JPH04274801A - Method and device for manufacturing thin web h-beam - Google Patents

Abstract

PURPOSE:To realize the manufacture of thin web H-beam in which a web wave is not generated, and also, toughness of a flange part is not deteriorated. CONSTITUTION:On the delivery of a finishing rolling mill 6 of an H-beam steel rolling mill consisting of a rough rolling mill 4, an edging mill 5 and the finishing rolling mill 6, a forced cooling system 7 formed by arranging alternately plural strong water-cooling banks and weak water-cooling banks is provided, and forced cooling is executed to a flange so that a flange surface temperature enters within a temperature range of MS point to {MS+50 deg.C}, and the system is controlled so that an average temperature difference between the flange and a web at the time when cooling is stopped becomes a prescribed value or below.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for manufacturing thin-walled H-section steel.

0002

2. Description of the Related Art In general, the cross-sectional shape of an H-section steel is such that the thickness of the flange 1 is thicker than the thickness of the web 2, as shown in FIG. Considering that this H-shaped steel is used as a structural member such as a beam or column, the contribution rate of the web 2 to the bending rigidity is small, so it is an economical design to make the web thickness as thin as possible to reduce the unit weight. Become. H made by welding flat plates
In a shaped steel (hereinafter referred to as a welded H-shaped steel), residual stress in the web 2 is small, so shape defects such as web waves due to buckling are less likely to occur, and the web 2 can be made thinner relatively easily.

On the other hand, in H-section steel manufactured by hot rolling (hereinafter referred to as rolled H-section steel), the above-mentioned flange 1
Due to the difference in thickness between the web 2 and the flange 2, the cooling rate of the web 2 becomes faster than that of the flange 1 during rolling and cooling, resulting in a temperature difference between the two, as shown in FIG. A tensile residual stress is generated in the flange 1 and a compressive longitudinal residual stress is generated in the web 2. Therefore, the thinning of the web 2 in the rolled H-beam increases the residual stress and the web 2 becomes thinner.
In order to reduce the critical buckling stress of the material, web waves are generated and the material becomes defective in shape, making it unusable as a product.

However, despite this, rolled H-section steel is cheaper than welded H-section steel, and the material of fillet portion 3 at the boundary between flange 1 and web 2 is stable. Because of the advantages of rolling thin web H
Shaped steel is strongly requested by the market. Here, thin web rolled H-beam steel has a ratio of flange thickness TF to web thickness TW (TF /TW) of 2 or more, and a ratio of web height HW to web thickness TW (HW /TW). )
refers to H-beam steel with a diameter of 65 or more.

By the way, Japanese Patent Application Laid-Open No. 1-205028 discloses a method for manufacturing a thin web H-beam steel.
When water-cooling a flange after hot finish rolling, this method uses the lower limit of the temperature difference between the flange and the web immediately after water-cooling, at which web waves do not occur during water-cooling, and the flange immediately after water-cooling, at which web waves do not occur until the temperature reaches room temperature after water-cooling. The upper limit of the temperature difference between the web and the web is determined for each size of H-beam steel and cooling water flow density, and the flange is forcibly cooled so that the temperature difference immediately after water cooling falls within the upper and lower limits of the temperature difference. However, according to experiments conducted by the inventors, this method tends to generate web waves both during and after water cooling when the web becomes thin, and the upper and lower limits of the temperature difference between the flange and the web immediately after water cooling are extremely limited. In many cases, the wave becomes small or the upper and lower limits do not exist, so it has not been possible to completely prevent web waves. Furthermore, when the flange is water-cooled, the flange surface temperature may drop below the MS point, which is the martensitic transformation start temperature. Problems such as deterioration of toughness, which is a parameter for elongation and bending workability, also occurred.

In addition, Japanese Patent Publication No. 60-37856 describes a method for manufacturing H-section steel without web waves, in which a web wave evaluation index for evaluating shape defects of web waves is determined as a function of the finishing temperature and cross-sectional dimensions of the flange and web. A proposed method is to use the functional formula to determine the finishing temperature of the flange and web that does not generate web waves, and to keep the web warm or water-cool the flange in the process before final finishing rolling to reach this finishing temperature. However, TF /TW, HW
For thin web H-beam steel with a large /TW as described above, finishing temperature conditions cannot be satisfied by insulating only web 1, and there is a problem of web wave generation during air cooling after rolling, and marten The problem of toughness deterioration due to site formation has arisen in each case.

