Surface-reinforced high-temperature alloy for underground coal gasification downhole tool and preparation method for surface-reinforced high-temperature alloy

Abstract

The present invention provides a surface-reinforced high-temperature alloy for an underground coal gasification downhole tool and a preparation method for a surface-reinforced high-temperature alloy. The method comprises: placing a first portion of a reinforcing agent into a container, adding a high-temperature alloy matrix material, covering the high-temperature alloy matrix material by using a second portion of a reinforcing agent, and sealing the container; heating the container and maintaining the temperature, stopping heating when the duration for maintaining the temperature is reached, and cooling the container to room temperature; taking out the high-temperature alloy matrix material, removing sintered matter from the surface of the high-temperature alloy matrix material, and obtaining a surface-reinforced high-temperature alloy for an underground coal gasification downhole tool. The present invention further provides a surface-reinforced high-temperature alloy obtained by means of the described method. The present invention fuses the excellent high-temperature mechanical properties of a high-temperature alloy and the excellent wear resistance of a metal-based wear-resistant material, providing the major advantages in performance of both a high-temperature alloy and a metal-based wear-resistant material, while further improving the oxidation resistance.

Description

A surface-strengthened high-temperature alloy for underground coal gasification downhole tools and its preparation method Technical Field

[0001] The invention relates to a surface-strengthened high-temperature alloy for underground coal gasification downhole tools and a preparation method thereof, belonging to the technical field of petroleum and natural gas tool equipment materials. Background Art

[0002] Underground coal gasification (UCG) technology enables the closed development of coal underground. The product is a mixed gas composed of multiple combustible components, with no solid waste emissions. It is an emerging clean energy development technology that integrates oil drilling, conventional coal mining, and coal-to-gas technologies. The core technology of UCG consists of several key technologies: coal mine site selection, gasifier construction, gasification agent and gasification tool equipment development, and surface processing of raw coal gas.

[0003] The most significant limitation to the large-scale promotion of UCG technology is the lack of a breakthrough in the key technical bottlenecks that ensure the safe, stable, smooth, and efficient operation of the entire UCG process. This is primarily reflected in the following aspects: First, in the already mature "controlled injection point retreat" process, the coal seam combustion gasification area, the front end of the horizontal well, and the bottom of the production well are the weakest links in the entire UCG channel. The gasification channel equipment is exposed to high temperatures of around 800°C for a long time, and the raw coal gas flowing through contains complex corrosive media such as CO2 and H2S. Combined with the high temperature conditions, these conditions severely test the heat resistance and corrosion resistance of the relevant tools and equipment. Second, high-temperature gas-borne particle erosion and wear are one of the most demanding operating conditions in the UCG process. Its characteristics are similar to those of aircraft engines, mainly characterized by high temperatures and high-speed micro-cutting with abrasive materials, which also severely tests the material's high-temperature strength and high-temperature wear resistance.

[0004] Summary of the Invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a surface-strengthened high-temperature alloy and a preparation method thereof, wherein the high-temperature alloy can meet the use requirements of underground coal gasification downhole tools.

[0006] To achieve the above object, the present invention provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which comprises the following steps:

[0007] placing a first portion of the strengthening agent in a container, adding a high-temperature alloy matrix material, then covering the high-temperature alloy matrix material with a second portion of the strengthening agent, and sealing the container;

[0008] The container is heated and kept warm, and heating is stopped after the holding time is reached, and the container is cooled to room temperature;

[0009] Taking out the high-temperature alloy base material and removing the sintered material on the surface of the high-temperature alloy base material to obtain the surface-strengthened high-temperature alloy for underground coal gasification downhole tools;

[0010] Wherein, the high-temperature alloy matrix material includes nickel-based high-temperature alloy and / or cobalt-based high-temperature alloy;

[0011] The reinforcing agent includes a metal-based reinforcing agent and / or a ceramic-based reinforcing agent.

[0012] In the above preparation method, preferably, the nickel-based high-temperature alloy includes nickel-based high-temperature alloy GH3536, and the cobalt-based high-temperature alloy includes cobalt-based high-temperature alloy GH5188.

[0013] In the above preparation method, preferably, the composition of the metal-based strengthening agent includes, by mass percentage, 17%-21% ferroboron, 40%-44% KBF4, 14%-18% SiC, and 21%-25% charcoal; more preferably, the composition of the metal-based strengthening agent includes: 19% ferroboron, 42% KBF4, 16% SiC, and 23% charcoal.

