Converter slagging agent as well as preparation and use methods thereof

Abstract

The invention discloses a converter slag melting agent and a preparation and use method thereof. The converter slag melting agent is prepared from the following raw materials in percentage by weight: 18-23% of iron powder, 27-33% of oxidized scale and 45-55% of limestone. Phenolic resin is added as a binder, and the addition amount of the binder is 1.5-2.5% of the mass of the converter slagging agent. Particularly, under the conditions that the molten iron phosphorus content is high, the finished product phosphorus content and the finished product nitrogen content are low, and converter single-slag-method dephosphorization is difficult, converter early-stage rapid slagging can be achieved, the converter dephosphorization effect is improved, the coal gas recovery amount is increased, oxygen consumption is reduced, and the converter smelting end-point nitrogen content is reduced. And meanwhile, the oxide scale resource is fully and reasonably utilized, the consumption of steel and iron materials is reduced through converter smelting, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a converter slagging agent and its preparation and application methods. Background Technology

[0002] During the continuous casting and rolling processes in the steel industry, a certain amount of iron oxide scale will be generated on the surface of the steel billet due to its high temperature. The main chemical component of the iron oxide scale is iron(III) oxide, with very low sulfur and phosphorus content. Since the iron oxide scale generated by the continuous casting and rolling processes contains a certain amount of iron, it can be recycled back into the steel process. However, how to make full and reasonable use of it remains a widely concerned issue for steel companies.

[0003] Patent application No. 201910502677.8 discloses a "method for preparing sintered ore using rolled iron oxide scale and the prepared sintered ore", characterized in that the method includes the following raw material proportions by mass percentage: rolled iron oxide scale 1%–5%, iron ore powder A 10%–25%, iron ore powder B 8%–30%, iron ore powder C 0%–15%, iron concentrate D 15%–35%, steel slag powder 2.0%–5.0%, limestone 4.0%–8.0%, dolomite 3.0%–6.0%, quicklime 1.0%–3.5%, coke powder 2.0%–7.0%, and recycled ore 8.0%–13.0%; mixing the raw materials with water and granulating to obtain a mixture; and sintering the mixture to obtain sintered ore. This invention can effectively utilize rolled iron oxide scale, achieving its recycling and reducing feedstock costs. Furthermore, the utilization coefficient and drum strength of the prepared sinter are significantly improved compared to existing technologies. However, this invention adds iron oxide scale to the sintering process, failing to achieve more direct and economical utilization of the iron element within the scale. Additionally, the added scale only accounts for 1% to 5%, hindering its rapid utilization.

[0004] Patent application No. 201310423350.4 discloses a "Bulking Process for Steelmaking Converter Dust and Sludge and Continuous Casting Oxide Scale," characterized by using simple equipment to mix steelmaking converter dust and sludge with continuous casting iron oxide scale, which is then briquetted into pellets by a briquetting machine to become auxiliary materials for converter steelmaking. The sludge and iron oxide scale are transported to the briquetting machine via a silo and belt conveyor. Qualified pellets are transported to the finished product yard via a sieve, while unqualified pellets are returned to the briquetting machine via a belt conveyor. Continuous casting generates a large amount of iron oxide scale during production. This invention quantitatively mixes steelmaking converter dust and sludge with the iron oxide scale produced during continuous casting, achieving complete utilization of the steelmaking converter dust and sludge. However, after adding the iron oxide pellets, the iron oxide scale in the pellets has an excessively high FeO content, which easily leads to slag runoff during the blowing process, negatively impacting the consumption of converter steel materials. It also generates a high concentration of ferrous oxide in the early stages, rather than calcium ferrite, failing to improve the dephosphorization effect of the converter.

