JPH04123802A - Rolling method for preventing generation of seam flaw of hot sheet - Google Patents

Abstract

PURPOSE:To prevent the generation of seam flaw by heating the edge parts in the width direction of a rough sheet bar in a specified temp. range before finish rolling at the time of the finish rolling of the rough sheet bar for hot rolled sheet. CONSTITUTION:A heated slab is roughly rolled into a rough sheet bar and, at the time of the finish rolling of this rough sheet bar, the edge parts in the width direction of the rough sheet bar is heated in the high temp. range of >=1300 deg.C with a device for heating edge part before finish rolling. After that, finish rolling is executed. In this way, the seam flaw that is generated on the rough sheet bar is eliminated by heating at >=1300 deg.C and the seam flaw after finish rolling can be reduced easily, surely, stably and drastically.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to seams extending in the rolling direction that occur on the front and back surfaces at the widthwise ends of the steel plate when manufacturing a steel plate such as a stainless steel plate by hot rolling. The present invention relates to a rolling method that can suppress flaws (linear flaws).

<Prior art> In hot rolling of steel plates, a slab (for example, 120 to 300 mm thick) heated to about 1250°C is rolled into a rough sheet bar (for example, 15 to 60 mm thick) by a group of rough rolling mills.
m), and after cutting and removing crops and removing surface scale, finish rolling is performed in a group of finishing mills to obtain a product with a predetermined thickness. This finishing temperature is usually 900°
It is said to be around C.

In such hot rolling, seam flaws along the rolling direction occur on the front and back surfaces of the rough sheet bar at the width direction ends after rough rolling. These seam defects are formed when the side surfaces of the slab come out onto the surface of the rolled material due to width expansion during rough rolling.

In order to prevent such seam flaws, the following rolling methods have been proposed in the past.

(i) JP-A No. 53-28542 Hot rolling in which a reduction is applied only to the edge portion of the metal material in the rough rolling step in hot rolling, or a reduction of 5 to 15 mm is applied only to the center portion of the edge and side surfaces. Method.

Gi) Japanese Unexamined Patent Publication No. 58-138502 A method for manufacturing a hot-rolled steel sheet with fewer edge surface defects, in which a material slab is formed into a concave shape with opposite short sides recessed inward in its cross section.

<Problems to be Solved by the Invention> In the above-mentioned method of processing the end face of the slab at the slab stage or the stage between rough rolling stands, the slab may have longitudinal camber or bending at the leading and trailing ends. Therefore, it is very difficult to give the slab a desired shape evenly on the left and right sides over the entire length of the slab using vertical rolls. Further, in the rough rolling process, if there is a variation in the rough rolling pass schedule, it becomes difficult to apply rolling to the central portion of the side surface of the slab using the limited rough rolling stands. Therefore, the method of adding processing as described above cannot reliably prevent seam flaws.

In addition, JP-A-1-321009 discloses that an induction heating coil is used to heat the widthwise ends and longitudinal ends of a rough sheet bar to prevent material defects at the side ends and the leading and trailing ends. However, this compensates for the temperature drop at the side edges and the front and rear edges, but cannot reduce seam flaws.

This invention was made to solve the above-mentioned problems, and its purpose is to provide a hot-sealing method that can easily, reliably, and stably reduce seam defects that occur at the widthwise ends of steel plates. An object of the present invention is to provide a method for rolling a steel plate that prevents the occurrence of seam defects.

<Means for Solving the Problems> As shown in FIGS. 1 and 2, the present invention rough-rolls a heated slab into a rough sheet bar, and when finishing rolling the rough sheet bar, the finishing rolling process is performed. The ends of the rough sheet bar 3 in the width direction are first heated to a high temperature range of 1300'C or higher using an end heating bag W5, and then finish rolling is performed.

The end heating device 5 may be a gas burner, radiant heating, etc., but induction heating is preferable.

<Function> As shown in FIG. 3, the phase sheet bar 3 after rough rolling has the following properties:
Approximately 0.17 nu+ diagonally to the top or bottom surface
+ seam flaw 4 has occurred.

Such seam flaws 4 are heated to 1300°C using an edge heating device 5.
When heated to -1, the crystal grains are fused and destroyed, and the cracks (gap) 4a are brought into close contact with each other, and the cracks, that is, the seam flaws are erased.

When this is finished rolled, the seam flaw removed part has a depth of 0.
This results in fine flaws of about 0.2 mm, and in the conventional case, the cracked portion 4a is rolled and remains as it is, whereas in the present invention, most of the seam flaws are eliminated.

