RH (Ruhrstahl Heraeus) vacuum refining method for synergistically blowing argon-hydrogen mixed gas and composite refining agent

Abstract

The invention belongs to the technical field of steel metallurgy, and particularly relates to an argon-hydrogen mixed gas and composite refining agent synergistic blowing RH vacuum refining method. In order to solve the problem that the traditional RH blowing refining process is difficult to realize synergistic and efficient removal of oxygen, sulfur and nitrogen impurities and the like, the invention provides a synergistic blowing method, during first-stage blowing and second-stage blowing, argon / hydrogen mixed gas and a composite refining agent are simultaneously injected into an RH ascending pipe, during third-stage blowing, only argon is blown, and during third-stage blowing, only nitrogen is blown; and the gas flow and the dosage of the composite refining agent in each injection stage are controlled, so that synchronous deep removal of oxygen, nitrogen and sulfur in the molten steel is realized, the refining efficiency is greatly improved, and the method particularly has important value for short-process high-cleanliness steel efficient smelting and has remarkable industrial popularization prospects.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel metallurgy, and particularly relates to a RH vacuum refining method with argon-hydrogen mixed gas and composite refining agent. BACKGROUND

[0002] In modern steel smelting processes, the RH (Ruhrstahl-Heraeus) vacuum refining technology has become an important refining means for producing high-quality steel materials due to its good degassing, impurity removal and homogenization capabilities. With the development of the steel industry towards a short process, high efficiency and low carbon emission, the traditional RH process has exposed the problem of insufficient efficiency in deep removal of nitrogen, sulfur and other difficult impurities, and it is urgent to further improve its multi-element collaborative removal capability and overall refining efficiency through technological innovation.

[0003] In the RH vacuum refining process, the presence of a large amount of interfacial active elements such as oxygen and sulfur in the molten steel makes it difficult to efficiently remove nitrogen. Oxygen and sulfur elements will preferentially enrich at the gas bubble / steel liquid interface under the action of the "bubble pump" effect, occupying the interface sites, thereby inhibiting the desorption and migration of nitrogen elements, severely restricting the progress of the denitrification reaction, and making it difficult to further reduce the nitrogen content. In theory, the denitrification environment can be improved by deep deoxidation or desulfurization first, but there are many limitations in actual operation. On the one hand, deep deoxidation usually relies on the addition of a large amount of aluminum and other strong deoxidizers, which can reduce the dissolved oxygen in the molten steel, but will generate a large amount of sharp Al2O3 inclusions, thereby worsening the inclusion control environment, and it is difficult to continuously change the bubble surface microenvironment, which has limited effect on improving the denitrification efficiency. On the other hand, deep desulfurization also has similar limitations. In the RH process, desulfurizing agents are usually added by top blowing or charging in the charging bin, but under vacuum conditions, powder particles are difficult to fully disperse in the molten steel, resulting in limited effective reaction interface, low desulfurization reaction efficiency, and difficulty in establishing an ideal low-sulfur environment to synergistically promote denitrification. Therefore, in the traditional RH blowing refining process, the means of relying on deep deoxidation or deep desulfurization to improve the denitrification conditions all face practical bottlenecks, and it is difficult to achieve the collaborative and efficient removal of oxygen, sulfur and nitrogen impurities.

[0004] In view of the above problems, the existing research is investigated. The Research Status and Prospect of Hydrogen Metallurgical Steelmaking Technology clearly points out that hydrogen metallurgical steelmaking has unique advantages in energy saving and consumption reduction and product quality improvement. On the one hand, “hydrogen” has a high-efficiency smelting effect, which can effectively reduce the energy consumption of steelmaking. On the other hand, “hydrogen” has a non-polluting refining effect, which can significantly improve the cleanliness of molten steel. Related research and patent technologies also explore the application path of hydrogen in the RH system. For example, Chinese patents CN113621759A and CN117512273A propose introducing pure hydrogen gas injection at specific positions in the RH riser or vacuum chamber to improve the removal effect of carbon, nitrogen, sulfur and other impurities and help maintain the temperature of molten steel; CN109628705A shows that hydrogen also has certain advantages in ensuring the yield of alloying elements and reducing the content of oxygen / carbon / hydrogen. However, these technologies still cannot achieve deep removal of oxygen, nitrogen and sulfur in molten steel, and the inclusion control effect is also limited. In addition, Chinese patent CN101603115A proposes using argon / hydrogen mixed gas to spray from the bottom of the ladle through a gas permeable brick, which shows good performance in removing oxygen and carbon elements, and the nitrogen content is also reduced, but it still cannot achieve deep removal of nitrogen and sulfur elements, and the inclusion removal rate is not significantly improved. Therefore, simply relying on the change of the type of injected gas cannot achieve the simultaneous and efficient removal of multiple harmful elements in molten steel.

