JPS61204360A - Production of molybdenum alloy plate - Google Patents

Abstract

PURPOSE:To obtain an Mo alloy plate which decreases the grain boundaries to be the cause for grain boundary cracking by subjecting a sintered body of an Mo alloy contg. K or/and Si at a prescribed ratio to area reduction at a specific reduction ratio or above then to a high-temp. heating treatment. CONSTITUTION:The sintered body of the Mo alloy contg. 0.003-0.05wt.%, more preferably 0.01-0.05wt.% K or/and Si is manufactured. The sintered body is then subjected to the area reduction by forging or rolling, etc. in a temp. region of a room temp. - primary recrystallization temp. in such a man ner that the direction for elongating the sintered body is >=2 directions crossing with the plane of the working plate. The reduction rate in this case is made >=60%, more preferably >=80%. At least one reduction rate of the above- mentioned orthogonal reduction rate is preferably >=20%, more particularly preferably >=40%. Such worked material is subjected to the 1st heating treat ment in a 1,200-1,500 deg.C range then to the 2nd heating treatment in a 1,700-2,000 deg.C range, by which the intended Mo alloy plate is obtd.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a method for manufacturing a molybdenum alloy plate.

[Technical background of the invention]

Generally, molybdenum alloy plates with a polycrystalline structure, which have a high melting point and high high-temperature strength, are used for structural materials used at high temperatures, such as boats for firing ceramics and metal powder, and furnace parts.

[Problems with background technology]

However, the polycrystalline molybdenum alloy plate has a major drawback of brittle grain boundaries, which causes grain boundary cracking due to grain boundary grooves during use.

As a result, molybdenum's inherent properties of high high-temperature strength cannot be fully demonstrated, and its uses have been limited. Therefore, there is a need to develop a molybdenum alloy plate with fewer grain boundaries that cause grain boundary cracking.

[Purpose 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 grain boundary cracking is reduced.

[Summary of the invention]

In the present invention, one or both of K and sr are added in an amount of 0.00%.
This method is characterized in that a sintered body of a molybdenum alloy containing 3 to 0.05% is subjected to surface reduction processing at a processing rate of 60% or more, and then the processed material is subjected to high-temperature heat treatment. According to the present invention, it is possible to obtain a molybdenum alloy plate in which the number of grain boundaries that cause grain boundary cracking is reduced as described above.

The present invention will be explained in detail below.

First, one or two of K and S;
A sintered body of a molybdenum alloy containing 0.05% O, preferably 0.01 to 0.05% is produced. To this, sr
is added to cause the recrystallized grains of the molybdenum alloy plate to grow large by high-temperature heat treatment described below, to create a large grain structure with one or less crystal grains per 100 m2, or to create a single crystal structure. It is an ingredient. Therefore, if the amount of these additive components is less than 0.00311%, the effect will be small, and even after high-temperature heat treatment after processing, a molybdenum alloy plate with a conventional polycrystalline structure with many grain boundaries will be obtained. on the other hand,
If the amount of these added components exceeds 0.05% by weight, S+ suppresses the effect of increasing recrystallized grains in the molybdenum alloy plate, even though they are finely and abundantly dispersed in the molybdenum alloy during high-temperature heat treatment.

Next, the produced sintered body is forged in a temperature range from V temperature to below the primary recrystallization temperature so that the direction in which the sintered body is stretched by 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 Sl 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.

