Process for smelting molten steel by adopting RE-Si-Fe composite deoxidizer

Abstract

The invention belongs to the technical field of steelmaking, and particularly relates to a process for smelting molten steel by adopting an RE-Si-Fe composite deoxidizer, which comprises the following steps: adding pretreated molten iron into a converter for smelting, and adding the RE-Si-Fe composite deoxidizer in the tapping process of the converter; and steel ladle top slag modification is carried out after steel tapping is completed. The RE-Si-Fe composite deoxidizer added in the converter tapping process can simultaneously exert the deoxidation and microalloying effects of rare earth in steel, stable reaction and retention of the rare earth in the steel are achieved while a good deoxidation effect is achieved, and inclusion control is facilitated. And the conventional calcium treatment operation for modifying the aluminum deoxidation product can be completely canceled, so that the production cost and the production treatment time of the smelting process are further reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of steelmaking, in particular to a process for steel liquid smelting by using RE-Si-Fe composite deoxidizer. BACKGROUND

[0002] The steelmaking process is to remove impurities such as carbon, silicon, manganese, phosphorus, sulfur in molten iron to the lower limit requirement or nothing by oxidation reaction. However, the oxygen element in the steel liquid will affect the mechanical properties and strength of the steel, so the steel liquid needs to be deoxidized. The conventional sedimentation deoxidation method is to add deoxidizer to the steel liquid to directly react with the oxygen in the steel liquid, and the large-size deoxidation product is insoluble in the steel liquid and finally floats in the slag for removal.

[0003] The traditional aluminum deoxidation method is to add aluminum blocks or aluminum-iron alloy to the steel to make Al and O in the steel liquid react to generate Al2O3, which is then floated to the top slag of the ladle. The aluminum deoxidation has the advantages of easy operation and good deoxidation effect, but the cost of aluminum material is high, and the preparation process is a typical high-energy consumption and high-pollution process. At the same time, the Al2O3 produced by deoxidation is a hard inclusion, which can seriously affect the strength and ductility of the steel. Al2O3 in the steel liquid is easy to collide and grow into large-size inclusions or generate hard spinel inclusions with other elements, which seriously affects the service life and performance of high-grade steel. The traditional converter aluminum deoxidation method also needs to add calcium treatment in the subsequent LF or RH refining process, which takes 5-7 min / furnace. The large-size aluminum deoxidation product Al2O3 inclusions in the steel are treated, which further increases the production cost and production process time of the smelting process. In addition, after calcium treatment, large-size calcium aluminate and calcium-silicon-magnesium-aluminate and other high-melting-point complex inclusions are easy to be produced in the steel, which seriously affects the fatigue resistance of the steel, and also causes the problem of welding spatter during steel welding.

[0004] The principle of rare earth deoxidation is to utilize the high reducing property of rare earth elements to react with oxygen to form rare earth oxides or to combine with sulfur to form oxysulfides. The advantages of this method are good deoxidation effect, small size of deoxidation products, good combination with steel due to the round shape of the deoxidation products, and effective improvement of the organization continuity and comprehensive performance of the steel. The general method of adding rare earth in steel is to add pure rare earth or rare earth alloy at the end of the refining process. However, this method has the following disadvantages: the rare earth elements added at the end of the refining process do not have sufficient time to fully react with oxygen in the steel, the content of rare earth elements in the steel fluctuates greatly, and accurate quantitative control cannot be achieved, which seriously affects the treatment effect of rare earth deoxidation. In addition, the method of adding rare earth alloy at the end of the refining process also causes the rare earth elements to continue to react and flocculate in the inner wall of the nozzle during casting, resulting in the problem of unstable continuous casting. In addition, the uneven distribution of rare earth elements in the steel under this process condition is also a major bottleneck problem that prevents stable batch production in industrial production.

