JPH10128426A - Descaling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the scale thickness of a steel plate in hot-rolling and the developing ratio of a scale fault. SOLUTION: In a descaling in a hot-rolling process, the high pressure water is injected on the surface of the steel plate at one or more times and the super high pressure water is injected on the surface of the steel plate within about 10sec after removing the scale on the surface layer to remove the scale which can not remove in the descaling with the high pressure water. The super pressure water is injected within about 10sec after injecting the high pressure water on the surface of the steel plate 3 at the outlet side of a rough-rolling mill 1 and a finish-rolling is executed within about 10sec after this descaling. In such a case, the pressure of the high pressure water is made to 120-180kgf/cm<2> and the pressure of the super high pressure water is made to >=250kgf/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to descaling of a hot-rolled steel sheet.

[0002]

2. Description of the Related Art Descaling is the removal of a scale layer consisting of several oxides of iron formed on the surface of a steel sheet at a high temperature. At higher temperatures, thicker scales are formed, the thickness of the outer layer being 0.5-2% Fe ₂ O ₃ ,
Fe ₃ O _{4 is} 10 to 15% and FeO is 85 to 90%. Immediately after the heating furnace extraction, the thickness of the scale layer is 1-2 mm
However, if this is subjected to rolling as it is, the scale bites into the surface of the product, and a surface defect called scale flaw occurs.

[0003] Although the mechanism of the generation of scale flaws has not been completely elucidated, a difference in mechanical properties such as ductility between the scale layer and the base material is one of the causes. Since the scale flaw generating portion is a surface defect, it needs to be cut off as a defective product, which is a factor of worsening the manufacturing cost. In order to suppress the occurrence of scale flaws, the scale layer must be removed. In a process of handling a steel sheet at a high temperature such as a hot rolling process, it is practically impossible to eliminate the scale layer entirely. An ideal scale layer is one that maintains a thin and uniform scale layer on the steel sheet surface.

Conventionally, descaling at the exit side of a rough rolling mill involves applying high-pressure water of about 150 kgf / cm ² to the surface of a steel sheet.
It is common to perform rolling once or twice for rolling. A method of performing descaling by water injection in two stages is proposed in, for example, JP-A-6-114432. This method is a method in which, after extraction in a heating furnace, an upper layer mainly composed of wustite of a primary scale is removed by water jetting, and then the steel sheet is rolled by water jetting again.

However, in the conventional two-stage water injection system, the descaling effect has been reduced by half since the elapsed time from the primary injection to the secondary injection is not taken into account. That is, after the primary scale is removed by the primary injection,
For example, after elapse of one minute, the scale grows again on the surface of the steel sheet, and the effect of removing the primary scale decreases.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a descaling method capable of reducing the scale thickness of a steel sheet in hot rolling and reducing the incidence of scale flaws.

[0007]

The present invention has the following features. (1) In the descaling of the hot rolling step, first, high-pressure water is sprayed on the steel sheet surface at least once to remove the scale of the surface layer, and then ultra-high-pressure water is sprayed on the steel sheet surface within about 10 seconds. A descaling method characterized by removing scale that could not be removed by descaling with high-pressure water. (2) In the descaling of the hot rolling step, first, ultra-high pressure water is sprayed on the surface of the steel sheet to remove the scale of the surface layer, and then the high-pressure water is sprayed on the surface of the steel sheet within about 10 seconds. A descaling method characterized by removing a scale that could not be removed by the descaling in (1).

(3) After high-pressure water or ultra-high-pressure water is sprayed on the steel sheet surface at the exit side of the rough rolling mill, ultra-high-pressure water or high-pressure water is injected within about 10 seconds to perform descaling. A hot rolling method, wherein finish rolling is performed within about 10 seconds. (4) A high-pressure water descaling device for injecting high-pressure water onto the surface of a steel sheet, an ultra-high-pressure water descaling device for injecting ultra-high-pressure water, and a finishing mill are arranged in this order in the rough rolling mill exit side. Hot rolling equipment.

(5) An ultra-high-pressure water descaling device for injecting ultra-high-pressure water onto the steel sheet surface, a high-pressure water descaling device for injecting high-pressure water, and a finishing mill are arranged in this order in the exit side of the rough rolling mill. Hot rolling equipment. (6) The pressure of the high-pressure water is 120 to 180 kgf / cm ²
The descaling method according to any one of (1) to (5), wherein the pressure of the ultra-high pressure water is 250 kgf / cm ² or more;
Hot rolling method and hot rolling equipment.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. FIG. 1 shows a hot rolling facility in which a high-pressure water and ultra-high-pressure water jet descaling apparatus according to the present invention is arranged. FIG.
As shown in (1), before the steel sheet 3 which has been roughly rolled by the rough rolling mill 1 is bitten into the finishing rolling mill 2, first, the scale on the surface is removed by high-pressure water of about 150 kgf / cm ^{2 by the} descaling device A. Then, the descaling device B installed immediately after the descaling device A
The surface layer scale is further removed by descaling with ultrahigh-pressure water of kgf / cm ² , and the steel sheet is bitten into the finishing mill 2 within 10 seconds after passing through the descaling device B.

