WO2008078914A1

WO2008078914A1 - Method for producing hot-dip aluminized stainless steel sheet using atmospheric pressure plasma

Info

Publication number: WO2008078914A1
Application number: PCT/KR2007/006720
Authority: WO
Inventors: Jae Hwa Hong; Hyoung Kuk Park; Yong Tae Shin; Ki Jang Oh
Original assignee: Posco
Priority date: 2006-12-27
Filing date: 2007-12-21
Publication date: 2008-07-03
Also published as: KR101372624B1; CN101568663A; KR20080060988A; JP2010514925A

Abstract

The invention relates to a method for producing a hot-dip aluminized stainless steel sheet that improves wettability and adhesion between the stainless steel sheet and aluminum by performing atmospheric plasma processing on the stainless steel sheet and hot-dip aluminizing the stainless steel sheet. A method for producing a hot-dip aluminized stainless steel sheet using an atmospheric plasma according to an aspect of the invention includes heating a stainless steel sheet at predetermined temperature; performing atmospheric plasma processing on the surface of the heated stainless steel sheet; and passing the stainless steel sheet subjected to the atmospheric plasma processing through a hot-dip aluminum plating bath to hot-dip aluminize the stainless steel sheet.

Description

METHOD FOR PRODUCING HOT-DIP ALUMINIZED STAINLESS STEEL SHEET USING ATMOSPHERIC PRESSURE

PLASMA

Technical Field

[1] The present invention relates to a method for producing a hot-dip aluminized stainless steel sheet, and more particularly, to a method for producing a hot-dip aluminized stainless steel sheet that improves wettability and adhesion between the stainless steel sheet and aluminum by hot-dip aluminizing the stainless steel sheet after atmospheric plasma processing on the stainless steel sheet.

[2]

Background Art

[3] A plasma is an ionized gas. Unlike a high-temperature gas that only contains electrically neutral atoms, particles having opposite charges to each other, that is, electrons and nucleuses are mixed with each other in the plasma. The plasma is neutral as a whole. However, in part, an electric field is generated by charge separation b etween cations and electrons and a magnetic field of current is generated by the flow of charge.

[4]

[5] The plasma can be divided into a low-temperature plasma and a high-temperature plasma according to the temperature when the plasma is generated. Also, according to the pressure applied when the plasma is generated, the plasma can be divided into a low-pressure plasma (several mTorr to several Torr) and an atmospheric (up to 760 Torr) plasma. Among them, since the atmospheric plasma is generated at atmospheric pressure, a high-cost vacuum system is not required when generating the low-pressure plasma. For this reason, the atmospheric plasma is being widely used for industrial use.

[6]

[7] Stainless steel itself has excellent corrosion resistance. However, aluminized stainless steel has significantly improved corrosion resistance. The aluminized stainless steel has been judged to be good materials for a vehicle exhaust system or good building materials. Recently, the use of the aluminized stainless steel has been extended to electrodes or separators of a fuel cell. Further, when stainless steel is plated with aluminum or an aluminum alloy, it has excellent heat or corrosion resistance. Therefore, the plated stainless steel has been wieldy used for heat or corrosion resistance. In a case of the heat resistance, the stainless steel plated with the aluminum or the aluminum alloy has been generally used as parts that constitute combustion apparatuses, heating apparatuses, or vehicle exhaust pipes.

[8]

[9] As a method for aluminizing stainless steel, hot-dip plating is one of the most economical methods. However, in general, it is very difficult to aluminize stainless steel by hot-dip plating due to poor wettability between the surface of stainless steel and the molten aluminum. It is generally known that a dense chrome oxide layer formed at the surface of stainless steel reduces wettability between the stainless steel and the molten aluminum.

