JP2002224704A - High performance h-shaped steel and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance H-shaped steel having fillet parts with excellent mechanical properties, especially toughness, and its manufacturing method. SOLUTION: An H-shaped steel is manufactured by rough rolling, intermediate rolling, and finish rolling in sequence. The axis of a horizontal roll is arranged at a location upstream of the rolling direction relative to the axis of a vertical roll on the final pass of the intermediate rolling, and/or on the pass of finish rolling, to reduce the inter-web width of the material-being-rolled by more than 40 mm. Consequently, an H-shaped steel is obtained such that the crystal grain size in the microstructure is 8.0 or more in the grain size number and the fillet parts have finer crystal grains than that of the central part of the web height or of the 1/4 width part from the end of the flange.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a high-performance H-section steel excellent in mechanical properties and a method for producing the same.

[0002]

2. Description of the Related Art H-section steel is made from a raw material such as a beam blank or a slab by a double-hole type roll roughing mill (hereinafter referred to as a BD rolling mill). Intermediate rolling, in which a rough material is rolled in a plurality of passes of an intermediate rolling mill row including one or two universal rough rolling mills and a double or four-roll edger rolling mill; It is manufactured by sequentially passing through finish rolling by one universal finishing mill.

FIG. 1 is a schematic diagram showing a cross-sectional shape of an H-section steel. Reference numeral 1 denotes a web, 2 denotes a flange, and 3 denotes a fillet portion. H is the web height, H _W is web inner width, B is the flange width, Tw is the web thickness, Tf is the flange thickness. b
1, b2 is the distance from the web to the tip of the flange (hereafter,
In the web, the depths b1, b2
Is called the web center deviation.

In recent years, high toughness has been required in all sections of H-section steel for the purpose of improving the earthquake resistance of buildings. That is, high toughness is required not only in the web 1 and the flange 2 in FIG. 1 but also in the fillet portion 3 which is a boundary portion between the web and the flange.

[0005] Since the web and the flange portion are directly rolled down by a roll and the total rolling reduction from the material to the product is large, high toughness is secured. Particularly, the web is rolled at a low temperature in the intermediate rolling under the influence of the roll cooling water, so that extremely high toughness can be obtained.

However, the temperature of the fillet is 100 ° C. or more higher than that of the web or the flange through rough rolling to finish rolling, it is difficult to directly reduce the fillet, and materials such as beam blanks and slabs are cast in the fillet. The mechanical properties of the fillet portion are inferior to those of the web or the flange due to, for example, inclusions accumulating during the process, and the variation in toughness is particularly large.

Further, a method has been proposed in which the temperature difference in the cross section is reduced by cooling the fillet portion with water during rolling to improve the toughness of the fillet portion. However, this method has a problem that the cooling of the cross section tends to be uneven.

Therefore, a method of improving the toughness of the fillet portion by adjusting the composition of the steel has been studied. However, the method of adjusting the components by adding an alloy element such as titanium has a problem that the production cost is increased.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the conventional problems and to provide a high-performance H-section steel having a fillet portion excellent in mechanical properties, particularly toughness, and a method for producing the same.

[0010]

In order to solve the above-mentioned problems, the present inventor has conceived a method of improving the toughness of a fillet portion by promoting metal flow from a web to a flange side in intermediate rolling or finish rolling. And diligently consider this method,
The following findings were obtained.

(A) In the final pass of intermediate rolling or the pass of finish rolling, the metal flows from the web to the flange side by reducing the inner width of the web by squeezing the flange in the height direction of the web. That is, the web of the material to be rolled before reducing the inner width of the web is finely grained by the reduction between the rough rolling and the intermediate rolling, and the metal at both ends of the web moves to the fillet portion due to the reduction in the inner width of the web. The fillet portion has a structure with a fine crystal grain size, and the toughness of the fillet portion is improved.

FIG. 2 is a schematic diagram illustrating the inner width of the web.
FIG. 3A is a cross-sectional view of a material to be rolled before finish rolling, and FIG.
Indicates the cross section of the H-beam after finish rolling. FIG. 2 (a),
As shown in (b), the inner web width H _W is defined by the intersection points 3 _P and 3 _{P of a} line A orthogonal to the rolling direction and passing through the center of the web thickness and a line B orthogonal to the rolling direction and passing through a plane inside the flange. Refers to the distance between Also, the fillet portion refers to a region including an intersection 3 _P at the boundary portion of the web and the flange. Note that FIG.
In (a) and (b), H is the web height, 1 is the web,
2 indicates a flange.

