TWI553128B - The Method of Making Spinning Steel and the Method of Refining in Material - Google Patents

Description

Method for producing aging steel and method for miniaturizing

The present invention relates to a method for producing a aging steel and a method for miniaturizing a medium.

Since the aging steel has a very high tensile length of about 2000 MPa, it is used in various parts requiring high strength, such as rocket parts, centrifugal separator parts, aircraft parts, parts for gearless parts of automobile engines, molds, and the like. on.

The aging steel usually contains an appropriate amount of molybdenum (Mo) or titanium (Ti) as a strengthening element, and after aging treatment, an intermetallic compound such as Ni ₃ Mo, Ni ₃ Ti, Fe ₂ Mo is precipitated, and high strength can be obtained. . A representative composition of the aging alloy including such molybdenum (Mo) and titanium (Ti) can be exemplified by mass percentage, 18% Ni-8% Co-5% Mo-0.45% Ti-0.1% Al. -bal.Fe.

However, although the aging steel can obtain a very high tensile strength, on the other hand, the fatigue strength is not necessarily high. The biggest cause of this fatigue strength degradation There is a non-metallic intervening substance (hereinafter referred to as "intermediate") called a nitride or a carbonitride such as TiN or TiCN. In particular, TiN is often a cube shape with sharp corners. The sharp corners of the cube become the starting point for expanding the crack within the metal matrix. As the crack expands, the metal material is destroyed. If the size of these media is fine, it is not easy to become a starting point for the destruction of the metal material. However, if these intervening substances grow in a large amount in the metal material, fatigue damage will occur from these intermediates.

In order to reduce the aforementioned intervening material, a vacuum arc remelting method (hereinafter referred to as "VAR") is employed. The aging steel produced by such a VAR has a small amount of segregation and homogeneity, and has an advantage that the amount of matter is reduced.

However, in the aging steel produced by the vacuum arc remelting device, a large nitride or carbonitride such as TiN or TiCN remains, and the larger dielectric remains after the VAR is subjected to hot forging and heat treatment. After hot rolling and cold rolling, it remains in the original aging steel. The residual larger intervening material becomes the cause of fatigue damage caused by the intermediate matter

In order to solve this problem of mediation, there is a proposal to refine the matter. For example, Japanese Laid-Open Patent Publication No. 2001-214212 (Patent Document 1) discloses a method for producing Ti-containing steel by melting a raw material containing TiN-based material but containing Ti steel by a vacuum induction furnace. In the casting, the Ti-containing steel material to be produced is used as an electrode to carry out VAR, and the TiN system is made fine.

Further, it has been proposed to refine the titanium system such as TiN or TiCN. For example, Japanese Patent No. 4,692,282 (Patent Document 2) proposes a method for producing a steel block including a magnesium oxide forming step in which magnesium is added to a molten metal to adjust turbidity in one vacuum melting. The oxide composition in the molten steel is such that MgO becomes the main body; the consumable electrode step is obtained, after the magnesium oxide is formed, the molten steel is solidified to retain the magnesium oxide; and the dissociation step is performed by using the aforementioned consumption electrode Compared with the magnesium oxide forming step, the vacuum degree of the atmosphere (environment) is further reduced, the consumable electrode is remelted, the magnesium oxide in the melt is decomposed into magnesium and oxygen, and the magnesium content is set in the foregoing. 50% or less of the magnesium oxide forming step.

[Previous Technical Literature] (Patent Literature)

Patent Document 1: Japanese Laid-Open Patent Publication No. 2001-214212

Patent Document 2: Japanese Patent No. 4,692,282

The method proposed in the above Patent Document 1 is characterized in that a titanium-based dielectric material containing no TiN or TiCN is used, but a titanium-based steel material is used, whereby the titanium-based intervening substance can be made fine. The quality management of the raw material itself is a means of reducing the amount of titanium in the medium. High-quality raw materials are inevitably high-priced raw materials, so there is a problem of cost increase. In addition, the generation of titanium-based mediators also depends on the melting conditions and the like. Therefore, depending on the melting conditions, etc., in the manufacturing process, sometimes titanium The media will grow in large numbers. Therefore, the management of raw materials must be fully addressed.

On the other hand, the method of miniaturizing the material disclosed in Patent Document 2 is a method for refining a medium by using magnesium, and in particular, it is possible to further refine the titanium-based intervening substance, which is a very effective method. As in the method described in Patent Document 2, it is possible to further refine the titanium-based intervening material, and to further uniformize the size of the titanium intervening material due to the difference in the position of the steel block after remelting, thereby further obtaining the aging-effect steel product. Stable quality and characteristics.

An object of the present invention is to provide a method for producing a aging steel and a method for refining a medium, which can further refine the titanium-based intervening material and can uniformize the size of the titanium-based intervening material due to the position of the steel block. .

The present inventors reviewed the method of further refining the titanium system of the aging steel. As a result, in the case of a vacuum arc remelting method, when a consumable electrode composed of a magnesia-containing steel containing magnesium oxide is melted and produced into a steel block, a gas having a high thermal conductivity is introduced between the steel block and the mold. By cooling the steel block with the gas to improve the cooling efficiency of the steel block, it has been found that the titanium-based intervening material can be further refined, and the size of the titanium-based intervening material due to the difference in the position of the steel block can be made uniform. The present invention has thus been completed.

