H-beam manufacturing method

Abstract

To provide a manufacturing method of an H-shaped steel capable of reducing variations of a flange width of a flange portion of the H-shaped steel in a longitudinal direction after finish rolling, by devising a rough rolling process using a breakdown rolling machine.SOLUTION: In a rough rolling process in a manufacturing method of an H-shaped steel, a rolling pass that presses only a flange width of a flange portion S1F of an H-shaped steel material S1 is provided, and a flange width B4 of a flange portion S2F of a rough shaped steel piece S2 after the rough rolling process ends is molded to be equal to or smaller than a target flange width Bf of a flange portion F of the H-shaped steel H after a finish rolling process.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing H-beam steel including a rough rolling step, an intermediate rolling step, and a finish rolling step. [Background technology]

[0002] Generally, H-beams are manufactured through a rough rolling process, an intermediate rolling process, and a finish rolling process. In the rough rolling process, H-beam material heated in a heating furnace is roughly rolled in a breakdown rolling mill to produce rough steel billets. In the intermediate rolling process, the rough steel billets rough rolled in the rough rolling process are rolled in an intermediate universal rolling mill and an intermediate edging rolling mill to produce rolled material for finish rolling that has approximate product dimensions. In the finish rolling process, the rolled material for finish rolling that has approximate product dimensions rolled in the intermediate rolling process is finish rolled in a finish universal rolling mill to produce H-beams with the product dimensions.

[0003] Conventionally, methods for manufacturing this type of H-section steel have been proposed, for example, as shown in Patent Documents 1 to 5. The rolling method for rough billets for H-shaped steel shown in Patent Document 1 includes a step of rolling rough billets for H-shaped steel using a double reversible rolling mill, in which, when rolling the rough billets for H-shaped steel, two or more adjacent forming dies having the same web depth share the web portions of two forming dies that match the web height of the rough billets, and inserting the rough billets across the web portions of the two shared forming dies to reduce the flange width.

[0004] According to the rolling method for rough steel billets for H-section steel shown in Patent Document 1, no groove is required for reducing the flange width, so it is possible to roll H-section steel with a high web height and narrow flange width from a beam blank with a single cross section.

[0005] In addition, the rolling method for H-beam steel shown in Patent Document 2 involves subjecting a raw steel billet to rough rolling, which involves breakdown rolling, rough universal rolling, and edging rolling, followed by finish universal rolling, in which the flange width distribution in the longitudinal direction of the pre-rolled material after finish universal rolling or rough universal rolling is determined. Then, based on the flange width distribution, either or both of the flange thickness reduction rate and web thickness reduction rate in the rough universal rolling of the subsequent material are changed using the set values ​​for the pre-rolled material as a reference.

[0006] According to the H-beam rolling method disclosed in Patent Document 2, it is possible to stably manufacture H-beams with good flange width accuracy in the product length direction without using any special equipment.

[0007] Furthermore, the rolling method for H-section steel shown in Patent Document 3 is a rolling method for H-section steel in which a raw steel billet is subjected to rough rolling, which involves breakdown rolling, rough universal rolling, and edging rolling, and then finish universal rolling, in which either or both of the flange thickness reduction rate and the web thickness reduction rate are changed in the longitudinal direction of the rolled material during rough universal rolling.

[0008] According to the rolling method for H-section steel disclosed in Patent Document 3, it is possible to stably manufacture H-section steel with good flange width accuracy in the product length direction.

[0009] Furthermore, a variable flange width rolling method for rough-rolled H-section steel material shown in Patent Document 4 uses a double-calibrated roll having a plurality of flange-widening grooves each having a central bulge at the center of the width direction of the hole bottom and grooves on both sides of the central bulge, and a shaping groove for rolling down the web and flange portions, and uses a rectangular cross-section steel billet as a material to perform intrusion and width-widening rolling on the side surfaces corresponding to the flanges of the H-section steel, and then performs shaping rolling.The flange width of the rolled material after the final pass through each of the flange-widening grooves except for the first groove and the shaping groove is made narrower than the groove bottom width of the groove, and rolling is performed so that the flange-corresponding portions of the rolled material do not fill each groove.

[0010] According to the variable flange width rolling method for rough rolled H-section steel material shown in Patent Document 4, when rough rolled H-section steel material is produced using a rectangular cross-section slab as raw material in a breakdown mill with double-groove rolls, multiple series of rough rolled material with different flange widths but the same web height can be rolled using only one set of roll pairs without changing the roll combinations.

[0011] Furthermore, the rolling method for producing a rough shaped billet for structural steel shown in Patent Document 5 is such that, in a rough shaping rolling process for producing a rough shaped billet from a material, after the web height is enlarged or reduced to a target dimension, when the flange tip is reduced to reduce the flange width using the flat portion of the web part of the grooved roll, the flange tip reduction and the shaping rolling using the shaping groove are each performed a required number of times or alternately.

[0012] According to the rolling method for rough shaped steel billets for structural steel shown in Patent Document 5, it is possible to use the same grooved rolls to form multiple series of rough shaped steel billets corresponding to structural steel products with different flange widths without generating defects that could cause product defects. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Japanese Patent Application Publication No. 207901 / 1999 [Patent Document 2] Japanese Patent Application Publication No. 11-151512 [Patent Document 3] Japanese Patent Application Publication No. 11-156414 [Patent Document 4] Japanese Patent Application Publication No. 2-169103 Summary of the Invention [Problem to be solved by the invention]

[0014] Here, when manufacturing H-shaped steel beams, there has traditionally been a problem in that the flange width of the H-shaped steel beam, which has been formed into the product shape by finish rolling, varies in the longitudinal direction of the H-shaped steel beam, significantly reducing the manufacturing yield.

[0015] Figure 8 shows an example of the longitudinal distribution of flange width at the flange portion of an H-beam after finish rolling, with Figure 8(a) showing a good example in which the flange width is within the target tolerance range over the entire longitudinal length of the H-beam. Figure 8(b) shows a bad example in which the flange width is within the target tolerance range at the leading and trailing ends of the H-beam in the longitudinal direction, but is smaller than the lower limit of the tolerance at the center (steady portion) of the H-beam in the longitudinal direction.

[0016] If the flange width at the center (steady section) of the H-shaped steel in the longitudinal direction is smaller than the lower limit of the tolerance, as shown in Figure 8(b), such an H-shaped steel cannot be used as a product and will be rejected, resulting in a significant drop in manufacturing yield.

[0017] The rolling method for rough billets for H-section steel shown in Patent Document 1 does not require a groove for reducing the flange width, so it is possible to roll H-section steel with a high web height and narrow flange width from a beam blank with a single cross section. However, this is not a technology for reducing the longitudinal variation in flange width of H-section steel after finish rolling.

