Special deslagging primer for nickel-based alloy and preparation method thereof

Abstract

This invention belongs to the field of steelmaking continuous casting technology, specifically relating to a special slag for nickel-based alloy casting and its preparation method. The special slag for nickel-based alloy casting of this invention, by weight percentage, comprises: Ca-Al alloy powder: 4.0%~5.0%, Fe2O3: (2.3~3.0)×(Ca-Al alloy powder), Li2O: 3~5%, F... ‑ The composition of the nickel-based alloy casting slag is as follows: Na2O: 6-9%, Al2O3: <0.5%, MgO <1.0%, free carbon (FC) <0.3%, with the remainder being CaO, SiO2, and unavoidable impurities. This invention utilizes a precisely proportioned Ca-Al alloy powder and Fe2O3 heating oxidation system to achieve a combination of instantaneous and continuous heat release, fully compensating for heat loss from molten steel during the initial casting stage. Furthermore, the residual Fe2O3 after the reaction further promotes rapid slag formation in the protective slag, balancing ignition capability, heat release stability, and overall slag formation efficiency, significantly improving slag layer stability during the initial casting stage.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking continuous casting technology, specifically relating to a special casting slag for nickel-based alloys and its preparation method. Background Technology

[0002] Nickel-based alloys, due to their excellent high-temperature strength, corrosion resistance, and oxidation resistance, are widely used in high-end fields such as aerospace, petrochemicals, and nuclear industry. However, nickel-based alloys face several technical challenges during the initial casting stage: First, the liquidus temperature of nickel-based alloys is low, typically around 1400℃. Large temperature fluctuations in molten steel during initial casting, coupled with the incompatible melting characteristics of conventional initial casting slag, easily lead to insufficient slag formation and insufficient slag thickness during the initial casting stage. Second, the high content of alloying elements such as Ni, Cr, and Mo in nickel-based alloys results in low thermal conductivity and large solidification shrinkage, easily forming air gaps in the crystallizer, leading to uneven heat transfer and surface cracking. Third, existing initial casting slags are mostly designed for ordinary carbon steel and alloy steel, and their chemical composition and physicochemical properties cannot meet the special heat transfer and lubrication requirements of nickel-based alloys, affecting billet quality. Fourth, the rapid heat dissipation of molten steel in the crystallizer during the initial casting stage, combined with the heat absorption of the melting protective slag, further exacerbates the temperature drop, easily causing cold steel to form on the molten steel surface, affecting the smooth casting process.

[0003] In the existing technology, the relevant open casting slag patents all have obvious adaptability defects. For example, the pre-melted exothermic open casting slag disclosed in patent CN1163329C, the open casting method for reducing longitudinal cracks on the surface of thick plate continuous casting billets disclosed in CN110640106A, and the continuous casting open casting slag for casting peritectic steel disclosed in patent CN112756570A are all applicable to steel grades with peritectic reaction. Their high basicity slag system cannot adapt to the heat transfer and lubrication requirements of nickel-based alloys. Although the open casting slag for stainless steel continuous casting in patent CN113290216A solves a series of problems in stainless steel open casting, the heating characteristics of the iron filings and ferrosilicon alloy exothermic agent used are not good, and the melting point of the open casting slag is too high, which cannot meet the rapid slag formation requirements of nickel-based alloy open casting.

[0004] The existing start-up slag systems, with their alkalinity, composition, exothermic agent, and oxidant systems, are designed for carbon steel or stainless steel with higher casting temperatures. However, their exothermic efficiency and melting characteristics cannot meet the rapid slag formation requirements for nickel-based alloys during start-up casting. Therefore, developing a specialized start-up slag that is highly targeted and adapted to the start-up casting needs of nickel-based alloys has become a pressing technical problem for the industry. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a special slag for nickel-based alloy casting and its preparation method.

[0006] Specifically, the present invention is achieved through the following technical solutions: A special slag for nickel-based alloy casting, comprising, by weight percentage: Ca-Al alloy powder: 4.0%~5.0%, Fe2O3: (2.3~3.0)×(Ca-Al alloy powder), Li2O: 3~5%, F - : 9~11%, Na2O: 6~9%, Al2O3: <0.5%, MgO <1.0%, free carbon FC <0.3%, the remainder is CaO and SiO2 and unavoidable impurities.

