KR19990018149A - Method for manufacturing hot-dip galvanized hot-dip galvanized steel plate with excellent black resistance - Google Patents

Abstract

The present invention relates to a method for producing a zero-spangle hot-dip galvanized hot rolled steel sheet having excellent black-black resistance of the plating surface even if the plating surface is rubbing or Cr-treated and stored for a long time in a high temperature and high humidity atmosphere. The purpose is to prevent the zinc plated surface from turning black by preventing O ₂ from penetrating.

The present invention relates to a method for producing a zero-spangle hot-dip galvanized hot-rolled steel sheet in a continuous hot-dip galvanizing facility, wherein in the zero-spangle apparatus for producing a zero-spangle on a surface of a molten zinc metal in a semi-molten state after hot-dip plating. _After spraying a mixture of ₄ H ₂ PO ₄ and 0.25 to 0.5% by weight of Co ₃ (PO ₄ ) ₂ · 8H ₂ O to inhibit the growth of the spangles on the surface of the plating, and temper rolling to completely remove the spangles on the surface of the plating. The technical gist of the present invention is to prepare a zero-spangle hot dip galvanized hot rolled steel sheet by Cr treatment to prevent the galvanized surface from turning black.

Description

Manufacturing method of zero spangle hot dip galvanized hot rolled steel sheet with excellent black resistance

The present invention relates to a method for producing a zero-spangle hot-dip galvanized hot-rolled steel sheet which does not turn black even after being stored for a long time in a high temperature and high humidity atmosphere. More specifically, it contains 0.05 to 0.12% of Pb. Zero spangle hot dip galvanized with excellent blackness by spraying a mixture of NH ₄ H ₂ PO ₄ and Co ₃ (PO ₄ ) ₂ · 8H ₂ O after the hot dip of zinc on the surface after plating in the hot dip galvanizing bath To manufacture a hot rolled steel sheet.

In general, hot-dip galvanized hot-rolled steel sheet has a regular-spangle product having a flower pattern on the plating surface and a zero-spangle product without a flower pattern, and manufactures two products in one plating facility. Doing. In general, 0.18 to 0.25% by weight of Al is added to obtain a plating adhesion as a component of the plating bath for manufacturing hot-dip galvanized hot rolled steel sheet, and 0.05 to 0.12% by weight of Pb for forming and growing spangles. To prepare a regular spangle. In addition, in the manufacture of hot-spread hot-dip galvanized hot-rolled steel sheet, the hot-rolled steel sheet is plated using the same plating bath as that of regular spangle. The cooling of the metal prevents the growth of the spangles, and the size of the spangles is 1 mm or less, and is produced by skin pass rolling to remove the spangles of the plating surface. It is also subjected to chromium (Cr) treatment to improve the corrosion resistance of the plating surface.

However, the zero-spangle hot-dip galvanized hot-rolled steel sheet manufactured by such a general method is often changed to a blue or black color during transportation or warehouse storage, which is called black stools. As such, the black plated surface is rough and the glossiness of this part is poor. On the other hand, as the demand for hot-dip galvanized steel sheet is gradually increased and the usage is diversified, it is strongly required to improve the quality of appearance and corrosion resistance. Therefore, studies to prevent the occurrence of black stools on the surface of the plating has been conducted, mainly a method by adjusting the composition of the Cr solution has been proposed, but there is a disadvantage that the corrosion resistance (white blue blue and blue blue resistance) is relatively poor when improving the black blue resistance The improvement of the blackening resistance of the plating surface by the improvement of the Cr processing method has not acquired the satisfactory effect. In addition, Japanese Laid-Open Patent Publication No. 59-177381 discloses that a plated steel sheet is immersed in NiSO ₄ · 6H ₂ O aqueous solution or CoSO ₄ · 7H ₂ O aqueous solution prior to Cr treatment to attach Ni or Co to the plating surface to improve black resistance. Although the method is proposed, there is a drawback of deterioration of gloss due to corrosion of zinc on the plating surface while the zinc plating surface is immersed in NiSO ₄ · 6H ₂ O aqueous solution or CoSO ₄ · 7H ₂ O aqueous solution. In order to apply to existing galvanizing equipment, it is difficult to apply because it needs extra space to install necessary equipment.