[0005] In summary, existing technologies using continuous casting and rolling processes to produce iron oxide scale, and employing sintering processes, cannot achieve more direct and economical utilization of the iron element in the iron oxide scale. Furthermore, the addition of iron oxide scale is only 1%–5%, failing to ensure rapid utilization. The direct pelletizing process for iron oxide scale results in excessively high FeO content in the scale, leading to slag runoff during blowing, affecting converter steelmaking material consumption, and preventing the formation of calcium ferrite in the early stages, thus hindering the improvement of converter dephosphorization efficiency. Therefore, there is an urgent need to develop a converter slagging agent and its preparation and application methods to achieve rapid slagging in the early stages of converter smelting, improve converter dephosphorization efficiency, increase gas recovery, and solve the problem of producing steel grades with high phosphorus and nitrogen content requirements under the single-slag method for high-phosphorus hot metal smelting. Simultaneously, this approach ensures the full and rational utilization of iron oxide scale resources, reduces steelmaking material consumption in converter smelting, and lowers production costs. Summary of the Invention

[0006] The purpose of this invention is to provide a converter slagging agent and its preparation and application methods, particularly for cases where molten iron has a high phosphorus content but the finished product has a low phosphorus content, and dephosphorization using the single-slag method in the converter is difficult. This invention enables rapid slagging in the early stages of converter smelting, improving the dephosphorization effect. It also increases gas recovery, reduces oxygen consumption, and lowers the nitrogen content at the converter smelting endpoint. Simultaneously, it ensures the full and rational utilization of iron oxide scale resources, reducing steelmaking material consumption and lowering production costs in converter smelting.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A converter slagging agent, the constituent raw materials of the converter slagging agent include, by weight percentage: iron powder: 18% to 23%, iron oxide scale: 27% to 33%, limestone: 45% to 55%; phenolic resin is added as a binder, the amount of binder added is 1.5% to 2.5% of the mass of the converter slagging agent.

[0008] The iron powder has a particle size of 50-500 μm and an iron content of more than 99%.

[0009] The iron oxide scale has a particle size of 0.2-3 mm and an FeO content greater than 98%.

[0010] The limestone has a particle size of 0.5–5 mm and a CaCO3 content greater than 95%.

[0011] The reasons for setting the weight percentage content range of the converter slagging agent in this invention are as follows: Iron powder: After the converter slagging agent is added to the converter, during the blowing process, the iron powder in the slagging agent can directly react with the blown-in oxygen to release heat, increasing the melting rate of the converter slagging agent. Simultaneously, ferrous oxide is generated, which reacts with calcium oxide in the converter slagging agent under the high-temperature conditions inside the converter to form calcium ferrite. If too much iron powder is added, the converter slagging agent directly enters the molten steel in the converter, failing to achieve rapid slagging and calcium ferrite dephosphorization effects. If too little iron powder is added, the iron powder cannot provide sufficient heat to promote rapid slagging. Therefore, the iron powder content should be controlled within the range of 18% to 23%.

[0012] Iron oxide scale: In order to improve the utilization rate of iron oxide scale in steel rolling, as much iron oxide scale as possible should be added when preparing converter slag agent. However, if too much iron oxide scale is added, the amount of limestone will be reduced accordingly, which is not conducive to the production of calcium ferrite and affects the slag dephosphorization effect in the early stage of converter. Therefore, the iron oxide scale content should be controlled in the range of 27% to 33%.

[0013] Limestone: After the slag-forming agent is added to the converter, limestone decomposes under the conditions of iron powder combustion to produce lime and carbon dioxide. Among them, lime reacts with FeO to produce calcium ferrite, and carbon dioxide reacts with carbon in the molten iron to produce carbon monoxide twice the volume, increasing the amount of converter gas recovered. If too much limestone is added, it will increase the calcium oxide content, raise the melting point of the slag-forming agent, and be detrimental to the formation of calcium ferrite. If too little limestone is added, it will also raise the melting point of the slag-forming agent, which is detrimental to the melting of the slag-forming agent. Therefore, the limestone content should be controlled in the range of 45% to 55%.

[0014] A method for preparing a converter slagging agent includes batching, mixing, and pelletizing, specifically comprising: Ingredients: Weigh the iron powder, iron oxide scale, limestone and phenolic resin required for preparing the converter slagging agent separately.

