JP5211735B2 - Manufacturing method of hot-dip galvanized steel sheet with excellent degreasing properties - Google Patents

Description

  The present invention relates to a method for producing a hot dip galvanized steel sheet having excellent degreasing properties.

  Conventionally, hot-dip galvanized steel sheets having excellent rust resistance have been used as steel sheets for automobile bodies. Among hot-dip galvanized steel sheets, galvannealed steel sheets, in particular, are excellent in press formability and are therefore used as steel sheets for vehicle body exteriors such as automobile body doors. Typical car body manufacturing processes at automakers include blanking process for steel sheet materials, oil washing process for washing steel sheets with oil, press forming process, joining (adhesion, spot welding) process, degreasing process, chemical conversion treatment process, and painting. It has a process.

  Of each process of manufacturing the car body, the degreasing process is a process of cleaning the steel sheet having press oil (or rust preventive oil or a mixture thereof) on the surface with an alkaline degreasing liquid. If it is insufficient, it will adversely affect the subsequent chemical conversion properties and paintability. However, in recent years, from the viewpoint of environmental protection, it has been difficult to require high degreasing performance for the degreasing liquid used in the degreasing process. Therefore, even when the oil on the surface of the steel sheet is washed with a degreasing liquid having a poor degreasing property, it is necessary to provide a steel sheet on which the surface oil is easily washed, that is, a steel sheet with good degreasing properties. In addition, against the backdrop of strong demand from automobile manufacturers, it may be left for more than a month from press molding to degreasing and chemical conversion treatment line, in such cases, the adsorption with oil becomes significant, There arises a problem that the degreasing property is remarkably deteriorated. Therefore, the problem is that only the so-called initial degreasing property is evaluated and the performance required for the galvannealed steel sheet by the current automobile manufacturer or the like is not satisfied. Therefore, the degreasing property to be aimed at is to improve the degreasing property under the cured conditions.

  As a method for obtaining an alloyed hot-dip galvanized steel sheet having excellent degreasing properties, for example, Patent Document 1 discloses that Teflon ("Teflon" is a registered trademark; the same applies hereinafter) particles are discretely attached to the alloyed hot-dip galvanized steel sheet. Is disclosed.

In addition, for the purpose of improving the slidability of the plated steel sheet, a technique for improving the degreasing property when an oxide layer is formed on the surface of the plated steel sheet is disclosed. For example, Patent Documents 2 to 4 disclose a method of forming an oxide layer on a steel sheet surface by bringing the steel sheet surface into contact with an acidic solution after temper rolling. Specifically, Patent Document 2 discloses a method of washing with an aqueous solution having a pH of 7.0 to 12.0 containing a sodium salt or potassium salt of a specific acid. Patent Document 3 discloses that a phosphorus concentration is 0.5 to 5000 ppm. A method of washing with a phosphorous-containing aqueous solution is disclosed in Patent Document 4 in which it is brought into contact with an aqueous solution having a pH of more than 7 and less than 10.
JP 2000-38648 A JP 2007-16266 A JP 2007-16267 A JP 2007-92093 A

  However, in any of the prior documents, a performance that sufficiently satisfies the degreasing property aimed by the present invention was not obtained. In addition, when the Teflon particles are adhered to the steel sheet surface as in Patent Document 1, when the oil on the steel sheet surface is washed with the degreasing liquid, the Teflon particles are also dropped together with the oil, and the degreasing liquid is contaminated. There was a problem.

  Moreover, in the method of patent documents 2-4, it is premised on forming an oxide layer on the steel plate surface using an acidic solution, and when the said acidic solution remains on the steel plate surface, degreasing of a steel plate is carried out. In some cases, the sexiness decreased. Therefore, after forming the oxide layer, the acidic solution remaining on the steel sheet surface must be washed and neutralized. In the case where an oxide layer is not formed on the surface of the steel sheet, there has been no disclosure of a method for producing a hot-dip galvanized steel sheet that has excellent degreasing properties of the steel sheet. Then, this invention makes it a subject to provide the manufacturing method of the hot dip galvanized steel plate which can manufacture the hot dip galvanized steel plate excellent in degreasing property irrespective of the surface state of a hot dip galvanized steel plate.

