A WC-Co cemented carbide composite post-treatment strengthening method

Abstract

The present invention belongs to the technical field of cemented carbide and discloses a WC-Co cemented carbide composite post-treatment strengthening method. The method is applicable to WC-Co cemented carbide prepared by powder metallurgy with a binder phase Co content of 5% to 20% and a WC grain size of 0.1μm to 5μm. The composite post-treatment strengthening process comprises one or more composite group treatments consisting of cryogenic treatment and pulsed electric field treatment. The method can significantly increase the martensitic transformation degree of the binder phase Co in the cemented carbide, reduce the internal residual stress of the cemented carbide, and improve the strength, hardness, fracture toughness and wear resistance of the cemented carbide. The method is particularly suitable for the rapid strengthening of cemented carbide products. The present invention has a reasonable design, a simple and controllable post-treatment process, a low production cost, and can be produced and applied on a large scale in an industrialized manner.

Description

Technical Field

[0001] The invention relates to the technical field of cemented carbide, and in particular to a WC-Co cemented carbide composite post-processing strengthening method. Background Art

[0002] WC-Co cemented carbide (WC-Co cemented carbide) is the simplest and most widely used cemented carbide. It is a multiphase material composed of refractory metal carbide (WC) and a binder metal (Co) produced using powder metallurgy. Due to its high strength, hardness, and excellent wear resistance, WC-Co cemented carbide is widely used in metal cutting tools, hot rolling rolls, and oil and mining drilling tools. Although WC-Co cemented carbide exhibits excellent overall performance, its primary failure cause remains wear and fracture caused by stress under high temperatures and extreme operating conditions. Cemented carbide modification techniques, such as microstructure refinement, sintering process optimization, and surface strengthening, have become the mainstream approach to improving the service life of WC-Co cemented carbide. However, these improvements still have drawbacks, including the high cost and complexity of equipment and the difficulty in preparing new cemented carbide materials, which have hindered the development and application of WC-Co cemented carbide. Furthermore, the widespread application of difficult-to-machine materials has placed higher demands on the performance, environmental friendliness, and sustainable manufacturing capabilities of cemented carbide. Previous methods often involve considerable cost and time investment, hindering sustainable manufacturing.

[0003] In recent years, clean and environmentally friendly post-processing strengthening methods have gradually become the mainstream way to strengthen WC-Co cemented carbide. Common post-processing strengthening methods include cryogenic treatment, heat treatment, pulsed magnetic field treatment, and electromagnetic coupling treatment. After the post-processing strengthening process, the mechanical properties, wear resistance, and corrosion resistance of cemented carbide have been improved to a certain extent. This is mainly due to the martensitic transformation of α-Co to ε-Co, the precipitation of carbides such as Co3W3C, and the evolution of residual stress during the post-processing process. However, the degree of martensitic transformation of the bonding phase Co, the precipitation of carbides, and the evolution of residual stress in a single post-processing strengthening process is relatively limited, and can no longer meet the needs of further strengthening cemented carbide and improving the service life of cemented carbide. Summary of the Invention

[0004] The present invention aims to overcome the limitations of single post-treatment strengthening on the strengthening of WC-Co cemented carbide and proposes a composite post-treatment strengthening process combining cryogenic treatment and pulsed electric field treatment. After multiple combined treatments of cryogenic treatment and pulsed electric field treatment, the composite post-treatment strengthening process can significantly improve the martensitic transformation degree of the binder phase Co in the WC-Co cemented carbide, reduce the internal residual stress of the cemented carbide, and improve the strength and wear resistance of the cemented carbide. The composite post-treatment strengthening process is particularly suitable for the rapid strengthening of various WC-Co cemented carbide products.

[0005] The technical solution of the present invention is as follows: a WC-Co cemented carbide composite post-treatment strengthening method, wherein the WC-Co cemented carbide is prepared by a powder metallurgy method, and the Co content of the binder phase is 5% to 20%, and the WC grain size is 0.1μm to 5μm; the composite post-treatment strengthening method is composed of a combination of deep cryogenic treatment and pulsed electric field treatment.

