A method of refining inclusions in invar alloys and invar alloys

Abstract

The application discloses a smelting method for refining inclusions in invar alloy and invar alloy, and a large-size invar alloy steel ingot is prepared through an induction furnace smelting, AOD furnace refining, LF furnace refining, VD furnace refining and mold casting process; Al-Si-Mn composite deoxidizer is used for deoxidation in the AOD furnace refining process; and Ni-Mg alloy is added in the LF furnace refining process to decompose and refine inclusions, so that the inclusions are controlled to be Al2O3-MgO-SiO2 inclusions, and the A-type, B-type, C-type and D-type inclusion ratings are less than or equal to 0.5 level, and the Ds-type inclusion rating is 0 level. The application can effectively refine the inclusion size in the invar alloy liquid, reduce the occurrence rate of the local peeling defect on the surface of the cold-rolled strip caused by the large-size deoxidation product, and improve the invar alloy strip product quality and the material yield.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting, and more particularly to a smelting method for refining the size of inclusions in Invar alloys and Invar alloys. Background Technology

[0002] Invar alloy is a binary austenitic Fe-Ni alloy, belonging to the category of precision alloys with anomalous or controllable thermal expansion characteristics. It is widely used in fields such as electronic components where high material expansion performance is required. This alloy has a low coefficient of thermal expansion, with a coefficient of thermal expansion of ≤1.5×10⁻⁶ at 20–100℃. -6 The expansion temperature is only 1 / 5 to 1 / 10 that of ordinary steel. Currently, commercially available Invar alloys are mainly Fe-Ni based alloys, such as 4J36 Invar alloy for aircraft composite molds, Ni36 Invar alloy for thin-film LNG ships, and high-strength H36 Invar alloy for high-voltage capacity conductors. Besides Fe-Ni based Invar alloys, Fe-Ni-Co based super Invar alloys are widely used in the aerospace field due to their excellent ultra-low expansion properties. Their composition is mainly C≤0.04%, Si≤0.25%, 0.2%≤Mn≤0.4%, S≤0.0015%, P≤0.008%, 35%≤Ni≤36.5%, 3%≤Co≤4%, with the remainder being Fe. This alloy requires an expansion performance of 1~2×10⁻⁶ within the operating temperature range of -180~0℃. -6 / ℃. In recent years, the demand for Invar alloy cold-rolled strip has been substantial. However, due to its predominantly application in electronic components and energy transportation, the surface quality requirements for the strip are high, and any defects such as scale or peeling are unacceptable. Under these usage requirements and technological context, the size requirements for inclusions in Invar alloy molten steel are even higher; inclusions exceeding grade 1 are not permitted in the molten steel. Traditional Invar alloys are highly sensitive to the content of gases such as oxygen. During the smelting and deoxidation process, a single deoxidizer such as Al is used for strong deoxidation, resulting in a high content of Al oxides in the alloy, with sizes reaching 100 micrometers or larger. In subsequent cold rolling, large inclusions easily lead to poor surface plasticity of the strip, causing defects such as peeling and scale.

[0003] Chinese patent publication CN119410860A discloses a method for preparing and using a composite deoxidizer for LF slag forming. The main purpose is to deoxidize and modify the top slag of the ladle after tapping from a converter or electric furnace, thereby improving its desulfurization, deoxidation, and inclusion removal functions. However, this method only improves the desulfurization and deoxidation capabilities, and does not provide an effective solution for how to refine and remove high-melting-point inclusions such as Al2O3.

[0004] Chinese patent publication number CN119351859A discloses a green invar alloy smelting method that uses direct reduced iron and scrap steel as raw materials for an electric arc furnace and employs a gaseous nitrogen-enhancing process in the VD process, eliminating the need for expensive nitriding alloy raw materials. However, this technology also does not provide effective methods for refining inclusions.

[0005] Chinese Patent Publication No. CN111519098A discloses a method for deoxidizing low-carbon steel and controlling inclusions in low-carbon steel. The method involves adding deoxidizers such as Ca, Si, Al, Ti, and Mn during a refining process. The mass fraction ratio of Ca to O is 0.5–1.2, and the mass fraction ratio of Ti to Al is 0.5–1.0. This technique can control inclusions into a dispersed Al-Ti-Ca-O inclusion structure, with all inclusions rated ≤0.5, and inclusions with a size ≤5 micrometers accounting for over 99%. However, this method uses Ca and Ti deoxidizers, which can deteriorate the expansion properties of Invar alloys, thus rendering it unusable in the Invar alloy field.

