KR20120074068A - Surface treatment method for high strength steel and coating method - Google Patents

Abstract

PURPOSE: A high-strength steel surface treatment method and a plating method are provided to improve platability by removing oxides rapidly though the power of CW(Continuous Wave) laser is low and the irradiation speed of CW laser is rapid. CONSTITUTION: A high-strength steel surface treatment method is as follows. A high strength steel including one or more Mn(Manganese)/Al(Aluminum)/Si(Silicon) based oxides is supplied. CW laser having lower than 1064nm wavelength is irradiated to the surface of a high strength steel to remove an oxide coating film.

Description

Surface Treatment Method For High Strength Steel And Coating Method

The present invention relates to a surface treatment method and a plating method of high strength steel, and specifically, a surface of a high strength steel for removing at least one of Mn oxide, Al oxide, and Si oxide formed on the surface during annealing of the high strength steel through a laser. It is about a processing method and a plating method.

Recently, advanced high strength steels with a tensile strength of 490 MPa or more, such as TWIP steel (TWinning Induced Plasticity Steel) or TRIP (TRransformation Induced Plasticity Steel), have been developed.

However, such AHSS forms Si / Mn / Al-based oxides of several tens to hundreds of nm as the Si / Mn / Al contained in the high-strength steel is diffused on the surface of the steel sheet during annealing. Such Si / Mn / Al type oxide prevents adhesion of molten zinc during hot dip galvanizing and causes unplating.

As can be seen from the surface analysis and depth profile of the TWIP steel shown in FIGS. 1A and 1B, it can be seen that Mn oxide and Al oxide exist on the surface of the TWIP steel to prevent zinc from adhering to the TWIP steel.

On the other hand, FIGS. 2A and 2B show surface analysis and depth profiles of TRIP steel. It can be seen that the Si-based oxide and the Mn-based oxide exist on the surface of the TRIP steel, and due to the Si- and Mn-based oxides, the TRIP steel is also difficult to be galvanized like the TWIP steel.

Since zinc plating has an electrochemical protection effect of steel, if it is not galvanized, it is not suitable for an external frame due to its low corrosion resistance, so that the high strength TWIP steel or TRIP steel cannot be used as an external frame despite the high rigidity. There is.

Accordingly, there is a request for technology development to remove Si / Mn / Al-based oxides on the surface of AHSS. In this regard, attempts have been made to remove Si / Mn / Al-based oxides from the surface of AHSS in various ways or to prevent the formation of Si / Mn / Al-based oxides, but no results have yet been made.

In particular, the Si / Mn / Al oxide film is arranged in the form of islands or networks on the surface of the high-strength steel, it is difficult to remove it.

The present invention is to solve the above problems, specifically, to remove the one or more of the Mn-based oxides, Al-based oxides, and Si-based oxides of the surface generated when heating high-strength steel to make the plating possible It is done.

Moreover, an object of this invention is to provide the surface treatment method and plating method which can be plated by a continuous process after annealing.

The present invention provides a surface treatment method of high strength steel as follows to achieve the above object.

The present invention comprises the steps of supplying a high-strength steel formed with at least one of Mn oxide, Al oxide, Si-based oxide; It provides a high-strength steel surface treatment method comprising a laser treatment step of irradiating a CW laser having a wavelength of 1064nm or less to the surface of the high-strength steel to remove the oxide film.

In this case, the laser spot irradiated from the laser treatment stage may have a spot size of 50 μm or less.

The method may further include an atmosphere forming step of supplying nitrogen to form a nitrogen atmosphere to prevent carbonization of the surface of the base material before the laser treatment step.

Furthermore, the present invention is a plating method for annealing and galvanizing high strength steel, and between the annealing and zinc plating, the above-described method for surface treatment of high strength steel can be performed.

The present invention makes it possible to plate by removing one or more of the Mn-based oxides, Al-based oxides, and Si-based oxides of the surface generated when heating the high-strength steel through the above configuration.

In addition, the present invention provides a surface treatment method and a plating method capable of plating in a continuous process after annealing.

