KR20010018653A - A method for manufacturing hot-dip galvanized steel sheets having good coating quality properties - Google Patents

Abstract

PURPOSE: A method for manufacturing hot-dipped galvanized coils and sheets having superior plating quality characteristics is provided to manufacture regular spangle having a uniform and appropriate size by regulating contents of Pb and Sb in the same composition of a zinc plating bath. CONSTITUTION: A method for manufacturing hot-dipped galvanized coils and sheets having superior plating quality characteristics consists the processes of manufacturing minimized spangle hot-dipped galvanized coils and sheets having a spangle size of 0.5 mm or less by spraying phosphate solution on the plated steel plate after plating an electrolytic cleaned and annealed rolled steel plate (1) in a plating bath (6) having a composition comprising 0.13 to 0.25 wt.% of Al, 0.06 to 0.12 wt.% of Sb, 0.005 wt.% or less of Pb, a balance of Zn and inevitable impurities; and manufacturing zero spangle (12) in which the spangle is not observed with naked eye by skin pass milling the minimized spangle hot-dipped galvanized coils and sheets. The phosphate solution is ammonium hydrogen phosphate or sodium hydrogen phosphate in a powder from, and sprayed in a concentration of 0.5 to 3.0 and amount of 80 to 120 g/m3.

Description

Method for manufacturing hot-dip galvanized steel sheet with excellent plating quality characteristics {A METHOD FOR MANUFACTURING HOT-DIP GALVANIZED STEEL SHEETS HAVING GOOD COATING QUALITY PROPERTIES}

The present invention relates to a method for manufacturing hot-dip galvanized steel sheet used in various building materials, home appliances, automobiles, and the like, in particular, by the same plating bath composition, the plating surface is smooth and plating quality characteristics such as blackening resistance, peeling resistance at inner diameter, glossiness, etc. The present invention relates to a method for producing this excellent regular spangle, minimized spangle, and zero spangle hot-dip galvanized steel sheet.

In general, hot-dip galvanized steel sheet has a regular spangle (Regular-spangle), Minimized-spangle, and zero-sight without the flower pattern according to the size of the flower-shaped zinc crystal formed on the plating surface. It is classified as Zero-spangle.

The spangles formed on the plating surface affect the smoothness, blackening resistance and glossiness of the plating surface according to their shape and uniformity, and are determined by the components of the plating bath and the manufacturing method.

To further explain this, hot-dip galvanized steel sheet is manufactured by alkali-cleaning and annealing the rolled steel sheet and then passing it through a galvanizing bath to hot-dip galvanizing the steel sheet and forcing it to cool or spraying Zn powder before the coated steel sheet is solidified. Done. The chemical composition of the hot dip galvanizing bath is aluminum (Al): 0.10 to 0.30, lead (Pb) or antimony (Sb): 0.05 to 0.15, the remainder is zinc (Zn), and cadmium (Cd), bismuth ( Bi) and the like.

Al is an important element that determines the plating quality in the hot dip galvanizing bath. When the steel sheet is immersed in the hot dip galvanizing bath, Al preferentially reacts with Fe and Zn at the interface between the steel sheet and the plating bath, and the thin Fe-Al- A film of Zn is formed to prevent the production of out-burst (Fe-Zn compound), which is a reactant of Fe and Zn.

The outburst has high hardness and brittleness, so once the hot-dip galvanized steel sheet with outburst is formed at the interface between the steel sheet and zinc, the outburst is broken and the plated film is peeled off from the steel sheet.

In addition, the Al is combined with Fe eluted from the steel plate in the plating bath to form dross (Fe ₂ Al ₅ ), which is an intermetallic compound of Fe and Al, to rise above the plating bath, where Fe is accumulated in the lower portion of the plating bath. It serves to prevent.

Pb or Sb is added to the plating bath to adjust the size of the spangle, and exclusively used, that is, Sb becomes an impurity when Pb is used, and Pb becomes an impurity when Sb is used.

Pb is easy to manufacture minimized spangles, but it precipitates at Zn grain boundary to promote grain boundary corrosion, resulting in time-lapse peeling (a phenomenon in which the plating layer falls from the base steel when processing after 3 months after molten zinc plating). Sb has a drawback that spangles remain even when forced cooling and Zn powder is sprayed.

Recently, in order to solve this problem, there is a tendency to manufacture minimize or zero spangle without adding Pb or Sb to the plating bath, but it is impossible to manufacture regular spangle. There is a problem that does not satisfy the desire.