[0007] The above-mentioned nickel-based alloy special casting slag has the following CaO and SiO2 content: CaO / SiO2 = 0.65~0.75.

[0008] The aforementioned nickel-based alloy special casting slag contains Ca content of 35~45 wt.% and Al content of 55~65 wt.% in the Ca-Al alloy powder.

[0009] A method for preparing a special casting slag for nickel-based alloys, comprising: (1) Mix wollastonite, quartz sand, fluorite powder, sodium carbonate, lithium carbonate and sodium fluoride in a certain proportion and add them to an electric furnace and heat until completely melted to obtain liquid slag; (2) The liquid slag is poured into water for water quenching treatment to obtain water-quenched slag; (3) The water-quenched slag is dried and ground to obtain a pre-melted base material; (4) The pre-melted base material is mixed with Fe2O3 and Ca-Al alloy powder in proportion to obtain the special casting slag for nickel-based alloy.

[0010] In the above-mentioned method for preparing nickel-based alloy special casting slag, the heating is carried out in an electric furnace at a temperature of 1500±50℃.

[0011] In the above-mentioned method for preparing special slag for nickel-based alloys, the temperature of the water is ≤60℃.

[0012] In the above-mentioned method for preparing nickel-based alloy special casting slag, the drying temperature is ≤300℃.

[0013] The above-mentioned method for preparing special casting slag for nickel-based alloys, wherein the pre-melted base material has a moisture content of <0.3wt.% and a particle size of -200 mesh >98%.

[0014] In the above-mentioned method for preparing nickel-based alloy special casting slag, the mixing time is 40-60 minutes.

[0015] A special slag for nickel-based alloy casting is prepared using the above-mentioned preparation method.

[0016] The technical solution of the present invention has the following beneficial effects: (1) The nickel-based alloy special casting slag of the present invention adopts a heating oxidation system with Ca-Al alloy powder and Fe2O3 in precise proportion to achieve a combination of instantaneous heat release and continuous heat release, which fully compensates for the heat loss of molten steel during the casting stage. Moreover, the Fe2O3 remaining after the reaction can further promote the rapid formation of protective slag, taking into account ignition capability, heat release stability and overall slag formation efficiency, and greatly improving the stability of slag layer during the casting stage.

[0017] (2) The preparation method of the nickel-based alloy special casting slag of the present invention adopts the preparation process of pre-melted base material combined with post-mixed functional powder. Under the premise of retaining the reducing property of Ca-Al alloy powder and the oxidizing property of Fe2O3, the melting uniformity of casting slag is improved and the finished product performance is stable.

[0018] (3) This invention addresses the material characteristics of nickel-based alloys, such as low liquidus temperature and low thermal conductivity. Through the design of a composition system with low melting point, low viscosity and low alkalinity, it achieves rapid slag formation and forms a stable liquid slag layer, effectively avoiding problems such as cold steel forming on the surface of molten steel and cracks on the surface of the billet. At the same time, it matches the special heat transfer and lubrication requirements of continuous casting of nickel-based alloys, ensuring the smooth operation of the casting process.

[0019] (4) By precisely designing the composition system and preparation process of the slag, the present invention enables the slag to match the properties of nickel-based alloys such as low liquidus temperature and low thermal conductivity, thereby achieving rapid slag formation, stable heating, uniform melting, uniform heat transfer and good lubrication. This solves the problems of insufficient slag formation, cold steel formation and surface cracks of the billet in the initial casting stage of nickel-based alloy continuous casting, ensuring smooth casting and improving the quality of the billet. Detailed Implementation

[0020] To fully understand the purpose, features, and effects of this invention, the following detailed embodiments are provided. Except as described below, the process methods of this invention employ conventional methods or apparatus in the art. Unless otherwise specified, the terms and expressions used below have the meanings commonly understood by those skilled in the art.

