Method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy through two-chamber vacuum induction furnace

Abstract

The invention relates to the technical field of high-temperature alloy preparation, and discloses a method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace, which comprises the following specific steps: step 1, preparing materials according to components of the nitrogen-containing cobalt-chromium-molybdenum alloy; step 2, sequentially arranging a Si layer, a Mo layer, an N layer, a Cr layer and a Co layer from the bottom of the crucible to the top; and step 3, vacuum melting: S1, vacuumizing treatment; then filling nitrogen; s2, heating and melting, wherein the power of a smelting chamber is set to be 340-360 KW; the power of the smelting chamber is set to be 180-200 KW, and heat preservation refining is carried out; s3, power failure and standing; s4, electrifying again, and adding Mn into the molten steel when the power of the smelting chamber is increased to 300KW; and 4, pouring is conducted, specifically, pouring is started when the temperature of the molten steel rises to 1520-1530 DEG C. The nitrogen-containing cobalt-chromium-molybdenum alloy which is smooth in surface and free of pores inside can be prepared.

Description

Technical Field

[0001] The invention relates to the technical field of high-temperature alloy preparation, and in particular to a method for preparing a nitrogen-containing cobalt-chromium-molybdenum alloy using a two-chamber vacuum induction furnace. Background Art

[0002] Cobalt-chromium-molybdenum alloy has excellent mechanical properties, corrosion resistance and biocompatibility, and is an important material for orthopedic metal implants. Forged cobalt-chromium-molybdenum alloy is used in high-end cobalt-chromium-molybdenum artificial joints due to its more excellent mechanical properties.

[0003] In the preparation of nitrogen-containing cobalt-chromium-molybdenum alloys, failure to properly control each link in the preparation process will affect the product quality: if the casting speed is too fast, the flow state of the alloy liquid in the mold will become turbulent. This will cause the alloy liquid to be unable to fill smoothly in the mold, and it is easy to be drawn into the gas and form pores; and the fast-flowing alloy liquid has an enhanced scouring effect on the mold wall, which may destroy the initial solidification layer already formed on the mold surface, making the surface of the solidified alloy rough; using an inappropriate casting method, such as casting the alloy liquid from a high place, the alloy liquid will be fully in contact with nitrogen during the falling process and easily absorb gas: during the solidification process, these gases will form pores. At the same time, the impact of the alloy liquid may damage the existing protective coating (if any) in the mold, increase the reaction probability of the alloy and the mold, and lead to a decrease in surface quality; during the cooling process, if the cooling rate is uneven, the shrinkage degree of different parts of the alloy will be different. For example, if the surface cooling rate is fast and the internal cooling rate is slow, thermal stress will be generated. This thermal stress may cause cracks or unevenness on the alloy surface. At the same time, uneven cooling will make the gas precipitation position inside the alloy uneven, which is easy to form pores; if the smelting time is too long, the elements in the alloy liquid may be excessively burned, and long-term smelting will increase the chance of the alloy liquid reacting with external impurities. For example, chromium may be oxidized under long-term high-temperature smelting, and the generated chromium oxide may be suspended in the alloy liquid, affecting the solidification quality of the alloy and causing the surface to be rough. If the smelting time is too short, the alloy composition may be uneven, nitrogen cannot be well dissolved in the alloy, and it will exist in the form of pores during the solidification process. In addition, the uneven composition will also cause different solidification speeds in different parts, making the surface rough; if the smelting temperature is too high, the viscosity of the alloy liquid will decrease and the fluidity will increase. In this case, the reaction between the liquid and the surrounding environment (such as air, furnace lining materials, etc.) will intensify; if the temperature is too high, the solubility of nitrogen may be too high, and during the cooling process, excessive nitrogen will precipitate to form pores. Therefore, higher requirements are placed on the smelting process. Summary of the invention

[0004] Purpose of the invention: In view of the problems existing in the prior art, the present invention provides a method for preparing a nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace. The present invention can prepare a nitrogen-containing cobalt-chromium-molybdenum alloy with a smooth surface and no pores inside.

