Cr12MoV cold work die steel repairing method based on laser cladding technology and application of Cr12MoV cold work die steel repairing method

Abstract

The invention provides a Cr12MoV cold work die steel repairing method based on a laser cladding technology and application of the Cr12MoV cold work die steel repairing method. Ultrasonic-assisted laser cladding is adopted, and a Ni60 / WC ceramic metal composite coating is formed; the mixed powder material for laser cladding comprises the following components in percentage by weight: 10 to 25 percent of WC ceramic powder, 0.2 to 1 percent of Zr powder, 0.2 to 1 percent of La2O3 rare earth powder and the balance of Ni60 alloy powder. According to the Cr12MoV cold work die steel repairing method based on the laser cladding technology and the application, the ultrasonic-assisted laser cladding technology is adopted, a cladding coating which is few or free of pore cracks, compact in structure and small in grain size is obtained, the compactness and uniformity of the coating are improved, the quality of the coating can be effectively improved while the operation technology is simplified, and the service life of the coating is prolonged. And the microstructure and the macroscopic performance of the coating are optimized, and the coating can be suitable for repairing the surface of the Cr12MoV cold roller.

Description

Technical Field

[0001] The present invention relates to the technical field of laser repair, and more particularly, to a repair method and application of Cr12MoV cold work die steel based on laser cladding technology. Background Art

[0002] Cr12MoV is used as a cold work die material because of its excellent hardenability and quenching penetration, and high economic efficiency. The service environment of Cr12MoV dies is harsh, the surface bears cyclic alternating loads, stress concentration occurs in local areas, and surface failure phenomena such as wear and shedding, fracture and chipping are prone to occur, and then they are scrapped. Therefore, it is necessary to repair these failed surfaces to extend the service life and reduce costs.

[0003] Laser repair technology is a processing method that uses a laser beam to heat and melt the metal surface, and uses the liquid phase formed by the molten pool to melt and deposit metal powder on the surface to repair surface defects and damages. Laser repair technology has the advantages of high efficiency, precision, low cost, non-destructive, and small heat input. The main factors affecting the cladding layer in laser repair technology are the cladding powder and process parameters, which can affect the surface quality and mechanical properties of the cladding layer.

[0004] Patent CN110565087A discloses a laser cladding synthesized ceramic phase reinforced cobalt-based cladding layer and its preparation method. The technical solution steps adopted in the present invention are as follows: (1) Substrate pretreatment: Remove rust from the surface of the processed Cr12MoV steel substrate, and polish it with a angle grinder to obtain a flat and smooth surface; (2) Preparation of alloy composite powder: The alloy composite powder is uniformly mixed in proportion. The alloy composite powder is composed of cobalt-based alloy powder, B4C powder, Cr3C2 powder and binder, and its mass composition is: 86-87% cobalt-based alloy powder, 6-8% B4C powder, 1-2% Cr3C2 powder, 4-5% binder; First, mix 86-87% by mass of 200-230 mesh cobalt-based alloy powder, 6-8% by mass of 260-280 mesh B4C powder and 1-2% by mass of 260-280 mesh Cr3C2 powder evenly in a ball mill for 2-3 hours, then add 4-5% by mass of binder and continue to mix for 1-1.5 hours to prepare the alloy composite powder; (3) Laser cladding: Adopt the pre-placed powder method, apply the prepared alloy composite powder on the surface of the Cr12MoV steel substrate, let it dry naturally, and then carry out laser cladding under argon protection. The cladding material reacts to generate ceramic hard phases during the laser cladding process. In the alloy composite powder of this invention technology, a binder needs to be added, and the powder is pre-placed on the surface of the steel substrate by using the binder method and then cladded. The operation process is complex; moreover, in the actual production process, the thickness of the pre-placed coating has a great influence on the forming quality of the coating. For complex curved surface workpieces, it is difficult to pre-place the coating, which is not conducive to automated production and cannot meet the actual working conditions of complex curved surfaces.