[0014] In the above preparation method, preferably, the composition of the ceramic-based strengthening agent includes, by mass percentage, 10%-14% B4C, 51%-55% KBF4, 12%-16% SiC, and 19%-23% graphite; more preferably, the composition of the metal-based strengthening agent includes: 12% B4C, 53% KBF4, 14% SiC, and 21% charcoal.

[0015] In the above preparation method, preferably, the laying height of the first part of the reinforcing agent is 5-10 mm, and the laying height of the second part of the reinforcing agent is 5-10 mm.

[0016] In the above preparation method, preferably, the minimum distance between the high-temperature alloy base material and the inner wall of the container is greater than 5 mm, more preferably greater than 10 mm.

[0017] In the above preparation method, preferably, the heating temperature is 900-1000° C., and the insulation time is 4-5 hours.

[0018] According to a specific embodiment of the present invention, the preparation method provided by the present invention comprises the following specific steps:

[0019] 1) Selecting a high-temperature alloy substrate material for surface strengthening treatment;

[0020] 2) Select ceramic-based strengthening agent or metal-based strengthening agent according to the content of Fe, Cr and Mo elements in the high-temperature alloy matrix material. When the total content of the above elements is less than 10%, metal-based strengthening agent must be used;

[0021] 3) Using a corundum container, first lay the first part of the powdered strengthening agent to a thickness of 5-10mm, then add the base material, and finally use the second part of the strengthening agent to completely cover the base material to a thickness of 5-10mm. The minimum distance between the base material and the inner wall of the container is more than 5mm. After the filling is completed, the container is covered and sealed;

[0022] 4) heating and holding the container containing the strengthening agent and the matrix material at a specific heating temperature and holding time, stopping heating after the holding time is up, and allowing the container to cool to room temperature in the furnace;

[0023] 5) The base material is taken out from the container, and sintered materials on the surface of the material are removed by mechanical grinding or other methods, thereby obtaining a surface-enhanced thermal insulation alloy specifically for underground coal gasification.

[0024] The present invention's method for preparing a surface-hardened high-temperature alloy specifically for underground coal gasification downhole tools involves heating a solid powdered hardener to a high-temperature alloy substrate material under specific heating temperatures and holding times, causing a vigorous metallurgical reaction between the hardener and the substrate surface, ultimately forming a high-hardness, reinforced layer of a defined thickness. This method is simple to operate, highly safe, and has no shape or size requirements for the workpiece being processed, regardless of the substrate material type, shape, or size. It has a wide range of applications and can be used to surface-harden materials used in various high-temperature, harsh operating conditions, such as underground coal gasification.

[0025] The present invention also provides a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which is prepared by the above-mentioned preparation method.

[0026] According to a specific embodiment of the present invention, preferably, the surface macro-hardness of the surface strengthened high-temperature alloy is not less than 52HRC.

[0027] According to a specific embodiment of the present invention, preferably, the yield strength of the surface-strengthened high-temperature alloy at 800° C. is not less than 35% of that at room temperature, and more preferably not less than 50%.

[0028] According to a specific embodiment of the present invention, preferably, the thickness of the surface strengthening layer of the surface strengthened high-temperature alloy is not less than 500 μm.

[0029] According to a specific embodiment of the present invention, preferably, the impact toughness value of the surface-strengthened high-temperature alloy is not less than 60J.

[0030] According to a specific embodiment of the present invention, preferably, the thickness of the surface strengthening layer of the surface strengthened high-temperature alloy is not less than 500 μm, more preferably 0.5-1 mm.

[0031] According to a specific embodiment of the present invention, preferably, the microhardness of the surface strengthening layer of the surface strengthened high-temperature alloy is above 1100 HV.

[0032] The surface-strengthened high-temperature alloy provided by the present invention has high surface hardness, excellent high-temperature strength and toughness.

[0033] The surface-strengthening high-temperature alloy specially used for underground coal gasification downhole tools provided by the present invention has excellent high-temperature strength.

[0034] While retaining the performance characteristics of the original high-temperature alloy matrix, the alloy surface treated by the present method possesses a strengthening layer exceeding 500 μm in thickness, far exceeding the thickness achievable with existing similar processes. This strengthening layer also exhibits a high hardness, reaching a maximum microhardness exceeding 1100 HV, sufficient to withstand the erosive wear and tear of various high-temperature, particulate-laden fluids encountered in underground coal gasification and other underground operating conditions. Furthermore, the strengthening layer further enhances the high-temperature oxidation resistance of the matrix alloy.

