Method for preventing internal oxidation of Fe-Cr-Si alloy material

Abstract

The invention discloses a method for preventing internal oxidation of a Fe-Cr-Si alloy material, and belongs to the technical field of metal corrosion prevention. The production method comprises the steps of alloy component design, preparation and pre-oxidation treatment. The alloy comprises the following components in percentage by mass: 88-92% of Fe, 6-8% of Cr and 2-4% of Si. The method mainly comprises the following steps: optimizing a Fe-Cr-Si alloy component system by regulating and controlling the proportion of Cr and Si elements, preparing an alloy by utilizing an electric arc melting process, then cladding a coating with the same components on the surface of the prepared alloy by combining a laser cladding technology, and finally carrying out low-oxygen-pressure pre-oxidation treatment on the prepared alloy to form a compact Cr2O3 and SiO2 oxidation film. And oxygen ions diffused into the coating are prevented, so that the formation of oxidation in the alloy is avoided. The internal oxidation problem of the Fe-Cr-Si alloy is solved, and the application of the system alloy in the fields of high temperature, corrosion, scouring and the like is effectively expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of metal anti-corrosion, and particularly relates to a method for preventing internal oxidation of a Fe-Cr-Si alloy material. Background Art

[0002] Most metal components in the mechanical equipment industry serve in harsh environments and are subject to environmental influences such as high temperature and corrosion. They are prone to surface oxidation, which affects mechanical coordination and significantly reduces the service life of the equipment. There is an urgent need to develop new materials and surface modification methods to extend the life of components.

[0003] Fe-Cr-Si alloys are corrosion-resistant, wear-resistant, and anti-oxidation, making them suitable for metal component applications in the metallurgical industry, such as repair materials for blast furnace TRT blades (which are susceptible to corrosion and wear in service environments), rotor hub surfaces, and fan and roll surfaces. The Cr and Si elements in the alloy form a protective oxide film in high-temperature environments, preventing further contact between oxygen and the metal or alloying elements, thus avoiding oxidation reactions. The main problem with current materials is that while Cr and Si can significantly improve the alloy's high-temperature resistance, adding excessive amounts of alloying elements deteriorates the alloy's mechanical properties. For example, excessive Si content increases the material's brittleness, making large, low-temperature parts prone to cracking. Too few antioxidants in the alloy prevent the formation of a complete, protective oxide film on the alloy surface. In addition, when the material application environment temperature is high, the protective elements Cr and Si in the alloy are affected by the diffusion coefficient and do not have time to diffuse to the surface to form a dense oxide layer. Non-dense and poorly resistant iron oxide will be produced on the surface of the material, causing oxygen or oxygen ions to further diffuse into the interior of the alloy, causing internal oxidation. The Fe element is not protected, further leading to Fe oxidation. This cycle is repeated, seriously affecting the performance of the material.

[0004] CN110453170A discloses a method for forming a dense oxide layer on the surface of an Fe-Cr-Si alloy. The method utilizes thermal spraying technology to apply a coating having the same composition to the alloy surface, and then forms an oxide layer on the alloy surface in a low oxygen pressure environment. This method does not take into account the following aspects: the bonding mode of thermal spraying is mechanical bonding, and the bonding between the coating and the substrate is poor. In particular, the coating and the substrate are prone to separation in a high temperature environment. In addition, spraying is prone to generate pores, which makes it impossible to form a dense oxide film. Oxygen or oxygen ions will gradually enter the coating through the pores, resulting in poor effect. The present invention utilizes laser cladding technology to clad the coating material on the surface of the substrate, and the cladding layer forms a complete metallurgical bond with the surface of the substrate material. Compared with the thermal spraying process in CN110453170A, a method for forming a dense oxide layer on the surface of an Fe-Cr-Si alloy, the present invention belongs to a "green and environmentally friendly treatment process". In addition, the coating obtained by the laser cladding technology has a dense structure and fine grains. The antioxidant elements diffuse quickly to the surface in a high-temperature environment, and an oxide layer with good density and strong bonding can be formed in a high-temperature environment.

