Preparation method of molybdenum alloy plug with long service life and molybdenum alloy plug prepared through preparation method

Abstract

The invention relates to the technical field of alloy materials, in particular to a preparation method of a long-service-life molybdenum alloy plug and the molybdenum alloy plug prepared through the preparation method. Rare earth oxide powder, titanium hydride powder, zirconium hydride powder, carbon powder and molybdenum powder are subjected to wet grinding and mixing, and after drying and sieving, needed alloy doped powder is obtained; and carrying out cold isostatic pressing and multi-section atmosphere sintering to obtain the molybdenum-alloy-doped plug. According to the preparation method, the carbon potential in the sintering furnace is controlled by adopting a segmented sintering process and controlling the sintering atmosphere, and the molybdenum alloy plug with excellent performance and long service life is prepared. The plug manufactured through the method has many carbide phases on the surface layer and high surface strength and hardness, and the method has the advantages of being easy and convenient to operate and low in cost.

Description

Technical Field

[0001] The invention relates to the technical field of alloy materials, and in particular to a method for preparing a long-life molybdenum alloy plug and the prepared molybdenum alloy plug. Background Art

[0002] Molybdenum alloy plugs are mainly used for the perforation of seamless steel pipes such as stainless steel, drill steel and high-temperature alloy steel. During the perforation process, the plug is in direct contact with the inner wall of the high-temperature tube blank. Due to the combined effects of high temperature and friction, the plug is very easy to wear. With the increasing scarcity of molybdenum resources and the continuous rise in prices, in order to ensure the quality and high productivity of seamless steel pipes, improving the wear resistance and service life of molybdenum plugs is an urgent problem to be solved.

[0003] During the sintering process, the tip and surface of the plug are prone to decarburization, which affects its composition and mechanical properties. The reasons for plug decarburization may be moisture, oxygen, sintering atmosphere, etc. Among them, hydrogen in the sintering atmosphere has the greatest impact and is also the key technology that restricts the sintering of long-life plugs. In recent years, researchers have done a lot of work on improving the life of plugs. However, there are few studies on the sintering atmosphere of plugs, and usually only the effects of composition, structure, surface coating, thermal processing, etc. on the plug are studied.

[0004] Patent CN102534604B, published on April 9, 2014, discloses a method for improving the service life of seamless steel pipe perforation plugs, introducing high-energy arc alloying technology into the preparation technology of perforation plug surface coating. Patent CN208245448U, published on December 18, 2018, discloses a design method for plug shape, by adjusting the specific design parameters of the top, leveling section, flat section and reverse cone section, and providing a connected conical hole at the top of the threaded hole, thereby increasing the service life of the plug. Patent CN104911428A, published on September 16, 2015, discloses a wear-resistant molybdenum alloy plug and its preparation method, by changing the component materials and proportions of the plug to obtain a wear-resistant molybdenum alloy plug.

[0005] However, in the existing technology, the molybdenum alloy plug has poor sintering consistency during the sintering process and severe surface decarburization, which leads to reduced wear resistance and service life. Summary of the invention

[0006] In order to improve the wear resistance and service life of the molybdenum plug, the present invention provides a method for preparing a molybdenum alloy plug, and the technical scheme thereof is as follows: The present invention provides a method for preparing a long-life molybdenum alloy plug, comprising the following steps: S1, placing appropriate amounts of molybdenum powder, rare earth oxide powder, titanium hydride powder, zirconium hydride powder and carbon powder in a sealed ball mill according to a certain weight ratio, ball milling, and then drying and sieving to obtain a mixed powder; S2, cold isostatic pressing the mixed powder obtained in S1 to obtain a blank; S3, turning and shaping the blank obtained in S2, and then sintering it in a hydrogen and methane atmosphere, wherein, when the sintering temperature is lower than 900°C, the volume ratio of methane is 2%-10%, and the volume ratio of hydrogen is 90%-98%; when the sintering temperature is 900-1850°C, the volume ratio of methane is 13%-30%, and the volume ratio of hydrogen is 70%-87%; when the sintering temperature is 1850-2100°C, the volume ratio of methane is 5%-10%, and the volume ratio of hydrogen is 90%-95%; finally, at a temperature of 1900-2100°C, the temperature is maintained for 5-10 h, and the molybdenum alloy plug is obtained after cooling with the furnace.