[0006] In summary, there is an urgent need to develop a smelting method that refines the size of inclusions in Invar alloys and can effectively remove large-particle oxides such as Al2O3 from steel. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a smelting method and Invar alloy that refines the size of inclusions in Invar alloy molten steel. This method can effectively refine the size of inclusions in Invar alloy molten steel, reduce the incidence of localized peeling defects on the surface of cold-rolled strip caused by large-sized deoxidation products, and improve the product quality and yield of Invar alloy strip.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A first aspect of the present invention provides a smelting method for refining the size of inclusions in Invar alloys, comprising the following steps:

[0010] S1, induction furnace smelting, uses pure nickel plates and pure iron as Invar alloy raw materials, and the raw materials are formulated according to the chemical composition of Invar alloy. Molten steel is obtained by induction furnace smelting.

[0011] S2, AOD furnace refining, involves adding molten steel to an AOD ladle furnace for refining, blowing oxygen to decarburize, and adding pure nickel plates and pure iron for alloying. At the same time, quicklime is added in batches. When the C content in the molten steel is ≤0.03%, Al-Si-Mn composite deoxidizer is added for deoxidation. After deoxidation, slag removal is performed.

[0012] After slag removal in the S3 LF furnace, the ladle is hoisted to the LF furnace for refining. Aluminum shot is added to the LF furnace to adjust the aluminum content in the molten steel to 0.1-0.2%, ensuring that the sulfur content in the molten steel is ≤0.001%. The composition is finely adjusted according to the composition analysis. After the chemical composition is stable, Ni-Mg alloy is added in the later stage of smelting. Then, bottom blowing argon gas is used for stirring and cooling. When the temperature of the molten steel is ≤1650℃, the LF furnace refining is completed.

[0013] S4, VD furnace refining, after the LF furnace refining is completed, the ladle is transported to the VD process, the ladle furnace is controlled to pump in vacuum, after the pump is withdrawn, the temperature is measured and the synthesis slag is added, and then the pump continues to pump in for bottom blowing argon gas weak stirring.

[0014] S5, ingot casting, argon gas protection is used throughout the casting process, and protective slag is added to the ingot mold in batches to obtain Invar alloy steel ingots weighing 15-25t.

[0015] In the Invar alloy steel ingot, the inclusions of type A, type B, type C, and type D are ≤0.5 grade, and the inclusions of type Ds are 0 grade.

[0016] Preferably, in step S1:

[0017] The pure nickel plate contains 98-99.5% Ni, and the amount of pure nickel plate added is 26-46% of the total weight of the Invar alloy raw material; the amount of pure iron added is 50-70% of the total weight of the Invar alloy raw material; and / or

[0018] The composition of the molten steel by mass percentage is as follows: C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 25%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements.

[0019] Step S1 above is the raw material smelting process, which uses pure nickel plate and pure iron as Invar alloy raw materials. The raw materials are formulated according to the standard chemical composition content of the target Invar alloy product and melted into molten steel that meets the above composition requirements in a 100t induction furnace. Preferably, the C content in the molten steel needs to be further controlled to ≤3.0%.

[0020] Preferably, in step S2:

[0021] The total amount of quicklime added is 4-5 tons per furnace; and / or

[0022] The mass ratio of Al to Si and Mn in the Al-Si-Mn composite deoxidizer is 4-6:2-3:1-4, and the amount of Al-Si-Mn composite deoxidizer added satisfies: m ≥ 0.02L + 0.1, where m is the amount of Al-Si-Mn composite deoxidizer added in tons (t); L is the mass of molten steel in tons; and / or

[0023] During the deoxidation process of the Al-Si-Mn composite deoxidizer, the reduction intensity is controlled to be 1.1 to 1.3.

[0024] Step S2 is the AOD furnace refining process. During oxygen blowing decarburization, pure nickel plates and pure iron are added for alloying. The amount of pure nickel plates and pure iron added can be determined through composition analysis, specifically based on the target composition of the molten steel refined from the AOD furnace. Simultaneously, quicklime is added in batches during oxygen blowing decarburization, primarily to form slag, adsorb deoxidation products, adjust slag basicity, promote the decarburization reaction, and protect the furnace lining. When the carbon content in the molten steel is ≤0.03%, an Al-Si-Mn composite deoxidizer is used. The amount of Al-Si-Mn composite deoxidizer used is adjusted according to the weight of the molten steel. For example, when the weight of the molten steel is approximately 100t, the amount of Al-Si-Mn composite deoxidizer added is m≥2.1t. The Al-Si-Mn composite deoxidizer is added to the molten steel in batches, such as three or four batches, to ensure sufficient deoxidation. After reduction, a slag removal operation is performed to ensure thorough and clean removal of the slag.

