A method for controlling porosity in high-W nickel-based superalloy castings

Abstract

The present invention provides a method for controlling porosity of a high-W nickel-based superalloy and its castings. The preparation method includes: preparing a wax pattern assembly; immersing the wax pattern assembly in refractory coating, sprinkling sand, and performing drying and strengthening treatment; coating the thicker parts of the mold shell prone to shrinkage porosity with wax material. After the wax material cools and solidifies, directly immerse the mold shell in the refractory coating to complete the preparation of the remaining backing layer; dewaxing and roasting; wrapping the pouring cup with a heat-insulating layer; preheating, pouring, and cleaning the residual shell after the alloy liquid cools and solidifies to obtain the casting. The present invention applies wax material with a relatively low melting point and good coating property to the parts of the casting prone to shrinkage porosity, accelerating local heat dissipation. At the same time, by different ways of wrapping cotton on the pouring cup and the body of the mold shell with different thicknesses, there is sufficient liquid for the casting to be supplemented during the pouring process, reducing the occurrence of shrinkage porosity in the casting. This method is applicable to castings of different sizes, and has a simple process, strong operability, and effectively improves the yield of the casting.

Description

Technical Field

[0001] The present invention belongs to the technical field of investment precision casting of superalloys, and particularly relates to a method for controlling porosity of high-W nickel-based superalloy castings. Background Art

[0002] Nickel-based superalloys have good comprehensive mechanical properties, oxidation resistance and tissue stability, and are widely used in the preparation of hot-end components of aeroengines. The main strengthening methods are solid solution strengthening, γ'-phase strengthening and carbide strengthening. High alloying is one of the main methods to improve the solid solution strengthening level of alloys. At present, a large amount of refractory elements such as W, Mo, Ta, Re, etc. are mainly added to the alloy to increase the primary melting temperature of the γ / γ'-phase. Especially for high-generation nickel-based single crystal superalloys, more than 5% of Re element is added in the composition design. Although the temperature-bearing capacity of the alloy is improved, the use cost of the alloy also increases significantly. Among many refractory elements, metal W is inexpensive and has excellent strengthening effect in nickel-based superalloys, and is an alloy element that can significantly improve the temperature-bearing capacity of alloys. Therefore, high-W nickel-based alloys have the advantages of good tensile properties, creep properties and low cost. However, due to the relatively large amount of W added, the initial solidification temperature of the alloy is relatively high, the solidification range is relatively wide, and the solidification time is relatively long, resulting in a relatively large total heat release during the solidification of the alloy. Thermal joints are easily formed at the transitions with sudden size changes, causing large-area porosity.

[0003] Investment casting is one of the important processes for obtaining precision castings, and is usually used for the preparation of parts with high dimensional accuracy requirements, and is applied to many fields such as aviation, aerospace, shipbuilding, automobiles, energy, medical treatment, etc. During the investment casting process, porosity is one of the common defects. Especially for superalloys with complex compositions and wide solidification windows, due to the large number of elements in the alloy (usually more than ten added elements), and the solidification temperature differences of each element are relatively large, up to more than 1000 °C. When the casting structure is complex and the volume of the area with sudden size change is large, the transition part is easily the main area where thermal joints are generated. During solidification, the upper area often solidifies first and cannot effectively compensate for shrinkage, and finally a large amount of solidification porosity appears in this area, which becomes one of the main reasons for the rejection of alloy castings.

[0004] Research shows that the main heat sources for the formation of hot spots during the solidification of castings are the accumulation of heat released during the solidification of the molten metal around this area and the large amount of heat storage generated in the mold shell in this area after the alloy liquid is poured in. The former is mainly controlled by the part design structure and size, while the latter is mainly controlled by the mold shell preparation process. To eliminate or transfer the hot spots, the method of increasing the heat conduction of the cooling components near the area prone to form hot spots can be adopted, such as using methods like adding risers, adding chill irons or graphite blocks, etc. However, these methods are usually complex in operation and high in implementation cost. Especially for small-sized castings, it is difficult to achieve mass production in the actual production process.

[0005] Therefore, for high-W nickel-based superalloys with a relatively wide solidification temperature range, a simple and effective process method is needed to control the porosity ratio at the transition of the size mutation area of their alloy castings, which not only helps to improve the qualification rate of the castings, but also helps to develop the application potential of such low-cost and high-performance alloys. From the technical and economic perspectives, it has profound strategic significance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for controlling the porosity of high-W nickel-based superalloy castings in view of the deficiencies of the above-mentioned prior art. This method smears a wax material with a relatively low melting point and good coating property on the parts of the casting prone to shrinkage porosity, accelerating local heat dissipation. At the same time, by wrapping cotton in different thicknesses at the pouring cup and the main body of the mold shell, there is sufficient liquid for the casting during the pouring process, reducing the generation of shrinkage porosity in the casting. This method is applicable to castings of different sizes, with simple process and strong operability, effectively improving the yield of the castings.

