JP2005314725A - METHOD FOR MANUFACTURING Si-CONTAINING STEEL SHEET - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a Si-containing steel sheet, which inhibits yellowing from occurring in a pickling step after a continuous annealing step. <P>SOLUTION: The manufacturing method is applied to the steel sheet containing 0.05 mass% or more Si; uses a yellowing inhibitor comprising one or more compounds selected from (A) a polyamine with an average molecular weight of 200 to 10,000, (B) a phosphonic acid (B1) and/or a salt (B2) thereof having chelating properties, and (C) a low-molecular carboxylic acid (C1) and/or a salt (C2) thereof; and when defining a period of time after having finished a pickling step and before starting the yellowing-inhibiting treatment step as t1 (second), a period of time while the steel sheet contacts with the yellowing inhibitor as t2 (second), a period of time after having finished the yellowing-inhibiting treatment step and before starting a washing step as t3 (second), a Si content in the steel sheet as S (mass%), and a temperature of the steel sheet when having finished the pickling step as T (°C), controls the factors so as to satisfy the following expressions (a) and (b): (a) t1≤-0.02×S×T+5.0, and (b) t2≥0.3×S-0.2×t3+0.8. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a thin steel plate, and more particularly to a method for manufacturing a thin steel plate including a step of performing a surface treatment including pickling after continuous annealing.

  In recent years, the use of high-tensile steel plates for automobile parts has been promoted for the purpose of ensuring collision safety, energy saving, and environmental measures. With the expansion of applicable parts of high-tensile steel plates, the performance required for these high-strength steel plates has also become stricter, and the workability for producing complex shapes that were not a problem in the past and the beautiful appearance after painting have been achieved. The surface treatment for ensuring, or the surface appearance improvement of the high-tensile steel plate itself has been a problem.

  These high-strength steel sheets are made by adding many alloying elements in the steel, hot rolling, cold rolling, heating to a predetermined temperature with a continuous annealing facility, and then applying a predetermined mechanical strength such as high tension by microstructure control by rapid cooling. It is common practice to ensure the characteristics.

  As a rapid cooling method in the continuous annealing equipment, since a higher cooling rate is advantageous in the production of a high-tensile steel plate, for example, called water quench, a method of directly immersing a steel plate in a water-cooled tank, called air-water cooling, A method of spraying a refrigerant obtained by mixing water and atmospheric gas in a mist form on a steel plate is employed.

  In these rapid cooling methods, water is used as a refrigerant, and thus an oxide film is formed on the surface of the steel sheet. In order to remove the formed oxide film, it is pickled after annealing.

  However, as will be described later, in a steel sheet containing Si in steel, after the pickling, oxidation coloring of the surface called yellowing is likely to occur. Conventionally, even if yellowing has occurred, there is often no problem, but with the expansion of the application parts of high-strength steel sheets, the appearance of poor appearance due to yellowing is becoming pointed out by customers.

  As a method for preventing discoloration after pickling in such a continuous annealing facility, for example, Patent Document 1 attempts to prevent discoloration by the concentration, temperature, and line speed of the pickling solution. Further, Patent Document 2 discloses a method for suppressing discoloration by controlling the temperature of the plate entering the pickling.

  However, in the case of Si-added steel, it is difficult to suppress the yellowing described above only by changing the concentration and temperature of the pickling solution.

  On the other hand, the following three types of surface discoloration problems and countermeasures are generally known.

  First, there is a problem of discoloration that occurs when the pickling line stops or slows down in the pickling process after hot rolling. As a countermeasure against this problem, for example, Patent Document 3 discloses a method of applying a discoloration preventing agent to a steel plate portion that is not immersed in a treatment liquid in a water washing section after pickling when the pickling line is stopped. Patent Document 4 discloses a method of washing with water after applying a chelating agent to a steel plate taken out from a pickling tank when the pickling line is stopped or gradually moved.

