A high-nitrogen iron-nickel-based alloy protective slag

Abstract

The application belongs to the technical field of continuous casting and particularly relates to a high-nitrogen Fe-Ni-based alloy protective slag. According to mass percentage, the high-nitrogen Fe-Ni-based alloy protective slag comprises SrO: 14-16%, CaF2: 11.5-13.5%, SiO2: 24-26%, Na2O+K2O: 12-14%, B2O3: 7-9%, Al2O3: <1%, MgO: 8-10%, La2O3: 10-12%, and the rest is carbonaceous material and inevitable impurities. Through accurate slag system design and component regulation, the protective slag has excellent performances of rapid slag formation, high lubrication and phased heat control, effectively solves the crack problem in the high-nitrogen Fe-Ni-based alloy continuous casting process, and meets the actual needs of the large-scale production of the continuous casting.

Description

Technical Field

[0001] This invention belongs to the field of continuous casting technology, specifically relating to a high-nitrogen iron-nickel-based alloy protective slag. Background Technology

[0002] High-nitrogen iron-nickel-based alloys possess excellent strength, corrosion resistance, and structural stability. Through solid solution strengthening and grain refinement by nitrogen, the high-temperature mechanical properties and pitting corrosion resistance of the alloys can be significantly improved, making them key structural materials in high-end equipment fields such as aerospace, energy equipment, nuclear power, and petrochemicals.

[0003] However, due to their high alloy element content, iron-nickel-based alloys suffer from poor high-temperature plasticity, low thermal conductivity and coefficient of thermal expansion, and are extremely susceptible to cracking. The high nitrogen content further exacerbates crack formation, posing a significant challenge to their production. Limited by their compositional characteristics, these steel grades have traditionally been produced using ingot casting. To achieve large-scale continuous casting production, three core challenges must be overcome: First, the low liquidus temperature of these alloys necessitates a protective slag with excellent rapid slag-forming capabilities to match the pace of continuous casting. Second, given the high high-temperature strength, poor plasticity, and low thermal conductivity of these alloys, the protective slag film must achieve phased heat control—initial strong heat transfer to rapidly form a sufficiently thick initial shell on the billet, preventing initial cracks; and subsequent weak heat transfer to allow the shell to cool slowly, reducing cracks caused by thermal stress. Third, the protective slag film must also possess long-lasting lubrication properties to ensure smooth billet casting and avoid surface defects.

[0004] Currently, conventional continuous casting mold fluxes are unable to meet the three core requirements of "high lubrication, staged heat control, and rapid melting," and cannot satisfy the actual requirements of large-scale, high-quality production of high-nitrogen iron-nickel-based alloys, thus becoming a key bottleneck restricting the promotion and application of its continuous casting process. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a high-nitrogen iron-nickel-based alloy protective slag.

[0006] Specifically, the present invention is achieved through the following technical solutions: A high-nitrogen iron-nickel-based alloy protective slag, by mass percentage, comprises: SrO: 14~16%, CaF2: 11.5~13.5%, SiO2: 24~26%, Na2O+K2O: 12-14%, B2O3: 7~9%, Al2O3: <1%, MgO: 8-10%, La2O3: 10~12%, with the remainder being carbonaceous materials and unavoidable impurities.

[0007] The above-mentioned high-nitrogen iron-nickel-based alloy protective slag has (SrO+0.7CaF2) / SiO2=0.8~1.0 and K2O / (La2O3+MgO)=0.32~0.71.

[0008] The above-mentioned high-nitrogen iron-nickel-based alloy protective slag has a softening point temperature of <910℃ and a melting point of 1020~1050℃.

[0009] The aforementioned high-nitrogen iron-nickel-based alloy protective slag is heated at a heating rate of 1℃ / min, and the glass crystallization temperature of the protective slag is 600~690℃.

[0010] The aforementioned high-nitrogen iron-nickel-based alloy protective slag is cooled at a rate of 15°C / min, and the melt crystallization temperature of the protective slag is 1100-1150°C.

[0011] The aforementioned high-nitrogen iron-nickel-based alloy protective slag has a transition temperature of 920-950℃.

[0012] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The present invention adds B2O3 and K2O to lower the softening point temperature of the protective slag, and adds and controls the ratio of MgO and La2O3 to increase the nucleation points of the protective slag in the glassy state. The two work together to enhance the migration ability of molecular units in the glassy protective slag, enhance and promote the transformation from the glassy state to the crystalline state, and enhance the heat transfer control ability of the protective slag in the later stage.

[0013] (2) Through precise slag system design and component control, the present invention enables the protective slag to simultaneously possess excellent properties such as rapid slag formation, high lubricity, and phased heat control, effectively solving the cracking problem in the continuous casting process of high nitrogen type iron-nickel based alloys and adapting to the actual needs of its large-scale continuous casting production. Detailed Implementation

[0014] 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.

[0015] To address the problem of cracking in continuous casting of high-nitrogen nickel-based alloys, the inventors of this invention have developed a high-nitrogen iron-nickel-based alloy protective slag. By precisely controlling the proportions of key components such as SrO, CaF2, B2O3, MgO, and La2O3, the invention achieves synergistic performance in rapid slag formation, high lubrication, and staged heat control.