1A and B are graphs illustrating surface analysis and depth profiles of TWIP steels.
2A and B are graphs illustrating the surface analysis and depth profile of TRIP steel.
3 shows an example of a surface treatment apparatus for removing an oxide film of high strength steel with a plasma irradiation apparatus.
4A and 4B are graphs showing the surface analysis and the depth profile of the TWIP steel when the plasma was irradiated for 1 second at a distance of 3 mm from the base metal with a 350W atmospheric pressure plasma irradiation apparatus.
FIG. 5 is a graph showing the depth profile of the TWIP steel when the plasma was irradiated for 20 seconds at a distance of 3 mm from the base metal with a 350 W atmospheric plasma irradiation apparatus.
6A and 6B show an example of a plasma generator for irradiating plasma and arc together.
7A and 7B are graphs showing surface analysis and depth profiles of TWIP steel when the plasma and the arc are irradiated with the atmospheric pressure plasma irradiation apparatus.
8A and 8B are graphs showing surface analysis and depth profiles of TRIP steel when the plasma and the arc are irradiated with the atmospheric pressure plasma irradiation apparatus.
9 is a schematic diagram of a surface treatment apparatus for removing an oxide film from high strength steel with a laser irradiation apparatus.
10A and 10B are graphs illustrating surface analysis and depth profiles of TWIP steel after examining the surface of the TWIP steel with a seedable oil laser 25W.
FIG. 11A is a surface photograph when irradiating a pulse laser in an air atmosphere, and FIG. 11B is a surface photograph when irradiating a pulse laser in a nitrogen atmosphere.
12A is a schematic diagram of a conventional zinc plating process, and FIG. 12B is a schematic diagram of a zinc plating process according to the present invention.
13 is a partial cross-sectional view of the sealing roll in the galvanizing process according to the present invention.

Conventionally, a technique for removing the Fe oxide layer on the surface of a steel sheet using a laser has been proposed. However, unlike the Fe oxide layer on the surface of the steel sheet, the oxide layer generated on the surface of the high-strength steel during the annealing process is formed in the form of islands (TWIP steel) or network (TRIP) in a thin layer of about tens to hundreds of nm. In addition, since Si / Mn / Al-based oxides have a ten times more bonding force than Fe oxide layers, a new approach is needed to remove the oxides.

Thus, a method of removing Si / Mn / Al-based oxides using a plasma, a laser, or a plasma and a laser is invented. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and analytical data.

In the present invention, the Si / Mn / Al-based oxide, oxide film, oxide layer means an oxide, oxide film, oxide layer containing at least one of Si-based oxide, Mn-based oxide, Al-based oxide.

Si / Mn / Al based oxide removal using plasma

The surface treatment apparatus used in the present invention is shown in FIG. The plasma generator 20 was disposed above the base material S of the support part 25, and was configured such that the plasma P from the plasma generator 20 could be irradiated onto the base material surface.

In the plasma generator 20, the plasma P decreases as the distance l from the plasma generator 20 increases, and when the temperature of the plasma P decreases, the plasma P decreases. ) Provides energy to the base material S. In the present invention, the distance (L) between the plasma generator 20 and the base material (S) in the plasma generator 20 of the same output (350W) was investigated using this point, the irradiation results are shown in Table 1 below. Is shown. At this time, the base material (S) used TWIP steel.

Model Distance to base material (L) Survey time Plating quality improvement after plasma irradiation Inventory 1 1mm 1 sec ○ Inventory 2 3mm 1 sec △ Inventory 3 3mm 20 seconds ○ Comparative Example 1 6 mm 1 sec ×

In the above table, the improvement of plating quality after plasma irradiation means that the zinc plating quality is improved compared to before plasma irradiation when zinc-coated specimens are plasma-plated, and '○' is a marked improvement, '△' Is a slight improvement, and '×' means no improvement.

As shown in the above table, even when the plasma of the same output, even if the distance (L) between the plasma (P) and the base material (S) is close, it was confirmed that the plating property is improved after the plasma (P) is irradiated.

However, when the distance L from the base material S became far, even if plasma P was irradiated, plating property did not improve. In the plasma generator 20 used in the present experiment, when the distance from the base material S was 6 mm or more, the temperature of the plasma P was 200 ° C. or lower. Therefore, the plasma P should be at least 200 ° C. at the surface of the base material. It can be seen that through the Si / Mn / Al base oxide can be removed through.

However, when the temperature of the plasma exceeds 900 ℃, since the damage to the base material due to the plasma, the temperature of the plasma at least on the surface of the base material is preferably up to 900 ℃.