[0005] Gu Xuekun, Du Maohua, etc. Research on the effect of wide-band laser cladding Cr12MoV powder on the surface of rolling rolls [J]. Laser Journal, 2024, 45(9): 188 provides a repair method for Cr12MoV rolling rolls. This literature uses Cr12MoV powder as raw material and adopts laser cladding technology to repair the rolling rolls. Before cladding repair, the substrate is preheated at 200°C, and the average hardness of the coating is 677HV, reaching 96% of the performance of the rolling rolls. The pre-welding preheating step in this literature makes the process complicated, and the coating has low hardness and poor wear resistance.

[0006] In view of this, the present invention is specifically proposed. Summary of the Invention

[0007] The purpose of the present invention is to provide a repair method and application of Cr12MoV cold work die steel based on laser cladding technology in view of the deficiencies of the prior art. By using ultrasonic-assisted laser cladding technology, a cladding coating with few or no pores and cracks, dense structure and fine grains can be obtained, improving the density and uniformity of the coating. While simplifying the operation process, it can also effectively improve the quality of the coating, optimize the microstructure and macroscopic properties of the coating.

[0008] To achieve the above object of the present invention, the following technical solutions are specifically adopted:

[0009] A repair method of Cr12MoV cold work die steel based on laser cladding technology, which adopts ultrasonic-assisted laser cladding to form a Ni60 / WC ceramic-metal composite coating.

[0010] Furthermore, the mixed powder material for laser cladding includes: 10-25 wt.% of WC ceramic powder, 0.2-1 wt.% of Zr powder, 0.2-1 wt.% of La2O3 rare earth powder, and the balance is Ni60 alloy powder.

[0011] Furthermore, the laser cladding is coaxial powder feeding laser cladding, and the processing conditions are: semiconductor laser power 1800-2800 W, spot diameter 3-4 mm, scanning speed 20-30 mm / s, overlapping rate 30-50%, protective gas flow rate 10-15 L / min, alloy powder carrier gas flow rate 6-9 L / min.

[0012] Furthermore, after the laser cladding processing is completed, the workpiece is wrapped with heat preservation cotton until the workpiece cools naturally.

[0013] Furthermore, the protective gas is an inert gas.

[0014] Furthermore, the ultrasonic power is 600-1000 W, and the ultrasonic working frequency is 10-22 kHz.

[0015] Furthermore, the preparation method of the mixed powder material for laser cladding is: putting WC ceramic powder, Zr powder, La2O3 rare earth powder, and Ni60 alloy powder into a ball milling tank according to the mass ratio for mixing and vacuum drying.

[0016] Furthermore, the WC ceramic powder, the Zr powder, the La2O3 rare earth powder, and the Ni60 alloy powder are all spherical powders.

[0017] Furthermore, the particle size of the Ni60 alloy powder is 45-105 μm; the Ni60 alloy powder includes: 0.5-1 wt.% of C, 14-19 wt.% of Cr, 3.5-5 wt.% of Si, 3-4.5 wt.% of B, Fe < 8 wt.%, and the balance is Ni.

[0018] Furthermore, the particle size of the WC ceramic powder is 53-105 μm; the WC ceramic powder includes: 6.13 wt.% of C, 0.08 wt.% of O, 0.005 wt.% of Fe, and the balance is WC.

[0019] Further, the particle size of the Zr powder is 45 - 105 μm; the Zr powder includes: 0.005 wt.% O, and the balance is Zr.

[0020] Further, the particle size of the La2O3 rare earth powder is 100 - 500 nm; the La2O3 rare earth powder includes: 0.005 wt.% Fe2O3, and the balance is La2O3.

