JPS63154202A - Reducing method for residual stress in h-shape steel - Google Patents

Abstract

PURPOSE:To reduce residual stresses, to increase a web height, and to reduce a web thickness by elongating the web in its height direction when a temp. of a part of flanges is not higher than the Ar1 transformation point. CONSTITUTION:A shape steel 1 is held by a web elongation device 3 installed in the downstream of a finishing rolling mill; a web 2 is elongated in its height direction when the temp. of at least one part of flanges is not higher than the Ar1 transformation point. A desirable working ratio for the web 2 is 0.5-2%. A web shape of the H shape steel is improved because residual stresses in the steel is remarkably reduced by this method.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for significantly reducing the residual stress inherent in H-section steel.

<Prior art> The cross-sectional shape of H-beam steel is usually flange 1 as shown in Fig. 3.
is thicker than the thickness of the web 2, and since it is rolled in this shape, the cooling water in the flange part falls, but the cooling water in the web part remains as it is.
During the hot rolling process, the cooling rate of web 2 tends to be faster than that of flange 1, and the temperature of veranib is about 150°C lower than that of the flange, which causes large residual stress to occur after cooling (e.g. , iron and steel, 69.m3
(+983), see 412). Residual stress in iIH section steel generally tends to be distributed as shown in Figure 4. For example, if the a direction indicated by the arrow is tensile stress and the b direction is compressive direction, then the central part of flange 1 is under tensile stress. This causes stress, and compressive stress occurs at both ends of the width of the flange l and at the web 2. Further, depending on the case, the width side of the flange l may also become tensile stress.

In rolled H-section steel, the maximum value of the compressive stress of the web tends to increase as the width of the flange Ig/web thickness and web height 77572 increases. Therefore, Hli”
The presence of residual stress in il causes deformation of the material, causing serious defects such as a decrease in yield strength, poor shape, and cracks during cutting.

For the above reasons, various methods have been proposed to reduce the residual stress of H-shaped steel. No. 47-33012 discloses a method of cooling the flange portion during rolling or cooling, and JP-A No. 48-4458 discloses a method of insulating the reverse web to reduce residual stress. As a method, JP-A-56-83+, No. 7 discloses a method in which the flange portion is stretched and rolled.

<Problems to be Solved by the Invention> However, in the flange water cooling method, it is difficult to avoid the splashing of cooling water onto the web, which may further increase the temperature difference, and in the web heat insulation method, it is difficult to avoid the splashing of cooling water onto the web. It takes a long time to cover, which increases the rolling cycle time.
There are disadvantages such as the difficulty of processing the insulation material, but on the other hand,
When using the flange stretch rolling method, a small reduction must be applied to the four surfaces of the upper, lower, left, and right flanges, and compared to thick plate rolling, H-beam steel manufactured using the universal rolling method has a large thickness variation. , requires complex control,
There is a problem that it is not always possible to obtain something satisfactory.

Furthermore, in the case of an H-beam steel with a thin web and a high web height, it is impossible to manufacture the steel by any of the above methods because the web waving phenomenon occurs.

The present invention has been made in consideration of the above-mentioned circumstances, and an object of the present invention is to provide a method for reducing residual stress in H-beam steel that is easy to work with and is highly effective.

<Means for Solving the Problems> The present invention is characterized in that the web is stretched in the height direction of the web of the H-section steel when at least a part of the flange is at a temperature below the Ar + transformation point. This is a method for reducing residual stress in H-beam steel.

As a result of various studies on reducing residual stress in H-beam steel, the present inventors found that the main cause of residual stress is that the finish temperature of the web is lower than that of the flange, and as the flange cools, the flange becomes closer to the web. They focused on the fact that tensile stress is generated in the flange and compressive stress is generated in the web due to the relatively short length, and found that it is effective to correct these by plastic deformation during cooling. In other words, in order to shrink the web in the longitudinal direction of the rolling direction (hereinafter referred to as the "downward direction") by an amount corresponding to the amount by which the flange becomes relatively shorter than the web, the web is rolled as known from the effect of Poisson's ratio. What is necessary is just to extend in the web height direction (hereinafter referred to as the C direction) perpendicular to the direction.

Note that when the temperature of the flange is Ar, the temperature is higher than the transformation point, the yield point of the material is low and residual stress is less likely to occur, so even if the web direction shrinkage is performed by stretching the web in the C direction, the implementation effect is low.