[0025] Preferably, in step S2, the composition of the molten steel after refining in the AOD furnace is as follows by mass percentage: C≤0.03%, Si≤1.0%, Mn≤0.5%, P≤0.02%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.2%, with the remainder being Fe and unavoidable residual elements.

[0026] Preferably, in step S3:

[0027] The amount of aluminum shot added is 1-2 kg / t of molten steel; and / or

[0028] In the Ni-Mg alloy, the Ni content is 60-70 wt% and the Mg content is 20-30 wt%; the amount of Ni-Mg alloy added satisfies: m 合金 ≥3×L+20, where m 合金 The amount of Ni-Mg alloy added is expressed in kg; L is the mass of molten steel in tons; and / or

[0029] The bottom-blown argon gas supply intensity is controlled at 5–8 L / min / t of molten steel, and the stirring time is 10–20 min; and / or

[0030] When the temperature of the molten steel is 1600-1650℃, the refining process in the LF furnace is completed.

[0031] Step S3 is the LF furnace refining process. After adding aluminum shot to adjust the aluminum content in the steel, Ni-Mg alloy is added, mainly to inhibit the aggregation and growth of Al2O3 oxide. The amount added can be 320-500 kg / furnace.

[0032] Preferably, in step S4:

[0033] The vacuuming time for the ladle furnace pump is ≥20 min; and / or

[0034] In the synthesized slag, the mass ratio of Al2O3 to SiO2 is 1–3:7–9; and / or

[0035] The amount of the synthetic slag added is 200-300 kg / furnace; and / or

[0036] The argon gas weak stirring time is ≥60 min.

[0037] Step S4 is the VD furnace refining process. The vacuuming time during the ladle furnace pumping process must be ≥20 minutes. After pumping out, a sample is taken for temperature measurement, and synthetic slag is added. Under vacuum conditions, bottom blowing of argon gas into the ladle furnace is more conducive to the flotation and removal of inclusions in the molten steel. Simultaneously, the addition of synthetic slag in this process increases the viscosity and fluidity of the slag in the molten steel. When weak stirring with bottom blowing argon gas is performed during the VD process, the slag, with its good fluidity and viscosity, can fully adsorb inclusions in the molten steel.

[0038] Preferably, in step S5:

[0039] During the process of adding the protective slag to the steel ingot mold in batches, 20-30 kg of protective slag is suspended at the bottom of each steel ingot mold before casting, and the remaining 20-30 kg of protective slag is added successively during the casting process; and / or

[0040] The mass ratio of CaO, MgO, SiO2, and Al2O3 in the protective slag is 2-4:1-2:1-2:2-3.

[0041] The second aspect of the present invention provides an Invar alloy prepared by the smelting method for refining the size of inclusions in Invar alloy as described in the first aspect of the present invention, the composition of which is as follows by mass percentage: C≤0.03%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.05%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements.

[0042] Preferably, the inclusions in the Invar alloy are MgO-Al2O3-SiO2 type inclusions;

[0043] The inclusions are classified as follows: Class A, Class B, Class C, and Class D inclusions are classified as having a grade of ≤0.5, and Class Ds inclusions are classified as having a grade of 0.

[0044] The composition design principle of the Invar alloy of this invention is as follows.

[0045] C: C is an austenitic strengthening element, and increasing the C content can effectively reduce the nitrogen saturation solubility in molten steel. In terms of mechanical properties, while C increases the strength of the alloy, it reduces the toughness and low-temperature expansion properties. Therefore, to ensure the strength and toughness of the alloy, the C content in this invention is controlled to be C≤0.03%.

[0046] Si: As a deoxidizer in molten steel, Si can strengthen the matrix and improve the high-temperature oxidation resistance of steel. An appropriate amount of Si can improve the steel's resistance to strong acid corrosion, but too much Si will reduce the steel's hot workability and toughness, and affect its magnetic permeability. Therefore, in this invention, the Si content is controlled at ≤0.8%.

[0047] Mn: Mn is an austenite-forming element with a very strong ability to stabilize the austenite phase, effectively controlling the low-temperature phase transformation of martensite. Therefore, the Mn content in this invention is required to be ≤0.5%.

[0048] P and S are harmful elements. These two elements tend to segregate near the columnar grain boundaries of steel ingots, which can have a detrimental effect on the welding performance of the material. Therefore, P and S elements are controlled within a low range. Based on the P and S content level of the raw materials, P ≤ 0.020% and S ≤ 0.05% are required.

