JP2010037651A - Method for producing titanium-ingot by vacuum arc melting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a titanium-ingot by a vacuum arc melting method by which the defective casting surface of the produced titanium ingot can be restrained. <P>SOLUTION: The titanium-ingot 6 is produced by: generating an arc 4 between a consumable electrode 1 made of titanium and suspended in a vacuum arc furnace 2 and a titanium starting material spread all over the bottom part of a water-cooled copper crucible 3 in the vacuum arc furnace 2; dripping the molten titanium droplet from the consumable electrode 1; and cooling and solidifying a molten pool 5 formed by collecting the molten titanium droplet. In this case, the titanium-ingot 6 is produced by stirring the molten pool 5 while rotating the arc 4 at the rotational speed of 4.0-20.0 sec/rotation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing a titanium ingot by a vacuum arc melting method in which a titanium ingot is produced from a titanium material such as sponge titanium using a vacuum arc melting method, and more specifically, a titanium ingot is produced using a vacuum arc melting method. In manufacturing, the present invention relates to a method for manufacturing a titanium ingot by a vacuum arc melting method capable of suppressing the occurrence of casting surface defects (surface defects) of the manufactured titanium ingot.

  Titanium (Ti) is an active metal that is violently oxidized by air at the melting temperature, and it is difficult to dissolve in an air atmosphere with a refractory crucible like a steel material. Therefore, various special melting techniques have been developed. At present, titanium ingots are manufactured by vacuum arc melting, plasma arc melting, electron beam melting, cold crucible induction melting, and the like. Among these manufacturing methods, the vacuum arc melting method is most frequently used for manufacturing titanium ingots.

  Conventionally, titanium ingots have been manufactured from titanium materials such as sponge titanium using this vacuum arc melting method, but the surface of the manufactured titanium ingot has irregular castings such as irregularities, wrinkles and shrinkage nests (surface defects). If a titanium ingot with a defective casting surface is used and machine processing such as forging or rolling is performed in the next step, the defective casting surface may become a surface defect. There was a problem that it was taken over as it was.

  Therefore, when a casting surface defect of a certain depth or more occurs in a titanium ingot, it is necessary to perform work to remove the surface with a grinder, a lathe, etc. It also had the problem of being wasted.

  In order to prevent the above various problems from occurring, when manufacturing a titanium ingot by using the vacuum arc melting method, the titanium ingot to be manufactured should not have a defective casting surface. It is necessary to produce an ingot. For this reason, various attempts have been made to improve various manufacturing methods as described below, and the occurrence of casting surface defects has been actually suppressed. According to those conventional techniques, although it was possible to obtain a certain casting surface defect occurrence suppression effect, the casting surface defect is still occurring to some extent, and it is possible to reliably suppress the occurrence of the casting surface defect. It could not be said that the production method can. In addition, there are manufacturing methods that require various additional materials for manufacturing titanium ingots, and it has been difficult to put into practical use.

Patent Document 1, CaO system the inner surface of the crucible and forming the prismatic provided with R at the four corners of water-cooled copper crucible used for production of such titanium ingots, ZrO ₂ system, TiO ₂ system, _Al 2 _{O 3} system A method of manufacturing a titanium ingot or the like by lining with a refractory material such as and applying a magnetic field of 5 to 75 gauss in the vertical direction inside the crucible when the electrode is melted is disclosed.

  In Patent Document 2, in the production of an ingot of a metal or alloy such as stainless steel, a metal to be melted is used as a consumable electrode, and this is melted and dropped into a water-cooled copper mold by each heat source to produce the ingot. In addition, there is disclosed a method of manufacturing an ingot by filling a gap between a mold and an ingot formed by melting and dropping melted and dropped in the mold into a molten metal.

  Patent Document 3 discloses a method of melting in an ingot using a consumable electrode made of titanium sponge as a main raw material. The melted ingot is cooled in a furnace, and the surface temperature becomes 300 to 700 ° C. A method is disclosed in which it is discharged to the outside of the furnace in stages, water-cooled until the surface temperature of the ingot reaches 100 to 200 ° C., and then the surface is dried.