[0007] In some embodiments, in step S1, by weight percentage, the rare earth oxide powder is 1-2%, the titanium hydride powder is 0.5%-2%, the zirconium hydride powder is 0.3%-1.5%, the carbon powder is 0.2%-0.8%, and the rest is molybdenum powder.

[0008] In some embodiments, in step S1, the rare earth oxide is one or more of lanthanum oxide powder, yttrium oxide powder, and cerium oxide powder.

[0009] Preferably, the rare earth oxide is cerium oxide powder.

[0010] In some embodiments, in step S1, the grinding balls used in ball milling are molybdenum balls, tungsten balls or other cemented carbide balls.

[0011] Preferably, the grinding balls are molybdenum balls.

[0012] In some embodiments, in step S1, the ball milling process is a wet mixing process.

[0013] In some embodiments, in step S1, the ball-to-material ratio is 5-10:1, and the rotation speed is 50-120 rpm.

[0014] In some embodiments, in step S1, the ball milling time is 4-10 h.

[0015] In some embodiments, in step S1, the ball milling medium is anhydrous ethanol.

[0016] In some embodiments, in step S2, the molding pressure used in cold isostatic pressing is 180-210 MPa, and the holding time is 3-10 min.

[0017] The present invention also provides a long-life molybdenum alloy plug, which is prepared according to the method for preparing the long-life molybdenum alloy plug as described above.

[0018] Compared with the prior art, the preparation method of the molybdenum alloy plug provided by the present invention has the following beneficial effects: the present invention ensures that the plug achieves good sintering consistency in a suitable atmosphere and reduces surface decarburization by adjusting the intake amount of two gases during the sintering process. When the sintering temperature is below 900°C, water vapor and hydride decomposition are removed; when the sintering temperature is 900-1850°C, at 900-1350°C, low-melting-point impurity elements are volatilized, oxygen in the sintered body is removed, and at the same time, carbon loss of the plug caused by deoxidation is reduced. At 1350-1850°C, high-melting-point impurities are removed, and as many carbide phases as possible are generated; when the sintering temperature is 1850-2100°C, the main process is the plug densification process, and at the same time, decarburization of carbides in a hydrogen atmosphere is prevented. In addition, the present invention controls the atmosphere through staged sintering, thereby controlling the carbon potential in the furnace, thereby controlling the carbon balance of the sintered body; the present invention also controls the change of the carbon potential in the furnace, thereby controlling the carbon loss of the carbide hard phase, thereby controlling the organization and strengthening effect of the sintered body to obtain higher mechanical properties. The sintering process of the present invention is simple and easy to accurately control. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 The metallographic microstructure diagram of the plug surface layer prepared in Example 1 provided by the present invention; Figure 2 The metallographic microstructure diagram of the plug surface layer prepared in Comparative Example 1 provided by the present invention; Figure 3 This is a metallographic microstructure diagram of the plug surface layer prepared in Comparative Example 2 provided by the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] In order to demonstrate that the method for preparing a molybdenum alloy plug provided by the present invention has outstanding technical effects compared with the prior art, the present invention will be described in conjunction with the following embodiments and comparative examples to illustrate the beneficial effects of the present invention.

[0023] Example 1 S1. In terms of weight percentage, 1.0% cerium oxide powder, 1.3% titanium hydride powder, 0.8% zirconium hydride powder, 0.65% carbon powder, and the rest molybdenum powder are accurately weighed and placed together in a ball mill, molybdenum balls are used as ball milling balls, the ball-to-material ratio is 8:1, anhydrous ethanol is used as the ball milling medium, the rotation speed is 70 rpm, the ball milling time is 5 h, and the mixed powder is dried in a dryer and then sieved to obtain a mixed powder; S2, cold isostatic pressing the mixed powder obtained in S1 at a forming pressure of 200 MPa and holding the pressure for 5 min to obtain a molybdenum alloy green body; S3, the molybdenum alloy green body obtained in S2 is turned and shaped and then sintered. The atmosphere used in the sintering is a mixed atmosphere of methane and hydrogen. Specifically, the sintering temperature is: when the sintering temperature is lower than 900°C, the volume ratio of methane is 8%; when the sintering temperature is 900-1850°C, the volume ratio of methane is 15%; when the sintering temperature is 1850-2000°C, the volume ratio of methane is 6%. Finally, the sintering temperature is kept at 2000°C for 6 hours, and the molybdenum alloy plug is obtained after cooling with the furnace.

