JP2021112745A - H-steel production method - Google Patents

Abstract

To provide an H-steel production method capable of more efficiently uniformizing a flange temperature distribution in a limited time during rolling or/and after rolling.SOLUTION: An H-steel production method includes setting a cooling water impact width Ds in a flange width direction to satisfy 0.12≤Ds/B≤0.4 when defining the cooling water impact width as Ds during or after rough rolling and further setting an effective impact flow rate Ve of a cooling water ejected from a cooling nozzle 11 to the fillet part to satisfy Wd=Qn/Sn/0.4B, Ve=Wd1/2 (Pn/ρf)1/4, and Ve≥1.0 when defining the flow of a cooling nozzle as Qn, a feed water pressure as Pn, a cooling nozzle pitch in a rolling direction as Sn, a density of the cooling water as ρf, and a flow density as Wd to cool a fillet part of the H-steel having a flange width B.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method for producing H-section steel.

In recent years, there has been a demand for thick H-beams (hereinafter referred to as "extremely thick H-beams") in North America and Southeast Asia as pillars for large-scale buildings such as skyscrapers and stadiums, and for civil engineering structures. Is expanding. Along with this, there is an increasing demand for higher-strength materials, and there is an increasing need for 60k-class extra-thick H-beams in addition to the conventional 40k to 50k-class.
In the past, increasing the strength of H-section steel was often dealt with by increasing the alloy component, but especially when the flange thickness t _f becomes thicker, in addition to the strength, the required toughness (for example, 1/6 from the top of the flange) At the position of width (B / 6 from the upper end of the flange when the width of the flange is B) (hereinafter referred to as 1 / 6F), the position is 1/4 thickness from the outer surface side in the thickness direction (hereinafter referred to as 1 / 4t). In order to secure vE- ₂₀ ≧ 40J), it was difficult to deal with it only by adding the alloy component.

Therefore, there is known an online quenching device capable of uniformly cooling the entire steel material by injecting cooling water all around.
As shown in FIG. 1, this online quenching device 6 is installed behind the finishing rolling mill 5, and after rolling, predetermined temperature conditions (for the outer surface temperature of the flange of 1 / 6F, for example, quenching start temperature: 840 ° C., quenching end). Temperature: 640 ° C (hereinafter, "quenching end temperature" means "temperature after reheating" after quenching is completed, and "after reheating" is released after the surface temperature that has dropped significantly during quenching is completed. By cooling the H-shaped steel at the time when it rises due to the heat transferred from the inside during cooling and reaches the peak value)), the structure is made finer and both strength and toughness are achieved even in the ultra-thick H-shaped steel. It became possible to plan.
In FIG. 1, reference numeral 1 indicates a rolling facility. The rolling equipment 1 includes a heating furnace 2 that heats slabs in order of transport direction, a breakdown rolling mill 3 that rolls slabs heated by the heating furnace 2 into a substantially H shape, and rough rolling that rolls slabs into an H shape close to the product shape. Machine 4, finish rolling machine 5 for finish rolling to product shape, online quenching device 6 for cooling and quenching H-shaped steel finished and rolled by finish rolling machine 5 to a predetermined temperature, H cooled by online quenching device 6. It is provided with a sawing device 7 for sawing shaped steel to a predetermined length.

However, in the actual manufacturing process, in the case of extra-thick H-section steel, remarkable temperature unevenness occurs in the flange part during rolling, and the temperature of the fillet part (intersection of the web and the flange) becomes remarkable, so online. Temperature unevenness remains as it is after quenching, and the temperature distribution after quenching (hereinafter, "after quenching" in online quenching means "after reheating" after quenching) is necessary to ensure the characteristics. It has been found that it is difficult to keep the temperature within a range (for example, 640 ± 50 ° C.).

Conventionally, as a means for eliminating the high temperature of the fillet portion of the H-section steel, a method of selectively cooling the outer surface of the flange, particularly the fillet portion, during or after rolling has been known (for example, Patent Document 1 and 2). However, until now, it has been mainly developed _{for H-section steels having a flange thickness t f} of 40 mm or less and having a web thickness t _w relatively thinner than the flange thickness t _f. In this case, a high temperature is limited to a relatively narrow range in the vicinity of the fillet portion (approximately the range of 2 times the width of the web thickness t _w), by appropriately cooling the part, relatively easily flange temperature It was possible to make the distribution uniform.

On the other hand, especially in the case of an extra-thick H-section steel having a _{flange thickness t f of more than 40 mm, not only the flange thickness t f} is thick and the fillet portion becomes hot due to the influence of the web, but also as seen in the example of FIG. 2 described later. As a result, the cooling effect from the end face is added and the temperature difference between 1 / 2F and 1 / 6F is widened. Therefore, a larger amount of cooling is required to make the temperature distribution uniform.

