A smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel

Abstract

The invention discloses a smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel. The smelting method comprises the following steps: KR molten iron pre-desulfurization, converter smelting, argon station top slag modification, RH refining, and continuous casting to form ingots. In the RH refining step, the invention adds rare earth La after desulfurization for alloying, then performs calcium treatment, and controls the soft blowing time before leaving the station to be ≥6 minutes, so that inclusions in the molten steel are fully floated and removed, thereby preventing nozzle blockage during the continuous casting process, thereby improving the continuous casting and pouring properties of the high-grade rare earth non-oriented silicon steel.

Description

Technical Field

[0001] The invention belongs to the technical field of silicon steel smelting, and particularly relates to a smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel. Background Art

[0002] High-grade non-oriented silicon steel boasts excellent properties such as low iron loss, high magnetic induction, and low noise. It is a key functional material for the manufacture of high-precision, cutting-edge iron cores used in electromagnetic converters. It is widely used in high-end emerging industries such as new energy vehicle drive motors, variable-frequency compressors, drone motors, and intelligent robot servo motors. However, the continuous casting and pouring properties of high-grade non-oriented silicon steel during smelting are poor, directly affecting the quality of the resulting high-grade non-oriented silicon steel.

[0003] Currently, the rare earth alloy yield during the smelting of high-grade rare earth non-oriented silicon steel is low, generally below 20%. Furthermore, during continuous pouring of molten steel, rare earth inclusions are easily adsorbed on the inner wall of the nozzle. As the adsorption of inclusions increases, the molten steel in the tundish cannot flow into the mold, causing casting to be interrupted and the production line to stop. Low rare earth alloy yield and poor continuous pourability during rare earth steel smelting have become common problems in the industry. Summary of the Invention

[0004] The object of the present invention is to provide a smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel. The high-grade rare earth non-oriented silicon steel smelted by the method of the present invention has very little change in the stopper rod position during the continuous casting process, and the continuous casting and pouring properties are not affected.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel, the smelting method comprising the following steps: KR molten iron pre-desulfurization - converter smelting - argon station top slag modification - RH refining - continuous casting into ingots;

[0007] In the KR hot metal pre-desulfurization step, after the blast furnace hot metal enters the KR station, the slag is skimmed to a metal bright surface of ≥95%, smokeless refining agent is added to the slag surface, and KR desulfurizer is added to pre-desulfurize to S≤0.0010%. After the desulfurization is completed, the slag is skimmed twice;

[0008] In the converter smelting step, the temperature of the molten iron in the converter is 1305-1370°C, the tapping P is controlled to be ≤0.012%, C: 0.035-0.055, O: 0.040%-0.070%, the ladle top slag thickness is ≤60mm, lime is added for slag washing after tapping, and the basicity CaO / SiO2 is required to be 3-3.5;

[0009] In the argon station top slag modification step, 0.80-1.5 kg / t steel top slag modifier with an Al content of 40% is added to modify the top slag;

[0010] In the RH refining step, decarburization is performed to a carbon content of ≤0.0015%, aluminum particles are added for deoxidation, and then the alloy composition is adjusted to meet the design requirements. After the alloy adjustment is completed, a desulfurizer is added for desulfurization to a carbon content of ≤0.0015%. After a 3-minute cycle, bauxite is added, and then a rare earth pure lanthanum-cerium alloy is added. After the alloy is added, the cycle time is ≥6 minutes before the steel is broken. After the steel is broken, the calcium wire is fed. Before leaving the station, the soft blowing time is ≥6 minutes, and the calming time is maintained for ≥20 minutes, so that the rare earth inclusions in the steel liquid can fully float up, thereby solving the problem of continuous casting and pouring of high-grade rare earth silicon steel.

[0011] In the continuous casting step, a filter is used in the tundish to replace the traditional retaining wall and dam, and argon is used to protect the casting throughout the entire process. The casting process adopts constant casting speed control, the casting speed range is 1.00-1.25m / min, the superheat is controlled at 10-30°C, electromagnetic stirring is used, and the automatic slag control device is controlled at the highest sensitivity level to prevent slag from contaminating the molten steel.

[0012] The chemical composition and weight percentage of the high-grade rare earth non-oriented silicon steel are as follows: C≤0.0020%, Mn0.10%~0.30%, S≤0.0010%, P≤0.015%, Si 2.3%~2.5%, Als 0.8%~1.3%, La+Ce0.002%~0.008%, N≤0.0015%, O≤0.0010%, and the rest are Fe and unavoidable impurities.

[0013] In the KR molten iron pre-desulfurization step, the molten iron temperature is ≥1250°C; the time interval between two slag removals is at least 5 minutes, preferably 5-10 minutes, and the metal bright surface of the molten iron ladle is ≥95%.