The invention relates to a method for manufacturing a aging steel, which adopts vacuum arc The vacuum arc remelting method of the melting device comprises at least a steel block manufacturing step of melting a consumable electrode composed of a magnesia-aged steel containing magnesium oxide in a mold of the foregoing device for manufacturing a steel block; Wherein, the steel block manufacturing step includes a cooling step of cooling the steel block by introducing a rare gas between the steel block and the mold.

On the other hand, the present invention relates to a method for miniaturizing the material of the aging steel by a vacuum arc remelting method using a vacuum arc remelting device, and a method for refining the intermediate of the aging steel, including at least a steel block. a manufacturing step of the steel block manufacturing step of melting a consumable electrode composed of a magnesia-aged steel containing magnesium oxide in a mold of the foregoing apparatus for manufacturing a steel block; Wherein, the steel block manufacturing step includes a cooling step of cooling the steel block by introducing a rare gas between the steel block and the mold.

According to the present invention, the titanium-based material remaining in the aging steel can be made finer and the size of the intervening material can be made uniform. As a result, it is possible to suppress fatigue fracture caused by the titanium-based medium as a starting point.

1‧‧‧Remelting consumable electrode

2‧‧‧ molten steel pool

3‧‧‧Steel

4‧‧‧Water-cooled copper mold

5‧‧‧ gas introduction nozzle

6‧‧‧Pressure measuring device

7‧‧‧Pressure control valve

8‧‧‧Pipe valve

10‧‧‧vacuum arc remelting device

A‧‧‧rare gas

Fig. 1 is a view showing an example of the structure of a vacuum arc remelting device for introducing a rare gas according to the present invention.

Hereinafter, the same state will be described with respect to an embodiment of the present invention. However, the present invention is not limited to the embodiments described below.

In the method for producing a aging steel of the present invention, the most important feature is that in the remelting step, a rare gas is introduced between the mold and the steel block in the VAR.

In the aging steel containing titanium, since the titanium intervening material formed in the steel has a high melting point, even when the consumable electrode is remelted, a part of the consumable electrode is not melted and remains, and is present in a solid form in the molten steel. In the pool. And it grows when the molten steel pool solidifies to form a steel block. If the cooling rate of the steel block can be increased, the steel block will be solidified immediately inside, and the growth time of the titanium-based medium can be shortened. Therefore, the titanium-based medium can be made finer. However, even if the speed of the melting consumable electrode is changed in the VAR, it is difficult to greatly change the cooling rate during solidification if the diameter of the same steel block is large. The reason for this is that in the VAR, a gap is formed between the steel block and the water-cooled copper mold due to solidification shrinkage of the steel block, and the conduction heat is isolated by the gap. Further, the following reason may be mentioned: In the prior art, since the gap described above is a reduced-pressure atmosphere, convective heat transfer is less likely to occur, and heat is mainly radiated only by radiant heat transfer, so that the steel block cannot be cooled. The heat transfer of the steel block is controlled by the heat transfer between the steel block and the mold. Therefore, in the prior art, the cooling rate of the VAR steel block is dependent on the diameter of the steel block.

Therefore, the manufacturing method of the present invention comprises a cooling step of using, for example, a rare gas guide in the gap between the steel block and the mold when manufacturing the steel block. An inlet nozzle or the like for introducing a rare gas and cooling it, thereby convecting heat between the steel block and the mold by convective heat transfer energy, and also increasing the cooling rate of the steel block during solidification. As a result, the growth of the titanium-based medium can be suppressed in the case of VAR. The titanization of the titanium-based medium is achieved. Further, by introducing a rare gas from the initial stage of the melting of the VAR, the cooling rate of the entire steel block can be increased, and the titanium-based medium coarsening in the longitudinal direction and the radial direction of the steel block can be suppressed, and the steel block can be made The titanium system caused by the difference in position is homogenized in the size of the object.

As described above, the present invention uses a rare gas to introduce the rare gas into the gap between the steel block and the mold. Rare gases do not chemically react with molten steel and steel blocks, so there is no need to worry about the formation of new chemical reactions. Furthermore, the use of rare gases can avoid the risk of explosion accidents caused by chemical reactions. Considering the cooling efficiency of the cooling steel block, it is preferable to use a rare gas having a high thermal conductivity in a rare gas, and the He (氦) gas is the most preferable in the rare gas. Further, when He gas is used, there is no problem even if He gas containing an impurity gas which can be ignored by chemical reaction with molten steel and steel blocks is used. In order to surely exert the cooling effect of He gas, the purity of He gas is preferably 99.9 volume% or more in terms of He gas.

