Sintering method of low-stress hard alloy die material
阅读说明：本技术 一种低应力硬质合金模具材料烧结方法 (Sintering method of low-stress hard alloy die material ) 是由 孙东平 杜伟 刘宾 刘勋 刘诗彪 叶楠敏 于 2021-05-20 设计创作，主要内容包括：本发明公开了一种低应力硬质合金模具材料烧结方法,步骤为：氢气正压脱蜡,氮气排氢,真空烧结,低压烧结,第一次降温冷却,返烧去应力：第一步升温至1200℃并保温,第二步升温至1300℃～1320℃并保温；第二次降温冷却：随炉自然冷却至60℃以下出炉,得到一种低应力硬质合金模具材料产品。本发明优点在于：本方法不需要额外新增退火回火炉、深冷处理炉、研磨机等设备以及相应的工作量,通过在原脱蜡-烧结一体式低压炉中新增步骤“返烧去应力”和“第二次降温冷却”即可有效降低产品烧结应力、提高产品断裂韧性。(The invention discloses a sintering method of a low-stress hard alloy die material, which comprises the following steps: hydrogen malleation dewaxing, nitrogen gas row hydrogen, vacuum sintering, low pressure sintering, the cooling of first cooling, burn back destressing: the first step is heating to 1200 ℃ and preserving heat, and the second step is heating to 1300-1320 ℃ and preserving heat; and (5) cooling for the second time: naturally cooling to below 60 ℃ along with the furnace, discharging to obtain a low-stress hard alloy die material product. The invention has the advantages that: the method does not need additional equipment such as an annealing tempering furnace, a cryogenic treatment furnace, a grinding machine and the like and corresponding workload, and can effectively reduce the sintering stress of the product and improve the fracture toughness of the product by adding the steps of 'burn-back stress removal' and 'secondary cooling' in the original dewaxing-sintering integrated low-pressure furnace.)
1. A low stress hard alloy die material sintering method is characterized in that:
(1) hydrogen positive pressure dewaxing: placing a die material plate pressed compact containing a forming agent on a graphite plate coated with an anti-sticking high-temperature coating, loading the die material plate pressed compact into a dewaxing-sintering integrated low-pressure furnace, heating the temperature from room temperature to 320-380 ℃ in the first step, preserving the temperature, heating the temperature to 650 ℃ in the second step, controlling the hydrogen flow to be 30-80 SLM in the whole process, and controlling the hearth pressure to be 10-20 mbar;
(2) hydrogen discharge by nitrogen: after the step (1) is finished, removing hydrogen in the furnace by adopting high-purity nitrogen, controlling the flow of the nitrogen to be 20-80SLM, and controlling the hydrogen removal time to be 40-80 min;
(3) and (3) vacuum sintering: after the step (2) is finished, starting a vacuum pump to pump out residual gas in the hearth, controlling the vacuum degree to be less than 30Pa, heating from 650 ℃ to 900-1000 ℃ in the first step, preserving heat, heating to 1200-1250 ℃ in the second step, preserving heat, and heating to 1400-1500 ℃ in the third step;
(4) low-pressure sintering: after the step (3) is finished, closing the vacuum pump, filling high-purity argon, controlling the pressure of the hearth to be 20-80bar, and preserving the heat for 60-200 min;
(5) cooling for the first time: after the step (4) is finished, naturally cooling the product to 100 ℃ along with the furnace;
(6) and (3) stress removal by back burning: after the step (5) is finished, the temperature is raised to 1200 ℃ in the first step and is kept, and the temperature is raised to 1300-1320 ℃ in the second step and is kept;
(7) and (5) cooling for the second time: and (4) naturally cooling the blank to below 60 ℃ along with the furnace after the step (6) is finished, and discharging the blank to obtain a low-stress hard alloy die material product.
2. The sintering method of low stress cemented carbide die material according to claim 1, characterized by: in the hydrogen positive pressure dewaxing, the temperature rising speed of the first step is 1.0-2.5 ℃/min, the heat preservation time is 300-900 min, and the temperature rising speed of the second step is 1.0-2.5 ℃/min.
3. The sintering method of low stress cemented carbide die material according to claim 1, characterized by: in the vacuum sintering, the first temperature rise, the second temperature rise and the third temperature rise are at the speed of 1.0-2.5 ℃/min, and the first heat preservation time and the second heat preservation time are 60-180 min.