[0021] Application of the above repair method of Cr12MoV cold work die steel based on laser cladding technology in repairing the surface of Cr12MoV cold rolling rolls.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] 1. The present invention adopts an ultrasonic-assisted laser cladding technology to obtain a cladding coating with few or no pores and cracks, dense structure, and fine grains; while the laser cladding forms a coating, the ultrasonic vibration technology is introduced. The ultrasonic-assisted technology can promote the uniform mixing of materials during the cladding process through its unique acoustic streaming effect and cavitation effect, reduce defects, improve the density and uniformity of the coating, effectively improve the quality of the coating, and optimize the microstructure and macroscopic properties of the coating.

[0024] 2. The mixed powder material for laser cladding in the present invention adds WC, Zr, and La2O3 powders on the basis of Ni60 alloy powder. Through the ultrasonic field-assisted laser cladding technology, a cladding coating with good density is formed without the need to add a binder; the thermal expansion coefficient of Ni60 alloy is similar to that of Cr12MoV steel and is applicable to the repair of Cr12MoV cold work die steel. However, due to the high thermal brittleness of quenched Cr12MoV steel, the matrix cracking tendency is relatively large during laser cladding. The preheating method at 300 - 400 °C is often used during cladding repair to reduce stress, and the strength and hardness of a single Ni60 coating are relatively low and cannot meet the service performance of Cr12MoV cold work die steel. The present invention introduces WC, Zr, and La2O3 powders into the coating and repairs it by ultrasonic-assisted laser cladding, reducing the risk of cracking while improving the coating strength; the pre-welding preheating step is not required, the operation process is simplified, and the danger and resource waste caused by long-term preheating can also be avoided.

[0025] 3. The mixed powder material for laser cladding in the present invention does not require the addition of a binder. Through the dual action of Zr element and La2O3 powder, the precipitation of brittle phases such as M6C at grain boundaries is reduced, and the uniform distribution of WC in the coating is achieved under the assistance of the ultrasonic field, obtaining a nano-ceramic metal cladding coating with high hardness and high wear resistance.

[0026] 4. The ultrasonic vibration of the present invention affects the distribution of WC particles in the coating by generating acoustic radiation force and changing the fluid drag force. When the ultrasonic frequency is fixed, the acoustic radiation force increases with the increase of the ultrasonic amplitude. At the same time, the acoustic pressure gradient generated by the ultrasonic forces the melt pool to convect, increasing the flow velocity of the melt pool and ultimately increasing the drag force of the molten metal on WC. When no ultrasonic vibration is applied, the Maragoni flow (Marangoni convection) in the melt pool is slow, and the generated drag force and buoyancy cannot overcome the gravity of WC, resulting in the resultant force on the WC particles in the melt pool being downward, and finally depositing at the bottom of the melt pool. When ultrasonic vibration is applied, the WC particles generate an upward resultant force under the action of the acoustic radiation force and the drag force, obtaining an upward acceleration. With the increase of the ultrasonic amplitude, the WC can quickly change its movement direction in a short time after entering the melt pool, showing an upward trend, and finally showing a more uniform distribution state.

[0027] 5. The stirring effect of the ultrasonic vibration of the present invention results in a uniform distribution of solutes and temperature gradients in the melt pool. On the one hand, it homogenizes the distribution of γ-(Fe,Ni) solid solution and Fe3Ni2 near the nucleation points. On the other hand, it destroys the tendency of the microscopic grains of the coating to preferentially grow along the direction of the large temperature gradient under single laser cladding. In addition, due to the addition of La2O3 rare earth elements and the enhanced melt pool convection by ultrasonic vibration, the diffusion effect of W and C elements in the melt pool is stronger and the content is higher, forming more and more uniform hard phases. At the same time, it also promotes the reasonable distribution of WC particles in the whole area of the coating. The W and C elements generated by the melting of WC combine with other metal elements in the melt pool to form phases such as Fe3W3C, (Fe,Cr,Ni)C, Ni17W3, and W2C. The compounds formed by C and W elements as hard phases distributed in the melt pool can play a role in dispersion strengthening, which is crucial for improving various properties of the coating such as hardness and wear resistance.

