Smelting method of green invar alloy

Abstract

The invention discloses a smelting method of a green invar alloy. The smelting method specifically comprises the following steps: adopting an electric arc furnace smelting, LF (ladle furnace) refining and VD (vacuum degassing) oxygen control and nitrogen increase triple smelting process; in the electric arc furnace smelting process, directly reducing iron within 30% is added, and the remaining proportion is scrap steel; in the LF refining process, precious metals such as a nickel plate, ferromolybdenum and ferrovanadium are added for alloying operation; and a gaseous nitrogen increasing process is adopted in the VD smelting process. According to the method, direct reduction iron and waste steel are adopted as raw materials of the electric arc furnace, the carbon emission in the smelting process is greatly reduced, the requirement for environmental protection is met, the gaseous nitrogen increasing technology is adopted in the VD process, precious nitroalloy raw materials do not need to be used, the smelting cost is reduced, energy consumption is reduced, and the steel grade is rich in'green steel 'labels.

Description

Technical Field

[0001] The invention relates to the technical field of metallurgy, in particular to a method for smelting green Invar alloy. Background Art

[0002] Under the background of the national "dual carbon" goal, short-process steelmaking in electric arc furnaces has become a trend in steelmaking technology, and the use of direct reduced iron to replace scrap steel for steelmaking has attracted more and more attention from scholars. Due to its extremely small expansion coefficient, Invar alloy is widely used in radio, precision instruments, instruments and other industries. Its preparation often adopts the "vacuum smelting + electroslag remelting" double smelting process; however, this process has high requirements on the quality of raw materials, and the proportion of scrap steel added is extremely limited, generally controlled within 5%; excessive scrap steel addition ratio will cause a series of problems such as increased content of harmful elements such as phosphorus, sulfur, copper, and tin in the ingot, increased inclusion content, etc., which will lead to a decrease in the mechanical properties of the material and fail to meet the product quality requirements. High-quality raw materials also lead to high smelting costs.

[0003] Under the dual smelting process of "vacuum smelting + electroslag remelting", the restriction on the proportion of scrap steel added is mainly due to the fact that there is no slag formation in the vacuum smelting stage, and harmful elements such as phosphorus, sulfur, copper, and tin in the steel cannot be effectively removed. Under the triple smelting process of "arc furnace + LF + VD", not only can the harmful elements in the scrap steel be removed to a certain extent, the scrap steel ratio can be increased, but also the equipment operation cost of smelting can be reduced, which is more than 20% lower than the original process. In the process of arc furnace smelting, a certain proportion of direct reduced iron can be added to dilute the harmful elements in the steel and improve the quality of smelting products. However, the quality of direct reduced iron products in the current market is uneven, and the quality gap of raw materials is too large, so that the energy consumption and slag basicity in the electric furnace smelting process cannot be stably controlled, which will seriously affect the quality of smelting products; and under the material composition system, the nitrogen addition process often adopts LF nitrogen addition and VD vacuum breaking nitrogen addition. This nitrogen addition process is difficult to meet the low control requirements of the material for oxygen content, and the nitrogen addition process generally adopts the method of adding nitrided alloys, which has a high smelting cost.

[0004] In order to smelt Invar alloy with qualified composition and excellent quality in this process and realize green smelting of the material, it is necessary to provide a green Invar alloy smelting method. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a green Invar alloy smelting method, which can not only reduce the smelting cost but also reduce energy consumption.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A green Invar alloy smelting method is specifically: adopting an electric arc furnace smelting, LF refining, and VD oxygen control and nitrogen enrichment triple smelting process.

[0008] Furthermore, in the electric arc furnace smelting process of the present invention, less than 30% of direct reduced iron is added, and the remaining proportion is scrap steel, and the smelting steel temperature is controlled at 150°C to 200°C above the liquidus line.

[0009] Furthermore, in order to reduce power consumption and ensure stable slag basicity, the electric arc furnace smelting process of the present invention requires that the direct reduced iron particle size be 5 to 10 mm, the total iron content be greater than 89%, C ≤ 3.4%, SiO 2 ≤3%、Al 2 O 3 ≤3%, P≤0.009%, S≤0.012%.

[0010] Furthermore, in the electric arc furnace smelting process of the present invention, the basicity of the slag is controlled at 2.1-2.3, no silicon-containing deoxidizer such as SiC is used, and the amount of deoxidizing Al added is strictly controlled, and 0.4-0.6 kg / t of steel core aluminum is added before steel tapping to achieve a terminal Si content of less than 0.03%.

