JP2001113302A - Rolling method for preventing rolling crack on continuously cast billet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rough-rolling method of a bar steel whose rolling crack at the inner and the outer parts is hardly generated by using flat rolls, even when a continuously cast billet is directly fed into a rolling line without cooling and continuously rolling after welding the cast billets. SOLUTION: In the continuous rolling of the bar steel continuously rolled after welding the cast billet, when the bar steel is produced with the rolling by directly feeding the continuously cast billet, this rolling method is executed by using the continuously cast billet having the round cross section, and using caliber rolls at the first pass for rough rolled forming pass and the flat rolls on and after the second pass for rougher roll. This rolling method has the peculiarity, in which the pushing force is loaded to the cast billet at the inlet side of the first pass for rough rolled forming pass to prevent the rolling crack in the continuously cast billet.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for rolling a steel bar such as a bar and a wire rod, and more particularly to a method for continuously rolling a steel bar by welding a billet slab manufactured by a continuous casting method.
The present invention relates to a rolling method capable of preventing a billet from rolling on the inner and outer surfaces and producing a high-quality strip.

[0002]

2. Description of the Related Art Generally, billet slabs are manufactured by reducing the cross-sectional size by continuous casting. Although the slab shape after billet continuous casting is generally a square cross section, there was a problem of internal cracking due to unevenness in the solidification process. In Japanese Patent Application Laid-Open No. 5-42304, uniformity of solidification in a mold is maintained by using a slab having a round cross-sectional shape obtained by continuous casting as a strip steel rolling material, and the solidified structure is caused by non-uniformity. There has been proposed a method for preventing cracking during solidification.

[0003] As a method for rolling a strip or wire rod using billet slabs, a rolling method using a hole-shaped roll is generally used.
For the purpose of improving the operation rate, a method called caliber-less rolling, in which rolling is performed in a plurality of passes using a flat roll in the rough rolling and intermediate rolling stages and a hole-shaped roll is used in the finishing pass, for example, is disclosed in Japanese Patent Publication No. -37582, JP-A-58-58
No. 23502, JP-A-58-68402 and the like. This rolling method has a low area reduction rate,
There is no need to change the roll depending on the product size,
Excellent economy. However, on the other hand, it is necessary to strongly reduce the pressure in the first pass of the rough rolling in order to increase the area reduction efficiency, and the flat roll is used, so that there is a problem that rolling cracks are easily generated on the billet side surface.

A technique of continuously welding and cutting billet slabs manufactured and cut by continuous casting in recent years using flash butt welding or the like is disclosed in Japanese Patent Laid-Open No. 9-66.
No. 301, JP-A-9-66302, JP-A-9-302
-85301.

[0005]

In rolling bar steel, billet slabs having a rectangular cross section manufactured by continuous casting are generally used. There is a problem that internal cracks are easily generated during rolling. However, even when this problem is avoided by using a billet slab having a round cross section, when the caliber-less rolling method using the flat roll is applied thereto,
In the rough rolling by the flat roll, the round section has a problem that the tensile stress in the rolling direction generated on the side face of the billet is larger than that of the square section, and the round section tends to cause rolling cracks.

When the caliber-less rolling method is applied at a high temperature without cooling the continuous cast billet irrespective of the cross-sectional shape, the billet slab is not transformed and has large crystal grains. There was a problem that the susceptibility to rolling crack was high.

[0007] Therefore, when rolling by a flat roll without cooling a continuous cast billet having a round cross section without cooling, there is a problem that rolling cracks are very likely to occur. When continuous rolling is applied here, in addition to the above-mentioned problems, the welded portion obtained by welding the billet slab has a high temperature, so that there is a problem that the material strength of the welded portion is reduced and further rolling cracks are likely to occur. .

[0008] The present invention solves the above-mentioned problems, and sends a continuously cast billet slab directly to a rolling line without cooling.
It is an object of the present invention to provide a method for rough rolling of a steel bar using flat rolls, in which even when a billet slab is welded to be continuous and rolled, internal and external rolling cracks are less likely to occur.

[0009]

The above object is achieved by the following invention. In producing a steel bar by direct-feed rolling from a continuous cast billet slab, in the continuous rolling of a steel bar in which the billet slab is welded and continuously rolled, using a continuous cast billet slab having a round cross section, a rough rolling forming pass In the rolling method, a hole roll is used in the first pass and a flat roll is used in the rough rolling in the second and subsequent passes, wherein the billet slab is formed on the entry side of the first pass of the rough rolling forming pass. A rolling method for preventing rolling cracks in a continuously cast billet slab, wherein a rolling force is applied to the billet.

