Large hard alloy product and dewaxing and sintering integrated process thereof

Abstract

The invention provides a hard alloy large product and a dewaxing and sintering integrated process thereof. The dewaxing and sintering integrated process comprises the following steps that firstly, positive pressure dewaxing is conducted on a hard alloy formed compact under the pulse pressure, mixed gas containing hydrogen and nitrogen is continuously introduced, and a paraffin forming agent is removed at the temperature not higher than 400 DEG C; after the paraffin forming agent is removed, inert gas is introduced to remove hydrogen; after hydrogen removal is finished, vacuumizing is carried out for vacuum sintering; and after vacuum sintering is finished, partial pressure sintering and pressure sintering are sequentially carried out, and the hard alloy large product is obtained after cooling. According to the dewaxing and sintering integrated process provided by the invention, the paraffin forming agent in the hard alloy large product can be more efficiently and uniformly removed, and the technical problems of difficult dewaxing, large internal and external carbon content gradient and relatively high gas cost of the hard alloy large product in the existing preparation process are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of cemented carbide material production, and in particular relates to a large cemented carbide product and a wax removal and sintering integrated process thereof. Background Art

[0002] Large cemented carbide products are high-performance alloy materials made of refractory metals and bonding metals through powder metallurgy. This material is widely used in the industrial field due to its high hardness, wear resistance, strength, heat resistance and corrosion resistance. However, during the powder metallurgy production process, it is necessary to add molding agents such as paraffin for pressing and molding, and the molding agents need to be removed before sintering, otherwise it will seriously affect the quality of large cemented carbide products.

[0003] Based on this, the prior art discloses many technical solutions for removing the paraffin molding agent from large cemented carbide products. For example, one technical solution is to remove wax under constant high pressure and high temperature, but this method is prone to cause wax removal dead corners, resulting in large differences in the carbon content of the product at different positions, and the higher wax removal temperature is more risky for cemented carbide products produced by the paraffin process; another technical solution is to use high-flow hydrogen to flush during the wax removal process, but in practice, hydrogen flushes the product at high temperature, which is prone to decarburization on the product surface, and the carbon content is not easy to control.

[0004] Therefore, in the art, there is an urgent need to develop a method for removing the wax molding agent in large cemented carbide products more uniformly and efficiently, and being able to accurately control the carbon content of the large cemented carbide products. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a large cemented carbide product and an integrated wax removal and sintering process thereof, so that the paraffin molding agent in the large cemented carbide product can be removed more efficiently and more evenly, aiming to solve the technical problems of wax removal difficulty, large internal and external carbon content gradient and high gas cost in the existing preparation process of large cemented carbide products.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a dewaxing and sintering integrated process for a large cemented carbide product, comprising the following steps:

[0008] S1. The cemented carbide forming blank is subjected to positive pressure dewaxing under pulse pressure, and a mixed gas containing hydrogen and nitrogen is continuously introduced to remove the paraffin molding agent at a temperature not higher than 400°C;

[0009] S2. After the paraffin molding agent is removed, an inert gas is introduced to remove hydrogen;

[0010] S3. After the hydrogen is removed, vacuum is evacuated for vacuum sintering;

[0011] S4. After the vacuum sintering is completed, partial pressure sintering and pressure sintering are performed in sequence, and the large cemented carbide product is obtained after cooling.

[0012] First, the present invention is carried out under pulse pressure by regulating the positive pressure dewaxing process. Compared with the constant positive pressure process, the advantage is that the pressure in the system is always in a changing state, so that the generation of wax removal dead angles can be avoided, so that the carbon uniformity of the system at different positions is better. Secondly, the present invention selects a mixed gas of hydrogen and nitrogen as the wax removal gas during positive pressure dewaxing. Since the density of nitrogen is much higher than that of hydrogen, after the mixed gas enters the furnace through the top of the sintering furnace, the heated nitrogen sinks rapidly, and since nitrogen has uniform temperature, the heat stored in nitrogen under the same volume is more than that of hydrogen. In the early low-temperature wax removal stage, the heat of the mixed gas itself can be transferred more quickly to the entire furnace, making the heat distribution in the furnace more uniform, thereby reducing the internal and external temperature difference of large cemented carbide products, and reducing the cracking probability of the product, while also greatly reducing the gas cost (the price difference between nitrogen and hydrogen is about 3 times). Finally, the present invention regulates the removal of paraffin molding agent at a temperature not higher than 400°C to avoid the risk of high-temperature wax removal that easily causes decarburization of the product.