[0007] To solve the above technical problem, the technical solution adopted by the present invention is: a method for controlling the porosity of high-W nickel-based superalloy castings, and this method is as follows:

[0008] S1. Inject wax into the product mold, and after the mold material cools, obtain the product wax mold to be cast; weld the wax mold with the gating system to obtain the wax mold assembly.

[0009] S2. After cleaning the surface oil film of the wax mold assembly obtained in S1, immerse it in the refractory coating so that its surface is evenly coated with the refractory coating. After sand spraying on the surface of the wax mold assembly with the refractory coating evenly coated on the surface and drying and hardening, form the first layer of backing layer. Repeat the operations of immersing in the refractory coating, sand spraying, and drying and hardening multiple times, and a total of n layers of backing layers are coated to obtain a shell with n layers; 5 ≤ n ≤ 7, and n is a natural number.

[0010] The method of sand spraying is: the sand spraying in the first layer of backing layer is corundum sand, and the sand spraying in the 2nd to nth layers of backing layers is mullite.

[0011] During the process of preparing the mold shell, a layer of wax material with a thickness of 1 mm to 1.4 mm is coated at the casting transition joint; after the wax material cools and solidifies, the mold shell is directly immersed in the refractory coating to complete the preparation of the remaining back layer; the casting flange transition joint is a thicker part prone to shrinkage porosity.

[0012] If the thickness of the casting transition joint < 5 mm, the wax material is coated on the (n - 1)-th layer of the mold shell.

[0013] If the thickness of the casting transition joint ≥ 5 mm, the wax material is coated on the (n - 2)-th layer of the mold shell.

[0014] The casting transition joint is a thicker part prone to shrinkage porosity. Since the wax material coated locally has not been cleaned and there is an oil film on the surface, the bonding force between its surface and the slurry is poor during dipping. When preparing the remaining back layer, only less slurry is dipped on this part, resulting in a thinner mold shell thickness, reducing the heat storage capacity of the mold shell, accelerating the solidification of the flange transition joint, avoiding overly thick dendrites, and thus reducing the generation of shrinkage porosity.

[0015] S3. Dewax the mold shell obtained in S2, and after dewaxing is completed, perform baking to obtain the baked mold shell.

[0016] S4. Wrap the pouring cup of the baked mold shell obtained in S3 with a heat-insulating layer to obtain the mold shell wrapped with the heat-insulating layer.

[0017] S5. Preheat the mold shell wrapped with the heat-insulating layer obtained in S4 and then pour high-W nickel-based superalloy liquid. After cooling and solidifying, clean the residual shell to obtain a high-W nickel-based superalloy casting.

[0018] The high-W nickel-based superalloy liquid is composed of raw materials with the following mass fractions: C: 0.13% - 0.19%, Cr: 8.00% - 9.50%, Co: 9.00% - 10.50%, W: 9.5% - 11.00%, Mo: 1.20% - 2.40%, Al: 5.10% - 6.00%, Ti: 2.10% - 2.90%, Nb 0.80% - 1.20%, Fe ≤ 1.0%, Zr ≤ 0.040%, B ≤ 0.035%, Ce ≤ 0.02%, Y ≤ 0.01%, Si ≤ 0.40%, and the balance is Ni.

[0019] Preferably, the refractory coating in S2 is a mixture of corundum powder and polymer silica sol; the particle size of the corundum powder is 20 - 45 μm, containing 99.3 - 99.5% alumina; the model of the polymer silica sol is Nalco ESB PRIME.

[0020] Preferably, the dewaxing method in S3 is as follows: the mold shell is dewaxed by steam pressurization using a dewaxing kettle, the sprue cup of the mold shell is placed downward, the dewaxing temperature is 180°C to 200°C, the dewaxing time is 13 min to 17 min, and the pressure is 7.9 bar to 8.5 bar.

[0021] Preferably, the roasting temperature in S3 is 940°C to 960°C, and the roasting time of the mold shell is ≥4 h.

[0022] Preferably, the material of the thermal insulation layer in S4 is cobalt aluminate cotton, and the thickness of each layer of the thermal insulation layer is 5 mm.

