Process method for reducing steelmaking cost and improving activity of steel slag

Abstract

The invention discloses a process method for reducing steelmaking cost and improving activity of steel slag, belongs to the field of steelmaking, and aims to solve the problems of high oxidability of converter terminal slag, low molten steel yield, high consumption of deoxidizer and alloy and low activity of steel slag due to influence of MgO and the like. According to the method, during blowing, MgO slag is not added, lime, ferric oxide and Al2O3-containing slag are added in batches, the basicity of the slag is controlled to be 2.5-3.5, the content of Al2O3 is larger than 4%, reduction gasification dephosphorization is carried out by adding a reducing agent (0.5-2 kg / t steel) in stages and stirring with nitrogen (40-90 ''), and the TFe content of terminal slag is controlled to be 9% or below. The process can deeply reduce the slag, prevent rephosphorization of the molten steel, reduce the steelmaking cost, greatly improve the activity of the steel slag, facilitate high-added-value utilization of the steel slag and digest Al2O3-containing materials such as Bayer process red mud magnetic separation substances.

Description

Technical Field

[0001] This invention relates to the field of steelmaking, specifically to technologies for reducing steelmaking costs and utilizing steel slag. Background Technology

[0002] During converter blowing, high oxidizability of the final slag leads to multiple problems: firstly, it affects the effectiveness of slag splashing for furnace protection; secondly, it significantly reduces steel yield; and thirdly, it results in higher oxidizability of the molten steel, thereby increasing the consumption of deoxidizers and alloys, and significantly raising steelmaking costs. Meanwhile, as a major byproduct of steelmaking, the low activity of steel slag severely limits its high-value-added utilization, and magnesium oxide (MgO) is one of the key factors causing this reduced activity.

[0003] The negative impact mechanism of MgO on the activity of steel slag

[0004] 1. Lattice disturbance and stability disruption: Mg 2+ The ionic radius (0.072 nm) and the Ca in the C2S lattice 2+ The difference (0.100nm) is significant. MgO can penetrate the C2S crystal structure to form a solid solution, which can destroy the metastable lattice integrity of β-C2S and reduce its thermodynamic stability.

[0005] 2. Accelerates the phase transformation kinetics: The presence of MgO reduces the activation energy of the β-C2S to γ-C2S phase transformation, allowing the phase transformation to occur at lower temperatures and in a shorter time. This promoting effect is more pronounced, especially during the slow cooling of steel slag.

[0006] 3. Stabilization induction of γ-C2S: MgO can form stable solid solutions with γ-C2S (such as Ca2(Si,Mg)O4), which further enhances the structural stability of γ-C2S and prevents its reverse transformation into β-C2S.

[0007] Actual influence patterns show that when the MgO content in steel slag is ≤3%, the phase transformation promoting effect is weak; when the MgO content is ≥5% (the common content in converter steel slag is 5%-10%), it will significantly accelerate the conversion of β-C2S to γ-C2S, leading to the large-scale generation of γ-C2S and a sharp decrease in the activity of steel slag; if the MgO content is too high (>10%), it may also generate an inert magnesium silicate calcium stone phase, further weakening the cementing performance.

[0008] The effect of Al2O3 on phase transformation of steel slag

[0009] In contrast to MgO, aluminum oxide (Al2O3) is an effective inhibitor of the β-C2S to γ-C2S phase transition, while phosphorus pentoxide (P2O5) has a weaker inhibitory effect and may even have a negative effect.

[0010] 1. Inhibitory effect of Al2O3: Al2O3 can form solid solutions with C2S (such as Ca2(Si,Al)O4), replacing Si in the C2S crystal structure. 4+ Al2O3 disrupts the stable lattice of γ-C2S, improves the thermodynamic stability of β-C2S, and delays its low-temperature phase transformation. However, this effect requires a certain content threshold; typically, an Al2O3 content ≥ 4% is needed to form a sufficient solid solution to exert its effect. Furthermore, Al2O3 can form aluminoferrite minerals (such as C4AF) with CaO and Fe2O3, further hindering the crystal growth of γ-C2S and enhancing the phase transformation inhibition effect. It is worth noting that controlling the Al2O3 content in silicate cement clinker to 4-7% can form calcium aluminate, improving early strength; adding an appropriate amount of Al2O3 slagging agent during converter blowing, maintaining an Al2O3 content of 4-7%, also facilitates slagging and prevents re-drying during mid-term blowing.

