KR100902216B1 - Method of manufacturing a hot dip galvanizing steel sheet containing Si - Google Patents

Abstract

The present invention is a method of manufacturing a hot-dip galvanized steel sheet with a silicon content of 0.3 ~ 3wt%, 0.5 ~ 10g / l copper ion on the surface of the steel sheet immediately after pickling in the pickling process for removing iron oxide present on the surface of the hot-rolled steel sheet Immersion in acid solution for 1 ~ 5 seconds or spray solution for 1 ~ 5 seconds on the surface of steel plate to make copper plating 0.05 ~ 3g / m ² on the surface of steel plate, and then cold roll with a rolling force of 0.3 ton per 1mm of steel plate width And a method for producing a silicon-containing hot dip galvanized steel sheet characterized by performing hot dip plating. According to the present invention, a hot dip galvanized steel sheet having a uniform surface and excellent plating adhesion can be produced.

Silicon, adhesion to adhesion, hot dip galvanized steel sheet

Description

Method of manufacturing a hot dip galvanizing steel sheet containing Si}

The present invention is a method for manufacturing a hot-dip galvanized steel sheet containing Si in steel, in the pickling process of hot-rolled steel sheet (hereinafter, hot-rolled steel sheet) by cold-rolling (hereinafter, cold-rolled steel) after replacing the plating on the surface of the steel sheet The present invention relates to a method for performing hot-dip plating, and more particularly, to a method of manufacturing hot-dip galvanized steel sheet having a uniform surface and excellent plating adhesion when the hot-dip plating is performed on a steel sheet having a Si concentration of 0.3 to 3 wt% in steel.

In general, hot-dip galvanized steel sheet is excellent in corrosion resistance and widely used in building materials, structures, home appliances and automobile bodies. In recent years, steel sheets coated with hot dip galvanized have been developed in accordance with high strength of buildings, light weight, and high strength of automobile bodies.

However, in order to obtain excellent machinability, Si-containing high tensile strength steel sheets need to be annealed at a high temperature of 800 ° C. or higher. By the way, in the ordinary reduction annealing method, Fe is a reducing atmosphere, while Si is an oxidizing atmosphere. Therefore, in the case of the steel sheet containing more than 0.3wt% of Si in the steel sheet, Si in the steel diffuses to the surface to form the Si oxide film. When these oxide films are present on the surface of the steel sheet, there is a problem in that the molten zinc is prevented from adhering to the steel sheet during hot dip galvanizing, thereby partially degrading the plating, or significantly reducing the adhesion even when plated.

As a hot dip galvanizing method of such a Si-containing high tensile strength steel sheet, Japanese Patent Application Laid-Open No. 11-199999 shows that Cu or Cu alloy is 0.002 ~ 2g / m ² on the surface of the steel sheet by electroplating or substitution plating method before reduction annealing of the high tensile strength steel sheet. During coating and annealing, Si, Mn, Cr, etc. are suppressed on the surface of the steel sheet to improve plating adhesion. When the Cu or Cu alloy layer is present on the surface of the steel sheet by this method, there is an effect of suppressing the surface concentration of the oxidized elements such as Si, Mn, Cr in the surface layer, thereby improving the plating adhesion of the hot-dip galvanized steel sheet. However, when Cu is coated on the surface of cold rolled steel sheet by substitution plating method, it is economical because no plating equipment is needed.However, since the adhesion between cold rolled steel sheet and Cu coating layer is weak, part of the coating layer is separated by friction with various rolls in the reduction annealing furnace. Contaminating the roll, and the fallen Cu coating layer locally adheres to the steel sheet, causing spot defects in the steel sheet after hot-dip plating, and the Cu coating layer weakly adhered to the steel sheet is released from the molten plating bath and reacts with the molten zinc. There is a problem that causes (Dross). Therefore, in order to improve the adhesive force of a Cu layer, there exists a method of coating Cu by the electroplating method. If Cu is plated on a cold rolled steel plate by the electroplating method, the Cu plated layer does not fall off even with friction with the roll in the reduction annealing furnace, because it does not cause the above problems, but an additional electroplating facility is required. Because of this, the equipment cost and the power cost increase, which is disadvantageous economically.