[0018] Furthermore, the rolling method for H-beams shown in Patent Document 2 allows for the stable production of H-beams with good flange width accuracy along the product length without the need for special equipment. However, this rolling method for H-beams involves changing either the flange thickness reduction rate or the web thickness reduction rate, or both, in the intermediate rolling process (rough universal rolling process), which has the problem of being less effective in uniforming the flange width along the length of the H-beams after finish rolling. Furthermore, when producing H-beams with large cross-sectional dimensions, such as a web height of 700 mm or more or a flange width of 350 mm or more, the effect of uniforming the flange width along the length of the H-beams may be particularly insufficient.

[0019] Furthermore, the rolling method for H-beams shown in Patent Document 3 also enables the stable production of H-beams with good flange width accuracy in the product's longitudinal direction. However, this rolling method for H-beams also involves varying either or both of the flange thickness reduction rate and the web thickness reduction rate in the intermediate rolling process (rough universal rolling process), which has the problem of being less effective in uniforming the flange width in the longitudinal direction of the H-beam after finish rolling. Furthermore, the method involves varying either or both of the flange thickness reduction rate and the web thickness reduction rate in the longitudinal direction of the H-beam during rough universal rolling, which has the problem of being difficult to implement in terms of equipment.

[0020] Furthermore, in the case of the variable flange width rolling method for rough rolled H-section steel material shown in Patent Document 4, when a rectangular cross-section slab is used as the raw material to produce rough rolled H-section steel material in a breakdown mill using double-calibrated rolls, it is possible to roll multiple series of rough rolled material with different flange widths but the same web height using only one set of roll pairs without changing the rolls. However, it is not possible to reduce the longitudinal variation in the flange width of the H-section steel after finish rolling.

[0021] Furthermore, in the case of the rolling method for rough shaped steel billets for shaped steel shown in Patent Document 5, it is possible to use the same grooved rolls to form multiple series of rough shaped steel billets corresponding to shaped steel products with different flange widths without generating defects that could cause product defects. However, it is not possible to reduce the longitudinal variation in flange width of H-shaped steel after finish rolling.

[0022] In addition, in conventional methods for manufacturing ordinary H-section steel, as disclosed in Patent Document 4, it has been common technical knowledge that the flange width of the rough steel billet after rough rolling by a breakdown rolling mill is finished to a dimension larger than the flange width of the product, and that the flange width is reduced to approach the product dimension after intermediate rolling by an intermediate universal rolling mill or the like.

[0023] Therefore, the present invention has been made to solve this conventional problem, and its object is to provide a method for manufacturing H-shaped steel that can reduce the longitudinal variation in the flange width of the flange portion of the H-shaped steel after finish rolling by improving the rough rolling process using a breakdown rolling mill. [Means for solving the problem]

[0024] The inventors investigated the reason why the flange width of the flange portion of the H-section steel after finish rolling becomes as shown in Figure 8(b), and focused on the rough rolling conditions using a breakdown rolling mill in order to find a solution that would bring the flange width within the target tolerance range over the entire length of the H-section steel, including the central portion (steady portion) in the longitudinal direction. Then, they changed the rough rolling conditions to various conditions and investigated how the cross-sectional shape of the flange portion of the rough steel billet after rough rolling changed.

[0025] The results are shown in Figure 9. Figure 9 is an enlarged view of the part indicated by the arrow 9 in Figure 2(b), which shows the cross-sectional shape of the rough steel billet after rough rolling. Figure 9(a) shows the cross-sectional shape of the flange portion of the rough-rolled H-beam blank when the rough-rolling process is performed under typical rolling conditions, where the rough-rolling process does not include a rolling pass that reduces only the flange width of the flange portion of the H-beam blank, and the flange width of the rough-rolled H-beam blank is 30 mm larger than the target flange width of the H-beam blank after the finish rolling process. In Figure 9(a), the cross-sectional area of ​​the flange portion (shown by the dashed line) at the longitudinal center (steady state portion) is smaller than the cross-sectional area of ​​the flange portion (shown by the solid line) at the longitudinal tail end. The flange thickness t4M of the flange portion at the longitudinal center is 130 mm, and the flange thickness t4B of the flange portion at the longitudinal tail end is 146 mm, making the former 16 mm smaller than the latter.

[0026] In contrast, Figure 9(b) shows the cross-sectional shape of the flange portion of the rough-shaped steel billet after rough rolling, when the H-shaped steel material is rough-rolled under rolling conditions in which a rolling pass is provided in the rough rolling process to reduce only the flange width of the flange portion of the H-shaped steel material, and the flange width of the flange portion of the rough-shaped steel billet after the rough rolling process is 30 mm smaller than the target flange width of the H-shaped steel flange portion after the finish rolling process. In Figure 9(b), the cross-sectional area of ​​the flange portion (shown by the dashed line) at the center (steady portion) in the longitudinal direction is approximately the same as the cross-sectional area of ​​the flange portion (shown by the solid line) at the tail end in the longitudinal direction, and the cross-sectional areas of the flange portions are consistent along the longitudinal direction. The reason for this is that a rolling pass is provided in the rough rolling process to reduce only the flange width of the flange portion of the H-beam material, and by making the flange width of the raw steel billet after the rough rolling process smaller than the target flange width of the H-beam flange after the finish rolling process, the thickness of the flange portion increases, and the thickness and width of the flange portion become uniform in the longitudinal direction. The flange thickness t4M of the flange portion at the longitudinal center is 150 mm, and the flange thickness t4B of the flange portion at the longitudinal tail end is 158 mm, with the difference between the former and latter being 8 mm, which is smaller than the case in Figure 9(a).

[0027] As shown in Figure 9(b), the cross-sectional area of ​​the flange at the longitudinal center (steady portion) is approximately the same as that at the longitudinal tail end, making the cross-sectional areas of the flanges uniform in the longitudinal direction. As a result, after finish rolling, which has been through the intermediate rolling process and the finish rolling process, not only is the thickness of the flange uniform in the longitudinal direction, but the flange width of the flange becomes nearly uniform in the longitudinal direction, making it possible to reduce the variation in the flange width of the flange after finish rolling.

[0028] In Figures 9(a) and (b), the cross-sectional shape of the longitudinal tail end of the flange portion is shown in addition to the longitudinal center portion (steady portion), but it has been confirmed that the longitudinal tip of the flange portion also has a cross-sectional shape similar to that of the longitudinal tail end.