[0028] 6. The added Zr atoms in the laser cladding coating of the present invention can fill vacancies and reduce the diffusion rate of elements at grain boundaries, thereby slowing down the climb of dislocations and strengthening the grain boundary bonding. At the same time, Zr atoms form a continuous and stable liquid film at the unit cell and grain boundaries, thereby realizing liquid backfill to relieve stress concentration. The Zr element can effectively reduce the precipitation of M6C carbides in grain boundaries, reducing the risk of coating cracking. And the Zr element forms Ni11Zr9 intermetallic compounds with Ni60 powder, which are pinned in the grain boundaries, forming a continuous skeleton structure, which is beneficial to improving the strength of the coating.

[0029] 7. The laser cladding of the present invention adopts a coaxial powder feeding laser cladding process, which has high degrees of freedom and automation and can be applied to the surface repair of complex curved workpieces.

[0030] 8. The repair method of the present invention can be applied to repair the surface of Cr12MoV cold-rolled rolls. The Cr12MoV steel used for cold-rolled rolls is in a quenched state, with high hardness and relatively large cracking strength. By using the repair method of the present invention, a crack-free and dense-structured coating can be effectively formed on the surface of high-hardness Cr12MoV steel. The average hardness of the coating reaches above 830HV, which is 1.3 times that of the roll, effectively improving the wear resistance of the roll and meeting the repair requirements of high-hardness rolls. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0032] Figure 1 Results of coating formation for Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0033] Figure 2 Results of microhardness measurement of coatings for Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0034] Figure 3 Results of wear measurement of coatings for Examples 1-3 and Comparative Examples 1-3 of the present invention;

[0035] Figure 4 Cross-sectional view of the coating of Example 1 of the present invention;

[0036] Figure 5 Comparison diagram of the microstructures of Example 1(a) and Comparative Example 1(b) of the present invention;

[0037] Figure 6 Comparison diagram of the morphologies at the bonding interface of the clad coatings of Comparative Example 3(a) and Example 1(b) of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the following described embodiments are some embodiments of the present invention, not all of them. They are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0039] Repair method of Cr12MoV cold work die steel based on laser cladding technology, using ultrasonic-assisted laser cladding to form a Ni60 / WC ceramic-metal composite coating;

[0040] Preferably, the mixed powder material for laser cladding includes: 10 - 25 wt.% of WC ceramic powder, including but not limited to 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, 16 wt.%, 17 wt.%, 18 wt.%, 19 wt.%, 20 wt.%, 21 wt.%, 22 wt.%, 23 wt.%, 24 wt.%, 25 wt.%, 0.2 - 1 wt.% of Zr powder, including but not limited to 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, 0.2 - 1 wt.% of La2O3 rare earth powder, including but not limited to 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, and the balance is Ni60 alloy powder;

[0041] Preferably, the laser cladding is coaxial powder feeding laser cladding, and the processing conditions are: semiconductor laser power 1800 - 2800 W, including but not limited to 1800 W, 1900 W, 2000 W, 2100 W, 2200 W, 2300 W, 2400 W, 2500 W, 2600 W, 2700 W, 2800 W, spot diameter 3 - 4 mm, including but not limited to 3 mm, 3.1 mm, 3.2 mm, 3.3 mm, 3.4 mm, 3.5 mm, 3.6 mm, 3.7 mm, 3.8 mm, 3.9 mm, 4 mm, scanning speed 20 - 30 mm / s, including but not limited to 20 mm / s, 21 mm / s, 22 mm / s, 23 mm / s, 24 mm / s, 25 mm / s, 26 mm / s, 27 mm / s, 28 mm / s, 29 mm / s, 30 mm / s, overlap rate 30 - 50%, including but not limited to 30%, 35%, 40%, 45%, 50%, alloy powder carrier gas flow rate 6 - 9 L / min, including but not limited to 6 L / min, 7 L / min, 8 L / min, 9 L / min, and protective gas flow rate 10 - 15 L / min, including but not limited to 10 L / min, 11 L / min, 12 L / min, 13 L / min, 14 L / min, 15 L / min;

