KR960010161B1 - Method for manufacturing galvanealed steel plates with an excellent workability and corrosion resistance after coatings - Google Patents

Abstract

fusion galvanizing a low carbon Al-killed steel sheet in a zinc plating bath so that zinc amount adhering on one side of the steel sheet is 80-100g/m3; performing heat treatment for alloying zinc and iron at 500-540 deg.C; and cooling at cooling rate of more than 30 deg.C/sec.. Adjustment of the zinc adhering amount, the temperature for heat treatment and the cooling rate improves workability and corrosion resistance after painting.

Description

Process for producing alloyed hot dip galvanized steel sheet with excellent workability and corrosion resistance after painting

1 is a graph showing the change in Fe concentration according to the alloying treatment temperature.

2 is a graph showing the change in workability according to the cooling rate after the alloying treatment.

3 is a graph showing the change in workability and corrosion resistance according to the coating amount.

The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet used for home appliances, automobile steel plates, and the like, and more particularly, to a method for producing an alloyed hot-dip galvanized steel sheet excellent in workability and corrosion resistance after coating. It is about.

Among hot-dip galvanized products, alloyed hot-dip galvanized steel sheet is widely used in home appliances and automotive steel plates because of its excellent weldability and paintability, but especially in the application of automotive steel sheets, high processability is required, It should be excellent in corrosion resistance after painting.

In general, alloyed hot-dip galvanized steel sheet is manufactured by alloying heat treatment of a strip passed through a galvanizing bath in a continuous hot-dip galvanizing line, and uses titanium or titanium-niobium composite additive ultra-low carbon steel as a material for manufacturing a steel sheet for processing. . The alloyed hot-dip galvanized steel sheet produced in the steel grade is peeled off the plating layer during processing, and the phenomenon of powdering and flaking occurs, the workability is lowered to improve the steel grade, pre-plating, hot-dip plating conditions, Research on alloying heat treatment conditions is actively underway.

As a well-known technique for improving the workability of alloyed hot-dip galvanized steel sheet, Japanese Patent Laid-Open No. 56-13470, which has been alloyed after galvanizing by adding a small amount of aluminum in a hot-dip galvanizing bath, iron, nickel on a pre-galvanized steel sheet Japanese Patent Laid-Open Publication No. 58-104163, Japanese Laid-Open Publication No. 60-110859, and the like, which have been plated first and then galvanized and alloyed, are known. In addition, the processability and coating property is excellent alloyed hot-dip zinc-coated steel sheet by known techniques is 01~4.0g / m ² coating the organic film on the one surface after plating and the alloying treatment of the plating bath by the addition of vanadium that Japanese Unexamined Patent Publication (Kokai) 5-44006 etc. are mentioned.

However, in the case of Japanese Patent Laid-Open No. 56-13470, the workability is improved to some extent, but there is a problem in that moldability is poor and corrosion resistance after coating is inferior.

In addition, in the case of Japanese Patent Laid-Open Publication No. 58-104163 and No. 60-110859, a separate pretreatment step must be added, which leads to a complicated manufacturing process and an increase in manufacturing cost. .

In addition, in the case of Japanese Patent Laid-Open No. 5-44006, since a separate post-treatment process has to be added, this also has a problem that the manufacturing process is complicated as well as an increase in manufacturing cost.

Therefore, the present invention adjusts the cooling rate after the alloying treatment at an appropriate temperature by adjusting the adhesion amount by plating and air spraying in a conventional galvanizing bath composition, thereby providing excellent powdering resistance during press working and excellent corrosion resistance after painting. To produce a method for economically manufacturing an alloyed hot-dip galvanized steel sheet, the purpose is.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is a method for producing a hot-dip galvanized galvanized steel sheet by immersing a low-carbon aluminum-kilted steel material in a hot-dip galvanizing bath, followed by alloying and melting, so that the one-sided adhesion amount is in the range of 80 to 100 g / m ² After galvanizing and alloying in a temperature range of 500 ~ 540 ℃ and then cooled to a cooling rate of 30 ℃ / sec or more relates to a method for producing an alloyed hot dip galvanized steel sheet excellent in workability and corrosion resistance after coating.

