JPH0938702A - Production of thin web wide flange shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a rolled wide flange shape having thin web, in which a waving deformation of the web part is not developed, at the time of producing the rolled wide flange shape by completing ferritic transformation in the web part during finish-rolling and thereafter, water-cooling the flange parts. SOLUTION: At the time of producing the wide flange shape in the hot- rolling, at least before executing the finish-rolling to the web part with a finish universal rolling mill 304, the web part temp. is lowered to near A3 transformation i.e., near ferritic transformation temp. For this purpose, the web part temp. is held or cooled by suitably operating a cooling device 305 of the web part and the flange parts before the finish-rolling and controlled near the ferritic transformation temp. just before the finish-rolling, and the finish-rolling is executed while cooling so that the ferritic transformation completes during finish- rolling the web part or after rolling. After completing the finish-rolling of the web part, the outer surface of the flange part in the obtd. rolled wide flange shape can be water-cooled.

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 H-section steel by hot rolling, and more particularly to a method for producing a thin web H-section steel which is susceptible to waviness.

[0002]

BACKGROUND OF THE INVENTION Although FIG. 1 is a cross-sectional view of H-section steel, H-section steel is generally used for beams in an I-shaped position. Therefore, from the viewpoint of economy, in order to increase the section modulus around the shaft 103 and the second moment of area, the sectional shape is
101 is thicker than web 102. That is, t ₁ <t ₂ .

Furthermore, H-shaped steel manufactured by rolling (hereinafter,
Rolled H-section steel) is usually rolled in an H-shape posture, and therefore cooling water or the like is likely to get on the upper surface of the web and excessively cool the web.

Therefore, for this reason, rolling H
In the case of shaped steel, the cooling rate of the web becomes faster than the cooling rate of the flange. Therefore, the flange may become hotter than the web by 200 ° C or more during hot rolling of rolled H-section steel. .

FIG. 2 shows the cooling process in the flange and the web of the H-section steel and the stress distribution after cooling. As can be seen from this, the compressive stress exists in the web 102 during cooling, If this residual stress exceeds the buckling stress of the web, the web 102 buckles and wavy deformation occurs.

Conventionally, a method for reducing the residual stress of the web,
Alternatively, as a method for preventing web waving, Japanese Patent Application Laid-Open
In JP 58-93819 A and JP 58-93820 A, H-section steel is subjected to web heat retention or flange water cooling during rolling or after finish rolling to reduce the temperature difference between the flange and the web. A method has been proposed in which the residual stress is reduced by stretching the flange in the longitudinal direction. However, such proposals in the prior art cannot prevent the corrugation of the flange,
The solution has been desired.

For example, in the method according to Japanese Patent Laid-Open No. 58-93819, depending on the size of the H-section steel, it is defined by the ratio of the average compressive residual stress of the web and the critical buckling stress, regardless of the rolling finish temperature of the flange / web. It is obvious that the manufactured web wave evaluation index is 1 or more, which makes it difficult to manufacture.
It is impossible to manufacture an H-section steel having a size of H550 × 200 × 6/12 (mm).

In addition, many proposals have been made so far as means for preventing wavy deformation of the web. However, all of them have been equipped with cooling means for minimizing the temperature difference between the web and the flange. This is intended, and there is no suggestion of the thin web H-section steel having a thickness of 10 mm or less as described above. Examples: Japanese Patent Publication No. 41-20336, Japanese Patent Publication No. 47-31481, Japanese Patent Publication No. 47-31481, Japanese Patent Publication No. 51-5607, Japanese Patent Publication No. 54-20442, and Japanese Patent Publication No. 50-133110. .

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for producing a rolled H-section steel, particularly a thin web, in which wavy deformation of the web does not occur during production of the rolled H-section steel. .

[0010]

By the way, it is known that steel changes its crystal structure when the temperature changes. In particular, as can be seen from the graph in which the length (volume) is plotted with respect to temperature in FIG. 4, it has the feature that the volume decreases or increases in a certain high temperature range.

In general, hot rolling of steel is performed in a temperature range of a crystal system of a body centered cubic lattice called δFe to a temperature range of a crystal system of a face centered cubic lattice called γFe. After that, in the cooling process, α of the crystal system of the body-centered cubic lattice is again obtained.
Transform into Fe. In this way, volume fluctuations are observed in the A ₃ transformation region from δFe to γFe and in the A ₁ transformation region from γFe to αFe.

However, when manufacturing H-section steel having a web thickness of 6 mm and a flange thickness of about 16 mm,
At the time of cooling the flange with water, the web 102 may have dropped to just above the transformation temperature to αFe. When flange water cooling is performed on such an H-section steel, the cooling water is transferred to the web 102.
By riding on, the web temperature is drastically lowered, and the web 102 is transformed from γFe to αFe. In that case, the volume of the web 102 is significantly increased by transforming from γFe to αFe. Therefore, the compressive stress exerted on the web 102 by the contraction of the flange 101 due to the flange water cooling and the phenomenon that the web 102 tends to extend in the longitudinal direction due to the transformation of the web 102 are combined, and a large compressive stress acts on the web 102 to 102 wavy deformation.

That is, in the case of a thin web size, even if the flange water cooling is simply strengthened, it is difficult to realize stable production unless the flange water cooling in the above temperature range is avoided.

However, due to the limitation of the withstand load of the rolling mill or the rolling torque, it is indispensable to cope with the thin thickness by increasing the number of rolling passes. Therefore, the temperature decrease cannot be avoided, and the countermeasure is difficult. Met.

By the way, in the method according to Japanese Patent Laid-Open No. 58-93820, the above phenomenon is not taken into consideration, and a thin web, that is, an H-section steel having a web thickness of 10 mm or less, particularly a web thickness of about 6 mm, is stabilized. Was difficult to manufacture.

