Method for improving continuous casting stability of low-carbon alloy steel by composite deoxidation and rare earth alloying

Abstract

The application belongs to the technical field of steel smelting, and particularly relates to a method for improving continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying, which comprises the following steps: S1, obtaining molten steel, a multi-element rare earth composite alloy and silicon-manganese alloy, the silicon-manganese alloy comprising a first silicon-manganese alloy and a second silicon-manganese alloy, adding lime to build slag at the initial tapping of the molten steel; simultaneously adding the multi-element rare earth composite alloy and the first silicon-manganese alloy and starting bottom argon blowing when the molten steel is tapped for 70-120 s; adding coke powder and a modifier when the molten steel is tapped for 180-240 s, and finally obtaining first molten steel; S2, adding the second silicon-manganese alloy to the first molten steel for refining to obtain second molten steel, and continuously casting the second molten steel to obtain low-carbon alloy steel. The application realizes full-oxygen stability control of the molten steel, efficient inheritance of rare earth, refinement and spheroidization of inclusions, stable manganese alloy yield and smooth continuous casting of the water gap by synergistically adding the rare earth composite alloy and the silicon-manganese alloy, and adding the silicon-manganese alloy again in the LF stage and controlling the temperature and the basicity of the slag.

Description

Technical Field

[0001] This application relates to the field of iron and steel smelting technology, specifically, to a method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying. Background Technology

[0002] In the smelting process of low-carbon plain carbon steel and low-alloy structural steel, the molten steel at the converter endpoint is in a strongly oxidizing state, with an active oxygen content typically as high as 300-600 ppm. Traditional processes often use aluminum blocks or aluminum-containing alloys for deoxidation. The aluminum mainly remains at the deoxidation level, easily forming polygonal, clustered, or coral-like high-melting-point Al2O3 inclusions. These inclusions are prone to depositing on the inner wall of the nozzle during casting and inducing nodule formation. During rolling, they easily form stress concentration sources, affecting the uniformity of steel hardness, fatigue performance, and low-temperature toughness. To alleviate nodule formation, existing technologies commonly use calcium treatment (feeding silicon-calcium wire) to liquefy and modify the inclusions. However, calcium has a low boiling point, large yield fluctuations, and when the sulfur content is high or the slag system is not properly controlled, it is easy to generate high-melting-point CaS, which increases the risk of nozzle blockage.

[0003] Rare earth elements (such as La and Ce) possess extremely strong deoxidizing affinity and excellent inclusion modification capabilities, theoretically making them an ideal alternative to calcium treatment. However, in the environment of highly oxidizing molten steel and strongly oxidizing converter top slag, rare earth elements exhibit extremely high chemical reactivity, easily leading to early oxidation and burn-off at the interface (slag loss). This not only results in extremely low and highly fluctuating rare earth recovery rates from steel but also causes severe imbalances in slag phase composition and basicity, preventing stable transfer of rare earth elements to the molten steel and hindering large-scale industrial application. Furthermore, existing rare earth treatment technologies typically focus on single deoxidation effects, lacking control over the coupling relationship between the addition sequence, FeO / MnO activity in the slag, refining slag basicity, La / Ce ratio, and manganese alloy recovery rate. Consequently, it is difficult to simultaneously achieve low oxygen, low burn-off, high rare earth transfer, and smooth nozzle operation.

[0004] Therefore, developing an integrated process that combines deep deoxidation, efficient rare earth inheritance, inclusion modification, and stable calcium substitution has become the key to the research and development of high-performance rare earth steel. Summary of the Invention

[0005] To solve the above technical problems, this application provides a method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying, comprising the following steps: S1, obtaining molten steel, a multi-element rare earth composite alloy, and a silicon-manganese alloy, wherein the silicon-manganese alloy comprises a first silicon-manganese alloy and a second silicon-manganese alloy, the mass ratio of the first silicon-manganese alloy to the second silicon-manganese alloy being (90-85):(10-15); when the molten steel is initially tapped, quicklime is added for slag formation; when the molten steel is tapped for 70-120 seconds, the multi-element rare earth composite alloy and the first silicon-manganese alloy are simultaneously added. A silicon-manganese alloy is used, and bottom-blowing argon gas is turned on. When the molten steel is tapped for 180-240 seconds, coke powder and a modifier are added to finally obtain the first molten steel. S2, the second silicon-manganese alloy is added to the first molten steel for refining to obtain the second molten steel. The second molten steel is continuously cast to obtain low-carbon alloy steel. The composition of the low-carbon alloy steel by mass percentage is: C≤0.25%, Si≤0.50%, Mn:0.30%-1.60%, La:5-32ppm, Ce:10-60ppm, with the remainder being Fe and unavoidable impurities.

