Smelting method for refining size of inclusions in invar alloy and invar alloy

Abstract

According to the smelting method for refining the size of the inclusions of the invar alloy and the invar alloy, a large-size invar alloy steel ingot is prepared through the processes of induction furnace smelting, AOD furnace refining, LF furnace refining, VD furnace refining and die casting, in the AOD furnace refining process, an Al-Si-Mn composite deoxidizing agent is adopted for deoxidizing, in the LF furnace refining process, Ni-Mg alloy is added, and in the VD furnace refining process, the Al-Si-Mn composite deoxidizing agent is adopted for deoxidizing; the impurities are decomposed and refined, the impurities are controlled to be Al2O3-MgO-SiO2 series impurities, the grade of the A type impurities, the grade of the B type impurities, the grade of the C type impurities and the grade of the D type impurities are smaller than or equal to 0.5 grade, and the grade of the Ds type impurities is 0 grade. The method can effectively refine the size of the inclusions in the invar alloy molten steel, reduce the occurrence rate of local peeling defects on the surface of the cold-rolled strip caused by large-size deoxidized products, and improve the product quality and the yield of the invar alloy strip.

Description

Technical Field

[0001] The present invention relates to the field of steel smelting, and in particular to a smelting method for refining the size of Invar alloy inclusions and Invar alloy. Background Art

[0002] Invar alloy is a binary austenitic Fe-Ni alloy. It is a precision alloy with abnormal thermal expansion characteristics or controllable thermal expansion characteristics. It is widely used in electronic components and other fields that require high material expansion performance. The alloy has a low expansion coefficient, and its expansion coefficient at 20-100℃ is ≤1.5×10 -6 / ℃, which is only 1 / 5 to 1 / 10 of that of ordinary steel. Currently, the commercially available Invar alloys are mainly Fe-Ni 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 double-capacity conductors. In addition to Fe-Ni Invar alloys, Fe-Ni-Co super Invar alloys are widely used in the aerospace field due to their excellent ultra-low expansion properties. Their main components are C≤0.04%, Si≤0.25%, 0.2%≤Mn≤0.4%, S≤0.0015%, P≤0.008%, 35%≤Ni≤36.5%, 3%≤Co≤4%, and the rest is Fe. The expansion performance requirement of this alloy is 1 to 2×10 -6 / ℃. In recent years, there has been a great demand for cold-rolled Invar alloy strips. However, since most of the applications are in electronic components and energy transportation, the surface quality of the strips is required to be high, and no linear scale or peeling defects are allowed. Under such usage requirements and technical background, the size requirements for inclusions in the Invar alloy molten steel are even higher, and no more than level 1 inclusion is allowed in the molten steel. Traditional Invar alloys are sensitive to the content of gases such as O. During the smelting and deoxidation process, a single deoxidizer such as Al is used for strong deoxidation, resulting in a high content of Al oxide in the alloy, and the size can reach 100 microns or more. In the subsequent cold rolling process, large-sized inclusions can easily lead to poor surface plasticity of the strip, and defects such as peeling and linear scale will appear on the surface.

[0003] Chinese patent publication number CN119410860A discloses a method for preparing and using a composite deoxidizer for LF slag making. The method mainly deoxidizes and modifies the ladle top slag after tapping from a converter or electric furnace to improve desulfurization, deoxidation, and inclusion removal. 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, which uses direct reduced iron and scrap steel as electric arc furnace raw materials and adopts a gaseous nitrogen addition process in the VD process, eliminating the need for expensive nitriding alloy raw materials. However, this technology also does not provide methods for effectively refining inclusions.

[0005] Chinese Patent Publication No. CN111519098A discloses a low-carbon steel and a method for controlling inclusions in the low-carbon steel. Deoxidizers such as Ca, Si, Al, Ti, and Mn are added during a refining process, wherein the mass fraction ratio of Ca to O is 0.5 to 1.2, and the mass fraction ratio of Ti to Al is 0.5 to 1.0. This technique can control inclusions to a dispersed size distribution of Al-Ti-Ca-O inclusions, with all inclusions rated ≤0.5, and inclusions ≤5 microns accounting for over 99%. However, this method uses Ca and Ti as deoxidizers, which degrade the expansion properties of Invar alloys, making it unsuitable for use in the Invar alloy field.