  The second problem is discoloration that occurs when the electrolytic cleaning line stops or slows down in the electrolytic cleaning step after cold rolling. As a countermeasure against this problem, for example, Patent Document 5 proposes a method of adding a discoloration preventing agent to cleaning water after electrolytic cleaning and stirring the cleaning water when the electrolytic cleaning line is stopped. Patent Document 6 discloses a method of discharging a cleaning liquid from the vicinity of an electrolytic electrode to the surface of a steel sheet when the electrolytic cleaning line is stopped.

  Further, as the above-mentioned discoloration preventing agent, for example, Patent Document 7 discloses a discoloration preventing agent for a steel plate made of cyclohexylamine or the like. Patent Document 8 discloses a discoloration inhibitor containing pentaethylenehexamine and hydrazine. Patent Document 9 discloses a discoloration inhibitor comprising an aliphatic dicarboxylic acid or a salt thereof and a polymer of an unsaturated carboxylic acid or a salt thereof. Patent Document 10 discloses a method of preventing discoloration by bringing a steel plate after pickling into contact with a liquid containing an anti-discoloring agent and then contacting with a rinsing liquid containing a compound having an amino group or a carboxyl group. Furthermore, in the above-mentioned Patent Document 3, several kinds of carboxylic acids are used in combination as an anti-discoloring agent, and in Patent Document 5, polyethylene polyamines, alkanolamines, aliphatic dibasic acids, oxyacids are used as rust inhibitors. It has been proposed that carboxylic acid or the like is used as a discoloration inhibitor.

Third, there is a problem of discoloration that occurs on the non-plated surface when performing single-sided plating in the electroplating line. As a countermeasure against this problem, for example, Patent Document 11 discloses a method of cleaning a non-plated surface after single-side plating and then bringing it into contact with washing water to which a discoloration inhibitor is added. In patent document 12, the method of wash | cleaning a steel plate with the aqueous solution of PH9-13 containing a specific chemical | medical agent after the water washing after single-sided plating is disclosed.
JP-A-6-212462 Japanese Unexamined Patent Publication No. 7-258873 JP-A-61-253389 JP 61-195983 A JP-A-2-305985 JP-A-8-3797 JP-A-1-225785 Japanese Patent Publication No. 3-29872 Japanese Examined Patent Publication No. 4-80119 Japanese Patent Publication No.7-835 Japanese Patent Laid-Open No. 55-14814 JP-A-61-588

  However, although the reaction mechanism itself is not clear, the yellowing phenomenon that occurs in Si-containing steel cannot be solved by simply diverting the conventional anti-discoloration technology from the time until the occurrence of discoloration and the degree of discoloration. It is not considered. Then, this invention makes it a subject to obtain the manufacturing method of the Si containing steel plate which can suppress the yellowing which arises by the pickling after continuous annealing.

First, yellowing after pickling of various steel sheets containing alloy elements such as Si and Mn was investigated. as a result,
(I) Si is dominant as an influence of alloying elements on yellowing, and yellowing is likely to occur in steel sheets containing 0.05 mass% or more of Si. The higher the Si content, the more yellowing occurs. Getting worse,
(II) It was found as a finding that the higher the steel plate temperature at the end of pickling, the worse the degree of yellowing.

  From these findings, the surface state after pickling differs between steel sheets containing Si and the other steel sheets. Therefore, the steel sheets containing Si are susceptible to yellowing, and this reaction is accelerated by the steel plate temperature. It is thought that it is done.

Furthermore, (III) In order to prevent yellowing after the pickling treatment after annealing the steel sheet containing Si, the steel plate surface after pickling is appropriately called an agent for preventing yellowing (hereinafter referred to as “yellowing inhibitor”). ) (Hereinafter referred to as “yellowing prevention treatment”) is effective,
(IV) At that time, the time from pickling to yellowing prevention treatment, the processing time of yellowing prevention treatment, and the time from yellowing prevention treatment to water washing include Si% in steel and steel plate immediately after pickling. It was found that there was an appropriate range (or constraint) in relation to temperature.

