Molybdenum strip sintered at medium and low temperature and preparation method thereof

Abstract

The invention discloses a medium and low temperature sintered molybdenum strip and a preparation method thereof, and belongs to the technical field of molybdenum strip preparation methods. The preparation method comprises the steps that molybdenum powder with the purity larger than or equal to 99.8% and the Fisher particle size of 1.2-6.8 micrometers is pressed and formed into a molybdenum blank strip through cold isostatic pressing; and under the reducing atmosphere, the molybdenum blank strip is subjected to medium and low temperature sintering including a plurality of temperature rising stages in a resistance furnace, and the highest sintering temperature of the medium and low temperature sintering is lower than 1850 DEG C. According to the preparation method, a resistance furnace with a simple structure can be adopted for sintering, and the low-oxygen and high-density metal molybdenum strip can be prepared under the temperature condition obviously lower than that of a traditional process.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molybdenum strip preparation method, and particularly relates to a middle-low temperature sintered molybdenum strip and a preparation method thereof. BACKGROUND

[0002] In the preparation of molybdenum and its alloy products, the pressing-sintering forming technology of powder metallurgy is mainly adopted, and the sintering process as the most core section of the production process plays a key role in the material performance, so it is of important practical significance to select a suitable sintering process.

[0003] Currently, there are mainly three sintering methods in the preparation of molybdenum materials: direct electric heating sintering (i.e. vertical melting sintering), intermediate frequency induction sintering and indirect resistance heating sintering. Among them, the vertical melting sintering generally makes the molybdenum product metallized and reduces the oxygen content and impurities by direct electric heating under hydrogen protection, but due to the limitation of equipment, it is only suitable for products with small single weight; the intermediate frequency induction sintering is a long-time high-temperature sintering in a intermediate frequency induction sintering furnace and hydrogen atmosphere, and it often needs to be repeated in the process of high-temperature sintering-low-temperature cooling, which not only has a complex equipment structure and high maintenance cost, but also causes serious loss of furnace bricks and long equipment repair cycle, thereby affecting the continuity and economy of production; and the indirect resistance heating sintering (resistance furnace sintering) is gradually attracting attention due to its relatively simple equipment and stable temperature control, however, the existing resistance furnace sintering process still has obvious defects when applied to molybdenum materials, including that the sintering temperature usually still needs to be maintained at a high level, the energy consumption is still significant, and there is a lack of systematic and mature process scheme for how to realize the full densification of molybdenum blanks and effective control of oxygen content in the middle-low temperature range, which limits the full play of its cost advantage and performance potential.

[0004] In summary, it is of urgent practical significance and important application value to develop a new method capable of fully utilizing the advantages of resistance furnace equipment and obtaining high-density, low-oxygen molybdenum products through an optimized middle-low temperature sintering process, so as to promote the technological progress of the industry, reduce the production cost and improve the product competitiveness. SUMMARY

[0005] In view of the defects of the prior art, the purpose of the present application is to provide a method for preparing molybdenum strips by middle-low temperature sintering through a resistance furnace, which can prepare low-oxygen, high-density molybdenum strips at a temperature significantly lower than that of the traditional process, thereby effectively overcoming the outstanding problems of complex equipment, high cost, high energy consumption and long production cycle in the prior art.

[0006] The technical scheme of the present application is as follows: A preparation method of a middle-low temperature sintered molybdenum strip, comprising the following steps: (1) Molybdenum powder with a purity ≥ 99.8% and a Fisher particle size of 1.2-6.8 μm is used as raw material; (2) The raw material is pressed into molybdenum billet strips by cold isostatic pressing; (3) Under a reducing atmosphere, the molybdenum billet is sintered in a resistance furnace at a medium and low temperature to obtain the medium and low temperature sintered molybdenum bar; the medium and low temperature sintering includes multiple heating stages, with the highest sintering temperature below 1850℃.

[0007] According to some preferred embodiments of the present invention, the pressure of the cold isostatic pressing is 145-195 MPa.

[0008] According to some preferred embodiments of the present invention, the pressing time of the cold isostatic pressing is 40-60 min.

[0009] According to some preferred embodiments of the present invention, the molybdenum billet is cylindrical with a diameter of 15-35 mm and a length of 550-750 mm.

[0010] According to some preferred embodiments of the present invention, the reducing atmosphere is hydrogen.