4. The sintering method of low stress cemented carbide die material according to claim 1, characterized by: in the stress removal by the back burning, the temperature rising speed of the first step is 1.5-3.5 ℃/min, the heat preservation time is 10-30 min, the temperature rising speed of the second step is 1.5-3.5 ℃/min, and the heat preservation time is 10-40 min.
Technical Field
The invention relates to the field of production and manufacturing of hard alloy die materials, in particular to a sintering method of a low-stress hard alloy die material.
Background
The hard alloy die is mostly made of (100-250) mmX (1.0-60.0) mm plates, and hard alloy parts such as a punch and a die are manufactured by machining methods such as wire electrical discharge machining and grinding and are used for stamping thin strips such as silicon steel, stainless steel and alloy copper at a high speed at a stamping speed of 200-800 times/min at a wear-resistant part and an impact-resistant part of a progressive die. Because the thermal expansion coefficient of the main component Co of the hard alloy is close to 3 times of WC, and the size of the hard alloy die material plate is larger, under the condition of the conventional sintering process, the cooling speed of the inside and the surface of the hard alloy is inconsistent, so that the residual sintering stress inside the hard alloy is large, and the stress is easily released instantly in the machining process to cause cracking and can not be used. Such as some cemented carbides cracking during grinding; such as some cemented carbides, crack during wire electrical discharge machining.
The conventional sintering process of WC-Co- (Ni) - (C) - (V) hard alloy is to quickly cool the hard alloy to 60 ℃ and discharge the hard alloy after heat preservation for 60-200 min at a high temperature of 1400-1500 ℃, and the sintering stress of the hard alloy is mainly formed at the stage. In the patent CN201510553910.7, the sintering stress of the hard alloy is reduced by adopting a cryogenic treatment and a cryogenic after-tempering process; patent CN 107350954A adopts cryogenic treatment firstly, then grinds in a roller by grinding fluid and grinding body, finally reduces the sintering stress of the hard alloy by the method of cleaning by alkaline solution and drying at normal temperature. The 2 methods all need to transfer the product in the original sintering furnace to other equipment for treatment, the single charging amount of the hard alloy is usually 300-1000 kg, and the transfer to other equipment needs a large amount of extra manpower and equipment investment, and has complex process and long flow. The two patent methods are not industrially popularized due to inconvenient production and are mainly suitable for single-weight small hard alloy products, and the method for producing the low-stress hard alloy die material product conveniently, quickly and efficiently is still the problem which needs to be solved urgently in the hard alloy production industry.
The liquidus point of the hard alloy is 1280-1340 ℃, after the liquid phase appears, the liquidity of the liquid phase Co is enhanced, the WC particles are rearranged and the dissolution and precipitation reaction is intensified, particularly in the high-temperature range of 1400-1500 ℃, the WC particles of the hard alloy grow rapidly through the dissolution and precipitation reaction, and the final densification of the alloy is completed. In the 'burn-back stress removal' stage in the 'sintering method for low-stress hard alloy die material', the product does not need to be transferred to other equipment, the selected high-temperature section is 1300-1320 ℃, the heat preservation time is 10-40 min, the hard alloy die material with different components is burned to 1300-1320 ℃, the heat preservation time is 10-40 min, then the alloy surface is cooled to below 60 ℃, an electron scanning microscope is adopted for observing the solidified morphology of a small amount of liquid phase Co (Ni), the alloy is confirmed to have the liquid phase at 1300-1320 ℃, the appearance of the liquid phase and the rearrangement of WC particles can effectively relax the stress between a bonding phase and a hard phase, passivate the WC sharp angle and improve the fracture resistance of the product, and simultaneously, the hardness of the hard alloy caused by the growth of crystal grains due to the dissolution precipitation reaction of the WC particles caused by excessive high-temperature liquid phase Co (Ni) is effectively inhibited, The wear resistance and the strength are reduced; in addition, compared with the stress caused by rapid cooling to the tapping temperature at the high temperature of 1400-1500 ℃, the stress formed by cooling the hard alloy from the lower temperature of 1300-1320 ℃ to the tapping temperature is smaller.
