A method for producing a straightening roll blank having high purity and low segregation

Abstract

The present application relates to a kind of preparation methods of straightening roll blank with high purity and low segregation, and the straightening roll blank is prepared by electric furnace, induction furnace, refining, vacuum degassing, electrode blank pouring, protective atmosphere electroslag mode, the raw materials are fully dephosphorized and inclusions by using strong oxidizing atmosphere of electric furnace, the noble alloy is melted by using intermediate frequency furnace, the basicity of refining slag is controlled, and the proportion of plastic inclusions in steel is improved by deep desulfurization and modification of oxide inclusions, the liquid steel is kept under ≤0.7mpa vacuum degree for ≥15min in vacuum process control, high aspect ratio ≥4 slender steel ingot mold is selected for pouring, argon protection pouring and riser insulation mode are used for pouring to reduce composition segregation in solidification process, ternary pre-melted slag system is selected for electroslag remelting process, inclusions in liquid steel are fully absorbed while the cooling speed of ingot is improved, so that the straightening roll blank with high purity, low segregation, high strength and toughness is obtained.

Description

Technical Field

[0001] This invention belongs to the field of steelmaking technology and relates to a method for preparing a straightening roll blank with high purity and low segregation. Background Technology

[0002] During the "2026-2030" period, my country has clearly proposed to develop strategic emerging industries such as new energy, new materials, aerospace and low-altitude economy, and high-end equipment manufacturing. Heavy plates, as key raw materials for components in marine equipment, energy and pressure vessels, and heavy machinery, are developing rapidly, with the largest heavy plate rolling mill currently reaching 5600mm in size. Straightening rolls, as key components of rolling mills, are subjected to high temperatures, high contact stress, continuous torsional stress, and impact forces during their service life. 4Cr5MoSiV1, as a hot work die steel, possesses good strength, toughness, resistance to high-temperature tempering, and hardness, making it one of the most commonly used materials for straightening rolls.

[0003] The performance of a material depends not only on its composition but also on metallurgical defects during its preparation. For 4Cr5MoSiV1, a commonly used material for straightening roll blanks, the preparation method typically involves an electric furnace followed by electroslag remelting. Metallurgical defects generated during preparation, such as macroscopic component segregation and non-metallic inclusions, severely impact product service life and cannot be improved through subsequent forging or heat treatment processes. These defects must be controlled during the smelting process. By selecting raw materials, refining the basicity control during refining, enhancing degassing, reducing electrode blank segregation, and optimizing the melting rate to improve the cooling intensity of the electroslag ingot, long-life straightening roll blanks with fine and uniform inclusions and minimal macroscopic component segregation can be produced. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a method for preparing a straightening roll blank with high purity and low segregation. The straightening roll blank is prepared by smelting through an electric furnace, induction furnace, refining, vacuum degassing, electrode blank casting, and protective atmosphere electroslag remelting. The composition of the prepared straightening roll blank meets the requirements of 4Cr5MoSiV1 in GB / T 1299-2014. Its inclusion level can reach the level of A, B, C, and D sum ≤ 2.0, Ds ≤ 1.0, and carbon segregation ≤ 0.04%.

