Smelting method for desulfurizing nickel-based superalloy by adding nickel-calcium alloy

Abstract

The invention relates to the technical field of metal smelting, in particular to a smelting method for desulfurizing a nickel-based superalloy by adding a nickel-calcium alloy, a small amount of nickel-calcium alloy is added into molten steel, the content of a harmful impurity sulfur element in the molten steel can be effectively reduced by adding the nickel-calcium alloy into the molten steel, the desulfurization rate exceeds 70%, and the nickel-based superalloy can be completely desulfurized. And the sulfur element in the finished product is controlled to be lower than 10 ppm, and the calcium content in the finished product is lower than 5 ppm, so that the subsequent process is not influenced, and the technical problems that the sulfur content in the finished product is relatively high, the high-temperature performance of the alloy is very low when the S element content of the alloy is 30 ppm and the requirement is difficult to meet due to the fact that desulfurization cannot be carried out in the smelting process and the vacuum self-consumption process in the prior art are solved in this way.

Description

Technical Field

[0001] The invention relates to the technical field of metal smelting, and in particular to a smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy. Background Art

[0002] High-temperature alloy refers to an alloy based on iron, nickel and cobalt. It is usually used stably for a long time at a temperature of up to 600℃. Due to the high degree of alloying, it usually contains a variety of main elements and trace elements, and is also called "superalloy". Trace elements at the ppm level can significantly affect the mechanical properties and structure of high-temperature alloys. Among them, the non-metallic element S is a harmful element, which has a great harmful effect on the durability, creep performance and tensile plasticity of high-temperature alloys. Its content must be controlled to the lowest possible level;

[0003] In order to improve the performance and stability of high-temperature alloy materials currently used in aerospace, the purity of materials is increasingly required, especially the sulfur content. The materials used in key components now require the sulfur content to be less than 15ppm. At present, the sulfur content of nickel-based high-temperature alloys, especially those using vacuum induction melting and vacuum consumable process routes, is often higher than 30ppm, which seriously affects the performance of the finished product; the S element mainly comes from the Cr metal raw materials in the raw materials. Taking GH648 as an example, its Cr content is 33%, and the sulfur content in the raw materials exceeds 30ppm.

[0004] However, the existing smelting process and vacuum consumable process are unable to carry out desulfurization, resulting in a high sulfur content in the finished product. When the S element content of the alloy is 30ppm, its high-temperature performance is very low and it is difficult to meet the demand. Summary of the invention

[0005] The purpose of the present invention is to provide a smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy, aiming to solve the technical problem that the smelting process and the vacuum consumable process in the prior art cannot perform desulfurization, resulting in a high sulfur content in the finished product. When the S element content of the alloy is 30ppm, its high-temperature performance is very low and it is difficult to meet the demand.

[0006] To achieve the above object, the present invention adopts a smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy.

[0007] The following steps are involved:

[0008] Step 1: Prepare the raw materials according to the alloy ratio, and calculate the harmful element S content in the ingredient list according to the quality assurance certificate provided by the raw material manufacturer;

[0009] Step 2: Use a 6T vacuum induction furnace to smelt the alloy and measure the leakage rate. If the leakage rate is ≤2Pa / min and the difference between the two leakage rates is ≤0.3Pa, the refining can be terminated, the induction heating can be turned off, and the temperature can be lowered to the specified temperature.

[0010] Step 3: Place the nickel-calcium alloy into the side feeding trough and add it into the furnace through the side feeding trough;

[0011] Step 4: Turn off the vacuum pump and fill with argon gas;

[0012] Step 5: Adjust the crucible heating power of the vacuum furnace to 200 kW, use this power to keep warm, and switch to the stirring mode to stir the crucible so that the liquid surface shakes slightly;

[0013] Step 6: Pour the molten steel into the mold and let the molten steel mold cool for a specified time without opening the air valve;

[0014] Step 7: Open the air valve to connect the pouring chamber to the atmosphere. After the molten steel solidifies and cools, cut a 100mm thick slice from the end of the alloy bar and drill a shavings sample at 1 / 2R of the slice. The sample weight is 20g.

[0015] Step 8: Analyze the sample and detect the sulfur content in the sample.

[0016] Wherein, in step 2, the gas leakage rate is measured after refining in a 6T vacuum induction furnace for 40 minutes.

[0017] Among them, in step 2, turning off the induction heating, and cooling to the specified temperature refers to cooling to 1460-1480°C.

[0018] Wherein, in step three, the amount of nickel-calcium alloy added is: 0.04-0.055% nickel-calcium alloy is added for every 10 ppm of S.

[0019] Wherein, in step 4, the vacuum pump is turned off and the pressure of the argon gas filled is 10000-15000Pa.