[0005] In addition to deep removal of impurity elements, some technologies attempt to introduce rare earth elements to spheroidize and modify inclusions, aiming to efficiently control the composition and size of inclusions. Although this process has shown effectiveness in some studies, there are still obvious problems in current industrial application. Most processes (such as CN111593252A, CN110438389A, CN108504926A and CN118256679A) use alloy bins to add rare earth metals or rare earth alloy blocks. In this way, the particle size of rare earth is large (5mm~200mm), which leads to uneven distribution of rare earth in molten steel, long mixing time, and easy formation of large and heavy rare earth inclusions, which are not easy to remove, all of which restrict the actual application effect.

[0006] In addition, the existing RH process generally uses a “step-by-step independent” mode in the process path design, i.e., gas injection, alloy addition and refining agent addition are carried out separately, and the impurity removal process lacks coordination. This “multiple-step addition” method not only increases the complexity of operation, but also easily leads to discontinuous processing, unstable impurity removal efficiency, and difficulty in achieving simultaneous deep removal of multiple impurities such as oxygen, nitrogen and sulfur. It is also difficult to meet the strict requirements of high-cleanliness steel for simultaneous control of composition and inclusions. In summary, the current RH refining still needs an integrated refining path that can achieve simultaneous and efficient removal of oxygen, nitrogen and sulfur impurities, precise control of inclusions, and has low energy consumption and high utilization rate. SUMMARY

[0007] To address the difficulty in simultaneously and efficiently removing oxygen, nitrogen, and sulfur in the traditional RH refining process, the present invention proposes an RH vacuum refining method based on the coordinated injection of an argon-hydrogen mixture and a composite refining agent. For an RH vacuum refining unit with a single furnace steel processing capacity of 50 to 150 tons, the specific implementation process mainly includes the following: (1) One-stage coordinated injection: After the RH refining starts, argon-hydrogen mixed gas and composite refining agent are injected into the riser simultaneously; the hydrogen gas volume fraction in the mixed gas is controlled within the range of 10%~30%, and the mixed gas flow rate is 50Nm 3 / h~525Nm 3 / h; the injection rate of the composite refining flux is 10kg / min~50kg / min, the total mass of the composite refining flux injected in this stage accounts for 0.5%~5.0% of the mass of the molten steel, and the coordinated injection time is 15min~30min.

[0008] (2) Second stage coordinated injection: After the first stage coordinated injection is completed, the second stage coordinated injection is carried out, and the argon-hydrogen mixed gas and the composite refining agent are injected into the riser at the same time; the hydrogen gas volume fraction in the mixed gas is adjusted to 5%~20%, and the mixed gas flow rate is 40Nm 3 / h~450Nm 3 / h; the injection rate of the composite refining flux is adjusted to 5kg / min~35kg / min. The total mass of the composite refining flux injected in this stage accounts for 0.3%~2.0% of the mass of the molten steel, and the coordinated injection time is 10min~20min.

[0009] (3) Three-stage pure argon injection: Pure argon injection is performed after the second stage coordinated injection is completed; the riser injection is switched to pure argon, and the argon flow rate is adjusted to 25Nm 3 / h~400Nm 3 / h, the injection amount of composite refining agent is reduced to 0, and the injection time is 8min~12min to further remove hydrogen and inclusions in the molten steel.

[0010] Furthermore, the composite refining agent is a mixture of an oxidative desulfurizer and rare earth alloy particles. The oxidative desulfurizer is primarily composed of oxides, supplemented by composite components such as calcium fluoride. The main components and contents of the oxidative desulfurizer are: 55.0wt.% to 70.0wt.% calcium oxide, 3.0wt.% to 10.0wt.% magnesium oxide, 5.0wt.% to 20.0wt.% aluminum oxide, 0.1wt.% to 2.5wt.% calcium fluoride, and 0.1wt.% to 10.0wt.% boron oxide. The above contents are calculated based on the total mass of the oxidative desulfurizer as 100%. The mass fraction of the rare earth alloy particles accounts for 0.5wt.% to 5.0wt.% of the composite refining agent, where the rare earth alloy is one or more combinations of RE-Fe alloy, RE-Si alloy, and RE-Al alloy.

[0011] The total amount of rare earth elements RE in the composite refining agent added to the molten steel is controlled to be 5ppm~250ppm, and the specific amount is based on the dynamic addition equation obtained by experimental fitting regression [ RE ] 添加 ≈(1.8[ O ]0+0.5[ S ]0)×(50%~150%), where [ O ]0、[ S ]0 are the mass contents of oxygen and sulfur in the initial molten steel before RH refining.

[0012] After mixing, the raw material components in the composite refining agent need to be pre-melted at a temperature of 1350° C. to 1600° C. for 1 hour to 3 hours. After pre-melting, the raw materials are cooled and crushed to a particle size of ≤3 mm to obtain oxidative desulfurization agent particles. The oxidative desulfurization agent particles are mixed with rare earth alloy particles to prepare the composite refining agent. No further treatment is required before mixing, and dry mixing is adopted.

[0013] Finally, the composite refining agent has the following physical properties: fluidity index (Carr index) ≤ 25%, bulk density 1.2g / cm 3 ~1.6g / cm 3 , sulfur capacity (C S )≥4.2×10 -3 kg / m 3 , significantly higher than the traditional lime-based refining agent (about 3.2×10 -3 kg / m 3 ).