[0011] The high oxidizability of the slag at the end of converter blowing has several negative consequences: first, it affects slag splashing and furnace protection operations; second, it reduces the steel yield; and third, the high oxidizability of the steel leads to an increase in the consumption of deoxidizers and alloys.

[0012] The silicate cement clinker contains 4-7% Al2O3, which forms calcium aluminate, improving the early strength of the cement. In addition, adding an appropriate amount of Al2O3 slagging agent during converter blowing, maintaining the Al2O3 content at 4-7%, is beneficial for slag formation and prevents re-drying during mid-stage blowing. When adding reducing agent to the slag at the end of blowing, stirring with nitrogen can achieve deep reduction of the slag at the same alkalinity, further reducing the oxidizability of the slag, increasing the steel yield, reducing the consumption of deoxidizers and alloys, and significantly reducing the cost of steelmaking. The slag contains a certain amount of Al2O3, which forms a network structure that is beneficial for the slag to adhere to the furnace lining and improves the effect of slag splashing and furnace protection.

[0013] On the other hand, the red mud magnetic separators from the Bayer process not only contain a large amount of iron resources, but also a certain amount of Al2O3; steel mill refining slag not only has a certain alkalinity, but also contains a large amount of Al2O3. Summary of the Invention

[0014] In view of the relationship between the oxidizability of the final slag and the steel yield and deoxidizer alloy consumption, as well as the correlation between the activity of steel slag and MgO, Al2O3, and FeO, this invention aims to develop a process method for deep reduction to reduce the oxidizability of the final slag, reduce steelmaking costs, and improve the activity of steel slag.

[0015] The technical solution of the present invention is as follows: no MgO slag is added during the blowing process, and lime, iron oxide and Al2O3-containing slag are added in batches. The slag basicity is controlled at 2.5-3.5, the Al2O3 content in the slag is adjusted to >4%, and the final slag TFe is controlled below 9%.

[0016] Furthermore, the control of TFe in the final slag to below 9% during the blowing process is based on different steel grades and the final situation. During the blowing process, or near the blowing end point, or at the blowing end point, 0.5-2 kg / t of steel is added as a reducing agent and the slag is stirred with nitrogen for 40-90 seconds to carry out reduction gasification dephosphorization. After carrying out reduction gasification dephosphorization near the blowing end point, the blowing process is continued for 1-2 minutes or at the same time as the blowing process ends and the lance is lifted, 0.5-2 kg / t of steel as a reducing agent is added again.

[0017] Furthermore, the process method for reducing steelmaking costs and improving the activity of steel slag is characterized in that, before adding a reducing agent and performing reduction gasification dephosphorization during the blowing process, the slag can be stirred with oxygen for 0-60″, and then the reducing agent can be added and the slag can be stirred with nitrogen for reduction gasification dephosphorization.

[0018] Furthermore, the Al2O3-containing slag material is one of the Bayer process red mud and its magnetic separators, refining slag, bauxite, and other Al2O3-containing slag materials.

[0019] Furthermore, the reducing agent is one of the following: a silicon-based reducing agent, a carbon-containing reducing agent, a silicon carbide reducing agent, or calcium carbide.

[0020] Furthermore, the carbon-containing reducing agent is one of coke particles, anthracite, coal gangue, carbon-containing dust, or blast furnace gas dust.

[0021] The mechanism of this invention: The main mineral phases of steel slag, dicalcium silicate and tricalcium silicate, together account for nearly 70%, similar to silicate cement clinker, but with high Fe2O3 content, low Al2O3 content, and high MgO content. FeO and MgO in the slag, either alone or forming the RO phase, lack activity and worsen the grindability of the steel slag. Simultaneously, magnesium oxide (MgO) in the steel slag significantly promotes the phase transformation from β-C2S to γ-C2S, which is one of the key factors leading to reduced steel slag activity. In practical applications, it is necessary to add stabilizers (such as Al2O3 and SO3) or use a rapid quenching process to counteract its negative effects. The presence of these factors greatly reduces the activity of the steel slag.