[0020] Wherein, in step five, the crucible is stirred so that the liquid surface is slightly shaken for a duration of 20 to 30 minutes.

[0021] Among them, in step six, the specified time for cooling the molten steel mold is 120 to 150 minutes.

[0022] In step eight, the sample is analyzed, and the equipment used to detect the sulfur content in the sample is Eltra CS-800 carbon-sulfur analyzer.

[0023] The present invention discloses a smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy. The method adopts the method of adding a small amount of nickel-calcium alloy, wherein the added weight accounts for only 0.14%, and is added to molten steel to effectively reduce the content of harmful impurity sulfur element in the molten steel. The desulfurization rate exceeds 70%, and the sulfur element in the finished product is controlled to be lower than 10ppm, and the calcium content in the finished product is lower than 5ppm, which will not affect the subsequent process. In this way, the technical problem that the smelting process and the vacuum consumable process in the prior art cannot be desulfurized, resulting in a high sulfur content in the finished product, and when the alloy S element content is 30ppm, its high-temperature performance is very low and it is difficult to meet the demand is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 It is a schematic diagram of the effect of the S element of the present invention on the high temperature plasticity of the nickel-based high temperature alloy.

[0026] Figure 2 It is a schematic diagram of the density of GH4738 of the present invention at different temperatures.

[0027] Figure 3 It is a schematic diagram of sulfur content in Test 1 of the present invention.

[0028] Figure 4 Schematic diagram of the disulfide content test of the present invention.

[0029] Figure 5 It is a schematic diagram of the test trisulfur content of the present invention.

[0030] Figure 6 This is a slag diagram on the surface of molten steel according to the present invention.

[0031] Figure 7 This is a diagram showing the desulfurization effect of an experiment conducted on GH648 for 8 batches according to the present invention. DETAILED DESCRIPTION

[0032] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0033] See also Figure 1 to Figure 7 ,in Figure 1 Schematic diagram of the effect of the S element on the high temperature plasticity of the nickel-based high temperature alloy of the present invention, Figure 2It is a schematic diagram of the density of GH4738 at different temperatures of the present invention, Figure 3 is a schematic diagram of sulfur content in test one of the present invention, Figure 4 is a schematic diagram of the test disulfide content of the present invention, Figure 5 is a schematic diagram of the test trisulfur content of the present invention, Figure 6 It is the slag diagram on the surface of molten steel of the present invention, Figure 7 This is a diagram showing the desulfurization effect of an experiment conducted on GH648 for 8 batches according to the present invention.

[0034] The present invention provides a smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy, comprising the following steps:

[0035] Step 1: Prepare the raw materials according to the alloy ratio, and calculate the harmful element S content in the ingredient list according to the quality assurance certificate provided by the raw material manufacturer;

[0036] Step 2: Use a 6T vacuum induction furnace to smelt the alloy and measure the leakage rate. If the leakage rate is ≤2Pa / min and the difference between the two leakage rates is ≤0.3Pa, the refining can be terminated, the induction heating can be turned off, and the temperature can be lowered to the specified temperature.

[0037] Step 3: Place the nickel-calcium alloy into the side feeding trough and add it into the furnace through the side feeding trough;

[0038] Step 4: Turn off the vacuum pump and fill with argon gas;

[0039] Step 5: Adjust the crucible heating power of the vacuum furnace to 200 kW, use this power to keep warm, and switch to the stirring mode to stir the crucible so that the liquid surface shakes slightly;

[0040] Step 6: Pour the molten steel into the mold and let the molten steel mold cool for a specified time without opening the air valve;

[0041] Step 7: Open the air valve to connect the pouring chamber to the atmosphere. After the molten steel solidifies and cools, cut a 100mm thick slice from the end of the alloy bar and drill a shavings sample at 1 / 2R of the slice. The sample weight is 20g.

[0042] Step 8: Analyze the sample and detect the sulfur content in the sample.

[0043] Wherein, in step 2, the gas leakage rate is measured after refining in a 6T vacuum induction furnace for 40 minutes.

[0044] Among them, in step 2, turning off the induction heating, and cooling to the specified temperature refers to cooling to 1460-1480°C.

[0045] Wherein, in step 4, the vacuum pump is turned off and the pressure of the argon gas filled is 10000-15000Pa.

[0046] Wherein, in step five, the crucible is stirred so that the liquid surface is slightly shaken for a duration of 20 to 30 minutes.

[0047] Among them, in step six, the specified time for cooling the molten steel mold is 120 to 150 minutes.

[0048] In step eight, the sample is analyzed, and the equipment used to detect the sulfur content in the sample is Eltra CS-800 carbon-sulfur analyzer.

