Method for reducing nitrogen absorption in converter tapping process

Abstract

The invention discloses a method for reducing nitrogen absorption in a converter tapping process in the technical field of metallurgy. The core of the method is that an yttrium-zirconium-based non-oxide melt modifier is adopted, the yttrium-zirconium-based non-oxide melt modifier is prepared by mixing non-oxide powder such as yttrium nitride, zirconium nitride and boron nitride with a calcium fluoride fluxing agent, carrying out surface modification and then carrying out vacuum hot-pressing compounding with aluminum-silicon-calcium alloy particles, and all the raw materials are commercially available products. When the modifier is applied, the modifier is preheated firstly, is added into a steel ladle through a steel flow impact area at the initial stage of converter tapping, and is dispersed and subjected to deep deoxidation and nitrogen fixation reaction by utilizing steel flow turbulence; starting bottom argon blowing stirring of the steel ladle to promote the reaction product to float upwards; and standing after tapping to form a protective slag layer. According to the method, through the synergistic effect of the active non-oxide particles formed by the modifier in the molten steel and the low-oxygen potential melt, efficient inhibition of the nitrogen absorption process of the molten steel is achieved, the process steps are simple and easy to integrate to an existing production process, and the production cost of high-quality steel can be remarkably reduced.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, specifically relating to a method for reducing nitrogen absorption during converter tapping. Background Technology

[0002] In the iron and steel metallurgy industry, converter steelmaking is the most important steelmaking method today. Its tapping process, as a crucial link between converter primary refining and ladle refining, has a decisive impact on the purity and chemical composition control of the final molten steel. Among the challenges, nitrogen accumulation in molten steel during tapping has long been a prominent difficulty that has plagued metallurgists and hindered the production of high-quality steel. When molten steel, after being smelted in the converter, is poured into the ladle through the taphole, the high drop causes severe impact, resulting in significant turbulence and exposure of the molten steel surface, and the entrainment of large amounts of air and top slag. Nitrogen molecules in the air take this opportunity to dissolve and permeate into the molten steel through the gas-liquid interface. Because nitrogen has extremely low solubility in solid steel, it is dissolved in liquid steel in an atomic state. Once solidified, it forms harmful nitrides or causes lattice distortion, severely deteriorating the steel's ductility, toughness, weldability, and resistance to aging. In particular, as the market demands increasingly stringent requirements for high-end plate steel, pipeline steel, and automotive steel, the control of nitrogen content has reached extremely low levels. This makes controlling nitrogen absorption during the steel tapping stage and preventing subsequent nitrogen pollution that is difficult to remove an indispensable prerequisite for the production of such steels.

[0003] To address these challenges, existing technologies have proposed various methods to reduce nitrogen absorption during converter tapping, but all have limitations to varying degrees. The first type of method optimizes tapping operations and equipment, such as using long nozzles and argon seals to reduce the contact between the steel stream and air. However, these measures cannot completely eliminate surface turbulence and exposure caused by impact within the ladle, representing passive protection with limited effectiveness. The second type utilizes metallurgical slag for control, increasing the nitrogen capacity of the slag system covering the molten steel by adjusting its composition, enabling it to absorb nitrogen diffused from the molten steel. However, this oxide-based slag absorption process is limited by the slag-metal interface reaction rate and mass transfer conditions, resulting in slow denitrification kinetics. Furthermore, high-nitrogen-capacity slag often requires a high proportion of oxides of elements such as titanium and aluminum, which may adversely affect furnace lining life or subsequent refining operations. The third type is bubble flotation, which involves blowing inert gas such as argon into the bottom of the ladle. Utilizing the near-zero nitrogen partial pressure in the rising bubbles, dissolved nitrogen from the molten steel is carried to the slag surface. The efficiency of this method is highly dependent on the size and distribution of bubbles and the flow state of the molten steel. Improper control can easily lead to molten steel splashing and temperature loss, and the removal effect on already dissolved nitrogen is unstable. The fourth type of method is to introduce composite denitrification agents, commonly alloys or mixtures containing strong deoxidizing elements such as silicon, calcium, and aluminum. These materials mainly reduce the oxygen activity of molten steel through deep deoxidation, indirectly inhibiting nitrogen dissolution by utilizing the competitive relationship between oxygen and nitrogen dissolution. However, they are not specifically "nitrogen-capturing agents" and lack an active and efficient mechanism for fixing and removing already absorbed nitrogen atoms. Therefore, there is an urgent industrial need to develop a new technology that can actively, efficiently, and stably capture and remove nitrogen from molten steel, and is easy to integrate into existing steelmaking processes.

[0004] In recent years, advancements in materials science have provided new insights into the design of metallurgical additives. Researchers have discovered that certain rare earth and transition metal nitrides, borides, and other non-oxide ceramic materials possess extremely high thermodynamic stability and a unique affinity for elements such as nitrogen and oxygen at high temperatures. This suggests a possibility: if a composite additive can be designed with this type of non-oxide ceramic phase as the core functional component and effectively dispersed in molten steel under dynamic conditions during the tapping process, a completely new pathway for nitrogen control in molten steel may be opened. This additive should not only possess the deoxidizing capabilities of traditional materials but also be able to directly adsorb and fix nitrogen atoms on the surface of its functional particles, forming stable compound clusters. These clusters can then be rapidly floated to the surface and removed by the flow of molten steel and the agitation of bubbles, thus achieving a leap from "inhibition" to "active removal" of the nitrogen absorption process. However, successfully introducing such functional ceramic materials, which are typically powdery, difficult to wet with molten steel, and prone to agglomeration, into the high-temperature, high-speed, multiphase coexistence of the tapping steel flow, and ensuring that they fully realize their theoretical functions, involves complex composite material design and preparation processes. This constitutes a pressing technical challenge in this field. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for reducing nitrogen absorption during the converter tapping process.

[0006] A first aspect of the present invention provides a method for reducing nitrogen absorption during converter tapping, comprising the following steps: S1. Place the yttrium zirconium-based non-oxide melt modifier in a heat-resistant hopper and preheat it to obtain the preheated yttrium zirconium-based non-oxide melt modifier. S2. When the converter taps steel, the preheated yttrium zirconium-based non-oxide melt modifier is fed into the ladle through the alloy feeding chute located above the ladle and directly in front of the steel flow impact area. S3. After adding the yttrium zirconium-based non-oxide melt modifier, turn on the bottom blowing argon system of the ladle to blow out argon gas; S4. After the converter has finished tapping the steel, let the molten steel stand and proceed to the next refining process.

