Smelting-electroslag remelting method for high-purity corrosion-resistant high-temperature alloy

Abstract

The invention discloses a smelting-electroslag remelting method for a high-purity corrosion-resistant high-temperature alloy. The high-purity corrosion-resistant high-temperature alloy comprises the following chemical components in percentage by weight: 0.067% of C, less than or equal to 0.31% of Si, less than or equal to 0.58% of Mn, less than or equal to 0.005% of P, less than or equal to 0.001% of S, 21.55% of Cr, 30.72% of Ni, less than or equal to 0.01% of Cu, 0.29% of Ti and 0.15% of Al. The method mainly comprises the steps of material preparation, EAF furnace smelting, AOD component adjustment, LF refining, VD, LF component adjustment, pouring and electroslag remelting. By the adoption of the smelting method, the C content can be controlled to be below 0.08%, meanwhile, the S content is reduced to be lower, and compared with a common smelting process route, after the electroslag process is added, the corrosion-resistant high-temperature alloy is more excellent in purity, structure, composition and physical and chemical properties.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and casting, and specifically relates to a method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloy. Background Art

[0002] As petrochemical and coal resources are increasingly depleted, the world is paying more and more attention to the development of the new energy industry. Solar energy is a new energy product that countries around the world are competing to develop, and it is an effective way to achieve the "dual carbon goals". High-purity polysilicon is the basic raw material for solar photovoltaic and electronic industries, and is the main raw material for the development of photovoltaic and electronic industries. With the development of solar energy applications, the use of high-purity polysilicon will also increase day by day. The production of high-purity polysilicon requires the use of core equipment such as cold hydrogenation reactors, because it needs to have high temperature and corrosion resistance in the production process of polysilicon. The main material of the design is a solid solution-strengthened heat-resistant alloy. Due to its excellent high-temperature strength and resistance to oxidation, nitriding and other forms of high-temperature corrosion, and good cold and hot processing and forming, the products involve rods, flange forgings, pipes, plates, etc., which are widely used in core pressure vessel equipment such as cold hydrogenation reactors, heat exchangers, towers, spherical tanks, reduction furnaces, etc. in the polysilicon industry. It can reduce the weight of the structure, save materials, and reduce production costs while maintaining the strength of the design structure. Summary of the invention

[0003] The technical problem to be solved by the present invention is to obtain a corrosion-resistant high-temperature alloy with better composition, performance, grain size and molten steel purity.

[0004] In order to solve the above technical problems, the present invention discloses a method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloy, comprising the following steps: EAF electric arc furnace smelting: The electric furnace quickly melts all the charges, and oxygen is blown appropriately during the melting process to assist melting. The carbon content reaches 0.5% after cleaning. Lime is added in the later stage to control the slag amount above 3%. Calcium silicon powder and ferrosilicon powder are added to reduce Cr2O3 in the slag. The composition before tapping is C: 0.50-0.70%, Si: 0.20-0.40%, Cr: 19.0-21.0%, Ni: 30.0-31.0%, and the tapping temperature is controlled at 1640-1660℃.

[0005] AOD Refining: (i) Add 3% (by weight of molten steel) of lime, bake in AOD furnace for 4 hours in advance, and the temperature of molten steel entering the furnace should be ≥1560℃.

[0006] (II) Blowing and decarbonization: The temperature during the decarbonization period is controlled at ≤1720℃. The blowing is divided into four steps. The first step is blowing C (O2:Ar=4:1) and adding 50-100kg of lime; the second step is blowing C (O2:Ar=1:1) to adjust the Mn composition and add 50-100kg of lime; the third step is blowing C (O2:Ar=1:3) and after the blowing is completed, take 6 carbon samples for analysis, add 50kg of lime, and immediately proceed to the fourth step of blowing; the fourth step is blowing C (O2:Ar=1:4), after the blowing is completed, take carbon samples for analysis and measure the temperature, and the carbon at the end of blowing is ≤0.030%.

