JP5344296B2 - TANDISH AND METHOD FOR PRODUCING R-T-B BASE ALLOY USING THE SAME - Google Patents

Description

  The present invention relates to a tundish and a method for producing an RTB-based alloy using the tundish.

  In recent years, rare earth magnets, particularly R-T-B based sintered magnets, have rapidly increased their production due to their high characteristics, and are used in a wide range of applications such as motors.

  As this kind of rare earth magnet, generally, a part of Nd is replaced with another rare earth element such as Pr or Dy, or a part of Fe is replaced with another transition metal such as Co or Ni. This is generically called an RTB-based sintered magnet including an Nd-Fe-B sintered magnet. Here, R is at least one of rare earth elements including Y. Further, T is a transition metal that requires Fe, and a part of Fe can be substituted with Co or Ni. B is boron, and a part thereof can be substituted with C or N. As the additive element, Cu, Al, Ti, V, Cr, Ga, Mn, Nb, Ta, Mo, W, Ca, Sn, Zr, Hf, or the like may be added alone or in combination.

The RTB-based sintered magnet is composed of a main phase composed of an R ₂ T ₁₄ B phase that is a ferromagnetic phase, and an R-rich phase in which rare earth elements are concentrated at the main phase grain boundary. It is considered that it is important for the coercive force to be uniformly dispersed.

  As a method for producing an RTB-based sintered magnet alloy (hereinafter referred to as an RTB-based alloy) in which the R-rich phase is uniformly dispersed, a molten raw material alloy adjusted to a predetermined composition is used as a roll surface. A strip casting method is known in which a slab-like R-T-B alloy is produced by pouring the mixture into a slab and cooling.

  In the production of the R-T-B type alloy by the strip casting method, a raw material alloy having a predetermined composition is melted by an induction heating method in an inert atmosphere such as argon to form a molten R-T-B type alloy. . Next, after this molten metal is kept at about 1350 ° C., it is rapidly cooled by a single roll method to obtain, for example, an RTB-based alloy having a thickness of 100 μm to 1000 μm.

  Patent Documents 1 and 2 disclose a method for producing an RTB-based alloy by strip casting.

JP-A-8-229641 JP-A-9-155507

  In the conventional manufacturing method of the R-T-B type alloy by strip casting, it is inevitable that the thickness varies in the R-T-B type alloy. If the variation in thickness is large, various structures will be mixed in the R-T-B type alloys produced by the same composition and the same process.

  When various structures are mixed, the particle size distribution becomes wide even if pulverized under certain conditions. As a result, the structure of the obtained sintered magnet is not uniform, and there is a possibility that predetermined magnetic characteristics may not be obtained.

  In the manufacturing method of the R-T-B type alloy disclosed in Patent Document 1, the central portion in the plate width direction of the R-T-B type alloy obtained because the upper surface of the molten metal on the tundish is a free surface is thick. , The edge becomes thinner. Moreover, since it is difficult to stabilize the supply amount of the molten metal, thickness variation in the length direction occurs.

  In Patent Document 2, the tundish has a shape that can receive the molten metal supplied from the crucible with an inclined receiving plate to stop the momentum of the molten metal and take a long flow path of the molten metal, and a shape that reduces a drop. Is intended to rectify the molten metal. In this method, the pouring gate becomes long, the temperature of the molten metal is difficult to keep constant, thickness variation occurs, and the alloy structure changes.

  An object of the present invention is to produce an RTB-based alloy having a small standard deviation in thickness by a tundish and a method for manufacturing an RTB-based alloy using the tundish.

The present invention
A main body composed of an inclined portion into which the molten metal melted in the crucible is poured and a flat portion into which the molten metal poured into the inclined portion flows;
A lid that is disposed opposite to the flat portion so as to form a predetermined distance;
A gate formed between the flat portion and the lid;
A tundish having heating means disposed on the lid.

  In a preferred embodiment of the present invention, the tundish heating means is a resistance heater.

