JPS5919761B2 - Method and device for blooming steel ingots for extra-thick steel materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION When a steel ingot for extra-thick steel material is bloomed and rolled, thickness reduction is performed by a press device between a rough rolling mill and a finishing mill, thereby reducing the amount of material present inside the steel ingot. The present invention relates to a method and an apparatus for manufacturing sound extra-thick steel material by crimping the scratches.

The common method of blooming rolling of steel ingots is to charge the molded steel ingot into a soaking furnace when the molten steel has completely solidified, and to perform blooming rolling after extraction. As shown in FIG. 1, the line has a construction in which a shear device 3 for cutting the top and bottom parts of the steel ingot is disposed between a rough rolling mill 2 and a finishing rolling mill 4.

1 indicates a soaking furnace. However, in the production of extra-thick steel plates with a thickness of 150 mm or more, extra-thick round pieces with a thickness of 350 mm or larger, and extra-thick square pieces with a thickness of 350 mm or more, the forging ratio is low, so that the scratches that exist inside the steel ingots remain unbonded. There was a problem.

For this reason, conventionally, in order to obtain a sound extra-thick steel material, a method has been used in which a heated steel ingot is pre-forged using a forging machine, then reheated and rolled.

However, this preliminary forging process is accompanied by a significant increase in manufacturing costs, which poses a problem in terms of economic efficiency.

On the other hand, in order to reduce manufacturing costs, there are methods to obtain sound steel products without scratches by rolling alone, such as the strong reduction rolling method that takes a large amount of reduction per pass, and the method that cools the surface of the steel billet to prevent internal and external damage. Although surface cooling rolling methods that involve rolling with a temperature difference are known, the reality is that sufficient effects have not yet been achieved.

This invention has been made in view of the above circumstances, and the gist of the invention is to provide a press device between a rough rolling mill and a finishing rolling mill, and to press at least the top of the steel ingot after rough rolling into the steel ingot by the press device. The method is characterized in that a portion corresponding to 20 to 50% of the total thickness is reduced in thickness, and then finish rolling is performed.

In this invention, the area where the thickness is reduced by the press device is limited to 20 to 50% of the top of the steel ingot for the following reason.

Figure 2 shows the distribution of cracks in the longitudinal direction of a steel plate manufactured only by rolling.As is clear from this diagram, the occurrence of cracks is observed in an area equivalent to 20 to 50% from the top of the steel ingot. It can be seen that the thickness reduction by the press device should be aimed at at least the above-mentioned range where occurrence of scratches is observed.

In this way, if the thickness of the steel ingot after rough rolling is reduced at least from the top part of the steel ingot by 20 to 50%, the scratches existing inside the steel ingot will be crimped and a sound extra-thick steel material can be obtained. This is possible.

Moreover, this invention has the great advantage of being cheaper to manufacture than the conventional pre-forging treatment method, since it is only necessary to incorporate a thickness reduction press device into a normal blooming rolling line.

Next, a device according to an embodiment of the present invention will be explained based on FIG.

In Fig. 3, 11 is a soaking furnace, 12 is a rough rolling mill, and 13
14 shows a press device, and 14 shows a finishing mill.

That is, the steel ingot 15-1 extracted from the soaking furnace 11 is
The intermediate rolled material 15-2 is roughly rolled to an intermediate shape by the rough rolling mill 12, and the intermediate rolled material 15-2 is pressed at least in a range of 20 to 50% from the top part by the press device 13 to form a pre-rolled material 18.
It becomes piece 15-3.

This pressing operation is performed as shown in Fig. 4.
5-2 intermittently or continuously press mold 13-1
The above range is divided into several times while sending the
Naturally, if the press capacity is as large as that, the press work will be completed with just one press forming.

In addition, this press forming enables the production of steel billets without surface flaws by using a U-shaped mold as shown in the figure.
Further, the amount of thickness reduction in the press is appropriately determined depending on the steel ingot dimensions, finished dimensions, and rolling pass schedule, but it is preferable to reduce the thickness by at least 50 mm.

After this press forming, the steel billet 15-3 is subsequently subjected to width and thickness reduction rolling by the finish rolling mill 14 to become a finished product 15-4.

Next: Examples of this invention will be explained.

Embodiment The blooming line of the present invention shown in FIG.
A steel ingot of mm thickness x 1200 mm width x 2900 mm height,
After rolling with a rough rolling mill to 45011tm thickness x 1050m width,
4 by pressing at a distance from the end face corresponding to the top part of the rough rolled steel ingot between 1000 mm and 3000 mm.
The thickness was reduced to 00 mm, 350 mm, and 300 mm, and then rolled to 200 mm using a finishing mill.

After rolling, U, S, and T flaw detection were performed to investigate the occurrence of scratches, and the results are shown in FIG.

The flaw detection range is 25 to 30% from the top of the steel ingot, and the flaw index a = (number of grid points where flaws remain/number of grid points detected) x 100 (%). The degree was shown.

As is clear from FIG. 5, the number of scratches on the steel slab is significantly reduced by the thickness reduction.

For comparison, the occurrence of pitting was observed in a steel slab that was subjected to blooming without being subjected to thickness reduction using a press.

As described above, according to the present invention, it is possible to easily crimp the scratches in the blooming and rolling line, so that a sound extra-thick steel material without scratches can be produced without causing a large increase in manufacturing costs. Obtainable.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing a conventional blooming rolling line, Fig. 2 is a chart showing the longitudinal direction roughness distribution of a steel plate manufactured only by rolling, and Fig. 3 is an explanatory diagram showing an embodiment of the present invention. FIG. 4 is an explanatory diagram showing the thickness reduction by the same press as described above, and FIG. 5 is a chart showing the function of the press thickness reduction amount and the Zaku index in the embodiment of the present invention. 11... soaking furnace, 12... rough rolling mill,
13... Press device, 14... Finish rolling mill, 15-1... Steel ingot, 15-2...
・Intermediate rolled material, 15-3... Steel billet after pressing, 1
5-4...Finished product.

Claims (1)

[Scope of Claims] 1. In the blooming of steel ingots for extra-thick steel materials, the steel ingot after rough rolling is processed by a press device between a rough rolling mill and a finishing mill to reduce at least 20 to 50% from the top of the steel ingot. 1. A method for blooming a steel ingot for use in extra-thick steel materials, characterized by performing thickness reduction on a considerable portion and then performing finish rolling. 2. In a blooming rolling line for steel ingots for extra-thick steel materials, between a rough rolling mill and a finishing mill, thickness reduction is performed on at least a portion equivalent to 20 to 50% from the top of the steel ingot after rough rolling. A method for blooming a steel ingot for extra-thick steel material, characterized by installing a press device.