[0042] Preferably, slow cooling treatment is carried out after laser cladding processing. After the laser cladding processing is completed, the workpiece is wrapped with heat preservation cotton until the workpiece cools naturally;

[0043] Preferably, the protective gas is an inert gas, preferably argon or nitrogen, and the laser cladding process is carried out under the protection of an inert gas atmosphere;

[0044] Preferably, the ultrasonic power is 600 - 1000 W, including but not limited to 600 W, 700 W, 800 W, 900 W, 1000 W, and the ultrasonic working frequency is 10 - 22 kHz, including but not limited to 10 kHz, 11 kHz, 12 kHz, 13 kHz, 14 kHz, 15 kHz, 16 kHz, 17 kHz, 18 kHz, 19 kHz, 20 kHz, 21 kHz, 22 kHz;

[0045] Preferably, the preparation method of the mixed powder material for laser cladding is as follows: WC ceramic powder, Zr powder, La2O3 rare earth powder, and Ni60 alloy powder are put into a ball milling tank according to the mass ratio and mixed for 2 - 3 h. After mixing, they are put into a vacuum drying oven and dried for 1 h;

[0046] Preferably, the WC ceramic powder, Zr powder, La2O3 rare earth powder, and Ni60 alloy powder are all spherical powders;

[0047] Preferably, the particle size of the Ni60 alloy powder is 45 - 105 μm, including but not limited to 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm; The Ni60 alloy powder includes: C 0.5 - 1 wt.%, Cr 14 - 19 wt.%, Si 3.5 - 5 wt.%, B 3 - 4.5 wt.%, Fe < 8 wt.%, and the balance is Ni;

[0048] Preferably, the particle size of the WC ceramic powder is 53 - 105 μm, including but not limited to 53 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm; The WC ceramic powder includes: C 6.13 wt.%, O 0.08 wt.%, Fe 0.005 wt.%, and the balance is WC;

[0049] Preferably, the particle size of the Zr powder is 45 - 105 μm, including but not limited to 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, 95 μm, 100 μm, 105 μm; The Zr powder includes: O 0.005 wt.%, and the balance is Zr;

[0050] Preferably, the particle size of the La2O3 rare earth powder is 100 - 500 nm, including but not limited to 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm; the La2O3 rare earth powder comprises: 0.005 wt.% of Fe2O3, and the balance is La2O3;

[0051] Application of the repair method of Cr12MoV cold work die steel based on laser cladding technology in repairing the surface of Cr12MoV cold rolling rolls.

[0052] Example 1

[0053] Weigh 90 g of Ni60 alloy powder with a particle size of 50 μm, 8.5 g of WC ceramic powder with a particle size of 53 μm, 1 g of Zr powder and 0.5 g of La2O3 rare earth powder, add them to a planetary ball mill and mix for 2 h, and then dry in a vacuum environment at 120 °C for 1 hour to obtain a mixed powder material for laser cladding.

[0054] Take a Cr12MoV steel alloy specimen with a specification of 40×40×20 mm. After rough grinding its surface with 180 - mesh metallographic sandpaper, clean it with acetone to remove oil stains, wipe it clean, then wipe it with alcohol and blow it dry to obtain a pretreated substrate material. The surface - treated Cr12MoV steel specimen is placed on the laser cladding workbench for use.

[0055] Adopt the co - axial powder feeding laser cladding method. Load the prepared alloy powder into the powder chamber of the laser cladding device, and adjust the laser cladding process parameters as follows: laser power 2500 W, spot diameter 3.5 mm, scanning speed 24 mm / s, overlapping rate 45%, carrier gas flow rate of alloy powder 9 L / min, protective gas flow rate 15 L / min. The power of the ultrasonic generator is 700 w, and the ultrasonic working frequency is controlled within the range of 10 - 22 kHz. Under the irradiation of laser energy, a coating metallurgically bonded to the substrate is formed on the surface of Cr12MoV steel.