  When the present inventors investigated the relationship between the degreasing property of a hot dip galvanized steel sheet and a manufacturing process, it turned out that the water which contacts the steel plate surface after temper rolling affects degreasing property. More specifically, when washed with so-called pure water such as ion-exchanged water immediately after temper rolling, the degreasing property of the steel sheet is not stable and good, and the steel sheet is brought into contact with an aqueous solution under specific conditions. Thus, the knowledge that the degreasing property of the steel sheet is extremely good was obtained, and the relationship between the components / concentration of the aqueous solution used for washing with water and the degreasing property was further investigated, and preferable conditions of the aqueous solution were specified.

  The reason is considered as follows. The plated surface after the temper rolling is mixed with an active surface that appears by contact with a temper rolling roll and an inactive surface that does not contact the roll. When rust preventive oil or press washing oil is applied to such a plated surface, extreme pressure additives and the like contained in the oil are particularly strongly adsorbed on the active surface. Here, when the plating surface before oiling is treated with an aqueous solution containing Ca and / or Mg and hydrogen carbonate ions, Ca and / or Mg and hydrogen carbonate are adsorbed on the plating surface, and the components in the oil are adsorbed. It is suppressed and the degreasing property is improved. Further, when the pH of the aqueous solution is adjusted to a weak alkali range, the plated surface is made uniform and the stain resistance is stably improved. The present invention has been made based on such knowledge and estimation.

  The present invention will be described below. In order to facilitate understanding of the present invention, reference numerals in the accompanying drawings are appended in parentheses, but the present invention is not limited to the illustrated embodiments.

  The first aspect of the present invention is a temper rolling process (S1) for temper rolling a hot dip galvanized steel sheet, and 15 ppm of Ca and / or Mg on the plated surface of the temper rolled steel sheet in the temper rolling process. It is characterized by comprising a contact step (S2) for contacting with an aqueous solution containing 60 ppm or more of hydrogen carbonate ions, and a drying step (S3) for drying the steel plate after the contact step. It is a manufacturing method (10) of the hot dip galvanized steel plate.

  Here, “temper rolling” refers to temper rolling of a general plated steel sheet that is rolled at a slight reduction rate. For purposes such as shape control, mechanical property imparting, gloss adjustment, and roughness imparting of the plated steel sheet. Done. In the present invention, after the temper rolling, the acid aqueous solution treatment is not performed and the oxide layer may not be formed. In the contacting step, “contact with aqueous solution” means a state in which the plating surface of the hot dip galvanized steel sheet is in contact with the aqueous solution, and the contact method is not particularly limited, and the plating surface of the steel sheet is immersed in the aqueous solution. And the aqueous solution may be contacted, or the aqueous solution may be sprayed and applied to the steel sheet. “Containing 15 ppm or more of Ca and / or Mg” may be adjusted by adding a reagent that generates Ca ions and / or Mg ions in pure water, or water such as rivers and lakes. In the case of being purified and used as industrial water, it suffices as long as it contains these components as a result. “Containing 60 ppm or more of hydrogen carbonate ions” may be adjusted by adding a reagent that generates hydrogen carbonate ions in pure water or blowing in carbon dioxide, or in water such as rivers and lakes. As a result, it is only necessary that the concentration of hydrogen carbonate ions falls within the specified range. “Drying the steel plate” in the drying step means drying the water present on the plated surface of the steel plate after the contacting step. The drying method is not particularly limited as long as the steel sheet can be dried, and is appropriately selected from drying with a hot air device, various infrared devices, an electromagnetic induction device, a microwave device, or natural drying.

  In 1st this invention, it is preferable not to include the process of forming an oxide layer intentionally on the plating surface of a steel plate between a temper rolling process and a contact process.