Japanese Unexamined Patent Publication No. 4-351220 Japanese Unexamined Patent Publication No. 9-8530

However, in the case of an extra-thick H-section steel having a flange thickness t _f of more than 40 mm, the cooling time that can be secured during or after rolling is limited due to the need to secure rolling efficiency, and a conventional cooling device has a sufficient temperature distribution. Could not be made uniform. Therefore, in order to reduce the temperature deviation of the extra-thick H-section steel, it is necessary to perform cooling much more efficiently than before.

The present invention has been made in view of the above circumstances, and provides a method for producing an H-section steel capable of more efficiently uniformizing the flange temperature distribution during and / or within a limited time after rolling. The purpose is.

The present inventors investigated the temperature distribution on the outer surface of the flange when the temperature of the extra-thick H-section steel was increased in order to obtain a method for producing an H-section steel capable of efficiently uniformizing the flange temperature distribution.
After finish rolling in FIG. 2 (product flange thickness t _f = 125 mm, web thickness t _w = 78 mm), it was cooled for 42 seconds with an online quenching device (water amount density for cooling the inner and outer surfaces of the flange: 2.0 m ³ / m ^{2 / min).} An example of actual measurement of the flange outer surface temperature distribution before and after quenching using a thermo-viewer is shown. The broken line is the temperature distribution on the outer surface of the flange before quenching and the solid line is after quenching. In addition, the dashed line (before quenching) and the solid line (after quenching) are marked at the center of the flange (hereinafter referred to as 1 / 2F), 1 / 6F, and the position 5/6 width from the top (hereinafter referred to as 5 / 6F). The mark is plotted. 1 / 2F, 1 / 6F, and 5 / 6F are often designated as control sites for collecting test pieces for mechanical property evaluation (strength / toughness) in various manufacturing standards for H-section steel, so that they are used for temperature control. Is also a reference site (see Fig. 3).

As can be seen from FIG. 2, a remarkable mountain-shaped temperature distribution has already occurred in the flange portion before quenching, and a temperature difference of about 70 ° C. occurs between 1 / 2F to 1 / 6F / 5 / 6F. .. Further, it can be seen that the same temperature distribution and the same temperature difference occur even after quenching, and that the temperature unevenness that occurred before quenching remains almost as it is after quenching.
The reason why such mountain-shaped temperature distribution becomes remarkable in ultra-thick H-section steel is
(1) Flange specifications: Since the flange thickness t _f is relatively thick with respect to the flange width B, the cooling effect due to heat removal from the flange end face during rolling tends to reach the 1 / 6F / 5 / 6F side, which is relative. The flange end side is easily cooled,
(2) Web specifications: In the case of extra-thick H-section steel used for column applications, it is necessary to increase the web thickness t _{w relative to the flange thickness t f} , and therefore the fillet portion in the center of the flange. However, the heat supply from the web makes it harder to cool and tends to get hotter.
It is considered that a chevron shape is likely to occur due to the combination of the factors (1) and (2).

That is, with respect to (1), the flange end face is cooled by allowing to cool or contact with the rolling roll during rolling, and the effect of this end face cooling appears at a length corresponding to _{approximately the flange thickness t f at both ends of the flange (1). As the flange thickness t f} becomes thicker with respect to the flange width B (the portion surrounded by the broken line in FIG. 2 (1)), the range in which the temperature drops on the end side becomes relatively longer.
(2) 2 times the approximate web thickness t _w is considered as a range to be high temperature for (a portion surrounded by a dotted line in FIG. 2 (2)), together the effect of (1) (2), pole _{It is considered that the thicker the flange thickness t f} is relative to the thick H-shaped steel, that is, the flange width B, the more remarkable mountain-shaped temperature distribution is formed during rolling.

Therefore, in order to flatten the mountain-shaped temperature distribution, the fillet cooling device and cooling nozzle were reviewed.
[Configuration example of fillet cooling device]
FIG. 4 shows a configuration example (image seen from above) of the fillet cooling device 10.
The cooling nozzles 11 are arranged at a predetermined nozzle pitch Sn in the transport direction of the H-shaped steel. Further, a set of an on-off valve 12, a flow rate adjusting valve 13, and a flow meter 14 is provided for each of a plurality of nozzles 11 (every four in the example of FIG. 4), and injection ON / OFF control and flow rate control of the cooling nozzle 11 are collectively performed. It is possible. Further, for each flow rate adjusting valve 13, a pressure gauge 15 is provided at one location in the pipe between the flow rate adjusting valve 13 and the cooling nozzle 11, so that the water supply pressure Pn of the cooling nozzle 11 can be measured.