[0029] The present invention was made based on this finding, and one embodiment of the present invention provides a method for manufacturing H-shaped steel beams, comprising a rough rolling process in which an H-shaped steel material is roughly rolled using a breakdown rolling mill to produce a rough steel billet; an intermediate rolling process in which the rough steel billet rough rolled in the rough rolling process is rolled using an intermediate rolling mill to produce a rolled material for finish rolling; and a finish rolling process in which the rolled material for finish rolling rolled in the intermediate rolling process is finish rolled using a finish rolling mill to produce an H-shaped steel beam of product dimensions.The gist of the present invention is that in the rough rolling process, a rolling pass is provided to reduce only the flange width of the flange portion of the H-shaped steel material, and the flange width of the flange portion of the rough steel billet after completion of the rough rolling process is shaped to be equal to or less than the target flange width of the flange portion of the H-shaped steel beam after the finish rolling process. [Effects of the Invention]

[0030] According to the manufacturing method of H-shaped steel of the present invention, by improving the rough rolling process using a breakdown rolling mill, it is possible to provide a manufacturing method of H-shaped steel that can reduce the longitudinal variation in the flange width of the flange portion of the H-shaped steel after finish rolling. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a schematic diagram of an H-beam rolling facility to which a method for manufacturing an H-beam according to one embodiment of the present invention is applied. [Figure 2] This explains the cross-sectional shapes of H-shaped steel material before rough rolling, rough steel billet after rough rolling, and H-shaped steel in its finished form, where (a) is a cross-sectional view of the H-shaped steel material before rough rolling, (b) is a cross-sectional view of the rough steel billet after rough rolling, and (c) is a cross-sectional view of H-shaped steel in its finished form. [Figure 3] FIG. 2 is a cross-sectional view showing the state of sizing rolling in the rough rolling step, together with a sizing rolling groove, a first web widening rolling groove, and a second web widening rolling groove. [Figure 4]This explains the web widening rolling process in the rough rolling process, where (a) is a cross-sectional view showing the first web widening rolling process together with the sizing rolling groove, the first web widening rolling groove, and the second web widening rolling groove, and (b) is a cross-sectional view showing the second web widening rolling process together with the sizing rolling groove, the first web widening rolling groove, and the second web widening rolling groove. [Figure 5] FIG. 10 is a cross-sectional view showing the state of edging rolling in the rough rolling step, together with a sizing rolling groove, a first web widening rolling groove, and a second web widening rolling groove. [Figure 6] This explains the intermediate rolling process and the finish rolling process, where (a) is a cross-sectional view for explaining the intermediate universal rolling process in the intermediate rolling process, (b) is a cross-sectional view for explaining the intermediate edging rolling process in the intermediate rolling process, and (c) is a cross-sectional view for explaining the finish rolling process. [Figure 7] This is a graph showing the relationship between the longitudinal deviation of the flange width of the flange portion of the H-shaped steel that has become the product after finish rolling and ΔB, which is the value obtained by subtracting the target flange width of the flange portion of the H-shaped steel after finish rolling from the flange width of the flange portion of the rough steel billet after rough rolling. [Figure 8] The graphs show an example of the longitudinal distribution of flange widths of the flanges of H-shaped steel after finish rolling. (a) is a graph showing a good example in which the flange width is within the target tolerance range over the entire longitudinal length of the H-shaped steel. (b) is a graph showing a bad example in which the flange width is within the target tolerance range at the leading and trailing ends of the H-shaped steel in the longitudinal direction, but the flange width is smaller than the lower limit of the tolerance at the center (steady part) of the H-shaped steel in the longitudinal direction. [Figure 9]The graph shows the results of an investigation into how the cross-sectional shape of the flange portion of the rough steel billet changes after rough rolling when the rough rolling conditions are changed to various conditions. (a) is a graph showing the cross-sectional shape of the flange portion of the rough steel billet after rough rolling when the H-shaped steel material is rough rolled under general rolling conditions in which no rolling pass is provided in the rough rolling process to reduce only the flange width of the flange portion of the H-shaped steel material, and the flange width of the flange portion of the rough steel billet after the rough rolling process is set to a dimension 30 mm larger than the target flange width of the flange portion of the H-shaped steel material after the finish rolling process. (b) is a graph showing the cross-sectional shape of the flange portion of the rough steel billet after rough rolling when the H-shaped steel material is rough rolled under rolling conditions in which a rolling pass is provided in the rough rolling process to reduce only the flange width of the flange portion of the H-shaped steel material, and the flange width of the flange portion of the rough steel billet after the rough rolling process is set to a dimension 30 mm smaller than the target flange width of the flange portion of the H-shaped steel material after the finish rolling process. [Figure 10] 1 is a graph showing the results of measuring the flange width at 20 positions along the entire longitudinal length of H-shaped steel after finish rolling using the manufacturing methods of Invention Example 1, Invention Example 2, Comparative Example 1, and Comparative Example 2 in the Examples. DETAILED DESCRIPTION OF THE INVENTION

[0032] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The embodiments shown below are examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention is not limited to the following embodiments in terms of the materials, shapes, structures, arrangements, etc. of the components.

[0033] In addition, the drawings are schematic, and therefore it should be noted that the relationship between thickness and planar dimensions, ratios, etc. may differ from the actual relationship, and the dimensional relationships and ratios may differ between the drawings.

[0034] The H-beam rolling equipment 1 shown in Figure 1 is composed of a heating furnace 2, a breakdown rolling mill 3, an intermediate universal rolling mill 4 and an intermediate edging rolling mill 5 as intermediate rolling mills, and a finishing universal rolling mill 6 as a finishing rolling mill, which are arranged in this order from the upstream side to the downstream side. The heating furnace 2 heats the H-beam steel material (see FIG. 2(a)) S1 to a predetermined temperature, which is to be subjected to rough rolling by the breakdown rolling mill 3.

[0035] As shown in Figure 2(a), the H-shaped steel material S1 is a steel material having a web portion S1W extending in the web height direction (left-right direction in Figure 2(a)), and a pair of flange portions S1F extending in the flange width direction (up-down direction in Figure 2(a)) at both ends of the web portion S1W in the web height direction. The H-shaped steel material S1 may be produced by directly casting a beam blank that has this shape through continuous casting, or may be formed into this shape from a slab by blooming.

[0036] The inner width of the web portion S1W of the H-shaped steel material S1 is W0, which is relatively short, and the thickness of the web portion S1W is T0, which is relatively thick. The web height of the H-shaped steel material S1 is H0, which is relatively small. The flange width of the flange portion S1F of the H-shaped steel material S1 is B0, which is relatively large, and the flange thickness is t0, which is relatively thick. The breakdown rolling mill 3 roughly rolls the H-beam material S1 conveyed on table rollers (not shown) from the heating furnace 2 to produce a rough steel billet (see FIG. 2(b)) S2 (rough rolling step).

