JPS625681B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for hot forming a bloomed steel billet or a continuously cast steel billet (hereinafter simply referred to as a steel billet). Generally, during hot rolling of steel billets, in order to ensure the width of the finished product, width reduction is performed in the first stage of the process.
As shown in the figure, a fishtail F is formed at the end of the steel piece S. Furthermore, recently, as the number of molds has been reduced in order to simplify continuous casting, it may be necessary to perform the width reduction more forcefully, and the fish tail F becomes larger. Since this fishtail portion is cut off after rolling, it is the biggest cause of lower yield. Furthermore, in hot rolling of steel billets, as shown in Figure 2, there is a problem of small width at the leading and trailing ends where the width of the leading and trailing ends is smaller than the width of the intermediate part, which also causes a decrease in yield. This is a major cause. Therefore, as a method for reducing fish tails, a method has been proposed in which the tip of a steel piece is pressed with a press to deform it into a narrow width, and then the width is reduced. However, in the case of such a method, there are concerns that the steel billet will escape during deformation by pressing, that a moment will act on the press body, and that the narrow width of the tip will be exacerbated due to the narrow width of the tip. This invention was proposed in view of the above-mentioned circumstances, and its purpose is to improve the stability of the steel billet during press forming, to prevent the generation of moment in the press body, and to improve the stability of the tip and rear ends. It is an object of the present invention to provide a method for hot forming a steel billet, which can reduce fishtail without promoting width reduction and improve yield. The method of hot forming a steel billet according to the present invention includes press-forming a portion of the steel billet into a narrow width at least at a distance that allows this end to retain its original shape from the end face of at least one end in the longitudinal direction. The steel strip is subjected to width reduction or thickness reduction using a subsequent rolling mill, thereby reducing the fish tail without making the end portions of the steel strip narrower in width. The present invention will be described below based on an illustrated embodiment. As shown in FIG. 3, a pair of press heads 1 for width reduction are provided at the front stage of the rolling mill, and the press heads 1 are moved forward and backward in the width direction by hydraulic cylinders 2. In such a press, the distance l from the end surface E of the steel billet S is removed before the width reduction and thickness reduction of the steel billet S is performed by the subsequent rolling mill.
Press-form the parts that are separated by a narrow width. However, the width of the steel piece end _S1 is not reduced. In other words, the distance l is a distance that allows at least this end portion _S1 to remain in its original shape. In addition, even if the shape of the width cutting notch is a wide U-shape,
A wide V-shape as shown in FIG. 8 may be used, and the width reduction amount is a and the press forming length is b for a steel piece having a width W. These a, b and l are appropriately determined depending on the thickness and width of the steel billet, the thickness and width of the finished product, the rolling method, etc. When such a width reducing notch is inserted, the end surface E has a shape in which the central portion in the width direction protrudes as shown in FIG. Next, when such a steel billet S is rolled in a subsequent rolling mill, the end portion _S1 is pushed out in the rolling direction to form a fishtail, but this is offset by the overhanging effect of the center portion in the width direction due to the formation of the width killing notch. and will be significantly reduced. Since the end portion _S1 of the steel billet is not press-formed, the effect on the narrowing of the end width is no different from that of a normal steel billet, and it is possible to reduce the fish tail without causing a narrowing of the end width. In the present invention, since the width reduction notch is formed, almost no moment acts on the press body, and furthermore, the steel piece does not escape in the longitudinal direction when deformed by the press. Further, when the method of the present invention is applied to both the front and rear ends of the steel billet, it is possible to easily form a notch with a predetermined width by simply moving the steel billet in the longitudinal direction. Furthermore, even in the rolling of blooms, billets, etc., which do not have the problem of small end widths, the method of the present invention reduces fish tails that occur at the ends. Next, a detailed explanation will be given using a specific example. A (thickness 270
mm, width 900mm, length 5000mm), B (thickness 270mm, width
1200mm, length 5000mm), C (thickness 270mm, width 1500mm)
Using three types of steel slabs (mm, length 5000mm), press width was removed at a portion l apart from the end face E under the conditions l/W = 0.45, a = 30mm, b = 650mm, as shown in Figure 8. After that, rolling was performed using a rolling mill with a width reduction amount (slab width - finished product width) of 50 mm to a finished product thickness of 35 mm. The following table shows a comparison of the fish tail lengths between the method of the present invention and the conventional method which does not perform press width reduction forming.

[Table] As is clear from this table, according to the method of the present invention, fish tails are significantly reduced, especially on the rear end side, and the yield improvement rate by cutting off fish tails at the tip and rear ends is 0.2 to 0.3%. Become. moreover,
The widths of the leading and trailing ends were almost the same without increasing compared to the conventional method. As described above, according to the hot forming method according to the present invention, the formation of fishtails can be significantly reduced without promoting a narrowing of the width of the leading end and trailing end, thereby improving the yield.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a conventional steel billet's body tail, FIG. 2 is a plan view showing a conventional steel billet with a small end width, and FIG. 3 is a plan view showing a steel billet forming method according to the present invention. , FIG. 4 is a sectional view taken along the - line in FIG. 3,
Fig. 5 is a plan view showing the steel billet after forming, Fig. 6 is a front view showing a press head used for forming, Fig. 7 is a front view showing a modification of the same press head, and Fig. 8 is the same as Fig. 7. 1 is a plan view showing a steel billet formed using the press head of FIG. 1...Press head, 2...Hydraulic cylinder, 3
...Broad killing notsuchi. S...Steel billet, _S1 ...Steel billet end, E...End face.

Claims (1)

[Claims] 1. During hot rolling of a slab-rolled or continuously cast steel billet, a portion of at least one longitudinal end of the billet separated from the end face by a distance that allows at least this end to retain its original shape is press-formed into a narrow width. 1. A method for hot forming a steel billet, characterized in that the steel billet is then subjected to width reduction and thickness reduction using a subsequent rolling mill.