JP2887921B2 - Method of manufacturing H-section steel without web wave - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an H-section steel without a web wave, and more particularly to a method of determining a cooling condition of a flange by a temperature difference between the flange and the web.

[0002]

2. Description of the Related Art As shown in FIG. 1, the cross-sectional shape of an H-section steel is generally such that the thickness of a flange 1 is greater than the thickness of a web 2, so that the cooling rate of the web 2 during the hot rolling process is reduced. 1, and the temperature of the flange may be 200 ° C. or more higher than the web temperature at the end of finish rolling. Due to the difference in the finishing temperature between the flange 1 and the web 2 at the end of the rolling, the flange 1 becomes relatively shorter than the web 2 when cooled to room temperature.
As shown in (1), a tensile residual stress is generated in the flange 1 and a compressive residual stress is generated in the web 2. When the compressive residual stress of the web 2 exceeds the buckling stress, a web wave is generated, resulting in a defective shape, and cannot be used as a product. Therefore, in order to prevent such a web wave, the compressive residual stress of the web must be suppressed to a value lower than the buckling stress.

Various methods have been disclosed for reducing the residual stress which causes the generation of web waves. One of the production methods which is excellent in terms of work efficiency is Japanese Patent Publication No. 41-20336 in which a flange is cooled during rolling. Production method disclosed in Japanese Patent Application Laid-open Publication
There is a manufacturing method disclosed in JP-A-7-31481. In any of these methods, the flange is cooled while the H-section steel is in a high temperature state, so that the temperature difference between the flange and the web, which causes residual stress, is reduced.

However, in order to carry out these methods, the finishing temperature or the temperature difference between the flange and the web when the flange is cooled during rolling is determined. It is necessary to specifically set the temperature or the temperature difference, but this has not been clarified in the conventional method.

In the case of a thin-walled H-section steel in which the ratio of the thickness of the flange to the thickness of the web is about 3, if the flange is not cooled, the temperature of the flange becomes higher than the web temperature by 200 ° C. or more at the end of rolling. Is common. In order to reduce this temperature difference by one flange cooling, it is necessary to perform strong flange cooling to increase the flange temperature drop. The present inventors have found that a web wave is generated during the cooling if the amount of drop in the flange temperature in one cooling is too large. This phenomenon is called the so-called plasticity in which when the flange is cooled strongly and shrinks greatly, a large compressive stress is generated in the web as a reaction force, and the web in which the yield stress is reduced in a high temperature state is easily plasticized and buckled. Due to buckling. Such buckling of the web during cooling of the flange is referred to as buckling during cooling. On the other hand, as described above, the buckling of the web that occurs when the flange is cooled to near room temperature after cooling is referred to as buckling after cooling. Buckling during cooling causes shape defects similarly to buckling after cooling, but cooling conditions for preventing it are not yet clear.

[0006]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the conventional example and the above-mentioned new problems discovered by the present inventors. To prevent post-buckling, the allowable temperature difference between the flange and the web after finish rolling (when the flange is cooled only during rolling) and the allowable temperature difference after cooling the flange after finish rolling (finish rolling) In the case where the flange is cooled later), the amount of flange temperature drop that is allowed in one cooling to prevent buckling during cooling of the web, and the necessary conditions for preventing buckling after cooling and buckling during cooling. By specifically setting the allowable temperature difference between the flange and the web at the start of the last flange cooling, it is possible to manufacture an H-beam without a web wave. To provide For the purpose.

[0007]

According to one aspect of the present invention, the following processing is performed to prevent buckling after cooling of a web. That is, in the method for producing an H-section steel in which the flange is cooled only during the rolling of the H-section steel, at the start of natural cooling after finish rolling, the difference between the average temperature of the flange and the average temperature of the web is represented by the following functional formula: After cooling, flange cooling during rolling is performed so as to be equal to or less than the buckling limit temperature difference ΔTa.

