Low heat semi-solid hardfacing process and its use

Abstract

The application relates to the technical field of corrosion-resistant alloy coating, in particular to a low-heat semi-solid surfacing process and application thereof, which comprises the following steps: using a plasma transferred arc surfacing gun with a double-gas channel, one channel is used for spraying low-heat semi-solid surfacing coating material, and the low-heat semi-solid surfacing coating material is heated to 6800-7800 DEG C through an ion source and is sprayed to the surface of a base material in a state of being protected by inert gas, and is scattered on the surface of the base material at an incident angle of 60-75 DEG; meanwhile, the other gas channel of the plasma transferred arc surfacing gun sprays alloy pellets to perform surfacing shot blasting, and a high-dense, continuous and uniform surfacing layer is formed on the surface of the base material; the low-heat semi-solid surfacing process has the advantages that the high-temperature corrosion resistance of the surface coating of important equipment such as thermal power, nuclear power, ocean, national defense and military industry can be improved.

Description

Technical Field

[0001] This application relates to the technical field of corrosion-resistant alloy coatings, and in particular to a low-heat semi-solid overlay welding process and its application. Background Technology

[0002] Traditional coating processes, such as thermal spraying, suffer from drawbacks such as loose structure, low interlayer bonding, and premature failure, failing to meet the requirements for long-term corrosion protection. Laser cladding and welding technologies, on the other hand, suffer from high heat input, potential damage and deformation of the base material, and are difficult and inefficient to apply on-site. Therefore, developing long-term corrosion protection technologies for equipment in harsh environments such as thermal power, nuclear power, marine, and defense industries, characterized by high temperatures, radiation, and high salinity and humidity, is of great significance. Summary of the Invention

[0003] To improve the high-temperature corrosion resistance of surface coatings on important equipment such as thermal power, nuclear power, marine, and defense equipment under harsh environments, this application provides a low-heat semi-solid surfacing welding process and its application.

[0004] In a first aspect, this application provides a low-heat semi-solid overlay welding process, employing the following technical solution:

[0005] A low-heat semi-solid cladding process includes the following steps:

[0006] The plasma transfer arc welding torch uses a dual-path gas system. One path sprays low-heat semi-solid coating material, heated to 6800-7800℃ by an ion source and protected by an inert gas. The powder is sprayed onto the substrate surface at a feed rate of 20-35 g / min. Under the combined action of gravity and carrier gas, the material is evenly distributed on the substrate surface at an incident angle of 60-75°. After traveling a certain distance to the substrate surface, the low-heat semi-solid coating material forms a semi-solid material, and the substrate surface temperature is maintained between 200-300℃. Simultaneously, the other path of the plasma transfer arc welding torch sprays alloy shot for shot peening, also protected by an inert gas. Under the action of the alloy shot peening, the coating further diffuses and forms a metallurgical bond with the substrate, forming a weld overlay layer.

[0007] In the process of shot peening, the alloy shot size is 0.3-0.6mm, the shot velocity is 30-50m / s, the shot peening gun moves at a constant speed of 3-8m / h, and the alloy shot has the same metal element composition as the coating material for low-heat semi-solid shot peening.

[0008] By adopting the above technical solutions, this application ensures that the coating material is uniformly distributed on the substrate surface by precisely controlling the powder feeding rate, incident angle, and heating temperature, thereby reducing spatter and material waste. The low-heat semi-solid surfacing coating material is heated to 7000℃, maintaining a semi-solid state upon reaching the substrate surface. Its temperature is reduced by the distance it travels from the sprayed surface, and the substrate temperature is consistently maintained at 200-300℃. Furthermore, the density and adhesion to the substrate are improved primarily through the size and velocity of the shot in the shot peening process. An in-situ shot peening device (shot size 0.3-0.6mm, velocity 30-50m / s) combined with inert gas protection allows the sprayed alloy shot to break up the surface oxide film, promote plastic flow of the material, enhance interfacial element diffusion, refine coating grains, reduce porosity, improve coating density and adhesion strength, and thus enhance the corrosion resistance of the substrate. Additionally, the moving speed of the welding gun ensures coating uniformity and stability while also increasing processing speed and efficiency.