In addition, the present invention is a method for producing a hot-dip galvanized coated steel sheet in a method of manufacturing a hot-dip galvanized steel sheet by immersing a titanium-niobium compound-added ultra low carbon steel material in a hot dip galvanizing bath, followed by hot dip galvanizing. After hot-dip galvanizing to the range of ² , the alloying treatment at a temperature range of 480 ~ 520 ℃, and then cooled at a cooling rate of 30 ℃ / sec or more to produce an alloyed hot dip galvanized steel sheet excellent in workability and corrosion resistance after coating It is about.

Hereinafter, the hot dip galvanizing and alloying process of the present invention will be described in detail.

The present invention is to control the alloying treatment temperature and the cooling rate after the alloying treatment in order to improve the workability during the production of alloyed hot-dip galvanized steel sheet, and to control the coating amount within the appropriate range to improve the corrosion resistance after coating. Factors affecting alloying reactivity include steel grade, continuous annealing conditions, plating conditions, and alloying treatment conditions. In particular, the aluminum concentration in the plating bath is adjusted in consideration of the strip passage speed and the alloy furnace length as factors affecting the alloying reaction rate, the alloy layer structure and the surface structure. Ultra-low carbon steel with added titanium as an effect of SOCHI steel grades, unlike aluminum-kilted low carbon steel, has a weak layer of iron-zinc-aluminum based zinc-iron-diffusion which suppresses zinc-iron interdiffusion during hot dip galvanizing. The compound is produced at the interface. These intermetallic compounds promote the diffusion of iron in the steel grades during the alloying process to increase the iron concentration in the alloy layer. If the iron concentration in the plating layer is increased above the optimum value, the capital gamma (Γ) layer is formed at the base iron / plating layer interface, and thus the powdering tendency is high during processing, and therefore, an appropriate temperature must be maintained during alloying heat treatment. Therefore, in the case of alloying treatment, steel with low titanium content, which is detrimental to workability, and mixed with small amount of niobium having the same purpose as titanium is used in many cases. The workability can be secured while preventing the formation of the capital gamma (Γ) layer at the base iron / plated layer interface. In the case of aluminum-kilted steel, a stable ternary alloy layer is formed by the reaction of aluminum and strip in the plating bath during hot dip plating, and the ternary alloy layer is added with a titanium-niobidium complex to maintain an appropriate iron concentration in the plating layer during alloying. 20 ° C higher temperature than ultralow carbon steel.

That is, in the case of aluminum-kilted low carbon steel, the temperature of iron in the plating layer is 9% or less even at temperatures of 500 ° C. or lower and 480 ° C. or lower in the titanium-niobidium-added ultra low carbon steel, and the structure of the plating layer is zeta + delta (ζ + δ). It is composed of phase, so that powdering property is good during press processing, but the press load is increased, so it is easy to cause poor press formability. In the case of aluminum-kilted low carbon steel, heat treatment at 540 ℃ or higher and titanium-niobidium-added ultra low carbon steel at 520 ℃ or higher results in an iron concentration of 12% or more, and is incapable of workability at the base iron / plated layer interface. Gamma (Γ) phases are not preferred because of the appearance.

Therefore, in the present invention, the alloying treatment temperature is preferably limited to 500 to 540 ° C for aluminum-kilted low carbon steel and 480 to 520 ° C for titanium-niobinium-added ultra low carbon steel.

Cooling after the alloying heat treatment is possible by a conventional cooling method, but quenching such as compressed air, water spray, steam-water spray, and water deposition is preferable, and is an important manufacturing factor related to the improvement of workability of the plating layer. In other words, as iron continues to diffuse into the plating layer during cooling after alloying, the iron concentration in the plating layer increases, resulting in deterioration of workability. Therefore, after alloying, the cooling rate is 30 ° C / sec or more to improve plating adhesion. The thickness of the capital gamma (Γ) layer at the plating layer interface should be minimized.

That is, after the alloying treatment, the cooling rate is preferably 30 ° C./sec or more without any distinction. At 30 ° C./sec or less, the iron concentration in the plating layer continuously increases during cooling, thereby degrading workability, and the plating layer in the hot strip is top rolled. It is not preferable because it is transferred from (Top-Roll) and surface stain occurs.

