JPH03184601A - Rolling method of shape steel - Google Patents

Abstract

PURPOSE:To regulate the height of a web with same number of pass as conventional rolling methods and to improve the efficiency of rolling by smoothing a projecting part in the middle part of the web and executing a finishing process where the reduction of area of the projecting part is transformed into the enlargement of the inside width of the web. CONSTITUTION:The projecting part is formed in the middle part of a web by rolling a material 1a to be rolled with a rolling mill. Next, the projecting part in the middle part of the web of a material 1b to be rolled which is formed by rolling with one side of annular sleeves 2c2 which is shown in two-dot chain lines by a finishing universal mill and flange parts are rolled with both annular sleeves 2c1 and vertical rolls 2c2. And the projecting part with the thickness Tcb is reduced to the thickness Tcc equal to the thickness Teb of both end parts and the whole surface of the web is smoothed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for rolling a section steel, and in particular to a hot rolling method that allows the web height of an H section steel to be freely adjusted during rolling. .

[Conventional technology]

Currently, there are a wide variety of types and sizes of shaped steel manufactured by hot rolling depending on the application, but in recent years, there has been an increase in the weight reduction and economical design of structures using these shaped steel. From this point of view, the variety of their dimensional sizes tends to further increase. If such a tendency is to be dealt with using known conventional techniques, the following problems will arise. For example, if we take universal rolling of H-section steel, which is the section steel with the largest production volume and size, the rolling mill arrangement is generally as shown in Figure 6 of the attached drawings, with breakdown rolling mill BD, 1st rough edging rolling mill RE, , 1st rough universal rolling mill RUI, 2nd rough universal rolling mill 1RU2, 2nd edging rolling mill 11E, , finishing universal rolling iF
It is rolled at U. As shown in FIG. 7, the dimensions of the H-section steel obtained by this conventional universal rolling method are as follows: web height [■, web inner width Ll+, flange thickness t2
has the relationship H=L11+2L2, and the inner width of the web Ll+
is the same as the horizontal roll width of the finishing universal rolling mill (LIIP in Figure 6) if the amount of heat shrinkage during cooling is ignored, so the web height H is the horizontal roll width of the finishing universal rolling mill and the flange thickness. Determined by For this reason, attempts were made to manufacture, for example, H-beam steel whose web height is constant regardless of the amount of change in flange thickness, or conversely, H-beam steel whose flange thickness is constant and whose web height can be adjusted to any dimension. In case, H rolling width of horizontal roll of universal rolling mill
It is necessary to prepare according to the size of the shaped steel. Therefore, an increase in the number of sizes to be rolled means an increase in the number of rolls owned, and furthermore, each time the rolling size changes, it becomes necessary to replace the rolls with rolls that match the size, which significantly reduces the operating efficiency. decreases to Further, during rolling, the rolling rolls are worn due to contact with the material to be rolled, and the width of the horizontal rolls, such as LIIF in FIG. 6, decreases, resulting in variations in the web height H or flange thickness t2 of the rolled product. Therefore, it is impossible to use the horizontal roll repeatedly for rolling of a certain rolling size for a long period of time. Due to these factors, it is almost impossible to economically manufacture products that satisfy the demands of consumers of a wider variety of products and sizes.

As methods for solving these problems, the following rolling methods are conventionally known, but each method has its own problems.

(1) JP-A No. 59-133902 "Hot rolling method for H-beam steel" The essential feature is that the web is partially rolled in a rough universal rolling mill and an edging mill. When the rolling part is rolled to make it smooth with a rolling mill, the web height is increased. However, in the edging rolling mill, the flange end of the rolled material is also rolled at the same time, so the rolling of the flange part acts to restrict the increase in web height, and the curvature of the flange and even the web. There is a risk that web buckling may occur due to restrictions on the amount of height expansion. To prevent this, it is necessary to reduce the rolling amount per pass in the rough universal rolling mill and reduce the protrusion at the center of the web, but in this case, the number of rolling passes increases and productivity decreases. There is.

(2) JP-A No. 59-178101 "Method for rolling H-beam steel with adjustable web height" The essence is that after forming protrusions on the web using the grooves of the roll,
The height of the web is expanded by rolling down the protrusion, and the height is regulated by the vertical roll or the caliber side wall, but by nature, it is difficult to adjust the volume of the web protrusion. Therefore, there is a high possibility that web buckling will occur due to rolling of the protrusions, and since the web height is regulated, the buckling is promoted. If a protrusion is formed to the extent that web buckling does not occur, its volume will be small, and therefore the amount of increase in web height will also be small, and the inherent effect will also be small. Furthermore, since a normal universal roll is used after the web protrusion is rolled down, it must be a horizontal roll with a width that matches the height of the web, and the number of rolls to be owned becomes large.

