Patent Application
20200122226
The present invention relates to a method for producing a metal ingot that melts a metal raw material by an electron beam melting process.
An ingot of commercially pure titanium or a titanium alloy or the like is produced by melting a titanium raw material such as titanium sponge or scrap. Examples of techniques for melting a metal raw material (hereunder, may be referred to simply as “raw material”) such as a titanium raw material include a vacuum arc remelting process, a plasma arc melting process, and an electron beam melting process. Among these, in the electron beam melting process, the raw material is melted by radiating an electron beam onto a solid raw material in an electron-beam melting furnace (hereunder, also referred to as “EB furnace”). To prevent dissipation of the energy of the electron beam, melting of the raw material by radiation of the electron beam in the EB furnace is performed inside a vacuum chamber. Molten titanium (hereunder, may also be referred to as “molten metal”) that is the melted raw material is refined in a hearth, and thereafter is solidified in a mold to form a titanium ingot. According to the electron beam melting process, because the radiation position of the electron beam that is the heat source can be accurately controlled by an electromagnetic force, heat can also be sufficiently supplied to molten metal in the vicinity of the mold. Therefore, it is possible to produce an ingot without deteriorating the surface quality thereof.
An EB furnace generally includes a raw material supplying portion that supplies a raw material such as titanium sponge, one or a plurality of electron guns for melting the supplied raw material, a hearth (for example, a water-cooled copper hearth) for accumulating the melted raw material, and a mold for forming an ingot by cooling molten titanium that was poured therein from the hearth. EB furnaces are broadly classified into two types according to differences between the configurations of the hearths. Specifically, for example, an EB furnace 1A that includes a melting hearth 31 and a refining hearth 33 as illustrated in
The EB furnace 1A illustrated in
On the other hand, the EB furnace 1B shown in
In the case of producing an ingot using a hearth and a mold by means of an electron beam melting process as described above, if impurities are mixed in with the ingot, the impurities will be the cause of cracks in the ingot. Therefore, there is a need for the development of electron beam melting technology that can ensure that impurities do not become mixed into molten metal that flows into a mold from a hearth. Impurities are mainly included in the raw material, and are classified into two kinds, namely, a HDI (High Density Inclusion) and a LDI (Low Density Inclusion). A HDI is, for example, an impurity in which tungsten is the principal component, and the density of the HDI is larger than the density of molten titanium. On the other hand, a LDI is an impurity in which the principal component is nitrided titanium or the like. The inside of the LDI is in a porous state, and therefore the density of the LDI is less than the relative density of molten titanium.
On the inner surface of a water-cooled copper hearth, a solidified layer is formed at which molten titanium that came in contact with the hearth solidified. The solidified layer is referred to as a “skull”. Among the aforementioned impurities, because the HDIs have a high relative density, the HDIs settle in the molten metal (molten titanium) in the hearth, and adhere to the surface of the skull and are thereby trapped, and hence the possibility of HDIs becoming mixed into the ingot is low. On the other hand, because the density of the LDIs is less than the density of molten titanium, a major portion of the LDIs float on the molten metal surface within the hearth. While the LDIs are floating on the molten metal surface, the nitrogen diffuses and is dissolved into the molten metal. In the case of using the long hearth illustrated in
Therefore, for example, Patent Document 1 discloses a method of electron beam melting for metallic titanium in which the surface of molten metal in a hearth is scanned with an electron beam in the opposite direction to the direction in which the molten metal flows into a mold, and the average temperature of molten metal in a region adjacent to a molten metal discharging opening in the hearth is made equal to or higher than the melting point of impurities. According to the technique disclosed in Patent Document 1, by scanning an electron beam in a zig-zag manner in the opposite direction to the flow direction of the molten metal, it is attempted to push back impurities that float on the molten metal surface to the upstream side so that the impurities do not flow into a mold on the downstream side.
However, according to the method disclosed in the aforementioned Patent Document 1, because an electron beam is scanned in the opposite direction to the flow direction of the molten metal, there is a possibility that, on the downstream side of the molten metal flow relative to the electron beam radiation position, impurities will pass through into the mold. In addition, on the downstream side relative to the electron beam radiation position, the flow of molten metal accelerates toward the mold and thus the residence time of the molten metal in the hearth becomes shorter, and there is the possibility that the rate of removal of impurities will decrease. Further, when impurities are present on the downstream side of the molten metal flow relative to the radiation position of the electron beam, the risk of those impurities riding on the flow of molten metal and flowing out into the mold increases. For these reasons, there is a possibility that impurities contained in molten metal within the hearth, particularly LDIs floating on the surface of the molten metal 5c, will flow out into the mold from the hearth and become mixed in the ingot that is formed in the mold. Therefore, there is a need for a method for producing a metal ingot that, by inhibiting the outflow of impurities such as LDIs from a hearth into a mold, can inhibit impurities from being mixed into an ingot.
An objective of the present invention, which has been made in consideration of the aforementioned problem, is to provide a novel and improved method for producing a metal ingot, which makes it possible to inhibit impurities contained in molten metal in a hearth from being mixed into an ingot.
To solve the aforementioned problem, according to an aspect of the present invention, there is provided a method for producing a metal ingot by using an electron-beam melting furnace having an electron gun capable of controlling a radiation position of an electron beam and a hearth that accumulates a molten metal of a metal raw material, the metal ingot containing 50% by mass or more in total of at least one metallic element selected from a group consisting of titanium, tantalum, niobium, vanadium, molybdenum and zirconium, wherein:
among a plurality of side walls of the hearth that accumulates the molten metal of the metal raw material, a first side wall is a side wall provided with a lip portion for causing the molten metal in the hearth to flow out into a mold, and a second side wall is at least one of the side walls other than the first side wall;
the metal raw material is supplied to a position on a supply line that is disposed along an inside face of the second side wall on a surface of the molten metal;
a first electron beam is radiated along a first irradiation line, the first irradiation line being disposed along the supply line and being closer to a central part of the hearth relative to the supply line on the surface of the molten metal; and
the radiation of the first electron beam along the first irradiation line increases a surface temperature (T2) of the molten metal at the first irradiation line above an average surface temperature (T0) of the entire surface of the molten metal in the hearth, and forms, in an outer layer of the molten metal, a first molten metal flow from the first irradiation line toward the supply line.
A configuration may be adopted so that a temperature gradient ΔT/L represented by Formula (A) below is −2.70 [K/mm] or more.
ΔT/L=(T2−T1)/L (A)
T1: surface temperature [K] of the molten metal at the supply line
T2: surface temperature [K] of the molten metal at the first irradiation line
L: distance [mm] between the first irradiation line and the supply line on the surface of the molten metal
A configuration may be adopted so that the aforementioned ΔT/L is 0.00 [K/mm] or more, and
the first molten metal flow that flows from the first irradiation line across the supply line toward an inside face of the second side wall is formed in the outer layer of the molten metal.
A configuration may be adopted so that the metal raw material is melted at a raw material supplying portion, and the melted metal raw material is caused to drip from the raw material supplying portion onto a position on the supply line of the molten metal in the hearth.
A configuration may be adopted so that, on the surface of the molten metal, both ends of the first irradiation line are positioned on an outer side in an extending direction of the supply line relative to both ends of the supply line.
