Preparation method of iron and horse dual-phase steel NM300TP

Abstract

The invention provides a preparation method of iron and horse dual-phase steel NM300TP, which comprises the following steps: refining initial molten steel: heating, adjusting alloy components, adjusting silicon content for the first time, deoxidizing and denitrifying, adjusting silicon content for the second time, and continuously casting to obtain a casting blank; wherein the step of deoxidizing and denitrifying comprises the following substeps of: adding an aluminum block or an aluminum wire into molten steel at one time to deoxidize and denitrify the molten steel; the step of adjusting the silicon content for the first time comprises adjusting the silicon content in the molten steel to 0.7-0.8 wt% by using ferrosilicon or silicomanganese, the step of adjusting the silicon content for the second time comprises adjusting the silicon content in the molten steel to 1.1-1.3 wt% by using ferrosilicon, and the Ca element content of the ferrosilicon used for the second time is 0.3-1.0 wt%. Through the synergistic effect of two-step silicon content adjustment and a one-time deep deoxidation and denitrification process, the technical bottleneck in high-aluminum steel continuous casting production is solved.

Description

Technical Field

[0001] This invention belongs to the field of steel continuous casting production technology, and particularly relates to a method for preparing NM300TP dual-phase steel for steel production. Background Technology

[0002] NM300TP steel is a high-silicon, high-alumina wear-resistant steel. Due to its excellent wear resistance and good cold-working formability, it has been widely used in the manufacture of key components of concrete mixer trucks (such as impellers and drum bodies), and is gradually replacing traditional 520JJ steel. With the expansion of downstream applications, market demand for this steel grade continues to grow. However, in the actual industrial production of NM300TP steel, a series of prominent technical challenges remain. First, due to its high aluminum content (Al content reaching 0.4%–0.6%), it is extremely prone to generating high-melting-point molecules during continuous casting. Inclusions cause nozzle blockage and abnormal rise of stopper rods, seriously affecting the smooth casting process. Secondly, the protective slag used in the existing continuous casting process is prone to react with high-alumina steel liquid and undergoes denaturation, causing frequent crystallizer sticking alarms, speed reduction, and even the risk of steel leakage. In addition, insufficient control of the cleanliness of the billet interior can easily lead to defects such as delamination and cracking during subsequent customer processing, seriously affecting the product yield and end-use performance.

[0003] Currently, studies addressing these issues have proposed introducing an RH (reverse annealing) vacuum refining process to deeply deoxidize, desulfurize, and control inclusions in molten steel, thereby improving steel purity and casting stability. However, RH treatment not only significantly increases process costs and energy consumption but also prolongs the smelting cycle, making it difficult to meet current demands for efficient, low-cost, and green production.

[0004] Therefore, there is an urgent need to develop a preparation method for high-alumina steel NM300TP that does not rely on RH vacuum treatment and can effectively solve problems such as stopper rod rise, mold flux deformation and adhesion, and poor internal quality of the billet during continuous casting. Summary of the Invention

[0005] The main objective of this invention is to provide a method for preparing NM300TP dual-phase steel for iron slag casting. This method aims to solve the production quality problems existing in the continuous casting process of NM300TP dual-phase steel for iron slag casting, such as frequent deformation and crystallizer adhesion alarms, severe rise of continuous casting stopper rods, and easy delamination of billets in subsequent processing. At the same time, it overcomes the problems of high cost and low efficiency caused by the reliance on RH vacuum treatment in traditional processes.

[0006] To achieve the above objectives, the present invention provides a method for preparing NM300TP dual-phase steel for ironworks, comprising the following steps: In some embodiments, the chemical composition of the initial molten steel, by mass percentage, is: C: 0.05%–0.10%, Si: 0.1%–0.8%, Mn: 0.7%–1.70%, P: ≤0.012%, with the remainder being Fe and unavoidable impurities.