[0013] Preferably, the pulse pressure in step S1 is 10mbar to 140mbar, preferably 20mbar to 80mbar, for example, it can be any range value between 10mbar, 20mbar, 30mbar, 40mbar, 50mbar, 60mbar, 70mbar, 80mbar, 90mbar, 100mbar, 110mbar, 120mbar, 130mbar, 140mbar and the like. The present invention solves the problem of wax discharge dead angle in the sintering furnace to the greatest extent by regulating the range of pulse pressure. If the pulse pressure is large, part of the paraffin discharged from the cemented carbide forming blank will overflow outside the graphite carbon felt, thereby adversely affecting the subsequent vacuum sintering process.

[0014] In the present invention, the device for realizing the pulse pressure exemplarily includes a pulse flame spraying device, so that the positive pressure dewaxing process always maintains pressure changes.

[0015] Preferably, the mixed gas in step S1 comprises a combination of hydrogen and nitrogen in a volume ratio of (2-4):1, preferably 3:1, for example, it can be 2:1, 2.2:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, etc.

[0016] Preferably, the flow rate of the mixed gas in step S1 is 10L / min to 100L / min, preferably 20L / min to 60L / min, for example, 10L / min, 20L / min, 25L / min, 30L / min, 35L / min, 40L / min, 45L / min, 50L / min, 55L / min, 60L / min, 70L / min, 80L / min, 90L / min, 100L / min, etc. The present invention minimizes the difference between the inside and outside of the cemented carbide forming blank by regulating the flow rate of the hydrogen-nitrogen mixed gas. If the flow rate of the hydrogen-nitrogen mixed gas is large, the difference in the cobalt magnetism inside and outside the prepared cemented carbide large product will be as high as 0.5 or more, thereby affecting the product quality.

[0017] Preferably, the heating process of the positive pressure dewaxing in step S1 is a staged heating and heat preservation process.

[0018] Preferably, the heating process of the positive pressure dewaxing is as follows: in the first stage, the temperature is raised from room temperature to 240°C to 260°C (for example, 240°C, 245°C, 250°C, 255°C, 260°C, etc.) at a heating rate of 1°C / min to 2°C / min (for example, 1°C / min, 1.2°C / min, 1.5°C / min, 1.8°C / min, 2°C / min, etc.), and kept at 240°C to 260°C for 60min to 140min (for example, 60min, 70min, 80min, 90min, 100min, 110min, in the second stage, the temperature is increased from 240°C to 260°C at a heating rate of 0.8°C / min to 1.5°C / min (for example, 0.8°C / min, 0.9°C / min, 1°C / min, 1.1°C / min, 1.2°C / min, 1.3°C / min, 1.4°C / min, 1.5°C / min, etc.) to 300°C to 330°C (for example, 300°C, 305°C, 310°C, 315°C, 320°C, 325°C, 330°C, etc.), and kept at 300°C to 330°C for 2 hours. The third stage is from 300°C to 330°C at 0.03°C / min to 0.15°C / min (for example, it can be 0.03°C / min, 0.05°C / min, 0.08°C / min, 0.1°C / min, 0.11°C / min, 0.12°C / min, 0.13°C / min, 0.15°C / min, etc.) The heating rate is increased to 360°C ~ 390°C (for example, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, etc.), and kept at 360°C ~ 390°C for 200min ~ 500min (for example, 200min, 220min, 250min, 280min, 300min, 320min, 350min, 380min, 400min, 420min, 450min, 480min, 500min, etc.), so as to remove the paraffin molding agent at a low temperature not higher than 400°C.

