A method for improving the internal quality of a 280x380 mm section bearing steel continuous casting billet by using rare earth Ce element

Abstract

The application discloses a method for improving the internal quality of 280*380 mm section bearing steel continuous casting billets by using rare earth Ce elements, and the process route is KR molten iron pretreatment-top and bottom combined blowing converter-LF refining-VD vacuum degassing-CCM 280*380 mm section continuous casting machine; wherein: the LF off-site molten steel temperature is 1620 DEG C >=T>=1635 DEG C; the slag basicity R is >=6.0, and the slag TFe is <=1.0%; after entering the VD process, the vacuum extraction operation is carried out; the deep vacuum time is >=15 minutes; after breaking the vacuum, the wire feeding operation is carried out, and after the wire feeding is finished, 30% content Ce ferroalloy is added; after the rare earth alloy is added, the refining soft blowing process is started, and the post-soft blowing time is >=15 minutes; after the soft blowing is finished, the steel is poured. The application utilizes the operation of rare earth Ce in the steel to refine the solidification structure grains, selects the appropriate process, reduces the proportion of dendritic crystal zone of the continuous casting billets, improves the proportion of equiaxed crystal of the continuous casting billets, and improves the internal quality of the continuous casting billets.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, and in particular to a method for improving the internal quality of a 280×380mm cross-section bearing steel continuous casting billet using rare earth element Ce. Background Technology

[0002] As the cross-sectional dimensions of continuously cast billets increase in width and thickness, the internal cooling conditions of large-section continuously cast billets, such as wide and thick slabs and large square billets, deteriorate significantly with prolonged solidification time. This is mainly manifested in the more developed columnar crystals and the increased macroscopic transport distance of molten steel rich in solute elements. Traditional light-reduction processes, due to their smaller deformation, cannot effectively penetrate to the core region of the billet, making it difficult to effectively improve internal quality defects such as center segregation, shrinkage cavities, and porosity. Furthermore, with the substantial increase in the shell thickness of large-section continuously cast billets, the skin effect becomes increasingly pronounced during electromagnetic stirring, significantly affecting the process's control over internal quality defects. Affected by these factors, internal quality problems such as center segregation, shrinkage cavities, and porosity in large-section continuously cast billets become increasingly prominent, seriously impacting the quality and yield of subsequent finished rolled products.

[0003] In the 1970s, Japan first developed a mechanical light reduction technology at the solidification end based on the shrinkage roll gap. By squeezing the solidification end of the continuously cast billet, it promoted the upstream discharge of molten steel rich in solute segregation elements, thereby effectively improving the center segregation defect of the billet. At the same time, it compensated for the solidification shrinkage of the billet and improved the center porosity defect. As the cross-sectional dimensions of continuously cast billets have become wider and thicker, the traditional light reduction process can no longer effectively improve the increasingly serious center segregation, shrinkage cavities, and porosity defects of large-section continuously cast billets such as wide and thick slabs and large square billets. In view of this, the heavy reduction technology at the solidification end was further developed based on the light reduction process.

[0004] Although continuous optimization of continuous casting equipment processes has improved the internal quality of billets, the uneven growth ratio of dendritic and equiaxed crystals during the solidification process of molten steel still leads to a decrease in the internal quality rating of billets under low magnification detection.

[0005] Therefore, given the current production situation of low internal quality rating of large billet continuously cast billets, it is necessary to propose a method to further improve the internal quality of continuously cast billets, effectively enhancing the internal quality of continuously cast billets without changing the equipment production process parameters. Summary of the Invention

[0006] The purpose of this invention is to provide a method for improving the internal quality of 280×380mm cross-section bearing steel continuous casting billets using rare earth element Ce. This method utilizes rare earth Ce to refine the solidification structure grains in the steel, and by selecting appropriate processes, reduces the proportion of dendritic crystal regions in the billet, increases the proportion of equiaxed crystals in the billet, and effectively improves the internal quality of the continuous casting billet.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] This invention discloses a method for improving the internal quality of 280×380mm cross-section bearing steel continuous casting billets using rare earth element Ce. The selected process route is KR hot metal pretreatment – ​​top and bottom blowing converter – LF refining – VD vacuum degassing – CCM 280×380mm cross-section continuous casting machine. The rare earth alloy used is a 30% Ce ferroalloy, added via VD station-thrown alloy addition. The addition process involves LF refining followed by VD vacuum degassing before adding the rare earth element. Specifically, the LF station temperature of the molten steel is... Ensure 1620℃≥T≥1635℃; slag basicity (CaO / SiO2)R≥6.0, slag TFe≤1.0%; after entering the VD process, perform vacuuming; deep vacuum time≥15 minutes; after breaking the vacuum, perform wire feeding, and after wire feeding, add 30% Ce ferroalloy, with the addition amount controlled at 0.2-0.25 kg / t; after the rare earth alloy is added, start the refining soft blowing process, with the argon flow rate controlled at 0.028-0.032 Nm. 3 / t·min, with a soft blowing time of ≥15 minutes; steel pouring after soft blowing.