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

[0007] In view of the defects existing in the prior art, the purpose of the present invention is to provide a smelting method and Invar alloy for refining the size of inclusions in Invar alloy, which can effectively refine the size of inclusions in Invar alloy steel liquid, reduce the incidence of local peeling defects on the surface of cold-rolled strip caused by large-sized deoxidation products, and improve the product quality and yield rate of Invar alloy strip.

[0008] To achieve the above object, the present invention adopts the following technical solutions:

[0009] A first aspect of the present invention provides a smelting method for refining the size of inclusions in Invar alloy, comprising the following steps: S1, induction furnace smelting, using pure nickel plate and pure iron as Invar alloy raw materials, the ingredients are prepared according to the chemical composition of Invar alloy, and molten steel is obtained by induction furnace smelting; S2, AOD furnace refining, the molten steel is added to the AOD ladle furnace for refining, oxygen is blown for decarburization, and pure nickel plates and pure iron are added for alloying. At the same time, quicklime is added in batches. When the carbon content in the molten steel is ≤0.03%, Al-Si-Mn composite deoxidizer is added for deoxidation. After deoxidation, the slag is skimmed; S3, LF furnace refining. After slag removal, the ladle is hoisted to the LF furnace for refining. Aluminum shots are added to the LF furnace to adjust the aluminum content in the molten steel to 0.1-0.2%, ensuring that the S content in the molten steel is ≤0.001%. The composition is fine-tuned according to component analysis. After the chemical composition is stable, Ni-Mg alloy is added in the later stage of smelting. Then, argon is blown from the bottom for stirring and cooling. When the molten steel temperature is ≤1650℃, the LF furnace refining is completed. 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 a vacuum. After the pump is withdrawn, sampling is performed to measure the temperature and synthetic slag is added. Then, the pump is continued to be pumped in for bottom blowing of argon gas for weak stirring. S5, mold casting, using argon protection pouring throughout the entire process, and adding mold slag into the ingot mold in batches to obtain an Invar alloy steel ingot weighing 15 to 25 tons;

[0010] In the Invar alloy steel ingot, the grades of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are ≤0.5, and the grade of Class Ds inclusions is 0.

[0011] Preferably, in step S1:

[0012] The Ni content of the pure nickel plate is 98-99.5%, and the amount of the pure nickel plate added is 26-46% of the total weight of the Invar alloy raw material; the amount of the pure iron added is 50-70% of the total weight of the Invar alloy raw material; and / or

[0013] The composition of the molten steel is as follows in percentage by mass: C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 25%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, and the rest are Fe and unavoidable residual elements.

[0014] Step S1 is a raw material smelting process, wherein pure nickel plate and pure iron are used as Invar alloy raw materials, and the ingredients are prepared according to the standard chemical composition content of the target Invar alloy product. The raw materials are melted into molten steel meeting the above-mentioned composition requirements in a 100t induction furnace. Preferably, the carbon content in the molten steel is further controlled to ≤3.0%.

[0015] Preferably, in step S2:

[0016] The total amount of quicklime added is 4 to 5 tons per furnace; and / or

[0017] 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 the Al-Si-Mn composite deoxidizer added satisfies: m≥0.02L+0.1, where m is the amount of the Al-Si-Mn composite deoxidizer added, in t; L is the mass of the molten steel, in t; and / or

[0018] The reduction intensity is controlled to be 1.1-1.3 during the deoxidation process of the Al-Si-Mn composite deoxidizer.

[0019] Step S2 is an AOD furnace refining process, and pure nickel plates and pure iron are added for alloying during the oxygen blowing decarburization process. The addition amount of the pure nickel plates and the pure iron can be determined according to the composition analysis, and can be determined according to the target composition of the molten steel refined by the AOD furnace. Meanwhile, the raw lime is added in batches during the oxygen blowing decarburization process, mainly to adsorb the deoxidation products, adjust the basicity of the slag, promote the decarburization reaction, and protect the furnace lining. When the C content in the molten steel is ≤0.03%, an Al-Si-Mn composite deoxidizer is used, and the amount of the Al-Si-Mn composite deoxidizer is adjusted according to the weight of the molten steel. For example, when the weight of the molten steel is about 100 t, the addition amount m of the Al-Si-Mn composite deoxidizer is ≥2.1 t. The Al-Si-Mn composite deoxidizer is added in batches, for example, in three or four batches. In this way, the Al-Si-Mn composite deoxidizer can be fully deoxidized. After the reduction is completed, the slag is removed to ensure that the slag is clean and sufficient.