[0016] Specifically, the high-nitrogen iron-nickel-based alloy protective slag provided by the present invention comprises, by mass percentage: SrO: 14~16%, CaF2: 11.5~13.5%, SiO2: 24~26%, Na2O+K2O: 12-14%, B2O3: 7~9%, Al2O3: <1%, MgO: 8-10%, La2O3: 10~12%, with the remainder being carbonaceous materials and unavoidable impurities.

[0017] In some preferred embodiments, the ratio of (SrO+0.7CaF2) / SiO2 is further controlled to be 0.8~1.0, and the ratio of K2O / (La2O3+MgO) is controlled to be 0.32~0.71.

[0018] To address the requirement for staged heat control of the protective slag film in high-nitrogen iron-nickel-based alloys, this invention improves the protective slag as follows: This invention effectively weakens the high-temperature crystallization ability of protective slag by controlling the effective alkalinity (SrO+0.7CaF2) / SiO2 to 0.8~1.0, ensuring the thickness of the liquid slag layer, improving the lubrication ability of protective slag, and reducing problems such as discontinuous slag film and insufficient lubrication caused by insufficient liquid slag, thereby reducing cracking problems.

[0019] Furthermore, by adding B2O3 and K2O, the softening point temperature of the protective slag is lowered, the migration ability of molecular units in the glassy protective slag is enhanced, the transformation from glassy to crystalline state is promoted, the heat transfer control ability of the protective slag in the later stage is improved, the heat transfer of the billet shell is uniform, and the generation of cracks is reduced.

[0020] Finally, by reasonably adding and controlling the ratio of MgO and La2O3, the nucleation sites in the glassy state of the protective slag are increased, further promoting the transformation from the glassy state to the crystalline state, enhancing the heat control effect in the later stage, and reducing the probability of thermal stress cracking.

[0021] Testing revealed that the softening point of the protective slag of this invention is <910℃, the melting point is 1020~1050℃, and when heated at a rate of 1℃ / min, the glass crystallization temperature of the protective slag is 600~690℃; when cooled at a rate of 15℃ / min, the melt crystallization temperature of the protective slag is 1100-1150℃; and the inflection point temperature of the protective slag is 920-950℃.

[0022] The melting point of the protective slag of this invention is 1020~1050℃, which is lower than that of the protective slag in the prior art. Therefore, the protective slag has a good ability to form slag quickly, so that the liquid slag has sufficient thickness and ensures a stable supply of protective slag liquid slag, effectively solving the problem of low liquidus temperature of high nitrogen type iron-nickel based alloy.

[0023] The preparation method of the high-nitrogen iron-nickel-based alloy protective slag of the present invention is as follows: strontium carbonate, fluorite powder, quartz sand, sodium carbonate and other raw materials are mixed in proportion, and then processed through pulping → atomization → drying → packaging.

[0024] In this invention, the types and proportions of raw materials used in preparing the protective slag are selected according to the target composition of the protective slag, and the technical parameters used in the preparation process are all in accordance with existing technologies, which will not be elaborated in detail in this invention.

[0025] 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.

[0026] Example 1: Casting N08120 iron-nickel-based alloy with a nitrogen content of 0.17% (1) The main components (wt.%) of N08120 iron-nickel based alloy steel liquid are: C: 0.04%, Cr: 24.6%, Ni: 36.7%, Nb: 0.44%, N: 0.17%.

[0027] (2) The effective component content (wt.%) of the protective slag used is as follows: SrO: 15.2%, CaF2: 12.5%, SiO2: 24.8%, Na2O+K2O: 13%, B2O3: 8.6%, Al2O3: 0.5%, MgO: 8.9%, La2O3: 11.3%, (SrO+0.7CaF2) / SiO2=0.96; K2O / (La2O3+MgO)=0.35, the remainder being carbonaceous materials and unavoidable impurities. The softening point temperature of the protective slag is 890℃, the melting point is 1036℃, the glass crystallization temperature is 665℃ (heating rate 1℃ / min), the melt crystallization temperature is 1135℃ (cooling rate 15℃ / min), and the inflection point temperature of the protective slag is 940℃.

[0028] (3) A vertical bending continuous casting machine is used, with a billet pulling speed of 1.15 m / min and a primary cooling water flow rate of 4000 / 370 L / min; the frictional stress of the crystallizer is 13.6 KN / m. 2 The thickness of the liquid slag layer is 10-12mm and the slag consumption is 0.46kg / t.

[0029] Inspection revealed that the produced billets had excellent surface quality and no longitudinal cracks.

[0030] Example 2: Casting N08120 iron-nickel-based alloy with a nitrogen content of 0.28% (1) The main components (wt.%) of N08120 iron-nickel based alloy steel liquid are: C: 0.08%, Cr: 25.3%, Ni: 35.2%, Nb: 0.52%, N: 0.28%.