[0007] (III) Pre-reduction: Add industrial silicon according to 3% Si content to reduce Cr2O3 in slag for 10-15min. Observe the slag sample. If the slag viscosity is high, add 50-100kg fluorite to increase the fluidity of the slag to improve the recovery rate of Cr. The slag should be removed by more than 95%; (IV) Slag making and desulfurization: Add lime to make new slag, 15-20kg / t lime, 3-5kg / t fluorite, and 1kg / t calcium silicate powder for deoxidation. If the desulfurization effect is not good, continue to make slag and desulfurize. The sulfur control target value is ≤0.005%.

[0008] (V) Steel tapping: The tapping temperature is controlled at 1640-1660℃, and the tapping composition is ≤0.03%. Except for Al and Ti elements, other elements are controlled within the internal control requirements.

[0009] First LF furnace refining: (i) Raise the temperature, add 5-10kg / t lime and 2kg / t fluorite to make slag, and add 2kg / t ferrosilicon powder to diffuse and deoxidize.

[0010] (ii) Adjust the slag volume according to the slag condition, keep the white slag for more than 30 minutes, add appropriate amount of silicon calcium powder and aluminum powder for deoxidation during the process, raise the temperature to 1680℃, and quickly lift the bag to the VD furnace for vacuuming.

[0011] VD furnace refining: Vacuum degree ≤ 67Pa, maintain pressure for 10min, and keep vacuum state for a certain period of time to remove gas and impurities; Steel tapping: take samples and measure temperature, hang the ladle to LF to adjust Al and Ti.

[0012] The second LF furnace is used to adjust the composition: The temperature is ≥1600℃, feed aluminum wire according to the aluminum content of 0.3-0.32% in the furnace charge mass ratio, stir for 5 minutes, add ferrotitanium according to the aluminum content of 0.28-0.30% in the furnace charge mass ratio, take samples for analysis, the carbon content is controlled at 0.05%-0.06%, soft blowing>15min, temperature 1520-1530℃, ladle casting to form electrode rods.

[0013] The electroslag remelting comprises the following steps: Slag preparation and baking: Prepare materials according to the mass percentage of CaF2: 50-60%; A1203: 15-20%; CaO: 20-25; Mg0: 1-4%; TiO: 3-6%, and prepare the slag according to 3-4% of the ingot weight. Put the prepared electroslag slag into the muffle furnace and bake it at 600±50℃ for 4-5 hours. After baking, keep it at 200℃. The baked slag must be taken out as needed. Usually, the time from taking it out from the heating furnace to slagging in the electroslag furnace shall not exceed 20 minutes.

[0014] (I) Preparation of electroslag consumable electrodes: Use arc furnace-AOD furnace-LF furnace-VD furnace-LF furnace for refining and then mold injection to make nickel-based high-temperature alloy electrode rods. During smelting, ensure that the alloy content of the electrode rods meets the standard requirements. The specifications of the consumable electrode rods are designed according to the specifications and dimensions of the electroslag furnace crystallizer. After injection molding, the electrode rods should be sawn flat at both ends and the surface should be descaled (if the electrode rods are not stored properly and are severely corroded, shot blasting is required). A dummy electrode is welded at one end of the processed consumable electrode rod. During welding, try to prevent the surface of the electrode rod from being contaminated by oil and rust.

[0015] (II) Furnace loading: Place the arc-starting plate on the copper plate of the bottom water tank, spread 2-3kg of bottom slag on the arc-starting plate, place the arc-starting agent, and spread asbestos cloth (be careful to prevent the bottom slag from drilling into the process). Lift the crystallizer to the fixed position of the low water tank in the smelting station. Confirm the specifications and materials of the smelting electrode rod again, install the electrode rod and put it vertically into the furnace, adjust it to the center, and make the end 50-100mm away from the arc-starting agent.

[0016] (III) Arcing and slag forming stage: After everything is ready, turn on the power and close the switch, quickly lower the electrode, add the slag evenly around the crystallizer after arcing, ensure that the current stabilizes quickly, control the arcing voltage between 50-66V, the current between 3000-7500A, and the arcing and slag forming time between 30-40 minutes, and ensure the stability of voltage and current to prevent sudden arc extinction.

