Technical field [0001] (Cross Reference of Related Applications) Thepresent application claims priority based on Japanese Patent Application No. 2018-007095 filed in Japan on January 19, 2018, and the content thereof is incorporated herein. [0002] 　The present invention relates to a manufacturing method for manufacturing an H-section steel using, for example, a slab having a rectangular cross section as a raw material. Background technology [0003] 　When manufacturing H-section steel, raw materials such as slabs and blooms extracted from a heating furnace are shaped into a rough shape material (so-called dogbone-shaped material to be rolled) by a rough rolling machine (BD), and intermediate universal rolling is performed. Machine is used to reduce the thickness of the web or flange of the rough material, and at the same time, an edger rolling machine adjacent to the intermediate universal rolling machine applies width reduction and edge face forging and shaping to the flange of the material to be rolled. . Then, the H-shaped steel product is formed by the finishing universal rolling machine. [0004] 　In the method for manufacturing the H-section steel as described above, when forming a so-called dogbone-shaped crude material from a slab material having a rectangular cross section, an interruption is made in the slab end face in the first hole die of the rough rolling step. After that, in the second and subsequent hole types, there is known a technique in which the interrupt is spread out or the interrupt depth is deepened, and the interrupt in the slab end face is erased in the subsequent hole types (for example, see Patent Document 1). ). [0005] 　Further, in the manufacture of H-section steel, after so-called edging rolling for edging the end surface (slab end surface) of a raw material such as a slab, the material to be rolled is rotated by 90 ° or 270 ° to reduce the portion corresponding to the web. It is known to perform rolling. In this flat shaping rolling, the portion corresponding to the flange is reduced and the portion corresponding to the flange is reduced as well as the portion corresponding to the web. However, when forming a large H-section steel product having a large web height, when a large material is used as a material to be rolled. In general flat shaping rolling, various problems may occur such as elongation in the web height direction and deformation of the flange-corresponding portion, and there are cases where correction of the shape is required. Specifically, as the web-corresponding portion is rolled down, the web-corresponding portion is stretched in the longitudinal direction, and the flange-corresponding portion is stretched in the longitudinal direction by being stretched by the stretching, and the flange-corresponding portion becomes thin. The phenomenon was a concern. [0006] 　Regarding such flat shaping rolling, for example, Patent Document 2 discloses a technique for selectively performing reduction to a web-corresponding portion. An unpressed lower portion is provided at the center of the web-corresponding portion, and a convex formed thereafter. By deleting a portion (corresponding to the raised portion of the present invention) and widening the portion corresponding to the web, it is possible to efficiently manufacture a large H-section steel. Advanced technical literature Patent literature [0007] Patent Document 1: JP-A-7-88501 JP Patent Document 2: JP-A-57-146405 Summary of the invention Problems to be Solved by the Invention [0008] 　As described above, in recent years, with the increase in the size of structures and the like, it has been desired to manufacture a large H-section steel product having a large web height and a large flange width. In particular, there is a demand for a product in which the flange, which greatly contributes to the strength and rigidity of H-section steel, is made wider than in the past. In order to manufacture an H-shaped steel product having a widened flange, it is necessary to form a material to be rolled having a wider flange width than that in the conventional method from the shaping in the rough rolling process. [0009] 　The technique disclosed in Patent Document 1 is a method of interrupting an end face (slab end face) of a material such as a slab, edging the end face, and performing rough rolling by utilizing the width expansion. However, in such a method of performing rough rolling, there is a limit to widening the flange. That is, in the conventional rough rolling method, in order to widen the flange width, the width expansion can be improved by techniques such as wedge design (interruption angle design), reduction adjustment, and lubrication adjustment. Since it does not contribute significantly, the width expansion ratio, which indicates the ratio of the expansion amount of the flange width to the edging amount, is about 0.8 even under the condition that the efficiency at the initial stage of edging is the highest. Further, it is known that under the condition of repeating edging with the same hole type, the width expansion ratio decreases as the amount of expansion of the flange width increases, and finally becomes about 0.5. It is also possible to enlarge the material itself such as slab and increase the edging amount, but due to the equipment limit of the rough rolling mill and the reduction amount etc., it is not possible to realize sufficient widening of the product flange. There are circumstances. [0010] 　Moreover, when manufacturing a large H-shaped steel product, a large-sized rough-shaped material may be roll-shaped in the rough-rolling