[0023] Preferably, the cup part of the sprue cup in S4 is wrapped with 2 layers of thermal insulation layer, and the pipe mouth part of the sprue cup is wrapped with 1 layer of thermal insulation layer; the mold shell body part far from the sprue cup is not wrapped with thermal insulation cotton, so as to form a temperature gradient that gradually increases along the direction from the sprue cup part of the mold shell to the mold shell body part during the solidification of the casting.

[0024] Preferably, the preheating temperature in S5 is 900°C to 1200°C, and the preheating time is 4 h to 8 h.

[0025] Preferably, the pouring temperature in S5 is 1450°C to 1500°C.

[0026] The present invention has the following advantages compared with the prior art:

[0027] A method for controlling porosity of a high-W nickel-based superalloy casting provided by the present invention has a design idea that during the preparation of the mold shell, a wax material with a lower melting point and better coating property is smeared on the locally thicker part of the casting where shrinkage porosity is likely to form. Since the thickness of the wax-coated part of the mold shell after dewaxing is thinner than that of the non-wax-coated part, the heat storage amount in the local area of the mold shell is reduced, and the heat dissipation of this part is accelerated, thereby reducing the formation of shrinkage porosity defects. At the same time, by wrapping the sprue cup and the mold shell body part of the mold shell with different thicknesses of cotton, a temperature gradient that gradually increases along the direction from the sprue cup part of the mold shell to the mold shell body part is formed during the solidification of the casting, so that there is sufficient liquid for the casting to be supplemented during the pouring process. By wrapping the thermal insulation layer in decreasing order of the number of layers from top to bottom, a temperature field condition for directional solidification of the casting is formed, thereby reducing the generation of shrinkage porosity in the casting and finally achieving the purpose of increasing the yield of alloy castings.

[0028] The following further describes the present invention in detail with reference to the drawings and embodiments. Description of the Drawings

[0029] Figure 1 It is a schematic diagram of wax material coated on the outer surface of the 5th layer of the mold shell in Embodiment 1 of the present invention.

[0030] Figure 2Schematic diagram of the 6-layer shell prepared in step S2 of Embodiment 1 of the present invention.

[0031] Figure 3 Schematic diagram of the shell of Embodiment 1 of the present invention wrapped with heat insulation cotton.

[0032] Figure 4 Schematic diagram of shrinkage porosity at the flange transition part of the K465 polycrystalline superalloy casting in Embodiment 1 of the present invention.

[0033] Figure 5 Schematic diagram of shrinkage porosity at the flange transition part of the K465 polycrystalline superalloy casting in Comparative Example 1 of the present invention.

[0034] Figure 6 Schematic diagram of shrinkage porosity at the flange transition part of the K465 polycrystalline superalloy casting prepared in Embodiment 2 of the present invention.

[0035] Figure 7 Schematic diagram of shrinkage porosity at the flange transition part of the K465 polycrystalline superalloy casting prepared in Embodiment 3 of the present invention. Detailed implementation manners

[0036] Embodiment 1

[0037] In this embodiment, a nickel-based superalloy casting with high W is used, and the thickness at the casting transition is 4.5 mm (<5 mm).

[0038] The method for controlling porosity of the nickel-based superalloy casting in this embodiment is as follows:

[0039] S1. Inject wax into the product mold (engine polycrystalline casting), and after the mold material cools, obtain the product wax mold to be cast; weld the wax mold with the gating system to obtain a wax mold assembly;

[0040] S2. After cleaning the surface oil film of the wax mold assembly obtained in S1, immerse it in a refractory coating so that its surface is evenly coated with the refractory coating. After sand spraying on the surface of the wax mold assembly with the evenly coated refractory coating and drying and hardening, form the first back layer. Repeat the operations of immersing in the refractory coating, sand spraying, and drying and hardening multiple times, and a total of 6 back layers are coated to obtain a 6-layer shell;

[0041] The refractory coating is a mixture of corundum powder and polymer silica sol, and the mass ratio of polymer silica sol to corundum powder is 1:3.5; the particle size of corundum powder is 20-45 μm, containing 99.3% alumina; the polymer silica sol model is Nalco ESB PRIME;

[0042] The method of sand spraying is as follows: the sand spraying for the first back layer is corundum sand, and the sand spraying for the 2nd to 6th back layers is mullite;