The high tensile strength steel sheet containing an element which is susceptible to oxidation, such as Si, has their oxides formed on the surface of the steel sheet, and the iron oxide on the surface of the steel sheet is reduced upon reduction annealing under ordinary reduction annealing conditions. Since Si is oxidized, Si in steel diffuses to the surface during annealing, and these oxides are concentrated on the surface of the steel sheet after reduction annealing. If the Si oxide is concentrated on the surface, the adhesion of the molten zinc in the hot dip galvanizing process causes unplating. Therefore, the method of improving the adhesion of molten zinc by suppressing the concentration of Si oxide on the surface of the steel sheet may be performed by electroplating or substitution plating on the surface of the steel sheet by plating a certain amount of unoxidized elements under different reducing annealing conditions. It is possible to improve the plating adhesion by suppressing the concentration of Si oxides. The method of plating non-oxidative element by electroplating method has the advantage of selecting various elements such as Ni, Fe, Cu, Co, but it is not economical because the processing cost is increased because power cost, electricity supply equipment, plating equipment, etc. are required. Substituted plating is a method of chemically plating by using the electrochemical potential difference between the base iron and the element to be plated, that is, the steel plate is deposited in an acidic solution containing a metal ion having an electrochemically higher potential than the base iron. In this case, electrons generated by dissolving Fe ions in the steel sheet are reduced to the metal ions in the solution and plated on the surface of the steel sheet. Although it has the advantages of being inexpensive and easy to install, the adhesion between the base iron and the plating layer is weak, so that the plating layer is dropped by friction with various rolls. There is a problem in that a plating material adhering to the surface of the steel sheet is dropped from the molten plating tank to form dross.

The present invention has been made in order to solve the above problems, by replacing the Cu on the surface of the steel sheet after pickling in the pickling process for removing iron oxide present on the surface of the hot rolled steel sheet for cold rolling the hot rolled steel sheet containing Si When cold rolling is performed, the substitution-plated Cu plating layer is strongly pressed onto the surface of the steel sheet and has excellent adhesion with the steel sheet.Therefore, there is no problem of roll contamination and dross formation since the plating layer does not drop even in friction with various rolls in the hot dip plating process. In the reduction annealing process of the hot-dip plating process, the present invention is proposed in view of the fact that the Si in the steel is prevented from being diffused and oxidized by the Cu present on the surface of the steel sheet, so that the adhesion and adhesion between the steel sheet and zinc are excellent. Was done.

In the present invention, in the hot-dip plating steel sheet added with 0.3 ~ 3wt% Si content in the steel, the surface of the steel sheet in the solution containing Cu ions after pickling in the pickling process to remove the iron oxide present on the surface of the hot-rolled steel sheet After immersing for 2 seconds or spraying the solution on the surface of steel sheet for 1 ~ 5 seconds, plating Cu ~ 0.05g / m ² on the surface of steel sheet and performing cold rolling to perform hot dip galvanizing in the usual way. The present invention provides a method for producing a hot-dip galvanized steel sheet having excellent adhesion and adhesion between the steel sheet and zinc by preventing Cu in the steel from diffusing into the steel sheet surface and oxidizing by Cu present on the surface of the steel sheet. There is this.

Hereinafter, the present invention will be described in detail.

Conventional hot-dip galvanized steel sheet is produced by degreasing cold rolled steel sheet, heating it to 750 ~ 850 ℃ in a reduced annealing furnace with H ₂ 10 ~ 20% -N ₂ atmosphere, and performing annealing. Cold rolling is performed by pickling iron oxide formed on the surface of a steel sheet by a hot rolling process to produce a cold rolled steel sheet.

In the present invention, in the hot-dip plating steel sheet added 0.3 ~ 3wt% Si content in the steel, the surface of the steel sheet after the pickling in the pickling process for removing iron oxide present on the surface of the hot-rolled steel sheet containing 0.5 ~ 10g / l and soaked for 1-5 seconds in an acidic solution, or by spraying the solution for 1-5 seconds on the surface of the steel sheet on the surface of the steel sheet and the Cu plating 0.05 ~ 3g / m ² substituted. Thereafter, cold rolling is performed with a rolling force of at least 0.3 ton per sheet width of 1 mm to manufacture cold rolled steel sheets, and the hot rolled steel sheets are annealed and plated by conventional annealing and plating methods to produce hot-dip galvanized steel sheets. It relates to a hot dip galvanizing method of Si-containing high tensile strength steel sheet.

The reason for limiting the concentration of Cu ions in the substitution plating solution to 0.5-10 g / l when replacing Cu on the surface of the hot-rolled steel sheet according to the present invention is that the target Cu deposition amount of 0.05-3 g / l is less than 0.5 g / l. It is not suitable for the facility of continuous plating at high speed due to the long processing time to obtain m ² , and there is no big problem even if the concentration exceeds 10 g / l, but the economical efficiency is low. The substitution plating solution may be acidic so that the hot-rolled steel sheet can be dissolved in the solution. When immersion or spray using the substitution plating solution, the lower limit of the processing time is limited to 1 second. It is not plated, but partially unplated, and there is no problem even if the treatment is performed for more than 5 seconds, but it is not economical because the length of the treatment tank has to be relatively long in a facility that is cold rolled at a high speed.