[0005] Current research on rare earth ferrosilicon alloy mainly includes preparation methods under different smelting equipment and smelting processes, and the main products are applied to inoculants and spherulitic agents in the cast iron industry. However, there is no specific deoxidation condition, deoxidation method, deoxidation control process, and deoxidation scheme for ensuring accurate control of the content of rare earth in steel according to the composition design of steel grades in the steelmaking industry and the matching of other alloy deoxidizers. For example, cold-rolled and galvanized products require silicon content <0.20wt% to avoid the difficulty of removing surface iron oxide scale caused by high silicon content, which affects the surface quality of the products. Therefore, the deoxidizer cannot be matched with the conventional silicon-manganese alloy that can simultaneously play the roles of deoxidation and alloying. For hot-rolled products, the requirement for surface quality is low, and the silicon content is designed to be ≥0.20wt% to replace valuable alloys to improve strength. Therefore, the deoxidizer can be matched with the conventional silicon-manganese alloy that can simultaneously play the roles of deoxidation and alloying. Therefore, it is necessary to design a detailed smelting process of rare earth ferrosilicon alloy according to the silicon content composition of the steel grade.

[0006] In summary, there is an urgent need for a deoxidizer and a deoxidation method that is low in cost, produces less deoxidation products, can exert the effect of rare earth in steel, and ensures stable and continuous casting during production, in order to meet the development needs of high-purity, low-cost, and high-value-added rare earth steel products. SUMMARY

[0007] To solve the problems in the prior art, the main purpose of the present application is to provide a process for smelting steel liquid by using RE-Si-Fe composite deoxidizer.

[0008] According to one aspect of the present application, the present application provides the following technical solution: A process for smelting steel liquid by using RE-Si-Fe composite deoxidizer, comprising the following steps: S1, hot metal desulfurization pretreatment; S2, after the pretreatment, the hot metal is added into a converter for smelting, low lance position and high oxygen supply intensity are adopted after the converter blowing starts; the temperature is controlled at 1300~1350℃ during the converter blowing dephosphorization period, the slag basicity is regulated to 1.8~2.2; the FeO content of the converter end-point slag is controlled to be >20wt%, the basicity is 4~6, so that the phosphorus content in the molten steel is stably controlled to be below 0.002wt%; an RE-Si-Fe composite deoxidizer is added during the converter tapping process, the RE-Si-Fe composite deoxidizer includes, in mass percentage, 30~40wt% of rare earth, 40~55wt% of silicon, and the balance of Fe and inevitable impurity elements; S3, after the tapping is completed, ladle top slag modification is carried out to realize the conditions of SiO2≤10wt% in the ladle top slag, CaO / Al2O3=1.2~1.5, and (MnO+FeO)≤2wt%.

[0009] The beneficial effects of the present application are as follows: The present application provides a process for molten steel smelting by using an RE-Si-Fe composite deoxidizer, the hot metal is added into a converter for smelting after pretreatment, the RE-Si-Fe composite deoxidizer is added during the converter tapping process; and the ladle top slag modification is carried out after the tapping is completed. The RE-Si-Fe composite deoxidizer added during the converter tapping process can simultaneously play the deoxidation and micro-alloying effects of rare earth in steel, good deoxidation effect is achieved while realizing the stable reaction and retention of the RE-Si-Fe composite deoxidizer in steel, and it is beneficial to the inclusion control. Moreover, the conventional calcium treatment operation for modifying the aluminum deoxidation product can be completely cancelled, and the production cost and production processing time of the smelting process are further reduced. DETAILED DESCRIPTION