[0022] High oxidizability of the slag at the end of converter blowing (i.e., high FeO content) has several negative impacts: firstly, it affects slag splashing for furnace protection; secondly, it significantly reduces steel yield; and thirdly, the high oxidizability of the steel leads to increased consumption of deoxidizers and alloys. In silicate cement clinker, the Al2O3 content is 4-7%, forming calcium aluminate, which improves the early strength of the cement. Simultaneously, adding an appropriate amount of Al2O3 slagging agent during converter blowing, maintaining an Al2O3 content ≥4-7%, is beneficial for slag formation, preventing re-drying during mid-stage blowing, and as a solid sulfur phase, it facilitates steel desulfurization. When a reducing agent is added to the slag at the end of blowing, under the same basicity, the slag becomes thinner due to the absence of MgO and the presence of an appropriate amount of Al2O3. This allows for deeper reduction of FeO in the slag at the end of blowing, further reducing slag oxidizability, increasing steel yield, reducing deoxidizer and alloy consumption, and significantly lowering steelmaking costs. The presence of a certain amount of Al2O3 in the slag forms a network structure, which is beneficial for slag adhesion to the furnace lining and improves the effectiveness of slag splashing for furnace protection. However, when the FeO content in the final slag is below 15%, phosphorus easily returns to the molten steel. The technical solution of this invention adds a reducing agent to the surface of the slag and uses gas to stir, reduce, and gasify the phosphorus. While reducing the oxidizing properties of the steel slag, it also reduces and gasifies a portion of the P2O5 in the slag, increasing the phosphorus capacity of the molten slag. This prevents phosphorus from returning to the molten steel due to a significant decrease in FeO content in the final slag, thus achieving the goal of reducing iron content and increasing efficiency of the process solution of this invention.

[0023] During the blowing process of medium and high carbon steel, the slag has a high P2O5 content at the beginning and end of the blowing process. At this time, the lance is lifted and a reducing agent such as silicon is added to the furnace (because CO is produced by the carbon-oxygen reaction in the molten pool at this time, carbon-based reducing agents are ineffective). Stirring with nitrogen for 30-60 seconds can reduce and gasify 40-60% of P2O5, increase the phosphorus capacity of the slag, and provide advance conditions for further dephosphorization, carbon retention at the end point, and iron reduction in subsequent blowing processes.

[0024] When smelting low-carbon steel and ultra-low-carbon steel, a carbonaceous reducing agent is added to the furnace near or at the end of the blowing process, while simultaneously stirring with nitrogen for 30-60 seconds. This significantly reduces iron oxide levels, while P2O5 is also reduced and gasified simultaneously. If the furnace is nearing the end of the blowing process after reduction and dephosphorization, continue blowing with the lance for 1-2 minutes. At the same time as stopping the blowing and raising the lance, add the carbonaceous reducing agent again. Adding it again at the end of the blowing process further reduces FeO in the slag. These three consecutive steps of reducing iron levels result in a deep reduction of FeO in the slag, preventing phosphorus reversion in the molten steel. If the final slag still does not meet the requirements, a carbonaceous reducing agent can be sprayed onto the slag surface during tapping to further reduce the FeO content in the slag.

[0025] The absence of MgO slag and the addition of an appropriate amount of Al2O3 during slag formation reduced the viscosity of the final slag, creating gaseous conditions for the deep reduction of FeO and the reduction and gasification of P2O5.

[0026] Further optimization details are as follows:

[0027] 1. Reduction gasification dephosphorization operation: Depending on the steel grade and the endpoint, add 0.5-2 kg / t steel of reducing agent during the blowing process, near the blowing endpoint or at the blowing endpoint, and stir the slag with nitrogen for 40-90″ to carry out reduction gasification dephosphorization operation; after carrying out reduction gasification dephosphorization operation near the blowing endpoint, continue blowing with the lance for 1-2 minutes, and add 0.5-2 kg / t steel of reducing agent again when lifting the lance at the end of blowing.