[0020] Preferably, in step S2, the composition of the molten steel after the AOD furnace refining is as follows: C≤0.03%, Si≤1.0%, Mn≤0.5%, P≤0.02%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.2%, and the rest is Fe and unavoidable residual elements.

[0021] Preferably, in step S3:

[0022] The addition amount of the aluminum pellets is 1-2 kg / t of molten steel; and / or

[0023] In the Ni-Mg alloy, the content of Ni is 60-70 wt%, and the content of Mg is 20-30 wt%. The addition amount of the Ni-Mg alloy satisfies the formula: m≥3×L+20, where m is the addition amount of the Ni-Mg alloy, kg; L is the mass of the molten steel, t; and / or 合金 合金 The addition amount of the Ni-Mg alloy satisfies the formula: m≥3×L+20, where m is the addition amount of the Ni-Mg alloy, kg; L is the mass of the molten steel, t; and / or

[0024] The gas supply intensity of the bottom argon blowing is controlled to be 5-8 L / min / t of molten steel, and the stirring time is 10-20 min; and / or

[0025] When the temperature of the molten steel is 1600-1650℃, the LF furnace refining is completed.

[0026] Step S3 is an LF furnace refining process, and the Ni-Mg alloy is added after the aluminum pellets are added to adjust the aluminum content in the steel. The main function is to hinder the aggregation and growth of Al2O3 oxide, and the addition amount can be 320-500 kg / heat.​

[0027] Preferably, in step S4:

[0028] The ladle furnace vacuum pumping time is ≥ 20min; and / or

[0029] In the synthetic slag, the mass ratio of Al2O3 to SiO2 is 1-3:7-9; and / or

[0030] The amount of synthetic slag added is 200-300 kg / furnace; and / or

[0031] The argon weak stirring time is ≥60 min.

[0032] Step S4 is the VD furnace refining process. The ladle furnace is pumped in for 20 minutes or longer. After the pump is removed, temperature is sampled and measured, and synthetic slag is added. Blowing argon from the bottom of the ladle furnace in a vacuum environment facilitates the removal of inclusions from the molten steel. Adding synthetic slag improves the slag's viscosity and fluidity. When weak stirring is achieved through bottom-blowing argon during the VD process, the slag, with its excellent fluidity and viscosity, can fully absorb inclusions from the molten steel.

[0033] Preferably, in step S5:

[0034] During the process of adding the protective slag into the ingot mold in batches, 20-30 kg of protective slag is hung at the bottom of each ingot mold before pouring, and the remaining 20-30 kg of protective slag is added successively during the pouring process; and / or

[0035] In the protective slag, the mass ratio of CaO, MgO, SiO2 and Al2O3 is 2-4:1-2:1-2:2-3.

[0036] A second aspect of the present invention provides an Invar alloy prepared by the smelting method for refining the size of Invar alloy inclusions according to the first aspect of the present invention, wherein the composition of the Invar alloy is as follows, in percentage by mass: 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 remainder is Fe and unavoidable residual elements.

[0037] Preferably, the inclusions of the Invar alloy are MgO-Al2O3-SiO2 inclusions; Among the inclusions, the grades of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are ≤0.5, and the grade of Class Ds inclusions is 0.

[0038] The composition design principle of the Invar alloy of the present invention is as follows.

[0039] C: C is an austenite-strengthening element. Increasing the C content effectively reduces the saturated solubility of nitrogen in molten steel. Regarding mechanical properties, C improves alloy strength while simultaneously reducing toughness and low-temperature expansion. Therefore, to ensure both strength and toughness, the C content in this invention is controlled to ≤ 0.03%.

[0040] Si: Si acts as a deoxidizer in molten steel, strengthening the matrix and improving the steel's high-temperature oxidation resistance. A moderate amount of Si can enhance the steel's resistance to strong acid corrosion, but excessive Si content can reduce the steel's hot workability and toughness, and affect its magnetic permeability. Therefore, in the present invention, the Si content is controlled to ≤ 0.8%.

[0041] Mn: Mn is an austenite-forming element with a strong ability to stabilize the austenite phase and effectively control the low-temperature martensite transformation. Therefore, the present invention requires that the Mn content be ≤ 0.5%.

[0042] P, S: are harmful elements. These two elements tend to segregate near the columnar grain boundaries of the steel ingot, which can have a negative impact on the welding performance. Therefore, the P and S elements are controlled in a lower range. Combined with the P and S content levels of the raw materials, P is required to be ≤ 0.020% and S ≤ 0.05%.