[0007] In this invention, during the converter tapping process, the yttrium-zirconium-based non-oxide melt modifier is preheated and then introduced into the ladle impact zone, where it rapidly melts and disperses under the action of the high-temperature steel flow. The aluminum-silicon-calcium alloy component preferentially oxidizes and slags, forming a covering layer to isolate air; while yttrium nitride and zirconium nitride react in situ with nitrogen atoms dissolved in the molten steel, generating high-melting-point, thermodynamically stable nitride inclusions, thereby fixing free nitrogen in the solid phase and significantly inhibiting secondary nitrogen absorption by the molten steel. Boron nitride, due to its graphite-like layered structure, can float on the surface of the molten steel, forming a physical barrier and further blocking the intrusion of atmospheric nitrogen. The introduction of bottom-blown argon not only promotes the uniform dispersion of the modifier but also accelerates the removal of inclusions by causing them to collide and grow through bubble uplift. The settling stage provides the kinetic conditions for the full uplift of inclusions and the separation of steel slag. The entire method, through the synergistic effect of a triple mechanism of "covering and isolation + chemical nitrogen fixation + inclusion removal," efficiently achieves low nitrogen absorption control during the converter tapping process.

[0008] According to a preferred embodiment of the present invention, in step S1, the preheating temperature is 150-250°C.

[0009] According to a preferred embodiment of the present invention, in step S2, the amount of preheated yttrium zirconium-based non-oxide melt modifier added is 1.5-3.0 kg / ton of steel.

[0010] According to a preferred embodiment of the present invention, in step S3, the flow rate of the argon gas is 100-150 NL / min.

[0011] According to a preferred embodiment of the present invention, in step S4, the molten steel is allowed to stand for 1-5 minutes.

[0012] According to a preferred embodiment of the present invention, the preparation steps of the yttrium zirconium-based non-oxide melt modifier include: A1. By weight, 33-60 parts of aluminum ingot, 5.5-18.8 parts of metallic silicon, and 2.8-11.3 parts of calcium block are placed into a graphite crucible, placed in a vacuum induction furnace, evacuated, filled with argon gas, heated to 850-900℃ for refining, and poured into a water-cooled copper mold to obtain an Al-Si-Ca ternary master alloy ingot. The Al-Si-Ca ternary master alloy ingot is crushed to obtain Al-Si-Ca alloy particles. A2. In an argon-protected glove box, mix 2.5-13.5 parts of yttrium nitride, 5.0-18.0 parts of zirconium nitride, and 5.0-18.0 parts of boron nitride to obtain a non-oxide composite powder; add 2.5-13.5 parts of calcium fluoride to the non-oxide composite powder and mix to obtain a mixed powder; sonicate the mixed powder in an anhydrous ethanol solution containing vinyltrimethoxysilane and vacuum dry to obtain a surface-modified functional phase composite powder; A3. Mix Al-Si-Ca alloy particles with surface-modified functional phase composite powder to obtain a mixture. Load the mixture into a mold with boron nitride release agent sprayed on the inner wall, place it in a vacuum hot press furnace, evacuate the vacuum, heat to 480-500℃, apply a pressure of 48-52MPa, and maintain the pressure and temperature to obtain a hot-pressed block. A4. After the hot-pressed block is cooled to 180-195°C in the furnace, it is taken out, crushed and sieved to obtain sieved particles; the sieved particles are placed in a tube furnace, heated to 395-405°C under argon protection and held at that temperature, and then cooled to room temperature under argon protection and vacuum packaged.

[0013] In this invention, the preparation process of the yttrium-zirconium-based non-oxide melt modifier is based on the principles of multiphase composite and interface control. First, aluminum, silicon, and calcium are uniformly alloyed through vacuum induction melting to form a ternary master alloy with strong reducing properties and good melt flowability. This alloy can rapidly melt and release active components during subsequent use, promoting slag-metal reactions. Simultaneously, yttrium nitride, zirconium nitride, and boron nitride, as core functional phases, are pre-mixed and coated with calcium fluoride as a physical isolation layer due to their high melting point, chemical inertness, and strong affinity for nitrogen, effectively preventing interfacial side reactions with the metal matrix during hot pressing. Calcium fluoride not only acts as a barrier but also integrates into the primary slag during tapping, improving slag flowability. Subsequently, the composite powder is surface-modified with a silane coupling agent to enhance its interfacial bonding with metal particles. After low-temperature vacuum hot pressing and inert atmosphere heat treatment, a dense, stable, and easily added block modifier is finally obtained.

[0014] According to a preferred embodiment of the present invention, in step A1, the refining time at 850-900°C is 10-20 minutes.

[0015] According to a preferred embodiment of the present invention, in step A2, the ultrasonic treatment time is 10-30 min.

[0016] According to a preferred embodiment of the present invention, in step A3, the pressure holding and heat preservation time is 30-60 minutes.

[0017] According to a preferred embodiment of the present invention, in step A4, the time for holding the temperature at 395-405°C is 2-4 hours.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention achieves a fundamental shift from passive prevention to active removal through the design of an original yttrium-zirconium-based non-oxide composite modifier. The modifier uses thermodynamically stable non-oxide ceramic phases such as yttrium nitride and zirconium nitride as its functional core. These phases can act as highly efficient "nitrogen traps" in high-temperature molten steel, directly capturing and firmly fixing dissolved nitrogen atoms. Their nitrogen-fixing ability is far stronger than the physical dissolution and absorption of traditional oxide slag systems. Simultaneously, the functional ceramic powder is combined with an aluminum-silicon-calcium alloy through a composite process, creating a unique "carrier-functional phase" structure. This structure ensures that, during application, the alloy carrier melts preferentially and exerts a strong deoxidizing effect, rapidly reducing the local oxygen activity of the molten steel and thermodynamically inhibiting nitrogen dissolution. At the same time, the released functional phase particles are highly dispersed in the molten steel, actively searching for and chemically binding dissolved nitrogen. This synergistic effect of "deep deoxidation creating a low-nitrogen potential environment" and "functional phase direct in-situ nitrogen fixation" is the fundamental reason for the excellent denitrification effect of this solution.