[0005] Chinese Patent Publication No. 200810033919.5 discloses a method for laser cladding of a cobalt-based alloy coating on a blast furnace tuyere. Laser cladding technology is used to prepare a wear-resistant and oxidation-resistant coating on the blast furnace tuyere outlet, which can extend the service life of the blast furnace tuyere. It has the advantages of low preparation cost and can be used for local repair of scrapped blast furnace tuyeres. As can be seen from the above, this patent can produce a coating with excellent performance by combining laser cladding technology. The difference between the present invention and this patent is that the material is subsequently pre-oxidized, which can further improve the material performance and application temperature. Chinese Patent Publication No. 201811328029.7 discloses a method for improving the thermal corrosion resistance of Co-Al-W high-temperature alloys by pre-oxidation. Under atmospheric conditions, the cobalt-based high-temperature alloy is pre-oxidized to obtain a pre-oxidation layer to enhance the thermal corrosion resistance. The difference between the present invention and the patent is that the present invention combines laser cladding technology, which has a fast cooling speed and can obtain materials with finer grains and denser structures. It also adopts a low-pressure oxidation environment, which can avoid cracking problems caused by large stress during the formation of the oxide layer. Summary of the Invention

[0006] The present invention aims to provide a method for preventing internal oxidation of Fe-Cr-Si alloy material. The alloy can be applied to the field of metal components requiring high temperature, corrosion and erosion requirements.

[0007] To solve the above technical problems, the technical solution adopted by the present invention is as follows: a method for preventing internal oxidation of Fe-Cr-Si alloy material, the method comprising the following steps: 1) Alloy preparation: Fe-Cr-Si alloy was prepared by arc melting process, with the composition of Fe: 88-92wt%, Cr: 6-8wt%, Si: 2-4wt%; 2) Coating preparation: Fe-Cr-Si coating with the same composition is clad on the surface of the alloy substrate by laser cladding technology; 3) Pre-oxidation treatment: The coating is pre-oxidized for 5 to 10 hours under low oxygen pressure and 500 to 600 ° C to form an oxide film mainly composed of Cr2O3 and SiO2.

[0008] The alloy preparation process in step (1) of the present invention comprises: placing the raw materials in an electric arc furnace, and evacuating the vacuum to ≤1.9×10 1 Pa, then fill with argon to a vacuum degree of -0.07 MPa for furnace cleaning; vacuumize for the second time to ≤9×10 -3 Pa, smelting at 1600-1700℃ for 5-6min, turning over and melting for ≥5 times to obtain Fe-Cr-Si alloy.

[0009] The coating preparation process parameters of step (2) of the present invention include: laser power of 1700-2000W, scanning speed of 350-550mm / min, and powder feeding rate of 7-13g / min. The parameters are designed by adopting a laser power interval of 1500-2000W and a scanning speed interval of 600-1000mm / min. Helium is used as the shielding gas and argon is used as the powder conveying gas. The optimal coating process parameters are selected to have a dilution rate of less than 10%, high bonding strength, no pores, and no cracks.

[0010] The main components of the oxide film pre-oxidized in step (3) of the present invention are oxides of Cr and Si.

[0011] The low oxygen pressure in step (3) of the present invention is 0.3 to 0.5 atm.

[0012] The Fe-Cr-Si alloy material oxide film obtained by the method of the present invention has a thickness of 0.5 to 1.5 μm and a hardness of 230 to 380 HV.

[0013] The present invention also provides an application of the Fe-Cr-Si alloy material prepared by the above method as a metal component in a high temperature, corrosive or erosive environment.

[0014] The present invention utilizes a Fe-Cr-Si coating of the same composition prepared on the surface of the obtained Fe-Cr-Si alloy material. The process comprises the following steps: optimizing the Fe-Cr-Si alloy by regulating the ratio of Cr and Si elements, preparing the alloy using an arc melting process, then cladding a coating of the same composition on the alloy surface using a laser cladding technique, and finally subjecting the alloy to a low-oxygen pressure pre-oxidation treatment. This allows the Cr and Si elements in the alloy time to diffuse to the alloy surface, forming a dense Cr2O3 and SiO2 oxide film on the coating surface, which prevents oxygen ions from diffusing into the coating interior, thereby preventing the formation of internal oxidation in the alloy. The present invention solves the internal oxidation problem of Fe-Cr-Si alloys, and the alloy can be applied to metal components requiring high temperatures, corrosion, and erosion.

