A method of using a barium-containing inoculant in the casting of thin-walled castings

Abstract

This invention discloses a method for using a barium-containing inoculant in the casting of thin-walled castings, belonging to the field of casting technology. First, molten iron is prepared, then an inoculant is added to the molten iron, mixed and allowed to stand. Finally, the molten iron inoculated in the ladle is transferred to the pouring station, where the barium-containing inoculant is added along with the molten iron flow. The inoculated molten iron is then poured into a sand mold and cooled to obtain a thin-walled casting. The barium-containing inoculant provided by this invention uses silicon-barium-iron alloy powder as the core material, and is sequentially composited with a rare earth-iron-based composite buffer layer, a silicon-calcium graphitization layer, and a PVA-AC vaporization protection layer. This four-layer composite structure forms a release reaction chain of vaporization transport, explosive graphitization, continuous core buffering, and long-term anti-fading. This barium-containing inoculant is released in a gradient throughout the entire process, effectively reducing the incidence of chilled white iron defects in thin-walled castings.

Description

Technical Field

[0001] This invention relates to the field of casting technology, and specifically to a method for casting thin-walled castings using a barium-containing inoculant. Background Technology

[0002] Thin-walled gray cast iron parts (wall thickness ≤ 8 mm) are widely used in air conditioner / refrigerator compressor housings, lightweight automotive components, and other fields. Their casting quality directly determines the mechanical properties, machinability, and service reliability of the products. However, according to statistics from 2025, the incidence of chilled white iron defects in thin-walled parts in small and medium-sized casting enterprises is generally 18-25%, and in some enterprises it is even higher than 30%. This defect has become a key bottleneck restricting the improvement of product quality. The formation mechanism of chilled white iron is that thin-walled parts cool extremely quickly, with the solidification time of molten iron in the mold cavity being only a few seconds to tens of seconds. If the number of graphitization nuclei is insufficient or unevenly distributed, the edges of the casting are prone to forming hard and brittle cementite structures instead of graphite, leading to a surge in hardness and increased brittleness, making subsequent machining difficult and even causing tool breakage. In addition, thin-walled parts are extremely sensitive to inoculation decay. If traditional ladle inoculation or in-flow inoculation agents are added too early or the dosage fluctuates, the nuclei begin to decay before the molten iron enters the mold cavity, failing to cover the entire solidification process.

[0003] The mainstream solutions in the industry to meet the inoculation requirements of thin-walled parts include the addition of traditional barium silicon inoculant inside the ladle, the in-flow inoculation of ordinary calcium silicon / strontium silicon particles, and the single-layer steel strip cored wire feeding technology. Currently, most technologies adopt a dual inoculation method of adding inoculant in the early stage and adding in-flow inoculant. The inoculant in the early stage needs to be completely added to the molten iron to avoid surface residues, while the in-flow inoculant needs to be precisely aligned with the pouring cup and added with the molten iron. However, these solutions have structural defects: traditional ladle inoculation has a narrow effective window due to early addition, and the pouring must be completed within 15 minutes, otherwise the degradation will be severe, making it difficult to adapt to the pace of large-scale production lines; although ordinary in-flow particles can be added with the molten iron, a large number of effective components are oxidized and burned off at high temperatures on the surface of the molten iron, with an absorption rate of only 30-40%, and the distribution is uneven, with local over-inoculation and under-inoculation coexisting; single-layer steel strip cored wire (such as silicon-calcium wire, silicon-barium wire) sends the core powder into the depth of the molten iron through a wire feeder, which significantly improves the absorption rate and uniformity, but its structure is only a binary design of steel strip outer skin + single powder core, and all effective components are released synchronously at the same time point in the molten iron, which cannot match the time sequence requirements of rapid cooling in the early stage of thin-walled parts, which require explosive nucleation, slow cooling in the middle stage, which require continuous nucleation supply, and solidification in the later stage, which require resistance to degradation. More importantly, the existing core material of the cored wire is directly exposed to molten iron without any buffer control on the outer layer, which leads to excessive initial burst and rapid exhaustion in the later stage. Defects such as white iron at the edge and shrinkage porosity in the center of thin-walled parts still occur frequently, making it difficult to steadily improve the white iron structure elimination rate and keeping the cost of compensation for machining tool damage high.

[0004] Given the current shortcomings, it is essential to propose a new method for using barium-containing inoculants in the casting of thin-walled castings. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for casting thin-walled castings using barium-containing inoculants.