Here, the processing rate is 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. . If the processing rate is less than 60%, the fibers S1 will not be sufficiently aligned along the fibrous structure described above, and recrystallized grains will not grow significantly 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 below, 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 was heated at 1200°C to 150°C.
, preferably in the temperature range of 1250'C to 1450°C.
After the heat treatment, a two-stage heat treatment is performed in which a second heat treatment is performed in a temperature range of 1700 to 2200°C, preferably 1900°C to 2200'C. As a result, the processed material is 1
The result is a molybdenum alloy plate having a large grain structure or a single crystal structure with one or less grains per 00 m. , S; is preferably in the above-mentioned temperature range because the second heat treatment is for bringing the recrystallized grains into a roughly arranged state that can effectively exhibit the effect of enlarging the recrystallized grains. The heat treatment is a process to make the crystal structure of the molybdenum alloy plate into a large crystal grain structure or a single crystal structure with one or less crystal grains per 1007111112, and the higher the heating temperature, the larger the recrystallized grains. If the second heat treatment temperature is lower than 1700°C, it will be difficult to form less than one crystal grain per 100 m2.On the other hand, if the second heat treatment temperature is lower than 2200°C, If it exceeds this, the vapor pressure of the K contained becomes higher than the strength of molybdenum, so pores are generated in this part, or adjacent pores combine to form defective holes, reducing the creep strength.Moreover, If the second heat treatment temperature exceeds 2200°C, impurities incidentally included in the molybdenum alloy may coalesce and become defects.
Molybdenum alloys are over-annealed, reducing their creep strength. Therefore, it is desirable that the second heat treatment temperature, which provides good leap strength and makes it difficult to cause grain boundary sliding, is within the above range.

[Embodiments of the invention]

First, MO powder and KCg in the weight% ratio shown in Table 1.
Or 2 S! A mixed powder sample of MO and K and a mixed powder sample of MO and 1Si were prepared by drying the bond mixed with the solution of 03.

Table 1 Next, each of the mixed powders was press-molded at a pressure of about 2 tOn/d, and the obtained molded body was sintered in a hydrogen furnace at 1830° C. for 7 hours. The content of s in these sintered bodies is shown in Table 2 below.

Next, for each of the sintered bodies, 1200 to 13 oo'c
After forging at a temperature of 700° C. to 1100° C., a plate material having a thickness of 2.5711111 mm and a processing rate of 90% was obtained.

Therefore, creep test pieces and 110
A test piece for metallographic observation of 05X100++ was prepared,
Both were heat-treated for 30 minutes in a hydrogen furnace at 1350°C, and then heat-treated for 14 hours in a vacuum furnace at 1950°C. The creep test piece subjected to the two-stage heat treatment was subjected to a creep test at a tensile stress of 1 Kg/lIn2 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 we observed the structure of the metal structure observation specimen after the two-stage heat treatment, Examples 1 to 7 (Samples 1 to 7) had a single crystal structure, and Example 8 (Sample 8) had a single crystal structure. It had a polycrystalline structure.

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 in a hydrogen furnace at 1350°C.
The results of a test piece that was heat-treated for 7 hours in a vacuum furnace at 2350°C after being heat-treated for 7 hours are also shown as a comparative example.

As is clear from Table 3 above, the molybdenum alloy plates manufactured by the method of the present invention (Examples 1 to 8) are different from the conventional pure molybdenum plate (Comparative Example 1) and the second heat treatment at 2350°C. Compared to the applied molybdenum alloy plate (Comparative Example 2), the creep strain rate per hour was 115 to 1/250, which was confirmed to have excellent high-temperature creep strength.

〔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, and its industrial value is great.

Claims (3)

[Claims] (1) 0.003 to 0.003% by weight of one or both of K and Si
A method for producing a molybdenum alloy plate, which comprises subjecting a sintered body of a molybdenum alloy containing 0.05% to an area reduction process of 60% or more, and then subjecting the processed material to high-temperature heat treatment. . (2) High temperature heat treatment at 1200°C to 1500°C
After the heat treatment, the second heat treatment at 1700-2200℃
The method for producing a molybdenum alloy plate according to claim 1, characterized in that the method is a two-stage heat treatment in which a heat treatment is performed. (3) The second recrystallized structure of the heat-treated molybdenum alloy plate is a large-grain structure or a single-crystal structure with one or less crystal grains per 100 mm^2. A method for producing a molybdenum alloy plate according to item 1.