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

Abstract

The invention provides a surface strengthening high-temperature alloy for a coal underground gasification downhole tool and a preparation method of the surface strengthening high-temperature alloy. The method comprises the following steps: putting a first part of reinforcer into a container, adding a high-temperature alloy matrix material, covering the high-temperature alloy matrix material with a second part of reinforcer, and sealing the container; heating and heat preservation treatment is conducted on the container, heating is stopped after the heat preservation time is up, and the container is cooled to the room temperature; and the high-temperature alloy base material is taken out, the sinter on the surface of the high-temperature alloy base material is removed, and the surface strengthening high-temperature alloy for the underground coal gasification downhole tool is obtained. The invention further provides the surface-strengthened high-temperature alloy obtained through the method. The high-temperature alloy material integrates the excellent high-temperature mechanical property of a high-temperature alloy and the excellent wear resistance of a metal-based wear-resistant material, has the two performance advantages of the high-temperature alloy and the metal-based wear-resistant material, and further improves the oxidation resistance at the same time.

Description

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 realizes 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 technology, conventional coal mining technology and coal-to-gas technology. The main body of underground coal gasification technology consists of several key technologies: coal mine resource site selection, gasification furnace construction, gasification agent and gasification tool equipment research and development, and raw coal gas surface processing.

[0003] The most important reason for limiting the large-scale promotion of UCG technology is that the key "neck" technical bottleneck to ensure the safe, stable, smooth and efficient operation of the entire underground coal gasification process has not been broken through. It is mainly reflected in the following aspects: First, in the "controlled injection point retreat" process that has been basically mature, the coal seam combustion gasification, the front end of the horizontal well and the bottom of the production well are the weakest links in the entire underground coal gasification channel. The gasification channel equipment is at a high temperature of about 800°C for a long time, and the raw coal gas flowing through contains complex corrosive media such as CO2 and H2S. Combined with high temperature conditions, it is a great test for the high temperature resistance and corrosion resistance of related tools and equipment; second, high-temperature gas-borne particle erosion and wear is one of the harsh working conditions in the underground coal gasification process. Its characteristics are similar to the working environment of aircraft engines, mainly high temperature and abrasive high-speed micro-cutting, which is also a great test for the high temperature strength and high temperature wear resistance of materials. Summary of the invention

[0004] In order to solve the above technical problems, the object 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.

[0005] 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:

[0006] 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;

[0007] 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;

[0008] 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;

[0009] Wherein, the high temperature alloy matrix material includes nickel-based high temperature alloy and / or cobalt-based high temperature alloy;

[0010] The reinforcing agent includes a metal-based reinforcing agent and / or a ceramic-based reinforcing agent.

[0011] 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.

[0012] In the above preparation method, preferably, the composition of the metal-based reinforcing 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 reinforcing agent includes: 19% ferroboron, 42% KBF4, 16% SiC, and 23% charcoal.

[0013] In the above preparation method, preferably, in terms of mass percentage, the composition of the ceramic-based reinforcing agent includes: 10%-14% B4C, 51%-55% KBF4, 12%-16% SiC, and 19%-23% graphite; more preferably, the composition of the metal-based reinforcing agent includes: 12% B4C, 53% KBF4, 14% SiC, and 21% charcoal.

[0014] 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.

[0015] In the above preparation method, preferably, the minimum distance between the high temperature alloy matrix material and the inner wall of the container is greater than 5 mm, and more preferably greater than 10 mm.

[0016] In the above preparation method, preferably, the heating temperature is 900-1000° C., and the insulation time is 4-5 h.

[0017] According to a specific embodiment of the present invention, the preparation method provided by the present invention comprises the following specific steps:

[0018] 1) Select high-temperature alloy matrix material for surface strengthening treatment;

[0019] 2) According to the content of Fe, Cr and Mo elements in the high-temperature alloy matrix material, select a ceramic-based strengthener or a metal-based strengthener. When the total content of the above elements is less than 10%, a metal-based strengthener must be used;

[0020] 3) Using a corundum container, first lay the first part of the powdered strengthening agent with a thickness of 5-10mm, then put in the base material, and finally use the second part of the strengthening agent to completely cover the base material with 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 loading is completed, the container is covered and sealed;

[0021] 4) Using a specific heating temperature and holding time, the container containing the strengthening agent and the matrix material is heated and held, and the heating is stopped after the holding time is reached, and the container is cooled to room temperature with the furnace;

[0022] 5) The base material is taken out from the container, and the sintered material on the surface of the material is removed by mechanical grinding or the like, so as to obtain a surface strengthening thermal insulation alloy specially used for underground coal gasification.