[0049] Ni (Ni): An austenite-forming element that improves the strength and corrosion resistance of steel. However, excessively high Ni content reduces the solubility of nitrogen in the steel, inhibits the precipitation of strengthening phases such as carbides and nitrides, affects strength, and increases cost. The effect of Ni content on the expansion properties of Invar alloys differs between low-temperature and high-temperature service temperature ranges. As the Ni content decreases, the Curie temperature decreases, moving closer to the low-temperature service temperature range. When the Ni content is below 28% or above 35%, its expansion properties do not meet user standards. Therefore, in this invention, the Ni content is controlled at 28% ≤ Ni ≤ 35%.

[0050] Mg and Al can further remove oxygen from Invar alloys and improve the hot plasticity of steel ingots, but their levels should not be too high. At the same time, adding Mg to Invar alloys can refine austenite grains, pinning them during hot working and inhibiting austenite grain growth; therefore, in this invention, Mg is controlled to be ≤0.1% and Al ≤0.20%.

[0051] This invention prepares large-size Invar alloy steel ingots using a process of smelting in a 100t induction furnace → AOD furnace refining → LF furnace refining → VD furnace refining → die casting. In the AOD furnace refining process, an Al-Si-Mn composite deoxidizer is used to effectively avoid excessive Al content in the molten steel caused by using only a strong Al deoxidizer, reducing the impact of Al on the welding performance of Invar alloy strips. Simultaneously, the application range and weight of each element in the composite deoxidizer are limited, ensuring that the Al, Si, and Mn composite deoxidation effectively removes O from the molten steel while preventing excessive residual deoxidizing elements from affecting the ingot's microstructure and welding performance. Meanwhile, a Ni-Mg alloy is added in the LF process. Mg alloying elements further inhibit the aggregation and growth of Al2O3 oxides, causing them to decompose into Al2O3-MgO-SiO2 composite oxides. This method ensures the strong deoxidation effect of Mg in the LF process and further refines the size of Al2O3 inclusions. The amount of Ni-Mg alloy added is m... 合金 ≥3×L+20, where m 合金 The amount of Ni-Mg alloy added is expressed in kg; L is the mass of molten steel in tons. If the amount added is less than this range, its effect on inhibiting the coarsening of oxides such as Al2O3 will be worse. In the VD process, the amount of synthetic slag added is 200–300 kg / furnace. If the amount of synthetic slag added is less than 200 kg, the slag fluidity will be poor, failing to achieve the effect of adsorbing inclusions in the molten steel. If the amount of synthetic slag added exceeds 300 kg, the synthetic slag cannot melt into the slag, leading to supersaturation and loss of fluidity, resulting in a worse adsorption effect on inclusions. Simultaneously, the mass ratio of Al2O3 to SiO2 in the synthetic slag is specified to be 1–3:7–9 to maintain a match between the basicity of the synthetic slag and the basicity of the slag, thus ensuring the adsorption performance of the slag. In the casting process, the mass ratio of CaO:MgO:SiO2:Al2O3 in the protective slag is controlled within the range of 2-4:1-2:1-2:2-3 to ensure that the dissolution temperature of the protective slag is lower than the casting temperature of the molten steel, thus avoiding the risk of slag entrapment due to incomplete slag formation in the molten steel. Compared with the prior art, the beneficial effects of this invention are:

[0052] 1. This invention employs an induction furnace smelting → AOD furnace refining → LF furnace refining → VD furnace refining → die casting process to prepare large-size Invar alloy steel ingots. In the AOD refining process, an Al-Si-Mn composite deoxidizer is used for deoxidation. In the LF refining process, Ni-Mg alloy is added to decompose and refine inclusions, controlling them to be Al2O3-MgO-SiO2 system inclusions. Furthermore, the ratings of Class A, B, C, and D inclusions are ≤0.5, and the rating of Class Ds inclusions is 0. This smelting method effectively refines the size of inclusions in the Invar alloy steel melt, reduces the incidence of localized peeling defects on the surface of cold-rolled strip caused by large-size deoxidation products, and improves the product quality and yield of Invar alloy strip.

[0053] 2. The Fe-Ni based Invar alloy prepared by the smelting method of the present invention can be widely used in aerospace, defense, energy transportation and other fields; the successful design and development of this alloy will bring extensive economic benefits and has broad market applications. Attached Figure Description

[0054] Figure 1 This is a morphological image of the inclusions in the Invar alloy steel ingot prepared in Example 1 of the present invention;

[0055] Figure 2 The image shows the inclusion morphology of the steel ingot prepared in Comparative Example 1. Detailed Implementation

[0056] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way.