[0006] The first aspect of this invention is to provide a barium-containing inoculant, prepared by the following steps: S1: Silicon barium iron alloy powder is dried and then made into core wire; S2: Add nano-cerium oxide to the binder to form a suspension slurry; S3: Pour the suspension slurry into the mixed powder of rare earth ferrosilicon powder and reduced iron powder, and stir to form a slurry; S4: Coat the core wire surface with paste and cure it under inert gas protection to obtain a coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire and cure it under inert gas protection to obtain a composite core wire; S6: The composite core wire is immersed in a PVA-AC mixture and dried to obtain a barium-containing inoculant.

[0007] In some embodiments, the barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; the core wire diameter is 3.5-4.2 mm.

[0008] In some embodiments, the binder is a mixture of water glass, kaolin and boric acid in a mass ratio of 100:4-6:2-4; nano-cerium oxide accounts for 7.5-8.6% of the binder mass.

[0009] In some embodiments, the mass ratio of rare earth ferrosilicon powder to reduced iron powder is 10-15:80-85; the mass ratio of suspension slurry to mixed powder is 0.8-1.2:2.2-2.5; in S5, the adhesive used for adhesion is a 35-40% aluminum dihydrogen phosphate solution.

[0010] In some embodiments, the PVA-AC mixture is prepared by the following steps: Polyvinyl alcohol was soaked in deionized water, stirred and dissolved, and then plasticizer, azodicarbonamide and defoamer were added. After standing, a PVA-AC mixture was obtained.

[0011] The polyvinyl alcohol used in this invention is PVA-1799.

[0012] In some embodiments, the plasticizer is selected from at least one of polyethylene glycol-400, glycerol, and sorbitol; the defoamer is an organosilicone defoamer; the mass ratio of polyvinyl alcohol, plasticizer, azodicarbonamide, and defoamer is 7-8:1.5-2:0.14-0.24:0.1, and the mass of deionized water is 11.5-13 times the mass of polyvinyl alcohol.

[0013] In some embodiments, soaking is performed at 0-10°C for 3.5-4.5 hours, stirring and dissolving is performed at 85-90°C for 25-35 minutes, and standing time is 1.5-2.5 hours.

[0014] In some embodiments, in S4, curing is performed at 120-150°C for 10-15 minutes; in S5, curing is performed at 180-220°C for 8-12 minutes; in S6, impregnation is performed at 40-50°C for 5-8 seconds, and drying is performed first at 60-70°C for 4-6 minutes, followed by drying at 105-115°C for 6-10 minutes.

[0015] A second aspect of the present invention is to provide a method for casting thin-walled castings using a barium-containing inoculant, comprising the following steps: (1) Preparing molten iron; (2) Add the inoculant from the ladle to the molten iron, mix and let stand; (3) Transfer the molten iron inoculated in step (2) to the casting station, add barium inoculant along with the molten iron flow, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting.

[0016] In some embodiments, the molten iron, by mass fraction, comprises the following components: carbon 3.3-3.4%, silicon 1.8-1.9%, manganese 0.6-0.8%, sulfur ≤0.1%, and phosphorus ≤0.1%; the inoculant in the ladle is composed of the following components by mass fraction: barium 2.5-3.5%, silicon 65-75%, aluminum 1.5-2%, calcium 1-1.5%, and the balance iron; the amount of inoculant added to the ladle is 0.6-0.8% of the weight of the molten iron; the amount of barium-containing inoculant added is 0.1-0.15% of the weight of the molten iron.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention provides a four-layer composite alloy wire as a barium-containing inoculant, with silicon-barium-iron alloy powder as the core material, and outer layers sequentially composited with a rare earth-iron-based composite buffer layer, a silicon-calcium graphitization layer, and a PVA-AC vaporization protection layer. The silicon-barium-iron alloy core material provides long-term resistance to fading nucleation, with slow barium diffusion and high stability, covering the middle and late stages of solidification. This ensures that thin-walled castings maintain sufficient graphitization nuclei even during the rapid cooling final solidification stage, effectively suppressing late-stage white iron formation and localized hard spots caused by inoculation fading, ensuring uniform microstructure and consistent machinability across the entire casting cross-section. The rare earth-iron-based composite buffer layer is composed of reduced iron powder, rare earth silicon-iron powder, nano-cerium oxide, and water glass-kaolin inorganic binder. The Ce / La in the rare earth silicon-iron powder reacts with O / S in the molten iron to generate high-melting-point rare earth oxysulfides, serving as a heterogeneous nucleation substrate. This allows the molten iron to possess a large number of readily available nuclei the moment it enters the mold cavity, shortening the formation time of the white iron sensitive zone. The invention establishes a time window for the formation of a nucleation site. Furthermore, the dispersed distribution of nano-CeO2, along with the gradual melting of iron powder, enables pulsed release, continuing to provide nucleation sites even after the explosive effect of the silicon-calcium layer decays. The silicon-calcium alloy powder in the silicon-calcium graphitized layer is solidified outside the buffer layer by an aluminum dihydrogen phosphate ceramic binder, rapidly melting upon contact with molten iron. The boiling and stirring of Ca, combined with the graphitization of Si, provides explosive nucleation, quickly suppressing cementite formation in the rapid cooling zone at the edge of thin-walled parts and controlling the depth of white iron. The PVA-AC vaporization protective layer, with a polyvinyl alcohol film-forming matrix carrying azodicarbonamide foaming agent, instantaneously vaporizes and peels off in high-temperature molten iron, uniformly exposing the internal active layer and penetrating deep into the center of the molten iron flow, preventing surface oxidation and burning. This four-layer composite structure forms a release reaction chain of vaporization transport, explosive graphitization, continuous nucleation buffering, and long-term anti-decay. The inoculant provided by this invention is released in a gradient throughout the entire process, effectively reducing the incidence of rapid cooling white iron defects in thin-walled castings.