[0005] Technical solution: The present invention provides a method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy using a two-chamber vacuum induction furnace, comprising the following steps: Step 1, ingredients: by mass percentage, the nitrogen-containing cobalt-chromium-molybdenum alloy components are as follows: C0.22-0.25%, Cr28.0-29.0%, Mo5.5-6.5%, Fe≤1%, Ni≤1%, Si≤1%, Mn≤0.6%, N0.1-0.2%, Co balance; Among them, C uses 100% pure graphite, Cr uses 99-99.2% pure metal chromium, Mo uses molybdenum bars, Si uses metal silicon, Mn uses manganese flakes, N uses chromium nitride (nitrogen content 10-11%), and Co uses electrolytic cobalt; Step 2, stacking: stacking the components in S1: from the bottom of the crucible upward, the components are stacked in the order of higher density and weaker oxidizing properties as they go up; Specifically, the stacking order of the components from the bottom of the crucible to the top is: C layer, Si layer, Mo layer, N layer, Cr layer and Co layer; among them, the amounts of carbon, silicon, molybdenum and chromium nitride (nitrogen) are relatively small, so they are added together and placed at the bottom layer.

[0006] The raw materials with low density and easy oxidation are placed on the bottom layer, and the raw materials with high density and not easy oxidation are placed on the top layer, in order to protect the easily oxidized metals from oxidation and burning. Among them, chromium nitride is placed on the bottom layer to increase the nitrogen recovery rate and maintain the nitrogen mass fraction between 0.16 and 0.2%. If chromium nitride is placed on the upper layer, it will directly contact the atmosphere above the molten steel, forming a dynamic chemical equilibrium, and nitrogen will continue to diffuse into the atmosphere above, resulting in a decrease in the nitrogen recovery rate of the molten steel, usually falling below 0.1%.

[0007] Step 3: Vacuum melting: S1. The smelting chamber is evacuated; followed by nitrogen filling; S2. Heat up and melt, set the melting chamber power to 340~360KW; until it is completely melted, set the melting chamber power to 180~200KW, and keep warm for refining; In the melting stage, the melting chamber is set to high power, which can quickly melt the solid metal into liquid, and prevent the solid metal from experiencing a long semi-solid stage during the melting process, which leads to component burnout, gas absorption and precipitation, and ultimately unqualified components; in the refining process, the melting chamber is set to low power to remove gas and inclusions in the molten steel. At this time, the power does not need to be too high, and it is enough to maintain the temperature of the molten steel and ensure that the molten steel rolls under the action of electromagnetic force; S3. Turn off the power and wait until a film appears on the surface of the molten steel; The purpose of static exhaust is achieved by power outage: after power outage, the molten steel no longer rolls and the temperature drops evenly. According to the principle of gas dynamic equilibrium, the gas solubility in the molten steel will decrease as the temperature decreases, achieving the effect of removing gas; S4. Turn on the power again, wait until the power of the melting chamber rises to 300KW, and add Mn to the molten steel (manganese is added later because it is a metal that is easily burned. Adding it later can protect manganese from being burned and improve the yield); Step 4: Pouring: When the temperature of the molten steel rises to 1520~1530℃, start pouring at a speed of 90~110KG / min.

[0008] The pouring temperature and pouring speed are set in this way, based on the specific device of the present invention, i.e., the two-chamber vacuum furnace, to ensure that the molten steel poured into the mold tube can contain the appropriate temperature and gas content, and obtain a master alloy material with good surface quality and qualified composition. The pouring temperature and pouring speed must be coordinated.

[0009] If the pouring temperature is lower than 1520~1530℃, the heat contained in the molten steel when poured into the mold tube is relatively low, and the relatively cold inner wall of the mold tube is chilled, resulting in the inability to eliminate the cold scar defects formed, resulting in a master alloy with poor surface quality. If the pouring temperature is higher than 1520~1530℃, the nitrogen content absorbed by the melt will increase, and the temperature will decrease when poured into the mold tube, and the absorbed gas will precipitate. If the precipitated gas does not overflow the mold tube in time, it will be wrapped in the master alloy, forming a porosity defect.

[0010] If the pouring speed is lower than 90~110KG / min, less molten steel will enter the mold tube per unit time, and the heat carried will be less, which will also cause severe surface cold scar defects. If the pouring speed is higher than 90~110KG / min, more molten steel will enter the mold tube per unit time, turbulence will be more serious, air entrainment will be serious, leading to invasive pores and forming pore defects.

[0011] Furthermore, the ingredients are new materials or a mixture of new materials and returned materials; wherein the mixture, calculated by mass percentage, includes 80% new materials and 20% returned materials.

[0012] Furthermore, the ingredients are a mixture of new materials and returned materials. When the materials are piled, the bottom of the crucible is the returned materials.

[0013] The return material is a large piece of metal block. When the material is piled, it is placed at the bottom to be more sensitive to magnetism and shorten the smelting time.

[0014] Furthermore, in S1, the furnace is evacuated until the pressure inside the furnace is less than 0.1 Pa, and the gas leakage rate is measured to be less than 2 Pa / min.

[0015] Furthermore, in S1, nitrogen is charged until the pressure inside the furnace is 0.03-0.04 MPa.