[0014] In the converter smelting step, the temperature of the molten steel is 1640-1670° C.; 2.0-2.5 kg / t of steel lime is added for slag washing, and the basicity CaO / SiO2 is required to be 3-3.5.

[0015] In the argon station top slag modification, 0.8-1.5 kg / t steel modifier is added to the slag surface before the molten steel leaves the station to modify the top slag. During the modification process, the bottom blowing gas is closed to prevent reaction with free oxygen in the molten steel.

[0016] In the RH refining step, the amount of bauxite added is 1.7-2.2 kg / t steel; the amount of rare earth pure lanthanum-cerium alloy added is 0.10-0.25 kg / t steel.

[0017] In the RH refining step, the target composition of the RH refining top slag is: CaO / SiO2≥5.0, CaO / Al2O31.5-1.8, ∑(FeO+MnO)≤1.5%.

[0018] In the continuous casting step, the water inlet, the space between the plates and the stopper rod are sealed with argon gas.

[0019] In the smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel provided by the present invention, in the KR molten iron pre-desulfurization step, after the blast furnace molten iron enters the KR station, the slag is skimmed to a metal bright surface of ≥95%, 0.40-0.60 kg / t of smokeless refining agent is added to the slag surface, and then 4-6 kg / t of KR desulfurizer is added for pre-desulfurization to S≤0.0010%. After the desulfurization is completed, two slag skimming treatments are performed, the time interval between the two skimmings is at least 5 minutes, preferably 5-10 minutes, the metal bright surface of the molten iron ladle is ≥95%, and the temperature of the molten iron entering the converter is ≥1250°C.

[0020] In the converter smelting step, the temperature of the molten iron in the converter is 1305-1370°C, the tapping P is controlled to be ≤0.012%, C: 0.035-0.055, O: 0.040%-0.070%, the ladle top slag thickness is ≤60mm, and after tapping, 2.0-2.5kg / t of steel lime is added for slag washing, and the basicity CaO / SiO2 is required to be 3-3.5;

[0021] In the top slag modification step of the argon station, 0.8 to 1.5 kg / t of steel top slag modifier is added to the slag surface before the molten steel leaves the station to modify the top slag. During the modification process, the bottom blowing gas is turned off to prevent reaction with free oxygen in the molten steel.

[0022] In the RH refining step, the molten steel is raised to a processing station. After the vacuum level in the vacuum tank drops to ≤67 Pa, the decarburization mode is entered. The decarburization time is ≥10 minutes. The steel is decarburized to a carbon content of ≤0.0012%. Aluminum particles are added for deoxidation. The alloy composition is then adjusted to meet design requirements. After the alloy adjustment is completed, a desulfurizer is added to desulfurize the steel to a sulfur content of ≤0.0015%. After a 3-minute cycle, 1.7-2.2 kg / t of bauxite is added to adjust the RH top slag composition. Then, 0.10-0.25 kg / t of pure lanthanum-cerium alloy of rare earth is added. After the alloy is added, the steel is discharged after a cycle of ≥6 minutes. The rare earth element is primarily used to modify inclusions in the desulfurized molten steel, causing fine inclusions ≤1 μm in the molten steel to aggregate, grow, float, and be removed, thereby improving the purity of the molten steel. The timing of adding rare earth alloys is critical. Adding them too early will easily vaporize and dislodge under extreme vacuum, resulting in a very low rare earth alloy yield. Adding rare earth alloys after the vacuum is broken will prevent the rare earth inclusions from floating up and being removed from the molten steel in time, easily blocking the pouring nozzle and seriously affecting continuous casting. The target composition of the top slag in RH refining is: CaO / SiO2 ≥ 5.0, CaO / Al2O3 1.5-1.8, ∑(FeO+MnO) ≤ 1.5%.

[0023] After the molten steel breaks through the air, it is fed into the calcium line at a rate of 0.8 to 2.2 m / t. The soft blowing time before leaving the station is ≥6 min, and the calming time is ≥20 min to ensure that the rare earth inclusions in the molten steel are fully floated, solving the problem of continuous casting and pouring of high-grade rare earth silicon steel. The purpose of calcium treatment is to convert inclusions that are easy to block the water outlet into low-melting-point composite oxides, which are conducive to the removal of polymerization growth from the molten steel.