  Here, the “step of intentionally forming an oxide layer” means a step of forming an oxide layer on the plated surface of a steel sheet with a specific purpose such as imparting slidability.

  In 1st this invention, it is preferable that pH of the aqueous solution used in a contact process is 6-12.

  Here, “the pH of the aqueous solution is 6 or more and 12 or less” means that the pH of the aqueous solution is adjusted to 6 or more and 12 or less, for example, by adding hydrochloric acid or sulfuric acid or blowing carbon dioxide gas. means.

  In the first aspect of the present invention, the temperature of the aqueous solution is preferably 5 ° C. or higher and 50 ° C. or lower, and the plating surface of the steel sheet and the aqueous solution are preferably contacted for 1 second or longer and 50 seconds or shorter.

  Moreover, in 1st this invention, it is preferable to provide the antirust oil application process (S4) which apply | coats antirust oil to the surface of a steel plate after a drying process.

  Furthermore, in the first aspect of the present invention, the hot dip galvanized steel sheet is preferably an alloyed hot dip galvanized steel sheet.

  According to 1st this invention, it is excellent in degreasing | defatting property by making the aqueous solution containing predetermined amount of Ca and / or Mg, and hydrogen carbonate ion contact the plating surface of a hot dip galvanized steel plate in a contact process. A hot dip galvanized steel sheet can be provided. The hot dip galvanized steel sheet can be cleaned using a degreasing solution having poor degreasing properties. Moreover, the degreasing property of a steel plate can be improved irrespective of the presence or absence of an oxide layer on the surface of the hot dip galvanized steel plate.

  In the first aspect of the present invention, it is considered that Ca and / or Mg can be appropriately adsorbed on the plating surface by adjusting the pH of the aqueous solution used in the contact step to a predetermined range, and as a result, stable. Good degreasing properties are obtained.

  Furthermore, in the first aspect of the present invention, the hot dip galvanized steel sheet having excellent degreasing properties, which is suitably used for automobile exterior materials, etc., by making the hot dip galvanized steel sheet an alloyed hot dip galvanized steel sheet having excellent press formability. Steel sheets can be manufactured.

  In the production of hot dip galvanized steel sheet, first, a base coil manufactured through steelmaking, hot rolling, cold rolling, annealing, etc. is heated in a continuous furnace and then impregnated in a pot containing zinc. Thus, a zinc component is adhered to the surface of the steel sheet, and then air-cooled to form a galvanized film on the surface of the base material. And after manufacturing the base material (henceforth a "plating steel strip") which has a galvanized film on the surface, it goes through the process including temper rolling, surface treatment, etc., and the hot dip galvanized steel plate excellent in degreasing It is said. The manufacturing method of the hot dip galvanized steel sheet according to the present invention includes the steps after the temper rolling of the plated steel strip.

  Embodiments of the present invention will be described below. In addition, in the form shown below, although an galvannealed steel plate is demonstrated, this invention is not limited to this, It is applicable to various hot dip galvanized steel plates. For example, the present invention may be applied to hot-dip galvanized steel sheets (not alloyed), Zn-Al-based plated steel sheets, Zn-Al-Mg-based plated steel sheets, and the like.

<1. Method 10 for producing alloyed hot-dip galvanized steel sheet>
FIG. 1: has shown the flowchart about each process of the manufacturing method 10 (henceforth "the manufacturing method 10") of the galvannealed steel plate concerning embodiment. The production method 10 includes a predetermined amount of Ca and / or Mg and hydrogen carbonate ions on the surface of the temper rolling step S1 for temper rolling the plated steel strip and the temper rolled steel sheet, Contact step S2 in which an aqueous solution adjusted to have a pH within a predetermined range (hereinafter, this aqueous solution is referred to as “aqueous solution of the present invention”), and after the contact step S2, the moisture on the steel sheet surface is blown off, A drying step S3 for drying the steel plate is provided, and an alloyed hot-dip galvanized steel plate having excellent degreasing properties is produced through these steps. Thereafter, the alloyed hot-dip galvanized steel sheet is coated with a rust-preventing oil on the surface thereof in the rust-preventing oil coating step S4, and the occurrence of rust is prevented.