[0006] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, in step S1, the tapping temperature of the molten steel is 1610-1650℃.

[0007] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, in step S1, the composition of the multi-element rare earth composite alloy, by mass percentage, is: RE: 29%-34%, Si: 44%-52%, with the remainder being Fe and unavoidable impurities, wherein RE is La and Ce, and the mass ratio of La to Ce is (30-40):(70-60); the composition of the silicon-manganese alloy, by mass percentage, is: Si: 17%-20%, Mn: 65%-72%, with the remainder being Fe and unavoidable impurities.

[0008] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, in step S1, the mass ratio of the multi-element rare earth composite alloy to the molten steel is (0.7-1.4):1000, and the mass ratio of the silicon-manganese alloy to the molten steel is (5-25):1000.

[0009] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, in step S1, the argon flow rate of the bottom-blown argon gas is 1000-1200 NL / min.

[0010] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, in step S2, the refining temperature is 1550-1580℃ and the refining time is 15-22min.

[0011] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, in step S2, the risk of nozzle clogging during continuous casting is reduced, and the continuous casting stability is improved.

[0012] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, the oxygen content of the molten steel is 300-800 ppm, the oxygen content of the first molten steel is 5-40 ppm, and the oxygen content of the second molten steel is 3-12 ppm.

[0013] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, the microstructure of the low-carbon alloy steel includes La-Ce rare earth composite oxysulfide inclusions, which are finely and dispersedly distributed.

[0014] As a preferred embodiment of the method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying as described in this application, the yield of La is ≥10%, the yield of Ce is ≥10%, and the yield of Mn is ≥90%.

[0015] Ce is the main active element for deoxidation and inclusion modification in light rare earth elements, possessing strong oxygen affinity and the ability to modify oxygen-sulfur inclusions. La, as a harmonizing and stabilizing element, can mitigate the problems of excessive reaction, easy aggregation of inclusions, or compositional fluctuations in single high-Ce systems. La and Ce have similar crystal structures, ionic radii, and chemical reactivity, exhibiting good miscibility and compositional homogeneity within the 35 / 65 (±5) range, and are less prone to phase separation, precipitation, or batch segregation, thus improving the compositional consistency of rare earth ferrosilicon alloys and their addition to molten steel. This La / Ce ratio is compatible with existing rare earth separation and downstream material preparation processes, with relatively uniform process windows for acid-base dissolution, extraction, carbonization crystallization, and subsequent alloying reactions, eliminating the need for significant parameter adjustments in downstream production.

[0016] This application proposes a method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying. The method involves the synergistic addition of rare earth composite alloy and silicon-manganese alloy within 70-120 seconds after tapping, the mid-to-late stage addition of coke powder and modifier, the re-addition of silicon-manganese alloy in the LF stage, and the control of temperature and slag basicity. This method achieves stable oxygen control in molten steel, efficient rare earth transfer, inclusion refinement and spheroidization, stable manganese alloy yield, and smooth continuous casting at the sprue. This application uses a multi-element rare earth composite alloy as the core deoxidation and rare earth transfer alloy. Its main chemical composition, by mass percentage, is RE: 29-34%, Si: 44-52%, and La / Ce mass ratio of 35 / 65 (±5). The amount added is 0.7-1.4 kg / t based on the mass of molten steel. The multi-element rare earth composite alloy is used in combination with silicon-manganese alloy, quicklime, coke powder, and modifiers to achieve deoxidation, rare earth transfer alloying, and inclusion modification through synergistic feeding. During the tapping stage, the first silicon-manganese alloy and the rare earth composite alloy are added synergistically. Silicon preferentially reduces the local oxygen potential and reduces the early burn-off of rare earth. The carbon in the coke powder reduces the activity of FeO and MnO in the slag, weakening the consumption of rare earth by the oxidizing top slag. During the LF stage, the composition is finely adjusted by the second silicon-manganese alloy, and the slag basicity is controlled to make the rare earth more stably transferred to the molten steel and billet.

