JPS60148661A - Formation of large-sized steel ingot - Google Patents

Abstract

PURPOSE:To eliminate inverse V segregation of a large-sized steel ingot by providing a casting mold in a pit, feeding water in the pit at the point of the time when 10min elapses after pouring a molten steel therein and releasing the generated steam through a discharge port provided near the head of the casting mold. CONSTITUTION:A casting mold 2 is installed via double molding boards 6 onto the molding board 4 in a pit 10 and a molten steel 16 is poured through a pouring pipe 8, a runner 18 and a sprue 20 into the mold 2. The molten steel surface is covered by a holding material 22. A steam discharge port 14 provided below a heat insulating material 12 is opened at the point of the time when about 20min elapses after completion of pouring and thereafter cooling water 24 is fed into the pit 10. The water level is maintained in the position below the port 14. The water 24 passes through the space between the mold 2 and the boards 6 and advances into the spacing 28 between the mold 2 and a soldified shell 26 to extract heat from the shell 26. Part of the cooling water is released in the form of steam through the port 14. The inverse V segregation of the large-sized steel ingot is eliminated and porosity defects are considerably decreased by such simple method.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing large-sized steel ingots, and more particularly to a method for producing sound steel ingots with extremely few inverted V segregation and grain defects.

The conventional method for manufacturing large flat steel ingots and chrysanthemum-shaped steel ingots uses cast iron molds and surface plates, and pours molten steel by top pouring or bottom pouring. Due to thermal contraction of the solidified shell at an early stage, a gap is generated between the solidified shell and the mold, and heat removal by the mold is suppressed, which not only prolongs the time until solidification is completed, but also causes damage to the inside of the steel ingot. It has been almost impossible to control the inverted V segregation that occurs and the pores that occur in the center of the steel ingot.

When trying to improve these internal defects in steel ingots using conventional technology, there are methods that use a wide mold or heat or keep the mold head warm, but these methods do not alleviate the cracks (
= had some effect, but it was not possible to improve the inverted V segregation at all. For this reason, in steel ingots manufactured using conventional techniques, inverted V segregation always appears in large steel ingots with a thickness of 500 to 600 m or more, and as the ingot thickness increases, the range of the inverted V segregation zone becomes wider. In addition, as the thickness of the steel ingot increases, grain defects become more noticeable2, and there is a drawback that the grains are not compressed even by forging or rolling and remain in the product as porous defects.

In order to eliminate the drawbacks of the above-mentioned conventional techniques and prevent or reduce inverse Vl analysis and roughness defects, the following various methods have been proposed.

(a) A method in which a heat transfer medium such as lead is injected into the gap created between the mold and the steel ingot.

(0) Method using a water-cooled surface plate.

e) A method of forcibly cooling the outer surface of the mold with gas or liquid.

2) A method of pressing the mold against the steel ingot by moving the mold and forming steel ingot relative to each other using jacks, etc.

All of these methods aim to accelerate the solidification rate of the steel ingot, but in method (a), it is difficult to inject lead, and the lead adhering to the surface of the steel ingot after forming the ingot is difficult. Post-processing is required. In addition, in the method, heat dissipation from the side walls of the mold remains unsolved, and in the e method, even if the outer surface of the mold is forcibly cooled, sufficient heat dissipation is achieved when the gap between the mold and the steel ingot remains intact and there is no contact. I can't expect that. Furthermore, although the method () has a significant effect when combined with the method (C), it requires large equipment such as a jacking device, mold division, etc. in order to integrate the process. Although many proposals have been made, they all have drawbacks and cannot be called effective methods.

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned conventional techniques to prevent or reduce reverse segregation and grain defects in large steel ingots, and to solve the problems of large steel ingots by a simple method that can be expected to have great effects. To provide an agglomeration method.

The gist of the present invention is as follows.

That is, the stage of injecting molten steel into a hind limb mold in which an ingot making device such as a cast iron mold with a removable steam outlet near the head and a surface plate is installed in the pit, and the stage of injecting molten steel into a hind limb mold in which an ingot making device such as a surface plate is installed in the pit, and when 10 minutes or more have passed after the molten steel injection. A method for making a large steel ingot, comprising the step of: opening the steam outlet at a point in time, and then injecting cooling water into the pit to reach a water level below the steam outlet. It is.

Prior to detailed explanation of the present invention, first, the solidification state of molten steel poured into a mold will be explained.

When molten steel is injected into the mold, a solidified shell begins to form from the parts that contact the mold body and surface plate. This solidified shell retains molten steel inside, so it is subjected to large static pressure.When the solidified shell is thin or hot, the molten steel is pressed against the mold body by this static pressure, but the solidified shell is As the thickness gradually increases and the temperature decreases, the deformation of the solidified shell due to the static pressure of the molten steel becomes less and eventually a void is formed between the solidified shell and the mold body. The time it takes for these voids to form varies depending on the size and shape of the steel ingot, but it usually takes 3 to 10 minutes after the completion of casting, and the voids gradually stabilize and expand.

Therefore, at the beginning of pouring molten steel, the solidified shell and the mold body are in contact, and the mold exerts a cooling effect on the steel ingot, but after voids are created, a gas layer intervenes, and the solidified shell is cooled. Rather, it acts as a heat insulator and the solidification rate is significantly reduced.