[0011] Furthermore, in the LF refining process of the present invention, precious metals such as nickel plate, ferromolybdenum and ferrovanadium are added, and the smelting process adopts submerged arc and slightly positive pressure operation to produce white slag, and the LF tapping temperature is controlled at 200°C to 230°C above the liquidus.

[0012] Furthermore, the VD smelting process of the present invention adopts a gaseous nitrogen enrichment process. After high vacuum degassing, the vacuum is stopped, nitrogen is filled into the furnace, the pressure is 40000-60000Pa, and then nitrogen is bottom blown to ensure that the exposed diameter of the molten steel is greater than 300mm, and the maintenance time is 20-25min. This operation not only ensures the smooth nitrogen enrichment of the molten steel, but also controls the oxygen content in the steel to below 0.0015%.

[0013] Furthermore, in the VD smelting process of the present invention, VD is cast after breaking the air, and the casting temperature is controlled at 50°C to 80°C above the liquidus line. After the casting is completed, the ingot mold is cooled for more than 3 hours and is hoisted into a slow cooling pit with the mold.

[0014] Furthermore, the chemical composition and mass percentage of the Invar alloy of the present invention are C: 0.1-0.3%, Ni: 32-40%, Mo: 0.30-1.00%, V: 0.50-1%, Si≤0.03%, O≤0.002%, N: 0.01-0.015%, and the balance is Fe and unavoidable impurities.

[0015] Furthermore, the invar alloy produced by the method of the present invention has a steel yield (ratio of the total mass of the cast steel liquid to the total mass of the raw material input) of more than 90%, and the inclusion density of the ingot is 30 / mm 2 the following.

[0016] The beneficial effects of adopting the above technical solution are:

[0017] The present invention adopts a triple smelting process of electric arc furnace smelting, LF refining and VD oxygen control and nitrogen addition. The electric arc furnace smelting process uses direct reduced iron and scrap steel as raw materials, which greatly reduces the carbon emission of the smelting process and meets the requirements of green environmental protection; the LF refining process performs alloying operation, which effectively avoids the burning of precious metals such as nickel, molybdenum and vanadium during the electric arc furnace smelting process and reduces the smelting cost; the VD process adopts a gaseous nitrogen addition process, and there is no need to use precious nitrided alloy raw materials, which not only reduces the smelting cost, but also reduces energy consumption, making the steel rich in the "green steel" label. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with specific examples. These examples are only for describing the best implementation of the present invention and are not intended to limit the scope of the present invention.

[0019] Examples 1-9

[0020] A green Invar alloy smelting method, wherein the smelting equipment is a 10t electric arc furnace and its supporting LF refining furnace and VD furnace; during the smelting process of the electric arc furnace, direct reduced iron with a particle size of 5-10mm and part of scrap steel are first added to the bottom of the furnace, the mass of the direct reduced iron accounts for less than 30% of the total weight of the smelting, the particle size of the direct reduced iron is 5-10mm, and the total iron content is greater than 89%, C≤3.4%, SiO 2 ≤3%、Al 2 O 3≤3%, P≤0.009%, S≤0.012%; after arcing steel, add the remaining scrap steel according to the furnace conditions, the slag basicity is controlled at 2.1-2.3, the final tapping temperature is controlled at 150℃-200℃ above the liquidus, and steel core aluminum is added to the molten steel at 0.4-0.6kg / t before tapping; submerged arc and slightly positive pressure operation are used in the LF refining process to produce white slag, and the nickel plate, ferromolybdenum and ferrovanadium required for this steel grade are added in this process, and the tapping temperature is controlled at 200℃-200℃ above the liquidus. 230℃; the VD process mainly involves oxygen control and nitrogen addition. After the ladle enters the VD station, it is first degassed in high vacuum. After a certain period of time, the vacuum is stopped, and then nitrogen is filled into the furnace with a pressure of 40,000 to 60,000Pa. Then nitrogen is blown from the bottom to ensure that the exposed diameter of the molten steel is greater than 300mm, and the holding time is 20 to 25min. After the VD breaks through the air, it enters the casting station, and the casting temperature is controlled at 50℃ to 80℃ above the liquidus line of the steel grade. After the casting is completed, the ingot mold is cooled for more than 3h and then hoisted into the slow cooling pit with the mold.

