KR100302396B1 - Method for removing scales by high pressure water containing abrasives - Google Patents

Abstract

PURPOSE: A method for peeling scales off hot rolled thin slab by high pressure water containing abrasives is provided. CONSTITUTION: The method includes the steps of (a) 5 to 60 vol.% of an abrasive selected from Al2O3, SiO2 and glass bead and (b) 2 to 10 vol.% of sodium polyacrylate dispersant are added in high pressure water; and spraying the high pressure water containing abrasives onto a hot rolled thin slab at 20 to 70 mm distance.

Description

Oxidation scale removal method by high pressure water containing abrasive

The present invention relates to a method for removing high-temperature oxidation scale formed in a reheating furnace for heating a slab at a high temperature for a long time to produce a hot rolled sheet and an oxide scale formed during thin slab casting by a mini mill. The present invention relates to a method for removing oxidative scale by high pressure water.

In general, in the steel manufacturing process, the sheet material is generated by a large amount of high temperature scale because it is reheated for a long time in a high temperature reheating furnace or continuously cast into a thin slab in the atmosphere. Therefore, it is essential to completely remove these scales in order to ensure the surface quality of the hot rolled sheet during hot rolling.

In recent years, as a method for increasing fuel efficiency in automobile steel sheets, etc., in order to maintain the formability and increase the strength of the steel, Si and the like have been added to increase the solid solution strengthening effect. A compound called ₂ SiO ₄ is made and is not easily removed when descaling with high pressure water which is a common method. The scale not removed in this way is known to cause red scale defects on the hot-rolled sheet surface. In addition, when thin slab casting by mini mill using an electric furnace not only contains a large amount of impurity components such as Cr, Ni, Cu, Sn, and Si, but also does not go through a reheating furnace, the oxide layer structure is different, so they are descaled by high pressure water. It is known that the surface quality of the hot rolled sheet is lower than that of the hot rolled sheet produced in the integrated steel mill using the blast furnace because the mill is not completely removed.

As described above, when the alloying element is added to change the manufacturing process in terms of production cost or to increase the mechanical properties of the steel, high pressure water alone is difficult to remove scale.

At present, the method of using high pressure water is mainly used for the removal of the oxide scale formed at the time of heating in a hot rolling furnace and thin slab casting. In the case of removing the oxidative scale using high pressure water, it is one method to increase the collision pressure when the removal of the scale is not easy.

The collision pressure can be expressed as in the following formula (1).

p∝PV / H2 ................. (1)

Where p is the impingement pressure, P is the hydraulic pressure, V is the flow rate, and H is the distance between the nozzle and the material. Therefore, in order to increase the collision pressure, the motor capacity must be increased to increase the water pressure or the quantity.

However, if the water pressure and quantity are increased too much, it is difficult to maintain the hot rolling finish temperature above the A ₃ transformation point.

Therefore, in consideration of the mechanical properties required in the steel, the load of the rolling mill, and the like, it is preferable to set an appropriate oxidation scale removal condition, so that the pressure and quantity of water cannot be increased indefinitely in terms of oxidation scale removal.

Therefore, in the case of steel grades containing a large amount of alloying elements, which are not easy to remove the scale, it is difficult to completely remove the hot-rolled sheet surface defects due to the scale.

In some cases, surface defects on the surface of the hot rolled sheet may need to be removed by grinding.

Therefore, the present inventors came to suggest that the present invention is focused on the fact that if the specific gravity is heavier than water and the powder which is stable at high temperature is sprayed with water, the scale removal efficiency will be increased.

That is, the present invention maximizes the collision energy by adding the abrasive and dispersant to the high pressure water and spraying the hot rolled thin slab under the proper spraying conditions to further remove the oxide scale formed during the heating in the hot rolling furnace and casting the thin slab. It is an object of the present invention to provide a method for removing oxidized scale by high pressure water containing an abrasive which can be improved.