[0017] (IV) Current increasing stage: When the slag is cleared, capacitors are added, the current rises to 11500-13500A, and the voltage is controlled between 54-63V.

[0018] (V) Electroslag remelting stage: Entering the normal and stable smelting process, the current and voltage are controlled at the upper and lower limits of the current increase stage respectively.

[0019] (VI) Shrinkage-feeding stage: In the later stage of electroslag remelting, the shrinkage-feeding filling is carried out by gradually reducing the flow rate. Each time the flow rate is controlled at 1000-1200A, it is ensured that the filling and shrinkage-feeding are sufficient and the top surface of the electroslag ingot is flat and without concave center.

[0020] (VII) ESR ingot cold mold stage: After the shrinkage compensation is completed, the power is turned off, but the cooling system operates normally. After the ESR ingot is kept warm in the water-cooled crystallizer for 60-80 minutes, it is lifted out of the crystallizer and covered with a heat preservation cover for slow cooling.

[0021] (VIII) Demolding the electroslag remelting ingot: After the electroslag ingot is heat-insulated, it is demolded and transferred into an annealing furnace for stress relief annealing at a temperature of 100°C, thereby completing the process steps of the present invention.

[0022] Beneficial effect: The present invention provides a method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloys. Through the steps of material preparation, EAF furnace smelting, AOD composition adjustment, LF refining, VD, LF composition adjustment, pouring, electroslag remelting and the like, the C content can be controlled below 0.08%, and the S content can be reduced to a lower level. Compared with the conventional smelting process route, the purity, structure, composition, and physical and chemical properties of the corrosion-resistant high-temperature alloy are better after the electroslag process is added. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a microstructure photograph of the corrosion-resistant high-temperature alloy forging of the embodiment. DETAILED DESCRIPTION

[0024] The steel smelted by the smelting method of the present invention is a corrosion-resistant high-temperature alloy, and its composition is as follows: C 0.067%, Si 0.31%, Mn 0.58%, P 0.005%, S 0.001%, Cr 21.55%, Ni 30.72%, Cu 0.01%, Ti 0.29%, and Al 0.15%.

[0025] The specific steps of the present invention are as follows: Step 1: Rapidly melt all the charge, add lime later to control the slag volume above 3%, the composition before steelmaking is C0.60%, Si0.30%, Cr20%, Ni30%, and the steelmaking temperature is controlled at 1660℃.

[0026] Step 2 AOD smelting includes the following: (i) Add 300kg of lime, bake in AOD furnace for 4h in advance, and the temperature of molten steel entering the furnace should be ≥1560℃.

[0027] (II) Blowing and decarbonization: The temperature during the decarbonization period is controlled at 1720℃. The blowing is divided into four steps. The first step is blowing C (O2:Ar=4:1) by adding a certain amount of 80kg lime; the second step is blowing C (O2:Ar=1:1) by adjusting the Mn composition and adding 100kg lime; the third step is blowing C (O2:Ar=1:3), after the blowing is completed, take a carbon sample for analysis, add 50kg lime, and immediately proceed to the fourth step of blowing; the fourth step is blowing C (O2:Ar=1:4), after the blowing is completed, take a carbon sample for analysis and measure the temperature again, and the carbon at the end of blowing is 0.030%.

[0028] (III) Pre-reduction: Add 300kg of Cr2O3 to the industrial silicon reduction slag for 15 minutes and observe the slag sample. If the slag viscosity is high, add 50kg of fluorite to increase the fluidity of the slag to improve the recovery rate of Cr. (IV) Slag making and desulfurization: Add lime to make new slag, add 250kg lime in two batches each to change the slag, and the sulfur control target value is 0.002%.

[0029] (V) Steel tapping: The tapping temperature is controlled at 1660°C, the tapping composition C is 0.027%, and except for Al and Ti elements, other elements are controlled within the internal control requirements.

[0030] The LF smelting in step 3 includes the following: (i) Raise the temperature, add 150kg lime and 30kg fluorite to make slag, and at the same time add 30kg ferrosilicon powder for diffusion deoxidation.