(B) If the reduction amount of the inner width of the web is small, the metal flow is small. (C) The reduction amount in the final pass of the intermediate rolling, or the reduction amount in the finishing rolling pass, or the total reduction amount of the reduction amount in the final pass of the intermediate rolling and the reduction amount in the finishing rolling pass. Is set to 40 mm or more, the ferrite crystal grain size of the fillet portion can be 8.0 or more as a crystal grain size number without water cooling the fillet portion during rolling. Thereby, the ferrite grain size number of the fillet portion is the same as the ferrite grain size number of the web height center portion or the flange 1/4 width portion, or the ferrite grain size number of the web height center portion or the flange 1/4 width portion. Can be larger. In addition, a fillet portion having higher toughness than the central portion of the web height or the 1/4 width of the flange can be obtained. In addition, the 1/4 width portion of the flange means a portion located at a position 1/4 of the flange width from the end of the flange toward the center of the flange.

(D) When the flange is narrowed in the height direction of the web by a universal rolling mill such as a universal rough rolling mill or a universal finishing mill, and the inner width of the web is reduced by 40 mm or more, the vertical roll is less than the horizontal roll. If the metal contacts the material to be rolled first, the central portion of the web height may buckle, and the metal flow from the web to the flange side may be insufficient.

(E) The horizontal roll axis of the universal roughing mill or the universal finishing mill is arranged so as to be upstream of the vertical roll axis in the rolling direction, and the thickness of the web is determined by the horizontal roll. After the rolling in the vertical direction is started, the flange is narrowed in the vertical direction of the web with a vertical roll to reduce the inner width of the web, thereby suppressing the buckling of the central portion of the web height. The flow can be increased. Further, since the buckling is suppressed, the occurrence of the deviation of the web center due to the reduction in the inner width of the web is also suppressed.

(F) In order to promote the metal flow,
The distance between the horizontal roll axis and the vertical roll axis in the rolling direction is preferably 40 mm or more. (G) When reducing the inner width of the web by 40 mm or more with a universal rolling mill such as a universal rough rolling mill or a universal finishing mill, the diameter of the vertical roll of the universal rolling mill (D
_{If V} ) is relatively larger than the horizontal roll diameter (D _H ), the restraint of the fillet portion by the horizontal roll is reduced, so that web buckling may occur and the center deviation of the web may increase.

(H) FIG. 3 shows the web center deviation of the product obtained by finishing rolling after reducing the inner width of the web by 50 mm in the final pass of the universal roughing mill and the diameter of the vertical roll of the universal roughing mill. it is a graph showing the relationship between the roll diameter ratio (D _V / D _H) and (D _V) and the horizontal roll diameter (D _H). As shown in FIG. 3, the roll diameter ratio (D _V /
By setting D _H ) to 0.6 or less, the web center deviation can be reduced.

The present invention has been completed based on the above findings, and the gist thereof is as follows. (1) An H-section steel manufactured by hot rolling,
A high-performance H-section steel, wherein the fillet portion of the section steel has a structure in which the ferrite grain size is 8.0 or more in grain size number.

(2) An H-section steel manufactured by hot rolling, wherein the ferrite grain size number at the fillet portion of the H-section steel is at the center of the web height or at the 1/4 width portion of the flange. A high-performance H-section steel having the same ferrite grain size as that of the ferrite grain size at the center of the web height or the quarter width portion of the flange.

(3) A method for producing an H-section steel through intermediate rolling in a plurality of passes by an intermediate rolling mill train and finish rolling in a single pass by a universal finish rolling mill, wherein the finish rolling is performed in a web of a material to be rolled. A method for producing a high-performance H-section steel, wherein the width is reduced by 40 mm or more.

(4) A method of manufacturing an H-section steel through a plurality of passes of intermediate rolling by a row of intermediate rolling mills and a finishing pass of one pass by a universal finishing mill, wherein a material to be rolled is produced in the final pass of the intermediate rolling. A method for producing a high-performance H-section steel, wherein the inner width of the web is reduced by 40 mm or more.

(5) A method for producing an H-section steel through a plurality of passes of intermediate rolling by a row of intermediate rolling mills and a finishing pass of one pass by a universal finishing mill, wherein the final pass of the intermediate rolling and the finish rolling A method for producing a high-performance H-section steel, wherein the web inner width of the material to be rolled is reduced by a total of 40 mm or more.

(6) The universal finishing mill according to the above (3) or (5), wherein the axis of the horizontal roll in the universal finishing mill is arranged upstream of the axis of the vertical roll in the rolling direction. Manufacturing method of high performance H-section steel.

(7) The intermediate rolling mill row is composed of two universal rough rolling mills and an edger rolling mill, and one of the two universal rough rolling mills has a horizontal roll of one universal rough rolling mill. The method for producing a high-performance H-section steel according to the above item (4) or (5), wherein the shaft core is disposed upstream of the shaft center of the vertical roll in the rolling direction.

(8) The high performance according to the above (6) or (7), wherein the distance between the axis of the horizontal roll and the axis of the vertical roll in the rolling direction is 40 mm or more. Method for producing H-section steel.