Thus, the gist of the present invention is
A steel plate containing 0.05% by mass or more of Si is subjected to continuous annealing, followed by surface treatment including pickling, wherein the surface treatment is a pickling step of pickling the steel plate, A yellowing prevention treatment step of bringing a treatment liquid containing a yellowing inhibitor into contact with the steel sheet surface, and a water washing step of washing the steel sheet in contact with the treatment liquid,
The yellowing inhibitor is
(A) a polyamine having an average molecular weight of 200 to 10,000,
(B) a chelating agent phosphonic acid (B1) and / or a salt thereof (B2);
(C) a low molecular carboxylic acid (C1) and / or a salt thereof (C2);
Including one or more selected from:
The time from the end of the pickling step to the start of the yellowing prevention treatment step is t1 (seconds),
Time t2 (second) for the steel sheet to contact the treatment liquid,
The time from the end of the yellowing prevention treatment process to the start of the water washing process is t3 (seconds),
The Si content of the steel sheet is S (mass%),
When the temperature of the steel sheet at the end of the pickling step is T (° C.),
It exists in the manufacturing method of the steel plate characterized by following formula (a) and (b) being materialized.
t1 ≦ −0.02 × S × T + 5.0 (a)
t2 ≧ 0.3 × S−0.2 × t3 + 0.8 (b)

  Here, the “low molecular carboxylic acid” in the present invention refers to a carboxylic acid having a molecular weight of 150 or less.

  The polyamine (A) having an average molecular weight of 200 to 10,000 is dicyandiamide / formalin polycondensate, dicyandiamide / diethylenetriamine polycondensate, epichlorohydrin / dimethylamine addition polymer, diallyldimethylammonium chloride / sulfur dioxide polymer, diallyldimethylammonium. Polymer of chloride, polyethyleneimine, pentaethylenehexamine, polycondensate of metaxylenediamine and epichlorohydrin, polymer of diallylamine hydrochloride and sulfur dioxide, polyarylamine, one or more Is preferred.

  The chelating agent phosphonic acid (B1) is any one of aminotrimethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, hexamethylenediaminephosphonic acid, or two or more thereof. Preferably there is.

  The low-molecular carboxylic acid (C1) is preferably one or more of formic acid, glycolic acid, oxalic acid, malonic acid, and succinic acid.

  The salt of the chelating agent phosphonic acid (B2) and / or the salt of the low molecular carboxylic acid (C2) is any one or two of sodium salt, potassium salt, ammonium salt, amine salt, and alkanolamine salt The above is preferable.

  Any of (A) polyamine having an average molecular weight of 200 to 10,000, (B) a chelating agent phosphonic acid and / or salt thereof, and (C) a low molecular carboxylic acid and / or salt thereof has an average molecular weight of 10,000 or less. Preferably there is.

  The treatment liquid preferably contains 10 to 10000 mg of the yellowing inhibitor in 1 L of the medium.

  According to the present invention, when producing a steel sheet containing 0.05% by mass or more of Si as an alloying element in steel, it is possible to effectively prevent yellowing that was likely to occur during pickling after annealing. It is possible to satisfy the quality demands of the changing customers. Such an operation and a gain of the present invention will be clarified from the best mode for carrying out the invention described below.

  Hereinafter, the manufacturing method of the steel plate concerning this invention is concretely demonstrated by embodiment of invention.

1. Base Steel The manufacturing method of the present invention is particularly effective when manufacturing a thin steel plate to which 0.05% by mass or more of Si is added. This is because, as described above, the yellowing phenomenon after continuous annealing is particularly remarkable in a thin steel sheet containing 0.05% by mass or more of Si.

2. Pickling process The manufacturing method of the present invention includes a surface treatment process including pickling after the annealing process. In the present invention, batch annealing and continuous annealing can be employed as the annealing method, but continuous annealing is preferable from the viewpoint of productivity. In the case of continuous annealing, an overaging treatment step is often provided after the annealing step, but this overaging treatment step may be any before or after the pickling step. This will be described with reference to the schematic diagram of the continuous annealing equipment shown in FIGS.