[0024] During the continuous casting process, filters replace traditional retaining walls and dams in the tundish to effectively remove inclusions from the molten steel. Argon is used throughout the pouring process, and the water inlet, interplate space, and stopper are sealed with argon to prevent secondary oxidation of the molten steel during the pouring process, which could lead to Al2O3 loss and increase in Al2O3 inclusions. Constant casting speed control is used during the pouring process to prevent slag contamination caused by liquid level fluctuations. The casting speed range is 1.00-1.25 m / min, and the superheat is controlled between 10°C and 30°C. Electromagnetic stirring is used to increase the proportion of equiaxed grains, and the automatic slag discharge control device is set to the highest sensitivity setting to prevent slag contamination of the molten steel.

[0025] The present invention also provides a high-grade rare earth non-oriented silicon steel. The smelting of the high-grade rare earth non-oriented silicon steel is carried out by the above-mentioned smelting method. The high-grade rare earth non-oriented silicon steel obtained by the smelting method has stable casting quality and low inclusion content, and can provide high-quality castings for high-grade rare earth silicon steel finished products.

[0026] The smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel provided by the present invention is characterized in that the whole process is linked controlled, a refining agent is added to the slag surface during KR pre-desulfurization treatment, and then a KR desulfurizer is added for desulfurization, the top slag of the iron ladle is adjusted, and the desulfurization efficiency is improved by using the top slag desulfurization and the addition of the KR desulfurizer for desulfurization, and the melting point of the top slag is increased, so that the top slag with a very high sulfur content is easy to be scraped off and cleaned, thereby preventing sulfur from returning to the converter, reducing the amount of desulfurizer added in the RH vacuum link, and reducing the content of exogenous inclusions in the steel; a top slag modifier is added in the CAS station to reduce the oxygen content in the slag, which is conducive to improving the RH desulfurization efficiency and reducing the amount of desulfurizer added and the content of exogenous inclusions; and bauxite is added after the RH desulfurizer is added to adjust the top slag composition, which is conducive to improving the ability of the top slag to absorb inclusions. Through the above measures, the amount of RH desulfurizer added is reduced to reduce the number of exogenous inclusions. Finally, pure rare earth lanthanum-cerium alloy is added to the RH vacuum tank for alloying, and then calcium treatment is performed to modify the inclusions in the steel to generate low-melting-point composite inclusions. The fine inclusions ≤1um in the molten steel are aggregated and grown and then floated up for removal, thereby improving the purity of the molten steel. The soft blowing time before leaving the station is controlled to be ≥6min, so that the inclusions in the molten steel are fully floated and removed, preventing the nozzle from being blocked during the continuous casting process and causing the pouring to be stopped, thereby improving the continuous casting and pouring of high-grade rare earth non-oriented silicon steel. The present invention optimizes the steelmaking process and utilizes rare earths to denature inclusions in the steel, thereby reducing the number of fine inclusions ≤1 μm in the steel. Calcium treatment and appropriate soft blowing time are then used to greatly reduce the content of composite rare earth inclusions in the steel. Simultaneously, a filter device is used in the tundish during continuous casting to further reduce the content of rare earth inclusions in the steel, thereby preventing rare earth inclusions from adhering to the inner wall of the nozzle and blocking the nozzle, thereby improving continuous casting and pouring properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 A flow control device for a continuous casting tundish used in the present invention;

[0028] Figure 2 This is the curve of stopper rod position change during the continuous casting process of rare earth high-grade non-oriented electrical steel in Example 1;

[0029] Figure 3 The following are typical results of fine inclusion detection in steel with and without rare earth addition in Example 1, where (a) is without rare earth addition and (b) is with rare earth addition.

[0030] Figure 4 This is the curve of stopper rod position change during the continuous casting process of rare earth high-grade non-oriented electrical steel in Example 2;

[0031] Figure 5 The following are typical results of fine inclusion detection in steel with and without rare earth addition in Example 2, where (a) is without rare earth addition and (b) is with rare earth addition.

[0032] Figure 6This is the curve of stopper rod position change during the continuous casting process of rare earth high-grade non-oriented electrical steel in Example 3;

[0033] Figure 7 Typical results of fine inclusion detection in steel with and without rare earth addition in Example 3, where (a) is without rare earth addition and (b) is with rare earth addition;

[0034] Figure 8 This is the curve of stopper rod position change during continuous casting of rare earth high-grade non-oriented electrical steel in Comparative Example 1;

[0035] Figure 9 This is the curve of the stopper rod position change during the continuous casting process of the rare earth high-grade non-oriented electrical steel in Comparative Example 2. DETAILED DESCRIPTION

[0036] The present invention is described in detail below with reference to the embodiments.

[0037] The present invention adopts a 210t top and bottom combined blown converter for smelting, and selects high-grade rare earth silicon steel XG300WG-C, the composition design of which is shown in Table 1.