A configuration may be adopted so that a second molten metal flow toward the lip portion is formed in a belt-shaped region between the supply line and the first irradiation line, and
a second electron beam is spot-radiated onto the second molten metal flow.
A configuration may be adopted so that the second electron beam is spot-radiated onto the second molten metal flow at a position of an irradiation spot that is disposed at an end portion on the lip portion side of the belt-shaped region.
A configuration may be adopted so that a third electron beam is radiated along a second irradiation line, the second irradiation line being disposed such that the second irradiation line blocks the lip portion on the surface of the molten metal and both ends of the second irradiation line are positioned in a vicinity of the first side wall.
The metal raw material may contain 50% by mass or more of a titanium element.
According to the present invention as described above, the mixing of impurities contained in molten metal in a hearth into an ingot can be inhibited.
Hereunder, preferred embodiments of the present invention are described in detail while referring to the accompanying drawings. Note that, in the present specification and the accompanying drawings, constituent elements having substantially the same functional configuration are denoted by the same reference characters and a duplicate description thereof is omitted.
First, a method for producing a metal ingot according to a first embodiment of the present invention will be described.
[1.1. Configuration of Electron-Beam Melting Furnace]
First, referring to
As illustrated in
The refining hearth 30 (hereunder, referred to as “hearth 30”) is an apparatus for refining a molten metal 5c of a metal raw material 5 (hereunder, referred to as “raw material 5”) while accumulating the molten metal 5c, to thereby remove impurities contained in the molten metal 5c. The hearth 30 according to the present embodiment is constituted by, for example, a water-cooled copper hearth having a rectangular shape. A lip portion 36 is provided in a side wall at an end on one side in the longitudinal direction (Y direction) of the hearth 30. The lip portion 36 is an outlet for causing the molten metal 5c inside the hearth 30 to flow out into the mold 40.
The mold 40 is an apparatus for cooling and solidifying the molten metal 5c of the raw material 5, to thereby produce a metal ingot 50 (for example, a titanium ingot or titanium alloy ingot). The mold 40 is, for example, constituted by a water-cooled copper mold that has a rectangular tube shape. The mold 40 is disposed underneath the lip portion 36 of the hearth 30, and cools the molten metal 5c that is poured therein from the hearth 30 that is above the mold 40. As a result, the molten metal 5c within the mold 40 solidifies progressively toward the lower part of the mold 40, and a solid ingot 50 is formed.
The raw material supplying portion 10 is an apparatus for supplying the raw material 5 into the hearth 30. The raw material 5 is, for example, a titanium raw material such as titanium sponge or scrap. In the present embodiment, for example, as illustrated in
Thus, in the present embodiment, in order to supply the raw material 5 into the hearth 30, the solid raw material 5 is melted by radiating electron beams onto the raw material 5 in the raw material supplying portion 10, and the melted raw material 5 (melted metal) is dripped into the molten metal 5c in the hearth 30 from inner edge portions of the raw material supplying portion 10. In other words, the raw material 5 is supplied into the hearth 30 by first melting the raw material 5 beforehand outside of the hearth 30, and then allowing the melted metal to drip into the molten metal 5c in the hearth 30. Drip lines that represent the positions at which the melted metal drips from the raw material supplying portion 10 onto the surface of the molten metal 5c in the hearth 30 in this way correspond to supply lines 26 that are described later (see
Note that a method for supplying the raw material 5 is not limited to dripping as described in the aforementioned example. For example, the solid raw material 5 may be introduced as it is into the molten metal 5c in the hearth 30 from the raw material supplying portion 10. The introduced solid raw material 5 is then melted in the high-temperature molten metal 5c and thereby added to the molten metal 5c. In this case, introduction lines that represent the positions at which the solid raw material 5 is introduced into the molten metal 5c in the hearth 30 correspond to the supply lines 26 that are described later (see
To implement an electron beam melting process, the electron guns 20 radiate electron beams onto the raw material 5 or the molten metal 5c. As illustrated in
The electron guns 20A and 20B radiate electron beams onto the solid raw material 5 placed on the raw material supplying portion 10 to thereby heat and melt the raw material 5. The electron gun 20C heats the molten metal 5c and maintains the molten metal 5c at a predetermined temperature by radiating an electron beam over a wide range with respect to the surface of the molten metal 5c in the hearth 30. The electron gun 20D radiates an electron beam onto the surface of the molten metal 5c in the mold 40 to thereby heat the molten metal 5c at the upper part thereof and maintain the molten metal 5c that is at the upper part at a predetermined temperature so that the molten metal 5c at the upper part in the mold 40 does not solidify. The electron gun 20E radiates an electron beam in a concentrated manner along an irradiation line 25 (see
Thus, the present embodiment is characterized in that the present embodiment prevents an outflow of impurities by, for example, radiating (line radiation) an electron beam in a concentrated manner along the irradiation line 25 at the surface of the molten metal 5c using the electron gun 20E. This characteristic will be described in detail later. Note that, in the EB furnace 1 according to the present embodiment, the electron gun 20E for line radiation as illustrated in
[1.2. Outline of Method for Producing Metal Ingot]
Next, an outline of the method for producing a metal ingot according to the present embodiment will be described referring to
A problem to be solved by the method for producing a metal ingot according to the present embodiment is, when producing a metal ingot 50 of commercially pure titanium or a titanium alloy or the like, to inhibit impurities from mixing into the ingot 50, by inhibiting impurities contained in melted metal (the molten metal 5c) into which the solid raw material 5 was melted from flowing into the mold 40 from the hearth 30. According to the method for producing a metal ingot of the present embodiment, in particular, a titanium raw material as a metal raw material is taken as an object, and the method for producing a metal ingot solves the problem of inhibiting the occurrence of a situation in which LDIs that, among the impurities contained in the titanium raw material, have a density that is smaller than the density of molten metal of titanium (molten titanium) become mixed into the ingot 50 of titanium or a titanium alloy. Note that, the term “titanium” or “titanium alloy” as used herein refers to a metal containing 50% by mass or more of titanium as an element.
To solve the aforementioned problem, in the method for producing a metal ingot according to the present embodiment, as illustrated in
The supply lines 26 (corresponds to “supply line” of the present invention) are imaginary lines representing positions at which the raw material 5 is supplied from outside of the hearth 30 into the molten metal 5c in the hearth 30. The supply lines 26 are disposed on the surface of the molten metal 5c at positions along the respective inside faces of the side walls 37A and 37B of the hearth 30.
In the present embodiment, the melted raw material 5 is dripped into the hearth 30 from inner edge portions of the raw material supplying portion 10 disposed at an upper part of the side walls 37A and 37B on the long sides of the hearth 30 as illustrated in
The irradiation line 25 (corresponds to “first irradiation line” of the present invention) is an imaginary line that represents the path of positions at which an electron beam (corresponds to “first electron beam” of the present invention) is radiated in a concentrated manner onto the surface of the molten metal 5c in the hearth 30. The irradiation line 25 is disposed along the supply line 26 of the raw material 5, on the surface of the molten metal 5c. As long as the irradiation line 25 is a linear shape extending along the supply line 26, the irradiation line 25 need not have a strictly straight-line shape, and, for example, may be a broken-line shape, a dotted-line shape, a curve shape, a wavy line shape, a zigzag shape, a double line shape, a belt shape, a polygonal line shape or the like.
