KR0146886B1 - Method for manufacturing hot-dipped zn-alloy coated steel sheet for the good machinability and anti-corrossion - Google Patents

Abstract

The present invention is to produce an alloyed hot-dip galvanized steel sheet having excellent powdering resistance during press working and excellent corrosion resistance after coating by performing the alloying treatment at a suitable temperature through the coating amount adjustment by plating and air spraying in a conventional galvanizing bath composition. The purpose is to provide as much as possible.

The present invention is an annealing and hot-dip galvanizing titanium-phosphorus composite addition ultra low carbon steel, and then alloyed to produce an alloyed hot-dip galvanized steel sheet, the plating deposition amount during the hot-dip galvanizing ranges from 80-100g / ㎡ The present invention provides a method for producing an alloyed hot-dip galvanized steel sheet excellent in workability and corrosion resistance by performing hot dip galvanizing and then alloying in a temperature range of 500-540 ° C.

Description

Manufacturing method of high tensile alloyed hot dip galvanized steel sheet with excellent workability and corrosion resistance

1 is a graph showing the change in workability and corrosion resistance according to the coating weight of the present invention.

2 is a graph showing the Fe concentration change according to the alloying treatment temperature of the present invention.

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

Among the 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. For this purpose, the corrosion resistance after coating of steel sheet should be excellent.

In general, alloyed hot-dip galvanized steel sheet is produced by alloying heat treatment of the strip passed through the galvanizing bath in a continuous hot dip galvanizing line. The steel sheet used in such an alloying heat treatment is an ultra low carbon steel, which usually contains 0.03-0.06 wt% titanium alone or a combination of 0.02-0.05 wt% titanium and 0.015-0.03 wt% niobium to improve workability. It also contains 0.04-0.2 wt% phosphorus to improve strength.

When an alloy layer vulnerable to the zinc plated layer and the base iron interface of the alloyed hot-dip galvanized steel sheet manufactured using the steel grades as described above is produced, the plating layer is peeled off during processing to cause powdering and flaking phenomenon. In order to improve the workability, research on steel grades, pre-plating conditions, hot-dip plating conditions, and alloying heat treatment conditions is actively underway.

As a result, various conventional methods have been proposed to improve the workability of alloyed hot-dip galvanized steel sheet, and representative methods include Japanese Patent Laid-Open No. 56-13470, Japanese Patent Laid-Open No. 58-104163, Japanese Patent Laid-Open No. 60-110859, Japanese Laid-Open Patent Publication No. 5-44006.

Japanese Patent Application Laid-Open No. 56-13470 is a method of alloying after hot-dip galvanizing by adding a small amount of aluminum in a hot dip galvanizing bath. Although workability is somewhat improved, there is a problem of poor moldability and poor corrosion resistance after coating.

Japanese Patent Laid-Open Nos. 58-104163 and 60-110859 are methods of first plating iron, nickel, etc. on a steel sheet before galvanizing, followed by galvanizing and alloying. However, in this case, since a separate pretreatment process must be added, the manufacturing process is complicated and there is a problem of increasing the manufacturing cost.

Japanese Patent Laid-Open No. 5-44006 is a method for coating 0.1-4.0 g / m 2 of an organic coating on one side after plating and alloying by adding vanadium in a hot dip plating bath. Since the treatment process has to be added, there is a problem that the manufacturing process is not only complicated but also increases the manufacturing cost.

Accordingly, the present inventors have proposed the present invention as a result of the research and experiment to solve the above problems, the present invention is an ordinary zinc plating bath after annealing the Ti-P composite addition ultra-low carbon steel in a certain condition Plating in the composition, alloying treatment at an appropriate temperature by adjusting the adhesion amount by air injection provides a method for producing an alloyed hot-dip galvanized steel sheet having excellent powder resistance during press working and excellent corrosion resistance after coating. There is a purpose.

Hereinafter, the present invention will be described.

The present invention is a method of producing an alloyed hot-dip galvanized steel sheet by annealing and hot-dip galvanizing titanium-phosphorus composite ultra low carbon steel, alloying, 0.03-0.06% titanium and 0.05-0.15% phosphorus composite After the added ultra low carbon steel is annealed at a temperature range of 780-830 ° C., it is passed through a hot dip galvanizing bath and subjected to hot dip galvanizing to adjust the coating amount to be in the range of 80-100 g / m 2, followed by 500-540 ° C. The present invention relates to a method for producing an alloyed hot-dip galvanized steel sheet excellent in workability and corrosion resistance by alloying in a temperature range.