[0057] Examples 1-7

[0058] This embodiment of a smelting method for refining the size of Invar alloy inclusions includes the following steps:

[0059] Using pure nickel plates (Ni content 98-99.5%) and pure iron as raw materials for Invar alloy, the raw materials are batched according to the standard chemical composition of the target Invar alloy product. The Invar alloy raw materials are melted into molten steel in a 100t induction furnace. The chemical composition of the molten steel by mass percentage is: C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 30%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements. The obtained molten steel is added to an AOD ladle furnace for refining. Nickel plates are added during the oxygen blowing and decarburization process in the AOD furnace for alloying, and quicklime (CaO) is added in batches, totaling 4-5 tons of CaO. When the carbon content is controlled to ≤0.03%, an Al-Si-Mn composite deoxidizer is added. The mass ratio of Al:Si:Mn in the composite deoxidizer is 4-6:2-3:1-4, and the addition amount satisfies m≥0.02L+0.1=2.1t (where L=100t, m can be 2.1-2.7t). It is added to the ladle in three batches, and the reduction strength is controlled within the range of 1.1-1.3. Slag removal is necessary before adding the composite deoxidizer. The composition of the molten steel after refining in the AOD furnace is as follows by mass percentage: C: 0.03%, Si: 0.08%, Mn: 0.4%, P: 0.02%, S: 0.06%, Ni: 28%, Mg: 0.05%, Al: 0.1%, with the remainder being Fe and unavoidable residual elements. After slag removal, the ladle is hoisted to the LF furnace. 1-2 kg / t of aluminum shot is added to the LF furnace to adjust the aluminum content in the steel, controlling the Al content to 0.1-0.2% to ensure the S content is ≤0.001%. Other components are fine-tuned based on composition analysis results. Once the chemical composition is stable, 320-500 kg of a Ni-Mg alloy (70% Ni, 30% Mg) is added in the later stages of smelting (meeting m... 合金≥3×L+20=320, where L=100t), after adding, the ladle is stirred and cooled by bottom blowing argon gas. The gas supply intensity is controlled at 5~8L / min / t of molten steel, and the stirring time is 10~20min. When the molten steel temperature is 1600~1650℃, the LF furnace refining process is completed. After the LF refining process is completed, the ladle is switched to the VD process. The vacuum time of the ladle furnace pump is required to be ≥20min (e.g., 20~26min). After the pump is withdrawn, a sample is taken for temperature measurement and 200~300kg of synthetic slag is added. The composition ratio of Al2O3 to SiO2 in the synthetic slag is 1~3:7~9. Then, continue to use argon gas for weak stirring at the bottom of the pump for ≥60 minutes. During the casting process, use Ar gas for protection throughout the casting process and add 40-60 kg of protective slag. The mass ratio of CaO:MgO:SiO2:Al2O3 in the protective slag is 2-4:1-2:1-2:2-3. The protective slag is added to the ingot mold in batches. Before casting, 20-30 kg of protective slag is suspended at the bottom of each ingot mold. During the casting process, the remaining 20-30 kg of protective slag is added in batches. Finally, Invar alloy steel ingots with a weight of 15-25 t are obtained.

[0060] The specific parameters of the above smelting process are shown in Table 1, and the composition of the prepared Invar alloy steel ingot is shown in Table 2. The specific composition by mass percentage is as follows: C: 0.017-0.029%, Si: 0.4-0.8%, Mn: 0.3-0.5%, P: 0.006-0.010%, S: 0.03-0.05%, Ni: 30.1-35.0%, Mg: 0.06-0.09%, Al: 0.013-0.19%, with the remainder being Fe and unavoidable residual elements.

[0061] The inclusions in the steel ingot are MgO-Al2O3-SiO2 series inclusions. The inclusion grades are shown in Table 3. The grade range of Class A, Class B, Class C, and Class D inclusions is 0 to 0.5, and the grade of Class Ds inclusions is 0.

[0062] Comparative Example 1

[0063] The smelting process of the Invar alloy in this comparative example is as follows:

[0064] Using nickel-iron as the raw material for Invar alloy, the raw materials were formulated according to the standard chemical composition of the target Invar alloy product. The Invar alloy raw materials were melted into molten steel in a 100t induction furnace. The chemical composition of the molten steel was as follows (mass percentage): C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 30%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements. The resulting molten steel was then added to an AOD ladle furnace for refining. During the oxygen blowing and decarburization process in the AOD furnace, nickel plates were added for alloying, and quicklime (CaO) was added in batches, totaling 4 tons of CaO. When the C content was controlled to ≤0.03%, Al deoxidizer was added, with a weight of 2.1t, in three batches to the ladle. The reduction strength was further controlled to 1.1. The steel composition after refining in the AOD furnace is as follows (by mass percentage): C: 0.04%, Si: 0.10%, Mn: 0.9%, P: 0.09%, S: 0.07%, Ni: 36%, Mg: 0.09%, Al: 0.3%, with the remainder being Fe and unavoidable residual elements. After slag removal, the ladle is hoisted to the LF furnace, where 1-2 kg / t of aluminum shot is added to adjust the aluminum content in the steel. Other components are fine-tuned based on the composition analysis results. After completion, argon gas is blown into the ladle for bottom stirring and cooling, with the gas supply controlled at 5 L / min / t of molten steel and the stirring time at 10 min. When the molten steel temperature reaches 1600-1650℃, the LF furnace refining process is complete. After the LF refining process is finished, the ladle is transferred to the VD process. The vacuum time for the ladle furnace pump is required to be ≥20 min. After pump withdrawal, a sample is taken for temperature measurement, and 300 kg of synthetic slag is added. The ratio of Al2O3 to SiO2 in the synthetic slag is 2:8. Then, continue to blow argon gas into the bottom of the pump for weak stirring for ≥60 minutes. During the casting process, Ar gas is used for protection throughout the casting process, and protective slag is added to the steel ingot mold in batches. Before casting, 25 kg of protective slag is suspended at the bottom of each steel ingot mold, and the remaining 25 kg of protective slag is added in batches during the casting process, finally obtaining an Invar alloy steel ingot with a weight of 20 t.

[0065] The composition of the Invar alloy steel ingot prepared in this comparative example is shown in Table 2. Its inclusions are Al2O3. The inclusion grades are shown in Table 3. The grades of Class A, Class B, and Class D inclusions are all grade 1, and the grades of Class C and Class Ds inclusions are 1.5.

[0066] Comparative Example 2

[0067] The smelting process of the Invar alloy in this comparative example is as follows:

[0068] Using ferronickel as the raw material for Invar alloys, the raw materials are formulated according to the standard chemical composition of the target Invar alloy product. The ferronickel alloy is melted into molten steel in a 100t induction furnace. The chemical composition of the molten steel is as follows (mass percentage): C≤0.08%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.05%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements. The obtained molten steel is then added to an AOD ladle furnace for refining. During the oxygen blowing and decarburization process in the AOD furnace, nickel plates are added for alloying, and quicklime (CaO) is added in batches, totaling 6 tons of CaO. The C content is controlled to 0.05%, and 2 tons of Al-Si-Mn composite deoxidizer are added. The mass ratio of Al:Si:Mn in the composite deoxidizer is 6:3:1, and it is added to the ladle in three batches. The reduction strength is controlled to 1.4. Slag removal is required before adding the composite deoxidizer. After slag removal, the ladle is hoisted to the LF furnace. 3 kg / t of aluminum shot is added to the LF furnace to adjust the aluminum content in the steel. Other components are fine-tuned based on composition analysis results. Once the composition is stable, 230 kg of a Ni-Mg alloy with 70% Ni and 30% Mg is added in the later stages of smelting. After adjustment, the ladle is bottom-blown and stirred to cool. When the molten steel temperature reaches 1600℃, the LF furnace refining process is complete. After the LF refining process is finished, the ladle is moved to the VD process. The vacuum time for the ladle furnace pump is required to be ≥20 min. After the pump is withdrawn, a sample is taken for temperature measurement, and 40 kg of synthetic slag is added. The ratio of Al2O3 to SiO2 in the synthetic slag is 1:3. Afterwards, continue to blow argon gas into the bottom of the pump for weak stirring for 30 minutes. Ar gas is used for protection during the entire casting process, and protective slag is added to the steel ingot mold in batches. Before casting, 40 kg of protective slag is suspended at the bottom of each steel ingot mold. During the casting process, the remaining 15 kg of protective slag is added in batches. The composition of the cast steel ingot is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The inclusion grades are shown in Table 3. The grades of inclusions A, B, C, and D are all grade 1, and the grade of inclusion Ds is 1.5.

[0069] Comparative Example 3

[0070] Most of the process parameters in this comparative example are the same as in Example 3, except that the mass ratio of Al:Si:Mn in the Al-Si-Mn composite deoxidizer used in the AOD furnace refining process is 3:4:3, the amount added is 2.4t, and it is added to the ladle in three batches. The reduction strength is further controlled to 1.0.

[0071] The composition of the steel ingots obtained after ingot casting in this comparative example is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The inclusion grades are shown in Table 3. The grades of inclusions A, B, C, and D are all grade 1, and the grade of inclusions Ds is 0.5.

[0072] Comparative Example 4

[0073] Most of the process parameters in this comparative example are the same as those in Example 3. The difference is that the mass ratio of Al:Si:Mn in the Al-Si-Mn composite deoxidizer used in the AOD furnace refining process is 2:5:3, the amount added is 2.7t, and it is added to the ladle in three batches. The reduction strength is further controlled to 1.5.