[0035] This invention combines the excellent high-temperature mechanical properties of high-temperature alloys with the superior wear resistance of metal-based wear-resistant materials, combining the performance advantages of both high-temperature alloys and metal-based wear-resistant materials while further enhancing oxidation resistance. This makes it the only material capable of meeting the demanding operating conditions of underground coal gasification, such as high temperatures, high pressures, complex loads, and fluid particle erosion.

[0036] The high-temperature alloy provided by the present invention is a new type of surface-reinforced high-temperature structural material developed based on the working conditions of underground coal gasification channels. It can have sufficient service time under wear conditions and is the key to solving the "bottleneck" technology of domestic underground coal gasification and promoting its industrialization and large-scale practical application. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a state diagram of the sample after heating and heat preservation in the embodiment.

[0038] Figure 2 is a diagram of a high-temperature plate tensile specimen.

[0039] FIG3 is a cross-sectional SEM morphology of the surface-strengthened high-temperature alloy of Example 1. DETAILED DESCRIPTION

[0040] In order to have a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention is now described in detail below, but it should not be understood as limiting the scope of implementation of the present invention.

[0041] Example 1

[0042] This embodiment provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which includes the following steps:

[0043] Nickel-based high-temperature alloy GH3536 is used as the matrix material, and a ceramic-based reinforcing agent is selected as the reinforcing agent. The raw material type and content of the ceramic-based reinforcing agent are shown in Table 1, and the hardness of the matrix material body is shown in Table 2;

[0044] Use a corundum container, first lay the first part of the powdered strengthening agent, the laying thickness is 5mm, then put the base material, and finally use the second part of the strengthening agent to completely cover the base material, the covering thickness is 5mm, and the minimum distance between the base material and the inner wall of the container is 5mm. After the filling is completed, the container is covered and sealed;

[0045] The container containing the strengthening agent and the matrix material is heated and kept at 950°C. After the holding time reaches 4 hours, the heating is stopped and the container is allowed to cool to room temperature along with the furnace.

[0046] After heating and holding, the corundum crucible was unsealed, and the sintered material on the sample surface was removed by grinding with a grinding wheel to obtain a surface-strengthened high-temperature alloy for underground coal gasification downhole tools. The surface morphology is shown in the left figure in Figure 1, and the Rockwell hardness of the surface-strengthened high-temperature alloy is shown in Table 2.

[0047] Using the same process, the high-temperature tensile specimen was subjected to surface strengthening treatment, as shown in Figure 2.

[0048] Surface-strengthened high-temperature tensile specimens were used to conduct room-temperature and high-temperature tensile tests to test yield strength, tensile strength, and elongation at break. The test results are shown in Table 3.

[0049] The impact toughness test was conducted using a 10 mm × 10 mm × 55 mm V-notch standard impact specimen. Before the test, the specimen surface was strengthened using the same process. The test results are shown in Table 4.

[0050] The sample that has completed the surface strengthening treatment was cut along the direction perpendicular to the strengthening layer, and the cross section was ground, polished, and etched to make a metallographic surface. The metallographic surface was observed using a scanning electron microscope, and the morphology is shown in Figure 3.

[0051] The surface-strengthened high-temperature alloy sample obtained in Example 1 and the unstrengthened sample (i.e., the base material) of the same specification were subjected to an oxidation weight gain test at 800° C. and a holding temperature of 5 h. The test results are shown in Table 5.

[0052] On the metallographic surface shown in FIG3 , the micro-Vickers hardness at sections at different distances from the strengthening layer was measured, and the results are shown in Table 6.

[0053] Example 2

[0054] This embodiment provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which includes the following steps:

[0055] Cobalt-based high-temperature alloy GH5188 is used as the matrix material, and a ceramic-based reinforcing agent is selected as the reinforcing agent. The raw material type and content of the ceramic-based reinforcing agent are shown in Table 1, and the hardness of the matrix material body is shown in Table 2;

[0056] Use a corundum container, first lay the first part of the powdered strengthening agent, the laying thickness is 5mm, then put the base material, and finally use the second part of the strengthening agent to completely cover the base material, the covering thickness is 5mm, and the minimum distance between the base material and the inner wall of the container is 5mm. After the filling is completed, the container is covered and sealed;

[0057] The container containing the strengthening agent and the matrix material is heated and kept at 950°C. After the holding time reaches 4 hours, the heating is stopped and the container is allowed to cool to room temperature along with the furnace.