  Patent Document 4 discloses a method for producing a titanium ingot by melting a consumable electrode by an arc and solidifying dripping titanium or a titanium alloy. Disclosed is a method for producing a titanium ingot with 15 to 80% of the Stirling current, 35 to 100% of the reversal time, or more than 80 to 100% of the Stirling current and 35 to 95% of the reversal time, respectively, in the stationary phase. .

  In Patent Document 5, when an ingot is produced by dissolving a refractory metal in a copper water-cooled vessel in an inert atmosphere, a coating material containing 30% or more of a refractory metal (Ti) oxide is formed on the inner surface. A method of manufacturing an ingot using a coated copper water cooled vessel is disclosed.

  As described above, all of the techniques described in these patent documents can suppress the occurrence of casting surface defects to some extent, but there is still room for improvement or practical use. It is a technology that is difficult to make, and the development of new technology is underway, and a new method for manufacturing a titanium ingot that can more reliably suppress the occurrence of defective casting surface It was a long-awaited development of technology.

JP-A 61-143528 JP-A-9-70656 JP 2003-41330 A JP 2003-221630 A JP 2003-239025 A

  The present invention has been made to solve the above-described conventional problems, and in producing a titanium ingot using the vacuum arc melting method, it suppresses the occurrence of defective casting surface (surface defects) of the produced titanium ingot. It is an object of the present invention to provide a method for producing a titanium ingot by a vacuum arc melting method capable of ensuring the above.

  The invention according to claim 1 generates an arc between a consumable electrode made of titanium suspended in a vacuum arc furnace and a titanium start material laid on the bottom of a water-cooled copper crucible of the vacuum arc furnace, and the consumable In a titanium ingot manufacturing method by a vacuum arc melting method in which titanium droplets are sequentially dropped from an electrode and a molten pool formed by collecting the titanium droplets is cooled and solidified to produce a titanium ingot. The titanium ingot is manufactured by a vacuum arc melting method, wherein the titanium ingot is manufactured by stirring the molten pool by rotating at a rotational speed of 4.0 to 20.0 sec / rotation.

  The invention according to claim 2 is the vacuum arc melting according to claim 1, wherein the titanium ingot is a JIS type KS40 titanium ingot, and the arc rotates at a rotation speed of 6.7 to 10.0 sec / rotation. It is the manufacturing method of the titanium ingot by a method.

  The invention according to claim 3 is the vacuum arc melting according to claim 1, wherein the titanium ingot is a JIS type 2 KS50 titanium ingot, and the arc rotates at a rotational speed of 4.0 to 6.7 sec / rotation. It is the manufacturing method of the titanium ingot by a method.

  According to the method of manufacturing a titanium ingot by the vacuum arc melting method according to claim 1 of the present invention, when manufacturing the titanium ingot using the vacuum arc melting method, the titanium ingot adheres to the inner wall of the water-cooled copper crucible that causes a defective casting surface. The formed splash can be redissolved, and it is possible to reliably suppress the occurrence of casting surface defects (surface defects) of the manufactured titanium ingot.

  According to the method of manufacturing a titanium ingot by the vacuum arc melting method according to claim 2 of the present invention, water-cooled copper which causes a defective casting surface in manufacturing a JIS type KS40 titanium ingot using the vacuum arc melting method. The splash formed on the inner wall of the crucible can be remelted more reliably, and the occurrence of defective casting surface (surface defects) of the manufactured titanium ingot can be further reliably suppressed.

  According to the method for producing a titanium ingot by the vacuum arc melting method according to claim 3 of the present invention, in producing a JIS type 2 KS50 type titanium ingot by using the vacuum arc melting method, water-cooled copper which causes a defective casting surface. The splash formed on the inner wall of the crucible can be remelted more reliably, and the occurrence of defective casting surface (surface defects) of the manufactured titanium ingot can be further reliably suppressed.

It is a longitudinal cross-sectional view of the vacuum arc furnace which shows the method of manufacturing a titanium ingot using a vacuum arc melting method. It is explanatory drawing which shows the breakdown of the consumable electrode and charge material which were used for manufacture of the titanium ingot which consists of KS40M in the Example of this invention. It is explanatory drawing which shows the breakdown of the consumable electrode and charge material which were used for manufacture of the titanium ingot which consists of KS50 in the Example of this invention. It is explanatory drawing which shows the relationship between the arc rotational speed (sec / rotation) at the time of manufacture of all the titanium ingots manufactured in the Example, and a casting surface defective area rate. It is explanatory drawing which shows the relationship between the frequency (Hz) of an arc voltage, and an arc rotational speed (sec / rotation). It is explanatory drawing which shows the relationship between the arc rotational speed (sec / rotation) at the time of manufacture of the KS40 type | system | group titanium ingot manufactured in the Example, and a casting surface defect area rate. It is explanatory drawing which shows the relationship between the arc rotational speed (sec / rotation) at the time of manufacture of the KS50 type | system | group titanium ingot manufactured in the Example, and a casting surface defect area rate.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.