  As shown in FIG. 1, the steel sheet manufacturing method of the present invention is performed after the steel sheet 1 is heated and annealed in the soaking zone 2, and then slowly cooled to a predetermined temperature in the air-water cooling zone 3, and then overheated in the overaging zone 4. An aging treatment may be performed, followed by a pickling treatment in the pickling treatment equipment 5, or rapid cooling in the water cooling zone 7 through roll cooling or gas jet cooling in the slow cooling zone 6 as shown in FIG. After that, pickling treatment with the pickling equipment 5 may be performed, followed by overaging treatment with the overaging band 4.

  The method for producing a steel sheet of the present invention includes a pickling process for pickling the steel sheet after annealing, a yellowing prevention treatment process for bringing the pickled steel sheet into contact with a treatment liquid containing a yellowing inhibitor, and yellowing prevention. And a surface treatment comprising a water washing step of washing the steel sheet in contact with the treatment liquid containing the agent. In FIG. 3, the outline of an example of the pickling processing equipment 5 is shown. The steel sheet is pickled in the pickling tank 10 and the pickling spray 11. As the acid used for pickling, hydrochloric acid or sulfuric acid having a concentration of about 1 to 20%, which is widely used, can be used. At that time, an appropriate amount of a corrosion inhibitor may be contained in the acid solution so that the surface of the steel sheet is not excessively etched. The pickled steel sheet is sprayed with a treatment liquid containing a yellowing inhibitor by a treatment liquid application spray 9. The treatment liquid application sprays 9 are arranged side by side in the longitudinal direction of the steel sheet, and the application time can be controlled. Instead of such a spray method, a dipping method in which the steel sheet is immersed in the treatment liquid bath may be used. The treatment liquid containing the yellowing prevention agent is supplied from the tank 14 through the inlet side pipe 15 by the pump 17 and is collected to the tank through the outlet side pipe 16 or is led out of the system as a waste liquid. 18 is a pressure gauge and a pressure controller, 19 is a flow meter and a flow controller. Subsequent to the yellowing prevention treatment step, a water washing step of washing the steel sheet surface with water is carried out with the water washing spray 13 and the water washing tank 12.

In the present invention, in the surface treatment, it is essential to perform the treatment so as to satisfy the following expressions (a) and (b).
t1 ≦ −0.02 × S × T + 5.0 (a)
t2 ≧ 0.3 × S−0.2 × t3 + 0.8 (b)
However,
t1: Time (seconds) from the end of the pickling process to the start of the yellowing prevention treatment process
t2: Time (seconds) that the steel sheet contacts the treatment liquid
t3: Time (seconds) from the end of the yellowing prevention treatment process to the start of the water washing process
S: Si content of steel sheet (% by mass)
T: Temperature of the steel sheet at the end of the pickling process (° C)
It is. In the surface treatment, yellowing of the surface of the steel sheet after pickling can be effectively prevented by setting process conditions that satisfy both the above formulas (a) and (b).

3. Yellowing inhibitor The yellowing inhibitor according to the production method of the present invention is:
(A) Polyamine having an average molecular weight of 200 to 10,000 (B) Chelating agent phosphonic acid (B1) and / or a salt thereof (B2)
(C) Low molecular carboxylic acid (C1) and / or its salt (C2)
1 type or 2 types or more selected from.

  Usually, a pickled steel sheet is often subjected to chemical conversion treatment in the next step. Therefore, it is preferable to select an anti-yellowing agent that does not affect the chemical conversion treatment of the next step by the yellowing prevention treatment step. From this viewpoint, preferred yellowing treatment agents are as follows.

  Examples of polyamines (A) having an average molecular weight of 200 to 10,000 include dicyandiamide and formalin polycondensate, dicyandiamide and diethylenetriamine polycondensate, epichlorohydrin and dimethylamine addition polymer, diallyldimethylammonium chloride and sulfur dioxide polymer, diallyldimethylammonium Polymer of chloride, polyethyleneimine, pentaethylenehexamine, polycondensate of metaxylenediamine and epichlorohydrin, polymer of diallylamine hydrochloride and sulfur dioxide, polyarylamine, one or more Is preferred.