[0019] Further preferably, the heating process of the positive pressure dewaxing is as follows: in the first stage, the temperature is increased from room temperature to 240°C to 260°C at a heating rate of 1.2°C / min to 1.6°C / min, and kept at 240°C to 260°C for 80min to 120min; in the second stage, the temperature is increased from 240°C to 260°C to 300°C to 330°C at a heating rate of 1.0°C / min to 1.4°C / min, and kept at 300°C to 330°C for 200min to 300min; in the third stage, the temperature is increased from room temperature to 240°C to 260°C at a heating rate of 1.2°C / min to 1.6°C / min, and kept at 240°C to 260°C for 80min to 120min. The temperature is increased from 300℃~330℃ to 360℃~380℃ at a heating rate of 0.05℃ / min~0.1℃ / min in the first stage, and then kept at 360℃~380℃ for 300min~500min. The specific actual heating rate and holding time need to be comprehensively determined based on the actual size of the cemented carbide forming blank product and the actual weight of the furnace. The larger the product, the slower the heating rate and the longer the holding time. In this way, the paraffin molding agent can be eliminated at a low temperature not higher than 400℃.

[0020] The present invention controls the heating process of positive pressure dewaxing to perform dewaxing treatment at a low temperature, completely removes the paraffin in large cemented carbide products at a temperature below 400° C., and eliminates the risk of decarburization of the product caused by high-temperature dewaxing.

[0021] The paraffin removed by the present invention is highly refined paraffin with a melting point of 42-56°C.

[0022] Preferably, the time for introducing the inert gas in step S2 is 60 min to 80 min, for example, it can be 60 min, 62 min, 65 min, 68 min, 70 min, 72 min, 75 min, 78 min, 80 min, etc.

[0023] In the present invention, the inert gas in step S2 is nitrogen.

[0024] Preferably, the vacuum degree of the system evacuated in step S3 is less than 100 Pa, for example, it can be 20 Pa, 30 Pa, 40 Pa, 50 Pa, 60 Pa, 70 Pa, 80 Pa, 90 Pa, 95 Pa, etc.

[0025] Preferably, the heating process of vacuum sintering in step S3 includes: firstly heating from 360°C to 390°C (for example, 360°C, 365°C, 370°C, 375°C, 380°C, 385°C, 390°C, etc.) at a heating rate of 2°C / min to 5°C / min (for example, 2°C / min, 2.5°C / min, 3°C / min, 3.5°C / min, 4°C / min, 4.5°C / min, 5°C / min, etc.) to 800°C to 900°C (for example, 80 0°C, 820°C, 850°C, 880°C, 900°C, etc.) and keep warm for 30min to 120min (for example, 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min, etc.), then increase the temperature at 3°C / min to 5°C / min (for example, 3°C / min, 3.2°C / min, 3.5°C / min, 3.8°C / min, 4°C / min, 4.2°C / min). in, 4.5°C / min, 4.8°C / min, 5°C / min, etc.) to 1100°C-1150°C (for example, 1100°C, 1110°C, 1120°C, 1130°C, 1140°C, 1150°C, etc.) and keep warm for 40min-120min (for example, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min, etc.), and finally heat at 2°C / The temperature is raised to 1250°C to 1280°C (for example, 1250°C, 1255°C, 1260°C, 1265°C, 1270°C, 1275°C, 1280°C, etc.) at a heating rate of min to 3°C / min (for example, 2°C / min, 2.2°C / min, 2.5°C / min, 2.8°C / min, 3°C / min, etc.) and kept warm for 20min to 30min (for example, 20min, 22min, 25min, 28min, 30min, etc.).