[0017] After tapping begins, quicklime is added first to achieve initial slag formation by utilizing the impact of the steel flow. Within 70-120 seconds after tapping begins, multi-element rare earth composite alloy and silicon-manganese alloy are simultaneously added to the steel flow impact zone, while bottom-blowing argon gas is turned on (flow rate 1000-1200 NL / min). This allows the silicon-manganese alloy to preferentially reduce the local oxygen potential of the molten steel and form a thermodynamic protective environment for the addition of rare earth elements, promoting the rapid melting, dispersion, and stable entry of the rare earth alloy into the molten steel. In the middle and later stages of tapping, coke powder and modifiers are added. The carbon in the coke powder is used to reduce the activity of FeO and MnO in the slag and inhibit the reaction between rare earth elements and oxidizing slag, while the modifier is used to maintain the adsorption capacity of inclusions in the alkaline slag system. After the ladle is transported to the LF refining station, it is first heated. The heating time before placement is 10-12 minutes, and the placement temperature is controlled at 1550-1580℃. This temperature range can reduce the viscosity of the molten steel, increase the melting and diffusion rate of the alloy, and at the same time avoid excessive reaction between rare earth elements and top slag and furnace lining at excessively high temperatures. It can also appropriately improve the stability of rare earth inheritance. This process eliminates the conventional calcium treatment (feeding silicon-calcium wire) process and relies on the rare earth elements that are stably inherited into the steel to modify inclusions and prevent nozzle nodule formation.

[0018] The alkalinity of the refined slag is controlled at 2.0-2.5 after slag formation. With the aforementioned synergistic addition and LF refining control, the average deoxidation rate of the molten steel reaches over 96%. Rare earth elements were detected in the refined slag samples, unrefined slag samples, and tundish samples. Furthermore, the cost per ton of deoxidized steel is reduced by 1-3.5 yuan / ton compared to the aluminum block deoxidation process.

[0019] By controlling the amount of rare earth added to achieve a Ce element equivalent of 10-60 ppm in the billet, smooth flow of the continuous casting process without nozzle clogging is achieved. The multi-element rare earth composite alloy and the silicon-manganese alloy are added synergistically within 70-120 seconds after tapping. Compared to adding rare earth earlier or later than silicon-manganese, this synergistic addition can reduce the burn-off caused by the reaction of rare earth with highly oxidizing top slag and avoid the decrease in slag basicity caused by early silicon oxidation.

[0020] The carbon in the coke powder is used to reduce the activity of FeO and MnO in the refining slag, maintain the adsorption capacity of the alkaline slag system for oxide inclusions, and reduce the oxidation loss of rare earth elements into the slag. The first silicon-manganese alloy is added simultaneously with the rare earth composite alloy during the tapping stage, mainly to reduce the local oxygen potential and protect the rare earth elements; the second silicon-manganese alloy is added during the LF stage for fine-tuning the composition and stabilizing the Mn yield. Adding in batches avoids the localized silicon oxidation, decrease in slag basicity, and accelerated rare earth burn-off that can occur with a single addition.

[0021] The La / Ce mass ratio is 30 / 70-40 / 60, preferably 35 / 65 (±5); this balances the rapid deoxidation modification effect of Ce with the regulating effect of La on the system's reaction intensity, inclusion fine dispersion, and batch-to-batch stability. Within this mass ratio range, the components are uniformly miscible, without phase separation or precipitation, and are suitable for the acid-base dissolution, extraction, carbonization crystallization, and subsequent alloying process windows in rare earth separation.

[0022] The method described is applicable to low-carbon, medium- and low-manganese low-alloy steels with a carbon content of no more than 0.25% and a silicon content of no more than 0.50%. It can reduce the proportion of hard Al2O3 inclusions and large-size composite inclusions, improve the cleanliness of the steel, and enhance the stability of its mechanical properties during subsequent rolling. Compared with existing technologies, this application has the following significant advantages: (1) Deep deoxidation and efficient inheritance: Rare earth composite alloy with a La / Ce mass ratio of 35 / 65 (±5) and silicon-manganese alloy are added synergistically within 70-120s after the start of steel tapping. Silicon preferentially reduces the local oxygen potential in the steel flow impact zone and provides thermodynamic protection for rare earth. The average deoxidation rate can exceed 96%, the oxygen content at the point of departure is less than 20ppm, and the Ce retention in the billet is stable at 10-60ppm. Rare earth elements can be detected in the samples of the refining process in the experimental furnace, the samples of the refining process in place, the samples of the refining process in place and the samples of the tundish, proving that rare earth has process inheritance.

[0023] (2) Inclusion Refinement and Performance Stabilization: The synergistic effect of La / Ce transforms hard inclusions such as Al2O3 and SiO2 into rounded and dispersed rare earth composite oxysulfide inclusions. This method can reduce the proportion of large particle inclusions larger than 100 μm and increase the proportion of small particle inclusions smaller than 20 μm. The reduction of large particle inclusions and the increase of small particle inclusions indicate a trend towards smaller and more dispersed inclusions. Compared with the blank furnace, the experimental furnace showed a reduction in large particle inclusions and an increase in small particle inclusions in subsequent processes. Rare earth elements were detected in the small particle inclusions, reducing the impact of large-size hard inclusions on subsequent rolling, fatigue performance, and low-temperature toughness.