[0018] 2. This invention employs a dual inoculation method: in-ladle inoculation and in-flow inoculation. In-ladle inoculation uses barium-silicon-aluminum-calcium particles added during tapping. The inoculant is automatically stirred and dispersed using the kinetic energy of the molten iron, ensuring uniform distribution throughout the ladle and establishing a basic graphitization core density. Barium's slow diffusion and high stability, combined with the deoxidizing and refining effects of aluminum and the desulfurizing and purifying effects of calcium, effectively extend the inoculation window. In-flow inoculation is added before the molten iron enters the mold cavity, effectively compensating for the decline losses of in-ladle inoculation. Furthermore, the synergistic effect of in-ladle and in-flow inoculation, targeting the edge strengthening nucleation of thin-walled, rapidly cooling castings, significantly reduces the incidence of white iron defects in the castings, and significantly improves process tolerance and batch stability. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to specific embodiments.

[0020] Example 1 A barium-containing inoculant is prepared by the following steps: S1: Silicon-barium-iron alloy powder is dried and then made into a core wire with a diameter of 3.8 mm; wherein, the barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; S2: Nano-cerium oxide is added to the binder to form a suspension slurry; wherein the binder is a mixture of water glass, kaolin and boric acid in a mass ratio of 100:5:3, and nano-cerium oxide accounts for 8% of the mass of the binder; S3: Pour the suspension slurry into a mixture of rare earth ferrosilicon powder and reduced iron powder in a mass ratio of 12:82, and stir to form a slurry; wherein the mass ratio of the suspension slurry to the mixed powder is 1:2.3; S4: Coat the core wire surface with paste, and cure at 135°C for 12 minutes under inert gas protection to obtain the coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire, and cure it at 200°C for 10 minutes under inert gas protection to obtain a composite core wire; wherein, the adhesive used for adhesion is a 38% aluminum dihydrogen phosphate solution. S6: Immerse the composite core wire in a PVA-AC mixture at 45°C for 6 seconds. After immersion, remove the composite core wire and dry it at 65°C for 5 minutes, then dry it at 110°C for 8 minutes to obtain a barium-containing inoculant.

[0021] The PVA-AC mixture is prepared by the following steps: PVA-1799 was soaked in deionized water at 5°C for 4 hours, stirred at 85°C for 30 minutes, and then polyethylene glycol-400, azodicarbonamide, and silicone defoamer-BYK-024 were added. After standing for 2 hours, a PVA-AC mixture was obtained. The mass ratio of polyvinyl alcohol, polyethylene glycol-400, azodicarbonamide, and defoamer BYK-024 was 7.5:1.8:0.19:0.1, and the mass of deionized water was 12 times the mass of polyvinyl alcohol.