(9) The ratio (D _V / D _H ) of the diameter (D _V ) of the vertical roll to the diameter (D _H ) of the horizontal roll is 0.
The method for producing a high-performance H-section steel according to any one of the above (6) to (8), wherein the number is 6 or less.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a high-performance H-section steel and a method of manufacturing the same according to the present invention will be described with reference to the accompanying drawings.

FIG. 4 is a schematic view showing a production line for high-performance H-section steel for explaining the embodiment. FIG. 4 (a) shows a universal rough rolling mill (UR mill) behind a BD rolling mill (BD mill). And a double finishing edge mill (E mill), and a production line in which a universal finishing mill (UF mill) is arranged behind the row of intermediate rolling mills. FIG. A row of intermediate rolling mills consisting of a universal roughing mill (UR1 mill), a double edger rolling mill (E mill) and a universal roughing mill (UR2) is arranged behind the mill (BD mill). It is a figure which shows the manufacturing line in which the finishing mill (UF1 mill) was arranged.
4A and 4B, reference numeral 11 denotes a heating furnace, 12 denotes a BD mill, 13 denotes a UR mill, 14 denotes an E mill, 15 denotes a UF mill,
16 represents a UR1 mill, 17 represents a UR2 mill, and 18 represents a UF1 mill.

The heating furnace 11 shown in FIGS. 4A and 4B is a known heating furnace for heating a slab or a beam blank, which is a material of the H-section steel, to a predetermined temperature. BD of FIGS. 4A and 4B
The mill 12 is a known double-type rolling mill for rolling a beam blank or a slab into a coarse material.

The UR mill 13 shown in FIG. 4 (a) includes a pair of horizontal rolls and a pair of vertical rolls. The horizontal roll lowers the web in the thickness direction, and the horizontal roll and the vertical roll form a flange. It is a well-known universal rolling mill that reduces in the direction.

The E-mill 14 shown in FIGS. 4A and 4B is a known double-type rolling mill for adjusting the flange width by pressing down the flange in the width direction. FIG. 5 shows the UF mill 1 shown in FIG.
It is a schematic diagram which shows the positional relationship of the horizontal roll axis and the vertical roll axis of No. 5. Reference numeral 15a denotes a horizontal roll, 15b denotes a vertical roll, 15a-1 denotes a line passing through the horizontal roll axis and parallel to the vertical roll axis, 15b-1 denotes a vertical roll axis, and L denotes a horizontal roll axis. And the distance in the rolling direction between the vertical roll and the axis of the vertical roll.

As shown in FIG. 5, the UF mill 15 includes a pair of horizontal rolls 15a and a pair of vertical rolls 15b.
The horizontal roll 15a is arranged such that the axial position of the horizontal roll 15a is upstream of the vertical roll axial position in the rolling direction at a distance L in the rolling direction between the horizontal roll axis and the vertical roll axis. In the UF mill, the web is reduced in the thickness direction by the horizontal roll 15a, and the horizontal roll 15a and the vertical roll 15 are pressed.
b, the flange is reduced in the thickness direction, and the vertical roll 15a is used to narrow the flange in the web height direction to reduce the inner width of the web.

The UR1 mill 16 shown in FIG. 4 (b) includes a pair of horizontal rolls and a pair of vertical rolls, and the web is pressed down in the thickness direction by the horizontal rolls, and the flange is formed by the horizontal rolls and the vertical rolls in the thickness direction. Is a known universal rolling mill.

FIG. 6 is a schematic diagram showing the positional relationship between the horizontal roll axis and the vertical roll axis of the UR2 mill 17 in FIG. 4 (b). 17a is a horizontal roll, 17b is a vertical roll, 17a-1 is a line passing through the axis of the horizontal roll and parallel to the axis of the vertical roll, 17b-1 is the axis of the vertical roll,
L represents the distance in the rolling direction between the axis of the horizontal roll and the axis of the vertical roll.

As shown in FIG. 6, the UR2 mill 17 includes a pair of horizontal rolls 17a and a pair of vertical rolls 17b, and a distance in the rolling direction between the axis of the horizontal roll and the axis of the vertical roll. In L, it is arranged such that the axis position of the horizontal roll is upstream of the axis position of the vertical roll in the rolling direction.
In the UR2 mill, the web is reduced in the thickness direction by a horizontal roll 17a, and a horizontal roll 17a and a vertical roll 17b are pressed.
Then, the flange is lowered in the thickness direction, and further, the flange is narrowed in the web height direction by the vertical roll 17a to reduce the inner width of the web.

FIG. 7 is a schematic diagram showing an example of the shape of the horizontal roll and the vertical roll of the UR2 mill 17 of FIG. 4B. Reference numeral 17a denotes a horizontal roll, 17b denotes a vertical roll, 20 denotes a hole formed by a horizontal roll and a vertical roll, and 21 denotes a material to be rolled.