[0015] Mixing: Mix the iron powder, iron oxide scale, and limestone once for 5-7 minutes, then add phenolic resin and mix again for 6-10 minutes.

[0016] Briquetting: The mixed raw materials are briquetting using a briquetting machine. The briquetting pressure is 0.2–0.4 MPa, the briquetting diameter is 30–40 mm, and the preparation speed is 20–30 t / h ("t" is "ton"). The slag-reducing agent briquetting is then stored in a dry and ventilated place for later use.

[0017] A method for using a converter slag-forming agent includes: adding the dried spherical slag-forming agent to the converter hopper; adding scrap steel to the converter; mixing in molten iron; and then igniting and blowing the converter. Initially, the oxygen lance height is 2.4–2.5 m. Within 1–3 minutes of blowing, the spherical slag-forming agent is added at a rate of 2–3 kg / t. The iron powder in the slag-forming agent burns and rapidly oxidizes into ferrous oxide, releasing heat and causing the limestone in the slag-forming agent to decompose rapidly into calcium oxide and carbon dioxide. The carbon dioxide combines with the carbon in the molten steel to generate twice the amount of carbon monoxide, increasing the recovery of converter gas. During the converter smelting process, as the amount of generated gas increases, nitrogen atoms in the molten steel spontaneously diffuse towards the surface of bubbles with low nitrogen partial pressure, and on the surface of these bubbles, nitrogen atoms combine to form nitrogen molecules, continuously carrying carbon monoxide bubbles out of the molten steel, thereby reducing the nitrogen content in the molten steel. Nitrogen atoms move about 100 times slower than hydrogen atoms in molten steel, making denitrification difficult even under RH vacuum conditions. Therefore, for steel grades requiring high nitrogen content in the finished product, the initial nitrogen content of the molten steel must be low before vacuum treatment. Removing more nitrogen from the molten steel during converter blowing is an effective method. Simultaneously, the oxidation products of iron powder react with FeO in the slagging agent and calcium oxide from the decomposition of limestone to form calcium ferrite, further lowering the melting point of the slag and achieving rapid melting.

[0018] Then, add appropriate amounts of active lime and dolomite from the silo to adjust the basicity and magnesium oxide content of the converter slag. The binary basicity of the final converter slag is controlled at 3.2-3.5, the magnesium oxide content is controlled at 6%-8%, and the final converter temperature is controlled at 1660-1690℃. This achieves rapid melting and dephosphorization of the slag in the early stage of the converter. In the molten slag, ferrous oxide provides oxidizing properties, and calcium oxide provides basicity, fixing the [P] in the molten steel to oxidize into P2O5 and transfer it to the slag.

[0019] 3CaO+5FeO+2[P]=Ca3(PO4)2+5[Fe] The converter steel produced using the above process achieves rapid slag melting in the early stages, a final dephosphorization rate of 94-96%, and a converter gas recovery rate of 115.4-115.8 m³. 3 / t, converter oxygen consumption is 49.7~49.9m 3 / t, the nitrogen content of the molten steel at the end of the converter smelting is below 0.0008%. The addition of slag-reducing agent reduces the oxidation of iron in the molten steel. The consumption of steelmaking materials in the converter is 1063.3~1064.5kg / t, which achieves a good dephosphorization effect in the converter, makes full use of resources, and reduces production costs.

[0020] After tapping from the converter, the molten steel undergoes LF refining, temperature adjustment, and alloying. During the LF refining process, air ionization and nitrogen introduction into the alloy occur, resulting in a nitrogen increase of over 0.0040% in the molten steel. It then undergoes RH vacuum degassing treatment before continuous casting. The phosphorus content in the finished steel is controlled between 0.0060% and 0.0080%, and the nitrogen content is controlled between 0.0030% and 0.0040%.