[0037] The rough steel billet S2 after rough rolling is a steel material having a web portion S2W extending in the web height direction and a pair of flange portions S2F extending in the flange width direction at both ends of the web height direction of the web portion S2W, as shown in Figure 2(b).

[0038] The inner width of the web portion S2W of the rough shaped steel billet S2 is W4, which is larger than the inner width W0 of the web portion S1W of the H-shaped steel material S1. The thickness of the web portion S2W of the rough shaped steel billet S2 is T4, which is thinner than the thickness T0 of the web portion S1W of the H-shaped steel material S1. The web height of the rough shaped steel billet S2 is H4, which is larger than the web height H0 of the H-shaped steel material S1, and is shaped to fit the web height Hw of the H-shaped steel H in the product shape after finish rolling shown in Figure 2(c). Furthermore, the flange width of the flange portion S2F of the rough shaped steel billet S2 is B4, which is smaller than the flange width B0 of the flange portion S1F of the H-shaped steel material S1, and is also smaller than the flange width Bf (target flange width) of the flange portion F of the H-shaped steel H in the product shape after finish rolling. In addition, the thickness of the flange portion S2F of the rough steel billet S2 is t4, which is thinner than the thickness t0 of the flange portion S1F of the H-shaped steel material S1, and is shaped to be thicker than the thickness tF of the flange portion F of the H-shaped steel H in the product shape after finish rolling.

[0039] Here, the thickness of the flange portion S2F (flange thickness) has a distribution in the flange height (width) direction, and t4 represents the average value. The roughing rolling process using the breakdown mill 3 will be described in detail with reference to Figures 3 to 5. Figure 3 is a cross-sectional view showing the sizing rolling process in the roughing rolling process, along with a sizing rolling groove, a first web widening rolling groove, and a second web widening rolling groove. Figure 4 explains the web widening rolling process in the roughing rolling process, with (a) being a cross-sectional view showing the first web widening rolling process together with a sizing rolling groove, a first web widening rolling groove, and a second web widening rolling groove, and (b) being a cross-sectional view showing the second web widening rolling process together with a sizing rolling groove, a first web widening rolling groove, and a second web widening rolling groove. Figure 5 is a cross-sectional view showing the edging rolling process in the roughing rolling process, along with a sizing rolling groove, a first web widening rolling groove, and a second web widening rolling groove.

[0040] The rough rolling process by the breakdown mill 3 includes a sizing rolling process, a web widening rolling process, and an edging rolling process. In the sizing rolling process, as shown in FIG. 3, a sizing groove 33 formed on the peripheral surfaces of an upper roll 31 and a lower roll 32 of a breakdown mill 3 is used to roll the web portion S1W of the H-shaped steel material S1 in the thickness direction and roll the flange portion S1F of the H-shaped steel material S1 in the width direction in multiple passes. As a result, the thickness (web thickness) of the web portion S1W of the H-shaped steel material S1 is reduced from T0 to T1 and set to the thickness (web thickness) T1. The inner width of the web portion S1W of the H-shaped steel material S1 is expanded from W0 to W1. The flange width of the flange portion S1F of the H-shaped steel material S1 is reduced from B0 to B1. The thickness (flange thickness) of the flange portion S1F of the H-shaped steel material S1 is reduced from t0 to t1. The web height of the H-shaped steel material S1 is expanded from H0 to H1.

[0041] In addition, the web widening rolling process includes a first web widening rolling process shown in Figure 4(a) and a second web widening rolling process shown in Figure 4(b), and widens the inner width of the web portion S1W of the H-shaped steel material S1 that has been rough rolled in the sizing process.

[0042] In the first web widening rolling process, as shown in Figure 4(a), the inner width of the web portion S1W of the H-shaped steel material S1, which has been rough rolled in the sizing process in multiple passes, is widened from W1 to W2 using a first web widening rolling groove 34 formed on the peripheral surfaces of an upper reduction roll 31 and a lower reduction roll 32 provided in a breakdown rolling mill 3. At this time, the web height of the H-shaped steel material S1 is widened from H1 to H2. In addition, the flange width of the flange portion S1F of the H-shaped steel material S1 changes from B1 to B2. However, in this example, the groove depth b2 (see FIG. 4(b)) of the flange rolling portion 34a in the first web widening rolling groove 34, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, is the same as the groove depth b1 (see FIG. 4(b)) of the flange rolling portion 33a in the sizing rolling groove 33, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, and B2 is approximately equal to B1. Also, the thickness (web thickness) of the flange portion S1F of the H-shaped steel material S1 changes from t1 to t2, but t2 is approximately equal to t1. Furthermore, the thickness (web thickness) of the web portion S1W of the H-shaped steel material S1 changes from T1 to T2, but in the first web widening rolling process, active thickness reduction of the web portion S1W of the H-shaped steel material S1 is not performed, and T2 is approximately equal to T1.

[0043] In the second web widening rolling process, as shown in FIG. 4(b), the inner width of the web portion S1W of the H-shaped steel material S1 rolled in the first web widening rolling process is widened from W2 to W3 using a second web widening rolling groove 35 formed on the peripheral surfaces of the upper roll 31 and the lower roll 32 of the breakdown mill 3. During this process, the web height of the H-shaped steel material S1 is widened from H2 to H3. The thickness of the flange portion S1F of the H-shaped steel material S1 (flange thickness) changes from t2 to t3, but t3 is approximately equal to t2. Furthermore, the thickness of the web portion S1W of the H-shaped steel material S1 (web thickness) changes from T2 to T3. However, in the second web widening rolling process, the web portion S1W of the H-shaped steel material S1 is not actively reduced in thickness, and T3 is approximately equal to T2.

[0044] In this example, the flange width of the flange portion S1F of the H-shaped steel material S1 is reduced from B2 to B3. The groove depth b3 (see FIG. 4(b)) of the flange rolling portion 35a in the second web widening rolling groove 35, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, is shallower than the groove depth b2 of the flange rolling portion 34a in the first web widening rolling groove 34, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction. The groove depth b1 of the flange rolling portion 33a in the sizing rolling groove 33, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, is equal to the groove depth b2 of the flange rolling portion 34a in the first web widening rolling groove 34, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction. Therefore, the groove depth b3 of the flange rolling portion 35a in the web widening second rolling groove 35, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, is shallower than the groove depth b1 of the flange rolling portion 33a in the sizing rolling groove 33, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction (b3 <b2=b1)。

[0045] By doing this, the flange width of the flange portion S1F of the H-shaped steel material S1 can be reduced during the web widening rolling process, and the flange width of the flange portion S2F of the rough steel billet S2 after rough rolling can be made more uniform in the longitudinal direction.