[0011] According to some preferred embodiments of the present invention, the reducing atmosphere is continuously introduced during the medium-low temperature sintering process, and the flow rate of the reducing atmosphere is 2-6 m³ / s. 3 / h.

[0012] According to some preferred embodiments of the present invention, the medium-low temperature sintering includes the following process: heating from room temperature to 1100-1300℃ over 60-300 min, and then holding at that temperature for 60-300 min; continuing to heat to 1300-1500℃ over 60-360 min, and then holding at that temperature for 60-360 min; continuing to heat to 1400-1700℃ over 60-360 min, and then holding at that temperature for 60-360 min; continuing to heat to 1600-1850℃ over 60-480 min, and then holding at that temperature for 180-1200 min.

[0013] In the preferred embodiments of the present invention, the temperature below 1100-1300℃ is a low-temperature sintering platform. This stage can be coordinated with the rapid oxygen and impurity removal process within the molybdenum billet, which helps to quickly reduce the oxygen content and the content of other low-melting-point impurity elements. During this process, the grains within the molybdenum billet particles do not change, the particle shape remains essentially unchanged, the entire billet does not shrink significantly, and the density does not increase substantially. The stage from 1100-1300℃ to 1400-1700℃ is the sintering neck growth and viscoplastic flow stage, during which the entire billet shrinks significantly and at a relatively fast rate. (Mainly due to the rapid shrinkage of the billet due to the large disappearance of pores) The heat preservation platform set at this stage helps to enhance the degree of sintering shrinkage; after sintering to the highest temperature of 1600-1850℃, as the sintering temperature increases, the grains grow and the grain boundaries move across the pores. In the areas swept by the grain boundaries, the pores disappear in large quantities. After sintering at high temperature and holding for a period of time, the shrinkage trend slows down and the sintering behavior is basically completed. Molybdenum strips with uniform grain size, fine grain scale, uniform distribution of closed pores, basically no abnormal closed pores, and dense and uniform density distribution can be obtained.

[0014] According to some preferred embodiments of the present invention, the medium-low temperature sintering includes the following process: heating from room temperature to 1100-1200℃ over 15-240 min, and then holding at that temperature for 60-240 min; continuing to heat to 1200-1300℃ over 15-300 min, and then holding at that temperature for 60-240 min; continuing to heat to 1300-1400℃ over 15-300 min, and then holding at that temperature for 0-240 min; continuing to heat to 1400-1500℃ over 15-300 min, and then holding at that temperature for 0-240 min; continuing to heat to 1600-1850℃ over 15-300 min, and then holding at that temperature for 300-960 min.

[0015] According to some preferred embodiments of the present invention, the medium-low temperature sintering includes the following process: heating from room temperature to 1100-1200℃ over 15-240 min, and then holding at that temperature for 60-180 min; continuing to heat to 1230-1300℃ over 15-180 min, and then holding at that temperature for 60-180 min; continuing to heat to 1330-1400℃ over 30-180 min, and then holding at that temperature for 30-180 min; continuing to heat to 1430-1500℃ over 15-180 min, and then holding at that temperature for 0-180 min; continuing to heat to 1630-1800℃ over 60-180 min, and then holding at that temperature for 0-180 min; continuing to heat to 1750-1850℃ over 30-180 min, and then holding at that temperature for 480-720 min.

[0016] According to some preferred embodiments of the present invention, hydrogen gas is continuously introduced during the medium-low temperature sintering process, and the flow rate of the hydrogen gas is 2-6 m³ / h. 3 / h.

[0017] According to some preferred embodiments of the present invention, the preparation method further includes: after completing the medium-low temperature sintering, shutting down the furnace and cooling it down until the temperature drops below 200°C, then introducing an inert atmosphere into the resistance furnace and opening the furnace to remove the material.

[0018] The present invention further provides a medium-low temperature sintered molybdenum bar prepared according to the above preparation method.