[0006] The cryogenic treatment and pulse electric field treatment are carried out sequentially, and the two form a composite group treatment, and the composite group is one or more groups; when the composite group is multiple groups, the temperature of the cryogenic treatment is sequentially reduced, and the pulse current and pulse frequency of the pulse electric field treatment are sequentially increased.

[0007] When the composite group consists of two groups, the following steps are followed:

[0008] Step 1: cryogenic treatment: cryogenically treat the WC-Co cemented carbide prepared by powder metallurgy, and then restore it to room temperature in air after a period of cryogenic treatment;

[0009] Step 2: One-time pulse electric field treatment: Connect electrodes at both ends of the WC-Co cemented carbide recovered to room temperature obtained in step 1, apply pulse current through a pulse power supply, and recover to room temperature in an air environment after the pulse electric field treatment;

[0010] Step 3: Secondary cryogenic treatment: The WC-Co cemented carbide obtained in step 2 is cryogenically treated again and then returned to room temperature;

[0011] Step 4: Secondary pulse electric field treatment: Connect electrodes at both ends of the WC-Co cemented carbide after secondary cryogenic treatment obtained in step 3, apply pulse current through a pulse power supply, and after a period of treatment, restore to room temperature in an air environment.

[0012] The step 1 specifically includes: placing the WC-Co cemented carbide in a liquid nitrogen cryogenic box, controlling the cryogenic temperature at -130 to -80°C, the cooling rate at 35 to 75°C / h, and the holding time at 12 to 24 hours; and returning to room temperature in the air after the holding period.

[0013] The second step specifically includes: connecting the two ends of the WC-Co cemented carbide obtained in the first step and restored to room temperature to positive and negative electrodes, applying a pulse current through a pulse power supply, the pulse current is 70 to 120A, the pulse frequency is 0.1 to 1Hz, and the pulse electric field treatment time is 10 to 30 minutes; after the pulse electric field treatment, the mixture is restored to room temperature in the air.

[0014] The step three specifically includes: placing the WC-Co cemented carbide obtained in step two and restored to room temperature into a liquid nitrogen cryogenic box, controlling the cryogenic temperature at -196 to -130°C, the cooling rate at 35 to 75°C / h, and the holding time at 24 to 48 hours; and returning to room temperature in the air after the holding period.

[0015] The fourth step specifically includes: connecting the two ends of the WC-Co cemented carbide restored to room temperature obtained in the third step to positive and negative electrodes, applying a pulse current through a pulse power supply, the current size is 200 to 500A, the pulse frequency is 1 to 100Hz, and the pulse electric field treatment time is 10 to 30 minutes; after the pulse electric field treatment is completed, the mixture is restored to room temperature in the air.

[0016] The beneficial effects of the present invention are as follows: the present invention realizes for the first time the strengthening of WC-Co cemented carbide by a composite post-treatment process of cryogenic treatment and pulsed electric field. Through the combined action of cryogenic treatment and pulsed electric field, while reducing the residual stress inside the alloy, the martensitic transformation content of the bonding phase Co in the alloy is increased, thereby enhancing the strength of the cemented carbide and significantly improving the hardness, fracture toughness, wear resistance and other related properties of the cemented carbide.

[0017] The composite post-processing strengthening process is a composite strengthening process that combines cryogenic treatment and pulsed electric field to provide an economical, efficient, green, environmentally friendly, highly applicable, and easy industrial production. The strengthening process does not make special requirements on cemented carbide workpieces and is suitable for rapid strengthening of workpieces of various sizes and complex structures. It solves the problems of the existing post-processing strengthening process, such as the lack of obvious strengthening effect, long strengthening cycle, and high cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The residual stresses in the X and Y directions after the two groups of composite post-treatment strengthening processes are adopted in Example 2.

[0019] Figure 2 The residual stresses in the X and Y directions after single cryogenic strengthening in comparative example 3 are shown.