(3) JP-A No. 59-212101 "Rolling method capable of changing web height, rolling mill row" The essence is that the width of the horizontal rolls of the roughing universal rolling mill group and the finishing universal rolling mill is a constant width. The amount of increase in web height is not large, and the effect of reducing the number of rolls possessed is small, making it impractical in order to accommodate a wide variety of products and sizes.

(4) JP-A No. 60-82201 "Hot rolling method for H-beam steel" Illegal method is to roll the unrolled part of the center of the web in the first rough universal rolling mill into a second rough universal rolling mill by dividing the horizontal roll into three parts. It has the characteristic of being rolled to a smooth surface using a machine. In this case, in order to prevent web buckling in the second rough universal rolling mill, it is necessary to increase the rolling reduction of the flange by the vertical rolls of the rolling mill to balance the stretching of the web and the flange. The horizontal roll of the machine is divided into three parts, and the thin left and right divided rolls must receive the rolling blade of the flange, which poses a problem in the strength of the rolls.

Therefore, the amount of rolling reduction per pass inevitably decreases, and the rolling efficiency decreases.

(5) JP-A No. 61-135403 "Hot rolling method for H-section steel" The essence of the method is to use split rolls whose axial positions are variable for each pass, and the split rolls and fixed rolls that go into a rough universal rolling mill. Partial rolling of the flange ends and center part by the split rolls and vertical rolls, Partial rolling of the unrolled parts on both sides of the web center part by the split rolls in the edging rolling mill, and Rolling of the flange ends by the split rolls. Characterized by repeated
In reality, since the edging mill rolls the unrolled parts on both sides of the center of the web and simultaneously rolls the flange ends, flange curvature or web buckling is likely to occur, and to prevent this, the rolling schedule is adjusted accordingly. Due to the addition of significant restrictions and the horizontal roll of the rough universal rolling mill being divided into three parts, the rolling efficiency is reduced due to the strength of the rolls and the inability to reduce the flange part to a large extent.

(6) JP-A-61-108,10 and JP-A-63-
No. 30362 "Method for rolling a section with flanges 1" This method is a method of expanding the web height of the material to be rolled using a diagonal roll type rolling mill installed between a rough universal rolling mill and a finishing mill. , most of the increase in web height due to its nature is due to stretching of the web by diagonal rolls in contact with the inner surface of the flange, so depending on the amount of stretching or web temperature, web constriction, flange collapse, and There is a risk of scratches caused by the oblique rolls on the inner surface of the flange.Also, in order to improve the product yield of shaped steel, the length per slab I is generally increased to 100 m or more. , Therefore, there is a significant temperature difference between the head and pressure part of the rolled material.
Due to this temperature difference, it is possible that the web height cannot be expanded evenly. Furthermore, the web height is not uniformly expanded to the vicinity of the crop at the rolling head end and tail end, resulting in a lower product yield. Moreover, in order to prevent this, a new prevention device is required.

(7) JP-A No. 61-283401 ``Hot rolling method for shaped steel'' The essence of the method is to divide the horizontal rolls of a universal rolling mill so that the width of the rolls can be changed mutually in the roll axis direction. The web part is partially rolled, and the next edging rolling machine is also divided to remove the web part of the section steel and rolled by configuring so that only the flange part can be rolled, and in the same way, the horizontal roll of the universal rolling mill in the next process. In this method, the unrolled portion of the web part is rolled by horizontal rolls in the previous step, but according to the inventors' experiments with a similar rolling method using a model rolling mill, the above-mentioned (1), (4), (5) ) problems in the known example, that is, the curvature of the flange or the buckling of the web, can be solved, but the unrolled part by the universal rolling mill becomes asymmetrical with respect to the rolled material, causing twisting of the rolled material during rolling. It turned out to be impractical for rolling operations.