Since the alloying hot-dip galvanized steel sheet has a high iron concentration in the plating layer, it is common to evaluate corrosion resistance after coating rather than corrosion resistance of the plating layer itself. The deposition amount is determined by the air spray nozzle pressure and the gap between the strip and the nozzle after hot dip plating in the galvanizing bath. In the thin plating, the thick anti-corrosive property of zinc in the plating layer is deteriorated, and thus thicker after plating is required. However, in the post-plating manufacturing of alloyed hot-dip galvanized steel sheet, the plating adhesion is rapidly deteriorated, which is not preferable, so it should be limited to an appropriate plating thickness range that satisfies the processability and corrosion resistance proposed by the present invention.

That is, when the thickness of the plating layer is 80g / m ² or less, the swelling occurrence time of the swelling is shortened, and the corrosion resistance is deteriorated.In 100g / m ² or more, the corrosion resistance is increased, but as the thickness of the plating layer is increased, a higher temperature is required during alloying heat treatment. The workability is deteriorated and unalloyment occurs at the edge of the strip, making it impossible to produce a product with uniform color.

Therefore, in this invention, it is preferable to limit the adhesion amount (thickness) of a plating layer to 80-100 g / m <^2> .

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

Example

After the reduction heat treatment annealing of cold carbon steel sheet of 0.8 mm thick carbon low carbon aluminum (Al-K) and titanium-niobium complex ultra-low carbon steel (Ti-Nb) was carried out at 760 ℃, 820 ℃, respectively, After the hot-dip galvanized steel sheet by hot-dip and alloying treatment under the same conditions as in Table 1, the specimens were taken to measure workability and corrosion resistance after coating, and the measurement results are shown in Tables 1 and 2-3 below. It was.

On the other hand, the Fe concentration change in the alloying temperature range of 440-560 degreeC was observed, and the result is shown in FIG.

TABLE 1

1) Attachment amount: one side, g / m ²

2) Workability: Comparison by weight difference before and after Erichen processing

3) Corrosion resistance: Comparison of coating film swelling width 1 ~ 2mm before and after adhesion coating

As shown in FIGS. 1-2 and Table 1, the ultra-low carbon steel with aluminum-kilted steel 500 to 540 ° C. and the titanium-niobidium composite additive has a steel content of 9 to 12% in the plating layer at 480 to 520 ° C. It can be seen that it can be prepared and the cooling rate is 30 ℃ / sec or more it can be seen that the corrosion resistance and workability is good.

On the other hand, as shown in FIG. 3, the steel sheet whose plating adhesion was controlled in the range of 80 to 100 g / m ² on a one-side basis while satisfying the manufacturing conditions for each steel type in FIGS. Known for excellence.

As described above, the present invention has an effect of providing a hot-dip zinc alloy plated steel sheet excellent in workability and corrosion resistance after coating by appropriately adjusting the deposition amount and the alloying treatment conditions under the plating conditions and the cooling rate.

Claims (2)

In a method of manufacturing a hot-dip galvanized steel sheet by immersing a low-carbon aluminum-kilted steel material in a hot-dip galvanizing bath, followed by alloying, hot-dip galvanized so that the one-sided deposition amount is in the range of 80 to 100 g / m ² . After, after the alloying treatment in the temperature range of 500 ~ 540 ℃, and the cooling method at a cooling rate of 30 ℃ / sec or more characterized in that the workability and corrosion resistance after coating excellent alloyed hot dip galvanized steel sheet manufacturing method. In a method of producing a hot-dip galvanized steel sheet by immersing a titanium-niobidium-added ultra low carbon steel material in a hot dip galvanizing bath, followed by galvanizing, an alloy having a single sided adhesion amount of 80 to 100 g / m ² After hot-dip galvanizing to a range, the alloying treatment at a temperature range of 480 ~ 520 ℃, and then cooled at a cooling rate of 30 ℃ / sec or more, characterized in that the production of alloyed hot-dip galvanized steel sheet excellent in workability and corrosion resistance after coating Way.