FIG. 2 is a diagram schematically showing a production line 20 for alloyed hot-dip galvanized steel sheets (hereinafter referred to as “production line 20”) provided with the steps of the production method 10. The production line 20 includes a temper rolling mill 2, a tension leveler 3, a post-processing unit 4, a drying unit 5, an exit side looper 6, a flying shear 7, and an oil application unit 8. An alloyed hot-dip galvanized steel strip 1 (hereinafter referred to as “plated steel strip 1”) runs on the production line 20 having these 2 to 8 and is alloyed with excellent degreasing properties after each step. The hot-dip galvanized steel sheet 30 (hereinafter referred to as “plated steel sheet 30”) is used.
Hereafter, each process of the manufacturing method 10 is demonstrated with the manufacturing line 20 referring FIG. 1, FIG.

(1.1. Temper rolling step S1)
In the temper rolling step S 1, the plated steel strip 1 is rolled by the temper rolling mill 2. In the production line 20, a skin pass mill is used as the temper rolling mill 2. The plated steel strip 1 is lightly rolled by the temper rolling machine 2 so that the mechanical properties, surface gloss, etc. are adjusted to appropriate ones. Further, in the temper rolling step S1, conditioned water (pressure conditioned liquid) may be used so that the plating film of the plated steel strip 1 is not transferred to the roll of the temper rolling mill 2. In this temper rolling process, an active surface appears on the surface in contact with the roll.

(1.2. Contacting step S2)
Contact process S2 (and drying process S3 described in detail later) may be performed at any timing between temper rolling S1 and oil coating process S4. In a normal continuous hot-dip galvanized steel sheet production line, a plurality of water washing facilities and drying facilities are provided between the temper rolling mill 2 and the oil application means 8, but the contact step S2 (and the drying step S3) of the present invention is performed. Such water washing and drying equipment can be utilized. For example, by spraying the aqueous solution according to the present invention immediately after the temper rolling mill 2, in the post-processing means 4 or in part or all of the water-washing equipment immediately after the post-processing means 4 (for the purpose of cleaning the steel sheet surface) It can also be brought into contact with the steel sheet surface. Further, pure water may be used in the water washing facility after the aqueous solution of the present invention is used in a certain water washing facility. Below, the case where contact process S2 is made immediately after the temper rolling mill 2 is demonstrated.

  Conventionally, pure water such as ion exchange water has been used as cleaning water for the surface of the plated steel sheet after temper rolling. In the manufacturing method 10, the aqueous solution of the present invention is used as the washing water.

  The aqueous solution of the present invention used in the present embodiment contains 15 ppm or more of Ca and / or Mg. From the viewpoint of improving the degreasing property, the lower limit of the content of Ca and / or Mg is preferably 20 ppm or more. The upper limit of the Ca and / or Mg content is not particularly defined, but is preferably 200 ppm or less, more preferably 100 ppm or less, from the viewpoint of solubility. Furthermore, the aqueous solution of the present invention used in this embodiment contains 60 ppm or more of hydrogen carbonate ions. When the bicarbonate ion concentration is low, the formation of carbonate and bicarbonate is not sufficient, and the degreasing properties described later cannot be sufficiently improved. Since the solubility of hydrogen carbonate ions is determined by the balance with the amount of Ca and / or Mg as the paired cations, it is important that Ca and / or Mg is contained in the aqueous solution at a predetermined concentration or more.