[10]

[11] In order to solve the problem, various methods and processes are used in the related art. For example, like a Kilbane process, a Boston process, or a Jasper process, each of which is a known process, Japanese Laid-open Publication No. 1995-337022 (published in September 5, 1995) provides a method of hot-dip aluminizing stainless steel by using a process that controls the temperature of the stainless steel before hot- dip aluminizing the stainless steel so as to rigorously control the dew point and components of an atmosphere gas before the hot-dip aluminizing. However, in the above-described process, since the dew point of the atmosphere gas needs to be very rigorously controlled, it is very difficult to satisfy process conditions. That is, in order to reduce the amount of oxygen introduced into the atmosphere gas to the minimum value, an advanced oxygen-scavenging technique needs to be used, and a technique and equipment for preventing penetration of oxygen from the outside into the atmosphere gas need to be used. Since it is difficult to implement the method and the equipment by a general method, it is difficult to apply the method and the equipment to a general hot-dip aluminizing line.

[12]

[13] Further, Korean Patent Publication No. 2005-0104667 (published in November 3,

2005) discloses a method of hot-dip aluminizing stainless steel in an aluminum plating bath. According to the method, the stainless steel is aluminized by controlling partial pressures of nitrogen and hydrogen. Since the partial pressures of nitrogen and hydrogen need to be rigorously controlled, it is difficult to meet process conditions.

[14] In addition, a method for plating stainless steel with nickel or iron having good wettability before aluminizing the stainless steel may be used. However, this method requires additional equipment for plating the stainless steel with an intermediate plating layer first. The use of the additional equipment makes it very difficult to apply the method to a general hot-dip plating line, and also results in an increase in manufacturing costs.

[15] Disclosure of Invention

Technical Problem

[16] An aspect of the present invention provides a method for producing a hot-dip aluminized stainless steel using an atmospheric plasma that improves wettability and adhesion between stainless steel and aluminum by pre-treating the surface of the stainless steel by using the atmospheric plasma and then hot-dip aluminizing the stainless steel.

[17]

Technical Solution

[18] According to an aspect of the present invention, there is provided a method for producing a hot-dip aluminized stainless steel sheet using an atmospheric plasma, the method including: heating a stainless steel sheet at predetermined temperature, performing atmospheric plasma processing on the surface of the heated stainless steel sheet, and passing the stainless steel sheet subjected to the atmospheric plasma processing through a hot-dip aluminum plating bath to hot-dip aluminize the stainless steel sheet.

[19] The method may further include performing atmospheric plasma processing on the surface of the stainless steel sheet before the heating of the stainelss steel.

[20]

[21] The performing atmospheric plasma processing may include generating an atmospheric plasma by applying a direct or alternating power source to a pair of electrodes facing each other with a predetermined interval therebetween and passing the stainless steel sheet between the pair of electrodes where the atmospheric plasma is generated.

[22]

Advantageous Effects

[23] As set forth above, according to the present invention, stainless steel can be aluminized by simply adding an atmospheric plasma processing unit to the existing plating line, and an aluminized stainless steel having excellent wettability and adhesion can be produced by a simple method.

[24]

Brief Description of the Drawings

[25] FIG. 1 is a view illustrating a continuous hot-dip aluminizing process to which the present invention can be implemented;

[26] FIG. 2 is a flowchart illustrating a method for producing hot-dip aluminized stainless steel according to the present invention;

[27] FIG. 3 is an exemplified view illustrating the shape of aluminum on stainless steel before and after performing atmospheric plasma processing according to the present invention; and

[28] FIG. 4 is a view illustrating pictures of stainless steel and results of carrying out an experiment on wettability of molten aluminum before and after performing actual atmospheric plasma processing according to an embodiment of the present invention.

[29]

Best Mode for Carrying Out the Invention

[30] Hereinafter, exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Only, in describing operations of the exemplary embodiments in detail, when it is considered that a detailed description on related well-known functions or constitutions unnecessarily may make essential points of the present invention be unclear, the detailed description will be omitted.

[31] FIG. 1 is a view illustrating a continuous hot-dip aluminizing process to which the present invention can be implemented.

[32] As shown in FIG. 1, stainless steel 10 is subjected to an electrolytic cleaning process in an electrolytic cleaning unit 20 so that foreign materials on the surface of the stainless steel 10 are removed. In this way, the foreign materials on the surface of the stainless steel 10 are removed by the electrolytic cleaning process, such that plating characteristics can be improved in a subsequent process. The stainless steel 10 passing through the electrolytic cleaning unit 20 is input to a preheating and reducing unit 30.