[0022] The application of the above-mentioned barium-containing inoculant in the casting of thin-walled castings includes the following steps: (1) Preparation of molten iron; wherein, the molten iron, by mass fraction, includes the following components: carbon 3.35%, silicon 1.85%, manganese 0.7%, sulfur ≤0.1%, phosphorus ≤0.1%; (2) Add the ladle inoculant to the molten iron, mix and let stand; wherein, the ladle inoculant is composed of the following components by mass fraction: barium 3%, silicon 70%, aluminum 1.8%, calcium 1.2%, balance iron; the amount of ladle inoculant added is 0.7% of the weight of molten iron; (3) Transfer the molten iron inoculated in step (2) to the casting station, add barium inoculant along with the molten iron, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting; wherein, the amount of barium inoculant added is 0.12% of the weight of the molten iron.

[0023] Example 2 A barium-containing inoculant is prepared by the following steps: S1: Silicon-barium-iron alloy powder is dried and then made into a core wire with a diameter of 4.2 mm; wherein, the barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; S2: Nano-cerium oxide is added to the binder to form a suspension slurry; wherein the binder is a mixture of water glass, kaolin and boric acid in a mass ratio of 100:6:4, and nano-cerium oxide accounts for 8.6% of the mass of the binder; S3: Pour the suspension slurry into a mixture of rare earth ferrosilicon powder and reduced iron powder in a mass ratio of 15:85, and stir to form a slurry; wherein the mass ratio of the suspension slurry to the mixed powder is 1.2:2.5; S4: Coat the core wire surface with paste, and cure at 150°C for 10 minutes under inert gas protection to obtain the coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire, and cure it at 220°C for 8 minutes under inert gas protection to obtain a composite core wire; wherein, the adhesive used for adhesion is a 40% aluminum dihydrogen phosphate solution. S6: Immerse the composite core wire in a PVA-AC mixture at 50°C for 5 seconds. After immersion, remove the composite core wire and dry it at 70°C for 4 minutes, then dry it at 115°C for 6 minutes to obtain a barium-containing inoculant.

[0024] The PVA-AC mixture is prepared by the following steps: PVA-1799 was soaked in deionized water at 10℃ for 3.5h, stirred at 90℃ for 25min, and then glycerol, azodicarbonamide and silicone defoamer SXP-101 were added. After standing for 2.5h, a PVA-AC mixture was obtained. The mass ratio of polyvinyl alcohol, glycerol, azodicarbonamide and defoamer SXP-101 was 8:2:0.24:0.1, and the mass of deionized water was 13 times the mass of polyvinyl alcohol.

[0025] The application of the above-mentioned barium-containing inoculant in the casting of thin-walled castings includes the following steps: (1) Preparation of molten iron; wherein, the molten iron, by mass fraction, includes the following components: carbon 3.4%, silicon 1.9%, manganese 0.8%, sulfur ≤0.1%, phosphorus ≤0.1%; (2) Add the ladle inoculant to the molten iron, mix and let stand; wherein, the ladle inoculant is composed of the following components by mass fraction: barium 2.5%, silicon 65%, aluminum 1.5%, calcium 1%, balance iron; the amount of ladle inoculant added is 0.8% of the weight of the molten iron; (3) Transfer the molten iron inoculated in step (2) to the casting station, add barium inoculant along with the molten iron, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting; wherein, the amount of barium inoculant added is 0.15% of the weight of the molten iron.

[0026] Example 3 A barium-containing inoculant is prepared by the following steps: S1: Silicon-barium-iron alloy powder is dried and then made into a core wire with a diameter of 3.5 mm; wherein, the barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; S2: Nano-cerium oxide is added to the binder to form a suspension slurry; wherein the binder is a mixture of water glass, kaolin and boric acid in a mass ratio of 100:4:2, and nano-cerium oxide accounts for 7.5% of the mass of the binder; S3: Pour the suspension slurry into a mixture of rare earth ferrosilicon powder and reduced iron powder at a mass ratio of 10:80, and stir to form a slurry; wherein the mass ratio of the suspension slurry to the mixed powder is 0.8:2.2; S4: Coat the core wire surface with paste, and cure at 120°C for 15 minutes under inert gas protection to obtain the coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire, and cure it at 180°C for 12 minutes under inert gas protection to obtain a composite core wire; wherein, the adhesive used for adhesion is a 35% aluminum dihydrogen phosphate solution. S6: Immerse the composite core wire in a PVA-AC mixture at 40°C for 8 seconds. After immersion, remove the composite core wire and dry it at 60°C for 6 minutes, then dry it at 105°C for 10 minutes to obtain a barium-containing inoculant.

