JP2009191317A - Method for manufacturing hot dip galvanized steel sheet having excellent degreasing property - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot dip galvanized steel sheet having excellent degreasing property. <P>SOLUTION: The method for manufacturing the hot dip galvanized steel sheet includes: a temper-rolling step for temper-rolling the hot dip galvanized steel sheet; a contact step of bringing an aqueous solution containing ≥0.1 mmol/L to ≤50 mmol/L pyrophosphate radical into contact with the plating surface of steel sheet temper-rolled in a temper-rolling step; and a drying step of drying the steel sheet after the contact step. <P>COPYRIGHT: (C)2009,JPO&INPIT

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, the types of degreasing liquids used in the degreasing process are limited, and the degreasing performance of such degreasing liquids is not necessarily high compared to conventional ones. Therefore, even when the oil on the surface of the steel sheet is washed with a degreasing liquid that is inferior in degreasing properties, the performance on the steel sheet side is improved so that the surface oil is easily washed, that is, a steel sheet with good degreasing properties. There is a demand to improve. In addition, against the backdrop of vigorous demand from automobile manufacturers, there is a case where it is left for one month or longer after press molding until it passes through a degreasing and chemical conversion treatment line. In such a case, even if the degreasing property is good soon after oiling, the degreasing property after being left to stand may be remarkably deteriorated. Therefore, not only the degreasing property immediately after oiling but also the degreasing property after being left for a certain period after oiling is important. As a method for obtaining an alloyed hot-dip galvanized steel sheet excellent in degreasing properties, a method of discretely attaching Teflon (registered trademark) particles to an alloyed hot-dip galvanized steel sheet as disclosed in Patent Document 1 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 exceeding 7 and less than 10.
JP 2000-38648 A JP 2007-16266 A JP 2007-16267 A JP 2007-92093 A

  However, by any of the above methods, the performance sufficiently satisfying the degreasing property aimed by the present invention was not obtained. In addition, as in Patent Document 1, when the Teflon (registered trademark) particles are adhered to the steel sheet surface, the Teflon (registered trademark) particles are dropped together with the oil when the oil on the steel sheet surface is washed with the degreasing liquid, There was a problem of contaminating the degreasing liquid.

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 the oxide layer is not formed on the surface of the steel sheet, there is no disclosure in the prior art regarding a method for producing a hot-dip galvanized steel sheet that has excellent degreasing properties.
Furthermore, when the steel sheet is left for a long time in the above situation, uneven rust called stain is generated on the plating surface, and the surface appearance may be significantly impaired. If oxides are not actively formed on the surface, a problem that stain is more likely to occur may occur.

Therefore, the present invention provides a method for producing a hot dip galvanized steel sheet capable of producing a hot dip galvanized steel sheet having excellent degreasing properties and stain resistance regardless of the surface state of the hot dip galvanized steel sheet. And

When the present inventors investigated the relationship between the degreasing property of an alloyed hot-dip galvanized steel sheet and a manufacturing process, it turned out that the water which wash | cleans the steel plate surface after temper rolling affects degreasing property. More specifically, when the steel sheet is washed with so-called pure water such as ion-exchanged water immediately after temper rolling as in the prior art, the degreasing property of the steel sheet is not good, and instead the steel sheet is treated with an aqueous solution containing pyrophosphoric acid. It was found that washing with water has better degreasing properties and better stain resistance.
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, if the plating surface before oiling is treated with a pyrophosphoric acid-containing aqueous solution, components derived from pyrophosphate roots are adsorbed on the plating surface to suppress the adsorption of components in the oil, and the degreasing property is improved. Furthermore, when the pH of the aqueous solution containing pyrophosphoric acid 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 0.1 mmol / A hot-dip galvanized steel sheet comprising: a contact step (S2) in which an aqueous solution containing L to 50 mmol / L is brought into contact; and a drying step (S3) in which the steel plate is dried after the contact step. The manufacturing method (10).

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. “Aqueous solution containing 0.1 to 50 mmol / L of pyrophosphate radical” means that 0.1 to 50 mmol / L of pyrophosphate radical in terms of P ₂ O ₇ is contained in the aqueous solution. To do. The aqueous solution may contain fine dispersed particles, a trace amount of carbonate, etc. inevitably mixed in the air, in addition to the pyrophosphate radical. “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 appropriately included by adding an alkali component or the like in an amount that does not impair the degreasing properties of the hot-dip galvanized steel sheet in the contact step. Is adjusted to 6 or more and 12 or less.

  In the first aspect of the present invention, the temperature of the aqueous solution is preferably 5 ° C. or more and 50 ° C. or less, and the plating surface of the steel sheet and the aqueous solution are preferably brought into contact with each other for 1 second or more and 50 seconds or less.

  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 the first aspect of the present invention, in the contacting step, by contacting the plated surface of the hot dip galvanized steel sheet with an aqueous solution containing a predetermined amount of pyrophosphate radicals, compared with the case of contacting with pure water, Since it is a hot-dip galvanized steel sheet having excellent degreasing properties, it can be cleaned using a degreasing solution having poor degreasing properties. In addition, stain resistance can be improved.