[0021] The control parameters of the smelting process of each embodiment are shown in Table 1, the DRI reduced iron components added in the electric arc furnace smelting of each embodiment are shown in Table 2; the chemical composition and mass percentage of the green Invar alloy of each embodiment are shown in Table 3; the steel production rate and inclusion density of the Invar alloy of each embodiment are shown in Table 4.

[0022] Table 1 Smelting process parameter control of each embodiment

[0023]

[0024] In Table 1, TL is the liquidus temperature.

[0025] Table 2 DRI reduced iron composition in arc furnace smelting process of each embodiment

[0026]

[0027]

[0028] Table 3 Chemical composition and mass percentage of Invar alloy in each embodiment

[0029] C Ni Mo V Si O N Example 1 0.20 32 0.65 0.55 0.023 0.0013 0.0132 Example 2 0.15 38.5 0.30 0.65 0.028 0.0012 0.0122 Example 3 0.21 36.5 0.55 0.50 0.019 0.0014 0.0141 Example 4 0.30 34.6 0.88 0.68 0.022 0.0015 0.0128 Example 5 0.25 39.2 0.95 0.85 0.019 0.0011 0.0133 Example 6 0.19 40 0.66 0.55 0.024 0.0013 0.0146 Example 7 0.21 35.5 0.35 0.73 0.028 0.0014 0.0121 Example 8 0.29 32.5 1.0 0.95 0.025 0.0010 0.0109 Example 9 0.10 38.6 0.55 1.0 0.018 0.0013 0.0115

[0030] Table 4 Steel production rate and inclusion density of ingots in various examples of Invar alloy smelting

[0031] Steel tapping rate, % <![CDATA[Inclusion density, / mm 2 > Example 1 90.6 28.6 Example 2 90.3 30.0 Example 3 90.8 26.4 Example 4 90.7 29.7 Example 5 90.1 28.4 Example 6 90.3 27.8 Example 7 91.2 29.6 Example 8 90.0 27.5 Example 9 91.7 28.1

Claims

1. A green Invar alloy smelting method, characterized in that: The triple smelting process of electric arc furnace smelting, LF refining and VD oxygen control and nitrogen addition is adopted.

2. A green Invar alloy smelting method according to claim 1, characterized in that: In the electric arc furnace smelting process, less than 30% direct reduced iron is added, and the remaining proportion is scrap steel. The smelting steel temperature is controlled at 150°C to 200°C above the liquidus line.

3. A green Invar alloy smelting method according to claim 2, characterized in that: The direct reduced iron has a particle size of 5 to 10 mm, a total iron content greater than 89%, C≤3.4%, SiO2≤3%, Al2O3≤3%, P≤0.009%, and S≤0.012%.

4. The green Invar alloy smelting method according to claim 1, characterized in that: In the electric arc furnace smelting process, the basicity of the slag is controlled at 2.1-2.3, no silicon-containing deoxidizer is used, and 0.4-0.6 kg / t of steel core aluminum is added before steel tapping to achieve a terminal Si content of less than 0.03%.

5. The green Invar alloy smelting method according to claim 1, characterized in that: In the LF refining process, nickel plate, ferromolybdenum and ferrovanadium precious metals are added, and the smelting process adopts submerged arc and slightly positive pressure operation to produce white slag, and the LF tapping temperature is controlled at 200°C to 230°C above the liquidus line.

6. The green Invar alloy smelting method according to claim 1, characterized in that: The VD smelting process adopts a gaseous nitrogen enrichment process. After high vacuum degassing, the vacuum is stopped, nitrogen is filled into the furnace at a pressure of 40,000 to 60,000 Pa, and then nitrogen is bottom blown to ensure that the exposed diameter of the molten steel is greater than 300 mm, and the maintenance time is 20 to 25 minutes.

7. The green Invar alloy smelting method according to claim 1, characterized in that: In the VD smelting process, VD is cast after breaking the air, and the casting temperature is controlled at 50°C to 80°C above the liquidus line. After the casting is completed, the ingot mold is cooled for more than 3 hours and is hoisted into a slow cooling pit with the mold.

8. The green Invar alloy smelting method according to claim 1, characterized in that: The chemical composition and mass percentage of the Invar alloy are C: 0.1-0.3%, Ni: 32-40%, Mo: 0.30-1.00%, V: 0.50-1%, Si≤0.03%, O≤0.002%, N: 0.01-0.015%, and the balance is Fe and unavoidable impurities.

9. The green Invar alloy smelting method according to claim 1, characterized in that: The invar alloy produced by the method has a steel yield of more than 90%, and the inclusion density of the ingot is 30 / mm 2 the following.

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