Preparation method of ultra-thick hard alloy

Abstract

The invention discloses a preparation method of an ultra-coarse hard alloy, which comprises the following steps: carrying out ball milling on coarse-particle tungsten carbide powder with the Fisher particle size of 20-30 [mu] m and the HCP value of 3.5-4.0 KA / m and cobalt powder according to the ball-to-material ratio; 1.5: 1-2: 1; the ball milling time is 5-10 hours; a grinding body used for ball milling is a rod-shaped alloy with the diameter phi of 5.5-10.5 mm, and alloy rods with different sizes are adopted; after ball milling, the mixture is subjected to compression molding, and the ultra-coarse hard alloy is obtained after sintering; according to the method, a conventional hard alloy method is adopted, the steps are simple, the ball milling time is short, special treatment on WC is not needed, a prefabricated mixture is not needed, new equipment does not need to be investment, and the manufacturing cost is low. The combined rods with different sizes are added as grinding bodies, so that the cobalt powder and the WC powder can be uniformly dispersed in a short time, and the common problems of cobalt aggregation and non-uniform WC grain distribution in the domestic ultra-thick hard alloy are effectively solved.

Description

Technical Field

[0001] The invention belongs to the technical field of powder metallurgy, and in particular relates to a method for preparing 5-7μm ultra-coarse WC-Co cemented carbide. Background Art

[0002] Ultra-coarse grained cemented carbide refers to a cemented carbide with an average grain size of WC greater than 3.5 microns. Under the same cobalt content, ultra-coarse grained alloys have higher fracture toughness, impact toughness and thermal conductivity than traditional medium and coarse grained alloys, and have better resistance to thermal fatigue and thermal shock. Therefore, in applications where thermal fatigue and thermoplastic transformation are the main wear modes and there are also high impact loads, such as road milling tools, rotary drilling and tunneling tools, coal cutting tools and other types of "soft rock" cutting tools, ultra-coarse grained cemented carbide has the best performance. At present, the main technologies for preparing ultra-coarse cemented carbide are: using flexible ball milling technology, using WC treated by special methods as raw materials, adding nano powder or ultra-fine WC powder during the preparation process, cobalt coating technology, prefabricated mixtures and other methods. The above methods have their own advantages and disadvantages: flexible ball milling technology uses a low ball-to-material ratio. Due to the small amount of grinding body, WC agglomerates and cobalt powder agglomerates have a certain probability of not being ground, resulting in cobalt agglomerates or WC agglomerates remaining in the alloy. The addition of nanometer powder or ultrafine WC powder and prefabricated mixture in the preparation process is cumbersome and increases production costs. Cobalt coating technology and the use of WC treated by special methods as raw materials require increased equipment investment. Summary of the invention

[0003] In view of the shortcomings of the above-mentioned existing process technology, the present invention provides a method for preparing ultra-coarse cemented carbide, which has simple steps, short ball milling time, no need for special treatment of WC, no need for prefabricated mixed materials, no need for investment in new equipment, and low manufacturing cost. Compared with the traditional use of a single alloy rod as a grinding body, adding combined rods of different sizes as a grinding body can make cobalt powder and WC powder dispersed evenly in a short time, effectively solving the problems of cobalt aggregation and uneven distribution of WC grains commonly found in domestic ultra-coarse cemented carbide.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is:

[0005] Four or five or more alloy rods of different sizes (diameter Φ*length L, unit: mm) are used as grinding bodies, and the alloy rods are combined in different proportions; general ultra-coarse WC (HCP value 3.5-4.0KA / m) is used as raw material; and the ball-to-material ratio is 1.5:1-2:1. The ball-to-material ratio is the ratio of the mass of the grinding body to the mass of the raw materials of tungsten carbide and cobalt powder. The ball milling is carried out for a short time of 5-10 hours, and the ball milled material paddle is spray-dried to obtain a mixed material, which is then pressed into shape, and sintered at a pressure of 4-6MPa and a temperature of 1450-1550°C to obtain an ultra-coarse-grained cemented carbide with an average particle size of 5-7μm.

[0006] The sizes of the alloy rods of different sizes (diameter Φ*length L, unit: mm) are mainly the following categories: 5.5*14.0, 7.3*15.6, 8.6*16.3, 9.5*16.7, 10.5*17.