[0023] The method for preparing a surface-reinforced high-temperature alloy for underground coal gasification downhole tools of the present invention uses a solid powder reinforcing agent and a high-temperature alloy matrix material, and at a specific heating temperature and insulation time, causes the reinforcing agent and the matrix material surface to undergo a violent metallurgical reaction, and finally forms a high-hardness reinforcing layer with a certain thickness. The method is easy to operate, highly safe, and has no shape and size requirements for the workpiece to be processed, is not limited by the type, shape and size of the matrix material, has a wide range of applications, and can be used for surface strengthening treatment of materials serving under various high-temperature and harsh working conditions such as underground coal gasification.

[0024] 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.

[0025] 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.

[0026] According to a specific embodiment of the present invention, preferably, the yield strength of the surface-hardened high-temperature alloy at 800° C. is not less than 35% of that at room temperature, and more preferably not less than 50%.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The surface-strengthened high-temperature alloy provided by the present invention has high surface hardness, excellent high-temperature strength and toughness.

[0032] The surface-strengthening high-temperature alloy specially used for underground coal gasification downhole tools provided by the present invention has excellent high-temperature strength.

[0033] On the basis of retaining the performance characteristics of the original high-temperature alloy matrix material, the alloy surface treated by the preparation method of the present invention has a strengthening layer with a thickness of more than 500 μm, which is much thicker than the strengthening layer thickness that can be achieved by existing similar process technologies. The strengthening layer also has a very high hardness level, with the highest microhardness reaching more than 1100 HV, which is sufficient to withstand various high-temperature particle-containing fluid erosion and wear underground working conditions such as underground coal gasification. In addition, the strengthening layer also has the function of further improving the high-temperature oxidation resistance of the matrix alloy.

[0034] The invention combines the excellent high-temperature mechanical properties of high-temperature alloys and the excellent wear resistance of metal-based wear-resistant materials, and has the two major performance advantages of high-temperature alloys and metal-based wear-resistant materials, while further improving the anti-oxidation performance. It becomes the only material that can meet the harsh working conditions of underground coal gasification, such as high temperature, high pressure, complex load, fluid particle erosion, etc.

[0035] The high-temperature alloy provided by the present invention is a new type of surface-strengthened 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

[0036] Figure 1 This is a state diagram of the sample after heating and heat preservation in the embodiment.

[0037] Figure 2 This is a picture of a high temperature plate tensile specimen.

[0038] Figure 3 This is a cross-sectional SEM morphology of the surface-strengthened high-temperature alloy of Example 1. DETAILED DESCRIPTION

[0039] In order to have a clearer understanding of the technical features, purposes 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 construed as limiting the applicable scope of the present invention.

[0040] Example 1

[0041] This embodiment provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which comprises the following steps:

[0042] 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;

[0043] 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 loading is completed, the container is covered and sealed;

[0044] 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 cooled to room temperature along with the furnace.

[0045] After heating and heat preservation, the corundum crucible was unsealed, and the sintered material on the sample surface was removed by grinding with a grinder to obtain a surface-strengthened high-temperature alloy for underground coal gasification downhole tools. The surface morphology is as follows: Figure 1 As shown in the left figure, the Rockwell hardness of the surface-hardened high-temperature alloy is shown in Table 2.

[0046] Using the same process, the high temperature tensile specimens were subjected to surface strengthening treatment. Figure 2 shown.

[0047] The room temperature and high temperature tensile tests were carried out using surface-strengthened high temperature tensile specimens to test the yield strength, tensile strength and elongation at break. The test results are shown in Table 3.

[0048] The impact toughness test was carried out using a 10mm×10mm×55mm V-notch standard impact specimen. Before the test, the surface of the specimen was strengthened using the same process. The test results are shown in Table 4.

[0049] 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. The morphology was as follows: Figure 3 shown.

[0050] The surface-strengthened high-temperature alloy sample obtained in Example 1 and the unstrengthened sample (i.e., the matrix material) of the same specification were subjected to an oxidation weight gain test at 800° C. and heat preservation for 5 hours. The test results are shown in Table 5.

[0051] exist Figure 3 On the metallographic surface shown, the micro-Vickers hardness at cross sections at different distances from the strengthening layer was measured, and the results are shown in Table 6.

[0052] Example 2

[0053] This embodiment provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which comprises the following steps:

[0054] 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;

[0055] 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 loading is completed, the container is covered and sealed;

[0056] 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 cooled to room temperature along with the furnace.

[0057] After heating and heat preservation, the corundum crucible was unsealed, and the sintered material on the sample surface was removed by grinding with a grinder to obtain a surface-strengthened high-temperature alloy for underground coal gasification downhole tools. The surface morphology is as follows: Figure 1 As shown in the middle figure in , the Rockwell hardness of the surface-hardened high-temperature alloy is shown in Table 2.

[0058] Using the same process, the high temperature tensile specimens were subjected to surface strengthening treatment. Figure 2 shown.

[0059] The room temperature and high temperature tensile tests were carried out using surface-strengthened high temperature tensile specimens to test the yield strength, tensile strength and elongation at break. The test results are shown in Table 3.