(8) JP-A No. 63-260602 “Method for rolling section steel”
The essence of this method is to reverse roll the section steel using only upper and lower horizontal rolls that are movably divided into two parts on the same axis, and sequentially widen and roll the inside of the web of the rolled material, but this method does not actively roll the web. At best, the flange and the web can only be attached by rolling down the extra thickness that has been pre-bottomed at the root. Therefore, the amount of increase in web height per bus is small;
If the required amount of expansion is large, an increase in the number of buses will be required, which will significantly reduce rolling efficiency. In addition, ■ If the web is compressed extremely in order to increase the amount of expansion per bath, protrusions or roll marks will occur on the web at the dividing part of the upper and lower horizontal rolls, which will make the product look unattractive and cause problems. However, Honbo has no way to prevent or solve this problem.

[Problems to be Solved by the Invention] In the conventional method, as mentioned above, the roll body length is fixed or constant for each roll, so it is necessary to prepare rolling rolls according to the rolling size. The amount of work required is enormous. ■ Operational efficiency is significantly reduced due to the need to rearrange the rolls.

Furthermore, due to roll wear during rolling, there are problems such as (1) variation in product dimensions, and (2) inability to repeatedly use the same rolling roll for the same size for a long period of time.

In addition, even with the above-mentioned known methods (1) to (8) for solving these problems, ■ occurrence of flange bending or web buckling or twisting; ■ decrease in rolling efficiency due to an increase in the number of rolling baths. , ■ Decreased product yield due to inability to ensure uniformity over the entire length of the rolled material, and ■ Only the number of rolls in some rolling mills can be reduced, with little overall reduction effect. .

The present invention was made in order to solve the above-mentioned problems, and it is possible to ensure high quality and high yield without increasing the number of rolls owned by one, without reducing the operation rate and rolling efficiency. At the same time, it is an object of the present invention to provide a method for rolling a section steel with good workability and in which the web height can be freely adjusted.

(Means for Solving the Problems) According to the present invention, the above object is achieved by using a first roughing universal rolling mill and a first roughing rolling mill, or a double-type first roughing mill, or a breakdown rolling mill. In the second rough rolling step of rolling the rolled material that has been rolled into the approximate product shape by the machine, two rolling annular sleeves are installed coaxially and with the roll shaft in the normal second rough rolling mill group. Adding a rolling mill equipped with a pair of upper and lower rolls, which are fitted so as to be integrally rotatable and at least one of the annular sleeves is movable in the axial direction of the rolls;
After the material to be rolled is rolled once or multiple times in the above-mentioned normal second rough rolling mill group to a predetermined size, the outer width of both annular sleeves of the rolling rolls of the added rolling mill is adjusted to the width of the rolled material. By rolling with the inner width of the web set larger than the inner width of the web, most of the area reduction at both ends of the web of the material to be rolled rolled with the annular sleeve is converted into an increase in the inner width of the web, and the inner width of the web is expanded between the two annular sleeves. a convex part forming step in which a convex part is formed in the central part of the web in a caliber section, and a finishing universal rolling mill in which rolling rolls having a similar structure to the rolling mill added to the second rough rolling mill group are incorporated into horizontal rolls. By rolling with the outer width of both annular sleeves of the horizontal roll set larger than the inner width of the web of the rolled material rolled in the above step, the rolled material web formed in the above protrusion forming step is rolled. This is achieved by performing a finish rolling process that smoothes the convex portion in the central portion and converts most of the area reduction of the convex portion into an increase in the inner width of the web.

[Effect]

In the present invention as described above, the rolled material that has been rolled one or more times to a predetermined size in a normal second rough rolling mill group has a convex portion formed in the center of the web, and In the post-finish rolling step, the convex portions are rolled and the web portion is stretched.

〔Example〕

Hereinafter, the present invention will be described in detail based on FIGS. 1 to 5 of the accompanying drawings.

In this example, in the conventional H-beam rolling mill arrangement shown in FIG. 6, a rolling mill with the roll configuration shown in FIG. 3 is added to the rear of the second etching rolling mill RE, and a finishing universal rolling The roll configuration of the machine FU is shown in FIG.

FIG. 5 is an example of a rolling mill arrangement according to this embodiment,
In the figure, RB indicates a rolling mill with the roll configuration shown in FIG. 3, and the finishing universal rolling mill FU has the roll configuration shown in FIG. 4 (8) or (B). Needless to say, there is no problem in placing it in

Next, the role configuration will be explained. As shown in FIG. 3, the roll configuration of the rolling iRB includes two rolling annular sleeves 2b fitted coaxially and rotatably together with the roll shaft 3b, and at least one of the annular sleeves 2b fitted on the roll shaft 3b. This is a pair of upper and lower horizontal rolls that are movable in the roll axis direction and the width between the annular sleeves 2b can be arbitrarily set, and the width of the annular sleeves 2b is equal on the left and right sides. This rolling iRB rolls down both ends of the web with the annular sleeve 2b, and forms a convex portion in the center of the web with the caliber portion formed between the circumferential annular sleeves 2b.

