KR101325400B1 - Semi-alloyed hot-rolled hot-dip galvanizing steel sheet and method for manufacturing the same - Google Patents

Abstract

The present invention is to provide a semi-alloyed hot-dip galvanized steel sheet excellent in surface appearance, workability and corrosion resistance without performing a pickling process and alloying process,
Preparing a hot rolled steel sheet;
High pressure spraying the slurry mixed with the high pressure water and the abrasive to the hot rolled steel sheet to remove the hot rolled scale; And
It provides a method of manufacturing a semi-alloyed hot-rolled hot-dip galvanized steel sheet comprising the step of immersing the hot-rolled steel sheet from which the hot-rolled scale has been removed in a hot-dip galvanizing bath and a semi-alloyed hot-dip hot-dip galvanized steel sheet produced by the same.

Description

Semi-alloyed hot-dip galvanized steel sheet and its manufacturing method {SEMI-ALLOYED HOT-ROLLED HOT-DIP GALVANIZING STEEL SHEET AND METHOD FOR MANUFACTURING THE SAME}

The present invention relates to an alloyed hot-rolled hot-dip galvanized steel sheet, and more particularly, to a semi-alloyed hot-rolled hot-dip galvanized steel sheet having a characteristic of an alloyed steel sheet without a separate alloying treatment after hot-dip galvanizing and a method of manufacturing the same. will be.

In general, an alloyed hot-rolled hot-dip galvanized steel sheet passes through a pickling process and an annealing process for hot-rolled scale removal after hot rolling, and is subjected to hot dip galvanizing in a zinc plating bath, and then the hot dip galvanizing solution on the steel sheet is not completely solidified. After heating in a galvannealing furnace installed at the top to form an iron-zinc alloy having an iron content of 10-12 wt% in the plating layer, it is manufactured through a cooling process. The alloyed hot-rolled hot-dip galvanized steel sheet produced by the above process has excellent weldability and corrosion resistance after coating, compared to hot-hot-dip galvanized steel sheet.

Alloying hot-dip galvanized steel sheet is composed of zeta phase (ζ, FeZn ₁₃ ), delta phase (δ, FeZn ₇ ), and capital gamma (Γ, Fe ₃ Zn ₁₀ ) according to the iron content in the alloy layer. Very different processability, weldability and corrosion resistance are shown depending on the configuration.

In particular, when a large amount of the capital gamma phase is contained, powdering occurs during processing due to a weakening of the bonding force between the base layers, which results in deterioration of workability. Therefore, it is important to suppress the formation of the capital gamma image as much as possible.

In general, in the manufacture of alloyed hot-dip galvanized steel sheet, the aluminum in the plating bath is lowered to 0.14 wt% or less for smooth alloying reaction of iron and zinc, and the iron-aluminum-zinc ternary alloy layer formed on the interface is weakly formed. By easily breaking in the alloying heat treatment furnace to achieve the alloying reaction.

In the alloying heat treatment furnace, the alloying is performed for about 10 to 15 seconds, and the iron content in the alloy layer is changed according to the alloying temperature and the type of steel at this time, and thereafter, the additional facilities required for additional cooling and quenching are passed.

In the alloying hot-dip galvanized steel sheet, the plating layer thickness is reduced compared to the hot-dip galvanized steel sheet due to the formation of an intermetallic compound of iron-zinc during the alloying process. For this reason, alloyed hot-dip galvanized steel sheet has better weldability than hot-dip galvanized steel sheet, but has a disadvantage in that corrosion resistance is degraded. In order to overcome this problem, the coating adhesion amount should be increased. In this case, when the alloying process is performed, a powder gamma phase is formed at the interface between the plating layer and the base layer due to excessive heat treatment, and powdering may occur, thereby degrading workability.

In addition, in the production of an alloyed hot-rolled hot-dip galvanized steel sheet, a hot-rolled scale removing process present in the surface layer of the steel sheet after hot rolling is essential. In general, the hot rolled scale is removed by a picking process using high temperature hydrochloric acid or mixed acid.

However, the method of descaling through pickling with strong acid is due to the increase in the length of equipment due to the use of many pickling tanks and washing tanks, the inhibition of the working environment due to the generation of acid vapor, the generation of environmental hazards due to waste acid treatment, the recovery of acid and acid-resistant facilities. Various problems have been pointed out such as an increase in auxiliary facilities, a difference in scale removability due to steel grades, and poor quality of the steel sheet stayed in the acid solution and the flush tank when the line is stopped.

One aspect of the present invention is to provide a method for producing a semi-alloyed hot-dip hot-dip galvanized steel sheet having excellent surface appearance, processability and corrosion resistance without performing a pickling process and alloying process and a semi-alloyed hot-dip galvanized steel sheet using the same .