  In 1st this invention, the stain resistance of a steel plate improves stably by making pH of the aqueous solution used for a contact process into a predetermined range. In addition, the stain resistance can be stably improved by setting the temperature of the aqueous solution used in the contact step and the contact time between the plated steel sheet and the aqueous solution in the contact step within a predetermined range.

  Furthermore, the hot dip galvanized steel sheet having excellent degreasing properties, which is preferably used for automobile exterior materials, etc., by making the hot dip galvanized steel sheet excellent in press formability in the first invention. 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. If necessary, re-heating to about 600 ° C. to perform alloying of plating. 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 manufacturing method 10 includes a temper rolling step S1 for temper rolling a plated steel strip, a contact step S2 for bringing an aqueous solution containing pyrophosphate roots into contact with the plated surface of the temper rolled steel sheet, and the contact step. After S2, it comprises a drying step S3, in which moisture on the surface of the steel sheet is blown off and the steel sheet is dried. Through these steps, an alloyed hot-dip galvanized steel sheet having excellent degreasing properties is produced. 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 S <b> 1, in order to prevent the plating film of the plated steel strip 1 from being transferred to the roll of the temper rolling mill 2, conditioned water (pressure conditioned liquid) may be used. 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) 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, and the contact step and the drying step of the present invention are such water washing. And drying facilities can be utilized. For example, the steel sheet is sprayed with the aqueous solution according to the present invention using part or all of the water washing equipment immediately after the temper rolling mill 2 or in or after the post-processing means 4 (also for the purpose of cleaning the steel sheet surface). The surface can be contacted. Moreover, you may use a pure water in the washing equipment after using the aqueous solution which concerns on this invention with a certain washing equipment. 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 containing a pyrophosphate radical is used as washing water.

The pyrophosphate root-containing aqueous solution used in the present embodiment has a pyrophosphate root concentration in the aqueous solution of 0.1 mmol / L or more and 50 mmol / L or less, preferably 0.2 mmol / L or more and 25 mmol / L in terms of P ₂ O _7. L or less, particularly preferably 0.3 mmol / L or more and 10 mmol / L or less. When the pyrophosphate radical concentration in the aqueous solution is low, the degreasing property of the plated steel sheet may be inferior. On the other hand, when the pyrophosphate radical concentration exceeds 50 mmol / L, the improvement in degreasing properties is saturated and not only is economically wasteful, but also the stability of the chemical solution is decreased, or excessive adsorption on the active surface is caused. Stain properties may decrease.

  The pH of the aqueous solution used in the present embodiment is preferably 6 or more and 12 or less, more preferably 6 or more and 11 or less, and particularly preferably 7 or more and 10.5 or less. Since zinc is an amphoteric metal, 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 the phosphorus component is prevented from adsorbing on the plating surface. In order to improve the stain resistance, it is preferable to make the aqueous solution weakly alkaline. Moreover, in adjusting the pH of the pyrophosphate group-containing aqueous solution, it is preferable to use an aqueous solution containing ammonium ions, various metal ions such as alkali metal ions, and the like as a pH adjuster.

  The liquid temperature of the aqueous solution used in the present embodiment is preferably 5 ° C. or higher and 50 ° C. or lower, and more preferably 5 ° C. or higher and 40 ° C. or lower. If it exceeds 50 ° C, pyrophosphoric acid may react excessively and stain resistance may decrease. Moreover, if it is less than 5 degreeC, an active surface may remain and degreasing may fall.

  It is considered that the phosphorus component can remain on the plating surface by washing the plating surface with the pyrophosphate root-containing aqueous solution prepared as described above. When the press oil and rust preventive oil adhering to the plating surface are washed by the degreasing liquid in the degreasing process, the adsorption of the extreme pressure additive component to the active surface is inhibited by the phosphorus component remaining on the plating surface, Since the phosphorus component is easily desorbed together with press oil, rust preventive oil, and the like, the degreasing property of the plated steel sheet can be improved as compared with the case where the plating surface is washed with pure water.

  In the contact step S2, it is considered that the degreasing property and the like are improved by leaving the phosphorus component on the plating surface of the plated steel strip 1 as described above. Therefore, it is preferable that the cleaning time of the pressure-regulating water component (contact time between the plating surface and the pyrophosphate group-containing aqueous solution) be 1 second or more and 50 seconds or less. When it is less than 1 second, it is considered that a sufficient amount of phosphorus component cannot be present on the plating surface. Moreover, even if it is 50 seconds or more, the surface adjustment effect of the plating surface is saturated, and the improvement of the degreasing property becomes constant, so that the efficiency is poor.

  Moreover, when leaving a phosphorus component on the plating surface, a surface treatment liquid containing pyrophosphoric acid, which is used for subjecting a steel material surface to a zinc phosphate treatment, can also be used. Zinc phosphate treatment is a treatment that is generally performed for the purpose of densely forming a zinc phosphate coating on the plating surface of a steel material. The surface treatment solution used is composed mainly of pyrophosphoric acid, titania or zirconia. And the like in which fine particles are dispersed. In the contact step S2, a commercially available drug used as such a surface conditioning solution can be used as an aqueous solution in the contact step S2 according to the present invention by adjusting the concentration and pH to a predetermined range.