Hereinafter, the present invention will be described in more detail.

In the present invention, the alloying treatment conditions are controlled to maintain strength and improve workability during the production of hot-dip galvanized steel sheet, and to control the coating amount within an appropriate range to improve corrosion resistance after coating.

Factors affecting the reactivity in the alloying treatment include steel grade, annealing conditions, plating conditions and alloying treatment conditions.In particular, aluminum commonly contained in a concentration range of 0.12-0.14% in the plating bath is alloying reaction rate and alloy. Factors affecting layer structure and surface texture are adjusted taking into account the strip passage speed and the length of the alloying furnace.

In the present invention, a titanium-phosphorus composite ultra low carbon steel is used as a plated steel sheet for workability and strength.

In general, when hot-dip galvanized steel sheet, a thin film layer of iron-zinc-aluminum based on suppressing mutual diffusion of zinc-iron at the plated layer and the base iron interface is produced. At this time, if the base steel is an ultra-low carbon steel containing titanium, unlike the aluminum-kilted low carbon steel, the thin film layer of the iron-zinc-aluminum system is vulnerable, and thus a zinc-iron intermetallic compound is formed on the plating layer and the base iron interface.

As such, the intermetallic compound formed at the zinc-plated layer and the base iron interface of the titanium-added ultra low carbon steel promotes the diffusion of iron in the steel grade during the alloying process, thereby increasing the iron concentration in the plating layer, and as a result, the iron concentration in the plating layer is higher than the optimum value. Increasing to increases the powder gamma (Γ) layer at the base iron / plated layer interface to increase the powdering tendency during processing, thereby deteriorating the workability.

In order to improve the processability, the amount of titanium added is preferably limited to the range of 0.03-0.06%. The reason is that when the titanium content is 0.03% or less, the workability is lowered, and when 0.06% or more, alloying proceeds quickly. This is because the plating layer is unstable and there is a high risk of powdering during processing.

In addition, phosphorus, which is usually added in the range of 0.04-0.2% in order to maintain the appropriate strength, precipitates at the grain boundary during alloying to slow the diffusion of iron in the steel grades. Therefore, in the titanium-phosphorus composite additive steel, proper temperature must be maintained during alloying heat treatment. If the phosphorus is added to 0.05% or less in the steel, it is not possible to secure the tensile strength of the steel sheet, when 0.15% or more is added, the phosphorus in the steel precipitates a large amount at the grain boundary during the alloying process, thereby delaying the alloying reaction. In addition, when alloying a plated steel sheet containing 0.15% or more of phosphorus, a high alloying temperature is required to maintain an appropriate alloying degree. ) Layer is formed, the workability of the alloy layer is degraded.

Therefore, in the present invention, the phosphorus added in the steel is preferably limited to the range of 0.05% -0.15%.

In order to recrystallize the titanium-phosphorus composite additive steel sheet as described above to give ductility and workability, annealing is carried out at a temperature range of 780-830 ° C. by a conventional method, followed by galvanizing through a conventional hot dip galvanizing bath and air. Spray to adjust plating amount.

At this time, the coating amount is determined by the pressure of the air spray nozzle and the distance between the strip and the nozzle after hot-dip galvanizing in the hot dip galvanizing bath.If the amount of coating is less than 80g / m2 per flight, the swelling time is shortened and the corrosion resistance is reduced. Corrosion resistance is increased when it is over 100g / ㎡, but as the thickness of the plating layer is increased, a higher temperature is required during alloying heat treatment, and thus, workability is deteriorated and unalloyed phenomenon occurs at the edge of the strip. There is a problem that the production of alloyed hot-dip galvanized steel sheet is impossible.

Therefore, in the present invention, the deposition amount of the plating layer is preferably limited to 80-100 g / m 2 and the titanium-phosphorus composite ultra low carbon steel hot-dip galvanized in the adhesion amount range is subjected to alloying treatment.

In the case of alloying titanium-added ultra low carbon steel, which is widely used as a high-processing steel, when heat-treated at a temperature range of 480-520 ° C, a weak capital gamma at the interface of the base iron / plated layer ( Processability can be ensured, preventing a layer from being produced.

