A method for recycling a metal workpiece covered with a ceramic coating

Abstract

The present invention belongs to the technical field of metal recycling, and particularly relates to a method for recycling metal workpieces covered with ceramic coatings, comprising the following steps: S1. Ultrasonic decontamination of the metal workpieces with ceramic coatings; S2. Primary oxidation: The ultrasonically decontaminated metal workpieces are subjected to primary oxidation to obtain metal workpiece A1, and then subjected to primary water quenching treatment to obtain metal workpiece A2; S3. Secondary oxidation: Metal workpiece A2 is subjected to secondary oxidation to obtain metal workpiece B1, and then subjected to secondary water quenching treatment to obtain metal workpiece B2; S4. Induction heating: Metal workpiece B2 is subjected to induction heating to obtain metal workpiece C1, and then subjected to three times of water quenching treatment to obtain metal workpiece C2; S5. The metal workpiece C3 is subjected to sandblasting treatment to obtain metal workpiece D1; S6. The metal workpiece D1 is subjected to cold straightening to obtain the recycled metal workpiece. The present invention can achieve the effect of recycling the metal substrate with a relatively simple process method, relatively low production cost and relatively high production efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal recycling, and particularly relates to a method for recycling metal workpieces covered with ceramic coatings. Background Art

[0002] With the development of the metal and its extended product industries, the impact of heavy metal wastewater and waste generated in the production and processing processes on the soil and surface water environment has become increasingly prominent. The pollution problem is seriously restricting the healthy and sustainable development of the stainless steel industry. The rapid development of the stainless steel industry has greatly driven the demand for metal elements such as chromium, iron, and manganese. The traditional predatory and extensive development methods are no longer sufficient to support the rapid development of the steel industry. The contradiction between the supply and demand of metal resources has become increasingly acute, and the bottleneck effect of resource constraints has become more evident. Therefore, the renewable utilization of steel resources is becoming increasingly important.

[0003] Metal-based ceramic coatings are the general term for heat-resistant inorganic protective layers or surface films applied on the metal surface. It can change the morphology, structure, and chemical composition of the outer surface of the metal substrate and endow the substrate with new properties. Metal-based ceramic coatings are widely used in industries such as aerospace and power electronics due to their properties such as the toughness, strength, and electrical conductivity of metals, as well as the high hardness, high strength, wear resistance, high temperature resistance, and corrosion resistance of ceramic materials. However, how to achieve the recycling of metal-based materials is of great practical significance for resource conservation in future industrial development. Currently, there is no effective solution. Therefore, how to remove the ceramic coating on the metal substrate to achieve the recycling of the metal substrate is the key problem to be solved currently.

[0004] CN106346146B discloses a high-energy short-pulse laser processing method for removing ceramic coatings on metal surfaces. The method includes the following steps: (1) In a vacuum environment or a nitrogen protection atmosphere, a circular overlapping method with a large-diameter focused light spot irradiation is used to quickly remove the ceramic coating in a large area; (2) A circular overlapping method with a small-diameter focused light spot irradiation is used to accurately remove the remaining small-area ceramic coating.

[0005] CN104858792A discloses a method for quickly removing thermal spray coatings. The abrasive material for sandblasting uses alloy sand with a particle size of 0.5 - 5.0 mm, special-shaped alloy sand with an aspect ratio of 1.0 - 5.0, and ceramic sand with a mesh size of 10 - 50. The mass ratio of the three raw materials of the alloy sand, special-shaped alloy sand, and ceramic sand is (1 - 4):(1 - 4):1; before sandblasting, the three raw materials are first evenly poured into an iron bucket at the same time to facilitate the mixing between the raw materials, and then the mixed sand in the iron bucket is poured into a sand tank for sandblasting. The air source pressure for sandblasting is 0.5 - 0.9 MPa.

[0006] CN105792951A discloses a method for removing a ceramic thermal barrier coating system. Laser energy is applied to the thermal barrier coating system in the presence of a flux material to form a melt. When the energy is removed, the melt solidifies to form a layer of slag that adheres less tightly to the underlying metal substrate compared to the initial thermal barrier coating system. The slag is then broken up by a mechanical process such as sandblasting and released from the substrate. Sufficient energy can be applied to melt the entire depth of the coating system along with a thin layer of the substrate, thereby forming a refurbished surface on the substrate when it re-solidifies.