[0007] The initial molten steel is heated in an LF furnace, the alloy composition is adjusted, the silicon content is adjusted for the first time, deoxidized and denitrogenated, the silicon content is adjusted for the second time, and then continuously cast to obtain a billet. The deoxidation and denitrification steps include: adding aluminum blocks or aluminum wires to the molten steel in one go to deoxidize and denitrify the molten steel; The initial adjustment of silicon content involves using ferrosilicon or ferromanganese to adjust the silicon content in the molten steel to 0.7-0.8 wt%. The second step of adjusting the silicon content includes: adjusting the silicon content in the molten steel to 1.1~1.3 wt% using ferrosilicon, with the ferrosilicon used in the second step containing 0.3~1.0 wt% Ca.

[0008] The method for preparing NM300TP dual-phase steel provided by this invention solves the technical bottlenecks of traditional processes by employing an innovative process in an LF furnace, combining two-step silicon content adjustment with one-time deep deoxidation and denitrification. The first step precisely adjusts the silicon content to 0.7~0.8wt%, creating a suitable reducing environment that allows the subsequently added aluminum to fully react and form... Deoxidation products; the one-time addition of aluminum blocks or wires instantly achieves a deep deoxidation state in the molten steel, promoting... The deoxidation products aggregate into clusters, significantly increasing their flotation rate and removal efficiency. Simultaneously, dissolved nitrogen in the steel combines with aluminum to form AlN inclusions, which float and are removed along with the deoxidation products, fundamentally solving the problem of excessive nitrogen content in high-silicon steel. After deoxidation and denitrification, a second silicon content adjustment is performed to 1.1%-1.3% wt%. The second application of ferrosilicon with a Ca element content of 0.3-1.0 wt% acts as a calcium treatment, modifying the small Al2O3 particles that do not float in the molten steel into spherical liquid 12CaO·7Al2O3, which easily floats and is removed from the molten steel, preventing the continuous casting stopper rod from rising. This process completely replaces the traditional RH vacuum degassing process, significantly shortening the production cycle, reducing energy consumption and production costs. Furthermore, by optimizing the morphology and removal path of the deoxidation products, it effectively prevents nozzle blockage and continuous casting interruptions.

[0009] Specifically, an innovative process combining two-step silicon content adjustment with one-time deep deoxidation and denitrification is employed in the LF furnace. The first step precisely adjusts the silicon content to 0.7-0.8 wt%, creating a suitable reducing environment that allows subsequently added aluminum to fully react and form Al2O3 deoxidation products. The one-time addition of aluminum blocks or wire instantly achieves deep deoxidation in the molten steel, causing the Al2O3 deoxidation products to aggregate into clusters, significantly increasing their flotation rate and removal efficiency. Simultaneously, dissolved nitrogen in the steel combines with aluminum to form AlN inclusions, which float and are removed along with the deoxidation products, fundamentally solving the problem of excessive nitrogen content in high-silicon steel. The second step uses ferrosilicon containing 0.3-1.0 wt% Ca, which acts as a calcium treatment, modifying the small Al2O3 particles that haven't floated in the molten steel into spherical liquid 12CaO·7Al2O3, making them easier to float and remove, and preventing the continuous casting stopper rod from rising. This synergistic mechanism of step-by-step adjustment and one-time deep deoxidation effectively reduces the total oxygen content and nitrogen content in molten steel, significantly improving the purity of molten steel. It replaces the traditional RH vacuum degassing process, greatly shortens the production cycle, and reduces energy consumption and production costs.

[0010] In some embodiments, after the deoxygenation and denitrification but before the second adjustment of silicon content, a first soft-blowing argon gas process is also performed; After completing the second adjustment of silicon content, a second soft-blowing argon process is also included.

[0011] In some embodiments, the continuous casting process includes pouring molten steel from a ladle into a tundish, and then pouring it from the tundish into a crystallizer to solidify into a billet shell. Before pouring molten steel from the ladle into the tundish, the tundish is purged and filled with CO2 gas with a purity of ≥90% for ≥3 minutes.