The present invention comprises the steps of preparing a hot rolled steel sheet;

High pressure spraying the slurry mixed with the high pressure water and the abrasive to the hot rolled steel sheet to remove the hot rolled scale; And

It provides a method of manufacturing a semi-alloyed hot-rolled hot-dip galvanized steel sheet comprising the step of immersing the hot-rolled steel sheet from which the hot-rolled scale is removed in the hot dip galvanizing bath.

The present invention also provides a semi-alloyed hot-rolled hot dip galvanized steel sheet having a Fe content of 10 wt% or less in the plating layer.

The present invention can produce a semi-alloyed hot-dip galvanized steel sheet by promoting the alloying reaction in the plating bath by applying a compressive residual stress to the surface of the hot-rolled steel sheet through the hot rolled scale removal process through slurry high pressure spraying. According to the present invention, it is possible to manufacture a semi-alloyed hot-dip galvanized steel sheet having a high plating deposition amount without additional alloying heat treatment, and the steel sheet has excellent surface appearance, workability and corrosion resistance.

1 is a schematic diagram of a manufacturing process of a conventional alloyed hot-dip galvanized steel sheet.
Figure 2 is a schematic diagram of the manufacturing process of the semi-alloyed hot-rolled hot-dip galvanized steel sheet of the present invention.
Figure 3 is a schematic diagram of the slurry high pressure injection of the present invention.

Hereinafter, the present invention will be described in detail.

The manufacturing process of the conventional alloyed hot-dip galvanized steel sheet is shown in FIG. In the hot-rolled hot-dip galvanized steel sheet, the scale breaker (4) and three to four pickling tanks (5) are continuously arranged after hot rolling to remove scale, and washed with water through a washing tank (6), followed by a reduction heating furnace ( 7), it is immersed in the hot-dip plating tank 8 and hot-dip zinc plating is performed. After performing the hot dip galvanizing, it is cooled in the cooling zone 11 via the alloying apparatus 10.

As described above, in order to manufacture a conventional alloyed hot-dip galvanized steel sheet, pickling is performed, there are problems of environmental pollution and high cost, and there is a problem of requiring a separate alloying treatment.

Thus, the present inventors have studied the method for obtaining an effect similar to that performed by the alloying treatment even without performing the pickling process and the alloying treatment.

The present invention first prepares a hot rolled steel sheet subjected to hot rolling. The hot rolled steel sheet subjected to the hot rolling has a scale formed on its surface. Such scales require removal because they degrade the plating bath adhesion during plating and cause a decrease in surface quality.

Thereafter, the slurry mixed with the high pressure water and the abrasive is high-pressure sprayed on the hot rolled steel sheet to remove the hot rolled scale. In the present invention, the hot rolled scale is removed by high-pressure spraying a slurry of a mixture of high-pressure water and an abrasive in place of hydrochloric acid or mixed acid pickling used in the conventional scale removal.

An example of the slurry high pressure injection nozzle is shown in FIG. 3. As shown in FIG. 3, the abrasive sucked through the negative pressure formed by the injection of high pressure water is mixed on the surface of the hot rolled steel strip having a flat shape to form a slurry, and a high pressure slurry kinetic energy forms a high pressure slurry stream. After making it uniformly sprayed in the width direction to remove the scale.

The abrasive is preferably a glass bead (Glass Bead), a shot ball (Shot ball), steel grit (Steel Grit), ceramic beads (Ceramic Bead), stainless steel beads (Stainless Bead) and the like.

On the other hand, the size of the abrasive is preferably 10 ~ 400㎛ in diameter. If the diameter is too small, less than 10 μm, the effect of descaling is insufficient, and if the abrasive material is too large in excess of 400 μm, the surface roughness of the hot-rolled steel sheet is too large to secure the target plating quality.

Moreover, as for the speed | rate of the abrasive injected to a steel plate, 50-200 m / s is preferable. If the abrasive speed is too small, less than 50m / s, the scale removal ability is insufficient, if the abrasive speed is too fast exceeding 200m / s leaving a defect on the surface of the steel sheet, there is a problem that the surface roughness is very high.

In the slurry high pressure injection, the injection pressure of the high pressure water is preferably 100 ~ 500bar. When the injection pressure is less than 100bar, the scale removal efficiency is insufficient, and when the pressure is higher than 500bar, the surface roughness of the hot rolled steel sheet is increased, and the power cost and equipment cost are increased.

When spraying, the spray nozzle should be installed in the upper and lower parts of the hot-rolled steel sheet at regular intervals in consideration of the nozzle spraying angle and the distance to the steel sheet according to the width of the hot-rolled steel sheet to achieve a uniform spray pattern. As such, the scale removed by the slurry high pressure injection may vary depending on the line speed of the hot rolled steel strip or the number of heads installed. However, the scale of the surface layer of the hot rolled steel strip may be removed under appropriate conditions.