[0007] The above technical solutions all describe how to remove the ceramic coating on the surface of the metal substrate and have predictable good effects on the plate-shaped metal substrate coated with the ceramic coating. However, firstly, the equipment and raw materials involved in the above solutions are relatively expensive, resulting in high costs, and the processes themselves are unfriendly to the environment; secondly, they are not applicable to the removal of ceramic coatings on the surfaces of shaped processed parts. Summary of the Invention

[0008] To solve the above problems, the present invention provides a method for recycling a metal substrate covered with a ceramic coating. This method has a wide range of applications, reduces damage to the substrate before and after processing, and provides a new design idea for the recycling and secondary utilization of metal substrates.

[0009] To achieve the above object, the present invention provides a method for recycling a metal workpiece covered with a ceramic coating, including the following steps:

[0010] S1. Ultrasonically decontaminate the metal workpiece with a ceramic coating.

[0011] S2. Primary oxidation: Subject the ultrasonically decontaminated metal workpiece to primary oxidation to obtain metal workpiece A1, and then perform primary water quenching treatment to obtain metal workpiece A2.

[0012] S3. Secondary oxidation: Subject metal workpiece A2 to secondary oxidation to obtain metal workpiece B1, and then perform secondary water quenching treatment to obtain metal workpiece B2.

[0013] S4. Induction heating: Subject metal workpiece B2 to induction heating to obtain metal workpiece C1, and then perform tertiary water quenching treatment to obtain metal workpiece C2.

[0014] S5. Sandblast metal workpiece C2 to obtain metal workpiece D1.

[0015] S6. Cold straighten metal workpiece D1 to obtain the recycled metal workpiece.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. The method of the present invention uses two high-temperature oxidations, induction heating combined with three water quenches, which can significantly improve the defects of the ceramic coating and reduce the bonding strength between the ceramic and the substrate, facilitating the removal of the ceramic coating from the metal substrate.

[0018] 2. After removing the ceramic coating, the damage to the substrate can be minimized as much as possible, and the overall loss to the substrate is 10 - 500 μm.

[0019] 3. The method provided by the present invention is suitable for the recycling of metal workpieces of any shape and size, with a wide application range.

[0020] 4. The method provided by the present invention realizes the reuse of metal workpieces, has the advantages of simple process, low production cost, high production efficiency, no secondary pollution and waste, and is conducive to cost control in industrial production. The equipment used in the present invention are all common equipment, with low equipment cost, high operability of the process, small operation difficulty, and play a crucial role in the industrial promotion of metal recycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a cross-sectional view of the metal workpiece in the present invention;

[0022] Figure 2 is the effect diagram of the substrate processed by the method of Example 1;

[0023] Figure 3 is the effect diagram of the substrate processed by the method of Example 2;

[0024] Figure 4 is the effect diagram of the substrate processed by the method of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0025] The endpoints and any values disclosed herein are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values and individual point values of each range, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0026] The present invention provides a method for recycling metal workpieces covered with ceramic coatings, including the following steps:

[0027] S1. Ultrasonically decontaminate the metal workpiece with a ceramic coating;

[0028] S2. Primary oxidation: Subject the ultrasonically decontaminated metal workpiece to primary oxidation to obtain metal workpiece A1, and then perform primary water quench treatment to obtain metal workpiece A2;

[0029] S3. Secondary oxidation: The metal workpiece A2 is subjected to secondary oxidation to obtain the metal workpiece B1, and then subjected to secondary water quenching treatment to obtain the metal workpiece B2;

[0030] S4. Induction heating: The metal workpiece B2 is subjected to induction heating to obtain the metal workpiece C1, and then subjected to three - time water quenching treatment to obtain the metal workpiece C2;

[0031] S5. The metal workpiece C2 is subjected to sandblasting treatment to obtain the metal workpiece D1;

[0032] S6. The metal workpiece D1 is subjected to cold straightening to obtain the recycled metal workpiece.

[0033] In the present invention, ultrasonic decontamination can remove the stains on the surface of the metal workpiece, improving the efficiency of subsequent processing. In the step S1, the conditions of ultrasonic decontamination are: the ultrasonic medium is anhydrous ethanol, the ultrasonic frequency is 0.5 - 1.5 KHz, and the ultrasonic time is 20 - 40 min.