[0007] Preferably, the combination ratio of alloy rods of different sizes is 5%-15% for alloy rods of 5.5*14.0mm; 15%-20% for alloy rods of 7.3*15.6mm; 25%-30% for alloy rods of 8.6*16.3mm; 25%-35% for alloy rods of 9.5*16.7mm; 0%-30% for alloy rods of 10.5*17mm. Preferably, the ball-to-material ratio is 1.5:1-2:1, and the ball milling time is 5-10 hours.

[0008] Preferably, the WC raw material is a coarse particle tungsten carbide powder of 20-30 microns, the carbon content of the tungsten carbide powder is above 6.10%, the tungsten carbide powder has high crystal integrity, coarse sub-grain size, small microscopic strain, and few structural defects. The HCP value of tungsten carbide is 3.5-4.0KA / m.

[0009] Preferably, the sintering temperature of the low-pressure sintering furnace is 1480-1550° C., the high-temperature holding pressure is 5-6 MPa, and the holding time is 60-90 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The technical solution will be described clearly and completely below in conjunction with the accompanying drawings. It is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments.

[0011] Figure 1 This is a 200-fold metallographic photograph of the ultra-coarse-grained cemented carbide prepared in Example 1;

[0012] Figure 2 This is a 50x metallographic photograph of the ultra-coarse grain cemented carbide prepared in Comparative Example 2;

[0013] Figure 3This is a 200-fold metallographic photograph of the ultra-coarse-grained cemented carbide prepared in Example 2;

[0014] Figure 4 This is a 200-fold metallographic photograph of the ultra-coarse-grained cemented carbide prepared in Control Example 2.

[0015] Figure 5 This is a 200-fold metallographic photograph of the ultra-coarse-grained cemented carbide prepared in Example 3;

[0016] Figure 6 This is a 200-fold metallographic photograph of the ultra-coarse-grained cemented carbide prepared in Control Example 3. DETAILED DESCRIPTION

[0017] The above contents of the invention are further described in detail below in conjunction with the specific implementation methods of the embodiments. However, this should not be understood as the scope of the above subject matter of the invention being limited to the following examples. Various substitutions or changes made according to common technical knowledge and customary means in the art without departing from the above technical ideas of the invention should be included in the scope of the invention.

[0018] In the following embodiments, the WC raw material used is a coarse particle tungsten carbide powder of 20-30 microns, the combined carbon content in the tungsten carbide powder is above 6.10%, and the HCP value of the tungsten carbide is 3.5-4.0KA / m.

[0019] Example 1

[0020] This embodiment provides a method for preparing an ultra-coarse-grained cemented carbide, comprising the following steps:

[0021] Step 1: Take 5.5*14.0mm alloy rods, accounting for 10%; take 7.3*15.6mm alloy rods, accounting for 15%; take 8.6*16.3mm alloy rods, accounting for 30%; take 9.5*16.7mm alloy rods, accounting for 30%; take 10.5*17mm alloy rods, accounting for 15%; combine them into the required grinding body. As shown in Table 2.

[0022] Step 2: Mix the grinding body of step 1 with 94% coarse-grained tungsten carbide powder and 6% cobalt powder in a weight ratio of 1.5:1 and place in a ball mill. Add a molding agent accounting for 2% of the total weight of the raw materials and a ball milling medium with a material-liquid ratio of 5.5kg / L. After wet grinding for 5 hours, spray dry the slurry to obtain a mixture, and then press the mixture to obtain a compact. Finally, keep the compact at 6.0MPa and 1550℃ for 90 minutes and sinter to obtain an ultra-coarse-grained cemented carbide. The metallographic test results are shown in Table 1. The metallographic photos are shown in Figure 1 .

[0023] Comparative Example 1

[0024] Step 1: Take a 10.5*17mm alloy rod, which accounts for 100% of the required grinding body.

[0025] Step 2: Mix the grinding body of step 1 with 94% coarse-grained tungsten carbide powder and 6% cobalt powder in a weight ratio of 1.0:1 and place in a ball mill. Add a molding agent accounting for 2% of the total weight of the raw materials and a ball milling medium with a material-liquid ratio of 5.5kg / L. After wet grinding for 5 hours, spray dry the slurry to obtain a mixture, and then press the mixture to obtain a compact. Finally, keep the compact at 6.0MPa and 1550℃ for 90 minutes and sinter to obtain an ultra-coarse-grained cemented carbide. The metallographic test results are shown in Table 1. The metallographic photos are as follows Figure 2 .