  The pH of the aqueous solution of the present invention used in the present embodiment is 6 or more and 12 or less, preferably 6.5 or more and 10 or less, and particularly preferably 6.5 or more and 8 or less. Zinc used as plating is an amphoteric metal, and the galvannealed steel sheet is eluted even if the pH is too high or too low. When elution of zinc occurs on the surface of the galvannealed steel sheet, it is considered that Ca and / or Mg and bicarbonate ions are prevented from adsorbing on the plating surface. In order to obtain stable degreasing properties, the aqueous solution of the present invention should be neutral to weakly alkaline. Examples of the method for adjusting the pH of the aqueous solution of the present invention include adjusting an acidic side by adding an acidic solution such as hydrochloric acid or sulfuric acid or blowing carbon dioxide gas.

  The liquid temperature of the aqueous solution of the present invention used in the present embodiment is preferably 5 ° C. or higher and 50 ° C. or lower, more preferably 5 ° C. or higher and 30 ° C. or lower, and more preferably 5 ° C. or higher and 20 ° C. or lower. It is particularly preferred. By setting it to an appropriate liquid temperature, it is possible to manufacture a plated steel sheet 30 that is further excellent in degreasing properties. If the liquid temperature is too high, the solubility of carbon dioxide in the aqueous solution of the present invention decreases due to the temperature rise, leading to a decrease in the amount of bicarbonate dissolved. For this reason, the temperature of the aqueous solution of the present invention should be kept as low as possible.

  By washing the plating surface with the aqueous solution of the present invention prepared as described above, the pressure-regulating water component and the plating powder can be removed from the plating surface, and Ca and / or Mg and hydrogen carbonate ions are appropriately applied to the plating surface. It is thought that the compound or salt consisting of can be adsorbed. And, by appropriately adsorbing a compound or salt composed of Ca and / or Mg and hydrogen carbonate ions on the plating surface, the wettability with the water on the plating surface is improved or the adsorptivity of the rust preventive oil is reduced. It is considered that the degreasing liquid can be easily drawn into the coated rust preventive oil / plating interface, and the degreasing property of the plated steel sheet can be improved. In addition, it is considered that hydrogen carbonate ions react with Ca and / or Mg in the vicinity of the plating surface to form carbonate or hydrogen carbonate, so that Ca and / or Mg is easily adsorbed on the plating surface.

  In the contact step S2, as described above, it is considered that the plating surface is washed and Ca and / or Mg is adsorbed on the plating surface of the plated steel strip 1. In order for Ca and / or Mg to be appropriately adsorbed on the plating surface of the plated steel strip 1, the cleaning time (contact time between the plating surface and the aqueous solution of the present invention) is preferably 1 second or more and 50 seconds or less. . When it is 1 second or less, it is considered that a sufficient amount of Ca and / or Mg is not adsorbed on the plating surface. Moreover, even if it is 50 seconds or more, since the surface adjustment effect of the plating surface is saturated and the improvement of degreasing property is constant, it is considered that the efficiency is poor.

  In the contact step S2, means are not particularly limited as long as the plated steel strip 1 can be brought into contact with the aqueous solution of the present invention, and means for spraying the aqueous solution of the present invention onto the plated steel strip 1 or a plated steel strip. A means for immersing 1 in the aqueous solution of the present invention can be mentioned.

(1.3. Drying step S3)
In the contact step S2, the aqueous solution and the plated steel strip 1 are brought into contact with each other, and then the water in the aqueous solution is blown from the surface of the plated steel strip 1 through the drying step S3. It will be in the state in which the component made into the excellent plated steel plate 30 remained. In the drying step S <b> 3, a drying device is used, and the drying device corresponds to the drying unit 5 in the production line 20. As the drying means 5, a commonly used drying device such as a hot air device, various infrared devices, an electromagnetic induction device, a microwave device, or the like is used. Further, natural drying may be performed without using the drying means 5.

  In the production line 20, after the drying step S3, the plated steel strip 1 is subjected to running shearing by the flying shear 7 via the exit side looper 6, wound into a coil shape, and a plated steel plate 30 having excellent degreasing properties. Manufactured. In the production line 20, the exit side looper 6 does not have to be in the form shown in the drawing as long as the plated steel strip 1 can be temporarily held when the coil is replaced. Moreover, although the flying shear 8 was illustrated as a shear in the manufacturing line 20, if it is an apparatus which can be sheared, it will not specifically limit, For example, it is good also as a stop cut shear.