[0024] (3) Smooth casting without calcification: Without feeding silicon-calcium wire, the risk of nozzle clogging in continuous casting is reduced and the stability of continuous casting is improved by modifying rare earth inclusions and stabilizing the alkaline slag system. By using La and Ce rare earth elements to modify Al2O3 inclusions, the inclusions are transformed from hard, polygonal or coral-like Al2O3 into fine and dispersed rare earth composite oxygen sulfides, reducing the tendency of inclusions to deposit and sinter on the inner wall of the nozzle; at the same time, the fluctuation of calcium yield and the risk of CaS blockage caused by conventional calcium treatment are avoided, thereby improving the castability of molten steel and reducing the risk of nozzle clogging.

[0025] (4) Slag system, alloying and cost synergy: The carbon in coke powder reduces the activity of FeO and MnO in the slag, reduces the loss of rare earth oxidation, and is conducive to the stable entry of manganese into the molten steel, thus improving the manganese (Mn) yield. Experiments show that the average TFe in the slag from converter to refining is reduced by about 92%, and rare earth ferrosilicon has a cost reduction space of about 1-3.5 yuan / t steel compared with aluminum block deoxidation. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a SEM image of the La-Ce rare earth complex oxysulfide inclusions in the low-carbon alloy steel prepared in Example 1 of this application.

[0028] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0029] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0030] This application provides a method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying, comprising the following steps: S1. Obtain molten steel, a multi-element rare earth composite alloy, and a silicon-manganese alloy. The silicon-manganese alloy includes a first silicon-manganese alloy and a second silicon-manganese alloy, with a mass ratio of (90-85):(10-15). Initially, quicklime is added to the molten steel during tapping to form slag. When the molten steel tapps for 70-120 seconds, the multi-element rare earth composite alloy and the first silicon-manganese alloy are added simultaneously, and bottom-blowing argon gas is activated. When the molten steel tapps for 180-240 seconds, coke powder and a modifier are added to finally obtain the first molten steel. The tapping temperature of the molten steel is 1610-1650℃; the composition of the multi-element rare earth composite alloy by mass percentage is: RE: 29%-34%, Si: 44%-52%, with the remainder being Fe and unavoidable impurities, wherein RE is La and Ce, and the mass ratio of La to Ce is (30-40):(70-60); the composition of the silicon-manganese alloy by mass percentage is: Si: 17%-20%, Mn: 65%-72%, with the remainder being Fe and unavoidable impurities; the mass ratio of the multi-element rare earth composite alloy to the molten steel is (0.7-1.4):1000, and the mass ratio of the silicon-manganese alloy to the molten steel is (5-25):1000; the argon flow rate of the bottom-blown argon gas is 1000-1200 NL / min; S2. The second silicon-manganese alloy is added to the first molten steel and refined to obtain the second molten steel. The second molten steel is then continuously cast to obtain low-carbon alloy steel. The composition of the low-carbon alloy steel, by mass percentage, is: C≤0.25%, Si≤0.50%, Mn:0.30%-1.60%, La:5-32ppm, Ce:10-60ppm, with the remainder being Fe and unavoidable impurities. The refining temperature is 1550-1580℃, and the refining time is 15-22 minutes; the continuous casting process reduces the risk of nozzle clogging and improves continuous casting stability; the oxygen content of the molten steel is 300-800 ppm, the oxygen content of the first molten steel is 5-40 ppm, and the oxygen content of the second molten steel is 3-12 ppm; the microstructure of the low-carbon alloy steel includes La-Ce rare earth complex oxysulfide inclusions, which are finely dispersed; the yield of La is ≥10%, the yield of Ce is ≥10%, and the yield of Mn is ≥90%.

[0031] The technical solution of this application will be further described below with reference to specific embodiments.