[0027] The PVA-AC mixture is prepared by the following steps: PVA-1799 was soaked in deionized water at 2℃ for 4.5 hours, stirred at 85℃ for 35 minutes, and then sorbitol, azodicarbonamide, and silicone defoamer BYK-024 were added. After standing for 1.5 hours, a PVA-AC mixture was obtained. The mass ratio of polyvinyl alcohol, sorbitol, azodicarbonamide, and defoamer BYK-024 was 7:1.5:0.14:0.1, and the mass of deionized water was 11.5 times the mass of polyvinyl alcohol.

[0028] The application of the above-mentioned barium-containing inoculant in the casting of thin-walled castings includes the following steps: (1) Preparation of molten iron; wherein, the molten iron, by mass fraction, includes the following components: carbon 3.3%, silicon 1.8%, manganese 0.6%, sulfur ≤0.1%, phosphorus ≤0.1%; (2) Add the ladle inoculant to the molten iron, mix and let stand; wherein, the ladle inoculant is composed of the following components by mass fraction: barium 3.5%, silicon 75%, aluminum 2%, calcium 1.5%, balance iron; the amount of ladle inoculant added is 0.6% of the weight of the molten iron; (3) Transfer the molten iron inoculated in step (2) to the casting station, add barium inoculant along with the molten iron, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting; wherein, the amount of barium inoculant added is 0.1% of the weight of the molten iron.

[0029] Example 4 A barium-containing inoculant is prepared by the following steps: S1: Silicon-barium-iron alloy powder is dried and then made into a core wire with a diameter of 3.7 mm; wherein, the barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; S2: Nano-cerium oxide is added to the binder to form a suspension slurry; wherein the binder is a mixture of water glass, kaolin and boric acid in a mass ratio of 100:4.5:3.5, and nano-cerium oxide accounts for 7.7% of the mass of the binder; S3: Pour the suspension slurry into a mixture of rare earth ferrosilicon powder and reduced iron powder in a mass ratio of 11:81, and stir to form a slurry; wherein the mass ratio of the suspension slurry to the mixed powder is 0.9:2.3; S4: Coat the core wire surface with paste, and cure at 130°C for 11 minutes under inert gas protection to obtain the coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire, and cure it at 190°C for 11 minutes under inert gas protection to obtain a composite core wire; wherein, the adhesive used for adhesion is a 36% aluminum dihydrogen phosphate solution. S6: Immerse the composite core wire in a PVA-AC mixture at 42°C for 6 seconds. After immersion, remove the composite core wire and dry it at 62°C for 5 minutes, then dry it at 108°C for 9 minutes to obtain a barium-containing inoculant.

[0030] The PVA-AC mixture is prepared by the following steps: PVA-1799 was soaked in deionized water at 0℃ for 4 hours, stirred at 87℃ for 28 minutes, and then polyethylene glycol-400, azodicarbonamide, and silicone defoamer SXP-101 were added. After standing for 1.6 hours, a PVA-AC mixture was obtained. The mass ratio of polyvinyl alcohol, polyethylene glycol-400, azodicarbonamide, and defoamer SXP-101 was 7.2:1.6:0.16:0.1, and the mass of deionized water was 12 times the mass of polyvinyl alcohol.

[0031] The application of the above-mentioned barium-containing inoculant in the casting of thin-walled castings includes the following steps: (1) Preparation of molten iron; wherein, the molten iron, by mass fraction, includes the following components: carbon 3.3%, silicon 1.9%, manganese 0.6%, sulfur ≤0.1%, phosphorus ≤0.1%; (2) Add the ladle inoculant to the molten iron, mix and let stand; wherein, the ladle inoculant is composed of the following components by mass fraction: barium 2.7%, silicon 68%, aluminum 1.6%, calcium 1.1%, balance iron; the amount of ladle inoculant added is 0.65% of the weight of molten iron; (3) Transfer the molten iron inoculated in step (2) to the casting station, add the barium inoculant along with the molten iron, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting; wherein, the amount of barium inoculant added is 0.11% of the weight of the molten iron.