[0034] In the present invention, the primary water quenching can increase the defect rate of the ceramic coating, laying a foundation for sufficient oxidation in the secondary oxidation; this requires ensuring the temperature difference from high temperature to low temperature during primary water quenching and the effectiveness of primary water quenching, that is, the rationality of the heating temperature and the timeliness of water quenching. Under preferred conditions, the conditions of the primary oxidation include: the oxidation temperature is 600 - 1200 °C, and the holding time is 30 - 60 min; the process of the primary water quenching treatment includes: putting the metal workpiece A1 obtained by primary oxidation into water and cooling it to room temperature (25 °C ± 5 °C).

[0035] According to the present invention, performing secondary water quenching after secondary oxidation can further increase the defect degree of the coating; under preferred conditions, the conditions of the secondary oxidation include: oxidizing in an air atmosphere, the oxidation temperature is 600 - 900 °C, and the holding time is 100 - 200 h. By subjecting the metal workpiece A2 to long - time secondary oxidation, the metal interface in contact with the ceramic coating undergoes oxidation to form an interface oxidation layer; by extending the temperature and time of secondary oxidation, the thickness of the interface oxidation layer can be increased, reducing the bonding strength between the ceramic coating and the metal substrate. However, if the temperature and / or time of secondary oxidation is too long, it will cause excessive oxidation of the metal substrate and an increase in the loss of the metal substrate; the process of the secondary water quenching treatment includes: putting the metal workpiece B1 obtained by secondary oxidation into water and cooling it to room temperature (25 °C ± 5 °C).

[0036] In the present invention, induction heating has the following characteristics: 1. It can rapidly heat and cool the metal substrate; 2. Induction heating has no heating effect on the ceramic coating. Induction heating of the metal workpiece B2 can increase the thermal expansion difference between the metal substrate and the ceramic coating, thereby increasing the defect rate of the metal workpiece C1 after three times of water quenching, further reducing the bonding strength between the ceramic coating and the metal substrate, and causing part of the ceramic coating to peel off from the metal substrate; Under preferred conditions, the conditions of the induction heating are: the heating current is 70 - 250 A, the heating temperature is 800 - 1200 °C, and the heating time is 5 - 15 s. The process of the three - time water quenching treatment includes: putting the metal workpiece C1 obtained by induction heating into water and cooling it to room temperature (25 °C ± 5 °C).

[0037] In the present invention, one - time induction heating or multiple - time induction heating can be carried out according to the size and shape of the metal workpiece. For example, for a regularly shaped metal plate, one - time induction heating can be used; for a metal workpiece with a special - shaped structure, multiple - time induction heating can be used to reduce the temperature difference inside the workpiece.

[0038] According to the present invention, the primary water quenching treatment, the secondary water quenching treatment, and the three - time water quenching treatment are all to put the heated substrate into an aqueous solution and cool it to 20 - 30 °C. The purpose of using multiple - time water quenching treatment is to increase the degree of defects caused by rapid cooling of the ceramic coating, making it easier for air to enter the coating to achieve the purpose of oxidizing the substrate. In some alternative embodiments of the present invention, the water quenching treatment only provides a cooling medium to enable the metal workpiece to rapidly cool from a high - temperature condition. Therefore, the present invention does not have a special limitation on the type of the cooling medium, which can be known to those skilled in the art. For example, the primary water quenching treatment, the secondary water quenching treatment, and the three - time water quenching treatment can also be replaced with oil quenching treatment.

[0039] In the present invention, in order to increase the removal rate of the ceramic coating, at least one of the steps S2 to S4 can be appropriately repeated according to the type and thickness of the ceramic coating. For example, the steps S2 to S4 can be repeated 2 - 4 times, or the step S4 can be repeated 2 - 4 times.

[0040] According to the present invention, the ceramic coating can be completely peeled off from the substrate through sandblasting treatment. To ensure that the ceramic on the surface of the metal substrate can be completely (or basically completely) removed in the sandblasting process, good sandblasting pressure and effective reduction of the bonding force between the coating and the substrate during the pre - oxidation and water quenching processes need to be grasped. Since there are certain gaps between the ceramic coating and the metal substrate after multiple pre - heating and water quenching treatments, oblique sandblasting is more likely to expand these gaps and cause the ceramic to peel off. Under preferred conditions, the conditions of the sandblasting treatment are: the sandblasting pressure is 5 - 10 MPa, the sandblasting angle is 30 - 60 °, and the sandblasting method is bidirectional (forward and reverse).