[0056] Use a coloring penetrant flaw detector to conduct penetrant flaw detection on Example 1 to detect whether there are defects such as pores and cracks. Before coloring flaw detection, first clean the surface of the coating with alcohol, and then conduct penetrant flaw detection. The flaw detection results are as Figure 1 shown.

[0057] Use an HVS - 1000 type Vickers micro - hardness tester to measure the micro - hardness of the coating. Set the load of the micro - hardness tester to 300 g and the holding time to 15 s. Take points along the depth direction from the top of the coating layer, with the distance between each measurement point along the depth direction being 100 μm. Conduct 3 tests on the same horizontal line, with the lateral horizontal distance between the 3 test points being 100 μm, and take the average value of the 3 measurements as the average micro - hardness in this horizontal direction. The micro - hardness results are asFigure 2 as shown

[0058] The friction and wear experiments were carried out on an HT-1000 friction and wear testing machine. Si3N4 ceramic balls were selected as the friction pair. The motor speed was 500 r / min, the wear time was 30 min, the test load was 10 N, and the friction radius was 3 mm. The upper and lower planes of the specimen to be worn were smooth and parallel. Before the test, the specimens were ultrasonically cleaned. After the experiment, a MT-500 probe-type material surface scratch measuring instrument was used to measure the cross-sectional profile and wear volume of the surface of the specimen scratch. Measurements were taken at three different positions on the scratch, and then the average value was taken to obtain the wear amount of the specimen. The wear amount results are as Figure 3 as shown

[0059] The coating cross-section of Example 1 is as Figure 4 as shown

[0060] Example 2

[0061] Weigh 89 g of Ni60 alloy powder with a particle size of 75 μm, 10 g of WC powder with a particle size of 75 μm, 0.8 g of Zr powder with a particle size of 75 μm, and 0.7 g of rare earth powder La2O3 with a particle size of 100 nm, add them to a ball mill and mix for 2 h, and then dry them in a vacuum environment at 120 °C for 1 hour to obtain a mixed powder material for laser cladding. The Cr12MoV steel pretreated by the pretreatment method in Example 1 was used as the substrate, and the laser cladding process parameters were adjusted as follows: laser power 1800 W, spot diameter 3 mm, scanning speed 20 mm / s, overlapping rate 40%, alloy powder carrier gas flow rate 9 L / min, protective gas flow rate 15 L / min. The power of the ultrasonic generator was 600 w, and the ultrasonic working frequency was controlled within the range of 10 - 22 kHz. The mixed powder was cladded on the substrate surface.

[0062] According to the testing method of Example 1, the hardness and wear resistance of the cladding layer were detected. The coating flaw detection results are as Figure 1 as shown. The wear rate detection results are as Figure 3 as shown, and the microhardness is as Figure 2 as shown

[0063] Example 3

[0064] Weigh 84 g of Ni60 alloy powder with a particle size of 53 μm, 15 g of WC powder with a particle size of 53 μm, 0.5 g of Zr powder with a particle size of 75 μm, and 0.5 g of rare earth La2O3 powder with a particle size of 500 nm. Add them to a ball mill and mix for 2 h, then dry in a vacuum environment at 120 °C for 1 h to obtain the mixed powder for laser cladding. Use the Cr12MoV steel pretreated by the pretreatment method in Example 1 as the substrate, and adjust the laser cladding process parameters as follows: laser power 2800 W, spot diameter 4 mm, scanning speed 25 mm / s, overlapping rate 50%, carrier gas flow rate of alloy powder 9 L / min, shielding gas flow rate 15 L / min. The power of the ultrasonic generator is 800 w, and the ultrasonic working frequency is controlled within the range of 10 - 22 kHz. Clad the mixed powder on the substrate surface.