A guide plate 16 is installed in front of the cooling nozzle 11 in order to prevent the H-shaped steel from colliding with the cooling nozzle 11. The guide plate 16 is provided with holes (hereinafter, referred to as “injection holes”) in accordance with the positions of the cooling nozzles 11 so that the cooling water injected from the individual cooling nozzles 11 can pass through.
Further, in order to keep the distance between the guide plate 16 and the flange surface of the H-shaped steel constant, vertical rolls (hereinafter referred to as “guide rolls”) 17 are installed on both the entrance side and the exit side of the fillet cooling device 10. ing. The guide roll 17 protrudes from the guide plate 16 about 50 mm inside the transport line, and even if the steel material (H-shaped steel) deviates slightly laterally from the transport line during transport, the guide roll 17 receives the steel material while rotating. Therefore, the steel material is pushed back to the inside of the transport line to prevent it from directly hitting the guide plate 16. Further, this makes it possible to keep the distance between the flange surface of the H-shaped steel being conveyed and the guide plate 16 within the range of 50 ± 20 to 30 mm.

The guide plate 16 and the guide roll 17 have a web height H so that the distance between the guide plate 16 and the flange outer surface is maintained within the above range even when the size of the H-section steel (web height H) changes. At the same time, it is possible to move the steel in the vertical direction (direction orthogonal to the H-shaped steel transport line) in FIG. At this time, by moving the cooling nozzle 11 together with the guide plate 16, the distance between the cooling nozzle 11 and the outer surface of the flange can be kept substantially constant.
Further, when the flange width B of the H-section steel changes, the height (= B / 2) of the fillet portion corresponding to the central portion from the pass line changes, so that the central height of the cooling water collision area becomes B / 2. As described above, the inclination angle γ of the cooling nozzle 11 can be adjusted. The injection holes provided in the guide plate 16 are elongated holes in the vertical direction according to the tilt angle changeable range of the cooling nozzle 11, so that the cooling water can be guided even when the tilt angle γ of the cooling nozzle 11 is changed. It can pass through the plate 16.

[Cooling nozzle]
FIG. 5 shows a cooling nozzle 11 (schematic image) of the fillet cooling device. In the H-shaped steel rolling line where hot rolling is performed in the H posture, in order to selectively cool the fillet portion in the center of the flange, the fillet portion is aimed at and is generally perpendicular to the flange surface from both sides toward the outer surface of the flange. Alternatively, the cooling water is injected from the cooling nozzle 11 by tilting it downward by a predetermined angle (inclination angle γ, see FIG. 5B) (in FIG. 5A, only the cooling nozzle 11 on one side (front side) is shown).
As the cooling nozzle 11, a spray nozzle having a mountain-shaped flow rate distribution is used. If the spray nozzle is used, the cooling water can be sprayed in the form of droplets, and it is possible to select a cooling water jet having an appropriate spread according to the distance from the object and the range in which cooling is required. In particular, a flat spray nozzle in which the shape of the collision portion of the cooling water is substantially strip-shaped, or an elliptical spray nozzle in which the shape of the collision portion of the cooling water is substantially elliptical may be used.

The reason is that the collision pressure of the cooling water is relatively high among various sprays, and it is likely to occur on the cooling surface especially when cooling the high temperature steel material during rolling, and it penetrates the steam film that hinders the collision of the cooling water and hinders the cooling. It has a large capacity, high cooling capacity can be obtained in the cooling water collision area, and the flow velocity of the cooling water flow (hereinafter referred to as "secondary flow") in which the cooling water flows along the surface of the steel material after colliding with the steel material is relatively high. This is because it is large and easily scatters from the steel material, so that there is an advantage that uneven cooling due to the secondary flow other than the collision portion is unlikely to occur.

Further, the inclination angle γ is usually 15 to 15 to prevent the cooling water scattered upward in the secondary flow from exceeding the flange and riding on the upper surface of the web when the cooling water is injected onto the outer surface of the flange. The temperature is set to about 30 degrees and the cooling water is tilted downward to reduce the amount of cooling water scattered upward. However, in the case of cooling the fillet portion, since the cooling water is injected only to the fillet portion, even if γ = 0 °, scattered water that goes beyond the flange and wraps around the web is unlikely to occur. Further, when the inclination angle γ is increased, the degree of uneven cooling in the vertical direction of the fillet portion increases, so that the angle may be smaller than usual (γ = 0 to 15 °).

As described above, if a spray nozzle is used as the cooling nozzle 11, a mountain-shaped flow rate distribution can be easily formed.
Therefore, the inventors thought that if this mountain-shaped flow rate distribution corresponds to the flange temperature distribution of the H-section steel, appropriate fillet cooling would be possible.