[33] The preheating and reducing unit 30 heats the stainless steel 10 at appropriate temperature before hot-dip aluminizing the stainless steel 10. At this time, reductive gas is preferably used as atmosphere gas. Further, the dew point is controlled to be as low as possible. However, the preheating and reducing process may be differently performed according to the kind, thickness, width, and transfer speed of the stainless steel 10. Therefore, preferably, in consideration of such variables, the optimum conditions are ensured. The stainless steel 10 which is heated by the preheating and reducing unit 30 at the appropriate temperature is put into an aluminum plating bath 50.

[34]

[35] Here, according to an embodiment of the invention, plasma processing units 40 and

41 are provided at an inlet and an outlet of the preheating and reducing unit 30, respectively. The inlet plasma processing unit 40 performs primary plasma processing on the surface of the stainless steel 10 subjected to the electrolyte cleaning process. The outlet plasma processing unit 41 performs secondary plasma processing on the stainless steel 10 before the stainless steel 10 enters the aluminum plating bath 50. At this time, preferably, primary and secondary plasmas 70 are atmospheric plasmas, which are advantageous in terms of the process. Since the plasma is processed at atmospheric pressure, the atmospheric plasma can be easily processed. Further, the atmospheric plasma has the advantage over a high-pressure plasma in terms of required equipment and facilities. The atmospheric plasma processing is performed as follows. A pair of electrodes facing each other at a predetermined interval therebetween are formed. A current is applied to the electrodes to generate the direct or alternating atmospheric plasma 70 between the electrodes. The stainless steel 10 passes between the two electrodes where the atmospheric plasma 70 is generated. In this way, ions by the atmospheric plasma collide against the surface of the stainless steel 10, such that the surface of the stainless steel 10 can be modified.

[36]

[37] Herein, according to another embodiment of the invention, the inlet plasma processing unit 40 may be selectively removed. In this case, the atmospheric plasma processing may be performed only once before the stainless steel 10 enters the aluminum plating bath 50. The atmospheric plasma processing may be performed once or twice according to a result of performing the atmospheric plasma processing.

[38] An AC or DC power source may be used to generate the atmospheric plasma 70 according to the embodiment of the invention. In general, a voltage in the range of 2 to 20 kV is used. A pulsed power source may be used as the DC power source. In this case, in general, the frequency in the range of 1 to 10 kHz is used. The stainless steel 10 passes through the atmospheric plasma 70 generated between the two electrodes, thereby performing the atmospheric plasma processing. When the atmospheric plasma 70 is generated, X-rays are generated together with the atmospheric plasma 70. Therefore, preferably, a shielding device may be installed for safety around a part where the plasma is generated. The shielding device prevents a person from directly seeing the X-rays.

[39]

[40] The atmospheric plasma processing is performed before the stainless steel 10 enters the hot-dip aluminum plating bath 50. Then, the stainless steel 10 is input to the hot- dip aluminum plating bath 50. As such, after subjected to the atmospheric plasma processing, the stainless steel 10 passes through the plating bath 50 so that the stainless steel 10 is aluminized. After the stainless steel 10 is aluminized, the stainless steel 10 escapes from the plating bath 50 in a vertical direction. At this time, air is appropriately sprayed by an air knife 60 to control the plating amount.

[41]

[42] FIG. 2 is a flowchart illustrating a method for producing a hot-dip aluminized stainless steel according to an embodiment of the present invention. [43] Referring to FIG. 2, foreign materials are removed from the surface of the stainless steel 10 by an electrolyte cleaning process (S200). Primary plasma processing is performed on the surface of the stainless steel 10 from which the foreign materials are removed (S202). Then, after the primary plasma processing on the stainless steel 10 is completed, the preheating and reducing unit 30 heats the stainless steel 10 at appropriate temperature in order to aluminize the stainless steel 10 (S204).