[0043] Ni: an austenite-forming element that can improve the strength and corrosion resistance of steel. However, if the Ni content is too high, it will reduce the solubility of nitrogen in the steel, inhibit the precipitation of strengthening phase carbon and nitrides, affect the strength, and increase the cost. The influence of Ni content on the expansion properties of Invar alloy in the low-temperature service temperature range and the high-temperature service temperature range is different. As the Ni content decreases, the Curie temperature decreases and is closer to the low-temperature service temperature range. When the Ni content is lower than 28% or higher than 35%, its expansion performance does not meet the user's standard requirements. Therefore, the Ni content in the present invention is controlled at 28%≤Ni≤35%.

[0044] Mg and Al: Mg and Al can further remove oxygen from Invar alloy, improving the thermoplasticity of the steel ingot. However, their contents should not be too high. Adding Mg to Invar alloy also refines austenite grains, pinning them during hot working and inhibiting their growth. Therefore, in the present invention, Mg is controlled to ≤ 0.1% and Al ≤ 0.20%.

[0045] The present invention prepares large-sized Invar alloy steel ingots by adopting a 100t induction furnace smelting → AOD furnace refining → LF furnace refining → VD furnace refining → die casting process; in the AOD furnace refining process, Al-Si-Mn composite deoxidizer is used for deoxidation, which effectively avoids the excessive Al content in the molten steel caused by the single use of Al strong deoxidizer, reduces the influence of Al element on the welding performance of Invar alloy strip, and at the same time limits the use range and weight of each element of the composite deoxidizer, ensuring that the composite deoxidation of Al, Si, and Mn elements can not only completely remove the O element in the molten steel, but also avoid excessive deoxidizing elements remaining in the molten steel to affect the structure and welding performance of the ingot. At the same time, Ni-Mg alloy is added in the LF process, and the Mg alloy element can further hinder the aggregation and growth of Al2O3 oxide, causing it to decompose into Al2O3-MgO-SiO2 composite oxide. The above method not only ensures the strong deoxidation effect of Mg element in the LF process stage, but also further refines the size of Al2O3 inclusions; the addition amount of Ni-Mg alloy m 合金 ≥3×L+20, where m 合金 is the amount of Ni-Mg alloy added, in kg; L is the mass of molten steel, in t; if the addition amount is less than this range, its effect of inhibiting the coarsening of oxides such as Al2O3 will deteriorate. Synthetic slag is added in an amount of 200-300 kg / furnace during the VD process. If the amount of synthetic slag added is less than 200 kg, the fluidity of the slag is poor and the effect of adsorbing inclusions in the molten steel cannot be achieved. If the amount of synthetic slag added exceeds 300 kg, the synthetic slag cannot be melted into the slag, resulting in oversaturation of the slag, which loses fluidity and deteriorates the effect of adsorbing inclusions. At the same time, the mass ratio of Al2O3 to SiO2 in the synthetic slag is specified to be 1-3:7-9, and the basicity of the synthetic slag is kept matched with that of the slag, maintaining the required basicity of the slag to ensure the adsorption performance of the slag. During the casting process, the mass ratio of CaO:MgO:SiO2:Al2O3 in the mold slag is controlled within the range of 2-4:1-2:1-2:2-3, ensuring that the melting temperature of the mold slag is lower than the pouring temperature of the molten steel, thereby avoiding the risk of slag inclusion caused by the mold slag not being dissolved in the molten steel. Compared with the prior art, the present invention has the following advantages: 1. The present invention adopts an induction furnace smelting → AOD furnace refining → LF furnace refining → VD furnace refining → die casting process to prepare large-sized Invar alloy steel ingots. An Al-Si-Mn composite deoxidizer is used for deoxidation in the AOD refining process, and a Ni-Mg alloy is added in the LF refining process to decompose and refine inclusions, controlling the inclusions to be Al2O3-MgO-SiO2 inclusions, and the ratings of Class A, Class B, Class C, and Class D inclusions are ≤0.5, and the rating of Class Ds inclusions is 0. The smelting method of the present invention effectively refines the size of inclusions in the Invar alloy steel liquid, reduces the incidence of local peeling defects on the surface of the cold-rolled strip caused by large-sized deoxidation products, and improves the product quality and yield rate of the Invar alloy strip. 2, The Fe-Ni-based invar alloy prepared by the smelting method can be widely applied in the fields of aerospace, national defense and military industry, energy transportation and the like; the successful design and development of the alloy will bring wide economic benefits and has wide market application. BRIEF DESCRIPTION OF DRAWINGS

[0046] Figure 1 Inclusion morphology chart of the invar alloy ingot prepared in Example 1 of the present application;

[0047] Figure 2 Inclusion morphology chart of the ingot prepared in Comparative Example 1. DETAILED DESCRIPTION

[0048] The present application will be described in detail below with reference to specific examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form.

