Method for replacing calcium line feeding process with rare earth treatment for aluminum deoxidized steel

Abstract

The invention discloses a method for replacing a calcium wire feeding process with rare earth treatment for aluminum deoxidized steel, which comprises the following steps of: 1, controlling a narrow window process in a smelting process to meet the cleanliness condition of molten steel before rare earth is added, optimizing and executing the following processes to realize better molten steel cleanliness in the steel, meanwhile, the control range of the content of acid-soluble aluminum [Al] in the steel is 0.020-0.050%; and 2, adding rare earth, namely adding a certain amount of rare earth cerium-iron alloy at the last stage after LF refining deoxidation alloying according to the content of acid-soluble aluminum [Al] in different ranges in the steel. The invention aims to effectively improve the production time sequence of the smelting process, further realize the control effect of high-cleanliness molten steel through the deep purification effect of strong deoxidation and desulfurization of high-reducibility lanthanum-cerium rare earth on the molten steel, simultaneously realize the purpose of reducing the manufacturing cost, and eliminate the problem of smoking caused by a calcium treatment process.

Description

Technical Field

[0001] The present invention belongs to the technical field of steelmaking, and particularly relates to a method for replacing the process of feeding calcium wire with rare earth treatment for aluminum-deoxidized steel. Background Art

[0002] The conventional smelting process for aluminum-deoxidized steel adopts the process flow of converter + LF furnace + continuous casting. After the converter smelting is completed, aluminum deoxidation is adopted during the tapping process to achieve calm tapping, and then the ladle furnace refining calcium treatment process is adopted after the LF refining is completed.

[0003] The purpose of the ladle furnace refining calcium treatment process is to add calcium alloy into the deep part of the molten steel by means of injection metallurgy method or wire feeding method, so as to achieve the metallurgical effects of modifying non-metallic inclusions represented by Al2O3, deoxidation, and desulfurization. However, the recovery rate of high-calcium wire / ferro-calcium wire used in the refining site is only 10-30%. Other impurity oxides in the calcium wire and the violent tumbling generated during the process of feeding calcium wire are likely to cause secondary pollution to the molten steel, seriously affecting the strict requirements of high-quality steel for cleanliness. The unit price cost of the calcium wire is relatively high, about 10,000 yuan per ton of steel in the market. At the same time, the consumption of the refining calcium wire feeding process is relatively large, directly increasing the manufacturing cost of the product during the smelting process, and the large amount of smoke generated during the process of feeding calcium wire also does not meet the increasingly strict environmental inspection requirements.

[0004] Due to its unique outer electron structure, rare earth has strong chemical activity, variable valence states, and large atomic size and other characteristics, and has become an important micro-alloying element for deep purification agents of steel, modifiers of inclusions, and high-value-added steel materials. There is no relevant report on completely replacing the traditional refining calcium treatment process through the rare earth treatment process. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for replacing the process of feeding calcium wire with rare earth treatment for aluminum-deoxidized steel. By mainly controlling the cleanliness of the narrow window during the smelting process and the precise addition process of rare earth steel, the traditional refining calcium treatment process is broken through, and finally a method for replacing the traditional refining calcium wire feeding process with rare earth treatment is realized. It can effectively improve the production sequence during the smelting process, and through the deep purification effect of strongly deoxidizing and desulfurizing the molten steel by high-reducing lanthanum-cerium rare earth, further achieve the control effect of high-cleanliness molten steel, and at the same time achieve the purpose of reducing the manufacturing cost and eliminating the smoking problem caused by the calcium treatment process.

[0006] To solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for replacing the process of feeding calcium wire with rare earth treatment for aluminum-deoxidized steel according to the present invention includes:

[0008] In the first step, in order to control the narrow window process during the smelting process and meet the cleanliness conditions of the molten steel before the addition of rare earth, the following process is executed:

[0009] (1) Converter process: Molten iron is smelted in a converter and then tapped to obtain molten steel. During tapping, slagging-off tapping is adopted to control the slag amount per ton of molten steel not exceeding 5 kg / t steel. When the tapping amount is between 1 / 5 and 2 / 5, 4.2 kg - 5.4 kg of ferrosilicon aluminum is added to the molten steel per ton of steel for deoxidation and alloying. When the tapping amount is between 3 / 5 and 4 / 5, ferrosilicon is added to the molten steel for alloying according to the design of the molten steel composition. Slag modification of the ladle is carried out, and it is required to control the basicity R of the ladle slag ≥ 2.5, and w(FeO + MnO) in the slag < 4%;