[0041] In the present invention, preferably, during the clamping process before sandblasting, a stainless steel plate is padded at the bottom of the metal substrate to avoid substrate deformation caused by sandblasting.

[0042] To ensure that the substrate can be effectively corrected finally, according to the different usage channels of the substrate, cold correction or hot correction can be selected here, and cold correction is preferably used. The conditions for cold correction are: the cold correction pressure is 10 - 30 MPa, and the pressure holding time is 5 - 30 min.

[0043] In the present invention, the types of the ceramic coating can be known to those skilled in the art, including but not limited to at least one of oxide ceramic coatings, nitride ceramic coatings, carbide ceramic coatings, boride ceramic coatings, silicide ceramic coatings, fluoride ceramic coatings, and sulfide ceramic coatings; in the present invention, an oxide ceramic coating is preferably used, and the oxide ceramic coating includes but not limited to ceramic coatings with perovskite, spinel, hexaaluminate, or cordierite structures.

[0044] The method provided in the present invention is suitable for removing ceramic coatings of various thicknesses. Exemplarily, the thickness of the ceramic coating is 10 - 500 μm.

[0045] It should be noted that in actual applications, according to different application scenarios, the surface of the ceramic coating may also be coated with other metal coatings, such as a silver plating layer, but the presence of the silver plating layer does not have too much impact on the removal rate of the ceramic coating.

[0046] The metal substrate described in the present invention is an iron-containing alloy, and its types can be known to those skilled in the art, including but not limited to stainless steel.

[0047] The method provided by the present invention is applicable not only to plate-shaped metal workpieces (i.e., metal plates), but also to shaped metal workpieces, such as metal rings, metal columns, and crankshafts, etc.

[0048] The present invention improves the utilization rate and reusability of metal materials. On the premise of ensuring the minimum damage to the substrate, the ceramic coating on the surface of the metal substrate is peeled off from the substrate without affecting the secondary use of the metal substrate. On the basis of ensuring the performance of the substrate, the present invention enables the metal substrate to have a longer service life, reduces the production cost of enterprises, and improves the effective utilization rate of resources.

[0049] The following further illustrates the present invention through examples. The metal workpiece is a SUS430 stainless steel substrate coated with a La 0.8 Sr 0.2 MnO3 ceramic coating, and its metallographic diagram is as Figure 1 shown. As can be seen from Figure 1 , the thickness of the ceramic coating on the surface of the metal workpiece is about 100 μm;

[0050] Removal rate test method: Use the area test software Image pro to measure the total number of pixels of the ceramic coating in the metal workpiece, which represents the area S of the ceramic coating;

[0051] Among them, the coating area S1 of the original untreated sample is the average value of the coating areas S1' of 10 untreated samples, and the coating area S2 of the treated sample is the average value of the coating areas S2' of 10 treated samples;

[0052] The calculation formula for the removal rate ψ of the coating on the sample surface is as follows:

[0053] Loss amount test method: Measure the initial thickness d1 of the stainless steel substrate and the thickness d2 of the treated stainless steel substrate through metallographic diagrams, and the loss amount Δd = d1 - d2.

[0054] Example 1

[0055] A method for recycling metal workpieces covered with ceramic coatings includes the following steps:

[0056] S1. Ultrasonic the metal workpiece in absolute ethanol for 20 minutes, and the ultrasonic frequency is 0.5 KHz;

[0057] S2. Primary oxidation: Put the ultrasonically decontaminated sample into a muffle furnace for primary oxidation, keep it at 600 °C for 30 minutes to obtain metal workpiece A1;

[0058] Primary water quenching: After taking out metal workpiece A1 from the muffle furnace, quickly immerse it in water (25 ± 5 °C) until the whole sample cools to room temperature and take it out to obtain metal workpiece A2, and its metallographic diagram is as Figure 2 shown in (a);

[0059] S3. Secondary oxidation: Put metal workpiece A2 into a muffle furnace for secondary oxidation in an air atmosphere, keep it at 600 °C for 100 hours to obtain metal workpiece B1;

[0060] Secondary water quenching: After taking out metal workpiece B1 from the muffle furnace, quickly immerse it in water (25 ± 5 °C) until the whole sample cools to room temperature and take it out to obtain metal workpiece B2, and its metallographic diagram is as Figure 2 shown in (b);