4A and 4B show graphs showing the surface analysis and depth profile of the TWIP steel when the plasma was irradiated for 1 second at a distance of 3 mm from the base metal with a 350 W atmospheric plasma irradiation apparatus (Invention Example 2 in Table 1). It is. Although not significantly different from the surface analysis and depth profile (see FIGS. 1A and B) of the TWIP steel before irradiation, it can be seen that the amount of Mn and Al oxides on the surface was reduced.

Specifically, FIG. 4A shows that the amplitudes of Mn1 and Al2 are smaller than those of FIG. 1A, but the amplitude of Fe3 is increased. When the plasma is irradiated for 1 second at a distance of 3 mm from the base metal with an atmospheric plasma irradiation apparatus, the Mn / Al oxide is Decreases and Fe is exposed to the surface instead.

In addition, as can be seen by comparing the depth profiles of FIGS. 4B and 1B, the fraction of Mn1 and Al2 in the early sputter time (surface) decreases when the plasma is irradiated for 1 second at a distance of 3 mm from the base material using an atmospheric pressure plasma irradiation apparatus. Therefore, it can be seen from this that the Mn / Al-based oxide on the surface of the base material was reduced. That is, since the fraction of Mn / Al was relatively reduced compared to the Fe fraction, it can be seen from this that the Mn / Al-based oxide on the surface of the base material was reduced.

For reference, in the surface analysis and the depth profile of the present invention, 20 μm × 20 μm specimens were analyzed. In the depth profile, the sputter rate was 0 to 15 minutes at 1.5 nm / minute and 15 to 30 minutes at 4.5 nm / minute. The invention is the same for all surface analysis and depth profiles.

In addition, FIG. 5 shows a graph showing the depth profile of the TWIP steel when the plasma was irradiated for 20 seconds with a distance of 3 mm from the base metal with a 350 W atmospheric plasma irradiation apparatus (Invention Example 3 in Table 1). Looking at the graph of Figure 5 it can be seen that the Mn / Al-based oxide is reduced compared to the Figure 4b.

That is, when compared to Figure 1b, Figure 1b, it can be clearly seen that the Mn / Al-based oxide is reduced, as shown in Figure 5 of Al oxide it can be seen that significantly reduced in the surface, Mn oxide also significantly reduced. On the other hand, it can be seen that the fraction of Fe on the surface is greatly increased (Fe in Figure 1b is rarely present on the surface, but in Figure 5 can be seen more than 15% Fe). This is due to the irradiation of the plasma, Mn / Al-based oxide is evaporated to remove from the surface, the Fe inside.

In the present invention, in order to prevent carbonization during plasma irradiation, the plasma generator uses nitrogen gas as a feeding gas. In addition, the experiment was conducted in an atmospheric atmosphere without forming a separate atmosphere.

Removal of Si / Mn / Al Oxides Using Plasma and Plasma Arc

In the experiment, the plasma arc was generated around the nozzle. In general, since the plasma arc can damage the surface of the base material and the plasma arc is generated only around the plasma nozzle, the plasma arc can be irradiated only when it is very close to the plasma generator, so it is not usually used with the plasma.

In the case of Si / Mn / Al-based oxide on the surface of high strength steel, it is formed in an island or network shape on the surface, which means that the oxide layer is located at a relatively high position relative to the base material surface. In the case of plasma arc, since it is supplied to a high position similar to lightning, this point was utilized to remove the plasma arc energy for the Si / Mn / Al-based oxide.

In addition, in the case of the plasma arc, the experimental plasma generator (output: 350 W) is generated only around the plasma nozzle, so that the base material is grounded to the cathode, thereby accelerating ions to maximize the ion bombardment effect, and the plasma arc surface of the base material. Pulled down.

6A shows a surface treatment apparatus for irradiating a plasma, and FIG. 6B shows a surface treatment apparatus for irradiating a plasma arc together with a plasma.

As shown in FIG. 6A, in the general plasma generator 20, the plasma arc A is irradiated only up to a short distance l1 as compared to the plasma irradiation distance. However, in FIG. 6B, the base material S is grounded to the cathode 30. Accordingly, the plasma P is accelerated, and the distance l2 at which the plasma arc is irradiated is increased along with the plasma acceleration.

At this time, nitrogen gas was used as the feeding gas of the plasma generator 20 to prevent oxidation on the surface of the base material.

7A and 7B are graphs showing the surface analysis and the depth profile of the TWIP steel when the plasma and the arc were irradiated with the 350 W atmospheric plasma irradiation apparatus for 10 seconds.

