Smelting method for producing W600 non-oriented silicon steel through CSP technology

Abstract

The invention belongs to the technical field of metallurgical processes, and particularly discloses a smelting method for producing W600 non-oriented silicon steel through a CSP process. The technological process comprises the steps of molten iron in a metal mixer, molten iron pretreatment, BOF converter smelting, RH furnace refining and CSP continuous casting. In the molten iron pretreatment, passivated metal magnesium powder and passivated lime powder are added in stages, so that the desulfurization effect is effectively ensured; slag tapping is strictly controlled in the BOF tapping process, a deoxidizing agent and steel ladle synthetic slag are not added in the tapping process, 3-4.5 kg of small-particle lime is added along with steel flow when tapping is conducted to 1 / 5, and bottom argon blowing is stopped after adding is finished; the RH ensures sufficient floating removal of inclusions through efficient decarburization, effective deoxidation net cycle time and sufficient standing time; according to the CSP, slag entrapment of a crystallizer is avoided and the cleanliness of molten steel is guaranteed through measures such as steel ladle protection pouring, roughing slag detection, tundish air curtain retaining wall, casting powder special for silicon steel and crystallizer liquid level fluctuation control within + / -3.5%.

Description

Technical Field

[0001] The invention belongs to the technical field of non-oriented electrical steel smelting, and relates to a CSP process for producing W600 non-oriented silicon steel smelting method. Background Art

[0002] CSP is suitable for the production of low iron loss, high magnetic induction non-oriented silicon steel due to its advantages such as thin ingot, fast cooling rate, fine grains and high equiaxed crystal ratio. However, the cleanliness of molten steel in the CSP metallurgical process is difficult to control, which directly affects the magnetic properties of non-oriented electrical steel. Therefore, effective control of the metallurgical process at each stage, from molten iron desulfurization to BOF, from RH to CSP, determines the quality of the ingot produced by the CSP process for non-oriented silicon steel, which is very important for the CSP process for producing non-oriented silicon steel.

[0003] The patent with application number CN201710892667 discloses a method for preventing the increase of silicon content during the smelting process of ultra-low carbon and ultra-low silicon steel, including the following steps: 1) desulfurization of molten iron; 2) converter smelting: the final carbon mass content is controlled at 0.030% to 0.055%, the oxygen mass content is controlled at 0.045% to 0.070%, and the sulfur mass content is controlled below 0.005%; 3) argon blowing; 4) RH refining: decarburization and deoxidation of molten steel, control the carbon mass content in the molten steel to below 0.005%, the free oxygen mass content to below 20ppm, and the aluminum mass content to below 0.005%; and deoxidation of the slag surface; 5) continuous casting: the temperature control target of the tundish is: the liquidus temperature of the molten steel is +20 to 35°C, and the free oxygen mass content of the tundish is controlled below 50ppm. This method successfully solves the problem of increasing silicon in the smelting process of ultra-low carbon and ultra-low silicon steel.

[0004] The patent with application number 202110081809 announced that the present invention provides a method for smelting silicon-manganese-killed non-oriented silicon steel. The chemical composition mass percentage is C≤0.005%, Si: 0.25%-1.20%, Mn: 0.2%-0.8%, P: 0.015%-0.065%, S≤0.005%, Als≤0.005%, and the balance is Fe and inevitable impurities. The production method includes adding lime and slag surface deoxidizer to adjust the slag after the converter tapping is completed; deoxidation and alloying are carried out after the RH vacuum refining and decarburization are completed, and synthetic slag is added from the vacuum chamber silo 3-5min after alloying. After a period of treatment, the net circulation is 8-12min, and the steel is tapped and transported to continuous casting. The invention can control the type of non-metallic inclusions in steel, improve the cleanliness of molten steel, and improve the erosion of refractory materials during the smelting process.

[0005] Patent application number CN201010617395 discloses a method for smelting silicon steel, which includes converter smelting, refining outside the furnace, and vacuum furnace smelting. In the silicon steel smelting method, the converter smelting adopts the method of controlling the amount of steel slag and adjusting the basicity of steel slag to make the iron oxide content below 5%, and then after LF furnace smelting, the weight content of iron oxide can be reduced to below 1.5%, and then after RH vacuum furnace smelting, the iron oxide in the molten steel is basically zero, which can ensure that the continuous casting machine can roll the steel billet normally without the phenomenon of crystallizer water nozzle blockage.