(1.4. Antirust oil application process S4)
In the manufacturing method 10, in order to prevent rust of the plated steel plate 30, it is preferable that a rust preventive oil is applied to the surface of the plated steel plate 30 in the rust preventive oil application step S4. The apparatus used for applying the antirust oil (oil applying means 8 in the production line 20) is not particularly limited as long as it is an apparatus that can apply the antirust oil to the surface of the plated steel sheet 30, and forward roll, reverse A roll, a gravure, a doctor blade, a slot die, a spray coating apparatus, or the like can be used. Since the plated steel sheet 30 manufactured by the manufacturing method 10 is excellent in degreasing properties, even if the rust preventive oil is applied to the surface of the plated steel sheet 30 in the rust preventive oil application step S4, Ca and / or Mg and hydrogen carbonate. Adsorption of compounds such as ions or salts, adsorption of components such as extreme pressure additives contained in the rust-preventing oil due to passivation of the galvanized surface can be suppressed, and the rust-preventing oil is easily washed with an alkaline degreasing solution.

(1.5. Others)
In the description of the present invention so far, the contact process S2 according to the manufacturing method 10 has been described as being applied to the plated steel strip 1 that has passed through the tension leveler 3, but the contact process S2 includes the temper rolling process S1 and the drying process. There is no particular limitation as long as it is between S3. For example, the plated steel strip 1 may pass through the tension leveler 3 after passing through the contact step S2.

  According to the production method 10 according to the present invention, a hot-dip galvanized steel sheet having excellent degreasing properties can be produced regardless of the presence or absence of an oxide layer on the surface of the hot-dip galvanized steel sheet. Moreover, since the manufacturing method 10 can integrate the process of providing degreasing properties and the cleaning process, the number of processes is reduced and the efficiency of the entire process is good. The hot dip galvanized steel sheet manufactured by the manufacturing method 10, especially the alloyed hot dip galvanized steel sheet is excellent in degreasing properties even when left for a long period of time. It can be degreased, and the chemical conversion treatment property and the coating property in the subsequent chemical conversion treatment step and coating step can be improved.

  Prepare a plurality of 70 mm × 150 mm specimens (hereinafter simply referred to as “test specimens”) cut out from the alloyed hot-dip galvanized steel sheet, and immerse each in an aqueous solution containing different components or ion-exchanged water, After the surface adjustment, the degreasing properties of each surface-adjusted specimen were evaluated.

(Examples 1 to 7, Comparative Examples 1 to 5)
As an aqueous solution for immersing the test material, after adding a predetermined amount of calcium hydroxide or magnesium hydroxide to ion-exchanged water, further adding hydrochloric acid or sulfuric acid, or blowing carbon dioxide gas to adjust the pH. Examples 1 to 7 include cases in which an aqueous solution containing 15 ppm or more of Ca and / or Mg, 60 ppm or more of hydrogen carbonate ions, and having a pH of 6 or more and 12 or less is used. It was. Moreover, it was set as Comparative Examples 1-5 when it carried out similarly to Example 1- Example 7 except containing Ca and / or Mg less than 15 ppm, or containing hydrogencarbonate ion less than 60 ppm. The components of these aqueous solutions are shown in Table 1. The concentrations of Ca, Mg, Cl, and SO ₄ shown in Table 1 are values calculated from the added amounts of calcium hydroxide, magnesium hydroxide, hydrochloric acid, and sulfuric acid, respectively. The concentration of hydrogen carbonate ions is a value measured by a total carbonic acid titration method defined in JIS K0101.

(Conventional example 1)
In order to compare with the aqueous solution of the present invention, the case of using ion-exchanged water was defined as Conventional Example 1.