process. When a large-sized rough shaped material is roll-shaped by a method different from the conventional method and the shape of the rough-shaped material is shaped closer to the H-shaped steel, flat shaping rolling is performed by the technique described in Patent Document 2 above. It has been found that when this is done, problems such as elongation in the web height direction and deformation of the flange equivalent portion occur. [0011] 　In view of such a point, the present inventors have made an evaluation in the entire overall process including the erasing of the unpressurized lower part in the subsequent process. Specifically, as described in an embodiment of the present invention to be described later, for example, when a 300-thick slab is used as a material, the unpressurized lower part has a width of 25% or more and 50% or less of a web internal method of a material to be rolled. It has been found that setting the width enhances the flange generation efficiency. At the same time, regarding the unpressurized part, due to the difference in shape between the pressed part and the unpressed part in the web of the material to be rolled, threading failure may occur during flat forming rolling, which may result in shape failure. The present invention has also been discovered and has led to the present invention. [0012] 　In view of the above circumstances, an object of the present invention is to perform a rough rolling process using a die for manufacturing an H-section steel to deeply interrupt a projecting portion having an acute-angled tip shape on an end surface of a rectangular cross-section material such as a slab. In the flat modeling rolling that is carried out after so-called edging rolling, in which the H-shaped steel rough-shaped cross section having a larger flange width than that in the past is obtained by inserting and sequentially bending the flange portions formed thereby, the elongation in the web height direction and the flange To provide a technology for efficiently and stably manufacturing a large H-section steel product by improving the efficiency of flange formation without causing a problem such as deformation of a considerable part, performing flat forming rolling of a large rough shape material. It is in. Means for solving the problems [0013] 　In order to achieve the above-mentioned object, according to the present invention, there is provided a method for producing an H-section steel including a rough rolling step, an intermediate rolling step, and a finish rolling step, wherein a rectangular cross-section slab having a thickness of 290 mm or more and 310 mm or less is used as a material. In the rough rolling step, the edging rolling step of rolling and shaping the material to be rolled into a predetermined dogbone shape and the rolling of the web portion by rotating the material to be rolled by 90 ° or 270 ° after completion of the edging rolling step are performed. In the upper and lower hole type rolls having at least one hole type among the hole types for performing the above flat rolling step, there is a dent portion for forming a raised portion at the center of the web portion of the material to be rolled, The width of the raised portion formed in the central portion of the roll cylinder length of the die roll and formed in the flat rolling step is set to 25% or more and 50% or less of the method in the web portion of the material to be rolled, and the width is set in the flat rolling step. The thickness of the formed web portion is set to a predetermined thickness that is thicker than the thickness of the web portion at the start of the intermediate rolling step. [0014] 　The hole type for performing the flat rolling step may further include a raised portion erasing hole type for pressing down the raised portion with respect to the rolled material on which the raised portion is formed. [0015] 　The hole type performing the flat rolling step includes one or a plurality of types in which the web portion is rolled and shaped substantially flat and the widening rolling is performed on the material to be rolled after being shaped by the raised portion erasing hole type. A widening hole type may be further included. [0016] 　The thickness of the web portion rolled in the flat rolling step may be set to a predetermined thickness with the lower limit of the following equation (3). Y = −0.118X 2 + 11.732X−121.15 (3) Here, Y: web thickness (mm), X: escape rate (%). [0017] 　A rolling mill that performs the rough rolling step is engraved with a plurality of six or more hole dies for rolling and shaping the material to be rolled, and in the plurality of die cavities, one or more pass shaping of the material to be rolled is performed. Of the plurality of hole types, the first hole type and the second hole type are provided with protrusions that insert a vertical interruption in the width direction of the material to be rolled to form a divided portion at the end of the material to be rolled, Among the plurality of hole dies, the third and subsequent hole dies other than the hole dies for performing the flat rolling step, which are located at the subsequent stage, have projections that abut the interrupt and sequentially bend the formed divided portions. It may be formed. The invention's effect [0018] 　According to the present invention, in a rough rolling process using a hole die for manufacturing H-section steel, a protrusion having an acute-angled tip shape is deeply interrupted at an end face of a rectangular cross-section material such as a slab, thereby forming After the so-called dog bone