[0012] The first soft argon blowing (after deoxidation and denitrogenation, and before the second silicon content adjustment) controlled the argon flow rate to create a micro-fluctuation state on the molten steel surface, greatly promoting the flotation and removal of Al2O3 clusters and AlN composite inclusions. This reduced the total oxygen and nitrogen content in the molten steel, creating a clean metallurgical environment for the second silicon adjustment and avoiding side reactions between the added ferrosilicon and residual inclusions. The second soft argon blowing not only homogenized the final composition but, more importantly, through reasonable blowing time and flow rate control, ensured the full flotation of newly formed spherical liquid 12CaO·7Al2O3 inclusions due to the addition of ferrosilicon. Simultaneously, it adjusted the temperature field distribution of the molten steel, providing uniform molten steel with minimal temperature fluctuations for continuous casting, significantly improving the solidification quality of the cast billet. In the continuous casting process, using CO2 gas with a purity ≥90% to purge and fill the tundish (for ≥3 minutes) can reduce the oxygen and nitrogen levels within the tundish.

[0013] In some embodiments, during continuous casting, a protective slag is also added, comprising the following components: basicity of 1.30–1.40, melting point of 1040°C–1100°C, viscosity of 0.05 Pa·s–0.10 Pa·s, and by mass percentage comprising the following components: SiO2 25%–30%, CaO 35%–40%, Al2O3 ≤1.0%, C 3.0%–5.0%, Na2O 4.0%–7.0%, Li2O 2.0%–5.0%, with the balance being unavoidable impurities.

[0014] In some embodiments, electromagnetic stirring is used during the continuous casting process, with a stirring current of 200~300A and a frequency of 4~7HZ.

[0015] In some embodiments, the continuous casting process employs light reduction, wherein the solid fraction reduction range is 0.45~0.99 and the reduction amount is 7~8mm.

[0016] Under the above conditions, it can effectively break up primary dendrites and promote the formation of equiaxed crystals, while avoiding the risk of slag entrainment caused by excessive stirring.

[0017] In some embodiments, after refining and before continuous casting, the temperature of the molten steel is 40°C to 60°C higher than the seed liquidus temperature.

[0018] Under the above conditions, the molten steel is ensured to have optimal fluidity, avoiding nozzle blockage during the continuous casting process of high-alumina steel, while ensuring uniform solidification of the billet and reducing surface cracks and center segregation.