The roll configuration of the finishing universal rolling mill FU is shown in Figure 4 (
As shown in A) and (B), two rolling annular sleeves 2cI are coaxially attached to the roll shaft 3c, and the roll shaft 3c
At least one annular sleeve 2c+ is formed to be movable in the roll axis direction, and the annular sleeve 2c has a pair of upper and lower horizontal rolls whose width can be arbitrarily set, and their left and right sides. Vertical roll 2cz is placed on the top. It should be noted that the annular sleeve 2c has different body widths between the left and right sides, and in the case of a larger width annular sleeve, the convex portion formed by the rolling mill RB is set to be rolled smoothly. Further, the annular sleeve 2c and the vertical roll 2cz roll down the flange.

FIG. 1 shows the web height enlarging process according to this embodiment in the order of its steps, which will be explained below. Step (a) in Figure 1 is a normal second roughing universal rolling mill RU.
, and shows a rolled material having a general product shape that has been rolled in one pass or several passes in the second etching rolling mill RE2. Since this rolled material 1a is rolled in a normal rolling mill, if the same roll is used, the web inner width LI
IA is constant, and the thickness of the central part of the web Tca (
The value in step (a) for the thickness Tc of the central part of the web is shown, and the value Tcb in step (b) and step (C) is shown.
, Tcc, Tcd. The thickness Te at the web end and the thickness Tf at the flange are also shown below. ) and the thickness Tea at both ends of the web are also equal.

However, this web thickness is adjusted to have a thickness that is suitable for increasing the web height in the next step (b). Further, the flange thickness Tfa is rolled to be slightly thicker than the flange thickness at the completion of finish rolling (rfc in step (C) in FIG. 1).

Next, the above-mentioned rolled material 1a is rolled by IRQ in step (b) in FIG.
) to roll. In this case, the outer width LII between the rolling annular sleeves 2b indicated by the two-dot chain line in step (b) of FIG.
B and the thickness Tab at both ends of the web are set approximately in the following relationship.

Ll184((Lll^-1)(Tea-Teb)+
l (Tea-Tcb) l /Tab+LIl
8 Here, l is the width of the caliber portion at the center of the web formed to set the annular sleeve 2b to the outer width LIIB. Further, α is a coefficient, which represents the ratio at which the web area reduction amount in the main rolling is converted to the web height. When L II A = L II B, α is around 0.4, and most of the web area reduction extends in the length direction (rolling direction), which causes buckling in the web.

Therefore, in order to prevent this, the value of α should be as close to l as possible, and preferably 0.9 or more. Further, the thickness Teb of both ends of the web, that is, the web reduction ratio in the main rolling step (b) is determined in consideration of the rolling limit of the material to be rolled in the main rolling, etc.

By performing such rolling, most of the web loss is converted into an increase in the web height, no web buckling occurs, and the flange is not pulled in the length direction, so the flange width and thickness are reduced. Tfb also hardly changed, and Tf
The desired web height LllI3 is approximately equal to a. The thickness Tcb of the convex portion at the center of the web formed in the caliber portion is almost the same as the web thickness Tea at the previous stage, although it depends on the rolling reduction ratio at both ends thereof. Moreover, the broken line in the figure shows the state before rolling, that is, the state in step (a) of FIG. 1.

Step (C) in FIG. 1 shows the situation of rolling with the finishing universal rolling iFU, and the annular sleeve 2c is indicated by a two-dot chain line in the figure.
, shows a situation in which the convex part of the web central part of the rolled material tb formed by rolling in step (b) of FIG. ing. In the main rolling step (C), the convex portion having a thickness Tab is rolled down to a thickness Tcc equal to the thickness Tab at both ends thereof, thereby smoothing the entire surface of the web. Therefore, the web thickness Tcc and Tec in the main rolling are equal to the thickness Tab of both ends of the web in the previous stage.

Further, when a convex portion having a thickness of Tcb is rolled to a thickness of Tcc,
The web inner width LIIC of the rolled material 1c is expressed by the following formula.