[0026] Further preferably, the heating process of vacuum sintering in step S3 includes: first heating from 360℃~380℃ to 800℃~900℃ at a heating rate of 2℃ / min~4℃ / min and keeping warm for 30min~60min, then heating to 1100℃~1150℃ at a heating rate of 4℃ / min~5℃ / min and keeping warm for 50min~100min, and finally heating to 1250℃~1280℃ at a heating rate of 2.5℃ / min~3℃ / min and keeping warm for 20min~30min.

[0027] The vacuum sintering stage adopted by the present invention adopts a rapid heating method, thereby accelerating the deoxidation rate of the green body. The ideal heating rate range is 2°C / min to 5°C / min. By adjusting the heating rate range in the vacuum sintering stage, the internal pores, cobalt aggregation and bubbling of large cemented carbide products can be reduced.

[0028] Preferably, the partial pressure sintering in step S4 is performed under an inert atmosphere, and the inert atmosphere is argon.

[0029] Preferably, the flow rate of the inert atmosphere is 15 L / min to 30 L / min, for example, it can be 15 L / min, 18 L / min, 20 L / min, 22 L / min, 25 L / min, 28 L / min, 30 L / min, etc.

[0030] Preferably, the pressure of the partial pressure sintering in step S4 is 7 mbar to 10 mbar, for example, 7 mbar, 8 mbar, 9 mbar, 10 mbar, etc. The present invention reduces the precipitation of cobalt in the green body during liquid phase sintering by regulating the pressure of the partial pressure sintering.

[0031] Preferably, the heating process of the partial pressure sintering in step S4 includes: heating from 1250℃~1280℃ (for example, it can be 1250℃, 1255℃, 1260℃, 1265℃, 1270℃, 1275℃, 1280℃, etc.) at a heating rate of 1℃ / min~3℃ / min (for example, it can be 1℃ / min, 1.2℃ / min, 1.5℃ / min, 1.8℃ / min, 2℃ / min, 2.2℃ / min, 2.5℃ / min, 2.8℃ / min, 3℃ / min, etc.) to 1430℃~1450℃ (for example, it can be 1430℃, 1435℃, 1440℃, 1445℃, 1450℃, etc.) and keeping warm for 30min~50min (for example, it can be 30min, 35min, 40min, 45min, 50min, etc.).

[0032] The present invention adjusts the heating speed in the partial pressure sintering stage according to the size of the large cemented carbide product, so that it is a slow heating process, thereby reducing the generation of temperature gradient inside and outside the large cemented carbide product and avoiding sintering deformation.

[0033] Preferably, the pressure sintering in step S4 is performed under an inert atmosphere, and the inert atmosphere is argon.

[0034] Preferably, the pressure of the pressure sintering in step S4 is 50 bar to 55 bar, for example, it can be 50 bar, 51 bar, 52 bar, 53 bar, 54 bar, 55 bar, etc.

[0035] Preferably, the heating process of pressure sintering in step S4 includes: keeping warm at a temperature of 1430°C to 1450°C (for example, 1430°C, 1435°C, 1440°C, 1445°C, 1450°C, etc.) for 30min to 60min (for example, 30min, 35min, 40min, 45min, 50min, 55min, 60min, etc.).

[0036] The purity of the gas used in the wax removal and sintering integration process adopted by the present invention is ≥99.99%.

[0037] The equipment used in the dewaxing and sintering integration process adopted by the present invention exemplarily includes a low-pressure sintering furnace with positive pressure dewaxing and sintering integration functions.