In contrast to the results of the surface analysis of the TWIP steel before irradiation, Figure 7a, b compared with the results of Figure 1a, b, it can be seen that Mn was reduced by about 66% by irradiation for 10 seconds, Al for approximately 10 seconds by irradiation It can be seen that about 90% is reduced. In addition, in FIG. 7B, the atomic fraction of Mn and Al on the surface was greatly reduced, and the atomic fraction of Fe was increased.

This is similar to the result obtained by irradiating the plasma only for 20 seconds, and it can be seen that the irradiation time can be greatly reduced when the plasma arc is used together with the plasma. In the case of irradiating plasma and plasma arc together, it is possible to remove sufficient Si / Mn / Al-based oxides with only a short time of irradiation, so that a device for irradiating the plasma and plasma arc together on the strip during the continuous process is provided. It can be performed continuously until. A specific zinc plating process will be described later.

Similarly to Figs. 7A and 7B, the results of irradiating the plasma arc with the plasma on the TRIP are shown in Figs. 8A and 8B.

In contrast to the results of FIGS. 8A and 8B, which are the surface analysis results of the TRIP steel before irradiation, Si and Mn were irretrievably reduced in the graph by irradiating the plasma and the plasma arc together for 10 seconds. . In addition, in FIG. 8B, the atomic fractions of Mn and Si on the surface were greatly reduced, and the atomic fractions of Fe were increased. In addition, since Fe appeared on the surface, the plating property of the TRIP steel was increased after irradiation.

In order to ground a base material by a cathode, it is also possible to ground the base material directly, but the support part which supports a base material consists of a conductive member, and the method of grounding a support part is more preferable. By grounding the support in this way, the base material can be freely moved or placed.

Laser Removal of Si / Mn / Al-based Oxides

In the present invention, in order to remove the Si / Mn / Al-based oxide, a laser was irradiated to the base material, Figure 9 shows a surface treatment apparatus including a laser irradiation apparatus according to the present invention.

As shown in FIG. 9, the surface treatment apparatus disposed the laser generator 10 above the base material S of the support part 25 and irradiated a laser to the surface of the base material, and moved the laser generator 10 to move the surface of the base material surface. The laser L was irradiated at a constant speed with respect to the predetermined area. After the laser was irradiated, the surface of the irradiated specimen was analyzed and then galvanized.

Table 2 below and Figure 10a, b shows the experimental results.

Model Laser type Output (W) Count speed
(mm / s) Plating quality improvement after laser irradiation Honorable 4 Pulse laser 35 250 ○ Inventory 5 Continuous Laser 25 3000 ○ Comparative Example 2 Pulse laser 24 3000 × Comparative Example 3 Pulse laser 22 3000 × Comparative Example 4 Pulse laser 18 3000 ×

Nd YAG 1064nm pulse laser (Pulse) and seed laser (Continuous Laser) was alternately tested as a laser, and the experiment was performed while changing the output and the irradiation speed.

In the above table, the improvement of plating quality after laser irradiation means that the zinc plating quality is improved compared to before laser irradiation when zinc-coated specimens are laser-plated, and '○' is a marked improvement. Means no improvement.

As can be seen in [Table 2], in the case of the pulse laser used to remove the Fe oxide due to the impact amount, the oxide could be removed when the output was large and the irradiation speed was low. It was confirmed that the plating property was improved even when the irradiation speed was low and fast.

Therefore, it can be seen that the high power 1064nm Nd YAG pulse laser and the 1064nm Nd YAG double oil laser can remove the Si / Mn / Al oxide.

In particular, when the laser having the same output power was used, the seedable oil laser (Invention Example 5) was significantly different in the plating property improvement compared to the pulse laser (Comparative Example 2). It is advantageous for removing / Mn / Al oxide.

In addition, in the case of a seed oil laser, it is possible to irradiate a laser beam with a laser beam, so that the width can be irradiated at one time. Therefore, the seed oil can be used for surface treatment of a strip during a continuous process.

10a and b show graphs illustrating the surface analysis and depth profile of a TWIP steel after examining the surface of the TWIP steel with a seedable oil seed oil.

