JPH06312202A - Manufacture of hot rolled strip - Google Patents

Abstract

PURPOSE:To obtain a hot rolled steel sheet whose surface ruggedness is minimized, fine and uniform in its distribution by adjusting the surface roughness of a steel strip in a specified range by passing the strip through a skin pass mill in which dull rolls are used for upper and lower work rolls after pickling a hot rolled steel sheet. CONSTITUTION:By passing the hot rolled steel strip through the skin pass mill in which the dull rolls are used for the upper and lower work rolls, surface properties of the hot rolled/pickled steel sheet is improved. At this time, the surface roughness Ra of the steel strip is adjusted in the range of 0.4-0.8mum. In this way, the steel strip excellent in surface properties whose surface ruggedness is minimized, fine and its distribution is uniform such that buffing is omitted is made. Where, the dull roll is a roll on the surface of which fine ruggedness is unifomly provided. Thus, the hot rolled steel strip which is excellent in the adhesive strength of paint and requires the smaller application amount of oil for preventing rust is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hot-rolled steel strip, and more specifically, after hot-rolled steel strip (coil of steel sheet) is pickled to remove oxide scale on the surface of the steel sheet, The present invention relates to a method of adjusting surface roughness to improve surface properties.

[0002]

2. Description of the Related Art A hot-rolled steel strip subjected to pickling treatment is called a hot-rolled pickled steel strip. Conventionally, such a hot-rolled pickled steel strip manufacturing method, after hot rolling the slab in a hot strip mill, or after further temper rolling, if necessary,
This is performed by a step of removing the oxide scale on the surface by pickling. The hot rolled pickled steel strip produced in this manner is currently being shipped to customers immediately.

[0003]

However, in the above-mentioned conventional manufacturing method, the surface properties of the hot-rolled pickled steel strip (steel plate) obtained are not sufficient, and are used as they are (after the pickling treatment). However, there is a problem in that the buffing, which is very troublesome for the customer side, must be performed as an additional step.

That is, when the above-mentioned hot rolled pickled steel strip after pickling treatment is microscopically evaluated for the surface properties of the steel sheet, the surface roughness Ra is compared with Ra of the cold rolled steel strip subjected to surface finishing. In addition, the distribution of surface irregularities is also uneven. Therefore, when the surface after plating is required to have a uniform and beautiful luster, as typified by chrome-plated steel pipes for automobile parts, motorcycle frames, furniture, etc., on the customer side, the hot rolled pickled steel strip is used. It cannot be used as it is, and there is no choice but to carry out buffing.

Since such buffing is very troublesome and costly and time consuming, this is a very serious problem. Against the background of recent trends of cost reduction and labor saving,
The solution is strongly desired. In other words, there is a strong demand for the development and supply of hot rolled pickled steel strips which have fine surface irregularities with a small amount of surface irregularity and which are excellent in the surface properties so that buffing can be omitted.

The present invention has been made by paying attention to such a situation, and its object is to solve the above-mentioned problems of the conventional one and to improve the surface quality of the hot-rolled pickled steel strip. A technique that can be improved by a simpler method than buff polishing, that is, a surface that is fine and has a uniform distribution with few surface irregularities before buff polishing can be omitted, as compared to the case where buff polishing is added. An object of the present invention is to provide a hot rolled steel strip manufacturing method capable of manufacturing a hot rolled steel strip having excellent properties.

[0007]

In order to achieve the above object, the present invention provides a method for producing a hot rolled steel strip having the following constitution. That is, the method for producing a hot-rolled steel strip according to the present invention, after the hot-rolled steel strip is pickled, the surface roughness Ra of the steel strip by passing through a skin pass mill using dull rolls for the upper and lower work rolls. Is adjusted to 0.4 to 0.8 μm.