[0015] The advantages of the present invention are: 1. Different materials, by regulating the alloying elements, the present invention can achieve the effect of protecting the substrate even if a small amount of alloying elements is added, effectively avoiding the problem of cracking during the formation of the oxide layer caused by excessive alloying amount; 2. Different material preparation processes, the material prepared by laser cladding technology has a dense structure and fine grains; 3. The present invention performs a low-oxygen pressure pre-oxidation treatment on the material, by reducing the oxygen partial pressure of the oxidizing atmosphere and using medium to high temperatures, so that the alloy Cr and Si elements have sufficient time to diffuse and enrich to the coating surface, thereby forming an oxide film with good density.

[0016] The beneficial effects of the above technical solution are as follows: 1. Based on a reasonable composition design, the present invention regulates the amount of alloying elements added, thereby avoiding the material brittleness problem caused by excessive Si content and controlling the amount of alloying elements added as little as possible while ensuring that the alloying elements can form an oxide film. 2. The present invention utilizes an arc melting process to prepare an Fe-Cr-Si alloy under a high vacuum environment, and uses laser cladding technology to clad a layer of Fe-Cr-Si coating with the same composition onto the surface of the alloy. Pre-oxidation treatment is performed by controlling the oxygen partial pressure, allowing the alloying elements to fully diffuse to the surface to form a dense and protective Cr2O3 and SiO2 oxide layer, thereby preventing internal oxidation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 A cross-sectional view of the alloy oxide layer of Example 1 (the red dashed lines in the figure are protective Cr2O3 and SiO2 oxide layers); Figure 2 A cross-sectional view of the alloy oxide layer of Example 2 (the red dashed lines in the figure are protective Cr2O3 and SiO2 oxide layers); Figure 3 A cross-sectional view of the alloy oxide layer of Example 3 (the red dashed lines in the figure are protective Cr2O3 and SiO2 oxide layers); Figure 4This is a cross-sectional view of the internal oxidation of the alloy of Comparative Example 1; Figure 5 This is a cross-sectional view of the internal oxidation of the alloy of Comparative Example 2. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Example 1

[0019] A method for internal oxidation of a Fe-Cr-Si alloy material, comprising alloy preparation (composition design), coating preparation, and pre-oxidation treatment, specifically as follows: 1) Alloy preparation: The alloy composition and its mass fraction are as follows: Fe: 88%, Cr: 8%, Si: 4%. The prepared raw materials are placed in an electric arc furnace and the furnace is evacuated to a vacuum of 1.9×10 1 Pa, then fill with argon gas to a vacuum degree of -0.07 MPa to clean the furnace, and then evacuate to a vacuum degree of 8.5×10 -3 Pa, arc melting at 1600℃ for 5min, flip melting 5 times to obtain Fe-Cr-Si alloy.

[0020] 2) Coating Preparation: The powder raw materials were mixed and dried. The laser power was controlled at 1700W, the scanning speed at 400mm / min, and the powder feed rate at 7g / min. Based on the above scheme, parameters were designed with laser power intervals of 1500W and scanning speed intervals of 600mm / min. Helium was used as the shielding gas and argon as the powder transport gas. Coatings with various parameters were obtained. The optimal coating process parameters were selected to achieve a dilution rate below 10%, high bonding strength, and no pores or cracks.

[0021] 3) Pre-oxidation treatment: The oxidation conditions were 0.3 atm atmospheric pressure, 500 °C pre-oxidation temperature, and 5 h pre-oxidation time. The total mass fraction of Cr and Si oxides in the oxide film is shown in Table 1.

[0022] The obtained Fe-Cr-Si alloy material has an oxide film thickness of 0.8 μm and a hardness of 380 HV. Example 2

[0023] A method for internal oxidation of a Fe-Cr-Si alloy material, comprising alloy preparation (composition design), coating preparation, and pre-oxidation treatment, specifically as follows: 1) Alloy preparation: The alloy composition and its mass fraction are as follows: Fe: 92%, Cr: 6%, Si: 2%. The prepared raw materials are placed in an electric arc furnace and the furnace is evacuated to a vacuum of 1.8×10 1 Pa, then fill with argon gas to a vacuum degree of -0.07 MPa to clean the furnace, and then pump it to a vacuum degree of 9×10 -3Pa, arc melting at 1670℃ for 6min, flip melting 6 times to obtain Fe-Cr-Si alloy.

