A low-dross high-yield La-containing high-temperature alloy smelting method

Abstract

The application discloses a low-dross high-yield La-containing high-temperature alloy smelting method, which comprises the following steps: raw material pretreatment and batching, calcium-based pre-purification treatment, La micro-zoning addition and dispersion, bottom argon blowing dross floating control, dross removal and surface layer purification, pouring atmosphere and condensation pressure control and the like. First, the melt is pre-purified by Ni-Ca intermediate alloy to reduce the oxygen and sulfur content in the melt; then, La particles coated by Ni foil are added in batches under the protection of argon and uniformly dispersed by electromagnetic stirring; then, micro-bubble flow field is formed by bottom argon blowing to adsorb and capture La oxide inclusions and composite inclusions and remove the same; finally, the pouring and solidification processes are completed under the protection of argon and micro-positive pressure to inhibit the secondary oxidation of La. Through the synergistic effect of calcium-based pre-purification, La slow-release addition, micro-bubble inclusion capture and micro-positive pressure protection in the solidification stage, the application can effectively reduce the dross generation amount, improve the La yield and the purity of the alloy, and can be widely applied to the preparation of K6188, K417G, GH4169 and other La-containing high-temperature alloys.

Description

Technical Field

[0001] This invention relates to the field of high-temperature alloy smelting technology, specifically to a method for smelting high-temperature alloys containing La with low slag and high yield. Background Technology

[0002] La can improve the grain boundary structure of nickel-based superalloys, enhance their oxidation resistance and hot corrosion resistance, and is therefore widely used in aero-engine blades, gas turbine guide vanes and high-temperature hot-end components.

[0003] However, La is an extremely reactive rare earth element, and it readily reacts with oxygen and sulfur during vacuum induction melting to form La2O3 and La2O2S inclusions.

[0004] Because these inclusions have low density, fine particle size, and slow floating speed, they easily form a large amount of scum and remain inside the alloy liquid.

[0005] The existing processes mainly employ: - Vacuum degassing; - Electromagnetic stirring; -Argon protection; -Standard scraping; Control methods are used.

[0006] But it still exists: -La was severely burned; -Large amount of scum; -Low rare earth recovery rate; - The alloy has a high oxygen content; - Excessive inclusions in the casting; Issues such as...

[0007] Therefore, it is necessary to develop a new smelting process that can simultaneously improve the La yield and reduce the amount of slag generated. Summary of the Invention

[0008] The purpose of this invention is to provide a method for smelting high-temperature alloys containing La with low slag and high yield, so as to solve the existing technical problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for smelting high-temperature alloys containing La with low slag and high yield, by establishing: - Pre-purification stage; -Rare earth slow-release addition stage; - Microbubble entrainment capture stage; - Slight positive pressure protection during the solidification stage; Four-level collaborative control system accomplish: - Scum content ≤ 0.3%; -La harvest rate ≥70%; -Oxygen content ≤10ppm; Significantly improves the purity of high-temperature alloys.

[0010] A method for smelting high-temperature alloys containing La with low slag and high yield includes the following steps: S1 raw material pretreatment:

[0011] Alloying elements other than La are subjected to shot peening or pickling. La is made into particles with a diameter of 3-5 mm; Slow-release coated particles are formed by completely coating with nickel foil with a thickness of 0.05 to 0.10 mm. S2 Vacuum Melting:

[0012] Add the raw materials into the vacuum induction furnace; Use MgO or CaO crucibles; Evacuate to: 10^-2~10^-3 Pa; Heat it to 1520-1550℃ until it is completely melted. S3 Calcium-Based Deep Purification:

[0013] Add a Ni-Ca master alloy to the melt; Addition amount: 0.08~0.12wt%.

[0014] Maintain electromagnetic stirring at 400-500 rpm; Refine for 20-30 minutes.

[0015] Ca preferentially combines with oxygen and sulfur to form stable inclusions that then float to the surface.

[0016] This reduces the oxygen content of the melt to below 20 ppm. S4 Rare Earth Gradient Slow-Release Addition: S5

[0017] Stop vacuum pumping; Argon gas with a purity of 99.999% or higher is introduced into the furnace; Pressure control: 0.3~0.5MPa.

[0018] The nickel foil-coated La particles are added in 3 to 5 batches through a vacuum feeding chamber.

[0019] Interval between adjacent batches: 2-3 minutes.

[0020] Total addition amount: 0.05~0.10wt%.

[0021] Simultaneously, electromagnetic stirring at 500-600 rpm is performed.

[0022] The nickel foil releases the element La after melting.

[0023] Reduce the probability of direct contact between La and oxygen. S5 microbubble trapping and purification:

[0024] After La is added, the bottom blowing system is activated.

[0025] Breathable bricks produce microbubbles of 0.5–2 mm.