[0026] Example 2

[0027] This embodiment provides a method for preparing an ultra-coarse-grained cemented carbide, comprising the following steps:

[0028] Step 1: Take 5.5*14.0mm alloy rods, accounting for 15%; take 7.3*15.6mm alloy rods, accounting for 20%; take 8.6*16.3mm alloy rods, accounting for 30%; take 9.5*16.7mm alloy rods, accounting for 25%; take 10.5*17mm alloy rods, accounting for 10%; combine them into the required grinding body. As shown in Table 2.

[0029] Step 2: Mix the grinding body of step 1 with 92% coarse-grained tungsten carbide powder and 8% cobalt powder in a weight ratio of 1.7:1 and place in a ball mill. Add a molding agent accounting for 2% of the total weight of the raw materials and a ball milling medium with a material-liquid ratio of 4.5kg / L. After wet grinding for 7 hours, spray dry the slurry to obtain a mixture, and then press the mixture to obtain a compact. Finally, keep the compact at 5.6MPa and 1520℃ for 60 minutes and sinter to obtain an ultra-coarse-grained cemented carbide. The metallographic test results are shown in Table 1. Metallographic photos are shown in Figure 3 .

[0030] Comparative Example 2

[0031] Step 1: Take a 10.5*17mm alloy rod, which accounts for 100% of the required grinding body.

[0032] Step 2: Mix the grinding body of step 1 with 92% coarse-grained tungsten carbide powder and 8% cobalt powder in a weight ratio of 1.2:1 and place in a ball mill. Add a molding agent accounting for 2% of the total weight of the raw materials and a ball milling medium with a material-liquid ratio of 4.5kg / L. After wet grinding for 10 hours, spray dry the slurry to obtain a mixture, and then press the mixture to obtain a compact. Finally, keep the compact at 5.6MPa and 1520℃ for 60 minutes and sinter to obtain an ultra-coarse-grained cemented carbide. The metallographic test results are shown in Table 1. Metallographic photos are shown in Figure 4 .

[0033] Example 3

[0034] This embodiment provides a method for preparing an ultra-coarse-grained cemented carbide, comprising the following steps:

[0035] Step 1: Take 5.5*14.0mm alloy rods, accounting for 15%; take 7.3*15.6mm alloy rods, accounting for 25%; take 8.6*16.3mm alloy rods, accounting for 30%; take 9.5*16.7mm alloy rods, accounting for 40%; combine them into the required grinding body, as shown in Table 2.

[0036] Step 2: Mix the grinding body of step 1 with 93% coarse-grained tungsten carbide powder and 7% cobalt powder in a weight ratio of 2:1 and place in a ball mill. Add a molding agent accounting for 20% of the total weight of the raw materials and a ball milling medium with a material-liquid ratio of 3.5 kg / L. After wet grinding for 10 hours, spray dry the slurry to obtain a mixture, and then press the mixture to obtain a compact. Finally, keep the compact at 5 MPa and 1480°C for 80 minutes and sinter to obtain an ultra-coarse-grained cemented carbide. The metallographic test results are shown in Table 1. The metallographic photos are shown in Table 1. Figure 5 .

[0037] Comparative Example 3

[0038] Step 1: Take a 10.5*17mm alloy rod, which accounts for 100% of the required grinding body.

[0039] Step 2: Mix the grinding body of step 1 with 93% coarse-grained tungsten carbide powder and 7% cobalt powder in a weight ratio of 1.5:1 and place in a ball mill. Add a molding agent accounting for 20% of the total weight of the raw materials and a ball milling medium with a material-liquid ratio of 3.5kg / L. After wet grinding for 12 hours, spray dry the slurry to obtain a mixture, and then press the mixture to obtain a compact. Finally, keep the compact at 5MPa and 1480℃ for 80 minutes and sinter to obtain an ultra-coarse-grained cemented carbide. The metallographic test results are shown in Table 1. The metallographic photos are as follows Figure 6 .

[0040] Table 1 Metallographic detection of examples and control examples

[0041] Case Number Unetched 100 times Cobalt phase distribution Grain size um (intercept method) Example 1 A02B00C00 ---- 7.96 Comparative Example 1 A02B04C04 Cobalt Pool 8.21 Example 2 A02B00C00 ---- 7.20 Comparative Example 2 A02B00C00 ---- 7.21 Example 3 A02B00C00 ---- 5.71 Comparative Example 3 A02B00C00 ---- 5.64

[0042] Table 2 Size ratio of grinding bodies

[0043]