Fig. 1 is a schematic view showing an example of the structure of a vacuum remelting device for introducing a rare gas according to the present invention. This figure is used to explain the case where the above-described cooling step contains a rare gas introduction step of introducing a rare gas into a mold of the vacuum arc remelting device by a rare gas introduction pipe. will The vacuum arc remelting device 10 of Fig. 1 is operated, whereby the remelting consumable electrode is dropped to form the molten steel pool 2, and the steel block 3 is further formed. The water-cooled copper mold 4 is used to cool the steel block 3. The rare gas A is introduced from the rare gas cylinder (not shown) through the gas introduction nozzle 5, and is introduced between the steel block 3 and the water-cooled copper mold 4 to cool the steel block 3. The introduction pressure of the rare gas A is measured by the pressure measuring device 6 to measure the gas sent from the rare gas cylinder to the water-cooled copper mold 4, and the pressure suppression valve 7 is provided, whereby the pressure can be controlled.

By increasing the pressure of the rare gas, the heat capacity per unit volume of the gas can be increased, and the effect of convective heat transfer can be improved. From this point of view, when the pressure in the gas pipe is less than 100 Pa, the effect of convective heat transfer is low, so that the effect of increasing the cooling rate is low. In addition, the vacuum arc remelting device is often operated under a reduced pressure gas, and even if the pressure of the rare gas introduced into the gap between the steel block and the mold is increased, the rare gas is leaked from the contact portion between the steel block and the mold by the vacuum pump. Exhaust rare gases. Further, if the rare gas for cooling the steel block leaks from the contact portion between the steel block and the mold, the gas may intrude into the region between the molten electrode and the molten steel pool. At this time, the arc is unstable due to the invading rare gas, which may increase the amount of the medium. Furthermore, even if the pressure of the rare gas is excessively increased, it is difficult to improve the convective heat transfer effect. Further, in order to promote denitrification and magnesium evaporation from the molten steel, it is preferred to set the reduced pressure gas as much as possible. Therefore, introduction of too much rare gas hinders denitrification and magnesium evaporation and is therefore poor. In consideration of the above factors, the pressure in the piping into which the rare gas is introduced is preferably in the range of 100 Pa to 3,000 Pa. The lower limit of the pressure in the piping into which the rare gas is introduced is preferably 100 Pa, preferably 600 Pa, more preferably 1000 Pa. Such as up to 1000Pa The above pressure makes the molten pool shallower more obvious. Therefore, the solid-liquid coexistence region in which the TiN crystal grows is also narrowed, so that the effect of refining TiN can be obtained more reliably, and therefore it is particularly preferable. Further, the upper limit of the pressure in the piping into which helium gas is introduced is preferably 300 Pa, preferably 2,500 Pa, more preferably 1,900 Pa. Although the cooling rate can be increased by increasing the pressure of helium, even if the pressure is excessively increased, it will be evacuated by vacuum, which does not contribute to cooling, and the effect is small.

The method for producing aging steel is particularly effective for steel blocks having an average diameter of 300 mm to 800 mm. The reason is that the larger the diameter of the steel block, the greater the thermal resistance of the steel block itself due to the influence of the convective heat transfer between the steel block and the mold, and the cooling rate of the steel block is related to the diameter of the steel block. The smaller the thermal conductivity, the stronger the tendency of the cooling rate of the steel block to be related to the diameter of the steel block, and the average diameter of the steel block is 300 mm or more, and the effect of increasing the cooling rate of the steel block becomes remarkable. If the average diameter of the steel block is less than 300 mm, the cooling rate is very fast even when the rare gas is not introduced. Therefore, when the rare gas is introduced, the effect of increasing the cooling rate is small. On the other hand, if the average diameter of the steel block exceeds 800 mm, even if a rare gas is introduced to improve the convective heat transfer between the steel block and the mold, the heat resistance of the steel block itself hinders heat dissipation, and the cooling rate is raised to the center of the steel block. The effect of the department may become smaller. Therefore, the average diameter of the steel block is preferably from 300 mm to 800 mm.

In addition, in the manufacture of the aging steel, the diameter of the steel block is not necessarily the same, and some differences may occur. Therefore, the average diameter of the steel block is calculated and the diameter of the steel block is specified.

In addition, the cooling rate of the steel block can reach 0.01 ° C / sec to 0.1 ° C / sec. this The cold speed of the steel block at the location refers to the cooling rate at the center of the steel block. It is difficult to measure the measured value of the cooling rate in actual operation. Therefore, it is preferable to measure the cooling rate in advance by simulation before melting.

In addition, in order to more reliably obtain the effect of increasing the cooling rate of the steel block by introduction of the aforementioned rare gas, for example, a plurality of rare gas introduction ports are provided, and a rare gas is introduced into the steel block manufacturing step to solidify the steel block. The structure that can always introduce fresh rare gas is most effective.

In the method for producing aging steel, the consumable electrode is composed of aging-age steel containing magnesium oxide. The consumable electrode is melted in a mold of a vacuum arc remelting device for manufacturing a steel block (steel block manufacturing step). The titanium-based intervening material is easily crystallized in the form of a titanium-based intervening-MgO composite, and the titanium-based intervening-MgO composite is an oxide mainly composed of magnesium oxide (MgO). Therefore, the aging steel contains magnesium oxide, whereby the titanium-based material can be present in a form in which the material is finely dispersed. Therefore, when a consumable electrode composed of a aging-containing steel containing magnesium oxide is used and a manufacturing method of a steel block manufacturing step including a cooling step is employed, the titanium-based intervening material remaining in the aging steel can be made fine. And it can make the size of the medium uniform.