In the hot dip galvanizing, if the plating surface is rubbed, even if the plated product is stored indoors, the plating surface becomes unstable and the plating surface is oxidized to generate black side. Cr treatment of the hot dip galvanized surface improves corrosion resistance but decreases black rust resistance. The reason is that when the hot-dip galvanized surface is Cr treated, the amount of O ₂ penetrating into the plating surface by Cr ^{+ 3} is limited, and zinc oxidation occurs in a state where oxygen is insufficient in the lower portion of the Cr film. Microscopic observation of the structure of the plated layer in which black stools occurred was confirmed to be oxygen-deficient zinc oxide (ZnO _1-x ). Thus, the need to increase the amount of Cr ⁺⁶ to prevent the O ₂ from penetrating in the galvanized surface reacts with O ₂ in order to prevent the heukcheong generated by the process, but if the amount of Cr in Cr ⁺⁶ Cr solution increases galvanized Since the surface turns yellow to impair the appearance, and Cr ⁺³ is relatively reduced, the effect of improving the corrosion resistance by Cr treatment is reduced. Therefore, it is impossible to increase the amount of Cr ⁺⁶ to prevent the black side of the plating surface. . Therefore, in the present invention, in order to prevent O ₂ from penetrating the zinc plated surface, zero spangles of a mixture of NH ₄ H ₂ PO ₄ and Co ₃ (PO) ₄ · 8H ₂ O after hot dip galvanizing before metal zinc solidifies. Co-attached to the plating surface by spraying from the manufacturing equipment to prevent O ₂ from penetrating into the plating surface, and utilizes a zero-spangle manufacturing device with excellent black resistance without installing a separate oxygen-deficient device. By doing so, it is conceived that zero spangle hot dip galvanized hot rolled steel sheet excellent in blackening resistance can be manufactured without additionally installing an additional device.

Therefore, the present invention has been made to solve the problems of the prior art described above, and even if the plating surface is rubbing or Cr treatment and stored for a long time in a high temperature and high humidity atmosphere, the black surface resistance and corrosion resistance of the plating surface is excellent, and the treatment method The purpose of the present invention is to provide a method for manufacturing a hot-splash hot-dip galvanized hot-rolled steel sheet that does not require additional equipment improvement by utilizing an existing zero-spangle manufacturing apparatus.

In order to achieve the above object, in the present invention, the hot-rolled steel sheet subjected to pickling treatment and reduction heat treatment in a facility for continuously manufacturing hot-dip galvanized hot-rolled steel sheet in a plating bath of 0.18 to 0.25 wt% Al, 0.05 to 0.12 wt% Pb After immersion and plating, the coating amount was adjusted by gas wiping, and then, on the molten zinc metal surface in the semi-melt state, 1 to 2 wt% NH ₄ H ₂ PO ₄ and 0.25 to 0.5 wt% Co ₃ (PO ₄ ) The plating surface is smooth, the white spots are zero, and the size of the spangle is 0.5 mm or less, characterized by spraying a mixture of ₂ · 8H ₂ O with 60 to 100 ml / m ² . Provided is a method for producing a zero-spangle hot dip galvanized hot rolled steel sheet excellent in blackening resistance.

Hereinafter, the present invention will be described in detail.

In the present invention, the components of the plating bath are 0.18 to 0.25 wt% Al, 0.05 to 0.12 wt% Pb, and the plating bath is dipped by immersing the hot rolled steel sheet which has passed through the pickling facility and the heating furnace in a non-oxidizing atmosphere, and then plating. The coating amount is adjusted by wiping (air or nitrogen wiping), and then, on the surface of the molten zinc metal in the semi-molten state, 1-2 wt% NH ₄ H ₂ PO ₄ and 0.25 to 0.5 wt% Spray the mixture of Co ₃ (PO ₄ ) ₂ · 8H ₂ O to 60 ~ 100mℓ / m ² to suppress the growth of spangles on the surface of the plating and make the size of the spangle 0.5 mm or less After the pungle is completely removed, Cr treatment is performed to prepare a zero spangle hot dip galvanized hot rolled steel sheet having excellent blackening resistance.

In the present invention, the Al concentration is limited in order to prevent growth of Fe-Zn alloy layers having poor workability by uniformly forming an alloy layer of Fe-Al-Zn at the interface between the plating layer and the base iron. The upper limit of Al concentration is to prevent damage to weldability when Al is excessively present on the plating surface.

Pb is an element that forms the nucleus of the spangle and determines the size of the spangle. The concentration of Pb is used to make regular and zero spangles in one plating bath, and the lower limit of the Pb concentration is regular. is the minimum concentration capable of producing the panggeul, the upper limit is a maximum density that is capable of spraying a liquid mixture of NH ₄ H ₂ PO ₄ and _{Co 3 (PO 4) 2 ·} 8H 2 O to produce a zero's panggeul. The size of the spangle is 5 to 15 mm when preparing the regular spangle, and the size of the spangle is 0.5 mm or less when producing the zero spangle.

The lower limit of the concentration of NH ₄ H ₂ PO ₄ is the minimum concentration at which the zero spangle can be produced in the plating bath composition of the present invention, and the upper limit produces the zero spangle of the smooth plating surface without generating white spots on the plating surface. This is the highest concentration you can.