[0065] According to the testing method of Example 1, detect the hardness and wear resistance of the clad layer. The coating flaw detection results are as Figure 1 shown. The wear rate detection results are as Figure 3 shown, and the microhardness is as Figure 2 shown.

[0066] Comparative Example 1

[0067] Weigh 80 g of Ni60 alloy powder with a particle size of 75 μm and 20 g of WC powder with a particle size of 75 μm. Add them to a ball mill and mix for 2 h, then dry in a vacuum environment at 120 °C for 1 h to obtain the mixed powder for laser cladding. Use the Cr12MoV steel pretreated by the pretreatment method in Example 1 as the substrate, and clad the alloy powder on the substrate surface according to the laser cladding parameters and ultrasonic energy field conditions in Example 1.

[0068] According to the testing method of Example 1, perform penetrant flaw detection on the coating and detect the microhardness and wear resistance of the clad layer. The coating flaw detection results are as Figure 1 shown, and the comparison of the microstructures is as Figure 5 shown. It can be seen from the comparison of the microstructures between Comparative Example 1 and Example 1 that under the combined action of the cavitation effect and the acoustic streaming effect of ultrasonic waves in the clad layer of Example 1, the dendrites in the molten pool are broken, the grains are refined, and the crystallization of the molten pool is delayed; the added La2O3 powder reduces the high surface energy of WC particles, and together with the Zr powder, the cracking risk is reduced, and the tissue distribution is relatively uniform. The tissue distribution of Comparative Example 1 is relatively disordered. Due to the lack of addition of Zr powder, brittle phases precipitate at the grain boundaries, and the agglomeration of WC particles leads to through cracks at the WC particles; due to the agglomeration phenomenon and high surface energy of the added WC particles in the coating, the coating cracks during the cladding process. The cracking phenomenon of the coating in Comparative Example 1 is as Figure 1 shown.

[0069] The wear rate detection results of Comparative Example 1 are as Figure 3 shown, and the microhardness is asFigure 2 As shown, the wear resistance and microhardness of Comparative Example 1 are inferior to those of Example 1.

[0070] Comparative Example 2

[0071] Weigh 80 g of Ni60 alloy powder with a particle size of 75 μm and 20 g of WC powder with a particle size of 75 μm, add them to a ball mill and mix for 2 h, and then dry for 1 h in a vacuum environment at 120 °C to obtain the mixed powder for laser cladding. Use the Cr12MoV steel pretreated by the pretreatment method in Example 1 as the substrate, and according to the laser cladding parameter conditions of Example 1, the difference is that ultrasonic energy field assistance is not used, and the alloy powder is cladded on the surface of the substrate.

[0072] According to the testing method of Example 1, the coating was subjected to penetrant inspection and the microhardness and wear resistance of the cladding layer were detected. The inspection results of the coating are as Figure 1 shown. Compared with the structure of Example 1, serious cracking occurred in the coating of Comparative Example 2, and multiple transverse cracks appeared in the coating. The test results of the wear rate are as Figure 3 shown, and the microhardness is as Figure 2 shown. The wear resistance and microhardness of Comparative Example 2 are significantly inferior to those of Example 1. Since Zr metal powder and La2O3 rare earth powder were not added to the cladding powder in Comparative Example 2, the carbide distribution in the cladding layer was uneven, resulting in an increase in the crack sensitivity of the cladding layer. Moreover, without ultrasonic energy field assistance, WC particles settled and agglomerated, the plasticity and toughness of the cladding layer decreased, and the crack sensitivity further increased, thus promoting the initiation and propagation of cracks. The wear resistance and microhardness of Comparative Example 2 are significantly inferior to those of Comparative Example 1.

[0073] Comparative Example 3

[0074] The difference from the steps of Example 1 is only that: ultrasonic energy field assistance is not applied during the laser cladding process. According to the testing method of Example 1, the coating was subjected to penetrant inspection and the microhardness and wear resistance of the cladding layer were detected.