[0010] (2) LF refining process: Rapid slag formation is achieved by rapid heating, submerged arc, stirring, and adding slag formers in batches, using a CaO - Al2O3 - SiO2 slag system; Bottom blowing argon system, in the early stage of refining (within 10 minutes after starting treatment), the bottom blowing argon flow rate is controlled at 3.0 - 4.0 NL / (min·t) for stirring and desulfurization, in the middle stage of refining (10 - 15 minutes after starting treatment), the bottom blowing intensity is controlled at 3.0 NL / min / t - 2.0 NL / min / t, and in the late stage of refining (15 - 25 minutes after starting treatment), the bottom blowing intensity is controlled at 2.0 NL / min / t - 1.5 NL / min / t; After LF refining, the slag composition is controlled as CaO ≥ 50%, SiO2 ≤ 10%, 23% ≤ Al2O3 ≤ 33%, MgO ≤ 10%, TFe + MnO ≤ 1.2%. The thickness of the ladle slag is controlled at 150 - 200 mm to ensure that the top slag is in the liquid region, has good fluidity, and has a strong adsorption capacity for deoxidation products; After refining, to ensure the slag viscosity and promote inclusions to float to the steel slag, the stirring intensity is controlled at 0.5 - 1.0 L / (min·t) with argon, specifically based on the principle that the liquid surface fluctuates but does not expose the steel liquid surface, and the holding time is required to be > 10 min;

[0011] Through the above treatment, better cleanliness of the molten steel in the steel is achieved, and at the same time, the acid-soluble aluminum [Al] content in the steel is controlled within the range of 0.020 - 0.050%;

[0012] Second step, rare earth addition process: According to the acid-soluble aluminum [Al] content in different ranges in the steel, a certain amount of rare earth cerium iron alloy is added at the end of LF refining deoxidation alloying.

[0013] Furthermore, 0.2 - 0.4 kg / t of aluminum powder is added according to the deoxidation situation, 70 - 90 kg of active lime and 15 - 20 kg of bauxite are added additionally to ensure that the basicity of the slag is greater than 3.0, and the white slag holding time should be > 12 minutes.

[0014] Furthermore, the rare earth cerium iron alloy contains 30% cerium.

[0015] Furthermore, the rare earth alloy addition plan for the aluminum content in the steel of 0.010% - 0.020%:

[0016]

[0018] Further, the addition plan of rare earth alloy with aluminum content of 0.020%-0.030% in steel:

[0019] Further, the addition plan of rare earth alloy with aluminum content of 0.030%-0.040% in steel:

[0020]

[0021]

[0022] Further, the addition plan of rare earth alloy with aluminum content of 0.040%-0.050% in steel:

[0023]

[0024] Compared with the prior art, the beneficial technical effects of the present invention:

[0025] The present invention provides a method for replacing the refining calcium wire feeding process with rare earth treatment for aluminum deoxidized steel, aiming to break through the traditional refining calcium treatment process through narrow window cleanliness control during the smelting process and precise addition process of rare earth steel, and finally realize the method of replacing the traditional refining calcium wire feeding process with rare earth treatment. After taking the above measures, it can directly reduce the operation time of the calcium treatment process for each furnace of steel and the time for the bottom blowing argon gas supporting the calcium treatment products to float, effectively improving the production sequence during the smelting process, and using the strong deoxidation and desulfurization deep purification effect of high-reducing lanthanum and cerium rare earth on the molten steel to further realize the control effect of high cleanliness molten steel, while achieving the purpose of reducing the manufacturing cost and eliminating the smoking problem caused by the calcium treatment process, providing technical guidance and process path for improving the quality of the production line and developing high cleanliness high-grade products. Brief Description of the Drawings

[0026] The present invention will be further described below in conjunction with the drawings.