[0026] Argon flow rate: 1.5~3.0L / min.

[0027] Continuous blowing: 15-25 minutes.

[0028] Simultaneously maintain a weak electromagnetic stirring speed of 200-300 rpm.

[0029] Microbubbles adsorb La2O3 inclusions and promote their aggregation and growth.

[0030] Improve the efficiency of inclusions rising to the surface. S6 surface scum removal:

[0031] Let stand for 3 to 5 minutes.

[0032] A slag removal device is used to remove surface slag.

[0033] Subsequently covered with: CaF2-CaO composite protective slag.

[0034] Protective slag thickness: 5-10mm. S7 micro-positive pressure protected casting:

[0035] Heat the alloy liquid to 1480-1500℃.

[0036] High-purity argon gas is continuously introduced during the pouring process.

[0037] Flow rate: 5-10 L / min.

[0038] After pouring, maintain a slight positive pressure of 0.05 to 0.08 MPa.

[0039] Until the casting temperature drops below 900℃.

[0040] To prevent secondary oxidation of La caused by solidification shrinkage and air absorption.

[0041] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention: It adopts a calcium-based deep purification process.

[0042] Before the addition of La, the oxygen content was reduced to below 20 ppm.

[0043] Reduce La oxidation at the source.

[0044] 2. This invention: It adopts a nickel foil slow-release coating structure.

[0045] La release rate is controlled.

[0046] Reduce instantaneous oxidation and burn-off.

[0047] La yield increased to over 70%. 3. This invention: A microbubble entrainment and trapping mechanism is employed.

[0048] The average particle size of La2O3 inclusions increased from 2–5 μm to 15–30 μm.

[0049] The buoyancy efficiency is increased by 5 to 8 times.

[0050] 4. This invention: Establish a micro-positive pressure protection mechanism for the entire solidification process.

[0051] It effectively inhibits secondary oxidation.

[0052] Reduce inclusion formation.

[0053] 5. This invention: Final result: - Scum content ≤ 0.3% -La yield 70-80% -Oxygen content ≤10ppm - Casting qualification rate ≥ 95% High-purity high-temperature alloy. Attached Figure Description

[0054] Figure 1 This is a system block diagram of the method for smelting high-temperature alloys containing La in this invention. Detailed Implementation

[0055] In the description of this invention, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," "tail," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0056] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0057] like Figure 1 As shown, the present invention provides a technical solution: a method for smelting high-temperature alloys containing La with low slag and high yield, characterized by comprising the following steps: S1. Raw material pretreatment: The metal raw materials other than La in the high-temperature alloy raw materials containing La are surface-purified, and La is prepared into granules and coated with nickel foil to form a slow-release structure. S2. Vacuum melting: The metal raw material is added into a vacuum induction furnace and melted under vacuum to form an alloy melt. S3, Calcium-based pre-purification: Ni-Ca master alloy is added to the alloy melt for deoxidation and desulfurization refining to reduce the oxygen and sulfur content in the melt; S4, La gradient addition: Under an argon protective atmosphere, the nickel foil-coated La particles are added to the alloy melt in batches, and the La element is uniformly dispersed by electromagnetic stirring; S5. Bottom blowing purification: Argon microbubbles are blown into the alloy melt through a venting device set at the bottom of the crucible, so that the inclusions in the melt are adsorbed on the surface of the microbubbles and float to the surface and accumulate. S6. Slag removal: Remove the slag inclusions floating on the surface of the melt and cover the surface of the melt with a protective slag layer; S7. Protective casting: Casting is completed under argon protection conditions, and a slightly positive pressure argon atmosphere is maintained continuously during the solidification process of the casting to prevent secondary oxidation of La. Among them, through the synergistic effect of calcium-based pre-purification, La gradient addition, microbubble inclusion capture, and micro-positive pressure protection during the solidification stage, the amount of scum generated is reduced to below 0.3%, and the La recovery rate is increased to 65% to 80%.

[0058] Example 1:

[0059] Comparative Example 1: Eliminate calcium-based pre-purification in S3; Except for the absence of Ni-Ca master alloy, the process is the same as in Example 1.

[0060] Comparative Example 2: S4 is omitted (Ni foil coating is omitted); La is added directly to the melt. All other conditions remain unchanged.

[0061] Comparative Example 3: Eliminate S5 (remove bottom-blowing argon); After adding La, the slag is removed and the mixture is poured directly. Microbubble purification is not performed.

[0062] Comparative Example 4: S7 was removed (solidification micro-positive pressure was removed); Argon protection was stopped after casting was completed. Conventional cooling was then used.

[0063] The testing items are conducted in accordance with the testing specifications for high-temperature alloys in aerospace castings: La yield; total slag content; oxygen content; inclusion rating; casting pass rate.

