JPS5921253B2 - Manufacturing method of steel ingots - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention involves pouring molten steel around a core in a mold to form a hollow steel ingot, and then remelting and filling the hollow part by vacuum arc melting to form a hollow steel ingot at the center of the steel ingot. The present invention relates to a method for manufacturing steel ingots with improved quality.

There is a method in which the axial core of a steel ingot is made hollow and this hollow part is filled by electroslag melting.

The method of filling the hollow part of a hollow steel ingot by vacuum arc melting is a completely new method, and this method provides the following effects compared to the method of filling the hollow part by electroslag melting.

(1) Absorption of hydrogen gas can be prevented.

(2) Low-quality consumable electrodes that are not vacuum-cast or vacuum-degassed can be used.

However, a technical obstacle that makes it difficult to fill the hollow space by vacuum arc melting is the obstacle caused by molten metal splashes during vacuum melting, which has already been widely experienced in the vacuum arc melting method.

In the vacuum arc melting method, molten metal droplets adhere to the side wall of the water-cooled mold, and elements such as manganese, which have a relatively high vapor pressure in the molten metal, are deposited thereon.

As vacuum arc melting progresses, these deposits are remelted, but due to the cooling effect of the water-cooled mold in the vacuum arc furnace, the deposits that should be remelted may not be sufficiently melted or may not be dissolved uniformly within the steel ingot. Sometimes I don't.

As a result, defects in the cast surface of the steel ingot and abnormal segregation of manganese and the like occur in shallow subcutaneous locations.

Therefore, the outer layer of the steel ingot obtained by vacuum arc melting generally requires turning.

The purpose of the present invention is to solve the problems when filling the hollow part of a hollow steel ingot by vacuum arc melting, and to produce a steel ingot with higher quality in the center of the steel ingot than the hollow part filling method using electroslag melting. It is in providing the law.

. In the present invention, a hollow core made of steel plate is placed on a water-cooled surface plate, molten steel is poured between the core and a steel ingot mold to form a hollow steel ingot, and the inside of the core is subsequently evacuated. The consumable electrode, the core, and a part of the ingot-formed hollow steel ingot are melted by vacuum arc melting using a consumable electrode, and the hollow part is filled with overlay.

For the reasons mentioned above, it was thought that it would be difficult to vacuum arc melt the hollow part of the hollow steel ingot, but as a result of the inventor's study, it was possible to remelt the hollow part of the hollow steel ingot without providing any special water cooling effect, and to make a steel plate core. By melting a part of the lumped hollow steel ingot, not only the deposit-resistant material but also the vicinity of the core of the base material is remelted, forming a filled part with high compositional uniformity. It was determined that no casting defects occurred.

Depending on the degree of deoxidation of the hollow steel ingot, boiling of the molten metal may occur during remelting under vacuum, but this can be prevented by controlling the degree of vacuum, such as by introducing argon gas.

In the present invention, a hollow core made of a steel plate is placed in a steel ingot mold, and molten steel is poured around the core to produce a hollow steel ingot.

As for the method of manufacturing hollow steel ingots, mechanical drilling, whether hot or cold, involves huge processing costs and a decrease in steel ingot yield, making it difficult to implement from an economic point of view.

In the present invention, a known hollow steel ingot manufacturing method (Japanese Unexamined Patent Publication No. 51-32
431), a hollow steel ingot is manufactured using a hollow core made of a steel plate, and the hollow core made of a steel plate is welded to molten steel.

For vacuum arc melting, it is necessary to place a steel plate hollow core on a water-cooled surface plate.

The water-cooled surface plate plays an important role as a chiller in the initial process of vacuum arc melting work.

If the bottom of the steel plate hollow core is a metal surface plate that is not specially cooled, the surface plate will definitely melt due to the initial energization of vacuum arc melting, and the metal filled with overlay will be welded to the surface plate. do.

For this reason, it becomes impossible to repeat and industrially carry out a series of processes in which the hollow steel ingot manufacturing process and the filling process of the hollow portion are successively performed.

Furthermore, the melted metal from the surface plate at this time mixes with the bottom of the steel ingot remelting section, causing component contamination.

A water-cooled surface plate can solve these problems.

Furthermore, the water-cooled surface plate also has the function of adjusting excessive penetration of the steel ingot base material due to unsteady energization conditions at the initial stage of vacuum arc melting.