[0028] 2. Pretreatment optimization: Before adding the reducing agent and performing reduction gasification dephosphorization, the slag can be stirred with oxygen for 0-60″, and then the reducing agent can be added and the slag stirred with nitrogen to complete the reduction gasification dephosphorization operation.

[0029] 3. Raw material selection: The Al2O3-containing slag is one of Bayer process red mud and its magnetic separators, refining slag, bauxite and other Al2O3-containing slag; the reducing agent is one of siliceous reducing agent, carbon-containing reducing agent, silicon carbide reducing agent and calcium carbide; wherein the carbon-containing reducing agent is one of coke particles, anthracite, coal gangue, carbon-containing dust removal ash and blast furnace gas dust.

[0030] Technical Mechanism: The main mineral phases of steel slag, dicalcium silicate and tricalcium silicate, together account for nearly 70%, similar to silicate cement clinker. However, conventional steel slag suffers from high Fe2O3 content, low Al2O3 content, and high MgO content. The presence of FeO and MgO alone, or the RO phase formed by them, lacks activity and reduces the grindability of the steel slag. These factors collectively lead to low activity in the steel slag. This invention, by omitting MgO and adding an appropriate amount of Al2O3, reduces the final slag viscosity, creating favorable gaseous conditions for deep reduction of FeO and reduction gasification of P2O5. When a reducing agent is added to the final slag of the blowing process and stirred with nitrogen, under the same basicity, the slag becomes thinner because there is no MgO and there is an appropriate amount of Al2O3 in the slag. This allows for deep reduction of FeO in the final slag, further reducing the slag's oxidizing properties, increasing steel yield, reducing the consumption of deoxidizers and alloys, and significantly reducing steelmaking costs. At the same time, the slag contains a certain amount of Al2O3, which can form a network structure, which is beneficial for the slag to adhere to the furnace lining and improve the slag splashing and furnace protection effect.

[0031] It should be noted that when the FeO content in the final slag is below 15%, phosphorus is easily returned to the molten steel. However, this invention adds a reducing agent to the surface of the slag and uses gas stirring to achieve reduction and gasification dephosphorization. While reducing the oxidizing properties of the steel slag, it also reduces and gasifies some of the P2O5 in the slag, increasing the phosphorus capacity of the molten slag. This prevents phosphorus from returning to the molten steel due to a significant decrease in FeO content in the final slag, thus ensuring the achievement of the goal of reducing iron content and increasing efficiency.

[0032] Operational suitability for different steel grades:

[0033] 1. Medium and high carbon steel smelting: At the end of the initial blowing stage, the slag has a high P2O5 content. At this time, the lance is lifted and a reducing agent such as silicon is added to the furnace (because CO is produced by the carbon-oxygen reaction in the molten pool at this time, carbon reducing agents are ineffective). Stir with nitrogen for 30-60 seconds, which can reduce and gasify 40-60% of P2O5, increase the phosphorus capacity of the slag, and provide the preconditions for further dephosphorization, carbon retention at the end point and iron reduction in subsequent blowing.

[0034] 2. Smelting of low-carbon steel and ultra-low-carbon steel: Near or at the end of the blowing process, add a carbonaceous reducing agent to the furnace while simultaneously stirring with nitrogen for 30-60 seconds. This significantly reduces iron oxide while simultaneously reducing and gasifying P2O5. If the furnace is near the end of the blowing process after reduction and dephosphorization, continue blowing with the lance for 1-2 minutes. While stopping the blowing and raising the lance, add the carbonaceous reducing agent again to further reduce FeO in the slag. Through these three consecutive steps of reducing iron, deep reduction of FeO in the slag is achieved without phosphorus reversion in the molten steel. If the slag at the end of the process still does not meet the requirements, a carbonaceous reducing agent can be sprayed onto the slag surface during tapping to further reduce the FeO content in the slag.