Further, in the method of manufacturing an H-section steel in which the flange is cooled only after the finish rolling of the H-section steel or during the rolling and after the finish rolling, the natural cooling is started after the flange is cooled after the finish rolling. In the above, flange cooling is performed after finish rolling, or at the time of rolling and after finish rolling so that the difference between the average temperature of the flange and the average temperature of the web is equal to or less than the buckling limit temperature difference ΔTa after cooling represented by the following functional formula. ΔTa = ｛(1 + Aw / Af) σ _cr / E−3 × 10 ⁻⁴ ｝ × 10 ⁵ (1) σ _cr = Min ｛3.6E (tw / Hw) ² , σ _y ｝ Aw, Af: web and flange of the cross-sectional area E: Young's modulus at room temperature tw: web thickness Hw: inner width of the web sigma _y: yield stress of the web at room temperature .DELTA.Ta: unit ℃ here, the average temperature of the flange flange outer side inner and The average temperature of the sides, the average temperature of the web is the surface temperature at the center of the web or the average temperature at some point on the web surface.

According to the study of the present inventors, when the flange is cooled only during the rolling, the difference between the average temperature of the flange and the average temperature of the web at the start of natural cooling after the finish rolling, or after the finish rolling, or during the rolling. And when the flange is cooled after finish rolling, the difference between the flange average temperature and the web average temperature at the start of natural cooling after cooling after finish rolling is determined by the shape and material constant of the H-section steel. It has been found that buckling does not occur after cooling of the web if the buckling limit temperature difference ΔTa is equal to or smaller than ΔTa. At the time of rolling, after finishing rolling or after rolling and after finishing rolling, as shown in FIG. 3, the difference between the average temperature of the flange and the average temperature of the web at the start of natural cooling is not more than the limit temperature difference of buckling after cooling. As shown, by performing flange water cooling using the flange water cooling device 3, it is possible to manufacture an H-section steel without web waves.

According to another aspect of the present invention, the following processing is performed to prevent buckling during cooling of the web. That is, at the time of rolling, after finishing rolling, or when cooling the flange at the time of rolling and finish rolling, the flange shall be cooled one or more times, and the amount of decrease in the average temperature of the flange by one cooling is reduced. The cooling of the flange is performed so as to be equal to or less than the buckling limit temperature drop ΔTb during cooling represented by the following functional expression.

When tf ≦ 20 mm and Af / Aw ≦ 1.7, or when tf> 20 mm ΔTb = 20.4 (Af / Aw) ² -139 (Af / Aw) +296 (2) When tf ≦ 20 mm When Af / Aw> 1.7 ΔTb = 120 (3) In the method of manufacturing an H-section steel in which the flange is cooled only at the time of rolling, the average temperature drop of the flange is usually the highest in the flange cooling performed immediately before finish rolling. The risk of buckling during the cooling of the web during this cooling is high. In the method of manufacturing an H-section steel in which a flange is cooled only after finish rolling or after rolling and after finishing rolling, the amount of flange temperature drop in cooling performed after finish rolling is usually the largest, and buckling occurs during cooling in this cooling. High risk. The present inventors have found that in such cooling in which the risk of buckling during cooling is high, the average temperature drop of the flange is determined by the buckling during cooling determined by the cross-sectional area ratio of the flange to the web of the H-section steel and the flange thickness. It has been found that buckling does not occur during cooling if the temperature drop is smaller than the critical temperature drop ΔTb. That is, when cooling the flange only at the time of rolling, in the flange cooling just before finish rolling, only after finishing rolling, or when cooling the flange during rolling and after finishing rolling, in the flange cooling after finish rolling, As shown in FIG. 3, when performing flange water cooling, if cooling is performed within a range in which the average temperature drop of the flange is equal to or less than the limit temperature drop of buckling during cooling, buckling during web cooling can be prevented.

This is merely an example, and in all of the flange cooling performed once or more than once, the average temperature drop of the flange must be within the limit temperature drop of buckling during cooling. Then, by performing cooling within this range, the difference between the average temperature of the flange and the average temperature of the web after the finish rolling or the cooling after the finish rolling as described above is set to be equal to or less than the limit temperature difference of buckling after cooling. Thus, buckling after cooling of the web can be prevented, and an H-section steel without web undulations can be manufactured.