LIIC=(βl(Tcb-Tcc))/T
cc+LIIB where β is a coefficient and the main rolling process (C
) represents the rate at which the area reduction of the convex portion changes to increase the web height. This value is greatly influenced by the caliber width i and Tcb-Tcc, that is, the height of the convex part, in other words, the rolling reduction rate of the convex part when there is no flange reduction by the vertical rolls, but when there is a reduction by the vertical rolls, this value is Most of it depends on L118 and LHC,
- Since LIICξLIIB is used for boat fishing, the area reduction due to convex rolling changes in the length direction, resulting in a situation where web buckling is likely to occur. To prevent this, LIIC is set larger than LIIB in the outer width between the two top-shaped sleeves 2c. In this case, β is determined in consideration of the amount of reduction of the convex portion and the amount of extension in the length direction due to the reduction of the flange of the vertical roll. Therefore, β is a coefficient that varies depending on the size, but if it is set to a value of approximately 0.5 or more, web buckling will not occur and it is good.

In addition, if an extra thickness shown in Fig. 2, which is known from Japanese Patent Publication No. 57-4402, is added before finishing rolling, it becomes possible to further increase the web height in finishing rolling, so LIIC can be further improved. Can be set large.

Additionally, the flange of the rolled material 1b is generally 3° to 10°.
It has a certain angle. This reduces the amount of wear on the rolls of the conventional universal rolling mill in the previous stage, and the outer width of the roll is larger than the inner width of the web in the previous stage (LII
When rolling with rolls (B and LIIC), this is installed to improve the bite, but in finishing rolling, this angle is rolled with an annular sleeve 2c+ and a vertical roll 2ct to approximately 0°. Stand the flange upright and make the flange finish thickness rfc.

Furthermore, since the rolling method of the present invention is characterized in that the web including the crop is rolled from the rolling head end to the rolling end end, the amount of web height expansion is uniform over the entire length of the rolled material.

As described above, the above-mentioned problems can be solved and it becomes possible to manufacture an H-beam steel whose web height is adjustable.

Next, the rolling apparatus of this embodiment will be explained using FIG. 1 and FIG. 5. As the rolling material, a beam blank cast by a continuous casting machine was used, and a breakdown rolling mill BD, a first roughing rolling mill RE,
, 1st rough universal rolling mill R1l, , 2nd rough universal rolling aRU, , 2nd edge rolling 4m RE
The conventional H type t is used for Z! A rolling roll for A300 x 200 (mm) was incorporated, and the rolling mill RB and finishing universal rolling mill FU were rolls adapted to this example shown in FIGS. 3 and 4.

First, the reheated beam blank is passed through the breakdown universal machine BD for 7 baths and the first rough rolling mill R1 (RIE
+ and R11,), and 5 passes of reverse rolling by continuous rolling of the second rough universal rolling mill RU and the second edging rolling mill IRU, to form a workpiece having the predetermined dimensions shown in step (a) of Fig. 1. It was referred to as rolled material 1a. The number of passes of this rolling is exactly the same as that of the conventional H-type 8500 x 200 (mm).

In the rolling by the second rough universal rolling mill R112 and the second engine rolling mill 17E2, rolling by rolling mill RB is performed as a dummy pass until the fourth pass, and in the fifth pass, rolling by rolling mill RB is performed to a predetermined roll gap. The rolling shown in step (b) in FIG. 1 is completed by setting the rolls and performing Kundem rolling with three rolling mills: the second rough universal rolling mill RU2, the second aging rolling mill RE, and the rolling mill RB. Ta.

The convex part of the web center part and the flange of the rolled material 1b rolled in the above manner are finished by a universal rolling machine FU.
Pass rolling was performed, and the rolling shown in step (C) in FIG. 1 was completed.

In this case, there was concern about the strength of the narrower body of the rolling annular sleeve 2c shown in FIG. There wasn't.

Table 1 shows an example of the rolling results of the present invention and, for comparison, the rolling results of conventional H-section steel 500 x 200 x 10 x 16 (mm). The dimensions of the rolled material in Table 1 are cold measurements obtained by taking samples from the rolled material in each rolling mill.

As shown in Table 1, normal H3O0X200 xlOx
Compared to the web height of 16 (mm), the rolling method in this example increases the height by about 34 mm, and the web height can be adjusted at least within that range. Furthermore, it can be seen that the number of rolling baths is exactly the same, and the rolling efficiency is also the same as that of the conventional method.

Furthermore, we closely observed the product after finishing rolling, but we could not find any peculiar flaws that were presumed to have occurred due to the method used in this example, and there were no shape defects such as web buckling, and the dimensions were uniform over the entire length. It was a good quality product.