[0010] The technical solutions in the embodiments will be described below in a clear and complete manner. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0011] According to one aspect of the present application, the present application provides the following technical solutions: A process for molten steel smelting by using an RE-Si-Fe composite deoxidizer, comprising the following steps: S1, hot metal desulfurization pretreatment; S2, after pretreatment, hot metal is added into the converter for smelting, low lance position and high oxygen supply intensity are adopted after converter blowing starts; the temperature is controlled at 1300~1350℃ during the dephosphorization stage of converter blowing, and the slag basicity is regulated to 1.8~2.2; the FeO content of the converter end-point slag is controlled to be >20wt%, and the basicity is 4~6, so that the phosphorus content in the molten steel is stably controlled to be below 0.002wt%; during the converter tapping process, a RE-Si-Fe composite deoxidizer is added, the RE-Si-Fe composite deoxidizer comprises, in mass percentage, 30~40wt% of rare earth, 40~55wt% of silicon, and the balance of Fe and inevitable impurity elements; S3, after the tapping is completed, the ladle top slag is modified, so that the conditions of SiO2≤10wt%, CaO / Al2O3=1.2~1.5, and (MnO+FeO)≤2wt% in the ladle top slag are realized.

[0012] The present application can effectively reduce the consumption of traditional high-cost aluminum materials, realize the effect of reducing Al2O3 hard oxide inclusions in steel, reduce the manufacturing cost in the smelting production process, the rare earth elements fully react with the impurity elements in the steel, and the nozzle clogging problem does not occur in the continuous casting process. The retention amount of rare earth in the steel is stable, the precise control of the content of rare earth in the steel can be realized, the stable application of the effect of rare earth in the steel is realized, and an effective technical approach for developing high-value-added rare earth steel products is provided.

[0013] Preferably, in the step S1, the hot metal slagging rate is above 95%, and the sulfur content of the hot metal is controlled to be <0.0010wt%.

[0014] The RE-Si-Fe composite deoxidizer contains rare earth alloy elements with strong oxygen affinity, can realize the effect of leaving rare earth in the steel, and the reaction of rare earth and oxygen can generate deoxidation products with small particles, which are not easy to aggregate and grow, and are dispersedly distributed in the steel, so that the morphology and characteristics of conventional inclusions in the steel can be improved, and the performance of the steel can be improved. At the same time, the silicon element in the RE-Si-Fe composite deoxidizer can react with oxygen to generate silicon oxide and float to the ladle top slag, avoiding the influence of large size hard Al2O3 inclusions generated by aluminum deoxidation process on the performance of the steel, and realizing the steel liquid with high purity, meeting the needs of high-grade product development. In addition, the deoxidation cost of the RE-Si-Fe composite deoxidizer is lower than that of the traditional aluminum deoxidizer. In order to exert the strong deoxidation effect of rare earth and consider the manufacturing cost of the product, the content of rare earth in the RE-Si-Fe composite deoxidizer is 30-40wt%, and the content of silicon is 40-55wt%. At the same time, it is found that when the content of silicon is less than 40wt%, the overall carbon reduction reaction of the preparation process of the RE-Si-Fe composite deoxidizer is insufficient, the temperature of the liquid furnace charge at the bottom of the furnace is less than 1500℃, which causes poor flowability of the material at the bottom of the furnace during discharging, and even production accidents such as crust rising. When the content of silicon is greater than 55wt%, the furnace charge is pulverized and cannot be bonded into a shape, so that the block product suitable for deoxidation of converter steelmaking cannot be produced. Preferably, in the step S2, the content of rare earth in the RE-Si-Fe composite deoxidizer can be any one of 30wt%, 31wt%, 32wt%, 33wt%, 34wt%, 35wt%, 36wt%, 37wt%, 38wt%, 39wt% and 40wt%, or a range between any two of them; the content of silicon in the RE-Si-Fe composite deoxidizer can be any one of 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, 46wt%, 47wt%, 48wt%, 49wt%, 50wt%, 51wt%, 52wt%, 53wt%, 54wt% and 55wt%, or a range between any two of them. Further preferably, in the step S2, the rare earth is lanthanum and cerium.

[0015] Preferably, the preparation process of the RE-Si-Fe composite deoxidizer is as follows: The first step, briquetting, involves mixing the rare earth oxide raw materials in the following weight percentages: 5-10wt% corn gum, 12-16wt% semi-coke, and the balance rare earth oxide. The raw materials are fed from the raw material bin via a vibrating feeder and conveyed on a conveyor belt to a mixer. Water, representing 10wt% of the total input, is added and stirred to ensure uniform distribution. After mixing, the raw materials enter the briquetting machine through the mixer's outlet. The pressurized material is removed from the mold using the machine's built-in mold slots and hydraulic system. The resulting spherical rare earth oxide spheres, 5-15mm in diameter, are then released.

