JP5805213B2 - Tungsten sintered alloy - Google Patents

Description

  The present invention generally relates to a tungsten sintered alloy, and more particularly to a tungsten sintered alloy used as a radiation shielding material in radiological medical equipment, nuclear reactor related equipment, and the like.

  The use of a tungsten-based alloy material mainly composed of tungsten as a radiation shielding material has been known.

  For example, in Japanese Patent Laid-Open No. 9-71828 (hereinafter referred to as Patent Document 1), a sintered body containing 85% by weight or more of tungsten as a main component and the balance of nickel and iron or copper is subjected to plastic working, A tungsten-based alloy material for radiation shielding, which has a layered structure in which particles and a nickel-containing binder layer are flattened and these flat layers overlap, is disclosed. This tungsten-based alloy material is obtained by rolling a sintered body obtained by sintering a molded body at 1470 ° C. at a heating temperature of 1300 ° C. so that the total processing rate is about 60%. It is obtained by flattening the particles and the binder layer.

  JP-A-9-235641 discloses that tungsten is 80 to 97% by weight, nickel is 2 to 15%, and one or more of iron, copper, and cobalt is 1 to 2 in total. A tungsten polymerized gold plate containing 10%, having a thickness of 0.3 mm or less and having both sides having dimensions of 200 times or more of the thickness is disclosed. This polymer metal plate is prepared by mixing raw material powders, forming a thin plate having a thickness of 0.35 mm or less with a powder rolling press, sintering in a non-oxidizing atmosphere, and performing hot rolling and / or cooling as necessary. It is obtained by carrying out hot rolling and then performing finish rolling for flattening and smoothing.

Japanese Patent Laid-Open No. 9-71828 Japanese Patent Laid-Open No. 9-235641

  As disclosed in Patent Document 1, a tungsten sintered alloy containing 85 mass% or more of tungsten has a radiation shielding effect, and is therefore used as a radiation shielding material in radiological medical equipment, reactor related equipment, and the like. . In the case of using a tungsten sintered alloy for such an application, it is necessary to produce a flat plate-like tungsten sintered alloy having a wide area of a certain extent or more.

  However, since the conventional tungsten sintered alloy does not have sufficient elongation as a material property, there is a problem that a flat radiation shielding member having a complicated shape cannot be formed by pressing or forging.

  Accordingly, an object of the present invention is to provide a flat plate-like tungsten sintered alloy that can be formed into a complicated shape by pressing or forging.

  The tungsten sintered alloy according to the present invention is at least one selected from the group consisting of 85% to 98% by weight of tungsten, 1.4% to 11% by weight of nickel, iron, copper and cobalt. Is a flat plate-like tungsten sintered alloy containing 0.6 mass% or more and 6 mass% or less. The flat plate-like tungsten sintered alloy has an elongation percentage in the plane direction of 20% or more.

  In the tungsten sintered alloy according to the present invention, it is preferable that the flat tungsten sintered alloy has a thickness of 1.5 mm or less.

  Further, in the tungsten sintered alloy according to the present invention, the X-ray diffraction intensity ratio of the (111) plane of the Ni— (Fe, Cu, Co) phase on the flat plate surface of the flat plate-like tungsten sintered alloy (where, When the X-ray diffraction intensities of the (111) plane, (100) plane, (110) plane, and (311) plane are I (111), I (100), I (110), and I (311), The X-ray diffraction intensity ratio of the (111) plane is [I (111) / {I (111) + I (100) + I (110) + I (311)}]) of 0.68 or more and 0.9 or less. Preferably there is.

  ADVANTAGE OF THE INVENTION According to this invention, the flat-plate-shaped tungsten sintered alloy which can be shape | molded in a complicated shape by press work or a forge process can be provided.

It is an optical microscope photograph which shows the cross section of the flat-plate-shaped tungsten sintered alloy after a sintering process was performed in the middle of preparation of Example 1 of this invention. It is an optical microscope photograph which shows the cross section of the flat-plate-shaped tungsten sintered alloy after the strain introduction process and the heat processing process were performed in the middle of preparation of Example 1 of this invention. It is an optical microscope photograph which shows the cross section of the flat tungsten sintered alloy produced in Example 1 of this invention. It is an optical microscope photograph which shows the cross section of the flat tungsten sintered alloy produced by the comparative example 2 of this invention. It is a typical perspective view which shows two cross sections observed in the flat-plate-shaped tungsten sintered alloy produced as an intermediate product in the Example and comparative example of this invention. It is a scanning electron microscope (SEM) photograph which shows the cross-sectional part observed in the flat-plate-shaped tungsten sintered alloy produced as an intermediate product in Example 1 of this invention. The figure which shows typically the thickness and length of the tungsten crystal grain measured in the cross-sectional part observed in the flat-plate-shaped tungsten sintered alloy produced as an intermediate product in the Example and comparative example of this invention. is there. It is the top view (A) and side view (B) which show the dimension of the tensile test piece produced from the flat-plate-shaped tungsten sintered alloy as the final product produced by the Example and comparative example of this invention.

  The flat tungsten sintered alloy as the intermediate product of the present invention is tungsten (W) 85 mass% to 98 mass%, nickel (Ni) 1.4 mass% to 11 mass%, iron (Fe ), At least one selected from the group consisting of copper (Cu) and cobalt (Co) is contained in an amount of 0.6 mass% to 6 mass%. This tungsten sintered alloy has a structure in which a plurality of flat tungsten crystal grains extending along the direction in which the plane of the flat tungsten sintered alloy extends are laminated. A first cross section along a thickness direction orthogonal to a direction in which a plane of the flat tungsten sintered alloy extends, and a thickness direction orthogonal to a direction in which the flat surface of the flat tungsten sintered alloy extends. A first cross-sectional portion having a constant width and a constant thickness selected from the first cross-section, and a second cross-section perpendicular to the first cross-section, and a second cross-section Average of a plurality of tungsten crystal grains intersecting a center line passing through the center of the constant width and extending in the constant thickness direction, observed in the second cross-sectional portion having the selected constant width and constant thickness The ratio of the average length to the thickness is 9 or more and 125 or less.