is formed from the rectangular cross-section slab by sequentially bending the formed flanges, the flatness forming rolling does not cause problems such as elongation in the web height direction and deformation of the flange equivalent part, and the flange generation efficiency. Therefore, it is possible to perform flat forming rolling of a large-sized rough shaped material. Brief description of the drawings [0019] FIG. 1 is a schematic explanatory view of an H-section steel production line. FIG. 2 is a schematic explanatory diagram of a first hole type. FIG. 3 is a schematic explanatory view of a second hole type. FIG. 4 is a schematic explanatory view of a third hole type. FIG. 5 is a schematic explanatory view of a fourth hole type. FIG. 6 is a schematic explanatory view of a fifth hole type. FIG. 7 is a schematic explanatory view of a sixth hole type. FIG. 8 is a graph showing the relationship between the relief rate and the flange width increase / decrease rate after H-shaped rough material molding. FIG. 9 is an explanatory diagram regarding warpage of a material to be rolled. FIG. 10 is a graph showing the relationship between warpage and web thickness. FIG. 11 is a graph showing the relationship between the escape rate and the minimum web thickness that ensures good formability. FIG. 12 is a graph showing an average flange thickness after flat rolling shaping according to an example and an average flange thickness after flat rolling shaping according to a comparative example. MODE FOR CARRYING OUT THE INVENTION [0020] 　Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and the drawings, components having substantially the same function or the same configuration are designated by the same reference numeral, and a duplicate description will be omitted. [0021] 　FIG. 1 is an explanatory diagram of an H-section steel production line T including a rolling facility 1 according to the present embodiment. As shown in FIG. 1, in the production line T, a heating furnace 2, a sizing mill 3, a rough rolling mill 4, an intermediate universal rolling mill 5, and a finish universal rolling mill 8 are arranged in this order from the upstream side. Further, an edger rolling mill 9 is provided near the intermediate universal rolling mill 5. In the following, for the sake of explanation, the steel material in the production line T may be generically referred to as "rolled material A", and the shape thereof may be appropriately illustrated by using broken lines, diagonal lines, etc. in each drawing. [0022] 　As shown in FIG. 1, in the production line T, a rectangular cross-section material (later rolled material A), for example, a slab 11 extracted from the heating furnace 2 is roughly rolled in a sizing mill 3 and a rough rolling mill 4. Then, it is subjected to intermediate rolling in the intermediate universal rolling mill 5. At the time of this intermediate rolling, the edger rolling machine 9 performs reduction on the flange tip portion (flange corresponding portion 12) of the material to be rolled, if necessary. Usually, the sizing mill 3 and the rolls of the rough rolling mill 4 are engraved with a so-called flat-shaped hole die that reduces the thickness of the edging hole die and the web portion to form the shape of the flange portion. Then, the H-shaped rough material 13 is formed by reverse rolling of a plurality of passes, and the H-shaped rough material 13 is formed by using a rolling mill train including two rolling mills of the intermediate universal rolling mill 5 to the edger rolling mill 9. , A plurality of passes of reduction are applied to form the intermediate material 14. Then, the intermediate material 14 is finish-rolled by the finish universal rolling machine 8 into a product shape, and the H-shaped steel product 16 is manufactured. [0023] 　Here, the slab thickness of the slab 11 extracted from the heating furnace 2 is within the range of 290 mm or more and 310 mm or less, for example. This is a dimension of a so-called 300-thick slab raw material used when manufacturing a large H-section steel product. [0024] 　Next, the hole configuration and the hole shape engraved in the sizing mill 3 and the rough rolling mill 4 shown in FIG. 1 will be described with reference to the drawings. FIG. 2 to FIG. 7 are schematic explanatory views of a hole die formed in the sizing mill 3 and the rough rolling machine 4 for performing the rough rolling process. Here, the first hole type to the sixth hole type described below may be all engraved on the sizing mill 3, and the sizing mill 3 and the rough rolling mill 4 have six holes of the first hole type to the sixth hole type. The hole types may be engraved separately. That is, the first hole type to the sixth hole type may be engraved over both the sizing mill 3 and the rough rolling mill 4, or may be engraved on either one of the rolling mills. In the rough rolling process in the production of ordinary H-section steel, modeling is performed in one or a plurality of passes in each of these hole dies. [0025] 　Further, in the present embodiment, the case where the number of hole types to be engraved is 6 will be described as an example, but the number of the hole types does not necessarily have to be the 6-hole type and may be 6 or less or 6 or more. It may be the number of holes. For example, a configuration may be adopted in which a general widening rolling die is provided in the subsequent stage of the sixth die K6 described later. That is, any hole-type structure suitable for forming the H-shaped rough material 13 may be used. 2 to 7, the outline final pass shape of the material