JPS5935855A - Production of steel ingot - Google Patents

Abstract

PURPOSE:To produce a steel ingot having no internal defects such as segregation and loose structure by positioning an internally sound billet which is beforehand cleaned of the surface in a casting mold, and charging molten steel into the mold while bubbling the surface of the billet with gas thereby casting the ingot. CONSTITUTION:An internally sound billet or steel plate 5 which is beforehand cleaned of the surface is fixed in the central part of a casting mold by a weight 6 for supporting. The inside of the mold 1 is under neutral atmosphere formed of the inert gas blown through an inert gas blow pipe 12 prior to the commencement of casting, then the casting through a casting port 4 is started. When the melt level arrives at the intermediate position between a molding board 8 and the bottom of the billet 5 to be embedded by casting, the bubbling of an inert gas 9 is started from a gas blowing hole 10 and the casting through the port 4 is continued. The part of the billet 5 in contact with the molten steel 7 at the bottom and over entire side surface thereof is washed by the gas bubbling whereby the solidification is progressed. The gas bubbling is executed right after the end of the casting. The internally sound steel ingot is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming steel ingots (or steel slabs), etc.

In recent years, continuous casting has been adopted to replace the ingot making method, and the production of steel ingots or steel slabs (hereinafter referred to as steel ingots) by the ingot making method is decreasing. It is difficult to apply the continuous casting method to large unit heavy steel plates or small lot products, and it is thought that they will continue to be manufactured by the ingot-forming method.

Conventionally, component macro segregation or "zaku" such as V segregation, inverted V segregation, bottom precipitated crystal negative segregation, and -order secondary vibes exist inside steel ingots manufactured by the ingot making method. Defects in the properties of steel ingots have had various negative effects on products after rolling the steel ingots. Therefore, in order to reduce various defects such as the aforementioned component macro segregation and "graininess", (1) a method of improving by optimizing conditions such as the height, width, thickness, taper, etc. of the mold; (2)
A method to reduce and control the components of steel, that is, the components that tend to segregate as much as possible. Although some improvements have been made, the current situation is that no fundamental solution has yet been found.

The present invention addresses the above-mentioned characteristics of conventional steel ingots, ie, bamboo segregation,
The purpose of this method is to produce steel ingots free of internal defects such as "Zaku", and the gist of this method is to place an internally sound steel billet or steel plate whose surface has been cleaned in advance in a mold, and This ingot-forming method is characterized by injecting molten steel into a mold while bubbling gas on the surface of the steel plate, and it is a method that completely eliminates defects such as macro-segregation of the components of the steel ingot.

Next, the present invention will be explained in more detail based on the flow pattern drawings which are examples of embodiments of the present invention. FIG. 1 is a schematic diagram for explaining the steel ingot manufacturing method of the present invention, and FIG. 2 is a plan view for explaining the set positions of gas discharge holes in the surface plate.

FIG. 1 shows an example in which the present invention is applied to a bottom pouring ingot method, but the present invention is not limited to this embodiment. In Fig. 1, the inner surface 2 of the mold 1 has been thoroughly cleaned to remove fine refractory dust, etc., and the runner 3 and spout 4 in particular have been thoroughly cleaned. A steel piece 5 of good quality is suspended from a support weight 6 and fixed to the upper part of the mold 1 by the support weight 6.

7 is molten steel, and the internally sound steel billet 5 is an ingot or a cast billet cast by an ingot method, a continuous casting method, an electrocasting method, etc., or a component macro segregation by processing such as rolling or forging. A steel piece or steel plate is used that has no defects such as scratches or has been reduced to a non-problematic level, and its surface is cleaned by gas scarf, surface machining (sapa grinder), shot plastin ink, pickling, etc. Afterwards, it is desirable to perform oxidation prevention treatment with mineral oil, vegetable oil, paraffin, etc. The weight of the steel billet or steel plate 5 to be cast is preferably 1/10 or more of the steel ingot to be produced, and the thickness of the molten steel 7 to be cast (the distance between the surface of the steel billet or steel plate 5 and the mold inner surface 2) is 400. -The following is desirable.

The surface plate 8 on which the mold 1 is placed has gas discharge holes 10 for bubbling inert gas 9 during pouring of the molten steel 7 from the pouring port 4 to the entire side surface and bottom of the steel piece 5 that surrounds the cast iron. .