The lower limit of the concentration of Co ₃ (PO ₄ ) ₂ · 8H ₂ O is the minimum concentration that can prevent the formation of black blue in a high wettability atmosphere even if the plating surface is rubbed during transportation of the product, and the upper limit is for economical efficiency.

Limiting the injection amount of the mixture of NH ₄ H ₂ PO ₄ and Co ₃ (PO ₄ ) ₂ · 8H ₂ O is the minimum amount to produce a zero spangle, and the upper limit is smooth and free of white spots on the plating surface. This is the highest amount of plating surface that can be produced.

Temper rolling is in the range of 0.5 ~ 2%, which is a commonly used rolling reduction rate, and Cr solution is also used in which 100% Cr ⁺⁶ 100% solution or Cr ⁺³ / Cr ⁺⁶ molar ratio is used. You may also do it.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

In a facility for continuously manufacturing hot-dip galvanized hot rolled steel sheets, low carbon steel with a plate thickness of 1.2 to 3.5 mm is immersed in a plating bath by pickling and reducing heat treated hot rolled steel sheets at a rate of 50 to 100 meters per minute in a plating bath. By adjusting the plating amount by 200 to 600 g / m ^2, and then on the surface of the molten zinc metal in the semi-melt state by 1 to 2 wt% NH ₄ H ₂ PO ₄ and 0.25 to 0.5 wt% Co ₃ ( The mixture of PO ₄ ) ₂ · 8H ₂ O is sprayed to suppress the growth of the spangles on the surface of the plating, and the temper rolling is used to completely remove the spangles on the surface of the plating, followed by Cr treatment to prepare a zero-spangle hot dip galvanized hot rolled steel sheet. In Table 1, the experimental conditions and evaluation results of the quality characteristics of the plated products are shown.

Comparative Example 1

In a facility for continuously manufacturing hot-dip galvanized hot rolled steel sheets, low carbon steel with a plate thickness of 1.2 to 3.5 mm is immersed in a plating bath by pickling and reducing heat treated hot rolled steel sheets at a rate of 50 to 100 meters per minute in a plating bath. By adjusting the plating amount by 200 to 600 g / m ^2, and then on the surface of the molten zinc metal in the semi-melt state by 1 to 2 wt% NH ₄ H ₂ PO ₄ and 0.25 to 1.0 wt% Co (NO ₃ ) Spraying a mixture of ₂ · 6H ₂ O to suppress the growth of the spangles on the surface of the plating, and temper rolling to completely remove the spangles on the surface of the plating, followed by Cr treatment to prepare a zero spangle hot dip galvanized hot rolled steel sheet. Table 1 shows the experimental conditions and evaluation results of the quality characteristics of the plated products.

Comparative Example 2

In a facility for continuously manufacturing hot-dip galvanized hot rolled steel sheets, low carbon steel with a plate thickness of 1.2 to 3.5 mm is immersed in a plating bath by pickling and reducing heat treated hot rolled steel sheets at a rate of 50 to 100 meters per minute in a plating bath. By adjusting the plating amount by 200 to 600 g / m ^2, and then spraying an aqueous solution of 0.25 to ₃ wt% 5Co ₃ (PO ₄ ) ₂ · 8H ₂ O with a zero-spangle manufacturing apparatus on the surface of the molten zinc metal in a semi-melt state. In order to suppress the growth of the spangles on the surface of the coating, and after the temper rolling, Cr treatment was performed to prepare a zero-spangle hot-dip galvanized hot-rolled steel sheet, and the experimental conditions and evaluation results of the quality characteristics of the plated products are shown in Table 1.

Comparative Example 3

In a facility for continuously manufacturing hot-dip galvanized hot rolled steel sheets, low carbon steel with a plate thickness of 1.2 to 3.5 mm is immersed in a plating bath by pickling and reducing heat treated hot rolled steel sheets at a rate of 50 to 100 meters per minute in a plating bath. By adjusting the plating amount by 200 to 600 g / m ^2, and then spraying an aqueous solution of ₁ to 2 wt% NH ₄ H ₂ PO _{4 on} the surface of the molten zinc metal in a semi-melt state by using a zero-spangle manufacturing apparatus. In order to suppress the growth of the pangle and to remove the spangles on the surface of the plating by temper rolling, the product is immersed in an aqueous solution of 1 to 5% by weight of CoSO ₄ · 7H ₂ O in a separate facility for 2 seconds and washed with Cr after washing with Cr. The pangle hot-dip galvanized hot-rolled steel sheet was manufactured, and the test results and evaluation results of the quality characteristics of the plated product are shown in Table 1.