  After the plating surface is dried after the contact step S2, it is preferable that no components other than the components necessary for improving the above-described degreasing property remain on the plated steel plate surface. Therefore, it is preferable that components other than the predetermined amount of pyrophosphate radical and pH adjuster are not contained in the aqueous solution as much as possible. However, in the pyrophosphate root-containing aqueous solution according to the present embodiment, fine particles such as the above-mentioned titania and zirconia, and a trace amount unavoidably mixed in the air, as long as the degreasing property and stain resistance of the plated steel plate are not impaired. There is no problem even if carbonates, bicarbonates, etc. are mixed.

  The contact means in the contact step S2 is not particularly limited as long as it can contact the plated steel strip 1 and the aqueous solution, and means for spraying the aqueous solution onto the plated steel strip 1 or the plated steel strip 1 in the aqueous solution. Means for immersing 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, adsorption of components derived from pyrophosphoric acid, Passivation can suppress adsorption of extreme pressure components and the like, and the rust preventive oil is easily washed with a degreasing liquid.

  Moreover, in the said description, although contact process S2 concerning the manufacturing method 10 was demonstrated as what is given to the plating steel strip 1 which passed through the tension leveler 3, contact process S2 is temper rolling process S1, drying process S3, If it is between, it will not be restricted in particular. 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 above-mentioned stain resistance can be improved at the same time, and the chemical conversion treatment and coating properties in the subsequent chemical conversion treatment step and coating step can be improved.

  In the examples, a 70 mm × 150 mm alloyed hot dip galvanized steel sheet test material was used, which was not surface-treated with an aqueous pyrophosphate solution, etc., and was an uncoated oiled active galvanized steel sheet. (Hereinafter simply referred to as “test material”) were prepared, and each was immersed in an aqueous solution whose components were adjusted as shown in Table 1. The following performance was evaluated for each immersed specimen.

(Degreasing evaluation)
Each test material was coated with 1.5 g / m ² of antirust oil (550S manufactured by Parker Kosan Co., Ltd.). After oiling, it was placed in a drier in an air atmosphere and cured at 60 ° C. for 4 days. In addition, curing at 60 ° C. for 4 days is equivalent to leaving it at room temperature for about 1 month.

  After completion of curing, it was immersed for 2 minutes in a commercially available alkaline degreasing solution (SD280Z manufactured by Nippon Paint Co., Ltd., 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 wet state of the surface after 10 seconds is visually observed, and the ratio of the wetted area (hereinafter referred to as the wetted area ratio (%)) is degreased. It was used as an index. If the wetted area ratio is 90% or more, it can be said that the degreasing property is good.

(Stain resistance evaluation)
The stain resistance was obtained by applying 1.5 g / m ² of antirust oil (550S manufactured by Parker Kosan Co., Ltd.) to each test material. Thereafter, five steel plates were stacked to form a stack with a torque of 5 Nm. After creating the stack, it was left for 30 days at 50 ° C. and 95% humidity, and after standing, the appearance of each steel sheet was examined to investigate the discoloration. Further, the stain resistance was visually determined by the appearance of the steel plate. The determination results are shown below.
A: No discoloration (very good)
○: Partially discolored (almost good)
×: Extremely unsatisfactory

  Table 1 shows the components of the aqueous solution brought into contact with the test material, and the evaluation results of degreasing and stain resistance.

  From the results of Table 1, when the aqueous solution according to Examples 1 to 22 in which the pyrophosphate concentration in the aqueous solution is in the range of 0.1 mmol / L to 50 mmol / L is brought into contact with the test material, The water wettability of each exceeded 90%, the degreasing property was improved, and the stain resistance was also good. Further, when the pyrophosphate root concentration is less than 0.1 mmol / L, the degreasing property is adversely affected (Comparative Examples 1 to 7), and when the pyrophosphate root concentration is more than 50 mmol / L, the stain resistance is adversely affected. It was found that there was a case (Comparative Example 8).

  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 (6)

Temper rolling of galvanized steel sheet, temper rolling,
A contact step in which an aqueous solution containing 0.1 to 50 mmol / L of pyrophosphate radicals is brought into contact with the plated surface of the steel sheet that has been temper-rolled in the temper rolling step;
The manufacturing method of the hot dip galvanized steel sheet characterized by including the drying process of drying the steel plate after the contact process. The hot dip galvanized steel sheet according to claim 1, wherein a step of intentionally forming an oxide layer on the plated surface of the steel sheet is not included between the temper rolling step and the contact step. Manufacturing method. The method for producing a hot-dip galvanized steel sheet according to claim 1 or 2, 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. The manufacturing method of the hot dip galvanized steel plate as described in any one of -3. The hot-dip galvanized steel sheet according to any one of claims 1 to 4, 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 5, wherein the hot dip galvanized steel sheet is an alloyed hot dip galvanized steel sheet.

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