The disposition of the irradiation line 25 and the supply lines 26 will now be described in further detail. As illustrated in
The lip portion 36 for causing the molten metal 5c in the hearth 30 to flow out into the mold 40 is provided in the side wall 37D that is one of the short sides. On the other hand, the lip portion 36 is not provided in the three side walls 37A, 37B and 37C that are the side walls other than the side wall 37D. Therefore, the side wall 37D corresponds to “first side wall” in which a lip portion is provided, and the side walls 37A, 37B and 37C correspond to “second side wall(s)” in which the lip portion 36 is not provided.
In the example illustrated in
In the present embodiment, a special temperature gradient is formed at the surface of the molten metal 5c in the hearth 30 by radiating an electron beam in a concentrated manner along the irradiation line 25 on the surface of the molten metal 5c as mentioned above, and flowage of the molten metal 5c is thereby controlled. The temperature distribution on the surface of the molten metal 5c in the hearth 30 will now be described.
In general, in the electron beam melting process, in order to prevent the molten metal 5c in the hearth 30 from solidifying, an electron beam is uniformly radiated by, for example, the electron gun 20C onto a heat-retention radiation region 23 that occupies a wide area of the surface of the molten metal 5c, to thereby maintain the temperature of the molten metal 5c in the hearth 30. By performing such radiation of an electron beam for heat retention, all of the molten metal 5c accumulated in the hearth 30 is heated, and an average surface temperature T0 (hereunder, referred to as “molten metal surface temperature T0”) of the entire surface of the molten metal 5c is maintained at a predetermined temperature. The molten metal surface temperature T0 is for example, in the range of 1923 K (melting point of titanium alloy) to 2323 K, and preferably is in the range of 1973 K to 2273 K.
In the present embodiment, at the aforementioned raw material supplying portion 10, electron beams are radiated onto the solid raw material 5 by the electron guns 20A and 20B to melt the raw material 5, and the melted metal of a high temperature that was melted drips onto the positions of the supply lines 26 of the molten metal 5c in the hearth 30 to thereby supply the raw material 5 to the hearth 30. Therefore, among the entire molten metal 5c in the hearth 30, impurities such as LDIs contained in the raw material 5 are mainly present in the vicinity of the supply lines 26. Further, because the high-temperature melted metal is supplied continuously or discontinuously to the supply lines 26, a high temperature region (see region S1 in
In addition, according to the method for producing a metal ingot of the present embodiment, separately to radiation of the aforementioned electron beam for heat retention onto the heat-retention radiation region 23 of the molten metal 5c, an electron beam is radiated in a concentrated manner by the electron gun 20E onto the surface of the molten metal 5c along the irradiation line 25. Specifically, the radiation position of the electron beam radiated by the electron gun 20E is moved on the irradiation line 25 on surface of the molten metal 5c. By such concentrated radiation of an electron beam along the irradiation line 25, a high temperature region (see region S2 in
Thus, according to the method for producing a metal ingot of the present embodiment, by radiating in a concentrated manner an electron beam along the irradiation line 25 on the surface of the molten metal 5c, a high temperature region of the molten metal 5c is also formed in the vicinity of the irradiation line 25, and not just the vicinity of the supply lines 26. By this means, as illustrated in
By means of the molten metal flow 61, the flowage of impurities such as LDIs that are present in a large amount in the vicinity of the supply lines 26 is controlled, and the impurities can be prevented from flowing toward the lip portion 36. Specifically, by means of the molten metal flow 61, impurities such as LDIs that are floating on the surface of the molten metal 5c in regions in the vicinity of the supply lines 26 are caused to move toward the side walls 37A and 37B of the hearth 30, and thus the impurities such as LDIs can be trapped by a skull 7 formed on the inside faces of the side walls 37A and 37B. Further, by radiating an electron beam along the irradiation lines 25 to increase the line irradiation temperature T2, dissolving of nitrided titanium or the like that is a principal component of the LDIs floating in the molten metal 5c in the vicinity of the irradiation line 25 can be promoted.
Thus, in the method for producing a metal ingot according to the present embodiment, electron beams are radiated along the irradiation lines 25, 25 that are closer to the central part (inner side) of the hearth 30 relative to the supply lines 26, 26. By this means, a high temperature region of the molten metal 5c is formed in the vicinity of each irradiation line 25, and by means of the molten metal flow 61 from the high temperature regions, impurities such as LDIs that are present in the vicinity of the supply lines 26 are caused to flow toward the side walls 37A and 37B, thus preventing the impurities from flowing toward the lip portion 36. Therefore, the impurities can be inhibited from flowing out from the hearth 30 to the mold 40.
[1.3. Flowage of Molten Metal Generated by Line Radiation]
Next, a flowage of the molten metal 5c within the hearth 30 that is generated by line radiation of an electron beam will be described in further detail referring to
As described above, in the present embodiment, raw material supplying portions 10A and 10B are disposed above the side walls 37A and 37B on the long sides of the hearth 30, respectively, and electron beams are radiated by the electron guns 20A and 20B onto the solid raw material 5 on the raw material supplying portions 10A and 10B to thereby melt the raw material 5. The melted raw material 5 is dripped onto the positions of the supply lines 26, 26 of the molten metal 5c in the hearth 30 from the raw material supplying portions 10A and 10B. Thus, in the present embodiment, the raw material 5 is supplied into the hearth 30 by causing the melted metal of the raw material 5 to drip onto the molten metal 5c in the hearth 30. In this respect, the supply lines 26 according to the present embodiment correspond to imaginary lines (drip lines) that represent the positions at which melted metal of the raw material 5 is dripped onto the surface of the molten metal 5c.
The molten metal 5c that is accumulated inside the hearth 30 is refined while residing in the hearth 30, and thereafter flows out from the lip portion 36 and is discharged into the mold 40. As illustrated in
Further, as illustrated in
Therefore, in the method for producing a metal ingot according to the present embodiment, electron beams are radiated in a concentrated manner along the irradiation lines 25, 25 that are on the inner side relative to the supply lines 26, 26 on the surface of the molten metal 5c in the hearth 30. By this means, the Marangoni convection is generated by a temperature gradient at the surface of the molten metal 5c, and as illustrated in
When a temperature gradient arises at the outer layer of a fluid, a gradient also arises in the surface tension of the fluid, and such a gradient causes the occurrence of convection in the fluid. Such convection in the fluid is called “Marangoni convection”. In a case where the fluid is molten titanium or a molten titanium alloy, the Marangoni convection is a flow from a high temperature region toward a low temperature region of the fluid. This is because molten titanium and a molten titanium alloy have a property such that when the temperature thereof is high, the surface tension weakens.
Here, as a comparative example of the present embodiment, as illustrated in
Thus, as illustrated in
Therefore, in the present embodiment, as illustrated in
The flowage of the molten metal 5c generated by line radiation that is mentioned above will now be described in further detail.
