Production method for improving cleanliness of wear-resistant steel casting blank

Abstract

The invention discloses a production method for improving cleanliness of a wear-resistant steel casting blank, and relates to the technical field of metal material smelting and continuous casting. The method comprises the following steps: optimizing electric arc furnace smelting, and reducing the oxygen content of molten steel by adopting a specific deoxidation system; a double-slag method is adopted in the LF refining stage, the size of inclusions is reduced through Ca treatment and rare earth denaturation, and the plasticity of the inclusions is improved; the vacuum degree and the degassing time are controlled in the RH degassing process, and the gas content in the molten steel is further reduced; and finally, an optimized protective casting process is adopted in the continuous casting process, a flow field is optimized in combination with electromagnetic stirring (EMS), and formation of secondary inclusions is reduced. By means of the method, the total amount of inclusions of the wear-resistant steel casting blank can be reduced by 30%-50%, the oxygen content is reduced to 0.0010% or below, the cleanliness of the casting blank is remarkably improved, and the comprehensive performance of the wear-resistant steel is improved. The method is stable in process and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of metal smelting and continuous casting technology, and particularly relates to a production method for improving the cleanliness of wear-resistant steel billets. Background Technology

[0002] Wear-resistant steel is widely used in mining, construction, metallurgy, and other industries, operating in harsh environments that demand high wear resistance and strength. However, in traditional production processes, wear-resistant steel billets are often affected by defects such as inclusions, segregation, and porosity, leading to a decline in the quality of the final product. Current common methods include optimizing the smelting process and improving the level of protective casting in continuous casting, but these still struggle to significantly improve the cleanliness of the billets. Therefore, an innovative production method is urgently needed to further reduce the inclusion content of the billets and improve the quality of the finished product. Summary of the Invention

[0003] The purpose of this invention is to provide a production method for improving the cleanliness of wear-resistant steel billets. By optimizing the smelting process, refining measures and continuous casting process, the content of inclusions in the billets is significantly reduced, the internal quality of the billets is improved, and thus the mechanical properties and service life of wear-resistant steel are improved.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] This invention discloses a production method for improving the cleanliness of wear-resistant steel billets, comprising electric furnace smelting, LF refining, RH vacuum degassing, and continuous casting; characterized in that, specifically:

[0006] (1) Electric arc furnace smelting: During the electric arc furnace smelting process, the raw material ratio is optimized, and high-quality scrap steel with a mass ratio of 75%-85% and pig iron with a mass ratio of 15%-25% are used as raw materials; oxygen injection and carbon-oxygen balance control technology are used during smelting to reduce the oxygen content of the molten steel and control the final oxygen content at 50-60ppm; the deoxidation system adopts aluminum-calcium-silicon composite deoxidation process, and aluminum powder is added in batches for pre-deoxidation before tapping the steel at the end point, and then silicon-calcium alloy is added for deep deoxidation to ensure that the total oxygen content of the molten steel is reduced to ≤0.0010%; rare earth micro-alloying treatment is added before tapping the steel, and 0.005%~0.015% La-Ce rare earth alloy is added; slag-steel interface control technology is adopted to increase the slag basicity to CaO / SiO2 mass ratio of 2.5~3.2, and the final sulfur content is ≤0.005% and phosphorus content is ≤0.015%;

[0007] (2) LF refining: The double slag method is adopted to control the slag composition, so that the slag contains 50% to 55% CaO, 20% to 30% Al2O3, and 5% to 10% MgO, forming a good desulfurization and deoxidation environment to ensure the aggregation and flotation of inclusions in the molten steel; Ca-Si wire is fed in to modify inclusions; in the later stage of LF refining, 0.002% to 0.008% La-Ce rare earth alloy is added; Argon gas stirring is used to control the flow field of molten steel to ensure that inclusions float fully, and the refining time is controlled at 30 to 45 minutes to make the cleanliness of molten steel reach the optimal level;

[0008] (3) RH vacuum degassing: The RH vacuum treatment method is used, and the system vacuum degree is maintained at 0.60~0.68kPa for 15~20min. Ar gas is used for bottom stirring to ensure the stable flow state of molten steel in the vacuum tank and improve the degassing effect.

[0009] (4) Continuous casting: During the continuous casting process, a full-process protective casting process is adopted, including argon-sealed tundish and immersion nozzle protection to prevent the molten steel from being oxidized during the casting process; the superheat of the molten steel in the crystallizer is controlled at 10-15℃ to avoid excessive superheat causing inclusions to deposit in the center of the billet; electromagnetic stirring of the crystallizer is adopted with a stirring frequency of 3.0-4.0Hz to optimize the flow field of the molten steel, so that the inclusions are more evenly distributed in the billet and promote the floating of the inclusions; flexible cooling technology is adopted to control the flow rate of cooling water, so that the internal structure of the billet is more uniform and cracks and segregation defects are reduced.