[0038] Table 1 List of design composition values ​​of high grade rare earth silicon steel XG300WG-C of the present invention

[0039]

[0040] Example 1

[0041] Because the number of steelmaking furnaces must match the production of hot rolling heating furnaces, a maximum of 6 furnaces can be produced at a time. If too many furnaces are produced, hot rolling cannot be carried out in time, cracks are easily generated after the casting is cooled, and the casting is prone to breakage during the hot rolling process. Therefore, this embodiment arranges one tundish for continuous casting of 6 furnaces of steel, the iron bag loading capacity is 204±1t, the total loading capacity is 240±2t, and the steel output is 225~235t.

[0042] 1. Process control

[0043] (1) KR pre-desulfurization, the specific parameters are shown in Table 2.

[0044] Table 2

[0045]

[0046]

[0047] (2) Converter smelting, the specific parameter control is shown in Table 3.

[0048] Table 3

[0049]

[0050] (3) RH refining, the specific parameter control is shown in Table 4.

[0051] Table 4 RH refining process control parameters

[0052]

[0053] (4) Continuous casting

[0054] The continuous casting tundish uses a filter to remove inclusions in the molten steel. Argon is used to protect the casting process. The water inlet, the plate space and the stopper are sealed with argon. A constant casting speed of 1.15m / min is used. The slag detection of the large ladle is adjusted to the highest sensitivity level to prevent slag. The composition of the tundish sample analysis is shown in Table 5, and the change curve of the tundish stopper is shown in Figure 2 .

[0055] Table 5 Composition of molten steel in continuous casting (%)

[0056]

[0057]

[0058] As can be seen from Table 1, the yield of rare earth alloy is relatively high when the process of the present invention is used, which is basically maintained above 46% and the highest reaches 52.25%. Figure 2 It can be seen that the liquid level is relatively stable throughout the entire pouring process. The liquid level fluctuates slightly starting from the fourth furnace, but the stopper rod does not show an upward trend, and the continuous pouring performance is good.

[0059] The overall results of the smelting of high-grade rare earth non-oriented electrical steel using this patented process show a high rare earth alloy yield, excellent continuous casting performance, and no interruptions caused by water blockage, demonstrating a significant continuous casting effect. The casting results of this example suggest that the number of continuous casting furnaces could be further extended. However, due to the matching of our steelmaking and hot rolling furnaces, this was not further extended for verification.

[0060] 2. Inclusion detection results of ingots

[0061] The same grade of steel as the present invention without rare earth addition (other things are the same as Example 1, except that rare earth is not added) and the low-magnification sample of Example 1 were taken and processed to observe the fine inclusions (≤1um) under the microscope. During the detection process, the magnification was kept at 15000 to observe the inclusions smaller than 1μm. 30 fields of view were randomly selected during the observation. The corresponding statistical results are shown in Table 6. The typical fields of view are as follows: Figure 3 shown.

[0062] Table 6 Statistics of the number of fine inclusions (<1 μm) in steel after rare earth treatment

[0063] La+Ce content in steel (ppm) <![CDATA[Number density of inclusions (per mm 2 )]]> Not added 840.0 56 168.0

[0064] As can be seen from the table and figure above, the number density of fine inclusions (≤1um) in the ingot without rare earth addition reaches 840 / mm 2 After adding rare earth, the number density of fine inclusions in the ingot is reduced to 168 / mm 2 The addition of rare earth significantly reduces the content of fine inclusions in the ingot and improves the purity of the molten steel.

[0065] Example 2

[0066] In this embodiment, one tundish is arranged to continuously cast six heats of steel, the iron loading is 204±1t, the total loading is 240±2t, and the steel output is 225-235t. The process of the present invention is taken as an example to further illustrate the present invention.

[0067] 1. Process control

[0068] (1) KR pre-desulfurization, the specific parameter control is shown in Table 7.

[0069] Table 7

[0070]

[0071] (2) Converter smelting, the specific parameter control is shown in Table 8.

[0072] Table 8

[0073]

[0074] (3) RH refining, the specific parameter control is shown in Table 9.

[0075] Table 9 RH refining process control parameters

[0076]

[0077] (4) Continuous casting

[0078] The continuous casting tundish uses a filter to remove inclusions in the molten steel. Argon is used to protect the casting process. The water inlet, the plate space and the stopper are sealed with argon. A constant casting speed of 1.20m / min is used. The slag detection of the large ladle is adjusted to the highest sensitivity level to prevent slag. The composition of the tundish sample analysis is shown in Table 10, and the change curve of the tundish stopper is shown in Figure 4 .