As described above, in a case where the molten metal 5c is molten titanium, Marangoni convection is a flow from a high temperature region toward a low temperature region of the molten metal 5c. When an electron beam is radiated in a concentrated manner along the irradiation line 25, the region S2 in the vicinity of the irradiation line 25 onto which the electron beam is radiated is heated and becomes a high temperature region. Accordingly, Marangoni convection occurs from the region S2 toward a low temperature region around the region S2. As a result, as illustrated in
In this case, it is preferable that, in the outer layer of the molten metal 5c, a temperature distribution is formed such that the line irradiation temperature T2 is higher than the raw material supplying temperature T1, and the surface temperature of the molten metal 5c progressively decreases from the irradiation line 25 to the supply line 26. By realizing such a temperature distribution, as illustrated in
As a result, as illustrated in
In general, the distance L1 between the supply line 26 at which the raw material 5 is dripped and the side wall 37B is small. Therefore, if the LDIs 8 that float in the vicinity of the supply line 26 are caused to move toward the side wall 37B of the hearth 30 by the molten metal flow 61, the LDIs 8 easily adhere to the skull 7 that is formed on the inside face of the side wall 37B. Accordingly, by forming the molten metal flow 61 in the outer layer of the molten metal 5c by line radiation of an electron beam, the LDIs 8 that float in the region S1 in the vicinity of the supply line 26 can be efficiently trapped by the skull 7 on the inside face of the side wall 37B and thereby removed from the molten metal 5c.
Further, the contamination source of the LDIs 8 that float in the molten metal 5c inside the hearth 30 is the melted metal that is dripped into the hearth 30 from outside, and at least one part of the LDIs 8 contained in the melted metal that is dripped on the supply lines 26 dissolves in the molten metal 5c or adheres to the skull 7 while residing inside the hearth 30. Therefore, it is considered that almost no LDIs 8 float in the molten metal 5c in regions other than the vicinity of the supply lines 26. Accordingly, as illustrated in
[1.4. Disposition of Irradiation Line]
Next, the disposition of the irradiation line 25 along which an electron beam is radiated in a concentrated manner will be described in detail.
According to the method for producing a metal ingot of the present embodiment, as illustrated in
From the viewpoint of accurately preventing an outflow of impurities by means of line radiation, it is preferable that the supply lines 26, 26 have a straight-line shape that is substantially parallel to the inside face of the side walls 37A and 37B that are the pair of long sides of the hearth 30. In addition, each irradiation line 25 is preferably a straight-line shape that is substantially parallel to each supply line 26.
Here, the term “substantially parallel” refers not only to a case where the relevant two objects are strictly parallel (the angular difference is 0°), but also includes a case where an angular difference between the relevant two objects is not greater than a predetermined angle. As a specific example, if an angular difference between the supply lines 26 and the inside faces of the side walls 37A and 37B of the hearth 30 is not more than 6°, the effect of the present invention is obtained. However, this does not apply to a case where the supply lines 26 are too close to the side walls 37A and 37B, specifically, a case where the supply lines 26 are around 5 mm or less from the side walls 37A and 37B and a hindrance thus arises with respect to supplying the melted metal. Further, with regard to the irradiation lines 25 also, the effect of the present invention can be expected to be obtained if an angular difference with respect to the corresponding supply line 26 is not more than 4°. However, this does not apply to a case where the relevant irradiation line 25 is too close to the corresponding supply line 26, specifically, a case where the irradiation line 25 is around 5 mm or less from the supply line 26, and a hindrance thus arises with respect to formation of the molten metal flow 61 that is described later.
In the method for producing a metal ingot according to the present embodiment, as illustrated in
Therefore, in the present embodiment, as illustrated in
Next, the distance L between each irradiation line 25 and the corresponding supply line 26 will be described. As illustrated in
If the distance L is less than 5 mm, the irradiation line 25 will be too close to the supply line 26, and the high temperature region S2 and the high temperature region S1 illustrated in
Further, as illustrated in
[1.5. Settings of Electron Beam for Line Radiation]
Next, the settings with respect to the electron beam for line radiation (first electron beam) that is radiated in a concentrated manner along the aforementioned irradiation line 25 will be described.
In order to push back the molten metal flow 62 from the supply lines 26 (see
The heat transfer amount [W] of the electron beam is a parameter that influences an increase in the temperature of the molten metal 5c at the irradiation line 25, and the flow velocity of the Marangoni convection (the molten metal flow 61) that occurs due to the temperature increase in question. If the heat transfer amount of the electron beam is small, a molten metal flow 61 that overcomes the molten metal flow 62 from the supply lines 26 cannot be formed. Accordingly, the larger that the heat transfer amount of the electron beam is, the more preferable it is, and for example, the heat transfer amount is in the range of 0.15 to 0.60 [MW].
The scanning speed [m/s] of the electron beam is a parameter that influences the flow velocity of the aforementioned molten metal flow 61. When radiating an electron beam along the irradiation line 25, the irradiation line 25 on the surface of the molten metal 5c is repeatedly scanned with an electron beam emitted from the electron gun 20E. If the scanning speed of the electron beam at such time is slow, positions at which the electron beam is not radiated for a long time will arise on the irradiation line 25. The surface temperature of the molten metal 5c will rapidly decrease at a position at which the electron beam is not radiated, and the flow velocity of the molten metal flow 61 that arises from the position in question will decrease. In such a case, it will be difficult to suppress the molten metal flow 62 from the supply lines 26 by means of the molten metal flow 61, and the possibility that the molten metal flow 62 will pass through the irradiation line 25 will increase. Therefore, the scanning speed of the electron beam is preferably as fast as possible, and for example is within a range of 1.0 to 20.0 [m/s].
The heat flux distribution at the surface of the molten metal 5c that is produced by the electron beam is a parameter that influences the heat transfer amount imparted to the molten metal 5c from the electron beam. The heat flux distribution corresponds to the size of the aperture of the electron beam. The smaller that the aperture of the electron beam is, the greater the degree to which a steep heat flux distribution can be imparted to the molten metal 5c. The heat flux distribution at the surface of the molten metal 5c is, for example, represented by the following Formula (1) (for example, see Non-Patent Document 1). The following Formula (1) represents that a heat flux is exponentially attenuated in accordance with the distance from the electron beam spot.
Where, (x,y) represents a position of the molten metal surface, (x0,y0) represents the electron beam spot, and σ represents the standard deviation of the heat flux distribution. In addition, as illustrated in the above Formula (2), the heat transfer amount Q of the electron gun is set to become the total sum of the heat flux q with respect to the surface of the entire molten metal 5c within the hearth 30. With respect to these parameters, for example, by means of a heat flow simulation or the like, values may be determined and set so as to cause the molten metal flows 62 that flow from the supply lines 26 toward the central part of the hearth 30 to flow toward the side walls 37A and 37B of the hearth 30 by Marangoni convection that is generated by radiation of an electron beam along the irradiation lines 25.
At such time, if the flow velocity of the molten metal flows 61 from the irradiation lines 25 to the supply lines 26 is greater than the flow velocity of the molten metal flows 62 from the supply lines 26 to the central part of the hearth 30, the molten metal flows 61 can more reliably stop the molten metal flows 62 and can push back the molten metal flows 62 toward the inside faces of the side walls 37A and 37B of the hearth 30.