[0014] Furthermore, the method of the present invention is applicable to various steel grades such as Q345, 20CrMnTi, GCr15, SUS304, and T91, wherein the initial oxygen content in the molten steel is 80ppm to 120ppm, the nitrogen content is 50ppm to 100ppm, the sulfur content is 40ppm to 80ppm, and the hydrogen content is 2ppm to 5ppm; During the RH refining process, the vacuum degree is controlled between 5 Torr and 10 Torr, and the mixed gas injection intensity is controlled at 0.5 Nm based on the mass of the molten steel. 3 / h·t -1 ~3.5Nm 3 / h·t -1 ; The method of the present invention can make the temperature fluctuation of molten steel in the whole RH refining process not exceed ±5°C; Compared with the prior art, the RH vacuum refining process effectively breaks through the kinetic bottleneck of gas-liquid-slag multiphase interface reaction. The results of the scaled-down experiment under simulated industrial conditions show that: during the refining process, the temperature fluctuation of the molten steel is controlled within ±5℃, the oxygen content in the final molten steel can be stably reduced to 7.6ppm~8.7ppm, the nitrogen content is reduced to 24.9ppm~35.0ppm, the sulfur content is reduced to 14.1ppm~24.8ppm, and the hydrogen content is reduced to 0.50ppm~0.98ppm. Correspondingly, the deoxidation rate is 91.3%~92.4%, the denitrogenation rate is 52.6%~66.3%, the desulfurization rate is 61.4%~78.1%, and the dehydrogenation rate is 67.3%~83.3%. The rare earth yield is stably in the range of 51%~65% under ideal pilot conditions, the micro-inclusion density is controlled in the range of 10~20 / mm 2 2, which is reduced by 4.8%~52.4% compared with the traditional process; the CO2 emission per ton of steel is reduced by 25kg / t·steel~45kg / t·steel, and the reduction is 25.0%~56.3%. The process ensures the efficiency of impurity removal while realizing the synergistic removal of various interface active elements, significantly improves the cleanliness of molten steel, and has excellent energy saving and consumption reduction potential and industrial promotion value.

[0015] The method sprays argon-hydrogen mixed gas and composite refining agent with optimized particle size into the RH riser, fully utilizes the natural enrichment characteristics of oxygen and sulfur at the bubble / steel liquid interface, and forms a "bubble pump" effect by the buoyancy-driven bubble movement and its interfacial tension regulation effect, so that in-situ reaction of oxygen, sulfur and hydrogen gas and the composite refining agent is realized at the interface. The reaction products are carried by the bubbles and float up, effectively realizing the deep removal of oxygen and sulfur. At the same time, the denitrogenation active sites on the surface of the bubbles are significantly released, promoting the desorption reaction of nitrogen element, and realizing the synergistic and efficient removal of oxygen, nitrogen and sulfur. The bubbles can also carry inclusions to float up during the movement, which helps to improve the overall cleanliness of the molten steel. The rare earth alloy component in the composite refining agent further spheroidizes and modifies the morphology and composition of the inclusions, effectively improving the controllability of the inclusions and the stability of the continuous casting process. The present application constructs a multiphase coupling interface reaction path, breaks through the process bottleneck of "step-by-step impurity removal and stage separation" in the traditional RH refining, and forms an integrated refining closed loop of "initial strong reduction and impurity removal-middle stage inclusion modification-end stage pure argon cleaning".

[0016] The method is suitable for Q345, 20CrMnTi, GCr15, SUS304, T91 and other steel grades, and is particularly suitable for smelting high-end steel with high requirements for impurity control precision and molten steel heat balance stability. Compared with the traditional RH injection refining method, the present application can not only simultaneously achieve deep removal of oxygen, nitrogen and sulfur in the molten steel, but also has significant advantages in energy saving, refining agent utilization rate and inclusion control, and has good industrial application prospect and popularization value.

[0017] In addition, the process takes into account efficient removal of impurities and optimization of thermal efficiency, showing outstanding energy-saving and emission-reducing effects. The synergistic injection of argon-hydrogen mixed gas and composite refining agent not only optimizes the impurity migration path and reaction kinetics, but also significantly reduces energy consumption and carbon emissions in the refining process by reducing argon consumption and improving heat compensation efficiency, meeting the requirements of green metallurgy. The combustion reaction of hydrogen under vacuum conditions can release heat, effectively making up for the heat loss of the molten steel due to bubble disturbance and vacuum heat absorption, so that the molten steel temperature is stably controlled at 1640℃±5℃ during the entire RH refining process. In contrast, the traditional pure argon injection process is often accompanied by a temperature drop of 10℃~20℃, and frequent secondary heating is required to maintain thermal balance, significantly increasing energy consumption.