[0006] In the "Research on Desulfurization Technology of 120t Converter Smelting Non-oriented Silicon Steel", it was announced that when smelting silicon steel, the final slag basicity is 3.0-3.5, w((FeO))≤20%, the final molten steel temperature is greater than or equal to 1680℃, and increasing the bottom blowing stirring intensity can improve the converter desulfurization effect. The average mass fraction of sulfur in silicon steel is 0.0048%. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a smelting method for producing W600 non-oriented silicon steel by CSP process.

[0008] In order to achieve the above object, a smelting method for producing W600 non-oriented silicon steel by CSP process designed by the present invention comprises the following steps: 6) Hot metal pretreatment: The hot metal pretreatment is carried out by spraying metallic magnesium powder and passivation lime powder. The molten iron is first sprayed with 0.35-0.42 kg / t of passivation lime powder, and then with metallic magnesium powder and passivation lime powder for desulfurization. The ratio of metallic magnesium powder to passivation lime powder is 1:4-1:6. After the theoretical amount of material is discharged, the passivation lime powder is continued to be sprayed at 0.4-0.6 kg / t. The S of the hot metal entering the furnace is ≤0.004%. 7) BOF converter: endpoint control [C]: 0.03-0.05%, [P]: ≤0.025%, [S]: ≤0.0035%, T=1690-1710℃, carbon-oxygen product ≤0.0023; slag is strictly controlled during steel tapping, the thickness of the ladle slag layer is less than 70mm, no deoxidizer is added during steel tapping, no ladle synthetic slag is added, small-grain lime is added with the steel flow when 1 / 5 of the steel is tapped, the addition amount is 3-4.5kg / t steel, and the bottom argon blowing is turned off after the addition is completed. 8) RH furnace: turn off bottom argon blowing throughout the process. RH furnace inlet temperature ≥1625℃, carbon content ≤0.045%, oxygen content 400~600ppm, inlet slag thickness ≤200mm; RH determines the oxygen supplement amount according to the inlet carbon content, oxygen content and residual oxygen content control targets, and the residual oxygen content target is controlled at 300~450ppm. 9) RH vacuum treatment time is 28 to 35 minutes. After the vacuum treatment is completed, 40 kg of steel slag modification agent is evenly spread on the slag surface. After the addition of steel slag modification agent is completed, the hydraulic jacking is lowered to the lower limit, and the ladle car is driven to the wire feeding position to keep the molten steel still for 15 to 20 minutes. Before leaving the station, 80 to 100 kg of carbon-free covering agent is added. The mass percentage of the RH steel molten steel composition is: [C]: 0.0015 to 0.0035%, [Mn]: 0.30 to 0.45%, [Si] 1.3 to 1.5%, [P]: ≤0.020%, [S]: ≤0.0030%, [Als]: 0.30 to 0.40%, [N]: ≤0.0030%, [O]: ≤0.0040%, [Nb+V+Ti]: ≤0.0025%, and the remainder is Fe and Ca and unavoidable impurities. 10) The molten steel obtained in step 4) is cast into W600 non-oriented silicon steel billet by CSP continuous casting.

[0009] Furthermore, in the step 1), the pre-desulfurized molten iron has 0.50%≤Si≤0.85%, and S≤0.060%.

[0010] Furthermore, in step 2), the BOF converter adopts full bottom blowing of argon, and the bottom blowing intensity is ≥0.05m 3 / (t·min). The amount of lime added is determined based on the Si content of molten iron, and the slag basicity is controlled at 2.9-3.5. Before the end of the converter, ensure that the oxygen lance low-position deep blowing time is ≥2min. It is forbidden to add iron ore near the end, and other raw materials can be used for temperature adjustment.

[0011] Furthermore, the RH treatment in step 3) must ensure that the gas pipeline for inserting the tube to lift is well permeable; leak detection is performed before production to ensure that the minimum vacuum can reach below 67 Pa. Before smelting non-oriented silicon steel, the RH furnace must be washed with low-carbon steel, the molten steel requires low-carbon boiling steel, and no deoxidizer is added to the converter.