[0049] Since most vacuum induction furnaces now use magnesium oxide aluminum dry pots instead of calcium oxide crucibles, it is necessary to add Ca elements for desulfurization; taking GH4738 as an example, its density is still higher than 7g / cm3 at 1500℃, while the density of calcium is only 1.55g / cm 3 When calcium is added, the calcium element cannot penetrate into the molten steel for desulfurization; therefore, this application uses nickel-calcium alloy for desulfurization, which has a density of about 8.4g / cm3 and can effectively penetrate into the molten steel to achieve the desulfurization effect;

[0050] A 6T vacuum induction furnace was selected, and the crucible wall was made of MgO and Al2O3 crucible to smelt GH648 and GH738 alloys. The alloy composition is shown in Table 1 and Table 2:

[0051] Table 1 Chemical composition of GH648 alloy wt%

[0052]

[0053] Table 2 GH738 alloy chemical composition wt%

[0054]

[0055] Test 1:

[0056] In a 6t vacuum induction furnace, two furnaces of GH648 and two furnaces of GH738 were tested. The sulfur content of the raw materials was 30ppm and 20ppm respectively. After all the alloy materials were melted, the alloy material composition was adjusted. 0.046% nickel-calcium alloy was added for every 10ppmS content. Argon was filled after 10 minutes, and steel was tapped after 20 minutes. The sulfur content results were as follows: Figure 3 :

[0057] It was found that after adding Ni-Ca, the sulfur content reduction effect was not very good, the sulfur content in the finished product was still high, and the expected desulfurization effect was not achieved;

[0058] Test 2:

[0059] In a 6t vacuum induction furnace, two furnaces of GH648 and two furnaces of GH738 were tested. During the smelting of GH648, the sulfur content of the raw materials was 30ppm. After all the alloy materials were melted, 9kg of nickel-calcium alloy was added to the furnace. After 10 minutes, argon gas was filled and steel was tapped after 20 minutes.

[0060] During the smelting of GH738, the sulfur content brought into the raw materials is about 20ppm. After all the alloy materials are melted, 0.046% nickel-calcium alloy is added to the furnace for every 10ppmS content. Argon gas is filled after 10 minutes, and steel is tapped after 20 minutes.

[0061] The sulfur content results are shown in Figure 4 It was found that the Ni-Ca content was increased this time, but the sulfur content did not decrease in direct proportion. The sulfur content in the finished product was still high, and the expected desulfurization effect was not achieved.

[0062] Test 3

[0063] In a 6t vacuum induction furnace, two furnaces of GH648 and two furnaces of GH738 were tested, and the nickel-calcium alloy was adjusted to be added after the argon gas was filled;

[0064] During the smelting of GH648, the sulfur content of the raw materials is 30ppm. After all the alloy materials are melted, they are kept warm for 10 minutes and then filled with argon gas. 0.046% of nickel-calcium alloy is added to the furnace for every 10ppmS content, and the steel is tapped after keeping warm for 20 minutes.

[0065] During the smelting process of GH738, the sulfur content brought into the raw materials is about 20ppm. After all the alloy materials are melted, they are kept warm for 10 minutes and then filled with argon gas. 6kg of nickel-calcium alloy is added to the furnace and the steel is produced after 20 minutes.

[0066] The sulfur content results are as follows: Figure 5 It was found that after the adjustment of this test plan, the desulfurization effect of Ni-Ca alloy was significantly improved, and the sulfur content was controlled below 10ppm, achieving the expected desulfurization effect.

[0067] Method summary:

[0068] According to the above experience, it is found that the strong binding force between Ca and S can be used to effectively desulfurize by adding nickel calcium. The main reason for the failure of Experiments 1 and 2 is that the temperature of the molten steel is 1480-1500℃ after the refining period, and Ca is very easy to volatilize under high temperature vacuum (boiling point 1484℃), so the added nickel calcium does not combine with the free sulfur element in the molten steel before volatilization, and the desulfurization effect is not achieved.

[0069] In the third test, it was modified to be added before steel tapping and after argon filling. The temperature before steel tapping was 1400-1480℃. The lower temperature and the protective atmosphere after argon filling made sulfur less likely to volatilize, and it could fully combine with sulfur to achieve the desulfurization effect.

[0070] The conventional vacuum furnace uses a CaO crucible for desulfurization, generating 3CaO·Al2O3 slag that adheres to the inner wall of the crucible for desulfurization; the crucible of the present application uses MgO and Al2O3 crucibles, and the Ca element is added to react with S to generate CaS, forming light inclusions that float on the surface of the molten steel. After being poured into the chute, the inclusions float on the upper layer of the molten steel in the chute, and are blocked in the chute by the slag baffle and the filter, effectively reducing the sulfur content in the molten steel, thereby achieving a desulfurization effect.