In the present invention, the growth of the titanium-based medium is inhibited in the steel block manufacturing step. The above-mentioned consumable electrode composed of the aging-containing steel containing magnesium oxide used in this step can be produced by, for example, adding magnesium to the aging steel and vacuum-melting it (consumption electrode manufacturing step).

In the consumable electrode production step, a remelting consumable electrode containing a magnesium oxide-containing aging steel can be obtained. In such a step, the titanium-based material is easily crystallized by using an oxide mainly composed of MgO as a core, and thus can be used as a form of a titanium-based intervening-MgO composite. Further, in the consumable electrode, the titanium-based material can be present in a form in which the substance is finely dispersed.

In order to use the oxide in the consumable electrode as an oxide mainly composed of magnesium oxide, the amount of magnesium added is preferably in the range of 10 ppm to 200 ppm in the consumable electrode production step.

When VAR is performed using the aforementioned consumable electrode, the degree of vacuum is set as much as possible under a reduced pressure gas, whereby remelting can promote the evaporation of magnesium from the surface of the molten steel. By the evaporation of magnesium, the part of MgO which forms part of the Ti-based Mg-MgO composite disappears, whereby the residual Ti-based medium is finely dispersed, thereby promoting thermal decomposition and enabling the Ti-based medium to be in the molten steel. Completely melted. That is, if the titanium-based medium is completely melted in the VAR, the size of the titanium-based medium is related to the growth in solidification of the VAR. Therefore, the effect of introducing the aforementioned rare gas can be sufficiently exerted.

As described above, the method for producing the aging steel of the present invention can exert an effect on the refinement of the titanium-based medium. Therefore, the target aging steel is particularly effective for the aging steel which is actively added with titanium. The best specific composition is as follows. In addition, the content is expressed in terms of mass percentage.

Titanium is a fine intermetallic compound formed by aging treatment, and is a key element necessary for strengthening by precipitation. It is preferably contained in an amount of 0.2% or more. However, if the content exceeds 3.0%, ductility and toughness may deteriorate. Therefore, it is preferable to set the titanium content to 3.0% or less.

Oxygen (O) is an element that forms an oxide-based intervening substance. It is preferred to reduce the oxygen content of the oxide-forming intermediate. Therefore, it is preferable to limit the oxygen content to less than 0.001%.

Nitrogen (N) is an element that forms a nitride and carbonitride intervening material. In the present invention, the nitride-based intervening substance can be made fine, but it is preferable to reduce the nitrogen content of the nitride-based intervening substance in advance. Therefore, it is preferable to limit the nitrogen content to less than 0.0015%.

Regarding carbon (C), in order to form carbides and carbonitrides, to reduce the amount of precipitation of intermetallic compounds and to reduce fatigue strength, it is preferable to set the upper limit of the carbon content to 0.01% or less.

Nickel (Ni) is an essential element for forming a matrix structure having high toughness. However, if it is less than 8%, the toughness deteriorates. On the other hand, if it exceeds 22%, the Austenite is stable, and it is difficult to form a Martensite structure. Therefore, the nickel content is preferably set at 8 to 22%.

Cobalt (Co) does not greatly affect the stability of the matrix, ie, the structure of the martensite, and can lower the solid solubility of molybdenum (Mo), thereby promoting the formation of fine intermetallic compounds and precipitation of molybdenum, which is helpful. To strengthen the elements of precipitation. However, if the content is less than 5%, a sufficient effect is not necessarily obtained, and if it exceeds 20%, embrittlement tends to occur. Therefore, the cobalt content is preferably set at 5 to 20%.

Molybdenum (Mo) is formed by a aging treatment to form a fine intermetallic compound and precipitated as a matrix, thereby contributing to strengthening. However, when the content is less than 2%, the effect is small, and if the content exceeds 9%, coarse precipitates having deteriorated ductility and toughness are likely to be formed. Therefore, the content of molybdenum is preferably set to 2 to 9%.

Aluminum (Al) not only contributes to aging precipitation strengthening and deoxidation, but the content of aluminum is preferably 0.01% or more, and if the content exceeds 1.7%, the toughness is deteriorated. Therefore, the content of aluminum is preferably set to 1.7% or less.

In addition to the above-mentioned elements, iron (Fe), for example, boron (B), can be used, and is an element effective for refining crystal particles. Therefore, the content may not be deteriorated by 0.01% or less. In addition, it may contain impurities elements that are inevitably contained.

Next, a method of refining the intermediate of the aging steel of the present invention will be described. This miniaturization method is a method of refining the intervening material of the aging steel by the vacuum arc remelting method of the vacuum arc remelting device. And the method at least Including a steel block manufacturing step, the steel block manufacturing step is to melt a consumable electrode composed of a magnesia-aged steel containing magnesium oxide in the above-mentioned device mold to manufacture a steel block.