[0027] Figure 1 For the liquid level and stopper rod curves during the continuous casting process of the conventional calcium wire treatment process;

[0028] Figure 2 For the liquid level and stopper rod curves during the continuous casting process of implementing the rare earth treatment process of the present invention;

[0029] Figure 3 For the inclusion detection in the finished steel plate of the conventional calcium treatment process;

[0030] Figure 4For the detection of inclusions in the finished product of the calcium-free treatment plus rare earth process steel plate of the present invention. Specific embodiments

[0031] Embodiment 1:

[0032] On the hot strip mill production line of a steel plant, a converter with a capacity of 240 tons was matched. A production trial comparison was carried out between the implementation of the present invention and the conventional calcium treatment process. The chemical compositions of the aluminum-killed low-alloy high-strength steel HC500LA produced are shown in Table 1 (the aluminum content in the steel is 0.020%-0.030%). A production trial comparison of the production sequence and the stability of the casting process was carried out by implementing the present invention and the conventional calcium treatment.

[0033] Table 1 Chemical composition Unit: %

[0034] Chemical element C Si Mn P S Alt Ti Target 0.17 0.02 0.95 0.015 0.005 0.025 0.075

[0035] The specific process of implementing the present invention is as follows:

[0036] Converter process: After the hot metal is smelted in the converter and the molten steel is obtained, slag blocking is adopted during the tapping process, and the slag volume per ton of molten steel is 2 kg / t steel; when the tapping volume reaches 2 / 5, ferrotitanium (containing 40% aluminum) is added to the molten steel at 4.5 kg per ton of steel for deoxidation and alloying. When the tapping volume reaches 3 / 5, ferrosilicon is added to the molten steel according to the molten steel composition design for alloying. Slag modification of the ladle is carried out, and it is required to control the basicity R of the ladle slag to be 3.1, and w(FeO + MnO) in the slag is 2%.

[0037] LF refining process: Rapid slag formation is achieved by rapid heating, submerged arc, stirring, and adding slag formers in batches reasonably, and the CaO-Al2O3-SiO2 slag system is adopted; the bottom blowing argon gas system. In the early stage of refining (within 10 minutes after the start of treatment), the bottom blowing argon gas flow rate is controlled at 3.4 NL / (min·t) for stirring and desulfurization. In the middle stage of refining (10-15 minutes after the start of treatment), the bottom blowing intensity is controlled at 2.3 NL / min / t. In the later stage of refining (15-25 minutes after the start of treatment), the bottom blowing intensity is controlled at 1.7 NL / min / t; the oxygen content of the molten steel tapped from the converter is 670 ppm, 0.34 kg / t of aluminum powder is added, 82 kg of active lime and 17 kg of bauxite are added additionally, the slag basicity is 3.6, and the white slag holding time is 16 minutes. After the LF refining is completed, the slag composition is CaO 54%, SiO2 7%, Al2O3 29%, MgO 9%, TFe + MnO 0.9%, and the ladle slag thickness is controlled at 175 mm. After the refining is completed, in order to ensure the slag viscosity and promote the floating of inclusions to the steel slag, argon gas controlled stirring at 0.78 L / (min·t) is adopted, and the holding time is 13 min. Finally, the content of acid-soluble aluminum [Al] in the steel is controlled within the range of 0.027%.

[0038] Rare earth addition process: According to the requirement of acid-soluble aluminum [Al] content in steel being 0.020% - 0.030%, 38 kg of rare earth cerium iron alloy (containing 30% cerium) was added at the end of LF refining, deoxidation, and alloying. In the ladle furnace treatment process of the conventional calcium treatment process, 300 meters of calcium wire was fed. The results of the trial production process are as follows:

[0039] In the ladle furnace treatment process of the conventional calcium wire treatment process ( Figure 1 ), there was no obvious steel flocculation at the stopper rod of the tundish during the casting process of the ladle furnace treated by the process of the present invention ( Figure 2 ). The rare earth treatment replacing the conventional calcium treatment did not affect the smooth casting.

[0040] There was an obvious smoking phenomenon during the operation process of the conventional calcium wire treatment process, while there was no smoking situation during the operation process of the present invention.

[0041] The cost generated by the operation of the conventional calcium wire treatment process was 300 m * 0.4 kg / m * 9000 yuan / ton of calcium wire / 240 tons of steel, resulting in a manufacturing cost of 4.5 yuan / ton of steel. While the cost generated by the present invention was 38 kg of rare earth cerium iron alloy (containing 30% cerium) * 15000 yuan / ton of rare earth alloy / 240 tons of steel, resulting in a manufacturing cost of 2.38 yuan / ton of steel, showing an obvious cost advantage.