[0032] Example 5 A barium-containing inoculant is prepared by the following steps: S1: Silicon-barium-iron alloy powder is dried and then made into a core wire with a diameter of 4.1 mm; wherein, the barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; S2: Nano-cerium oxide is added to the binder to form a suspension slurry; wherein the binder is a mixture of water glass, kaolin and boric acid in a mass ratio of 100:5.5:2.5, and nano-cerium oxide accounts for 8.4% of the mass of the binder; S3: Pour the suspension slurry into a mixture of rare earth ferrosilicon powder and reduced iron powder in a mass ratio of 14:84, and stir to form a slurry; wherein the mass ratio of the suspension slurry to the mixed powder is 1.1:2.4; S4: Coat the core wire surface with paste, and cure at 145°C for 14 minutes under inert gas protection to obtain the coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire, and cure it at 210°C for 11 minutes under inert gas protection to obtain a composite core wire; wherein, the adhesive used for adhesion is a 38% aluminum dihydrogen phosphate solution. S6: Immerse the composite core wire in a PVA-AC mixture at 48°C for 7 seconds. After immersion, remove the composite core wire and dry it at 68°C for 5 minutes, then dry it at 112°C for 8 minutes to obtain a barium-containing inoculant.

[0033] The PVA-AC mixture is prepared by the following steps: PVA-1799 was soaked in deionized water at 8°C for 4.2 hours, stirred at 88°C for 32 minutes, and then glycerol, azodicarbonamide, and silicone defoamer SXP-101 were added. The mixture was allowed to stand for 2.3 hours to obtain a PVA-AC mixture. The mass ratio of polyvinyl alcohol, glycerol, azodicarbonamide, and defoamer SXP-101 was 7.5:1.9:0.22:0.1, and the mass of deionized water was 12.5 times the mass of polyvinyl alcohol.

[0034] The application of the above-mentioned barium-containing inoculant in the casting of thin-walled castings includes the following steps: (1) Preparation of molten iron; wherein, the molten iron, by mass fraction, includes the following components: carbon 3.4%, silicon 1.9%, manganese 0.8%, sulfur ≤0.1%, phosphorus ≤0.1%; (2) Add the ladle inoculant to the molten iron, mix and let stand; wherein, the ladle inoculant is composed of the following components by mass fraction: barium 3.2%, silicon 72%, aluminum 1.9%, calcium 1.4%, balance iron; the amount of ladle inoculant added is 0.78% of the weight of molten iron; (3) Transfer the molten iron inoculated in step (2) to the casting station, add barium inoculant along with the molten iron, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting; wherein, the amount of barium inoculant added is 0.14% of the weight of the molten iron.

[0035] Comparative Example 1 The process is basically the same as in Example 1, except that the traditional in-bottle inoculation method is adopted, that is, no barium inoculant is added and no in-flow inoculation method is adopted. Step (3) is omitted in the casting of thin-walled castings. After the in-bottle inoculation in step (2) is completed, the casting is completed and the mass of barium inoculant is added to the in-bottle inoculation.

[0036] Comparative Example 2 It is basically the same as Example 1, except that: the barium-containing inoculant is added together with the inoculant in the package, that is, the in-flow inoculant method is not used.

[0037] Comparative Example 3 The results are basically the same as in Example 1, except that the outer layer of the barium inoculant is not covered with a rare earth-iron-based composite buffer layer, a silicon-calcium graphitization layer and a PVA-AC vaporization protection layer, i.e., S2-S6 are omitted, and the barium inoculant is a silicon-barium-iron alloy wire.

[0038] Comparative Example 4 It is basically the same as Example 1, except that the outer layer of the barium inoculant is not covered with a rare earth-iron-based composite buffer layer, that is, S2-S4 are omitted in the preparation steps of the barium inoculant.

[0039] Comparative Example 5 It is basically the same as Example 1, except that the outer layer of the barium inoculant is not covered with a silicon-calcium graphitization layer, that is, S5 is omitted in the preparation step of the barium inoculant.

[0040] Comparative Example 6 The process is basically the same as in Example 1, except that the outer layer of the barium-containing inoculant is not covered with a PVA-AC vaporization protective layer, that is, step S6 is omitted in the preparation step of the barium-containing inoculant.

[0041] Comparative Example 7 It is basically the same as Example 1, except that azodicarbonamide (foaming agent AC) is not added.

[0042] Comparative Example 8 The results are basically the same as in Example 1, except that the nano-cerium oxide and rare earth silicon iron powder in S2-S3 are replaced with reduced iron powder, that is, the rare earth-iron-based composite buffer layer is replaced with an iron powder buffer layer.

[0043] The thin-walled castings prepared in Examples 1-5 and Comparative Examples 1-8 were subjected to performance tests, and the test results are shown in Table 1.