The titanium-based intervening material is easily crystallized in the form of a titanium-based intervening-MgO composite, and the titanium-based intervening-MgO composite is an oxide mainly composed of magnesium oxide (MgO). Therefore, the aging steel contains magnesium oxide, whereby the titanium-based material can be present in a form in which the material is finely dispersed. Therefore, when a consumable electrode composed of a aging-containing steel containing magnesium oxide is used, and a refining method for a steel block manufacturing step including a cooling step is employed, the titanium-based intervening material remaining in the aging steel is made fine. And can make the size of the medium uniform.

The steel block manufacturing step includes a cooling step of cooling the steel block by introducing a rare gas between the steel block and the mold. The heat can be dissipated by convection heat transfer between the steel block and the mold, thereby increasing the cooling rate of the steel block during solidification. As a result, it is possible to suppress the growth of the titanium-based intervening substance in the case of VAR, and to achieve the refinement of the titanium-based intervening substance. Furthermore, since the rare gas is introduced at the initial stage of the melting of the VAR, the cooling rate of the entire steel block can be increased, so that the titanium in the longitudinal direction and the radial direction of the steel block can be suppressed from coarsening, and the steel block can be obtained. Titanium is caused by the difference in position to homogenize the size of the object.

In addition, the cooling rate of the steel block can be set at 0.01 ° C / sec to 0.1 ° C / sec. Here, the cooling rate of the steel block means the cooling rate of the center portion of the steel block.

In the present invention, a gas introduced into the gap between the steel block and the mold is a rare gas. The rare gas does not chemically react with the molten steel and the steel block, so there is no need to worry about the formation of a new intermediate. If the cooling efficiency for cooling the steel block is considered, it is preferable to use a rare gas having a high thermal conductivity in the rare gas, wherein Helium (He) gas has the highest thermal conductivity in rare gases and is therefore the best. The use of rare gases can avoid the danger of explosion accidents caused by chemical reactions. In addition, when helium is used, there is no problem even if helium gas containing an impurity gas which can be neglected by chemical reaction with molten steel and steel blocks is used. In order to surely exert the cooling effect of helium, the purity of the crucible is preferably 99.9 volume percent or more.

The cooling step may include a rare gas introduction step of introducing the rare gas into the mold by a rare gas introduction pipe. By increasing the pressure of the rare gas, the average heat capacity per unit volume of the gas can be increased to improve the effect of convective heat transfer. Therefore, if the pressure in the gas pipe is lower than 100 Pa, the effect of convective heat transfer becomes low and the cooling rate cannot be increased. Further, since the vacuum arc remelting device is often operated under reduced pressure, the rare gas is discharged by the vacuum pump even if the pressure of the rare gas introduced into the gap between the steel block and the mold is increased. Therefore, even if the rare gas pressure is set to a pressure exceeding 3000 Pa, it is difficult to increase the convective heat transfer effect. Further, in order to promote denitrification and magnesium evaporation from the molten steel, it is preferable to set the decompressed gas as much as possible. Therefore, introduction of excess rare gas hinders denitrification and magnesium evaporation and is therefore not good. Therefore, the pressure in the piping into which the rare gas is introduced is preferably in the range of 100 Pa to 3000 Pa. The lower pressure limit in the piping into which the rare gas is introduced is preferably 100 Pa, preferably 600 Pa, more preferably It is 1000pa. Further, the upper limit of the pressure in the piping into which helium gas is introduced is preferably 3,000 Pa, preferably 2,500 Pa, more preferably 1900 Pa.

The method of refining the interfacial material of the aging steel is particularly effective for a steel block having an average diameter of 300 mm to 800 mm. The reason is that the larger the diameter of the steel block, the greater the influence of the convective heat transfer between the steel block and the mold on the thermal resistance of the steel block itself, and the cooling rate of the steel block depends on the diameter of the steel block. The smaller the thermal conductivity, the stronger the tendency of the cooling rate of the steel block to depend on the diameter of the steel block, and the average diameter of the steel block is 300 mm or more, and the effect of increasing the cooling rate of the steel block becomes obvious. If the average diameter of the steel block is less than 300 mm, the cooling rate is very fast even when the rare gas is not introduced. Therefore, when the rare gas is introduced, the effect of increasing the cooling rate is small. On the other hand, if the average diameter of the steel block exceeds 800 mm, even if a rare gas is introduced to improve the convective heat transfer between the steel block and the mold, the heat resistance of the steel block itself hinders heat dissipation, and the cooling rate is raised to the center of the steel block. The effect of the department may become smaller. Therefore, the average diameter of the steel block is preferably from 300 mm to 800 mm.

In addition, in the manufacture of the aging steel, the diameter of the steel block is not necessarily the same, and some differences may occur. Therefore, the average diameter of the steel block is calculated and the diameter of the steel block is specified.

In the present invention, the growth of the titanium-based medium is inhibited in the steel block manufacturing step. The above-mentioned consumable electrode composed of the aging-containing steel containing magnesium oxide used in this step can be produced by, for example, adding magnesium to the aging steel and vacuum-melting it (consumption electrode manufacturing step).

In the consumable electrode production step, a remelting consumable electrode containing a magnesium oxide-containing aging steel can be obtained. According to this step, since the titanium-based oxide containing MgO is easily crystallized as a core, it can be used as a form of a titanium-based intervening-MgO composite. Further, in the consumable electrode, the titanium-based material can be present in a form in which the substance is finely dispersed.