A desirable set position of the gas discharge hole 10 on the surface plate 8 is the second position.
As shown in the figure. In Figure 2, (a) is a square steel ingot, (b)
) is an example of a flat steel ingot, 2 is the inner surface of mold 1, and 14
is the outer periphery of the billet 5 to be cast, and the setting position of the gas discharge hole 1o of the surface plate 8 is preferably the hatched portion 15, and is uniform over the entire side surface and bottom, which is the contact portion of the billet to be cast with the molten steel. An important requirement is to set it in a position that surrounds the sides so that gas bubbling can be performed. The pouring port 4 for the molten steel 7 is a surface plate 8 when manufacturing round steel ingots and square steel ingots.
One location is installed in the center, but two locations are usually installed in the case of flat blocks. FIG. 1 shows an example of bottom pouring casting from one casting hole. The inert gas for gas bubbling is argon or the like, and gas is bubbled from the gas discharge hole 10 via the gas blowing pipe 11 conducted into the surface plate 8 as described above. If the bubbling gas discharge hole 10 is made of various porous refractories or a nozzle made of a refractory filled with a large number of thin metal tubes such as stainless steel, the bubbling effect will be greater.

An inert gas blowing pipe 12 is provided from the upper part of the mold toward the inside of the mold 1, and the inside of the mold 1 is always maintained in a neutral atmosphere before and during casting.

13 is a riser frame.

First, before starting casting, the inside of the mold 1 is replaced with an inert gas such as argon to create a neutral atmosphere and casting is started. When the molten metal level reaches the intermediate position between the surface plate 8 and the bottom of the steel billet 5 to be cast, bubbling of inert gas such as argon is started from the gas discharge hole 10 and pouring from the pouring port 4 is continued. .

Casting 9 As shown in FIG. 1, the bottom and all sides of the steel piece 5 to be cast, which are in contact with the molten steel 7, are washed by gas bubbling while solidification progresses. Gas bubbling is carried out until immediately after the completion of casting.

The molten steel that is cast by casting a steel billet or steel plate into molten steel is not removed from the mold, but is also cooled from inside the steel billet or steel plate, so that the steel ingot after solidification contains macroscopic particles. A steel ingot with extremely good internal quality is obtained without internal defects such as segregation and "rub".

By performing this type of casting, not only does the contact between the steel billet and the molten steel to be cast occur uniformly (but also the molten steel is well washed at the interface, resulting in a cast with an extremely sound internal quality). EXAMPLES Next, the present invention will be explained by way of examples.

Example Two 50 ton steel ingots were manufactured under the manufacturing conditions shown in Table 1 below.

Table 1 Test casting conditions: Two identical 50 ton molds were placed on the same surface plate truck, and the same 50 kg class molten steel was simultaneously injected using the same injection pipe. The first steel ingot mold performs normal bottom pouring, and the second steel ingot mold is used to suspend cast steel pieces (weighing 6 tons) as shown in Figure 1. Using a bubbling device with porous bricks set on a surface plate, the casting method was carried out at the position corresponding to Figure 2 (bl). Continuously cast slab material with internally sound properties was cold scarfed on the surface and coated with rapeseed oil. Argon gas was used for bubbling, the casting temperature was 1590°C, and the casting time was approximately 20 minutes. Ta.

Next, the cast first steel ingot and second steel ingot were bloomed and rolled, and an extremely thick steel plate with a thickness of 150 fins was manufactured using a plate mill, and an internal quality investigation was conducted17. As a result, there was a problematic ultrasonic defect in the top middle part of the steel plate of the first steel ingot (conventional method), as well as reverse ■ segregation and V segregation, and furthermore, the bottom part had a thick middle part. In contrast, the steel plate of the second steel ingot produced by the method of the present invention was found to be extremely sound with no negative segregation present at all.

As described above, the present invention is a completely new steel ingot manufacturing method that eliminates defects such as component macro segregation of steel ingots. change,
This invention can also be used in a method for manufacturing clad steel plates, etc., and has industrial effects as well.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram for explaining the embodiment of the present invention, and Fig. 2 is an explanatory diagram for showing the set position of the gas discharge hole in the surface plate. An example of a case of a 5-sided steel ingot is shown. 1: Mold, 2: Mold inner surface, 4: Casting port, 5: Steel piece, 7:
Molten steel, 8: surface plate, 10: gas discharge hole, 14: outer periphery of the steel piece to be cast, 15: gas discharge hole set position. Agent Patent Attorney Sanro Kimura Figure 1

Claims (3)

[Claims] (1) A method for manufacturing an internally sound steel ingot, which comprises placing an internally sound steel piece or steel plate in a mold in advance, and pouring and casting molten steel into the mold. (2) The method according to claim 1, characterized in that the molten steel is poured while bubbling the surface of the steel billet or steel plate with an inert gas; (3) The method according to claim 41, characterized in that molten steel is injected from the lower part of the mold.