Therefore, it is good to set the radiation conditions of the electron beam for line radiation so that, as illustrated in
Note that, the aforementioned radiation conditions such as the heat transfer amount, scanning speed and heat flux distribution of the electron beam for line radiation are constrained by the specifications of the equipment that radiates the electron beam. Accordingly, when setting the radiation conditions of the electron beam it is good to make the heat transfer amount as large as possible, the scanning speed as fast as possible, and the heat flux distribution as narrow as possible (make the aperture of the electron beam as small as possible) within the range of the equipment specifications. Further, radiation of an electron beam with respect to the irradiation line 25 may be performed by a single electron gun or may be performed by a plurality of electron guns. In addition, as the electron gun for line radiation described here, the electron gun 20E for exclusive use for line radiation (see
[1.6. Temperature Gradient ΔT/L]
Next, the influence that a temperature gradient ΔT/L between the irradiation lines 25 and the supply lines 26 has on the flowage of the molten metal 5c in the hearth 30 will be described referring to
The strength of the aforementioned molten metal flow 61 flowing from each irradiation line 25 toward the corresponding supply line 26 changes depending on a temperature gradient ΔT/L between the irradiation line 25 and the corresponding supply line 26. Here, a temperature gradient ΔT/L [K/mm] is represented by Formula (A) below.
ΔT/L=(T2−T1)/L (A)
T1: surface temperature of the molten metal 5c at the supply line 26 (raw material supplying temperature) [K]
T2: surface temperature of the molten metal 5c at the irradiation line 25 (line irradiation temperature) [K]
L: distance between the irradiation line 25 and the supply line 26 on the surface of the molten metal 5c [mm]
The temperature gradient ΔT/L is preferably −2.70 [K/mm] or more (ΔT/L−2.70 K/mm), and more preferably 0.00 [K/mm] or more (ΔT/L≥0.00 K/mm). Thus, the molten metal flow 61 that flows from the irradiation line 25 to the supply line 26 can be appropriately formed. Therefore, in the belt-shaped region S3 between the irradiation line 25 and the supply line 26, impurities such as the LDIs 8 floating in the vicinity of the supply lines 26 can be inhibited from flowing toward the lip portion 36, and the outflow amount of impurities from the lip portion 36 can be favorably suppressed. The reason is described in detail hereunder.
(1) Case where “ΔT/L≥0.00”
First, a case where the temperature gradient ΔT/L is 0.00 [K/mm] or more will be described referring to
Accordingly, as illustrated in
(2) Case where “−2.70≤ΔT/L<0.00” Next, a case where the temperature gradient ΔT/L is −2.70 [K/mm] or more and less than 0.00 [K/mm] will be described referring to
Accordingly, as illustrated in
(3) Case where “ΔT/L<−2.70”
Next, a case where the temperature gradient ΔT/L is less than −2.70 [K/mm] will be described referring to
Specifically, as illustrated in
Therefore, there is a possibility that, in the belt-shaped region S3 between the irradiation line 25 and the supply line 26, the molten metal flow 66 that flows toward the lip portion 36 will be formed, and a molten metal flow 67 that flows from the supply line 26 and flows across the irradiation line 25 toward the central part in the width direction of the hearth 30 will be formed. Hence, there is a risk that the LDIs 8 that ride on the molten metal flow 66 or the molten metal flow 67 and reside in the vicinity of the supply lines 26 will flow out from the lip portion 36.
However, even in a case where ΔT/L<−2.70, the molten metal flow 62 from the supply line 26 can be suppressed to a certain extent by the molten metal flow 61 from the irradiation line 25. Therefore, the LDIs 8 which were stopped from entering the central part in the width direction of the hearth 30 by the molten metal flow 61 are gradually dissolved while residing in the belt-shaped region S3. Hence, since impurities such as the LDIs 8 in the vicinity of the supply lines 26 can be inhibited to a certain extent from flowing toward the lip portion 36, the outflow amount of impurities from the lip portion 36 can be reduced to, for example, 5% or less in comparison to a case where electron beams are not radiated along the irradiation lines 25.
Therefore, in order to form an appropriate molten metal flow 61 by line radiation and reduce the outflow amount of impurities, a preferable temperature gradient ΔT/L is −2.70 [K/mm] or more, and more preferably is 0.00 [K/mm] or more. It suffices to appropriately set the radiation conditions of the electron beam for line radiation (for example, the heat transfer amount, scanning speed and heat flux distribution of the electron beam), the temperatures T0, T1 and T2 of the molten metal 5c, or the disposition of the irradiation lines 25 and the supply lines 26 or distances L and L1 and the like so that a temperature gradient ΔT/L that is within the relevant suitable numerical value range is obtained.
Note that, the larger that the value of the temperature gradient ΔT/L is, the better the value is from the viewpoint of suppressing the outflow amount of impurities. However, an upper limit value of the temperature gradient ΔT/L is constrained by the specifications of the equipment that radiates the electron beam. Because of such constraints with regard to the equipment specifications, for example, the upper limit value of the temperature gradient ΔT/L is preferably 64.0 [K/mm] or less, and more preferably is 10.0 [K/mm] or less.
[1.7. Modification]
Next, a modification of the first embodiment that is described above will be described. In the foregoing, an example was described in which, as illustrated in
For example, as illustrated in
Further, as illustrated in
Further, although not illustrated in the drawings, for example, there are also cases where side walls of the hearth are a curved shape such as elliptical shape or an oval shape. In such a case, the supply line 26 and the irradiation line 25 that have a curved shape may be disposed along the curved side walls of the hearth.
[1.8. Summary]
A method for producing a metal ingot according to the first embodiment of the present invention has been described above. According to the present embodiment, the irradiation lines 25 are disposed along the supply lines 26 at positions closer to the central part in the width direction of the hearth 30 relative to the supply lines 26, and electron beams are radiated in a concentrated manner along the irradiation lines 25. By this means, as illustrated in
In addition, by making ΔT/L≥0.00, as illustrated in
Further, by making ΔT/L≥−2.70, as illustrated in
Further, according to the method for producing a metal ingot of the present embodiment, since it is not necessary to change the shape of an existing hearth 30, the method can be easily implemented and special maintenance is also not required.
In the conventional methods for producing an ingot of a titanium or a titanium alloy, it is common to remove impurities by causing the molten metal to reside for a long time period in the hearth to thereby dissolve LDIs in the molten metal while also causing HDIs to adhere to a skull formed on the bottom face of the hearth. Consequently, conventionally, a long hearth has generally been used to thereby secure the residence time of the molten metal in the hearth. However, according to the present embodiment, since impurities can be appropriately removed even in a case where the residence time of molten metal in the hearth is comparatively short, it is possible to use a short hearth. Accordingly, by using a short hearth in the EB furnace 1, the running cost of the EB furnace 1 can be decreased. In addition, if a short hearth is used, the yield of the ingot 50 can be improved even without reutilizing the skull 7 that remained in the hearth.
Next, a method for producing a metal ingot according to a second embodiment of the present invention will be described.