[0043] Before preparing the last layer (the 6th layer) of the mold shell, put solid red wax into a crucible and heat it. After it is completely melted, evenly apply it to the thicker part of the mold shell where shrinkage porosity is likely to form (such as the transition part of the casting flange). Coat it with a layer of wax material with a thickness of 1 mm (see Figure 1 ), that is, apply the wax material to the 5th layer of the mold shell; after the wax material cools and solidifies, directly immerse the mold shell into the refractory coating, sprinkle sand and dry to complete the preparation of the last layer of the mold shell (see Figure 2 ); Figure 2 Since the wax material coated locally has not been cleaned and there is an oil film on the surface, the bonding force between its surface and the slurry is poor during slurry dipping, and only less slurry is dipped on this part;

[0044] S3. Dewax the mold shell obtained in S2. After dewaxing, the thickness of the mold shell at the part coated with wax material is about 56 mm, and the thickness of the mold shell at the part not coated with wax material is about 70 mm. After dewaxing, perform roasting to obtain the roasted mold shell; the method of dewaxing is: use a dewaxing kettle to perform steam pressure dewaxing on the mold shell. Place the sprue cup of the mold shell downward and place it steadily on the dewaxing cart. When the indicated pressure reaches 8.2 bar, gently push the loading cart into the dewaxing kettle, close and lock the door, immediately open the air inlet valve. The dewaxing temperature is 190 °C, and the dewaxing time is 15 min. After the operation program ends, take out the cavity mold shell; the roasting temperature is 950 °C, and the roasting time of the mold shell is 4 h;

[0045] S4. Wrap the sprue cup of the roasted mold shell obtained in S3 with a heat insulation layer to obtain a mold shell wrapped with a heat insulation layer; the material of the heat insulation layer is cobalt aluminate cotton, and the thickness of each layer of the heat insulation layer is 5 mm;

[0046] Wrap 2 layers of heat insulation layer around the cup part of the sprue cup, and wrap 1 layer of heat insulation layer at the pipe mouth of the sprue cup (see Figure 3 ); Do not wrap the heat insulation cotton on the part of the mold shell body far from the sprue cup, so as to form a temperature gradient that gradually increases along the direction from the sprue cup part to the mold shell body part of the casting during solidification. The heat insulation layer wrapping the sprue cup realizes a gradually increasing thickness by adjusting the number of layers. By wrapping the heat insulation layer with the number of layers decreasing from top to bottom in sequence, it is more likely to form the temperature field conditions for directional solidification of the ingot material, thereby reducing the shrinkage porosity of the casting;

[0047] S5. Preheat the mold shell wrapped with a heat insulation layer obtained in S4 at a temperature of 1000 °C for 6 h, then pour high-W nickel-based superalloy liquid at 1480 °C. After cooling and solidifying, clean the residual shell to obtain a high-W nickel-based superalloy casting (that is, K465 polycrystalline superalloy casting). Dissect the transition part of the casting flange. The schematic diagram of the shrinkage porosity morphology after dissection is shown in Figure 4 , and no shrinkage porosity phenomenon is observed.

[0048] The high-W nickel-based superalloy liquid (K465 nickel-based superalloy liquid) consists of raw materials with the following mass fractions: C: 0.17 wt.%, Cr: 8.50 w.t%, Co: 10.00 wt.%, W: 10.50 wt.%, Mo: 2.00 wt.%, Al: 5.50 wt.%, Ti: 2.50 wt.%, Nb: 1.00 wt.%, Zr: 0.020 wt.%, B: 0.015 wt.%, and the balance is Ni;

[0049] Among them, 40 kg of master alloy ingots are prepared according to the composition requirements of the high-W nickel-based superalloy liquid, and the master alloy smelting process is as follows:

[0050] Put the raw materials into the smelting crucible in the order of C, Co, Cr, Mo, Nb, W, Ni from bottom to top, close the furnace lid, and turn on the vacuum pump group to pump the vacuum degree to below 100 Pa shown on the meter, and turn on the heating power to melt the materials;

[0051] Wrap elements such as Al, Ti, B, Zr, Ce, Y with nickel foil for standby;

[0052] When the raw materials in the furnace are completely melted and there are no continuous bubbles on the surface of the alloy liquid, adjust the melt temperature to 1510 °C, keep it warm for 25 min according to the weight of the materials, and conduct primary refining;

[0053] After the primary refining is completed, cut off the power and cool down until the solidification characteristics appear on the surface of the alloy liquid, input the heating power to the primary refining holding power, quickly remelt the alloy liquid, and at this time add the remaining raw materials wrapped with nickel foil such as Al, Ti, B, Zr, Ce, Y to carry out the alloying process;

[0054] When there are no continuous bubbles on the surface of the alloy liquid, cut off the power and cool down to 1390 °C, keep it warm for 40 min according to the weight of the materials, and conduct secondary refining;

[0055] After the secondary refining is completed, raise the melt temperature to 1400 °C and pour it into the standby ingot mold to obtain the master alloy ingot. After cutting off the riser and grinding the surface, an alloy ingot that can be used for casting is obtained.