Therefore, the surface plate must have a water-cooled structure, and the outer diameter of the surface plate must be made larger than the outer diameter of the steel plate hollow core so that the steel plate hollow core can be placed on the water-cooled surface plate.

It has become clear that the present invention can substantially overcome the obstacles associated with remelting and filling the hollow parts of hollow steel ingots, which are expected from conventional vacuum arc melting methods.

As a method of overlaying the hollow part of a hollow steel ingot, the benefits of using vacuum arc melting compared to electroslag melting will be further explained.

The purpose of such a process is to remelt and fill the center of a large cross-section steel ingot, but the biggest weakness of the electroslag melting method is the absorption of hydrogen gas from the atmospheric atmosphere and slag due to remelting.

In electroslag melting, countermeasures are taken such as blowing argon gas into the slag and molten metal pool during melting to eliminate hydrogen gas, or sealing the slag with dry air or inert gas for melting. , 2py to hydrogen content in steel
This is just a measure to maintain the concentration around n and prevent it from becoming enriched.

Moreover, it is generally necessary to use a consumable electrode that has been vacuum cast or vacuum degassed.

On the other hand, in vacuum arc melting, since the melting is carried out under vacuum, hydrogen is not absorbed, but rather hydrogen gas and other harmful gas components are actively degassed. I can do it.

This feature regarding the hydrogen content of the remelted filler metal has an extremely large effect on the material quality from the perspective of overlay work on the center of a large cross-section steel ingot.

In other words, it is difficult for the hydrogen element in the center to be easily diffused and dehydrogenated by the diffusion heating that accompanies hot working. When tested, it was found that white dot cracking defects caused by the hydrogen content frequently occurred as internal defects in the product.

Products processed by vacuum arc melting according to the present invention had no white spot defects due to hydrogen content.

In the present invention, the hollow core made of steel plate plays the role of a vacuum vessel in vacuum arc melting.

A hollow core made of a steel plate is airtightly connected to a vacuum barrel of a vacuum arc furnace, evacuated, and a consumable electrode is inserted into the core and energized to produce a consumable electrode, a hollow core made of a steel plate, and a steel ingot base material. A part of the steel is re-melted to fill the hollow part to obtain a steel ingot with improved internal quality.

By using the hollow steel ingot mold assembly as it is as the lower molding device of the vacuum arc melting furnace, it is possible to start overlay filling of the hollow part by vacuum arc melting at the same time as the ingot forming of the hollow steel ingot is completed. Huge economic effects such as elimination of the hot or cold drilling process, reduction in yield, and shortening of manufacturing process time can be cited.

Embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view of an embodiment of the present invention.

FIG. 1 shows a mold configuration that is almost the same as that of the conventional hollow steel ingot manufacturing method, in which a feeder refractory 11 is arranged at the top of the steel ingot mold 1, and a surface plate 2 has a mold structure similar to that of the present embodiment. Because it is a bottom pouring ingot method,
A runner brick 9 assembled with an injection port brick 10 and a runner metal frame 4 is installed in communication with each other.

A steel plate hollow core 12, which is a feature of this hollow steel ingot manufacturing method, is placed on a water-cooled surface plate 3 via a core bottom plate 7.

The water cooling surface plate is made of copper and has an outer diameter larger than the outer diameter of the core 12, and has a cooling water port 6 and a cooling water outlet 5.

The bottom end of the steel plate hollow core is welded to a core bottom plate 7, and a steel ingot mold 1 is placed and fixed on a part of the core bottom plate γ as shown.

The molten steel passes through the runner bricks and fills the gap between the steel plate hollow core 12 and the steel ingot mold 1.

From the initial stage of casting to the hollow steel ingot base material, the steel plate hollow core 12
receives high heat from the molten steel and steel ingot, becomes plastic and deforms in response to solidification shrinkage and cooling shrinkage of the steel ingot.

Therefore, no steel ingot cracking occurs in the hollow steel ingot 13, and the ingot making process of the hollow steel ingot is completed.