  First, a method for producing a titanium ingot using a general vacuum arc melting method will be described with reference to FIG. First, the purchased granular titanium material such as titanium sponge is made into a briquette by a compact press. Some of the briquette titanium is joined by plasma welding to form a rod-shaped consumable electrode 1 as shown in FIG. The consumable electrode 1 is suspended in a vacuum arc furnace 2 as a primary electrode, and a high-current arc 4 is placed between a lower end of the consumable electrode 1 and a titanium start material (not shown) spread on the bottom of the water-cooled copper crucible 3. When generated, the arc 4 melts titanium from the lower end of the consumable electrode 1 to form droplets and melts sequentially. The melted droplets gathered and the molten pool 5 formed in the water-cooled copper crucible 3 is cooled from the lower part and solidified to obtain a titanium ingot 6.

  In order to obtain a titanium ingot 6 of good quality, homogenization of the components is not sufficient only by this primary melting, so that the titanium ingot 6 obtained by the primary melting is used again as the consumable electrode 1, and the secondary melting, In the vacuum arc melting method, a method of obtaining the final titanium ingot 6 by performing the third melting after the second melting or the number of times more than that, if necessary, is generally used.

  The general vacuum arc melting method is performed according to the procedure described above. However, in order to perform the vacuum arc melting more efficiently, the titanium scrap and the steel scrap are formed between the water-cooled copper crucible 3 of the consumable electrode 1 during the primary melting. A method of reducing the melting time and power consumption by continuously charging a charge material (not shown) mixed with sponge titanium has also been implemented.

  In the present invention, at least when melting to obtain the final titanium ingot 6 (for example, when melting twice, in the secondary melting), the arc 4 is rotated by electromagnetic stirring so that the molten pool 5 is formed. The titanium ingot 6 is manufactured by stirring. If the arc 4 is concentrated in one place, only the temperature of the portion where the arc 4 is concentrated becomes high, and the possibility that the titanium ingot 6 having a casting defect is manufactured is increased, and therefore the arc 4 is rotated. Moreover, by stirring the molten pool 5, the molten metal is vigorously brought into contact with the inner wall of the water-cooled copper crucible 3, and there is also an effect of adhering to the water-cooled copper crucible 3 and melting the splash that causes the occurrence of casting surface defects.

  The rotation of the arc 4 and the stirring of the molten pool 5 are performed by passing a current through a solenoid coil 7 arranged in a spiral shape so as to surround the outer periphery of the water-cooled copper crucible 3. In the vacuum arc melting method, an arc 4 is generated by passing a current between the consumable electrode 1 and the water-cooled copper crucible 3. At that time, current flows radially in the horizontal direction on the surface of the molten pool 5. On the other hand, when a current is passed through the solenoid coil 7, a magnetic field is generated in the vertical direction of the molten pool 5. A force acts in the circumferential direction under the influence of the magnetic field generated by the solenoid coil 7, the arc 4 rotates, and the molten pool 5 is agitated.

  As a result of earnest research, the inventors have re-melted the splash formed on the inner wall of the water-cooled copper crucible 3 by controlling the rotation of the arc 4 within a specific range, among the parameters related to operation, It has been found that the occurrence of skin defects is suppressed.

  In the method for producing a titanium ingot of the present invention, the molten pool 5 is agitated by rotating the arc 4 at a rotational speed of 4.0 to 20.0 sec / rotation at least during melting when obtaining the final titanium ingot 6. Thus, the titanium ingot 6 is manufactured, and the area ratio of defective casting surface generated on the surface of the titanium ingot 6 can be suppressed to a range in which no problem occurs in the subsequent forging process and rolling process.