[0031] (ii) Adjust the slag volume according to the slag condition, keep the white slag for more than 30 minutes, add appropriate amount of silicon calcium powder and aluminum powder for deoxidation during the process, raise the temperature to 1680℃, and quickly lift the bag to VD for vacuuming.

[0032] Step 4: The VD furnace includes the following: VD: vacuum degree 111Pa, pressure maintenance 10min, maintain vacuum state for a certain period of time to remove gas and impurities; The LF furnace in step five includes the following: temperature 1605°C, feeding aluminum wire at 0.32% aluminum content, stirring for 5 minutes, adding 0.30% ferrotitanium, sampling and analysis, carbon content controlled at 0.06%, soft blowing for 15 minutes, and ladle pouring at 1530°C.

[0033] The electroslag remelting in step 6 includes the following: (I) Preparation and baking of electroslag: The slag is prepared in the proportions of CaF2: 55%; A1203: 17%; CaO: 23%; Mg0: 2%; TiO: 3%. The total mass of the prepared slag is 140 kg. The prepared electroslag is placed in a muffle furnace and baked at 650°C for 5 hours. After baking, it is kept warm at 200°C for use in the test.

[0034] (II) Preparation of consumable electrodes: Three 3.3-ton UNS nickel-based high-temperature alloy electrode rods were molded after refining in an electric arc furnace. The alloy content of the electrode rods is: C 0.067%, Si 0.31%, Mn 0.58%, P0.005%, S 0.005%, Cr21.55%, Ni 30.72%, Cu0.01%, Ti 0.29%, Al 0.15%. After sawing and flattening the ends of the electrode rods and removing the oxide scale on the surface, a dummy electrode was welded on one end.

[0035] (III) Furnace loading: Place the arc-starting plate on the copper plate of the bottom water tank, spread 3kg of bottom slag on the arc-starting plate, place the arc-starting agent, spread asbestos cloth, and hoist the crystallizer to the fixed position of the low water tank. Confirm the specifications and materials of the smelting electrode rods again, clamp the electrode rods, and put them vertically into the furnace, adjust them to the center, and make the end 50mm away from the arc-starting agent.

[0036] (IV) Arcing and slag forming stage: After everything is ready, turn on the power and close the switch, quickly lower the electrode, add the slag evenly around the crystallizer after arcing, ensure that the current stabilizes quickly, control the arcing voltage between 50-66V, the current between 3000-7500A, and the arcing and slag forming time within 40 minutes.

[0037] (V) Current increasing stage: When the slag is cleared, capacitors are added, the current rises to 11500-13500A, and the voltage is controlled between 54-63V.

[0038] (VI) Electroslag remelting stage: entering the normal and stable smelting process, with the current and voltage controlled at 13500A and 54V respectively.

[0039] (VII) Shrinkage compensation stage: In the later stage of electroslag remelting, the shrinkage compensation filling is carried out by gradually reducing the flow rate, and each time the flow rate is controlled at 1100A.

[0040] (VIII) Electroslag ingot cold mold stage: After the shrinkage compensation is completed, the power is turned off to ensure the normal operation of the cooling system. After the electroslag ingot is kept warm in the water-cooled crystallizer for 80 minutes, it is lifted out of the crystallizer and covered with a heat preservation cover for slow cooling.

[0041] (IX) Demolding the electroslag remelting steel ingot: After the electroslag ingot is heat-insulated, it is demolded and transferred into an annealing furnace for stress relief annealing when the temperature is 100°C, thereby completing the process steps of the present invention.

[0042] Implementation effect: The materials produced by the above process operation not only meet the technical requirements, but also the gas content of the finished steel can be controlled at O: 25ppm; H: 1.8ppm; N: 130ppm; the injection molded steel ingot has no large chemical deviation along the ingot body and in the direction perpendicular to the ingot body; the electroslag ingot alloy content obtained by the above process method is: C 0.067%, Si 0.31%, Mn 0.58%, P 0.005%, S 0.001%, Cr 21.55%, Ni 30.72%, Cu 0.01%, Ti 0.29%, Al 0.15%. The content of active elements C, Si and Mn in the slag ingot is basically not burned, and further desulfurization is played through electroslag remelting.

