A method for improving the bendability of a molybdenum alloy article

Abstract

The application discloses a method for improving the bending performance of molybdenum alloy products, and mainly comprises the following steps: doping molybdenum powder, pressing, medium-frequency sintering, rolling, bending, annealing and post-treatment, and finally obtaining molybdenum alloy products with excellent performance. In the bending process, a high-frequency heating device is used to heat the bending part, so as to utilize the characteristics of the high-frequency heating with shallow depth, and the deformation characteristics of the bending part, thereby avoiding the problems of brittle fracture of the bending part due to improper heating. The method can be used to prepare high-performance molybdenum alloy product bending parts with good mechanical properties and obviously improved bending yield.

Description

Technical Field

[0001] This invention relates to the field of high-performance molybdenum profile processing, specifically a method for improving the bending performance of molybdenum alloy products. Background Technology

[0002] Molybdenum alloy products are widely used in aerospace, automotive, and metallurgical industries due to their excellent thermal and electrical conductivity and superior high-temperature mechanical properties. During their use, there is an unavoidable demand for irregularly shaped parts, and bent parts are a common type of such part. However, current processes for manufacturing bent parts suffer from problems such as brittle fracture, cracks at the bend, and edge chipping, which severely affect the yield of bent irregularly shaped parts.

[0003] Therefore, improving the bending performance of molybdenum alloy products has become the key to increasing the yield of bent parts. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for improving the bending performance of molybdenum alloy products. This method can improve the bending performance of molybdenum alloy products and ensure the yield of molybdenum alloy products in the bending and shaping process.

[0005] To achieve the above objectives, the specific solution adopted by the present invention is as follows:

[0006] A method for improving the bending performance of molybdenum alloy products, characterized in that molybdenum-doped powder is subjected to cold isostatic pressing, medium-frequency sintering, rolling, bending, annealing, and post-treatment to obtain molybdenum-doped alloy products.

[0007] The rolling process employs bidirectional rolling to ensure that the rolled sheet does not bend or break due to anisotropy. The rolling temperature is 1000–1250℃, the single heating time is 0.5–2 hours, and the reheating temperature is reduced by 50–100℃ each time.

[0008] In the bending process, the rolled part is first heated to 800-1000℃ using a high-frequency heating device, and then bent. Using a high-frequency heating device can avoid the material recrystallization and breakage caused by bending heating.

[0009] As a preferred embodiment, the molybdenum powder is doped with boron powder at a mass fraction of 0.5% to 5%.

[0010] As a preferred option, the average particle size of the selected molybdenum powder and boron powder is 2.0 to 4.2 μm, the purity of the molybdenum powder is 99.95%, and the purity of the boron powder is 99.95%. The molybdenum powder and boron powder are sieved, mixed, and blended to obtain a uniformly mixed doped molybdenum powder.

[0011] As a preferred option, the pressure of cold isostatic pressing is 160-240 MPa, and the holding time is 10-30 min.

[0012] As a preferred option, the medium-frequency sintering temperature is 1800–1950℃, and the holding time is 2–6 hours.

[0013] As a preferred option, the density ρ2 of the sintered billet obtained after medium-frequency sintering satisfies: ρ2≥95%ρ1, where ρ1 represents the theoretical density of the molybdenum alloy folded product.

[0014] As a preferred option, in the rolling process, the deformation amount of unidirectional rolling passes is 15-20%. After each rolling pass is completed, the rolling direction is rotated 90°. Each rolled surface is counted as one pass, and the total deformation amount must be ≥70%.

[0015] As a preferred option, the bent parts are annealed in a vacuum furnace at a temperature of 700–900°C for 1–2 hours.

[0016] As a preferred option, the post-processing steps include machining to obtain the product, product cleaning, inspection, and packaging.

[0017] It should be noted that the present invention adds 0.5% to 5% B during the preparation of molybdenum alloy products. The main function of B is to refine the grains and improve the mechanical properties of the alloy by increasing the grain boundary strength. According to engineering practice research, too high or too low B content will affect the strengthening effect of Mo-B alloy.