As shown in FIG. 7, in the UR2 mill, it is desirable that the horizontal roll 17a and the vertical roll 17b form a die 20 and the horizontal roll 17a restrains the front end of the flange of the material 21 to be rolled. . By restricting the flange tip and rolling as described above, it is possible to suppress the deviation of the web center, which tends to occur with the reduction of the inner width of the web.

The UF1 mill 18 shown in FIG. 4B is provided with a pair of horizontal rolls and a pair of vertical rolls. The horizontal rolls lower the web in the thickness direction, and the horizontal rolls and the vertical rolls form the flange in the thickness direction. A known universal rolling mill may be used, and the same as the UF mill 15 described above may be used.

In the production line shown in FIG.
1. A material such as a beam blank or a slab heated to a predetermined temperature in step 1 is rolled into a H-shaped steel rough material by a BD mill 12, and the rough material is then intermediate-rolled into a UR mill 13 and an E mill 14. A predetermined shape is formed by reciprocating rolling in a plurality of passes in the machine train, and the H-shaped steel having the target dimensions is finished in one pass of the final UF mill 15.

The method of the present invention reduces the inner width of the web by narrowing the flange in the height direction of the web in the final pass of the UF mill 15 when manufacturing the H-section steel on the manufacturing line shown in FIG. Hereinafter, this method is referred to as a first method.

The reduction of the inner web width in the first method is as follows.
This is possible by making the horizontal roll width of the UR mill 13 larger than the horizontal roll width of the UF mill 15. By reducing the inner width of the web by the UF mill pass, metal flows from the web to the flange side, and the fillet portion becomes a fine-grained structure and the toughness is improved. In order to adjust the reduction amount of the inner web width, it is desirable to use a variable width roll having a variable horizontal roll width as the horizontal roll of the UF mill.

In the production line shown in FIG.
The material such as a beam blank or a slab heated to a predetermined temperature is rolled into a H-shaped steel coarse material by a BD mill 12, and then,
The coarse material is formed into a predetermined shape by reciprocating rolling in a plurality of passes of an intermediate rolling mill train including a UR1 mill 16, an E-mill 14, and a UR2 mill 17, and a final pass of the UF1 mill 18 produces an H-beam having the desired dimensions. Finish.

According to another method of the present invention, in the production of an H-section steel in the production line shown in FIG. 4B, the flange of the material to be rolled is narrowed in the web height direction in the final pass of the UR2 mill 17 to reduce the web height. Reduce inner width. Hereinafter, this method is referred to as a second method.

The reduction of the web inner width in the second method is as follows.
This is possible by making the horizontal roll width of the UR1 mill 16 larger than the horizontal roll width of the UR2 mill 17. UR
By reducing the inner web width in the final 2 mil pass,
The metal flows from the web to the flange side, and the fillet portion becomes a fine-grained structure, improving the toughness. In addition,
In order to adjust the reduction amount of the inner web width, it is desirable to use a variable width roll having a variable horizontal roll width as the horizontal roll of the UR1 mill.

In these methods, the reduction amount of the inner width of the web is set to 40 mm or more. If the reduction amount is less than 40 mm, the flow of the metal from the web to the flange side is insufficient, and the improvement in the toughness of the fillet portion may be insufficient. The upper limit of the reduction amount is not particularly limited, but practically, the upper limit is about 100 mm from the viewpoint of biting properties.

In the first method, in one pass of the UF mill, and in the second method, in the last pass of the UR2 mill, the reduction amount is set to 40 mm or more to reduce the inner width of the web. In the production line of (1), the reduction of the inner web width may be performed in both the last pass of the UR2 mill and one pass of the UF1 mill. In this case, the reduction amount of the web inner width is
The sum of the reduction amount in the final pass of the UR2 mill and the reduction amount in the UF1 mill should be 40 mm or more. This method is called a third method.

In the first method, as shown in FIG.
The axial center position of the horizontal roll 15a of the mill 15 is set to the vertical roll 1
It is preferable that the web 5b is arranged so as to be upstream of the axial center position in the rolling direction, and the inner width of the web is reduced in the final pass of the UF mill.

In the second method, as shown in FIG. 6, the axis of the horizontal roll 17a of the UR2 mill 17 is arranged upstream of the axis of the vertical roll 17b in the rolling direction. It is desirable to reduce the inner web width in the final pass of the UR2 mill.

In the third method, the position of the axis of the horizontal roll 17a of the UR2 mill 17 is arranged upstream of the position of the axis of the vertical roll 17b in the rolling direction.
The inner width of the web is reduced in the final pass of the mill, and the UF1
It is desirable to arrange the axis position of the horizontal roll of the mill 18 so as to be upstream of the axis position of the vertical roll in the rolling direction, and to reduce the inner width of the web in the final pass of the UF1 mill.

