JPH0829324B2 - Manufacturing method by rolling H-section steel whose web thickness is thinner than flange thickness - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Purpose of the Invention> Industrial field of application The present invention relates to a method for manufacturing H-section steel having a web thickness thinner than the flange thickness by rolling, and more specifically, flange thickness / web thickness >> 1. The present invention relates to a method for manufacturing thin H-section steel by rolling a breakdown mill, a rough universal mill and a finishing universal mill.

2. Description of the Related Art H-section steel is widely used in steel structures.

Depending on the application, there is a demand for weight reduction as much as possible even if the rigidity is about the same.

Responding to this requirement will reduce the web thickness, which contributes less to the stiffness. An H-section steel having a web thickness smaller than the flange thickness is generally called a thin-wall H-section steel.

Conventionally, in thin H-section steel, the ratio of the web thickness (hereinafter referred to as tw) to the flange thickness (hereinafter referred to as tf) is tf / t.
W >> 1 size H-section steel is difficult to roll and is manufactured by welding.

On the other hand, the H-section steel manufactured by rolling is superior to the H-section steel manufactured by welding in terms of both cost and quality.

For this reason, it is desired that thin H-section steel with tf / tw >> 1 is also manufactured by rolling, but it is said that it cannot be manufactured by rolling.

That is, since the thin H-section steel has tf >> tw, the temperature difference between the web and the flange becomes significantly large during cooling after rolling, and a large difference in shrinkage amount between the web and the flange occurs after cooling. There is a problem that so-called web waves are generated due to the buckling phenomenon on the web surface.

As a method to prevent the generation of this web wave,
No. -20336 discloses that the flange is water-cooled during the universal mill rolling, thereby reducing the temperature difference between the web and the flange at the time of finishing.

However, in the case of rolling thin H-section steel, the web thickness and the flange thickness itself are thin, and the rolling finish temperature itself is usually low. Therefore, if water cooling is further applied to this, the temperature of the H-section steel will drop considerably. , Low temperature rolling.

As a result, insufficient elongation may occur and the product may be out of specification.

Problems to be Solved by the Invention The present invention aims to solve the above problems, and specifically,
After rolling is finished with a breakdown mill, the rough billet is reheated to raise the web temperature to a temperature higher than the temperature of the flange thickness, and after rough rolling and finish rolling with a universal mill and subsequent cooling. In this paper, we propose a rolling method of thin H-section steel which can minimize the residual stress and prevent the generation of web waves.

Furthermore, according to this method, when reheating after the completion of breakdown rolling, the web thickness is the smallest compared to the flange thickness, so the rate of temperature rise of the web is considerably higher than that of the flange. For this reason, the temperature difference between the flange and the web can be approximated and even reversed simply by charging into the furnace for reheating.

<Structure of the Invention> Means for Solving Problems and Its Action That is, the method of the present invention is a universal rolling mill group,
When rolling and manufacturing a thin H-section steel having a web thickness thinner than the flange thickness, the flange thickness / web thickness ratio is 1 during or after rolling by a breakdown mill.
When the temperature rises by 40 to 70%, it is charged into the heating furnace and reheated to raise the temperature of the web above the temperature of the flange, and then rolled through the universal rough mill and universal finishing mill. It is characterized by performing predetermined cooling after finish rolling.

The structure and operation of these means will be described below with reference to the drawings.

Note that FIG. 1 is a graph showing the temperature history of the web and the flange when the material is sent back to the heating furnace and heated again after the completion of the breakdown rolling in the method of the present invention.

FIG. 2 compares the case of reheating with a heating furnace on the way according to the method of the present invention and rolling, and the case of rolling according to the comparative method, and shows the residual after cooling after rolling with a universal finishing mill for each. It is a graph which shows stress.

FIG. 3 is a graph showing a temperature history in each process during H-shaped steel rolling.

FIG. 4 is a graph showing a temperature history during cooling after finishing rolling by a universal finishing mill.

First, when thin H-section steel is manufactured by rolling, rolling is performed in the process of heating furnace extraction → breakdown mill → universal rough mill → universal finishing mill. When the temperature history of each process during rolling was obtained, it was as shown in FIG. As is clear from FIG. 3, there is a large temperature difference between the web and the flange.

That is, during the rolling by the breakdown mill and the rolling by the universal rough mill, although the plate thickness difference is considerably large, the processing heat is generated, so that the temperature difference is not so large.

Rather, a large temperature difference appears from the end of breakdown rolling to biting into No. 1 of the universal rough mill, during which the rough billet is air-cooled, which causes a temperature difference. .

In addition, this temperature difference is widened during the rough rolling in the universal rough mill, and when it reaches the universal finishing mill, it is about 10
The temperature difference is close to 0 ° C.

In the cooling after finish rolling in the universal finishing mill, the temperature difference further increases with time, as shown in FIG.

Therefore, on the assumption that this is the case, the generation mechanism of the web waves generated in the H-section steel during cooling is as follows. Thermal expansion that occurs when passing the transformation points Ar _{3 to} Ar ₁ in the web and the flange, This is based on the fact that the passage points of the transformation points Ar _{3 to} Ar _{1 in} the flange are shifted, and the yield point is lowered at high temperature. In other words, due to the plastic strain due to the temperature difference, the web has elongation strain,
Compressive strain will remain on the flange.

Therefore, as shown in FIGS. 3 and 4, in the cooling process after the universal finishing mill rolling, web waves are generated by the generation mechanism.

The method of the present invention has been established on the premise of the points shown in FIGS. 3 and 4, and in particular, has been established by examining the mechanism of generation of the web wave obtained from this point.