If the Cu plated layer deposited on the surface of the hot-rolled steel sheet is less than 0.05 g / m ² , the effect of inhibiting Si oxide thickening is weak during the annealing of the hot dip plating process. Even if the adhesion amount exceeds 3 g / m ² , there is no problem in hot-dip plating. Since it falls, it is preferable to limit to 0.05-3 g / m ² .

In addition, when the cold rolling of a steel plate coated with 0.05 to 3 g / m ^{2 of} Cu is less than 0.3 ton per 1 mm of the steel plate width, the plated Cu is partially annealed by friction with various rolls in the annealing and plating process. In addition, it is preferable that the lower limit of the rolling force of the cold rolled roll is limited to 0.3 ton per 1 mm of steel width, since not only the whole is dropped and contaminates the equipment, but also the dropped Cu is reattached to the steel sheet in the form of lumps to cause swelling of the plated layer. Do. In addition, there is no problem in quality even if the reduction of the rolling force greatly increases, and the upper limit of the rolling force depends on the cold rolling rate, so that the upper limit of the rolling reduction is not particularly limited at or below 90% as in the general cold rolled steel manufacturing process. no need.

As described above, the Cu-substituted plating was carried out at 0.05 to 3 g / m ² immediately after pickling the hot rolled steel sheet according to the solution composition and processing conditions in the range defined by the present invention, and cold rolling was performed at a rolling force of 0.3 ton per 1 mm of steel sheet width. When manufacturing a cold rolled steel sheet, Cu is strongly pressed on the surface of the cold rolled steel sheet, and thus a Cu plated layer pressed on the surface of the steel sheet exists to prevent the diffusion of Si into the surface during reduction annealing, thereby suppressing the surface concentration of Si and allowing the surface to be Since it is not formed on the oxide layer, it improves the adhesion and adhesion of the base of molten zinc during hot dip plating. Also, Cu is strongly pressed onto the surface of the steel sheet, so Cu plated on the surface by friction with various rolls in the annealing and plating process It prevents contamination of various equipments because there is no problem of falling off, and also prevents swelling defect of plated layer caused by re-attach of the dropped Cu to the steel sheet in the form of lumps. Can.

The present invention will be described in more detail with reference to the following Examples.

Example 1

High tensile hot rolled steel sheets containing Si in steel were pickled by a conventional pickling method in a 70%, 17% hydrochloric acid solution, and immediately after pickling, Cu substitution plating was carried out under the composition and conditions shown in Table 1 and washed with water. Substituted plating solution was prepared at the corresponding concentration using a copper sulfate solution, the solution was adjusted to pH 2 using hydrochloric acid. Immersion plating is complete, the hot-rolled steel sheet is cooled to 800 ℃, reduction and annealing the steel sheet for 60 seconds in a push-down force to a cold rolling after 12% H ₂ -N ₂ atmosphere to prepare a cold-rolled steel sheet to silsi the same as in Tables 1 to 460 ℃ Then, after hot-dip plating in a hot dip galvanizing bath having a bath temperature of 460 ° C., N ₂ wipping was performed such that the plating adhesion amount was 60 g / m ^{2 on one} side. The plated steel sheet was visually observed for the presence of unplated portions to evaluate plating adhesion, and the presence of plating layer swelling defects was examined. In addition, the plated steel sheet was bent at 60 degrees to evaluate plating adhesion as the degree of plating layer dropping. In addition, after each plating was finished by checking the equipment contamination.

division number Si content in steel (wt%) Cu plating Cu ion concentration (g / l) Plating Process Processing time (seconds) Cold rolling rolling force (ton) per steel plate width 1mm Invention One 0.4 U 0.5 Immersion One 0.3 2 0.5 U 0.5 Immersion 3 0.5 3 One U One Immersion 3 0.5 4 One U 2 Immersion One 0.5 5 One U 5 Immersion 3 0.5 6 One U 5 spray 3 0.7 7 2 U 5 Immersion 3 0.7 8 2 U 5 Immersion 5 0.7 9 2 U 10 spray 5 0.7 10 3 U 10 Immersion One 0.7 11 3 U 10 Immersion 5 0.7 Comparative example One 0.5 radish - - 0.5 2 1.5 radish - - 0.7 3 3 radish - - 0.7 4 One U One Immersion 0.5 0.5 5 One U 0.2 Immersion 2 0.5 6 One U One Immersion 2 0.2

division number Cu deposition amount (g / m ² ) Plating adhesion Plating adhesion No plating defects Facility pollution Invention One 0.05 One One radish radish 2 0.12 One One radish radish 3 0.21 One One radish radish 4 0.15 2 One radish radish 5 1.44 One One radish radish 6 1.72 One One radish radish 7 1.41 One One radish radish 8 2.35 One One radish radish 9 2.89 One One radish radish 10 0.74 One One radish radish 11 2.56 One One radish radish Comparative example One - 3 3 radish radish 2 - 4 4 radish radish 3 - 4 4 radish radish 4 0.02 3 4 radish radish 5 0.06 3 2 radish radish 6 0.08 3 2 U U