[0044] White iron depth testing: The test is conducted in accordance with the standard GB / T 7216-2009. Samples are taken from the thin-walled part of the casting (wall thickness ≤ 8 mm), metallographic specimens are ground, and the depth of the white iron layer is measured.

[0045] Graphite morphology and distribution test: The proportion of type A graphite was tested in accordance with the standard GB / T 7216-2009.

[0046] Brinell hardness test: Refer to standard GB / T 231.1-2018, test at thin-walled and thick-walled sections of the casting, and calculate the hardness difference.

[0047] Table 1

[0048] As can be seen from Table 1, the white iron depth of the thin-walled castings prepared in the embodiments of the present invention is about 0.3 mm, and there are almost no chilling white iron defects at the edges of the thin-walled castings; the proportion of type A graphite is more than 86%, indicating that the graphite morphology is mainly uniformly distributed flake graphite. This graphite morphology endows cast iron with excellent damping, wear resistance and machinability. The hardness difference of the casting cross section is only about 10 HBW, the microstructure of the thin-walled part and the thick-walled part are uniform and consistent, and the surface quality of the machined part is stable.

[0049] As can be seen from the comparative examples, Comparative Example 1 uses the traditional in-bundle inoculation method without adding barium-containing inoculant via in-flow inoculation. Although the traditional barium-containing inoculant contains barium, it decays quickly, has a coarse distribution, and lacks end compensation. The traditional barium-containing solution alone is insufficient to solve the white iron problem of thin-walled parts. Comparative Example 2 adds the barium-containing inoculant and the in-bundle inoculant at the same time. Although the white iron depth is improved compared to Comparative Example 1, the composite layer structure loses its function. The silicon-calcium burst, rare earth continuation, and nanopulse cannot be released at the correct time, still resulting in white iron defects and uneven graphite distribution. Comparative Example 3 uses bare silicon-barium-iron alloy wire. After feeding the bare silicon-barium-iron alloy wire (only the core material, without the vaporization layer, silicon-calcium layer, or rare earth buffer layer) into the molten iron, the core material is directly exposed, and all barium and silicon elements dissolve simultaneously, causing the white iron depth to increase to 1.5 mm and the performance to deteriorate significantly.

[0050] Comparative Example 4 uses a barium-containing inoculant without a rare-earth-iron-based composite buffer layer. Without the rare-earth-iron-based buffer layer, the silicon-calcium layer is directly adjacent to the core material. After the silicon-calcium eruption, the dissolution rate of the core material's silicon and barium is affected by the iron powder. The silicon and calcium are exhausted, but the silicon and barium have not yet been released, leading to a sharp drop in the core density of the molten iron. Secondary white iron forms at the edges of thin-walled parts, resulting in a hardness difference of 7. The apparent small HBW is due to excessive silicon-calcium explosion leading to localized softness and overall performance degradation. Comparative Example 5 uses a barium-containing inoculant without an outer silicon-calcium graphitization layer. By omitting the silicon-calcium layer, the outer layer is directly in contact with the molten iron as a rare earth buffer layer. The rare earth oxide sulfide nucleation efficiency is high, but the lack of calcium boiling and stirring effect results in insufficient local mixing of the molten iron, slow establishment of nucleation density, and white iron appearance at the edges. The rare earth layer reaction is mild with no explosion peak, and the overall graphitization degree is moderate. Comparative Example 6 uses a barium-containing inoculant without a PVA-AC vaporization protection layer. Without the protection of the vaporization layer, the silicon-calcium layer and rare earth buffer layer are in direct contact with the air and the slag layer on the surface of the molten iron. During wire feeding, the outer powder is oxidized at high temperature on the surface of the molten iron, and some of the effective components are burned off. Even if some enter the molten iron, due to the lack of micro-explosion dispersion effect, the wire melts and accumulates locally, resulting in uneven distribution and obvious white iron defects and uneven graphite distribution.

[0051] Comparative Example 7 did not add azodicarbonamide (foaming agent AC), meaning it had a PVA vaporization layer but no AC foaming agent, thus losing its instantaneous vaporization function. PVA required several seconds to completely decompose in molten iron, during which time a viscous carbonaceous residue formed on the surface of the wire, hindering the rapid exposure of the inner layer. At the same time, without the impact force of micro-explosion, the wire tended to float and melt along the surface of the molten iron rather than penetrate into the center, resulting in an increase in the white iron depth. Comparative Example 8 replaced the rare earth-iron-based buffer layer with a pure iron powder layer, retaining the buffer layer structure but removing rare earth silicon iron powder and nano CeO2, replacing it with traditional pure iron powder physical buffer. The iron powder layer only delayed the release of the core material and had no pre-nucleation activity. The window period after the silicon-calcium explosion still existed, with a white iron depth of 0.8 mm and 78% type A graphite.