[0021] Definitions: Initial pouring slag refers to the protective slag used at the beginning of continuous casting, specifically for the initial stage of pouring.

[0022] Pre-melted base material refers to a powdered semi-finished product made by pre-melting and homogenizing the base slag material of protective slag at high temperature, and then cooling and crushing it.

[0023] The Fe2O3 ratio "(2.3~3.0)×(Ca-Al alloy powder)" indicates that the Fe2O3 content is 2.3~3.0 times that of the Ca-Al alloy powder.

[0024] Specifically, the nickel-based alloy special casting slag provided by this invention, by weight percentage, comprises: Ca-Al alloy powder: 4.0%~5.0%, Fe2O3: (2.3~3.0)×(Ca-Al alloy powder), Li2O: 3~5%, F - : 9~11%, Na2O: 6~9%, Al2O3: <0.5%, MgO <1.0%, free carbon FC <0.3%, the remainder is CaO and SiO2 and unavoidable impurities.

[0025] Among them, the following effective components in the nickel-based alloy special casting slag of the present invention are Li2O and F. - Na2O, Al2O3, MgO, free carbon FC, CaO, and SiO2 are derived from the pre-melted base material.

[0026] In the nickel-based alloy-specific casting slag of this invention, Li2O and F - The content of Na2O, especially Li2O, is much higher than that of conventional casting slag, which can effectively reduce the melting point and viscosity of the casting slag, enabling it to melt quickly to form liquid slag, meeting the basic requirements of nickel-based alloys for casting slag. At the same time, the viscosity value is similar to that of protective slag, improving its compatibility with protective slag.

[0027] This invention uses Ca-Al alloy powder as a heating agent. The aluminum component can release heat instantly, thereby breaking up the cold slag and thawing the meniscus; the calcium component can release heat gently and continuously, keeping the liquid slag layer stable for 20 to 30 seconds.

[0028] In some preferred embodiments, based on the requirement that nickel-based alloys have a lower casting temperature and require higher heat in the early stage, the present invention controls the mass percentage of calcium in the Ca-Al alloy powder to be 35% to 45% and the mass percentage of aluminum to be 55% to 65%. The resulting Ca-Al alloy powder simultaneously takes into account ignition capability, heat release stability and slag formation efficiency, thereby effectively solving the problem of rapid heat dissipation of molten steel in the crystallizer during the initial casting stage of nickel-based alloys, which easily leads to cold steel condensation on the surface of the molten steel.

[0029] In the nickel-based alloy special casting slag of this invention, Fe2O3 acts as a strong oxidant and exothermic agent, reacting with Ca-Al alloy powder to release heat, compensating for heat loss during continuous casting and preventing the formation of cold steel. Through extensive theoretical calculations and experimental verification, the inventors determined that the Fe2O3 content must satisfy: w(Fe2O3) = (2.3~3.0) × w(Ca-Al alloy powder). This ensures that after the reaction is complete, some Fe2O3 remains in the liquid slag. When the mold flux is subsequently added, the remaining Fe2O3 reacts with free carbon in the flux, accelerating the combustion of carbonaceous materials and further promoting the rapid formation of liquid slag, thus improving the overall slag formation effect.

[0030] Nickel-based alloys have a much lower thermal conductivity than conventional steels. If the basicity of the initial slag is too high, it can lead to uneven and excessively thin initial shell thickness in the mold, making the cast billet prone to cracking in subsequent processes. To avoid this defect, in some preferred embodiments, the present invention controls the binary basicity CaO / SiO2 in the initial slag to 0.65~0.75, ensuring that the initial shell thickness is uniform and meets the standard, thus avoiding cracking defects.

[0031] According to testing, the melting point of the nickel-based alloy special casting slag of this invention is 950~1000℃, and the viscosity is 0.10~0.15Pa.s.

[0032] On the other hand, the present invention also provides a method for preparing a special slag for nickel-based alloys. The present invention abandons the traditional direct mixing process and adopts a preparation process of first preparing a pre-melted base material and then mixing functional powders. Under the premise of ensuring the reducibility of calcium-aluminum alloy powder and the oxidizing property of Fe2O3 (without affecting the heating effect), the melting uniformity of the slag is greatly improved.