[0021] Compared with the prior art, the beneficial effects of the present invention are: By employing converter slagging agents, compared to using sintering feedstock, the converter utilizes iron from iron oxide scale more directly and economically. This achieves rapid slagging in the early stages of converter smelting, increasing the overall dephosphorization rate and reducing the pressure on converter dephosphorization. The slagging agent releases heat, increases gas recovery, reduces oxygen consumption, and lowers the nitrogen content at the converter's final smelting stage. Simultaneously, it ensures the full and rational utilization of iron oxide scale resources, reduces iron oxidation in molten steel, and lowers steelmaking costs through converter smelting. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of this invention clearer, the specific implementation methods of this invention will be further described below in conjunction with the embodiments. The following embodiments are used to specifically illustrate the content of this invention. These embodiments are only general descriptions of the content of this invention and do not limit the content of this invention.

[0023] The present invention will be described in detail below with reference to the embodiments. However, the implementation of the present invention is not limited thereto. Obviously, the embodiments described below are only some embodiments of the present invention. For those skilled in the art, other similar embodiments can be obtained without creative effort and all fall within the protection scope of the present invention.

[0024] The converter slagging agent of this invention is mainly composed of iron powder, iron oxide scale, and limestone. The weight percentage content of each component is as follows: iron powder: 18%–23%, iron oxide scale: 27%–33%, limestone: 45%–55%. The particle size of the iron powder is 50–500 μm, and the iron content is greater than 99%. The particle size of the iron oxide scale is 0.2–3 mm, and the FeO content is greater than 98%. The particle size of the limestone is 0.5–5 mm, and the CaCO3 content is greater than 95%. Phenolic resin is used as a binder, and its addition amount accounts for 1.5–2.5% of the total amount of converter slagging agent. The raw material composition and content of the converter slagging agent provided in the embodiments of this invention are shown in Table 1.

[0025] Table 1. Raw material composition and content (wt%) of converter slagging agents in Examples 1-5 The preparation method of converter slagging agent includes steps such as batching, mixing, and briquetting.

[0026] S1. Ingredients: Weigh the iron powder, iron oxide scale, limestone and phenolic resin required for preparing the converter slagging agent.

[0027] S2. Mixing: Put the iron powder, iron oxide scale, and limestone together and mix them once using a mixer for 5-7 minutes. Then add phenolic resin and mix again for 6-10 minutes to obtain a fully mixed slag-reducing agent raw material.

[0028] S3. Briquetting: The above-mentioned slag-reducing agent raw materials are briquettingd using a briquetting machine. The briquetting pressure is 0.2–0.4 MPa, the briquetting diameter is 30–40 mm, and the preparation speed is 20–30 t / h. The briquetting agent briquettes are stored in a dry and ventilated place for later use.

[0029] The preparation process parameters of the converter slagging agent in this embodiment of the invention are shown in Table 2.

[0030] Table 2. Preparation process parameters of converter slagging agent in the examples The method of using converter slag-forming agent is as follows: add the dried spherical slag-forming agent to the converter hopper, add scrap steel to the converter, and then add molten iron. After ignition and blowing, the oxygen lance height is 2.4-2.5m in the early stage (0.1-0.2m lower than the furnace without slag-forming agent). Add the spherical slag-forming agent within 1-3 minutes of blowing, at a rate of 2-3kg / t. The iron powder in the slag-forming agent burns and is rapidly oxidized into ferrous oxide, releasing heat at the same time. This causes the limestone in the slag-forming agent to decompose rapidly into calcium oxide and carbon dioxide. The carbon dioxide combines with the carbon in the molten steel to generate twice the amount of carbon monoxide, increasing the recovery of converter gas. At the same time, the oxidation products of iron powder react with FeO in the slag-forming agent and the calcium oxide after the decomposition of limestone to form calcium ferrite, further lowering the melting point of the slag and achieving rapid melting. Then, add appropriate amounts of active lime and dolomite from the silo to adjust the basicity and magnesium oxide content of the converter slag. The binary basicity of the final converter slag is controlled at 3.2-3.5, the magnesium oxide content is controlled at 6%-8%, and the final converter temperature is controlled at 1660-1690℃. This achieves rapid melting and dephosphorization of the slag in the early stage of the converter. In the molten slag, ferrous oxide provides oxidizing properties, and calcium oxide provides basicity, fixing the [P] in the molten steel to oxidize into P2O5 and transfer it to the slag.