[0005] The objective of this invention is achieved as follows: Step 1), Initial smelting of molten steel: Step 1.1) Smelting is carried out using raw materials fed into the electric furnace. The raw materials consist of 20%-30% pig iron and 70%-80% CrMo steel scrap. During the smelting process, oxygen is blown and slag is flowed simultaneously. During this period, 3-10 kg / t of C powder is injected in batches and 20-40 kg / t of lime is added to create foamy slag. This process is used to dephosphorize and remove inclusions from the molten steel. The smelting ends when the C content is 0.05%-0.10% and the molten steel temperature is ≥1620℃. Step 1.2) Use an intermediate frequency furnace to smelt the ferroalloy and raw material. The raw materials entering the furnace consist of 70-75% medium carbon ferrochrome, 10-15% ferromolybdenum, and 10-15% ferrovanadium. The smelting end condition is: the temperature of the molten steel is 1580℃-1620℃. Step 1.3) The molten steel from the electric furnace and the medium-frequency furnace is sequentially added to the ladle to obtain primary molten steel. When tapping steel from the electric furnace, 2-4 kg / t of lime, 2-4 kg / t of aluminum blocks, and 10-14 kg / t of ferrosilicon are added to the ladle along with the steel flow to induce slag formation and alloying. The ferrosilicon used above contains 72% Si by mass, and the lime contains 92% CaO by mass. Step 2) LF refining: The molten steel from the initial refining process is poured into the refining furnace; Step 2.1) Slag-forming stage: Slag-forming is performed by power supply, with the molten steel temperature ≥1580℃. Samples are taken to test the composition. Based on the deviation between the chemical composition and the target value, the required alloy is added to adjust the composition. The mass of silicon dioxide entering the slag is obtained by subtracting the mass of silicon in the molten steel from the mass of silicon in the ferrosilicon added in Step 1.3). Based on the mass of silicon dioxide in the slag, 2-4 kg / t of lime is added to the ladle to adjust the theoretical basicity of the refining slag to 3-4, i.e., CaO:SiO2=3-4, to improve the refining slag's adsorption capacity for non-metallic oxides and its deoxidation capacity for molten steel. During this period, the chemical composition is adjusted as required. Step 2.2) After the chemical composition meets the requirements, add 1-2 kg / t of silica to the slag to adjust the theoretical basicity of the refining slag to 2-3, i.e., CaO:SiO2 = 2-3. This increases the activity of [Si] in the steel and reduces the content of Al2O3 in the composite oxide inclusions in the steel, transforming them into plastic inclusions. At the same time, it creates a favorable environment for the steel slag mixing and inclusion modification in the subsequent vacuum degassing process. The silica used above has a SiO2 content of 99%. Step 2.3) Throughout the refining process, add a total of 1.5-2.5 kg / t of carbon powder and ferrosilicon powder to the slag surface in small batches and multiple batches. The carbon powder and ferrosilicon powder are prepared in a 1:1 ratio to maintain a reducing atmosphere. Step 3), Vacuum degassing: Step 3.1) Hoist the ladle into the vacuum tank, start the vacuum pump, and maintain the molten steel at a vacuum of ≤0.7 MPa for more than 15 minutes, during which time the bottom-blown argon flow rate should be greater than 70 NL / m³.3 This process fully degasses and promotes steel slag mixing, maximizing the contact area between molten steel and slag layer, further reducing the Al2O3 content in composite oxide inclusions in steel, and transforming brittle inclusions in steel into ductile inclusions. Step 3.2) After the vacuum is broken, the bottom-blown argon flow rate is reduced to 10-30 NL / m³. 3 Weak stirring is carried out and the time is ≥10min to further adsorb the inclusions in the steel that collided, agglomerated and grew during the vacuum degassing process but did not have time to float to the surface. Step 4) Steel ingot casting: Step 4.1) Select a fine external riser type ingot mold with an ingot height-to-diameter ratio ≥4, and a riser ratio ≥8%. Preheat to 30℃-100℃ before use, and suspend 1-2kg / t of carbon-free protective slag inside the mold before casting. Step 4.2) Use argon gas injection for protection during casting. Control the molten steel level to rise steadily during the casting process. When the steel reaches two-thirds of the riser, add 1-2 kg / t of exothermic agent and 0.5-1.5 kg / t of carbonized rice husk into the riser in sequence to take into account both the rapid cooling effect of the slender ingot mold and the feeding effect of the riser. Step 4.3) After solidification, the riser is hot-cut to remove all inclusions and shrinkage defects that floated into the riser during solidification, thereby obtaining a high-quality electrode blank with low segregation and few inclusions. Step 4.4) The high-quality electrode billet with hot-cut risers is hot-sent to the electroslag workshop for electroslag remelting; Step 5), Electroslag Remelting: Step 5.1) Select a ternary pre-melted slag with a mass percentage of CaF:Al2O3:SiO2 = 65%:25%:10%, and add 2% SiO2 to the pre-melted slag to suppress the reduction reaction of Al2O3 in the slag. Step 5.2) Send the electrode blank with the welded dummy electrode to the bottom of the crystallizer and energize it for cold arc starting. The melting rate during the remelting stage is controlled at 0.6-65 times the diameter of the crystallizer to improve the cooling rate of the ingot during the remelting process and reduce the segregation of the electroslag ingot components. Step 5.3) The electroslag process is protected by compressed air. The compressed air flow rate is 50-200 NL / min. At the beginning of the remelting stage, add 40-50g of calcium silicate powder every 5 minutes. During the feeding stage, reduce the addition rate of calcium silicate powder to 10-20g every 5 minutes to ensure good feeding. After remelting, cool the mold for 50-80 minutes and then demold.