[0019] The present invention has the following beneficial effects: The preparation method of this invention changes the traditional sintering method, changing the medium-frequency high-temperature sintering to low-temperature sintering in a resistance furnace. The quality, impurity content, density, grain size and other indicators of the medium-low temperature sintered molybdenum bars prepared by this invention have reached the effect of high-temperature sintering (2000-2200℃) using medium-frequency induction heating, which can realize continuous batch production with low energy consumption. Traditional powder metallurgy methods for producing molybdenum products employ medium-frequency furnaces with temperatures as high as 2000-2200℃. These furnaces, being enclosed, operate on a single-furnace, intermittent production model, resulting in lengthy heating and cooling phases, a long overall sintering cycle, and high energy consumption. Furthermore, the frequent heating and cooling necessitates frequent replacement of refractory materials, insulation materials, and various auxiliary materials within the furnace, leading to high sintering costs. In contrast to traditional medium-frequency furnace sintering, the method of this invention significantly shortens the production cycle, reduces energy consumption and costs, and simultaneously extends the service life of equipment and related materials. The medium- and low-temperature sintered molybdenum strips prepared by this invention have a purity of over 99.9%, an oxygen content of less than 800 ppm, uniform grain size, uniform distribution of sintered agglomerates with relatively consistent closure degree and similar pore size, and a density of over 94%, with a macroscopic density of 9.3 g / cm³. 3 above. Attached Figure Description

[0020] Figure 1 This is a low-temperature sintering process in a resistance furnace used in Example 4.

[0021] Figure 2 The high-temperature sintering procedure of the medium-frequency furnace used in Example 4.

[0022] Figure 3 The images shown are sampling and detection images of the broken morphology of the molybdenum strip in Example 4, where (a) is a SEM image magnified 1000 times and (b) is a SEM image magnified 2000 times. Detailed Implementation

[0023] The technical solutions of the present invention will be further described below with reference to embodiments thereof. The embodiments described below are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort should fall within the scope of protection of the present invention.

[0024] In the following examples, the density was determined by the water displacement method, and the SEM images were obtained by observing the fracture morphology of the molybdenum strips using a scanning electron microscope.

[0025] Example 1 Molybdenum bars are prepared through the following process: (1) Molybdenum powder with a purity ≥99.8% and an average Fisher particle size of 4.98 μm was used as raw material. Its elemental composition is shown in Table 1: Table 1. Elemental composition (wt%) and average particle size (μm) of molybdenum powder in Example 1

[0026] (2) Under a pressure of 185-195MPa and a pressing time of 50-60min, the raw material is formed into a molybdenum billet with a diameter of 25mm and a length of 650mm (Ф25×h650mm) by cold isostatic pressing; (3) Under the protection of hydrogen, the molybdenum billet was sintered in a resistance furnace through the following medium-low temperature sintering procedure to obtain the molybdenum bar: Table 2 Sintering procedure for Example 1

[0027] The heating time refers to the time it takes to reach the end temperature of that stage, and the holding time is the time it takes to hold the temperature at that end temperature. For example, the heating time from room temperature to 1150℃ is 2 hours, and the holding time at 1150℃ is 3 hours. The heating time to 1250℃ is 2 hours, and the holding time at 1250℃ is 3 hours.

[0028] The obtained molybdenum strips were subjected to elemental analysis and density determination, and the results are shown in Table 3 below: Table 3. Elemental composition (wt%) and density (g.cm³) of molybdenum strips in Example 1 -3 )

[0029] As shown in Table 3, the density of the molybdenum strips obtained in Example 1 is 9.74 g / cm³. 3 The oxygen content is 58 ppm.

[0030] Example 2 Molybdenum bars are prepared through the following process: (1) Molybdenum powder with a purity ≥99.8% and an average Fisher particle size of 3.39 μm was used as raw material. Its elemental composition is shown in Table 4: Table 4. Elemental composition of molybdenum powder in Example 2 (wt%)

[0031] (2) Under a pressure of 165-185 MPa and a pressing time of 40-50 min, the raw material is formed into a molybdenum billet with a diameter of 25 mm and a length of 650 mm (Ф25×h650 mm) by cold isostatic pressing; (3) Under the protection of hydrogen, the molybdenum billet was sintered in a resistance furnace through the following medium-low temperature sintering procedure to obtain the molybdenum bar: Table 5 Sintering procedure for Example 2

[0032] The obtained molybdenum strips were subjected to elemental analysis and density determination, and the results are shown in Table 6 below: Table 6. Elemental composition (wt%) and density (g / cm³) of molybdenum strips in Example 2. -3 )

[0033] As shown in Table 6, the density of the molybdenum strips obtained in Example 2 is 9.67 g / cm³. 3 The oxygen content is 65 ppm.