[0049] Examples 1-7

[0050] The smelting method for refining the inclusion size of the invar alloy of the present embodiment comprises the following steps:

[0051] Pure nickel plates (Ni content of 98-99.5%) and pure iron are used as raw materials for Invar alloy, and the ingredients are prepared according to the standard chemical composition content of the target product of Invar alloy. The raw materials for Invar alloy are melted into molten steel in a 100t induction furnace. The chemical composition of the molten steel is as follows: C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 30%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, and the rest are Fe and inevitable residual elements. The obtained molten steel is added to an AOD ladle furnace for refining. Nickel plates are added for alloying during the oxygen decarburization process of the AOD furnace. Quicklime CaO is added in batches, and a total of 4-5 tons of CaO is added. 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. 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 reducing strength is controlled within the range of 1.1-1.3. Slag removal must be performed 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%, and the rest is Fe and unavoidable residual elements. After the slag is removed, 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, controlling the Al content in the steel to 0.1-0.2% to ensure that the S content in the steel is ≤ 0.001%. Other components are fine-tuned based on the component analysis results. After the chemical composition stabilizes, 320-500 kg of Ni-Mg alloy with a Ni content of 70% and a Mg content of 30% is added in the later stage of smelting (to meet the requirements of m 合金≥3×L+20=320, where L=100t). After addition, argon is blown from the bottom of the ladle for stirring and cooling. 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 reaches 1600-1650℃, the LF furnace refining process is completed. After the LF refining process is completed, the ladle is transferred to the VD process. The vacuum pumping time of the ladle furnace is required to be ≥20min (for example, 20-26min). After the pump is removed, samples are taken for temperature measurement and 200-300kg of synthetic slag is added. The composition ratio of Al2O3 and SiO2 in the synthetic slag is 1-3:7-9. Then continue to pump argon into the bottom for weak stirring, and the stirring time is ≥60min; use Ar gas to protect the pouring throughout the pouring process, and add 40-60kg of protective slag, the mass ratio of CaO:MgO:SiO2:Al2O3 in the protective slag is 2-4:1-2:1-2:2-3, and the protective slag is added to the ingot mold in batches, and 20-30kg of protective slag is hung at the bottom of each ingot mold before pouring. The remaining 20-30kg of protective slag is added in batches during the pouring process, and finally an Invar alloy steel ingot weighing 15-25t is obtained.

[0052] The specific parameters of the above smelting process are shown in Table 1. The composition of the prepared Invar alloy steel ingot is shown in Table 2. The specific composition is as follows in percentage by mass: 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%, and the rest are Fe and unavoidable residual elements.

[0053] The inclusions in the steel ingot are MgO-Al2O3-SiO2 system inclusions. The grades of the inclusions are shown in Table 3. The grades of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions range from 0 to 0.5, and the grade of Class Ds inclusions is 0.

[0054] Comparative Example 1

[0055] The smelting process of the Invar alloy of this comparative example is as follows:

[0056] Using nickel-ferroin as the raw material for Invar alloy, the ingredients are proportioned according to the standard chemical composition of the target Invar alloy product. The Invar alloy raw material is melted into molten steel in a 100-ton induction furnace. The chemical composition of the molten steel is as follows: 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 is then refined in an AOD ladle furnace. Nickel plates are added for alloying during the oxygen decarburization process in the AOD furnace. Quicklime (CaO) is then added in batches, totaling 4 tons of CaO. Once the carbon content is controlled to ≤ 0.03%, 2.1 tons of Al deoxidizer are added to the ladle in three batches. The reducing strength is further controlled to 1.1. The composition of the molten steel after refining in the AOD furnace is as follows by mass: 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 deslagging, the ladle is hoisted to the LF furnace, where 1-2 kg / t of aluminum shot is added to adjust the aluminum content. Other components are fine-tuned based on the compositional analysis results. After completion, argon is blown from the bottom of the ladle for stirring and cooling, with the gas supply controlled at 5 L / min / t of molten steel and a stirring time of 10 minutes. When the molten steel temperature reaches 1600-1650°C, the LF furnace refining process is completed. After the LF refining process is completed, the ladle is transferred to the VD process. The ladle furnace must be vacuumed for ≥20 minutes. After the pump is removed, a sample is taken to measure the temperature, and 300 kg of synthetic slag is added. The ratio of Al2O3 to SiO2 in the synthetic slag is 2:8. Then continue to pump argon into the bottom for weak stirring, and the stirring time is ≥60min; use Ar gas to protect the pouring throughout the pouring process, and add the protective slag into the ingot mold in batches. Before pouring, hang 25kg of protective slag at the bottom of each ingot mold, and add the remaining 25kg of protective slag in batches during the pouring process, and finally obtain an Invar alloy steel ingot weighing 20t.