[0061] S4. Induction heating: Induction heat metal workpiece B2, with a heating current of 120 A, a heating temperature of 800 °C, and a heating time of 5 s to obtain metal workpiece C1;

[0062] Tertiary water quenching: Quickly immerse metal workpiece C1 in water (25 ± 5 °C) until the whole sample cools to room temperature and take it out to obtain metal workpiece C2, and its metallographic diagram is as Figure 2as shown in (c);

[0063] S5. Sandblast the metal workpiece C2 with a sandblasting pressure of 5 MPa, a sandblasting angle of 30°, and a bidirectional sandblasting method (forward and reverse). During the clamping process before sandblasting, a thick stainless steel plate is placed under the sample to prevent the substrate from deforming due to sandblasting, obtaining the metal workpiece D1. Its metallographic diagram is as Figure 2 shown in (d);

[0064] S6. Cold correct the metal workpiece D1 with a pressure of 10 MPa and a pressure holding time of 5 min to obtain the recycled metal workpiece. The relevant experimental parameters and experimental results in this embodiment are shown in Table 1.

[0065] From Figure 2 Figure (a), it can be seen that the defect degree of the ceramic coating is significantly increased after the first water quenching, and obvious dot-like and linear defects appear in the ceramic coating; from Figure 2 Figure (b), it can be seen that after the secondary oxidation and secondary water quenching, an oxide layer appears at the cross-section of the ceramic coating and the substrate, and there is an obvious "separation" phenomenon between the ceramic coating and the substrate, and the defects of the ceramic coating are further deepened; from Figure 2 Figure (c), it can be seen that when the ceramic coating undergoes induction heating and three times of water quenching, the ceramic coating shows "splitting"; from Figure 2 Figure (d), it can be seen that after the sandblasting treatment, the ceramic coating is basically removed from the substrate.

[0066] Example 2

[0067] A method for recycling a metal workpiece covered with a ceramic coating, comprising the following steps:

[0068] S1. Ultrasonic clean the metal workpiece in absolute ethanol for 30 min with an ultrasonic frequency of 1 kHz;

[0069] S2. Primary oxidation: Put the ultrasonically decontaminated sample into a muffle furnace for primary oxidation, keep it at 1000 °C for 40 min to obtain the metal workpiece A1;

[0070] Primary water quenching: Take out the metal workpiece A1 from the muffle furnace and quickly immerse it in water (25 ± 5 °C) until the whole sample cools to room temperature and then take it out to obtain the metal workpiece A2. Its metallographic diagram is as Figure 3 shown in (a);

[0071] S3. Secondary oxidation: Put the metal workpiece A2 into a muffle furnace for secondary oxidation in an air atmosphere, keep it at 700 °C for 150 h to obtain the metal workpiece B1;

[0072] Secondary water quenching: Take out the metal workpiece B1 from the muffle furnace and quickly immerse it in water (25 ± 5 °C) until the whole sample cools to room temperature and then take it out to obtain the metal workpiece B2. Its metallographic diagram is as Figure 3as shown in (b);

[0073] S4. Induction heating: Induction heat the metal workpiece B2 with a heating current of 120 A, a heating temperature of 900 °C, and a heating time of 8 s to obtain the metal workpiece C1;

[0074] Three - time water quenching: Quickly immerse the metal workpiece C1 in water (25 ± 5 °C) until the whole sample cools to room temperature and then take it out to obtain the metal workpiece C2, and its metallographic diagram is as shown in Figure 3 (c);

[0075] S5. Sandblasting the metal workpiece C2 with a sandblasting pressure of 8 MPa, a sandblasting angle of 50°, and a sandblasting method of forward and reverse two - way. During the clamping process before sandblasting, a thick stainless - steel plate is placed under the sample to avoid substrate deformation caused by sandblasting, and the metal workpiece D1 is obtained, and its metallographic diagram is as shown in Figure 3 (d);

[0076] S6. Cold - straightening the metal workpiece D1 with a pressure of 20 MPa and a pressure - holding time of 20 min to obtain the recycled metal workpiece; The relevant experimental parameters and experimental results in this embodiment are shown in Table 1.