FIG. 6 shows the flow rate density (flow rate per unit width / unit time in the spreading direction) of a flat spray nozzle (hereinafter referred to as a spray nozzle) having a mountain-shaped flow rate distribution in the spray spreading direction (direction parallel to the collision line). An example of distribution is shown (nozzle flow rate Qn = 100 L / min, injection distance Ln = 300 mm, spread angle α = 53 °). Here, the collision line is the center line of the belt-shaped cooling water collision area (when the collision area is elliptical, its long axis, see FIG. 7), and the effective collision length De (flow density is in the range of 20% or more of the maximum value). Length and definition, see FIG. 6), the distance between the cooling water outlet of the spray nozzle and the steel material (cooling water injection surface) is the injection distance (described as injection height in FIG. 6) Ln, and the relationship between the spread angle α is α = arctan. It can be represented by (De / 2 / Ln) * 2.

These effective collision length De, injection distance Ln, and spread angle α are important parameters for properly cooling the fillet portion, but the cooling water from the spray nozzle is injected with an inclination (torsion angle β) with respect to the fillet portion. Will be done. Even if the effective collision length De is large, if the twist angle is large, the amount of cooling water that collides with the fillet portion becomes small. Therefore, rather than adjusting these parameters, the amount of cooling water that actually collides with the fillet portion, that is, the cooling water collision width Ds in the flange width direction in the fillinget portion cooling as shown on the right side in FIG. 7 is adjusted. I thought it was important to do it.

[Definition of cooling water collision width Ds]
FIG. 7 shows the flow rate density distribution in the flange width direction with the collision surface of the cooling water from the spray nozzle. Regarding the cooling water injected from the cooling nozzle (spray nozzle) to the outer surface of the flange, the flow rate density distribution in the flange width direction calculated by integrating the flow rates in the longitudinal direction of the H-shaped steel is the same as the definition of the effective collision length De. , The range of 20% or more of the maximum value is defined as the cooling water collision width Ds.
The reason why the width of 20% or more of the maximum value is defined as the cooling water collision width Ds is that the flow rate of the cooling water jetted in that range covers approximately 95% or more of the total flow rate jetted from the spray nozzle. Therefore, it is considered to correspond to the effective cooling range in the sense that it is the main injection range of the cooling nozzle (spray nozzle) and therefore a substantial cooling effect can be obtained, and the jet density drops sharply outside that range. Therefore, it almost coincides with the boundary of the water jet injected from the apparent cooling nozzle.

[Examination of efficiency of fillet cooling system]
In order to perform cooling such that the flange temperature distribution is flattened, it is important to adjust the cooling water collision width Ds appropriately with respect to the fillet portion.
For example, the cooling water collides width Ds is be cooled adjusted to 2 times the web thickness t _w, can not always properly fillet portion cooling. Various sizes of H-beams are manufactured on the production line. Depending on the size of the H-section steel, the amount of heat (latent heat) latent in the H-section steel also differs. If the cooling water collision width Ds can be adjusted regardless of the amount of latent heat, in other words, regardless of the size of the H-section steel, universally efficient uniform flange temperature distribution becomes possible.
As mentioned above, the main causes of the mountain-shaped temperature distribution are considered to be (1) flange specifications and (2) web specifications. Therefore, if the inventors estimate the latent heat using these (or one of them) and standardize the cooling water collision width Ds with respect to the fillet portion to determine the cooling width (that is, the cooling water collision width Ds). (If the optimization is performed), it is thought that cooling that can flatten the flange temperature distribution is possible.

The method for producing an H-section steel of the present invention is based on the above, and is a method for producing an H-section steel having a flange width of B (m).
During rough rolling and / and after rough rolling
When the cooling water collision width in the flange width direction is Ds (m),
The cooling water collision width Ds is set so that 0.12 ≦ Ds / B ≦ 0.4, and the cooling water collision width Ds is set.
The flow rate of the cooling nozzle is Qn (m ³ / min), the water supply pressure is Pn (Pa), the cooling nozzle pitch in the rolling direction is Sn (m), the density of the cooling water is ρ _f (kg / m ³ ), and the flow rate density is When Wd (m ³ / m ² / min) and the effective collision flow velocity of the cooling water injected from the cooling nozzle to the fillet are Ve (m / s),
Wd = Qn / Sn / 0.4B
Ve = Wd ^1/2 · (Pn / ρ _f ) ^1/4
Ve ≧ 1.0
It is characterized in that the fillet portion is cooled by setting the effective collision flow velocity Ve (m / s) so as to be.

Further, in the above-mentioned configuration of the present invention, the flange thickness t _f of the H-shaped steel to be manufactured may exceed 40 mm.

Further, in the above-mentioned configuration of the present invention, after rough rolling, finish rolling may be performed and quenching may be performed.

According to the present invention, the flange temperature distribution can be more efficiently made uniform during and / or within a limited time after rough rolling, and the H-beam can be efficiently made without deteriorating the manufacturing efficiency. Steel can be manufactured.
In particular, even when manufacturing ultra-thick H-beams with a flange thickness of more than 40 mm, which was difficult to homogenize in the past, the temperature distribution can be made uniform, meeting the demand for H-beams that require larger sizes. Will be possible.