[0008]

[Function] As the upper and lower work rolls of the skin pass mill for temper rolling, dull rolls are used in place of the normal rolls used for temper rolling, and hot rolled steel strips (after hot rolling and pickling are used. The treated steel sheet, hot rolled steel, temper-rolled steel sheet, and then pickled) are passed through the steel strip (steel sheet) to measure the surface roughness and scan the steel sheet surface. Observation with a scanning electron microscope (SEM) was performed. As a result, by passing the hot-rolled steel strip through a skin pass mill using dull rolls for the upper and lower work rolls, the surface texture of the hot-rolled pickled steel strip can be improved, and at this time the surface roughness Ra of the steel strip is increased.
It has been found that by adjusting the value of 0.4 to 0.8 μm, a hot rolled steel strip can be obtained which has fine surface irregularities with a small amount of surface irregularity before buffing can be omitted and has a uniform distribution of surface properties. The present invention has been made based on these findings. Here, the dull roll is a roll having fine irregularities uniformly provided on the surface. The surface roughness Ra is the center line average roughness.

Therefore, according to the method for producing a hot-rolled steel strip of the present invention, as described above, the hot-rolled steel strip is subjected to pickling treatment and then passed through a skin pass mill using dull rolls for the upper and lower work rolls. Surface roughness Ra of steel strip is 0.4 to 0.8 μm
It was adjusted to. Passing a steel strip (hot rolled pickling steel strip) through such a skin pass mill is an extremely simple means than buffing. Therefore, the surface texture of the hot-rolled pickled steel strip can be improved by a simpler method than buffing. That is,
According to the method for manufacturing a hot-rolled steel strip according to the present invention, as compared with the case where buff polishing is added, a surface having a small amount of surface irregularities and a uniform distribution thereof before buff polishing can be omitted. A hot rolled steel strip having excellent properties can be manufactured.

The surface roughness Ra of the steel strip after passing through the skin pass mill is numerically limited to 0.4 to 0.8 μm for the following reason. That is, in order to make buff polishing omissible
Ra needs to be 0.8 μm or less, and if it exceeds 0.8 μm, buffing cannot be omitted, and at least one buffing is indispensable, and the time and labor required for buffing increase as Ra increases. To do. On the other hand, when using a steel strip, Ra should be as low as 0.8 μm or less from the viewpoint of the surface appearance after plating, but Ra: 0.4 μm reduces the frictional force on the surface of the steel strip, and therefore There is a concern that the end faces of the coil after removal may become uneven, or surface defects such as scratches and misalignment may occur. From this, the surface roughness Ra
It is adjusted to 0.4 to 0.8 μm.

The surface roughness Ra is adjusted according to the type of steel strip (physical properties such as composition and hardness) and the surface properties of the steel strip after pickling, etc. ) Or by adjusting the pressure applied at the time of skin pass. In particular, regarding dull rolls, by using dull rolls whose surface roughness is varied according to the grain size of the grid projected on the roll surface, it is possible to variously control the surface roughness Ra of the steel strip after passing the skin pass mill. . Further, when a laser dull roll obtained by uniformly engraving fine irregularities on the roll surface with a laser is used, it is possible to obtain a steel strip having further excellent image clarity.

[0012]

EXAMPLES Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to the examples.

[0013]

[Table 1]

[0014]

[Table 2]

A method (a method according to an embodiment of the present invention) in which a hot-rolled steel strip is pickled to remove oxide scale on the surface and then passed through a skin pass mill using dull rolls as upper and lower work rolls 14 coils of hot rolled steel strip were manufactured.
At this time, as the dull roll, a roll material made of 5% Cr forged steel and having a roll surface roughness Ra adjusted to 0.8 to 1.5 μm was used. Two types of steel strips A and B were used as the hot rolled steel strips. These steel strips A and B have different chemical components as shown in Table 1, and different mechanical properties as shown in Table 2.
Especially, the strength is different. The surface roughness Ra is defined by JIS B 0601.

For comparison, 24 coils of hot rolled steel strip were manufactured by a conventional manufacturing method (method of pickling a hot rolled pickled steel strip). For these hot-rolled steel strips, and hot-rolled steel strips obtained by the method according to the embodiment of the present invention, the surface roughness is measured to obtain a distribution of surface roughness Ra and a representative roughness chart, or The surface of the steel sheet was observed with a scanning electron microscope (SEM) and photographed.

