JPS5829178B2 - Metal ingot making method with less cracking - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming metal ingots with fewer cracks, and particularly provides a method for forming metal ingots with fewer cracks in steel ingots for rolling.

As is well known, when pouring molten metal into a mold to produce a cast product or obtaining a steel ingot for rolling, various mold paints are applied to the inner surface of the mold to coat the surface of the cast product. Methods to improve properties and improve turbid flow have been widely put into practical use.

By the way, all of the well-known methods involve applying a mold coating to the entire surface of the mold that comes in contact with the molten metal, and the inventors of the present invention have also applied organic or inorganic paints, or an appropriate proportion of these paints, to the entire surface of the mold for many years. By applying a mixed mold paint and casting, we succeeded in obtaining a steel ingot with an excellent casting surface, but occasionally some of the cast steel ingots had cracks, especially vertical ones. Cracks may occur, and as a result of investigating the cause and researching a method of agglomeration that does not cause cracks, it was possible to significantly reduce the occurrence of the cracks by developing the method of the present invention.

The mechanism by which vertical splitting of a steel ingot/)"L occurs is explained in Fig. 1. In general, when molten steel is injected into the steel ingot casting mold 1 in Fig. 1 and solidified and shrunk, the convex corner of the steel ingot is Sections (hereinafter referred to as steel ingot corner parts) A, B, and C.

D solidifies and shrinks faster than other parts because heat is removed from the mold to a large extent, and it separates from the mold (releases the mold) earlier, so an air gap 2 is created after the mold is released, and heat is removed from the steel ingot to the mold faster than other parts. becomes smaller.

For this reason, the solidified shell 3 of part A of the steel ingot corner (in addition to the above A)
~ D) is thinner than other parts, and receives tensile stress from the solidified shells 4 and 5 in the straight parts on both sides of the corner part at high temperature.
It is considered that vertical corner cracks 7 occur.

Vertical cracks in the planar part excluding a part of the steel ingot corner are caused by adhesion of splash to the mold wall surface or entrainment of scum during the melting process, which reduces the heat conduction from the molten steel to the mold in that part. Therefore, the solidified shell 8 becomes thinner, and the above-mentioned thermal stress is also concentrated in this portion, causing vertical cracks 9 to occur on the surface.

The above-mentioned convex corner part of the steel ingot is one in which the angle θ (θ1 to θ4) formed by both sides of the corner of the steel ingot shown in FIGS. 2 and 3 is 1.
Parts A and B with an angle of 200 or less.

C and D, and refers to a range of 100 mm on both sides from the center of the corner.

On the other hand, when mold paint is used, the residual smell of the mold paint tends to exist in some corners of the mold, which impairs heat conduction between the mold and the steel ingot, and also releases the mold quickly, making it difficult for heat to be removed from the steel ingot to the mold. Further, the problem arises that the steel ingot corner cracks occur frequently.

The present invention addresses the above-mentioned drawbacks of conventional metal ingot making methods,
(In particular, the purpose is to solve the problem of cracking in some corners of the steel ingot and provide a steel ingot with no surface flaws.)

The gist of this method is to inject molten metal into a metal mold whose inner wall surface is coated with mold paint, and to create a corresponding mold for the part where the release of the ingot from the inner wall surface of the mold starts to slow due to solidification shrinkage. This is a metal ingot making method with less cracking, characterized in that a mold paint is selectively applied to the inner wall surface, and the mold surface corresponding to the part where mold release starts early is left uncoated or lightly coated.

The present invention will be explained in detail below.

The mold paint according to the present invention refers to an inorganic or organic paint, or a well-known paint made by appropriately mixing organic and inorganic materials, while "molten steel metal" mainly refers to pure iron, carbon, which is a steel material. It refers to steel, alloy steel, cast steel, and cast iron, but does not exclude these as it can also be used for non-ferrous metals.

Further, when molten steel metal is injected into a mold and the ingot is formed, the part where the mold release between the inner wall surface of the mold and the ingot starts early due to solidification shrinkage is, for example, from the center to both sides 100 of the above-mentioned convex corner of the steel ingot. This refers to the areas where corner cracks are likely to occur, and the areas where mold release starts late refers to the areas excluding some of the above-mentioned convex corners.

Next, the procedure for applying the mold paint will be explained in detail.

To simplify the explanation, a case will be described in which the flat mold shown in FIG. 2 is used.

(1) In the case of brush coating or roller coating, it is relatively easy to apply no mold paint or apply a thin coat of mold paint only to a 100 mm range on both sides, including parts A, B, C, and D of the mold corners.

Here, thin coating means a coating amount of 20f/rr? This is an amount that has no significant difference in its effect on the surface of the steel ingot compared to when no coating is applied.

(2) In the case of spray application ■ Four adjustable angle plates are installed near the outer periphery of the paint spraying nozzle in the direction of a part of the corner of the mold, that is, diagonally, or the corner of the steel ingot on the inner surface of the casting fan is installed. Part A,
A method in which one plate is hung so as to cover the surfaces corresponding to B, C, and D, and no or only a thin coating of mold paint is applied.

■ When spraying by moving only up and down without rotating a spraying device that has a large number of paint spraying nozzles, some mold corners A and B are used depending on the dimensions of the various molds.