[0056] Comparative Example 1

[0057] This comparative example uses the same high-W nickel-based superalloy casting as in the example.

[0058] Similarly, taking the polycrystalline casting of an engine as an example, first select a product mold according to process requirements for wax injection. After the mold material cools, visually inspect the wax mold. If the surface finish is high and there are no defects such as inclusions, air bubbles, and oil streaks, it can be welded with the gating system to obtain a wax mold assembly; after cleaning the surface oil of the wax mold assembly, immerse it in a refractory coating composed of corundum powder + polymer-containing silica sol (mass ratio 3.5:1) to evenly coat its surface, then sprinkle a layer of corundum sand on its surface, and then perform drying and strengthening treatment. The remaining back layer is sprinkled with mullite, and a 6-layer mold shell is formed after repeated dipping and sanding. After preparing each layer of the mold shell, dry it for more than 4 hours to make it fully hardened;

[0059] Use a dewaxing kettle to perform steam pressure dewaxing on the prepared mold shell. Place the mold shell's pouring cup downward and place it steadily on the dewaxing cart. When the indicated pressure reaches 8.2 bar, gently push the loading cart into the dewaxing kettle, close the door and lock it, and immediately open the intake valve. The dewaxing kettle automatically times. The dewaxing time of the mold shell is 14 minutes, and the dewaxing temperature is 190 °C. After the operation program ends, take out the hollow mold shell. After dewaxing, perform mold shell roasting. The mold shell roasting temperature is 950 °C, and the mold shell roasting time ≥ 4 hours.

[0060] Wrap the roasted mold shell with a heat insulation layer made of cobalt aluminate cotton with a thickness of about 5 mm, and wrap the entire mold shell including the pouring cup and the mold shell body part with 2 layers of 10 mm thick cobalt aluminate cotton.

[0061] Preheat the mold shell. The mold shell preheating temperature is 1000 °C, and the mold shell preheating time is 6 hours. Pour high-W nickel-based superalloy liquid (the same formula as in Example 1) into the preheated mold shell, where the pouring temperature is 1480 °C. After the alloy liquid cools and solidifies, clean the remaining shell to obtain a casting (i.e., a K465 polycrystalline superalloy casting). Dissect the flange transition part of the casting. The schematic diagram of the shrinkage porosity morphology after dissection is shown in Figure 5 , and it is observed that the shrinkage porosity range is large and the depth is relatively deep, about 200 - 300 μm.

[0062] The main differences between this comparative example and Example 1 are whether wax is applied during the mold shell preparation process and the differences during the mold shell cotton wrapping process. The effect difference is reflected in the shrinkage porosity situation.

[0063] Example 2

[0064] This example uses a high-W nickel-based superalloy casting, and the thickness of the casting transition part is 6.5 mm (>5 mm).

[0065] The method for controlling the porosity of the nickel-based superalloy casting in this example is as follows:

[0066] S1. Inject wax into a product mold (i.e., a K465 polycrystalline superalloy casting). After the mold material cools, obtain the product wax mold to be cast; weld the wax mold with the gating system to obtain a wax mold assembly;

[0067] S2. After cleaning the surface oil film of the wax mold module obtained in S1, immerse it in a refractory coating so that its surface is evenly coated with the refractory coating. After sand spraying on the surface of the wax mold module with the refractory coating evenly coated on the surface and drying and hardening, form the first layer of back layer. Repeat the operations of immersing in the refractory coating, sand spraying, and then drying and hardening multiple times, and coat a total of 7 layers of back layer to obtain a 7-layer mold shell.

[0068] The refractory coating is a mixture of corundum powder and polymer silica sol. The mass ratio of polymer silica sol to corundum powder is 1:3.5; the particle size of corundum powder is 20 - 45 μm, containing 99.5% alumina; the model of the polymer silica sol is Nalco ESB PRIME.

[0069] The method of sand spraying is as follows: the sand spraying for the first layer of back layer is corundum sand, and the sand spraying for the 2nd - 7th layers of back layer is mullite.

[0070] After preparing the 5th layer of mold shell, put solid red wax into a crucible and heat it. After it is completely melted, evenly apply it to the thicker part of the mold shell where shrinkage porosity is likely to form (such as the transition part of the casting flange). Coat a layer of wax material with a thickness of 1.4 mm, that is, coat the wax material on the 5th layer of mold shell. After the wax material cools and solidifies, directly immerse the mold shell into the refractory coating, and complete the preparation of the remaining 2 layers of mold shell by sand spraying and drying.