[0038] In a second aspect, the present invention provides a large cemented carbide product, which is prepared by the wax removal and sintering integrated process for the large cemented carbide product according to the first aspect.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] The present invention provides an integrated dewaxing and sintering process for large cemented carbide products. First, the present invention regulates the positive pressure dewaxing process under pulse pressure. Compared with the constant positive pressure process, the advantage is that the pressure in the system is always in a changing state, so that the generation of dewaxing dead corners can be avoided, so that the carbon content uniformity of the system at different positions is better. Secondly, the present invention selects a mixed gas of hydrogen and nitrogen as the dewaxing gas during positive pressure dewaxing. Since the density of nitrogen is much higher than that of hydrogen, after the mixed gas enters the furnace through the top of the sintering furnace, the heated nitrogen sinks rapidly, and since nitrogen has uniform temperature, the heat stored in nitrogen under the same volume is more than that of hydrogen. In the early low-temperature dewaxing stage, the heat of the mixed gas itself can be transferred to the entire furnace more quickly, making the heat distribution in the furnace more uniform, thereby reducing the internal and external temperature difference of large cemented carbide products, and reducing the cracking probability of the product, while also greatly reducing the gas cost (the price difference between nitrogen and hydrogen is about 3 times). Finally, the present invention regulates the removal of the paraffin molding agent at a temperature not higher than 400° C., thereby avoiding the risk of decarburization of the product due to high-temperature wax removal. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a curve diagram of the integrated process of wax removal and sintering of large cemented carbide products provided by the present invention.

[0042] Figure 2 This is the metallographic diagram of the large cemented carbide product provided in Example 1. DETAILED DESCRIPTION

[0043] The technical solution of the present invention is further described below by combining the accompanying drawings and specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0044] The test method of the large cemented carbide products provided in the embodiments and comparative examples of the present invention is as follows:

[0045] (1) Density: Tested in accordance with GB / T3850 standard.

[0046] (2) Hardness: Tested in accordance with GB / 3849 standard.

[0047] (3) Cobalt magnet: tested in accordance with GB / T23369 standard.

[0048] (4) Magnetic force: tested in accordance with GB / T3848 standard.

[0049] (5) Strength: Tested in accordance with GB / T3851 standard.

[0050] Example 1

[0051] This embodiment provides a large cemented carbide product and its dewaxing and sintering integration process. A cemented carbide forming green sheet with a wall thickness of 200 mm is placed in a low-pressure sintering furnace with a positive pressure dewaxing and sintering integration function for sintering. Figure 1 As shown, the dewaxing and sintering integrated process comprises the following steps:

[0052] (1) After the vacuum leak test is qualified, positive pressure dewaxing is carried out. Nitrogen-hydrogen mixed gas (composed of hydrogen and nitrogen with a volume ratio of 3:1) is used as the dewaxing gas. The flow rate of the nitrogen-hydrogen mixed gas is 40L / min. Pulse ignition is adopted, and the flame pressure is set to 30mbar~100mbar. When the pressure in the wax collecting tank reaches 100mbar, the ignition valve automatically opens, and the nitrogen-hydrogen mixed gas in the furnace is ejected and burned through the ignition port to reduce the pressure in the furnace. When the pressure in the wax collecting tank drops to 30mbar, the ignition valve is automatically closed. This cycle is repeated until the hydrogen removal is completed.

[0053] The heating process is as follows: starting from room temperature (20°C), heating to 260°C in 160 minutes, and keeping warm for 120 minutes, then heating to 330°C in 70 minutes, and keeping warm for 300 minutes, then heating to 380°C in 600 minutes and keeping warm for 300 minutes, so as to remove the paraffin molding agent.

[0054] (2) The hydrogen removal process is as follows: after the wax molding agent is removed, the hydrogen valve is closed and nitrogen is introduced to remove the hydrogen. The hydrogen removal time is 70 minutes. After the hydrogen removal is completed, the nitrogen is stopped and the vacuum is evacuated until the vacuum degree in the furnace is less than 100 Pa to start vacuum sintering.

[0055] (3) Vacuum sintering: evacuate the furnace until the vacuum degree is less than 100 Pa.