[0074] The composition of the steel ingots obtained after ingot casting in this comparative example is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The inclusion grades are shown in Table 3. The grades of inclusions A, B, C, and D are all 1.0, and the grade of inclusions Ds is 1.0.

[0075] Comparative Example 5

[0076] Most of the process parameters in this comparative example are the same as those in Example 3, except that Ni-Mg alloy is not added in the later stage of the LF furnace refining process.

[0077] The composition of the steel ingots obtained after ingot casting in this comparative example is shown in Table 2. The inclusions are Al2O3-SiO2. The inclusion grades are shown in Table 3. The grades of inclusions A, B, C, and D are all 1.5, and the grade of inclusions Ds is 1.0.

[0078] Comparative Example 6

[0079] Most of the process parameters in this comparative example are the same as those in Example 3. The difference is that 250 kg of Ni-Mg alloy is added in the later stage of the LF furnace refining process.

[0080] The composition of the steel ingots obtained after ingot casting in this comparative example is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The inclusion grades are shown in Table 3. The grades of inclusions A, B, C, and D are all 1.0, and the grade of inclusions Ds is 0.5.

[0081] Table 1 Process parameters of the embodiment

[0082]

[0083] Table 2 Chemical composition of steel ingots (wt%)

[0084]

[0085] Table 3 Inclusion grades in steel ingots

[0086]

[0087] Figure 1 The image shows the inclusion morphology of the Invar alloy steel ingot prepared in Example 1 of this invention. In the image, the components of 1 and 4 are Al2O3, the component of 2 is MgO, and the component of 3 is SiO2. It can be seen that the inclusions are MgO-Al2O3-SiO2 type inclusions.

[0088] Figure 2 The image shows the inclusion morphology of the steel ingot prepared in Comparative Example 1. The components of 1 and 2 in the image are both Al2O3, which shows that the inclusions are Al2O3 inclusions.

[0089] As shown in Examples 1-7, the inclusions in the Invar alloy steel ingots prepared in the embodiments of the present invention are MgO-Al2O3-SiO2 system inclusions. The inclusions of type A, type B, type C, and type D are ≤0.5 grade, and the inclusions of type Ds are 0 grade.

[0090] As can be seen from Example 3 and Comparative Example 2, by adjusting the amount of Ni-Mg alloy from the original 350kg to 230kg, while the composition range and amount of Al-Si-Mn and other composite deoxidizers are within the range set by this invention, the reduction strength exceeds the range set by this invention. By comparison, the inclusion ratings of A, B, C, D, and Ds show different degrees of increase.

[0091] As can be seen from Example 3 and Comparative Examples 3 and 4, by adjusting the proportion and amount of the composite deoxidizer components, its reduction strength changes significantly, and the final inclusion rating increases significantly.

[0092] Based on Example 3 and Comparative Examples 5 and 6, it can be seen that Comparative Example 5 did not add Ni-Mg alloy, resulting in its deoxidation products mainly being Al2O3-SiO2, with a high rating and large deoxidation product size. Although Comparative Example 6 added Ni-Mg alloy, its addition amount was lower than the range set in this invention, and the effect of inhibiting the coarsening of oxides such as Al2O3 was relatively poor, which led to a significant increase in the final inclusion grade.

[0093] Compared with Comparative Examples 1-6, the Invar alloy of this invention exhibits better inclusion control, with smaller Ds-type inclusions, reducing the incidence of localized peeling defects on the surface of cold-rolled strip caused by large inclusions, and improving the product quality and yield of Invar alloy strip. The Fe-Ni based Invar alloy prepared by this invention can be widely used in aerospace, defense, energy transportation, and other fields. Due to its excellent hot working properties and superior expansion performance, the successful design and development of this alloy will bring extensive economic benefits and broad market applications.

