JPS6331542B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to a method for manufacturing a molybdenum alloy plate. [Technical Background of the Invention] In general, molybdenum alloy plates with a polycrystalline structure and a high melting point and high temperature strength are used for structural materials used at high temperatures, such as boats for firing ceramics and metal powder, and furnace parts. ing. [Problems with the Background Art] However, the polycrystalline molybdenum alloy plate has a major drawback of brittle grain boundaries.
During use, intergranular cracking occurs due to intergranular sliding.
As a result, the inherent property of molybdenum, which is high high-temperature strength, cannot be fully demonstrated, and its uses have been limited. Therefore, there is a need for the development of a molybdenum alloy plate with fewer grain boundaries that cause grain boundary cracking. [Object of the Invention] The present invention aims to provide a method for manufacturing a molybdenum alloy plate in which the number of grain boundaries that cause intergranular cracking is reduced. [Summary of the invention] The present invention provides one or both of K and Si in weight%.
A step of reducing the area of a sintered body of a molybdenum alloy containing 0.003 to 0.05% at a working rate of 60% or more, and a first heat treatment of this processed material at 1200 to 1500°C, A second heat treatment at 1700 to 2200°C is performed to obtain a large crystal structure or a single crystal structure having one or less crystal grains per 100 ^mm2 . This is a method for manufacturing a molybdenum alloy plate. According to this invention,
As mentioned above, it is possible to obtain a molybdenum alloy plate with fewer grain boundaries that cause grain boundary cracking. The present invention will be explained in detail below. First, add one or two of K and Si to 0.003% by weight.
A sintered body of a molybdenum alloy containing ~0.05%, preferably 0.01~0.05% is produced. This K, Si is
It is added to make the recrystallized grains of the molybdenum alloy plate grow large through high-temperature heat treatment to be described later to create a large grain structure with one or less crystal grains per 100 ^mm2 , or to create a single crystal structure. It is a component that
Therefore, if the amount of these additive components is less than 0.003% by weight, the effect will be small, and even after high-temperature heat treatment after processing, a molybdenum alloy plate will have a conventional polycrystalline structure with many grain boundaries. On the other hand, if the amount of these added components exceeds 0.05% by weight, K and Si, which are finely and abundantly dispersed in the molybdenum alloy during high-temperature heat treatment, suppress the effect of increasing the recrystallized grains of the molybdenum alloy plate. Next, the produced sintered body is forged in a temperature range from room temperature to below the primary recrystallization temperature so that the direction in which the sintered body is stretched during processing is a direction that crosses two or more directions with respect to the plane of the processed plate. The area is reduced by rolling or rolling. At this time, if the processing temperature exceeds the primary recrystallization temperature, problems arise such as the development of the processed fiber structure and the inability to arrange K and Si particles along the processed fiber structure. Note that for forging, rolling, etc., conventional methods may be applied as they are. Further, by the processing, the structure of the sintered body is crushed in the thickness direction and stretched in the processing direction, so that the structure as a whole is arranged in a texture parallel to the plane of the processed plate. At this time, most of the K and Si contained are arranged along the aforementioned fibrous structure. In addition, some of it is dispersed within the fibrous tissue to increase the strength of that tissue. Furthermore, the processing requires at least two directions with respect to the plane of the molybdenum alloy plate, and the processing rate must be 60% or more, preferably 80% or more. In this case, it is desirable that at least one of the processing rates perpendicular to each other is 20% or more, preferably 40% or more.
The processing rate here refers to the percentage value obtained by dividing the decrease in the cross-sectional area of the molybdenum alloy plate before and after processing by the cross-sectional area before processing, and the larger this value, the more advanced the processing is. . Processing rate is 60%
If K is less than
and Si are not sufficiently aligned, and recrystallized grains do not grow large during the heat treatment described below. In addition, if the processing rate in one of the processing directions is less than 20%, during the heat treatment described later, the recrystallized grains will be arranged long in the processing direction with a large processing rate and short in the direction with a small processing rate, resulting in a cylindrical shape. There is a risk that it will happen. Next, the obtained processed material is heated at 1200℃ to 1500℃,
Preferably, after performing the first heat treatment at a temperature range of 1250°C to 1450°C, the heating temperature is preferably 1700°C to 2200°C, preferably 1900°C.
A two-stage heat treatment is performed in which a second heat treatment is performed in a temperature range of .degree. C. to 2200.degree. As a result, the processed material becomes a molybdenum alloy plate having a large grain structure or a single crystal structure with one or less crystal grains per 100 mm ² . Here, the first heat treatment brings K and Si, which were present along the fibrous structure during the processing stage, into a size and arrangement state that can effectively exhibit the effect of enlarging recrystallized grains. Since this is a treatment for The second heat treatment is a process for changing the crystal structure of the molybdenum alloy plate into a large-grain structure or a single-crystal structure having one or less crystal grains per 100 ^mm2 , and the higher the heating temperature, the higher the heating temperature. This is effective in enlarging recrystallized grains. This second heat treatment temperature
If the temperature is lower than 1700°C, it becomes difficult to form crystal grains of one or less per 100 mm ² . On the other hand, if the temperature of the second heat treatment exceeds 2200°C, the vapor pressure of the K contained becomes higher than the strength of molybdenum, so pores may be generated in this area or adjacent pores may coalesce. This results in defective holes and reduces creep strength. Furthermore, if the second heat treatment temperature exceeds 2200°C, impurities incidentally included in the molybdenum alloy may coalesce and become defects, or the molybdenum alloy may be excessively annealed, reducing its creep strength. . Therefore, it is desirable that the second heat treatment temperature, which provides good creep strength and prevents grain boundary slippage, is within the above range. [Embodiments of the Invention] First, Mo powder and a solution of KCl or K ₂ SiO ₃ are mixed in the weight percent ratio shown in Table 1, and then dried to form a Mo and K mixed powder sample and a Mo and K powder sample. , a mixed powder sample of Si was prepared.