[0057] The composition of the Invar alloy steel ingot prepared in this comparative example is shown in Table 2. The inclusion is Al2O3. The grade of the inclusion is shown in Table 3. The ratings of Class A inclusions, Class B inclusions, and Class D inclusions are all Class 1, and the ratings of Class C inclusions and Class Ds inclusions are Class 1.5.

[0058] Comparative Example 2

[0059] The smelting process of the Invar alloy of this comparative example is as follows:

[0060] The nickel-iron is used as the raw material of the inconel alloy, and the nickel-iron alloy is melted into molten steel in a 100t induction furnace according to the target product standard chemical composition content of the inconel alloy. The mass percentage of the chemical composition of the molten steel is as follows: C≤0.08%, 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. The obtained molten steel is poured into an AOD ladle furnace for refining, and a nickel plate alloy is added during the oxygen decarburization process of the AOD furnace. A total of 6 tons of CaO are added in batches. The C component 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 the composite deoxidizer is added in three batches into the ladle. The reduction intensity is controlled to be 1.4, and the slag must be removed before the composite deoxidizer is added. After the slag removal is completed, the ladle is lifted to the LF furnace. 3kg / t of aluminum pellets are added to the LF furnace to adjust the aluminum content in the steel. According to the composition analysis results, the other components are adjusted. After the composition is stable, 230kg of Ni-Mg alloy with Ni content of 70% and Mg content of 30% is added in the late smelting stage. After adjustment, the ladle is cooled by bottom blowing stirring. When the temperature of the molten steel is 1600℃, the LF refining treatment is completed. After the LF refining treatment is completed, the ladle is adjusted to the VD process. The pump pumping time of the ladle furnace is required to be≥20min. After the pump is removed, the sample is taken and the temperature is measured, and 40kg of synthetic slag is added. The Al2O3 and SiO2 composition ratio of the synthetic slag is 1:3. Then continue to pump bottom blowing argon gas and weak stirring for 30min. During the pouring process, Ar gas protection is used throughout the pouring process, and the remaining 15kg of protective slag is added into the ingot mold in batches. The composition of the poured ingot is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The inclusion level is shown in Table 3. The ratings of A-type inclusions, B-type inclusions, C-type inclusions and D-type inclusions are all 1 level. The rating of Ds-type inclusions is 1.5 level.

[0061] Comparative Example 3

[0062] Most of the process parameters of the present comparative example are the same as those of Example 3. The difference lies in that the mass ratio of Al:Si:Mn in the Al-Si-Mn composite deoxidizer used in the AOD refining process is 3:4:3, the amount added is 2.4t, and the composite deoxidizer is added in three batches into the ladle. The reduction intensity is further controlled to be 1.0:

[0063] The composition of the ingot obtained after mold casting of the present comparative example is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The inclusion level is shown in Table 3. The ratings of A-type inclusions, B-type inclusions, C-type inclusions and D-type inclusions are all 1 level. The rating of Ds-type inclusions is 0.5 level.

[0064] Comparative Example 4

[0065] Most of the process parameters of this comparative example are the same as those of 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 2:5:3, the addition amount is 2.7t, and it is added to the ladle in three batches, and the reducing strength is further controlled to 1.5;

[0066] The composition of the steel ingot obtained after die casting in this comparative example is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The grades of the inclusions are shown in Table 3. The ratings of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are all 1.0, and the rating of Class Ds inclusions is 1.0.

[0067] Comparative Example 5

[0068] Most of the process parameters of this comparative example are the same as those of Example 3, except that in the LF furnace refining process, no Ni-Mg alloy is added in the later stage of smelting.