[0010] Furthermore, in the LF refining process, 1.0 to 1.5 kg / t of Ca-Si wire is fed in.

[0011] Furthermore, in the LF refining process, the flow rate of argon gas stirring is 15-20 L / min.

[0012] Furthermore, in the RH vacuum degassing process, the flow rate of Ar gas at the bottom is 20-25 L / min.

[0013] Furthermore, the chemical composition of the wear-resistant steel billet comprises the following percentages by mass: C 0.25–0.35%, Si 0.20–0.50%, Mn 1.00–1.50%, P ≤0.015%, S ≤0.005%, Cr 0.90–1.20%, Mo 0.20–0.40%, Ni 0.30–0.50%, B 0.0005–0.0020%, V 0.08–0.15%, Re 0.005–0.015%, with the remainder being Fe and unavoidable trace impurities, totaling 100% by mass.

[0014] Furthermore, by optimizing the electric arc furnace smelting, LF refining, RH degassing, and continuous casting processes, the total amount of inclusions and oxygen content in the wear-resistant steel billets were effectively reduced.

[0015] Furthermore, compared to traditional processes, inclusions are reduced by 30%-50%, oxygen content is reduced by 30%-50%, and the cleanliness of the cast billet is significantly improved.

[0016] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0017] (1) By optimizing the electric arc furnace smelting, LF refining, RH vacuum degassing, and continuous casting processes, this invention effectively reduces the oxygen content and total amount of inclusions in molten steel, reducing the total oxygen content of the billet to ≤0.0007%, controlling the inclusion size to ≤10μm, and reducing the total amount of inclusions by more than 50%, significantly improving the cleanliness of the billet and extending the service life of wear-resistant steel. (2) By employing Ca treatment and rare earth modification technology, alumina inclusions in molten steel are transformed into highly ductile CaO-Al2O3 composite inclusions, reducing brittle inclusions and improving the deformability of inclusions, thereby improving the impact toughness and fatigue resistance of wear-resistant steel and ensuring its excellent service performance under complex working conditions. (3) By controlling key process parameters such as refining time, vacuum degree, casting superheat, and electromagnetic stirring frequency, this invention achieves a stable improvement in the cleanliness of wear-resistant steel billets, ensuring the operability and consistency of the production process. This method is suitable for large-scale industrial production, effectively reducing quality fluctuations, improving product qualification rate, and meeting the application needs of high-end wear-resistant steel. Detailed Implementation

[0018] The following is a detailed description of a production method for improving the cleanliness of wear-resistant steel billets according to the present invention.

[0019] Example 1: This example is a preferred embodiment of the various embodiments of the present invention.

[0020] This embodiment describes a production method for improving the cleanliness of wear-resistant steel billets. The steel grade is NM500RE, and its chemical composition by mass percentage includes: C 0.30%, Si 0.35%, Mn 1.25%, P 0.010%, S 0.002%, Cr 0.90%, Mo 0.30%, Ni 0.40%, B 0.0009%, V 0.1%, Re 0.009%, with the remainder being Fe and unavoidable trace impurities, totaling 100% by mass.

[0021] Chemical composition design principles:

[0022] C: Ensure the strength and hardness of wear-resistant steel, while controlling the carbon content to avoid reducing toughness and weldability;

[0023] Si: Improves the oxidation resistance of steel and, to some extent, increases its strength;

[0024] Mn: Improves hardenability and enhances wear resistance;

[0025] P and S: Strictly control harmful elements to reduce steel brittleness and improve toughness and fatigue performance;

[0026] Cr: Enhances wear resistance, improves tempering stability, and prevents softening at high temperatures;

[0027] Mo: Improves the tempering resistance to softening and enhances the thermal stability of wear-resistant steel;

[0028] Ni: Improves low-temperature impact toughness, enabling steel to maintain good wear resistance even at low temperatures;

[0029] B: A very small amount of boron can significantly improve hardenability, and increase the hardness and impact resistance of wear-resistant steel;

[0030] V: Refines grain size, improving the strength, toughness, and fatigue resistance of wear-resistant steel;

[0031] Re: Rare earth microalloying treatment is carried out to optimize the morphology of inclusions and improve the toughness and fatigue life of steel.

[0032] One production method for improving the cleanliness of wear-resistant steel billets in this embodiment is: electric furnace smelting, LF refining, RH vacuum degassing, and continuous casting.