[0009] Preferably, the coating material for low-heat semi-solid surfacing includes the following raw materials in the following mass percentages: 13-20% chromium powder, 2-4% manganese powder, 0.7-1.5% niobium powder, 1-3% tungsten powder, 1-3% cerium powder, and 1-3% additives, with the balance being nickel powder; the additives are vanadium carbide or titanium diboride, or a mixture of vanadium carbide and titanium diboride.

[0010] By adopting the above technical solution and optimizing the alloy ratio, the coating material for low-heat semi-solid surfacing can reach a lower temperature and a wider temperature range in the semi-solid state, thus reducing the sensitivity to construction parameters. In its formula, the nickel-based matrix provides good toughness and corrosion resistance, chromium enhances the coating's oxidation resistance and wear resistance, manganese improves deoxidation and strength, and niobium and tungsten refine the grains and improve high-temperature performance. Cerium not only purifies grain boundaries and improves thermal stability but also enhances the coating's ductility, allowing the coating to adhere evenly and fully to the substrate surface, improving wettability and metallurgical bonding strength, thereby improving the coating's corrosion resistance. Furthermore, the additives (vanadium carbide / titanium diboride) further refine the grains during the melting and recrystallization of the semi-solid coating material, preventing further grain growth, thereby improving the adhesion and strength between the coating and the substrate, making the coating suitable for high-load environments.

[0011] Preferably, the additive is a mixture of vanadium carbide and titanium diboride, and the mass ratio of vanadium carbide to titanium diboride is (1-3):1.

[0012] By adopting the above technical solutions, vanadium carbide can refine the grains and improve the hardness and wear resistance of the coating. In addition to refining the grains, titanium diboride can also improve the toughness and thermal shock resistance of the coating. When vanadium carbide or titanium diboride is added alone, it is easy to cause the coating to become brittle or the strength improvement is small. When added together, the coating can have the advantages of high strength, high hardness and crack resistance. Furthermore, the mechanical properties of the coating are improved by this additive, and it has no significant effect on the semi-solid heating temperature of the coating, making it more suitable for the implementation of shot surfacing technology.

[0013] Preferably, the particle size of the additive is ≤100nm.

[0014] By adopting the above technical solution, nanoscale additives can be uniformly dispersed in the matrix, reducing stress concentration. At the same time, the coating strength, wear resistance and thermal stability are further improved through dispersion strengthening and pinning effect, without affecting the process flowability.

[0015] As a preferred embodiment, the preparation method of the low-heat semi-solid overlay coating material is as follows:

[0016] Nickel powder, chromium powder, manganese powder, niobium powder, tungsten powder and cerium powder are mixed, and then the mixed powder is ground to a particle size of 15-45μm. Additives are then added and mixed evenly to obtain a low-heat semi-solid overlay coating material.

[0017] By adopting the above technical solution, the main metal powder is first mixed and then ground to 15-45μm, which can ensure the uniformity of the composition.

[0018] Preferably, the average particle size of the alloy projectile is 0.45 mm.

[0019] By adopting the above technical solution, when the projectile velocity is within a certain range, if the particle size of the projectile is too small, it may embed into the coating; if the particle size of the projectile is too large, the coating is easily shattered and the substrate is damaged. Therefore, a particle size of 0.45 mm is the optimal particle size.

[0020] Preferably, the velocity of the elastic flow is 40 m / s.

[0021] By adopting the above technical solution, when the projectile size is within a certain range, this projectile velocity is the optimal choice, which is not easy to penetrate the coating and can also play a good forging role for the coating.

[0022] Preferably, the thickness of the weld overlay is 0.3-0.5 mm.

[0023] By adopting the above technical solution, good and long-lasting high corrosion resistance can be achieved even with a relatively thin thickness.

[0024] Preferably, the substrate is pretreated by cleaning, grinding and shot peening, and the surface roughness after pretreatment is 10-20 μm.