[0043] The present invention provides a method for smelting and electroslag remelting of a high-purity corrosion-resistant high-temperature alloy. Through the steps of material preparation, EAF furnace smelting, AOD composition adjustment, LF refining, VD, LF composition adjustment, pouring, electroslag remelting and the like, the C content is controlled below 0.08%, and the S content is reduced to a lower level. Compared with the conventional smelting process route, the purity, structure, composition and physical and chemical properties of the corrosion-resistant high-temperature alloy after adding the electroslag process are more excellent.

[0044] Table 1 Mechanical properties test results of corrosion-resistant high-temperature alloy forgings of the embodiment Table 2 Corrosion test results of corrosion-resistant high-temperature alloy forgings in Example Tables 1 and 2 illustrate the temperature resistance and corrosion resistance of the product of the present invention, which are better than the standard requirements.

Claims

1. A method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloys, characterized in that The chemical composition of the alloy is composed of the following components in weight percentage: C: 0.05-0.08%, Si≤0.31%, Mn≤1.5%, P≤0.025%, S≤0.010%, Cr: 19.0-23.0%, Ni: 30.0-35.0%, Cu≤0.75%, Ti: 0.15-0.60%, Al: 0.15-0.60%; The process route is EAF electric arc furnace → AOD furnace → first LF furnace → VD furnace → second LF furnace → mold casting electrode ingot → electroslag remelting.

2. The method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloy according to claim 1, characterized in that: The electroslag remelting comprises the following steps: Preparation and baking of electroslag slag: The slag is prepared according to the mass percentage of CaF2: 50-60%, A12O3: 15-20%, CaO: 20-25%, MgO: 1-4%; TiO: 3-6%, and the slag amount is prepared according to 3-4% of the ingot weight. The prepared electroslag slag is placed in a muffle furnace and baked at 600±50℃ for 4-5 hours. After baking, it is kept warm at 200℃ for use. It can be taken out as needed. The electroslag slag must be used in the electroslag furnace within 20 minutes after it is taken out; Preparation of consumable electrode: using an electric arc furnace and refining outside the furnace to mold a nickel-based high-temperature alloy electrode rod, the alloy content of the electrode rod is as described in claim 1, the specifications of the consumable electrode rod are designed according to the specifications and dimensions of the electroslag furnace crystallizer, and the two ends of the electrode rod are sawn flat and the surface is descaled, and a dummy electrode is welded at one end; Furnace loading stage: Place the arc-starting plate on the copper plate of the bottom water tank, spread 2-3kg of bottom slag on the arc-starting plate, place the arc-starting agent, spread asbestos cloth, hoist the crystallizer to the fixed position of the low water tank, confirm the specifications and materials of the electrode rods again, install the electrode rods and put them vertically into the furnace, adjust them to the center, and make the end 50-100mm away from the arc-starting agent; Arcing and slag forming stage: After power on and closing the switch, the electrode is quickly lowered. After arcing, the slag is evenly added around the crystallizer. The arcing voltage is controlled between 50-66V, the current is controlled between 3000-7500A, and the arcing and slag forming time is controlled within 30-40 minutes; Current increasing stage: when the slag is cleared, capacitors are added, the current rises to 11500-13500A, and the voltage is controlled between 54-63V; Electroslag remelting stage: entering the normal and stable smelting process, the current and voltage are controlled at 13500A and 54V respectively; Shrinkage feeding stage: In the later stage of electroslag remelting, the shrinkage filling is carried out by gradually reducing the flow, and each time the flow is controlled at 1000-1200A; ESR ingot cold mold stage: after the shrinkage is completed, the power is turned off to ensure the normal operation of the cooling system. The ESR ingot is introduced into the water-cooled crystallizer. After being kept warm in the water-cooled crystallizer for 60-80 minutes, it is lifted out of the water-cooled crystallizer and covered with a heat preservation cover for slow cooling; (IX) Demolding of electroslag remelting ingot: After the electroslag ingot is heat-insulated, it is demolded and transferred to the annealing furnace for stress relief annealing when the temperature reaches 100°C.