[0035] Beneficial effects

[0036] The process of this invention has multiple advantages: First, it can deeply reduce FeO in the final slag, improve steel yield, reduce deoxidizer consumption, and significantly reduce steelmaking costs; second, it is beneficial for the final control of medium and high carbon steel smelting, and can also significantly reduce the final oxidation of low carbon and ultra-low carbon steel, further improving steel yield and reducing deoxidizer consumption; third, it optimizes slag performance, which is beneficial for slag splashing and furnace protection operations and their furnace protection effect, and the slag remaining in the furnace can also provide assistance for the next batch of dephosphorization; fourth, the activity of the steel slag poured out of the furnace is greatly improved, and all high-value-added utilization can be achieved; fifth, it can digest and fully utilize the iron and aluminum resources in Bayer process red mud and its magnetic separators; sixth, it helps to prevent dryness during converter blowing, further ensuring smelting stability. Detailed Implementation

[0037] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a deep understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0038] The core implementation process of this invention is as follows: After the converter performs slag retention operation, scrap steel is added, molten iron is added, and the slag is successfully ignited by lowering the hood and lowering the lance, Al2O3 slag, lime, red mud briquettes and other slag materials are added in batches; at the end of the initial blowing stage (about 3-5 minutes), the lance is lifted and reducing agents such as silicon are added, and the slag is stirred with nitrogen for 30-60 seconds, then the oxygen lance is switched to continue blowing until the end; or the blowing is directly carried out until near the end or at the end of the blowing, the lance is lifted and reducing agents such as carbon are added, and the slag is stirred with nitrogen for 30-60 seconds and then the blowing ends; or the oxygen lance is switched to continue blowing for 0-60 seconds and then the blowing ends, and at the same time as the blowing stops and the lance is lifted, 0.5-1.5 kg / t of carbonaceous reducing agent is added again.

[0039] Example 1

[0040] 1. Equipment and raw materials: 120t converter, smelting steel grade is 65# spring steel, reducing agent is silicon-calcium deoxidizer with particle size of 10-20mm (CaSi 73%).

[0041] 2. Operation Process: After the previous heat of steel is tapped, 50% of the slag is poured out, leaving 50% as the slag. After completing the slag splashing and furnace protection operation, the remaining slag is left in the furnace. Add 20.2t of scrap steel, 110t of molten iron, and 1t of red mud magnetic separator. Turn the converter mouth upwards to the zero position, lower the lance and ignite it. Use constant pressure and variable lance position operation, with an oxygen supply flow rate of 3.6 Nm / t / min. Control the smelting lance position at 1.2-1.8m. When blowing for 3 minutes and 5 seconds, lift the lance, stir the slag with oxygen for 30 seconds, add 250kg of calcium silicate powder, and stir with nitrogen for 60 seconds. Then lower the lance and continue blowing. Add a total of 5.4t of lime and 600kg of Bayer process magnetic separation red mud briquettes in three batches at 2-minute intervals. After blowing for 13 minutes and 6 seconds, lift the lance and add 120kg of anthracite coal at the same time. After standing for 40 seconds, tap the steel.

[0042] 3. Results: At the end of the converter smelting, the final temperature was 1628℃, the final phosphorus content was 0.009%, the final slag basicity was 3.0, the final slag FeO content was 6.6%, Al2O3 content was 5.8%, and MgO content was 0%. The final molten steel had [C] content of 0.65%, [P] content of 0.011%, and oxygen activity of molten steel of 105ppm. After tapping, the slag viscosity was suitable. After pouring out part of the slag, the slag splashing operation was carried out directly, and the slag splashing operation lasted for 2 minutes and 2 seconds.

[0043] 4. Effect Analysis: In this heat of high-carbon steel, oxygen stirring was used for 30″ during the lance raising process. The oxidation of iron beads and carbon in the slag was exothermic, increasing the FeO content and decreasing the viscosity of the slag, thus improving the gasification and dephosphorization effect. The final [C] reached 0.65%. Because the slag contained 5.8% Al2O3 and no MgO, the slag viscosity was relatively low. Adding anthracite when the blowing stopped and the lance was raised could further reduce the oxidizability of the slag. After the initial blowing was completed and the lance was raised, a silicon-calcium reducing agent was added and stirred with nitrogen. Part of the P2O5 was reduced and gasified, which provided a key prerequisite for the final slag reduction and iron reduction and prevented the molten steel from returning to phosphorus.

