A refining method and continuous casting application for reducing subsurface gas bubbles in aluminum-free non-oriented silicon steel cast slab

Abstract

The application discloses a refining method for reducing subcutaneous gas bubbles of aluminum-free non-oriented silicon steel cast billets and a continuous casting application, and the refining method comprises the following steps: (1) performing desulfurization treatment on molten steel to ensure that the content of S in the molten steel is below 0.002%, and obtaining desulfurized molten steel; (2) when the molten steel reaches RH refining, ensuring that the temperature is between 1600-1650 DEG C, the content of C element is between 0.02-0.05 %, and the content of O element is between 400-850 ppm; (3) during the RH refining, deep decarburization treatment is adopted, oxygen is determined after decarburization for 15-20 min, and then aluminum is added for deoxidization to below 300 ppm; (4) phosphorus iron, silicon iron and manganese iron are added successively for alloying, so that the free oxygen in the final molten steel is reduced to below 20 ppm, the net circulation treatment time is greater than or equal to 8 min after the chemical composition reaches the standard, and after oxygen measurement and oxygen determination, the space is broken and the molten steel is discharged. The molten steel after refining is continuously cast by controlling relevant parameters, so that the subsequent silicon steel cast billets can not produce subcutaneous gas bubble defects, and short strip-shaped buckles cannot be formed on the surface of the hot coil after hot rolling of the cast billets.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting technology, specifically relating to a refining and continuous casting application that reduces subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets. Background Technology

[0002] During the production of aluminum-free high-strength non-oriented silicon steel (Al≤50ppm), due to the high dissolved oxygen and low Al content in the steel, the [O] precipitated during the solidification of the molten steel mainly reacts with [C] to generate CO, which makes the cast steel billet prone to subcutaneous bubble defects. This results in a large number of short strip-shaped peeling skins forming on the surface of the hot-rolled coil after hot rolling, causing serious loss of yield.

[0003] Therefore, there is an urgent need to develop a refining and continuous casting method to reduce subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets in order to solve the aforementioned problems. Summary of the Invention

[0004] Purpose of the invention: This invention provides a refining method and continuous casting application for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets, to solve the problem of subcutaneous bubble defects in continuously cast aluminum-free, non-oriented silicon steel billets.

[0005] Technical solution:

[0006] A refining method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets includes the following steps:

[0007] (1) Desulfurize the molten steel to ensure that the mass content of S in the molten steel is less than 0.002% to obtain desulfurized molten steel;

[0008] (2) When the molten steel reaches the RH refining stage, ensure that the temperature is between 1600-1650℃, the C element mass content is between 0.02-0.05%, and the O element content is between 400-850ppm;

[0009] (3) When performing RH refining, deep decarburization treatment is adopted. After decarburization for 15-20 minutes, oxygen is determined, and then aluminum is added to deoxidize to below 300 ppm.

[0010] (4) Phosphorus iron, silicon iron and manganese iron are added in sequence to ensure that the free oxygen in the final molten steel is reduced to below 20 ppm. After all chemical components meet the standards, the net circulation treatment time is ≥8 min. After oxygen is measured and determined, the air is broken and the steel is discharged.

[0011] Furthermore, in step (3), when adding aluminum particles for deoxidation, 0.15-0.3 kg / ton of aluminum is added for deoxidation at a rate of 100 ppm O content.

[0012] Furthermore, in step (4), the ferrosilicon includes deoxidized ferrosilicon and component ferrosilicon.

[0013] Furthermore, in step (4): ferromanganese is ferromanganese containing 97% manganese, ferrosilicon is low-carbon ferrosilicon containing 74% silicon and ≤0.02% carbon, and ferrophosphorus is low-carbon ferrophosphorus containing 25% phosphorus and ≤0.02% carbon.

[0014] A continuous casting method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets involves hoisting molten steel to a slab continuous casting machine for pouring. During continuous casting, the argon flow rate for protective casting at the stopper rod and the upper gate is controlled at 2-5 L / min, the superheat is controlled between 30-50℃, the insertion depth of the submerged entry nozzle is controlled at 150-180 mm, and the continuous casting speed is 0.9-1.1 m / min.

[0015] Beneficial effects:

[0016] (1) According to the oxygen content of the molten steel, the present invention accurately adds metallic aluminum to deoxidize the steel, and then adds ferrophosphorus, ferrosilicon and ferromanganese in sequence to alloy the molten steel, ensuring that the free oxygen in the molten steel is reduced to below 20ppm at the end point, avoiding the generation of CO bubbles by carbon-oxygen reaction, and ensuring that the subsequent silicon steel billet does not produce subcutaneous bubble defects.

[0017] (2) In the continuous casting process of this invention, by controlling the appropriate argon blowing flow rate, the argon bubbles brought into the molten steel are reduced, which can ensure that the subsequent silicon steel billet does not produce subcutaneous bubble defects.

[0018] (3) In the continuous casting process of this invention, by controlling the superheat, the insertion depth of the submerged nozzle and the continuous casting speed within a specific range, it is ensured that the bubbles entering the crystallizer can be quickly and effectively removed, which can ensure that the subsequent silicon steel billet does not produce subcutaneous bubble defects, and further ensure that short strips of peeling skin will not form on the surface of the hot-rolled coil, thereby ensuring a high yield. Attached Figure Description

[0019] Figure 1 A schematic diagram showing the normal surface state of a hot-rolled aluminum-free, non-oriented silicon steel slab after rolling.