[0056] The heating process is as follows: starting from 380°C, heating to 800°C in 120 minutes and keeping the temperature for 80 minutes, then heating from 800°C to 1150°C in 100 minutes and keeping the temperature for 80 minutes, then heating from 1150°C to 1250°C in 40 minutes and keeping the temperature for 30 minutes, then introducing argon gas and switching to partial pressure sintering;

[0057] (4) Partial pressure sintering, maintaining the pressure in the furnace at 8 mbar and continuously filling with argon at a flow rate of 20 L / min;

[0058] The heating process is as follows: starting from 1250°C, heating to 1440°C in 120 minutes and keeping the temperature for 30 minutes, then switching to pressure sintering;

[0059] (5) Pressure sintering: Maintain the temperature at 1440°C and introduce argon gas to make the pressure in the furnace reach 50 bar, and perform pressure sintering. Maintain the temperature and pressure at 1440°C for 40 minutes, and then cool naturally. The metallographic structure of the obtained cemented carbide large product is as follows: Figure 2 shown.

[0060] The test results are shown in Table 1:

[0061] Table 1

[0062]

[0063] Example 2

[0064] The difference between this embodiment and embodiment 1 is that step S1 is specifically as follows: the pulse flame pressure is 30mbar to 100mbar, and the heating process of positive pressure dewaxing is as follows: heating starts from room temperature (20°C) and heats up to 260°C in 120min, and keeps warm for 100min, then heats up to 330°C in 47min, and keeps warm for 200min, then heats up to 380°C in 330min, and keeps warm for 200min; the rest is the same as embodiment 1. The test results are shown in Table 2:

[0065] Table 2

[0066]

[0067] Example 3

[0068] The difference between this embodiment and embodiment 1 is that step S1 is specifically as follows: the pulse flame pressure is 30mbar to 100mbar, and the heating process of positive pressure dewaxing is as follows: heating starts from room temperature (20°C) and heats up to 260°C in 240min, and keeps warm for 140min, then heats up to 330°C in 87min, and keeps warm for 400min, then heats up to 380°C in 1600min, and keeps warm for 500min, and the rest is the same as embodiment 1. The test results are shown in Table 3:

[0069] Table 3

[0070]

[0071]

[0072] Example 4

[0073] The difference between this embodiment and embodiment 1 is that step S1 is specifically as follows: the pulse flame pressure is 30mbar to 100mbar, and the heating process of positive pressure dewaxing is as follows: heating from room temperature (20°C) to 240°C in 146 minutes, and keeping the temperature for 120 minutes, then heating to 300°C in 60 minutes, and keeping the temperature for 300 minutes, then heating to 360°C in 750 minutes, and keeping the temperature for 300 minutes, and the rest is the same as embodiment 1. The test results are shown in Table 4:

[0074] Table 4

[0075]

[0076] Example 5

[0077] The difference between this embodiment and embodiment 1 is that step S1 is specifically as follows: the pulse flame pressure is 30mbar to 100mbar, and the heating process of positive pressure dewaxing is as follows: heating from room temperature (20°C) to 260°C in 160min, and keeping the temperature for 120min, then heating to 330°C in 70min, and keeping the temperature for 300min, then heating to 390°C in 750min, and keeping the temperature for 300min, and the rest is the same as embodiment 1. The test results are shown in Table 5:

[0078] Table 5

[0079]

[0080] Example 6

[0081] The difference between this embodiment and embodiment 1 is that the mixed gas is replaced with hydrogen gas in step S1, and the rest is the same as embodiment 1. The test results are shown in Table 6:

[0082] Table 6

[0083]

[0084] Example 7

[0085] The difference between this embodiment and embodiment 1 is that the flow rate of the mixed gas in step S1 is 100 L / min, and the rest is the same as embodiment 1. The test results are shown in Table 7:

[0086] Table 7

[0087]

[0088] Comparative Example 1

[0089] The difference between this comparative example and Example 1 is that the positive pressure dewaxing in step S1 is carried out at a constant pressure of 1000 mbar, and the rest is the same as Example 1. The test results are shown in Table 8:

[0090] Table 8

[0091]