In the present invention, direct rolling refers to rolling a cast billet at a high temperature without cooling it to a temperature below the A3 transformation point, and includes a case where a small amount of heating is performed for reheating before rolling. It is. In the present invention, since a round cross-sectional shape is used as a billet slab, internal cracks are less likely to occur during the solidification process and rough rolling than when a square cross-section is used. Furthermore, by using a grooved roll in the first pass of rough rolling, the billet side surface is compressed in the width direction by the grooved slope,
The tensile stress in the rolling direction generated when the side surface of the billet is stretched in the rolling direction is smaller than that in flat roll rolling, so that even when a round cross-section billet is used, rolling cracks on the side surface of the billet are less likely to occur. In addition, due to the restraint of the grooved roll, a surface reduction efficiency equivalent to that of the flat roll can be obtained with a small rolling reduction, and the tensile stress in the rolling direction generated on the side surface of the billet becomes smaller than that of the flat roll rolling. Rolling cracks on the side surface are less likely to occur. The temperature of the side of the welded portion of the billet slab where the material strength is reduced due to the high temperature is reduced by heat removal by the hole-shaped slope of the hole-shaped roll, so that the material strength is increased and rolling cracks occur. It becomes difficult.

If a pushing force is applied to the billet slab at the entry side of the first pass of the rough rolling forming pass, the rolling occurs in the entire cross-sectional rolling direction of the billet slab during rolling in the first pass of the rough rolling forming pass. Tensile stress is reduced by the indentation force. In particular, this effect is remarkable on the side of the billet slab that does not touch the rolling roll during rolling, so that rolling cracks on the side of the billet slab hardly occur. When the pushing roller is not driven, the pushing roller is pulled out, but in the present invention, a pushing force is applied by using a driving type pushing roller.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A billet having a round cross section used in the present invention is manufactured by a continuous casting method. A round billet cast by a continuous casting machine at two or more locations and cut to a predetermined length,
Rolling is performed after direct feeding at high temperature without cooling and joining by flash butt welding. The welding for the continuity may be high-frequency heating welding, a laser welding method, or the like. After welding, the joint is deburred, and a rolling roller having a driving source is used to press the billet slab into the rolling mill, which is arranged on the entry side of the first pass of the rough rolling forming pass, and applies a pressing force in the rolling direction, Rolling is continuously performed by a rolling mill train to produce a steel bar product. If the temperature of the billet decreases during the transportation, heating may be performed before rolling. FIG. 1 shows an embodiment of the present invention. FIG. 1 shows the change in the shape of the billet in the cross-sectional direction in each step (pass) of the process of the present invention and the rough rolling. The flash butt welding device 1, the deburring device 2,
The pushing drive roller 3 and the rough rolling mill 4 are arranged in this order. Using a round-section billet 5 as a continuous cast billet slab, a hole roll for the first rolling (rough one pass) of rough rolling.
Roll 6 in the longitudinal direction (or transverse direction), and then the flat roll 7 in the second rolling (rough 2 passes) of the rough rolling
In the subsequent rough rolling process, flat rolls are alternately arranged in a direction orthogonal to the previous pass to perform rough rolling. For the subsequent finish rolling, bar and wire products will be manufactured using the commonly used hole rolls. In the intermediate rolling, a flat roll may be used, or a grooved roll may be used. In the subsequent finish rolling, a flat roll may be used halfway and a grooved roll may be used for the minimum number of passes, or a bar / wire product may be manufactured using a holed roll for all passes. . If a roll of an oval caliber or a box caliber is used as the roll of the hole type, there is an effect of preventing cracking.

As the pushing roller, a vertical or horizontal roller can be used. If the first pass of the rough rolling forming pass is a horizontal rolling (rolling roll axis is horizontal), a vertical roll is used. When the first pass of the rough rolling forming pass is vertical rolling (the roll axis of the rolling is vertical), a horizontal roll is used to perform the rolling of the first pass of the rough rolling forming pass of the billet slab. This is more effective because the side surface at can be slightly reduced. Although the material strength of the high-temperature welded portion of the billet slab continuous by welding has decreased, the material strength increases due to heat removal due to the contact of the pushing roller with the side surface of the billet slab, and at the same time the effect of light pressure reduction Therefore, the crystals on the side surfaces of the billet slab are refined by dynamic recrystallization to improve the breaking strength, reduce the rolling crack susceptibility, and reduce the occurrence of rolling cracks on the side surfaces of the billet slab.

The pushing force can be set arbitrarily by changing the number of rotations of the pushing roller. Since the billet slab that has been continuous by welding is bitten into the multi-stage rolling roll, it is easy to apply a constant pushing force, and there is no clogging on the entry side of the roll, so a large pushing force is applied. It is also possible.