[0018] Beneficial effects:

[0019] 1) This invention uses a sieving and mixing method to mix boron powder and Mo powder in a certain proportion, presses them into shape, and then sinterstens them in an induction furnace. After a series of subsequent processing such as rolling and machining, a molybdenum alloy bending product with a certain degree of alloying is obtained. The molybdenum alloy product has a dense alloy structure and excellent tensile-elongation properties. The bending yield is over 97%, which aims to lay a theoretical and practical foundation for improving the yield of bending products.

[0020] 2) The sheet material needs to be bidirectionally rolled to eliminate anisotropy. During the bending process, the bending direction can be not only along the rolling direction, but also along a direction perpendicular to the rolling direction. This can easily lead to obvious anisotropy in the rolled sheet. The present invention uses a bidirectional rolling method to eliminate the anisotropy of the rolled sheet, thereby making the sheet material less prone to breakage during bending.

[0021] 3) In the bending process, bent parts with a thickness ≥1mm often require a certain temperature to undergo significant deformation and achieve bending. Current production processes often experience brittle fracture at the bending point. This is mainly due to the inconsistency in deformation between the inner and outer surfaces of the material at the bending point; that is, the outer surface deforms more than the core. Conventional heating methods, such as electric furnace heating or oxy-acetylene flame heating, are not conducive to bending deformation at low temperatures (leading to low-temperature brittle fracture). Increasing the temperature, on the other hand, leads to grain growth within the material, reducing its toughness and plasticity (resulting in brittle fracture during bending due to grain growth). This invention uses a high-frequency heating device (heating depth 0.2-2mm), which ensures that after appropriately increasing the bending temperature, the temperature of the external induction heating area is slightly higher than the internal heat transfer heating area. Combined with the bending deformation characteristics (larger deformation on the outside and smaller deformation in the core), this effectively improves the yield of bent Mo alloy products. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0023] This invention discloses a method for improving the bending performance of molybdenum alloy products, comprising the following preparation steps:

[0024] Step 1: Powder selection: The average particle size of molybdenum powder and boron powder is 2.0-4.2μm, the purity of molybdenum powder is 99.95%, and the purity of boron powder is 99.95%.

[0025] Step 2, Powder Mixing: Boron powder and Mo powder are mixed in proportion using a sieving and mixing method. The mixing time is 12h-24h to obtain mixed powder. The mass fraction of boron powder is 0.05%-1.5%, and the mass fraction of Mo is 95%-99.5%.

[0026] Step 3, pressing: After loading the powder into the appropriate mold, press it for 10-30 minutes using a cold isostatic press at a pressure of 160-240 MPa, and then set it aside.

[0027] Step 4, medium-frequency sintering. The pressed billet obtained in Step 3 is sintered at 1800℃-1950℃ using a hydrogen medium-frequency sintering furnace for 2-6 hours to obtain a sintered billet for later use.

[0028] Step 5, Rolling: The sintered billet undergoes bidirectional rolling. During rolling, the deformation per unidirectional rolling pass is 15-20%. After each rolling pass, the billet is rotated 90° along the rolling direction. Each rolled surface is counted as one pass, and the total deformation must be ≥70%. After each rolling pass, the billet needs to be reheated in the furnace. The initial rolling temperature is 1000℃-1250℃, and the heating time for each reheat is 0.5-2 hours. The reheating temperature decreases by 50-100℃ with each subsequent reheat.

[0029] Step Six: Bending: After cutting the rolled plate to the target size, it is heated briefly by a high-frequency heating device and then bent. Heating time: 3-10 minutes; high-frequency heating temperature: 600℃-1000℃, the specific temperature needs to be determined according to the situation.

[0030] Step 7: Annealing: Place the bent workpiece in a vacuum furnace and anneal it at 800℃-900℃ for 1-2 hours.

[0031] Step 8, Post-processing: This includes machining to obtain the product, cleaning the product, inspecting it, and packaging it to obtain the final product.

[0032] It should be noted that in the bending process of step six, the bent part can be bent into shape in one go or in multiple bends; when bending into shape in multiple bends, a short heating time is required before each bend, time: 3-5 minutes, high frequency heating temperature: 600℃-800℃.