The WC-Co- (Ni) - (C) - (V) hard alloy with the Co (Ni) binder mass fraction higher than 20 omega t percent is not suitable for the method of the invention because the liquid phase amount is large and the dissolution and precipitation reaction of WC particles is severe to cause the particles to be increased rapidly and cause the reduction of hardness, wear resistance and strength even under the conditions that the temperature is 1300-1320 ℃ and the holding time is 10-40 min.
Disclosure of Invention
The invention aims to provide a sintering method of a low-stress hard alloy die material, which improves the stability of hard alloy in the machining process, improves the fracture toughness of a product under the condition of not reducing the strength and the wear resistance and enlarges the application range of the product.
In order to achieve the purpose, the technical scheme of the invention comprises the following specific implementation steps: a low stress hard alloy die material sintering method is characterized in that:
(1) hydrogen positive pressure dewaxing: placing a die material plate pressed compact containing a forming agent on a graphite plate coated with an anti-sticking high-temperature coating, loading the die material plate pressed compact into a dewaxing-sintering integrated low-pressure furnace, heating the temperature from room temperature to 320-380 ℃ in the first step, preserving the temperature, heating the temperature to 650 ℃ in the second step, controlling the hydrogen flow to be 30-80 SLM in the whole process, and controlling the hearth pressure to be 10-20 mbar;
(2) hydrogen discharge by nitrogen: after the step (1) is finished, removing hydrogen in the furnace by adopting high-purity nitrogen, controlling the flow of the nitrogen to be 20-80SLM, and controlling the hydrogen removal time to be 40-80 min;
(3) and (3) vacuum sintering: after the step (2) is finished, starting a vacuum pump to pump out residual gas in the hearth, controlling the vacuum degree to be less than 30Pa, heating from 650 ℃ to 900-1000 ℃ in the first step, preserving heat, heating to 1200-1250 ℃ in the second step, preserving heat, and heating to 1400-1500 ℃ in the third step;
(4) low-pressure sintering: after the step (3) is finished, closing the vacuum pump, filling high-purity argon, controlling the pressure of the hearth to be 20-80bar, and preserving the heat for 60-200 min;
(5) cooling for the first time: after the step (4) is finished, naturally cooling the product to 100 ℃ along with the furnace;
(6) and (3) stress removal by back burning: after the step (5) is finished, the temperature is raised to 1200 ℃ in the first step and is kept, and the temperature is raised to 1300-1320 ℃ in the second step and is kept;
(7) and (5) cooling for the second time: and (4) naturally cooling the blank to below 60 ℃ along with the furnace after the step (6) is finished, and discharging the blank to obtain a low-stress hard alloy die material product.
Further, in the hydrogen positive pressure dewaxing, the first temperature rise speed is 1.0-2.5 ℃/min, the heat preservation time is 300-900 min, and the second temperature rise speed is 1.0-2.5 ℃/min.
Further, in the vacuum sintering, the first temperature rise, the second temperature rise and the third temperature rise are carried out at the speed of 1.0-2.5 ℃/min, and the first heat preservation time and the second heat preservation time are carried out for 60-180 min.
Further, in the stress removal by the back burning, the first temperature rise speed is 1.5-3.5 ℃/min, the heat preservation time is 10-30 min, and the temperature of each part of the product is balanced; and in the second step, the temperature rising speed is 1.5-3.5 ℃/min, the temperature is kept for 10-40 min, and the temperature of each part of the product is equalized again.
The invention has the advantages that: (1) the temperature rise speed selected before the step 6 is 1.0-2.5 ℃/min, so that the uniform temperature rise, dewaxing speed and oxide reduction rate of each part of the product in the sintering process can be effectively ensured to be uniform, the defects of cracking, porosity and the like of the product caused by too high or unbalanced dewaxing speed and insufficient or unbalanced oxide reduction can not be caused, and the low production efficiency caused by too low temperature rise speed can not be caused; (2) according to the method, the high-temperature section selected in the step 6 is 1300-1320 ℃, the heat preservation time is 10-40 min, multiple tests confirm that under the condition, liquid phase Co (Ni) appears in the alloy with different components, the stress between the binding phase and the hard phase can be effectively relaxed by the appearance of the liquid phase and the rearrangement of WC particles, the WC sharp angle is passivated, the fracture resistance of the product is improved, and the reduction of the hardness, the wear resistance and the strength of the hard alloy caused by the growth of crystal grains due to the dissolution and precipitation reaction of the WC particles is effectively inhibited; (3) according to the method, equipment such as an annealing tempering furnace, a cryogenic treatment furnace, a grinding machine and the like and corresponding workload are not additionally added, and the sintering stress of the product can be effectively reduced and the fracture toughness of the product can be improved by additionally adding the step 6 of're-sintering stress removal' and the step 7 of 'secondary cooling' in the original dewaxing-sintering integrated low-pressure furnace. (4) The method has the characteristics of simple process, short flow and low production cost, and is suitable for industrial production; the cracking rate of the hard alloy die material plate treated by the method is reduced to below 1% through mechanical processing such as grinding, linear cutting and the like, and is obviously improved by more than 10% compared with the cracking rate of the hard alloy die material plate not subjected to stress removal processing.