[0020] Figure 3 The residual stress in the X and Y directions after strengthening by single pulse electric field treatment in comparative example 4. DETAILED DESCRIPTION

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The embodiments of the present invention are intended to enable those skilled in the art to better understand the present invention and are not intended to limit the present invention in any way. The workflow and working principle of the present invention will be further described below using a preferred embodiment of the present invention.

[0022] Example 1: WC-10Co ultrafine-grained cemented carbide composite post-treatment strengthening

[0023] Step 1: Preparation of WC-10Co Ultrafine-Grained Cemented Carbide: This experiment uses powder metallurgy to prepare ultrafine-grained cemented carbide with a binder phase Co content of 10% and a WC grain size of 0.3 microns. The carbide is 20 mm long and 10 mm wide, respectively, and 5 mm thick.

[0024] Step 2: cryogenic treatment of WC-10Co ultrafine-grained cemented carbide: Place the WC-10Co ultrafine-grained cemented carbide prepared in step 1 in a liquid nitrogen cryogenic box for cryogenic treatment, set the cooling rate to 40°C / h, the treatment temperature to -80°C, the treatment time to 12 hours, and then return to room temperature in an air environment.

[0025] Step 3: One-time pulse electric field treatment of WC-10Co ultrafine-grained cemented carbide: Connect the positive and negative electrodes at both ends of the WC-10Co ultrafine-grained cemented carbide restored to room temperature obtained in step 2, apply a pulse current through a pulse power supply, the current is 70A, the pulse frequency is 1Hz, the pulse electric field treatment time is 30 minutes, and then return to room temperature in air.

[0026] Comparative Example 1:

[0027] The difference between this comparative example and Example 1 is that the WC-10Co ultrafine-grained cemented carbide obtained in step 1 is subjected to only one cryogenic treatment in step 2, and no pulse electric field treatment is performed.

[0028] Comparative Example 2:

[0029] The difference between this comparative example and Example 1 is that the WC-10Co ultrafine-grained cemented carbide obtained in step 1 is subjected to only one pulse electric field treatment in step 3, without undergoing cryogenic treatment.

[0030] Example 2: WC-10Co ultrafine-grained cemented carbide two-group composite post-treatment strengthening

[0031] Step 1: Preparation of WC-10Co Ultrafine-Grained Cemented Carbide: This experiment uses powder metallurgy to prepare ultrafine-grained cemented carbide with a binder phase Co content of 10% and a WC grain size of 0.3 microns. The carbide is 20 mm long and 10 mm wide, respectively, and 5 mm thick.

[0032] Step 2: cryogenic treatment of WC-10Co ultrafine-grained cemented carbide: Place the WC-10Co ultrafine-grained cemented carbide prepared in step 1 in a liquid nitrogen cryogenic box for cryogenic treatment, set the cooling rate to 40°C / h, the treatment temperature to -80°C, the treatment time to 12 hours, and then return to room temperature in an air environment.

[0033] Step 3: One-time pulse electric field treatment of WC-10Co ultrafine-grained cemented carbide: Connect the positive and negative electrodes at both ends of the WC-10Co ultrafine-grained cemented carbide restored to room temperature obtained in step 2, apply a pulse current through a pulse power supply, the current is 70A, the pulse frequency is 1Hz, the pulse electric field treatment time is 30 minutes, and then return to room temperature in air.

[0034] Step 4: Secondary cryogenic treatment of WC-10Co ultrafine-grained cemented carbide: The WC-10Co ultrafine-grained cemented carbide obtained in step 3 and restored to room temperature is placed in a liquid nitrogen cryogenic box, the cryogenic temperature is controlled at -196°C, the cooling rate is 75°C / h, and the holding time is 24 hours; after the holding period, it is restored to room temperature in air.

[0035] Step 5: Secondary pulse electric field treatment of WC-10Co ultrafine-grained cemented carbide: Connect the positive and negative electrodes at both ends of the WC-10Co ultrafine-grained cemented carbide sample that has been restored to room temperature obtained in step 4, and apply a pulse current of 200A and a pulse frequency of 100Hz through a pulse power supply. The pulse electric field treatment time is 30 minutes. After the pulse electric field treatment, the sample is restored to room temperature in air. Figure 1 shown.