[0033] The following specific embodiments and comparative examples illustrate that the Mo-B alloy prepared by the technical solution of the present invention possesses excellent bending properties.

[0034] Example 1

[0035] A method for improving the bending performance of molybdenum alloy products includes the following preparation steps:

[0036] Step 1: Powder Selection: The average particle size of molybdenum powder and boron powder is 2.0 μm, and the purity of molybdenum powder is 99.95%, and the purity of boron powder is 99.95%. Step 2: Powder Mixing: Boron powder and Mo powder are mixed in a specific ratio using a sieving and mixing method for 12 hours to obtain a mixed powder. In this mixed powder, the mass fraction of boron powder is 0.5%, and the mass fraction of Mo is 99.5%.

[0037] Step 3, pressing: After loading the powder into the appropriate mold, press it for 10 minutes using a cold isostatic press at a pressure of 160 MPa to obtain a pressed blank for later use.

[0038] Step 4, Medium-frequency sintering: The pressed billet obtained in Step 3 is sintered at 1800℃ using a hydrogen medium-frequency sintering furnace, with a high-temperature holding time of 6 hours, to obtain a sintered billet for later use.

[0039] Step 5, Rolling: The sintered billet is rolled bidirectionally. The deformation per unidirectional rolling pass is 15%. After each rolling pass, the billet is rotated 90° along the rolling direction. Each rolled surface is counted as one pass. The total deformation is 75%. After each rolling pass, the billet needs to be reheated in the furnace. The initial rolling temperature is 1000℃, and the reheating temperature decreases by 50℃ each time. The heating time for each reheating is 0.5 hours, resulting in a 3mm thick rolled plate.

[0040] Step 6, Bending: After the rolled plate is cut to the required size, it is heated for a short time by a high-frequency heating device and then bent. The high-frequency heating temperature is 1000℃.

[0041] Step 7, Annealing: Place the bent part in a vacuum furnace and anneal at 900℃ for 1 hour;

[0042] Step 8, Post-processing: This includes machining to obtain the product, cleaning the product, inspecting it, and packaging it to obtain the final product.

[0043] Example 2

[0044] A method for improving the bending performance of molybdenum alloy products includes the following preparation steps:

[0045] Step 1: Powder Selection: The average particle size of molybdenum powder and boron powder is 4μm, and the purity of molybdenum powder is 99.95% and that of boron powder is 99.95%. Step 2: Powder Mixing: Boron powder and Mo powder are mixed in a specific ratio using a sieving and mixing method for 12 hours to obtain a mixed powder. The mass fraction of boron powder in this mixed powder is 5%, and the mass fraction of Mo is 95%.

[0046] Step 3, pressing: After loading the powder into the appropriate mold, press it for 30 minutes at a pressure of 240 MPa using a cold isostatic press, and then set it aside for later use;

[0047] Step 4, Medium-frequency sintering: The pressed billet obtained in Step 3 is sintered at 1950℃ using a hydrogen medium-frequency sintering furnace, with a high-temperature holding time of 6 hours, to obtain a sintered billet for later use.

[0048] Step 5, Rolling: The sintered billet is subjected to bidirectional rolling. The deformation per unidirectional rolling pass is 20%. After each rolling pass, the billet is rotated 90° along the rolling direction. Each rolled surface is counted as one pass. The total deformation is 80%. After each rolling pass, the billet needs to be reheated in the furnace. The initial rolling temperature is 1250℃, and the reheating temperature decreases by 50℃ each time. The heating time for each reheating is 0.5 hours, resulting in a 1mm thick rolled plate.

[0049] Step 6, Bending: After the rolled plate is cut to the required size, it is heated for a short time by a high-frequency heating device and then bent. The high-frequency heating temperature is 800℃.

[0050] Step 7: Annealing: Place the bent workpiece in a vacuum furnace and anneal at 800℃ for 2 hours.

[0051] Step 8, Post-processing: This includes machining the product, cleaning the product, inspection, and packaging.

[0052] Comparative Example 1

[0053] The only difference between Comparative Example 1 and Example 1 is that no boron powder was added, i.e., the Mo powder content was 100%.