In order to reduce the inner width of the web and allow the metal to flow from the web to the flange side, it is important to prevent the buckling of the web. However, as shown in FIGS. By arranging the center of the web to be upstream of the axis of the vertical roll in the rolling direction, the deformation of the web due to the reduction of the inner width of the web is concentrated at both ends of the web, so that the web buckles. Can be suppressed.

It is desirable that the distance between the axis of the horizontal roll and the axis of the vertical roll in the rolling direction is 40 mm or more. If the distance is less than 40 mm, the buckling of the web may occur, particularly when the amount of reduction in the inner width of the web is large.

When reducing the inner width of the web, it is important to reduce the center deviation of the web. When the roll diameter ratio of the universal mill used for reducing the inner width of the web is 0.6 or less, the occurrence of the center deviation of the web is reduced. Can be suppressed. Therefore, in the first method, the roll diameter ratio of the UF mill is set to 0. In the second method, the roll diameter ratio of the UR 2 mill is set to 0.
It is desirable to set it to 6 or less. In the third method, U
It is desirable that the roll diameter ratio between the F1 mill and the UR2 mill be 0.6 or less.

By these methods, an H-section steel having a fillet portion having a structure having a ferrite grain size of 8.0 or more in grain size number and having high toughness in all cross sections can be obtained. Further, according to these methods, the ferrite grain size number is the same as the ferrite grain size number at the center of the web height or the 1/4 width of the flange, or the ferrite grain size at the center of the web height or the 1/4 width of the flange. An H-section steel having a fillet portion having a structure larger than the number and having high toughness in all cross sections is obtained. The above structure may be a sized structure or a striped structure. In the case of a striped structure, the ferrite grain size refers to the grain size of ferrite in a ferrite band. Here, the fillet portion is, as described above, a boundary portion between the web and the flange, but in this specification, for convenience, a line perpendicular to the rolling direction and passing through the center of the web thickness, and a flange perpendicular to the rolling direction, It refers to a region including an intersection with a line passing through the inner plane, and the region refers to a range in which the crystal grain size can be measured. Therefore, the ferrite grain size at the intersection is defined as the ferrite grain size at the fillet portion.

In the present invention, for example, C: 0.06 to 0.2
4% by mass, Si: 0.10 to 0.55% by mass, Mn:
It is suitable for an H-beam containing a chemical component of 0.5 to 1.6% by mass.

[0055]

(Example 1) A UF mill as shown in FIG. 5 was arranged on the production line shown in FIG. 4 (a). The distance L between the axis of the horizontal roll of the UF mill and the axis of the vertical roll in the rolling direction is 50 mm, the horizontal roll of the UF mill is a variable width roll, and the horizontal roll width of the UF mill is 468 mm, UR
The horizontal roll width of the mill was 508 mm.

Using this apparatus, a web height of 500 m
m, a flange width of 200 mm, a web thickness of 10 mm, and a test for producing an H-section steel having a flange thickness of 16 mm were performed. That is, a web height of 700 mm, a flange width of 450 mm,
After heating a beam blank made of low carbon steel (C: 0.12% by mass, Si: 0.36% by mass, Mn: 0.80% by mass) having a web thickness of 120 mm to 1250 ° C. in a heating furnace, B
9 passes of D mill, web height 690mm, web thickness 45
mm of H-section steel. Next, reciprocating rolling of 9 passes is performed in an intermediate rolling mill train composed of a UR mill and an E mill to reduce the inner width of the web to 508 mm. H
It was finished in a shape steel (Test No. 1).

For comparison, in the production line of FIG.
The horizontal roll width of the UR mill is set to 468 mm, which is the same as the horizontal roll width of the UF mill, and the beam blank is made into a rough piece having a web height of 650 mm and a web thickness of 45 mm by a BD mill. 9 rows of reciprocating rolling are performed in a row, and finally the H
A test for finishing into a shaped steel was performed (Test No. 2). Test No. In the case of 2, the reduction amount of the web inner width in the UF mill is 0 m
m. In the following, Test No. After each reciprocating rolling of Nos. 1 and 2, the material to be rolled before the final finishing pass is referred to as a UR release material.

The microstructure and ferrite grain size of the center of the web height, the 1/4 width of the flange, and the fillet of the H-section steel obtained by this rolling were investigated.
The toughness values of the central portion of the web height, the 1/4 width of the flange, and the fillet portion in the H-section steel and the UR free material were measured.

FIG. 8 is a cross-sectional view of the UR release material and the H-section steel showing the measurement position of the toughness. FIG.
(B) is an H-section steel. The symbol is the center of the web height of the H-section steel, the 1/4 width portion of the flange of the H-section steel, the fillet of the H-section steel, the center of the web height of the UR release material,
Is a fillet portion of the UR release material.

Table 1 shows the results of the investigation of the microstructure and ferrite grain size of the H-section steel, and Table 2 shows the results of measurement of the toughness values of the H-section steel and the UR as-cast material.