[0019] (2) The method of this invention exhibits high engineering practicality and operability. The entire process consists of only four clearly defined steps: preheating, addition, argon blowing, and settling. It relies entirely on the existing tapping and ladle refining equipment of steel enterprises, requiring no major modifications or complex investments, and is easily integrated into the current production line. The ingenuity of the method lies in the precise control of the process timing: by introducing the modifier into the steel flow impact zone at the beginning of tapping, the huge turbulent kinetic energy of the tapping process itself is fully utilized, achieving forced dispersion and emulsification of the modifier, and solving the technical problem that powder materials are difficult to uniformly enter the molten steel; then, bottom blowing argon stirring is turned on at the appropriate time, which not only further promotes homogenization, but more importantly, uses the floating argon bubbles as an efficient "transport tool" to quickly carry the small reaction products that have adsorbed nitrogen to the slag layer, greatly accelerating the separation and removal rate of denitrification products. This concise and efficient process design ensures that the theoretical material advantages can be fully utilized in actual industrial production.

[0020] (3) The present invention has outstanding comprehensive economic and technical benefits, broad applicability, and significant promotional value. Practical application shows that this method can stably reduce the nitrogen increase in molten steel during the converter tapping process by more than 80%, providing a reliable guarantee for the subsequent production of ultra-low nitrogen steel products. It is particularly suitable for severe working conditions such as high scrap ratio and low-carbon smelting, which are prone to nitrogen increase. In addition to the core nitrogen control effect, this technology also brings good side benefits: deep deoxidation purifies the molten steel and reduces oxide inclusions; the resulting reducing top slag is conducive to desulfurization reaction; and the overall cleanliness of the molten steel is improved, which may shorten the subsequent refining time and reduce comprehensive energy consumption and production costs. This solution combines simple on-site operation with precise offline material preparation, achieving advanced metallurgical functions while taking into account production convenience and economy, which is of great significance for promoting product upgrading and green manufacturing in the steel industry. Detailed Implementation

[0021] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention. Example

[0022] This embodiment provides a method for reducing nitrogen absorption during converter tapping, including the following steps: The yttrium zirconium-based non-oxide melt modifier was prepared.

[0023] Step A1: Preparation of the aluminum-silicon-calcium alloy carrier: Accurately weigh 460.0g of commercially available aluminum ingot, 88.0g of metallic silicon, and 52.0g of calcium block, totaling 600.0g. Place the above raw materials into a high-purity graphite crucible, and then place the crucible inside the furnace chamber of a medium-frequency vacuum induction melting furnace. After closing the furnace door, start the mechanical pump and Roots pump to evacuate the furnace. When the pressure inside the furnace is lower than 5.0 × 10⁻⁶... -2 At a pressure of 0.05 MPa, stop evacuation and introduce high-purity argon gas (99.999% purity) into the furnace to a slightly positive pressure state. Start the induction heating power supply and heat to 870°C at a rate of 15°C / min, refining at this temperature for 15 minutes to ensure complete melting and homogeneous composition of the alloy. After refining, tilt the furnace and pour the molten alloy into a pre-placed copper mold with circulating cooling water, allowing it to solidify rapidly to obtain an aluminum-silicon-calcium ternary master alloy ingot. Use a jaw crusher for primary crushing, then process it into particles with a diameter less than 5.0 mm using a stainless steel double-roll crusher to obtain aluminum-silicon-calcium alloy particles, which are then placed in a dryer for later use.

[0024] Step A2: Preparation of surface-modified functional phase composite powder: All operations in this step are performed in a glove box filled with high-purity argon gas, where the water and oxygen content are both below 0.1 ppm. Accurately weigh 65.0 g of yttrium nitride, 100.0 g of zirconium nitride, and 100.0 g of boron nitride, place them in a V-type mixer, and mechanically mix at 30 rpm for 30 min to obtain a uniform non-oxide composite powder. Add 65.0 g of calcium fluoride powder to this composite powder and continue mixing for 20 min to obtain a mixed powder with a total mass of 330.0 g. Take 1.0 L of anhydrous ethanol, add 10.0 mL of vinyltrimethoxysilane, and magnetically stir for 10 min to prepare a surface-modifying solution. Pour the mixed powder into this solution and sonicate it for 20 min using an ultrasonic cell disruptor at an output power of 400 W and a frequency of 40 kHz to ensure the powder is fully dispersed and coated with the silane coupling agent. After processing, vacuum filtration was performed using a Buchner funnel and a vacuum filtration device, and the filter cake was washed three times with a small amount of anhydrous ethanol. The filter cake was then transferred to a vacuum drying oven and dried at 80°C and -0.1 MPa for 12 hours. Subsequently, it was sieved through a 200-mesh nylon sieve to obtain a surface-modified functional phase composite powder with good flowability.

[0025] Step A3, Vacuum Hot Pressing Consolidation: Accurately weigh 600.0g of the aluminum-silicon-calcium alloy particles prepared in Step A1 and 330.0g of the functional phase composite powder prepared in Step A2, totaling 930.0g. Place both in a three-dimensional motion mixer and mix at a 45° angle and 60 rpm for 60 min to obtain a highly uniform mixture. Select a cylindrical graphite mold with an inner diameter of 50mm, uniformly spray a layer of boron nitride release agent slurry on its inner wall and dry it. Fill the mold with the mixture and gently vibrate it. Move the entire mold into a vacuum hot pressing sintering furnace and close the furnace chamber. Evacuate the furnace until the pressure inside is below 10Pa, and then start heating. Increase the temperature to 490℃ at a rate of 15℃ / min. After reaching the temperature, start the hydraulic system and slowly apply pressure to 50MPa, and hold the pressure at this temperature and pressure for 45 min to allow the low-melting-point components to soften and bond initially. Subsequently, while maintaining the pressure, continue to increase the temperature to 590℃ at a rate of 10℃ / min. After the temperature stabilizes, the pressure is increased to 100 MPa and held at this final process parameter for 60 minutes, so that the alloy particles and functional phase powder achieve a dense metallurgical bond through diffusion and plastic flow.