[0024] 2) Coating Preparation: The powder raw materials were mixed and dried. The laser power was controlled at 1850W, the scanning speed at 350mm / min, and the powder feed rate at 13g / min. Based on the above scheme, parameters were designed with laser power intervals of 2000W and scanning speed intervals of 1000mm / min. Helium was used as the shielding gas and argon as the powder delivery gas. Coatings with various parameters were obtained. The optimal coating process parameters were selected to achieve a dilution rate below 10%, high bonding strength, and no pores or cracks.

[0025] 3) Pre-oxidation treatment: The oxidation conditions were 0.5 atm atmospheric pressure, 600 °C pre-oxidation temperature, and 10 h pre-oxidation time. The total mass fraction of Cr and Si oxides in the oxide film is shown in Table 1.

[0026] The obtained Fe-Cr-Si alloy material has an oxide film of 1.5 μm and a hardness of 330 HV. Example 3

[0027] A method for internal oxidation of a Fe-Cr-Si alloy material, comprising alloy preparation (composition design), coating preparation, and pre-oxidation treatment, specifically as follows: 1) Alloy preparation: The alloy composition and its mass fraction are as follows: Fe: 90%, Cr: 7%, Si: 3%. The raw materials are placed in an electric arc furnace and the furnace is evacuated to a vacuum of 1.5×10 1 Pa, then fill with argon gas to a vacuum degree of -0.07 MPa to clean the furnace, and then pump it to a vacuum degree of 8×10 -3 Pa, arc melting at 1700℃ for 6min, flip melting 7 times to obtain Fe-Cr-Si alloy.

[0028] 2) Coating Preparation: The powder raw materials were mixed and dried. The laser power was controlled at 2000W, the scanning speed at 550mm / min, and the powder feed rate at 10g / min. Based on the above scheme, parameters were designed with laser power intervals of 1500W and scanning speed intervals of 800mm / min. Helium was used as the shielding gas and argon as the powder transport gas. Coatings with various parameters were obtained. The optimal coating process parameters were selected to achieve a dilution rate below 10%, high bonding strength, and no pores or cracks.

[0029] 3) Pre-oxidation treatment: The oxidation conditions were 0.4 atm atmospheric pressure, 550 °C pre-oxidation temperature, and 7.5 h pre-oxidation time. The total mass fraction of Cr and Si oxides in the oxide film is shown in Table 1.

[0030] The obtained Fe-Cr-Si alloy material has an oxide film thickness of 0.5 μm and a hardness of 230 HV.

[0031] Comparative Example 1 A method for internal oxidation of a Fe-Cr-Si alloy material includes alloy preparation (composition design), specifically as follows: 1) Alloy preparation: The alloy composition and its mass fraction are as follows: Fe: 82%, Cr: 10%, Si: 8%. The prepared raw materials are placed in an electric arc furnace and the furnace is evacuated to a vacuum of 1.7×10 1 Pa, then fill with argon gas to a vacuum degree of -0.07 MPa to clean the furnace, and then pump it to a vacuum degree of 8×10 -3 Pa, arc melting at 1650℃ for 5min, flip melting 5 times to obtain Fe-Cr-Si alloy.

[0032] 2) The alloy was directly applied to 900°C to obtain Oxidation Comparative Example 1.

[0033] Comparative Example 2 A method for internal oxidation of a Fe-Cr-Si alloy material includes alloy preparation (composition design), specifically as follows: 1) Alloy preparation: The alloy composition and its mass fraction are as follows: Fe: 95%, Cr: 4%, Si: 1%. The prepared raw materials are placed in an electric arc furnace and the furnace is evacuated to a vacuum of 1.4×10 1 Pa, then fill with argon gas to a vacuum degree of -0.07 MPa to clean the furnace, and then pump it to a vacuum degree of 9×10 -3 Pa, arc melting at 1630℃ for 5min, flip melting 7 times to obtain Fe-Cr-Si alloy.

[0034] 2) The alloy was directly applied to 900°C to obtain Oxidation Comparative Example 2.

[0035] Table 1 Oxide layer composition in each example (wt%)

[0036] Depend on Figure 1 、 Figure 2 and Figure 3 It can be seen that all three examples of the alloys formed a complete and dense oxide layer. This is because the low oxygen partial pressure and slow oxidation allow alloying elements sufficient time to diffuse to the surface and form an oxide scale. Furthermore, the oxide particles are small, dense, and highly adherent, so the alloys do not experience internal oxidation. The composition of the oxide layer in each example is shown in Table 1. It can be seen that the main components of the oxide layer in each example are Cr and Si oxides.