[Table] Next, each of the above mixed powders was mixed at approximately 2 tons/cm ²
Press molded at a pressure of 1830°C.
The material was sintered in a hydrogen furnace for 7 hours. The contents of K and Si in these sintered bodies are shown in Table 2 below. Next, each of the sintered bodies was forged at a temperature of 1200 to 1300°C, and then rolled at a temperature of 700 to 1100°C to obtain a plate material with a thickness of 2.5 mm and a processing rate of 90%. A creep test piece and a 100 mm x 100 mm test piece for metallographic observation were prepared from each of the plate materials obtained, and both were heat treated in a hydrogen furnace at 1350°C for 30 minutes. Heat treatment was performed for 14 hours in a vacuum furnace. The creep test piece subjected to this two-stage heat treatment was subjected to a creep test at a tensile stress of 1 Kg/mm ² in an argon atmosphere furnace at 1800° C., and the creep strain rate per hour was calculated.
The results of these tests are shown in Table 3. In addition, when the structure of the test piece for metallographic observation after two-stage heat treatment was observed, Examples 1 to 7 (Sample 1
~7) had a single crystal structure, and Example 8 (sample 8) had a polycrystalline structure with 6 crystal grains. Table 3 shows the results of a pure molybdenum plate test piece made under the same conditions as in the above example, and a creep test piece made from the sample 6 plate subjected to heat treatment for 30 minutes in a hydrogen furnace at 1350°C. After applying 2350℃
The results of a test piece that was heat-treated for 7 hours in a vacuum furnace are also shown as a comparative example.

【table】

【table】

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to reduce the number of grain boundaries that cause intergranular cracking in materials for high-temperature structures such as firing boats and furnace parts used at high temperatures, thereby significantly extending the fracture life. It is possible to provide a method for producing a molybdenum alloy plate that can be stretched, stabilized for a long time, and significantly improved in reliability. Furthermore, by using the molybdenum alloy plate produced according to the present invention, it is possible to effectively utilize rare metals, which has great industrial value.

Claims (1)

[Claims] 1 0.003 to 0.05 by weight of one or both of K and Si
A process of reducing the area of a sintered body of a molybdenum alloy with a processing rate of 60% or more, and then subjecting this processed material to a first heat treatment at 1200 to 1500°C. A molybdenum alloy characterized by comprising a step of performing a second heat treatment at 2200°C to obtain a large crystal structure or a single crystal structure having one or less crystal grains per 100 ^mm2 . Method of manufacturing the board.