Next, the ignition plate 14 for starting vacuum arc melting is placed at the bottom of the hollow part of this hollow steel ingot, and if necessary, after adding auxiliary materials necessary for maintaining the arc, such as daiko, to the surrounding area, the consumable electrode 16 is assembled by tightly inserting the flange 29 of the hollow core made of steel plate and the flange 27 of the vacuum cylinder through an electrical insulating material 28 which also serves as a vacuum seal.

The vacuum vessel constituted by the vacuum shell 25 and the steel plate hollow core 12 is evacuated via the exhaust hole 26 by a separately prepared vacuum exhaust system.

The consumable electrode 16 is raised and lowered by the electrode stub 18 and its gripping device 19 via a pulley 22 and the like by a lifting wire drum 23.

The elevating wire drum 23 is rotated forward and backward by a drive shaft 24 vacuum-sealed with the vacuum cylinder 25 using a separately prepared electric motor.

Although the explanation of the control of the electric motor will be omitted, it is assumed that it is automatically controlled according to the vacuum arc melting conditions.

The sliding bushing 20 and the guide shaft 21 prevent the consumable electrode from moving when moving up and down, and are connected to a power source via power supply cables and power supply intake busbars 30 and 31.

For example, in the case of DC melting, generally 30 is negative, 31
is connected positively.

When the degree of vacuum reached the predetermined level, the ignition plate 1 was inserted.
An electric arc, ie, an arc 17, is generated between the tip of the consumable electrode 16 and the tip of the consumable electrode 16, and then the consumable electrode 16 is remelted by automatic control while maintaining a stable electric arc and an appropriate melting rate. form.

In this case, the hollow steel ingot 13 itself may be in the state of a red material after solidification, or may be a gold material cooled to near room temperature.

Thermal conditions for overlaying both middle parts can be arbitrarily determined by taking into consideration thermal energy loss and the amount of melt penetration into the base material.

The consumable electrode 16 for vacuum arc melting may have the same chemical composition as the hollow steel ingot base material, or may be intentionally selected to have a different chemical composition.

However, it is generally preferable that the steel plate hollow core 12 be made of mild steel, and a remelted filling part is formed by the consumable electrode, the melting part of the hollow steel ingot base material, and the steel plate hollow core. The composition of the filling part is adjusted by calculating the distribution of the amounts of these three components.

A distinctive feature of the present invention is that the hollow core made of steel plate used for manufacturing the hollow steel ingot 13 completely disappears by vacuum arc melting, and is completely melted together with droplets and deposits during vacuum mark melting, and is consumed. The point is that a high-quality vacuum degassed shaft core remelting filling part 15 is formed together with the electrode and the base material melting part.

Furthermore, an extremely economical manufacturing method has been established by utilizing the hollow core 12 made of a steel plate as a vacuum container or mold in an expendable manner.

In addition, for the sake of convenience, the manufacturing of hollow steel ingots described here involves the installation of a mold by the bottom pouring ingot method, but the runner brick type 9
And 10, the case of using the top pouring method in which the runner metal frame 4 is omitted can also be carried out.

[Brief explanation of the drawing]

FIG. 1 is a front sectional view showing an example of an apparatus for carrying out the method of the present invention. 1... Steel ingot mold, 2... Surface plate, 3...
...Water cooling surface plate, 5...Cooling water inlet, 6...
... Cooling water outlet, γ ... Core bottom plate, 12.
...Hollow core made of steel plate, 13...Hollow steel ingot, 14...Ignition plate, 15...Remelting part, 16... Consumable electrode, 11... Arc, 18... Electrode stub, 19... Gripping device, 20... Sliding bush 21...
Guide shaft, 22... Pulley, 23... Lowering wire drum, 25... Vacuum cylinder, 26...
...Exhaust hole, 27...Vacuum barrel flange, 28
...Electrical insulation material, 29 ... Core flange, 30 ... O bus bar, 31 ...... ■
Bus bar.

Claims (1)

[Claims] 1 A step of forming a hollow steel ingot by pouring molten steel between a steel ingot mold and a steel plate hollow core on a water-cooled surface plate, and airtightly connecting the steel plate hollow core with a vacuum arc furnace vacuum shell. Then, the inside of the core is evacuated, and vacuum arc melting is performed inside the core using a consumable electrode to melt the consumable electrode, the core, and a part of the ingot-formed hollow steel ingot, thereby fleshing out the hollow part. A method for manufacturing steel ingots characterized by filling.