[0061]

[Table 1]

[0062]

[Table 2]

As shown in Tables 1 and 2, Test No. In No. 1, an H-section steel having a fillet portion having a finer grain than the 1/4 width portion of the flange and having a ferrite crystal grain size of 8.3 with a grain size number of 8.3 is obtained. However, the toughness value of the fillet portion as the H-section steel was the same as in Test No. This was greatly improved as compared with No. 2 and showed a high toughness value in all cross sections. On the other hand, Test No. In Comparative Example 2, the ferrite crystal grain size of the fillet portion of the H-section steel was 6.7.

Example 2 A UR2 mill as shown in FIG. 6 was arranged on the production line shown in FIG. 4B. The horizontal distance between the axis of the horizontal roll of the UR2 mill and the axis of the vertical roll is 55 mm, the horizontal roll of the UR1 mill is a variable width roll, and the horizontal roll width of the UR1 mill is 610 m.
m, the horizontal roll width of the UR2 mill was 560 mm.

Using this apparatus, a web height of 600 m
m, a flange width of 300 mm, a web thickness of 12 mm, and a test for producing an H-section steel having a flange thickness of 20 mm were performed. That is, made of low-carbon steel having a width of 1500 mm and a thickness of 250 mm (C: 0.12% by mass, Si: 0.36% by mass, Mn:
0.80% by mass) was heated to 1250 ° C. in a heating furnace, and the web height was 850 mm with 19 passes of a BD mill.
It was rolled into a beam blank having a web thickness of 80 mm. Next, reciprocating rolling of 15 passes is performed between the UR1 mill and the E mill, and in the final 15th pass, the inner web width is reduced by 50 mm by the UR2 mill to reduce the inner web width to 560 mm.
An H-section steel having a target size was finished with a UF1 mill with the reduction amount of the inner width of the web being 0 mm (Test No. 3). In addition,
In the UR2 mill, as shown in FIG. 6, a hole was formed by a horizontal roll and a vertical roll, and the front end of the flange was constrained by a horizontal roll to prevent the center of the web from being decentered due to the reduction in the inner width of the web.

For comparison, in the production line of FIG.
The horizontal roll width of the UR1 mill is 560 mm, which is the same as the horizontal roll width of the UR2 mill. The slab is formed into a coarse piece having a web height of 800 mm and a web thickness of 45 mm by a BD mill. And the final 15th pass was further rolled by a UR2 mill, and then a test was performed by a UF1 mill to finish it into an H-beam having the desired dimensions (Test No. 4). Test No. In No. 4, in the UR2 mill and the UF1 mill, the reduction amount of the inner width of the web is both 0 mm. In the following, Test No. 3,
The material to be rolled after each reciprocating rolling of No. 4 is referred to as a UR release material.

In the same manner as in Example 1, the microstructure and ferrite crystal grain size of the central portion of the web height, the 1/4 width of the flange, and the fillet portion of the H-section steel obtained by this rolling were investigated, and the H-section steel was obtained. Then, the toughness values of the web height center portion, the flange 1/4 width portion, and the fillet portion of the UR release material were measured.

Table 3 shows the results of investigation of the microstructure and ferrite grain size of the H-section steel, and Table 4 shows the results of measurement of the toughness values of the H-section steel and the UR as-cast material.

[0069]

[Table 3]

[0070]

[Table 4]

As shown in Tables 3 and 4, Test No. In No. 3, an H-section steel having a fillet portion having a finer grain than the 1/4 width portion of the flange and having a ferrite crystal grain size of 8.3 with a grain size number of 8.3 is obtained. In both cases, the toughness value of the fillet portion was the same as in Test No. 4 was significantly improved as compared with No. 4 and showed a high toughness value in all cross sections. on the other hand,
Test No. In Comparative Example No. 4, the ferrite grain size of the fillet portion of the H-section steel was 6.5.

Example 3 A UR2 mill as shown in FIG. 6 was arranged on the production line shown in FIG. 4B. In the UR2 mill, the horizontal distance between the horizontal roll axis and the vertical roll axis is 50 mm, and the roll diameter ratio is 0.55.
The horizontal roll was a fixed width roll having a horizontal roll width of 468 mm. The horizontal roll width of the UR1 mill was 518 mm. Using this device, web height 500mm, flange width 200mm, web thickness 10mm, flange thickness 16
A test was conducted to produce an H-section steel of mm.