[0031] (2) The effective component content (wt.%) of the protective slag used is as follows: SrO: 14.3%, CaF2: 11.8%, SiO2: 25.6%, Na2O+K2O: 13.5%, B2O3: 8.4%, Al2O3: 0.6%, MgO: 8.3%, La2O3: 10.5%; (SrO+0.7CaF2) / SiO2=0.88, K2O / (La2O3+MgO)=0.40, the remainder being carbonaceous materials and unavoidable impurities. The softening point temperature of the protective slag is 886℃, the melting point is 1042℃, the glass crystallization temperature is 613℃ (heating rate 1℃ / min), the melt crystallization temperature is 1127℃ (cooling rate 15℃ / min), and the inflection point temperature is 929℃.

[0032] (3) A vertical bending continuous casting machine is used, with a billet pulling speed of 1.0 m / min and a primary cooling water flow rate of 4000 / 370 L / min; the frictional stress of the crystallizer is 12.9 KN / m. 2 The thickness of the liquid slag layer is 9-12mm and the slag consumption is 0.45kg / t.

[0033] Inspection revealed that the surface quality of the cast billet was excellent, with no longitudinal cracks.

[0034] Comparative Example 1: N08120 iron-nickel-based alloy with a nitrogen content of 0.17% (cast) (1) The composition of N08120 iron-nickel based alloy steel liquid is the same as that in Example 1.

[0035] (2) The effective component content (wt.%) of the protective slag used is as follows: CaO: 33.64%, SiO2: 31.42%, Al2O3: 6.62%, MgO: 1.29%, Na2O: 6.71%, F - The composition is 6.5%, with the remainder consisting of carbonaceous materials and unavoidable impurities. Testing revealed that the softening point of the protective slag is 1109℃, the melting point is 1117℃, the glass crystallization temperature is 1079℃ (heating rate 1℃ / min), the melt crystallization temperature is 1193℃ (cooling rate 15℃ / min), and the inflection point temperature of the protective slag is 1203℃.

[0036] (3) A vertical bending continuous casting machine is used, with a billet pulling speed of 1.15 m / min and a primary cooling water flow rate of 4000 / 370 L / min; the frictional stress of the crystallizer is 19.3 KN / m. 2 The thickness of the liquid slag layer is 6-9mm and the slag consumption is 0.40kg / t.

[0037] Tests revealed that the longitudinal crack rate on the surface of the cast billet reached 35%.

[0038] Comparative Example 2: N08120 iron-nickel based alloy with a nitrogen content of 0.28% (cast) (1) The composition of N08120 iron-nickel based alloy steel liquid is the same as in Example 2.

[0039] (2) The effective component content (wt.%) of the protective slag used is as follows: CaO: 33.64%, SiO2: 31.42%, Al2O3: 6.62%, MgO: 1.29%, Na2O: 6.71%, F-: 6.5%, with the remainder being carbonaceous materials and unavoidable impurities. The softening point temperature of the protective slag is 1109℃, the melting point is 1117℃, the glass crystallization temperature is 1079℃ (heating rate 1℃ / min), the melt crystallization temperature is 1193℃ (cooling rate 15℃ / min), and the inflection point temperature is 1203℃.

[0040] (3) A vertical bending continuous casting machine is used, with a billet pulling speed of 1.0 m / min and a primary cooling water flow rate of 4000 / 370 L / min; the frictional stress of the crystallizer is 20.9 KN / m. 2 The thickness of the liquid slag layer is 7-9 mm and the slag consumption is 0.39 kg / t.

[0041] Tests revealed that the longitudinal crack rate on the surface of the cast billet reached 51%.

[0042] 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.

[0043] 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.

[0044] 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 high-nitrogen iron-nickel-based alloy protective slag, characterized in that, By mass percentage, it includes: SrO: 14~16%, CaF2: 11.5~13.5%, SiO2: 24~26%, Na2O+K2O: 12-14%, B2O3: 7~9%, Al2O3: <1%, MgO: 8-10%, La2O3: 10~12%, with the remainder being carbonaceous materials and unavoidable impurities.

2. The high-nitrogen iron-nickel-based alloy protective slag according to claim 1, characterized in that, (SrO+0.7CaF2) / SiO2=0.8~1.0, K2O / (La2O3+MgO)=0.32~0.

71.

3. The high-nitrogen iron-nickel-based alloy protective slag according to claim 1, characterized in that, The softening point of the protective slag is <910℃, and the melting point is 1020~1050℃.

4. The high-nitrogen iron-nickel-based alloy protective slag according to claim 1, characterized in that, The protective slag is heated at a heating rate of 1℃ / min, and the glass crystallization temperature of the protective slag is 600~690℃.

5. The high-nitrogen iron-nickel based alloy protective slag according to claim 1, characterized in that, The protective slag is cooled at a rate of 15℃ / min, and the melt crystallization temperature of the protective slag is 1100-1150℃.

6. The high-nitrogen iron-nickel-based alloy protective slag according to claim 1, characterized in that, The inflection point temperature of the protective slag is 920-950℃.