As a result, regarding the distribution of the surface roughness Ra, as shown in FIG. 1, the surface roughness Ra of the hot-rolled steel strip obtained by the method according to the embodiment of the present invention is 0.4 to 0.8 μm. Within the range, of the hot rolled steel strip obtained by the conventional manufacturing method
Ra: 0.6 to 1 μm, the surface roughness Ra of the method according to the embodiment of the present invention is at a lower level than the conventional manufacturing method. This is because the method according to the embodiment of the present invention can control the surface roughness Ra to a low level as compared with the case of the conventional manufacturing method,
Moreover, it is shown that the surface roughness Ra can be adjusted to 0.4 to 0.8 μm.

Further, as shown in FIG. 2 (representative roughness chart), the hot-rolled steel strip obtained by the conventional manufacturing method has uneven surface irregularities, whereas the embodiment of the present invention. The hot-rolled steel strip obtained by the method has the surface irregularities uniformly pressed down by a dull roll and smoothed. Furthermore, FIG.
As shown in (SEM photo showing the metallographic structure of the surface), in the hot rolled steel strip obtained by the conventional manufacturing method,
The light and shade showing the height of the surface irregularities is remarkably shown, and the distribution state is also non-uniform, whereas the hot-rolled steel strip obtained by the method according to the example of the present invention is rolled down with a dull roll. Marks are observed, and the surface irregularities are evenly distributed. From the above, the manufacturing method according to the present invention is smaller than the case of the conventional manufacturing method in the surface of the hot-rolled steel strip having less surface unevenness by buffing omission, and its distribution is uniform, that is, It was confirmed quantitatively and visually that the desired hot rolled steel strip with excellent surface properties could be produced.

Further, the hot-rolled steel strip obtained by the method according to the above-mentioned embodiment of the present invention has a beautiful luster not seen in the hot-rolled steel strip obtained by the conventional manufacturing method, It had a surface quality that made buffing unnecessary, and satisfied the demands of consumers. It was also excellent in paint adhesion, and was a material more suitable for coating applications than the hot-rolled steel strip obtained by the conventional method. Moreover,
Since the surface roughness Ra was controlled to a low level, it was also found that a sufficient amount of rust preventive function can be obtained by applying a smaller amount of oil than the hot rolled steel strip obtained by the conventional method.

Therefore, according to the manufacturing method of the present invention,
In addition to having the surface quality that allows buffing before plating by the customer to be omitted, it also has excellent paint adhesion and a hot rolled steel strip that requires a small amount of oil for rust prevention.

[0021]

According to the method for producing a hot rolled steel strip according to the present invention, the surface texture of the hot rolled pickled steel strip can be improved by a simpler method than the buff polishing. In other words, buff polishing is added. As compared with the case of performing the above, it becomes possible to easily manufacture a hot-rolled steel strip which has a small surface irregularity and is fine and has a uniform distribution so that buffing can be omitted. Moreover, a hot-rolled steel strip having such excellent surface properties, excellent paint adhesion, and a small amount of oil for rust prevention can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a distribution of surface roughness Ra of a hot rolled steel strip obtained by a method according to an example of the present invention and a conventional method.

FIG. 2 is a diagram showing a representative roughness chart of hot-rolled steel strips obtained by a method according to an example of the present invention and a conventional method.

FIG. 3 is a drawing-substituting photograph showing a metallographic structure of a surface of a hot-rolled steel strip obtained by a method according to an example of the present invention and a conventional method by a scanning electron microscope.

Claims (1)

[Claims] 1. The surface roughness Ra of the steel strip is adjusted to 0.4 to 0.8 μm by pickling the hot-rolled steel strip and then passing it through a skin pass mill using dull rolls for the upper and lower work rolls. A method for producing a hot rolled steel strip.