[0025] By adopting the above technical solutions, through cleaning, grinding and shot peening pretreatment, the roughness is controlled at 10-20μm, which increases the mechanical interlocking area between the coating and the substrate, significantly improves the bonding strength, and reduces the risk of peeling.

[0026] Secondly, this application provides an application of a low-heat semi-solid overlay welding process, employing the following technical solution:

[0027] An application of a low-heat semi-solid cladding process, which is applied to iron-based materials and stainless steel-based materials.

[0028] By adopting the above technical solution, the low heat input characteristics (semi-solid) of this process are particularly suitable for easily deformable iron-based and stainless steel substrates. It can repair or strengthen components (such as boiler heating surfaces, turbine components, etc.) without affecting the properties of the substrate, thus expanding the application scope of surfacing technology.

[0029] In summary, this application includes at least one of the following beneficial technical effects:

[0030] 1. This application ensures uniform distribution of coating material on the substrate surface by precisely controlling the powder feeding rate, incident angle, and heating temperature, reducing spatter and material waste. The low-heat semi-solid surfacing coating material is heated to 7000℃, maintaining a semi-solid state upon reaching the substrate surface. Its temperature is reduced as it travels a distance from the substrate surface, and the substrate temperature is consistently maintained at 200-300℃. Furthermore, the coating's density and adhesion to the substrate are improved primarily through the size and velocity of the shot in the shot peening process. An in-situ shot peening device (shot size 0.3-0.6mm, shot velocity 30-50m / s) combined with inert gas protection is used. The blasted alloy shot can break the surface oxide film, promote plastic flow of the material, enhance interfacial element diffusion, refine coating grains, reduce porosity, improve coating density and adhesion strength, and thus enhance the substrate's corrosion resistance. Additionally, the moving speed of the surfacing gun ensures coating uniformity and stability while also increasing processing speed and efficiency.

[0031] 2. The coatings prepared on the surface of iron-based substrates using the low-heat semi-solid surfacing process described in this application exhibit substrate bond strengths between 237-260 MPa, coating hardness between 649-740 HV, molten pool depths of approximately 1 μm, and corrosion weight loss of 12.7 mg / cm³. 2 The lowest concentration can reach 9.3 mg / cm³. 2This demonstrates that the coating prepared by the low-heat semi-solid overlay welding process of this application has good metallurgical bonding strength with the substrate, does not damage the substrate, has high construction efficiency, and excellent anti-corrosion performance. Attached Figure Description

[0032] Figure 1 This is a metallographic image of a coating sample of an iron-based substrate prepared by a low-heat semi-solid overlay welding process according to Example 1.

[0033] Figure 2 This is a metallographic image of a coating sample of an iron-based substrate prepared by a low-heat semi-solid overlay welding process, as shown in Comparative Example 1. Detailed Implementation

[0034] The following provides a more detailed description of this application in conjunction with specific details.

[0035] raw material

[0036] All raw materials used in this application are commercially available products.

[0037] Preparation Example 1

[0038] A low-heat semi-solid overlay coating material, the raw materials and their amounts are shown in Table 1, and its preparation method is as follows:

[0039] Nickel powder, chromium powder, manganese powder, niobium powder, tungsten powder, and cerium powder are mixed, and then the mixed powder is ground to an average particle size of 15 μm. Then, an additive is added and mixed evenly to obtain a coating material for low-heat semi-solid overlay welding. The additive is a mixture of vanadium carbide and titanium diboride, with a mass ratio of vanadium carbide to titanium diboride of 2:1. The average particle size of both vanadium carbide and titanium diboride is 50 nm.

[0040] Table 1. Amounts (g) of each raw material used in Preparation Example 1

[0041]

[0042] Preparation Example 2

[0043] A low-heat semi-solid overlay coating material differs from Preparation Example 1 in that its additive is vanadium carbide, while the remaining steps are the same as in Preparation Example 1.

[0044] Preparation Example 3

[0045] A low-heat semi-solid overlay coating material differs from Preparation Example 1 in that its additive is titanium diboride, while the remaining steps are the same as those in Preparation Example 1.