[0071] S3. Dewax the mold shell obtained in S2. After dewaxing is completed, perform roasting to obtain the roasted mold shell; the method of dewaxing is: use a dewaxing kettle to perform steam pressure dewaxing on the mold shell. Place the sprue cup of the mold shell downward and place it stably on the dewaxing cart. When the indicated pressure reaches 7.9 bar, gently push the loading cart into the dewaxing kettle, close the door and lock it, immediately open the air inlet valve. The dewaxing temperature is 180 °C, and the dewaxing time is 17 min. After the operation program ends, take out the cavity mold shell; the roasting temperature is 940 °C, and the roasting time of the mold shell is 8 h (≥4 h is acceptable).

[0072] S4. Wrap the sprue cup of the roasted mold shell obtained in S3 with a heat-insulating layer to obtain the mold shell wrapped with the heat-insulating layer; the material of the heat-insulating layer is cobalt aluminate cotton, and the thickness of each layer of heat-insulating layer is 5 mm.

[0073] S5. Preheat the mold shell wrapped with the heat-insulating layer obtained in S4 at 900 °C for 8 h, then pour high-W nickel-based superalloy liquid at 1450 °C. After cooling and solidifying, clean the residual shell to obtain a high-W nickel-based superalloy casting. Dissect the transition part of the casting flange. The schematic diagram of the shrinkage porosity morphology after dissection is shown in Figure 6 , and no shrinkage porosity phenomenon is observed.

[0074] The cup part of the pouring cup is wrapped with two layers of heat insulation layers, and the pipe opening of the pouring cup is wrapped with one layer of heat insulation layer; the part of the mold shell body far from the pouring cup is not wrapped with heat insulation cotton, so as to form a temperature gradient that gradually increases in the direction from the pouring cup part of the mold shell to the mold shell body part during the solidification of the casting. The heat insulation layer wrapping the pouring cup realizes a gradually increasing thickness by adjusting the change in the number of layers. By wrapping the heat insulation layer with the number of layers decreasing successively from top to bottom, it is more conducive to forming a temperature field condition for directional solidification of the ingot material, thereby reducing the shrinkage porosity of the casting;

[0075] The high-W nickel-based superalloy liquid consists of raw materials with the following mass fractions: C: 0.13wt%, Cr: 9.50%, Co: 9.00%, W: 9.5%, Mo: 1.20%, Al: 6.00%, Ti: 2.10%, Nb 1.20%, Fe: 1.0%, Zr: 0.020%, B: 0.035%, Ce: 0.01%, Y: 0.01%, Si: 0.20%, and the balance is Ni;

[0076] Among them, 40 kg of master alloy ingots are prepared according to the component requirements of the high-W nickel-based superalloy liquid. The master alloy smelting process is as follows:

[0077] Put the raw materials into the smelting crucible in the order of C, Co, Cr, Mo, Nb, W, Ni from bottom to top, close the furnace lid, and turn on the vacuum pump group to pump the vacuum degree to below 100 Pa shown on the meter, and turn on the heating power to melt the materials;

[0078] Wrap elements such as Al, Ti, B, Zr, Ce, Y with nickel foil for later use;

[0079] When the raw materials in the furnace are completely melted and there are no continuous bubbles on the surface of the alloy liquid, adjust the melt temperature to 1500 °C, keep it warm for 10 min according to the weight of the material, and conduct a primary refining;

[0080] After the primary refining is completed, cut off the power and cool down until solidification characteristics appear on the surface of the alloy liquid, input the heating power to the primary refining holding power, quickly remelt the alloy liquid, and at this time add the remaining raw materials wrapped with nickel foil such as Al, Ti, B, Zr, Ce, Y to carry out the alloying process;

[0081] When there are no continuous bubbles on the surface of the alloy liquid, cut off the power and cool down to 1380 °C, keep it warm for 10 min according to the weight of the material, and conduct a secondary refining;

[0082] After the secondary refining is completed, raise the melt temperature to 1390 °C and pour it into the spare ingot mold to obtain the master alloy ingot. After cutting off the riser and grinding the surface, an alloy ingot that can be used for casting is obtained.

[0083] Example 3

[0084] This embodiment uses a high-W nickel-based superalloy casting, and the thickness of the casting transition part is 5 mm.