  In the plate-like tungsten sintered alloy as the intermediate product configured as described above, the ratio of the average length to the average thickness of the tungsten crystal grains observed as described above is 9 or more and 125 or less. High strength can be obtained at a high temperature as compared with the prior art. If the ratio of the average length to the average thickness of the tungsten crystal grains observed as described above is less than 9, there is a possibility that a sufficiently high strength cannot be obtained at a high temperature. When the ratio of the average length to the average thickness of the tungsten crystal grains observed as described above exceeds 125, there is a possibility that cracking may occur.

  In order to realize the above ratio, the average thickness of tungsten crystal grains observed as described above is 2 μm or more and 10 μm or less, and the average length of tungsten crystal grains observed as described above is 30 μm or more and 250 μm or less. It is preferable that It is difficult to make the average thickness of the tungsten crystal grains less than 2 μm, or to make the average length exceed 250 μm.

  When the average thickness of tungsten crystal grains observed as described above is 2 μm or more and 3 μm or less, the average length of tungsten crystal grains observed as described above is preferably in the range of 30 μm or more and 250 μm or less. The ratio of the average length to the average thickness is preferably 10 or more and 125 or less.

  In addition, when the average thickness of the tungsten crystal grains observed as described above exceeds 3 μm and is 6 μm or less, the average of the tungsten crystal grains observed as described above is required to obtain a sufficiently high strength at a high temperature. The length is preferably in the range of 54 μm to 250 μm, and the ratio of the average length to the average thickness is preferably 9 to 84.

  Further, when the average thickness of the tungsten crystal grains observed as described above exceeds 6 μm and is 10 μm or less, the average of the tungsten crystal grains observed as described above is obtained in order to obtain a sufficiently high strength at a high temperature. The length is preferably in the range of 90 μm to 250 μm, and the ratio of the average length to the average thickness is preferably 9 to 42.

  The shape of the tungsten crystal grains in the planar direction of the flat plate-like tungsten sintered alloy has various shapes such as a substantially circular shape, a substantially elliptical shape, a substantially square shape, a substantially rectangular shape, and an indefinite shape.

  The flat tungsten sintered alloy as the intermediate product of the present invention includes (1) raw material preparation step, (2) mixing step, (3) forming step, (4) sintering step, and (5) strain described later. It is manufactured through an introduction step, (6) a heat treatment step, and (7) a hot rolling step.

  In summary, the method for producing a flat plate-shaped tungsten sintered alloy as an intermediate product of the present invention includes tungsten in an amount of 85 to 98% by mass, nickel in an amount of 1.4 to 11% by mass, iron, A method for producing a tungsten sintered alloy containing at least one selected from the group consisting of copper and cobalt in an amount of 0.6 mass% to 6 mass%, wherein strain is introduced into the sintered body and strain is introduced. After the sintered body is heat treated, the sintered body is hot-rolled at a rolling rate of 60% or more.

  The plate-like tungsten sintered alloy thus produced can have a structure in which the ratio of the average length to the average thickness of the tungsten crystal grains observed as described above is 9 or more and 125 or less. Higher strength than conventional can be obtained at temperature.

  In particular, for a tungsten sintered alloy (sintered body) having tungsten crystal grains with a grain size of 30 to 50 μm produced by a conventionally known production method (mixing step, forming step and sintering step of raw material powder). By applying a certain heat treatment after applying a certain strain, the grain size of the tungsten crystal grains in the tungsten sintered alloy can be reduced to a certain value or less (5 to 20 μm). Thereafter, the thickness of the tungsten crystal grains is reduced below a certain value and the length of the tungsten crystal grains is increased above a certain value by hot rolling the sintered body at a rolling processing rate of 60% or more. Thus, it is possible to obtain a tungsten sintered alloy having a structure in which a plurality of flat tungsten crystal grains extending in the planar direction of the flat tungsten sintered alloy are stacked. Thereby, the high intensity | strength compared with the former can be acquired at high temperature.

  The flat tungsten sintered alloy according to the present invention was selected from the group consisting of 85 mass% to 98 mass% tungsten, 1.4 mass% to 11 mass% nickel, iron, copper and cobalt. At least one kind is contained in an amount of 0.6 mass% to 6 mass%. The flat plate-like tungsten sintered alloy has an elongation percentage in the plane direction of 20% or more.

  In the flat plate-like tungsten sintered alloy configured as described above, the flat plate-like tungsten sintered alloy has an elongation percentage in the plane direction of 20% or more. It becomes possible to mold the bond gold into a complicated shape.

  If the flat plate-like tungsten sintered alloy has an elongation percentage of less than 20%, there is no difference in elongation rate from the conventional tungsten sintered alloy. There is a possibility that it cannot be formed into a complicated shape. The upper limit of the elongation in the plane direction of the flat plate-like tungsten sintered alloy is 45%. It is difficult to obtain a flat tungsten sintered alloy having an elongation percentage in the plane direction exceeding 45%.

  The flat plate-like tungsten sintered alloy according to the present invention has the following (1) raw material preparation step, (2) mixing step, (3) forming step, (4) sintering step, (5) strain introducing step, (6) It is manufactured through a heat treatment step, (7) a hot rolling step, and (8) a heat treatment step.

  In summary, the method for producing a flat tungsten sintered alloy according to the present invention includes tungsten in an amount of 85 mass% to 98 mass%, nickel in an amount of 1.4 mass% to 11 mass%, iron, copper, and cobalt. A method for producing a tungsten sintered alloy containing at least one selected from the group consisting of 0.6% by mass and 6% by mass, wherein strain is introduced into the sintered body and the strain is introduced. After the body is heat-treated, the sintered body is hot-rolled at a rolling processing rate of 60% or more, and the hot-rolled sintered body is further heat-treated.

  The flat plate-like tungsten sintered alloy thus manufactured can increase the flat plate-like tungsten sintered alloy in the planar direction by 20% or more, and is flat plate-like tungsten by pressing or forging. It becomes possible to form a sintered alloy into a complicated shape.

  In particular, the flat tungsten sintered alloy according to the present invention is obtained by further heat-treating the flat tungsten sintered alloy as the intermediate product of the present invention. By this heat treatment, the flat tungsten sintered alloy does not have the structure of the tungsten sintered alloy as the intermediate product of the present invention, but has a structure very close to the structure of the conventional tungsten sintered alloy immediately after sintering. Have. However, in the tungsten sintered alloy according to the present invention, the structure of the tungsten sintered alloy as the intermediate product of the present invention is returned to the structure very close to the structure of the conventional tungsten sintered alloy. . As a result, defects existing in the interface between the tungsten crystal grains and the binder (nickel, iron, etc.) and in the binder, which caused the decrease in elongation in the conventional tungsten sintered alloy, are almost eliminated, so the tungsten crystal grains Becomes slippery in the binder component. As a result, the elongation of the tungsten sintered alloy according to the present invention is improved.