It is a figure which shows the schematic structure of the rolling equipment provided with the fillet cooling device which concerns on embodiment of this invention. It is a graph which shows the actual measurement example of the temperature distribution of the flange outer surface before and after quenching. It is a figure for demonstrating the control part which collects the test piece of the mechanical property evaluation (strength / toughness) of H-section steel. It is a figure which shows the schematic structure of the fillet cooling device which concerns on embodiment of this invention. The positional relationship between the cooling nozzle and the H-shaped steel according to the embodiment of the present invention is shown, and (a) a perspective view and (b) is a front view. It is a figure which shows the distribution example of the flow rate density of the flat spray nozzle which has the mountain-shaped flow rate distribution in the spread direction of a spray, which concerns on embodiment of this invention. It is a figure which shows the collision surface of the cooling water from a cooling nozzle, and the flow density distribution in the flange width direction. It is a graph which shows the result of plotting the change of the required water amount of a cooling device with respect to the cooling water collision width. The graph shows the results of plotting the ratio of the cooling water collision width to the flange width on the horizontal axis and the ratio of the required water amount to the minimum value of the required water amount for each size on the vertical axis. It is a graph which shows the result of plotting the change of the reduction rate of the temperature deviation in the flange 1 / 4t after quenching by fillet cooling when the ratio of the cooling water collision width and the flange width is taken on the horizontal axis. In the same graph, the results of the transfer speeds that can be secured are arranged by taking the flow rate density on the horizontal axis. In the same graph, the results of the transfer speeds that can be secured are arranged by taking the effective collision flow velocity on the horizontal axis.

Hereinafter, embodiments of the method for producing H-section steel according to the present invention will be described with reference to the drawings.
In the present embodiment, the fillet portion of the flange of the H-shaped steel is cooled by the fillet cooling device 10 shown in FIG. Since the configuration of the fillet cooling device 10 has been described above, the description here will be omitted.

In the method for producing H-shaped steel of the present embodiment, cooling water is injected from the cooling nozzle 11 of the fillet cooling device 10 to the fillet portion of the H-shaped steel during and / or after rough rolling.
In this case, when the cooling water collision width in the flange width direction is Ds (m),
The cooling water collision width Ds is set so that 0.12 ≦ Ds / B ≦ 0.4, and the cooling water collision width Ds is set.
The flow rate of the cooling nozzle 11 is Qn (m ³ / min), the water supply pressure is Pn (Pa), the cooling nozzle pitch in the rolling direction is Sn (m), the density of the cooling water is ρ _f (kg / m ³ ), and the flow rate density. Is Wd (m ³ / m ² / min), and the effective collision flow velocity of the cooling water injected from the cooling nozzle 11 to the fillet is Ve (m / s).
Wd = Qn / Sn / 0.4B
Ve = Wd ^1/2 · (Pn / ρ _f ) ^1/4
Ve ≧ 1.0
The effective collision flow velocity Ve (m / s) is set so as to be, and the fillet portion is cooled.

By cooling the fillet portion in this way, the flange temperature distribution can be more efficiently made uniform during and / or within the limited time after rough rolling, and the manufacturing efficiency is deteriorated. H-shaped steel can be manufactured efficiently without any problems.

_{In this case, the flange thickness t f} of the H-shaped steel to be manufactured may exceed 40 mm. As described above, in particular, even when manufacturing an extra-thick H-section steel having a flange thickness of more than 40 mm, which has been difficult to homogenize in the past, it is possible to make the temperature distribution uniform, and the H-section steel is required to be increased in size. It will be possible to meet the demand of.
Further, after rough rolling, finish rolling may be performed and quenching may be performed.

Here, the following studies were conducted in optimizing the cooling water collision width Ds.
[Examination of the optimum range of cooling water collision width Ds]
In the fillet cooling device shown in FIG. 4, a flat spray nozzle is used as the cooling nozzle 11, and the cooling water collision width Ds is determined by changing the twist angle β of the cooling nozzle 11 under the six conditions A to F shown in Table 1. The temperature distribution after cooling the fillet portion and the temperature distribution after cooling using the online quenching device 6 shown in FIG. 1 after cooling the fillet portion were analyzed. Here, the torsion angle β is defined as the angle (0 ° to 90 °) formed by the collision line (the long axis of the collision area when the collision area is elliptical) and the horizontal line on the collision surface (flange outer surface) of the cooling water (0 ° to 90 °). (See FIG. 5). Conditions A and B in which the cooling water collision width Ds was small were both adjusted to β = 0 °, and Ds was adjusted using cooling nozzles 11 having different nozzle holes. The flow rate Qn shown in Table 1 is the flow rate when the water supply pressure Pn is 0.3 MPa, and the Qn can be changed by changing the Pn.