[0079] Table 10 Composition of molten steel in continuous casting (%)

[0080] Furnace number C Mn S P Si Als La+Ce O N Rare earth recovery rate, % 2-01401 0.0018 0.14 0.0009 0.014 2.41 0.98 0.0062 0.0009 0.0014 46.97 2-01402 0.0020 0.15 0.0008 0.014 2.42 0.91 0.0066 0.0008 0.0012 50.00 2-01403 0.0019 0.13 0.0010 0.013 2.45 0.99 0.0064 0.0010 0.0015 48.48 2-01404 0.0017 0.12 0.0009 0.011 2.43 0.93 0.0066 0.0009 0.0008 50.00 2-01405 0.0019 0.14 0.0008 0.012 2.42 1.01 0.0065 0.0009 0.0012 49.24 2-01406 0.0018 0.12 0.0007 0.010 2.41 0.98 0.0068 0.0007 0.0014 51.52

[0081] As can be seen from the table above, the yield of rare earth alloys is relatively high when the process of the present invention is used, which is basically maintained at above 46%, and the highest reaches 51.52%. Figure 4It can be seen that the liquid level in the crystallizer did not rise in the first two batches of pouring. Starting from the third batch, the liquid level slowly rose by about 6 mm. However, from the fourth batch until the end of pouring, the liquid level was stable and no upward trend appeared.

[0082] Judging from the overall situation of the smelting of high-grade rare earth non-oriented electrical steel using this patented process, the rare earth alloy yield is high, and the continuous casting has good pourability. In the middle and late stages of continuous casting, the liquid level did not show a trend of continuing to rise, and there was no water blockage resulting in interruption of casting. The continuous casting effect is significant.

[0083] 2. Inclusion detection results of ingots

[0084] In Example 2, a low-magnification sample was processed and then observed for fine inclusions (≤1 μm) under a microscope. During the inspection, the magnification was maintained at 15,000 to observe inclusions smaller than 1 μm. 30 fields of view were randomly selected during the observation. The corresponding statistical results are shown in Table 11. Typical fields of view are as follows: Figure 5 shown.

[0085] Table 11 Statistics of the number of fine inclusions (<1μm) in steel after rare earth treatment

[0086] La+Ce content in steel (ppm) <![CDATA[Number density of inclusions (per mm 2 )]]> Not added 840.0 66 140.0

[0087] From the above table and Figure 5 It can be seen that the number density of fine inclusions (≤1 μm) in the billet after adopting the process of the present invention is reduced from 840 / mm to 1000 / mm compared with the billet without rare earth addition. 2 Reduced to 140 pieces / mm 2 The addition of rare earth significantly reduces the content of fine inclusions in the ingot and improves the purity of the molten steel.

[0088] Example 3

[0089] In this embodiment, one tundish is arranged to continuously cast six heats of steel, the iron loading is 204±1t, the total loading is 240±2t, and the steel output is 225-235t. The process of the present invention is taken as an example to further illustrate the present invention.

[0090] 1. Process control

[0091] (1) KR pre-desulfurization, the specific parameter control is shown in Table 12.

[0092] Table 12

[0093]

[0094] (2) Converter smelting: the specific parameter control is shown in Table 13.

[0095] Table 13

[0096]

[0097] (3) RH refining, the specific parameter control is shown in Table 14.

[0098] Table 14 RH refining process control parameters

[0099]

[0100] (4) Continuous casting

[0101] The continuous casting tundish uses a filter to remove inclusions in the molten steel. Argon is used to protect the casting process. The water inlet, the plate space and the stopper are sealed with argon. A constant casting speed of 1.15m / min is used. The slag detection of the large ladle is adjusted to the highest sensitivity level to prevent slag. The composition of the tundish sample analysis is shown in Table 15 below, and the change curve of the tundish stopper is shown in Figure 6 .

[0102] Table 15 Composition of molten steel in continuous casting (%)

[0103] Furnace number C Mn S P Si Als La+Ce O N Rare earth recovery rate, % 2-01489 0.0019 0.13 0.0010 0.014 2.48 1.02 0.0076 0.0010 0.0011 49.35 2-01490 0.0018 0.15 0.0009 0.015 2.43 0.98 0.0073 0.0009 0.0009 47.40 2-01491 0.0020 0.14 0.0009 0.012 2.40 0.94 0.0076 0.0008 0.0006 49.35 2-01492 0.0016 0.14 0.0008 0.009 2.41 0.99 0.0078 0.0010 0.0009 50.65 2-01493 0.0019 0.12 0.0010 0.013 2.45 0.93 0.0072 0.0008 0.0010 46.75 2-01494 0.0020 0.13 0.0008 0.011 2.43 0.99 0.0079 0.0007 0.0011 51.30

[0104] As can be seen from the table above, the yield of rare earth alloys is relatively high when the process of the present invention is used, which is basically maintained at above 46%, and the highest reaches 51.30%. Figure 6 It can be seen that the liquid level in the crystallizer did not rise during the pouring of the first furnace. From the start of the second furnace to the end of pouring, the liquid level rose slowly by about 10 mm, which did not affect the continuous casting and pouring performance.