[0006] The beneficial effects of this invention are as follows: This invention employs an electric furnace + electroslag remelting method. The preparation process is optimized in terms of improving steel purity, reducing the proportion of brittle inclusions in the steel, and suppressing component segregation in electroslag ingots. Through the interaction of various stages such as electric furnace, refining, vacuum pumping, electrode billet casting, and electroslag remelting, high-purity and low-segregation billets for straightening rolls are prepared. The process route is reasonably designed and highly operable. Detailed Implementation

[0007] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0008] Example 1: A method for preparing a high-purity and low-segregation straightening roll blank, characterized by: preparing the straightening roll blank through an electric furnace, induction furnace, refining, vacuum degassing, electrode blank casting, and protective atmosphere electroslag remelting. The composition of the prepared straightening roll blank meets the requirements of 4Cr5MoSiV1 in GB / T 1299-2014. The specific preparation steps are as follows: Step 1), Initial smelting of molten steel: Step 1.1) Smelting is carried out using raw materials fed into the electric furnace. The raw materials include 23% pig iron and 77% chromium-molybdenum steel scrap. During the smelting process, oxygen is blown and slag is flowed simultaneously. During this period, carbon powder with a total mass of 4 kg / t is injected in batches and lime with a total mass of 30 kg / t is added to create foam slag. The steel is dephosphorized and inclusions are removed. After the smelting is completed, a sample is taken with a carbon content of 0.05% and the temperature of the steel is measured at 1634℃. Step 1.2) Use an intermediate frequency furnace to smelt the ferroalloy and the raw material. The raw materials fed into the furnace according to the mass percentage consist of 72% medium carbon ferrochrome, 14% ferromolybdenum, and 14% ferrovanadium. After smelting, the temperature of the molten steel is measured at 1600℃. Step 1.3) The molten steel from the electric furnace and the medium-frequency furnace is sequentially added to the ladle to obtain primary molten steel. When tapping steel from the electric furnace, 4 kg / t of lime, 2 kg / t of aluminum blocks, and 11 kg / t of ferrosilicon are added to the ladle along with the steel flow to slag and alloy in advance. The mass percentage of Si in the ferrosilicon used above is 72%, and the mass percentage of CaO in the lime is 92%. Step 2) LF refining: The molten steel from the initial refining process is poured into the refining furnace; Step 2.1) Slag-making stage: Slag-making is carried out by power supply. The temperature of the molten steel is ≥1580℃. The chemical composition is sampled and tested. The ferrosilicon oxide content is 1 kg / t, and the silica content in the slag is 1.54 kg / t. 2.7 kg / t of lime is added to the ladle to adjust the theoretical basicity of the refining slag to 4 (CaO:SiO2). The high basicity of the refining slag ensures the adsorption capacity of non-metallic oxides and the deoxidation capacity of the molten steel. Then, alloying operation is carried out. The silica in the slag is from ferrosilicon and is added during the electric furnace tapping stage. The calcium oxide in the slag is from lime and is added during the electric furnace tapping stage and the LF refining slag-making stage. Step 2.2) After the chemical composition meets the requirements, 1.4 kg / t of silica is added to the slag to adjust the theoretical basicity of the refining slag to 2.5 (CaO:SiO2) in order to increase the activity of [Si] in the steel, reduce the content of Al2O3 in the composite oxide inclusions in the steel, transform them into plastic inclusions, and create a favorable environment for steel slag mixing and inclusion modification in the subsequent vacuum degassing process. The silica used above has a SiO2 content of 99%. Step 2.3) Throughout the refining process, add a total of 1.5-2.5 kg / t of carbon powder and ferrosilicon powder to the slag surface in small batches and multiple batches. The carbon powder and ferrosilicon powder are prepared in a 1:1 ratio to maintain a reducing atmosphere. Step 3) Vacuum degassing: Step 3.1) Hoist the ladle into the vacuum tank, start the vacuum pump, and maintain the molten steel at a vacuum of ≤0.7 MPa for 17 minutes, during which the bottom-blown argon flow rate is 70-90 NL / m³. 3 This process fully degasses and promotes steel slag mixing, maximizing the contact area between molten steel and slag layer, further reducing the Al2O3 content in composite oxide inclusions in steel, and increasing the proportion of plastic inclusions. Step 3.2) After the vacuum is broken, use bottom-blown argon gas for weak stirring, with an argon gas flow rate of 10-30 NL / m³. 3 Keep it for 12 minutes to allow the large-sized inclusions that have grown