In addition, the present invention
A step of introducing a raw material into a crucible so as to have a predetermined composition and then heating to prepare a molten R-T-B alloy;
A main body composed of an inclined portion into which the molten metal melted in the crucible is poured, and a flat portion through which the molten metal poured into the inclined portion flows, a lid that is arranged to face the flat portion at a predetermined interval, and the flat portion Preparing a tundish having a gate formed between a portion and the lid, and heating means disposed on the lid;
Preparing a cooling roll having a surface roughness Ra of 1.2 μm or more;
The RTB alloy is poured into the inclined portion of the tundish, and poured into the cooling roll via the gate heated from the inclined portion, thereby rapidly cooling the RTB alloy. Process,
It is a manufacturing method of the RTB type alloy which consists of.

  According to the present invention, it is possible to produce an RTB-based alloy having a thickness variation (standard deviation) that is less than half that of the prior art.

Schematic diagram of fabrication of alloy for RTB-based sintered magnet of the present invention Sectional drawing which shows the structure of the tundish of this invention Schematic diagram of conventional alloy preparation for RTB-based sintered magnet The figure which shows the abundance ratio of the thickness of the R-T-B type | system | group alloy produced by this invention, and the R-T-B type | system | group alloy produced not according to this invention The figure which shows the relationship between the average thickness of a R-T-B type alloy, and D50 The figure which shows the grinding | pulverization particle size of the RTB system alloy by this invention, and the RTB system alloy which is not this invention The figure which shows the squareness of the RTB system sintered magnet by this invention for every tempering temperature, and the RTB system sintered magnet which is not this invention

[Tundish]
1 and 2, the tundish 1 of the present invention is disposed so as to face the main body 3 having an inclined portion and a flat portion that form a flow path of the molten metal, and with a predetermined distance from the flat portion. It comprises a lid 4 and heating means 5 disposed on the lid.

The main body 3 and the lid 4 of the tundish 1 are preferably made of a material having high heat resistance and low reaction with rare earth elements. As the material, for example, BN, be included such as Al ₂ O ₃ known materials.

  In the present invention, the melt 6 of the R-T-B alloy is a rectangular spout 7 formed by the lid 4 and the flat portion of the main body 3 from the inclined portion of the main body of the tundish shown in FIGS. The hot water is poured into the cooling roll 8.

  The main body 3 of the tundish 1 of the present invention has an inclined portion into which the molten metal 6 is poured from the crucible 2. Depending on the composition, the molten metal 6 of the R-T-B alloy may have poor flowability. If there is no inclined part, the molten metal of the R-T-B alloy will start at the start, middle and end of the molten metal. The amount of discharged hot water differs, and the thickness of the RTB-based alloy after cooling with the roll 8 varies. Since the portion where the molten metal 6 is poured from the crucible 2 has an inclination, the molten metal 6 of the R—T—B system alloy is smoothly conveyed from the crucible 2 to the tundish gate 7.

  In the main body 3 of the tundish 1 of the present invention, the inclination angle θ of the inclined portion where the molten metal is poured from the crucible 2 is preferably set to 5 ° to 80 °. More preferably, the angle is 10 ° to 50 °. By setting the inclination angle θ of the inclined portion where the molten metal 6 is poured from the crucible 2 to a range of 10 ° to 50 °, the RTB-based alloy at the beginning of the pouring, during the pouring, immediately before the hot water runs out The amount of hot water discharged from the spout 7 described later of the molten metal 6 can be made substantially constant.

  Further, in the main body 3, a gate 7 is formed by the flat portion and a lid that is disposed to face the flat portion at a predetermined interval. In the present invention, the size of the gate 7 can be easily adjusted by changing the distance H between the main body 3 and the lid 4.

  The distance H between the gates 7 of the preferred tundish 1 of the present invention is determined by the hot water rate and the gate width, but is preferably 1 mm or more and 5 mm or less.

  The rectangular gate 7 formed by the main body 3 and the lid 4 is preferably 20 mm or more in length. The length of 20 mm or more rectifies the molten metal flow. Furthermore, the temperature of the molten metal 6 of the R—T—B system alloy can be kept constant in combination with the heating means 5 described later. Moreover, by making the gate 7 rectangular and making the length 20 mm or more, the flow of the molten metal is rectified, and the amount of hot water discharged in the plate width direction of the R-T-B system alloy can be made almost constant.