In order to solve the above-mentioned problems, various methods have been proposed. Japanese Patent Laid-Open Publication No. 53-128539 discloses a plating bath having Al: 0.2 to 17, Sb: 0.02 to 0.15, and Pb: 0.02 or less. Flow patterns occur at Al concentrations of 0.25 and above, and regular spangles are not possible at Sb concentrations of 0.05 and below. At the concentration of Sb concentrations of 0.10 and above, spangles having a size of 2 mm or more remain during the production of minimized sponges. If the concentration is 0.008 or more, Pb is precipitated at the Zn grain boundary, and thus there is a disadvantage in that time-dependent peeling is caused by the promotion of grain boundary corrosion.

In addition, KR-90426 discloses a plating bath with Al: 0.15 to 0.20 and Sb: 0.03 to 0.14. However, a flow pattern occurs at an Sb concentration of 0.06 or less, and commercial regular spangles cannot be produced. Above 0.10, not only has a disadvantage in that spangles having a size of 2 mm or more remain in the production of minimized spangles, but no method for producing minimized and zero spangles is disclosed.

Further, Japanese Patent Laid-Open No. 8-74018 discloses Al: 0.1 to 0.3, Sb: 0.003 to 0.10, Ni and Cr in one or a total, in a plating bath of 0.001 to 2.0 or less, followed by quenching and mist. The present invention provides a method for producing zero spangle by cooling, but in the case of zero spangle, since the spangle having a size of 2 mm remains as shown in the examples, the high quality molten zinc does not allow the spangle to be seen by the naked eye. It is impossible to manufacture a plated zero spangle, and furthermore, there is a problem in that it cannot be used industrially since no method for producing zero spangle is proposed.

The present invention was devised to solve the above problems in view of the above-mentioned conventional problems, and includes regular spangles and minimized plates having a smooth plating surface and excellent plating quality characteristics such as blackening resistance, peeling resistance and gloss resistance. It is an object of the present invention to provide a method for manufacturing a spangle and a zero spangle hot dip galvanized steel sheet.

1 is a schematic view showing a hot-dip galvanizing facility for producing a hot-dip galvanized steel sheet excellent in plating quality characteristics according to the present invention.

<Description of the code | symbol about the principal part of drawing>

1: rolled steel sheet 2: electrolytic cleaning equipment

3: steel sheet storage facility 4: annealing furnace

5: Snout 6: Zinc plating bath

7: Plating amount adjusting equipment 8: Regular spangle

9: Minimize Spangle Manufacturing Equipment

10: Minimize Spangle 11: Temper Rolling Mill

12: Zero Spangle

In order to achieve the above object, in the method of manufacturing a hot-dip galvanized steel sheet, Al: 0.13 to 0.25, Sb: 0.06 to 0.12, Pb: 0.005 or less, the remainder is electrolytic cleaning and annealing in a plating bath composed of Zn and unavoidable impurities After plating the treated rolled steel sheet, spraying a phosphate solution on the plated steel sheet to produce a minimized spangle hot-dip galvanized steel sheet having a spangle size of 0.5 mm or less, and the minimized spangle hot-dip galvanized steel sheet. There is provided a hot dip galvanized steel sheet manufacturing method having excellent plating quality characteristics, comprising the step of manufacturing a zero spangle by temper rolling and the spangles are not visually observed.

In the present invention as described above, the phosphate solution is powdered as ammonium hydrogen phosphate or sodium hydrogen phosphate, and is characterized in that it is sprayed at 80 to 120 g / m 2 at a concentration of 0.5 to 3.0.

The pressure of the phosphate solution and air for injecting the phosphate solution was set to 1.8 to 2.3 kg / cm 2 and 3.0 to 3.5 kg / cm 2, respectively.

In addition, the rolling load of the temper rolling in the present invention is characterized in that 30 to 500 Ton.

Hereinafter, the manufacturing conditions of the present invention will be described in detail.

First, the description of the production of regular spangles showed that the minimum concentration of Al without plating peeling was derived as 0.13 by uniformly forming a Fe-Al-Zn film at the interface between the base iron and the Zn plating layer through experiments. When the concentration of Al is increased in the plating bath of 0.25 or more, a flow pattern is generated on the surface of the plating and the base iron is eroded, so that dross occurs excessively, resulting in a plating surface defect. Therefore, the concentration of Al is limited to 0.13 to 0.25.

Since Pb precipitates at the Zn grain boundary and generates black stools and time-lapse peeling, the lower the composition ratio is, the better.The higher the wettability test (plating layer peeling test after 48 hours at 95 ° C and 95 RH) shows that the concentration does not occur over time. Derived at 0.008 or less, the minimum amount that can be inevitably incorporated in the production of Zn is 0.004, so the concentration of Pb allowed in the plating bath is limited to 0.005 or less.