According to another aspect of the present invention, the following treatment is performed to prevent buckling of the web after cooling and buckling during cooling. That is, at the time of rolling, or when cooling the flange during rolling and after finish rolling, at the start of the last cooling of the flange cooling performed a plurality of times, the difference between the average temperature of the flange and the average temperature of the web is the post-cooling seat. The flange is cooled during rough rolling or before finish rolling so as to be smaller than ΔTa + ΔTb, which is the sum of the critical temperature difference ΔTa of buckling and the critical temperature drop ΔTb of buckling during cooling.

As described above, if the difference between the average temperature of the flange at the start of natural cooling and the average temperature of the web is not more than ΔTa, buckling does not occur after cooling the web. Further, as described above, if the amount of decrease in the average temperature of the flange in one flange cooling is equal to or less than ΔTb in all flange cooling, buckling does not occur during cooling of the web. Therefore, if the difference between the average temperature of the flange and the average temperature of the web at the start of the last flange cooling is smaller than ΔTa + ΔTb, the average temperature of the flange is set to ΔTb at which buckling does not occur during cooling of the web.
And the difference between the average temperature of the flange at the start of natural cooling and the average temperature of the web can be set to ΔTa or less, at which buckling does not occur after cooling. That is, flange water cooling is performed during rough rolling or before finish rolling as shown in FIG. 3 so that the difference between the average temperature of the flange and the average temperature of the web at the start of the last flange cooling is smaller than ΔTa + ΔTb. As shown in FIG. 3, the flange water cooling reduces the average temperature drop of the flange to ΔTb or less so that the difference between the average temperature of the flange and the average temperature of the web at the start of natural cooling after cooling is ΔTa or less. By cooling the flange within a certain range, buckling during cooling and buckling after cooling can be prevented, and an H-section steel without web waves can be manufactured.

[0015]

EXAMPLES Table 1 shows the results when an H-section steel of steel type SS41 was manufactured. All the temperatures in the table are average temperatures.

[0016]

[Table 1]

With the size of the H-section steel of Case 1, the temperature difference during natural cooling is 95 ° C., and the limit temperature difference ΔTa of buckling after cooling.
= 113 ° C. and the critical temperature drop ΔTb = 163 ° C. during cooling. As shown in Case 1, with this size, an H-section steel without a web wave could be manufactured by performing flange water cooling after finish rolling to lower the flange temperature by 81 ° C. Since the temperature drop of the flange was set to 81 ° C. smaller than ΔTb and the temperature difference between the flange and the web during natural cooling was set to 95 ° C. smaller than ΔTa, buckling during cooling and buckling after cooling could be prevented.

As shown in Case 2, the web wave was generated in the anhydrous cooling, but the temperature difference between the flange and the web during natural cooling was 167 ° C., which was larger than ΔTa, and buckling occurred after cooling. It is.

In the sizes of the H-section steels of cases 3 to 6, ΔT
a = 93 ° C., ΔTb = 120 ° C., and the critical temperature difference at the start of flange water cooling after finish rolling is ΔTa + ΔTb = 213 ° C. As shown in Case 3, in this size, H-section steel without web corrugation was obtained by performing flange water cooling during rolling to lower the flange temperature by 60 ° C. and water cooling after finish rolling to lower the flange temperature by 102 ° C. It could be manufactured. The temperature difference between the flange and the web at the start of flange water cooling after finish rolling by flange water cooling during rolling is smaller than ΔTa + ΔTb.
8 ° C., the temperature drop of the flange due to water cooling after finish rolling was 102 ° C. smaller than ΔTb, and the temperature difference between the flange and the web during natural cooling was 87 ° C. smaller than ΔTa. Crouching could be prevented. Incidentally, as shown in Cases 4 and 5, web waves were generated in the case of anhydrous cooling and in the case where the flange temperature was lowered by 103 ° C. by water cooling only after finish rolling. Temperature difference during natural cooling is Δ
Buckling occurred after cooling due to exceeding Ta.