  The ratio between the length L1 of the flat part of the main body and the length L2 of the inclined part is preferably 1: 2 to 1: 4. When the ratio of L1 is small, the flow rate of the molten metal cannot be made constant. When the ratio of L1 is large, the molten metal is cooled. On the other hand, when the ratio of L2 is small, the molten metal discharge rate at the beginning of the pouring, during the pouring, and immediately before the hot water runs out fluctuates. If the ratio of L2 is large, it will be difficult to maintain a uniform temperature by the heating means 5 described later. The length L1 of the flat portion of the main body is preferably longer than the length of the lid 4. If the length L1 of the flat part of the main body is shorter than the length of the lid 4, the lid 4 protrudes and uniform pouring of the roll cannot be performed.

  The lid 4 is provided with heating means 5. The heating means 5 prevents the molten metal 6 of the R—T—B system alloy from being hardened at the gate 7 having a rectangular shape. Moreover, the heating means 5 can maintain the amount of hot water to be constant by keeping the temperature of the molten metal 6 of the RTB-based alloy constant.

  Since the heating means 5 needs to heat the peripheral members to an approximate temperature in order to maintain the molten metal temperature constant, a resistance heater that also heats the heater periphery is suitable.

[R-T-B alloy production process]
The above alloy is produced by quenching a molten R-T-B alloy by, for example, a strip casting method. Hereinafter, details of the preparation of the RTB-based alloy rapidly solidified by the strip casting method will be described.

FIG. 1 shows a schematic diagram of an apparatus for producing an RTB-based alloy by the strip casting method of the present invention. The RTB-based alloy is melted using the refractory crucible 2 in a vacuum or an inert gas atmosphere because of its active properties. The melted molten alloy 6 is maintained at 1350-1500 ° C. for a predetermined time, and then supplied to the casting rotary roll 8 whose interior is water-cooled via the tundish 1 and from 10 ² K / s to 10 ^5. Quench rapidly at a rate of K / s.

  Here, the tundish 1 has the gate 7 in a rectangular shape as described above. The temperature of the tundish 1 is kept constant by the heating means 5 so that the molten metal 6 does not harden at the rectangular spout 7. The temperature is set in the range of 700 ° C to 1500 ° C. Preferably, it is 800 degreeC or more and 1200 degrees C or less. At a set temperature of 800 ° C. or lower, the melt viscosity may decrease. Further, in order to set the set temperature to 1200 ° C. or higher, it becomes difficult to select a heater wire.

  In general, the supply speed of the molten metal 6 and the rotational speed of the roll 8 are controlled by appropriately setting conditions according to the desired thickness of the alloy. The rotation speed of the roll 8 is arbitrarily set within the range of 0.5 to 3 m / s as the peripheral speed.

  The material of the casting roll 8 is preferably copper or a copper alloy from the viewpoint of good thermal conductivity and easy availability. Depending on the material of the roll 8 and the surface state of the roll 8, a molten metal residue may adhere to the surface of the casting roll 8, so that a cleaning device for cleaning the roll surface can be installed as necessary. The R—T—B type alloy solidified on the roll 8 is detached from the roll 8 and is recovered as a slab-like R—T—B type alloy in a collection container (not shown). A uniform alloy structure can be maintained by providing a heating and cooling mechanism for the collection container.

  The surface roughness of the casting roll 8 surface is preferably 1.2 μm or more in terms of arithmetic average roughness Ra. When Ra is less than 1.2 μm, the wettability of the roll 8 with respect to the molten metal 6 of the R—T—B alloy is deteriorated, and the production of the R—T—B alloy that becomes a slab shape is not stable. If Ra exceeds 6 μm, the cooling efficiency is lowered and the desired alloy structure cannot be obtained, so 6 μm or less is preferable.

  When the temperature of the cooling water used for cooling the RTB-based alloy by the roll 8 is too high, excessive energy is required for maintaining the temperature of the cooling water. Therefore, it is desirable to make it 70 degrees C or less. More preferably, it is desirable to make it 50 degrees C or less.

  In the manufacturing method according to the present invention, it is possible to produce an RTB-based alloy having a thickness variation (standard deviation) of less than half that of the conventional one.

  A raw material blended with metal neodymium, ferroboron, cobalt, aluminum, copper, iron, or the like so as to have the composition shown in Table 1 is used with an alumina crucible and argon gas in an atmosphere of 0.10 atm. Melting was performed in a melting furnace.