A method in which a solenoid valve is attached to the spray nozzle facing the inner surface of the mold corresponding to C and D to selectively apply no paint or apply a thin coat of paint.

■ After undercoating only a portion of the mold corner with a hydrophobic combustible paint, apply a water-soluble mold paint or a mold paint mixed with water to the entire inner surface of the mold.

In this case, it is difficult for the mold paint to be applied to some of the mold corners,
Even if it is applied thinly, the undercoat paint on some corners burns well when molten steel is poured, making it difficult for residual scent to adhere.

and so on.

The aforementioned flange plate may be made of any material that has good heat resistance, impact resistance, and abrasion resistance so that it can be used for a long time at a mold temperature of 100 to 500°C.

Among them, it may be a metal plate, pipe, or rod, but it is preferable to make it as light as possible from the viewpoint of operation and handling.

100m on both sides including part of the mold corner A, B, C, D
The reason for setting the range of m is based on experiments, and it is recognized that if no coating or thin coating is applied beyond this range, the incidence of surface flaws will increase, and if it is less than 10 mm, the effect of preventing vertical cracks will be weakened.

Now, as mentioned above, porcelain paint can be applied by brushing, spraying,
Using a coating method such as roller coating or dipping, some corners of the mold are left uncoated or coated thinly, and other than some corners are selectively coated on areas deemed necessary.

Since the viscosity of the mold paint has an appropriate viscosity depending on the application method, it is preferable to adjust the viscosity to an appropriate value depending on which application method is used.

Now, the coating amount of the mold paint of the present invention is 20 to 100 as a solid after drying. /? ? Good results can be obtained when used within the range of Z2.

If it is less than 20i/-, the coating amount will be small and it will be difficult to apply it uniformly to the mold wall, and the surface texture of the cast steel ingot will be slightly inferior, and the coating amount will be less than 1000f/lr. With the above coating, the workability of coating and drying is poor, the result is saturated, and the economical efficiency is also poor.

In addition, in general, in mass production processes such as those in pig steel mills, molds are used repeatedly, so they remain at relatively high temperatures and are heated to around 300 ml when applying mold paint before pouring molten steel. It may maintain a temperature of around ℃.

If the mold temperature is 50 to 300°C, the paint film will dry in a relatively short time when applying with a solution, so preheating the mold or drying after applying the paint can be done by other means such as gas heating, electric heating, There is no need to raise the temperature using heating means such as infrared heating, and the work can be performed more economically.

However, if the mold has been cooled to near room temperature or if a new mold is used, it is necessary to preheat the mold or mold paint, or to dry it after applying the paint.

In any case, it is preferable to dry the coating sufficiently before pressing the button.

Next, embodiments of the present invention will be described in detail.

Example 1 Low carbon rimmed steel was melted in a 170 ton pure oxygen top blowing furnace,
The mold paint shown in Table 1 was applied by brush or spray so that some corners of the inner surface of the flat mold were not coated or lightly coated (coating amount less than 20?/lr?) or normally coated (~100 f/i). After pouring into the mold and producing a 16 ton steel ingot,
After the blooming process, the surface of the steel ingot with a thickness of 17n7IL was hot-rolled, and after cooling, the vertical cracks in the steel ingot were determined, and the results are shown in Table 1.

Note (1) A coating device with one nozzle attached horizontally to the end of a pipe for pumping paint was inserted into the mold from a gantry crane and the coating was applied manually.

Some parts of the mold corners were lightly coated due to paint scattering.

As shown in Table 1, the method of selectively applying the mold paint of the present invention can reduce the number of vertical cracks and sagging defects compared to the entire surface coating, and therefore can improve the yield.

The present invention is a casting method that reduces vertical cracking in steel ingots by applying a mold paint to the entire inner surface of the mold, and using a selective coating method that has not been thought of in the past in cases where vertical cracking has occurred in some steel ingots. It had a very good effect.

As explained in detail above, the ingot making method of the present invention makes it possible to produce a steel ingot with an extremely good skin when casting a steel ingot, and the steel ingot with the excellent skin has a high yield rate since it has no defects. The practical effects of the present invention are extremely remarkable, as it enables the production of final products with good quality and no defects, that is, high-quality strip steel plates and long steel products.

The ingot making method of the present invention can be expected to produce excellent results not only in making ordinary steel ingots, but also in making special steel ingots and non-ferrous metal ingots.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional plan view to explain the vertical cracking of a steel ingot that occurs during solidification after molten steel is poured into a flat mold. Figures 2 and 3 are cross-sectional plan views of a flat steel ingot and a deformed steel ingot. . 1...Mold, 2...Air gap, 3
．． 4.5 and 8... Solidified shell, 6...
- Unsolidified part, 7, 9... Vertical crack, A, B, C and D... Corner part (θ≦1200).

Claims (1)

[Claims] 1. In the method of injecting molten metal into a metal mold whose inner wall surface is coated with mold paint, the inner wall surface of the mold corresponding to the part where the separation between the inner wall surface of the mold and the agglomerate starts to slow due to solidification shrinkage. A metal ingot forming method for reducing cracks, characterized in that a mold paint is selectively applied to the inner wall surface of the mold, and the inner wall surface of the mold corresponding to the part where mold release starts early is left uncoated or lightly coated.