[0044] Example 2

[0045] 1. Equipment and raw materials: 120t converter, steel grade X65, reducing agent is anthracite (C93%) with a particle size of 10-20mm.

[0046] 2. Operation Process: After the previous heat of steel is tapped, 50% of the slag is poured out, leaving 50% as the slag is retained. After completing the slag splashing and furnace protection operation, the remaining slag is left in the furnace. Add 21.3t of scrap steel, 112t of molten iron, and 1.5t of red mud magnetic separator. Turn the converter mouth upwards to the zero position, lower the lance for ignition, and use constant pressure variable lance position operation with an oxygen supply flow rate of 3.6 Nm / t / min. Add a total of 5.5t of lime and 500kg of Bayer process dust and mud magnetic separator briquettes in three batches at 2-minute intervals. After blowing for 13 minutes and 9 seconds, lift the lance and add 122kg of coke particles. Stir with nitrogen for 40″, then continue blowing with the lance for 90″ before stopping. At the same time as lifting the lance, add another 120kg of anthracite. After standing for 20″, tap the steel.

[0047] 3. Results: At the end of the converter smelting, the final temperature was 1623℃, the final phosphorus content was 0.0010%, the final slag basicity was 3.1, the final slag FeO content was 7.3%, Al2O3 content was 6.8%, and MgO content was 0.1%; the final molten steel had [C] content of 0.04%, [P] content of 0.009%, and oxygen activity of molten steel of 112ppm; the slag viscosity after tapping was suitable, and after pouring out part of the slag, the slag splashing operation was carried out directly, with a splashing time of 2′10″. After splashing, the slag was left for the next heat operation.

[0048] 4. Effect Analysis: In this embodiment, low-carbon steel is smelted with a high final oxidation state. The three-step operation of "reduction gasification dephosphorization to reduce iron oxide in slag - continued lance blowing to further reduce iron - adding carbonaceous reducing agent to deeply reduce iron when blowing stops and the lance is lifted" is adopted. Because the first step of reduction gasification dephosphorization increases the phosphorus capacity of slag, it provides the prerequisite for the subsequent continuous reduction of slag FeO and effectively avoids the problem of phosphorus return in molten steel.

[0049] Example 3

[0050] 1. Equipment and raw materials: 120t converter, steel grade X65, reducing agent is anthracite (C93%) with a particle size of 10-20mm.

[0051] 2. Operation process: After the previous heat of steel is tapped, all slag is retained. After the slag splashing and furnace protection operation is completed, the remaining slag is left in the furnace. Add 23t of scrap steel, 115t of molten iron, and 3t of Bayer process dust and sludge magnetic separator briquettes; turn the converter mouth upwards to the zero position, lower the lance for ignition, and use constant pressure variable lance position operation with an oxygen supply flow rate of 3.6 Nm / t / min; add a total of 4t of lime and 600kg of Bayer process dust and sludge magnetic separator briquettes in three batches at 2-minute intervals; after blowing for 13min01s, lift the lance, add 140kg of coke particles, stir with nitrogen for 38″, and then continue blowing with the lance for 60″ to finish. At the same time as lifting the lance, add another 150kg of anthracite, let it stand for 30″, and then tap the steel.

[0052] 3. Results: At the end of the converter smelting, the final temperature was 1635℃, the final phosphorus content was 0.0012%, the final slag basicity was 2.9, the final slag FeO content was 7.1%, Al2O3 content was 6.8%, and MgO content was 0.3%; the final molten steel had [C] content of 0.03%, [P] content of 0.011%, and oxygen activity of molten steel of 105ppm; the slag viscosity after tapping was suitable, and after pouring out part of the slag, the slag splashing operation was carried out directly, with a splashing time of 2 minutes and 20 seconds. After splashing, the slag was left for the next heat operation.

[0053] Example 4

[0054] 1. Equipment and raw materials: 120t converter, smelting steel grade is 65# spring steel, reducing agent is anthracite coal (C93%) with a particle size of 10-20mm.