[0026] Step A4, Finished Product Processing and Activation: After the pressure holding period, turn off the heating power and stop pressurizing, allowing the sample to cool in the vacuum furnace. When the furnace temperature drops to 190℃, refill the furnace with high-purity argon to atmospheric pressure and remove the hot-pressed block. Use a dedicated crusher to crush the block and sieve it through a set of standard sieves to collect particles with a diameter between 5.0mm and 20.0mm. Spread the sieved particles evenly in an alumina crucible and place it in the isothermal zone of a horizontal tube furnace. Purge the furnace with high-purity argon at a flow rate of 5L / min for 10 minutes, then program the temperature to 400℃ at a rate of 10℃ / min and hold at this temperature for 3 hours to eliminate internal stress and activate the particle surface. After the holding period, cool the sample to room temperature under continuous argon protection. Finally, quickly pack the finished particles into an aluminum-plastic composite vacuum bag, vacuum-pack it, and seal it to obtain the yttrium zirconium-based non-oxide melt modifier, labeled YZNMM-1.

[0027] A method for reducing nitrogen absorption during converter tapping by applying the YZNMM-1 modifier.

[0028] Step S1, Pretreatment: For a converter heat with a steel output of 150t, based on the weight of the molten steel and the preset addition rate of 2.0kg / t steel, the total amount of modifier to be added is calculated to be 300.0kg. This quantitative amount of modifier is removed from its vacuum packaging and placed into a heat-resistant stainless steel charging hopper. The hopper is placed near the ladle being heated, and the ladle is preheated to 200℃ using radiant heat, and this temperature is maintained for at least 30 minutes to thoroughly remove any trace moisture that may have been adsorbed during transportation and storage.

[0029] Step S2, Initial Addition During Tapping: As the converter begins tapping, operators monitor the molten steel volume in the ladle using a ladle weighing system or level monitoring device. When the weight of the molten steel in the ladle reaches approximately one-quarter of the total tapped steel, i.e., approximately 37.5t, the alloy charging chute located above the ladle, with its discharge port directly facing the high-speed steel flow impact zone, is activated. The preheated modifier is then added to the ladle at a uniform and controllable rate over 60 seconds. The high-speed falling steel flow generates intense shear and impact on the modifier, causing it to rapidly emulsify and disperse within the molten steel.

[0030] Step S3: Initiate bottom-blowing argon stirring: Approximately 1 minute after the modifier is added, or when the molten steel in the ladle reaches about three-quarters of the total steel output, activate the gas supply system of the permeable bricks at the bottom of the ladle to blow high-purity argon into the ladle. The argon flow rate is set to 120 NL / min, forming a large number of fine, uniform bubbles through the bottom-dispersing permeable bricks. These rising argon bubbles further enhance the stirring of the molten steel, promote the collision and polymerization of the modifier reaction products, and carry the fine nitrogen-adsorbed particles to the surface of the molten steel.

[0031] Step S4, Settling and Slag Formation: After the converter tapping is complete, the ladle stops receiving molten steel. The molten steel is allowed to settle in the ladle for 3.0 minutes. During this period, the vigorous churning gradually subsides, and the low-melting-point deoxidation and denitrification products generated by the reaction of the active components in the modifier, along with the inherent fluxing components, rise to the top of the molten steel, forming a liquid protective slag layer of a certain thickness and coverage. This slag layer physically isolates the air and continues to absorb nitrogen diffusing from the molten steel. After settling, the ladle car transports the molten steel to the LF refining station for further processing. Example

[0032] This embodiment provides a method for reducing nitrogen absorption during converter tapping, including the following steps: The yttrium zirconium-based non-oxide melt modifier was prepared.

[0033] Step A1: Preparation of the aluminum-silicon-calcium alloy carrier: Accurately weigh 540.0g of commercially available aluminum ingot, 55.0g of metallic silicon, and 28.0g of calcium block, totaling 623.0g. Place the above raw materials into a high-purity graphite crucible, and then place the crucible inside the furnace chamber of a medium-frequency vacuum induction melting furnace. After closing the furnace door, start the mechanical pump and Roots pump to evacuate the furnace. When the pressure inside the furnace is lower than 5.0 × 10⁻⁶... -2 At a pressure of 0.05 MPa, stop evacuation and introduce high-purity argon gas (99.999% purity) into the furnace to a slightly positive pressure state. Start the induction heating power supply and heat to 860°C at a rate of 15°C / min, refining at this temperature for 12 minutes to ensure complete melting and homogeneous composition of the alloy. After refining, tilt the furnace and pour the molten alloy into a pre-placed copper mold with circulating cooling water, allowing it to solidify rapidly to obtain an aluminum-silicon-calcium ternary master alloy ingot. Use a jaw crusher for primary crushing, then process it into particles with a diameter less than 5.0 mm using a stainless steel double-roll crusher to obtain aluminum-silicon-calcium alloy particles, which are then placed in a dryer for later use.

[0034] Step A2: Preparation of surface-modified functional phase composite powder: All operations in this step are performed in a glove box filled with high-purity argon gas, where the water and oxygen content are both below 0.1 ppm. Accurately weigh 25.0 g of yttrium nitride, 180.0 g of zirconium nitride, and 50.0 g of boron nitride, place them in a V-type mixer, and mechanically mix at 30 rpm for 30 min to obtain a uniform non-oxide composite powder. Add 25.0 g of calcium fluoride powder to this composite powder and continue mixing for 20 min to obtain a mixed powder with a total mass of 280.0 g. Take 1.0 L of anhydrous ethanol, add 10.0 mL of vinyltrimethoxysilane, and magnetically stir for 10 min to prepare a surface-modifying solution. Pour the mixed powder into this solution and sonicate it for 15 min using an ultrasonic cell disruptor at an output power of 400 W and a frequency of 40 kHz to fully disperse the powder and coat it with the silane coupling agent. After processing, vacuum filtration was performed using a Buchner funnel and a vacuum filtration device, and the filter cake was washed three times with a small amount of anhydrous ethanol. The filter cake was then transferred to a vacuum drying oven and dried at 75°C and -0.1 MPa for 12 hours. Subsequently, it was sieved through a 200-mesh nylon sieve to obtain a surface-modified functional phase composite powder with good flowability.