On the other hand, phosphorus added for the production of high tensile steel can increase the tensile strength without degrading the workability of the base steel, so the titanium-in composite additive steel is mainly used as the base steel sheet when manufacturing high tensile alloyed hot-dip galvanized steel sheet for processing. . The hot-dip galvanizing properties of titanium-phosphorus composite steels are similar to those of titanium-added ultra-low carbon high processing steels, but the alloying properties of the titanium-phosphorus composites are localized due to the shift of phosphorus to the grain boundaries of the ferrous iron, which stabilizes the grain boundaries. By suppressing, the alloying reaction is delayed. Therefore, the alloying temperature should be set 20 ° C higher than the titanium-added ultra low carbon steel in order to maintain the same alloying degree as the titanium-added ultra low carbon high processing steel during alloying of titanium-phosphorus-added ultra low carbon steel.

That is, when the alloying temperature of the titanium-phosphorus composite ultra low carbon steel is alloyed at 500 ° C. or less, the iron concentration in the coating layer is 9% or less, resulting in poor coating adhesion and corrosion resistance after coating, and coating layer structure being zeta +. It is composed of delta (ζ + δ), so the powdering property is good during press processing, but the press load is increased, so it is easy to cause poor press formability, and the swelling phenomenon occurs during cationic electrodeposition coating, resulting in poor workability and corrosion resistance. . In addition, alloying heat treatment of titanium-phosphorus-added ultra low carbon steel at a temperature above 540 ℃ results in a poor powderability due to poor workability due to the iron concentration in the plating layer being more than 12%. Vulnerable Capital Gamma ( The appearance of) phase is undesirable.

Therefore, in the present invention, the alloying treatment temperature is preferably limited to 500-540 ° C.

In this way, the corrosion resistance of the alloyed hot-dip galvanized steel sheet has a high iron concentration in the plating layer, so it is common to evaluate the corrosion resistance after coating rather than the corrosion resistance of the plating layer itself.

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

Example 1

By weight%, 0.04% titanium and 0.07% phosphorus are added in combination, and cold rolled 0.8mm thick ultra low carbon steel is subjected to reduction heat treatment at 820 ° C for 1 minute, and then the Al content is 0.14wt% and the temperature is 460 ° C. Passing through the usual hot-dip galvanizing bath and blowing the air was carried out hot-dip galvanized in the deposition amount shown in Table 1. In addition, after the hot-dip galvanized alloying treatment was applied by applying the alloying temperature shown in Table 1 below to prepare an alloyed hot-dip galvanized steel sheet.

The workability of the alloyed hot-dip galvanized steel sheet prepared as described above was measured and the results are shown in Table 1 below. At this time, the workability was measured by comparing the difference in weight before and after the Erichen processing.

In addition, the alloyed hot-dip galvanized steel sheet was immersed in an electrodeposition coating solution at 29 ° C. having an electrodeposition voltage and current of 220-280 V and 10 A, respectively, for 1 minute and 30 seconds to measure corrosion resistance after electrodeposition coating, and the results are shown in Table 1 below. . At this time, the corrosion resistance after coating made 'X'-shaped scratches on the coating film, and put the sample into the salt spray tester (SST) maintained at 35 ° C and saturated humidity, and then took it out after a certain period of time. The coating film swelling width before and after electrodeposition coating was measured as an occurrence time of 1-2 mm.

As shown in Table 1, in the case of the invention material (1-12) satisfying the plating deposition amount and the alloying treatment temperature range of the present invention, while excellent in workability and corrosion resistance after coating, the comparative material (outside the scope of the present invention) ( In the case of AL), it can be seen that the processability and corrosion resistance after painting are deteriorated compared to the invention material.

On the other hand, as shown in FIG. 1, the workability and corrosion resistance after coating according to the coating weight were shown in the range of 80-100 g / mm2, and the coating performance was excellent in the workability and corrosion resistance after coating, and alloyed at 440-560 ° C. As a result of measuring the Fe concentration change of the alloying plated layer in the temperature range and shown in FIG. .

As described above, the present invention provides an alloyed hot-dip galvanized steel sheet having excellent workability and corrosion resistance after coating by controlling the amount of coating during hot dip galvanizing and adjusting the alloying treatment temperature after annealing the Ti-P composite additive carbon steel under certain conditions. There is an effect that can be produced.

Claims (1)

Titanium-phosphorus composite addition Annealing and hot dip galvanizing, followed by alloying to produce an alloyed hot-dip galvanized steel sheet, comprising 0.03-0.06% titanium and 0.05-0.15% phosphorus After annealing the low-carbon steel at a temperature range of 780-830 ° C, it is passed through a hot dip galvanizing bath and hot-dip galvanized to adjust the coating amount to be in the range of 80-100 g / m2, and then in the temperature range of 500-540 ° C. A method for producing an alloyed hot-dip galvanized steel sheet excellent in workability and corrosion resistance, characterized in that the alloying treatment.