[0032] Example 1

[0033] This application provides a method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying, comprising the following steps: S1. Obtain molten steel, a multi-element rare earth composite alloy, and a silicon-manganese alloy. The silicon-manganese alloy includes a first silicon-manganese alloy and a second silicon-manganese alloy, with a mass ratio of 88:12. At the initial stage of tapping the molten steel, quicklime is added for slag formation. 100 seconds after tapping the molten steel, the multi-element rare earth composite alloy and the first silicon-manganese alloy are added simultaneously, and bottom blowing argon gas is turned on. 210 seconds after tapping the molten steel, coke powder and a modifier are added to finally obtain the first molten steel. The tapping temperature of the molten steel is 1630℃; the composition of the multi-element rare earth composite alloy by mass percentage is: RE: 32%, Si: 48%, with the remainder being Fe and unavoidable impurities, wherein RE consists of La and Ce, and the mass ratio of La to Ce is 35:65; the composition of the silicon-manganese alloy by mass percentage is: Si: 18%, Mn: 69%, with the remainder being Fe and unavoidable impurities; the mass ratio of the multi-element rare earth composite alloy to the molten steel is 1.1:1000, and the mass ratio of the silicon-manganese alloy to the molten steel is 8:1000; the argon flow rate of the bottom-blown argon gas is 1100 NL / min; S2. The second silicon-manganese alloy is added to the first molten steel and refined to obtain the second molten steel. The second molten steel is continuously cast to obtain low-carbon alloy steel. The composition of the low-carbon alloy steel by mass percentage is: C: 0.16%, Si: 0.18%, Mn: 0.50%, La: 16ppm, Ce: 30ppm, with the remainder being Fe and unavoidable impurities. The refining temperature was 1560℃, and the refining time was 18 minutes; the risk of nozzle clogging was reduced and the stability of continuous casting was improved; the oxygen content of the molten steel was 498 ppm, the oxygen content of the first molten steel was 13 ppm, and the oxygen content of the second molten steel was 7 ppm; please refer to [link / reference]. Figure 1 , Figure 1This is a SEM image of the La-Ce rare earth composite oxysulfide inclusions in the low-carbon alloy steel prepared in Example 1 of this application; the microstructure of the low-carbon alloy steel includes La-Ce rare earth composite oxysulfide inclusions, which are finely and dispersedly distributed; the yield of La is 13.0%, the yield of Ce is 13.1%, and the yield of Mn is 90.6%.

[0034] Example 2

[0035] This application provides a method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying, comprising the following steps: S1. Obtain molten steel, a multi-element rare earth composite alloy, and a silicon-manganese alloy. The silicon-manganese alloy includes a first silicon-manganese alloy and a second silicon-manganese alloy, with a mass ratio of 90:10. At the initial stage of tapping the molten steel, quicklime is added for slag formation. 70 seconds after tapping the molten steel, the multi-element rare earth composite alloy and the first silicon-manganese alloy are added simultaneously, and bottom blowing argon gas is turned on. 180 seconds after tapping the molten steel, coke powder and a modifier are added to finally obtain the first molten steel. The tapping temperature of the molten steel is 1610℃; the composition of the multi-element rare earth composite alloy by mass percentage is: RE: 29%, Si: 44%, with the remainder being Fe and unavoidable impurities, wherein RE consists of La and Ce, and the mass ratio of La to Ce is 30:70; the composition of the silicon-manganese alloy by mass percentage is: Si: 17%, Mn: 65%, with the remainder being Fe and unavoidable impurities; the mass ratio of the multi-element rare earth composite alloy to the molten steel is 1.4:1000, and the mass ratio of the silicon-manganese alloy to the molten steel is 5:1000; the argon flow rate of the bottom-blown argon gas is 1000 NL / min; S2. The second silicon-manganese alloy is added to the first molten steel and refined to obtain the second molten steel. The second molten steel is continuously cast to obtain low-carbon alloy steel. The composition of the low-carbon alloy steel by mass percentage is: C: 0.12%, Si: 0.15%, Mn: 0.31%, La: 30ppm, Ce: 60ppm, with the remainder being Fe and unavoidable impurities. The refining temperature was 1550℃, and the refining time was 15 minutes. The risk of nozzle clogging was reduced and the stability of continuous casting was improved during the continuous casting process. The oxygen content of the molten steel was 787 ppm, the oxygen content of the first molten steel was 36 ppm, and the oxygen content of the second molten steel was 12 ppm. The microstructure of the low-carbon alloy steel included La-Ce rare earth complex oxygen sulfide inclusions, which were finely and dispersedly distributed. The yield of La was 24.6%, the yield of Ce was 21.1%, and the yield of Mn was 95.4%.