As such, the slurry high pressure spraying enables the removal of the scale breaker equipment for cracking the hot rolled steel sheet to promote pickling, and does not require a large capacity pickling equipment.

The hot rolled steel sheet after the slurry high pressure injection process has a compressive residual stress on the surface layer, and the compressive residual stress is preferably -100 to -300 MPa. Since the residual stress-containing layer formed on the surface layer has a thermodynamically high surface energy, in order to solve this problem, the residual stress-containing layer actively reacts with the hot dip galvanizing in the plating bath in the subsequent hot dip galvanizing process to promote the elution of iron. The compressive residual stress of the surface layer of the steel sheet is solved by the semi-alloy reaction in the plating bath, and enables the production of hot-dip galvanized steel sheet having excellent surface appearance and whiteness.

When the compressive residual stress is less than -100 MPa, the Fe content in the alloy layer is low, and when the compressive residual stress exceeds -300 MPa, the Fe content is high and the Fe content is high in the alloy layer.

Preferably, the method further includes a step of reducing heat treatment of the hot rolled steel sheet subjected to the descaling process in a reducing furnace. The reduction heat treatment is a conventional method, and is not particularly limited. As an example of the said reduction heat processing, it heats at the temperature of 500-550 degreeC in reducing atmosphere of 80-95% of nitrogen and 5-20% of hydrogen.

The hot rolled steel sheet from which the hot rolled scale has been removed is immersed in a hot dip galvanizing bath to perform hot dip galvanizing.

The concentration of the hot-dip plating bath is preferably 0.12 ~ 0.2wt% Al and the rest Zn and inevitable impurities. When the Al content exceeds 0.2wt%, the alloying reaction suppression layer of aluminum is formed thick at the interface to suppress the alloying reaction in the plating bath, and when the content is less than 0.12wt%, the alloying reaction is caused by the temperature change in the plating bath. This suddenly rises and it is difficult to obtain an appropriate degree of alloying.

The hot dip galvanizing is carried out under ordinary hot dip galvanizing conditions, and preferably the plating bath temperature is performed at 450 to 550 占 폚.

In the present invention, the hot rolled steel sheet from which the hot rolled scale is removed is alloyed in the process of immersing and plating the hot rolled steel plate in a molten zinc plating bath. This is distinguished from what is done in a separate alloying process after plating, and the Fe content in the plating layer is distinguished by alloying of 10wt% or less, and referred to as quasi-alloyed in the present invention.

The Fe content in the alloy layer of the semi-alloyed hot-dip galvanized steel sheet of the present invention is preferably about 2 to 8 wt%. The iron content in the plating layer increases as the temperature of the incoming steel sheet, the temperature of the plating bath and the plating bath immersion time increase. The smaller the Fe content, the more white the appearance of the surface appearance, the higher the Fe content is a darker color. Through the above method, it is possible to manufacture a semi-alloyed hot-dip galvanized steel sheet without using an alloying heat treatment furnace.

On the other hand, after the semi-alloy treatment proposed by the present invention may further include an alloying treatment step, the alloying treatment is possible at a temperature lower than the conventional alloying treatment temperature through the semi-alloying treatment, thereby conventional alloying and melting Compared with the manufacturing method of galvanized steel sheet, there is an advantage that the manufacturing cost can be lowered.

The manufacturing process of the semi-alloyed hot-dip galvanized steel sheet of the present invention is briefly shown in FIG. As shown in Figure 2, after performing the slurry high-pressure spraying 21, after washing with water and reducing heating, the hot-dip galvanized and hot-dip galvanized steel sheet shown in Figure 1 in that it is directly cooled without a separate alloying treatment There is a difference with the manufacture of.

Reference numerals in the accompanying drawings refer to the payoff reel 1, the welder 2, the looper 3, the gas wiping 9, the skin pass 12, the tension leveler 13, and the post treatment 14. And tension reel 15.

Hereinafter, embodiments of the present invention will be described in detail. The following examples are for the understanding of the present invention, and the present invention is not limited by the following examples.

(Example)

The hot rolled low carbon hot rolled steel sheet containing 0.04 wt% carbon, 0.2 wt% manganese, 0.01 wt% silicon, and the remainder containing Fe and unavoidable impurities was prepared using the slurry high pressure spray conditions, zinc plating bath conditions, and hot dip baths in Table 1. By changing the conditions, a semi-alloyed hot dip galvanized steel sheet was manufactured.

The steel sheet produced at this time is 120 mm wide, 200 mm long, 2.0 mm thick. Whiteness, workability, and corrosion resistance of the prepared steel sheet were evaluated, and the results are shown in Table 1.

In Table 1, the workability was expressed as a powdering index (P / I) to evaluate the powdering resistance. The smaller the powdering index was, the better the workability was, and the larger the poorer the index was.