[0033] Further: During the electric arc furnace smelting process, the raw material ratio is optimized, using high-quality scrap steel (75%-85%) and pig iron (15%-25%) as raw materials to reduce the impurity content introduced by the raw materials. Oxygen injection and carbon-oxygen balance control technology are employed during smelting to reduce the oxygen content of the molten steel, controlling the final oxygen content to 50-60 ppm. The deoxidation system uses an aluminum-calcium-silicon composite deoxidation process. Before tapping, aluminum powder (0.03%–0.05%) is added in batches for pre-deoxidation, followed by the addition of silicon-calcium alloy (0.08%–0.12%) for deep deoxidation, ensuring that the total oxygen content of the molten steel is reduced to ≤0.0010%, effectively reducing the formation of oxide inclusions. Rare earth microalloying is added before tapping. The addition of 0.005%–0.015% La-Ce rare earth alloy improves the morphology of inclusions, transforming them into highly ductile rare earth oxide composite inclusions, thereby enhancing the deformability of inclusions, reducing brittle inclusions, and improving the toughness of wear-resistant steel. Furthermore, the use of slag-steel interface control technology increases slag basicity (CaO / SiO2 mass ratio 2.5–3.2), reduces high-temperature oxidation, and simultaneously lowers the content of P and S impurities, resulting in a final sulfur content ≤0.005% and a phosphorus content ≤0.015%.

[0034] Further, LF refining employs a dual-slag process to enhance inclusion removal capabilities, and combines Ca treatment and rare earth modification techniques to optimize inclusion morphology. Slag composition is controlled to ensure 50%–55% CaO, 20%–30% Al₂O₃, and 5%–10% MgO, creating a favorable desulfurization and deoxidation environment to ensure the aggregation and flotation of inclusions in the molten steel. Ca-Si wire (1.0–1.5 kg / t) is fed in to modify inclusions, transforming Al₂O₃ inclusions into CaO-Al₂O₃ composite inclusions, improving their fluidity and reducing high-temperature inclusion deposition. In the later stages of LF refining, 0.002%–0.008% La is further added. -Ce rare earth alloy optimizes the morphology of inclusions, making them more uniformly distributed and improving the impact toughness and fatigue resistance of wear-resistant steel; Argon gas stirring (flow rate 15-20 L / min) is used to control the flow field of molten steel to ensure that inclusions float fully, and the refining time is controlled at 30-45 min to achieve the optimal level of cleanliness of molten steel; After LF refining, the total oxygen content in molten steel is reduced to ≤0.0008%, the inclusion size is controlled to ≤10μm, and the total amount of inclusions is reduced by more than 30%.

[0035] Further: By employing the RH vacuum treatment method, the system vacuum degree is maintained at 0.60–0.68 kPa for 15–20 min, effectively reducing the gas content in the molten steel; bottom Ar gas stirring (flow rate 20–25 L / min) is used to ensure stable flow of molten steel in the vacuum vessel and improve degassing effect; after RH treatment, the hydrogen content in the molten steel is reduced to ≤1.5 ppm, effectively reducing porosity defects in the billet, and the total oxygen content in the molten steel is further reduced to ≤0.0007%, significantly improving the cleanliness of the billet and reducing the total amount of inclusions by 40%–50%.

[0036] Furthermore, during continuous casting, a full-process protective casting process is adopted, including argon-sealed tundish and submerged nozzle protection to prevent oxidation of molten steel during pouring. The superheat of molten steel in the crystallizer is controlled at 10-15°C to avoid excessive superheat causing inclusions to deposit in the center of the billet. Electromagnetic stirring (EMS) in the crystallizer is used at a stirring frequency of 3.0-4.0 Hz to optimize the molten steel flow field, making inclusions more evenly distributed in the billet and promoting their flotation. Flexible cooling technology is used to control the cooling water flow rate, making the internal structure of the billet more uniform and reducing cracks and segregation defects. Through the optimization of this continuous casting process, the cleanliness of the final billet is significantly improved, the total amount of inclusions is reduced by more than 50%, and the oxygen content is controlled below 0.0007%, so that the quality of the wear-resistant steel billet meets the requirements of high-end applications.

[0037] Comparative Example 1:

[0038] In Comparative Example 1, the procedure was identical to that of Example 1 except that RH vacuum degassing was not performed. In this comparative example, the total amount of inclusions was 0.013%, and the oxygen content was 0.0013%.

[0039] Comparative Example 2:

[0040] In Comparative Example 2, except that electromagnetic stirring was not performed during continuous casting, it was exactly the same as Example 1. In this comparative example, the total amount of inclusions was 0.0115% and the oxygen content was 0.0011%.