[0092] Comparative Example 2

[0093] The difference between this comparative example and Example 1 is that the heating process of positive pressure dewaxing in step S1 is: heating from room temperature to 330°C in 250 minutes, and keeping the temperature for 400 minutes, then heating to 650°C in 267 minutes, and keeping the temperature for 200 minutes, then nitrogen exhausts hydrogen, and vacuum sintering starts at 650°C, and the rest is the same as Example 1. The test results are shown in Table 9:

[0094] Table 9

[0095]

[0096] It can be seen from Tables 1 to 9 that the integrated dewaxing and sintering process provided by the present invention can not only remove the paraffin molding agent at low temperature, but also reduce the internal and external temperature difference of large cemented carbide products and reduce the cracking probability of the products, while also significantly reducing the gas cost (the price difference between nitrogen and hydrogen is about 3 times).

[0097] Under the same furnace loading conditions, Example 2-Example 3 show that the present invention adjusts the range of the heating rate in the positive pressure dewaxing heating process, so that the internal and external differences of the prepared large cemented carbide products are smaller, and at the same time, with the continuous increase of the heating rate, the internal and external differences of the large cemented carbide products will also increase; Example 4-Example 5 show that the present invention adjusts the insulation value of different temperature points in the positive pressure dewaxing heating process, which will affect the internal and external differences of the large cemented carbide products. The closer the insulation point temperature is to the lower limit, the greater the internal and external differences of the large cemented carbide products.

[0098] Example 6 shows that when the mixed gas is replaced with pure hydrogen, although the sintering performance of the product will not be affected, the gas cost of the entire positive pressure dewaxing process will increase significantly; Example 7 shows that the flow rate of the mixed gas is increased, so that the gap between the inside and outside of large cemented carbide products increases under the flushing of a large flow of mixed gas.

[0099] By comparing Example 1 and Comparative Example 1, it can be seen that in Comparative Example 1, the gas pressure of the positive pressure dewaxing is changed to a constant value. Although the paraffin molding agent in the large cemented carbide product can be discharged, there is a wax discharge dead corner in the sintering furnace, resulting in a high cobalt magnetism in a certain part of the furnace, resulting in poor overall uniformity of the products in the furnace.

[0100] By comparing Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, the temperature of the positive pressure dewaxing is changed to 650°C. When the hydrogen dewaxing temperature is raised to such a high temperature, the material strength on the surface of the large cemented carbide product decreases significantly, and the carbon on the surface of the product is continuously lost under the flushing of high-temperature hydrogen, resulting in a decrease in the cobalt magnetism and strength of the large cemented carbide product, and the occurrence of decarburization.

[0101] The applicant declares that the present invention illustrates the process method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned process steps, that is, it does not mean that the present invention must rely on the above-mentioned process steps to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of the raw materials selected by the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A wax removal and sintering integrated process for large cemented carbide products, characterized in that: The following steps are involved: S1. The cemented carbide forming blank is subjected to positive pressure dewaxing under pulse pressure, and a mixed gas containing hydrogen and nitrogen is continuously introduced to remove the paraffin molding agent at a temperature not higher than 400°C; S2. After the paraffin molding agent is removed, an inert gas is introduced to remove hydrogen; S3. After the hydrogen is removed, vacuum is evacuated for vacuum sintering; S4. After the vacuum sintering is completed, partial pressure sintering and pressure sintering are performed in sequence, and the large cemented carbide product is obtained after cooling.

2. The dewaxing and sintering integrated process according to claim 1, characterized in that: The pulse pressure in step S1 is 10 mbar to 140 mbar, preferably 20 mbar to 80 mbar; Preferably, the mixed gas in step S1 comprises a combination of hydrogen and nitrogen in a volume ratio of (2-4):1, preferably 3:1; Preferably, the flow rate of the mixed gas in step S1 is 10 L / min to 100 L / min, preferably 20 L / min to 60 L / min.