Therefore, as a result of further study by the present inventors paying attention to the above phenomenon, as a result, at least the web finish rolling is performed during or immediately after the ferrite transformation of γFe → αFe, and then the flange is water-cooled. Then, the inventors have found that the occurrence of the waviness of the web can be minimized or substantially eliminated, and the present invention has been completed. In other words, the ferrite transformation is completed before the final water cooling of the flange.

Here, in the present invention, when H-section steel is manufactured by hot rolling, the ferrite transformation of the web is completed by the time of finish rolling, and then the flange is water-cooled. It is a method of manufacturing steel.

Broadly speaking, the present invention relates to H rolling in hot rolling.
A method for producing a thin-walled web H-section steel, which comprises finishing rolling and ferritic transformation of a web before final water cooling of a flange when producing the shape steel.

As described above, the present invention is not necessarily limited to the H-section steel of the thin-walled web. Since the corrugation of the web can be effectively prevented, the H-section steel of the thin-walled web is particularly economical. This is advantageous to the manufacturing method. There is no particular definition when referring to a thin web, and the present invention can be applied as long as waviness is a problem, but generally, a web having a thickness of 10 mm or less can be referred to as a thin web. It is preferably 6 mm or less.

[0020]

Next, the operation of the present invention will be described more specifically with reference to the accompanying drawings. FIG. 4 is a rolling process diagram of an H-section steel when performing the method according to the present invention.
Breakdown rolling mill 30 using rolls with hole shape
1 to produce a rolled material having a web and a flange by rolling a crude steel slab, and the rough universal rolling mill 302 and the edger rolling mill 303 perform reduction of the web, flange face and flange tip of the rolled material. Finally, the finish universal rolling machine 304 performs finish rolling to a predetermined size.

Here, an apparatus 305 for water cooling the web and the flange of the H-section steel is installed on the upstream side of the rough universal rolling mill 302 and on the downstream side of the edger rolling mill 303, and further, on the downstream side of the finishing rolling mill 304. Install a device 306 for water cooling the shaped steel flange.

According to the present invention, when H-section steel is manufactured by hot rolling according to the rolling process of FIG. 1, the web undergoes A ₁ transformation at least before the finish universal rolling machine 304 finish-rolls the web. That is, the temperature is lowered to near the ferrite transformation temperature.

For that purpose, before the finish rolling, the web and flange cooling device 305 is appropriately operated to keep or cool the web, and the web temperature immediately before the finish rolling is controlled to be near the ferrite transformation temperature to obtain the ferrite of the web. The finish rolling is carried out while cooling so that the transformation is completed before or after the web finish rolling.

As the web and flange cooling device 305, a known device can be used as it is, and no special device is required in the present invention. In the conventional method described above, it has been proposed to minimize the difference between the cooling temperatures of the web and the flange, and it is possible to easily control the heat retention and cooling of the web by appropriately selecting from a large number of devices.

After the web finish rolling, the outer surface of the flange of the obtained rolled H-section steel may be water-cooled by a conventional cooling method. Next, the working effects of the present invention will be described in more detail with reference to Examples.

[0026]

EXAMPLE In this example, an H-section steel having dimensions H550 × 200 × 6/16 (mm) was rolled and manufactured according to the rolling process chart shown in FIG.

In the example of the present invention, the cooling device 305 of FIG. 4 is operated so that the web temperature immediately before the finish rolling is 620 to 630 ° C., so that the temperature of the web becomes close to the A ₁ transformation point immediately before the finish rolling. The cooling was controlled so that the web completed ferrite transformation at least just before entering the finish rolling mill 304, or the ferrite transformation was completed during rolling. Further, in order to prevent the temperature difference between the web and the flange from increasing due to the web temperature control by the cooling device 305, the cooling device 305 also performed water cooling of the flange.

In the conventional example, the web did not undergo ferrite transformation even at the stage of the finish rolling mill 304, and ferrite transformation was observed at the cooling stage after completion of finish rolling.

Table 1 shows the chemical composition of the steel materials used in this example. The transformation end temperature of γFe to αFe of the steel used is about 62
It was 0 ° C. The results are summarized in Table 2.

In the conventional method, the rolling finish temperature of the web is in the temperature range immediately above the transformation temperature, and web waviness occurs during flange water cooling. However, as is clear from Table 2, according to the present invention, the thin web H-section steel could be stably manufactured.

As is clear from the above examples, the web is kept warm or cooled before the finish rolling, the web temperature immediately before the finish rolling is controlled to be near the ferrite transformation start temperature, and the ferrite transformation of the web is Finish rolling while cooling to complete, then
It has been found that the invention, in which the outer surface of the section steel flange is water-cooled, makes it possible to produce H-section steel without web waves.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

As is apparent from the above description, according to the present invention, the web is kept warm or cooled before the finish rolling, the web temperature immediately before the finish rolling is controlled to the ferrite transformation start temperature, and Finish rolling is performed while cooling so that the ferrite transformation of this web is preferably completed immediately before or during finish rolling, and then,
By water cooling the outer surface of the obtained H-section steel flange,
It is possible to produce H-section steel without web waviness.

[Brief description of drawings]

FIG. 1 is a sectional view of an H-section steel.

FIG. 2 is a diagram showing residual stress of H-section steel.

FIG. 3 is a graph showing a correlation between temperature and length.

FIG. 4 is a schematic view of an H-section steel manufacturing process according to the present invention.

Claims (1)

[Claims] 1. When manufacturing H-section steel in hot rolling,
A method for producing a thin web H-section steel, characterized in that the ferrite transformation of the web is completed before finish rolling, and then the flange is water-cooled.