[0054] Comparative Example 2

[0055] The only difference between Comparative Example 2 and Example 2 is that no boron powder was added, i.e., the Mo powder content was 100%.

[0056] Comparative Example 3

[0057] The only difference between Comparative Example 3 and Example 1 is that the bending process uses a conventional oxy-acetylene flame for heating, rather than a high-frequency heating device.

[0058] Performance testing

[0059] The performance of the sintered billets and rolled plates of Examples 1-2 and Comparative Examples 1-3 was tested. 500 products were prepared for each specific example. The yield of the products prepared in each example was statistically analyzed, and the results are shown in the table below.

[0060] Table 1. Performance test results for Examples 1-2 and Comparative Examples 1-3

[0061]

[0062] As shown in the table above, the density of the sintered billets in Examples 1-2 and Comparative Examples 1-3 is greater than 95% of the theoretical density of the molybdenum alloy products. The mechanical properties and bending yield of the rolled plate in Example 1 are superior to those in Comparative Example 1, and the mechanical properties and bending yield of the rolled plate in Example 2 are superior to those in Comparative Example 2. This indicates that doping molybdenum alloys with boron (B) can improve the bending performance of the products to a certain extent. The bending yield of Comparative Example 3 is higher than that of Comparative Example 1 but lower than that of Example 1. This indicates that although the bending yield of molybdenum alloy products prepared using the conventional heating method is higher than that of pure molybdenum products, the yield using the conventional method is significantly lower. This also shows that the doping of B improves the mechanical properties of the Mo alloy products to a certain extent, while the ordinary bending heating method leads to hard and brittle fracture, reducing the yield of Mo-B alloy bending. In summary, the method of this embodiment can obtain molybdenum alloy products with excellent bending performance.

[0063] Unless otherwise specified in the above embodiments and comparative examples, the conditions were performed under standard conditions or conditions recommended by the manufacturer. All reagents and instruments used, unless otherwise specified, were commercially available products.

[0064] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific implementation of the present invention with reference to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims.

Claims

1. A method of improving the bendability of a molybdenum alloy article, comprising: The molybdenum alloy product is prepared by cold isostatic pressing, medium-frequency sintering, rolling, bending, annealing and post-treatment of doped molybdenum powder, wherein the doped molybdenum powder is doped with boron powder with a mass fraction of 0.5-5%; During rolling, bidirectional rolling is adopted, and the rolling piece needs to be heated in a furnace after each pass, the first rolling temperature is 1000-1250℃, the temperature of each time of heating in the furnace is reduced by 50-100℃, and the single heating time is 0.5-2h; During the bending step, the rolling piece is heated to 800-1000℃ by using a high-frequency heating device, and then is bent; The deformation amount of each pass of unidirectional rolling is 15-20%, and the rolling piece is rotated by 90° along the rolling direction after each pass, each rolling of one side is recorded as one pass, and the total deformation amount is ≥70%; The bending piece is placed in a vacuum furnace for annealing treatment, the annealing temperature is 800-900℃, and the annealing time is 1-2h.

2. The method of claim 1, wherein the molybdenum alloy article is a tube. The average particle size of the selected molybdenum powder and boron powder is 2.0-4.2μm, the purity of the molybdenum powder is 99.95%, the purity of the boron powder is 99.95%, and the doped molybdenum powder with uniform mixture is obtained by screening and mixing the molybdenum powder and boron powder.

3. The method of claim 1, wherein the bend performance of the molybdenum alloy article is improved by: The pressure of cold isostatic pressing is 160-240MPa, and the pressure maintaining time is 10-30min. ​ 4. The method of claim 1, wherein the molybdenum alloy article is a tube. The medium-frequency sintering temperature is 1800-1950℃, and the holding time is 2-6h.

5. The method of claim 4, wherein the molybdenum alloy article is bent at a bend radius of 0.5 to 2.0 inches. The density ρ2 of the sintered blank obtained after medium-frequency sintering satisfies ρ2≥95%ρ1, wherein ρ1 represents the theoretical density of the molybdenum alloy product. ​ 6. The method of claim 1, wherein the molybdenum alloy article is a tube. The post-treatment step includes machining to obtain the product, product cleaning, inspection and packaging.

Images