[0075] It can be seen from the test results that under the dual action of Zr element and La2O3 rare earth powder in Comparative Example 3, the high surface energy of WC particles was reduced, and the precipitation of brittle phases was reduced. No cracking occurred in the coating, as Figure 1 shown. As Figure 6As shown, in Example 1, due to the application of an ultrasonic energy field, the molten pool interface is non-linearly distributed; in Comparative Example 3, without the application of an ultrasonic energy field, the molten pool interface is linearly distributed; in Comparative Example 3, due to the lack of ultrasonic energy field assistance, a large number of WC particles aggregate in the middle and lower parts of the coating, and the ceramic reinforcing phase WC particles are unevenly distributed inside the coating. There is agglomeration of WC particles at the bottom of the coating. Since the density of WC powder is about twice that of Ni60 alloy powder, the WC particles are extremely prone to deposit towards the lower part of the coating and are unevenly distributed, resulting in the microhardness and room-temperature wear resistance of the upper part of the coating under the parameters of Comparative Example 3 being significantly inferior to those of Example 1.

Claims

1. Repair method for Cr12MoV cold work die steel based on laser cladding technology, characterized in that, Ultrasonic-assisted laser cladding is adopted to form a Ni60 / WC ceramic-metal composite coating.

2. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 1, characterized in that, The mixed powder material for laser cladding includes: 10 - 25 wt.% of WC ceramic powder, 0.2 - 1 wt.% of Zr powder, 0.2 - 1 wt.% of La2O3 rare earth powder, and the balance is Ni60 alloy powder.

3. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 1 or 2, characterized in that, The laser cladding is coaxial powder feeding laser cladding, and the processing conditions are: semiconductor laser power of 1800 - 2800 W, spot diameter of 3 - 4 mm, scanning speed of 20 - 30 mm / s, overlapping rate of 30 - 50%, carrier gas flow rate of alloy powder of 6 - 9 L / min, and protective gas flow rate of 10 - 15 L / min.

4. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 3, characterized in that, After the laser cladding processing is completed, the workpiece is wrapped with heat insulation cotton until it cools naturally.

5. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 3, characterized in that, The protective gas is an inert gas.

6. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 1 or 2, characterized in that, The ultrasonic power is 600 - 1000 W, and the ultrasonic working frequency is 10 - 22 kHz.

7. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 2, characterized in that, The preparation method of the mixed powder material for laser cladding is: putting the WC ceramic powder, Zr powder, La2O3 rare earth powder, and Ni60 alloy powder into a ball milling tank according to the mass ratio for mixing and vacuum drying.

8. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 2, characterized in that, The WC ceramic powder, the Zr powder, the La2O3 rare earth powder, and the Ni60 alloy powder are all spherical powders.

9. The repair method of Cr12MoV cold work die steel based on laser cladding technology according to claim 2 or 8, characterized in that, It includes at least one of the following technical features: (1) The particle size of the Ni60 alloy powder is 45 - 105 μm; The Ni60 alloy powder includes: 0.5 - 1 wt.% of C, 14 - 19 wt.% of Cr, 3.5 - 5 wt.% of Si, 3 - 4.5 wt.% of B, Fe < 8 wt.%, and the balance is Ni; (2) The particle size of the WC ceramic powder is 53 - 105 μm; the WC ceramic powder includes: 6.13 wt.% of C, 0.08 wt.% of O, 0.005 wt.% of Fe, and the balance is WC; (3) The particle size of the Zr powder is 45 - 105 μm; the Zr powder includes: 0.005 wt.% of O, and the balance is Zr; (4) The particle size of the La2O3 rare earth powder is 100 - 500 nm; the La2O3 rare earth powder includes: 0.005 wt.% of Fe2O3, and the balance is La2O3.

10. The application of the repair method of Cr12MoV cold work die steel based on laser cladding technology according to any one of claims 1 - 9 in repairing the surface of a Cr12MoV cold rolling roll.

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