JPH03207518A - Descaling method for hot rolled steel strip - Google Patents

Abstract

PURPOSE:To reduce the equipment cost, to decrease the occupied space for equipment and to improve the efficiency of descaling by specifying the center line mean roughness of the surface of steel strip by applying rolling reduction to the hot rolled steel strip, radiating the electric discharging arc to the surface and then pickling it. CONSTITUTION:The steel strip 1 is rolled with the roll 21 with dull incorporated in the rolling mill 2, the crack is generated on the surface of steel strip and fine ruggedness are simultaneously formed and the center line mean roughness Ra of the surface of steel strip is made to 0.5-5mum. Next, the steel strip 1 is irradiated with the electric discharging arc from the discharging electrode 4 during passing in the insulating liquid 5 and the crack number of surface is increased. At final, the steel strip 1 is subjected to pickling in the pickling tank. Therefore, the good descaling is executed and the time required for the descaling can be shortened.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for descaling various hot rolled steel strips from ordinary steel to stainless steel.

(Conventional technology) Conventionally, in the descaling of hot rolled steel strips, in addition to the method of continuously immersing the steel strip in an acid solution, a method of performing mechanical descaling as a pretreatment for acid immersion has been adopted. has been done.

Specific examples of this method include a method in which cracks are created in the scale by rolling and bending or the like, or the surface of the steel strip with scale adhering to it is polished by shot blasting or the like and then immersed in an acid. For example, in Japanese Unexamined Patent Publication No. 57-47519, the present applicant has disclosed that after rolling a hot rolled steel strip at a reduction ratio of 3 to 10%, a tension leveler is used to reduce the temperature to zero.
．． We proposed a method of applying tensile bending of 5 to 3.0% and removing scale in a pickling bath. Also, JP-A-62-2801
In Publication No. 9, after applying reduction, instead of bending and tension,
A method of adding simple bending was disclosed.

By performing mechanical descaling in this manner, the time required for descaling can be shortened.

As mentioned above, hot-rolled steel strips are descaled by pickling, but the acid solution used for pickling differs between ordinary steel and stainless steel; hydrochloric acid is usually used for the former, while for the latter. A mixed acid of nitric acid and butsu acid (nitric acid/bututsu #1) is used. In particular, for descaling stainless steel, which is a material that is difficult to pickle, it is common to perform shot blasting and then immerse it in nitric acid. Therefore, ordinary steel and stainless steel are currently processed in separate pickling lines.

(Problems to be Solved by the Invention) As mentioned above, when pickling hot-rolled mesh strips, the lines are different for ordinary steel and stainless steel, and as a result, equipment costs and equipment installation space increase due to parallel installation of lines. was unavoidable.

In addition, looking at the individual equipment used for pickling, shot blasting, which is commonly used as a pre-treatment for pickling stainless steel, has high equipment costs and running costs.
Furthermore, the tension leveler used to perform the bending and tensioning process described above also has problems such as high equipment costs and a need for a large equipment space.

The present invention provides a method for descaling hot rolled steel strip that can be used for common steel and stainless steel, and can reduce equipment costs and space occupied by the equipment, as well as improve descaling efficiency. The purpose is to

(Means for Solving the Problems) The gist of the present invention is to apply rolling to a hot rolled steel strip, adjust the center line average roughness Ra of the steel strip surface to 0.5 to 5 μm, and ``A method for descaling hot rolled steel strip, which comprises irradiating the surface of the steel strip with a discharge arc and then pickling it.''
It is in.

The hot rolled steel strip may be of any type, such as not only ordinary steel but also low alloy steel and stainless steel.

The surface of the steel strip mentioned above is precisely the surface of the scale formed on the surface of the steel strip, but since the steel strip and the scale are considered to be one, it is simply referred to as the surface of the steel strip.

To adjust the surface roughness of this steel strip, if you use a dull roll that has been subjected to uneven processing (dull processing) on the surface of the roll, you can create minute irregularities on the surface of the steel strip while applying pressure to achieve the desired roughness. This is suitable because it allows

In order to irradiate a discharge arc, a discharge electrode is placed in an insulating liquid, and a discharge arc is started between this electrode and a steel strip passing through the insulating liquid. A large number of electrodes are provided in the width direction of the steel strip so that the entire width direction of the steel strip is irradiated with a discharge arc.

FIG. 1 is a schematic diagram showing the structure of an example of an apparatus for carrying out the present invention.

In the figure, 1 is a steel strip, 2 is a rolling mill incorporating a dull roll 2l, 3 is a priddle roll provided on the entry and exit sides of the rolling mill 2, and provides the necessary tension to the steel strip 1;
4 is a discharge electrode that is provided on the upper and lower surfaces of the steel strip and generates a discharge arc between the steel strip 1 passing through an insulating liquid 5; and 6 is a pickling tank.