[0034] Example 3 Molybdenum bars are prepared through the following process: (1) Molybdenum powder with a purity ≥99.8% and an average Fisher particle size of 2.20 μm was used as raw material. Its elemental composition is shown in Table 7: Table 7. Elemental composition of molybdenum powder in Example 3 (wt%)

[0035] (2) Press the raw material under a pressure of 145-165 MPa for 40-50 minutes and form it into a molybdenum billet with a diameter of 25 mm and a length of 650 mm (Ф25×h650 mm) by cold isostatic pressing; (3) Under the protection of hydrogen, the molybdenum billet was sintered in a resistance furnace through the following medium-low temperature sintering procedure to obtain the molybdenum bar: Table 8 Sintering procedure for Example 3

[0036] The obtained molybdenum strips were subjected to elemental analysis and density determination, and the results are shown in Table 9 below: Table 9. Elemental composition (wt%) and density (g / cm³) of molybdenum strips in Example 3. -3)

[0037] As shown in Table 9, the density of the molybdenum strips obtained in Example 3 is 9.49 g / cm³. 3 The oxygen content is 72 ppm.

[0038] Example 4 Molybdenum bars are prepared through the following process: (1) Multiple batches of molybdenum powder with a purity ≥99.8% and an average Fisher particle size of 1.2-6.8 μm were used as raw materials. The composition of impurity elements is shown in Table 10: Table 10. Impurity element content (ppm) of molybdenum powder in Example 4

[0039] (2) Under a pressure of 145-195MPa, each batch of raw materials is formed into molybdenum billets with a diameter of 25mm and a length of 650mm (Ф25×h650mm) by cold isostatic pressing for 40-60min; (3) Under the protection of hydrogen, the molybdenum billet was sintered in a resistance furnace through the following medium-low temperature sintering procedure to obtain the molybdenum bar: Table 11 Sintering procedure for Example 4

[0040] The sintering curves for molybdenum powder raw materials with an average Fisher particle size of 3.58 μm at medium and low temperatures are shown in the attached figure. Figure 1 As shown in Table 12 below.

[0041] Table 12 Sintering procedure for molybdenum powder raw material with an average Fisher particle size of 3.58 μm in Example 4

[0042] In contrast, the molybdenum billet was sintered using a traditional medium-frequency furnace high-temperature sintering method, and the sintering curve used is shown in the attached figure. Figure 2 As shown in Table 13 below: Table 13 High-Temperature Sintering Procedure for Traditional Medium-Frequency Furnaces

[0043] A cost comparison between the traditional sintering method and the sintering method of Example 4 is shown in Table 14 below: Table 14 Cost Comparison between Traditional Sintering and Medium-Low Temperature Sintering

[0044] It can be seen that, compared with the traditional high-temperature sintering in a medium-frequency furnace, the low-temperature sintering in the resistance furnace of this invention can directly reduce the sintering cost by 4.74 yuan / kg, saving 2,844 yuan per furnace and 443,700 yuan in sintering costs per year.

[0045] Regarding the effective sintering time, the total sintering time at medium and low temperatures in this invention is less than that at high temperatures, effectively shortening the sintering time and increasing production efficiency by 36.67%. A single furnace can sinter 600 kg, with an average of 10 furnaces per month and a monthly output of 6 tons. After the sintering cycle is shortened, the monthly output can be increased to 13 furnaces, with a monthly output of 7.8 tons and a total annual output of 93.6 tons.

[0046] The maximum sintering temperature of this invention is reduced from the conventional 2000℃ and above to below 1850℃, which significantly reduces the requirements for sintering equipment. Lower-cost insulation materials can be used, and medium-low temperature sintering can be used without replacing the insulation materials, extending the service life of the insulation materials by nearly 50% and directly reducing the production cost of replacing insulation materials.

[0047] Furthermore, elemental analysis of the obtained molybdenum strips revealed that the Mo content was above 99.90 wt%, and the contents of other impurity elements are shown in Table 15 below: Table 15 Impurity element content (ppm) of molybdenum strips in Example 4

[0048] As can be seen from the table, compared with the impurity content of the raw material molybdenum powder, the O content in the molybdenum bars is significantly reduced, and the C content is also reduced.

[0049] In addition, test blocks were sequentially cut from the upper, middle, and lower parts of the molybdenum strip using wire cutting, and the density value was tested using the water displacement method. The average test results are shown in Table 16 below: Table 16. Average density test results of molybdenum strips in Example 4

[0050] As can be seen from the table, the molybdenum billet bars did not exhibit significant differences in density uniformity after low-temperature resistance sintering, and the densification degree reached 94.1%, exceeding the national standard of 9.3 g / cm³. 3 It meets the density requirements and has excellent sintering density.