[0055] 2. Operation Process: After the previous heat of steel is tapped, 50% of the slag is poured out, leaving 50% as the slag. After completing the slag splashing and furnace protection operation, the remaining slag is left in the furnace. Add 20t of scrap steel, 113t of molten iron, and 2t of Bayer process magnetic separation material briquettes. Turn the converter mouth upwards to the zero position, lower the lance and ignite it. Use constant pressure and variable lance position operation, with an oxygen supply flow rate of 3.6 Nm / t / min. Control the smelting lance position at 1.2-1.8m. Blow for 3'22″ and then lift the lance. First, stir the slag with oxygen for 40″, then add 180kg of calcium silicate powder. Stir with nitrogen for 90″, then lower the lance and continue blowing. Add lime in three batches every 2 minutes, totaling 5.5t, and 600kg of Bayer process magnetic separation red mud briquettes. Blow for 14min05s and then lift the lance. At the same time, add 120kg of coke particles. After standing for 30″, tap the steel.

[0056] 3. Results: At the end of the converter smelting, the final temperature was 1626℃, the final phosphorus content was 0.009%, the final slag basicity was 3.0, the final slag FeO content was 9%, Al2O3 content was 6.5%, and MgO content was 0.1%. After tapping, the slag viscosity was suitable. After pouring out part of the slag, the slag splashing operation was carried out directly. The splashing time was 2 minutes and 20 seconds. After splashing, the slag was left for the next heat operation.

[0057] Comparative Example 1

[0058] 1. Equipment and raw materials: 120t converter, smelting steel grade is 65# spring steel, the Al2O3 regulation and reduction gasification dephosphorization process of the present invention was not adopted, and lightly calcined dolomite was added to introduce MgO.

[0059] 2. Operation process: After the previous heat of steel is tapped, 50% of the slag is poured out, leaving 50% as the slag. After completing the slag splashing and furnace protection operation, the remaining slag is left in the furnace. Add 20.2t of scrap steel, 110t of molten iron, and 1t of iron oxide scale; tilt the converter with the opening facing upwards to the zero position, lower the lance and ignite, add 1t of lightly calcined dolomite, and use constant pressure variable lance position operation, with an oxygen supply flow rate of 3.6 Nm / t / min, and control the smelting lance position at 1.2-1.8m; add a total of 5.4t of lime in three batches at 2-minute intervals, and blow until 14min06s, then lift the lance and tap the steel.

[0060] 3. Results: At the end of the converter smelting, the final temperature was 1628℃, the final phosphorus content was 0.009%, the final slag basicity was 3.0, the final slag FeO content was 11.6%, Al2O3 content was 2.8%, and MgO content was 7%; the final molten steel had [C] content of 0.65%, [P] content of 0.011%, and oxygen activity of molten steel of 151ppm; after tapping, some slag was poured out and slag splashing was carried out to protect the furnace, with the slag splashing operation lasting 2′40″.

[0061] Comparative Example 2

[0062] 1. Equipment and raw materials: 120t converter, smelting steel grade X65, without using the Al2O3 regulation and reduction gasification dephosphorization process of this invention.

[0063] 2. Operation process: After the previous heat of steel is tapped, all slag is retained. After the slag splashing and furnace protection operation is completed, the remaining slag is left in the furnace. Add 23t of scrap steel, 115t of molten iron, and 3t of iron oxide scale; turn the converter mouth upwards to the zero position, lower the lance for ignition, and use constant pressure variable lance position operation with an oxygen supply flow rate of 3.6 Nm / t / min; add a total of 4t of lime and 600kg of iron oxide scale in three batches at 2-minute intervals, and blow for 14min01s before lifting the lance to tap out the steel.

[0064] 3. Results: At the end of the converter smelting, the final temperature was 1635℃, the final phosphorus content was 0.0012%, the final slag basicity was 3.0, the final slag FeO content was 25%, Al2O3 content was 1.6%, and MgO content was 7%; the final molten steel had [C] content of 0.03% and [P] content of 0.011%, the final slag (∑FeO) content was 25%, the final molten steel [C] content was 0.04%, and the oxygen activity of the molten steel was 952ppm; after tapping, some slag was poured out and slag splashing was performed to protect the furnace, with a splashing time of 3 minutes and 20 seconds. After splashing, the slag was left for the next furnace operation.