  The chelating agent phosphonic acid (B1) is aminotrimethylphosphonic acid, 1-hydroxyethylidene-1,1 diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, hexamethylenediaminephosphonic acid, or two or more of them. Preferably there is.

  Low molecular carboxylic acid (C1) refers to a carboxylic acid having a molecular weight of 150 or less in the present invention. Such low-molecular carboxylic acid (C1) is preferably one or more of formic acid, glycolic acid, oxalic acid, malonic acid, and succinic acid.

  Chelate phosphonic acid salt (B2) and / or low molecular weight carboxylic acid salt (C2) is any one of sodium salt, potassium salt, ammonium salt, amine salt, alkanolamine salt, or two or more thereof It is preferable that

  The treatment liquid containing the yellowing inhibitor contains 10 to 10000 mg, preferably 30 to 5000 mg, more preferably 50 to 3000 mg of the yellowing inhibitor with respect to 1 L of water. When there is too little content of the yellowing prevention agent with respect to 1 L of water, there will be no yellowing prevention effect. On the other hand, it is not economical that the content of the yellowing inhibitor is too high, and the COD load during waste water treatment becomes high, which is not preferable.

  The treatment liquid containing the yellowing inhibitor may contain other discoloration inhibitors and rust inhibitors as needed in addition to the yellowing inhibitor. Other discoloration inhibitors include sodium, potassium, ammonium or amine salts such as aliphatic dicarboxylic acids such as sebacic acid and dodecanedioic acid, and oxycarboxylic acids such as gluconic acid. Examples of the rust preventive agent include amines such as diethanolamine and triethanolamine.

  Although the yellowing prevention mechanism of the yellowing inhibitor is not clear, the yellowing inhibitor selectively adsorbs on the active sites centered on Si present on the steel sheet surface by pickling to form a film. It is thought that yellowing is prevented by interfering with or delaying the oxidation reaction with oxygen or water. Furthermore, it is thought that yellowing is prevented by suppressing the elution of Fe ions from the steel sheet, which is considered to be a cause of yellowing.

[Yellow test Line test]
(Invention Example 1, Comparative Examples 1-3)
A steel sheet having a Si addition amount of 0.7 mass% was manufactured by passing through the continuous annealing equipment shown in FIG. In addition, the pickling processing equipment 5 in this equipment is shown in FIG. About 3.0% hydrochloric acid was used for pickling. Subsequent to the pickling, a treatment liquid containing 0.2% of pentaethylenehexamine was sprayed on the surface with a spray (spray flow rate 100 L / min), followed by washing with water. The yellowing state of the surface of such a steel sheet was visually evaluated, and the results were recorded according to the following criteria.
(Evaluation criteria for yellowing)
○: Little yellowing was observed visually.
X: Significant yellowing was observed.
The results are shown in Table 1. In addition, x and y in Table 1 are numerical values calculated by the following formula (the same applies to Table 6).
x = −0.02 × S × T + 5.0
y = 0.3 * S-0.2 * t3 + 0.8
That is, the equations (a) and (b) are
It is the same as t1 ≦ x and t2 ≧ y.
In the determination column of (a) and (b), “good” is displayed when the values of t1 and t2 satisfy the conditions of the expressions (a) and (b), respectively, and “no” is displayed when they are not satisfied ( The same applies to Table 6).

  Inventive Example 1, which satisfies both the above formulas (a) and (b), hardly yellowed, whereas in Comparative Examples 1 to 3 that did not satisfy either of the above formulas (a) or (b) A marked yellowing was observed.

  In FIG.4 and FIG.5, the result of having performed evaluation similar to Table 1 about the steel plate of Si content 0.05-1.4 mass% is shown. FIG. 4 shows the results of manufacturing under conditions that satisfy the above-described formula (b). In this case, the yellowing prevention effect was obtained as long as the conditions satisfied the above formula (a). FIG. 5 shows the results of manufacturing under conditions that satisfy the above-mentioned formula (a). In this case, the yellowing prevention effect was obtained as long as the conditions satisfied the above formula (b).