[0036] Example 3

[0037] This application provides a method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying, comprising the following steps: S1. Obtain molten steel, a multi-element rare earth composite alloy, and a silicon-manganese alloy. The silicon-manganese alloy includes a first silicon-manganese alloy and a second silicon-manganese alloy, with a mass ratio of 85:15. At the initial stage of tapping the molten steel, quicklime is added for slag formation. 120 seconds after tapping the molten steel, the multi-element rare earth composite alloy and the first silicon-manganese alloy are added simultaneously, and bottom blowing argon gas is turned on. 240 seconds after tapping the molten steel, coke powder and a modifier are added to finally obtain the first molten steel. The tapping temperature of the molten steel is 1650℃; the composition of the multi-element rare earth composite alloy by mass percentage is: RE: 34%, Si: 52%, with the remainder being Fe and unavoidable impurities, wherein RE consists of La and Ce, with a mass ratio of La to Ce of 40:60; the composition of the silicon-manganese alloy by mass percentage is: Si: 20%, Mn: 72%, with the remainder being Fe and unavoidable impurities; the mass ratio of the multi-element rare earth composite alloy to the molten steel is 0.7:1000, and the mass ratio of the silicon-manganese alloy to the molten steel is 22:1000; the argon flow rate of the bottom-blown argon gas is 1200 NL / min; S2. The second silicon-manganese alloy is added to the first molten steel and refined to obtain the second molten steel. The second molten steel is continuously cast to obtain low-carbon alloy steel. The composition of the low-carbon alloy steel by mass percentage is: C: 0.18%, Si: 0.30%, Mn: 1.50%, La: 10ppm, Ce: 15ppm, with the remainder being Fe and unavoidable impurities. The refining temperature was 1580℃, and the refining time was 22 minutes. The risk of nozzle clogging was reduced and the stability of continuous casting was improved during the continuous casting process. The oxygen content of the molten steel was 308 ppm, the oxygen content of the first molten steel was 7 ppm, and the oxygen content of the second molten steel was 3 ppm. The microstructure of the low-carbon alloy steel included La-Ce rare earth complex oxygen sulfide inclusions, which were finely and dispersedly distributed. The yield of La was 10.5%, the yield of Ce was 10.5%, and the yield of Mn was 94.7%.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that, in step S1, when the molten steel is tapped for 100 seconds, a multi-element rare earth composite alloy is added first, followed by a first silicon-manganese alloy. The other steps are the same as in Example 1.

[0039] The tendency of nozzle formation, steel castability, and continuous casting stability during continuous casting did not change significantly compared to Example 1. The oxygen content of the molten steel was 485 ppm, the oxygen content of the first molten steel was 31 ppm, and the oxygen content of the second molten steel was 12 ppm. No rare earth components were detected, and the Mn recovery rate was 93%.

[0040] Comparative Example 2 The difference between this comparative example and Example 1 is that, in step S1, when the molten steel is tapped for 100 seconds, the first silicon-manganese alloy is added first, followed by the multi-element rare earth composite alloy. The other steps are the same as in Example 1.

[0041] The continuous casting process carries a significant risk of nozzle clogging, which reduces the stability of continuous casting. The oxygen content of the molten steel is 410 ppm, the oxygen content of the first molten steel is 48 ppm, and the oxygen content of the second molten steel is 15 ppm. The microstructure of the low-carbon alloy steel includes La-Ce rare earth complex oxysulfide inclusions. The yield of La is 25.1%, the yield of Ce is 29.8%, and the yield of Mn is 83%.

[0042] Comparative Example 3 The difference between this comparative example and Example 1 is that the mass ratio of the first silicon-manganese alloy and the second silicon-manganese alloy in step S1 is 75:25, while the other steps are the same as in Example 1.

[0043] The tendency of nozzle formation, castability of molten steel, and stability of continuous casting did not change significantly compared with Example 1. The oxygen content of the molten steel was 488 ppm, the oxygen content of the first molten steel was 45 ppm, and the oxygen content of the second molten steel was 13 ppm. The microstructure of the low-carbon alloy steel included La-Ce rare earth complex oxysulfide inclusions. The yield of La was 5.4%, the yield of Ce was 6.0%, and the yield of Mn was ≥90%.

[0044] Comparative Example 4 The difference between this comparative example and Example 1 is that the mass ratio of the first silicon-manganese alloy and the second silicon-manganese alloy in step S1 is 95:5, while the other steps are the same as in Example 1.

[0045] The continuous casting process carries a significant risk of nozzle clogging, which reduces the stability of continuous casting. The oxygen content of the molten steel is 458 ppm, the oxygen content of the first molten steel is 13 ppm, and the oxygen content of the second molten steel is 10 ppm. The microstructure of the low-carbon alloy steel includes La-Ce rare earth complex oxysulfide inclusions. The yield of La is 25.4%, the yield of Ce is 29.0%, and the yield of Mn is 82%.

[0046] Comparative Example 5 The difference between this comparative example and Example 1 is that the mass ratio of La to Ce in step S1 is 20:80, while the other steps are the same as in Example 1.