[44] Secondary plasma processing is performed on the surface of the heated stainless steel 10 before dipping the stainless steel 10 in the hot-dip aluminum plating bath 50 (S206). When the secondary plasma processing is completed, the stainless steel 10 passes through the hot-dip aluminum plating bath 50, thereby aluminizing the stainless steel 10 (S208).

[45]

[46] According to the embodiment of the invention, preferably, the primary plasma processing and the secondary plasma processing are performed using the atmospheric plasmas 70. To this end, the atmospheric plasma 70 is generated by applying a DC or AC power source to a pair of electrodes facing each other with a predetermined interval therebetween. The stainless steel 20 passes between the two electrodes where the atmospheric plasma is generated. In this way, the atmospheric plasma processing is performed on the surface of the stainless steel 10. In this case, ions by the atmospheric plasma collide against the surface of the stainless steel 10, so that the surface of the stainless steel 10 can be mordified.

[47]

[48] Further, according to the embodiment of the invention, the primary plasma processing may be selectively omitted. That is, the stainless steel 10 may be subjected to the atmospheric plasma processing once before the stainless steel 10 is aluminized in the hot-dip aluminum plating bath 50.

[49] Further, the air knife 60 sprays air onto the surface of the stainless steel 10 that is completely aluminized and escapes from the aluminum plating bath 50 to thereby control the plating amount (S210).

[50]

[51] FIG. 3 is an exemplified view illustrating the shape of aluminum on stainless steel before and after atmospheric plasma processing according to an embodiment of the present invention. FIG. 4 is a view illustrating pictures of stainless steel and results of carrying out an experiment on wettability of molten aluminum before and after performing actual atmospheric plasma processing according to an embodiment of the present invention

[52] First, referring to FIG. 3, the shape of molten aluminum 80 on the stainless steel 10 before and after performing the atmospheric plasma processing according to the embodiment of the invention will be described. Before performing the atmospheric plasma processing, the molten aluminum 80 has a spherical shape due to poor adhesion between the molten aluminum 80 and the stainless steel 10. However, after performing the atmospheric plasma processing according to the embodiment of the invention, the molten aluminum 80 spreads over a wide area because of good adhesion between the molten aluminum 80 and the stainless steel 10. This also can be shown in results of the actual experiment according to the embodiment of the present invention.

[53]

[54] In FIG. 4, according to an embodiment of the invention, electrodes are disposed at front and rear surfaces of the stainless steel 10 while each of the electrodes is separated from the stainless steel 10 by an interval of 4 mm. A pulsed power source of 1 kV having a frequency of 300 Hz is applied to the electrodes to generate an atmospheric plasma. Pictures of the surface of the stainless steel 10 before and after carrying out this experiment are shown in FIG. 4(a). As shown in FIG. 4(a), since a portion subjected to the atmospheric plasma has roughness, the surface reformation occurs. Further, the oxidation of the surface occurs.

[55]

[56] Further, FIG. 4(b) and 4(c) are pictures illustrating results of carrying out an experiment on adhesion and wettability by dropping molten aluminum before and after performing the atmospheric plasma processing under the above-described experimental conditions. In FIG. 4(b), before the atmospheric plasma processing is performed, adhesion and wettability between the stainless steel and the molten aluminum are poor. In FIG. 4(c), after the atmospheric plasma processing is performed, adhesion and wettability between the stainless steel and the molten aluminum are excellent.

[57]

[58] While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

[1] A method for producing a hot-dip aluminized stainless steel sheet using an atmospheric plasma, the method comprising: heating a stainless steel sheet at a predetermined temperature; performing atmospheric plasma processing on the surface of the heated stainless steel sheet; and passing the stainless steel sheet subjected to the atmospheric plasma processing through a hot-dip aluminum plating bath to hot-dip aluminize the stainless steel sheet.

[2] The method according to claim 1, further comprising performing atmospheric plasma processing on the surface of the stainless steel sheet before the heating of the stainless steel sheet.

[3] The method according to claim 1 or 2, wherein the performing atmospheric plasma processing comprises generating an atmospheric plasma by applying a DC or AC power source to a pair of electrodes facing each other with a predetermined interval therebetween and passing the stainless steel sheet between the pair of electrodes where the atmospheric plasma is generated.