The heating temperature for the seam flaw 4 was set to 1300°C or higher because cracks along each grain boundary were heated to 130°C.
This is to bring each grain boundary into a fused state by heating to 0°C or higher.

Moreover, the position where the seam flaw 4 is heated is preferably in front of the finishing rolling mill 2. This is because a vertical roll is installed in each stand between the rough stands, and the vertical roll performs width reduction, so the material undergoes plastic deformation in the width direction. By heating the sheet after completing the plastic deformation in the width direction between the rough stands, a good result can be obtained without any turning around at one end of the rough sheet bar.

Embodiment> The present invention will be described below based on an illustrative embodiment. As shown in Fig. 1, a steel plate hot rolling line consists of a plurality of rough rolling mills 1 equipped with vertical scale breakers VSB or edger rolls E at the front stage, and a crop shear FC3 at the entry side, in order from the heating furnace side. A plurality of finishing rolling mills 2 having
After the slab is heated to about 1250°C in a heating furnace to remove scale, it is rough rolled while being etched, and the rough rolled sheet bar cuts and removes the crops at the front and rear ends. After that, it is finished rolled. Here, the steel plate temperature is usually 1100 to 100 on the exit side of the rough rolling mill.
0°C1 finish rolling mill entrance side Te 1000~900°C1 finish rolling mill side Tee 90θ~8o.

``It is said to be C.

In such a configuration, the induction heating device 5 is installed upstream of the crop shear FC3. The induction heating device 5 includes an induction heating coil 6, a support member 7, a control circuit, a high frequency power source, and the like, and heats a steel plate using Joule heat of a current induced by electromagnetic induction.

The induction heating coils 6 are installed in pairs, upper and lower, so as to sandwich the width direction ends of the rough sheet bar 3 from above and below, and two sets are arranged in the line direction to heat the seam flaw 4 portion to 1300° C. or higher. Further, the induction heating coil 6 can be adjusted to move in a direction perpendicular to the line so that it can accommodate rough sheet bars 3 of various widths. Further, although it is better that the gap between the induction coil 6 and the rough sheet bar 3 be narrow, it is preferable that the gap between the induction coil 6 and the rough sheet bar 3 be retractable so that the coil 6 is not damaged by warping of the rough sheet bar.

In the above structure, hot rolling was carried out under the following conditions, and the results shown in FIGS. 5 and 6 were obtained.

(i) Test material (11) Induction heating device specifications Frequency: 5001-fz Output Crab 4400KW GiD Slab dimensions: 201 mm x 1025
mm
mm x 107O hot dimension) (thickness) (width)
(Length) Rough sheet bar temperature: 1055°C (Rough rolling exit side) (■) Induction heating temperature: 1310°C (Edge part) (Vil Product dimensions: 3.2 mm x 1059
mm x 596 m (hot dimension) (thickness) (width)
(Length) Product temperature: 950°C (Final rolling exit side) As shown in Figures 5 and 6, according to the present invention, the beseam flaw width is approximately 15 nu+ compared to the conventional material (no processing or heating). The seam flaw depth can be reduced by approximately 0.2 mm. This makes it possible to significantly improve yield.

<Effects of the Invention> As mentioned above, the present invention provides the following advantages: After heating the width direction end portion of the rough sheet bar before finish rolling to a high temperature range of 1300°C or higher,
Because finish rolling is used, seam defects that occur on the rough sheet bar are erased by heating to over 1300°C.
Seam flaws after finish rolling can be easily, reliably and stably significantly reduced. This makes it possible to significantly improve yield.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a rolling line layout according to the present invention, FIG. 2 is a schematic perspective view showing a heating device according to the present invention, FIG. 3 is a sectional view showing seam flaws in a rough sheet bar, and FIG.
The figure is a sectional view showing a product according to the present invention, and FIGS. 5 and 6 are graphs showing seam flaw width and seam flaw depth. 1... Rough rolling mill, 2... Finishing rolling mill 3...
Rough sheet bar 4... Seam flaw 5... Induction heating device 6... Induction heating coil 7... Supporting member No.

Claims (1)

[Claims] (1) When the heated slab is roughly rolled into a rough sheet bar and this rough sheet bar is finish rolled, the widthwise end of the rough sheet bar is heated to a high temperature of 1300°C or higher using an end heating device before finishing rolling. 1. A method for rolling a hot steel sheet to prevent seam flaws, the method comprising heating a hot steel sheet to a temperature of 100° C. and then finishing rolling the sheet.