[0047] The tendency for nozzle formation during continuous casting is significantly increased, and the castability and stability of molten steel deteriorate. The oxygen content of the molten steel is 507 ppm, the oxygen content of the first molten steel is 11 ppm, and the oxygen content of the second molten steel is 5 ppm. The microstructure of the low-carbon alloy steel includes La-Ce rare earth complex oxysulfide inclusions. The yield of La is 15.4%, the yield of Ce is 28.3%, and the yield of Mn is 92%.

[0048] Comparative Example 6 The difference between this comparative example and Example 1 is that the mass ratio of La to Ce in step S1 is 50:50, while the other steps are the same as in Example 1.

[0049] The tendency of nozzle formation, castability of molten steel, and stability of continuous casting did not change significantly compared with Example 1; the oxygen content of the molten steel was 479 ppm, the oxygen content of the first molten steel was 26 ppm, and the oxygen content of the second molten steel was 14 ppm; the microstructure of the low-carbon alloy steel included La-Ce rare earth complex oxysulfide inclusions; the yield of La was 10.5%, the yield of Ce was 4.9%, and the yield of Mn was 86%.

[0050] Comparative Example 7 The difference between this comparative example and Example 1 is that the refining temperature in step S2 is 1530°C, while the other steps are the same as in Example 1.

[0051] The tendency of nozzle formation, steel castability, and continuous casting stability during continuous casting did not change significantly compared to Example 1; the oxygen content of the molten steel was 488 ppm, the oxygen content of the first molten steel was 25 ppm, and the oxygen content of the second molten steel was 16 ppm; the microstructure of the low-carbon alloy steel included La-Ce rare earth complex oxysulfide inclusions, with a La yield of 7.5%, a Ce yield of 8.5%, and a Mn yield of 79%.

[0052] Comparative Example 8 The difference between this comparative example and Example 1 is that the refining temperature in step S2 is 1600°C, while the other steps are the same as in Example 1.

[0053] The tendency of nozzle formation, steel castability, and continuous casting stability during continuous casting did not change significantly compared to Example 1; the oxygen content of the molten steel was 519 ppm, the oxygen content of the first molten steel was 14 ppm, and the oxygen content of the second molten steel was 10 ppm; the microstructure of the low-carbon alloy steel included La-Ce rare earth complex oxysulfide inclusions, with a La yield of 3.3%, a Ce yield of 3.5%, and a Mn yield of 83%.

[0054] As can be seen from the above examples and comparative examples: Example 1, combined with Comparative Example 1, shows that when the multi-element rare earth composite alloy is added before the first silicon-manganese alloy, rare earth elements undergo oxidation and burn-off in the high-oxygen potential molten steel and oxidizing slag, resulting in increased oxygen content in the first and second molten steel, and a significant decrease in Ce and La yields and rare earth retention in the billet. Example 1, combined with Comparative Example 2, shows that when the first silicon-manganese alloy is added before the multi-element rare earth composite alloy, the synergistic deoxidation sequence of the two is disrupted, and some Mn participates in deoxidation and oxidation into the slag in the high-oxygen potential molten steel, reducing the Mn yield; at the same time, although the Ce and La yields are improved, the Ce retention exceeds 60 ppm, the tendency of rare earth composite inclusions to aggregate is enhanced, leading to an increased risk of nozzle formation in continuous casting, and a decrease in the castability and continuous casting stability of the molten steel. Example 1, combined with Comparative Example 3, shows that when the proportion of the first silicon-manganese alloy is too low, the low-oxygen potential protective environment formed during the tapping stage is insufficient, the oxygen content of the first molten steel increases, the yield of Ce and La decreases, and the effect of rare earth stabilization is weakened. Although increasing the proportion of the second silicon-manganese alloy is beneficial to the retention of Mn during the LF refining stage, it cannot compensate for the adverse effects caused by rare earth oxidation and burning during the tapping stage. Example 1, combined with Comparative Example 4, shows that when the proportion of the first silicon-manganese alloy is too high and the proportion of the second silicon-manganese alloy is too low, more Mn participates in deoxidation and is lost through oxidation during the tapping stage, and the ability to fine-tune the Mn composition during the LF refining stage is insufficient, resulting in a decrease in Mn yield. At the same time, the high amount of rare earth retention increases the risk of nozzle clogging in continuous casting and reduces the stability of continuous casting. Example 1, combined with Comparative Example 5, shows that when the proportion of Ce in the La / Ce mass ratio is too high, the Ce yield and the Ce retention in the billet increase, and the Ce content exceeds 60 ppm, which easily promotes the aggregation of rare earth composite inclusions, increases the risk of nozzle clogging, and reduces the stability of continuous casting. Example 1, in conjunction with Comparative Example 6, shows that when the La proportion in the La / Ce mass ratio is too high, the system's rapid deoxidation capacity decreases, the oxygen content in the first and second molten steel increases, the proportion of Mn participating in deoxidation increases, the Mn yield decreases slightly, and the proportion of rare earth fine composite inclusions decreases, weakening the modification effect of rare earth composite inclusions. Example 1, in conjunction with Comparative Example 7, shows that when the LF refining temperature is too low, the melting, diffusion, and homogenization of the silicon-manganese alloy and the multi-element rare earth composite alloy are insufficient, the oxygen content in the second molten steel increases, and the yields of Ce, La, and Mn decrease. Example 1, in conjunction with Comparative Example 8, shows that when the LF refining temperature is too high, the reaction of rare earth elements with the top slag, furnace lining, and oxide inclusions intensifies, while the oxidation of Mn and slag loss increase, leading to a decrease in the yields of Ce, La, and Mn.