[0016] Furthermore, in S2, the heat preservation refining is specifically: heat preservation refining for 25-35 minutes, and the temperature of the molten steel after refining is 1550-1570°C.

[0017] Furthermore, in S3, the power is turned off and the mixture is left to stand for 10 to 30 minutes until a film appears on the surface of the molten steel, and the temperature of the molten steel is 1470 to 1490°C.

[0018] Furthermore, in step four, the pouring is specifically as follows: spraying boron nitride on the inner wall of the mold tube, then arranging the mold tube array, and assembling the mold tube, the diverter plate, and the filter plate from bottom to top; preheating the assembled device for 3 to 4 hours at a temperature of 500 to 800°C; finally, placing the preheated device into a vacuum induction furnace for melting, starting vacuuming, and pouring.

[0019] Preheating the assembled device can reduce the temperature difference between the molten steel and the mold, thereby improving the surface quality of the bar and reducing pores; Boron nitride is sprayed on the inner wall of the mold tube.

[0020] Furthermore, after step 4, step 5 is also included: placing the mold tube after casting in the furnace for 25-35 minutes, turning off the nitrogen and argon gases, and taking it out of the furnace. Placing the mold tube after casting in the furnace for a period of time and then turning off the gas after it is completely solidified can prevent the semi-solid steel liquid that is not completely solidified from escaping gas, resulting in porosity defects and unqualified composition defects.

[0021] Preferably, the specification of the two-chamber vacuum induction furnace is 500KG, and the specification of the mold tube is Φ54mm*620mm.

[0022] Beneficial effects: Compared with the prior art, the specific beneficial effects of the present invention are as follows: By strictly controlling the process, a nitrogen-containing cobalt-chromium-molybdenum alloy with a smooth surface and no pores inside is prepared: 1. The temperature difference between the molten steel and the mold tube is reduced, and the surface quality of the rod is improved; 2. Strict control of the melting temperature, time, pouring speed, etc. can effectively inhibit the precipitation of nitrogen in the molten steel during solidification, and can prevent the molten steel from being drawn into nitrogen to form pores, thereby achieving the purpose of preventing the occurrence of pores. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 The alloy prepared by pouring at a pouring temperature exceeding the pouring temperature set in the present invention (the pouring temperature is 1550-1560° C., and the pouring speed is 90-110 KG / min) has pore defects; Figure 2 The alloy prepared by pouring at a pouring temperature lower than the pouring temperature set in the present invention (the pouring temperature is 1490-1510° C., and the pouring speed is 90-110 KG / min) has a cold cadmium defect; Figure 3 The alloy prepared by pouring at a pouring speed exceeding the pouring speed set in the present invention (pouring temperature of 1520-1530° C., pouring speed of 180-220 KG / min) has pore defects; Figure 4 The alloy prepared by pouring at a pouring speed lower than that set by the present invention (pouring temperature is 1520-1530° C., pouring speed is 40-60 KG / min) has cold cadmium defects; Figure 5 The alloy prepared by pouring within the pouring temperature and pouring speed range set by the present invention has a smooth surface and is substantially free of pores. DETAILED DESCRIPTION

[0024] The present invention is described in detail below in conjunction with the embodiments.

[0025] Implementation 1: This embodiment provides a method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy using a two-chamber vacuum induction furnace. The vacuum induction furnace adopts a 500KG specification. The specific steps are as follows: 1. Ingredients: brand new ingredients; Among them, the raw material carbon uses graphite, chromium uses metallic chromium, molybdenum uses molybdenum bars, silicon uses metallic silicon, manganese uses manganese sheets, nitrogen and chromium use chromium nitride (nitrogen content 10~11%), and cobalt uses electrolytic cobalt. The ingredients after mixing are as follows:

[0026] 2. Stacking method: The stacking order of each component from the bottom of the crucible to the top is: C layer, Si layer, Mo layer, N layer, Cr layer and Co layer; among them, the amount of carbon, silicon, molybdenum and chromium nitride (nitrogen) is relatively small, add them together and put them at the bottom layer; 3. Evacuate the vacuum induction furnace until the pressure inside the furnace is less than 0.1Pa, and measure the gas leakage rate to make it less than 2Pa / min; 4. Fill the furnace with nitrogen to 0.03~0.04MPa; 5. Heat up and melt, and turn the power to 340~360KW; 6. After the purification is complete, the power is reduced to 180~200KW, and the temperature is kept at 1550~1570℃ for 30 minutes. 7. Turn off the power and wait for 10-30 minutes for a film to form on the surface of the molten steel. The temperature should be 1470-1490℃. 8. Turn on the power, the power rises to 300KW, and then manganese is added through the charging chamber; 9. When the temperature rises to 1520~1530℃, start pouring, and the pouring speed is controlled at 90~110KG / min; during pouring, the structure of mold tube, diverter plate and filter plate is adopted from bottom to top; the mold tube specification is Φ54mm*620mm, arranged in a 4*6 array, and two groups are set. Boron nitride is sprayed on the inner wall of the mold tube, and a diverter plate is placed on the mold tube to play the role of pouring each mold tube; a filter plate is placed on the diverter plate to receive the molten steel poured from the crucible and transition to the diverter plate; after the mold tube, diverter plate and filter plate are assembled, preheat for 3~4 hours at a temperature of 500~800℃, and then put into a vacuum induction furnace to start vacuuming and pouring; 10. After pouring, wait in the furnace for 30 minutes, turn off the nitrogen and argon, and take it out of the furnace.

[0027] Implementation 2: This embodiment is substantially the same as embodiment 1, except that, in this embodiment, the ingredients are 80% new material + 20% returned material; the stacking method is that the stacking order of the components from the bottom of the crucible to the top is: C layer, Si layer, Mo layer, N layer, Cr layer and Co layer; among them, the amount of carbon, silicon, molybdenum and chromium nitride (nitrogen) is relatively small, and they are added together and placed in the second bottom layer; the returned material is placed in the bottom layer.

[0028] Apart from this, this embodiment is completely the same as Embodiment 1 and will not be described in detail here.

[0029] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent transformation or modification made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy using a two-chamber vacuum induction furnace, characterized in that: The following steps are involved: Step 1, ingredients: by mass percentage, the nitrogen-containing cobalt-chromium-molybdenum alloy components are as follows: C0.22-0.25%, Cr28.0-29.0%, Mo5.5-6.5%, Fe≤1%, Ni≤1%, Si≤1%, Mn≤0.6%, N0.1-0.2%, Co balance; Step 2, stacking: stacking the components in S1: from the bottom of the crucible upward, the components are stacked in the order of higher density and weaker oxidizing properties as they go up; Step 3: Vacuum melting: S1. The smelting chamber is evacuated; followed by nitrogen filling; S2. Heat up and melt, set the melting chamber power to 340~360KW; until it is completely melted, set the melting chamber power to 180~200KW, and keep warm for refining; S3. Turn off the power and wait until a film appears on the surface of the molten steel; S4. Power on again, wait for the power of the melting chamber to rise to 300KW, and add Mn to the molten steel; Step 4: Pouring: When the temperature of the molten steel rises to 1520~1530℃, start pouring at a speed of 90~110KG / min.

2. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 1, characterized in that: The ingredients used are new materials or a mixture of new materials and returned materials; wherein the mixture, calculated by mass percentage, includes 80% new materials and 20% returned materials.

3. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 2, characterized in that: If the ingredients are a mixture of new materials and returned materials, the returned materials will be at the bottom of the crucible during stacking.

4. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 1, characterized in that: In S1, the vacuum treatment specifically includes: vacuuming until the pressure in the furnace is less than 0.1 Pa, measuring the gas leakage rate, and making the gas leakage rate less than 2 Pa / min.

5. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 1, characterized in that: In S1, nitrogen is filled until the pressure inside the furnace is 0.03~0.04MPa.

6. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 1, characterized in that: In S2, the heat preservation refining specifically includes: heat preservation refining for 25-35 minutes, and the temperature of the molten steel after refining is 1550-1570°C.

7. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 1, characterized in that: In S3, the power is turned off and the liquid is left to stand for 10 to 30 minutes until a film appears on the surface of the molten steel. The temperature of the molten steel is 1470 to 1490°C.

8. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 1, characterized in that: In step 4, the pouring is specifically as follows: spraying boron nitride on the inner wall of the mold tube, then arranging the mold tube array, assembling the mold tube, the diverter plate, and the filter plate from bottom to top; preheating the assembled device for 3 to 4 hours at a temperature of 500 to 800°C; finally, placing the preheated device into a vacuum induction furnace for melting, and starting vacuuming, melting, and pouring.

9. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 8, characterized in that: Step 5 is also included after step 4: placing the mold tube after casting in the furnace for 25-35 minutes, turning off nitrogen and argon, and taking it out of the furnace.

10. The method for preparing nitrogen-containing cobalt-chromium-molybdenum alloy by a two-chamber vacuum induction furnace according to claim 9, characterized in that: The specification of the two-chamber vacuum induction furnace is 500KG, and the specification of the mold tube is Φ54mm*620mm.

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