and agglomerated during the vacuum degassing process to float fully to the slag. Step 4) Steel ingot casting: Step 4.1) Select an external riser type ingot mold with an ingot mold height-to-diameter ratio of 4.5, with risers accounting for 8%. Preheat to 50°C before use, and suspend 1.5 kg / t of carbon-free protective slag inside the mold before casting. Step 4.2) Argon gas is used for bottom-pouring protection during casting. The molten steel level is controlled to rise steadily during the casting process. When the riser is two-thirds full, 1 kg / t of exothermic agent and 1 kg / t of carbonized rice husk are added to the riser in sequence. This takes into account both the rapid cooling effect of the slender ingot mold and the feeding effect of the riser. Step 4.3) After solidification, the riser is hot-cut to remove all inclusions and shrinkage defects that floated into the riser during solidification, thus obtaining a high-quality electrode blank with low segregation and few inclusions. Step 4.4) The high-quality electrode billet with hot-cut risers is hot-sent to the electroslag workshop for electroslag remelting; Step 5), Electroslag Remelting: Step 5.1) Select a ternary pre-melted slag with a mass percentage of CaF:Al2O3:SiO2 = 65%:25%:10%, and add 2% SiO2 to the pre-melted slag to inhibit the reduction reaction of Al2O3 in the slag. The above pre-melted slag is used after being baked at 600℃ for 4 hours. Step 5.2) The electrode blank with the welded dummy electrode is sent to the bottom of the crystallizer and energized for cold arc ignition. After slag removal, the remelting stage begins. The target melting rate for the remelting stage is 440 kg / h. During the remelting process, a low melting rate is used to increase the cooling rate of the electroslag ingot and reduce the segregation of the electroslag ingot components. When welding the dummy electrode, the dummy electrode is welded to the tail end of the ingot. During electroslag removal, the riser of the electrode blank serves as the tail end of the electroslag ingot for remelting. The average diameter of the crystallizer used in the electroslag removal process is 700 mm. The target melting rate is set at 0.63 of the average diameter of the crystallizer, i.e., the target melting rate is 440 kg / h. Step 5.3) The electroslag process is protected by compressed air with a flow rate of 80 NL / min. At the beginning of the remelting stage, add 45 g of calcium silicate powder every 5 minutes. During the feeding stage, reduce the addition rate of calcium silicate powder to 15 g every 5 minutes to ensure good feeding. After remelting, cool the mold for 50-80 minutes and then demold. Step 6) Finished product inspection Step 6.1) Samples were taken from the riser and the 1 / 2R position of the ingot tail of the forged electroslag ingot according to GB / T10561. The results are shown in Table 1. Table 1 Non-metallic inclusions in electroslag ingot forgings riser 0 0.5 0.5 0 0 0 0.5 1 0 Ingot tail 0 0.5 0.5 0 0 0 0.5 0.5 0 Step 6.2) Samples were taken from the riser and the center position of the ingot tail of the forged electroslag ingot and analyzed for C content. The results are shown in Table 2. Table 2. C content in electroslag ingot forgings riser 0.36 0.38 Ingot tail 0.38 0.39 Finally, it should be noted that the above descriptions are merely preferred embodiments 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 foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a straightening roll blank with high purity and low segregation, characterized in that: Straightening roll blanks were prepared by a smelting process involving an electric furnace, induction furnace, refining, vacuum degassing, electrode blank casting, and electroslag remelting under a protective atmosphere. The composition of the prepared straightening roll blanks met the requirements of 4Cr5MoSiV1 in GB / T 1299-2014. The specific preparation steps are as follows: Step 1), Initial smelting of molten steel: Step 1.1) Smelting is carried out using raw materials fed into the electric furnace. The raw materials fed into the furnace include 20%-30% pig iron and 70%-80% CrMo steel scrap by mass percentage. During the smelting process, oxygen is blown and slag is flowed simultaneously. During this period, 3-10 kg / t of C powder is injected in batches and 20-40 kg / t of lime is added to create foam slag. The steel is dephosphorized and inclusions are removed. The smelting ends when the C content is 0.05%-0.10% and the steel temperature is ≥1620℃. Step 1.2) Use an intermediate frequency furnace to smelt the ferroalloy and raw materials. The raw materials fed into the furnace according to the mass percentage include 70-75% medium carbon ferrochrome, 10-15% ferromolybdenum, and 10-15% ferrovanadium. The smelting end condition is: the temperature of the molten steel is 1580℃-1620℃. Step 1.3): The molten steel from the electric furnace and the medium-frequency furnace is sequentially added to the ladle to