[0018] In terms of vacuum control, the present application adopts a multi-stage control strategy consistent with conventional RH refining, i.e. in the RH refining start-up stage, the vacuum system rapidly pumps down to reduce the system pressure to below 10 Torr. Subsequently, in the main decontamination stage (synergistic injection stage), the vacuum degree is stably controlled between 5 Torr and 10 Torr (0.67 kPa~1.33 kPa) by adjusting the main pumping system and the gas supply system, to ensure the optimal synergistic conditions of the bubble reaction interface and hydrogen combustion heat release. Finally, when pure argon is used for cleaning and blowing in the late stage of refining, the vacuum degree can be moderately increased (but not higher than 15 Torr) to balance the inclusion migration rate and thermal efficiency. This process does not require constant vacuum throughout the process, but rather dynamic adjustment within the optimal reaction window at different stages. This parameter range is based on experimental data and combined with the actual RH equipment operation rules, and has good industrial adaptability and controllability.

[0019] The RH vacuum refining method of the present application, which involves synergistic injection of argon-hydrogen mixed gas and composite refining agent, is suitable for scenarios where the initial oxygen content in the molten steel is 80ppm~120ppm, nitrogen is 50ppm~100ppm, sulfur is 40ppm~80ppm, and hydrogen is 2ppm~5ppm, and meets the decontamination treatment needs of molten steel with medium and high impurity levels. This method is suitable for RH vacuum refining devices with a single furnace steel treatment capacity of 50~150 tons, and the recommended total gas injection flow rate range is 25Nm 3 / h~525Nm 3 / h, wherein the hydrogen volume fraction is controlled between 5% and 30%. Under different steel liquid treatment conditions, the mixed gas blowing intensity should be controlled in the range of 0.5 Nm 3 / h·t -1 ~3.5 Nm 3 / h·t -1 (standard cubic meters per ton of steel liquid) to ensure the synergy optimization of the bubble carrying interface, the decontamination reaction rate and the heat balance. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a schematic diagram of impurity element removal in the RH refining process of the application. DETAILED DESCRIPTION

[0021] In order to better understand the technical solutions described in the application, the following will describe the technical solutions of the application in detail and clearly in combination with specific examples and drawings, and the removal effects of oxygen, nitrogen, sulfur and other impurity elements will be described. It should be pointed out that the listed examples are only used to further explain and illustrate the content of the application, and do not limit the application range. Based on the application, all other examples obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0022] In order to verify the decontamination mechanism and process performance of the RH vacuum refining process described in the application, experiments were carried out under the typical working conditions of a 100-ton steel liquid treatment of a certain RH device. The rare earth yield recorded in the examples of the application is based on the sampling analysis of the experimental platform, and the average value interval is controlled between 51% and 65%, which reflects the effective improvement of the reaction conversion efficiency of rare earth by the synergistic blowing mode under the experimental scale. It should be noted that, due to the differences between the industrial RH device and the experimental platform in terms of vacuum fluctuation, material flow disturbance and stirring intensity, the rare earth elements may still have the loss paths of volatilization, adsorption and inclusion complex in the industrial actual, and the yield may be slightly lower than the existing results.

[0023] The temperature of the steel liquid in the refining process is controlled at 1640℃±5℃, and the vacuum degree is stably maintained in the range of 5 Torr~10 Torr (0.67 kPa~1.33 kPa), which conforms to the conventional RH process vacuum control mode, and is not a constant vacuum throughout the process. The initial chemical composition of the steel liquid is as follows: C: 1.02%; Cr: 1.52%; Mn: 0.30%; Si: 0.25%; P: 0.015%; S: 0.00643% (i.e. 64.3 ppm); N: 0.00738% (i.e. 73.8 ppm); O: 0.00997% (i.e. 99.7 ppm); H: 0.0003% (i.e. 3.0 ppm).

[0024] The composite refining agent used is Al2O3-CaO-MgO-CaF2-B2O3-rare earth alloy particle pre-melted synthetic refining agent (mass ratio: CaO 62.5%, MgO 7%, Al2O3 17%, CaF2 1.5%, B2O3 7%, and rare earth alloy 5%), with a particle size of 0.5 mm to 1.5 mm. The rare earth component is a rare earth alloy powder composed of RE-Fe alloy, RE-Si alloy, and RE-Al alloy, with a particle size of 0.3 mm to 0.8 mm, and a mass percentage composition as follows: Ce 30%, La 25%, Nd 10%, Fe 10%, Si 15%, and Al 10% (which can be adjusted according to the specific raw materials). The total amount of rare earth elements added to the steel liquid is controlled to be 5 ppm to 250 ppm, and the synergistic components are formed by compounding with the oxidizing desulfurizing agent particles and sprayed into the steel liquid in powder form.

[0025] To further evaluate the process adaptability, three groups of different spraying intensities were designed for comparative study. Some parameters (such as inclusion migration path and rare earth reaction interface behavior) were supplemented by CFD modeling and reaction kinetics analysis, and the error between experimental and simulation results was controlled within ±10%.

[0026] According to the traditional RH refining process, two control groups were set up for comparison with the embodiments of the present application. The amount of molten steel in the control groups was the same as in the embodiments.

[0027] Control group 1 The traditional lime-based refining process (without rare earth elements and using the traditional feeding method).