  In addition, it is preferable that the thickness of the flat tungsten sintered alloy according to the present invention is 1.5 mm or less.

  Further, in the tungsten sintered alloy according to the present invention, the X-ray diffraction intensity ratio of the (111) plane of the Ni— (Fe, Cu, Co) phase on the flat plate surface of the flat plate-like tungsten sintered alloy (where, When the X-ray diffraction intensities of the (111) plane, (100) plane, (110) plane, and (311) plane are I (111), I (100), I (110), and I (311), The X-ray diffraction intensity ratio of the (111) plane is [I (111) / {I (111) + I (100) + I (110) + I (311)}]) of 0.68 or more and 0.9 or less. Preferably there is.

  Thus, the reason why the X-ray diffraction intensity ratio of the (111) plane of the Ni— (Fe, Cu, Co) phase on the flat plate surface of the flat plate-like tungsten sintered alloy of the present invention is high, and the function and effect thereof are as follows. It can be explained as follows. In the hot rolling step (7), when a flat structure of tungsten crystal grains having an extremely high aspect ratio is formed, the Ni— (Fe, Cu, Co) phase that is a binder phase is also elongated in the plane direction. As a result, in the Ni— (Fe, Cu, Co) phase that is the binder phase, the (111) plane that is the slip surface of the FCC (face centered cubic) structure is oriented in parallel to the plane direction. Thereafter, after the heat treatment step (8), the (111) plane orientation remains in the flat tungsten sintered alloy as the final product. Thus, since the sliding surface of the binder surface is oriented parallel to the planar direction, the tungsten crystal grains can be easily slipped in the binder component. Then, the heat treatment can substantially eliminate the defects present in the tungsten sintered alloy, and can further improve the planar elongation of the tungsten sintered alloy.

  In conventional tungsten sintered alloys, warping and distortion occur, and it is difficult to form a thin flat plate immediately after sintering. In addition, when a conventional tungsten sintered alloy is subjected to a rolling process with a rolling rate of 60% or more, cracks and the like are generated. Therefore, in order to obtain a thin flat plate, it is necessary to finally perform grinding and polishing. Thereby, there exists a problem that manufacturing cost becomes high.

  On the other hand, in the method for producing a tungsten sintered alloy according to the present invention, strain is introduced into the sintered body, and the sintered body into which the strain has been introduced is subjected to a heat rolling process after heat treatment. The sintered body can be hot-rolled at a rolling rate of at least%. Thereby, a flat tungsten sintered alloy having a thickness of 1.5 mm or less can be formed. Therefore, the manufacturing method of the present invention is particularly advantageous for obtaining a thin flat plate, and the manufacturing cost can be reduced.

  In particular, in the method for producing a tungsten sintered alloy according to the present invention, since the heat treatment is further performed after the hot rolling process, the elongation can be increased. For this reason, the obtained flat plate-like tungsten sintered alloy can be further thinned by rolling or the like. The lower limit of the thickness of the flat tungsten sintered alloy according to the present invention is 0.05 mm. It is difficult to make the thickness of the flat tungsten sintered alloy less than 0.05 mm.

  In addition, the tungsten sintered alloy according to the present invention contains elements other than nickel (Ni), iron (Fe), copper (Cu), and cobalt (Co) as long as the effects of the present invention are not impaired. For example, manganese (Mn), molybdenum (Mo), silicon (Si), rhenium (Re), chromium (Cr), titanium (Ti), vanadium (V), niobium (Nb), tantalum (Ta ) And the like may be contained in an amount of 0% by mass to 2% by mass.

  Hereinafter, the manufacturing method of the flat tungsten sintered alloy of this invention is demonstrated.

(1) Raw material preparation step Tungsten powder, nickel powder, and at least one metal powder selected from the group consisting of iron, copper, and cobalt are prepared. The raw material is tungsten powder of 85% by mass to 98% by mass, nickel powder of 1.4% by mass to 11% by mass, and at least one metal powder selected from the group consisting of iron, copper and cobalt is 0.00. The raw material is prepared so as to be included at a blending ratio of 6% by mass or more and 6% by mass or less.

  If the blending ratio of the tungsten powder is less than 85% by mass, the strength of the obtained tungsten sintered alloy may not be sufficient. When the blending ratio of the tungsten powder exceeds 98% by mass, the binder component is insufficient, and the obtained tungsten sintered alloy may be cracked in the rolling process.

  When the blending ratio of the nickel powder is less than 1.4% by mass, the obtained tungsten sintered alloy may be cracked in the rolling process. If the blending ratio of the nickel powder exceeds 11% by mass, the strength of the obtained tungsten sintered alloy may not be sufficient.

  Iron, copper and cobalt act as sintering aids. If the blending ratio of at least one metal powder selected from the group consisting of iron, copper and cobalt is less than 0.6% by mass, a dense sintered body cannot be obtained. There is a risk of cracking in the rolling process. When the blending ratio of the above metal powder exceeds 6% by mass, the binder component is excessively cured, so that the toughness of the obtained tungsten sintered alloy itself may be lowered.

  The average particle size of each of the tungsten powder, the nickel powder, and the metal powder is preferably 1 μm or more and 10 μm or less. If the average particle size of each of these powders is less than 1 μm, the production cost may increase. When the average particle diameter of each of these powders exceeds 10 μm, voids are easily formed in the obtained tungsten sintered alloy, and the tungsten sintered alloy may be cracked in the rolling process.

(2) Mixing step The tungsten powder prepared above, nickel powder, and at least one metal powder selected from the group consisting of iron, copper and cobalt are mixed to obtain a mixture. Mixing can be performed using a Redige mixer, an attritor, a ball mill, or the like. A solvent and a binder may be added to the raw material powder during mixing. As the binder, camphor, melball, stearic acid, paraffin or the like can be used. As the solvent, ethanol, methanol, acetone or the like can be used.