[0046] In this embodiment, the web widening rolling process is performed in two stages: a first web widening rolling process using a first web widening rolling groove 34, and a second web widening rolling process using a second web widening rolling groove 35. However, the web widening rolling process may be performed in one stage using one web widening rolling groove, or in three or more stages using three or more web widening rolling grooves. Furthermore, if the inner width W1 or web height H1 of the web portion S1W of the H-section steel material S1 rolled in the sizing rolling process is a groove that matches the inner width or web height of the web portion S2W of the rough steel billet S2 after the intermediate rolling process using the intermediate universal rolling mill 4 and intermediate edging rolling mill 5 described below, the web widening rolling process itself is not necessary.

[0047] In the edging rolling process, as shown in FIG. 5, a sizing groove 33 formed on the peripheral surfaces of an upper roll 31 and a lower roll 32 of a breakdown mill 3 and an adjacent web widening first rolling groove 34 are used to reduce only the flange width of the flange portion S1F of the H-shaped steel material S1 rolled in the web widening rolling process, thereby forming the flange width of the flange portion S2F of the rough steel billet S2 after the rough rolling process to be equal to or smaller than the target flange width of the flange portion HF of the H-shaped steel H after the finish rolling process described below. In other words, in the edging rolling process, only the flange width of the flange portion S1F of the H-shaped steel material S1 rolled in the web widening second rolling process is reduced to reduce the flange width from B3 to B4. The flange width B4 of this rough steel billet S2 is equal to or smaller than the target flange width Bf (see FIG. 2(c)) of the flange portion F of the H-shaped steel H after the finish rolling process.

[0048] As a result, the thickness (flange thickness) of the flange portion S2F of the rough steel billet S2 increases, and the thickness and width of the flange portion S2F become uniform in the longitudinal direction, and as shown in Figure 9(b), the cross-sectional area of ​​the flange portion at the longitudinal center portion (steady portion) becomes approximately the same as the cross-sectional area of ​​the flange portion at the longitudinal tail end, and the cross-sectional areas of the flange portions become uniform in the longitudinal direction. As a result, after finish rolling via the intermediate rolling process and the finish rolling process, not only does the thickness of the flange portion (flange thickness) become uniform in the longitudinal direction, but the flange width of the flange portion becomes nearly uniform in the longitudinal direction, and longitudinal variation in the flange width of the flange portion after finish rolling can be reduced.

[0049] In this embodiment, the edging rolling process, which reduces only the flange width of the flange portion S1F of the H-shaped steel material S1, is performed in the final rolling pass of the rough rolling process after the web widening rolling process has been completed. This simplifies the design of the caliber and the rolling pass schedule, which is preferable. However, the reduction pass of the edging rolling process, which reduces only the flange width of the flange portion S1F of the H-shaped steel material S1, may be performed not only in the final rolling pass of the rough rolling process, but also in a rolling pass before the final rolling pass. For example, the caliber shape may be changed and the reduction pass of the edging rolling process may be performed between the first web widening rolling process and the second web widening rolling process.

[0050] The intermediate universal rolling mill 4 and the intermediate edging rolling mill 5 are installed downstream of the breakdown rolling mill 3, and as shown in Figures 6(a) and 6(b), the rough steel billet S2 roughly rolled in the rough rolling process by the breakdown rolling mill 3 is rolled into a rolled material S3 having a web portion S3W for finish rolling and a pair of flange portions S3F that have approximately the product dimensions (intermediate rolling process). Note that the approximate product dimensions here refer to dimensions that allow the rolled material to be made into the product dimensions in the finish rolling process.

[0051] The intermediate rolling process includes an intermediate universal rolling process using an intermediate universal rolling mill 4 shown in FIG. 6(a) and an intermediate edging rolling process using an intermediate edging rolling mill 5 shown in FIG. 6(b). As shown in FIG. 6(a), the intermediate universal rolling mill 4 has a pair of upper and lower horizontal rolls 41, 42 that rotate on a horizontal axis, and a pair of left and right vertical rolls 43, 44 that rotate on a vertical axis.

[0052] In the intermediate universal rolling process using the intermediate universal rolling mill 4, multiple passes of rolling are performed using reverse rolling, and as shown in Figure 6(a), the horizontal rolls 41 and 42 roll down the entire height of the web portion S2W of the rough steel billet S2 in the thickness direction, and the vertical rolls 43 and 44 and the sides of the horizontal rolls 41 and 42 roll down the flange portion S2F in the thickness direction.

[0053] In addition, the intermediate edging rolling mill 5 is installed downstream of the intermediate universal rolling mill 4, and as shown in Figure 6(b), it has a pair of upper and lower horizontal rolls 51, 52, each of which has a large diameter roll section and a small diameter roll section in the horizontal axis direction.

[0054] In the intermediate edging rolling process using the intermediate edging mill 5, multiple passes of rolling are performed by reverse rolling, and as shown in Figure 6(b), the large diameter roll portions of a pair of upper and lower horizontal rolls 51, 52 guide the web portion S2W of the rough steel billet S2 that has been intermediate universally rolled, and the small diameter roll portions press down the end faces of the flange portions S2F in the width direction, turning the rough steel billet S2 into rolled material S3 for finish rolling that has approximately the dimensions of the product.

[0055] Here, in this embodiment, as described above, the flange width B4 of the flange portion S2F of the rough steel billet S2 after the rough rolling process is formed to be equal to or smaller than the target flange width Bf of the flange portion F of the H-shaped steel H after the finish rolling process. Therefore, in the intermediate edging rolling process, the flange width of the flange portion S2F of the material becomes smaller than the intermediate edging groove depth (the distance between the small diameter roll portions of the pair of upper and lower horizontal rolls 51, 52) that is adjusted to the product flange width. Therefore, in the intermediate edging rolling process, a rolling pass occurs in which there is no reduction in the flange width (reduction amount is 0 mm).

[0056] However, in the edging rolling process of the rough rolling process, the thickness (flange thickness) of the flange portion S2F of the rough steel billet S2 is increased. Therefore, in the intermediate universal rolling process using the intermediate universal rolling mill 4, it is easy to perform a "strong flange reduction" in which the thickness reduction of the flange portion S2F is made relatively larger than the thickness reduction of the web portion S2W of the rough steel billet S2. By performing the "strong flange reduction", it is possible to promote the width expansion of the flange portion S2F in the intermediate universal rolling, and in the latter pass of the intermediate universal rolling, the flange width of the flange portion S2F can be made larger than the product flange width. Therefore, the amount of flange width reduction of the flange portion S2F can be ensured in the intermediate edging rolling process.

[0057] As described above, in order to enable "strong flange reduction" in the intermediate universal rolling process, the difference Σrf-Σrw between the total flange thickness reduction rate Σrf of the flange portion S2F and the total web thickness reduction rate Σrw of the web portion S2W in the intermediate rolling process is preferably 0.055 or more, and more preferably 0.060 or more.