[0028] This control group uses the common RH refining process in the current industry, using argon / hydrogen mixed gas spraying, but not using the composite refining agent synergistic spraying method in the present application. The refining agent does not undergo pre-melting treatment or add rare earth elements, but only adds traditional refining agents through the top conventional feeding method. The traditional refining agent is a lime-based refining agent (mass ratio: Al2O3 37.5%, CaO 27.5%, MgO 17.5%, and CaF2 17.5%), with a particle size of 0.5 mm to 1.5 mm. The specific operation is as follows: (1) First-stage spraying: After the start of RH refining, argon-hydrogen mixed gas is sprayed in the riser, with a hydrogen volume fraction of 10% and a total mixed gas flow rate of 100 Nm 3 / h. The lime-based refining agent is added through the top alloy bin, with a total addition amount of 500 kg, accounting for about 0.5% of the mass of the molten steel, and the spraying time is 20 min.

[0029] (2) Second-stage spraying: The argon-hydrogen mixed gas spraying is maintained, with the hydrogen volume fraction in the mixed gas adjusted to 5%, and the mixed gas flow rate maintained at 100 Nm 3 / h. The total amount of the lime-based refining agent was 306 kg, and the total amount of the refining agent accounted for about 0.3% of the mass of the molten steel. The continuous blowing time was 17 min.

[0030] (3) Three-stage argon blowing cleaning: switching to pure argon blowing, the flow rate was 80 Nm 3 / h, and the blowing time was 8 min without further feeding.

[0031] Under the process, the cooperative migration ability of the bubbles and the inclusions was limited, the inclusions were mainly large-particle sharp-cornered inclusions; hydrogen participated in part of the dehydrogenation reaction, but had weak influence on the interface reaction and the inclusions regulation. Due to the bubble disturbance and vacuum heat absorption, the temperature of the molten steel fluctuated greatly, the temperature drop was 10 ℃~20 ℃ during the whole RH process, and 1~2 times of electrode temperature compensation was needed.

[0032] The experimental results showed that (average value), the deoxidation rate of the molten steel after the RH refining was about 70%, the final oxygen content was about 30 ppm; the denitrogenation rate was about 26%, the final nitrogen content was about 55 ppm; the desulfurization rate was about 50%, the final sulfur content was about 32 ppm; the dehydrogenation rate was about 38%, the final hydrogen content was about 1.9 ppm; the density of the microscopic inclusions was ≥21 pieces / mm 2 , and most of the inclusions were irregular large-size inclusions; the CO2 emission per ton of steel was about 75 kg / t·steel~83 kg / t·steel.

[0033] Control group 2 The composite refining agent refining process (using a conventional feeding method).

[0034] In order to further verify the technical advantages of the "cooperative blowing" mode and the material advantages of the composite refining agent, another control group was set, the composite refining agent (Al2O3-CaO-MgO-CaF2-B2O3-rare earth alloy pre-melted synthesized refining agent) with the same composition as the example was used, but was added by the top conventional feeding method, the gas blowing conditions were consistent with those of Example 1, and the specific conditions were as follows: (1) One-stage blowing: after the start of the RH refining, argon-hydrogen mixed gas was blown in the riser pipe, the hydrogen volume fraction in the mixed gas was controlled at 10%, and the mixed gas flow rate was 100 Nm 3 / h. The composite refining agent was added through the top bin, and the composite refining agent added in this stage accounted for 0.5% of the mass of the molten steel. The blowing time was 20 min.

[0035] (2) Two-stage blowing: after the one-stage blowing was completed, two-stage blowing was carried out, the hydrogen volume fraction in the mixed gas was adjusted to 5%, and the mixed gas flow rate was kept at 100 Nm 3 / h. The composite refining agent was added through the top bin, and the composite refining agent added in this stage accounted for 0.3% of the mass of the molten steel. The blowing time was 17 min.

[0036] (3) Three-stage pure argon blowing: After the end of the second-stage blowing, pure argon blowing is carried out. The up-pipe blowing is switched to pure argon, and the blowing gas flow is adjusted to 80 Nm 3 / h, and lasts for 8 min without further charging.

[0037] The results of this group of experiments show that, due to the low melting point and good melting dispersibility of the composite refining agent, although it lacks the disturbance of blowing to promote the interfacial reaction in the traditional charging mode, it still has certain process advantages compared with the traditional lime-based refining agent. The steel liquid temperature is controlled at 1635±5℃, and no obvious secondary temperature compensation occurs, but due to the insufficient release of reaction heat, the overall temperature control relies on the external heating system to maintain. The deoxidation rate is 77%, the oxygen content is about 23 ppm; the denitrification rate is 33.8%, the nitrogen content is about 48 ppm; the desulfurization rate is 61.4%, the sulfur content is about 25 ppm; the dehydrogenation rate is 45.3%, and the hydrogen content is about 1.6 ppm; although the rare earth utilization rate is low in this control group, the inclusion spheroidization degree and removal rate are slightly improved compared with the control group 1. The rare earth recovery rate is 38%~44%, and the micro-inclusion density is about 16 pieces / mm 2 , part of which is spheroidized but the morphology is uneven. The CO2 emission per ton of steel is 55 kg / t·steel~62 kg / t·steel.