[0077] From Figure 3 It can be seen from (a) to 3(d) that the process of removing the ceramic coating from the substrate is basically the same as that in Example 1. However, because the primary heating temperature, secondary oxidation heating temperature, and tertiary induction heating temperature in this embodiment are all higher than those in Example 1, the removal rate of the ceramic coating in this embodiment is higher than that in Example 1.

[0078] Example 3

[0079] A method for recycling a metal workpiece covered with a ceramic coating, comprising the following steps:

[0080] S1. Ultrasonic the metal workpiece in absolute ethanol for 40 min with an ultrasonic frequency of 1.5 KHz;

[0081] S2. Primary oxidation: Put the ultrasonically decontaminated sample into a muffle furnace for primary oxidation, keep it at 1000 °C for 60 min to obtain the metal workpiece A1;

[0082] Primary water quenching: After taking out the metal workpiece A1 from the muffle furnace, quickly immerse it in water (25 ± 5 °C) until the whole sample cools to room temperature and then take it out to obtain the metal workpiece A2, and its metallographic diagram is as shown in Figure 4 (a);

[0083] S3. Secondary oxidation: Put the metal workpiece A2 into a muffle furnace for secondary oxidation in an air atmosphere, keep it at 800 °C for 200 h to obtain the metal workpiece B1;

[0084] Secondary water quenching: After taking out the metal workpiece B1 from the muffle furnace, it is quickly immersed in water (25 ± 5 °C) until the whole sample is cooled to room temperature and taken out, obtaining the metal workpiece B2, and its metallographic diagram is as shown in Figure 4 Figure (b);

[0085] S4. Induction heating: The metal workpiece B2 is subjected to induction heating with a heating current of 120 A, a heating temperature of 1000 °C, and a heating time of 10 s, obtaining the metal workpiece C1;

[0086] Tertiary water quenching: The metal workpiece C1 is quickly immersed in water (25 ± 5 °C) until the whole sample is cooled to room temperature and taken out, obtaining the metal workpiece C2, and its metallographic diagram is as shown in Figure 4 Figure (c);

[0087] S5. Sandblasting treatment is carried out on the metal workpiece C2 with a sandblasting pressure of 10 MPa, a sandblasting angle of 60°, and a sandblasting method of forward and reverse two-way. During the clamping process before sandblasting, a thick stainless steel plate is placed at the bottom of the sample to avoid substrate deformation caused by sandblasting, obtaining the metal workpiece D1, and its metallographic diagram is as shown in Figure 4 Figure (d);

[0088] S6. Cold straightening is carried out on the metal workpiece D1 with a pressure of 30 MPa and a pressure holding time of 30 min to obtain the recycled metal workpiece; The relevant experimental parameters and experimental results in this embodiment are shown in Table 1.

[0089] From Figure 4 Figures (a) to (d), it can be seen that the process of removing the coating from the substrate is basically the same as that in Example 1. However, because the primary heating temperature, secondary oxidation heating temperature, and tertiary induction heating temperature in this example are all higher than those in Examples 1 and 2, the coating removal rate in this example is also better than that in Examples 1 and 2.

[0090] Examples 4 - 8 and Comparative Examples 1 - 6

[0091] According to the method of Example 2, the difference is that the specific process conditions are shown in Table 1.

[0092] Table 1

[0093] Primary oxidation Secondary oxidation Induction heating Removal rate, % Loss amount, μm Example 1 600 °C, 30 min 600℃,100h 120 A, 800 °C, 5 s 88% 49 Example 2 1000 °C, 40 min 700℃,150h 120 A, 900 °C, 8 s 93% 63 Example 3 1000 °C, 60 min 800℃,200h 120 A, 1000 °C, 10 s 95% 71 Example 4 800 °C, 40 min Same as Example 2 Same as Example 2 89% 52 Example 5 1200 °C, 40 min Same as Example 2 Same as Example 2 97% 74 Comparative Example 1 400 °C, 40 min Same as Example 2 Same as Example 2 72% 43 Comparative Example 2 None Same as Example 2 Same as Example 2 66% 44 Example 6 Same as Example 2 600，150h Same as Example 2 90% 53 Example 7 Same as Example 2 900℃,150h Same as Example 2 97% 126 Comparative Example 3 Same as Example 2 300℃,150h Same as Example 2 53% 22 Comparative Example 4 Same as Example 2 None Same as Example 2 41% 14 Example 8 Same as Example 2 Same as Example 2 120 A, 800 °C, 8 s 88% 52 Example 9 Same as Example 2 Same as Example 2 120 A, 1200 °C, 12 s 95% 90 Comparative Example 5 Same as Example 2 Same as Example 2 None 74% 36