Compared with the results of the surface analysis of the TWIP steel before the irradiation of Figures 10a and b, it can be seen that the Al oxide layer was almost removed from the surface, Mn also significantly reduced (see Figure 10a) ). In addition, as shown in Figure 10b, it can be seen that exceeding 10%, which was only the atomic fraction 5% level before irradiation, it can be seen that the Fe layer on the surface of the TWIP steel by the seed oil laser irradiation.

11A shows the surface of the steel sheet when the laser is irradiated in an ambient temperature atmosphere. As shown in FIG. 11A, when the laser is irradiated in an atmospheric atmosphere, a carbonization layer is generated on the surface of the steel sheet due to carbonization, which later adversely affects the plating performance during zinc plating.

In FIG. 11B, the surface of the steel sheet is shown when the laser is irradiated in a nitrogen atmosphere. As shown in FIG. 11B, no carbonization occurred when the laser was irradiated in a nitrogen atmosphere, resulting in a clean surface, which is advantageous for zinc plating.

In addition, the spot size of the laser is preferably set to 1 mm or less or in the case of a laser beam, the laser beam width is 1 mm or less. When the steel sheet was irradiated with different spot sizes of the laser in the same atmosphere, that is, in the atmospheric atmosphere, carbonization did not occur even in the atmospheric atmosphere in the spot size of the laser of 1 mm or less. Therefore, it is considered that carbonization can be prevented when the spot size is set to 1 mm or less even in a nitrogen atmosphere.

In addition, experiments were performed while changing the wavelength of the laser to 1064 nm, 532 nm, and 355 nm, and it was confirmed that the Si / Mn / Al oxide was removed at all of the 1064 nm, 532 nm, and 355 nm. However, in terms of energy efficiency, the laser wavelength is preferably 1064 nm.

Applied to galvanizing process

12A shows a conventional zinc plating process.

The steel sheet 100 of the cold rolled coil is continuously heated through a pay-off reel (not shown) and a welding machine (not shown), and heat-treated in the annealing facility 110 that rises to a maximum temperature of 700 ° C. to 800 ° C. to remove residual stress. The heated steel sheet 100 is introduced into the plating bath 130 filled with the plating liquid, that is, the molten zinc 130a while being maintained at a suitable temperature for zinc plating.

At this time, the equipment connected between the annealing equipment 110 and the plating bath 130 of the galvanizing equipment, the snout 120 is provided to prevent surface oxidation due to exposure of the steel sheet heat-treated at high temperature to the atmosphere (snout) )to be. The inside of the known snout 120 is filled with an inert gas to prevent plating failure of the steel sheet by surface oxidation.

In addition, the plated steel sheet 100 passing through the heating furnace 110, the snout 120, and the sink roll 132 and the stabilizing rolls 134 of the plating bath 130 may be disposed directly above the plating bath. In the knife 140, the demand is adjusted to the desired plating amount.

Then, the plated steel sheet after the plating amount adjustment is completed is subjected to a temper rolling mill (not shown), cut by a cutter (not shown) through proper surface roughness and shape correction, and then wound on a tension reel (not shown) to obtain final plating. It is produced as a coil product.

In the high-strength steel, the Si / Mn / Al-based oxide film is formed on the surface during heat treatment during annealing, so the zinc plating process for high strength steel of the present invention in which a surface treatment apparatus is disposed in the snout between the annealing facility and the zinc plating facility is illustrated. It is shown in 12b. Since the galvanizing process of the present invention is disposed in the snout, it is possible to apply only by changing the snout in the conventional equipment, so the utilization is high.

The steel sheet 200 of the high-strength steel (for example, TWIP, TRIP) coil is continuously passed through a pay-off reel (not shown) and a welding machine (not shown), and heat-treated in the annealing facility 210 while Si / Mn / Al The oxide film is formed, and the steel sheet 200 on which the oxide film is formed passes through the surface treatment facility disposed inside the snout 220 and then is introduced into the plating bath 230 filled with the molten zinc 230a of the zinc plating facility.

Since the surface treatment facility 300 has to continuously surface-treat the surface of the steel sheet 200 which is continuously supplied, the plasma generating apparatus may remove the Si / Mn / Al-based oxide film formed on the surface of the high strength steel sheet in a short time. 310 and 311 and laser generators 320 and 321 are disposed on both surfaces, respectively. The windows 322 and 323 are installed in the middle of the laser light emitted from the laser generators 320 and 321, and a pump 336 for supplying a feeding gas is connected to the plasma generators 310 and 311.