[0042] The operation time for feeding calcium wire in the ladle furnace treatment process of the conventional calcium wire treatment process was 5.5 minutes, and the time for promoting the floating of calcium treatment products by bottom blowing argon was 13.5 minutes. While for the ladle furnace treated by the process of the present invention, no additional treatment time was generated, effectively reducing the production time sequence by 19 minutes per furnace of steel.

[0043] Implementation case two:

[0044] In a hot strip mill production line of a steel plant, a converter with a capacity of 240 tons was matched. A production trial comparison was carried out between the process of the present invention and the conventional calcium treatment process. The chemical composition of the aluminum-deoxidized structural steel Q355B produced is shown in Table 2 (the requirement for aluminum content in steel is 0.030% - 0.040%). A production trial comparison was carried out to improve the inclusion effect and cost by implementing the process of the present invention and the conventional calcium treatment.

[0045] Table 2 Chemical composition Unit: %

[0046] Chemical element C Si Mn P S Alt Target 0.18 0.15 1.15 0.015 0.005 0.035

[0047] The specific process of implementing the process of the present invention is as follows:

[0048] Converter process: Molten iron is smelted in a converter and then tapped to obtain molten steel. During tapping, slag blocking tapping is adopted, and the slag volume per ton of molten steel is 2.5 kg / t steel. When the tapping amount reaches 2 / 5, ferrosilicon aluminum (containing 40% aluminum) is added to the molten steel at a rate of 4.9 kg / ton of steel for deoxidation and alloying. When the tapping amount reaches 3 / 5, ferrosilicon is added to the molten steel according to the molten steel composition design for alloying. Slag modification of the ladle is carried out, and the basicity R of the ladle slag is required to be controlled at 3.5, and w(FeO + MnO) in the slag is 1.8%.

[0049] LF refining process: Rapid slag formation is achieved by rapid heating, submerged arc, stirring, and reasonable addition of slag formers in batches, using a CaO-Al2O3-SiO2 slag system; bottom blowing argon system. In the early stage of refining (within 10 minutes after starting treatment), the bottom blowing argon flow rate is controlled at 3.7 NL / (min·t) for stirring and desulfurization. In the middle stage of refining (10 - 15 minutes after starting treatment), the bottom blowing intensity is controlled at 2.7 NL / min / t. In the late stage of refining (15 - 25 minutes after starting treatment), the bottom blowing intensity is controlled at 1.9 NL / min / t. The oxygen content in the converter tapping is 745 ppm, 0.36 kg / t of aluminum powder is added, 78 kg of active lime and 19 kg of bauxite are added additionally, the slag basicity is 4.3, and the white slag holding time is 15 minutes. After the LF refining is completed, the slag composition is CaO 56.5%, SiO2 8.4%, Al2O3 27.6%, MgO 7.9%, TFe + MnO 0.87%, and the ladle slag thickness is controlled at 183 mm. After the refining is completed, to ensure the slag viscosity and promote the floating of inclusions to the steel slag, argon-controlled stirring at 0.75 L / (min·t) is adopted, and the holding time is 12 min. Finally, the content of acid-soluble aluminum [Al] in the steel is controlled within the range of 0.035%.

[0050] Rare earth addition process: According to the requirement of the acid-soluble aluminum [Al] content in the steel being 0.030% - 0.040%, 36 kg of rare earth cerium iron alloy (containing 30% cerium) is added at the end of the LF refining deoxidation and alloying. For the furnace charges with the conventional calcium treatment process, 250 meters of calcium wire is fed. Samples of the refining off-position slag properties, tundish, and steel plate are taken respectively for inclusion detection. The trial production results are as follows:

[0051] By analyzing the components of the LF refining off-position slag samples corresponding to the conventional calcium treatment and the furnace charges with the calcium-free treatment process plus rare earth process described in the present invention, the results of the slag sample component analysis show that the basicities of the ladle top slag corresponding to the conventional calcium treatment process and the calcium-free treatment plus rare earth process described in the present invention are 7.55 and 7.05 respectively, the T.FeO in the slag is 0.83% and 0.85% respectively, and the CaO / Al2O3 is 1.95 and 2.11 respectively. The control ranges of indexes such as the adsorption capacity of deoxidation products, the total oxygen content in the slag, and the steel slag fluidity are the same under the two process conditions, ensuring good steel slag properties.