[0007]

[Problems to be Solved by the Invention] The present invention provides TF/T
In manufacturing H-section steel with large W, HW /TW, that is, thin-walled H-section steel, by rolling, the problems of the conventional technology as described above are solved, and the generation of web waves is efficiently prevented. In addition, it is an object of the present invention to provide a method and apparatus for manufacturing a thin-walled web H-section steel having excellent toughness.

[0008]

[Means for Solving the Problems] A first aspect of the present invention is
In a method of manufacturing thin-walled H-section steel by forced cooling of the flange in the process after final finish rolling of H-section steel, the flange surface temperature is set at the MS point of martensitic transformation start temperature or higher and below {MS point +50°C} The flange is forcibly cooled so that the temperature falls within the temperature range of This is a method for manufacturing a characteristic thin-walled web H-beam steel.

[0009] A second aspect of the present invention is an H-section steel manufacturing apparatus comprising a rough rolling mill, an edging mill, and a finishing mill. This is an apparatus for manufacturing thin-walled H-section steel, characterized in that a forced cooling device is arranged in which the following elements are arranged alternately.

0010

[Function] The first point of the present invention is to adopt a method of forced cooling of the flange in the process after finish rolling, and according to research by the present inventor, the web waves generated during cooling are This is elastic buckling, and is based on the discovery that even if web waves are generated during water cooling, the web waves will disappear if the compressive thermal stress of the web becomes less than the buckling stress while cooling to room temperature. In other words, the previously mentioned Unexamined Patent Publication No. 1-2050
No. 28 states that “web waves must not be generated during water cooling”
However, in reality, the web waves during water cooling are unrelated to the web waves at room temperature after cooling, and in order to prevent web waves at room temperature, a lower limit value of the temperature difference between the flange and the web immediately after water cooling is specified. That makes no sense. However, if forced cooling is performed too much, the temperature of the flange surface becomes below the MS point, and in this case, a martensitic structure is generated and the toughness of the flange is deteriorated. Therefore, as the second point of the present invention, it is necessary to add conditions for forced cooling so that the flange surface temperature does not fall below the MS point. However, in this case, the MS point will be determined by the type of steel, including its chemical composition.

On the other hand, in order to prevent web waves from occurring at room temperature after cooling, the average temperature difference ΔT in the thickness direction between the flange and the web during forced cooling, that is, the difference between the flange average temperature and the web average temperature, must be set to a certain limit. It is necessary to make the value ΔTc or less, which is the third point of the present invention. In addition,
This critical temperature difference ΔTc is determined by the steel type and the cross-sectional dimensions of the H-section steel. Therefore, this average temperature difference Δ
To make T less than the critical temperature difference ΔTc, thick-walled flanges can be forcedly cooled, but in order to efficiently reduce the average flange temperature in a short time, the flange surface temperature should be maintained at the MS point where material deterioration does not occur. do it. however,
In reality, maintaining the flange surface temperature near the MS point requires advanced cooling technology, and an error of about 50°C is expected. Therefore, the fourth point of the present invention is that the upper limit of the flange surface temperature during forced cooling is set to {MS point +50° C.}. Note that the upper limit of the flange surface temperature during forced cooling is {MS
If the temperature exceeds +50°C, the time required for cooling will significantly increase, which will increase the size of the forced cooling equipment and increase production costs, and the temperature of the thin web will drop too much and the material quality of the web will deteriorate (deterioration of toughness). Problems such as the occurrence of

Next, the configuration of the manufacturing apparatus used in the present invention will be explained. As shown in FIG.
, an edging mill 5, a finishing mill 6, and a forced cooling device 7, and the hot-rolled H-beam 10 moves in the direction of the arrow in the final stage. The forced cooling device 7 is divided into a plurality of small banks 7a, 7b, 7c, 7d, 7.
As shown in FIG. 2, each bank 7a,... has a large number of cooling nozzles 8 arranged on the side surface of the side guide 11 on the table roller 9, so that the flow rate of the cooling water can be adjusted. It has become.