That is, a slab made of low-carbon steel (C: 0.12% by mass, Si: 0.36% by mass, Mn: 0.80% by mass) was heated to 1250 ° C. in a heating furnace, and then heated by a BD mill. Web height 738mm (Web width 518m) with 15 passes
m, flange thickness 110 mm) and a web blank with a web thickness of 80 mm. Next, reciprocating rolling of 9 passes is performed between the UR1 mill and the E mill, and the inner width of the web is reduced by 50 mm and the inner width of the web is reduced to 468 by the UR2 mill in the final 9th pass.
mm, the reduction amount of the web inner width is set to 0 mm, and the UF
Finished in 1 mil into H-section steel of desired dimensions (Test N
o. 5). In the UR2 mill, as shown in FIG.
A hole was formed by the horizontal roll and the vertical roll, and the front end of the flange was restrained by the horizontal roll in order to prevent the web center deviation due to the reduction in the inner width of the web.

For comparison, in the production line shown in FIG. 4B, the horizontal roll width of the UR1 mill was 468 mm, which is the same as the horizontal roll width of the UR2 mill, and the slab was 708 mm in web height and 80 mm in web thickness in a BD mill. Rolled into a beam blank, followed by reciprocating rolling of 9 passes by a UR1 mill and an E mill, and further rolling by a UR2 mill in the final 9th pass, and thereafter, an H-shape of a target size by a UF1 mill A test for finishing steel was performed (Test No. 6). Test N
o. 6, in both UR2 mill and UF1 mill,
The reduction amount of the web inner width is 0 mm.

The microstructure and ferrite grain size of the center of the web height, the 1/4 width of the flange, and the fillet of the H-section steel obtained by this rolling were investigated.
The toughness values of the web height center, flange 1/4 width and fillet were measured.

Table 5 shows the microstructure and ferrite grain size of the H-section steel, and Table 6 shows the measurement results of the toughness of the H-section steel.
Shown in

[0077]

[Table 5]

[0078]

[Table 6]

As shown in Tables 5 and 6, Test No. In No. 5, an H-section steel having a fillet portion having a stripe structure with a grain size smaller than the quarter width of the flange and having a ferrite crystal grain size of 8.8 is obtained, and the toughness value of the fillet portion of the H-section steel is as follows. Test No. 6 significantly improved, and showed a high toughness value in all cross sections. On the other hand, Test No. In No. 6, the ferrite grain size of the fillet portion of the H-section steel was 6.7 in grain size number.
Met.

The test No. In No. 5, the web center deviation was small and good. (Example 4) A UR2 mill as shown in FIG. 6 was arranged on the production line shown in FIG. 4 (b). In the UR2 mill, the horizontal distance between the horizontal roll axis and the vertical roll axis was 50 mm, the roll diameter ratio was 0.55, the horizontal roll was a variable width roll, and the horizontal roll width was 860 mm. . The horizontal roll width of the UR1 mill was 910 mm.
Using this apparatus, a test for producing an H-section steel having a web height of 900 mm, a flange width of 300 mm, a web thickness of 16 mm, and a flange thickness of 28 mm was performed.

That is, a slab made of low-carbon steel (C: 0.12% by mass, Si: 0.36% by mass, Mn: 0.80% by mass) is heated to 1250 ° C. in a heating furnace, and then is heated by a BD mill. Web height 1130mm (Web inner width 910) in 15 passes
mm, flange thickness 110 mm) and a web blank having a web thickness of 80 mm. Next, reciprocating rolling of 9 passes is performed between the UR1 mill and the E mill, and UR2 is passed in the last 9 passes.
The inner width of the web was reduced by 50 mm with a mill and the inner width of the web was reduced to 86 mm.
0 mm, and further increase the inner width of the web by 8 mm with a UF1 mill.
It was finished to the H-shaped steel of the target size while reducing (Test No. 7). In the UR2 mill, as shown in FIG. 6, a hole was formed by a horizontal roll and a vertical roll, and the front end of the flange was restrained by a horizontal roll in order to prevent the center of the web from being decentered due to the reduction in the inner width of the web.

For comparison, in the production line shown in FIG. 4B, the horizontal roll width of the UR1 mill is 468 mm, which is the same as the horizontal roll width of the UR2 mill, and the slab is 844 mm in web height and 80 mm in web thickness in a BD mill. Rolled into a beam blank, followed by reciprocating rolling of 9 passes by a UR1 mill and an E mill, and further rolling by a UR2 mill in the final 9th pass, and thereafter, an H-shape of a target size by a UF1 mill A test for finishing steel was performed (Test No. 8).

The microstructure and ferrite grain size of the central portion of the web height, the 1/4 width of the flange, and the fillet portion of the H-section steel obtained by this rolling were investigated.
The toughness values of the web height center and fillet were measured.

Table 7 shows the results of investigation of the microstructure and ferrite grain size of the H-section steel, and Table 8 shows the results of measurement of the toughness value of the H-section steel.
Shown in

[0085]

[Table 7]

[0086]

[Table 8]

As shown in Tables 7 and 8, Test No. In No. 7, an H-section steel having a fillet portion having a stripe structure with a ferrite grain size smaller than the 1/4 width portion of the flange and having a ferrite crystal grain size of 8.5 by particle number is obtained. The toughness value of the fillet portion of the H-section steel is Test No. The value was greatly improved as compared with No. 8, and a high toughness value was exhibited in all cross sections. On the other hand, Test No. In No. 8, the ferrite grain size of the fillet portion of the H-section steel was 6.5 in grain size number.
Met.