[0058] After heating and holding, the corundum crucible was unsealed, and the sintered material on the sample surface was removed by grinding with a grinding wheel to obtain a surface-strengthened high-temperature alloy for underground coal gasification downhole tools. The surface morphology is shown in the middle figure in Figure 1, and the Rockwell hardness of the surface-strengthened high-temperature alloy is shown in Table 2.

[0059] Using the same process, the high-temperature tensile specimen was subjected to surface strengthening treatment, as shown in Figure 2.

[0060] Surface-strengthened high-temperature tensile specimens were used to conduct room-temperature and high-temperature tensile tests to test yield strength, tensile strength, and elongation at break. The test results are shown in Table 3.

[0061] Example 3

[0062] This embodiment provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which includes the following steps:

[0063] Cobalt-based high-temperature alloy GH5188 is used as the base material, and a metal-based strengthener is selected as the strengthener. The raw material type and content of the metal-based strengthener are shown in Table 1, and the hardness of the base material is shown in Table 2.

[0064] Use a corundum container, first lay the first part of the powdered strengthening agent, the laying thickness is 5mm, then put the base material, and finally use the second part of the strengthening agent to completely cover the base material, the covering thickness is 5mm, and the minimum distance between the base material and the inner wall of the container is 5mm. After the filling is completed, the container is covered and sealed;

[0065] The container containing the strengthening agent and the matrix material is heated and kept at 950°C. After the holding time reaches 4 hours, the heating is stopped and the container is allowed to cool to room temperature along with the furnace.

[0066] After heating and holding, the corundum crucible was unsealed, and the sintered material on the sample surface was removed by grinding with a grinding wheel to obtain a surface-strengthened high-temperature alloy for underground coal gasification downhole tools. The surface morphology is shown in the right figure in Figure 1, and the Rockwell hardness of the surface-strengthened high-temperature alloy is shown in Table 2.

[0067] The impact toughness test was conducted using a 10 mm × 10 mm × 55 mm V-notch standard impact specimen. Before the test, the specimen surface was strengthened using the same process. The test results are shown in Table 4.

[0068] Table 1 Composition of ceramic-based reinforcement and metal reinforcement

[0069] Table 2 Hardness of base material and surface reinforcement material in each embodiment

[0070] It can be seen from the experimental results in Table 2 that the surface strengthening method provided in the examples can significantly improve the hardness of the body material, wherein Example 1 improves by 279.2% and Example 2 improves by 50.7%.

[0071] Table 3 High temperature tensile test results of various examples

[0072] According to the experimental results in Table 3, it can be seen that the surface-strengthened high-temperature alloy provided in the embodiment has higher yield strength, tensile strength and elongation.

[0073] Table 4 Impact toughness test results of each embodiment

[0074] According to the experimental results in Table 4, it can be seen that the surface-strengthened high-temperature alloy provided in Example 1 has a high impact energy, indicating that it has good impact resistance; the surface-strengthened high-temperature alloy provided in Example 3 has a very high impact energy, indicating that it has excellent impact resistance.

[0075] Table 5 High temperature oxidation weight gain test results of Example 1

[0076] According to the experimental results in Table 5, it can be seen that the surface-strengthened high-temperature alloy provided in the embodiment has relatively high high-temperature oxidation resistance.

[0077] Table 6 Microhardness test results of different cross-sectional positions of the specimens of Example 1

[0078] According to the experimental results in Table 6, it can be seen that the strengthening layer on the surface of the surface-strengthened high-temperature alloy provided in the embodiment has very high hardness, and the strengthening depth range reaches 1.1 mm below the surface layer.

[0079] In summary, based on a high-temperature alloy substrate, this invention utilizes a special process to strengthen the substrate surface, resulting in a high-performance, reinforced surface layer with a thickness of 0.5-1 mm and a maximum hardness of 1100 HV. Compared to similar processes, this layer achieves significantly higher thickness and hardness.

[0080] Due to the strengthening layer, the high-temperature alloy provided by the present invention combines the excellent high-temperature yield strength and toughness of high-temperature alloys with the high hardness and excellent wear resistance of metal-based wear-resistant materials, while the high-temperature oxidation resistance is further improved.