In this device, [F1 is rolled down by the dull roll 21 incorporated in the rolling m2, and at the same time a crank is generated on the surface of the steel strip, minute irregularities are formed. Next, the steel strip 1 is irradiated with a discharge arc by the discharge electrode 4 while passing through the insulating liquid 5, and the number of cranks on the surface increases. Insulating oil is suitable as the insulating liquid, but water may also be used.

Finally, the rope strap 1 is pickled in a pickling tank. As an acid solution,
Hydrochloric acid or sulfuric acid of normal concentration is used.

(Function) Generally, if minute cracks are formed in the scale layer before pickling, the pickling solution will penetrate into the cracks and the pickling speed will increase. However, the shape of the crank (hereinafter referred to as
(referred to as "scale breaking"), there is a limit to the number of cranks, and the pickling speed cannot be increased any further. The present invention was made based on the fact that increasing the number of cranks would increase the pickling speed.
The discharge arc creates minute cranks in the scale layer, increasing the pickling speed.

Even if scale breaking is performed only by discharge arc, the discharge arc will be concentrated locally and the number of cracks will not increase. However, in the method of the present invention, minute irregularities are formed on the entire surface of the strap by a rolling machine before discharge, so that the discharge arc is uniformly distributed on the surface of the strap. Arcing occurs and uniformly distributed cracks form.

A certain relationship is recognized between the size of these minute irregularities, that is, the roughness, and the scale breaking effect due to the discharge arc.

FIG. 2 is a graph showing the relationship between the discharge time and the number of cracks in the cross section of the scale when the surface roughness of the ordinary mesh is changed. In the same figure, the surface roughness is JIS B 0.
It was expressed as center line average roughness (Ra) defined in 601.

The unit of the number of cross-sectional cranks on the vertical axis is the number of cranks 8 per 10 mm of length in the cross-section of the scale 7 (see FIG. 3).

As is clear from Figure 2, the steel strip surface roughness (Ra) is 0.
．． When the thickness is less than 5 μm, the scale breaking effect is small.

Moreover, if Ra exceeds 5 μm, the product will have a rough surface.

FIG. 4 is a graph showing the relationship between the number of cross-sectional cracks and pickling time for common steel. From the same figure, it can be seen that as the number of cross-sectional cracks increases, the pickling time decreases significantly.

From the above, the minute irregularities that form on the steel strip surface have an Ra of 0.
．． The thickness was adjusted to be in the range of 5 to 5 μm.

(Example) The equipment shown in the first section above was installed on the entrance side of a cold rolling mill, and a line speed of 10 m/min was set to a thickness of 3.5 m/min. 0mm, width 1
200mm Ferrai 1~ series stainless steel (sus 4
10) was passed through the hot rolled steel strip, and descaling was performed by applying the method of the present invention.

The thickness of the scale was approximately 10 μm.

The rolling roll with dullness used had a diameter of 800 mm and a surface roughness (
Ra) was 3.5 μm, and the rolling reduction was 1%.

The discharge electrode is IOOV・2A=200W per electrode, and the arc irradiation area is 500cm" (width 5cm x length 100cm).
cm), and the number of electrodes was 24 in the width direction of the coil and 10 rows in the longitudinal direction of the coil.

The pickling tank consists of two 20m long tanks arranged in series, with a concentration of 10
% hydrochloric acid (bath temperature 85°C) was used.

For comparison, the same hot rolled steel strip was descaled using the conventional method of shot blasting followed by pickling. Four pickling tanks each having a length of 20 m were arranged in series, and nitric acid (10% nitric acid + 3% hydrofluoric acid, bath temperature 60°C) was used as the acid solution.

As a result of applying the method of the present invention, good descaling was achieved, and the surface of the steel strip after cold rolling was no different from that when the conventional pickling method was applied.

Further, the time required for descaling was significantly shortened to 0.5 minutes in the method of the present invention, compared to 1.5 minutes in the conventional method.

According to the method of the invention, stainless steel can also be treated with hydrochloric acid, and the time required is significantly reduced.

The method of the present invention was also applicable to other stainless steels, ordinary steels, and low alloy steels.

(Effects of the Invention) The descaling method of the present invention is applicable to various steels from ordinary steel to stainless steel, the same descaling line can be used for both, and the descaling efficiency is significantly improved. Furthermore, since equipment such as a shot blaster and a tension leveler is not required, it is possible to reduce the equipment cost and the space occupied by the equipment.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of an example of an apparatus for carrying out the method of the present invention. FIG. 2 is a diagram showing the relationship between the discharge time and the crank number of the scale cross section when the surface roughness of the steel strip is changed. FIG. 3 is a schematic diagram showing the occurrence of cracks in a scale cross section. FIG. 4 is a diagram showing the relationship between the number of cracks in the scale cross section and the pickling time.

Claims (1)

[Claims] It is characterized by applying pressure to the hot rolled steel strip, adjusting the center line average roughness Ra of the steel strip surface to 0.5 to 5 μm, irradiating the surface of the steel strip with a discharge arc, and then pickling. A method for descaling hot rolled steel strip.