[0060] Example 3

[0061] This embodiment provides a method for preparing a surface-strengthened high-temperature alloy for underground coal gasification downhole tools, which comprises the following steps:

[0062] Cobalt-based high-temperature alloy GH5188 is used as the matrix material, and the reinforcing agent is a metal-based reinforcing agent. The raw material type and content of the metal-based reinforcing agent are shown in Table 1, and the hardness of the matrix material body is shown in Table 2;

[0063] 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 loading is completed, the container is covered and sealed;

[0064] 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 cooled to room temperature along with the furnace.

[0065] After heating and heat preservation, the corundum crucible was unsealed, and the sintered material on the sample surface was removed by grinding with a grinder to obtain a surface-strengthened high-temperature alloy for underground coal gasification downhole tools. The surface morphology is as follows: Figure 1 As shown in the right figure, the Rockwell hardness of the surface-hardened high-temperature alloy is shown in Table 2.

[0066] The impact toughness test was carried out using a 10mm×10mm×55mm V-notch standard impact specimen. Before the test, the surface of the specimen was strengthened using the same process. The test results are shown in Table 4.

[0067] Table 1 Composition of ceramic-based reinforcing agents and metal reinforcing agents

[0068]

[0069] Table 2 Hardness of base material and hardness of surface reinforcement material in various embodiments

[0070] Hardness before strengthening / HRC Hardness after strengthening / HRC Example 1 14.4 54.6 Example 2 35.3 53.2

[0071] It can be seen from the experimental results in Table 2 that the surface strengthening method provided in the embodiments can significantly improve the hardness of the body material, wherein the hardness of the embodiment 1 is improved by 279.2% and the hardness of the embodiment 2 is improved by 50.7%.

[0072] Table 3 High temperature tensile test results of various embodiments

[0073]

[0074] It can be seen from the experimental results in Table 3 that the surface-strengthened high-temperature alloy provided in the embodiment has higher yield strength, tensile strength and elongation.

[0075] Table 4 Impact toughness test results of each embodiment

[0076] Base material type Impact energy / J Example 1 63.5 Example 3 278.7

[0077] 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 higher 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.

[0078] Table 5 High temperature oxidation weight gain test results of Example 1

[0079] Specimen type Before weight gain / g After weight gain / g Increase Example 1 64.90 64.91 0.015％ GH3536 alloy 67.80 67.88 0.118％

[0080] It can be seen from the experimental results in Table 5 that the surface-strengthened high-temperature alloy provided in the embodiment has a relatively high high-temperature oxidation resistance.

[0081] Table 6 Microhardness test results of the samples of Example 1 at different cross-sectional positions

[0082] Distance to surface / mm Hardness / HV 0.15 1168 0.2 1146 0.25 1138 0.3 1198 0.5 1050 0.7 1053 0.9 1060 1.1 739 1.4 241 1.6 249

[0083] It can be seen from the experimental results in Table 6 that the strengthening layer on the surface of the surface-strengthened high-temperature alloy provided in the embodiment has a very high hardness, and the strengthening depth range reaches 1.1 mm below the surface layer.

[0084] In summary, based on the high-temperature alloy matrix material, the present invention strengthens the surface of the matrix material through a special process, so that a high-performance strengthened surface layer with a thickness of 0.5-1mm and a maximum hardness of 1100HV can be obtained. Compared with similar process technologies, the thickness and hardness of the strengthened layer are at a significantly leading level.

[0085] Due to the strengthening layer, the high-temperature alloy provided by the present invention has both the excellent high-temperature yield strength and toughness of the high-temperature alloy and the high hardness and excellent wear resistance of the metal-based wear-resistant material, while the high-temperature oxidation resistance is further improved.

[0086] 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 subjected to fine processing pretreatment 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, geothermal mining, etc.

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 greater than 5 mm, preferably greater than 10 mm.

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

7. 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 6.

8. The surface-hardened high-temperature alloy according to claim 7, wherein: The surface macro-hardness of the surface strengthened high-temperature alloy is not less than 52HRC.

9. The surface-strengthened high-temperature alloy according to claim 7, wherein: The yield strength of the surface-strengthened high-temperature alloy at 800° C. is not less than 35% of that at room temperature, preferably not less than 50%.

10. The surface-hardened high-temperature alloy according to claim 7, wherein: The thickness of the surface strengthening layer of the surface strengthened high-temperature alloy is not less than 500 μm.

11. The surface-hardened high-temperature alloy according to claim 7, wherein: The impact toughness value of the surface-strengthened high-temperature alloy is not less than 60J.

12. The surface-hardened high-temperature alloy according to claim 7, wherein: The thickness of the surface strengthening layer of the surface strengthened high temperature alloy is not less than 500 μm, and more preferably 0.5-1 mm.

13. The surface-hardened high-temperature alloy according to claim 7 or 12, wherein: The microhardness of the surface strengthening layer of the surface strengthened high temperature alloy is above 1100 HV.

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