Sb forms and grows spangles, and the size of the spangles is determined by the Sb concentration, and thus the size of commercially produced regular spangles is 5 to 15 mm.

The minimum Sb concentration, which can produce a spangle with a size of 5 mm or more, was derived as 0.05. As a result, it was confirmed that a flow pattern occurred at an Sb concentration of less than 0.06.

In addition, the maximum Sb concentration that can produce the size of the spangle to 15 mm or less and the phosphate solution having a large cooling effect when spraying the minimaized sponge, the size of the spangle becomes 0.5 mm or less, when producing zero spangle Even when temper rolling with a rolling load of 30-500 Ton, the Sb concentration which does not produce delamination with time was 0.12.

Therefore, the concentration range of Sb is limited to 0.06 to 0.12.

On the other hand, the temperature of the plating bath in the present invention is set to be the same as the temperature of the general hot dip galvanizing bath 440 ~ 480 ℃.

Next, a description will be made of the minimized spangles. Minimized spangles were prepared by spraying a phosphate solution before zinc in the plated steel sheet having a temperature composition range of about 418 to 420 ° C. plated in the above-described plating bath was solidified.

The phosphate for preparing the minimized spangles used an ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ) or sodium hydrogen phosphate (Na ₂ HPO ₄ .12H ₂ O) having a large cooling effect due to an endothermic reaction during pyrolysis. At this time, the concentration of the phosphate is preferably 0.5 to 3.0, which is the minimum concentration for preparing the phosphate concentration of 0.5 to less than 0.5 mm, if the concentration is increased to 3.0 or more, the cooling effect is increased but the phosphate This is because phosphorus (P) in the residue remains on the plated steel sheet, causing black stools.

In addition, the injection amount of the phosphate is limited to 80 ~ 120 g / ㎡, the phosphate injection amount of 80 g / ㎡ is the minimum concentration for producing the size of the spangle to 0.5 mm or less, the cooling capacity is increased above 120 g / ㎡ Therefore, the effect of reducing the size of the spangle is limited because it causes a surface defect such as large spots or white spots on the plating surface, thereby lowering the glossiness.

At this time, the phosphate solution should be sprayed on the surface of the coating to make the phosphate solution into fine powder (Mist) in order to increase the cooling effect and not to produce white spots. The pressure of the phosphate solution and air supplied to the spray nozzle was important, and the pressure of the phosphate solution was 1.8-2.3 kg / cm 2 and the pressure of air was 3.0-3.5 kg / cm 2.

The lower limit (1.8, 3.0 kg / cm 2) of the above-mentioned pressure conditions is the minimum pressure for producing the size of the spangle to 0.5 mm or less as a powder without the solution flowing down, and the upper limit of the pressure conditions (2.3, 3.5 kg / cm 2) ) Is defined as the maximum pressure at which white spots do not occur.

Next, referring to the production of zero spangles, as a result of temper rolling the minimized spangles manufactured as described above with a rolling load of 30 to 500 Ton, zero spangles having a smooth surface without visible visuals of spangles on the plated surface were produced. It became.

The lower limit of the rolling load (30 Ton) is the minimum load for producing a zero spangle by rough rolling so that the minimized spangle of the plating surface is not visually observed, and the upper limit of the rolling load (500 Ton) is The plating layer prepared at the upper limit of the plating bath component is the maximum load that does not cause delamination during the production of zero spangle by temper rolling.

1 is a schematic view showing a hot dip galvanizing facility for manufacturing a hot dip galvanized steel sheet having excellent plating quality characteristics according to the present invention. Referring to this, the rolled steel sheet 1 is degreased in an electrolytic cleaning facility 2, and the steel sheet is stored. After the annealing furnace 4 is annealed at 700 to 830 ° C. in the non-oxidizing atmosphere of the annealing furnace 4, the rolled steel sheet 1 passes through the snout 5 and the galvanizing bath 6 is 1 to 1. 2 seconds was passed.

At this time, the temperature of the galvanizing bath (6) was a general composition range of 440 ~ 480 ℃, after adjusting the coating amount in the coating amount adjusting equipment (7) the steel plate coated with a large amount of molten zinc from the galvanizing bath (6) When the hot-dip galvanized steel sheet 8 has a temperature range of 418 to 420 ° C. in the minimized spangle manufacturing equipment 9, a solution of phosphate (ammonium hydrogen phosphate or sodium hydrogen phosphate) having a concentration of 0.5 to 3.0 is sprayed. Minimized spangle 10 was prepared.