[0020] Figure 2 A schematic diagram of subcutaneous air bubbles in an aluminum-free, non-oriented silicon steel slab.

[0021] Figure 3 This is a schematic diagram showing short strips of peeling skin on the surface of hot-rolled steel slabs caused by air bubbles.

[0022] Figure 4 This is a bar chart showing the relationship between the overheating degree of continuous casting and the incidence of bubbles and peeling on the surface of hot-rolled coils. Detailed Implementation

[0023] The following embodiments are provided to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0024] A refining method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets and its application in continuous casting are disclosed. The process flow is as follows: converter smelting → RH refining → continuous casting. The ladle used has a capacity of 200 tons, and the molten steel weighs 175-185 tons. The invention is further illustrated using this process as an example.

[0025] This application provides a refining method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets, comprising the following steps:

[0026] (1) KR steel pretreatment: desulfurize the steel to ensure that the S content in the steel is below 0.002% to obtain desulfurized steel;

[0027] (2) When the molten steel reaches the RH refining stage, ensure that the temperature is between 1600-1650℃, the C element content is between 0.02-0.05%, and the O element content is between 400-850ppm;

[0028] (3) When RH refining is carried out, deep decarburization is adopted. After decarburization for 15-20 minutes, oxygen is determined, and then aluminum particles are added to deoxidize to below 300ppm. When adding aluminum particles for deoxidation, 0.15-0.3kg / ton of aluminum is added for deoxidation at every 100ppm O content.

[0029] (4) Phosphorus iron, deoxidized silicon iron, composition silicon iron, and manganese iron are added in sequence to ensure that the free oxygen in the final molten steel is reduced to below 20 ppm. After all chemical components meet the standards, the net circulation treatment time is ≥8 min. After oxygen is measured and determined, the air is broken and the steel is discharged. The manganese iron is ferromanganese iron containing 97% manganese, the silicon iron is low carbon silicon iron containing 74% silicon and C≤0.02%, and the phosphorus iron is low carbon phosphorus iron containing 25% phosphorus and C≤0.02%.

[0030] The molten steel obtained after processing according to steps one to four of the above RH refining method is hoisted to the slab continuous casting machine for pouring. During continuous casting, the argon flow rate for protective casting at the stopper rod and the upper gate is controlled at 2-5 L / min, the superheat is controlled between 30-50℃, the insertion depth of the submerged entry nozzle is controlled at 150-180 mm, and the continuous casting speed is 0.9-1.1 m / min.

[0031] In Examples 1-7, the process data for obtaining aluminum-free, non-oriented silicon steel billets and the effect of reducing bubbles are shown in Tables 1 and 2. The billets obtained in all 7 examples showed no subcutaneous bubbles.

[0032] The RH arrival temperature of molten steel, RH arrival oxygen content, oxygen content before alloying, and RH final oxygen content are shown in Table 1.

[0033] Table 1

[0034]

[0035] Table 2 shows the argon blowing volume of the stopper rod and the argon blowing volume of the top nozzle during continuous casting, the continuous casting speed, the degree of superheat in continuous casting, and the number of bubbles and scale detected.

[0036] Table 2

[0037]

[0038] The aluminum-free, non-oriented silicon steel billets produced according to this process did not exhibit any bubble-like peeling.

[0039] The above technical solutions illustrate the technical concept of the present invention, but should not be construed as limiting the scope of protection of the present invention. Any modifications or alterations made to the above technical solutions based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the scope of protection of the technical solutions of the present invention.

Claims

1. A refining method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets, characterized in that, Includes the following steps: (1) Desulfurize the molten steel to ensure that the mass content of S in the molten steel is less than 0.002% to obtain desulfurized molten steel; (2) When the molten steel reaches RH refining, ensure that the temperature is between 1600-1650 ℃, the C element mass content is between 0.02-0.05 % and the O element content is between 400-850 ppm; (3) When RH refining is carried out, deep decarburization is adopted. After decarburization for 15-20 min, oxygen is determined, and then aluminum is added to deoxidize to below 300 ppm. When adding aluminum particles for deoxidation, 0.15-0.3 kg / ton of aluminum is added for deoxidation per 100 ppm O content. (4) Phosphorus iron, deoxidized silicon iron, component silicon iron, and manganese iron are added in sequence to ensure that the free oxygen in the final molten steel is reduced to below 20 ppm. After all chemical components meet the standards, the net circulation treatment time is ≥ 8 min. After oxygen is measured and determined, the air is broken and the steel is discharged.

2. The refining method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets according to claim 1, characterized in that, In step (4): ferromanganese is ferromanganese containing 97% manganese, ferrosilicon is low-carbon ferrosilicon containing 74% silicon and ≤ 0.02% carbon, and ferrophosphorus is low-carbon ferrophosphorus containing 25% phosphorus and ≤ 0.02% carbon.

3. A continuous casting method for molten steel obtained based on the refining method for reducing subcutaneous bubbles in aluminum-free, non-oriented silicon steel billets as described in claim 1, characterized in that... Molten steel is hoisted to the slab continuous casting machine for pouring. During continuous casting, the argon blowing rate of the stopper rod is 3L / min, the argon blowing rate of the upper nozzle is 3L / min, the superheat is controlled between 30-50℃, the insertion depth of the submerged entry nozzle is controlled between 150-180 mm, and the continuous casting speed is 0.9-1.1 m / min.

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