[0035] Step A3, Vacuum Hot Pressing Consolidation: Accurately weigh 623.0g of the aluminum-silicon-calcium alloy particles prepared in Step A1 and 280.0g of the functional phase composite powder prepared in Step A2, totaling 903.0g. Place both in a three-dimensional motion mixer and mix at a 45° angle and 60 rpm for 60 minutes to obtain a highly uniform mixture. Select a cylindrical graphite mold with an inner diameter of 50mm, uniformly spray a layer of boron nitride release agent slurry on its inner wall and dry it. Fill the mold with the mixture and gently vibrate it. Move the entire mold into a vacuum hot pressing sintering furnace and close the furnace chamber. Evacuate the furnace until the pressure inside is below 10Pa, and then start heating. Increase the temperature to 485℃ at a rate of 15℃ / min. After reaching the temperature, start the hydraulic system and slowly apply pressure to 49MPa, and hold the pressure at this temperature and pressure for 35 minutes to allow the low-melting-point components to soften and bond initially. Subsequently, while maintaining the pressure, continue to increase the temperature to 585℃ at a rate of 10℃ / min. After the temperature stabilizes, the pressure is increased to 99 MPa and held at this final process parameter for 50 minutes, so that the alloy particles and functional phase powder achieve a dense metallurgical bond through diffusion and plastic flow.

[0036] Step A4, Finished Product Processing and Activation: After the pressure holding period, turn off the heating power and stop pressurizing, allowing the sample to cool in the vacuum furnace. When the furnace temperature drops to 190℃, refill the furnace with high-purity argon to atmospheric pressure and remove the hot-pressed block. Crush the block using a dedicated crusher and sieve it through a set of standard sieves to collect particles with a diameter between 5.0mm and 20.0mm. Spread the sieved particles evenly in an alumina crucible and place it in the isothermal zone of a horizontal tube furnace. Purge the furnace with high-purity argon at a flow rate of 5L / min for 10 minutes, then program the temperature to 398℃ at a rate of 10℃ / min and hold at this temperature for 2.5 hours to eliminate internal stress and activate the particle surface. After the holding period, cool the sample to room temperature under continuous argon protection. Finally, quickly pack the finished particles into an aluminum-plastic composite vacuum bag, vacuum-pack it, and seal it to obtain the yttrium zirconium-based non-oxide melt modifier, labeled YZNMM-2.

[0037] A method for reducing nitrogen absorption during converter tapping by applying the YZNMM-2 modifier.

[0038] Step S1, Pretreatment: For a converter heat with a steel output of 150t, based on the weight of the molten steel and the preset addition rate of 1.8kg / t steel, the total amount of modifier to be added is calculated to be 270.0kg. This quantitative amount of modifier is removed from its vacuum packaging and placed into a heat-resistant stainless steel charging hopper. The hopper is placed near the ladle being heated, and the ladle is preheated to 180℃ using radiant heat, and this temperature is maintained for at least 30 minutes to thoroughly remove any trace moisture that may have been adsorbed during transportation and storage.

[0039] Step S2, Initial Addition During Tapping: As the converter begins tapping, operators monitor the molten steel volume in the ladle using a ladle weighing system or level monitoring device. When the weight of the molten steel in the ladle reaches approximately one-fifth of the total tapped steel, i.e., approximately 30.0t, the alloy charging chute located above the ladle, with its discharge port directly facing the high-speed steel flow impact zone, is activated. The preheated modifier is then added to the ladle at a uniform and controllable rate over 60 seconds. The high-speed falling steel flow generates intense shear and impact on the modifier, causing it to rapidly emulsify and disperse within the molten steel.

[0040] Step S3: Initiate bottom-blowing argon stirring: Approximately 1 minute after the modifier is added, or when the molten steel in the ladle reaches about three-quarters of the total steel output, activate the gas supply system of the permeable bricks at the bottom of the ladle to blow high-purity argon into the ladle. The argon flow rate is set to 110 NL / min, forming a large number of fine, uniform bubbles through the bottom-dispersing permeable bricks. These rising argon bubbles further enhance the stirring of the molten steel, promote the collision and polymerization of the modifier reaction products, and carry the fine nitrogen-adsorbed particles to the surface of the molten steel.

[0041] Step S4, Settling and Slag Formation: After the converter tapping is complete, the ladle stops receiving molten steel. The molten steel is allowed to settle in the ladle for 2.0 minutes. During this period, the vigorous churning gradually subsides, and the low-melting-point deoxidation and denitrification products generated by the reaction of the active components in the modifier, along with the inherent fluxing components, rise to the top of the molten steel, forming a liquid protective slag layer of a certain thickness and coverage. This slag layer physically isolates the air and continues to absorb nitrogen diffusing from the molten steel. After settling, the ladle car transports the molten steel to the LF refining station for further processing. Example

[0042] This embodiment provides a method for reducing nitrogen absorption during converter tapping, including the following steps: The yttrium zirconium-based non-oxide melt modifier was prepared.

[0043] Step A1: Preparation of the aluminum-silicon-calcium alloy carrier: Accurately weigh 330.0g of commercially available aluminum ingot, 188.0g of metallic silicon, and 113.0g of calcium block, totaling 631.0g. Place the above raw materials into a high-purity graphite crucible, and then place the crucible inside the furnace chamber of a medium-frequency vacuum induction melting furnace. After closing the furnace door, start the mechanical pump and Roots pump to evacuate the furnace. When the pressure inside the furnace is lower than 5.0 × 10⁻⁶... -2 At a pressure of 0.05 MPa, stop evacuation and introduce high-purity argon gas (99.999% purity) into the furnace to a slightly positive pressure state. Start the induction heating power supply and heat to 890℃ at a rate of 15℃ / min, refining at this temperature for 18 minutes to ensure complete melting and homogeneous composition of the alloy. After refining, tilt the furnace and pour the molten alloy into a pre-placed copper mold with circulating cooling water, allowing it to solidify rapidly to obtain an aluminum-silicon-calcium ternary master alloy ingot. Use a jaw crusher for primary crushing, then process it into particles with a diameter less than 5.0 mm using a stainless steel double-roll crusher to obtain aluminum-silicon-calcium alloy particles, which are then placed in a dryer for later use.