[0046] Example 1

[0047] A low-heat semi-solid cladding process includes the following steps:

[0048] S1. Pretreatment of iron-based substrate

[0049] The heated surface of the iron-based substrate is cleaned to remove oil and dirt, and then the surface oxide layer is removed by grinding to a depth of 0.15mm. Then, sandblasting is performed to make the roughness of the heated surface of the iron-based substrate Ra 15μm.

[0050] S2, weld overlay

[0051] The plasma transfer arc welding torch is designed with dual gas paths. One path is used to spray low-heat semi-solid welding coating material, which is delivered to the welding area through a powder feeding system. The low-heat semi-solid welding coating material is heated to 7000℃ by an ion source and protected by inert gas. It is then sprayed onto the surface of the iron-based substrate. After traveling a certain distance to the substrate surface, the low-heat semi-solid welding coating material forms a semi-solid material, and the substrate surface temperature is maintained between 200-300℃ (in actual operation, the spraying distance can also be set according to this temperature). At the same time, the other gas path of the plasma transfer arc welding torch sprays alloy shot for welding shot peening, and inert gas is introduced for protection. Under the action of alloy shot peening, the coating further diffuses and forms a metallurgical bond with the substrate, resulting in a highly dense, continuous and uniform welding layer with a coating thickness of 0.4mm on the surface of the iron-based substrate.

[0052] The relevant parameters are as follows: the powder feeding rate is precisely controlled within the range of 20 g / min. When the low-heat semi-solid cladding coating material leaves the powder feeding nozzle, it is uniformly distributed on the surface of the pretreated iron-based substrate at an incident angle of 60° under the dual action of gravity and carrier gas. The low-heat semi-solid cladding coating material comes from Preparation Example 1.

[0053] The alloy shot used in the shot peening process (the metallic element composition of the alloy shot is the same as that of the coating material for low-heat semi-solid surfacing, and the alloy shot is obtained by melting and granulating the coating material for low-heat semi-solid surfacing and then ball milling) has a size of 0.45 mm and a projectile velocity of 40 m / s. The surfacing gun moves at a constant speed of 5 m / h. The total mass of the alloy shot sprayed per unit time is the same as the powder feeding amount per unit time of the plasma transfer arc surfacing gun, forming a continuous and uniform coating deposition.

[0054] Example 2

[0055] A low-heat semi-solid cladding process differs from Example 1 in that the coating material for the low-heat semi-solid cladding is derived from Preparation Example 2, while the remaining steps are the same as in Example 1.

[0056] Example 3

[0057] A low-heat semi-solid cladding process differs from Example 1 in that the coating material for the low-heat semi-solid cladding is derived from Preparation Example 3, while the remaining steps are the same as in Example 1.

[0058] Example 4

[0059] A low-heat semi-solid surfacing process differs from Example 1 in that the alloy shot size used in the shot peening during S2 is 0.3 mm, while the remaining steps are the same as in Example 1.

[0060] Example 5

[0061] A low-heat semi-solid surfacing process differs from Example 1 in that the alloy shot size used in the shot peening during S2 is 0.6 mm, while the remaining steps are the same as in Example 1.

[0062] Example 6

[0063] A low-heat semi-solid cladding process differs from Example 1 in that the blast velocity in S2 is 30 m / s, while the remaining steps are the same as in Example 1.

[0064] Example 7

[0065] A low-heat semi-solid cladding process differs from Example 1 in that the blast velocity in S2 is 50 m / s, while the remaining steps are the same as in Example 1.

[0066] Example 8

[0067] A low-heat semi-solid overlay welding process differs from Example 1 in that the coating thickness in S2 is 0.3 mm, while the remaining steps are the same as in Example 1.

[0068] Example 9

[0069] A low-heat semi-solid cladding process differs from Example 1 in that the coating thickness in S2 is 0.5 mm, while the remaining steps are the same as in Example 1.