[0085] The method for controlling porosity of the nickel-based superalloy casting in this embodiment is as follows:

[0086] S1. Inject wax into the product mold (i.e., K465 polycrystalline superalloy casting). After the mold material cools, obtain the product wax mold to be cast; weld the wax mold with the gating system to obtain a wax mold assembly.

[0087] S2. After cleaning the surface oil film of the wax mold assembly obtained in S1, immerse it in a refractory coating so that its surface is evenly coated with the refractory coating. After spraying sand on the surface of the wax mold assembly with the refractory coating evenly coated on its surface and drying and hardening, form the first layer of back layer. Repeat the operations of immersing in the refractory coating, spraying sand, and drying and hardening multiple times, and a total of 5 layers of back layers are coated to obtain a 5-layer shell mold; the refractory coating is a mixture of corundum powder and polymer silica sol, and the mass ratio of polymer silica sol to corundum powder is 1:3.5; the particle size of corundum powder is 20 - 45 μm, containing 99.5% alumina; the model of the polymer silica sol is Nalco ESBPRIME.

[0088] The method for spraying sand is: the sand sprayed in the first layer of back layer is corundum sand, and the sand sprayed in the 2nd - nth layer of back layer is mullite.

[0089] After preparing the bottom 3 layers of shell mold, put solid red wax into a crucible and heat it. After it is completely melted, evenly apply it to the thicker part of the shell mold where shrinkage porosity is likely to form (such as the casting flange transition part), and coat a layer of wax material with a thickness of 1.2 mm, that is, coat the wax material on the 3rd layer of shell mold; after the wax material cools and solidifies, directly immerse the shell mold in the refractory coating, spray sand and dry to complete the preparation of the remaining 2 layers of shell mold.

[0090] S3. Dewax the shell mold obtained in S2. After dewaxing, perform roasting to obtain the roasted shell mold; the method for dewaxing is: use a dewaxing kettle to perform steam pressure dewaxing on the shell mold. Place the sprue cup of the shell mold downward and place it stably on the dewaxing cart. When the indicated pressure reaches 8.5 bar, gently push the loading cart into the dewaxing kettle, close and lock the door, immediately open the air inlet valve, the dewaxing temperature is 190 °C, the dewaxing time is 13 min, and after the operation program ends, take out the cavity shell mold; the roasting temperature is 960 °C, and the roasting time of the shell mold is 6 h.

[0091] S4. Wrap the sprue cup of the roasted shell mold obtained in S3 with a heat-insulating layer to obtain the shell mold wrapped with a heat-insulating layer; the material of the heat-insulating layer is cobalt aluminate cotton, and the thickness of each layer of heat-insulating layer is 5 mm.

[0092] S5. After preheating the shell of the package insulation layer obtained in S4 at 1200 °C for 4 h, pour the high-W nickel-based superalloy liquid at 1500 °C. After cooling and solidifying, clean the residual shell to obtain a high-W nickel-based superalloy casting. Dissect the flange transition part of the casting. The schematic diagram of the shrinkage porosity morphology after dissection is shown in Figure 7 , and no shrinkage porosity phenomenon is observed;

[0093] The cup part of the pouring cup is wrapped with 2 layers of insulation layer, and the pipe mouth of the pouring cup is wrapped with 1 layer of insulation layer; the part of the shell body far from the pouring cup is not wrapped with insulating cotton, so as to form a temperature gradient that gradually increases along the direction from the pouring cup part of the shell to the shell body part during the solidification of the casting. The insulation layer wrapping the pouring cup realizes the gradual increase of the thickness by adjusting the change of the number of layers. By wrapping the insulation layer with the number of layers decreasing successively from top to bottom, it is more likely to form the temperature field conditions for directional solidification of the ingot material, thereby reducing the shrinkage porosity of the casting;

[0094] The high-W nickel-based superalloy liquid is composed of the following raw materials by mass fraction: C: 0.19%, Cr: 8.00%, Co: 10.50%, W: 11.00%, Mo: 2.40%, Al: 5.10%, Ti: 2.90%, Nb 0.80%, Fe: 0.2%, Zr: 0.040%, B: 0.023%, Ce: 0.02%, Y: 0.005%, Si: 0.40%, and the balance is Ni;

[0095] Among them, prepare a 40 kg master alloy ingot according to the composition requirements of the high-W nickel-based superalloy liquid. The master alloy smelting process is as follows:

[0096] Put the raw materials into the smelting crucible in the order of C, Co, Cr, Mo, Nb, W, Ni from bottom to top, close the furnace lid, and turn on the vacuum pump group to pump the vacuum degree to below 100 Pa shown on the meter, and turn on the heating power supply to melt the materials;