(3) Molding step Pressure is applied to the mixture obtained above to mold it to obtain a molded body. Pressure is applied to the mixture using a cold isostatic press (CIP), dry CIP, mechanical press or the like. The pressure applied during molding is preferably 49 MPa or more and less than 294 MPa. If the pressure is less than 49 MPa, the molded body may not be obtained, and even if the molded body can be obtained, the molded body may be damaged in handling of the molded body or in a subsequent process. There is no problem even if the pressure is increased to 294 MPa or more, but the action for obtaining the molded body is not increased.

(4) Sintering step The molded body obtained above is sintered to obtain a sintered body. As an atmosphere for sintering the compact, an atmosphere of hydrogen gas, vacuum, or inert gas can be used. A batch furnace, a continuous pusher furnace, or the like can be used as a sintering furnace that accommodates the compact.

  The sintering temperature is preferably 1200 ° C. or higher and 1550 ° C. or lower. If the sintering temperature is less than 1200 ° C., a dense sintered body cannot be obtained, so that the obtained tungsten sintered alloy may break in the rolling process. If the sintering temperature exceeds 1550 ° C, the sintered body may be melted.

  The sintering time is preferably 10 minutes or more and 300 minutes or less at the maximum sintering temperature. If the sintering time is less than 10 minutes, a dense sintered body cannot be obtained, so that the obtained tungsten sintered alloy may break in the rolling process. If the sintering time exceeds 300 minutes, the tungsten crystal grains become too coarse, and there is a possibility that the tungsten crystal grains cannot be sufficiently refined in the subsequent process.

  In addition, you may perform a formation process and a sintering process simultaneously using a hot isostatic press (HIP). In that case, an inert gas such as nitrogen gas or argon gas can be used as the atmosphere.

  The pressure is preferably 500 MPa or more and 1500 MPa or less. If the pressure is less than 500 MPa, a dense sintered body cannot be obtained, so that the obtained tungsten sintered alloy may break in the rolling process. There is no problem even if the pressure exceeds 1500 MPa, but the action for obtaining the sintered body is not increased.

  The temperature is preferably 1200 ° C. or higher and 1550 ° C. or lower. If the temperature is less than 1200 ° C., a dense sintered body cannot be obtained, so that the obtained tungsten sintered alloy may break in the rolling process. If the temperature exceeds 1550 ° C, the sintered body may be melted.

(5) Strain introduction step Strain is introduced into the sintered body (tungsten sintered alloy) obtained above. For example, it is preferable to introduce strain into the sintered body by deforming the flat sintered body in the thickness direction at a deformation rate of 20% to 50%. If the deformation rate is less than 20%, the amount of strain introduced into the sintered body is insufficient, so that fine crystal grains may not be formed even if heat treatment is performed in a subsequent process. If the deformation rate exceeds 50%, the sintered body may be broken.

  The temperature of the sintered body at the time of introducing strain is preferably 0 ° C. or higher and 600 ° C. or lower. If the temperature is less than 0 ° C., the sintered body becomes hard and may crack. When the temperature exceeds 600 ° C., the introduced strain is released, so that fine crystal grains may not be formed even if heat treatment is performed in a later step.

  In addition, as a method of introducing strain into the sintered body, it can be performed by deforming the sintered body by forging, mechanical pressing, cold rolling or the like.

(6) Heat treatment step The sintered body (tungsten sintered alloy) in which strain is introduced as described above is heat treated. By this heat treatment, the strain introduced into the sintered body is appropriately recovered and the tungsten crystal grains are refined.

  As an atmosphere for heat-treating the sintered body, an atmosphere of vacuum, hydrogen gas, nitrogen gas, argon gas, or carbon monoxide gas can be used.

  The temperature of the heat treatment is preferably 900 ° C. or higher and 1400 ° C. or lower. If the temperature of the heat treatment is less than 900 ° C., the recovery of strain is insufficient and the tungsten crystal grains are not refined, so that the sintered body may break in the subsequent hot rolling process. When the temperature of the heat treatment exceeds 1400 ° C., the distortion is completely recovered and the tungsten crystal grains are coarsened, so that the sintered body may be broken in the subsequent hot rolling process.

  The heat treatment time is preferably 20 minutes or more and 5 hours or less. When the heat treatment time is less than 20 minutes, the recovery of strain is insufficient and the tungsten crystal grains are not refined, so that the sintered body may break in the subsequent hot rolling process. If the heat treatment time exceeds 5 hours, the distortion is completely recovered and the tungsten crystal grains are coarsened, so that the sintered body may be broken in the subsequent hot rolling process.

  The average grain size of the tungsten crystal grains in the sintered tungsten alloy after the heat treatment is preferably 5 μm or more and 20 μm or less. It is difficult to make the average grain size of tungsten crystal grains less than 5 μm. If the average grain size of the tungsten crystal grains exceeds 20 μm, the sintered body may break in the subsequent hot rolling process.

(7) Hot rolling step In the state where the sintered body (tungsten sintered alloy) heat-treated as described above is heated, it is rolled at a rolling rate of 60% or more. As an atmosphere for heating the sintered body, an atmosphere of hydrogen gas, nitrogen gas, argon gas, or the like can be used.

  The rolling temperature is preferably 800 ° C. or higher and 1400 ° C. or lower. If the temperature of the rolling process is less than 800 ° C., the load applied to the rolling mill increases, and the rolling process cannot be performed or the sintered body may be broken. If the temperature of the rolling process exceeds 1400 ° C., the tungsten crystal grains are coarsened.

  It is preferable that the rolling process rate per time is 5% or more and 30% or less. If the rolling process rate of one time is less than 5%, the number of rolling operations for making the rolling process rate 60% or more in total increases, and the manufacturing cost increases. When the rolling processing rate of one time exceeds 30%, the load applied to the rolling mill increases, and rolling processing cannot be performed or the sintered body may be broken.

  The total rolling ratio is preferably 60% or more and 95% or less. If the total rolling ratio is less than 60%, the tungsten crystal grains do not become flat particles, so that the strength of the tungsten sintered alloy at a high temperature may not be sufficiently increased. If the total rolling ratio exceeds 95%, the sintered body may be broken by rolling.

  In addition, (5) Strain introduction process and (6) Heat treatment process are not performed on the conventional tungsten sintered alloy, and (7) Hot rolling process is performed on the tungsten sintered alloy immediately after sintering. However, rolling at a rolling rate of about 60% is the limit. For example, even if a hot rolling process is performed on a flat plate-like tungsten sintered alloy having a plane of about 100 mm × 100 mm or more, only a tungsten sintered alloy having a thickness of about 2 mm can be obtained.