[0012] Furthermore, in the step 4), low carbon ferromanganese and ferrophosphorus are added when the RH is vacuumed for 5 minutes, and the addition is completed before the vacuum for 9 minutes; when the CO and CO2 in the exhaust gas are ≤3% after 12 minutes of vacuum, 4-6 kg / t steel of deoxidizer aluminum shots and 4-4.5 kg / t steel of synthetic slag are added; when the vacuum is applied for 15 minutes, 14.5-17 kg / t steel of ultra-low carbon ferrosilicon is added, and the pure degassing time after addition is ≥5 minutes), Als is controlled at 2500-3500 ppm during vacuum treatment. After the vacuum treatment is completed, 40 kg of slag modifier and 20 kg of aluminum shots are evenly spread on the slag surface.

[0013] Furthermore, in step 5), the CSP casting machine adopts full-process protection casting, and the argon flow rate of the protective casing is 7-9m 3 / h, the CSP tundish uses an air curtain retaining wall, controls the argon pressure to 0.08-0.10MPa, and adopts low-carbon and low-silicon covering agent + argon protection; the CSP molten steel superheat is 20-25℃, the crystallizer uses special protective slag for silicon steel, the crystallizer liquid level fluctuation is controlled at ±3.5%, and the pulling speed is 3.8-4.5m / min.

[0014] The beneficial effects of the present invention are: (1) Pretreatment of hot metal desulfurization, by adding metal magnesium powder and passivation lime powder in stages, effectively ensures the desulfurization effect; (2) The carbon-oxygen product of the converter is ≤0.0023 at the end point. The slag is strictly controlled during the converter tapping process. No deoxidizer is added during the converter tapping process, and no ladle synthetic slag is added. When the steel is tapped to 1 / 5, 3 to 4.5 kg / t of small lime is added with the steel flow. After the addition is completed, the bottom argon blowing is turned off, which is conducive to the control of non-metallic inclusions. (3) The RH refining process ensures the full floating removal of inclusions and improves the castability of the molten steel through efficient decarburization, effective deoxidation net cycle time and sufficient standing time. (4) CSP thin slab continuous casting: Through ladle protection pouring, slag detection and tundish air curtain retaining wall, special protective slag for silicon steel, low carbon and low silicon covering agent + argon protection, and crystallizer liquid level fluctuation control within ±3.5%, the secondary oxidation of molten steel and slag roll-up in the crystallizer are avoided, thus ensuring the cleanliness of the molten steel. DETAILED DESCRIPTION

[0015] The present invention is described in detail with reference to the following embodiments:

[0016] Example 1

[0017] The smelting method of producing W600 non-oriented silicon steel adopts the CSP thin slab continuous casting and rolling process, and the process flow is: molten iron in a mixing furnace → molten iron desulfurization pretreatment → BOF converter smelting → RH furnace refining → CSP thin slab continuous casting, wherein:

[0018] The molten iron in the mixing furnace: temperature 1315°C, Si: 0.68%, S: 0.065%

[0019] The hot metal desulfurization pretreatment is carried out by spraying metal magnesium powder and passivation lime powder. The hot metal is first sprayed with 50 kg of passivation lime powder, and then 150 kg of metal magnesium powder and 650 kg of passivation lime powder for desulfurization. After the material is unloaded, 70 kg of passivation lime powder is continued to be sprayed. The S of the hot metal before pretreatment is 0.065%, and the S of the hot metal after pretreatment is 0.002%. The S of the hot metal entering the furnace is ≤ 0.004%.

[0020] The BOF converter smelting: adopts a 120-ton BOF top and bottom blown converter, and the smelting process adopts bottom blowing argon throughout the process, and the bottom blowing gas supply intensity is ≥0.05m3 / (t*min); Determine the amount of lime added based on the Si content of molten iron, and the slag basicity is 3.15. Before the end of the converter, ensure that the oxygen lance low-position deep blowing time is ≥2min. It is forbidden to add iron ore near the end, and other raw materials can be used for temperature adjustment. End point [C]: 0.030%, [P]: 0.020%, [S]: 0.0035%, T = 1698℃, molten steel [O]: 670ppm; Strictly control the slag during steel tapping, the thickness of the ladle slag layer is less than 70mm, no deoxidizer is added during the steel tapping process, and no ladle synthetic slag is added. When the steel tapping reaches 1 / 5, 400kg of small-grain lime is added with the steel flow. After the addition is completed, the bottom blowing of argon is turned off.