[2.1. Outline of Method for Producing Metal Ingot]
First, an outline of the method for producing a metal ingot according to the second embodiment will be described referring to
As illustrated in
In the second embodiment also, by radiating an electron beam along the aforementioned irradiation lines 25, the high temperature region S2 is formed in the vicinity of each irradiation line 25, and the molten metal flows 61 are formed that flow from each irradiation line 25 toward the corresponding supply line 26. By this means, the flowage of the molten metal 5c is controlled between the irradiation lines 25 and the side walls 37 of the hearth 30, and impurities such as the LDIs 8 that float in the vicinity of the supply lines 26 are restricted so as not to flow toward the lip portion 36. In addition, in the second embodiment also, if the molten metal flows 61 are formed from the irradiation lines 25 toward the side walls 37A and 37B, the LDIs 8 that reside in the vicinity of the supply lines 26 can be caused to be trapped by the skull 7 that is formed on the inside faces of the side walls 37 of the hearth 30 and can thus be removed from the molten metal 5c.
With regard to this point, in the aforementioned first embodiment, as described with reference to
However, as described with reference to
Therefore, in the second embodiment, as illustrated in
[2.2. Spot Irradiation Temperature]
The LDIs 8 are composed of titanium nitride and the like, and the melting point of titanium nitride is higher than the melting point of commercially pure titanium. Therefore, in a case where the molten metal surface temperature T0 is comparatively low, even if titanium that is the principal component of the molten metal 5c melts, titanium nitride that is a component of the LDIs 8 is liable not to dissolve and to remain as a granular solid. Therefore, at the aforementioned irradiation spots 27, an electron beam is radiated in a concentrated manner to increase a surface temperature T3 of the molten metal 5c at the relevant irradiation spot 27 (hereunder, referred to as “spot irradiation temperature T3”) by a large margin relative to the molten metal surface temperature T0. By this means, the spot irradiation temperature T3, for example, can be made higher than the melting point of titanium nitride, and thus the titanium nitride can be dissolved in the molten metal 5c to cause the nitrogen to diffuse and thereby change the titanium nitride to titanium. Accordingly, the LDIs 8 that are contained in the molten metal flows 66 that pass through the irradiation spots 27 can be reliably dissolved into the molten metal 5c and thereby removed. Note that, the melting point of titanium nitride varies depending on the nitrogen concentration. For example, in a case where the nitrogen concentration is in a range of 1.23 to 4% by mass, the melting point of the titanium nitride is 2300 K.
In this case, the spot irradiation temperature T3 is, for example, in the range of 2300 K to 3500 K, and preferably in the range of 2400 K to 2700 K. Preferably, the spot irradiation temperature T3 is higher than the aforementioned raw material supplying temperature T1 and line irradiation temperature T2 (T3>T1, and T3>T2). By this means, even in a case where the LDIs 8 are not dissolved and remain in a solid state when the raw material 5 is melted at the raw material supplying portion 10 (raw material supplying temperature T1) and when line radiation is performed (line irradiation temperature T2), since the LDIs 8 can be heated at the spot irradiation temperature T3 that is a higher temperature, the LDIs 8 can be more reliably dissolved.
[2.3. Position of Irradiation Spot]
First, the position in the Y direction of the respective irradiation spots 27 will be described. As illustrated in
Next, the position in the X direction of the respective irradiation spots 27 will be described. The irradiation spot 27 is disposed between the irradiation line 25 and the supply line 26. A distance L2 between the irradiation spot 27 and the supply line 26 is appropriately set in accordance with the raw material supplying temperature T1, the line irradiation temperature T2, and the radiation conditions for line radiation and spot radiation and the like, and the distance L2 is preferably around half of the distance L between the irradiation line 25 and the supply line 26. By this means, since the irradiation spot 27 can be appropriately disposed at a position of the molten metal flow 66 that flows through the belt-shaped region S3 between the irradiation line 25 and the supply line 26, the LDIs 8 contained in the molten metal flow 66 can be efficiently dissolved and removed.
Note that, in the example illustrated in
[2.4. Settings of Electron Beam for Spot Radiation]
In the second embodiment, as described above, a flow path of the LDIs 8 (the molten metal flow 66) is formed in the belt-shaped region S3 between the irradiation line 25 and the corresponding supply line 26, the irradiation spot 27 is disposed so as to cut off the flow path, and an electron beam is radiated in a concentrated manner onto the irradiation spot 27. By maintaining the spot irradiation temperature T3 at the irradiation spot 27 at a high temperature in this way, the LDIs 8 in the molten metal flow 66 that flows toward the lip portion 36 can be more reliably dissolved. In a case where the molten metal 5c is molten titanium, if the spot irradiation temperature T3 that is measured with a radiation thermometer is maintained at, for example, 2400 K or higher, the LDIs 8 contained in the molten titanium can be reliably dissolved.
Note that, as long as the spot irradiation temperature T3 can be maintained within a predetermined temperature range, the electron beam for spot radiation that dissolves impurities such as the LDIs 8 may be radiated continuously or may be radiated intermittently at the irradiation spot 27. Further, radiation conditions such as the heat transfer amount, scanning speed and heat flux distribution of the electron beam for spot radiation are constrained by the specifications of the equipment that radiates the electron beam. Accordingly, when setting the radiation conditions of the electron beam it is preferable to make the heat transfer amount of the electron beam as large as possible, the scanning speed as fast as possible, and the heat flux distribution as narrow as possible (make the aperture of the electron beam as small as possible) within the range of the equipment specifications.
Further, radiation of an electron beam at the irradiation spots 27 may be performed using a single electron gun or may be performed using a plurality of electron guns. In addition, preferably the aforementioned electron gun 20E for line radiation (see
[2.5. Modification]
Next, a modification of the foregoing second embodiment will be described. In the foregoing, an example was described in which, as illustrated in
For example, as illustrated in
Further, as illustrated in
[2.6. Summary]
The method for producing a metal ingot according to the second embodiment of the present invention has been described above. According to the second embodiment, the following effects are obtained in addition to the aforementioned effects of the first embodiment.
According to the second embodiment, when the molten metal flow 66 that flows toward the lip portion 36 is formed in the belt-shaped region S3 between the irradiation line 25 and the supply line 26, an electron beam for dissolving impurities is radiated in a concentrated manner onto the molten metal flow 66 at an irradiation spot 27 that is disposed at one end portion or both ends on the belt-shaped region S3. By this means, before impurities such as the LDIs 8 that are contained in the molten metal flow 66 arrive at the lip portion 36 from the belt-shaped region S3, the impurities can be dissolved at the high-temperature irradiation spot 27 and thereby removed from the molten metal. Hence, impurities such as the LDIs 8 can be more reliably inhibited from flowing out from the lip portion 36 to the mold 40.
In the foregoing first embodiment, in a case where the line irradiation temperature T2 is lower than the raw material supplying temperature T1 or a case where the temperature gradient ΔT/L between the supply line 26 and the irradiation line 25 is less than 0.00 due to the equipment specifications or other constraints, there is a possibility that a molten metal flow 66 that flows toward the lip portion 36 will be formed in the belt-shaped region S3, and that impurities which ride on the molten metal flow 66 will flow out to the lip portion 36. Even in such a case, in the method for producing a metal ingot according to the second embodiment, impurities can be more reliably inhibited from flowing out to the lip portion 36, and hence the method for producing a metal ingot according to the second embodiment is particularly useful.
Next, a method for producing a metal ingot according to a third embodiment of the present invention will be described.