The minimized spangles 10 thus prepared were temper-rolled in a rough rolling mill 11 at a rolling load of 30 to 500 Ton to produce a zero spangle 12 having a beautiful and uniform surface.

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

<Example 1>

(1) The rolled steel sheet (Al-Killed: C: 0.035 to 0.04, Mn: 0.25, P: 0.02 or less) is degreased in the electrolytic cleaning facility (2), and then passed through the steel sheet storage facility (3) to the annealing furnace (4). Annealed at 700 to 760 ° C, the annealed rolled steel sheet 1 was passed through a snout 5 and a galvanizing bath 6 having a temperature of 440 to 480 ° C. Regular spangles 8 were prepared by adjusting to g / m 2 and cooling naturally.

At this time, the zinc plating bath (6) is Al: 0.13 ~ 0.25, Sb: 0.06 ~ 0.12, Pb: 0.005 or less, the balance is composed of Zn and unavoidable impurities, the experimental conditions and evaluation results are shown in Table 1 below .

Plating surface Plating bath components Gilding Quality Total judgment Al concentration () Sb concentration () Pb concentration () Spangle Size (mm) Flow Glossiness Plating Peeling inside diameter Comparative Example 1 Regular Pangle 0.12 0.45 Less than 0.005 × × ○ × ○ × Comparative Example 2 0.13 0.06 ○ ○ ○ ○ ○ ○ Comparative Example 3 0.13 0.12 ○ ○ ○ ○ ○ ○ Comparative Example 4 0.25 0.06 ○ ○ ○ ○ ○ ○ Comparative Example 5 0.25 0.012 ○ ○ ○ ○ ○ ○ Comparative Example 6 0.26 0.045 × × ○ ○ ○ × Comparative Example 7 0.26 0.06 ○ × ○ ○ ○ ×

The criteria and terms used in Table 1 will be described.

-. Spangle size: The size was 5-15 mm, and it was judged that it was good ((circle)).

-. Flow pattern: Visually observed, it was determined that there was no flow pattern as good (○).

-. Glossiness: It measured at 20 degreeC by JIS Z 8741, and determined that it was 130 or more as good ((circle)).

-. Plating peeling: After the lock forming test, it was visually observed to determine that there was no peeling of the plating layer as good (○).

-. Peeling at Internal Diameter: After 48 hours of surface exposure at a relative humidity of 95 and a temperature of 95 ° C, it was determined that the plating peeling was 1 or less in the bending and taping tests.

<Example 2>

Rolled steel sheet (Ti-Nb-IFS (Interstitial Free Steel): C: 0.002, Mn: 0.10, P: 0.015 or less, Ti 0.030 ~ 0.032, Nb 0.010 ~ 0.013) (1) after degreasing in electrolytic clean facility (2) , Annealing at an annealing furnace (4) at 810 to 830 ° C. through a steel plate storage facility (3) and sintering the annealed rolled steel sheet (5) and a galvanizing bath (6) having a temperature of 440 to 480 ° C. A phosphate solution having a concentration of 0.5 to 3.0 at a temperature of 418 to 420 ° C., which is produced by adjusting the plating amount to 90 to 600 g / m 2 in the plating amount adjusting equipment 7 through Minimized spangles 10 were prepared by spraying g / m 2.

At this time, the zinc plating bath (6) was Al: 0.13 to 0.25, Sb: 0.06 to 0.12, Pb: 0.005 or less, the balance was made of Zn and unavoidable impurities, and the minimized spangle manufacturing equipment (9) The pressures of the powdered phosphate solution and air supplied to the injection nozzle were 1.8 to 2.3 kg / cm 2 and 3.0 to 3.5 kg / cm 2, respectively, and the experimental conditions and evaluation results thereof are shown in Table 2 below.

In the preparation conditions of Table 2, * Solution Types 1 and 2 exclusively used ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ) or sodium hydrogen phosphate (Na ₂ HPO ₄ · 12H ₂ O).

The criteria and terminology used in Table 2 will be described.

-. Spangle size: 0.5 mm or less in size and uniform were judged as good ((circle)).

-. Flow pattern: Visually observed, it was determined that there was no flow pattern as good (○).

-. Point defects: The plating surface was visually observed to determine that there were no point defects.

-. Glossiness: It measured at 20 degreeC by JIS Z 8741, and determined that it was 180 or more as good ((circle)).

-. Resistance to blackening: No change in color after surface exposure for 144 hours at a relative humidity of 95 and a temperature of 50 ° C. was judged as good (○).