[Yellowing test lab test]
(Invention Examples 2-18)
The following yellowing prevention treatment was performed using a cold-rolled steel sheet (100 mm × 50 mm, thickness 1.5 mm) with an Si addition amount of 0.7 mass%.
1. Immerse in a 70%, 5% aqueous sodium hydroxide solution for 30 seconds. 2. Degreasing 3. Hot air drying Immerse it in a pickling solution at 50 ° C in which 50 g of hydrochloric acid and 20 g of ferrous chloride are dissolved in 1 liter of tap water (T = 60 ° C)
5). 5. Hold in air for 2 seconds after immersion A treatment liquid (35 ° C.) obtained by adding 100 mg of various yellowing inhibitors shown in Table 2 to 1 L of tap water was used, and the distance between the spray nozzle and the steel plate was 30 cm using a spray nozzle (1/4 MVEP65117TPVDF manufactured by Ikeuchi Co., Ltd.). Spray for 2 seconds (flow rate 5L / min)
7. Hold in the air for 1 second Use 8.35 ° C tap water spray nozzle (1/4 MVEP65117TPVDF Ikeuchi Co., Ltd.) and spray for 1 second (flow rate 5L / min) with 30cm distance between spray nozzle and steel plate
9. Immerse in tap water at 35 ° C for 5 seconds 10. Dry with hot air for 30 seconds

About the yellowing state of the obtained steel plate, it determined visually by the following reference | standard. In addition, the b value of the surface was measured with a spectrocolorimeter (CM-508C manufactured by Minolta). The b value is a numerical value in the Hunter Lab color system, and is a numerical value that is substantially correlated with the apparent yellow color.
The visual judgment of the yellowing state was performed based on the following criteria.
◎: No yellowing ○: Almost no yellowing △: Slightly yellowing ×: Extremely yellowing

  The results are shown in Table 2.

(Comparative Example 4)
The following treatment was performed using a high-tensile steel plate (Si content: 0.7% by mass, the same in Comparative Examples 5 to 11 below).
1. 2. Immerse in pickling solution described in Invention Examples 2 to 18 for 7 seconds. Hold in air for 2.10 seconds. A 35 ° C aqueous solution obtained by adding 100 mg of polyethyleneimine (average molecular weight 1800) to 1 liter of tap water is sprayed for 2 seconds using a spray nozzle (1/4 MVEP65117TPVDF, manufactured by Ikeuchi Co., Ltd.) and the distance between the spray nozzle and the steel plate is 30 cm. (Flow rate 5L / min)
4.1 Hold in the air for 1 second Tap water at 5.35 ° C using a spray nozzle (1/4 MVEP65117TPVDF Ikeuchi Co., Ltd.) and spray for 1 second with a distance of 30cm between the spray nozzle and the steel plate (flow rate 5L / min)
6. Soaked in tap water at 35 ° C. for 5 seconds 7. Dryer drying Table 3 shows the results.

(Comparative Example 5)
The following treatment was performed using a high-tensile steel plate.
1. 2. Soaked in the pickling solution described in Invention Examples 2 to 18 for 7 seconds and kept in air for 2.2 seconds. A 35 ° C aqueous solution obtained by adding 100 mg of polyethyleneimine (average molecular weight 1800) to 1 liter of tap water is used for 0.5 seconds using a spray nozzle (1/4 MVEP65117TPVDF, manufactured by Ikeuchi Co., Ltd.) and the distance between the spray nozzle and the steel plate is 30 cm. Spray (flow rate 5L / min)
4. Hold in the air for 1 second. Tap water at 5.35 ° C using a spray nozzle (1/4 MVEP65117TPVDF Ikeuchi Co., Ltd.) and spray for 1 second (flow rate 5L / min) with the distance between the spray nozzle and the steel plate set to 30cm.
6. Soaked in tap water at 35 ° C. for 5 seconds 7. Dryer dried for 30 seconds Table 3 shows the results.

(Comparative Example 6)
100 mg of pentaethylenehexamine (molecular weight 232) was added to 1 L of tap water. The test method and test conditions were the same as in Comparative Example 4. Table 3 shows the results.