[0033] Specifically, the steps of the method for preparing nickel-based alloy special casting slag of the present invention are as follows: (1) Mix wollastonite, quartz sand, fluorite powder, sodium carbonate, lithium carbonate and sodium fluoride in proportion and add them to an electric furnace for heating until completely melted to obtain liquid slag.

[0034] The proportions of wollastonite, quartz sand, fluorite powder, sodium carbonate, lithium carbonate, and sodium fluoride are based on the concentrations of Li₂O and F in the initial slag. - The contents of Na2O, Al2O3, MgO, free carbon FC, CaO, and SiO2 are calculated, but the present invention does not impose detailed limitations on these contents.

[0035] In some preferred embodiments, the heating is carried out in an electric furnace at a temperature of 1500±50°C.

[0036] (2) Pour the liquid slag into water for water quenching treatment to obtain water-quenched slag.

[0037] By water quenching the liquid slag, an amorphous structure can be rapidly formed.

[0038] In some preferred embodiments, the temperature of the water is ≤60°C.

[0039] (3) The water-quenched slag is dried and ground to obtain a pre-melted base material.

[0040] In some preferred embodiments, the drying temperature shall not exceed 300°C to prevent cold crystallization of water-quenched slag, which would affect melting characteristics and meet the requirements of the pre-melted base material.

[0041] In some preferred embodiments, the pre-melted base material has a moisture content of <0.3 wt.% and a particle size of -200 mesh >98%.

[0042] (4) The pre-melted base material is mixed with Fe2O3 and Ca-Al alloy powder in proportion to obtain the special casting slag for nickel-based alloy.

[0043] In some preferred embodiments, in order to ensure that the composition of the prepared slag is uniform, the mixing time of the pre-melted base material with Fe2O3 and Ca-Al alloy powder is controlled to be 40 to 60 minutes.

[0044] In some preferred embodiments, the pre-melted base material is mixed with Fe2O3 and Ca-Al alloy powder in a mixing dryer.

[0045] The preparation method of the present invention involves first mixing CaO, iO2, Li2O, and F... - Using Na2O-related raw materials to prepare pre-melted base material can ensure uniform composition and stable melting performance of the base material. By mixing the pre-melted base material with calcium aluminum powder and Fe2O3, the functional powder can be effectively prevented from reacting and losing its heat generation and oxidation functions during the high-temperature pre-melting stage. At the same time, it can ensure that the overall composition of the finished product is uniform and the melting uniformity meets the process requirements.

[0046] Example The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments, unless otherwise specified, are performed according to conventional methods and conditions.

[0047] Example 1 (1) Mix 35.7% wollastonite, 21.03% quartz sand, 20.09% fluorite powder, 11.40% sodium carbonate, 9.72% lithium carbonate and 2.06% sodium fluoride by weight percentage, and add them to an electric furnace at 1500±50℃ for melting until completely melted.

[0048] (2) Pour the liquid slag evenly into a flowing water pool at 20~50℃ for water quenching treatment so that the liquid slag can quickly form an amorphous structure.

[0049] (3) The water-quenched slag is dried and ground at 200±20℃ to obtain a pre-melted base material, wherein the water content of the pre-melted base material is 0.2% and the particle size is -200 mesh > 98%.

[0050] (4) The weight percentages of 85.15% pre-melted base material, 10.65% ferric oxide and 4.2% Ca-Al alloy powder are prepared and added to a mixing dryer. After mixing for 50 minutes and mixing evenly, the nickel-based alloy special casting slag product is obtained.

[0051] The finished slag has a melting point of 965℃ and a viscosity of 0.11 Pa. The effective component percentage content is as follows: Ca-Al alloy powder 4.2%, Fe2O3 10.75%, Li2O 3.5%, F - 9.6%, Na2O 7.2%, Al2O3 0.3%, MgO 0.7%, free carbon 0.2%, the remainder being CaO and SiO2, CaO / SiO2=0.72.