[0069] The composition of the steel ingot obtained after die casting in this comparative example is shown in Table 2. The inclusions are Al2O3-SiO2. The grades of the inclusions are shown in Table 3. The ratings of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are all 1.5, and the rating of Class Ds inclusions is 1.0.

[0070] Comparative Example 6

[0071] Most of the process parameters of this comparative example are the same as those of Example 3, except that in the LF furnace refining process, 250 kg of Ni-Mg alloy is added in the later stage of smelting.

[0072] The composition of the steel ingot obtained after die casting in this comparative example is shown in Table 2. The inclusions are MgO-Al2O3-SiO2. The grades of the inclusions are shown in Table 3. The ratings of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are all 1.0, and the rating of Class Ds inclusions is 0.5.

[0073] Table 1 Process parameters of the embodiment

[0074] Table 2 Chemical composition of steel ingot (wt%)

[0075] Table 3 Inclusion levels in steel ingots

[0076] Figure 1This is an inclusion morphology diagram of the Invar alloy steel ingot prepared in Example 1 of the present invention. In the figure, the components 1 and 4 are Al2O3, the component 2 is MgO, and the component 3 is SiO2. It can be seen that the inclusions are MgO-Al2O3-SiO2 inclusions.

[0077] Figure 2 This is the inclusion morphology of the steel ingot prepared in Comparative Example 1. The components of 1 and 2 in the figure are both Al2O3, which shows that the inclusions are Al2O3 inclusions.

[0078] As shown in Examples 1-7, the inclusions in the Invar alloy steel ingot prepared in the embodiments of the present invention are MgO-Al2O3-SiO2 inclusions, the grades of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are ≤0.5, and the grade of Class Ds inclusions is 0.

[0079] Combining Example 3 and Comparative Example 2, it can be seen that by adjusting the amount of Ni-Mg alloy from the original 350 kg to 230 kg, while the composition range and amount of composite deoxidizers such as Al-Si-Mn are within the range set by the present invention, the reduction strength exceeds the range set by the present invention. By comparing the A, B, C, D, and Ds inclusion assessment grades, there is a different degree of increase.

[0080] Combining Example 3 with Comparative Examples 3 and 4, it can be seen that by adjusting the ratio and dosage of the composite deoxidizer components, its reducing strength changes significantly, and the final inclusion assessment grade increases significantly.

[0081] Combining Example 3 with Comparative Examples 5 and 6, it can be seen that Comparative Example 5 does not add Ni-Mg alloy, resulting in its deoxidation product being mainly Al2O3-SiO2, with a higher evaluation grade and a larger deoxidation product size; although Comparative Example 6 adds Ni-Mg alloy, its addition amount is lower than the setting range of the present invention, and the effect of inhibiting the coarsening of oxides such as Al2O3 is relatively poor, thereby resulting in a significant increase in the final inclusion grade.

[0082] Compared with Comparative Examples 1-6, the Invar alloys prepared in the present invention exhibit better inclusion control and smaller Ds-type inclusions, reducing the incidence of localized surface peeling defects on the cold-rolled strip caused by large inclusions and improving the quality and yield of the Invar alloy strip. The Fe-Ni-based Invar alloys prepared in the present invention are widely applicable in aerospace, defense, energy transportation, and other fields. Due to their excellent hot working properties and superior expansion performance, the successful design and development of this alloy will bring broad economic benefits and a wide range of market applications.

[0083] 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 the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, and all of these should be included in the scope of the claims of the present invention.