Comparative Example 4

In a facility for continuously manufacturing hot-dip galvanized hot rolled steel sheets, low carbon steel with a plate thickness of 1.2 to 3.5 mm is immersed in a plating bath by pickling and reducing heat treated hot rolled steel sheets at a rate of 50 to 100 meters per minute in a plating bath. By adjusting the plating amount by 200 to 600 g / m ^2, and then spraying an aqueous solution of ₁ to 2 wt% NH ₄ H ₂ PO _{4 on} the surface of the molten zinc metal in a semi-melt state by using a zero-spangle manufacturing apparatus. In order to suppress the growth of the pangle and to perform the temper rolling to completely remove the spangles on the surface of the plating, Cr treatment was performed to prepare a zero-spangle hot-dip galvanized hot-rolled steel sheet. Marked on.

Sample number division Plating bath component (%) ZEROSPANGLE Aqueous Solution (%) Injection amount (ml / mm ² ) CoSO ₄ (%) Plating appearance Whiteness Glossiness Al Pb NH ₄ H ₂ PO ₄ Co ₃ (PO ₄ ) ₂ Co (NO ₃ ) ₂ One Inventive Example (Example) 0.18 to 0.25 0.05-0.12 One 0.25 85-92 ○ ○ ○ 2 One 0.5 80 to 85 ○ ○ ○ 3 2 0.25 75-82 ○ ○ ○ 4 2 0.5 60-70 ○ ○ ○ 5 Comparative Example 1 1 to 2 0.25 85-92 ○ △ △ 6 One 80 to 85 ○ △ △ 7 Comparative Example 2 0.25 80-140 × △ △ 8 3 80-120 × △ △ 9 Comparative Example 3 1 to 2 85-92 One ○ △ × 10 80 to 85 5 ○ △ × 11 Comparative Example 4 80-92 ○ × ○

The legend of the evaluation symbol used in Table 1 is as follows.

-Appearance of plating surface: Visually determine by using ruler after increasing the size of spangle by 10 times

○: Excellent (spangle size is 0.5 mm or less, uniform surface of plated steel sheet and no white spots)

(Triangle | delta): Normal (The size of a spangle is 1 mm or less but a partial nonuniformity and white spots appear.)

X: Poor (spangle of 2-3 mm in size with large number of white spots)

-Whiteness: Evaluation of blackness resistance by measuring the whiteness of plating surface after multiplying the surface by 0 ~ 720 hours in a sample with a relative humidity of 90% and a temperature of 50 ℃ using a multi spectro color meter. It was taken as an index.

○: excellent (whiteness 70 or more)

(Triangle | delta): Normal (white degree 69-65)

×: defective (less than whiteness 65)

-Glossiness: measured at 20。 by JIS Z 8741

○: Excellent (gloss 130 or more)

△: normal (glossiness 120 to 80)

X: Poor (less than glossiness 80)

As can be seen from the evaluation results of Table 1, in the case of the hot-rolled steel sheet manufactured by the embodiment according to the present invention, the appearance of the plating is not only good but also the whiteness is excellent, and the blackness is good. It can be seen that it is excellent. In addition, in Comparative Example 1, the plating appearance was excellent, but the whiteness and glossiness were normal. In Comparative Example 2, the plating appearance was poor and the whiteness and glossiness were normal. In Comparative Example 3, whiteness was normal and glossiness was poor, whereas in Comparative Example 4, whiteness was poor.

As a result of applying the present invention to a facility for continuously producing hot-dip galvanized hot-rolled steel sheet, as shown in the embodiment of the present invention, NH ₄ H ₂ PO ₄ in a zero-spangle manufacturing apparatus after the hot-dip galvanizing on the steel sheet after plating By spraying a mixture of and Co ₃ (PO ₄ ) ₂ · 8H ₂ O to produce a zero-spangle hot-dip galvanized hot-rolled steel sheet excellent in blackening resistance that does not turn black even after long-term storage in high temperature and high humidity atmosphere Is obtained.

Claims (1)

In a facility for continuously manufacturing hot-dip galvanized hot-rolled steel sheets, the hot-rolled steel sheets subjected to pickling treatment and reduction heat treatment are immersed in a plating bath containing 0.18 to 0.25 wt% Al and 0.05 to 0.12 wt% Pb, and then plated by gas wiping. After adjusting the plating amount, the molten zinc metal surface in the semi-molten state was prepared in a zero-spangle manufacturing apparatus of 1 to 2 wt% NH ₄ H ₂ PO ₄ and 0.25 to 0.5 wt% Co ₃ (PO ₄ ) ₂ · 8H ₂ O. A method for producing a hot-span galvanized hot-rolled steel sheet excellent in blackening resistance, characterized by spraying a mixed solution at 60 to 100 ml / m ² to zero-span the plating surface.