In order to use the oxide in the consumable electrode as an oxide mainly composed of magnesium oxide, the amount of magnesium added is preferably in the range of 10 ppm to 200 ppm in the consumable electrode production step.

When VAR is performed using the aforementioned consumable electrode, the degree of vacuum is set as much as possible under a reduced pressure gas, whereby remelting can promote the evaporation of magnesium from the surface of the molten steel. By the evaporation of magnesium, the MgO portion of the titanium-based Mg-MgO composite disappears, whereby the residual titanium is dispersed in the fine particles, thereby promoting thermal decomposition and enabling the titanium-based mediator to be in the molten steel. Completely melted. That is, if the titanium-based medium is completely melted in the VAR, the size of the titanium-based medium is related to the growth in solidification of the VAR. Therefore, the above-described effect of introducing a rare gas can be sufficiently exerted.

[Examples]

Hereinafter, the present invention will be specifically described based on examples and reference examples, but the present invention is not limited to the following examples.

(Example 1)

The present invention will be described in detail by way of Example 1. The consumable electrode manufacturing step is to manufacture a consumable electrode for vacuum arc remelting by vacuum melting. When manufacturing the consumable electrode, to form magnesium oxide, 14 ppm of magnesium was added, a test piece was taken from the consumable electrode, the test piece was dissolved by a nitric acid solution, and the solution was filtered with a 5 μm sieve, thereby leaving no nitric acid. The dissolved residue, that is, the intervening material is obtained from the consumable electrode. The obtained intervening substance was observed by a scanning electron microscope (SEM), and energy dispersive X-ray analysis (EDS) measurement was performed to investigate the presence or absence of magnesium oxide. As a result, it was confirmed that the intervening substance is a TiN-based intervening substance having MgO as a core. The consumable electrode was remelted in a VAR to produce a steel block.

In addition, the composition of the remelting electrode provided by the present invention example and the reference example is the same as the number and size of the electrode, and the manufacturing process of the consumable electrode is used, and the molten steel of the same shape is used, and the molten steel is simultaneously cast to produce two. Electrode for melting. Vacuum arc remelting is carried out using the vacuum arc remelting device 10 shown in Fig. 1. When the electrode 1 for remelting is remelted by VAR, the purity of the industrial helium gas is 4 N (99.99%) or more between the steel block 3 and the water-cooled copper mold 4, that is, the 氦 ratio is 99.99. The helium gas having a volume percentage or more is exemplified in the invention No. 1. When the remaining one of the remelting electrodes 1 was melted by the vacuum arc, helium gas was not introduced between the steel block 3 and the water-cooled copper mold 4, and was referred to as Reference Example No. 11. The steel blocks of the present invention and the reference examples have an average diameter of 500 mm.

The helium gas is cooled using the vacuum arc remelting furnace shown in Figure 1. The electrode 1 for remelting is provided and melted in the water-cooled copper mold 4. In the melting, the gas is introduced into the nozzle 5 from the lower portion of the water-cooled copper mold 4, and the helium gas is introduced into the gap between the steel block 3 and the mold 4. The pressure inside the pipe for conveying the gas from the helium gas cylinder to the mold is measured by the pressure measuring device 6, and the pressure control valve 7 is set, and the set helium gas pressure is constantly controlled to be constant. The introduced helium gas is filled in the gap between the steel block 3 and the water-cooled copper mold 4, and is radiated from the steel block 3, and the gas leaking from the gap is finally discharged to the outside by a vacuum pump (not shown).

In the melting, the pipe valve 8 provided in the pipe is opened, and after confirming the controlled helium pressure, the electrode for remelting is continuously melted. The helium pressure in the piping set in Example No. 1 was 1200 Pa. After the electrode melting is completed, the pipe valve 8 provided in the pipe is closed, and the set value of the pressure suppressing device is set to 0 Pa. The first table shows the composition of the electrode for remelting of Example No. 1 of the present invention and Reference Example No. 11, and the composition of the steel block.

Elements other than the above are Fe and unavoidable impurities.

Use [ ] to indicate that the element content is in ppm.

Secondly, a test piece for measuring the intervening material is collected from the top, the middle portion, and the bottom of the steel block of the aging steel which is remelted with VAR, and the steel block is perpendicular to the center. The direction of the shaft is cut at equal intervals, from the center of the steel block at the top, the middle, and the bottom of the steel block (D/2, D is the diameter of the steel block) and the middle of the steel block radius (D/4) The test piece for the measurement of the substance was 2 g each. The test piece for the measurement of the substance was dissolved in a nitric acid solution, and the TiN of TiN and TiCN which were not dissolved in the nitric acid solution were filtered through the sieve for the object. The residue on the sieve after filtration was observed by SEM, and the size of the titanium-based TiN and TiCN was measured.