  In contrast, in the present invention, after (5) the strain introduction step and (6) the heat treatment step are performed on the sintered body (tungsten sintered alloy) obtained in the (4) sintering step ( 7) By performing a hot rolling process, it is possible to perform rolling at a rolling processing rate of 60% or more and 95% or less, and to produce a flat tungsten sintered alloy as an intermediate product having a thickness of 1.5 mm or less. be able to. In addition, the lower limit of the thickness of the tungsten sintered alloy as the intermediate product of the present invention is 0.5 mm. Obtaining a tungsten sintered alloy having a thickness of less than 0.5 mm is difficult even if (7) the hot rolling step is performed after the (5) strain introducing step and the (6) heat treatment step.

(8) Heat treatment step The sintered body (tungsten sintered alloy) hot-rolled as described above is heat treated. By this heat treatment, the defects present in the interface between the tungsten crystal grains and the binder and in the binder can be almost eliminated, and the tungsten crystal grains easily slip in the binder component. As a result, the elongation of the tungsten sintered alloy is improved.

  As an atmosphere for heat-treating the hot-rolled sintered body, an atmosphere of vacuum, hydrogen gas, or inert gas can be used. As a furnace for heat treatment, a batch furnace or a continuous pusher furnace can be used.

  The heat treatment temperature is preferably 1300 ° C. or higher and 1550 ° C. or lower. If the temperature of the heat treatment is lower than 1300 ° C., the coarsening of the tungsten crystal grains is insufficient, and the cold workability may not be improved. If the temperature of the heat treatment exceeds 1550 ° C., the sintered body may be melted.

  The heat treatment time is preferably 10 minutes or more and 5 hours or less. If the heat treatment time is less than 10 minutes, the tungsten crystal grains are not sufficiently coarsened, and the cold workability may not be improved. If the heat treatment time exceeds 5 hours, the tungsten crystal grains become coarse and the workability deteriorates, so that the sintered body may be cracked when processing into a complicated shape.

  The average grain size of the tungsten crystal grains in the sintered tungsten alloy after the heat treatment is preferably 20 μm or more and 60 μm or less. If the average grain size of the tungsten crystal grains is less than 20 μm, the effect of the heat treatment is insufficient, a high elongation cannot be obtained, and cold workability may not be improved. If the average grain size of the tungsten crystal grains exceeds 60 μm, the tungsten crystal grains are coarsened and the workability is lowered, so that the sintered body may be cracked when processing into a complicated shape.

  Hereinafter, Examples 1 to 29 and Comparative Examples 1 to 13 of the present invention in which a flat plate-like tungsten sintered alloy was produced in order to confirm the effects of the above-described embodiment will be described below.

(Example 1)
In this example, a flat plate-like tungsten sintered alloy as an intermediate product of the present invention described above was produced. That is, a flat tungsten sintered alloy was produced by performing the above steps (1) to (7).

  First, 95% by mass of tungsten powder having an average particle size of 3 μm, 3.5% by mass of nickel powder having an average particle size of 4 μm, and 1.5% by mass of iron powder having an average particle size of 3 μm are included. ((1) Raw material preparation step).

  Next, the tungsten powder, nickel powder, and iron powder prepared above were mixed using a Redige mixer to obtain a mixture ((2) mixing step).

  Then, the mixture obtained above was molded by applying a pressure of 196 MPa using a cold isostatic press (CIP) to obtain a molded body ((3) molding step). The dimension of the obtained molded body was 176 mm × 176 mm × 8.2 mm.

  Furthermore, the molded body obtained above was sintered at a temperature of 1460 ° C. for 80 minutes in a hydrogen gas atmosphere furnace to obtain a sintered body ((4) sintering step). The size of the obtained sintered body was 150 mm × 150 mm × 7 mm.

  The optical microscope photograph which observed the cross section of the flat-plate-like tungsten sintered alloy obtained as mentioned above is shown in FIG.

  Thereafter, the obtained flat plate-like tungsten sintered alloy was deformed at a deformation rate of 30% in the thickness direction using a forging machine at a temperature of 25 ° C., thereby introducing strain into the tungsten sintered alloy ( (5) Strain introduction step). The dimension of the flat plate-like tungsten sintered alloy after introduction of strain was 177 mm × 177 mm × 5 mm.

  The flat plate-like tungsten sintered alloy into which strain was introduced was heat-treated in a vacuum furnace at a temperature of 1200 ° C. for 3 hours ((6) heat treatment step).

  The optical microscope photograph which observed the cross section of the flat-plate-like tungsten sintered alloy obtained as mentioned above is shown in FIG. As shown in FIG. 2, it can be seen that the tungsten crystal grains are refined and the average grain size is about 10 μm.

  Finally, after heating the heat-treated plate-like tungsten sintered alloy sample to a temperature of 1100 ° C. in a hydrogen gas atmosphere furnace, the sample is taken out of the furnace and immediately rolled at a rolling rate of about 10%. The rolling process was repeated until the total rolling ratio reached 80% ((7) hot rolling process). The dimension of the flat tungsten sintered alloy after hot rolling was 100 mm × 1070 mm × 1 mm.

  In this way, a flat plate-like tungsten sintered alloy was produced as an intermediate product of the present invention.

  The obtained flat plate-like tungsten sintered alloy as an intermediate product was heat-treated in a vacuum furnace at a temperature of 1450 ° C. for 60 minutes ((8) heat treatment step).

  The optical microscope photograph which observed the cross section of the flat-plate-shaped tungsten sintered alloy as the final product obtained as mentioned above is shown in FIG. As shown in FIG. 3, it can be seen that the tungsten crystal grains are coarsened and the average grain size is about 35 μm.

(Example 2)
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment temperature was 1300 ° C. in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 21 μm.

Example 3
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment temperature was changed to 1550 ° C. in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat plate-like tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 43 μm.

Example 4
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment time was 10 minutes in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 25 μm.

(Example 5)
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment time was 3 hours in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 39 μm.

Example 6
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment time was 5 hours in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 57 μm.

(Example 7)
Except that the strain was introduced into the sintered tungsten alloy by deforming at a deformation rate of 20% in the thickness direction in the strain introduction step, and that the heat treatment temperature was 1500 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, a flat tungsten sintered alloy having a thickness of 1.1 mm was produced. When the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 19 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 39 μm.