Drawings
FIG. 1 is a graph X5000 showing the surface morphology of a hard alloy material sintered at 1300-1320 ℃ in example 1.
FIG. 2 is a structural view of a 5000 XSEM image of cemented carbide sintered by a conventional process in example 1.
FIG. 3 is a structural diagram of a 5000 XSEM image of cemented carbide sintered by the method of the present invention in example 1.
FIG. 4 is an X5000 graph showing the surface morphology of the hard alloy material in the embodiment 2 at 1300-1320 ℃.
FIG. 5 is a structural view of a 5000 XSEM image of cemented carbide sintered by a conventional process in example 1.
FIG. 6 is a structural diagram of a 5000 XSEM image of cemented carbide sintered by the method of the present invention in example 1.
Detailed Description
Example 1
The WC-13.0 omega t percent Co hard alloy die material has the original WC granularity of 1.0 mu m and the appearance size of 105mm multiplied by 50mm, one piece is sintered by adopting the conventional process, the other piece is sintered by adopting the method, and the specific steps of the sintering by adopting the method are as follows:
1) hydrogen positive pressure dewaxing: the die material plate pressed compact containing the forming agent is placed on a graphite plate coated with anti-sticking high-temperature coating and is filled into a hearth with the volume of 0.1m3The dewaxing-sintering integrated low-pressure furnace is heated from room temperature to 350 ℃ at the heating rate of 1.8 ℃/min, is kept warm for 700min, is continuously heated to 650 ℃ at the heating rate of 1.8 ℃/min, the hydrogen flow in the whole process is controlled at 35SLM, and the hearth pressure is controlled at 10 mbar.
(2) Hydrogen discharge by nitrogen: and (3) after the step (1) is finished, removing hydrogen in the furnace by adopting high-purity nitrogen, controlling the flow of the nitrogen by 50SLM, and controlling the hydrogen removal time for 45 min.
(3) And (3) vacuum sintering: after the step (2) is finished, starting a vacuum pump to pump out residual gas in the hearth, controlling the vacuum degree to be less than 30Pa, heating from 650 ℃ to 950 ℃ at a heating rate of 1.8 ℃/min, keeping the temperature for 100min, continuing to heat to 1200 ℃ at a heating rate of 1.8 ℃/min, keeping the temperature for 100min, and continuing to heat to 1450 ℃ at a heating rate of 1.8 ℃/min.
(4) Low-pressure sintering: and (4) after the step (3) is finished, closing the vacuum pump, introducing high-purity argon, controlling the pressure of the hearth to be 70bar, and preserving the heat for 150 min.
(5) Cooling for the first time: and (4) after the step (4) is finished, naturally cooling the product to 100 ℃ along with the furnace.
(6) And (3) stress removal by back burning: after the step (5) is finished, the temperature is raised to 1200 ℃ according to the temperature raising speed of 2.2 ℃/min, the temperature is kept for 20min, and then the temperature is raised to 1310 ℃ according to the temperature raising speed of 2.2 ℃/min, and the temperature is kept for 30 min.
(7) And (5) cooling for the second time: and (5) naturally cooling to 50 ℃ along with the furnace after the step (6) is finished, and discharging to obtain a low-stress hard alloy die material product.
Compared with the conventional process and the method for sintering two products by adopting an electron scanning microscope, the internal structure of the two products can be obviously observed, the WC crystal grains with sharp corners, which are easy to generate stress concentration, in the hard alloy sintered by adopting the conventional process are more, and the WC crystal grains with sharp corners in the hard alloy sintered by adopting the method for sintering the hard alloy are obviously less. The internal stress of two sintered products is detected by adopting the conventional process and the method of the invention by adopting the homocline method of an X-ray diffractometer:
sintering process
Internal stress value/MPa
Conventional process
320±40
The method of the invention
250±35
The internal stress value of the hard alloy die material product sintered by the method is lower by more than 20 percent than that of the product produced by the conventional process.