[0094] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method of refining the size of inclusions in Invar alloys, characterized in that, Includes the following steps: S1, induction furnace smelting, uses pure nickel plates and pure iron as Invar alloy raw materials, and the raw materials are formulated according to the chemical composition of Invar alloy. Molten steel is obtained by induction furnace smelting. S2, AOD furnace refining, involves adding molten steel to an AOD ladle furnace for refining, blowing oxygen to decarburize, and adding pure nickel plates and pure iron for alloying. At the same time, quicklime is added in batches. When the C content in the molten steel is ≤0.03%, Al-Si-Mn composite deoxidizer is added for deoxidation. After deoxidation, slag removal is performed. The mass ratio of Al to Si and Mn in the Al-Si-Mn composite deoxidizer is 4-6:2-3:1-4, and the amount of Al-Si-Mn composite deoxidizer added satisfies: m≥0.02L+0.1, where m is the amount of Al-Si-Mn composite deoxidizer added in tons (t); and L is the mass of molten steel in tons. During the deoxidation process of the Al-Si-Mn composite deoxidizer, the reduction strength is controlled to be 1.1 to 1.3; After slag removal in the S3 LF furnace, the ladle is hoisted to the LF furnace for refining. Aluminum shot is added to the LF furnace to adjust the aluminum content in the molten steel to 0.1-0.2%, ensuring that the sulfur content in the molten steel is ≤0.001%. The composition is finely adjusted according to the composition analysis. After the composition is stabilized, Ni-Mg alloy is added in the later stage of smelting. Then, bottom blowing argon gas is used for stirring and cooling. When the temperature of the molten steel is ≤1650℃, the LF furnace refining is completed. The Ni-Mg alloy contains 60-70wt% of Ni and 20-30wt% of Mg; the added amount of the Ni-Mg alloy satisfies: m 合金 ≥ 3×L+20, wherein m 合金 is the added amount of the Ni-Mg alloy, kg; and L is the mass of the molten steel, t. S4, VD furnace refining, after the LF furnace refining is completed, the ladle is transported to the VD process, the ladle furnace is controlled to pump in vacuum, after the pump is withdrawn, the temperature is measured and the synthesis slag is added, and then the pump continues to pump in for bottom blowing argon gas weak stirring. S5, ingot casting, argon gas protection is used throughout the casting process, and protective slag is added to the ingot mold in batches to obtain Invar alloy steel ingots weighing 15-25t. In the Invar alloy steel ingot, the inclusions of type A, type B, type C, and type D are ≤0.5 grade, and the inclusions of type Ds are 0 grade.

2. The refining process of claim 1, wherein the refining process is a smelting process. In step S1: The pure nickel plate has a Ni content of 98-99.5%, and the amount of pure nickel plate added is 26-46% of the mass of the Invar alloy raw material; the amount of pure iron added is 50-70% of the mass of the Invar alloy raw material; and / or The composition of the molten steel by mass percentage is as follows: C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 25%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, with the remainder being Fe and unavoidable residual elements.

3. The method of refining Invar inclusion size according to claim 2, wherein, The steel composition has C ≤ 3.0%.

4. The method of refining Invar alloy inclusion size according to claim 1, wherein, In step S2: The total amount of quicklime added is 4 to 5 tons per furnace.

5. The method of refining Invar inclusion size according to claim 1 wherein, In step S2, the composition of the molten steel after refining in the AOD furnace is as follows by mass percentage: C≤0.03%, Si≤1.0%, Mn≤0.5%, P≤0.02%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.2%, with the remainder being Fe and unavoidable residual elements.

6. The method of refining Invar alloy inclusion size according to claim 1 wherein, In step S3: The amount of aluminum shot added is 1-2 kg / t of molten steel; and / or The argon supply intensity of the bottom blowing is controlled to be 5-8 L / min / t molten steel, and the stirring time is 10-20 min; and / or The temperature of the molten steel is 1600-1650 DEG C, and the LF furnace refining is ended.

7. The method of refining Invar alloy inclusion size according to claim 1 wherein, In step S4: The ladle furnace pumping vacuum time is greater than or equal to 20 min; and / or In the synthetic slag, the mass ratio of Al2O3 to SiO2 is 1-3:7-9; and / or The adding amount of the synthetic slag is 200-300 kg / heat; and / or The argon weak stirring time is greater than or equal to 60 min.

8. The method of refining Invar alloy inclusion size according to claim 1 wherein, In step S5: In the process of adding the protective slag into the ingot mold in batches, 20-30 kg of the protective slag is hung at the bottom of each ingot mold before pouring, and the remaining 20-30 kg of the protective slag is added successively during the pouring process; and / or In the protective slag, the mass ratio of CaO, MgO, SiO2 and Al2O3 is 2-4:1-2:1-2:2-3.

9. A wrought Invar alloy prepared by a smelting process according to one of claims 1 to 8, characterized in that The components are as follows in terms of mass percentage: C≤0.03%, Si≤0.8%, Mn≤0.5%, P≤0.020%, S≤0.05%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.20%, and the rest is Fe and inevitable residual elements.

10. The inconel alloy as claimed in claim 9, wherein, The inclusions of the invar alloy are MgO-Al2O3-SiO2 system inclusions; The grade of the A-type inclusions, the B-type inclusions, the C-type inclusions, the D-type inclusions and the like in the inclusions is less than or equal to 0.5 grade, and the grade of the Ds-type inclusions is 0 grade.

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