[0036] Comparative Example 3:

[0037] The difference between this comparative example and Example 2 is that the WC-10Co ultrafine-grained cemented carbide obtained in step 1 of Example 2 is subjected to only the first cryogenic treatment in step 2 and the second cryogenic treatment in step 4 of Example 2, without pulsed electric field treatment.

[0038] Comparative Example 4:

[0039] The difference between this comparative example and Example 2 is that the WC-10Co ultrafine-grained cemented carbide obtained in step 1 of Example 2 is only subjected to the single pulse electric field treatment in step 3 of Example 2 and the secondary pulse electric field treatment in step 5 of Example 2, without deep cryogenic treatment.

[0040] Comparative Example 5:

[0041] The difference between this comparative example and Example 2 is that the secondary cryogenic treatment temperature in step 4 is controlled at -50°C, which is higher than the primary cryogenic treatment temperature in step 2.

[0042] Comparative Example 6:

[0043] The difference between this comparative example and Example 2 is that the pulse current and pulse frequency in the secondary pulse electric field treatment in step five are 50 A and 0.5 Hz, respectively, which are lower than the pulse current and pulse frequency parameters of the primary pulse electric field treatment in step three.

[0044] The hardness and fracture toughness of Example 1 and Comparative Example 1, Comparative Example 2, Example 2 and Comparative Example 3, Comparative Example 4, Comparative Example 5 and Comparative Example 6 are shown in Table 1 below.

[0045] Table 1 Hardness and fracture toughness data of Example 1 and Comparative Example 1, Comparative Example 2, Example 2 and Comparative Example 3, Comparative Example 4, Comparative Example 5 and Comparative Example 6

[0046]

[0047] The contents of the α-Co phase and the ε-Co phase and the corresponding ratios according to Example 2, Comparative Examples 3 and 4 are shown in Table 2 below.

[0048] Table 2 The contents of α-Co phase and ε-Co phase and the corresponding ratio data of Example 2, Comparative Example 3 and Comparative Example 4

[0049]

[0050] The experimental data of Table 1 show that after implementing the WC-Co cemented carbide composite post-treatment strengthening process (one or two groups) of the present invention, the hardness and fracture toughness of the cemented carbide are improved to varying degrees compared to single cryogenic treatment strengthening (Comparative Example 1, Comparative Example 3) and single pulse electric field treatment strengthening (Comparative Example 2, Comparative Example 4). Among them, the maximum improvement of the hardness and fracture toughness of the WC-Co cemented carbide after one group of composite post-treatment strengthening is 6.14% and 18.65% respectively; the maximum improvement of the hardness and fracture toughness of the WC-Co cemented carbide after two groups of composite post-treatment strengthening is 11.37% and 27.24% respectively. This shows that the cemented carbide post-treatment strengthening process of the present invention is effective and significantly improves the overall mechanical properties of the WC-Co cemented carbide. In addition, the results of Example 1, Example 2, Comparative Example 5 and Comparative Example 6 in Table 1 show that when the composite group is multiple groups, the temperature of the cryogenic treatment is successively reduced, and the pulse current and pulse frequency of the pulse electric field treatment are successively increased, the strengthening effect is best.

[0051] When the composite group is two groups, it can be seen from the experimental data in Table 2 that after implementing the two groups of the WC-Co cemented carbide composite post-treatment strengthening process, the ε-Co phase content is significantly improved, and the ratio of the ε-Co phase to the α-Co phase is significantly increased compared with the single cryogenic treatment strengthening WC-Co cemented carbide (Comparative Example 3) and the single pulse electric field treatment strengthening WC-Co cemented carbide (Comparative Example 4). Combined with the accompanying drawings, the WC-Co cemented carbide composite post-treatment strengthening process of the present invention can increase the ε-Co phase content in the WC-Co cemented carbide and reduce the internal residual stress, which is the main reason for achieving WC-Co cemented carbide.