A to be rolled at the time of shaping in each hole die is shown by broken lines. [0026] 　FIG. 2 is a schematic explanatory view of the first hole type K1. The first hole type K1 is engraved on an upper hole type roll 20 and a lower hole type roll 21 which are a pair of horizontal rolls, and the material to be rolled A is rolled in the roll gap between the upper hole type roll 20 and the lower hole type roll 21. It is rolled down and shaped. Further, on the peripheral surface of the upper hole type roll 20 (that is, the upper surface of the first hole type K1), there is formed a protrusion 25 projecting toward the inside of the hole type. Further, on the peripheral surface of the lower hole type roll 21 (that is, the bottom surface of the first hole type K1), a projection portion 26 protruding toward the inside of the hole type is formed. These protrusions 25 and 26 have a tapered shape, and the protrusion length and the like of the protrusions 25 and 26 are equal. The height (projection length) of the protrusions 25 and 26 is h1, and the tip angle is θ1a. [0027] 　In the first hole type K1, the protrusions 25 and 26 are pressed against the upper and lower ends (slab end faces) of the material A to be rolled, and interrupts 28 and 29 are formed. Here, the tip end angle (also referred to as a wedge angle) θ1a of the protrusions 25 and 26 is preferably, for example, 25 ° or more and 40 ° or less. [0028] 　Here, it is preferable that the hole width of the first hole K1 is substantially equal to the thickness of the material A to be rolled (that is, the slab thickness). Specifically, the left and right centering properties of the material A to be rolled are preferably ensured by making the width of the hole die at the tip of the projections 25 and 26 formed in the first hole die K1 the same as the slab thickness. To be done. Further, by adopting such a configuration of the hole type dimension, as shown in FIG. 2, at the time of modeling with the first hole type K1, the projections are formed on the upper and lower end portions (slab end surface) of the material A to be rolled. Part 25, 26 and part of the hole type side surface (side wall) are in contact with the material A to be rolled, and the first hole is formed on the upper and lower ends of the slab divided into four elements (parts) by interruptions 28, 29. It is preferable that no positive rolling is performed on the top surface and the bottom surface of the mold K1. This is because the reduction by the top and bottom surfaces of the hole type causes elongation of the material A to be rolled in the longitudinal direction and reduces the production efficiency of the flange (flange portion 80 described later). That is, in the first hole type K1, the protrusions 25 and 26 are pressed against the upper and lower end portions (slab end faces) of the material A to be rolled, and the reduction in the protrusions 25 and 26 when the interruptions 28 and 29 are formed. The amount (wedge tip reduction amount) is made sufficiently larger than the reduction amount (slab end face reduction amount) at the upper and lower ends of the slab, whereby the interruptions 28 and 29 are formed. [0029] 　FIG. 3 is a schematic explanatory view of the second hole type K2. The second hole type K2 is engraved on an upper hole type roll 30 and a lower hole type roll 31 which are a pair of horizontal rolls. On the peripheral surface of the upper hole type roll 30 (that is, the upper surface of the second hole type K2), a projection portion 35 protruding toward the inside of the hole type is formed. Further, on the peripheral surface of the lower hole type roll 31 (that is, the bottom surface of the second hole type K2), a protrusion 36 protruding toward the inside of the hole type is formed. These protrusions 35 and 36 have a tapered shape, and the protrusion length and other dimensions of the protrusions 35 and 36 are equal. The angle of the tip of each of the protrusions 35 and 36 is preferably a wedge angle θ1b of 25 ° or more and 40 ° or less. [0030] 　The wedge angle θ1a of the first hole die K1 is the wedge angle of the second hole die K2 in the latter stage in order to secure the thickness of the tip end portion of the flange, enhance the inductivity, and ensure the stability of rolling. It is preferable that the angle is the same as θ1b. [0031] 　The height (projection length) h2 of the protrusions 35 and 36 is higher than the height h1 of the protrusions 25 and 26 of the first hole type K1, and h2> h1. Further, it is preferable in terms of rolling dimensional accuracy that the tip angles of the protrusions 35 and 36 are the same as the tip angles of the protrusions 25 and 26 of the first hole mold K1. In the roll gap between the upper hole type roll 30 and the lower hole type roll 31, the material A to be rolled after the first hole type K1 threading is further formed. [0032] 　Here, the height h2 of the protrusions 35, 36 formed on the second hole mold K2 is higher than the height h1 of the protrusions 25, 26 formed on the first hole mold K1. Similarly, the penetration length into the upper and lower ends (end face of the slab) of the second hole mold K2 is longer. The penetration depth of the protrusions 35 and 36 into the material A to be rolled in the second hole type K2 is the same as the height h2 of the protrusions 35 and 36. That is, the penetration depth h1 ′ of the protrusions 25 and 26 into the rolled material A in the first hole type K1 and the penetration depth h1 ′ of the protrusions 35 and 36 into the rolled material A in the second hole type K2. h2 has a relationship of h1 ′