JPS63281701A - Manufacture of h-shape steel - Google Patents

Abstract

PURPOSE:To manufacture an H-shape steel having no web wave by an on-line production by increasing a flange draft amount of a finishing universal mill when web waves are generated on the H-shape steel in the final pass stage. CONSTITUTION:When web waves are generated on an H-shape steel in the final pass stage of a finishing rolling, a draft amount of a finishing mill for a flange is increased. By that additional draft, the flange is given a rolling strain corresponding to a thermal strain amount at the limit stress for web waves generated by a temp. difference between a web and a flange to prevent generation of web waves. Hence, the producible size range of products is extended.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for manufacturing an H-section steel, and particularly to a method for manufacturing an H-section steel that prevents web waves caused by residual stress.

<Prior art and 8 points in between> The cross-sectional shape of H-beam steel is generally such that the thickness of the flange 1 is thicker than the thickness of the web 2 as shown in Fig. 4, so the cooling of the web 2 during the rolling process is difficult. The speed is faster than that of flange 1, and descaling water, etc. accumulates on web 2 and accelerates cooling, so the flange temperature may be 200°C or more higher than the web temperature at the end of finish rolling. .

Due to the finishing temperature conditions of flange 1 and web 2 at the end of rolling and the difference in cooling rate between flange 1 and web 2 after rolling, flange 1 is relatively shorter than web 2 when cooled to room temperature. As a result, as shown in FIG. 5, tensile residual stress is generated in the flange 1 and compressive longitudinal residual stress is generated in the web 2.

Then, when the compressive residual stress of the web 2 exceeds the critical buckling stress, web waves are generated in the web 2 and the shape becomes defective.

As a method for reducing this residual stress, for example, Japanese Patent Publication No. 41-20336, Japanese Patent Application Laid-Open No. 56-152928, and Japanese Patent Application Laid-open No. 58-93819 disclose a flange cooling means or a web heating means at the exit of a finishing rolling mill. Many proposals have been made to provide a.

However, installing such a flange cooling means and web heating means on an existing line is restricted by space, layout, temperature conditions, etc., which limits the manufacturing size of the product.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a method suitable for manufacturing an H-beam steel without web waves online without adding equipment.

Means for Solving the Problems> The present invention provides a method for solving the problems in the final pass process of finish rolling of H-section steel.
The above object is achieved by increasing the amount of reduction of the flange of the finishing universal rolling mill when web waves occur in the H-section steel to prevent the occurrence of web waves.

As a result of various studies on reducing the residual stress of H-section steel, the present inventors found that this residual stress is controlled by thermal strain generated by the difference between the web temperature and flange temperature during rolling. However, it was discovered that this thermal strain during rolling can be reduced by generating rolling strain by changing the rolling schedule, and based on this knowledge, the present invention was completed.

In other words, when web waves are generated due to residual stress during rolling of H-section steel, or when rolling H-section steel with a thin web that is less likely to generate web waves, thermal strain during rolling can be calculated and determined. , it is possible to reduce the residual stress in the H-section steel by controlling the rolling schedule accordingly.

The magnitude of residual stress in H-shaped steel is determined by its cross-sectional dimensions and finishing temperature.
It may be determined using the following formula (1) as described in Publication No. 19.

We-aa+a+・ΔTf"+az'ΔTw"+a
, ・in(Tf - where, ηC: Web wave evaluation index Tf, Tw: Finishing temperature of flange and web (C)t
Ltw: Thickness of flange and web (IIIIIIl)
H-: Inside the web II (n+a+) ao~as+ n++ nz 'Constant TAI r Ta2' Ferrite transformation start and end temperature (''C) Since most of this residual stress is thermal strain before finish rolling, finishing rolling mill When a web wave is generated at , the residual stress distribution curve vAA becomes the web wave limit stress B as shown in
It will exceed. Therefore, if the amount of reduction of web 2 remains unchanged and a strong reduction is applied to flange 1, the residual stress distribution becomes below the web wave limit stress as shown by curve C, and no web waves are generated. Residual stress is reduced by making the amount of reduction in step 1 larger than the amount of flange reduction when web waves are generated to generate rolling strain equivalent to thermal strain.

<Example> Below, an example of the present invention will be described based on FIG. 1. FIG. 1 is a flowchart showing the steps of the method of the present invention.