Corrosion resistance was measured by the salt spray test according to JIS Z-2371 until the time when the surface where the red dust (res dust) occurred over the entire surface of the specimen was 5%. Whiteness is the value of the L * value measured using a color difference meter, which is 0 for perfect black and 100 for perfect white.

division High pressure water (bar) Abrasive Type Abrasive Size (mm) Slurry amount (L) Plating bath Al content Plating bath temperature and dipping time (℃) Alloying Heat Treatment Temperature and Time (℃ Seconds) Alloying degree (wt%) One-sided coating weight (g / ㎡) Machinability (P / I) Corrosion Resistance (hours) Whiteness Inventory 1 250 Shortball 300 10 0.12 460, 5 - 6 120 One 72 86 Inventory 2 250 Steel grit 300 10 0.12 460, 5 - 6 120 One 72 88 Inventory 3 250 Glass bead 200 10 0.14 470, 5 - 6 100 One 72 90 Honorable 4 300 Glass bead 120 10 0.14 470, 5 - 3 90 One 72 93 Inventory 5 300 Ceramic bead 200 10 0.14 470, 10 - 5 100 One 72 86 Inventory 6 300 Stainless steel ball 120 10 0.14 470, 10 - 5 100 One 72 87 Comparative Example 1 - - - 0.12 460, 5 460, 10 11 60 2 48 70 Comparative Example 2 - - - 0.12 460, 5 470, 15 12 60 3 60 65 Comparative Example 3 - - - 0.12 460, 5 500. 15 13 100 3 72 68

As can be seen from the results of Table 1, in the inventive example of the present invention, it is confirmed that the processability is excellent, and the corrosion resistance is superior to the comparative example in which the scale is removed by the existing pickling treatment, and exhibits excellent surface appearance and whiteness.

Compared to the invention example, the comparative example does not remove the scale by slurry, and after the plating is subjected to a separate alloying treatment it can be seen that the workability is lower than the invention example, in particular Comparative Example 1 has a low alloying time, corrosion resistance is inferior to I can see that there is.

1 ..... payoff reel 2 ..... welder
3 ..... looper 4 ..... scale breaker
5 ..... Sanjo 6 .....
7 ..... Reduction Furnace 8 ..... Hot Plating Bath
9 ..... gas wiping 10 ..... alloy treatment
11 ... cooling stand 12 ..... skin pass
13 ..... tension leveler 14 .... postprocessing
15 ..... Tension Reel 21 ..... Slurry High Pressure Injection

Claims (10)

Removing the hot rolled scale by high pressure spraying the slurry mixed with the high pressure water and the abrasive on the hot rolled steel sheet; And
Hot-dip galvanizing the hot-rolled steel sheet from which the hot-rolled scale has been removed by immersing in a hot-dip galvanizing bath;
It includes, and the step of reducing heat treatment of the hot rolled steel sheet after removing the scale, wherein the reducing heat treatment is performed at a temperature of 500 ~ 550 ℃ in a reducing atmosphere of 80 to 95% nitrogen, 5 to 20% hydrogen Method of manufacturing a semi-alloyed hot-dip galvanized steel sheet.
The method according to claim 1,
After the high-pressure spraying the slurry to remove the hot rolled scale, the compressive residual stress of the hot rolled steel sheet is -100 ~ -300MPa method of manufacturing a semi-alloyed hot-rolled hot-dip galvanized steel sheet.
The method according to claim 1,
The abrasive is at least one semi-alloyed hot-rolled molten metal selected from the group consisting of glass beads, shot balls, steel grit, ceramic beads, and stainless beads. Method of manufacturing galvanized steel sheet.
The method according to claim 1,
The abrasive is a manufacturing method of a semi-alloyed hot-dip galvanized steel sheet having a diameter of 10 ~ 400㎛.
The method according to claim 1,
The speed of the abrasive sprayed on the hot rolled steel sheet is a manufacturing method of a semi-alloyed hot-rolled hot-dip galvanized steel sheet is 50 ~ 200m / s.
The method according to claim 1,
The high-pressure spraying method of manufacturing a semi-alloyed hot-dip galvanized steel sheet is carried out at a pressure of 100 ~ 500bar.
delete The method according to claim 1,
The hot-dip galvanizing is a method of producing a semi-alloyed hot-dip galvanized steel sheet containing aluminum content of 0.12 ~ 0.2wt%, the remainder in a plating bath made of Zn and inevitable impurities.
The method according to any one of claims 1 to 6 and 8,
The method of manufacturing a semi-alloyed hot-dip galvanized steel sheet having an alloying degree of Fe content of 10wt% or less in the hot dip galvanized layer.
The method of claim 9,
A method of manufacturing a semi-alloyed hot dip galvanized steel sheet having a Fe content of 2 to 8 wt% in the plating layer.

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