Regarding the fillet cooling device, the cooling device 10 (device length: 6 m (= number of nozzles x nozzle pitch)) shown in FIG. 4 is installed at two locations on the entry side and the exit side of the breakdown rolling mill 3 as shown in FIG. When the fillet portion was cooled in each of the rolling passes, the fillet cooling device 10 was passed through the entire length of the H-shaped steel for cooling. The number of passes for cooling the fillet portion was constant regardless of the conditions, and cooling was performed in 8 consecutive passes from the latter half pass to the final pass of rough rolling. The temperature of the flange 1 / 2F (1 / 4t) at the start of cooling the fillet is about 1075 ° C. and 77 mm when the flange is 125 mm thick (hereinafter, when the flange is OO mm thick, it is simply referred to as OO mm thick). The thickness was about 1060 ° C. and the thickness was about 1070 ° C. with a thickness of 43 mm. The rolling speed (= transport speed of H-section steel in the cooling device) when cooling the fillet was set to 2 m / s.

As for the size of the H-section steel, _{three types of cases with different flange thicknesses t f} (thickness after finish rolling ≈ product thickness) shown in Table 2 were examined. After rolling, quenching is performed using an online quenching device in which the water density for cooling the inner and outer surfaces of the flange is set to 2.0 m ³ / m ² / min and the water density for cooling the upper and lower surfaces of the web ^{is set to 0.5 m 3} / m ^{2 / min.} I decided. The time from the completion of cooling of the fillet to the start of quenching is constant at 90 seconds, and the quenching temperature conditions (outer surface temperatures of flanges 1 / 6F and 5 / 6F) are such that the quenching start temperature is 125 mm thick and 77 mm thick is 840 ° C. The thickness of 43 mm was 800 ° C., and the quenching end temperature was 630 to 640 ° C. for all sizes.

In cooling the fillet portion, the cooler the fillet portion is, the lower the temperature of the fillet portion is, and the temperature unevenness after rolling can be reduced. However, if the fillet part is cooled too much, the temperature of 1 / 2F will drop below the predetermined quenching start temperature before the completion of rolling, and the structure will change due to the occurrence of ferrite transformation during rolling. Problems such as loss of mechanical properties may occur.
Therefore, as the cooling condition of the fillet part, the temperature of 1 / 2F (1 / 4t) at the start of quenching is almost the same as the outer surface of 1 / 6F and 5 / 6F, with the aim of making it as uniform as possible within the range that does not impair the characteristics. Qn was adjusted so that the temperature was the same (that is, 840 ° C for 125 mm thickness and 77 mm thickness, 800 ° C for 43 mm thickness). That is, in the case of 125 mm thickness, Pn is set to 0.3 MPa, the cooling nozzle used is changed for each condition to set Qn, and in the case of 77 mm thickness and 43 mm thickness, the required flow rate is significantly reduced as compared with 125 mm thickness. Therefore, the number of nozzles used was reduced by closing a part of the on-off valve, and Pn was changed for each condition to adjust Qn.

[Conditions for maximizing cooling efficiency]
8 shows for the cooling water collides width Ds of the fillet cooling, the results of plotting the change in the required amount of water W _f of the cooling device. Here, the required water flow _{rate W f} adjusts the water supply pressure Pn to make the temperature distribution of the flange uniform (that is, the temperature of 1 / 2F (1 / 4t) at the start of quenching is the outer surface of 1 / 6F and 5 / 6F. It is a flow rate that can be (almost the same temperature), and the required water amount W _f is [flow rate Qn of cooling nozzles under each condition] x [number of nozzles used per cooling device] x 2 (2 before and after the breakdown rolling mill). Calculated by (based).
From FIG. 8, it can be seen that the _{required water amount W f increases significantly as the flange thickness increases.} Further, it can be seen that there are Ds having the minimum _{required water amount W f} in each size of the H-section steel.

9, the re-plotted by taking the ratio of the minimum value W _fm of the horizontal axis to the cooling water collides width Ds and the ratio of the flange width B, for each size of the required amount of water Wf and H-shaped steel on the vertical axis W _f The result is shown. From FIG. 9, _{the relationship between Ds / B and W f} / W _fm is organized by almost one line regardless of the size of the H-section steel, and W _f / W _fm becomes the minimum at around Ds / B = 0.2. It can be seen that the required flow rate increases significantly regardless of whether Ds / B is reduced or increased. By setting Ds / B in the range of 0.12 to 0.4 from FIG. 9, the required flow rate can be suppressed to within a range of approximately 40% more than the minimum value (within 1.4 times), and further, Ds / B can be suppressed. If is set to the range of 0.14 to 0.32, the minimum value can be suppressed to a range within about 20% increase (within 1.2 times).
The reason why the optimum range of Ds depends on the flange width B is that the chevron temperature distribution formed by combining the supercooling effect from the flange end face and the high temperature effect at the fillet is the flange thickness t. It is considered that this is because the shape is almost similar regardless of _f.