[0024] Example 2 The difference between Example 2 and Example 1 is that the sintering process is different, and the other component combinations and proportions, operation processes and methods are the same.

[0025] In the sintering process of Example 2, the sintering atmosphere is a mixed atmosphere of methane and hydrogen: specifically, the sintering temperature is: when the sintering temperature is lower than 900°C, the volume ratio of methane is 3%; when the sintering temperature is 900-1850°C, the volume ratio of methane is 25%; when the sintering temperature is 1850-2000°C, the volume ratio of methane is 7%. Finally, the sintering temperature is kept at 2000°C for 6 hours, and the molybdenum alloy plug is obtained after cooling with the furnace.

[0026] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the sintering process is different, and the other component combinations and proportions, operation processes and methods are the same.

[0027] In the sintering process of Comparative Example 1, the sintering atmosphere is a mixed atmosphere of methane and hydrogen: specifically, the sintering temperature is: when the sintering temperature is lower than 900°C, the volume ratio of methane is 6%; when the sintering temperature is 900-1850°C, the volume ratio of methane is 2%; when the sintering temperature is 1850-2000°C, the volume ratio of methane is 2%. Finally, the sintering temperature is kept at 2000°C for 6 hours, and the molybdenum alloy plug is obtained after cooling with the furnace.

[0028] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the sintering process is different, and the other component combinations and proportions, operation processes and methods are the same.

[0029] In the sintering process of Comparative Example 2, the sintering atmosphere is a mixed atmosphere of methane and hydrogen: specifically, the sintering temperature is: when the sintering temperature is lower than 900°C, the volume ratio of methane is 5%; when the sintering temperature is 900-1850°C, the volume ratio of methane is 25%; when the sintering temperature is 1850-2000°C, the volume ratio of methane is 20%, and finally, the sintering temperature is kept at 2000°C for 6 hours, and the molybdenum alloy plug is obtained after cooling with the furnace.

[0030] Comparative Example 3 The titanium hydride in the formula of Example 1 was replaced by titanium carbide, and the rest was the same as Example 1.

[0031] Performance Testing The molybdenum alloy plugs obtained in Examples 1-2 and Comparative Examples 1-3 were subjected to performance tests using the following method: Surface carbon content: Take a 1mm thick sample from the surface and use the CS-200 carbon-sulfur analyzer to test the carbon content; Surface hardness: Use HVS-1000 microhardness tester to measure the surface hardness of the plug; Service life: It is expressed by the amount of pipe penetration, which is the total weight of the 304 stainless steel pipe penetrated by the molybdenum alloy plug. The pipe is penetrated from the leftmost end to the rightmost end of the stainless steel pipe. The specification of the stainless steel pipe is 65mm*4.5-6mm (pipe diameter*wall thickness).

[0032] It should be noted that, in the technical field, the pipe penetration amount is generally used to indicate the service life of the plug.

[0033] The performance test results of Examples 1-2 and Comparative Examples 1-3 are shown in the following table: Table 1 Sample Surface carbon content / ppm Surface hardness / HV30 Pipe penetration / t Example 1 4853 221 11.2 Example 2 6125 235 12.9 Comparative Example 1 256 175 4.8 Comparative Example 2 12635 684 3.6 Comparative Example 3 5028 212 8.9 From the data in Table 1, it can be seen that in Example 1-2, the carbon content of the surface layer is kept in a relatively high range (4500-6500ppm) by using the sintering atmosphere control of the present invention, and more carbides are generated during the sintering process, which is manifested as high surface hardness, wear resistance, and long service life of the plug. In Comparative Example 1, the hydrogen flow rate exceeds the upper limit, the atmosphere has strong reducing property, the plug surface is severely decarburized, the hardness is low, the tip is collapsed, the arc surface wears quickly, the tonnage of the plug is small, and the service life is short.

[0034] In Comparative Example 2, the methane gas flow rate exceeded the upper limit, the carbon potential in the furnace was high, the surface of the plug was carburized, and a large amount of brittle molybdenum carbide phase was generated, which was prone to cracking during the pipe threading process.