FIG. 1 shows an example in which high-pressure water of 150 kgf / cm ² is injected by the descaling device A in the first stage and ultra-high-pressure water of 300 kgf / cm ² is injected by the descaling device B in the second stage. Although shown, the arrangement of the descaling devices A and B may be reversed. That is,
As shown in FIG. 2, the high-pressure water of 150 kgf / cm ² in the first stage, the degree even using an ultra high pressure water of 300 kgf / cm ² in the second stage, also descaling effect changes its order is the same Was confirmed.

The descaling conditions of the present invention will be described. First, regarding the injection pressure of water in descaling, as high-pressure water, 120 to 180 kgf / cm ²
Is within the proper range, and the ultra-high pressure water is 250 kgf
/ Cm ² or more is suitable.

The reason why the time until the steel sheet is descaled by the descaling device B after the descaling by the descaling device A is set to 10 seconds or less is as follows. That is, as shown in FIG. 3A, after descaling by the descaling device A, the scale remaining thickness increases with time, and within 10 seconds, the scale remaining thickness remains at the required level. This is because the scale layer grows too thick after a longer time.

The reason why the time until the steel sheet is finish-rolled after the descaling by the descaling device B is set to within about 10 seconds is, as shown in FIG. This is because if it is within the range, the scale remaining thickness remains at the required level.

According to the method of the present invention, the scale remaining thickness of the steel sheet on the entrance side of the finishing mill is, as shown in FIG.
About 30 μm, compared to about 120 μm by the conventional method,
Excellent descaling effect. Since there is a relationship between the residual scale thickness and the scale flaw occurrence rate as shown in FIG. 4B, that is, the smaller the residual scale thickness, the lower the scale flaw occurrence rate. In addition, according to the method of the present invention, the occurrence of scale flaws on the steel sheet is significantly improved.

[0016]

According to the present invention, the scale thickness of a steel plate in hot rolling can be reduced as compared with the conventional steel plate, thereby making it possible to reduce the occurrence of scale flaws.

[Brief description of the drawings]

FIG. 1 is a view showing a hot rolling facility in which a descaling apparatus of the present invention is arranged, wherein (a) is a top view and (b) is a side view.

FIG. 2 is an enlarged view of a surface layer of a steel sheet showing a mechanism of descaling by high-pressure water and ultra-high-pressure water injected from descaling apparatuses A and B of the present invention.

FIG. 3 is a graph illustrating the descaling condition of the present invention, wherein (a) shows the relationship between the time from the descaling device A to the descaling device B and the remaining thickness of the scale;
(B) shows the relationship between the time from the descaling device B to finish rolling and the scale flaw occurrence rate.

FIG. 4 is a graph showing the effect of the method of the present invention,
(A) is a graph comparing the scale residual thickness with the conventional method,
(B) is a graph showing the scale residual thickness and the scale flaw generation rate.

Claims (8)

[Claims] In the descaling of a hot rolling step,
After high-pressure water is sprayed on the steel sheet surface at least once to remove the surface scale, ultra-high-pressure water is sprayed on the steel sheet surface within about 10 seconds to remove the scale that could not be removed by the descaling with the high-pressure water. A descaling method characterized by removing. 2. The descaling of a hot rolling step,
After removing the scale of the surface layer by injecting ultra-high pressure water to the surface of the steel plate, the scale that could not be removed by the descaling with the ultra-high pressure water is removed by injecting the high pressure water to the surface of the steel plate within about 10 seconds. A descaling method characterized in that: 3. The pressure of high-pressure water is 120 to 180 kgf / c.
m ^2, and descaling method according to claim 1 or 2 pressure of ultra-high pressure water is 250 kgf / cm ² or more. 4. After high-pressure water is sprayed on the surface of the steel sheet at the exit side of the rough rolling mill, ultra-high-pressure water is sprayed within about 10 seconds to perform descaling, and finish rolling is performed within about 10 seconds after the descaling. A hot rolling method, characterized in that: 5. After ultra-high pressure water is sprayed on the surface of the steel sheet at the exit side of the rough rolling mill, high-pressure water is sprayed within about 10 seconds to perform descaling, and finish rolling is performed within about 10 seconds after the descaling. A hot rolling method, characterized in that: 6. A high-pressure water pressure of 120 to 180 kgf / c.
m ^2, and hot rolling method according to claim 4 or 5 pressure of ultra-high pressure water is 250 kgf / cm ² or more. 7. A high-pressure water descaling device for injecting high-pressure water onto the surface of a steel sheet, an ultra-high-pressure water descaling device for injecting ultra-high-pressure water, and a finishing mill are arranged in this order on the rough rolling mill exit side. A hot rolling facility characterized by the following. 8. An ultra-high-pressure water descaling device for injecting ultra-high-pressure water onto the surface of the steel sheet, a high-pressure water descaling device for injecting high-pressure water, and a finishing mill are arranged in this order in the exit side of the rough rolling mill. A hot rolling facility characterized by the following.