[0009] Furthermore, no aluminum element adjustment or calcium refining process is performed before entering the VD vacuum degassing process to ensure the deoxidation effect.

[0010] Furthermore, the vacuum level is ≤0.10 kPa.

[0011] Furthermore, the vacuum level is ≤0.06 kPa.

[0012] Furthermore, the argon flow rate is controlled at 0.03 Nm during soft blowing. 3 / t·min.

[0013] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0014] The method of this invention significantly improves the inspection results of continuous casting billets produced from large 280×380mm cross-section billets for rare earth bearing steel. Specifically, the inspection ratings for central porosity and shrinkage cavities show marked improvement. Attached Figure Description

[0015] The present invention will be further described below with reference to the accompanying drawings.

[0016] Figure 1 A hot acid photograph of a 280×380mm cross-section of a cast billet before the use of the patented method;

[0017] Figure 2The images show hot acid photographs of a 280×380mm cross-section of a cast billet after using the patented method (as shown in the first image, the central porosity is significantly improved; as shown in the second image, the isocrystalline region is significantly increased, which has a significant effect on improving the as-cast microstructure).

[0018] Figure 3 These are photos comparing the internal quality of the cast billet before and after using the patented method. Detailed Implementation

[0019] To better understand the above aspects, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments.

[0020] A method for improving the internal quality of 280×380mm cross-section bearing steel continuous casting billets using rare earth element Ce is proposed. The selected process route is KR hot metal pretreatment - top and bottom blowing converter - LF refining - VD vacuum degassing - CCM 280×380mm cross-section continuous casting machine. A 30% Ce ferroalloy is used as the rare earth alloy, added via alloy throwing at the VD station. The addition process involves LF refining followed by VD vacuum degassing before adding the rare earth element. The LF steel temperature is maintained between 1620℃ and 1635℃. Before entering the VD vacuum degassing stage, no aluminum element adjustment or refining calcium treatment is performed to ensure deoxidation effectiveness. The slag basicity (CaO / SiO2) R ≥ 6.0 and slag TFe ≤ 1.0%. After the VD process, a vacuum operation is performed with a vacuum degree ≤ 0.10 kPa and a target value ≤ 0.06 kPa; the deep vacuum time is ≥ 15 minutes. After the air gap is broken, wire feeding is performed. After wire feeding, a 30% Ce-containing ferroalloy is added at a rate controlled at 0.2-0.25 kg / t. Following the addition of the rare earth alloy, the refining soft-blowing process begins. During soft-blowing, the argon gas flow rate is controlled at 0.03 Nm³. 3 / t·min, followed by soft blowing time ≥15 minutes. After soft blowing is completed, steel is poured.

[0021] In the production of rare earth bearing steel from 280×380mm cross-section large square billets, the inspection results of continuously cast billets showed significant improvement. Specifically, the inspection ratings for central porosity and shrinkage cavities showed marked improvement. See Table 1 below:

[0022] Table 1

[0023]

[0024] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for improving the internal quality of a 280×380mm cross-section bearing steel continuous casting billet using rare earth element Ce, characterized in that, The selected process route is KR hot metal pretreatment - top and bottom blowing converter - LF refining - VD vacuum degassing - CCM280×380mm section continuous casting machine; the rare earth alloy used is 30% Ce ferroalloy, added by VD station throwing alloy addition, and the addition process is LF refining + VD vacuum degassing followed by rare earth element addition; wherein: the LF off-site molten steel temperature is guaranteed to be 1620℃≥T≥1635℃; slag basicity (CaO / SiO2) R≥6.

0. Slag TFe ≤ 1.0%; After entering the VD process, a vacuuming operation is performed; deep vacuum time ≥ 15 minutes; after breaking the vacuum, a wire feeding operation is performed, and after the wire feeding is completed, a 30% Ce iron alloy is added, with the addition amount controlled at 0.2-0.25 kg / t; after the rare earth alloy is added, the refining soft blowing process is started, and the argon flow rate is controlled at 0.028-0.032 Nm³ / t·min during soft blowing, and the soft blowing time is ≥ 15 minutes; after the soft blowing is completed, the steel is cast. Before entering the VD vacuum degassing process, no aluminum element adjustment or calcium refining process is performed to ensure the deoxidation effect.

2. The method for improving the internal quality of a 280×380mm cross-section bearing steel continuous casting billet using rare earth element Ce according to claim 1, characterized in that, Vacuum operation requirements: vacuum degree ≤ 0.10 kPa.

3. The method for improving the internal quality of a 280×380mm cross-section bearing steel continuous casting billet using rare earth element Ce according to claim 2, characterized in that, Vacuum degree ≤0.06KPa.

4. The method for improving the internal quality of a 280×380mm cross-section bearing steel continuous casting billet using rare earth element Ce according to claim 1, characterized in that, During soft blowing, the argon flow rate is controlled at 0.03 Nm³ / t·min.

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