[0031] 3CaO+5FeO+2[P]=Ca3(PO4)2+5[Fe] The process parameters for the slag-forming agent used in the example and the comparative example in the converter are shown in Table 3. The comparative example added active lime and lightly calcined dolomite to form slag during converter smelting. The scrap steel ratio of both the example and the comparative example was 15%.

[0032] Table 3 Process parameters for slagging agent in converter The effects of the slag-reducing agent in the example and the comparative example in the converter are shown in Table 4, and the changes in phosphorus and nitrogen content in the refining process and the finished product are shown in Table 5.

[0033] Table 4. Effects of slagging agents in converters Table 5 LF refining process and finished phosphorus and nitrogen content The converter steel produced using the above process exhibits rapid slag melting in the early stages, achieving a final dephosphorization rate of 94.9%–96%. This represents an average increase of 6.9% in the converter's dephosphorization rate and an average increase of 0.42 m³ in converter gas recovery. 3 / t, oxygen consumption decreased by an average of 0.3m 3 The core innovation of this invention lies in adding a converter slag-forming agent to the converter for smelting, which effectively reduces the phosphorus and nitrogen content at the converter's final stage. Under the single-slag smelting condition, the phosphorus content in the finished steel can be controlled at 0.0060-0.0080%, and the nitrogen content at 0.0030-0.0040%. This increases gas recovery, reduces oxygen consumption, and reduces the oxidation of iron in the molten steel. The average consumption of steelmaking materials in the converter is reduced by 1.31 kg / t, resources are fully utilized, and production costs are reduced.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A converter slagging agent, characterized in that, The raw materials of the converter slagging agent, by weight percentage, include: iron powder: 18% to 23%, iron oxide scale: 27% to 33%, limestone: 45% to 55%; phenolic resin is added as a binder, and the amount of binder added is 1.5% to 2.5% of the mass of the converter slagging agent.

2. The converter slagging agent according to claim 1, characterized in that: The iron powder has a particle size of 50-500 μm and an iron content of more than 99%.

3. The converter slagging agent according to claim 1, characterized in that: The iron oxide scale has a particle size of 0.2-3 mm and an FeO content greater than 98%.

4. The converter slagging agent according to claim 1, characterized in that: The limestone has a particle size of 0.5–5 mm and a CaCO3 content greater than 95%.

5. A method for preparing a converter slagging agent as described in any one of claims 1-4, characterized in that: The process includes ingredient preparation, mixing, and pelletizing; specific methods include: Mixing: Mix the iron powder, iron oxide scale, and limestone once for 5-7 minutes, then add phenolic resin and mix again for 6-10 minutes. Briquetting: The mixed raw materials are briquetting using a briquetting machine. The briquetting pressure is 0.2-0.4 MPa, the briquetting diameter is 30-40 mm, and the preparation speed is 20-30 t / h.

6. A method of using the converter slagging agent as described in any one of claims 1-4, characterized in that: Specifically, it includes: The dried slag-reducing agent is added to the converter hopper. Scrap steel is added to the converter, and molten iron is added. The process is then initiated by ignition and blowing. Initially, the oxygen lance height is 2.4–2.5 m. The slag-reducing agent is added within 1–3 minutes of blowing, at a rate of 2–3 kg / t. The iron powder in the slag-reducing agent burns, causing the limestone in the slag-reducing agent to decompose into calcium oxide and carbon dioxide. The carbon dioxide combines with the carbon in the molten steel to form carbon monoxide. At the same time, the oxidation products of the iron powder react with the FeO in the slag-reducing agent and the calcium oxide from the decomposition of limestone to form calcium ferrite. Then, add quicklime and dolomite from the silo to adjust the basicity and magnesium oxide content of the converter slag. The binary basicity of the final converter slag is controlled at 3.2-3.5, the magnesium oxide content is controlled at 6%-8%, and the final converter temperature is controlled at 1660-1690℃.

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