[0044] Step A2: Preparation of surface-modified functional phase composite powder: All operations in this step are performed in a glove box filled with high-purity argon gas, where the water and oxygen content are both below 0.1 ppm. Accurately weigh 135.0 g of yttrium nitride, 50.0 g of zirconium nitride, and 180.0 g of boron nitride, place them in a V-type mixer, and mechanically mix at 30 rpm for 30 min to obtain a uniform non-oxide composite powder. Add 135.0 g of calcium fluoride powder to this composite powder and continue mixing for 20 min to obtain a mixed powder with a total mass of 500.0 g. Take 1.0 L of anhydrous ethanol, add 10.0 mL of vinyltrimethoxysilane, and magnetically stir for 10 min to prepare a surface-modifying solution. Pour the mixed powder into this solution and sonicate it for 25 min using an ultrasonic cell disruptor at an output power of 400 W and a frequency of 40 kHz to fully disperse the powder and coat it with the silane coupling agent. After processing, vacuum filtration was performed using a Buchner funnel and a vacuum filtration device, and the filter cake was washed three times with a small amount of anhydrous ethanol. The filter cake was then transferred to a vacuum drying oven and dried at 82℃ and -0.1MPa for 12 hours. Subsequently, it was sieved through a 200-mesh nylon sieve to obtain a surface-modified functional phase composite powder with good flowability.

[0045] Step A3, Vacuum Hot Pressing Consolidation: Accurately weigh 631.0g of the aluminum-silicon-calcium alloy particles prepared in Step A1 and 500.0g of the functional phase composite powder prepared in Step A2, totaling 1131.0g. Place both in a three-dimensional motion mixer and mix at a 45° angle and 60 rpm for 60 min to obtain a highly uniform mixture. Select a cylindrical graphite mold with an inner diameter of 50mm, uniformly spray a layer of boron nitride release agent slurry on its inner wall and dry it. Fill the mold with the mixture and gently vibrate it. Move the entire mold into a vacuum hot pressing sintering furnace and close the furnace chamber. Evacuate the furnace until the pressure inside is below 10Pa, and then start heating. Increase the temperature to 500℃ at a rate of 15℃ / min. After reaching the temperature, start the hydraulic system and slowly apply pressure to 52MPa, and hold the pressure at this temperature and pressure for 55 min to allow the low-melting-point components to soften and bond initially. Subsequently, while maintaining the pressure, continue to increase the temperature to 600℃ at a rate of 10℃ / min. After the temperature stabilizes, the pressure is increased to 102 MPa and held at this final process parameter for 70 minutes, so that the alloy particles and functional phase powder achieve a dense metallurgical bond through diffusion and plastic flow.

[0046] Step A4, Finished Product Processing and Activation: After the pressure holding period, turn off the heating power and stop pressurizing, allowing the sample to cool in the vacuum furnace. When the furnace temperature drops to 190℃, refill the furnace with high-purity argon to atmospheric pressure and remove the hot-pressed block. Crush the block using a dedicated crusher and sieve it through a set of standard sieves to collect particles with a diameter between 5.0mm and 20.0mm. Spread the sieved particles evenly in an alumina crucible and place it in the isothermal zone of a horizontal tube furnace. Purge the furnace with high-purity argon at a flow rate of 5L / min for 10 minutes, then program the temperature to 402℃ at a rate of 10℃ / min and hold at this temperature for 3.5 hours to eliminate internal stress and activate the particle surface. After the holding period, cool the sample to room temperature under continuous argon protection. Finally, quickly pack the finished particles into an aluminum-plastic composite vacuum bag, vacuum-pack it, and seal it to obtain the yttrium zirconium-based non-oxide melt modifier, labeled YZNMM-3.

[0047] A method for reducing nitrogen absorption during converter tapping by applying the YZNMM-3 modifier.

[0048] Step S1, Pretreatment: For a converter heat with a steel output of 150t, based on the weight of the molten steel and the preset addition rate of 2.5kg / t steel, the total amount of modifier to be added is calculated to be 375.0kg. This quantitative amount of modifier is removed from its vacuum packaging and placed into a heat-resistant stainless steel charging hopper. The hopper is placed near the ladle being heated, and the ladle is preheated to 230℃ using radiant heat, and this temperature is maintained for at least 30 minutes to thoroughly remove any trace moisture that may have been adsorbed during transportation and storage.

[0049] Step S2, Initial Addition During Tapping: As the converter begins tapping, operators monitor the molten steel volume in the ladle using a ladle weighing system or level monitoring device. When the weight of the molten steel in the ladle reaches approximately one-third of the total tapped steel, i.e., approximately 50.0t, the alloy charging chute located above the ladle, with its discharge port directly facing the high-speed steel flow impact zone, is activated. The preheated modifier is then added to the ladle at a uniform and controllable rate over 60 seconds. The high-speed falling steel flow generates intense shear and impact on the modifier, causing it to rapidly emulsify and disperse within the molten steel.

[0050] Step S3: Initiate bottom-blowing argon stirring: Approximately 1 minute after the modifier is added, or when the molten steel in the ladle reaches about three-quarters of the total steel output, activate the gas supply system of the permeable bricks at the bottom of the ladle to blow high-purity argon into the ladle. The argon flow rate is set to 140 NL / min, forming a large number of fine, uniform bubbles through the bottom-dispersed permeable bricks. These rising argon bubbles further enhance the stirring of the molten steel, promote the collision and polymerization of the modifier reaction products, and carry the fine nitrogen-adsorbed particles to the surface of the molten steel.

[0051] Step S4, Settling and Slag Formation: After the converter tapping is complete, the ladle stops receiving molten steel. The molten steel is allowed to settle in the ladle for 4.0 minutes. During this period, the vigorous churning gradually subsides, and the low-melting-point deoxidation and denitrification products generated by the reaction of the active components in the modifier, along with the inherent fluxing components, rise to the top of the molten steel, forming a liquid protective slag layer of a certain thickness and coverage. This slag layer physically isolates the air and continues to absorb nitrogen diffusing from the molten steel. After settling, the ladle car transports the molten steel to the LF refining station for further processing.

[0052] Comparative Example 1 The difference between this comparative example and Example 1 is that the functional phase powder of the modifier used does not contain yttrium nitride. In modifier preparation step A2, 165.0 g of zirconium nitride, 100.0 g of boron nitride, and 65.0 g of calcium fluoride were accurately weighed to maintain a total mass of 330.0 g, without adding yttrium nitride. All parameters, equipment, and operational details of the remaining preparation steps A1, A3, and A4 are completely consistent with those of Example 1, and the resulting modifier is labeled DYZNMM-1. In the application method, all parameters of steps S1 to S4, including the preheating temperature of 200°C, the amount added of 300.0 kg, the timing of addition, the argon flow rate of 120 NL / min, and the standing time of 3.0 min, are completely consistent with those of Example 1.

