10 ~ 15 ㎖ / L for 5 to 15 minutes at 40 ~ 60 ℃ Surface treatment method.

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