Therefore, at this point, it is ideal to expose the steel ingot and directly cool it with forced water, but it is extremely dangerous and unethical to remove the mold when the solidified shell is thin, even in the case of a lower mold. Moreover, the reduction of internal defects in steel ingots (which is not dangerous in the case of a preferable top-wide mold, but is extremely difficult in actual operation).The present invention avoids such dangers and safely and effectively This method established a method for cooling lumps.

The details of the present invention will be explained in accordance with the working procedure with reference to the accompanying drawings. First, prior to the ingot-forming operation, the mold 2, surface plate 4, double surface plate 6, and injection pipe 8 used in the present invention are set in the piston 10. The mold 2 used in the present invention has a removable steam outlet 14 slightly below the heat insulating material 12 near the head. When the molten steel 16 transported in a ladle is injected from the injection pipe 8, it is injected into the mold 2 from the upper sprue 20 via the runner 18 formed in the surface plate 4. Molten steel 1
The work of adding the surface coating heat insulating material 22 to the surface of the molten steel 16 at the same time as the injection of the molten steel 16 to prevent oxidation of the molten steel 16 is almost conventional. After 20 minutes have elapsed from the completion of injection of molten steel 16, the removable steam outlet 14 is opened, and the injection of cooling water 24 into the piston 10 is started, and the highest water level reaches the lower position of the steam outlet 14. reach the point. The time from the completion of injection of molten steel 16 to the start of injection of cooling water 24 into the pit varies depending on the size, shape, etc. of the steel ingot, but it takes until a solidified shell 26 with a certain thickness is formed. It takes time and at least 1
It is necessary to allow 0 minutes or more to elapse.

In this example, 25 minutes elapsed from the completion of injection of molten steel 16 to the start of injection of cooling water 24.

The injected cooling water 24 passes through the gap between the mold 2 and the double surface plate 6 and enters the gap 28 between the mold 2 and the solidified shell 26.
Heat is removed from the solidified shell 26, the temperature of the solidified shell 26 rises, and a portion of it becomes steam, which rises and is discharged from the steam outlet 14. The reason why the steam outlet 14 is provided below the heat insulating material 12 at the head of the mold 20 is as follows.
If there were no steam outlet 14, the generated water vapor would rise within the gap 28 between the mold 2 and the solidified shell 26, and then rise and be released through the gap between the heat insulating material 12 and the mold 2. This is because the heat retaining effect of the heat insulating material 12 is lost. At this time, in the pipe 10, the cooling water 24 is supplied,
It is more preferable to keep the water temperature of the supplied cooling water 24 substantially constant by repeating the discharge circulation than to make the cooling effect of a large number of steel ingots uniform.

The shape of the example steel ingot has an average thickness of 1000n+m and an average width of 2200m.
A high Mn steel ingot with a Q% height of 2300 is used for ingot making according to the present invention, using a mold having a wide taper of 4 inches on one side of the long side of the mold and having a steam outlet 14 near the head according to the present invention. Casting was carried out using the following method. In this case, the injection of cooling water 24 into the pit 10 starts 25 minutes after the injection of molten steel 16 is completed, and the water level of the cooling water 24 in the pit 10 is lower than the lower end of the insulation material 12 at the head of the mold 2. 150 mm from the bottom of mold 2
It was at a height of 0+w+.

When we investigated the internal defects of the steel ingot obtained by the ingot-forming method of the present invention, we found that the roughness defects in the center were drastically reduced to 1/3 compared to the steel ingot made under the same conditions by the conventional method. Regarding inverted V segregation, in the conventional method, it occurred from a position of about 180 m from the steel ingot surface, but in the steel ingot according to the present invention, except for the heat retention area where the head insulation material 12 is applied, It was found that the steel ingot was extremely sound.

As is clear from the above embodiments, the present invention involves setting a complete molding device in a pit and forming a safe solidified shell for at least 10 minutes after the completion of pouring molten steel. We used a method of injecting water and letting it rise through the void formed between the mold and solidified shell to directly cool the steel ingot, and then releasing the generated steam from a steam outlet located near the mold head. The following effects were achieved.

(a) The equipment used in the present invention requires only a new pit and water supply and drainage equipment, and the existing equipment can be used as is except for slight modification of the mold, so the equipment cost is minimal.

(b) The cooling water in the pit can be used for circulation after cooling the steel ingot, and there is no need for any special equipment to forcibly inject it into the gaps in the mold, so operating costs are minimal.

(c) Since the cooling water enters the gap between the mold and the solidified shell and directly cools the steel ingot, the cooling effect is superior to any other method.

As a result of (2) and (e), there is almost no inverted V segregation in large steel ingots except for the heat retention area at the head of the steel ingot, and the roughness defects in the center have been significantly reduced to about 1/3 of the conventional value, making it extremely sound. I was able to obtain a steel ingot.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a mold device in a pit showing the ingot making method according to the present invention. 2... Mold 4... Surface plate 6... Double surface plate 8... Injection pipe 10... Pit 12... Insulation material 14... Steam outlet 16... Molten steel 24...・Cooling water 26...Solidified shell 28...Gap agent formed between the mold and the solidified shell Patent attorney Takeo Nakaji

Claims (1)

[Claims] (1) The step of injecting molten steel into a hind limb mold in which an ingot making device such as a cast iron mold with a removable steam outlet near the head and a surface plate is installed in the pit, and the step of injecting molten steel into the hind limb mold, which has a removable steam outlet near the head, and when 10 minutes or more have passed after the molten steel injection. The step of injecting cooling water into the pit after opening the steam outlet at a point in time to reach a water level below the steam outlet. Method.