-. Peeling at Internal Diameter: After 48 hours of surface exposure at a relative humidity of 95 and a temperature of 95 ° C, it was determined that the plating peeling was 1 or less in the bending and taping tests.

<Example 3>

(1) The rolled steel sheet (Ti-P-IFS: C: 0.003 to 0.004, Mn: 0.30, P: 0.06, Ti: 0.05) (1) is degreased in the electrolytic cleaning facility (2) and then annealed through the steel plate storage facility (3). In the furnace (4) annealing at 750 ~ 760 ℃, the annealed rolled steel sheet (1) is passed through the snout (5) and the galvanizing bath (6) having a temperature of 440 ~ 480 ℃ and in the plating amount adjusting equipment (7) When the temperature of the regular spangles 8 with the plating amount adjusted to 90 to 600 g / m 2 is 418 to 420 ° C., 80 to 120 g / m 2 is sprayed with a phosphate solution having a concentration of 0.5 to 3.0, thereby minimizing the spangles 10. Was prepared.

The minimized spangles 10 were temper-rolled in a rough rolling mill 11 of a continuous hot dip galvanizing facility with a rolling load of 30 to 500 tonnes to produce a smooth and uniform zero spangle 12. At this time, the zinc plating bath 6 was Al: 0.13 to 0.25, Sb: 0.06 to 0.12, Pb: 0.005 or less, the balance was made of Zn and unavoidable impurities in the same manner as in Examples 1 and 2. As described above, the pressures of the phosphate solution and air supplied to the injection nozzles of the minimized spangle manufacturing equipment 9 were 1.8 to 2.3 kg / cm 2 and 3.0 to 3.5 kg / cm 2, respectively. It is shown in Table 3.

In the preparation conditions of Table 3, * Solution Types 1 and 2 used exclusively ammonium hydrogen phosphate (NH ₄ H ₂ PO ₄ ) or sodium hydrogen phosphate (Na ₂ HPO ₄ · 12H ₂ O).

The criteria and terminology used in Table 3 will be described.

-. Spangle size: The plating surface was visually observed to determine that no spangles were found to be good (○).

-. Flow pattern: Visually observed, it was determined that there was no flow pattern as good (○).

-. Point defects: The plating surface was visually observed to determine that there were no point defects.

-. Glossiness: It measured at 20 degreeC by JIS Z 8741, and determined that it was 150 or more as good ((circle)).

-. Resistance to blackening: No change in color after surface exposure for 144 hours at a relative humidity of 95 and a temperature of 50 ° C. was judged as good (○).

-. Peeling at Internal Diameter: After 48 hours of surface exposure at a relative humidity of 95 and a temperature of 95 ° C, it was determined that the plating peeling was 1 or less in the bending and taping tests.

As described above, according to the present invention by controlling the Pb, Sb content in the same zinc plating bath composition to prevent the occurrence of black stools and time-lapse peeling, with the production of a regular spangle having a uniform and appropriate size, the supply amount of the phosphate solution, It is possible to manufacture minimized spangles with smooth and excellent glossiness and the size of spangles of 0.5 mm or less by adjusting the injection pressure and air pressure to appropriate conditions and forming a uniform plating surface with the prevention of white spot defects.

In addition, there is an effect that can be prepared of the zeros pangle in which the spangles are not visually observed by the temper rolling by appropriate load.

Claims (4)

In the method of manufacturing a hot-dip galvanized steel sheet, Al: 0.13 to 0.25, Sb: 0.06 to 0.12, Pb: 0.005 or less, and the remainder is plated with a rolled steel plate subjected to electrolytic cleaning and annealing in a plating bath composed of Zn and unavoidable impurities, and then sprayed with a phosphate solution on the plated steel sheet. Preparing a minimized spangle hot-dip galvanized steel sheet having a size of the spangle of 0.5 mm or less; The method of manufacturing a hot dip galvanized steel sheet having excellent plating quality characteristics, characterized in that it comprises the step of producing a zero spangle in which the spun is not visually observed by rolling the minimized spangle hot dip galvanized steel sheet. The hot-dip galvanized steel sheet having excellent plating quality characteristics according to claim 1, wherein the phosphate solution is powdered as ammonium hydrogen phosphate or sodium hydrogen phosphate and sprayed at 80 to 120 g / m 2 at a concentration of 0.5 to 3.0. Manufacturing method. The pressure of the phosphate solution and air for injecting the phosphate solution is 1.8 to 2.3 kg / cm 2 and 3.0 to 3.5 kg / cm 2, respectively. Hot-dip galvanized steel sheet manufacturing method. The method of claim 1, wherein the rolling load of the temper rolling is 30 to 500 Ton.