[0035] In Comparative Example 3, titanium hydride is replaced by titanium carbide, and titanium hydride will produce highly active titanium after dehydrogenation and decomposition. Part of the titanium will be dissolved into the molybdenum matrix to produce a solid solution strengthening effect. In Comparative Example 3, the solid solution strengthening of titanium is lacking, the hardness and strength of the organization will be relatively low, and the service life will be shorter than that of Example 1.

[0036] In addition, the present invention also provides the metallographic microstructure diagram of the plug surface layer of Example 1 and Comparative Examples 1-2: like Figure 1 As shown, the plug surface structure of Example 1 is uniform and fine, carbides are appropriate and evenly distributed, hardness and strength are high, brittleness is small, and wear resistance is good.

[0037] like Figure 2 As shown, the second phase carbide in the plug surface layer of Comparative Example 1 is less and the grains are relatively coarse, resulting in reduced hardness and strength.

[0038] like Figure 3 As shown, the amount of molybdenum carbide on the plug surface of Comparative Example 2 is large, the brittleness is large, the structure is strip-shaped and coarse, and cracks are easily generated after being subjected to force.

[0039] In summary, the preparation method of the molybdenum alloy plug provided by the present invention controls the intake amount of the two gases during the sintering process to ensure that the plug achieves good sintering consistency in a suitable atmosphere and reduces surface decarburization. The prepared molybdenum alloy plug generates more carbide phases during the sintering process, has high surface hardness, low brittleness, wear resistance, and long service life. In addition, the present invention controls the atmosphere through segmented sintering, and then controls the carbon potential in the furnace, thereby controlling the carbon balance of the sintered body and regulating the carbon loss of the carbide hard phase, thereby achieving the control of the organization and strengthening effect of the sintered body to obtain higher mechanical properties. The sintering process of the present invention is simple and easy to accurately control.

[0040] The preparation method provided by the present invention effectively reduces the decarburization of the surface layer of the plug and increases the service life of the plug, and the method has the characteristics of strong operability and low cost.

[0041] Although the terms such as sintering, carbon potential and atmosphere are used more frequently in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

[0042] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a long-life molybdenum alloy plug, characterized in that: The steps include: S1, placing appropriate amounts of molybdenum powder, rare earth oxide powder, titanium hydride powder, zirconium hydride powder and carbon powder in a sealed ball mill according to a certain weight ratio, ball milling, and then drying and sieving to obtain a mixed powder; S2, cold isostatic pressing the mixed powder obtained in S1 to obtain a blank; S3, turning and shaping the blank obtained in S2, and then sintering it in a hydrogen and methane atmosphere, wherein, when the sintering temperature is lower than 900°C, the volume ratio of methane is 2%-10%, and the volume ratio of hydrogen is 90%-98%; when the sintering temperature is 900-1850°C, the volume ratio of methane is 13%-30%, and the volume ratio of hydrogen is 70%-87%; when the sintering temperature is 1850-2100°C, the volume ratio of methane is 5%-10%, and the volume ratio of hydrogen is 90%-95%; finally, at a temperature of 1900-2100°C, the temperature is maintained for 5-10 h, and the molybdenum alloy plug is obtained after cooling with the furnace.

2. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, by weight percentage, the rare earth oxide powder is 1%-2%, the titanium hydride powder is 0.5%-2%, the zirconium hydride powder is 0.3%-1.5%, the carbon powder is 0.2%-0.8%, and the rest is molybdenum powder.

3. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, the rare earth oxide is one or more of lanthanum oxide powder, yttrium oxide powder, and cerium oxide powder.

4. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, the grinding balls used in ball milling are molybdenum balls, tungsten balls or other hard alloy balls.

5. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, the ball milling process is a wet mixing process.

6. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, the ball-to-material ratio is 5-10:1, and the rotation speed is 50-120 rpm.

7. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, the ball milling time is 4-10 h.

8. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S1, the ball milling medium is anhydrous ethanol.

9. The method for preparing a long-life molybdenum alloy plug according to claim 1, characterized in that: In step S2, the molding pressure used in the cold isostatic pressing is 180-210 MPa, and the holding time is 3-10 min.

10. A long-life molybdenum alloy plug, characterized in that: The long-life molybdenum alloy plug is prepared according to the method for preparing the long-life molybdenum alloy plug according to any one of claims 1 to 9.

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