In addition, the titanium-based TiN and TiCN-based media are selected by the SEM observation to select the titanium-based intervening substance, and the SEM photograph of the titanium-based intervening image is combined with the image analysis software to obtain a titanium-based intervening substance. The outline of the contour is calculated by image processing, and the area in the outline is calculated, and the area is converted into a circle diameter when the area is round. Next, the titanium-based mediator of the largest diameter is considered to be the maximum length titanium-based intervening agent in all titanium-based mediators observed on the screen. The second table and the third table are the dimensions of the titanium-based intervening material of TiN and TiCN which are confirmed at the top, the middle portion, and the bottom portion. The second table is from the center portion (D/2 portion) of the steel block, and the third table is the sample result collected from the middle portion (D/4 portion) of the radius of the steel block.

From the second table and the third table, it was confirmed that the titanium system of the present invention example No. 1 in which helium gas was introduced at any of the intermediate portion and the bottom portion had a small maximum length. In the case of Reference Example No. 11, there was a coarse titanium-based intervening material of about 7.8 μm, but in the present invention example No. 1, the largest titanium-based intervening material was about 7.2 μm. Therefore, when the aging billet is re-melted by vacuum arc, helium gas is introduced into the gap between the steel block and the mold, whereby the titanium-based intervening material can be confirmed to be fine.

In addition, the results of comparing the maximum length of the titanium in the top, the middle, and the bottom of the steel block, in the case of the reference example No. 11, according to the position in the longitudinal direction of the steel block and the position in the diameter direction, the titanium medium is the largest. The length is dispersed between 7.2 μm and 7.8 μm (Table 2, Table 3). On the other hand, in the case of the invention example No. 1, the maximum length of the titanium-based medium is in the range of 7.0 μm to 7.2 μm in accordance with the position in the longitudinal direction of the steel block and the position in the radial direction (second table, third table). The introduction of helium gas in the gap between the steel block and the mold enables the titanium system at the position of the steel block to be uniform in size. ,

(Example 2)

The present invention can be applied to the case where it is confirmed in Example 2 that the steel block diameter is larger than that of the above-described first embodiment for producing a large steel block. At this time, a steel block was produced under the condition that the helium pressure in the piping of the vacuum arc remelting device was changed. First, in the same manner as in the first embodiment, the consumable electrodes for re-melting the three vacuum arcs were produced by vacuum melting in the consumable electrode manufacturing step. When a consumable electrode is produced, magnesium is added to form a magnesium oxide. To investigate the presence or absence of magnesium oxide, use and implementation In the same manner as in Example 1, when a test piece was collected from a consumable electrode to investigate the presence or absence of magnesium oxide, the TiN system of the three consumable electrodes was made of MgO. These consumable electrodes were remelted with VAR to produce steel blocks.

In the three electrodes for remelting, when two electrodes for remelting are remelted by VAR, a helium gas having a ytterbium ratio of 99.9 vol% is introduced between the steel block 3 and the water-cooled copper mold 4 to produce a steel block. Inventive Examples No. 2 and No. 3). When the remaining one remelting electrode was subjected to vacuum arc remelting, helium gas was not introduced between the steel block 3 and the water-cooled copper mold 4 to produce a steel block (Reference Example No. 12). The average diameter of the steel block of the present invention and the reference example was 550 mm.

The cooling by helium gas was carried out in the same manner as in Example 1. In the case of cooling by helium gas, the helium gas pressure in the set pipe was 1300 Pa in the present invention example No. 2, and the sample No. 3 in the present invention was 1860 Pa. The fourth table shows the composition of the electrode for remelting of the examples of the present invention and the reference example, and the composition of the steel block to be produced.

Elements other than the above are Fe and unavoidable impurities.

Use [ ] to indicate that the element content is in ppm.

The re-melted aging steel was forged by VAR, and forged into a slab shape, the test piece for the measurement of the substance was collected from the top, the middle, and the bottom, and cut at equal intervals in the direction perpendicular to the central axis. In the center portion of each of the diameter direction and the thickness direction, 2 g of the test piece for interstitial measurement was collected. After the shape of the slab was forged, the test piece for the measurement of the interstitial was collected. Therefore, the distribution of the size of the titanium-based TiN in the diameter direction of the steel block was not investigated. Further, the size of the titanium-based intervening material such as TiN or TiCN was measured in the same manner as in Example 1, and the largest titanium-based intervening material was used as the titanium system in all the titanium-based intermediaries observed on the sieve. The maximum length of the object. The fifth table indicates the size of the titanium-based intervening material such as TiN or TiCN which is confirmed in the top, the intermediate portion, and the bottom portion of the slab stage.

As is apparent from the fifth table, in the examples No. 2 and No. 3 of the present invention in which helium gas was introduced at any of the top, the intermediate portion, and the bottom of the slab, the maximum length of the titanium-based intervening material was small. In the case of Reference Example No. 12, it was confirmed that there was a coarse titanium-based intervening material of about 7.5 μm to 8.1 μm. On the other hand, in the example of the present invention, the largest titanium-based medium was 7.26 μm. From the above results, it is understood that even if the diameter of the steel block is increased, the titanium-based intervening material is refined by introducing the cooling effect of the helium gas.