(Comparative Example 7)
100 mg of pentaethylenehexamine (molecular weight 232) was added to 1 L of tap water. The test method and test conditions were the same as in Comparative Example 5. Table 3 shows the results.

(Comparative Example 8)
100 mg of tetraethylenepentamine (molecular weight 189) was added to 1 L of tap water. The test method and test conditions were the same as in Examples 2 to 18 of the present invention. Table 3 shows the results.

(Comparative Example 9)
10 parts by mass of sebacic acid and 20 parts by mass of monoethanolamine were added, and 1000 mg of a yellowing inhibitor dissolved in tap water was added to 1 L of tap water. The test method and test conditions were the same as in Examples 2 to 18 of the present invention. Table 3 shows the results.

(Comparative Example 10)
10 parts by mass of dodecanedioic acid and 20 parts by mass of diethanolamine were added, and 1000 mg of a yellowing inhibitor dissolved in tap water was added to 1 L of tap water. The test method and test conditions were the same as in Examples 2 to 18 of the present invention. Table 3 shows the results.

(Comparative Example 11)
It implemented like Example 2-18 of this invention except not having used a yellowing prevention agent. Table 3 shows the results.

  Comparative Examples 4 to 7 were conditions that did not satisfy Formula (a) or Formula (b). Comparative Example 8 was a case where a substance that was a polyamine but had a molecular weight of less than 200 was used as an anti-yellowing agent. Comparative Examples 9 to 10 were cases where a substance not corresponding to any of (A), (B), and (C) was used as the yellowing inhibitor. In each of these comparative examples, a sufficient yellowing prevention effect could not be obtained. Further, the b values measured at the same time showed values of −1.0 or more, and the same tendency as the result of visual observation was recognized.

(Invention Examples 19 to 29)
Chemical conversion treatment was performed using the steel plates obtained in Invention Examples 2-12.
(1) Surface adjustment: A steel plate treated in the same manner as in Invention Examples 2 to 18 was immersed in a surface adjustment liquid (prepare (trade name) 2.5 g per 1 L of tap water, liquid temperature 25 ° C.) for 20 seconds. did.
(2) Chemical conversion treatment: treated with PB-L3007M (trade name) at 50 ° C. for 2 minutes. Then, after washing with tap water for 10 seconds and drying with a dryer for 30 seconds, the falling state of crystals of the chemical conversion coating film was determined by the following criteria with an electron microscope (S-4300, manufactured by Hitachi, Ltd.).
Judgment criteria:
◎: No dropout part ○: Almost no dropout part Δ: Some dropout part results are shown in Table 4.

(Comparative Example 12)
The yellowing prevention treatment was performed by the same test method as that of Invention Examples 2 to 18. However, 100 mg of polyethyleneimine (average molecular weight 20000) was added to 1 L of tap water as a yellowing prevention agent. Chemical conversion treatment was performed using the obtained steel plate. The chemical conversion treatment method and conditions were the same as those of Examples 19 to 29 of the present invention. Table 5 shows the results.

(Comparative Example 13)
The yellowing prevention treatment was performed by the same test method as that of Invention Examples 2 to 18. However, 100 mg of a polymer of diallyldimethylammonium chloride and sulfur dioxide (average molecular weight 100000) was added to 1 L of tap water as a yellowing inhibitor. Chemical conversion treatment was performed using the obtained steel plate. The chemical conversion treatment method and conditions were the same as those of Examples 19 to 29 of the present invention. Table 5 shows the results.

  Comparative Examples 12 and 13 are examples in which an anti-yellowing agent having an average molecular weight exceeding 10,000 was used, but both were slightly inferior in chemical conversion treatment.

  Finally, Table 6 summarizes the results of pass / fail judgments regarding whether or not t1 and t2 satisfy the formulas (a) and (b) for all the inventive examples and comparative examples described above.