[0065] Compared with Comparative Examples 1 and 2, Examples 1-4 showed a significant reduction in FeO in the final slag, an increase in Al2O3 content, and almost the disappearance of MgO. The molten steel did not revert to phosphorus, and the slag splashing time was shortened.

[0066] Example 5: Steel Slag Activity Test Verification

[0067] To verify the effect of the process of the present invention on improving the activity of steel slag, steel slag from Example 4 (corresponding to high-carbon steel smelting, final slag FeO 9%, Al2O3 6.5%, MgO 0.1%) and steel slag from Comparative Example 2 (corresponding to low-carbon steel smelting, final slag FeO 25%, Al2O3 1.6%, MgO 7%) were selected as test samples. Using silicate cement clinker as a reference, activity-related performance tests were conducted according to the standard "Steel Slag Powder for Cement and Concrete" (GB / T 20491-2017). The core difference in the tests stemmed from the different chemical compositions of the steel slag (Fe2O3, MgO, Al2O3 content). The specific performance is shown in the table below:

[0068]

[0069]

[0070] Test results show that the steel slag prepared by the process of this invention far surpasses the steel slag prepared by the process of this invention in key indicators such as setting time, strength development and stability. Some indicators are close to or even better than those of silicate cement clinker, which fully proves that the process of this invention can significantly improve the activity of steel slag.

[0071] In summary, as can be seen from the comparison of the specific embodiments and comparative examples, this technical solution can achieve deep reduction of slag at the blowing endpoint, significant reduction of iron oxide, no phosphorus return at the molten steel endpoint, shortened slag splashing operation time, and significantly improved steel slag activity. Any process adjustments made by those skilled in the art based on the principles of this invention, such as changes to process parameters and details like slag basicity, slag addition amount and time, and oxygen supply parameters, should fall within the scope of protection of the technical solution claimed in this invention.

Claims

1. A process for reducing steelmaking costs and improving the activity of steel slag, characterized in that: No MgO slag is added during the blowing process. Lime, iron oxide and Al2O3-containing slag are added in batches to control the slag basicity at 2.5-3.5, the Al2O3 content in the slag at >4%, and the final slag TFe content is controlled below 9%.

2. The process for reducing steelmaking costs and improving the activity of steel slag as described in claim 1, characterized in that: The endpoint slag TF e The method to control it below 9% is as follows: depending on the steel grade and the endpoint, during the blowing process or near the blowing endpoint, add 0.5-2 kg / t of reducing agent and use nitrogen to stir the slag for 40-90″ for reduction gasification dephosphorization operation; after the reduction gasification dephosphorization operation is completed near the blowing endpoint, continue blowing with the lance for 1-2 minutes, or add 0.5-2 kg / t of reducing agent again when lifting the lance at the end of blowing.

3. The process method for reducing steelmaking costs and improving the activity of steel slag as described in claim 1, characterized in that, Before adding the reducing agent and performing reduction gasification dephosphorization during the blowing process, the slag can be stirred with oxygen for 0-60″, and then the reducing agent can be added and the slag stirred with nitrogen for reduction gasification dephosphorization.

4. The process method for reducing steelmaking costs and improving steel slag activity as described in claim 1, characterized in that: The Al2O3-containing slag material is one of Bayer red mud, Bayer red mud magnetic separator, refining slag, and bauxite.

5. The process method for reducing steelmaking costs and improving the activity of steel slag as described in claim 2, characterized in that: The reducing agent is one of the following: siliceous reducing agent, carbon-containing reducing agent, silicon carbide reducing agent, and calcium carbide.

6. The process method for reducing steelmaking costs and improving steel slag activity as described in claim 5, characterized in that: The carbon-containing reducing agent is one of the following: coke particles, anthracite, coal gangue, carbon-containing dust, and blast furnace gas dust.

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