[0038] The following is an example, the composite refining agent used is Al2O3-CaO-MgO-CaF2-B2O3-rare earth alloy pre-melted synthetic refining agent, and the RH refining process is shown in Figure 1 .

[0039] Example 1 Low-intensity blowing condition under the RH refining process of the application.

[0040] (1) One-stage collaborative blowing: After the start of the RH refining, argon-hydrogen mixed gas and composite refining agent are blown in the up-pipe at the same time. The hydrogen volume fraction in the mixed gas is controlled at 10%, the mixed gas flow is 100 Nm 3 / h, and the composite refining agent blowing amount is 25 kg / min. The total mass of the composite refining agent blown in this stage accounts for 0.5% (500 kg) of the mass of the steel liquid, and the collaborative blowing time is 20 min.

[0041] (2) Two-stage collaborative blowing: After the end of the one-stage collaborative blowing, two-stage collaborative blowing is carried out, and argon-hydrogen mixed gas and composite refining agent are blown in the up-pipe at the same time. The hydrogen volume fraction in the mixed gas is adjusted to 5%, the mixed gas flow is kept at 100 Nm 3 / h, and the composite refining agent blowing amount is adjusted to 18 kg / min. The total mass of the composite refining agent blown in this stage accounts for 0.3% (306 kg) of the mass of the steel liquid, and the collaborative blowing time is 17 min.

[0042] (3) Three-stage pure argon blowing: After the end of the second-stage synergistic blowing, pure argon gas is blown. The up-pipe blowing is switched to pure argon gas, the blowing gas flow is adjusted to 80 Nm 3 / h, the composite refining agent blowing amount is reduced to 0 (stop adding the composite refining agent), and the blowing time is 8 min.

[0043] During the RH refining process, the temperature fluctuation of the molten steel is not more than ±5℃, and no secondary heating occurs. The experimental results show that after the end of the RH refining, the oxygen content in the molten steel is reduced to 7.9 ppm, the deoxidization rate is 92.1%, which is about 15.1% higher than that of the traditional argon-hydrogen mixed gas blowing process (control group 2) (the deoxidization rate of the control group 2 is about 77%); the nitrogen content is 30.1 ppm, the denitrification rate is 59.2%, which is about 25.4% higher than that of the traditional process (the denitrification rate of the control group 2 is about 33.8%); the sulfur content is 19.3 ppm, the desulfurization rate is 69.9%, which is about 8.5% higher than that of the traditional process (the desulfurization rate of the control group 2 is about 61.4%); the hydrogen content is reduced from 3 ppm to 0.98 ppm, the dehydrogenation rate is 67.3%, which is about 22% higher than that of the traditional process (the dehydrogenation rate of the control group 2 is about 45.3%); the rare earth yield is stably at 51%~56% (which is an interval value, and is affected by the particle size of the refining agent and the stirring intensity); the density of the microscopic inclusions is ≤15 pieces / mm 2 , which is reduced by 1 piece / mm 2 than that of the control group 2 (16 pieces / mm 2 ); the CO2 emission per ton of steel is 45 kg / t·steel~55 kg / t·steel.

[0044] Example 2 The present application is a RH refining process with medium-strength synergistic blowing.

[0045] (1) First-stage synergistic blowing: After the start of the RH refining, argon-hydrogen mixed gas and composite refining agent are blown in the up-pipe at the same time. The hydrogen volume fraction in the mixed gas is controlled at 20%, the mixed gas flow is 200 Nm 3 / h, and the composite refining agent blowing amount is 40 kg / min. The total mass of the composite refining agent blown in this stage accounts for 1.0% (1000 kg) of the mass of the molten steel, and the synergistic blowing time is 25 min.

[0046] (2) Second-stage synergistic blowing: After the end of the first-stage synergistic blowing, second-stage synergistic blowing is carried out, and argon-hydrogen mixed gas and composite refining agent are blown in the up-pipe at the same time. The hydrogen volume fraction in the mixed gas is adjusted to 10%, the mixed gas flow is adjusted to 180 Nm 3 / h, and the composite refining agent blowing amount is adjusted to 25 kg / min. The total mass of the composite refining agent blown in this stage accounts for about 0.5% (500 kg) of the mass of the molten steel, and the synergistic blowing time is 20 min.

[0047] (3) Three-stage pure argon blowing: After the end of the second-stage synergistic blowing, pure argon gas is blown. The up-pipe blowing is switched to pure argon gas, the blowing gas flow is adjusted to 120 Nm 3 / h, the composite refining agent blowing amount is reduced to 0 (stop adding the composite refining agent), and the blowing time is 10 min.