[3.1. Outline of Method for Producing a Metal Ingot]
First, an outline of the method for producing a metal ingot according to the third embodiment will be described referring to
As illustrated in
In the third embodiment also, by radiating an electron beam along the aforementioned irradiation lines 25, the high temperature region S2 is formed in the vicinity of each irradiation line 25, and the molten metal flows 61 are formed that flow from each irradiation line 25 toward the corresponding supply line 26. By this means, the flowage of the molten metal 5c is controlled between the irradiation lines 25 and the side walls 37 of the hearth 30, and impurities such as the LDIs 8 that float in the vicinity of the supply lines 26 are restricted so as not to flow toward the lip portion 36. In addition, in the third embodiment also, if the molten metal flows 61 can be formed from the irradiation lines 25 toward the side walls 37A and 37B, the LDIs 8 that reside in the vicinity of the supply lines 26 can be caused to be trapped by the skull 7 that is formed on the inside faces of the side walls 37 of the hearth 30 and can thus be removed from the molten metal.
However, as described with reference to
Therefore, in the third embodiment, as illustrated in
Hence, in the third embodiment, in comparison to the aforementioned first embodiment, impurities such as the LDIs 8 can be even more reliably prevented from flowing out from the lip portion 36 into the mold 40.
[3.2. Position of Radiation Line and Line Irradiation Temperature]
The irradiation line 28 is an imaginary line that represents the path of positions at which an electron beam is radiated in a concentrated manner onto the surface of the molten metal 5c in the hearth 30. The irradiation line 28 is disposed on the surface of the molten metal 5c so as to surround the lip portion 36. The two ends of the irradiation line 28 are positioned in the vicinity of the inside face of the side wall 37D (first side wall) of the hearth 30. As used here, the term “vicinity” means that a distance between the two ends of the irradiation line 28 and the inside face of the side wall 37 is within a range of not more than 5 mm. By disposing both ends of the irradiation line 28 in the vicinity of the side wall 37D, the occurrence of a situation in which impurities pass through gaps between the two ends of the irradiation line 28 and the side wall 37D and flow toward the lip portion 36 can be appropriately inhibited.
Note that, although the irradiation line 28 in the example illustrated in
By radiating an electron beam in a concentrated manner along the aforementioned irradiation line 28, a high temperature region having a surface temperature T4 that is higher than the aforementioned molten metal surface temperature T0 is formed in the vicinity of the irradiation line 28 on the surface of the molten metal 5c. Preferably, the surface temperature T4 (hereunder, referred to as “second line irradiation temperature T4”) of the molten metal 5c at the irradiation line 28 is higher than the aforementioned molten metal surface temperature T0 (T4>T0), and is higher than the aforementioned raw material supplying temperature T1 (T4>T1>T0). The second line irradiation temperature T4 is, for example, within a range of 1923 K to 2473 K, and preferably is within a range of 1973 K to 2423 K.
[3.3. Settings of Electron Beam for Second Line Radiation]
In the third embodiment, as illustrated in
Further, radiation of an electron beam along the irradiation line 28 (second line radiation) may be performed using a single electron gun or may be performed using a plurality of electron guns. In addition, preferably the aforementioned electron gun 20E for line radiation (see
[3.4. Modification]
Next, a modification of the aforementioned third embodiment will be described referring to
The method for producing a metal ingot according to this modification is an example in which spot radiation according to the aforementioned second embodiment (see
By combining the irradiation line 25, the irradiation spot 27 and the irradiation line 28 in this manner, even if impurities such as the LDIs 8 are not completely removed by the line radiation according to the first embodiment and the spot radiation according to the second embodiment, and some impurities ride on a molten metal flow and flow toward the lip portion 36, ultimately the impurities in question can be prevented from flowing into the lip portion 36 at the irradiation line 28 that is in the vicinity of the lip portion 36. Hence, impurities can be even more reliably prevented from flowing out from the lip portion 36 to the mold 40.
Next, examples of the present invention will be described. The following examples are merely concrete examples for verifying the effects of the present invention, and the present invention is not limited to the following examples.
(1) Examples of Line Radiation
First, referring to Table 1 and
With respect to the present examples, a molten metal flow inside the hearth 30 was simulated for a case where a titanium alloy, for example, was used as the raw material 5, and an electron beam was radiated along the irradiation line 25 with respect to the molten metal 5c of the titanium alloy that was accumulated inside the short hearth illustrated in
The simulation conditions and evaluation results of the present examples are shown in Table 1.
In the simulations of Examples 1 to 7 shown in Table 1, as illustrated in
On the other hand, as Comparative Example 1, as illustrated in
In Examples 1 to 7 and Comparative Example 1, the various temperatures T0, T1 and T2, an output Q2 of the electron beam for line radiation, a distance L between the irradiation line 25 and the supply line 26, a temperature gradient ΔT/L and the like were as shown in the aforementioned Table 1.
For each simulation, a transient calculation was performed because the flow and the temperature of the molten metal 5c change from moment to moment depending on radiation of an electron beam. The simulation was performed based on the assumption that the LDIs were titanium nitride, the grain size of the titanium nitride was 3.5 mm, and the density of the titanium nitride was 10% less than the molten metal 5c. Further, in Examples 1 to 7 and Comparative Example 1, an electron beam was radiated in a concentrated manner along each of the irradiation lines 25, 25 by scanning an electron beam from one end to the other end of each of the irradiation lines 25, 25 using one electron gun for line radiation. Although the line irradiation temperature T2 fluctuated temporally and spatially, the average value of the line irradiation temperature T2 was as shown in Table 1.
As illustrated in Table 1, in Examples 1 to 7 and Comparative Example 1, an LDI removal effect was evaluated on a four-grade scale (A grade to D grade). The outflow amount [g/min] of LDIs per unit time from the hearth 30 in the respective Examples 1 to 7 were evaluated based on the following evaluation criteria when taking the outflow amount [g/min] of LDIs per unit time from the hearth 30 in Comparative Example 1 as a reference value (100%).
A grade: outflow amount of LDIs is less than 0.1%, or outflow of LDIs is not detected
B grade: outflow amount of LDIs is 0.1% or more and less than 1%
C grade: outflow amount of LDIs is 1% or more and less than 5%
D grade: outflow amount of LDIs is 100% (reference value)
Next, the simulation results and the evaluation of the outflow amount of LDIs for Examples 1 to 7 and Comparative Example 1 will be described.
In Example 1, as illustrated in
Similarly, in Example 2 shown in
It is considered that the reason is as follows. In each of the aforementioned Examples 1 to 3, the line irradiation temperature T2 was higher than the raw material supplying temperature T1, and the temperature gradient ΔT/L between the supply lines 26 and the irradiation lines 25 was a large value of 0.00 K/mm or more. Therefore, it is considered that because strong molten metal flows 61 could be formed from the irradiation lines 25 that crossed over the supply lines 26 and flowed toward the side walls 37A and 37B, the LDIs were appropriately controlled so as not to flow toward the lip portion 36, and thus the LDIs could be reliably prevented from flowing out into the mold 40.