[0105] Judging from the overall situation of the smelting of high-grade rare earth non-oriented electrical steel using this patented process, the rare earth alloy yield is high, and the liquid level in the ladle of continuous casting for 6 batches of steel only rises by about 10mm. There is no water blockage resulting in interruption of casting, and the continuous casting effect is good.

[0106] 2. Inclusion detection results of ingots

[0107] In Example 3, a low-magnification sample was processed and then observed for fine inclusions (≤1 μm) under a microscope. During the inspection, the magnification was maintained at 15,000 to observe inclusions smaller than 1 μm. 30 fields of view were randomly selected during the observation. The corresponding statistical results are shown in the following table. Typical fields of view are as follows: Figure 7 shown.

[0108] Table 16 Statistics of fine inclusions (<1μm) in steel after rare earth treatment

[0109] La+Ce content in steel (ppm) <![CDATA[Number density of inclusions (per mm 2 )]]> Not added 840.0 76 112.0

[0110] From the above table and Figure 7It can be seen that the number density of fine inclusions (≤1 μm) in the billet after adopting the process of the present invention is reduced from 840 / mm to 1000 / mm compared with the billet without rare earth addition. 2 Reduced to 112 pieces / mm 2 The addition of rare earth significantly reduces the content of fine inclusions in the ingot and improves the purity of the molten steel.

[0111] Comparative Example 1

[0112] In this comparative example, a total of six heats of steel were cast continuously in one tundish, with a tundish loading of 204±1t, a total loading of 240±2t, and a tapping volume of 225-235t. Some processes were treated with process parameters outside the scope of the present invention as an example to illustrate the technical solution of the present invention.

[0113] 1. Process control

[0114] (1) KR pre-desulfurization

[0115] The KR process is performed according to the KR process of the present invention, and the specific parameters are shown in Table 17 below.

[0116] Table 17

[0117]

[0118] (2) Converter smelting

[0119] The converter smelting (converter + CAS process) process is carried out according to the process of the present invention, and the specific parameters are shown in Table 18 below.

[0120] Table 18

[0121]

[0122] (3)RH refining

[0123] In the RH refining process, the rare earth alloy of this comparative example is added in advance to after alloying and before desulfurization, and the remaining processes are carried out according to the process of the present invention. Specific parameters are shown in Table 19 below.

[0124] Table 19 RH refining process control parameters

[0125]

[0126] (4) Continuous casting

[0127] The continuous casting tundish uses a filter to remove inclusions in the molten steel. Argon is used to protect the casting process. The water inlet, the plate space and the stopper are sealed with argon. A constant casting speed of 1.15m / min is used. The slag detection of the large ladle is adjusted to the highest sensitivity level to prevent slag. The composition of the tundish sample analysis is shown in Table 20 below, and the change curve of the tundish stopper is shown in Figure 8 .

[0128] Table 20 Composition of molten steel in continuous casting (%)

[0129]

[0130]

[0131] As can be seen from the composition in the above table, this comparative example adopts a process outside the process range of the present invention. The rare earth alloy is added in advance, which leads to easy gasification and removal under extreme vacuum. The rare earth yield is very low, basically maintained below 25%, and the lowest reaches 16.36%. Figure 8 It can be seen that the liquid level is stable throughout the entire pouring process and there is no upward trend.

[0132] From the overall situation of the smelting of high-grade rare earth non-oriented electrical steel, the rare earth alloy is added before RH desulfurization, and the remaining processes are carried out according to the process parameters of the present invention. Although the continuous casting and pouring properties are good, the yield of rare earth alloy is very low. For actual production, the smelting cost is high and it is not worth promoting.

[0133] 2. Inclusion detection results of ingots

[0134] In this comparative example, a low-magnification sample was taken from the second casting furnace and processed to observe fine inclusions (≤1 μm) under a microscope. During the detection process, the magnification was maintained at 15,000 to observe inclusions smaller than 1 μm. 30 fields of view were randomly selected during the observation. The corresponding statistical results are shown in Table 21 below.

[0135] Table 21 Statistics of fine inclusions (<1μm) in steel after rare earth treatment

[0136] La+Ce content in steel (ppm) <![CDATA[Inclusion number density (number / mm 2 )]]> Not added 840.0 26 (Comparative Example 1) 532.0

[0137] As can be seen from the table above, the number density of fine inclusions (≤1 μm) in the billet after using the process outside the scope of the present invention is reduced from 840 / mm to 1000 / mm compared with the billet without rare earth addition. 2 Reduced to 532 pieces / mm 2 Although the addition of rare earth reduces the content of fine inclusions in the ingot, the effect is not obvious. The main reason is that the amount of rare earth actually participating in the modification of inclusions is small, and the yield of rare earth alloy is very low.