[0058] Here, if the flange thickness of the flange portion S3F after the intermediate rolling step is tI, the total flange thickness reduction rate Σrf is calculated as Σrf=(t4−tI) / t4.

[0059] Furthermore, if the web thickness of the web portion S3W after the intermediate rolling step is TI, the web total thickness reduction ratio Σrw is calculated as Σrw=(T4−TI) / T4. Normally, the flange thickness tI of the flange portion S3F and the web thickness TI of the web portion S3W after the intermediate rolling process are determined from the flange thickness tF of the flange portion F of the product (see Figure 2(c)) and the web thickness Tw of the web portion W (see Figure 2(c)), taking into account the thickness reduction rate required in finish rolling. Therefore, it is desirable to set the flange thickness t4 of the flange portion S2F and the web thickness T4 of the web portion S2W at the stage of the rough steel billet S2 so that Σrf - Σrw becomes the value mentioned above.

[0060] In addition, the finishing universal rolling mill 6 is installed downstream of the intermediate universal rolling mill 4 and the intermediate edging rolling mill 5, and as shown in Figure 6(c), the finishing rolling material S3 for finishing rolling, which has been rolled in the intermediate rolling process to approximately the product dimensions, is finish-rolled to produce H-shaped steel H of the product dimensions (see Figure 2(c)) (finish rolling process). H-beam steel H is manufactured through this finishing rolling process.

[0061] As shown in FIG. 6(c), the finishing universal rolling mill 6 is equipped with a pair of upper and lower horizontal rolls 61, 62 that rotate on horizontal axes, and a pair of left and right vertical rolls 63, 64 that rotate on vertical axes. In the finish rolling process using the finishing universal rolling mill 6, a pair of upper and lower horizontal rolls 61, 62 and a pair of left and right vertical rolls 63, 64 are used to reduce the web portion S3W and flange portion S3F of the rolled material S3 to the thickness of the product dimensions, and the angle of the flange portion S3F is also corrected. As a result, as shown in Figure 2(c), an H-beam H is obtained with product dimensions of a web height Hw, a flange width Bf of the flange portion F, a thickness of the web portion W (web thickness) Tw, and a thickness of the flange portion F (flange thickness) tF.

[0062] Figure 7 shows the relationship between the longitudinal deviation of the flange width of the flange portion F of the H-shaped steel H that has become the product after finish rolling and ΔB, which is the value obtained by subtracting the target flange width Bf of the flange portion F of the H-shaped steel H after finish rolling from the flange width B4 of the flange portion S2F of the rough steel billet S2 after rough rolling. Figure 7 shows the results of an investigation into the dimensions of the H-shaped steel H in the product shape, with a web height Hw of 1000 mm, a flange width of the flange portion F of 400 mm, a thickness of the web portion W (web thickness) Tw of 19 mm, and a thickness of the flange portion F (flange thickness) tF of 40 mm.

[0063] The tolerance, which is the difference between the upper and lower limits of the flange width tolerance shown in Figure 8, is ±2 mm for the H-shaped steel of the above dimensions. If the longitudinal deviation is 3 mm, that is, the target deviation in the longitudinal direction is ±1.5 mm, it was confirmed with reference to Figure 7 that ΔB is preferably 0 mm or less. For this reason, in the manufacturing method of H-shaped steel according to this embodiment, a rolling pass (edging rolling process) is provided in the rough rolling process to reduce only the flange width of the flange portion S1F of the H-shaped steel material S1. Then, the flange width B4 of the flange portion S2F of the raw steel billet S2 after the rough rolling process is shaped to be equal to or smaller than the target flange width Bf of the flange portion F of the H-shaped steel H after the finish rolling process.

[0064] Here, the condition of "setting ΔB to 0 mm or less" also satisfies the condition that the flange S2F width in the intermediate rolling process is made larger than before. This condition also has the effect of making the flange width Bf (equivalent to the target flange width after finish rolling) uniform in the longitudinal direction at the product stage.

[0065] However, if ΔB is made too small, the flange width expansion amount in the intermediate rolling process may be insufficient, and the flange width Bf of the product may not be secured. Therefore, it is preferable that ΔB is set to -10% or more of the flange width Bf of the product (-0.1Bf (mm)≦ΔB≦0 (mm)).

[0066] If edging is not performed in the rough rolling process, or if edging is performed in the rough rolling process but the reduction is small and ΔB exceeds 0 mm, the "thickening of the flange portion S2F" due to edging during rough rolling will be insufficient. As a result, as shown in Figure 9(a), the thickness (flange thickness) of the flange portion S2F will not be uniform in the longitudinal direction, and the cross-sectional area of ​​the flange portion at the longitudinal center (steady portion) will be smaller than the cross-sectional area of ​​the flange portion at the longitudinal leading and trailing ends. Therefore, after finish rolling via the intermediate rolling process and the finish rolling process, the flange width at the longitudinal center (steady portion) will be smaller than the target. This situation is particularly likely to occur in a cross section where the thickness (flange thickness) tF of the flange portion F is relatively thick compared to the thickness (web thickness) Tw of the web portion W (tF / Tw≧2), and the present invention is particularly effective.

[0067] As described above, according to the manufacturing method of the H-shaped steel according to this embodiment, a rolling pass (edging rolling process) is provided in the rough rolling process to reduce only the flange width of the flange portion S1F of the H-shaped steel material S1. Then, the flange width B4 of the flange portion S2F of the raw steel billet S2 after the rough rolling process is shaped to be equal to or smaller than the target flange width Bf of the flange portion F of the H-shaped steel H after the finish rolling process.

[0068] As a result, the thickness of the flange portion S2F of the rough steel billet S2 increases, the thickness and width of the flange portion S2F become uniform in the longitudinal direction, the cross-sectional area of ​​the flange portion at the longitudinal center portion (steady portion) becomes approximately the same as the cross-sectional area of ​​the flange portion at the longitudinal tail end, and the cross-sectional areas of the flange portions become uniform in the longitudinal direction. As a result, after finish rolling which has gone through the intermediate rolling process and the finish rolling process, not only does the thickness of the flange portion (flange thickness) become uniform in the longitudinal direction, but the flange width of the flange portion becomes nearly uniform in the longitudinal direction, and it is possible to reduce longitudinal variation in the flange width of the flange portion after finish rolling.

[0069] Furthermore, according to the manufacturing method of H-shaped steel in this embodiment, the aforementioned rolling pass in the rough rolling process is the final rolling pass in the rough rolling process, so that the design of the groove shape and the rolling pass schedule can be simplified when rolling down only the flange width of the flange portion S1F of the H-shaped steel material S1 in the rough rolling process.