[0052] Inclusions in the finished steel plate samples corresponding to the conventional calcium treatment process and the calcium-free treatment plus rare earth process furnace runs described in the present invention were detected and rated. The test results show that the overall rating of inclusions in the steel of the furnace runs implementing the present invention is superior to that of the conventional calcium treatment process (Table 3). Rare earth plays a role in modifying and refining inclusions in the steel. The metallographic test results show that the size of the products produced by rare earth in the steel ranges from 7 to 55 μm ( Figure 3 ), while the size of inclusions in the steel of the conventional calcium treatment process ranges from 3 to 5 μm ( Figure 4 ).

[0053] Table 3 Inspection Results of Inclusions in Plate Coils

[0054]

[0055] The embodiments described above are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel, characterized in that: include: The first step is to control the narrow window of the smelting process and meet the cleanliness conditions of the molten steel before adding rare earths. The following processes are performed: (1) Converter process: molten iron is smelted in a converter and then tapped to obtain molten steel. During the tapping process, slag blocking is used to control the slag amount under ton of molten steel to be no more than 5kg / t of steel. When the steel output is 1 / 5-2 / 5, ferroaluminum is added to the molten steel at 4.2kg-5.4kg / ton steel for deoxidation and alloying. When the steel output is 3 / 5-4 / 5, ferrosilicon is added to the molten steel for alloying according to the molten steel composition design. Ladle slag modification is adopted, and the ladle slag basicity R is controlled to be ≥2.5, and w(FeO+MnO) in the slag is <4%; (2) LF refining process: rapid slag formation is achieved through rapid heating, arc burial, stirring, and reasonable addition of slag-forming agents in batches, using CaO-Al2O3-SiO2 slag system; bottom blowing argon system, the bottom blowing argon flow rate is controlled at 3.0-4.0NL / (min·t)) in the early stage of refining for stirring and desulfurization, the bottom blowing intensity is controlled at 3.0NL / min / t-2.0NL / min / t in the middle stage of refining, and the bottom blowing intensity is controlled at 2.0NL / min / t-1.5NL / min / t in the late stage of refining; the slag composition at the end of LF refining is controlled at CaO≥50%, SiO2≤10%, 23%≤Al2O3≤33%, MgO≤10%, TFe+MnO≤1.2%, the ladle slag thickness is controlled at 150-200mm, to ensure that the top slag is in the liquid area, and maintains good fluidity, and has a strong adsorption capacity for deoxidation products; after refining, in order to ensure the viscosity of the slag and promote the floating of inclusions to the slag, argon is used to control the stirring intensity at 0.5-1.0L / (min·t), specifically, the liquid level fluctuates but the steel liquid surface is not exposed as a principle, and the holding time is required to be greater than 10min; The above treatment achieves better cleanliness of molten steel in the steel, and at the same time, the acid-soluble aluminum [Al] content in the steel is controlled within the range of 0.020-0.050%; The second step is rare earth addition process: according to the different ranges of acid-soluble aluminum [Al] content in the steel, a certain amount of rare earth ferrocerium alloy is added at the end of LF refining, deoxidation and alloying.

2. The method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel according to claim 1, characterized in that: According to the deoxidation situation, add 0.2-0.4kg / t aluminum powder, 70-90kg active lime and 15-20kg bauxite to ensure that the slag basicity is greater than 3.0 and the white slag retention time should be greater than 12 minutes.

3. The method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel according to claim 1, characterized in that: The rare earth ferrocerium alloy contains 30% cerium.

4. The method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel according to claim 1, characterized in that: Rare earth alloy addition scheme with aluminum content of 0.010%-0.020% in steel:

5. The method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel according to claim 1, characterized in that: Rare earth alloy addition scheme with aluminum content of 0.020%-0.030% in steel:

6. The method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel according to claim 1, characterized in that: Rare earth alloy addition scheme with aluminum content of 0.030%-0.040% in steel:

7. The method for replacing the calcium wire feeding process with rare earth treatment of aluminum deoxidized steel according to claim 1, characterized in that: Rare earth alloy addition scheme with aluminum content of 0.040%-0.050% in steel:

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