[0097] Wrap the elements such as Al, Ti, B, Zr, Ce, Y with nickel foil for standby;

[0098] When the raw materials in the furnace are completely melted and there are no continuous bubbles on the surface of the alloy liquid, adjust the melt temperature to 1520 °C, keep it warm for 60 min according to the weight of the material, and conduct primary refining;

[0099] After the primary refining is completed, cut off the power supply and cool down until the solidification characteristics appear on the surface of the alloy liquid, input the heating power to the primary refining holding power, quickly remelt the alloy liquid again, and at this time add the remaining raw materials wrapped with nickel foil such as Al, Ti, B, Zr, Ce, Y to carry out the alloying process;

[0100] When there are no continuous bubbles on the surface of the molten alloy, cut off the power supply to cool down to 1400 °C, keep warm for 60 minutes according to the weight of the material, and conduct secondary refining;

[0101] After the secondary refining is completed, raise the melt temperature to 1410 °C and pour it into the spare ingot mold to obtain the master alloy ingot. After cutting off the riser and grinding the surface, an alloy ingot that can be used for casting is obtained.

[0102] As described above, it is only a preferred embodiment of the present invention and does not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments based on the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for controlling the porosity of high W nickel-based high-temperature alloy castings, characterized in that: The method is: S1. Wax is injected into the product mold. After the mold material cools, a wax mold of the product to be cast is obtained; the wax mold is welded to the pouring system to obtain a wax mold module; the product mold is an engine polycrystalline casting or a K465 polycrystalline high-temperature alloy casting; S2. After cleaning the oil film on the surface of the wax mold obtained in S1, immerse it in a refractory coating, sprinkle sand on the surface of the wax mold, and dry and harden it after the surface is evenly coated with the refractory coating to form the first backing layer. Repeat the immersion in the refractory coating, the sanding, and the drying and hardening operations multiple times to apply n layers of backing layer to obtain an n-layer mold shell; 5≤n≤7, where n is a natural number; The sand scattering method is as follows: the sand scattering in the first back layer is corundum sand, and the sand scattering in the second to n back layers is mullite; During the preparation of the shell, a layer of wax with a thickness of 1 mm to 1.4 mm is applied to the transition of the casting; after the wax is cooled and solidified, the shell is directly immersed in the refractory coating to complete the preparation of the remaining back layer; If the thickness of the casting transition is less than 5mm, the wax material is applied to the n-1 layer of the shell; If the thickness of the casting transition is ≥5mm, the wax material is applied to the n-2 layer of the shell; The refractory coating in S2 is a mixture of corundum powder and polymer-containing silica sol; the polymer silica sol model is Nalco ESB PRIME; S3, dewaxing the shell obtained in S2, and after dewaxing, calcining to obtain a calcined shell; the dewaxing method in S3 is: using a dewaxing kettle to dewax the shell under steam pressure, placing the shell with the pouring cup facing downward, the dewaxing temperature is 180°C to 200°C, the dewaxing time is 13min to 17min, and the pressure is 7.9bar to 8.5bar; the calcining temperature in S3 is 940°C to 960°C, and the shell calcining time is ≥4h; S4, wrapping the pouring cup of the fired shell obtained in S3 with an insulation layer to obtain a shell wrapped with the insulation layer; the insulation layer in S4 is made of cobalt aluminate wool, and the thickness of each insulation layer is 5 mm; the cup portion of the pouring cup in S4 is wrapped with two layers of insulation layers, and the nozzle of the pouring cup is wrapped with one layer of insulation layer; S5, preheating the mold shell wrapped with the insulation layer obtained in S4, pouring high W nickel-based superalloy liquid into it, and cleaning the residual shell after cooling and solidification to obtain a high W nickel-based superalloy casting; The high-W nickel-based high-temperature alloy liquid is composed of the following raw materials by mass fraction: C: 0.13% to 0.19%, Cr: 8.00% to 9.50%, Co: 9.00% to 10.50%, W: 9.5% to 11.00%, Mo: 1.20% to 2.40%, Al: 5.10% to 6.00%, Ti: 2.10% to 2.90%, Nb 0.80% to 1.20%, Fe≤1.0%, Zr≤0.040%, B≤0.035%, Ce≤0.02%, Y≤0.01%, Si≤0.40%, and the balance is Ni; The preheating temperature in S5 is 900°C~1200°C, and the preheating time is 4h~8h; the pouring temperature in S5 is 1450°C~1500°C.

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