Therefore, according to the method of the present invention, the temperature difference between the web and the flange of the rough shaped billet that has passed through the breakdown mill is reduced or the temperature difference is reversed immediately before the start of rolling in the universal rough mill. This makes it possible to reduce the temperature difference during finish rolling in the universal finishing mill and prevent web waves. The method of the present invention was established by paying attention to this point.

 Therefore, more specifically, it is as follows.

The rolling process of H-section steel is performed through a heating furnace-breakdown mill-universal rough mill-universal finishing mill. In this rolling process, the web-to-flange plate thickness ratio becomes maximum during the breakdown mill rolling.

That is, even if the product plate thickness ratio (tf / tw) is 1 to 2, the plate thickness ratio further increases by 40 to 70% in the vicinity of the completion of the breakdown, and the web thickness (tw) becomes the flange thickness ( thinnest for tf). Such rolling is a factor that causes a temperature difference.

Therefore, in the method of the present invention, attention is paid to the vicinity of the completion of the breakdown mill rolling in which the difference in plate thickness is the largest as described above, and at this point, it is once returned to the heating furnace. Also, when not returning to the heating furnace, install a heating furnace near the breakdown mill,
This heating furnace purposely heats the rough steel slab, and by inserting this heating step, the temperature difference between the web and the flange is reversed (the temperature of the web is made higher than the temperature of the flange).

Rolling with a universal rough mill and a finishing mill in this state can reduce or reverse the finishing temperature difference, thereby preventing generation of web waves.

Examples Hereinafter, examples will be further described.

Web height 300 mm, flange width 150 mm, web thickness 3.2 m
A thin H-section steel with m and a flange thickness of 4.5 mm was manufactured by the method of the present invention, and it was as shown in FIG.

For comparison, when a universal rolling mill group is used for rolling and manufacturing as in the conventional example, as shown in FIG. 3, the gap between the web and the flange is rolled in a universal finishing mill. There was a temperature difference of about 100 ° C at the start and at the completion of finish rolling.

On the other hand, when rolling by the method of the present invention,
Since the flange thickness / web thickness ratio had increased by 40 to 70% at the completion of the breakdown mill rolling, the rough H-shaped steel billet was sent back to the heating furnace again and heated (7'30 ″ in Fig. 1). By the way).

Since the web thickness is considerably smaller than the flange thickness only after charging in the heating furnace, the rate of temperature rise of the web is extremely fast. The temperature difference between the B / 2 and B / 4 widths is reduced,
When the charging was continued for more than a minute, the temperature difference of 70 to 100 ° C was reversed and the web became hotter (see Fig. 1). In this state, send it to the universal rough mill for rough rolling, then
Finished and rolled with a universal finishing mill. The temperature difference between the web and the flange during the finish rolling became almost zero, the residual stress after the predetermined cooling was reduced as shown in FIG. 2, and the generation of web waves was not observed at all.

In FIG. 2, the vertical axis represents the residual stress at the center of the flange, and the rolling in the conventional method of the comparative example is indicated by the ● mark in the figure. As described above, the comparative example has a residual stress of -15 to -25 after the predetermined cooling after finishing rolling by the universal finishing mill.
It is distributed within the range of kg / mm ² and some web waves are observed.

On the other hand, in the case of the present invention, as indicated by a circle in the figure,
It is distributed in −10 to 0 kg / mm ² , and it can be seen that the residual stress is greatly reduced.

<Effects of the Invention> As described in detail above, the method of the present invention produces thin H-section steel having a web thickness thinner than the flange thickness by rolling in a universal rolling mill group.

In addition, since this rolling is carried out during or after the completion of the breakdown mill rolling, it is charged into the heating furnace and reheated, and then rough rolling and finish rolling are performed by the universal mill, so the residual stress after cooling is greatly reduced. It is possible to prevent the generation of web waves.

Also, since the web is charged into the heating furnace when it becomes the thinnest as compared with the flange thickness, the temperature of the web rises faster than the flange, and the temperature difference between the web and the flange is reduced while the furnace is still charged. You can reverse.

Therefore, according to the method of the present invention, it is possible to manufacture a thin H-section steel, which is said to be difficult to manufacture by rolling due to the generation of web waves, by rolling, which greatly contributes to cost and quality. be able to.

[Brief description of drawings]

FIG. 1 is a graph showing the temperature history of the web and the flange when the material is sent back to the heating furnace and heated again after the completion of breakdown rolling in the method of the present invention, and FIG. A graph showing the residual stress after cooling after rolling with a universal finishing mill for each case comparing the case of reheating and rolling and the case of rolling by the comparative method. FIG. 4 is a graph showing the temperature history in each process of FIG. 4, and FIG. 4 is a graph showing the temperature history during cooling after finishing rolling by the universal finishing mill.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Takafumi Hashimoto, Inventor 1-chome, Mizushima Kawasaki-dori, Kurashiki-shi, Okayama Prefecture (no address) Inside Mizushima Works, Kawasaki Steel Co., Ltd. (72) Harumi Nagashitayama, Kawashima-dori, Kurashiki-shi, Okayama Prefecture 1 chome (without street number) Kawasaki Steel Co., Ltd. Mizushima Steel Works (56) References Japanese Patent Publication Sho 53-48183 (JP, B2) Actual Publication Sho 57-58192 (JP, Y2)

Claims (1)

[Claims] 1. When rolling a thin H-section steel having a web thickness smaller than that of a flange in a universal rolling mill group to manufacture it, during the rolling by a breakdown mill or at the completion of rolling, the flange thickness / web Thickness ratio is 1 or more and is 40-70
% When the temperature rises, it is charged into a heating furnace and reheated to raise the temperature of the web above the temperature of the flange, and then rolled through a universal rough mill and universal finishing mill, and after this finishing rolling a prescribed cooling A manufacturing method by rolling H-section steel having a thinner web thickness than the flange thickness.