obtain primary molten steel. During tapping from the electric furnace, 2-4 kg / t of lime, 2-4 kg / t of aluminum blocks, and 10-14 kg / t of ferrosilicon are added to the ladle along with the steel flow to induce slag formation and alloying. The ferrosilicon used contains 72% Si by mass, and the lime contains 92% CaO by mass. Step 2) LF refining: The molten steel from the initial refining process is poured into the refining furnace; Step 2.1) Slag-forming stage: Slag-forming is performed by power supply, with the molten steel temperature ≥1580℃. Samples are taken to test the composition. Based on the deviation between the chemical composition and the target value, the required alloy is added to adjust the composition. The mass of SiO2 entering the slag is obtained by subtracting the mass of silicon in the molten steel from the mass of silicon in the ferrosilicon added in Step 1.3). Based on the mass of SiO2 in the slag, 2-4 kg / t of lime is added to the ladle to adjust the theoretical basicity of the refining slag to 3-4, i.e., CaO:SiO2=3-4, thereby improving the refining slag's adsorption capacity for non-metallic oxides and its deoxidation capacity for the molten steel. During this process, the chemical composition is adjusted as required. Step 2.2) After the chemical composition meets the requirements, add 1-2 kg / t of silica to the slag to adjust the theoretical basicity of the refining slag to 2-3, i.e., CaO:SiO2 = 2-3. This increases the activity of [Si] in the steel and reduces the content of Al2O3 in the composite oxide inclusions in the steel, transforming them into plastic inclusions. At the same time, it creates a favorable environment for the steel slag mixing and inclusion modification in the subsequent vacuum degassing process. The silica used above has a SiO2 content of 99%. Step 2.3) Throughout the refining process, add a total of 1.5-2.5 kg / t of carbon powder and ferrosilicon powder to the slag surface in small batches and multiple batches. The carbon powder and ferrosilicon powder are prepared in a 1:1 ratio to maintain a reducing atmosphere. Step 3), Vacuum degassing: Step 3.1) Hoist the ladle into the vacuum tank, start the vacuum pump, and maintain the molten steel at a vacuum of ≤0.7 MPa for more than 15 minutes, during which time the bottom-blown argon flow rate should be greater than 70 NL / m³. 3 This process fully degasses and promotes steel slag mixing, maximizing the contact area between molten steel and slag layer, further reducing the Al2O3 content in composite oxide inclusions in steel, and transforming brittle inclusions in steel into ductile inclusions. Step 3.2) After the vacuum is broken, the bottom-blown argon flow rate is reduced to 10-30 NL / m³. 3 Weak stirring is carried out and the time is ≥10min to further adsorb the inclusions in the steel that collided, agglomerated and grew during the vacuum degassing process but did not have time to float to the surface. Step 4) Steel ingot casting: Step 4.1) Select a fine external riser type ingot mold with an ingot height-to-diameter ratio ≥4, and a riser ratio ≥8%. Preheat to 30℃-100℃ before use, and suspend 1-2kg / t of carbon-free protective slag inside the mold before casting. Step 4.2) Use argon gas injection for protection during casting. Control the molten steel level to rise steadily during the casting process. When the steel reaches two-thirds of the riser, add 1-2 kg / t of exothermic agent and 0.5-1.5 kg / t of carbonized rice husk into the riser in sequence to take into account both the rapid cooling effect of the slender ingot mold and the feeding effect of the riser. Step 4.3) After solidification, the riser is hot-cut to remove all inclusions and shrinkage defects that floated into the riser during solidification, thereby obtaining a high-quality electrode blank with low segregation and few inclusions. Step 4.4) The high-quality electrode billet with hot-cut risers is hot-sent to the electroslag workshop for electroslag remelting; Step 5), Electroslag Remelting: Step 5.1) Select a ternary pre-melted slag with a mass percentage of CaF:Al2O3:SiO2 = 65%:25%:10%, and add 2% SiO2 to the pre-melted slag to suppress the reduction reaction of Al2O3 in the slag. Step 5.2) Send the electrode blank with the welded dummy electrode to the bottom of the crystallizer and energize it for cold arc starting. The melting rate during the remelting stage is controlled at 0.6-65 times the diameter of the crystallizer to improve the cooling rate of the ingot during the remelting process and reduce the segregation of the electroslag ingot components. Step 5.3) The electroslag process is protected by compressed air. The compressed air flow rate is 50-200 NL / min. At the beginning of the remelting stage, add 40-50g of calcium silicate powder every 5 minutes. During the feeding stage, reduce the addition rate of calcium silicate powder to 10-20g every 5 minutes to ensure good feeding. After remelting, cool the mold for 50-80 minutes and then demold.