  Then, each molten metal was poured on the roll surface on the conditions of Table 2, and the slab-like RTB system alloy was produced by the strip casting method. Here, the diameter of the rotary roll for casting is 235 mm, the material is chromium / zirconium copper, the inside is water-cooled, and the water temperature can be adjusted.

  As shown in Table 3, when 100 lots were measured per lot, the average thickness and standard deviation (thickness σ) of the slab-like R—T—B-based alloy were determined according to the present invention. No. which is a TB alloy. 1 to 3, no. From 9 to 17, the standard deviation (thickness σ) of the thickness of the RTB-based alloy was 8 μm to 15 μm. Here, the standard deviation of thickness (thickness σ) refers to the standard deviation of thickness in the length direction. Incidentally, the R-T-B alloy No. 1 prepared according to the present invention. When the thickness in the plate width direction was measured for No. 1, the standard deviation of thickness (thickness σ) was 15 μm or less.

  On the other hand, No. 1 which is an R-T-B alloy produced without using the present invention. 4 to 8, no. 18 to No. No. 26, the standard deviation (thickness σ) of the thickness of the RTB-based alloy was 26 to 55 μm.

  FIG. 4 shows a comparison of the abundance ratios of the thicknesses of the RTB-based alloy manufactured according to the present invention and the RTB-based alloy manufactured not according to the present invention. In FIG. 4, when the average thickness of the RTB-based alloy is 300 μm, the average thickness is 400 μm. As shown in FIG. 4, it can be seen that the RTB-based alloy produced by the present invention has almost the same thickness. On the other hand, it can be seen that the thickness distribution is broad in the R-T-B alloy produced without using the present invention.

  Next, seven lots of raw materials blended so as to have the composition of B alloy shown in Table 1 were prepared, and these raw materials were melted in a high frequency melting furnace in an atmosphere of 0.1 atm with argon gas using an alumina crucible. Molten metal was poured onto the roll surface under the conditions shown in Table 4 to produce slab-like RTB-based alloys having different thicknesses. Here, the diameter of the rotary roll for casting is 235 mm, the material is chromium / zirconium copper, the inside is water-cooled, and the water temperature can be adjusted.

  Using these alloys as raw materials, they were hydrogen embrittled in a hydrogen-pressurized atmosphere, and then heated and cooled in vacuum to 600 ° C. to obtain alloy coarse powder. 0.05% zinc stearate by mass ratio was added to and mixed with the coarse powder.

  Next, using an airflow pulverizer (jet mill device), dry pulverization was performed in a nitrogen airflow at a magnetic powder feed rate of 100 g / min and a gas pressure of 500 kPa to obtain an RTB-based alloy powder. At this time, the oxygen concentration in the pulverized gas is controlled to 8500 ppm or less. About the powder of the RTB system alloy after pulverization, the particle size D50 was measured by a laser diffraction method using an air flow dispersion method.

  The measurement results for each of the 7 lots are shown in Table 5 and FIG. As shown in FIG. 5, it can be seen that the average thickness of the slab-shaped RTB-based alloy and D50 increase proportionally as the average thickness increases. Thereby, since D50 and slab thickness correspond, desired D50 can be stably obtained by controlling the thickness of a R-T-B system alloy.

  Next, three lots of raw materials blended so as to have the composition of the B alloy shown in Table 1 were prepared, and these raw materials were melted in a high-frequency melting furnace in an atmosphere of 0.1 atm with argon gas using an alumina crucible. The molten metal was poured onto the roll surface under the three conditions shown in Table 6 to produce a slab-shaped R-T-B alloy. Here, the diameter of the rotary roll for casting is 235 mm, the material is chromium / zirconium copper, the inside is water-cooled, and the water temperature can be adjusted. The peripheral speed of the roll was 1.0 m / s.

  As shown in Table 7, when 100 lots were measured per lot, the average thickness and standard deviation of thickness (thickness σ) of the slab-shaped R-T-B alloy were prepared in the present invention. No. 34, 303 μm, 9 μm, No. 34 35 was 298 μm and 14 μm. On the other hand, no. 36 was 334 μm and 36 μm.