[0051] Furthermore, the molybdenum strip obtained in Example 4 was subjected to morphological analysis by breaking it apart, and the results are shown in the attached figure. Figure 3 As shown, the grain size is basically ≤45um, the grain size is relatively small, the closed pores are evenly distributed, and there are basically no abnormally closed pores, which makes the overall density of the molybdenum strip uniform.

[0052] It should be noted that the above descriptions are merely preferred embodiments of the present invention and should not limit the scope of protection of the technical solutions of the present invention. Any modifications made to the technical solutions described in the foregoing embodiments, or equivalent substitutions of technical features, by those skilled in the art within the spirit and principles of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for preparing medium- and low-temperature sintered molybdenum bars, characterized in that, It includes the following steps: (1) Molybdenum powder with a purity ≥ 99.8% and a Fisher particle size of 1.2-6.8 μm is used as raw material; (2) The raw material is pressed into molybdenum billet strips by cold isostatic pressing; (3) Under a reducing atmosphere, the molybdenum billet is sintered in a resistance furnace at a medium and low temperature to obtain the medium and low temperature sintered molybdenum bar; the medium and low temperature sintering includes multiple heating stages, with the highest sintering temperature below 1800℃.

2. The preparation method according to claim 1, characterized in that, in, The pressure of the cold isostatic pressing is 145-195 MPa; and / or the pressing time of the cold isostatic pressing is 40-60 min.

3. The preparation method according to claim 1, characterized in that, The molybdenum billet is cylindrical, with a diameter of 15-35 mm and a length of 550-750 mm.

4. The preparation method according to claim 1, characterized in that, The reducing atmosphere is hydrogen.

5. The preparation method according to claim 1, characterized in that, The medium-low temperature sintering includes the following process: heating from room temperature to 1100-1300℃ in 60-300 minutes, followed by holding at that temperature for 60-300 minutes; Continue heating to 1300-1500℃ over 60-360 minutes, then hold for 60-360 minutes; continue heating to 1400-1700℃ over 60-360 minutes, then hold for 60-360 minutes; continue heating to 1600-1850℃ over 60-480 minutes, then hold for 180-1200 minutes.

6. The preparation method according to claim 5, characterized in that, The medium-low temperature sintering process includes the following steps: heating from room temperature to 1100-1200℃ over 15-240 minutes, then holding at that temperature for 60-240 minutes; continuing to heat to 1200-1300℃ over 15-300 minutes, then holding at that temperature for 60-240 minutes; continuing to heat to 1300-1400℃ over 15-300 minutes, then holding at that temperature for 0-240 minutes; continuing to heat to 1400-1500℃ over 15-300 minutes, then holding at that temperature for 0-240 minutes; continuing to heat to 1600-1850℃ over 15-300 minutes, then holding at that temperature for 300-960 minutes.

7. The preparation method according to claim 5, characterized in that, The medium-low temperature sintering process includes the following steps: heating from room temperature to 1100-1200℃ over 15-240 minutes, then holding at that temperature for 60-180 minutes; continuing to heat to 1230-1300℃ over 15-180 minutes, then holding at that temperature for 60-180 minutes; continuing to heat to 1330-1400℃ over 30-180 minutes, then holding at that temperature for 30-180 minutes; continuing to heat to 1430-1500℃ over 15-180 minutes, then holding at that temperature for 0-180 minutes; continuing to heat to 1630-1800℃ over 60-180 minutes, then holding at that temperature for 0-180 minutes; continuing to heat to 1750-1850℃ over 30-180 minutes, then holding at that temperature for 480-720 minutes.

8. The preparation method according to claim 1, characterized in that, It also includes: after completing the medium-low temperature sintering, shutting down the furnace and cooling it down until the temperature drops below 200°C, then introducing an inert atmosphere into the resistance furnace and opening the furnace to remove the material.

9. The preparation method according to any one of claims 1-8, characterized in that, During the medium-low temperature sintering process, the reducing atmosphere is continuously introduced, and the flow rate of the reducing atmosphere is 2-6 m³ / h. 3 / h.

10. The medium-low temperature sintered molybdenum strip prepared by the preparation method according to any one of claims 1-9.

Images