  If the rotational speed of the arc 4 at the time of melting when the final titanium ingot 6 is obtained by the vacuum arc melting method is over 20.0 sec / rotation, defective casting surface generated on the surface of the manufactured titanium ingot 6 The area ratio may be so high that a problem occurs in the subsequent forging process or rolling process. In addition, even if the rotation speed of the arc 4 is less than 4.0 sec / rotation, the area ratio of defective casting surface generated on the surface of the titanium ingot 6 to be produced is such that a problem occurs in the subsequent forging process and rolling process. May be high. Therefore, when the titanium ingot 6 is manufactured by rotating the arc 4 at a rotational speed of 4.0 to 20.0 sec / rotation at least during melting when the final titanium ingot 6 is obtained, casting of the titanium ingot to be manufactured is performed. The occurrence of skin defects (surface defects) can be suppressed.

  Note that typical pure titanium used in general includes a JIS type 1 KS40 system and a JIS type 2 KS50 system. The difference between the KS40 system and the KS50 system is, for example, as shown in FIG. 2 and FIG. 3, which is the difference in the amount of raw material, and the KS40 system has a larger amount of sponge titanium than the KS50 system. One of the causes of defective casting surface is splash formed on the inner wall of the water-cooled copper crucible, but this splash is generated when sponge titanium is arc-melted and formed on the inner wall of the water-cooled copper crucible. The thickness of the splash is about 8 mm for the KS40 system and about 6 mm for the KS50 system. Therefore, a more preferable arc rotation speed for melting the splash is different between the KS40 system and the KS50 system.

  In the case of the KS40 system, if the rotation speed of the arc 5 is set to 6.7 to 10.0 sec / rotation, the area ratio of defective casting surface generated on the surface of the manufactured titanium ingot 6 becomes lower, and the manufactured titanium. Generation | occurrence | production of the casting surface defect (surface defect) of an ingot can be suppressed more reliably. On the other hand, in the KS50 system, by setting the rotation speed of the arc 5 to 4 to 6.7 sec / rotation, the area ratio of defective casting surface generated on the surface of the titanium ingot 6 to be manufactured becomes lower, and titanium to be manufactured is manufactured. Generation | occurrence | production of the casting surface defect (surface defect) of an ingot can be suppressed more reliably.

  In the present example, the occurrence of a casting surface defect of a titanium ingot obtained by two melting steps of primary melting and secondary melting was examined. The present invention is not limited to this example, and can be carried out with appropriate modifications within a range that can be adapted to the gist of the present invention, such as dissolving three times or more. Are included in the technical scope of the present invention.

  In this example, JIS1 type KS40 type KS40 type titanium ingots and JIS2 type KS50 type titanium ingots, which are representative pure titanium, are not affected by the difference in content of inevitable impurities contained in pure titanium. A total of 18 pieces of 9 pieces were produced. Titanium ingots of KS40M for KS40 and KS50 for KS50 were produced. Table 1 shows the component specifications of pure titanium. The total mass of the consumable electrode and the charge material used for manufacturing the titanium ingot in this example is 8400 kg, and details of the breakdown are as shown in FIG. 2 and FIG.

  First, the operation data (arc voltage, arc current, degree of vacuum, current flowing through the solenoid coil, etc.) obtained from the primary melting and the secondary melting were divided into a steady state and an unsteady state, and prior confirmation was performed.

  When melting of the consumable electrode in the vacuum arc furnace starts, the current is gradually increased, and when the current reaches around 38.5 kA, when the current stabilizes, melting of the consumable electrode is continued while maintaining that state. This is a steady state. Thereafter, the melting of the consumable electrode proceeds, and the current is lowered when the length of the consumable electrode becomes shorter than 1/10. This is an unsteady state. The dissolution time in the unsteady state is about 1.5 hours, and the proportion of the total operation time is large. However, the proportion of the total volume of the titanium ingot obtained by the dissolution in the unsteady state is less than 1/10, It is thought that the influence on the occurrence of defective casting surface of the titanium ingot is not great.

  Therefore, in this example, the range of titanium ingots obtained in a steady state where the current value is stable was examined. The range of the titanium ingot obtained in a steady state was divided into upper and lower 45 to 50, and each was made into one cell. The time required for manufacturing one cell is 4 to 5 minutes, which corresponds to about 50 mm of the height of the titanium ingot.