[0052] When applied to the continuous casting of N06625 nickel-based alloy, it resulted in sufficient slag formation, stable slag layer thickness, no condensation of cold steel, no cracks or defects on the surface of the billet, and smooth casting.

[0053] Example 2 (1) Mix 36.11% wollastonite, 20.44% quartz sand, 18.54% fluorite powder, 7.13% sodium carbonate, 11.03% lithium carbonate and 6.75% sodium fluoride by weight percentage, and add them to an electric furnace at 1500±50℃ for melting until completely melted.

[0054] (2) Pour the liquid slag evenly into a flowing water pool at 25~55℃ for water quenching treatment so that the liquid slag can quickly form an amorphous structure.

[0055] (3) The water-quenched slag is dried and ground at 200±20℃ to obtain a pre-melted base material, wherein the water content of the pre-melted base material is 0.2 wt.% and the particle size is -200 mesh > 98%.

[0056] (4) After preparing 82.82% pre-melted base material, 12.38% ferric oxide and 4.8% Ca-Al alloy powder by weight percentage, add them to a mixing dryer and mix for 50 minutes. After mixing evenly, the finished product of nickel-based alloy special casting slag is obtained.

[0057] The finished slag has a melting point of 975℃ and a viscosity of 0.11 Pa. The effective component percentage content is as follows: Ca-Al alloy powder 4.8%, Fe2O3 12.48%, Li2O 3.8%, F - 10.2%, Na2O 7.5%, Al2O3 0.3%, MgO 0.79%, free carbon 0.2%, the remainder being CaO and SiO2, CaO / SiO2=0.70.

[0058] When applied to the continuous casting of N08825 nickel-based alloy, it resulted in rapid slag formation, uniform liquid slag layer, no condensation of cold steel or air gaps, and a liquid slag thickness of up to 11 mm. The surface quality of the cast billet met the standards and was free of defects.

[0059] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0060] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0061] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A special slag for nickel-based alloy casting, characterized in that, By weight percentage, it includes: Ca-Al alloy powder: 4.0%~5.0%, Fe2O3: (2.3~3.0)×(Ca-Al alloy powder), Li2O: 3~5%, F - : 9~11%, Na2O: 6~9%, Al2O3: <0.5%, MgO <1.0%, free carbon FC <0.3%, the remainder is CaO and SiO2 and unavoidable impurities.

2. The special slag for nickel-based alloy casting according to claim 1, characterized in that, The contents of CaO and SiO2 satisfy the following condition: CaO / SiO2 = 0.65~0.

75.

3. The special slag for nickel-based alloy casting according to claim 1, characterized in that, The Ca-Al alloy powder contains 35-45 wt.% Ca and 55-65 wt.% Al.

4. The method for preparing the nickel-based alloy special casting slag according to any one of claims 1 to 3, characterized in that, include: (1) Mix wollastonite, quartz sand, fluorite powder, sodium carbonate, lithium carbonate and sodium fluoride in a certain proportion and add them to an electric furnace and heat until completely melted to obtain liquid slag; (2) The liquid slag is poured into water for water quenching treatment to obtain water-quenched slag; (3) The water-quenched slag is dried and ground to obtain a pre-melted base material; (4) The pre-melted base material is mixed with Fe2O3 and Ca-Al alloy powder in proportion to obtain the special casting slag for nickel-based alloy.

5. The preparation method according to claim 4, characterized in that, The heating is carried out in an electric furnace at a temperature of 1500±50℃.

6. The preparation method according to claim 4, characterized in that, The temperature of the water is ≤60℃.

7. The preparation method according to claim 4, characterized in that, The drying temperature is ≤300℃.

8. The preparation method according to claim 4, characterized in that, The moisture content of the pre-melted base material is <0.3wt.%, and the particle size is -200 mesh >98%.

9. The preparation method according to claim 4, characterized in that, The mixing time is 40-60 minutes.

10. A special slag for nickel-based alloy casting, characterized in that, It is prepared by the preparation method described in any one of claims 4 to 9.