[0019] In some embodiments, the casting speed is 0.8~1.5 m / min during the continuous casting process. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0022] To further illustrate the present invention, the following examples are provided: Example 1 This embodiment 1 provides a method for preparing NM300TP dual-phase steel for ironworks, specifically as follows: S1. Preparation of initial molten steel: Molten iron is directly fed into the converter for smelting (without pretreatment to reduce temperature drop). During the tapping process, alloys are added for deoxidation and alloying, and 200 kg of lime is added for slag washing. The chemical composition (mass percentage) of the resulting initial molten steel is: C: 0.05%, Si: 0.1%, Mn: 0.7%, P: ≤0.012%, with the remainder being Fe and unavoidable impurities. S2.1. The initial molten steel is heated by electrodes in the LF refining furnace to increase the temperature. The initial molten steel is heated by electrodes in the LF refining furnace at a heating rate of 3℃ / min to bring the temperature of the molten steel to 1580℃. S2.2. First adjustment of silicon content: When the temperature of molten steel in the LF refining furnace reaches 1580℃ and the refining time reaches 8min, the silicon content in the molten steel is reduced to 0.7% by ordinary ferrosilicon treatment. At the same time, other alloying elements to be added are adjusted to the internal control range to form a composition that is suitable for deep deoxidation environment and meets the performance requirements of the final product. S2.3. Deoxidation and denitrogenation: When the molten steel has completed the first silicon content adjustment and the refining time reaches 15 minutes, it undergoes a one-time deep deoxidation treatment. By adding aluminum blocks, the Al2O3 deoxidation products in the molten steel form a cluster structure, which is easy to float and separate. At the same time, the nitrogen in the molten steel combines with aluminum to form AlN inclusions and floats to the surface, effectively reducing the nitrogen content in the molten steel. After this treatment, the molten steel obtains good purity and a suitable compositional basis. S2.4. First soft argon blowing: The deoxidized and denitrogenated molten steel is treated with soft argon for ≥5 minutes, with an argon flow rate of 200NL / min. The argon flow rate is ≥5 minutes, and the molten steel surface is slightly fluctuated to promote the full floating of residual Al2O3 inclusions in the molten steel and further improve the purity of the molten steel. S2.5. Second adjustment of silicon content: After the first soft blowing argon treatment, the molten steel is treated with ferrosilicon in the later stage of refining to precisely adjust the silicon content in the molten steel to 1.1%. The ferrosilicon used in the second time contains 0.3~1.0wt% Ca element to achieve the purpose of calcium treatment and the target composition requirements. S2.6. The molten steel that has undergone the second silicon content adjustment is subjected to soft-blowing argon treatment for ≥6 minutes at a flow rate of 200 NL / min, with the molten steel surface slightly fluctuating. This process homogenizes the steel composition and further purifies it. After this treatment, the final chemical composition (mass percentage) of the molten steel is: C: 0.13%, Si: 1.1%, Mn: 1.60%, P: ≤0.015%, S: ≤0.003%, Al: 0.45%, Ti: 0.020%, Ca: 0.0010-0.0060%, with the remainder being Fe and unavoidable impurities. At the same time, the temperature of the molten steel is controlled at 40°C above the liquidus temperature of the steel grade, providing suitable conditions for the continuous casting process. S3.1. Tundish (The tundish is a transitional container located between the ladle and the crystallizer, used to receive molten steel from the ladle and stably supply steel to the crystallizer, while also having the functions of buffering, distributing the steel flow and promoting the floating of inclusions) Before receiving molten steel, it is purged and filled with CO2 gas with a purity of ≥90% for a purging time of ≥3 minutes, so that the nitrogen and oxygen in the tundish are fully replaced, providing a low-oxygen and low-nitrogen casting environment for the molten steel; S3.2. The refined molten steel is introduced into the pretreated tundish through a long nozzle. When the weight of the molten steel in the tundish reaches 20 tons, it flows into the crystallizer under the control of a stopper rod. The molten steel begins to solidify in the crystallizer at an initial pouring speed of 0.3 m / min, and after 90 seconds, it solidifies at an acceleration of 0.2 m / min. 2 Accelerate to 0.8 m / min; after stabilizing at 0.8 m / min for 120 seconds, accelerate again to 0.1 m / min. 2 Once the target casting speed is reached, the casting speed of the molten steel is controlled within the range of 0.8-1.5 m / min throughout the continuous casting process, and is dynamically adjusted according to the production rhythm. S3.3. A pre-melted protective slag is added to the surface of the molten steel in the crystallizer. The basicity of the protective slag is 1.27, the melting point is 1035℃, and the viscosity is 0.02 Pa·s. Its chemical composition (mass percentage) is: SiO2 26.6%, CaO 36%, Al2O3 ≤0.8%, C 3.2%, Na2O 4%, Li2O 3.0%, with the remainder being unavoidable impurities. It serves to lubricate the billet shell and copper plate in the crystallizer, control heat transfer, and effectively prevent secondary oxidation of the molten steel and slag entrapment. S3.4. During solidification, the molten steel is subjected to roller electromagnetic stirring with a stirring current of 200A and a frequency of 4Hz, making the solidified structure of the molten steel more uniform and dense. At the same time, the billet shell is lightly reduced, with the solid fraction controlled in the reduced range of 0.45-0.99 and the reduction amount of 7.0mm, which effectively improves the center segregation of the billet. After the above treatment, the center segregation of the billet is C-class ≤1.5, and the number of consecutive heats can reach 13. This realizes the stable, economical and mass production of NM300TP dual-phase steel, and eliminates the need for the RH process, significantly reducing production costs.

[0023] The surface quality of the cast billet product obtained in this embodiment is good, with no dents or cracks.

[0024] Example 2 This embodiment 2 provides a method for preparing NM300TP dual-phase steel for iron horses. The difference from embodiment 1 is that the silicon content is adjusted to 0.75% in the first adjustment and 1.2% in the second adjustment. Other process parameters are kept the same as in embodiment 1. After the above treatment, stable, economical and mass production of NM300TP dual-phase steel for iron horses is achieved, and no RH process is required. The surface quality of the cast billet product obtained in this embodiment is good, without dents and cracks.