Unlike the TWIP steel, in which the Mn / Al oxide film is formed at about 150 nm to 200 nm, the thickness of the Si / Mn oxide film is 50 nm or less in the case of TRIP steel, so that the laser generators 320 and 321 may vary depending on the grade of the steel species and the oxide. It may not be mounted.

Sealing rolls 342 and blocking portions 340 for fixing them are formed at both sides of the surface treatment facility 300 to separate spaces inside and outside the surface treatment facility 300, and to lift from the plating bath 230. To block the ingress of zinc vapor and foreign substances.

In the surface treatment facility 300, a nitrogen gas communication port 330 is formed on an outer wall thereof, and a pump 332 and a nitrogen gas storage part 333 are connected to the nitrogen gas communication hole 330. The pump 332 may supply nitrogen from the nitrogen gas storage unit 333 into the surface treatment facility 300 to initially form a nitrogen atmosphere.

On the other hand, an inlet 335 is formed on the outer wall of the blocking unit 340 or the surface treatment facility 300 to inhale nitrogen gas therein. In this inlet 335, nitrogen supplied from the nitrogen gas communication port is a high-temperature steel sheet. The high temperature nitrogen gas heated by 200 is sucked in. A pump 336 may be connected to the suction port 335 to suck nitrogen gas, and the sucked nitrogen gas may be supplied to the feeding gas of the plasma generators 310 and 311 or may be discharged to the outside.

In addition, since the sucked gas includes Si / Mn / Al-based oxide gas evaporated from the surface of the steel sheet 200, the sucked gas may be supplied to the plasma generators 310 and 311 after being collected. If necessary, the sucked gas is sent to a treatment facility, and nitrogen gas from the nitrogen gas storage unit 333 may be supplied to the plasma generator.

Since the pump 336 connected to the suction port 335 supplies high temperature nitrogen gas to the plasma generators 310 and 311, the plasma generators 310 and 311 provide higher nitrogen gas at room temperature than the feeding gas. The plasma of energy can be irradiated. Therefore, the performance of the high output plasma generator can be obtained through the low output plasma generator.

The suction port 335 may not only supply the feeding gas of the plasma generating apparatuses 310 and 311, but also simultaneously maintain the pressure inside the surface treatment facility 300 to be lower than atmospheric pressure. By maintaining the pressure inside the surface treatment facility 300 lower than atmospheric pressure, the plasma irradiation distance and the plasma arc irradiation distance of the plasma generating apparatuses 310 and 311 are increased, which is caused by the fluctuation of the steel plate 200. The 310 and 311 and the steel plate 200 are prevented from colliding or rubbing.

In addition, a sensor 360 for measuring the internal pressure is disposed in the surface treatment facility 300 to measure the internal pressure in real time to provide an internal pressure value to the controller 390.

The controller 390 is connected to the plasma generators 310 and 311, the laser generators 320 and 321, the pumps 332 and 336, and the sensor 360, and inputs information about the sensor 360 and the steel grade. And the plasma generators 310 and 311, the laser generators 320 and 321, and the pumps 332 and 336 in accordance with the user's operation.

In addition, the sealing roll 342 is made of a chargeable material, and the ground terminal 343 is mounted on the roll out 341 of the sealing roll 342 (see FIG. 13), and the ground terminal is grounded with a negative electrode. Accordingly, the steel sheet 200 entering the surface treatment facility 300 while contacting the sealing roll 340 and the sealing roll 340 is negatively grounded.

When the steel sheet 200 is not negatively grounded, the distance of the plasma arc irradiated from the plasma generators 310 and 311 becomes relatively shorter than when grounded. Therefore, in order to irradiate the plasma arc on the surface of the steel sheet 200, the distance between the steel sheet 200 and the plasma generators 310 and 311 should be maintained at a relatively narrow distance, but the steel sheet 200 may cause fluctuations during transportation. When the plasma generators 310 and 311 are arranged at such a narrow distance, physical friction or collision with the steel plate 200 cannot be avoided, and therefore, it is difficult to irradiate the steel plate with the plasma arc.

In the embodiment of the present invention, although the sealing roll 340 is used as the grounding roll, it is also possible to include a roll in contact with the steel sheet 200 inside the surface treatment facility, and to mount the ground terminal on the roll shaft of the roll to plate the steel sheet. Do.