(Example 8)
Except that the strain was introduced into the sintered tungsten alloy by deforming at a deformation rate of 40% in the thickness direction in the strain introduction step, and that the heat treatment temperature was 1500 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, a flat tungsten sintered alloy having a thickness of 0.9 mm was produced. In addition, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 10 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 38 μm.

Example 9
Except that the strain was introduced into the sintered tungsten alloy by deforming at a deformation rate of 50% in the thickness direction in the strain introduction step, and that the heat treatment temperature was 1500 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, a flat tungsten sintered alloy having a thickness of 0.7 mm was produced. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 39 μm.

Example 10
A flat plate-like tungsten sintered alloy having a thickness of 2.0 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling ratio reached 60% in the hot rolling process. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 39 μm.

Example 11
A flat plate-like tungsten sintered alloy having a thickness of 1.5 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling process rate reached 70% in the hot rolling process. In addition, when the cross section of the flat-plate-like tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 36 μm.

(Example 12)
In the hot rolling process, a flat plate-like tungsten sintered alloy having a thickness of 0.7 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling ratio reached 85%. . In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 37 μm.

(Example 13)
A flat plate-like tungsten sintered alloy having a thickness of 0.5 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling process rate reached 90% in the hot rolling process. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 37 μm.

(Example 14)
The same as in Example 1 except that the thickness of the sintered body obtained in the sintering process was 14 mm and that the rolling process was performed until the total rolling ratio in the hot rolling process reached 95%. Then, a flat tungsten sintered alloy having a thickness of 0.5 mm was produced. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 39 μm.

(Example 15)
The thickness of the sintered body obtained in the sintering step was 20 mm, the strain was introduced into the tungsten sintered alloy by being deformed at a deformation rate of 50% in the thickness direction in the strain introducing step, In the same manner as in Example 1, except that the rolling process was performed until the total rolling ratio became 95% in the rolling process, and the heat treatment temperature was set to 1300 ° C. in the heat treatment process after the hot rolling process, A flat tungsten sintered alloy having a thickness of 0.5 mm was produced. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 23 μm.

(Example 16)
The thickness of the sintered body obtained in the sintering step was 20 mm, the strain was introduced into the tungsten sintered alloy by being deformed at a deformation rate of 50% in the thickness direction in the strain introducing step, In the same manner as in Example 1 except that the rolling process was performed until the total rolling ratio reached 95% in the rolling process and that the heat treatment temperature was 1450 ° C. in the heat treatment process after the hot rolling process, A flat tungsten sintered alloy having a thickness of 0.5 mm was produced. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Further, in the same manner as in Example 1, when the cross section of the flat plate-like tungsten sintered alloy as the final product was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 37 μm.

(Example 17)
The thickness of the sintered body obtained in the sintering step was 20 mm, the strain was introduced into the tungsten sintered alloy by being deformed at a deformation rate of 50% in the thickness direction in the strain introducing step, In the same manner as in Example 1, except that the rolling process was performed until the total rolling ratio became 95% in the rolling process, and the heat treatment temperature was set to 1550 ° C. in the heat treatment process after the hot rolling process, A flat tungsten sintered alloy having a thickness of 0.5 mm was produced. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 47 μm.

(Example 18)
Using tungsten powder with an average particle diameter of 1 μm in the raw material preparation process, using copper powder instead of iron powder, and deforming at a deformation rate of 20% in the thickness direction in the strain introduction process, the tungsten sintered alloy Except for introducing strain, performing rolling until the total rolling rate reaches 60% in the hot rolling step, and setting the heat treatment temperature to 1300 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, a flat plate-like tungsten sintered alloy having a thickness of 2.2 mm was produced. When the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 19 μm. Further, in the same manner as in Example 1, when the cross section of the flat plate-like tungsten sintered alloy as the final product was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 21 μm.

(Example 19)
Using tungsten powder with an average particle size of 5 μm in the raw material preparation step, using copper powder instead of iron powder, and deforming at a deformation rate of 20% in the thickness direction in the strain introduction step, the tungsten sintered alloy Except for introducing strain, performing rolling until the total rolling ratio reaches 70% in the hot rolling step, and setting the heat treatment temperature to 1300 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, a flat plate-like tungsten sintered alloy having a thickness of 1.7 mm was produced. When the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 19 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 23 μm.

(Example 20)
Using tungsten powder with an average particle size of 10 μm in the raw material preparation process, using copper powder instead of iron powder, and deforming at a deformation rate of 20% in the thickness direction in the strain introduction process, the tungsten sintered alloy Except for introducing strain, performing rolling until the total rolling ratio reaches 90% in the hot rolling step, and setting the heat treatment temperature to 1300 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, a flat plate-like tungsten sintered alloy having a thickness of 0.7 mm was produced. When the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 19 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 22 μm.

(Example 21)
In the raw material preparation step, the tungsten powder was prepared to contain 85% by mass, the nickel powder was 10.5% by mass, and the iron powder was prepared to contain 4.5% by mass, and the total rolling ratio in the hot rolling step was The thickness was 0 as in Example 1, except that the rolling process was performed until 90% and that the heat treatment temperature was 1300 ° C. and the heat treatment time was 3 hours in the heat treatment step after the hot rolling step. A 5 mm flat plate-like tungsten sintered alloy was produced. When the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 9 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 24 μm.

(Example 22)
The raw material preparation step was prepared so as to include 90% by mass of tungsten powder, 7% by mass of nickel powder, and 3% by mass of iron powder, and the total rolling ratio in the hot rolling step was 90%. A flat plate having a thickness of 0.5 mm in the same manner as in Example 1 except that the rolling process was performed until the heat treatment temperature was 1300 ° C. and the heat treatment time was 3 hours in the heat treatment step after the hot rolling step. A tungsten sintered alloy was produced. In addition, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 10 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 24 μm.

(Example 23)
In the raw material preparation step, the tungsten powder was prepared to contain 98% by mass, the nickel powder was 1.4% by mass, and the iron powder was prepared to contain 0.6% by mass, and the total rolling ratio in the hot rolling step was The thickness was 0 as in Example 1, except that the rolling process was performed until 90% and that the heat treatment temperature was 1300 ° C. and the heat treatment time was 3 hours in the heat treatment step after the hot rolling step. A 5 mm flat plate-like tungsten sintered alloy was produced. In addition, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 10 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 26 μm.