[0094] It can be seen from Table 1 that

[0095] From the comparison between Examples 2, 4, 5 and Comparative Examples 1 - 2, it can be seen that as the primary oxidation temperature increases, the removal rate of the ceramic coating gradually increases. However, when the primary oxidation temperature reaches 1200 °C, the loss of the metal substrate increases, and the increase in the removal rate of the ceramic coating is not obvious.

[0096] It can be seen from the comparison of Examples 2, 6, 7 and Comparative Examples 3-4 that as the secondary oxidation temperature increases, the removal rate of the ceramic coating gradually increases. However, when the secondary oxidation temperature reaches 800 °C, the loss of the metal substrate increases, while the increase in the removal rate of the ceramic coating is not obvious.

[0097] It can be seen from the comparison of Examples 2, 8-9 and Comparative Example 5 that as the induction heating temperature increases, the removal rate of the ceramic coating gradually increases. However, when the induction temperature reaches 1200 °C, the loss of the metal substrate increases, while the increase in the removal rate of the ceramic coating is not obvious.

[0098] Examples 10-12

[0099] According to the method of Example 2, the difference is that the sandblasting angle is as shown in Table 2.

[0100] Table 2

[0101] Sandblasting Removal rate, % Loss amount, μm Example 2 8 MPa, 50 ° 93% 63 Example 10 8 MPa, 30 ° 96% 87 Example 11 8 MPa, 60 ° 83% 54 Example 12 8 MPa, 90 ° 79% 24

[0102] It can be seen from Table 2 that the sandblasting angle has an obvious influence on the removal rate of the ceramic on the substrate surface. The lower the inclination angle of the sandblasting, the higher the removal rate of the ceramic. And the loss of the substrate is related to the removal rate of the surface ceramic. Due to the barrier of the ceramic, even if the sandblasting angle becomes larger, the loss rate of the substrate is not very obvious.

[0103] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for recycling a metal workpiece covered with a ceramic coating, characterized in that, It includes the following steps: S1. Ultrasonically decontaminate the metal workpiece with a ceramic coating; S2. Primary oxidation: Subject the ultrasonically decontaminated metal workpiece to primary oxidation to obtain metal workpiece A1, and then perform primary water quenching treatment to obtain metal workpiece A2; S3. Secondary oxidation: Subject metal workpiece A2 to secondary oxidation to obtain metal workpiece B1, and then perform secondary water quenching treatment to obtain metal workpiece B2; S4. Induction heating: Subject metal workpiece B2 to induction heating to obtain metal workpiece C1, and then perform tertiary water quenching treatment to obtain metal workpiece C2; S5. Sandblast metal workpiece C2 to obtain metal workpiece D1; S6. Cold straighten metal workpiece D1 to obtain the recycled metal workpiece; The primary water quenching treatment, secondary water quenching treatment, and tertiary water quenching treatment are all to cool the heated metal workpiece in an aqueous solution to 20 - 30 °C; The conditions for the primary oxidation include: oxidation temperature of 600 - 1200 °C and holding time of 30 - 60 min; The conditions for the secondary oxidation include: oxidation temperature of 600 - 900 °C and holding time of 100 - 200 h; The conditions for the induction heating include: heating current of 70 - 250 A, heating temperature of 800 - 1200 °C, and heating time of 5 - 15 s; Any one of steps S2 to S4 is repeated once or multiple times; or Steps S2 to S4 as a whole are repeated once or multiple times; The conditions for the sandblasting treatment include: sandblasting pressure of 5 - 10 MPa and sandblasting angle of 30 - 60°; The conditions for the cold straightening include: cold straightening pressure of 10 - 30 MPa and pressure holding time of 5 - 30 min.

2. The method according to claim 1, characterized in that The ceramic coating is selected from at least one of oxide ceramic coatings, nitride ceramic coatings, carbide ceramic coatings, boride ceramic coatings, silicide ceramic coatings, fluoride ceramic coatings, and sulfide ceramic coatings.

3. The method according to claim 1, wherein The thickness of the ceramic coating is 10 - 500 μm.

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