(Hereinafter, blank space) [Effect of the invention] As described above, according to the present invention, both webs of the section steel ζ;
In the rolling of one part, by combining the amount of area reduction with the roll width, most of the area reduction can be converted into an increase in web height, and the convex part in the center of the web formed at that time is smoothed in the next rolling, Even in that case, most of the area reduction of the convex portion can be converted into an increase in web height by combining with the roll width, thereby providing a method for hot rolling a section steel that has a large effect of increasing the web height. Therefore, ■ The web height of the section steel can be adjusted with the same number of baths as in the conventional rolling method, and therefore the rolling efficiency is high. On the other hand, it is possible to share rolling rolls, so there is no need to increase the number of rolls owned as the number of sizes increases. ■ There is no risk of product defects such as web buckling, and the rolling rolls can be used over the entire length of the rolled material. The effect is that dimensional control accuracy is high, and therefore high-quality and high-yield manufacturing is possible.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the web height of an H-beam steel according to an embodiment of the present invention, and Fig. 2 is a cross-sectional view showing the web height of an H-beam steel according to an embodiment of the present invention. A cross-sectional view of a section steel showing the formation of excess thickness in a rolled material,
Figure 3 is a cross-sectional view showing the roll configuration for rolling both ends of the web of the ■4 section steel, and Figures 4 (A) and (B) are cross-sectional views showing the roll configuration of the finishing universal rolling mill in this example. , FIG. 5 is a diagram showing an example of the configuration of a rolling mill and the shape of the material to be rolled for embodying the rolling method of this embodiment, and FIG.
The figure shows the conventional H-beam rolling process, the roll configuration of each rolling mill, and the shape of the rolled material, and FIG. 7 is a cross-sectional view showing the dimensional relationship of the product. 1, la, lb, lc...... Rolled material 2b, 2c+...... Rolling annular three 73b, 3c...・・・・・・・・・
・Roll axis BD・・・・・・・・・・・・・・・・・・
...Breakdown rolling mill R1...
・・・・・・・・・First rough rolling mill group R2・・・・・・・・・
・・・・・・・・・・・・・・・Second rough rolling mill group F...
・・・・・・・・・・・・・・・・・・ Finishing rolling mill I
T pasting・・・・・・・・・・・・・・・First rough rolling mill RU,・・・・・・・・・・・・・・・・・・
...First rough universal rolling mill IIL1.・・・・・・
・・・・・・・・・・・・Second rough universal rolling mill R
Ez・・・・・・・・・・・・・・・・・・Second etching rolling mill FU・・・・・・・・・・・・・・・・・・
...Finishing universal rolling machine R...
・・・・・・・・・Rolling machine for rolling both ends of the web of H-shaped steel Tea, Tab + Tea・・・・Thickness of both ends of the web Tea, Tcb, Tcc・・・・・・
・Thickness of the central part of the web Tfa, Tfb, Tfc...
...Flange thickness LIIA, Lllll, LI
IC・・・・・・Web inner width dimension and roll outer dimension

Claims (1)

[Claims] In the second rough rolling process, which rolls the rolled material that has been rolled into the rough product shape in the first rough universal rolling mill, the first rough edging rolling mill, the double-type first rough rolling mill, or the breakdown rolling mill. In a normal second rough rolling mill group, two rolling annular sleeves are fitted to the roll shaft coaxially and rotatably together with the roll shaft, and at least one of the annular sleeves is movable in the roll axis direction. Added a rolling mill equipped with a pair of upper and lower rolling rolls,
After the material to be rolled is rolled once or multiple times in the above-mentioned normal second rough rolling mill group to a predetermined size, the outer width of both annular sleeves of the rolling rolls of the added rolling mill is adjusted to the width of the rolled material. By rolling with the inner width of the web set larger than the inner width of the web, most of the area reduction at both ends of the web of the material to be rolled rolled with the annular sleeve is converted into an increase in the inner width of the web, and the inner width of the web is expanded between the two annular sleeves. a convex part forming step in which a convex part is formed in the central part of the web in a caliber section, and a finishing universal rolling mill in which rolling rolls having a similar structure to the rolling mill added to the second rough rolling mill group are incorporated into horizontal rolls. By rolling with the outer width of both annular sleeves of the horizontal roll set larger than the inner width of the web of the rolled material rolled in the above step, the rolled material web formed in the above protrusion forming step is rolled. A method for rolling a section steel, comprising carrying out a finish rolling process in which a convex portion in the central portion is smoothed and most of the area reduction of the convex portion is converted into an increase in the inner width of the web.