[0041] As can be seen from the above embodiments and comparative examples, this invention effectively reduces the total amount of inclusions and oxygen content in wear-resistant steel billets by optimizing the electric arc furnace smelting, LF refining, RH degassing, and continuous casting processes. Compared with traditional processes, inclusions are reduced by 30%-50%, and oxygen content is reduced by 30%-50%, significantly improving the cleanliness of the billets. This invention has significant novelty, differing from existing technologies by employing a dual-slag refining method combined with rare earth modification treatment, and optimizing RH degassing and protective casting measures to achieve higher cleanliness of wear-resistant steel billets.

[0042] 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 production method for improving the cleanliness of wear-resistant steel billets, comprising electric furnace smelting, LF refining, RH vacuum degassing, and continuous casting; characterized in that, Specifically: Electric arc furnace smelting: During the electric arc furnace smelting process, the raw material ratio is optimized, using high-quality scrap steel (75%-85% by mass) and pig iron (15%-25% by mass) as raw materials; oxygen injection and carbon-oxygen balance control technology are used during smelting to reduce the oxygen content of the molten steel, controlling the final oxygen content to 50-60 ppm; the deoxidation system adopts an aluminum-calcium-silicon composite deoxidation process, adding aluminum powder in batches for pre-deoxidation before tapping, followed by adding silicon-calcium alloy for deep deoxidation, ensuring that the total oxygen content of the molten steel is reduced to ≤0.0010%; rare earth micro-alloying treatment is added before tapping, with 0.005%~0.015% La-Ce rare earth alloy added; slag-steel interface control technology is used to increase the slag basicity to a CaO / SiO2 mass ratio of 2.5~3.2, with a final sulfur content ≤0.005% and phosphorus content ≤0.015%; LF refining: A dual-slag method is used to control the slag composition, ensuring that the slag contains 50%–55% CaO, 20%–30% Al2O3, and 5%–10% MgO, creating a good desulfurization and deoxidation environment to ensure the aggregation and flotation of inclusions in the molten steel. A Ca-Si wire is fed in to modify the inclusions. In the later stage of LF refining, 0.002%–0.008% La-Ce rare earth alloy is further added. Argon gas stirring is used to control the flow field of the molten steel to ensure that the inclusions float fully. The refining time is controlled at 30–45 minutes to achieve the optimal level of cleanliness in the molten steel. RH vacuum degassing: The RH vacuum treatment method is used, and the system vacuum degree is maintained at 0.60-0.68 kPa for 15-20 min. Ar gas stirring is used at the bottom to ensure the stable flow of molten steel in the vacuum tank and improve the degassing effect. Continuous casting: During continuous casting, a full-process protective casting process is adopted, including argon-sealed tundish and submerged nozzle protection to prevent the molten steel from being oxidized during the pouring process; the superheat of the molten steel in the crystallizer is controlled at 10-15℃ to avoid excessive superheat causing inclusions to deposit in the center of the billet; electromagnetic stirring of the crystallizer is adopted with a stirring frequency of 3.0-4.0Hz to optimize the flow field of the molten steel, so that the inclusions are more evenly distributed in the billet and promote the floating of the inclusions.

2. The production method for improving the cleanliness of wear-resistant steel billets according to claim 1, characterized in that, In the LF refining process, 1.0 to 1.5 kg / t of Ca-Si wire is fed in.

3. The production method for improving the cleanliness of wear-resistant steel billets according to claim 1, characterized in that, In the LF refining process, the flow rate of argon gas stirring is 15-20 L / min.

4. The production method for improving the cleanliness of wear-resistant steel billets according to claim 1, characterized in that, During the RH vacuum degassing process, the flow rate of Ar gas at the bottom is 20-25 L / min.

5. The production method for improving the cleanliness of wear-resistant steel billets according to claim 1, characterized in that, The chemical composition of the wear-resistant steel billet comprises the following percentages by mass: C 0.25–0.35%, Si 0.20–0.50%, Mn 1.00–1.50%, P ≤0.015%, S ≤0.005%, Cr 0.90–1.20%, Mo 0.20–0.40%, Ni 0.30–0.50%, B 0.0005–0.0020%, V 0.08–0.15%, Re 0.005–0.015%, with the remainder being Fe and unavoidable trace impurities, totaling 100% by mass.

6. The production method for improving the cleanliness of wear-resistant steel billets according to claim 1, characterized in that, By optimizing the electric arc furnace smelting, LF refining, RH degassing, and continuous casting processes, the total amount of inclusions and oxygen content of wear-resistant steel billets were effectively reduced.

7. The production method for improving the cleanliness of wear-resistant steel billets according to claim 6, characterized in that, Compared with traditional processes, inclusions are reduced by 30%-50%, oxygen content is reduced by 30%-50%, and the cleanliness of the cast billet is greatly improved.