[0138] Comparative Example 2

[0139] This comparative example planned to continuously cast six heats of steel using one tundish. The iron loading was 204±1t, the total loading was 240±2t, and the tapping volume was 225-235t. The rare earth elements in the RH process were added via a cored wire feeder after the RH was broken. After a soft-blow time of ≥6 minutes, the steel was pulled out of the station and transferred to the continuous casting platform for casting. The remaining process parameters were implemented using the process parameters of the present invention. After the third heat of rare earth steel was poured, severe nozzle blockage occurred, leading to a casting halt.

[0140] 1. Process control

[0141] (1) KR pre-desulfurization

[0142] The KR process is performed according to the KR process of the present invention, and the specific parameters are shown in Table 22 below.

[0143] Table 22

[0144]

[0145] (2) Converter smelting

[0146] The converter smelting (converter + CAS process) process is carried out according to the process of the present invention, and the specific parameters are shown in Table 23 below.

[0147] Table 23

[0148]

[0149] (3)RH refining

[0150] During the RH refining process, the rare earth alloy of this comparative example was added in the form of cored wire via a wire feeder. This addition occurred after the RH was broken through the air. After the rare earth wire was added, bottom blowing and soft blowing were performed for ≥6 minutes. The remaining processes were carried out in accordance with the present invention. Specific parameters are shown in Table 24. After the rare earth was added, the ladle slag surface tumbled violently, and a large amount of slag curled into the molten steel, leading to secondary oxidation of the molten steel and increased aluminum loss.

[0151] Table 24 RH refining process control parameters

[0152]

[0153] (4) Continuous casting

[0154] The continuous casting tundish uses a filter to remove inclusions in the molten steel. Argon is used to protect the casting process. The water inlet, the plate space and the stopper are sealed with argon. A constant casting speed of 1.15m / min is used. The slag detection of the large ladle is adjusted to the highest sensitivity level to prevent slag. The composition of the tundish sample analysis is shown in Table 25 below, and the change curve of the tundish stopper is shown in Figure 9 .

[0155] Table 25 Composition of molten steel in continuous casting (%)

[0156] Furnace number C Mn S P Si Als La+Ce O N Rare earth recovery rate, % 2-01453 0.0019 0.12 0.0006 0.015 2.41 0.96 0.0061 0.0009 0.0011 55.45 2-01454 0.0020 0.14 0.0008 0.013 2.45 0.93 0.0059 0.0006 0.0009 53.64 2-01455 0.0017 0.11 0.0009 0.011 2.43 0.95 0.0065 0.0010 0.0013 59.09

[0157] As can be seen from the composition table above, this comparative example utilizes a process outside the scope of the present invention. The rare earth alloy is added to the feed line after RH refining is complete and the air is broken. While this yield is relatively high, it suffers from the following drawbacks: First, the slag interface reacts violently, causing significant slag tumbling, which results in significant slag entrainment and contamination of the molten steel, leading to significant Al(II) losses. Second, inclusions modified by the rare earth addition cannot be promptly floated and removed, remaining in the molten steel and causing sprue blockage during the pouring process. This comparative example was intended to pour six heats of steel, but severe sprue blockage interrupted the pouring process during the third heat.

[0158] From the overall situation of the smelting of rare earth high-grade non-oriented electrical steel, it can be seen that the rare earth alloy is added to the wire after the RH refining is completed and the air is broken, and the remaining processes are carried out according to the process parameters of the present invention. Although the yield is high, the rare earth inclusions are retained in the molten steel and block the water inlet, resulting in poor continuous casting and pouring properties.

[0159] 2. Inclusion detection results of ingots

[0160] In this comparative example, a low-magnification sample was taken from the second casting furnace and processed, and then fine inclusions (≤1 μm) were observed under a microscope. During the detection process, the magnification was maintained at 15,000, and inclusions smaller than 1 μm were observed. 30 fields of view were randomly selected during the observation. The corresponding statistical results are shown in Table 26 below.

[0161] Table 26 Statistics of fine inclusions (<1μm) in steel after rare earth treatment

[0162] La+Ce content in steel (ppm) <![CDATA[Number density of inclusions (per mm 2 )]]> Not added 840.0 59 (Comparative Example 2) 672.0

[0163] As can be seen from the table above, the number density of fine inclusions (≤1 μm) in the billet after using the process outside the scope of the present invention is reduced from 840 / mm to 1000 / mm compared with the billet without rare earth addition. 2 Reduced to 672 pieces / mm 2 Although the addition of rare earth reduces the content of fine inclusions in the ingot, the effect is not obvious. The main reasons are: first, the timing of adding rare earth is not good. After the rare earth modifies the inclusions, they are not floated up and removed in time and remain in the molten steel; second, when added through wire feeding, the rare earth reacts violently, causing the ladle slag surface to roll violently, and the slag enters the molten steel and pollutes the molten steel.