[0021] The RH furnace refining: RH treatment must ensure that the gas pipeline for inserting tube lifting is well permeable; leak detection is performed before production to ensure that the minimum vacuum can reach below 67 Pa. The bottom blowing argon is closed throughout the RH process, the RH furnace molten steel inlet temperature is 1628℃, the molten steel [O]: 550ppm, and the inlet slag thickness is 170mm; RH determines the oxygen supplement amount according to the inlet carbon content, oxygen content and residual oxygen content control targets, and the residual oxygen content is 400ppm. 180kg of ferrophosphorus and 450kg of low-carbon ferromanganese are added during the 5 minutes of vacuum; the addition is completed before the 9 minutes of vacuum; after 12 minutes of vacuum, CO and CO2 in the exhaust gas are ≤3%, 600kg of aluminum shots and 500kg of synthetic slag are added for deoxidation and alloying; 1900kg of ultra-low carbon ferrosilicon is added during the 15 minutes of vacuum, and the pure degassing time after addition is ≥5min; the vacuum treatment is ended after 28 minutes of vacuum cycle, and 30kg of slag modifier and 20kg of aluminum shots are evenly spread on the slag surface. After the addition is completed, the hydraulic jacking is lowered to the lower limit, and the ladle car is driven to the wire feeding position for 18 minutes to ensure the denaturation and spheroidization rate of non-metallic inclusions such as MnS and Al2O3 in the steel, so that the inclusions can fully float and improve the cleanliness and quality of the molten steel. Before leaving the station, 80-100kg of carbon-free covering agent is added.

[0022] The mass percentages of the RH outgoing molten steel composition are: [C]: 0.0030%, [Mn]: 0.275%, [Si]: 1.43%, [P]: 0.0252%, [S]: 0.0033%, [Als]: 0.300%, [N]: 0.0030%, T[O]: 0.0038%, [Nb+V+Ti]: 0.0023%, and the remainder are Fe, Ca and unavoidable impurities.

[0023] The CSP thin slab continuous casting: adopts a two-stream vertical bending CSP thin slab continuous casting process. The molten steel after converter smelting and LF furnace refining is produced by CSP process. The casting process requires ladle protection pouring and ladle slag detection and control. The protective casing argon flow rate is 9m 3 / h, the CSP tundish uses an air curtain retaining wall, the argon pressure is controlled at 0.10MPa, and low-carbon and low-silicon covering agent + argon protection is adopted; the CSP molten steel superheat is 20-25℃, the crystallizer uses special protective slag for silicon steel, the crystallizer liquid level fluctuation is controlled at ±3.5%, the pulling speed is 4.3m / min, the billet temperature before swing shear is 910℃, and the cooling curve uses DSC6# curve, and finally W600 silicon steel billet is obtained.

[0024] Example 2

[0025] The smelting method of producing W600 non-oriented silicon steel adopts the CSP thin slab continuous casting and rolling process, and the process flow is: molten iron in a mixing furnace → molten iron desulfurization pretreatment → BOF converter smelting → RH furnace refining → CSP thin slab continuous casting, wherein:

[0026] The molten iron in the mixing furnace: temperature 1330°C, Si: 0.65%, S: 0.064%

[0027] The molten iron desulfurization pretreatment: the molten iron is pretreated by spraying metal magnesium powder and passivating lime, the metal magnesium powder is 133kg, the passivating lime powder is 500kg, and the theoretical amount is completed after the feeding is completed. Before and after the spraying, 50kg of passivating lime powder needs to be sprayed separately. The S of the molten iron before pretreatment is 0.064%, and the S of the molten iron after pretreatment is 0.002%.

[0028] The BOF converter smelting: adopts a 120-ton BOF top and bottom double-blown converter, and the molten iron entering the converter is S: 0.002%; the smelting process adopts bottom blowing argon throughout the process, and the bottom blowing gas supply intensity is ≥0.05m 3 / (t*min); Determine the amount of lime added based on the Si content of molten iron, and the slag basicity is 2.98. Before the end of the converter, ensure that the oxygen lance low-position deep blowing time is ≥2min. It is forbidden to add iron ore near the end, and other raw materials can be used for temperature adjustment. End point molten steel [C]: 0.032%, [P]: 0.010%, [S]: 0.0030%, T=1690℃, T[O]: 667ppm; Slag is strictly controlled during steel tapping, and the thickness of the ladle slag layer is less than 70mm. No deoxidizer is added during the steel tapping process, and no ladle synthetic slag is added. When the steel tapping reaches 1 / 5, 380kg of small-grain lime is added with the steel flow. After the addition is completed, the bottom blowing of argon is turned off.