(Example 24)
Nickel powder with an average particle size of 1 μm was used in the raw material preparation step, cobalt powder was used instead of iron powder, and the heat treatment temperature was 1300 ° C. and the heat treatment time was 5 hours in the heat treatment step after the hot rolling step. Except for this, a flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1. When the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 11 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 28 μm.

(Example 25)
Nickel powder having an average particle size of 5 μm was used in the raw material preparation step, cobalt powder was used instead of iron powder, and the heat treatment temperature was 1300 ° C. and the heat treatment time was 5 hours in the heat treatment step after the hot rolling step. Except for this, a flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1. In addition, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 10 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 30 μm.

(Example 26)
Nickel powder having an average particle size of 10 μm was used in the raw material preparation step, cobalt powder was used instead of iron powder, and the heat treatment temperature was 1300 ° C. and the heat treatment time was 5 hours in the heat treatment step after the hot rolling step. Except for this, a flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1. In addition, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 10 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 27 μm.

(Example 27)
The use of iron powder having an average particle size of 1 μm in the raw material preparation step, the introduction of strain into the tungsten sintered alloy by deformation at a deformation rate of 50% in the thickness direction in the strain introduction step, and hot rolling A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling process rate reached 60% in the process. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 32 μm.

(Example 28)
The use of iron powder having an average particle size of 5 μm in the raw material preparation step, the introduction of strain into the tungsten sintered alloy by deformation at a deformation rate of 50% in the thickness direction in the strain introduction step, and hot rolling A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling process rate reached 60% in the process. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 35 μm.

(Example 29)
The use of iron powder having an average particle size of 10 μm in the raw material preparation step, the introduction of strain into the tungsten sintered alloy by deformation at a deformation rate of 50% in the thickness direction in the strain introduction step, and hot rolling A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling process rate reached 60% in the process. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat-plate-like tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 33 μm.

(Comparative Example 1)
A conventional tungsten sintered alloy produced by performing the above steps (1) to (4) was processed by grinding and polishing until the thickness became 1 mm.

(Comparative Example 2)
With respect to the conventional tungsten sintered alloy produced by performing the steps (1) to (4), the rolling process rate is 60 immediately after sintering without performing the steps (5) and (6). The hot rolling process of (7) was performed until the content became% (until the thickness became 2 mm). Then, the rolled tungsten sintered alloy was processed by grinding and polishing until the thickness became 1 mm.

  The optical microscope photograph which observed the cross section of the flat-plate-like tungsten sintered alloy obtained as mentioned above is shown in FIG.

(Comparative Example 3)
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment temperature was 1200 ° C. in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 18 μm.

(Comparative Example 4)
Except that the heat treatment temperature was 1600 ° C. in the heat treatment step after the hot rolling step, an attempt was made to produce a flat plate-like tungsten sintered alloy having a thickness of 1.0 mm in the same manner as in Example 1. The flat tungsten sintered alloy melted.

(Comparative Example 5)
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment time was 6 minutes in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 17 μm.

(Comparative Example 6)
A flat plate-like tungsten sintered alloy having a thickness of 1.0 mm was produced in the same manner as in Example 1 except that the heat treatment time was 6 hours in the heat treatment step after the hot rolling step. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 64 μm.

(Comparative Example 7)
Except that the strain was introduced into the sintered tungsten alloy by deformation at a deformation rate of 17% in the thickness direction in the strain introduction step, and that the heat treatment temperature was 1500 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, an attempt was made to produce a flat tungsten sintered alloy, but cracking occurred after the hot rolling step. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 24.3 μm. .

(Comparative Example 8)
Except that the strain was introduced into the sintered tungsten alloy by deforming at a deformation rate of 60% in the thickness direction in the strain introduction step, and that the heat treatment temperature was 1500 ° C. in the heat treatment step after the hot rolling step. In the same manner as in Example 1, an attempt was made to produce a flat tungsten sintered alloy, but cracking occurred in the strain introduction process.

(Comparative Example 9)
A flat plate-like tungsten sintered alloy having a thickness of 2.5 mm was produced in the same manner as in Example 1 except that the rolling process was performed until the total rolling process rate reached 50% in the hot rolling process. In addition, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 37 μm.

(Comparative Example 10)
An attempt was made to produce a flat tungsten sintered alloy in the same manner as in Example 1 except that the rolling process was performed until the total rolling ratio reached 97% in the hot rolling process. Cracks occurred after the hot rolling process.

(Comparative Example 11)
The thickness of the sintered body obtained in the sintering step was 20 mm, the strain was introduced into the tungsten sintered alloy by being deformed at a deformation rate of 50% in the thickness direction in the strain introducing step, In the same manner as in Example 1, except that the rolling process was performed until the total rolling ratio reached 95% in the rolling process and that the heat treatment temperature was 1200 ° C. in the heat treatment process after the hot rolling process, A flat tungsten sintered alloy having a thickness of 0.5 mm was produced. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm. Moreover, when the cross section of the flat tungsten sintered alloy as the final product was observed with an optical microscope in the same manner as in Example 1, the average grain size of the tungsten crystal grains was about 17 μm.

(Comparative Example 12)
The thickness of the sintered body obtained in the sintering step was 20 mm, the strain was introduced into the tungsten sintered alloy by being deformed at a deformation rate of 50% in the thickness direction in the strain introducing step, In the same manner as in Example 1, except that the rolling process was performed until the total rolling ratio reached 95% in the rolling process, and that the heat treatment temperature was 1600 ° C. in the heat treatment process after the hot rolling process, An attempt was made to produce a flat tungsten sintered alloy having a thickness of 0.5 mm, but the flat tungsten sintered alloy melted. As in Example 1, when the cross section of the flat plate-like tungsten sintered alloy after the heat treatment after the strain introducing step was observed with an optical microscope, the average grain size of the tungsten crystal grains was about 5 μm.

(Comparative Example 13)
With respect to the conventional tungsten sintered alloy produced by performing the steps (1) to (4) in Example 1, the heat of (7) until the rolling rate reaches 65% immediately after sintering. When the hot rolling process was performed, cracks occurred in the tungsten sintered alloy.