[0070] Comparative Example 1

[0071] A low-heat semi-solid cladding process differs from Example 1 in that the additives in the coating material are replaced with an equal mass of nickel powder, while the remaining steps are the same as in Example 1.

[0072] Comparative Example 2

[0073] A low-heat semi-solid cladding process differs from Example 1 in that the cerium powder in the coating material is replaced with an equal mass of nickel powder, while the remaining steps are the same as in Example 1.

[0074] Comparative Example 3

[0075] A low-heat semi-solid surfacing process differs from Example 1 in that the alloy shot size used in the shot peening during S2 is 0.2 mm, while the remaining steps are the same as in Example 1.

[0076] Comparative Example 4

[0077] A low-heat semi-solid cladding process differs from Example 1 in that the blast velocity in S2 is 55 m / s, while the remaining steps are the same as in Example 1.

[0078] Performance testing

[0079] Detection methods / test methods

[0080] The low-heat semi-solid surfacing processes of Examples 1-9 and Comparative Examples 1-4 were used to load coatings onto the surface of iron-based substrates in the same batch, and then the substrates were tested according to the following testing methods. The test results are shown in Table 2.

[0081] Coating hardness: Micro Vickers hardness was tested according to the test method in GB / T 9790.

[0082] Matrix bond strength: tested using the defect tensile method.

[0083] Resistance to high-temperature molten salt corrosion: This was tested by corrosion weight loss over a corrosion period of 200 hours under the following conditions:

[0084] Molten salt composition: 37.5% KCl + 50% NaCl + 12.5% ​​K3Na(SO4)2;

[0085] Test conditions: Atmosphere: O2: 5%; H2O: 2%; HCl: 0.08%; SO2: 0.01%; the remainder is N2; temperature: 600℃.

[0086] Table 2. Detection results of Examples 1-9 and Comparative Examples 1-4

[0087]

[0088] Furthermore, testing revealed that the molten pool depths in Examples 1-9 of this application were all between 0.7 and 1.5 μm. The test data from Examples 1-9 and Comparative Examples 1-4 show that the substrate bonding strength of the coatings prepared on the surface of the iron-based substrate using the designed low-heat semi-solid cladding process of this application are all between 237 and 260 MPa, the coating hardness is all between 649 and 740 HV, the molten pool depth is all around 1 μm, and the corrosion weight loss is all around 12.7 mg / cm³. 2 The lowest concentration can reach 9.3 mg / cm³. 2This demonstrates that the coating prepared using the low-heat semi-solid overlay welding process described in this application exhibits excellent metallurgical bonding strength with the substrate, does not damage the substrate, has high construction efficiency, and excellent corrosion resistance. Furthermore, through... Figure 1 and Figure 2 This also demonstrates that the coating prepared in this application shows no change in the coating and substrate surface after corrosion, exhibiting excellent corrosion resistance.

[0089] The test data from Examples 1-3 and Comparative Examples 1-2 show that by optimizing the alloy ratio, the coating material for low-heat semi-solid surfacing can reach a lower temperature and a wider temperature range in the semi-solid state, thus reducing the sensitivity to construction parameters. In its formulation, the nickel-based matrix provides good toughness and corrosion resistance, chromium enhances the coating's oxidation resistance and wear resistance, manganese improves deoxidation and strength, and niobium and tungsten refine the grains and improve high-temperature performance. Cerium not only purifies grain boundaries and improves thermal stability but also enhances coating ductility, allowing the coating to adhere evenly and fully to the substrate surface, improving wettability and metallurgical bonding strength, thereby improving the coating's corrosion resistance. Furthermore, the additives (vanadium carbide / titanium diboride) further refine the grains during the melting and recrystallization of the semi-solid coating material, preventing further grain growth, thereby improving the adhesion and strength between the coating and the substrate, making the coating suitable for high-load environments.

[0090] Furthermore, vanadium carbide can refine grains and improve coating hardness and wear resistance. In addition to refining grains, titanium diboride can also improve coating toughness and thermal shock resistance. When vanadium carbide or titanium diboride is added alone, although it can improve the strength of the coating, it can easily lead to brittleness or insufficient strength of the coating. Adding them together can make the coating have high strength, high hardness and crack resistance.