As shown in Case 6, a web wave was also generated when the flange temperature was lowered by 155 ° C. by water cooling only after finish rolling. Although the temperature difference at the time of natural cooling was smaller than ΔTa, buckling occurred during cooling because the temperature drop of the flange in one water cooling exceeded ΔTb.

[0021]

As is clear from the above embodiment, according to the present invention, while the cooling is restricted so that the average temperature drop of the flange by one flange cooling becomes smaller than ΔTb, the last flange is cooled. At the start of cooling, the difference between the average temperature of the flange and the average temperature of the web is smaller than ΔTa + ΔTb, and the average of the flange at the start of natural cooling after finish-rolling or after flange-cooling after finish-rolling is performed. By performing flange cooling during rolling or after finish rolling so that the difference between the temperature and the average temperature of the web becomes smaller than ΔTa, an H-section steel without web waves can be manufactured.

[Brief description of the drawings]

FIG. 1 is a sectional view of an H-section steel.

FIG. 2 is a cross-sectional view showing distribution of residual stress of an H-section steel.

FIG. 3 is a sectional view showing a water-cooled state of the flange of the H-section steel according to the present invention.

[Explanation of symbols]

 1 Flange 2 Web 3 Flange water cooling device

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Misao Makinohara 1-1-2 Marunouchi, Chiyoda-ku, Tokyo Inside Nippon Kokan Co., Ltd. (72) Inventor Joe Kataoka 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nippon Kokan Co., Ltd. (58) Field surveyed (Int.Cl. ⁶ , DB name) B21B 45 / 02,1 / 08,37 / 00 C21D 9/00

Claims (4)

(57) [Claims] 1. An H-section steel flange is cooled only at the time of rolling. At this time, at the start of natural cooling after finish rolling, the difference between the average temperature of the flange and the average temperature of the web is expressed by the following formula (1). ), Wherein the flange is cooled so as to be equal to or smaller than ΔTa. ΔTa = ｛(1 + Aw / Af) σ _cr / E−3 × 10 ⁻⁴ ｝ × 10 ⁵ (1) σ _cr = Min ｛3.6E (tw / Hw) ² , σ _y ｝ Aw, Af: web and flange of the cross-sectional area E: Young's modulus at room temperature tw: web thickness Hw: inner width of the web sigma _y: yield stress of the web at room temperature .DELTA.Ta: unit ℃ 2. The flange of the H-section steel is cooled only after finish rolling, or at the time of rolling and after finish rolling, and the average of the flanges at the start of natural cooling after the cooling after finish rolling is performed. A method for producing an H-section steel without a web wave, wherein the flange is cooled such that a difference between a temperature and an average temperature of the web is equal to or less than ΔTa represented by the following equation (1). ΔTa = ｛(1 + Aw / Af) σ _cr / E−3 × 10 ⁻⁴ ｝ × 10 ⁵ (1) σ _cr = Min ｛3.6E (tw / Hw) ² , σ _y ｝ Aw, Af: web and flange of the cross-sectional area E: Young's modulus at room temperature tw: web thickness Hw: inner width of the web sigma _y: yield stress of the web at room temperature .DELTA.Ta: unit ℃ 3. The method according to claim 1, wherein the flange is cooled one or more times. At this time, an average temperature drop of the flange by one cooling is equal to or less than ΔTb shown in the following equations (2) and (3). 3. The method according to claim 1, wherein the flange is cooled so as to fall within the range. Af / Aw ≦ 1 when tf ≦ 20 mm.
7 or when tf> 20 mm ΔTb = 20.4 (Af / Aw) ² −139 (Af / Aw) +296 (2) When Af / Aw> 1.7 when tf ≦ 20 mm ΔTb = 120 (3) tf: thickness of flange ΔTb: unit ° C 4. When the flange is cooled during rolling or after rolling and after finish rolling, when the flange is cooled a plurality of times, the average temperature of the flange and the web at the start of the last cooling are determined. 4. The method according to claim 3, wherein the flange is cooled during rough rolling or before finish rolling so that the difference from the average temperature is smaller than ΔTa + ΔTb.