Claims

1. A smelting method for refining the size of inclusions in Invar alloy, characterized in that: The following steps are involved: S1, induction furnace smelting, using pure nickel plate and pure iron as Invar alloy raw materials, the ingredients are prepared according to the chemical composition of Invar alloy, and molten steel is obtained by induction furnace smelting; S2, AOD furnace refining, the molten steel is added to the AOD ladle furnace for refining, oxygen is blown for decarburization, and pure nickel plates and pure iron are added for alloying. At the same time, quicklime is added in batches. When the carbon content in the molten steel is ≤0.03%, Al-Si-Mn composite deoxidizer is added for deoxidation. After deoxidation, the slag is skimmed; 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 the Al-Si-Mn composite deoxidizer added satisfies: m≥0.02L+0.1, where m is the amount of the Al-Si-Mn composite deoxidizer added, in t; L is the mass of the molten steel, in t; During the deoxidation process of the Al-Si-Mn composite deoxidizer, the reduction strength is controlled to be 1.1 to 1.3; S3, LF furnace refining. After slag removal, the ladle is hoisted to the LF furnace for refining. Aluminum shots are added to the LF furnace to adjust the aluminum content in the molten steel to 0.1-0.2%, and the sulfur content in the molten steel is ensured to be ≤0.001%. The composition is fine-tuned according to component analysis. After the composition is stable, Ni-Mg alloy is added in the later stage of smelting. Then, argon is blown from the bottom for stirring and cooling. When the molten steel temperature is ≤1650℃, the LF furnace refining is completed. In the Ni-Mg alloy, the Ni content accounts for 60-70wt%, and the Mg content accounts for 20-30wt%. The addition amount of the Ni-Mg alloy satisfies: 合金 ≥3×L+20, where m 合金 is the amount of Ni-Mg alloy added, in kg; L is the mass of molten steel, in 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 a vacuum. After the pump is withdrawn, sampling is performed to measure the temperature and synthetic slag is added. Then, the pump is continued to be pumped in for bottom blowing of argon gas for weak stirring. S5, mold casting, using argon protection pouring throughout the entire process, and adding mold slag into the ingot mold in batches to obtain an Invar alloy steel ingot weighing 15 to 25 tons; In the Invar alloy steel ingot, the grades of type A inclusions, type B inclusions, type C inclusions, and type D inclusions are ≤ grade 0.5, and the grade of type Ds inclusions is grade 0.

2. The smelting method for refining the size of Invar alloy inclusions according to claim 1, characterized in that: In step S1: The Ni content of the pure nickel plate is 98-99.5%, and the amount of the pure nickel plate added is 26-46% of the mass of the Invar alloy raw material; the amount of the pure iron added is 50-70% of the mass of the Invar alloy raw material; and / or The composition of the molten steel is as follows in percentage by mass: C≤5.0%, Si≤1.2%, Mn≤0.8%, P≤0.010%, S≤0.30%, 25%≤Ni≤45%, Mg≤0.5%, Al≤0.20%, and the rest are Fe and unavoidable residual elements.

3. The smelting method for refining the size of Invar alloy inclusions according to claim 2, characterized in that: In the composition of the molten steel, C≤3.0%.

4. The smelting method for refining the size of Invar alloy inclusions according to claim 1, characterized in that: In step S2: The total amount of quicklime added is 4 to 5 tons per furnace.

5. The smelting method for refining the size of Invar alloy inclusions according to claim 1, characterized in that: In step S2, the composition of the molten steel after refining and tapping the steel in the AOD furnace is as follows in percentage by mass: C≤0.03%, Si≤1.0%, Mn≤0.5%, P≤0.02%, S≤0.06%, 28%≤Ni≤35%, Mg≤0.1%, Al≤0.2%, and the rest are Fe and unavoidable residual elements.

6. The smelting method for refining the size of Invar alloy inclusions according to claim 1, characterized in that: In step S3: The amount of aluminum shot added is 1-2 kg / t molten steel; and / or The bottom blowing argon gas supply intensity is controlled to be 5-8 L / min / t molten steel, and the stirring time is 10-20 min; and / or When the temperature of the molten steel is 1600-1650°C, the LF furnace refining is completed.

7. The smelting method for refining the size of Invar alloy inclusions according to claim 1, characterized in that: In step S4: The ladle furnace vacuum pumping time is ≥ 20min; and / or In the synthetic slag, the mass ratio of Al2O3 to SiO2 is 1-3:7-9; and / or The amount of synthetic slag added is 200-300 kg / heat; and / or The argon weak stirring time is ≥60 min.

8. The smelting method for refining the size of Invar alloy inclusions according to claim 1, characterized in that: In step S5: During the process of adding the protective slag into the ingot mold in batches, 20-30 kg of protective slag is hung at the bottom of each ingot mold before pouring, and the remaining 20-30 kg of 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. An Invar alloy prepared by the smelting method for refining the size of Invar alloy inclusions according to any one of claims 1 to 8, characterized in that: Its composition 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%, and the rest are Fe and unavoidable residual elements.

10. The Invar alloy according to claim 9, wherein The inclusions of the Invar alloy are MgO-Al2O3-SiO2 inclusions; Among the inclusions, the grades of Class A inclusions, Class B inclusions, Class C inclusions, and Class D inclusions are ≤0.5, and the grade of Class Ds inclusions is 0.

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