[0064]

[0065]

[0066]

[0067] Comparative analysis of Example 1: Without calcium-based pre-purification, the melt contains high levels of oxygen and sulfur. When La is added, it readily reacts with oxygen and sulfur to form La2O3 and La2O2S inclusions, resulting in a significant increase in scum and a significant decrease in La recovery.

[0068] Comparative analysis of Example 2: When La is directly added to the melt, the contact area between La and residual oxygen is large, which intensifies the oxidation and burning loss, resulting in a decrease in La utilization and the formation of a large number of rare earth oxide inclusions.

[0069] Comparative analysis of Example 3: After the bottom-blowing argon gas was removed, the inclusions mainly relied on natural floating and electromagnetic stirring to migrate. Small inclusions were difficult to remove effectively, resulting in an increase in the amount of residual inclusions.

[0070] Comparative analysis of Example 4: After the micro-positive pressure protection during the solidification stage is removed, air is easily drawn in during the solidification shrinkage of the casting, which leads to secondary oxidation of La, increasing the oxygen content and inclusion defect rate.

[0071] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for smelting high-temperature alloys containing La with low slag and high yield, characterized in that, Includes the following steps: S1. Raw material pretreatment: The metal raw materials other than La in the high-temperature alloy raw materials containing La are surface-purified, and La is prepared into granules and coated with nickel foil to form a slow-release structure. S2. Vacuum melting: The metal raw material is added into a vacuum induction furnace and melted under vacuum to form an alloy melt. S3, Calcium-based pre-purification: Ni-Ca master alloy is added to the alloy melt for deoxidation and desulfurization refining to reduce the oxygen and sulfur content in the melt; S4, La gradient addition: Under an argon protective atmosphere, the nickel foil-coated La particles are added to the alloy melt in batches, and the La element is uniformly dispersed by electromagnetic stirring; S5. Bottom blowing purification: Argon microbubbles are blown into the alloy melt through a venting device set at the bottom of the crucible, so that the inclusions in the melt are adsorbed on the surface of the microbubbles and float to the surface and accumulate. S6. Slag removal: Remove the slag inclusions floating on the surface of the melt and cover the surface of the melt with a protective slag layer; S7. Protective casting: Casting is completed under argon protection conditions, and a slightly positive pressure argon atmosphere is maintained continuously during the solidification process of the casting to prevent secondary oxidation of La. Among them, through the synergistic effect of calcium-based pre-purification, La gradient addition, microbubble inclusion capture, and micro-positive pressure protection during the solidification stage, the amount of scum generated is reduced to below 0.3%, and the La recovery rate is increased to 65% to 80%.

2. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: The La particles in step S1 have a particle size of 3-5 mm, and the nickel foil used for coating has a thickness of 0.05-0.10 mm.

3. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: In step S2, the vacuum degree of vacuum melting is controlled at 10^-2 to 10^-3 Pa, and the melting temperature is controlled at 1520 to 1550℃.

4. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: In step S3, the amount of Ni-Ca master alloy added is 0.08 to 0.12 wt% of the total alloy mass, and the alloy is refined for 20 to 30 minutes using an electromagnetic stirring speed of 400 to 500 r / min. After step S3 is completed, the oxygen content in the alloy melt is controlled to be below 20 ppm before the La addition operation in step S4 is carried out.

5. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: In step S4, argon gas with a purity of not less than 99.999% is introduced, and the pressure inside the furnace is controlled at 0.3-0.5 MPa. La particles are added in 3-5 batches, with an interval of 2-3 minutes between each batch. In step S4, the total amount of La added is 0.05 to 0.10 wt% of the total alloy mass. After addition, it is dispersed and mixed using an electromagnetic stirring speed of 500 to 600 r / min for 5 to 8 min.

6. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: In step S5, the bottom-blowing argon flow rate is 1.5–3.0 L / min, the diameter of the formed bubbles is 0.5–2 mm, the bottom-blowing time is 15–25 min, and a weak electromagnetic stirring state of 200–300 r / min is maintained simultaneously.

7. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: The protective slag layer in step S6 is composed of CaF2 and CaO, and the thickness of the protective slag layer is 5-10 mm.

8. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: In step S7, the pouring temperature is controlled at 1480-1500℃, the argon flow rate is controlled at 5-10L / min during the pouring process, and after pouring, the argon micro-positive pressure of 0.05-0.08MPa is maintained until the casting temperature drops below 900℃.

9. The method for smelting a high-temperature alloy containing La with low slag and high yield according to claim 1, characterized in that: In step S5, microbubbles form bubble-inclusion complexes after contacting inclusion particles. Under weak electromagnetic stirring, the inclusion particles collide and aggregate with each other, increasing the average particle size of the inclusions by 3 to 10 times and increasing the floating speed of the inclusions by 5 to 8 times, thereby achieving rapid removal of La oxide inclusions and calcium-based composite inclusions.

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