3. The dewaxing and sintering integrated process according to claim 1 or 2, characterized in that: The heating process of the positive pressure dewaxing in step S1 is a staged heating and heat preservation process; Preferably, the heating process of the positive pressure dewaxing is as follows: in the first stage, the temperature is increased from room temperature to 240°C-260°C at a heating rate of 1°C / min-2°C / min, and kept at 240°C-260°C for 60min-140min; in the second stage, the temperature is increased from 240°C-260°C to 300°C-330°C at a heating rate of 0.8°C / min-1.5°C / min, and kept at 300°C-330°C for 200min-400min; in the third stage, the temperature is increased from 300°C-330°C to 360°C-390°C at a heating rate of 0.03°C / min-0.15°C / min, and kept at 360°C-390°C for 200min-500min, so as to remove the paraffin molding agent.

4. The integrated process of dewaxing and sintering according to claim 3, characterized in that: The heating process of the positive pressure dewaxing is as follows: in the first stage, the temperature is increased from room temperature to 240°C to 260°C at a heating rate of 1.2°C / min to 1.6°C / min, and kept at 240°C to 260°C for 80min to 120min; in the second stage, the temperature is increased from 240°C to 260°C to 300°C to 330°C at a heating rate of 1.0°C / min to 1.4°C / min, and kept at 300°C to 330°C for 200min to 300min; in the third stage, the temperature is increased from 300°C to 330°C to 360°C to 380°C at a heating rate of 0.05°C / min to 0.1°C / min, and kept at 360°C to 380°C for 300min to 500min, so as to remove the paraffin molding agent.

5. The integrated dewaxing and sintering process according to any one of claims 1 to 4, characterized in that: The time for introducing the inert gas in step S2 is 60 min to 80 min.

6. The integrated dewaxing and sintering process according to any one of claims 1 to 5, characterized in that: In step S3, the system is evacuated to a vacuum degree of less than 100 Pa; Preferably, the heating process of vacuum sintering in step S3 includes: first heating from 360℃~390℃ to 800℃~900℃ at a heating rate of 2℃ / min~5℃ / min and keeping warm for 30min~120min, then heating to 1100℃~1150℃ at a heating rate of 3℃ / min~5℃ / min and keeping warm for 40min~120min, and finally heating to 1250℃~1280℃ at a heating rate of 2℃ / min~3℃ / min and keeping warm for 20min~30min.

7. The integrated process of dewaxing and sintering according to claim 6, characterized in that: The heating process of vacuum sintering in step S3 includes: firstly heating from 360℃~380℃ to 800℃~900℃ at a heating rate of 2℃ / min~4℃ / min and keeping warm for 30min~60min, then heating to 1100℃~1150℃ at a heating rate of 4℃ / min~5℃ / min and keeping warm for 50min~100min, and finally heating to 1250℃~1280℃ at a heating rate of 2.5℃ / min~3℃ / min and keeping warm for 20min~30min.

8. The integrated dewaxing and sintering process according to any one of claims 1 to 7, characterized in that: The partial pressure sintering in step S4 is performed under an inert atmosphere; Preferably, the flow rate of the inert atmosphere is 15L / min to 30L / min; Preferably, the pressure of the partial pressure sintering in step S4 is 7 mbar to 10 mbar; Preferably, the heating process of the partial pressure sintering in step S4 includes: heating from 1250°C to 1280°C at a heating rate of 1°C / min to 3°C / min to 1430°C to 1450°C and keeping the temperature for 30min to 50min.

9. The integrated process for dewaxing and sintering according to any one of claims 1 to 8, characterized in that: The pressure sintering in step S4 is performed under an inert atmosphere; Preferably, the pressure of the pressure sintering in step S4 is 50 bar to 55 bar; Preferably, the heating process of the pressure sintering in step S4 includes: keeping the temperature at 1430° C. to 1450° C. for 30 min to 60 min.

10. A large cemented carbide product, characterized in that: The large cemented carbide product is prepared by the integrated process of dewaxing and sintering of the large cemented carbide product according to any one of claims 1-9.

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