JPS62161402A - Method for decreasing residual stress in web of wide flange beam - Google Patents

Abstract

PURPOSE:To improve the quality of a product and to reduce the cost of production by reheating a wide flange beam in the mid-way or upon completion of rolling with a break down mill then reducing the temp. difference between the web and flanges thereof and rolling the beam with a finishing mill. CONSTITUTION:The wide flange beam is reheated in a heating furnace, etc., in the mid-way or upon completion of rolling with the break down mill to make the reverse of the temp. difference of 70-100 deg.C between the web and the flanges so that the web is made higher in the temp. than the flange in the stage of rolling the wide flange beam with a universal rolling mill group, etc. The wide flange beam is subjected in such temp. state to universal rough rolling and finish rolling. The temp. difference after the finish rolling is offset in accordance with the difference in the thicknesses of the web and flanges by which the temp. difference is made approximately zero. The residual stress of the product after cooling is thus decreased and the product quality is improved by the above-mentioned method. The web waviness of the product is eliminated and the cost for reducing the thin-walled wide flange beam is reduced.

Description

[Detailed Description of the Invention] <Object of the Invention> Industrial Field of Application The present invention relates to a method for reducing web residual stress of 1-section steel, and more specifically, relates to a method for reducing web residual stress of 1-section steel. The present invention relates to a method for reducing web residual stress of section 11 steel that can be manufactured by rolling.

Conventional technology Sectional steel is widely used in steel structures, but depending on the application, there is a demand to reduce the weight as much as possible even though the rigidity is the same.

In response to such requirements, when the web thickness of Section 11 steel is larger than the flange thickness, the opening contributes to rigidity and the opening reduces the web thickness. A size with such a small web thickness is generally called a thin-walled 1-section steel.

This thin wall (web thickness ([W) of section 1 steel and flange thickness (t
For sizes with f) ratio tf/1w)1, welded 11-section steel is usually used, and for other sizes, rolled H-section steel is usually used. However, since rolled 11 section steel is superior to welded 11 section steel in terms of both loss and quality, rolled 14 section steel is desired even in the case of [f z'jW)1. However, due to jf, )tW, the temperature difference between the web and the flange becomes significant during cooling after rolling, and after cooling TiI, the difference in the amount of shrinkage between the web and the flange causes a l1YII'52 phenomenon (web wave) to sit on the web surface. 7S;), which is difficult to manufacture by rolling for certain thin wall sizes.

Rolling of thin-walled 11 section steel is done by heating extraction → plate down mill →
During rolling in the process of universal rough mill → universal finishing mill, a temperature difference occurs between the web and the flange, as shown in Figure 3.

That is, in breakdown rolling and universal rough mill rolling, due to processing heat, the temperature difference is not so large despite the difference in plate thickness, but rather from the completion of breakdown to universal rough mill In, 1 bite. Air cooling during the transportation process creates a temperature difference,
This results in a temperature difference of approximately 100°C in the universal finishing mill.

Further, even after finish rolling, the temperature difference is further exacerbated as shown in FIG.

In general, the web wave generation mechanism that occurs during cooling of section 11 steel is r3~Ar to the transformation point of the web and flange, thermal expansion during passage, low yield point at high temperature, and Ar3~Ar of the web and flange.

It is said that webs are generated during the cooling process after universal finishing mill rolling because the plastic strain caused by the difference in passing time, that is, the temperature difference, causes elongational strain to remain in the web and compressive strain to remain in the flange.

As a method for preventing the generation of web waves during cooling by the above mechanism, Japanese Patent Publication No. 41-20336 describes a method to reduce the temperature difference between the web and the flange at the time of separation by water cooling the flange during universal mill rolling. However, in the case of rolling thin-walled section 11 steel, the plate thickness is thin and the finishing temperature is usually low during rolling, so if further water cooling is carried out, the temperature of section 11 steel will drop and the temperature will decrease. This was unsuitable because there was a risk of rolling and non-standardization such as insufficient elongation.

Problems to be Solved by the Invention The purpose of the present invention is to solve these problems.Specifically, during rolling, the entire rough section of section 11 is reheated, and at this time, the flange thickness is is considerably larger than the web thickness, so the purpose of the 4-temperature speed is to take advantage of the fact that the web is larger than the flange, reduce the temperature difference between the 7 langes and the web after reheating, and prevent the generation of web waves. .

<Structure of the Invention> Means for Solving the Problems and Their Effects The present invention provides a means for solving the problem and its operation. , reduce the temperature difference between the web and flange,
Alternatively, the temperature difference between the finishing pressure Kl and the web and the flange is reduced by reversing the finishing pressure Kl.