In order to achieve the above object, the present invention provides a method for removing an oxidized scale formed on a hot rolled thin slab by spraying high pressure water, wherein the high pressure water contains an abrasive: 5-60% and a dispersant: 2-10% by volume. Next, the present invention relates to a method of removing oxide scale formed on a hot rolled thin slab by spraying the abrasive and dispersant high pressure water at a distance of 20 to 70 mm from the hot rolled thin slab.

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

In the present invention, it is preferable to select one of Al ₂ O ₃ , SiO ₂ , and glass beads stable at high temperature as the abrasive added to the high pressure water.

The reason for limiting the abrasive to 5-60% by volume ratio is that when the amount of the abrasive added is 5% or less, the impact force is reduced and the oxidative scale removal effect is reduced. This is because it is difficult to spray the high pressure water containing the abrasive and dispersant.

In the case of containing a large amount of alloying elements that are difficult to remove the oxidative scale, increasing the amount of the abrasive added was more effective in removing the oxidizing scale, in which case it is preferable to add at least 25% by volume ratio.

The dispersant is added to disperse the abrasive particles in the high pressure water, and the type thereof is sodium polyacrylate, and when the content is 2% or less, the abrasive particles are not dispersed well in the high pressure water but aggregated and added more than 10%. In one case, since the effect was saturated and there was no further effect, the addition amount is preferably limited to the range of 2 to 10%.

The high pressure water containing the abrasive and the dispersant, which is formed as described above, is sprayed on the thin slab in a conventional manner through the spray nozzle, and the abrasive particles are not sufficiently accelerated when the distance between the spray nozzle and the hot rolled thin slab is 20 mm or less. Rather, the oxide scale removal ability is lowered, and in the case of 70 mm or more, the acceleration is reduced and the oxidation scale removal ability is lowered. Therefore, the distance between the spray nozzle and the hot rolled thin slab is preferably selected to be 20-70 mm.

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

EXAMPLE

After maintaining the hot rolled sheet composed of the components shown in Table 1 for 1 hour at 1150 ℃, high pressure water mixed with 50% Al ₂ O ₃ as an abrasive, 5% sodium polyacrylate as a dispersant and high pressure water without mixing the abrasive After removing the high-temperature oxidation scale at the same water pressure using, and visually observed, the results are shown in Table 2 below.

TABLE 1

TABLE 2

◎: very good, 0: good, △: bad, x: very bad

As shown in Tables 1 and 2, in the case of S4, a steel grade containing little Si and alloying elements, even when the high-temperature oxidation scale was removed with only high pressure water, very good results were obtained. Even in the case of a good result.

However, when Si was added, when the oxide layer was removed only by high pressure water, there was a part where the oxide layer had not been peeled off.

In contrast, in the case of removing the oxide layer by adding an abrasive and a dispersant to the high pressure water according to the present invention, not only Si but S2 containing only alloying elements and S4 containing no alloying elements as well as Si Even in the case of containing S1 and S3, good results were obtained.

As described above, according to the present invention, the high-temperature oxidation scale is removed by spraying the high-pressure water in which the abrasive is dispersed, so that the interface between the oxide layer and the base material is not smoothed by the selective oxidation and contains a large amount of alloying elements. Due to the effect, the oxide layer is not easily peeled off and is applied to the case of the steel species containing Si, which is widely known to cause red scale generation, and thus, the high temperature scale can be effectively removed.

Claims (2)

A method of removing oxidized scale formed on a hot rolled thin slab by spraying high pressure water, wherein at least one abrasive selected from Al ₂ O ₃ , SiO ₂ , and glass beads in a volume ratio to the high pressure water is 5-60% and as a dispersant. Sodium polyacrylic acid: After adding 2-10%, high pressure water containing abrasive, wherein the high pressure water containing the abrasive and dispersant is sprayed on the hot rolled thin slab at a distance of 20-70 mm from the hot rolled thin slab. Oxidation scale removal method by. The method of claim 1, wherein the hot rolled thin slab contains an Si component.