[0081] In addition, compared with existing similar treatment processes, the surface strengthening treatment process involved in the present invention has a simple strengthening agent component composition, low toxicity, and high safety. It is suitable for all alloys containing Fe, Cr or Mo elements, including high-temperature alloys. The strengthening treatment process is easy to operate and does not require any protective atmosphere. It can be carried out only in atmospheric atmosphere. The base material does not need to be finely processed or pre-treated such as fine grinding and polishing before treatment. It can be carried out after simply cleaning the surface. The workpiece after strengthening treatment does not need further heat treatment. It has a wide range of applications and is very suitable for the preparation of tools and equipment under various high-temperature underground complex load and wear conditions such as underground coal gasification, heavy oil thermal recovery, and geothermal mining.

Claims

1. A method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, comprising the following steps: The first part of the strengthening agent is placed in a container, a high-temperature alloy matrix material is added, and the high-temperature alloy matrix material is covered with the second part of the strengthening agent, and the container is sealed; The container is heated and kept warm, and the heating is stopped after the warm-keeping time is reached, and the container is cooled to room temperature; Taking out the high-temperature alloy matrix material and removing the sintered material on the surface of the high-temperature alloy matrix material to obtain the surface-strengthened high-temperature alloy for underground coal gasification downhole tools; Wherein, the high temperature alloy matrix material includes nickel-based high temperature alloy and / or cobalt-based high temperature alloy; The reinforcing agent includes a metal-based reinforcing agent and / or a ceramic-based reinforcing agent; In terms of mass percentage, the composition of the metal-based reinforcing agent includes: 17%-21% of ferroboron, 40%-44% of KBF4, 14%-18% of SiC, and 21%-25% of charcoal; In terms of mass percentage, the ceramic-based reinforcing agent comprises: 10%-14% B4C, 51%-55% KBF4, 12%-16% SiC, and 19%-23% graphite.

2. The preparation method according to claim 1, wherein The nickel-based high-temperature alloy includes the nickel-based high-temperature alloy GH3536, and the cobalt-based high-temperature alloy includes the cobalt-based high-temperature alloy GH5188.

3. The preparation method according to claim 1, wherein The metal-based reinforcing agent comprises: 19% of ferroboron, 42% of KBF4, 16% of SiC, and 23% of charcoal.

4. The preparation method according to claim 1, wherein The metal-based reinforcing agent comprises: 12% B4C, 53% KBF4, 14% SiC and 21% charcoal.

5. The preparation method according to claim 1, wherein The laying height of the first part of the reinforcing agent is 5-10 mm, and the laying height of the second part of the reinforcing agent is 5-10 mm; The minimum distance between the high temperature alloy matrix material and the inner wall of the container is more than 5 mm.

6. The preparation method according to claim 1, wherein The minimum distance between the high temperature alloy matrix material and the inner wall of the container is more than 10 mm.

7. The preparation method according to claim 1, wherein The heating temperature is 900-1000° C., and the insulation time is 4-5 hours.

8. A surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which is prepared by the preparation method according to any one of claims 1 to 7.

9. The surface-strengthened high-temperature alloy according to claim 8, wherein: The surface macro-hardness of the surface strengthened high-temperature alloy is not less than 52HRC.

10. The surface-hardened high-temperature alloy according to claim 8, wherein: The yield strength of the surface-strengthened high-temperature alloy at 800° C. is not less than 35% of that at room temperature.

11. The surface-hardened high-temperature alloy according to claim 10, wherein: The yield strength of the surface-strengthened high-temperature alloy at 800° C. is not less than 50% of that at room temperature.

12. The surface-hardened high-temperature alloy according to claim 8, wherein: The thickness of the surface strengthening layer of the surface strengthened high-temperature alloy is not less than 500 μm.

13. The surface-strengthened high-temperature alloy according to claim 8, wherein: The impact toughness value of the surface-strengthened high-temperature alloy is not less than 60J.

14. The surface-strengthened high-temperature alloy according to claim 8, wherein: The thickness of the surface strengthening layer of the surface strengthened high-temperature alloy is not less than 500 μm.

15. The surface-hardened high-temperature alloy according to claim 14, wherein: The thickness of the surface strengthening layer of the surface strengthened high temperature alloy is 0.5-1 mm.

16. The surface-hardened high-temperature alloy according to claim 8, 14 or 15, wherein: The microhardness of the surface strengthening layer of the surface strengthened high temperature alloy is above 1100 HV.

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