The alloy hardness, bending strength, wear resistance and fracture toughness of two products sintered by the conventional process and the method are compared.
Sintering process
Rockwell hardness HRA
Flexural strength/MPa
Abrasion resistance/cm-3
Fracture toughness/MPm1/2
Conventional sintering
90.3
4480
6.40
11.2
The invention
90.3
4500
6.39
12.5
Compared with the conventional process sintered material, the hard alloy die material produced by the method has the advantages that the fracture toughness is improved by more than 10 percent under the condition of unchanged hardness, bending strength and wear resistance, so that the material has a wider application range.
Example 2:
the WC-16.0 omega t percent Co hard alloy die material has the original WC granularity of 3.0 mu m and the appearance size of 150mm multiplied by 60mm, one piece is sintered by adopting the conventional process, the other piece is sintered by adopting the method, and the specific steps of the sintering by adopting the method are as follows:
1) hydrogen positive pressure dewaxing: will containThe die material plate pressed compact of the forming agent is arranged on a graphite plate coated with anti-sticking high-temperature coating and is loaded into a hearth with the volume of 0.1m3The dewaxing-sintering integrated low-pressure furnace is heated from room temperature to 350 ℃ at the heating rate of 1.2 ℃/min, is kept warm for 800min, is continuously heated to 650 ℃ at the heating rate of 1.2 ℃/min, the hydrogen flow in the whole process is controlled at 35SLM, and the hearth pressure is controlled at 10 mbar.
(2) Hydrogen discharge by nitrogen: and (3) after the step (1) is finished, removing hydrogen in the furnace by adopting high-purity nitrogen, controlling the flow of the nitrogen by 50SLM, and controlling the hydrogen removal time for 45 min.
(3) And (3) vacuum sintering: and (3) after the step (2) is finished, starting a vacuum pump to pump out residual gas in the hearth, controlling the vacuum degree to be less than 30Pa, heating from 650 ℃ to 950 ℃ at the heating rate of 1.2 ℃/min, keeping the temperature for 150min, continuing to heat to 1250 ℃ at the heating rate of 1.2 ℃/min, keeping the temperature for 150min, and continuing to heat to 1410 ℃ at the heating rate of 1.2 ℃/min.
(4) Low-pressure sintering: and (4) after the step (3) is finished, closing the vacuum pump, introducing high-purity argon, controlling the pressure of the hearth to be 60bar, and preserving the heat for 140 min.
(5) Cooling for the first time: and (4) after the step (4) is finished, naturally cooling the product to 100 ℃ along with the furnace.
(6) And (3) stress removal by back burning: after the step (5) is finished, the temperature is raised to 1200 ℃ according to the temperature raising speed of 2.5 ℃/min, the temperature is kept for 30min, and then the temperature is raised to 1310 ℃ according to the temperature raising speed of 2.5 ℃/min, and the temperature is kept for 30 min.
(7) And (5) cooling for the second time: and (5) naturally cooling to 50 ℃ along with the furnace after the step (6) is finished, and discharging to obtain a low-stress hard alloy die material product.
Compared with the conventional process and the method for sintering two products by adopting an electron scanning microscope, the internal structure of the two products can be obviously observed, the WC crystal grains with sharp corners, which are easy to generate stress concentration, in the hard alloy sintered by adopting the conventional process are more, and the WC crystal grains with sharp corners in the hard alloy sintered by adopting the method for sintering the hard alloy are obviously less.
The internal stress of two sintered products is detected by adopting the conventional process and the method of the invention by adopting the homocline method of an X-ray diffractometer:
sintering process
Internal stress value/MPa
Conventional process
410±40
The method of the invention
300±35
The internal stress value of the hard alloy die material product sintered by the method is lower by more than 25 percent than that of the product produced by the conventional process.
The alloy hardness, bending strength, wear resistance and fracture toughness of two products sintered by the conventional process and the method are compared.
Compared with the conventional process sintered material, the hard alloy die material produced by the method has the advantages that the fracture toughness is improved by more than 10 percent under the condition of unchanged hardness, bending strength and wear resistance, so that the material has a wider application range.
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