[0037] Figure 3 、 Figure 4For alloy substrates that have not undergone laser cladding or pre-oxidation treatment, when the material is in a high-temperature environment, the alloy elements do not have time to diffuse to the surface, or the oxide layer cracks due to the large stress in the oxide layer, resulting in internal oxidation of the alloy (the internal oxidation area is shown in the circle in the figure). Example 4

[0038] Continuous high-temperature oxidation experiments were conducted in a muffle furnace for the samples obtained in Examples 1-3 and Comparative Examples 1 and 2: Standard specimens measuring 10 mm × 10 mm × 3 mm were cut from the center of the sample using wire cutting. The specimens were sanded to remove any machining marks and then polished with diamond polishing compound. Finally, they were cleaned with an ultrasonic cleaner using anhydrous ethanol and dried. The specimens were placed in a corundum crucible, which was heated to 800°C and baked for 2 hours before the experiment to remove any residue and ensure a constant crucible weight. High-temperature oxidation was performed at 900°C for 6, 12, 24, 48, 60, 72, 84, 96, 108, 120, 132, and 144 hours. Each specimen was placed in a separate crucible to prevent spallation of the formed oxides, which could affect the accuracy of the experimental data. Two identical specimens were selected for parallel experiments and removed at intervals. After cooling to room temperature, the specimens were analyzed. The total weight of the specimens and crucible was determined using an electronic balance with an accuracy of 10⁻¹⁴ g.

[0039] Results: After 144 h of oxidation, the total mass gains of the alloy materials of Examples 1-3 were 0.38, 0.44, and 0.50 g / m, respectively. 2 Under the same test conditions, the total mass gain of 45# steel in Comparative Example 1 and Comparative Example 2 reached 10.98g / m 2 , 11.07g / m 2 It is proved that the alloy material of the present invention can effectively avoid oxidation and can be applied to metal components in high temperature, corrosive or erosive environments.

[0040] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preventing internal oxidation of Fe-Cr-Si alloy material, characterized in that: The method comprises the following steps: 1) Alloy preparation: Fe-Cr-Si alloy was prepared by arc melting process, with the composition of Fe: 88-92wt%, Cr: 6-8wt%, Si: 2-4wt%; 2) Coating preparation: Fe-Cr-Si coating with the same composition is clad on the surface of the alloy substrate by laser cladding technology; 3) Pre-oxidation treatment: The coating is pre-oxidized for 5 to 10 hours under low oxygen pressure and 500 to 600 ° C to form an oxide film mainly composed of Cr2O3 and SiO2.

2. The method for preventing internal oxidation of Fe-Cr-Si alloy material according to claim 1, characterized in that: The alloy preparation process in step (1) comprises: placing the raw materials in an electric arc furnace and evacuating the vacuum to ≤1.9×10 1 Pa, then fill with argon to a vacuum degree of -0.07 MPa for furnace cleaning; vacuumize for the second time to ≤9×10 -3 Pa, smelting at 1600-1700℃ for 5-6min, turning over and melting for ≥5 times to obtain Fe-Cr-Si alloy.

3. The method for preventing internal oxidation of Fe-Cr-Si alloy material according to claim 1, characterized in that: The coating preparation process parameters of step (2) include: laser power 1700-2000W, scanning speed 350-550mm / min, and powder feeding rate 7-13g / min.

4. A method for preventing internal oxidation of a Fe-Cr-Si alloy material according to any one of claims 1 to 3, characterized in that: The main components of the oxide film pre-oxidized in step (3) are oxides of Cr and Si.

5. A method for preventing internal oxidation of a Fe-Cr-Si alloy material according to any one of claims 1 to 3, characterized in that: The low oxygen pressure in step (3) is 0.3 to 0.5 atm.

6. A method for preventing internal oxidation of a Fe-Cr-Si alloy material according to any one of claims 1 to 3, characterized in that: The Fe-Cr-Si alloy material obtained by the method has an oxide film of 0.5 to 1.5 μm and a hardness of 230 to 380 HV.

7. Use of the Fe-Cr-Si alloy material prepared by the method according to any one of claims 1 to 6 as a metal component in high temperature, corrosive or erosive environments.

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