[0044] As can be seen from Table 1, the average particle size of the ultra-coarse grained alloys obtained in Examples 1 to 3 is similar to that of the comparative alloy. Figures 1 to 6 It can be seen that compared with the ultra-coarse-grained alloy obtained by grinding only a single alloy rod in the conventional method, the cobalt phase (the black part in the photo, i.e., the place where the cobalt phase is corroded) and WC grain distribution of Examples 2 to 3 are more uniform; Example 1 can disperse the cobalt powder in a short time, avoiding defects such as cobalt pools and holes in the alloy.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing an ultra-coarse cemented carbide, characterized in that: The steps include: (1) Ingredients: tungsten carbide powder and cobalt powder are mixed according to the mass composition ratio: the tungsten carbide powder has a Fisher particle size of 20 μm to 30 μm and a HCP value of 3.5-4.0 KA / m; (2) Ball milling and drying: The material of step (1) is loaded into a ball mill for ball milling. The grinding body used for ball milling is a rod-shaped alloy with a diameter and length of 5.5*14.0 mm, 7.3*15.6 mm, 8.6*16.3 mm, 9.5*16.7 mm, and 10.5*17 mm. The alloy rod of 5.5*14.0 accounts for 5%-15%; the alloy rod of 7.3*15.6 accounts for 15%-20%; the alloy rod of 8.6*16.3 accounts for 25%-30%; the alloy rod of 9.5*16.7 accounts for 25%-35%; the alloy rod of 10.5*17 accounts for 0%-30%; the ball-to-material ratio is 1.5:1-2:1; the ball milling time is 5-10 h; after ball milling, the mixed powder is obtained by drying; (3) Pressing and forming; (4) Pressure sintering: After sintering, ultra-coarse-grained cemented carbide is obtained; the sintering process is: sintering temperature 1480°C to 1550°C, holding time 60-90 minutes, and pressure 5-6MPa.

2. The method according to claim 1, characterized in that The mass percentage of the cobalt powder in step (1) is 6%-8%, and the remainder is tungsten carbide powder.

3. The method according to claim 1, characterized in that In the step (2), the ball milling medium is hexane, and the material-to-ethane ratio is 3.5-5.5 kg / L.

4. The method according to claim 2, characterized in that In the step (1), the mass composition of tungsten carbide powder and cobalt powder is 94% tungsten carbide powder and 6% cobalt powder; the content of combined carbon in the tungsten carbide powder is above 6.10%; In the step (2), the material-liquid ratio of the material to ethane is 5.5 kg / L, the ball-to-material ratio is 1.5:1, and the ball milling time is 5 h; the grinding body combination is as follows: take 5.5*14.0 mm alloy rods, accounting for 10%; take 7.3*15.6 mm alloy rods, accounting for 15%; take 8.6*16.3 mm alloy rods, accounting for 30%; take 9.5*16.7 mm alloy rods, accounting for 30%; take 10.5*17 mm alloy rods, accounting for 15%; In the step (4), the sintering process is as follows: sintering temperature 1550° C., holding time 90 minutes, and pressure 6 MPa.

5. The method according to claim 2, characterized in that In the step (1), the mass composition of tungsten carbide powder and cobalt powder is 92% tungsten carbide powder and 8% cobalt powder; the content of combined carbon in the tungsten carbide powder is above 6.10%; In the step (2), the material-to-ethane ratio is 5.5 kg / L, the ball-to-material ratio is 1.7:1, and the ball milling time is 7 hours; the grinding body combination is as follows: take 5.5*14.0 mm alloy rods, accounting for 15%; take 7.3*15.6 mm alloy rods, accounting for 20%; take 8.6*16.3 mm alloy rods, accounting for 30%; take 9.5*16.7 mm alloy rods, accounting for 25%; take 10.5*17 mm alloy rods, accounting for 10%; In the step (4), the sintering process is as follows: sintering temperature 1520° C., holding time 60 minutes, and pressure 5.6 MPa.

6. The method according to claim 2, characterized in that In the step (1), the mass composition of tungsten carbide powder and cobalt powder is 94% tungsten carbide powder and 6% cobalt powder; the content of combined carbon in the tungsten carbide powder is above 6.10%; In the step (2), the material-liquid ratio of the material to ethane is 5.5 kg / L, the ball-to-material ratio is 1.3:1, and the ball milling time is 20 h; the grinding body combination is as follows: take 5.5*14.0 mm alloy rods, accounting for 15%; take 7.3*15.6 mm alloy rods, accounting for 25%; take 8.6*16.3 mm alloy rods, accounting for 30%; take 9.5*16.7 mm alloy rods, accounting for 40%; In the step (4), the sintering process is as follows: sintering temperature 1480° C., holding time 80 minutes, and pressure 5 MPa.

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