[0048] During the RH refining process, the temperature fluctuation of the molten steel is not more than ±5℃, and no secondary heating occurs. The experimental results show that after the end of the RH refining, the oxygen content in the molten steel is stably reduced to 8.7 ppm, the deoxidization rate is 91.3%, which is increased by 14.3% compared with the traditional argon-hydrogen mixed gas blowing process (control group 2) (the deoxidization rate in the control group 2 is about 77%); the nitrogen content is 35.0 ppm, the denitrification rate is 52.6%, which is increased by 18.8% compared with the traditional process (the denitrification rate in the control group 2 is about 33.8%); the sulfur content is 22.4 ppm, the desulfurization rate is 65.2%, which is increased by 3.8% compared with the traditional process (the desulfurization rate of the control group 2 is about 61.4%); the hydrogen content is reduced from 3.0 ppm to 0.81 ppm, the dehydrogenation rate is 73%, which is increased by 27.7% compared with the traditional process (the hydrogen removal rate in the control group 2 is about 45.3%); the rare earth yield is stably at 55%~60% (depending on the blowing stability); the micro-inclusion density is ≤20 pieces / mm 2 , the inclusion density is slightly higher than that of the control group 2; the CO2 emission per ton of steel is 42 kg / t·steel~58 kg / t·steel.

[0049] Example 3 The high-strength synergistic blowing condition under the RH refining process of the application.

[0050] (1) First-stage synergistic blowing: After the start of the RH refining, argon-hydrogen mixed gas and composite refining agent are blown in the up-pipe at the same time. The hydrogen volume fraction in the mixed gas is controlled at 30%, the mixed gas flow is 350 Nm 3 / h, and the composite refining agent blowing amount is 45 kg / min. The total mass of the composite refining agent blown in this stage accounts for 1.2% (1215 kg) of the mass of the molten steel, and the synergistic blowing time is 27 min.

[0051] (2) Second-stage synergistic blowing: After the end of the first-stage synergistic blowing, second-stage synergistic blowing is carried out, and argon-hydrogen mixed gas and composite refining agent are blown in the up-pipe at the same time. The hydrogen volume fraction in the mixed gas is adjusted to 20%, the mixed gas flow is adjusted to 300 Nm 3 / h, and the composite refining agent blowing amount is adjusted to 35 kg / min. The total mass of the composite refining agent blown in this stage accounts for 0.7% (700 kg) of the mass of the molten steel, and the synergistic blowing time is 20 min.

[0052] (3) Three-stage pure argon blowing: After the end of the second-stage synergistic blowing, pure argon blowing is carried out. The updraft pipe blowing is switched to pure argon, the blowing gas flow is adjusted to 200 Nm 3 / h, the composite refining agent blowing amount is reduced to 0 (stop adding the composite refining agent), and the blowing time is 12 min.

[0053] The experimental results show that after RH refining, the oxygen content in the molten steel is reduced to 7.6 ppm, the deoxidation rate is 92.4%, which is 15.4% higher than that of the traditional argon-hydrogen mixed gas blowing process (control group 2) (the deoxidation rate of control group 2 is about 77%); the nitrogen content is 24.9 ppm, the denitrification rate is 66.3%, which is 32.5% higher than that of the traditional process (the denitrification rate of control group 2 is about 33.8%); the sulfur content is 14.1 ppm, the desulfurization rate is 78.1%, which is 16.7% higher than that of the traditional process (the sulfur element removal rate of control group 2 is about 61.4%); the hydrogen content is reduced from 3.0 ppm to 0.50 ppm, the dehydrogenation rate is 83.3%, which is 38% higher than that of the traditional process (the hydrogen element removal rate of control group 2 is about 45.3%); the rare earth yield is stable at 60%~65% (the range value of multiple batches of detection); the micro-inclusion density is ≤10 pieces / mm 2 , which is 37.5% lower than that of control group 2; the CO2 emission per ton of steel is 30 kg / t steel~45 kg / t steel.

[0054] From example 1 to example 3, it can be seen that the increase of blowing intensity (including the increase of composite refining agent blowing rate and hydrogen concentration) shows a positive promoting effect on the removal of inclusions under the experimental platform. With the increase of working condition intensity, the removal rates of oxygen, nitrogen, sulfur and hydrogen, which are four interfacial active elements in the molten steel, show an overall upward trend, the rare earth yield is also improved, and the number and morphology of inclusions are further improved.

[0055] Specifically, in example 3, the deoxidation rate and the dehydrogenation rate are higher than 90% and 80%, respectively, the rare earth yield is stable at more than 60%, and the micro-inclusion density is reduced to ≤10 pieces / mm 2 , which shows that the synergistic blowing mechanism can effectively enhance the reactivity of rare earth and the migration ability of impurities. Although there are still differences between the experimental platform and the industrial working condition, the above results provide valuable trend judgment basis for engineering scale-up.

[0056] Note: The impurity end point content control results in each example are obtained by sampling determination and component analysis, and are consistent with the equivalent setting conditions of industrial RH operation parameters, verifying the adaptability and generalizability of the refining process of the present application under the real high-impurity steel liquid initial conditions. It should be noted that the CO2 emission data in the above examples are based on the equivalent conversion calculation results under the scaled experimental platform. Considering that the experimental platform uses electric heating and standard gas blowing modules, the power consumption and gas consumption during the treatment of unit mass of steel liquid can be accurately quantified, and the ton steel conversion and deduction are carried out through international standard emission factors (such as ISO14064 and GB / T 32151, etc.). In the specific conversion, the carbon emission factor of electric energy is 0.85 kg CO2 / kWh (national average power grid emission factor), and the carbon emission of gas is 0.16 kg CO2 / Nm 3 of argon and 10.7 kg CO2 / Nm 3 of hydrogen.