(Degreasing evaluation)
The sample material was immersed in each aqueous solution or ion-exchanged water (conventional example 1) according to Examples 1 to 7 and Comparative Examples 1 to 5 for 1 minute, pulled up, and dried with a dryer. Thereafter, each test material was coated with 1.5 g / m ² of rust preventive oil (550S manufactured by Parker Kosan Co., Ltd.). After oiling, the same steel plates were stacked and placed in a drier in the air atmosphere and cured at 60 ° C. for 4 days. In addition, curing at 60 ° C. for 4 days is equivalent to leaving at room temperature for about 1 month.

  After completion of curing, it was immersed for 2 minutes in a commercially available alkaline degreasing solution (Nippon Paint Co., Ltd. SD280Z, pH = 10.5, degreasing solution temperature 40 ° C.). After soaking, it was lifted and immediately washed with tap water for 30 seconds. The test specimen washed with water is kept substantially vertical, and the surface wet state of the surface after 10 seconds is visually observed, and the ratio of the wetted area (hereinafter, this ratio is referred to as “water wetted area ratio (%)”). .) Was used as a degreasing index. The higher the wetted area ratio, the better the degreasing property. Table 1 shows the respective aqueous solutions and ion-exchange components according to Examples 1 to 7 and Comparative Examples 1 to 5 brought into contact with the test material, and the water wetted area ratio of the test material.

  From the results shown in Table 1, when the aqueous solutions of the present invention (Examples 1 to 7) are used, the wettability is higher than when the aqueous solutions and ion-exchanged water (Conventional Example 1) according to Comparative Examples 1 to 5 are used. It can be seen that the area ratio increases. That is, it turns out that the degreasing property of the surface of a plated steel plate is improved by using the aqueous solution of this invention.

  Although the present invention has been described with reference to the most practical and preferred embodiments at the present time, the present invention is not limited to the embodiments disclosed herein. The invention can be changed as appropriate without departing from the scope or spirit of the invention that can be read from the claims and the entire specification, and a method of manufacturing a hot-dip galvanized steel sheet with such a change is also included in the technical scope of the present invention. Must be understood as being.

It is a flowchart which shows the process with which the manufacturing method 10 of this invention is equipped. It is a figure showing roughly about manufacturing line 20 with which manufacturing method 10 of the present invention is applied.

Explanation of symbols

S1 temper rolling process S2 contact process S3 drying process S4 rust preventive oil application process 1 plated steel strip 2 temper rolling mill 3 tension leveler 4 post-processing means 5 drying means 6 outlet looper 7 flying shear 8 oil application means 10 plated steel sheet Manufacturing method 20 Production line 30 Plated steel sheet

Claims (5)

Temper rolling of galvanized steel sheet, temper rolling,
A contact step in which an aqueous solution containing 15 ppm or more of Ca and / or Mg and 60 ppm or more of hydrogen carbonate ions is brought into contact with the plated surface of the steel sheet after being temper-rolled in the temper rolling step;
After the contacting step, drying the steel sheet, a drying step,
And a step of intentionally forming an oxide layer on the plated surface of the steel sheet between the temper rolling step and the contacting step is not included . The method for producing a hot-dip galvanized steel sheet according to claim 1, wherein the aqueous solution used in the contacting step has a pH of 6 or more and 12 or less. The liquid temperature of the aqueous solution is 5 ° C or higher and 50 ° C or lower in the contact step, and the plating surface of the steel sheet and the aqueous solution are contacted for 1 second or longer and 50 seconds or shorter. Or the manufacturing method of the hot dip galvanized steel plate of 2 . The hot-dip galvanized steel sheet according to any one of claims 1 to 3 , further comprising a rust-preventing oil coating step for applying a rust-preventing oil to the surface of the steel sheet after the drying step. Production method. The method for producing a hot dip galvanized steel sheet according to any one of claims 1 to 4 , wherein the hot dip galvanized steel sheet is an alloyed hot dip galvanized steel sheet.

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