 In the surface treatment facility 300, the plasma generators 310 and 311 have a temperature of 200 to 900 ° C. irradiated to the steel sheet, and are spaced apart from the steel sheet so that the plasma arc may be irradiated together. Since the steel sheet 200 is grounded to the cathode, the plasma arc may be irradiated with the plasma from the plasma generators 310 and 311 onto the steel sheet. Therefore, the oxide film formed on the surface of the steel sheet 200 can be removed quickly.

The plasma generating apparatuses 310 and 311 are preferably arranged in plural numbers so that the plasma and the plasma arc can be irradiated to the entire width of the steel sheet at one time.

In the present invention, the laser generators 320 and 321 irradiate a laser beam parallel to the width direction of the steel sheet 200. At this time, the laser beam is irradiated with 1064nm Nd-YAG double oil laser to quickly remove the oxide film formed on the surface of the steel sheet. In addition, the width of the laser beam is preferably 1 mm or less so as to prevent carbonization.

In addition, in the present invention, the laser irradiation unit 320, 321 is disposed so that the laser irradiated portion and the plasma generator 310, 311, the portion where the plasma is generated. Therefore, it is possible to continuously remove the oxide film formed on the surface of the steel sheet that is rapidly passed through the laser beam, the plasma, and the plasma arc at one point of the steel sheet 200.

In the present invention, it is preferable that the inside of the surface treatment facility 300 is maintained at 800 ° C. or lower, because an additional heating device is required when the surface treatment facility is maintained at 800 ° C. or higher. In addition, in the present invention, it is preferable that the inside of the surface treatment facility 300 is maintained at a temperature of 200 ° C. or higher, which means that the steel sheet 200 introduced into the zinc bath 230 should have a temperature of about 460 ° C. If the temperature inside the 300 is low, it is because the temperature of the steel sheet 200 drawn into the zinc bath 230 through the additional temperature raising device to increase the temperature.

The zinc plating process of the present invention is as follows.

The steel sheet 200 released from the coil passes through the annealing facility 210 and then flows into the surface treatment facility 300. The steel sheet 200 is grounded to the cathode by the sealing roll 342 while passing through the sealing roll 342 separating the inside and the outside of the surface treatment facility 300. The interior of the surface treatment facility 300 is maintained at a low pressure (below atmospheric pressure) nitrogen atmosphere through feedback control by the suction port 335, the nitrogen gas communication port 330, and the sensor 360.

In a low pressure nitrogen atmosphere, the steel sheet 200 is irradiated with a laser beam, a plasma, and a plasma arc on both surfaces. Accordingly, the Si / Mn / Al-based oxide film formed on the surface of the steel sheet 200 in the annealing facility 210 is removed, and the surface of the steel sheet 200 is surface treated through the sealing roll 342 in a state capable of galvanizing. Exit facility 300.

Thereafter, the steel sheet 200 passing through the surface treatment facility 300 is introduced into the plating tank 230, and the plated steel sheet passing through the sink roll 232 and the stabilizing rolls 234 of the plating tank 230 ( 200 is adjusted to the amount of plating desired by the demand in the air knife 240 disposed directly above the plating bath.

Next, the plated steel sheet after the plating amount adjustment is completed is subjected to a temper rolling mill (not shown), cut by a cutter (not shown) through proper surface roughness and shape correction, and then wound on a tension reel (not shown) to obtain final plating. Produced as a coiled product.

200: steel sheet 210: annealing equipment
220: snout 230: plating bath
240: air knife 300: surface treatment equipment
310, 311: plasma generator 320, 321: laser generator
330: nitrogen gas communication port 340: blocking unit
342: sealing roll 360: sensor
390: control unit

Claims (4)

Supplying a high strength steel on which at least one of an Mn oxide, an Al oxide, and an Si oxide is formed;
And a laser treatment step of irradiating a CW laser having a wavelength of 1064 nm or less on the surface of the high strength steel to remove the oxide film. The method of claim 1,
The laser beam irradiated from the laser treatment stage has a spot size of 1 mm or less, the surface treatment method of high strength steel. The method of claim 2,
And forming an atmosphere of nitrogen by supplying nitrogen to prevent carbonization of the surface of the base material before the laser treatment step. Plating method of annealing high strength steel and galvanizing
A plating method, characterized in that between the annealing and zinc plating, a method for surface treatment of the high strength steel according to any one of claims 1 to 3 is performed.

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