[0071] Subsequently, 8 batches of tests were conducted on GH648, and the values ​​of sulfur content and Ca content were collected. Figure 6 , using this desulfurization process, the desulfurization effect is stable, the sulfur content in the product is less than 10ppm, the desulfurization rate is greater than 70%, and the residual calcium content in the molten steel after desulfurization is completed is less than 5ppm;

[0072] A smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy according to the present embodiment is used. A small amount of nickel-calcium alloy is added, and the added weight accounts for only 0.14%. When added to the molten steel, the content of harmful impurity sulfur in the molten steel can be effectively reduced. The desulfurization rate exceeds 70%, and the sulfur content in the finished product is controlled to be lower than 10ppm, and the calcium content in the finished product is lower than 5ppm, which will not affect the subsequent process. In this way, the technical problem that the smelting process and the vacuum consumable process in the prior art cannot be desulfurized, resulting in a high sulfur content in the finished product, and when the alloy S element content is 30ppm, its high temperature performance is very low and it is difficult to meet the demand is solved.

[0073] The present invention has the following beneficial effects:

[0074] In order to control the sulfur content of the finished product to a lower level and ensure the purity of the material, the traditional method is to use purer raw materials, such as high-purity metallic chromium, but this will significantly increase the cost. The price of high-purity chromium is about 230% of metallic chromium. This solution only uses a small amount of nickel-calcium alloy, which is about 0.14% of the total weight of the molten steel, to reduce the sulfur content in the finished product. This method can reduce costs.

[0075] This method uses a nickel-calcium alloy with a Ca content of less than 6%, and the remaining 94% is nickel. More nickel can increase the density of the alloy, allowing it to sink into the lower part of the molten steel and fully combine with the sulfur element to achieve a desulfurization effect.

[0076] The method adopts appropriate temperature and timing to add nickel-calcium alloy, and adds the alloy when the temperature of molten steel is between 1400 and 1480°C and the furnace is filled with protective gas, so as to reduce the burning loss of calcium element.

[0077] After adding nickel and calcium, the heat preservation time is longer than 20 minutes, so that the calcium element and the sulfur element are combined to form light slag, which floats on the surface of the molten steel, reduces the slag content inside the molten steel, and improves the purity of the molten steel.

[0078] What is disclosed above is only a preferred embodiment of the present invention, and it certainly cannot be used to limit the scope of rights of the present invention. Ordinary technicians in this field can understand that all or part of the processes of the above embodiment and equivalent changes made according to the claims of the present invention still fall within the scope of the invention.

Claims

1. A smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy, It is characterized in that The following steps are involved: Step 1: Prepare the raw materials according to the alloy ratio, and calculate the harmful element S content in the ingredient list according to the quality assurance certificate provided by the raw material manufacturer; Step 2: Use a 6T vacuum induction furnace to smelt the alloy and measure the leakage rate. If the leakage rate is ≤2Pa / min and the difference between the two leakage rates is ≤0.3Pa, the refining can be terminated, the induction heating can be turned off, and the temperature can be lowered to the specified temperature. Step 3: Place the nickel-calcium alloy into the side feeding trough and add it into the furnace through the side feeding trough; Step 4: Turn off the vacuum pump and fill with argon gas; Step 5: Adjust the crucible heating power of the vacuum furnace to 200 kW, use this power to keep warm, and switch to the stirring mode to stir the crucible so that the liquid surface shakes slightly; Step 6: Pour the molten steel into the mold and let the molten steel mold cool for a specified time without opening the air valve; Step 7: Open the air valve to connect the pouring chamber to the atmosphere. After the molten steel solidifies and cools, cut a 100mm thick slice from the end of the alloy bar and drill a shavings sample at 1 / 2R of the slice. The sample weight is 20g. Step 8: Analyze the sample and detect the sulfur content in the sample.

2. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 1, characterized in that: In step 2, the gas leakage rate is measured after refining for 40 minutes using a 6T vacuum induction furnace.

3. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 2, characterized in that: In step 2, the induction heating is turned off, and cooling to a specified temperature refers to cooling to 1460-1480°C.

4. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 3, characterized in that: In step three, the amount of nickel-calcium alloy added is: 0.04-0.055% nickel-calcium alloy is added for every 10 ppm of S.

5. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 4, characterized in that: In step 4, the vacuum pump is turned off and the pressure of the argon gas filled is 10000-15000Pa.

6. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 5, characterized in that: In step five, the crucible is stirred so that the liquid surface is slightly shaken for 20 to 30 minutes.

7. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 6, characterized in that: In step six, the specified time for cooling the molten steel mold is 120 to 150 minutes.

8. The smelting method for desulfurizing a nickel-based high-temperature alloy by adding a nickel-calcium alloy as claimed in claim 7, characterized in that: In step eight, the sample is analyzed, and the equipment used to detect the sulfur content in the sample is Eltra CS-800 carbon sulfur analyzer.

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