[0052] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A barium-containing probiotic, characterized in that, It is prepared by the following steps: S1: Silicon barium iron alloy powder is dried and then made into core wire; S2: Add nano-cerium oxide to the binder to form a suspension slurry; S3: Pour the suspended slurry into a mixture of rare earth ferrosilicon powder and reduced iron powder, and stir to form a slurry; S4: Coat the surface of the core wire with the paste and cure it under inert gas protection to obtain a coated core wire; S5: Adhere silicon-calcium alloy powder to the surface of the coated core wire and cure it under inert gas protection to obtain a composite core wire; S6: The composite core wire is immersed in a PVA-AC mixture and dried to obtain a barium-containing inoculant.

2. The barium-containing probiotic according to claim 1, characterized in that, The barium content in the silicon-barium-iron alloy powder is >30%, the silicon content is >50%, and the balance is iron; the diameter of the core wire is 3.5-4.2 mm.

3. The barium-containing probiotic according to claim 1, characterized in that, The binder is composed of water glass, kaolin and boric acid in a mass ratio of 100:4-6:2-4; the nano-cerium oxide accounts for 7.5-8.6% of the mass of the binder.

4. The barium-containing probiotic according to claim 1, characterized in that, The mass ratio of rare earth ferrosilicon powder to reduced iron powder is 10-15:80-85; the mass ratio of the suspension slurry to the mixed powder is 0.8-1.2:2.2-2.5; in step S5, the adhesive used for adhesion is a 35-40% aluminum dihydrogen phosphate solution.

5. The barium-containing probiotic according to claim 1, characterized in that, The PVA-AC mixture was prepared by the following steps: Polyvinyl alcohol was soaked in deionized water, stirred and dissolved, and then plasticizer, azodicarbonamide and defoamer were added. The mixture was then allowed to stand to obtain the PVA-AC mixture.

6. The barium-containing inoculant according to claim 5, characterized in that, The plasticizer is selected from at least one of polyethylene glycol-400, glycerol, and sorbitol; the defoamer is an organosilicone defoamer; the mass ratio of polyvinyl alcohol, plasticizer, azodicarbonamide, and defoamer is 7-8:1.5-2:0.14-0.24:0.1, and the amount of deionized water used is 11.5-13 times the mass of polyvinyl alcohol.

7. The barium-containing inoculant according to claim 5, characterized in that, The soaking process involves soaking at 0-10℃ for 3.5-4.5 hours, the stirring and dissolving process involves stirring at 85-90℃ for 25-35 minutes, and the standing time is 1.5-2.5 hours.

8. The barium-containing probiotic according to claim 1, characterized in that, In step S4, curing is performed at 120-150℃ for 10-15 minutes; in step S5, curing is performed at 180-220℃ for 8-12 minutes; in step S6, impregnation is performed at 40-50℃ for 5-8 seconds, and drying is performed first at 60-70℃ for 4-6 minutes, followed by drying at 105-115℃ for 6-10 minutes.

9. A method for casting thin-walled castings using a barium-containing inoculant as described in any one of claims 1-8, characterized in that, Includes the following steps: (1) Preparing molten iron; (2) Add the inoculant to the molten iron, mix and let stand; (3) Transfer the molten iron inoculated in step (2) to the casting station, add the barium-containing inoculant along with the molten iron flow, and pour the inoculated molten iron into the sand mold to cool and obtain a thin-walled casting.

10. The method for using a barium-containing inoculant according to claim 9 in the casting of thin-walled castings, characterized in that, The molten iron, by mass fraction, comprises the following components: carbon 3.3-3.4%, silicon 1.8-1.9%, manganese 0.6-0.8%, sulfur ≤0.1%, and phosphorus ≤0.1%; the inoculant in the ladle is composed of the following components by mass fraction: barium 2.5-3.5%, silicon 65-75%, aluminum 1.5-2%, calcium 1-1.5%, and the balance iron; the amount of inoculant added to the ladle is 0.6-0.8% of the weight of the molten iron; the amount of barium-containing inoculant added is 0.1-0.15% of the weight of the molten iron.

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