[0070] In addition, according to the manufacturing method of H-shaped steel of this embodiment, the rough rolling process includes a sizing rolling process in which the web portion S1W of the H-shaped steel material S1 is rolled in the thickness direction and the flange portion S1F of the H-shaped steel material S1 is rolled in the width direction, a web widening rolling process in which the inner width of the web portion S1W of the H-shaped steel material S1 is widened, and an edging rolling process having a rolling pass in which only the flange width of the flange portion S1F of the H-shaped steel material S1 is rolled down.

[0071] As a result, in the rough rolling process, the web portion S1W of the H-shaped steel material S1 is rolled in the thickness direction in the sizing rolling process, and the flange portion S1F of the H-shaped steel material S1 is rolled in the width direction. Also, the inner width of the web portion S1W of the H-shaped steel material S1 is widened in the web widening rolling process. Furthermore, only the flange width of the flange portion S1F of the H-shaped steel material S1 is rolled down in the edging rolling process. As a result, the flange width B4 of the flange portion S2F of the rough steel billet S2 after the rough rolling process is shaped to be equal to or less than the target flange width Bf of the flange portion F of the H-shaped steel H after the finish rolling process.

[0072] Furthermore, according to the manufacturing method of H-shaped steel in this embodiment, the groove depth b3 of the flange rolling portion 35a that rolls the flange portion S1F of the H-shaped steel material S1 in the width direction in the web widening second rolling groove (web widening rolling groove) 35 used in the web widening second rolling process (web widening rolling process) is shallower than the groove depth b1 of the flange rolling portion 33a that rolls the flange portion S1F of the H-shaped steel material S1 in the width direction in the sizing rolling groove 33 used in the sizing rolling process.

[0073] This allows the flange width of the flange portion S1F of the H-shaped steel material S1 to be reduced during the web widening rolling process, and the flange width of the flange portion S2F of the rough steel billet S2 after rough rolling to be more uniform in the longitudinal direction. Although the embodiment of the present invention has been described above, the present invention is not limited to this and various modifications and improvements can be made.

[0074] For example, the reduction pass in the edging rolling process, which reduces only the flange width of the flange portion S1F of this H-beam steel material S1, may be performed not only in the final rolling pass in the rough rolling process, but also in a rolling pass before the final rolling pass.For example, the groove shape may be changed and the reduction pass in the edging rolling process may be performed between the first web widening rolling process and the second web widening rolling process.

[0075] Furthermore, the groove depth b3 of the flange rolling portion 35a in the web widening second rolling groove 35 used in the web widening second rolling process, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, does not necessarily have to be shallower than the groove depth b1 of the flange rolling portion 33a in the sizing rolling groove 33 used in the sizing rolling process, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction.

[0076] Furthermore, the flange rolling groove having a groove depth shallower than the groove depth b1 of the flange rolling portion 33a that rolls the flange portion S1F of the H-shaped steel material S1 in the width direction in the sizing rolling groove 33 used in the sizing rolling process is not limited to the web widening second rolling groove 35, but may be the web widening first rolling groove 34. Furthermore, when web widening rolling is performed in one stage using one web widening rolling groove, the flange rolling groove having a groove depth shallower than the groove depth b1 of the flange rolling portion 33a that rolls the flange portion S1F of the H-shaped steel material S1 in the width direction in the sizing rolling groove 33 may be this web widening rolling groove. Furthermore, when web widening rolling is performed in three or more stages using three or more web widening rolling grooves, any one of the three or more web widening rolling grooves may be used as a groove for the flange rolling section that has a groove depth shallower than the groove depth b1.

[0077] Furthermore, the H-beam steel material S1 is not limited to that which has been heated in the heating furnace 2, and may be that which has not been heated. In addition, in the intermediate rolling process, the rough steel billet S2 is rolled using an intermediate universal rolling mill 4 and an intermediate edging rolling mill 5, but other intermediate rolling mills may be used instead of the intermediate universal rolling mill 4 and the intermediate edging rolling mill 5.

[0078] In addition, in the finish rolling process, a finish universal rolling mill 6 is used to finish roll the rolled material S3 for finish rolling, which has approximate product dimensions, but other finish rolling mills may be used instead of the finish universal rolling mill 6. [Example]

[0079] In order to verify the effects of the present invention, H-section steel was manufactured under the following manufacturing conditions, and the flange width of the H-section steel manufactured (finish-rolled) as a result of the manufacturing process was measured over the entire length in the longitudinal direction.

[0080] <Manufacturing conditions> (1) Target cross-sectional dimensions of H-shaped steel products The cross-sectional designation is H1000 x 400 x 19 x 40. H-shaped steel H was manufactured with target product dimensions of web height Hw: 1000 mm, flange width Bf of flange part F: 400 mm (target flange width after finish rolling is 403.2 mm in hot dimension), thickness of web part W (web thickness) Tw: 19 mm, thickness of flange part F (flange thickness) tF: 40 mm.

[0081] (2) Rolls used in the rough rolling process The rolling rolls used in the rough rolling step are the upper rolling roll 31 and the lower rolling roll 32 shown in Figures 3 to 5. A sizing rolling groove 33, a first web widening rolling groove 34, and a second web widening rolling groove 35 are formed on the peripheral surfaces of the upper rolling roll 31 and the lower rolling roll 32. The groove depth b3 of the flange rolling portion 35a in the second web widening rolling groove 35, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction, is 5 mm shallower than the groove depth b1 of the flange rolling portion 33a in the sizing rolling groove 33, which rolls the flange portion S1F of the H-shaped steel material S1 in the width direction.

[0082] (3) Dimensions of H-beam material and rough-rolled billets The dimensions of the H-shaped steel material S1 were: web height H0 was 1160 mm, flange width B0 of flange portion S1F was 540 mm, thickness (web thickness) T0 of web portion S1W was 140 mm, and thickness (flange thickness) t0 of flange portion S1F was 210 mm. Dimensions of rough steel billet S2 after rough rolling: In the rough rolling step, the H-beam steel material S1 was rough rolled by the manufacturing methods of Inventive Example 1, Inventive Example 2, Comparative Example 1, and Comparative Example 2. In all of Inventive Example 1, Inventive Example 2, Comparative Example 1, and Comparative Example 2, sizing rolling and web widening rolling (first web widening rolling and second web widening rolling) were performed in the rough rolling step.

[0083] In addition, in the case of Invention Examples 1 and 2 and Comparative Example 1, edging rolling was performed after web widening rolling, and edging rolling was carried out in the final pass of the rough rolling process, but in the case of Comparative Example 2, edging rolling was not performed, and the rough rolling process was completed with web widening rolling.