[0052] Although the composite post-treatment strengthening process of ultrafine-grained WC-10Co cemented carbide applicable to the present invention is described above with reference to the accompanying drawings, the present invention is not limited to the above-mentioned cemented carbide system, and is also applicable to cemented carbides with other WC grain sizes and Co contents.

[0053] Although the present invention has been described above, the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many variations without departing from the purpose of the present invention, and these are all protected by the present invention.

Claims

1. A WC-Co cemented carbide composite post-treatment strengthening method, characterized in that: The WC-Co cemented carbide is prepared by a powder metallurgy method, and the Co content of the binder phase is 5% to 20%, and the WC grain size is 0.1μm to 5μm; the composite post-treatment strengthening method is composed of a combination of cryogenic treatment and pulse electric field treatment; the cryogenic treatment and pulse electric field treatment are carried out sequentially, and the two form a composite group, and the composite group is one or more groups; when the composite group is multiple groups, the temperature of the cryogenic treatment is sequentially reduced, and the pulse current and pulse frequency of the pulse electric field treatment are sequentially increased.

2. A WC-Co cemented carbide composite post-treatment strengthening method according to claim 1, characterized in that: When the composite group consists of two groups, the following steps are followed: Step 1: cryogenic treatment: cryogenically treat the WC-Co cemented carbide prepared by powder metallurgy, and then restore it to room temperature in air after a period of cryogenic treatment; Step 2: One-time pulse electric field treatment: Connect electrodes at both ends of the WC-Co cemented carbide recovered to room temperature obtained in step 1, apply pulse current through a pulse power supply, and recover to room temperature in an air environment after the pulse electric field treatment; Step 3: Secondary cryogenic treatment: The WC-Co cemented carbide obtained in step 2 is cryogenically treated again and then returned to room temperature; Step 4: Secondary pulse electric field treatment: Connect electrodes at both ends of the WC-Co cemented carbide after secondary cryogenic treatment obtained in step 3, apply pulse current through a pulse power supply, and after a period of treatment, restore to room temperature in an air environment.

3. A WC-Co cemented carbide composite post-treatment strengthening method according to claim 2, characterized in that: The step 1 specifically includes: placing the WC-Co cemented carbide in a liquid nitrogen cryogenic box, controlling the cryogenic temperature at -130 to -80°C, the cooling rate at 35 to 75°C / h, and the holding time at 12 to 24 hours; and returning to room temperature in the air after the holding period.

4. A WC-Co cemented carbide composite post-treatment strengthening method according to claim 2, characterized in that: The second step specifically includes: connecting the two ends of the WC-Co cemented carbide obtained in the first step and restored to room temperature to positive and negative electrodes, applying a pulse current through a pulse power supply, the pulse current is 70 to 120A, the pulse frequency is 0.1 to 1Hz, and the pulse electric field treatment time is 10 to 30 minutes; after the pulse electric field treatment, the mixture is restored to room temperature in the air.

5. A WC-Co cemented carbide composite post-treatment strengthening method according to claim 2, characterized in that: The step three specifically includes: placing the WC-Co cemented carbide obtained in step two and restored to room temperature into a liquid nitrogen cryogenic box, controlling the cryogenic temperature at -196 to -130°C, the cooling rate at 35 to 75°C / h, and the holding time at 24 to 48 hours; and returning to room temperature in the air after the holding period.

6. A WC-Co cemented carbide composite post-treatment strengthening method according to claim 2, characterized in that: The fourth step specifically includes: connecting the two ends of the WC-Co cemented carbide restored to room temperature obtained in the third step to positive and negative electrodes, applying a pulse current through a pulse power supply, the current size is 200 to 500A, the pulse frequency is 1 to 100Hz, and the pulse electric field treatment time is 10 to 30 minutes; after the pulse electric field treatment is completed, the mixture is restored to room temperature in the air.

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