  While the present invention has been described in connection with embodiments that are presently the most practical and preferred, the present invention is not limited to the embodiments disclosed herein. However, the present invention can be modified 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 for producing a Si-containing 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 figure which shows typically the structure of a continuous annealing equipment. It is a figure which shows typically the structure of another continuous annealing equipment. It is the schematic of the pickling processing equipment concerning the manufacturing method of this invention. It is a figure which shows the Example of this invention. It is a figure which shows the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Steel plate 2 Heating and soaking zone 3 Air-water cooling zone 4 Over-aging zone 5 Pickling processing equipment 6 Slow cooling zone 7 Water-cooling zone 8 Treatment liquid application device 9 Treatment liquid application spray 10 Pickling tank 11 Pickling spray 12 Water washing tank 13 Washing spray 14 Tank 15 Inlet piping 16 Outlet piping 17 Pump 18 Pressure gauge and pressure controller 19 Flow meter and flow controller

Claims (7)

A steel plate containing 0.05% by mass or more of Si is subjected to continuous annealing, followed by surface treatment including pickling, wherein the surface treatment is a pickling step of pickling the steel plate, A yellowing prevention treatment step of bringing a treatment liquid containing a yellowing inhibitor into contact with the steel sheet surface, and a water washing step of washing the steel sheet in contact with the treatment liquid,
The yellowing inhibitor is
(A) a polyamine having an average molecular weight of 200 to 10,000,
(B) a chelating agent phosphonic acid (B1) and / or a salt thereof (B2);
(C) a low molecular carboxylic acid (C1) and / or a salt thereof (C2);
Including one or more selected from:
The time from the end of the pickling step to the start of the yellowing prevention treatment step is t1 (seconds),
Time t2 (second) for the steel sheet to contact the treatment liquid,
The time from the end of the yellowing prevention treatment process to the start of the water washing process is t3 (seconds),
The Si content of the steel sheet is S (mass%),
When the temperature of the steel sheet at the end of the pickling step is T (° C.),
A method for manufacturing a steel sheet, characterized in that the following formulas (a) and (b) are satisfied.
t1 ≦ −0.02 × S × T + 5.0 (a)
t2 ≧ 0.3 × S−0.2 × t3 + 0.8 (b) The polyamine (A) having an average molecular weight of 200 to 10,000 is dicyandiamide and formalin polycondensate, dicyandiamide and diethylenetriamine polycondensate, epichlorohydrin and dimethylamine addition polymer, diallyldimethylammonium chloride and sulfur dioxide polymer, diallyldimethylammonium. Polymer of chloride, polyethyleneimine, pentaethylenehexamine, polycondensate of metaxylenediamine and epichlorohydrin, polymer of diallylamine hydrochloride and sulfur dioxide, polyarylamine, one or more The manufacturing method of the steel plate of Claim 1 characterized by these. The chelating agent phosphonic acid (B1) is aminotrimethylphosphonic acid, 1-hydroxyethylidene-1,1-diphosphonic acid, ethylenediaminetetramethylenephosphonic acid, hexamethylenediaminephosphonic acid, or one or more of them. The manufacturing method of the steel plate of Claim 1 or 2 characterized by the above-mentioned. The low-molecular carboxylic acid (C1) is any one of formic acid, glycolic acid, oxalic acid, malonic acid, and succinic acid, or two or more thereof. The manufacturing method of the steel plate of description. The salt of the chelating agent phosphonic acid (B2) and / or the salt of the low molecular carboxylic acid (C2) is any one or two of sodium salt, potassium salt, ammonium salt, amine salt, alkanolamine salt It is the above, The manufacturing method of the steel plate of any one of Claims 1-4 characterized by the above-mentioned. All of (A) polyamine having an average molecular weight of 200 to 10,000, (B) chelating agent phosphonic acid and / or salt thereof, and (C) low molecular weight carboxylic acid and / or salt thereof have an average molecular weight of 10,000 or less. It exists, The manufacturing method of the steel plate of any one of Claims 1-5 characterized by the above-mentioned. The method for producing a steel sheet according to any one of claims 1 to 6, wherein the treatment liquid contains 10 to 10,000 mg of the yellowing inhibitor in 1 L of a medium.

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