Next, in Example 4 and Example 5, as illustrated in
It is considered that the reason is as follows. In Examples 4 and 5, the line irradiation temperature T2 was lower than the raw material supplying temperature T1, and the temperature gradient ΔT/L was in the range of −2.70 K/mm to less than 0.00 K/mm, which was smaller than the temperature gradient ΔT/L in the aforementioned Examples 1 to 3. Therefore, in Examples 4 and 5, the molten metal flows 61 from the irradiation lines 25 toward the supply lines 26 that are illustrated in
Further, according to the results of comparing the aforementioned Examples 1 to 3 with Examples 4 and 5, it can be said that the effect of preventing an outflow of LDIs by line radiation is superior in Examples 1 to 3 (T2≥T1, ΔT/L≥0.00) compared to Examples 4 and 5 (T2<T1, −2.70≤ΔT/L<0.00).
Next, in Example 6 and Example 7, as illustrated in
It is considered that the reason is as follows. In Examples 6 and 7, the line irradiation temperature T2 was lower than the raw material supplying temperature T1, and the temperature gradient ΔT/L was less than −2.70 K/mm, which was even smaller than the temperature gradient ΔT/L in the aforementioned Examples 4 and 5. Therefore, in Examples 6 and 7, in a part of the region illustrated in
Further, according to the results of comparing Examples 1 to 5 with Examples 6 and 7, it can be said that the effect of preventing an outflow of LDIs by line radiation is superior in Examples 1 to 5 (ΔT/L≥−2.70) compared to Examples 6 and 7 (ΔT/L<−2.70).
In contrast, in Comparative Example 1, as illustrated in
The simulation results for Examples 1 to 7 and Comparative Example 1 have been described above. According to these results it can be said that is was verified that by performing line radiation of an electron beam in a concentrated manner along the irradiation lines 25 as described in Examples 1 to 7, a flowage of LDIs that reside in the vicinity of the supply lines 26 is restricted and the LDIs can be inhibited from flowing toward the lip portion 36, and thus an outflow amount of the LDIs from the lip portion 36 can be reduced to less than 5% of the outflow amount of the LDIs in Comparative Example 1. In particular, it can be said that it was verified that from the viewpoint of preventing an outflow of LDIs by line radiation and increasing the LDI removal effect, Examples 4 and 5 (−2.70≤ΔT/L<0.00) are preferable, and Examples 1 to 3 (ΔT/L≥0.00) are further preferable.
(2) Line Radiation and Spot Radiation Examples
Next, referring to Table 2 and
With respect to the present examples, a molten metal flow inside the hearth 30 was simulated for a case where a titanium alloy, for example, was used as the raw material 5, and with respect to the molten metal 5c of the titanium alloy that was accumulated inside the short hearth illustrated in
The simulation conditions and evaluation results for the present examples are shown in Table 2.
In the simulations of Examples 8 to 12 shown in Table 2, as illustrated in
On the other hand, as Comparative Example 2, as illustrated in
In Examples 8 to 12 and Comparative Example 2, the various temperatures T0, T1, T2 and T3, an output Q2 of the electron beam for line radiation, an output Q3 of the electron beam for spot radiation, a distance L between the irradiation line 25 and the supply line 26, a temperature gradient ΔT/L and the like were as shown in the aforementioned Table 2. The other conditions were made the same as the simulation conditions in the aforementioned Examples 1 to 7. Further, with regard to the evaluation criteria for evaluating the LDI removal effect (evaluation based on four grades from A to D), the evaluation criteria were made the same as in the aforementioned Examples 1 to 7 with the exception that Comparative Example 2 was adopted as a reference value (100%) instead of Comparative Example 1.
Next, the simulation results and the evaluation of outflow amount of LDIs for Example 8 to 12 and Comparative Example 2 will be described.
In Example 8, as illustrated in
Similarly, in Example 9 and Example 10 also, as illustrated in the flow line diagrams on the right side in
It is considered that the reason is as follows. In Examples 8 to 10, because the temperature gradient ΔT/L was in a range of −2.70 K/mm to less than 0.00 K/mm, the molten metal flows 61 from the irradiation lines 25 toward the supply lines 26 that are illustrated in
Next, in Example 11, as illustrated in
It is considered that the reason is as follows. In the aforementioned Example 11, the line irradiation temperature T2 was higher than the raw material supplying temperature T1, and the temperature gradient ΔT/L between the supply lines 26 and the irradiation lines 25 was +0.70 K/mm, which was sufficiently larger than 0.00 K/mm that is the aforementioned threshold value. Therefore, it is considered that because strong molten metal flows 61 could be formed from the irradiation lines 25 that crossed over the supply lines 26 and flowed toward the side walls 37A and 37B, the LDIs were appropriately controlled so as not to flow toward the lip portion 36, and thus the LDIs could be reliably prevented from flowing out into the mold 40. Accordingly, it is considered that with respect to Example 11, even if spot radiation were not performed, an outflow of LDIs could be adequately prevented.
Next, in Example 12, as illustrated in
It is considered that the reason is as follows. In Example 12, the line irradiation temperature T2 was lower than the raw material supplying temperature T1, and the temperature gradient ΔT/L was −3.60 K/mm, which was lower than −2.70 K/mm that is the aforementioned threshold value. Therefore, in Example 12, in a part of the region illustrated in
In contrast, in Comparative Example 2, as illustrated in
The simulation results for Examples 8 to 12 and Comparative Example 2 have been described above. According to these results it can be said that is was verified that by performing spot radiation of an electron beam in a concentrated manner on the irradiation spots 27 as described in Examples 8 to 12, LDIs contained in the molten metal flow 66 that flow in the Y direction in the belt-shaped regions S3 are dissolved and the LDIs can be inhibited from flowing toward the lip portion 36, and thus an outflow amount of the LDIs from the lip portion 36 can be reduced to less than 5% of the outflow amount of the LDIs in Comparative Example 2. In particular, it can be said that it was verified that, as in Examples 8 to 10, because ΔT/L is in the range of −2.70 K/mm to less than 0.00 K/mm, in a case where the molten metal flow 66 that flows in the Y direction toward the lip portion 36 is formed in the belt-shaped region S3 (see
Whilst preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to the above examples. It is clear that a person having common knowledge in the field of the art to which the present invention pertains will be able to contrive various examples of changes and modifications within the category of the technical idea described in the appended claims, and it should be understood that they also naturally belong to the technical scope of the present invention.
In the foregoing, examples of producing an ingot 50 of titanium using the hearth 30 and the mold 40 in which the metal raw material 5 that is the object of melting by the method for producing a metal ingot according to the present embodiments is, for example, a raw material of titanium or a titanium alloy have been mainly described. However, the method for producing a metal ingot of the present invention is also applicable to cases where various metal raw materials other than a titanium raw material are melted and an ingot of the relevant metal raw material is produced. In particular, the method for producing a metal ingot of the present invention is also applicable to a case of producing an ingot of a high-melting-point active metal with which it is possible to produce an ingot using an electron gun capable of controlling a radiation position of an electron beam and an electron-beam melting furnace having a hearth that accumulates a molten metal of a metal raw material, specifically, a case of producing an ingot of a metal raw material such as, apart from titanium, tantalum, niobium, vanadium, molybdenum or zirconium. In other words, the present invention can be applied particularly effectively to a case of producing an ingot containing the respective elements mentioned here in a total amount of 50% by mass or more.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-079732 | Apr 2017 | JP | national |
| 2017-079733 | Apr 2017 | JP | national |
| 2017-079734 | Apr 2017 | JP | national |
| 2017-079735 | Apr 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/015536 | 4/13/2018 | WO | 00 |