[0015]

EXAMPLE A billet with a round cross section produced by continuous casting was directly fed, and each billet was sequentially joined and integrated by flash butt welding, and after removing burrs at a welded portion, the first pass of a rough rolling forming pass was performed. A pushing roller having a drive source for pushing a billet slab into a rolling mill, which was arranged on the side, applied a pushing force in the rolling direction, and was conveyed to a rolling mill row to perform continuous rolling. The pushing roller arranged on the entry side of the first pass of the rough rolling forming pass is kept open until the tip of the billet at the start of continuous rolling is engaged with the rolling roll of the first pass, and the tip of the billet is moved to the first pass. After passing through the rolling roll, the gap between the pair of pushing rollers is gradually narrowed, and a predetermined reduction is applied to the side surface of the billet (the free side surface perpendicular to the rolling surface where the rolling roll does not contact). did. This rolling amount is sufficiently effective even when the billet diameter is about 1 to 2%, and the effect is further increased when the rolling amount is further reduced to about 2 to 4%. It is desirable that the contact surface of the pushing roller with the free side surface of the billet is formed in a shape conforming to the billet shape, and is a round or male having a radius of curvature of about 1.1 to 1.3 times the radius of the billet. -It was found that the effect was great when the shape was a bal. The billet temperature before applying the indentation force was 1020 ° C., and the temperature of the weld was 1145 ° C. The same process as in the case of using the production method of the present invention (the present invention example), in which the rough rolling is performed by using a grooved roll in the first rolling (rough one pass) and the flat roll in the following rolling. However, a comparison was made of a case where a conventional technique using a flat roll was used for the first rolling (coarse one pass) without applying a pushing force in the rolling direction by a pushing roller (Comparative Example). FIG. 2 shows a shape 12 after rolling when the continuous cast round section billet 10 of the present invention is rolled in the longitudinal direction by the hole roll 11 in one rough pass. The billet slab 10 has a round cross section with an initial diameter D of 200 mm and a rough one-pass
Reference numeral 11 denotes an oval caliber (radius of curvature R = 0.8 D). The driven pushing roller has a flange portion having a diameter of 200 mm, and a radius of curvature of a contact surface with the free side surface of the billet is 110 mm. The gap of the hole type roll is 125 mm
The roll gap of the pushing roller was changed in the state of being fixed to, and the presence or absence of cracks after one rough pass was observed. Table 1 shows the results. After that, rolling is performed with flat rolls up to 3 passes of finish rolling, and after slitting, using a hole type roll.
Round bars of two different diameters were manufactured. No cracks occurred in any of the manufacturing processes.

[0016]

[Table 1]

FIG. 3 shows a rolled shape 15 of a comparative example in which a continuous cast round section billet 13 is longitudinally rolled by a flat roll 14 in one rough pass. The round billet slab has a round cross section with a diameter of 200 mm and a flat roll diameter of 8
00 mm. Table 2 shows the results of rolling tests performed under various roll gap reduction conditions. As can be seen from Table 2, when the round billet is rolled down using a flat roll, rolling cracks occur frequently. Compared to FIG. 2, it can be seen that in FIG. 3, the deformation of the side surface of the billet after rolling is large, which causes rolling cracks on the side surface.

[0018]

[Table 2]

As described above, in the case of the comparative example in which flat rolls are all used for the rough rolling, which is a conventional technique, cracks occurred at the stage of one coarse pass. However, when the method of the present invention was used, cracks occurred. Could be prevented.

[0020]

According to the production method of the present invention, internal cracks are less likely to occur during the solidification process of the billet slab and during rough rolling, and cracks on the inner and outer surfaces during rough rolling can be prevented. In particular, rolling cracks on the side surfaces of the billet hardly occur. Therefore, rolling using flat rolls can be applied to continuous rolling of the bar steel, so that the product yield can be improved and the production efficiency can be increased.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a rolled shape of a rough one-pass round cross-section billet of the present invention.

FIG. 3 is a diagram showing a rolled shape of a conventional rough one-pass round cross-section billet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flash butt welding device 2 Deburring device 3 Pushing drive roller 4 Rough rolling mill 5 Round section billet 6 Rough 1 pass hole roll 7 Rough 2 pass flat roll 8 Rough 3 pass flat roll 9 Flat roll of coarse 4 pass 10 Continuous cast round cross section billet shape before coarse 1 pass rolling 11 Hole roll of coarse 1 pass rolling 12 Continuous cast round cross sectional billet shape after coarse 1 pass rolling 13 Before coarse 1 pass rolling Continuously cast round section billet shape 14 Flat roll of coarse 1 pass 15 Continuously cast round section billet shape after coarse 1 pass rolling

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Takashi Ariizumi, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Inside Nihon Kokan Co., Ltd. (72) Susumu Okawa 1-2-1, 1-2, Marunouchi, Chiyoda-ku, Tokyo Within Nippon Kokan Co., Ltd. (72) Inventor Hiroshi Wakasa 1-2-1 Marunouchi, Chiyoda-ku, Tokyo F-term within Nippon Kokan Co., Ltd. 4E002 AA02 AB02 AB06 AC12 AC14 BB06 BB07 BC01 BC04 BD05

Claims (1)

[Claims] 1. A method of manufacturing a steel bar by direct-feed rolling from a continuous cast billet slab, wherein a continuous cast billet slab having a round cross section is used in continuous rolling of a steel bar in which the billet slab is welded and continuously rolled. A rolling method in which a hole roll is used in the first pass of the rough rolling forming pass, and a flat roll is used in the rough rolling in the second and subsequent passes. Rolling method for preventing rolling cracks in a continuously cast billet slab, wherein a pressing force is applied to the billet slab.