[0029] The RH furnace refining: RH treatment must ensure that the gas pipeline for inserting tube lifting is well permeable; leak detection is performed before production to ensure that the minimum vacuum can reach below 67 Pa. Bottom argon blowing is closed throughout the RH process, the RH furnace molten steel inlet temperature is 1638°C, molten steel [O]: 550ppm, and the inlet slag thickness is 170mm; RH determines the oxygen supplement amount based on the inlet carbon content, oxygen content and residual oxygen content control targets, and the residual oxygen content target is controlled at 400ppm. Before RH deoxidation, add 190kg of ferrophosphorus and 400kg of low-carbon ferromanganese when the vacuum is on for 5min; the addition is completed before 9min of vacuum; 700kg of aluminum shots and 520kg of synthetic slag are added when the CO and CO2 in the exhaust gas are ≤3% for 12min of vacuum to carry out deoxidation and alloying; 1870kg of ultra-low carbon ferrosilicon is added for 15min of vacuum, and the pure degassing time after addition is ≥5min; the vacuum treatment time is 28min. After the vacuum treatment is completed, 40kg of slag modifier and 20kg of aluminum shots are evenly spread on the slag surface. After the addition is completed, the hydraulic jacking is lowered to the lower limit, and the ladle car is driven to the wire feeding position to keep the molten steel still for 20min to ensure the denaturation and spheroidization rate of non-metallic inclusions such as MnS and Al2O3 in the steel, so that the inclusions can fully float and improve the cleanliness and quality of the molten steel. Before leaving the station, 80-100kg of carbon-free covering agent is added.

[0030] The mass percentages of the RH outgoing molten steel composition are: [C]: 0.0022%, [Mn]: 0.295%, [Si]: 1.328%, [P]: 0.0256%, [S]: 0.0028%, [Als]: 0.335%, [N]: 0.0020%, T[O]: 0.0035%, [Nb+V+Ti]: 0.0018%, and the remainder are Fe, Ca and unavoidable impurities.

[0031] The CSP thin slab continuous casting adopts a two-strand vertical bending CSP thin slab continuous casting process, the molten steel after converter smelting and LF furnace refining treatment is produced by the CSP process, the casting process requires ladle protection pouring and ladle slag detection and control, the protective sleeve argon flow rate is 9m3 / h, the CSP tundish uses an air curtain retaining wall, the argon pressure is controlled to be 0.10MPa, and low-carbon and low-silicon covering agent + argon protection is adopted; the CSP molten steel superheat is 20-25°C, the crystallizer uses silicon steel special protective slag, the crystallizer liquid level fluctuation is controlled at ±3.5%, the pulling speed is 4.2m / min, the billet temperature before swing shear is 910°C, the cooling curve uses the DSC6# curve, and finally the W600 silicon steel billet is obtained.

Claims

1. A smelting method for producing W600 non-oriented silicon steel by CSP process, characterized in that: The following steps are involved: 1) Hot metal pretreatment: Hot metal pretreatment is carried out by spraying metal magnesium powder and passivation lime powder. The hot metal is first sprayed with 0.35-0.42 kg / t of passivation lime powder, and then with metal magnesium powder and passivation lime powder for desulfurization. The ratio of metal magnesium powder to passivation lime powder is 1:4-1:

6. After the theoretical amount of material is discharged, continue to spray 0.4-0.6 kg / t of passivation lime powder. The S of the hot metal entering the furnace is ≤0.004%. 2) BOF converter: endpoint control [C]: 0.03-0.05%, [P]: ≤0.025%, [S]: ≤0.0035%, T=1690-1710℃, carbon-oxygen product ≤0.0023; slag is strictly controlled during steel tapping, the thickness of the ladle slag layer is less than 70mm, no deoxidizer is added during steel tapping, no ladle synthetic slag is added, small-grain lime is added with the steel flow when 1 / 5 of the steel is tapped, the addition amount is 3-4.5kg / t steel, and the bottom argon blowing is turned off after the addition is completed. 3) RH furnace: Bottom blowing argon is turned off throughout the process. The inlet temperature of the RH furnace is ≥1625℃, the carbon content is ≤0.045%, the oxygen content is 400-600ppm, and the inlet slag thickness is ≤200mm; the RH furnace determines the oxygen supplement amount according to the inlet carbon content, oxygen content and residual oxygen content control targets, and the residual oxygen content target is controlled at 300-450ppm. 4) RH vacuum treatment time is 28 to 35 minutes. After the vacuum treatment is completed, 40 kg of steel slag modification agent is evenly spread on the slag surface. After the addition of steel slag modification agent is completed, the hydraulic jacking is lowered to the lower limit, and the ladle car is driven to the wire feeding position to keep the molten steel still for 15 to 20 minutes. Before leaving the station, 80 to 100 kg of carbon-free covering agent is added. The mass percentage of the RH steel molten steel composition is: [C]: 0.0015 to 0.0035%, [Mn]: 0.30 to 0.45%, [Si] 1.3 to 1.5%, [P]: ≤0.020%, [S]: ≤0.0030%, [Als]: 0.30 to 0.40%, [N]: ≤0.0030%, [O]: ≤0.0040%, [Nb+V+Ti]: ≤0.0025%, and the remainder is Fe and Ca and unavoidable impurities. 5) The molten steel obtained in step 4) is cast into W600 non-oriented silicon steel billet by CSP continuous casting.

2. The smelting method for producing W600 non-oriented silicon steel by CSP process according to claim 1, characterized in that: In the step 1), the molten iron is pre-desulfurized to 0.50%≤Si≤0.85%, S≤0.060%.

3. The smelting method for producing W600 non-oriented silicon steel by CSP process according to claim 1, characterized in that: In step 2), the BOF converter adopts full bottom blowing of argon, and the bottom blowing intensity is ≥ 0.05m 3 / (t·min). The amount of lime added is determined based on the Si content of molten iron, and the slag basicity is controlled at 2.9-3.

5. Before the end of the converter, ensure that the oxygen lance low-position deep blowing time is ≥2min. It is forbidden to add iron ore near the end, and other raw materials can be used for temperature adjustment.

4. The smelting method for producing W600 non-oriented silicon steel by CSP process according to claim 1, characterized in that: The RH treatment in step 3) must ensure that the gas pipeline for inserting the tube to lift is well permeable; leak detection is performed before production to ensure that the minimum vacuum can reach below 67 Pa. Before smelting non-oriented silicon steel, low-carbon steel must be used to wash the RH furnace, the molten steel requires low-carbon boiling steel, and no deoxidizer is added to the converter.

5. The smelting method for producing W600 non-oriented silicon steel by CSP process according to claim 1, characterized in that: In the step 4), low carbon ferromanganese and ferrophosphorus are added when the RH is in vacuum for 5 minutes, and the addition is completed before the vacuum for 9 minutes; when the CO and CO2 in the exhaust gas are ≤3% after 12 minutes of vacuum, 4-6 kg / t steel of deoxidizer aluminum shots and 4-4.5 kg / t steel of synthetic slag are added; when the vacuum is 15 minutes, 14.5-17 kg / t steel of ultra-low carbon ferrosilicon are added, and the pure degassing time after addition is ≥5 minutes), Als is controlled at 2500-3500 ppm during vacuum treatment. After the vacuum treatment is completed, 40 kg of slag modifier and 20 kg of aluminum shots are evenly spread on the slag surface.

6. The smelting method for producing W600 non-oriented silicon steel by CSP process according to claim 1, characterized in that: In step 5), the CSP casting machine adopts full-process protection casting, and the argon flow rate of the protective casing is 7-9m 3 / h, the CSP tundish uses an air curtain retaining wall, controls the argon pressure to 0.08-0.10MPa, and adopts low-carbon and low-silicon covering agent + argon protection; the CSP molten steel superheat is 20-25℃, the crystallizer uses special protective slag for silicon steel, the crystallizer liquid level fluctuation is controlled at ±3.5%, and the pulling speed is 3.8-4.5m / min.