[0164] The above-mentioned detailed description of a smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel with reference to the embodiment is illustrative rather than restrictive, and several embodiments can be listed according to the limited scope. Therefore, changes and modifications without departing from the overall concept of the present invention should fall within the scope of protection of the present invention.

Claims

1. A smelting method for improving the continuous casting and pouring properties of high-grade rare earth non-oriented silicon steel, characterized in that: The smelting method comprises the following steps: KR molten iron pre-desulfurization - converter smelting - argon station top slag modification - RH refining - continuous casting into ingots; In the KR hot metal pre-desulfurization step, after the blast furnace hot metal enters the KR station, the slag is skimmed to a metal bright surface ≥95%, smokeless refining agent is added to the slag surface, and then KR desulfurizer is added for pre-desulfurization to S ≤0.0010%. After the desulfurization is completed, two slag skimming treatments are performed; In the converter smelting step, the temperature of the molten iron in the converter is 1305-1370°C, the tapping P is controlled to be ≤0.012%, C: 0.035%-0.055%, O: 0.040%-0.070%, the ladle top slag thickness is ≤60mm, lime is added for slag washing after tapping, and the basicity CaO / SiO2 is required to be 3-3.5; In the argon station top slag modification step, a top slag modifier having an Al content of 40% and a concentration of 0.80-1.5 kg / t of steel is added to modify the top slag; In the RH refining step, decarburization is performed to C≤0.0012%, aluminum particles are added for deoxidation, and then the alloy composition is adjusted to meet the design requirements. After the alloy adjustment is completed, a desulfurizer is added to desulfurize to S≤0.0015%, and bauxite is added after a 3-minute cycle, and then a rare earth pure lanthanum-cerium alloy is added. After the rare earth pure lanthanum-cerium alloy is added, the cycle time is ≥6 minutes before breaking the air; after the molten steel is broken, the calcium line is fed, and the soft blowing time before leaving the station is ≥6 minutes, and the calming time is maintained for ≥20 minutes; In the continuous casting step of the ingot, a filter is used in the tundish to replace the traditional retaining wall and dam, and argon is used to protect the casting throughout the process. The casting process is controlled by constant casting speed, the casting speed range is 1.00~1.25m / min, the superheat is controlled at 10~30℃, electromagnetic stirring is used, and the automatic slag discharge control device is controlled at the highest sensitivity level.

2. The smelting method according to claim 1, characterized in that: The chemical composition and weight percentage of the high-grade rare earth non-oriented silicon steel are as follows: C≤0.0020%, Mn 0.10%~0.30%, S≤0.0010%, P≤0.015%, Si 2.3%~2.5%, Als 0.8%~1.3%, La+Ce 0.002%~0.008%, N≤0.0015%, O≤0.0010%, and the rest are Fe and unavoidable impurities.

3. The smelting method according to claim 1, characterized in that: In the KR molten iron pre-desulfurization step, the temperature of the molten iron entering the furnace is ≥1250°C; the time interval between two slag removals is at least 5 minutes, and the metal bright surface of the molten iron ladle is ≥95%.

4. The smelting method according to claim 1, characterized in that: In the converter smelting step, the temperature of the molten steel is 1640-1670° C.; 2.0-2.5 kg / t of steel lime is added for slag washing, and the basicity CaO / SiO2 is required to be 3-3.

5.

5. The smelting method according to claim 1, characterized in that: In the argon station top slag modification step, a top slag modifier is added to modify the top slag before the molten steel leaves the station, and the bottom blowing gas is turned off during the modification process.

6. The smelting method according to claim 1, characterized in that: In the RH refining step, the amount of bauxite added is 1.7-2.2 kg / t steel; the amount of rare earth pure lanthanum-cerium alloy added is 0.10-0.25 kg / t steel.

7. The smelting method according to claim 1, characterized in that: In the RH refining step, the target composition of the RH refining top slag is: CaO / SiO2≥5.0, CaO / Al2O3:1.5~1.8, ∑(FeO+MnO)≤1.5%.

8. The smelting method according to claim 1, characterized in that: In the continuous casting step to form the ingot, the water inlet, the space between the plates and the stopper rod are sealed with argon gas.

9. A high-grade rare earth non-oriented silicon steel, characterized in that: The high-grade rare earth non-oriented silicon steel is smelted by the smelting method according to any one of claims 1 to 8.

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