[0057] In addition, in order to ensure the industrial amplification adaptability of the test results, the experimental platform design strictly follows the fluid similarity criteria such as Froude number and Reynolds number, ensuring that the flow in the RH riser, the inclusion migration path and the reaction interface behavior have comparable kinetic response relationship with the industrial real furnace. Therefore, although the absolute value comes from the scaled experiment, the relative performance change trend between each example and the control group has good engineering consistency, which can be used to evaluate the decontamination effect, inclusion control ability and energy saving and emission reduction potential under different process paths.

[0058] The RH refining process described in the present application shows good decontamination ability under different blowing intensities, especially in the synergistic control of oxygen, nitrogen, sulfur and hydrogen four interfacially active impurities, which has significant advantages over traditional processes. In addition, thanks to the thermal compensation effect of argon-hydrogen mixed gas, the temperature stability of the steel liquid refining process is significantly improved, avoiding the energy consumption caused by secondary heating, which meets the development direction of green metallurgy.

Claims

1. A RH vacuum refining method using a combined injection of an argon-hydrogen gas mixture and a composite refining agent, characterized in that: Includes the following: (1) One-stage coordinated injection: After the RH refining starts, argon-hydrogen mixed gas and composite refining agent are injected into the riser simultaneously; the hydrogen volume fraction in the mixed gas is 10%~30%, and the mixed gas flow rate is 50Nm 3 / h~525Nm 3 / h; the injection rate of composite refining agent is 10kg / min~50kg / min; (2) Second stage coordinated injection: After the first stage coordinated injection is completed, the second stage coordinated injection is carried out, and the argon-hydrogen mixed gas and the composite refining agent are injected into the riser at the same time; the hydrogen volume fraction in the mixed gas is 5%~20%, and the mixed gas flow rate is 40Nm 3 / h~450Nm 3 / h; the injection rate of composite refining agent is 5kg / min~35kg / min; (3) Three-stage pure argon injection: pure argon injection is performed after the second stage coordinated injection is completed; the riser injection is switched to pure argon, and the argon flow rate is 25Nm 3 / h~400Nm 3 / h.

2. The RH vacuum refining method of claim 1, wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in combination, In step (1), the total mass of the sprayed composite refining agent accounts for 0.5% to 5.0% of the mass of the molten steel; in step (2), the total mass of the sprayed composite refining agent accounts for 0.3% to 2.0% of the mass of the molten steel.

3. The RH vacuum refining method of claim 1 wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in combination, The blowing time of step (1) is 15 min to 30 min; the blowing time of step (2) is 10 min to 20 min; and the blowing time of step (3) is 8 min to 12 min.

4. The RH vacuum refining method of claim 1 wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in coordination, characterized in that: The RH vacuum refining method is applicable to steel grades including Q345, 20CrMnTi, GCr15, SUS304, and T91.

5. The RH vacuum refining method of claim 1 wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in coordination, characterized in that: The composite refining agent has the following physical properties: fluidity index ≤ 25%, bulk density 1.2 g / cm 3 ~1.6g / cm 3 , sulfur capacity ≥4.2×10 -3 kg / m 3 .

6. The RH vacuum refining method of claim 1 wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in coordination, wherein: The composite refining agent is a mixture of an oxidative desulfurizer and rare earth alloy particles; the oxidative desulfurizer includes calcium oxide, magnesium oxide, aluminum oxide, calcium fluoride, and boron oxide, and the rare earth alloy particles include one or more combinations of RE-Fe alloy, RE-Si alloy, and RE-Al alloy.

7. The RH vacuum refining method of claim 6, wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in combination, The contents of the components of the oxidative desulfurizer are as follows: based on the total mass of the oxidative desulfurizer being 100%, calcium oxide 55.0 wt.% to 70.0 wt.%, magnesium oxide 3.0 wt.% to 10.0 wt.%, aluminum oxide 5.0 wt.% to 20.0 wt.%, calcium fluoride 0.1 wt.% to 2.5 wt.%, and boron oxide 0.1 wt.% to 10.0 wt.%.

8. The RH vacuum refining method of claim 6, wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in combination, The mass of the rare earth alloy particles accounts for 0.5 wt.% to 5.0 wt.% of the total mass of the composite refining agent.

9. The RH vacuum refining method of claim 8, wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in combination, The total amount of rare earth elements RE in the composite refining agent added to the molten steel is 5ppm~250ppm, [ RE ] 添加 ≈(1.8[ O ]0+0.5[ S ]0)×(50%~150%); in,[ O ]0、[ S ]0 are the mass contents of oxygen and sulfur in the initial molten steel before RH vacuum refining.

10. The RH vacuum refining method of claim 6, wherein the argon-hydrogen mixed gas and the composite refining agent are sprayed in coordination, The raw material components of the oxidative desulfurizer and the rare earth alloy particles are mixed and then pre-melted at a temperature of 1350° C. to 1600° C. for 1 to 3 hours. After pre-melting, the mixture is cooled and crushed to obtain the composite refining agent.

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