Therefore, in the forced cooling device 7, for example, 7a, 7c, 7e... are made into strong water cooling banks, and 7b, 7d are made into strong water cooling banks.
... are arranged alternately as weak water-cooled banks, and the H-shaped steel 10 that has finished finish rolling in the finish rolling mill 6 is repeatedly cooled with strong water and weak water in each bank of the forced cooling device 7, and the flange surface temperature is Above the MS point and {MS point +50℃}
Control the temperature to be within the following temperature range. Then, water cooling is stopped when the average temperature difference ΔT between the flange and the web becomes equal to or less than the limit temperature difference ΔTc.

FIG. 3 shows the flange surface temperature TF when strong water cooling and weak water cooling are alternately repeated using a 5-bank forced cooling device 7 consisting of strong water cooling banks 7a, 7c, 7e and weak water cooling banks 7b, 7d. and flange average temperature TFave
, is a characteristic diagram schematically showing the time course of the web average temperature TWave, and as shown in the figure, the flange surface temperature TF
is controlled between the MS point and {MS point +50°C}. As a result, the temperature difference ΔT between the flange average temperature TFave and the web average temperature TWave is controlled. Note that the input and output sides of the forced cooling device 7 are air-cooled.

[0015]

[Example] C: 0.0 mm was melted in a converter and then continuously cast.
Using a beam blank of steel type SM50 whose main components are Mn: 16 wt% and Mn: 1.35 wt%, the web height was 5.
50mm, flange width 200mm, web thickness 6mm,
Flange thickness 16mm (550 x 200 x 6 x 16)
It was hot rolled into a thin-walled H-beam steel. At this time, the forced cooling device 7 provided on the exit side of the finishing rolling mill 6 had five banks, and strong water cooling and weak water cooling were repeated as shown in FIG. 5 above.

Table 1 shows the results of an investigation on the presence or absence of martensite formation on the flange surface of the produced H-section steel and the presence or absence of web waves. Here, for comparison, only conventional strong water cooling and only air cooling without treatment were performed at the same time, and the investigation results are also shown in Table 1 as Conventional Examples 1 and 2. In addition, the MS point (lower limit T
LL) is 435°C, so its upper limit TUL(=
MS point +50°C) is 485°C, so the flange surface temperature TF should be within the range of 435 to 485°C.

[0017]

[Table 1]

As is clear from Table 1, in the example of the present invention, if the average temperature difference ΔT immediately after water cooling is stopped is within 10°C, it is possible to manufacture H-beam steel without material deterioration or web waves. However, it can be seen that this is not possible in Conventional Examples 1 and 2. In addition, if the steel type and cross-sectional shape are changed in the above-described embodiments, only the MS point and the critical temperature difference ΔTC at the time of water cooling stop are changed, so forced cooling may be performed accordingly.

[0019]

As explained above, according to the present invention, it is possible to inexpensively manufacture a thin-walled web H-beam steel without generating web waves or deteriorating the toughness of the flange portion.
Its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the configuration of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a cooling zone used in the present invention.

FIG. 3 is a characteristic diagram showing temperature changes at various parts of the H-section steel when the present invention is applied.

FIG. 4 is a cross-sectional view of a conventional H-section steel.

FIG. 5 is an explanatory diagram of the effect of stress on H-beam steel.

[Explanation of symbols]

1 Flange 2. Web 4 Rough rolling mill 5 Edging mill 6 Finishing rolling mill 7. Forced cooling device 8 Cooling nozzle 9 Table roller 10 H-beam steel 11 Side guide

Claims (2)

[Claims] Claim 1: A method for manufacturing a thin-walled H-section steel by forcedly cooling the flange in a process after final finish rolling of the H-section steel, wherein the flange surface temperature is set to a temperature equal to or higher than the MS point of the martensitic transformation start temperature, and {MS The flange is forcibly cooled so that the temperature falls within the temperature range of +50℃}, and the forced cooling is performed when the average temperature difference in the thickness direction between the flange and the web becomes smaller than the upper limit value determined in advance by the steel type and cross-sectional dimensions. A method for manufacturing a thin-walled web H-beam steel, characterized by stopping the process. 2. An H-section steel manufacturing apparatus comprising a rough rolling mill, an edging mill, and a finishing mill, wherein strong water-cooled banks and weak water-cooled banks are alternately arranged on the exit side of the finishing mill. A manufacturing device for thin-walled web H-beam steel, characterized in that a cooling device is provided.