[0055] Based on Examples 1-3 and Comparative Examples 1-8, it can be seen that by simultaneously adding the multi-element rare earth composite alloy and the first silicon-manganese alloy 70-120s after tapping, controlling the mass ratio of the first silicon-manganese alloy to the second silicon-manganese alloy to be 85:15 to 90:10, the mass ratio of La to Ce to be 30:70 to 40:60, and controlling the LF refining temperature at 1550-1580℃, the Mn yield in the examples can be ≥90%, while also taking into account deep deoxidation of molten steel, stable inheritance of rare earth elements, refinement and modification of rare earth composite inclusions, control of target Mn composition, and smooth operation of continuous casting nozzles and stability of continuous casting.

[0056] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for improving the continuous casting stability of low-carbon alloy steel through composite deoxidation and synergistic rare earth alloying, characterized in that, Includes the following steps: S1. Obtain molten steel, a multi-element rare earth composite alloy, and a silicon-manganese alloy. The silicon-manganese alloy includes a first silicon-manganese alloy and a second silicon-manganese alloy, with a mass ratio of (90-85):(10-15). Initially, quicklime is added to the molten steel during tapping to form slag. When the molten steel tapps for 70-120 seconds, the multi-element rare earth composite alloy and the first silicon-manganese alloy are added simultaneously, and bottom-blowing argon gas is activated. When the molten steel tapps for 180-240 seconds, coke powder and a modifier are added to finally obtain the first molten steel. S2. The second silicon-manganese alloy is added to the first molten steel and refined to obtain the second molten steel. The second molten steel is then continuously cast to obtain low-carbon alloy steel. The composition of the low-carbon alloy steel, by mass percentage, is: C≤0.25%, Si≤0.50%, Mn:0.30%-1.60%, La:5-32ppm, Ce:10-60ppm, with the remainder being Fe and unavoidable impurities.

2. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, In step S1, the tapping temperature of the molten steel is 1610-1650℃.

3. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, In step S1, the composition of the multi-element rare earth composite alloy, by mass percentage, is: RE: 29%-34%, Si: 44%-52%, with the remainder being Fe and unavoidable impurities, wherein RE is La and Ce, and the mass ratio of La to Ce is (30-40):(70-60); the composition of the silicon-manganese alloy, by mass percentage, is: Si: 17%-20%, Mn: 65%-72%, with the remainder being Fe and unavoidable impurities.

4. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, In step S1, the mass ratio of the multi-element rare earth composite alloy to the molten steel is (0.7-1.4):1000, and the mass ratio of the silicon-manganese alloy to the molten steel is (5-25):1000.

5. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, In step S1, the argon flow rate of the bottom-blown argon gas is 1000-1200 NL / min.

6. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, In step S2, the refining temperature is 1550-1580℃, and the refining time is 15-22 minutes.

7. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, In step S2, the risk of nozzle clogging during continuous casting is reduced, and the stability of continuous casting is improved.

8. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, The oxygen content of the molten steel is 300-800 ppm, the oxygen content of the first molten steel is 5-40 ppm, and the oxygen content of the second molten steel is 3-12 ppm.

9. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, The microstructure of the low-carbon alloy steel includes La-Ce rare earth complex oxysulfide inclusions, which are finely and dispersedly distributed.

10. The method for improving the continuous casting stability of low-carbon alloy steel by composite deoxidation and synergistic rare earth alloying according to claim 1, characterized in that, The yield of La is ≥10%, the yield of Ce is ≥10%, and the yield of Mn is ≥90%.

Images