■ Given the cross-sectional dimensions of the H-section steel (web thickness t!1, flange thickness tf, web inner width 1w) and the expected finishing temperatures θ, θf of the web and flange, calculate the web using equation (1) above. Find the generated residual stress σ.

(2) Next, calculate the thermal strain ε- from this residual stress σ-. At this time, since the finishing rolling mill is originally intended for forming, the amount of reduction is minute, and the following (2) is applied using the web thickness tw.
There is no major problem even if it is converted into thermal strain using the formula.

8w = σw / tw・・・・・・・・・・・・
・・−・・・−・・−・・−・−・−・・・−・・
−・・・・・・・・・−・・・・−・(2) ■ This thermal strain ε
Calculate the flange reduction amount corresponding to -. At this time, the additional reduction amount Δtr of the flange is determined by the following equation (3), where the rolling strain ε゛wζε− is used.

Δtf=(1-1/(1+gw))xαxtf −=
----(3) Here, α: correction coefficient (〉l) ■ Add the additional reduction amount Δtf obtained in the above (3) to the finishing reduction amount Δto of the final pass to obtain ts to the corrected reduction amount. .

Δts = Δto + Atf −・・・−・
−・・−１−−・−・・・・・・・・・−・−−m−・
・・・・・・−・・−・−(4) ■ This corrected reduction amount Δ
By incorporating ts into the rolling schedule, the H-section steel is subjected to heavy rolling.

Next, the present invention was developed using H-beam steel dimensions: web width 300 mm x
When the flange height is 150 m+a, the web thickness tn/flange thickness tf: 1/2, and the expected web finishing temperature θ-
An example applied to the case of near 00°C will be explained based on FIG. 3.

In Figure 3, the web wave generation limit of this H-beam is 11.
0kgf/am", but in the conventional example where the flange is not strongly compressed, the temperature difference Δθ between the normal web and the flange is 1
At 00℃, the residual stress is -16kg f/III
Since it becomes IIlt, a web wave is generated. Further, the thermal strain generated in the web at this time is -7.5Xl0-'.

On the other hand, in order to prevent web waves from occurring through the additional reduction of the present invention, the temperature difference between the web and the flange must be 1
Web wave critical stress generated at 00°C (-10kgf/
It is sufficient to apply a rolling strain corresponding to the amount of thermal strain 4.OX 10-'

When converting the rolling reduction rate ΔRtf applied to the finishing rolling mill at this time, ΔRtf-(1-(1+4.0X10-')-') X
α・−・・・(5) Here, α is the correction coefficient (〉l), so by adding a reduction amount greater than this value, the distortion occurring in the web can be reduced. Therefore, it is possible to prevent the generation of web waves.

In this example, the above-mentioned additional reduction amount is applied in the final pass of the finishing universal rolling mill, but if space permits, it is possible to use equipment that applies the reduction independently after the completion of finishing rolling. may be arranged.

Further, if the timing of applying this additional reduction amount is performed near the transformation point, for example, in combination with flange water cooling, the correction coefficient can be brought close to 1, which is efficient.

<Effects of the Invention> As explained above, according to the present invention, since rolling strain corresponding to the thermal strain generated in the web is applied to the flange, the following effects are achieved.

■ It is possible to expand the range of sizes that can be manufactured.

■ Since there is no need to modify the existing line, problems such as space can be solved.

(2) By combining the method of the present invention with web heating and flange cooling, it is possible to significantly reduce the thickness of the web.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the flat head of the method of the present invention, and FIG.
Cross-sectional diagram showing the distribution of residual stress during strong flange compression, Part 3
The figure is a characteristic diagram showing the relationship between the temperature difference between the web and the flange, residual stress, and rolling strain. Figure 4 is a cross-sectional view of the H-section steel. Figure 5 shows the distribution of residual stress occurring in the H-section steel. FIG. 1...Flange, 2...Web. A...Residual stress distribution curve. B... Web wave critical stress line. C... Residual stress distribution curve under strong pressure Figure 3 (xlσ4) Temperature difference between web and 7 langes 〇 (℃) Figure 2 Figure 5

Claims (1)

[Claims] In the final pass process of finish rolling of the H-section steel, when web waves are generated in the H-section steel, the rolling amount of the flange of the finishing universal rolling mill is increased to prevent the generation of web waves. Method of manufacturing section steel.