3. The method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloy according to claim 2, characterized in that: The smelting of the EAF electric arc furnace comprises the following steps: Melting charge: Melting charge, Oxidation: After purification, the carbon content reaches 0.5%, Reduction: Add calcium silicon powder and ferrosilicon powder to reduce Cr2O3 in the slag. Steel tapping: The composition before steel tapping is C: 0.50-0.70%, Si: 0.20-0.40%, Cr: 19.0-21.0%, Ni: 30.0-31.0%, and the steel tapping temperature is controlled at 1640-1660℃.

4. The high-purity corrosion-resistant high-temperature alloy smelting-electroslag remelting method as described in claim 2 is characterized in that: The smelting of the AOD furnace comprises the following steps: Add 3% lime by weight of molten steel, bake in AOD furnace for 4 hours in advance, and the temperature of molten steel entering the furnace should be ≥1560℃; Oxygen blowing decarbonization: the temperature is controlled at ≤1720℃, divided into 4 steps, the first step is to blow C, add 50-100kg lime, where O2:Ar=4:1; the second step is to blow C, where O2:Ar=1:1, adjust the Mn composition, and add 50-100kg lime; the third step is to blow C, where O2:Ar=1:3, take carbon sample for analysis after blowing, add 50-100kg lime, and immediately carry out the fourth step; the fourth step is to blow C, where O2:Ar=1:4, take carbon sample for analysis and temperature measurement after blowing, and the carbon at the end of blowing is ≤0.030%; Pre-reduction: After blowing, add industrial silicon according to 3% Si content to reduce Cr2O3 in the slag. The reduction time is 10-15min. Observe the slag sample. If the slag is viscous, add 50-100kg of fluorite to increase the fluidity of the slag to improve the recovery rate of Cr. The slag should be removed by more than 95%; Slag making and desulfurization: add lime to make new slag, 15-20kg / t lime, 3-5kg / t fluorite, add 1kg / t calcium silicate powder for desulfurization. If the desulfurization effect is not good, continue slag making and desulfurization, and the sulfur control target value is ≤0.005%; Steel tapping: The tapping temperature is controlled at 1640-1660°C, and the tapping composition C is ≤ 0.03%. Except for Al and Ti elements, other elements are controlled within the required range of claim 1.

5. The method for smelting and electroslag remelting of high-purity corrosion-resistant high-temperature alloy according to claim 2, characterized in that: The first LF furnace smelting comprises the following steps: Lime and fluorite are added to make slag, and ferrosilicon powder is added for diffusion deoxidation to turn the slag into white slag. At the same time, the white slag is kept for more than 30 minutes. During the process, calcium silicon powder and aluminum powder are appropriately added for deoxidation. The temperature is raised to 1680℃, and the bag is quickly lifted to VD for vacuuming.

6. The high-purity corrosion-resistant high-temperature alloy smelting-electroslag remelting method according to claim 2, characterized in that: The smelting of the VD furnace comprises the following steps: Carry out vacuum extraction and set the vacuum degree ≤67Pa. After maintaining it for about 10 minutes, take samples and measure the temperature. Hang the bag to the LF furnace to adjust Al and Ti.

7. The high-purity corrosion-resistant high-temperature alloy smelting-electroslag remelting method according to claim 2, characterized in that: The second LF furnace smelting comprises the following steps: Temperature ≥1600℃, feed aluminum wire according to the aluminum content of 0.3-0.32% in the furnace charge mass ratio, stir for 5 minutes, add ferrotitanium according to the aluminum content of 0.28-0.30% in the furnace charge mass ratio, take samples for analysis, the carbon content is controlled at 0.05%-0.06%, soft blowing>15min, hang the bag at the temperature of 1520-1530℃, and cast it into electrode rods.

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