A detailed explanation will be given below according to the drawings.

Figure 1 shows time on the horizontal axis and material temperature and thermal stress on the vertical axis, and shows changes in material temperature and thermal stress over time.
This is shown as an example.

In the figure, Ia and lb indicate the cooling curves of the flange center and web center, respectively, from the end of finish rolling to room temperature during normal cooling, and lb and 2b indicate the thermal stress at the flange center and web center, respectively, during normal cooling. The lines D, H indicate the mid-flange and mid-web thermal stress lines, respectively, according to the inventive implementation.

During normal cooling, the temperature changes over time.

Lunge ° Heat stress line in middle husband! Due to the transition of 1+- to 0-A-1, tension-, compression-, tensile and thermal stress act, and on the other hand, the thermal stress cotton 2b changes to 〇-・E-1J in the center of the web, and vice versa. A compressive-tension-pressure thermal stress of 11 h acts on the flange, resulting in a tensile residual stress of 1 h at room temperature.
However, compressive residual stress j is generated in the web.

Therefore, by applying the present invention in which at least a part of the flange is subjected to Ar (at a temperature below the transformation point, stretching processing is performed in the C direction perpendicular to the direction of rolling force of the web, the web can be
direction, resulting in a reduction in residual stress. In other words, as shown in Fig. 1, due to the stretching process in the C direction of the nib, the thermal stress at the center of the flange is transferred from point A to point B (in multiple lines,
The thermal stress at the center of the web moves from point E to point F. After cooling is completed, that is, at room temperature, residual stress of S, C, and C will be exhibited, respectively. This residual stress is the residual stress 1. caused by normal cooling. Much smaller than J
The effect of web stretching is obvious.

It should be noted that if the amount of web C-direction elongation is too small, the residual stress will not be reduced and the effect will be weak, whereas if it is too large, the product dimensions will fluctuate and the material will change, which is not preferable. According to the experience of the present inventors, it is appropriate to give an elongation of 0.5 to 2.1 stone. That is, if it is less than 0.5%, the residual stress will not be reduced, and if it is more than 2%, it will elongate too much, causing product dimensional fluctuations and material changes, which is not preferable. This amount of stretching is
There are appropriate values depending on the temperature, material, or product dimensions, and it is necessary to select the optimal value in conjunction with the cooling conditions.

Further, the stretching according to the method of the present invention is not limited to one time, but may be performed multiple times gradually in the web C direction.

<Example> An embodiment of the present invention will be described below based on FIG. 2.

In the figure, the web stretching device 3 is composed of four rolls 3a arranged corresponding to the upper, lower, left, and right flanges 1, and the roll position is set and driven by a roll position adjustment device and a drive device (not shown). .

The web stretching device 3 configured as described above was placed downstream of the finishing rolling mill, and stretching was performed in the web C direction under conditions not shown in Table 1. The results are shown in Table 1 together with comparative examples based on the prior art.

The dimensions of the F shape steel used in this example were a web height of 500 mm, a flange width of 200 m, a web thickness of IQms, and a flange thickness of 16 m, and the steel type was 5S41.

As is clear from Table 1, the residual stress after cooling in all of the invention examples is significantly reduced compared to the comparative example.

<Effects of the Invention> As explained above, according to the present invention, since the web is stretched, it is possible to form a type II! :21 residual stress can be significantly reduced, especially due to the conventional web waving phenomenon'! It is now possible to use H-beam steel, which has a thinner web and a higher web height, which was impossible to manufacture in A.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the temperature transition and thermal stress change at the center of the flange and web of the FI section steel, and FIG. 2 is a side view and cross section taken along the line A-A showing an embodiment of the present invention. Figure, Figure 3 is type II! Cross-sectional view showing the shape of +4, 4th
The figure is an explanatory diagram of the residual stress distribution of H-beam steel. l...flange, 2...web, 3...
Web stretching device, 3a...Roll Patent applicant: Kawasaki Steel Corporation Figure 1 Figure 2 (a) A (b) Figure 3 Figure 4

Claims (1)

[Claims] A method for reducing residual stress in an H-section steel, comprising stretching the web in the height direction of the H-section steel when at least a part of the flange is at a temperature below the Ar_1 transformation point.