Hereinafter, the structure and operation of the present invention will be explained with reference to the drawings.

FIG. 1 is a graph showing the temperature history of the web and flange due to reheating of the rough mill completion machine according to the method of the present invention;
Fig. 2 is a graph showing a comparison of the residual stress after cooling of the method of the present invention and the conventional method, Fig. 3 is a graph showing the temperature history during rolling of H-beam steel by the conventional method, and Fig. 4 is a graph showing a comparison of residual stress after cooling by the method of the present invention and the conventional method. 3 is a graph showing the cooling history from the completion of 11-shape rolling according to the method.

That is, in the present invention, immediately before the start of universal mill rolling, 1
We focused on the fact that by reducing the temperature difference between the web and flange of a rough section 1 steel billet, or reversing the temperature difference, it is possible to prevent reweb waves with a small temperature difference during finish rolling. It was completed. I (The rolling process for section steel consists of a heating furnace, a breakdown mill, a universal roughing mill, and a universal finishing mill. Generally, there is a point during breakdown mill rolling where the thickness ratio of the web to flange reaches its maximum, and the product thickness increases. Ratio (tf/1w) is 1 to 2
On the other hand, near the completion of breakdown, the plate thickness ratio is 40 to 70.
%Rise. The cracking is a factor that causes temperature differences, but in the present invention, near the completion of breakdown mill rolling where the difference in plate thickness is greatest, the plate is returned to the heating furnace, or heated in a heating furnace installed near the breakdown mill. By inserting and reversing the temperature difference between the web and the flange (increasing the temperature on the web side) and rolling with a universal rough and finish mill, the finish/temperature difference can be reduced or reversed, resulting in the generation of web waves. can be prevented.

Example This will be further explained below using examples.

As an example of the present invention, the web height is 300 mm, the flange width is 150 mm, the web thickness is 3.2 mm, and the flange thickness is 4.
Applicable to 5mm thin wall 11 section steel! An example is shown in Figure 1.

Normally, when rolling is performed, as shown in FIG. 1, as the rolling progresses, a temperature difference of about 100° C. is created between the web and the flange at the beginning of universal mill rolling and at the completion of finish rolling. If this is sent back to the heating furnace once the breakdown rolling is completed, the temperature difference between the center of the web and the 8/2 and B/4 widths of the flange will be reduced to 70 to 100°C after the furnace operation.
A reversal of the temperature difference occurs, and the web is in a state where the temperature is higher. By sending the web to a universal rough mill and rolling it in this state, the temperature difference between the web and the flange during finish rolling becomes approximately 4O, and the residual stress after cold FA is reduced compared to the conventional rolling method.

In other words, Figure 2 is a residual stress distribution diagram with the vertical axis representing the residual stress at the center of the flange of the H-section steel and the horizontal axis representing the residual stress at the center of the web. Residual stress after cooling is -15 to -25kq/m
m', and the occurrence of web waves can be seen in some data, but in the case of the present invention, as indicated by the ○ marks in the figure, the
g/mm2, and it can be seen that the residual stress is significantly reduced.

<Effects of the Invention> As explained above, the present invention utilizes the thickness difference between the web and the flange to reheat in a heating furnace during or at the completion of breakdown mill rolling, so that the temperature of the web increases less than that of the flange. A method for reducing residual stress by reducing the temperature difference between the web and the flange by rolling the web quickly or by reversing the temperature difference between the web and the flange after finishing rolling. It has become possible to manufacture thin-walled 11-section steel by rolling, which was difficult to manufacture by rolling due to the occurrence of steel, making it possible to make a significant contribution in terms of cost and quality.

[Brief explanation of drawings]

Fig. 1 is a graph showing the temperature history of the web and flange due to reheating after completion of rough milling by the method of the present invention, Fig. 2 is a graph showing a comparison of residual stress after cooling by the method of the present invention and the conventional method, and Fig. 3 The figure is a graph showing the temperature history during rolling of the H-shaped steel by the conventional method, and FIG. 4 is the graph showing the cold W history after completion of the 11-shape rolling by the conventional method.

Claims (1)

[Claims] When rolling H-beam steel in a universal rolling mill group, during or at the end of breakdown mill rolling, it is reheated in a heating furnace, etc. to reduce or reverse the temperature difference between the web and the flange, and to reduce the temperature difference between the web and the flange after finish rolling. A method for reducing residual stress in a web of H-beam steel, characterized by reducing the temperature difference between the web and the flange.