In FIG. 10, when the ratio of the cooling water collision width Ds and the flange width B is taken on the horizontal axis, the temperature deviation (1 / 2F and 1 / 6F / 5 / 6F) at the flange 1 / 4t after quenching by cooling the fillet portion. The result of plotting the change of the reduction rate (the reduction rate when the fillet part cooling is not used) of the temperature difference) is shown.
From FIG. 10, in the range where Ds / B is 0.4 or less, the temperature deviation reduction rate improves slightly as Ds / B increases, but the overall reduction rate does not depend much on Ds / B, and the fillet portion is cooled. Therefore, it can be seen that the temperature deviation can be reduced by about 40 to 50% in the case of 125 mm thickness and by about 40% in the case of 77 mm thickness and 43 mm thickness.
That is, by setting Ds / B in the range of Ds / B = 0.12 to 0.4, it is possible to achieve both improvement in cooling efficiency and stabilization of product characteristics regardless of the size of the H-section steel, and preferably Ds / B. By keeping it in the range of = 0.14 to 0.32, it is possible to maximize the efficiency of cooling while stabilizing the product characteristics.

In the above, the study was carried out in optimizing the cooling water collision width Ds. Just as the water supply pressure Pn was adjusted to adjust the flow rate Qn, the amount of cooling water ejected from the cooling nozzle is also related to the fillinget cooling. Therefore, it is necessary to control the amount of water in order to achieve both improvement of cooling efficiency and stabilization of product characteristics in the production of H-section steel. Therefore, the cooling capacity of the cooling nozzle was evaluated.

[Cooling nozzle cooling capacity evaluation index]
As an evaluation index of the cooling ability of the spray flow that can be easily calculated, when the spray flow from the spray nozzle (cooling nozzle) is replaced with a flow with a uniform density and flow velocity distribution such as a continuous flow, it is equivalent in terms of momentum. It is known to define and use such a collision flow velocity Ve (hereinafter referred to as "effective collision flow velocity").
That is, Wd: flow density at the collision surface [m ³ / (m ² s)], Vo: (average) droplet collision velocity [m / s], ρ _f : density of cooling water [kg / m ³ ]. Assuming that the momentum of the spray flow when colliding with a steel material is m _sf ,
m _sf = ρ _f・ Wd ・ Vo (1)
And if the momentum of the continuous jet is _mcf,
m _cf = ρ _f · Ve ² (Ve: collision flow velocity) (2).
And when m _sf = m _cf is set,
Ve = (Wd ・ Vo) ^1/2 (3)
Therefore, the effective collision flow velocity Ve of the spray flow can be defined by the equation (3).

Here, when the water supply pressure to the nozzle is Pn [Pa], the injection speed of the cooling water from the nozzle is proportional to the 1/2 power of Pn, so the collision speed of the droplets on the steel material is Vo [m / s]. ], Considering the deceleration due to pressure loss in the nozzle and the deceleration due to air resistance in the atmosphere,
Vo = Cv · Cn · (Pn / ρ _f ) ^1/2 (Cv: Atmospheric flow velocity attenuation coefficient, Cn: Nozzle flow coefficient) (5)
It is expressed in the form of.
Here, in the cooling device as used in the present invention, since the injection distance Ln is relatively short as 300 mm or less, it can be approximated to Cv≈1.0. The flow coefficient Cn of the cooling nozzle differs depending on the nozzle type, and is about 0.85 in the flat spray nozzle used in the embodiment of the present invention. However, for the sake of simplicity, Cn = 1. Set to 0. Therefore, in the present invention,
As Cv = Cn = 1.0 in Eq. (5), the effective collision flow velocity Ve obtained by substituting into Eq. (3) is used.
Ve = Wd ^1/2 · (Pn / ρ _f ) ^1/4 (6)
It was decided to evaluate the cooling capacity using.

[Definition of flow rate density Wd]
From FIG. 9, in order to selectively cool the fillet portion, it is effective to inject cooling water within a range of 0.4 times the flange width B (fillet center ± 0.2B) to cool the fillet portion. It turns out that there is. Therefore, as the definition of the flow rate density Wd for cooling the fillet portion, the area obtained by the product of 0.4 times the flange width B and the nozzle pitch Sn in the steel material transport direction is defined as the cooling range of each nozzle.
Wd = Qn / Sn / 0.4B (6)
Let us define the flow density Wd. As a result, the influence of the amount of cooling water injected into the region substantially effective for fillet cooling can be taken into consideration, and more accurate evaluation of the cooling capacity becomes possible.