[0084] The reduction amount in edging rolling in Inventive Example 1 was such that the flange width B4 of the flange portion S2F of the rough steel billet S2 after rough rolling was 13.2 mm smaller than the target flange width Bf of the flange portion F of the H-shaped steel H after finish rolling (the target flange width after finish rolling was 403.2 mm in hot dimension). Also, the reduction amount in edging rolling in Inventive Example 2 was such that the flange width B4 of the flange portion S2F of the rough steel billet S2 after rough rolling was 3.2 mm smaller than the target flange width Bf of the flange portion F of the H-shaped steel H after finish rolling (the target flange width after finish rolling was 403.2 mm in hot dimension). Furthermore, the reduction amount in the edging rolling in Comparative Example 1 was such that the flange width B4 of the flange portion S2F of the rough steel billet S2 after rough rolling was 6.8 mm larger than the target flange width Bf of the flange portion F of the H-shaped steel H after finish rolling (the target flange width after finish rolling was 403.2 mm in hot dimension).

[0085] As a result, the dimensions of the rough steel billet S2 after rough rolling were as follows: web height H4 was 1300 mm, and thickness (web thickness) T4 of web portion S2W was 55 mm for each of invention example 1, invention example 2, comparison example 1, and comparison example 2.

[0086] In addition, the flange width B4 of the flange part S2F is as follows: Invention example 1: 390mm (ΔB=-13.2mm) Invention Example 2: 400 mm (ΔB = -3.2 mm) Comparative example 1: 410mm (ΔB=+6.8mm) Comparative example 2: 430mm (ΔB=+26.8mm) It was.

[0087] Under the above flange width reduction conditions, the flange thickness t4 of the flange part S2F is the longitudinal steady part, Invention example 1: 144 mm Invention Example 2: 141 mm Comparative example 1: 137 mm Comparative example 2: 131mm After the intermediate rolling process, the target web thickness TI of the web portion S3W is 19.3 mm, the target flange thickness tI of the flange portion S3F is 41.2 mm, Σrw is 0.649, and (Σrf-Σrw) is Invention Example 1: 0.065 Invention Example 2: 0.058 Comparative Example 1: 0.050 Comparative Example 2: 0.036 This becomes:

[0088] (4) Number of rolling passes in the rough rolling process, intermediate rolling process, and finish rolling process Rough rolling process: 17 passes in the sizing rolling process, 2 passes in the web widening rolling process, and 2 passes in the edging rolling process, for a total of 21 passes. Intermediate rolling process: intermediate universal rolling and intermediate edging rolling each had 21 passes. Finish rolling process: 1 pass.

[0089] <Manufacturing results> 10 shows the results of measuring the flange width at 20 positions along the entire length of the H-shaped steel after finish rolling, which was manufactured by the manufacturing methods of each of Invention Example 1, Invention Example 2, Comparative Example 1, and Comparative Example 2. The 20 positions along the entire length of the H-shaped steel in the longitudinal direction are positions obtained by dividing the entire length of the H-shaped steel in the longitudinal direction into 20 equal parts. The flange width is the average value of the flange widths of a pair of flange portions, and the measurements were taken in the cold state.

[0090] In the case of Invention Example 1 (◯ in Figure 10: ΔB = -13.2 mm) and Invention Example 2 (△ in Figure 10: ΔB = -3.2 mm), the flange width over the entire longitudinal length was within the tolerance range, which was good, with the target flange width Bf being 400 mm, upper tolerance limit being 402 mm, and lower tolerance limit being 398 mm.

[0091] In contrast, in the case of Comparative Example 1 (□ in Figure 10: ΔB = +6.8 mm) and Comparative Example 2 (× in Figure 10: ΔB = +26.8 mm), the target flange width Bf was 400 mm, with the upper tolerance limit being 402 mm and the lower tolerance limit being 398 mm, and the flange width at the longitudinal center (steady part) was below the lower tolerance limit, resulting in a rejected product.

[0092] In addition, under the rough rolling conditions of Comparative Example 1 and Comparative Example 2, attempts were made to devise a pass schedule for intermediate rolling by referring to the rolling method for H-shaped steel described in Patent Document 2, but no matter what was done, it was not possible to make the flange width at the longitudinal center (steady portion) larger than the lower limit of the tolerance. In this way, it was confirmed that the present invention can reduce the variation in the flange width in the longitudinal direction of the flange portion after finish rolling. [Explanation of symbols]

[0093] 1. H-beam rolling equipment 2 Furnace 3 Breakdown rolling mill 4 Intermediate universal rolling mill 5. Intermediate edging rolling mill 6 Finishing rolling mill S1 H-shaped steel material S1W Web Section S1F flange S2 Rough shaped steel billet S2W Web Department S2F flange S3 Rolled material S3W Web Department S3F flange HH section steel W Web Department F flange

Claims

1. A method for manufacturing H-beam steel, comprising: a rough rolling step in which an H-beam steel material is roughly rolled by a breakdown rolling mill to form a rough steel billet; an intermediate rolling step in which the rough steel billet rough rolled in the rough rolling step is rolled by an intermediate rolling mill to form a rolled material for finish rolling; and a finish rolling step in which the rolled material for finish rolling rolled in the intermediate rolling step is finish rolled by a finish rolling mill to form an H-beam steel of product dimensions, In the rough rolling process, a rolling pass is provided that reduces only the flange width of the flange portion of the H-shaped steel material, and the flange width B4 of the flange portion of the rough steel billet after the rough rolling process is completed is set to be equal to or less than the target flange width Bf of the flange portion of the H-shaped steel after the finish rolling process, and ΔB, which is the value obtained by subtracting the target flange width Bf from the flange width B4, satisfies the formula: -0.1Bf (mm)≦ΔB≦0 (mm), thereby increasing the thickness of the flange portion of the rough steel billet.

2. The method for manufacturing H-beam steel according to claim 1 , wherein the rolling pass in the rough rolling step is a final rolling pass in the rough rolling step.

3. The rough rolling step includes: a sizing rolling process in which a web portion of the H-shaped steel material is rolled in a thickness direction and a flange portion of the H-shaped steel material is rolled in a width direction; a web widening rolling process for widening the inner width of the web portion of the H-shaped steel material; 3. The method for manufacturing H-beam steel according to claim 1, further comprising an edging rolling process having the rolling pass for rolling down only the flange width of the flange portion of the H-beam steel material.

4. The method for manufacturing H-shaped steel as described in claim 3, characterized in that the groove depth of the flange rolling portion in the web widening rolling groove used in the web widening rolling process, which rolls the flange portion of the H-shaped steel material in the width direction, is shallower than the groove depth of the flange rolling portion in the sizing rolling groove used in the sizing rolling process, which rolls the flange portion of the H-shaped steel material in the width direction.

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