[0091] The test data from Examples 1 and 4-7, as well as Comparative Examples 3-4, show that when the projectile velocity is within a certain range, if the projectile size is too small, it may embed into the coating; if the projectile size is too large, the coating is easily shattered, damaging the substrate. Therefore, a projectile size of 0.45 mm is the optimal particle size. Within a certain range, this projectile velocity is the preferred choice, as it is less likely to penetrate the coating while still providing a good forging effect.

[0092] The test data from Examples 1 and 8-9 show that, through the design of the coating material and the low-heat semi-solid overlay welding process, the coating can have good and long-lasting high corrosion resistance even with a relatively thin coating thickness.

[0093] This specific embodiment is merely an explanation of the present invention and is not intended to limit the invention. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they are within the scope of the claims of the present invention.

Claims

1. A low heat semi-solid surfacing process characterized by: It includes the following steps: The plasma transfer arc welding torch uses a dual-path gas system. One path sprays low-heat semi-solid coating material, heated to 6800-7800℃ by an ion source and protected by an inert gas. The powder is sprayed onto the substrate surface at a feed rate of 20-35 g / min. Under the combined action of gravity and carrier gas, the material is evenly distributed on the substrate surface at an incident angle of 60-75°. After traveling a certain distance to the substrate surface, the low-heat semi-solid coating material forms a semi-solid material, and the substrate surface temperature is maintained between 200-300℃. Simultaneously, the other path of the plasma transfer arc welding torch sprays alloy shot for shot peening, also protected by an inert gas. Under the action of the alloy shot peening, the coating further diffuses and forms a metallurgical bond with the substrate, forming a weld overlay layer. In the process of shot peening, the alloy shot size is 0.3-0.6mm, the shot velocity is 30-50m / s, the shot peening gun moves at a constant speed of 3-8m / h, and the alloy shot has the same metal element composition as the coating material for low-heat semi-solid shot peening.

2. A low heat semi-solid deposition welding process according to claim 1, characterized in that: The coating material for low-heat semi-solid surfacing includes the following raw materials in the following mass percentages: 13-20% chromium powder, 2-4% manganese powder, 0.7-1.5% niobium powder, 1-3% tungsten powder, 1-3% cerium powder, and 1-3% additives, with the balance being nickel powder; the additives are vanadium carbide or titanium diboride, or a mixture of vanadium carbide and titanium diboride.

3. A low heat semi-solid deposition welding process according to claim 2, characterized in that: The additive is a mixture of vanadium carbide and titanium diboride, and the mass ratio of vanadium carbide to titanium diboride is (1-3):

1.

4. A low heat semi-solid deposition welding process according to claim 2, characterized in that: The particle size of the additive is ≤100nm.

5. A low heat semi-solid surfacing process as claimed in claim 2, wherein: The preparation method of the coating material for low-heat semi-solid overlay welding is as follows: Nickel powder, chromium powder, manganese powder, niobium powder, tungsten powder and cerium powder are mixed, and then the mixed powder is ground to a particle size of 15-45μm. Additives are then added and mixed evenly to obtain a low-heat semi-solid overlay coating material.

6. A low heat semi-solid surfacing process as claimed in claim 1, wherein: The average particle size of the alloy projectile is 0.45 mm.

7. A low heat semi-solid surfacing process as claimed in claim 1, wherein: The velocity of the elastic stream is 40 m / s.

8. A low heat semi-solid surfacing process as claimed in claim 1, wherein: The thickness of the weld overlay is 0.3-0.5 mm.

9. A low heat semi-solid surfacing process as claimed in claim 1, wherein: The substrate is pretreated by cleaning, grinding and shot peening, and its surface roughness after pretreatment is 10-20 μm.

10. Use of the low heat semi-solid deposition welding process according to any one of claims 1 to 9, characterized in that: The low-heat semi-solid overlay welding process is applied to iron-based materials and stainless steel-based materials.

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