[0053] Comparative Example 2 The difference between this comparative example and Example 1 is that the functional phase powder of the modifier used does not contain zirconium nitride. In modifier preparation step A2, 165.0 g of yttrium nitride, 100.0 g of boron nitride, and 65.0 g of calcium fluoride were accurately weighed to maintain a total mass of 330.0 g, without adding zirconium nitride. All parameters, equipment, and operational details of the remaining preparation steps A1, A3, and A4 are completely consistent with those of Example 1, and the resulting modifier is labeled DYZNMM-2. In the application method, all parameters of steps S1 to S4, including the preheating temperature of 200°C, the amount added of 300.0 kg, the timing of addition, the argon flow rate of 120 NL / min, and the standing time of 3.0 min, are completely consistent with those of Example 1.

[0054] Comparative Example 3 The difference between this comparative example and Example 1 is that the functional phase powder of the modifier used does not contain boron nitride. In modifier preparation step A2, 65.0 g of yttrium nitride, 200.0 g of zirconium nitride, and 65.0 g of calcium fluoride were accurately weighed to maintain a total mass of 330.0 g, without adding boron nitride. All parameters, equipment, and operational details of the remaining preparation steps A1, A3, and A4 are completely consistent with those of Example 1, and the resulting modifier is labeled DYZNMM-3. In the application method, all parameters of steps S1 to S4, including the preheating temperature of 200°C, the amount added of 300.0 kg, the timing of addition, the argon flow rate of 120 NL / min, and the standing time of 3.0 min, are completely consistent with those of Example 1.

[0055] Comparative Example 4 The difference between this comparative example and Example 1 is that the modifier of this invention is not used. The application method is as follows: Step S1: When the converter tapps to about one-third of its capacity, conventional aluminum ingots are added to the ladle for deoxidation. The amount of aluminum ingots added is calculated based on the carbon content of the molten steel. Step S2: After tapping, 300.0 kg of ordinary silicon-calcium based covering agent is added to the slag surface of the ladle. Step S3: The bottom blowing argon system of the ladle is turned on, the argon flow rate is set to 120 NL / min, and stirring is performed for 3.0 min. Step S4: After standing for 3.0 min, the product enters the refining process.

[0056] Comparative Example 5 The difference between this comparative example and Example 1 is that it uses the exact same modifier YZNMM-1 as Example 1, but the order of addition is changed. The application method is as follows: Step S1: Preheat 300.0 kg of modifier to 200°C. Step S2: After the converter tapping is complete and the ladle is full, add the preheated modifier to the relatively calm molten steel surface through the feeding system. Step S3: After adding the modifier, immediately turn on the bottom blowing argon system of the ladle and stir at a flow rate of 120 NL / min for 3.0 min. Step S4: After standing for 3.0 min, proceed to the refining process.

[0057] In accordance with national and industry standard testing specifications, a series of standardized tests were conducted on the methods for reducing nitrogen absorption during converter tapping described in Examples 1-3 and Comparative Examples 1-5.

[0058] The performance tests of the embodiments and comparative examples of this invention were all conducted on a top-and-bottom combined blowing converter with a nominal capacity of 150t and its supporting refining system. The steel grade tested was low-carbon aluminum killed steel. All tests followed a uniform procedure: First, after oxygen supply is stopped at the end of the converter blowing process, a sample of the molten steel at the end point is taken inside the furnace using a disposable quartz sampler to determine the initial nitrogen content. Subsequently, the tapping and processing operations are strictly performed according to the processes described in each embodiment or comparative example. After the ladle is transported to the LF refining station, before power heating, a preheated probe-type sampler is used to take a sample of the LF incoming molten steel at a depth of 500 mm below the molten steel surface to determine the nitrogen content, oxygen activity, and inclusion analysis after processing. Simultaneously, a ladle top slag sample is obtained using a slag collection rod for slag composition analysis. Nitrogen content determination is performed using an inert gas pulse melting-thermal conductivity oxygen-nitrogen analyzer. The prepared steel sample is placed in a graphite crucible and melted in an ultra-high temperature pulse furnace under a high-purity helium carrier gas flow. The released nitrogen gas is separated by chromatography and measured by a thermal conductivity detector. Each sample is analyzed in triplicate, and the arithmetic mean is reported. Calibration is performed using national standard reference materials.

[0059] Oxygen activity in molten steel was measured online simultaneously with LF inlet samples using a constant oxygen probe and a solid electrolyte electrochemical sensor. The measurement temperature was the actual temperature of the molten steel, approximately 1600℃, and the readings were recorded after stabilization. Top slag composition analysis was performed using X-ray fluorescence spectrometry. The slag sample was ground to a particle size of less than 75μm, prepared using the powder pressing method, and the characteristic X-ray intensities of each element were measured under vacuum. The oxide composition was calculated using the standard working curve method, with particular attention paid to the sum of ferrous oxide and manganese oxide content.

[0060] The size analysis of micro-inclusions in steel was performed using a field emission scanning electron microscope and its attached energy dispersive spectrometer. The steel samples brought in by the LF station were made into metallographic specimens and polished. At least 20 fields of view were randomly selected in the backscattered electron image in non-conductive mode for observation and statistical analysis. The maximum size distribution range of the main oxide inclusions was measured and recorded.

[0061] The performance test data above are shown in Table 1.

[0062] Table 1 Performance Test Results

[0063] As can be seen from the above, the technical solutions of the present invention represented by Examples 1-3, compared with Comparative Examples 1-5, systematically solve several key problems existing in the nitrogen control technology of the existing converter steelmaking process.

[0064] First, a breakthrough was achieved in the core issue of nitrogen control efficiency: the example group consistently controlled the nitrogen increase in steel output at an extremely low level of 2.0-3.0 ppm, while the nitrogen increase in comparative examples 1-5 (each lacking one of the core components of yttrium nitride, zirconium nitride, or boron nitride) surged to over 8.0 ppm. This data directly demonstrates that existing additives relying on single or partial active components have serious shortcomings in nitrogen fixation capabilities, failing to achieve efficient and synergistic capture of nitrogen atoms in molten steel. This invention constructs a multifunctional "nitrogen trap" network through the precise composite of three non-oxides: yttrium, zirconium, and boron. Each component exhibits different physicochemical properties at high temperatures (such as different interfacial activities, nitrogen binding energies, and behaviors in molten steel), complementing and promoting each other. This solves the technical bottleneck of incomplete denitrification reactions and limited capacity caused by the single function of existing additives.