* Plating adhesion;

1: No unplated part 2: Unplated part exists as a fine point

3: 5 ~ 30% of unplated part 4: More than 31% of unplated part

* Plating adhesion;

1: Excellent 2: Good

3: bad 4: extremely bad

In the case of Inventive Example (1-11) according to the present invention as shown in Tables 1 and 2 above, Cu is coated with 0.05 to 2.89 g / m ² on the surface of the hot rolled steel sheet after Cu substitution plating, and the steel sheet is cold rolled. When cold-rolled at 0.3 ton per 1mm width of steel sheet, which is the rolling reduction defined in the present invention, the plating is performed. Was not present at all, or was present as a fine point, and the plating adhesion was excellent, and the plating adhesion was also excellent. In addition, no plating swelling defects occurred and there was no equipment contamination.

In the case of Comparative Example (1-3), the cold rolling and plating were performed by the usual process without performing Cu substitution plating after pickling of the hot rolled steel sheet. This was extremely poor and plating adhesion was also poor. However, Cu substitution plating was not performed on the steel sheet, so that no plating layer swelling defect or equipment contamination occurred.

On the other hand, in the case of Comparative Example (4), although Cu substitution plating was performed in the solution within the range defined in the present invention, the treatment time is less than the range defined in the present invention, and the Cu deposition amount is within the range defined in the present invention. The plating adhesion was relatively small due to the partial non-uniform plating, but the plating adhesion was poor. However, since the cold rolling force was rolled to 0.3 ton or more per 1 mm of steel sheet width, which is the pressing force limited by the present invention, the plating layer swelling defect and equipment contamination did not occur.

On the other hand, in the case of Comparative Example (5), the treatment time is in the range defined in the present invention, but the concentration of the solution is lower than the range defined in the present invention, so that the Cu adhesion amount is lower than the range defined in the present invention. It was poor. However, since the cold rolling force was rolled to 0.3 ton or more per 1 mm of steel sheet width, which is the pressing force limited by the present invention, the plating layer swelling defect and equipment contamination did not occur.

In Comparative Example (6), Cu substitution plating was carried out under the conditions defined in the present invention, and the Cu deposition amount was 0.08 g / m 2, which was within the range defined by the present invention. However, the rolling force during cold rolling of the steel sheet was limited in the present invention. In the annealing and plating process, a part of the Cu plating layer was dropped and adhered to the steel sheet in the form of agglomeration, resulting in a swelling defect of the plating layer, and equipment contamination occurred. In addition, the Cu plating layer plated on the surface of the steel sheet was eliminated during the annealing and plating process, and thus there was no effect of suppressing the diffusion of Si inside the steel to the surface, resulting in poor adhesion and adhesion.

As described above, according to the present invention, in order to cold-roll a hot-rolled steel sheet containing Si, in the pickling process for removing iron oxide present on the surface of the hot-rolled steel sheet, a cold plating is performed on the surface of the steel sheet by performing cold rolling after substitution with Cu. The plated Cu plating layer is strongly pressed onto the surface of the steel sheet, so it has excellent adhesion with the steel sheet, and the plating layer does not fall off even when friction with various rolls in the hot dip plating process. In the process, the Cu present on the surface of the steel sheet prevents Si in the steel from diffusing to the surface of the steel sheet and oxidizes, so that the adhesion and adhesion between the steel sheet and zinc are excellent.

Claims (3)

In the method of manufacturing a hot-dip galvanized steel sheet containing 0.3 to 3 wt% of silicon, the surface of the steel sheet in an acidic solution containing 0.5 to 10 g / l of copper ions immediately after pickling in a pickling process for removing iron oxide present on the surface of a hot rolled steel sheet Immerse for 1 ~ 5 seconds or spray solution for 1 ~ 5 seconds on the surface of steel plate to make copper plate 0.05 ~ 3g / m ² substitution plating on the surface of steel plate, and then cold roll and melt with a rolling force of 0.3 ton per 1mm of steel plate width A method for producing a silicon-containing hot dip galvanized steel sheet, characterized by plating. delete delete