Further, the variation in the size of the titanium-based medium is small in the example of the present invention, and particularly in the case of the examples No. 2 and No. 3 of the present invention, the maximum length in the top portion and the intermediate portion is 7.0 μm to 7.15 μm, respectively. Within the range of 7.2 μm to 7.3 μm. On the other hand, in Reference Example No. 12, the maximum length of the titanium-based medium in the top and the middle portion was 8.1 μm to 8.5 μm, respectively, and thus the results were inferior to those in the examples of the present invention.

The sixth table shows the results of calculation of the amount of heat radiation when the steel blocks were produced in the first and second embodiments. The amount of heat dissipation is as shown in the following formula (1). The average water temperature of the cooling water introduced into the water-cooled copper mold is multiplied by the water temperature of the cooling water discharged from the water-cooled copper mold after cooling the steel block. The temperature difference of the values is calculated. The water temperature of the cooling water of the first embodiment is the time when the operation state of the vacuum arc remelting furnace is stable, that is, the time from the start of the remelting time to the end of the remelting after 200 minutes after the start of the operation, that is, from the start of operation to the start of the operation. The measurement was carried out for 500 minutes. On the other hand, the water temperature of the cooling water of the second embodiment is the time when the operation state of the vacuum arc remelting furnace is stable, that is, the time from the start of the remelting time to the end of the remelting after 300 minutes after the start of the operation, that is, The measurement was carried out from the start of the operation to the time of 1000 minutes.

[Formula 1] Heat dissipation amount = (average water temperature at which cooling water is discharged - average water temperature at which cooling water is introduced) × flow rate (1)

Water temperature unit: °C

Flow unit: L/min

[Table 6]

As is apparent from the results of the sixth table, in the example of the present invention in which helium gas was introduced into the gap between the steel block and the mold, the heat radiation amount was increased as compared with the reference example. The cooling water introduced into the water-cooled copper mold not only cools the steel block, but also introduces helium gas to cool the steel block. By calculating the amount of heat dissipation, it is possible to confirm the heat dissipation effect of the crucible.

From the above results, it is understood that the helium gas is introduced into the gap between the steel block and the mold, and the steel block is cooled by the helium gas, so that the titanium system at the position of the steel block can be made uniform in size. Regarding the bottom of the billet, since it is connected to the bottom of the water-cooled copper mold 4, the cooling rate is larger than that of other regions. Therefore, the cooling effect of the mold and the cooling effect of the helium gas have a common effect, and it is considered that the titanium system can be made finer than the middle portion of the steel block and the middle portion of the steel block.

According to the above, when vacuum arc re-melting is performed on the aging steel, helium gas is introduced into the gap between the steel block and the mold, whereby the titanium-based medium can be made fine, and the position of the steel block can be suppressed. The titanium system is a variation in the size of the object. As a result, it is possible to suppress fatigue fracture starting from the intervening material of the aging steel, and it is possible to stabilize the quality and characteristics of the aging steel product.

Claims (10)

A method for manufacturing a aging steel is a vacuum arc remelting method using a vacuum arc remelting device, comprising at least a steel block manufacturing step, wherein the steel block manufacturing step comprises a consumable electrode composed of a magnesia-aged steel containing magnesium oxide in the foregoing The mold of the apparatus is melted to produce a steel block; wherein the step of manufacturing the steel block includes a cooling step of cooling the steel block by introducing a rare gas between the steel block and the mold. The method for producing a aging steel according to claim 1, wherein the rare gas contains 99.9 volume% or more of ruthenium. The method for producing a aging steel according to claim 1, wherein the cooling step includes a rare gas introduction step of introducing the rare gas into the mold by a rare gas introduction pipe; and introducing the rare gas The pressure of the rare gas in the tube is 100 Pa to 3000 Pa. The method for producing a aging steel according to claim 1, wherein the steel block has an average diameter of 300 mm to 800 mm. The method for producing a aging steel according to any one of claims 1 to 4, further comprising a consumable electrode manufacturing step of adding magnesium to the aging steel by vacuum melting To manufacture the aforementioned Consuming electrodes. A method for miniaturizing the material of the aging steel is a method for refining the intermediate of the aging steel by a vacuum arc remelting method using a vacuum arc remelting device, at least comprising a steel block manufacturing step, the steel block manufacturing a step of melting a consumable electrode composed of a magnesia-aged steel containing magnesium oxide in a mold of the foregoing apparatus for manufacturing a steel block; wherein the step of manufacturing the steel block includes a cooling step by introducing the steel block and The rare gas between the aforementioned molds cools the aforementioned steel block. The method for miniaturizing the aging steel according to claim 6, wherein the rare gas contains 99.9% by volume or more of ruthenium. The method for miniaturizing the aging steel according to claim 6, wherein the cooling step includes a rare gas introduction step of introducing the rare gas into the mold by a rare gas introduction pipe; The rare gas pressure in the rare gas introduction pipe is 100 Pa to 3000 Pa. The method for miniaturizing the aging steel according to claim 6, wherein the steel block has an average diameter of 300 mm to 800 mm. The invention of the aging steel according to any one of claim 6 to claim 9 The material refining method further includes a consumable electrode manufacturing step of adding magnesium to the aging steel and manufacturing the aforementioned consumable electrode by vacuum melting.