(Measurement of average thickness and average length of tungsten crystal grains)
As shown in FIG. 5, the plane 100 of the flat plate-like tungsten sintered alloy 1 obtained as an intermediate product of Examples 1 to 29 and Comparative Examples 1 to 6, 9, 11, and 12 is orthogonal to the extending direction. A first cross section 101 along the direction of the thickness T ₀ (1 mm) to be performed, and a cross section along the direction of the thickness T ₀ perpendicular to the direction in which the flat surface 100 of the flat plate-like tungsten sintered alloy 1 extends. A second cross section 102 perpendicular to the first cross section was observed with a scanning electron microscope (SEM).

  Specifically, in each of the first cross-section 101 and the second cross-section 102, a photograph of an arbitrary location (field of view) is taken at 1000 times, and the cross-section is taken along the direction in which the plane 100 extends from the location. A photograph of a portion (field of view) shifted in position is taken, and photographs of seven fields of view obtained by sequentially shifting are connected in the direction in which the plane 100 extends, and the thickness T is 70 μm and the width W is 500 μm. A photograph of the cross section was obtained. In this way, the first cross-section portion having the constant width W (500 μm) and the constant thickness T (70 μm) selected from the first cross-section 101 and the constant cross-section selected from the second cross-section 102 are selected. A photograph of a second cross-sectional portion having a width W (500 μm) and a constant thickness T (70 μm) was obtained. An example (Example 1) of a scanning electron microscope (SEM) photograph of the cross section is shown in FIG.

  FIG. 7 schematically shows the above cross-sectional portion. As shown in FIG. 7, in the photograph of the first cross-section portion 101a and the second cross-section portion 102a obtained as described above, it passes through the center of a constant width W (500 μm) and has a constant thickness T (70 μm). The thickness t and the length s of the plurality of tungsten crystal grains G1 to G4 intersecting with the center line 200 extending in the direction were measured. The average value of these measured values was determined and used as the average thickness and average length of the tungsten crystal grains. Moreover, the ratio of the average length with respect to the average thickness of a tungsten crystal grain was computed.

  Table 1 shows the average thickness and average length of the tungsten crystal grains calculated as described above, and the ratio of the average length to the average thickness.

(Measurement of elongation of tungsten sintered alloy)
From the flat-plate-like tungsten sintered alloy obtained as a final product in Examples 1 to 29 and Comparative Examples 1 to 5, 5, 6, 9, 11, and 12, tensile test pieces having a thickness T as shown in FIG. 10 was produced. The distance between the gauge points was 8 mm with the center line 20 as the center.

  The produced tensile test piece 10 was set in a tensile tester of model number 5867 manufactured by INSTRON Co., Ltd., and at 300 mm / min. Tensile tests were conducted until rupture at a tensile rate of. The increase rate of the distance between the gauge points of the test piece until it broke was defined as the elongation rate. In addition, also about the flat-plate-shaped tungsten sintered alloy obtained as an intermediate product in Example 1, the elongation rate was measured similarly to the above.

  Table 1 shows the measurement results of the elongation obtained as described above. In Table 1, “Example 1”, the numerical value in parentheses indicates the elongation of the flat plate-like tungsten sintered alloy obtained as an intermediate product in Example 1.

(Measurement of X-ray diffraction intensity ratio of (111) plane of Ni- (Fe, Cu, Co) phase)
From the flat tungsten sintered alloy obtained as a final product in Examples 1 to 29 and Comparative Examples 1 to 3, 5, 6, 9, 11, and 12, a flat surface having a thickness of 0.5 mm and 8 mm × 8 mm was obtained. A test piece was prepared.

  Using an X-ray diffractometer manufactured by Rigaku Co., Ltd., model number SmartLab-2D-PILATUS, X-rays were applied to the 8 mm x 8 mm plane of the test specimen, and Ni- (Fe, Cu, Co on the flat plate surface The X-ray diffraction intensities of the (111) plane, (100) plane, (110) plane, and (311) plane of the) phase were measured. The X-ray diffraction conditions were X-ray used: Cu-Kα, excitation condition: 45 kV, 200 mA, collimator: φ0.8 mm, and measurement method: θ-2θ method. An 8 mm × 8 mm flat surface as a measurement surface was mechanically polished and then subjected to alkaline electrolytic polishing.

  From the value of the X-ray diffraction intensity of each surface obtained, the X-ray diffraction intensity ratio of the (111) plane (here, (111) plane, (100) plane, (110) plane and (311) plane each) If the X-ray diffraction intensity is I (111), I (100), I (110), I (311), the X-ray diffraction intensity ratio of the (111) plane is [I (111) / {I (111) + I (100) + I (110) + I (311)}]).

  Table 1 shows the measurement results of the X-ray diffraction intensity ratio of the (111) plane of the Ni— (Fe, Cu, Co) phase obtained as described above.

  Table 1 shows that the sample of the Example of this invention shows high elongation.

  In addition, in the sample of the example of the present invention, it can be seen that the X-ray diffraction intensity ratio of the (111) plane of the Ni— (Fe, Cu, Co) phase shows a value of 0.68 or more and 0.9 or less.

  It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the claims, and is intended to include all modifications and variations within the meaning and scope equivalent to the claims.

  The sintered tungsten alloy of the present invention is used as a radiation shielding material in radiological medical equipment, reactor related equipment, and the like.

1: tungsten sintered alloy, 100: plane, 101: first cross section, 101a: first cross section, 102: second cross section, 102a: second cross section, 200: center line, G1 to G4: Tungsten crystal grains, T, T ₀ : thickness, W: width, t: thickness, s: length.

Claims (2)

85% by mass to 98% by mass of tungsten, 1.4% by mass to 11% by mass of nickel, and 0.6% by mass to 6% by mass of at least one selected from the group consisting of iron, copper and cobalt A flat plate-like tungsten sintered alloy comprising:
The flat plate-like tungsten sintered alloy has an elongation in the plane direction of 20% or more,
X-ray diffraction intensity ratio of the (111) plane of the Ni— (Fe, Cu, Co) phase on the flat plate surface of the flat plate-like tungsten sintered alloy (where (111) plane, (100) plane, (110) If the X-ray diffraction intensities of the plane and (311) plane are I (111), I (100), I (110), and I (311), the X-ray diffraction intensity ratio of the (111) plane is [I ( 111) / {I (111) + I (100) + I (110) + I (311)}] is 0.68 or more and 0.9 or less.   The tungsten sintered alloy according to claim 1, wherein a thickness of the flat tungsten sintered alloy is 1.5 mm or less.

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