[Evaluation of cooling capacity by effective collision flow velocity Ve]
In the fillet cooling device 10 (device length: 4 m (= number of nozzles x nozzle pitch)) shown in FIG. 4, a flat spray nozzle is used as the cooling nozzle 11, and the water supply pressure Pn and nozzle pitch of the cooling nozzle 11 are set under the conditions shown in Table 3. When Sn and the nozzle flow rate Qn were changed, the transport speed (rolling speed) Vp during cooling that could be cooled to the target temperature was investigated. If the transport speed Vp is small, the time for passing through the fillet cooling device becomes long, and the fillinget portion is cooled. The meaning of investigating the transport speed Vp is to grasp the amount of water required for cooling.
In a specific investigation of the transport speed Vp, when the fillet cooling device 10 is arranged at two locations on the entry side and the exit side of the breakdown rolling mill 3 shown in FIG. 1 and the fillet portion is cooled in each rolling path. Cooled by passing through the fillet cooling device 10 over the entire length of the H-shaped steel. The number of passes for cooling the fillet was constant regardless of the conditions, and cooling was performed in 8 consecutive passes from the latter half pass to the final pass of rough rolling. The H-section steel to be cooled has a flange thickness t _f = 125 mm shown in Table 2, and the temperature at the flange 1 / 2F (1 / 4t) at the start of quenching by the online quenching device 6 after cooling the fillet is almost a predetermined temperature. The transport speed Vp was adjusted so as to be 840 ° C. The temperature of 1 / 2F (1 / 4t) at the start of fillet cooling was about 1075 ° C. regardless of the conditions. Further, the injection distance of the cooling nozzle was set to Ln = 70 mm, the spread angle α = 97 °, the twist angle β = 45 °, and the cooling water collision width Ds = 132 mm (Ds / B = 0.29).

FIG. 11 shows the results of arranging the results of Vp that can be secured with the flow rate density Wd on the horizontal axis. As can be seen from FIG. 11, there is a large variation in the results (Comparative Examples 1 and 2 and Examples 1 to 3) when the water pressure Pn is changed while the flow rate Qn is constant, and the results may not be aligned on one line. Understand.
FIG. 12 shows the results when the effective collision flow velocity Ve is taken on the horizontal axis and arranged. As can be seen from FIG. 12, it can be almost arranged by a power approximation curve of 0.85 power regardless of conditions such as when the water pressure Pn and the flow rate Qn are changed. That is, it can be seen that the cooling capacity can be universally arranged regardless of the injection conditions of the cooling nozzle by using the effective collision flow velocity Ve defined by the equation (5) as an index.

[Ve conditions required to ensure rolling efficiency]
Further, in extra-thick H-beam rolling, rolling is usually performed at a rolling speed of 2.5 m / s to 3.5 m / s, and when the transport speed during fillet cooling falls below 2.5 m / s, rolling is performed. There will be a decrease in efficiency. From FIG. 12, it can be seen that in order to secure the transport speed of 2.5 m / s or more, it is necessary to secure the effective collision flow velocity Ve of the cooling water jet jet injected from the cooling nozzle at 1.0 m / s or more.
Therefore, by setting Ds / B = 0.12 to 0.40 and setting Ve to 1 or more, it is possible to achieve both improvement in cooling efficiency and stabilization of product characteristics regardless of the size of the H-section steel.

10 Fillet cooling device 11 Cooling nozzle 12 On-off valve 13 Flow control valve 14 Flow meter 15 Pressure gauge 16 Guide plate 17 Guide roll

Claims (3)

A method for manufacturing H-section steel with a flange width of B (m).
During rough rolling and / and after rough rolling
When the cooling water collision width in the flange width direction is Ds (m),
The cooling water collision width Ds is set so that 0.12 ≦ Ds / B ≦ 0.4, and the cooling water collision width Ds is set.
The flow rate of the cooling nozzle is Qn (m ³ / min), the water supply pressure is Pn (Pa), the cooling nozzle pitch in the rolling direction is Sn (m), the density of the cooling water is ρ _f (kg / m ³ ), and the flow rate density is When Wd (m ³ / m ² / min) and the effective collision flow velocity of the cooling water injected from the cooling nozzle to the fillet are Ve (m / s),
Wd = Qn / Sn / 0.4B
Ve = Wd ^1/2 · (Pn / ρ _f ) ^1/4
Ve ≧ 1.0
A method for producing an H-section steel, which comprises setting an effective collision flow velocity Ve (m / s) so as to cool the fillet portion. The method for producing an H- _{section steel according to claim 1, wherein the flange thickness t f} of the H-section steel to be produced exceeds 40 mm. The method for producing an H-section steel according to claim 1 or 2, wherein after rough rolling, finish rolling is performed and quenching is performed.

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