  Next, the casting surface defect area ratio in each cell is calculated (how to calculate will be described below), the vertical axis is the defective casting surface area ratio, the horizontal axis is the arc voltage frequency (Hz), and the graph Created. The graph is shown in FIG.

  For reference, when the arc rotation speed (sec / rotation) was confirmed with a monitor and measured, the arc voltage frequency (Hz) and the arc rotation speed (sec / rotation) were calculated as follows: arc voltage frequency (Hz) x arc It was confirmed that there was a relationship of rotational speed (sec / rotation) = 100. FIG. 5 shows this relationship.

  Table 2 is created based on the relationship of FIG. 4 and the arc voltage frequency (Hz) × arc rotation speed (sec / rotation) = 100. The defective casting surface area ratio was obtained from a surface sketch that marked a defective casting surface portion of the surface of a slab after forging and rolling a titanium ingot. The surface sketch was equally divided into 45 to 50 cells from the top part to the bottom part, and the defective casting surface area was determined for each cell. In one cell, the defective casting surface area / total area = the defective casting surface area ratio, and the average value of the obtained data is shown in Table 2 as the defective casting surface area ratio.

  If the defective surface area of the casting surface is less than 0.1, pass with ◎, if the defective surface area of the casting surface is less than 0.2, 0.1 or more, pass with ○, and the defective surface area of the casting surface is 0.2 or more. Is shown in the judgment column of Table 2 as x.

  According to Table 2 and FIG. 4, the arc rotation speed is 4.0 to 20.0 sec / rotation, and the defective surface area ratio of the casting surface is less than 0.2, and in particular, the arc rotation speed is 6.7 to At 10.0 sec / rotation, it was confirmed that the defective casting surface area ratio was less than 0.1.

  As described above, since the more preferable arc rotation speed is different between the KS40 system and the KS50 system, a more preferable range of the arc rotation speed is specified separately for the KS40 system and the KS50 system. .

  FIG. 6 and FIG. 7 are graphs created by dividing the graph of FIG. 4 into the KS40 system and the KS50 system. FIG. 6 shows the relationship between the arc voltage frequency (Hz) of the KS40 system and the defective casting surface area ratio. Indicates the relationship between the frequency (Hz) of arc voltage of the KS50 system and the defective surface area ratio of the casting surface.

  According to FIG. 6, the casting surface defect area ratio is less than 0.1 when the arc rotation speed is 6.7 to 10.0 sec / rotation. That is, in the case of the KS40 system, the occurrence of a casting surface defect (surface defect) of the titanium ingot can be more reliably suppressed by rotating the arc at a rotation speed of 6.7 to 10.0 sec / rotation.

  According to FIG. 7, the defective casting surface area ratio is less than 0.1 when the arc rotation speed is 4.0 to 6.7 sec / rotation. That is, in the case of the KS50 system, the occurrence of a casting surface defect (surface defect) of the titanium ingot can be more reliably suppressed by rotating the arc at a rotation speed of 4.0 to 6.7 sec / rotation.

DESCRIPTION OF SYMBOLS 1 ... Consumable electrode 2 ... Vacuum arc furnace 3 ... Water-cooled copper crucible 4 ... Arc 5 ... Molten pool 6 ... Titanium ingot 7 ... Solenoid coil

Claims (3)

An arc is generated between a consumable electrode made of titanium suspended in a vacuum arc furnace and a titanium start material laid on the bottom of the water-cooled copper crucible of the vacuum arc furnace, and titanium droplets are dropped sequentially from the consumable electrode. In the method for producing a titanium ingot by the vacuum arc melting method in which the molten pool formed by collecting the titanium droplets is cooled and solidified to produce a titanium ingot.
A method for producing a titanium ingot by a vacuum arc melting method, wherein the titanium ingot is produced by stirring the molten pool by rotating the arc at a rotation speed of 4.0 to 20.0 sec / rotation. The titanium ingot is a JIS1 type KS40 titanium ingot,
The method for producing a titanium ingot according to claim 1, wherein the arc rotates at a rotation speed of 6.7 to 10.0 sec / rotation. The titanium ingot is a JIS type 2 KS50 titanium ingot,
The method for producing a titanium ingot by the vacuum arc melting method according to claim 1, wherein the arc rotates at a rotation speed of 4.0 to 6.7 sec / rotation.

Images