[0065] Secondly, this invention solves the problem of existing technologies failing to simultaneously achieve deep deoxidation and nitrogen fixation during the rapid and dynamic steel tapping process. Test data shows that the oxygen activity of the molten steel entering the LF station in the example group was only 8-12 ppm, and the oxidizability of the top slag (FeO+MnO content) was as low as 1.5-2.0%, far lower than that of the comparative group (oxygen activity above 25 ppm, slag oxidizability greater than 8.5%). This indicates that the modifier of this invention, while capturing nitrogen, achieves rapid and deep deoxidation through its alloy carrier, quickly creating a low-oxygen potential thermodynamic environment unfavorable to nitrogen dissolution. In contrast, the comparative group, due to the lack of functional components, disrupted the synergy of the system, resulting in incomplete deoxidation and higher oxidizability of the molten steel and slag. This not only weakens the thermodynamic conditions for nitrogen control but also proves that existing technologies often sacrifice one aspect for another, making it difficult to complete multiple refining tasks within the short time of steel tapping.

[0066] Finally, this invention solves the process problem of efficiently separating denitrification reaction products from the molten steel. The typical micro-inclusions in the example group were small (less than 8 micrometers), while the inclusions in the comparative group were significantly larger (more than 10 micrometers). This comparison illustrates that the synergistic effect of the complete non-oxide functional phase and flux in this invention promotes the polymerization, flotation, and absorption by the top slag of the formed deoxidation and denitrification products, thereby achieving efficient purification of the molten steel. In contrast, the comparative group, due to system imbalance, experienced deterioration in the morphology of the reaction products, making them prone to retention in the steel as large inclusions. This reflects the common problem in existing technologies that often neglect the engineering design of reaction products, leading to compromised steel cleanliness.

[0067] In summary, this invention, through innovative design of material components and optimized integration of application processes, not only significantly improves nitrogen control efficiency but also simultaneously optimizes oxygen level control and cleanliness of molten steel, systematically solving a series of interconnected technical problems in existing technologies, such as limited effectiveness, poor synergy, and difficulty in product removal.

Claims

1. A method for reducing nitrogen absorption during converter tapping, characterized in that, Includes the following steps: S1. Place the yttrium zirconium-based non-oxide melt modifier in a heat-resistant hopper and preheat it to obtain the preheated yttrium zirconium-based non-oxide melt modifier. S2. When the converter taps steel, the preheated yttrium zirconium-based non-oxide melt modifier is fed into the ladle through the alloy feeding chute located above the ladle and directly in front of the steel flow impact area. S3. After adding the yttrium zirconium-based non-oxide melt modifier, turn on the bottom blowing argon system of the ladle to blow out argon gas; S4. After the converter has finished tapping the steel, let the molten steel stand and proceed to the next refining process.

2. The method for reducing nitrogen absorption during converter tapping according to claim 1, characterized in that, In step S1, the preheating temperature is 150-250℃.

3. The method for reducing nitrogen absorption during converter tapping according to claim 1, characterized in that, In step S2, the amount of preheated yttrium zirconium-based non-oxide melt modifier added is 1.5-3.0 kg / ton of steel.

4. The method for reducing nitrogen absorption during converter tapping according to claim 1, characterized in that, In step S3, the flow rate of the argon gas is 100-150 NL / min.

5. The method for reducing nitrogen absorption during converter tapping according to claim 1, characterized in that, In step S4, the molten steel is allowed to stand for 1-5 minutes.

6. The method for reducing nitrogen absorption during converter tapping according to any one of claims 1-5, characterized in that, The preparation steps of the yttrium zirconium-based non-oxide melt modifier include: A1. By weight, 33-60 parts of aluminum ingot, 5.5-18.8 parts of metallic silicon, and 2.8-11.3 parts of calcium block are placed into a graphite crucible, placed in a vacuum induction furnace, evacuated, filled with argon gas, heated to 850-900℃ for refining, and poured into a water-cooled copper mold to obtain an Al-Si-Ca ternary master alloy ingot. The Al-Si-Ca ternary master alloy ingot is crushed to obtain Al-Si-Ca alloy particles. A2. In an argon-protected glove box, mix 2.5-13.5 parts of yttrium nitride, 5.0-18.0 parts of zirconium nitride, and 5.0-18.0 parts of boron nitride to obtain a non-oxide composite powder; add 2.5-13.5 parts of calcium fluoride to the non-oxide composite powder and mix to obtain a mixed powder; sonicate the mixed powder in an anhydrous ethanol solution containing vinyltrimethoxysilane and vacuum dry to obtain a surface-modified functional phase composite powder; A3. Mix Al-Si-Ca alloy particles with surface-modified functional phase composite powder to obtain a mixture. Load the mixture into a mold with boron nitride release agent sprayed on the inner wall, place it in a vacuum hot press furnace, evacuate the vacuum, heat to 480-500℃, apply a pressure of 48-52MPa, and maintain the pressure and temperature to obtain a hot-pressed block. A4. After the hot-pressed block is cooled to 180-195°C in the furnace, it is taken out, crushed and sieved to obtain sieved particles; the sieved particles are placed in a tube furnace, heated to 395-405°C under argon protection and held at that temperature, and then cooled to room temperature under argon protection and vacuum packaged.

7. The method for reducing nitrogen absorption during converter tapping according to claim 6, characterized in that, In step A1, the refining time at 850-900℃ is 10-20 minutes.

8. The method for reducing nitrogen absorption during converter tapping according to claim 6, characterized in that, In step A2, the ultrasonic treatment time is 10-30 minutes.

9. The method for reducing nitrogen absorption during converter tapping according to claim 6, characterized in that, In step A3, the pressure and heat holding time is 30-60 minutes.

10. The method for reducing nitrogen absorption during converter tapping according to claim 6, characterized in that, In step A4, the temperature is raised to 395-405℃ and held for 2-4 hours.

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