[0025] Example 3 This embodiment 3 provides a method for preparing NM300TP dual-phase steel for iron horses. The difference from embodiment 1 is that the amount of aluminum block added in the deoxidation and denitrification step is 6.5 kg / ton of steel; other process parameters are consistent with those in embodiment 1. After the above treatment, the surface quality of the cast billet product obtained in this embodiment is good, without dents or cracks.

[0026] Example 4 This embodiment 4 provides a method for preparing NM300TP dual-phase steel for ironmaking. The difference from embodiment 1 is that the basicity of the protective slag covering the surface of the molten steel in the crystallizer is 1.35, while other process parameters remain the same as in embodiment 1. The strip steel product obtained in this embodiment has good surface quality, with no dents or cracks.

[0027] Comparative Example 1 Comparative Example 1 provides a method for preparing NM300TP dual-phase steel for iron and steel. The difference from Example 1 is that the traditional process route of iron, converter, LF refining, RH refining, continuous casting, hot rolling, and leveling is adopted. Due to the increase in the RH process, the production cost is increased, but the surface quality of the cast billet is generally poor, with slight depressions.

[0028] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing NM300TP dual-phase steel for iron and steel horses, characterized in that, Includes the following steps: The initial molten steel is refined, and the refining steps include: heating, adjusting the alloy composition, first adjustment of silicon content, deoxidation and denitrogenation, second adjustment of silicon content, and then continuous casting to obtain a billet; The deoxidation and denitrification steps include: adding aluminum blocks or aluminum wires to the molten steel in one go to deoxidize and denitrify the molten steel; The initial adjustment of silicon content involves using ferrosilicon or silicomanganese to adjust the silicon content in the molten steel to 0.7-0.8 wt%. The second step of adjusting the silicon content includes: adjusting the silicon content in the molten steel to 1.1~1.3wt% using ferrosilicon, with the ferrosilicon used the second time containing 0.3~1.0wt% Ca.

2. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, After deoxygenation and denitrification and before the second adjustment of silicon content, the process also includes a first soft blowing of argon gas. After completing the second adjustment of silicon content, a second soft-blowing argon process is also included.

3. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, The continuous casting process includes pouring molten steel from a ladle into a tundish, and then pouring it from the tundish into a crystallizer to solidify into a billet shell. Before pouring molten steel from the ladle into the tundish, it also includes using steel with a purity of ≥90%. The intermediate batch is purged and filled with gas for ≥3 minutes.

4. The method for preparing NM300TP dual-phase steel for ironworks according to claim 3, characterized in that, During continuous casting, a protective slag is also added, comprising the following components by mass percentage: 25%–30%, CaO 35%–40%, ≤1.0%, C 3.0%~5.0%, 4.0%~7.0%, 2.0% to 5.0%, with the balance being unavoidable impurities; The protective slag has an alkalinity of 1.30–1.40, a melting point of 1040℃–1100℃, and a viscosity of 0.05 Pa·s–0.10 Pa·s.

5. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, During the continuous casting process, electromagnetic stirring is used, with a stirring current of 200~300A and a frequency of 4~7HZ.

6. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, During the continuous casting process, a light reduction is adopted, wherein the solid fraction reduction range is 0.45~0.99 and the reduction amount is 7~8mm.

7. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, After refining and before continuous casting, the temperature of the molten steel is 40°C to 60°C higher than the seed liquidus temperature.

8. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, During the continuous casting process, the casting speed is 0.8~1.5m / min.

9. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, The method for preparing the initial molten steel includes: deoxidizing and alloying the molten iron and washing the slag to obtain the initial molten steel.

10. The method for preparing NM300TP dual-phase steel for ironworks according to claim 1, characterized in that, The initial molten steel has the following chemical composition by mass percentage: C: 0.05%–0.10%, Si: 0.1%–0.8%, Mn: 0.7%–1.70%, P: ≤0.012%, with the remainder being Fe and unavoidable impurities.