The test No. In No. 5, the web center deviation was small and good.

[0089]

According to the present invention, the toughness of the fillet can be effectively increased, and the H-shaped steel can be used for applications requiring higher strength as compared with the conventional steel. Combined with the fact that it is easy to manufacture, its practical significance is great.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a cross-sectional shape of an H-section steel.

FIGS. 2A and 2B are schematic diagrams illustrating the inner width of a web, wherein FIG. 2A shows a cross section of a material to be rolled before finish rolling, and FIG. 2B shows a cross section of an H-section steel after finish rolling.

FIG. 3 is a graph showing a relationship between a web center deviation and a roll diameter ratio (D _V / D _H ).

FIG. 4 is a schematic view showing a production line of a high-performance H-section steel for explaining an embodiment, and FIG. 4 (a) shows a BD rolling mill, an intermediate rolling mill row (a universal rough rolling mill and a double edger rolling mill). )
A production line in which a universal finishing mill is arranged, FIG. 12B shows a BD rolling mill, an intermediate rolling mill (universal rough rolling mill, double type edger rolling mill and universal rough rolling mill),
This production line has a universal finishing mill.

FIG. 5 is a schematic diagram showing a positional relationship between a horizontal roll axis and a vertical roll axis of the UF mill 15 in FIG.

FIG. 6 is a schematic diagram showing a positional relationship between a horizontal roll axis and a vertical roll axis of the UR2 mill 17 of FIG. 4 (b).

FIG. 7 is a schematic diagram showing an example of the shape of a horizontal roll and a vertical roll of the UR2 mill 17 of FIG. 4 (b).

FIG. 8 is a cross-sectional view of a UR release material and an H-section steel showing a measurement position of toughness, wherein FIG. 8A shows a UR release material and FIG. 8B shows an H-section steel.

[Explanation of symbols]

1: web, 2: flange, 3: fillet, 11:
Heating furnace, 12: BD mill, 13: UR mill, 14: E mill, 15: UF mill, 15a: horizontal roll, 15b: vertical roll, 16: UR1 mill, 17: UR2 mill, 17
a: Horizontal roll, 17b: Vertical roll 18: UF1 mill, 20: Hole type, 21: Rolled material.

Claims (9)

[Claims] 1. An H-shaped steel produced by hot rolling, wherein a fillet portion of the H-shaped steel has a structure in which a ferrite grain size is 8.0 or more in grain size number. H-section steel. 2. An H-section steel manufactured by hot rolling, wherein the ferrite grain size number of a fillet portion of the H-section steel is the same as the ferrite grain size number of a central portion of a web height or a 1/4 width portion of a flange. A high-performance H-section steel having the same or a larger ferrite grain size number at the center of the web height or the quarter width of the flange. 3. A method for producing an H-section steel through intermediate rolling in a plurality of passes by an intermediate rolling mill train and finish rolling in a single pass by a universal finish rolling mill, wherein the finish rolling includes a web inner width of a material to be rolled. A method for manufacturing a high-performance H-section steel, wherein 4. A method for producing an H-section steel through a plurality of passes of intermediate rolling by a row of intermediate rolling mills and a finish rolling of one pass by a universal finish rolling mill, wherein a material to be rolled is processed in a final pass of the intermediate rolling. A method for manufacturing a high-performance H-section steel, wherein the inner width of a web is reduced by 40 mm or more. 5. A method for producing an H-section steel through a plurality of passes of intermediate rolling by a row of intermediate rolling mills and a finishing pass of one pass by a universal finishing mill, wherein a final pass of the intermediate rolling, the finish rolling, A method for producing a high-performance H-section steel, characterized in that the web inner width of the material to be rolled is reduced by 40 mm or more in total. 6. The high-performance H-section steel according to claim 3, wherein the axis of the horizontal roll in the universal finishing mill is arranged upstream of the axis of the vertical roll in the rolling direction. Production method. 7. The intermediate rolling mill row is composed of two universal rough rolling mills and an edger rolling mill, and a horizontal roll shaft of one of the two universal rough rolling mills. The method for producing a high-performance H-section steel according to claim 4 or 5, wherein the core is disposed upstream of the axis of the vertical roll in the rolling direction. 8. The method for producing a high-performance H-section steel according to claim 6, wherein the distance between the axis of the horizontal roll and the axis of the vertical roll in the rolling direction is 40 mm or more. . 9. The ratio (D _V / D _H ) of the diameter (D _V ) of the vertical roll to the diameter (D _H ) of the horizontal roll is 0.6 or less. 9. The method for producing a high-performance H-section steel according to any one of 8.