  Using these alloys as raw materials, they were hydrogen embrittled in a hydrogen-pressurized atmosphere, and then heated and cooled in vacuum to 600 ° C. to obtain alloy coarse powder. 0.05% zinc stearate by mass ratio was added to and mixed with the coarse powder.

  Next, as shown in Table 8, using an airflow pulverizer (jet mill device), dry pulverization is performed in a nitrogen stream at a gas pressure of 500 kPa, and an R-T-B alloy having a D50 of about 4.5 μm. Of powder was obtained. At this time, the oxygen concentration in the pulverized gas is controlled to 8500 ppm or less.

  The particle size distribution after pulverization was graphed (FIG. 6). No. prepared in the present invention. 34 and no. No. 35 has a small distribution on the coarse grain side but was not prepared according to the present invention. No. 36 was confirmed to be widely distributed on the coarse grain side.

  The powder thus produced was molded by a press device to produce a molded body. Specifically, the powder particles were compressed in a magnetic field-oriented state in an applied magnetic field and pressed. Thereafter, the molded body was extracted from the press device and subjected to a sintering process at 1060 ° C. for 4 hours in a vacuum furnace.

  The sintered RTB-based sintered magnet was divided into three, and tempering at 440 ° C., 460 ° C., and 480 ° C. was applied to each in vacuum.

No. 34 to No. About each of 36, _HcJ (kA / m) and HK (kA / m) were measured, and the squareness was evaluated by the calculation formula of HK / _HcJ × 100. Table 9 shows the evaluation results.

  Of the results in Table 9, the squareness was graphed (FIG. 7). No. produced in the present invention. 34, no. In the 35 RTB sintered magnet, the squareness does not change in a wide range from 440 ° C to 480 ° C. On the other hand, no. The 36 RTB sintered magnets have a squareness lower than that of the present invention in the range of 440 ° C. to 480 ° C., especially when heat treatment at 440 ° C. is applied, compared with the sintered magnet according to the present invention. The squareness is as low as 10% or more.

  By having good squareness, there are advantages that a high magnetic flux density can be obtained with the same permeance, and that the production conditions of temper treatment are relaxed because the squareness does not change under a wide range of tempering conditions.

  When manufactured irrespective of the present invention, the thickness variation of the slab becomes large, and the pulverized particle size after pulverization is broadly distributed on the coarse particle side as shown in FIG. As a result, many sintered bodies having a large crystal grain size are included. In addition, the variation in crystal grain size becomes large. Therefore, it is presumed that the squareness was deteriorated. According to the present invention, the variation in the thickness of the RTB-based alloy is reduced, so that the structure becomes more homogeneous than before. By forming a homogeneous structure, it is considered that the variation in magnetic properties after magnetization, which has conventionally occurred in the same lot, is reduced. In addition, the sintered magnet using the RTB-based alloy of the present invention stably has a squareness of 95% or more.

  The present invention can be suitably used for the production of an RTB-based sintered magnet.

1 11 Tundish 2 12 Crucible 3 Main body 4 Lid 5 Heating means 6 16 Molten metal 7 Pouring gate 8 18 Roll 9 19 Crusher H Distance between pouring gates L1 Length of flat part L2 Length of inclined part

Claims (3)

A main body composed of an inclined portion into which the molten metal melted in the crucible is poured and a flat portion into which the molten metal poured into the inclined portion flows;
A lid that is disposed opposite to the flat portion so as to form a predetermined distance;
A gate formed between the flat portion and the lid;
A tundish having heating means disposed on the lid.   The tundish according to claim 1, wherein the heating means is a resistance heater. A step of introducing a raw material into a crucible so as to have a predetermined composition and then heating to prepare a molten R-T-B alloy;
  A main body composed of an inclined portion into which the molten metal melted in the crucible is poured, and a flat portion through which the molten metal poured into the inclined portion flows, a lid that is arranged to face the flat portion at a predetermined interval, and the flat portion Preparing a tundish having a gate formed between a portion and the lid, and heating means disposed on the lid;
  Preparing a cooling roll having a surface roughness Ra of 1.2 μm or more;
  The RTB alloy is poured into the inclined portion of the tundish, and poured into the cooling roll via the gate heated from the inclined portion, thereby rapidly cooling the RTB alloy. Process,
  The manufacturing method of the RTB type alloy which consists of these.

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