[0016] The second step is to put the materials into the furnace: rare earth oxide balls, semi-coke, silica and steel chips are placed in different silos, transported to the feeding pipe of the submerged arc furnace by a belt conveyor according to the established material ratio through the batching system, and enter the smelting area of ​​the submerged arc furnace. The material distribution principle is that semi-coke and rare earth oxide balls, silica and steel chips are distributed in layers.

[0017] The third step is the smelting process: the three-phase electrodes of the submerged arc furnace are inserted into the material. Under the support of electrode arcing and resistance heat, the temperature rises to the range of 1700~1800℃, and the material melts to reach the reaction temperature range. The semi-coke undergoes redox reactions with rare earth oxides and silica at the same time. At the same time, the silicon dioxide (silica) reduced by the semi-coke also participates in the reduction reaction of rare earth oxides to form rare earth silicon alloy. Steel chips can destroy the insoluble silicon carbide produced in the production process, so that the final product does not contain insoluble impurities. The smelting time is 2~3 hours.

[0018] The fourth step is the furnace discharge process: the rare earth ferrosilicon alloy formed by the complete reaction flows downward from the reaction zone of the ore-fired furnace into the molten pool area, the taphole is opened by the eye-opening machine, and the alloy liquid enters the pre-prepared molten iron ladle.

[0019] The fifth step is the casting process: the molten iron ladle is lifted to the casting point by a crane for casting. The alloy liquid is naturally cooled to below 300°C in the air. After cooling, the mold is turned sideways by a hydraulic device, and the material is demolded into the material trough. The operation is completed and the RE-Si-Fe composite deoxidizer is prepared.

[0020] Preferably, in step S2, according to the silicon content requirement of the steel grade, a RE-Si-Fe composite deoxidizer or a RE-Si-Fe composite deoxidizer and a silicon alloy are added during the converter tapping process, specifically: When the silicon content of the steel grade is required to be less than 0.2wt%, add 1.4~5.3kg / t during the converter tapping process. 钢 RE-Si-Fe composite deoxidizer; When the silicon content of steel is required to be ≥0.2wt%, add 0.4~1.1kg / t during the converter tapping process. 钢 RE-Si-Fe composite deoxidizer and 1.3~4.4kg / t钢 of silicon alloy.

[0021] Further preferably, in step S2, when the silicon content of the steel grade is required to be less than 0.2wt%, 1.4-5.3kg / t is added during the converter tapping process. 钢 Specifically, the oxygen content in the molten steel is measured before the converter is tapped, and the amount of the RE-Si-Fe composite deoxidizer added is determined based on the oxygen content. The amount of the RE-Si-Fe composite deoxidizer added during the converter tapping process can be, for example, 1.4 kg / t 钢 , 1.5kg / t 钢 、1.75kg / t 钢 , 2.0kg / t 钢 , 2.25kg / t 钢 , 2.5kg / t 钢 , 2.75kg / t 钢 、3.0kg / t 钢 、3.25kg / t 钢 、3.5kg / t 钢 、3.75kg / t 钢 , 4.0kg / t 钢 , 4.25kg / t 钢 , 4.5kg / t 钢 , 4.75kg / t 钢 、5.0kg / t 钢 , 5.2kg / t 钢 , 5.3kg / t 钢 Any one of them or the range between any two of them.

[0022] Further preferably, in step S2, when the silicon content of the steel grade is required to be ≥0.2wt%, 0.4-1.1kg / t is added during the converter tapping process. 钢 RE-Si-Fe composite deoxidizer and 1.3~4.4kg / t 钢 The silicon alloy is a silicon-manganese alloy, which includes: 25-35wt% silicon, 55-65wt% manganese, and the balance is Fe and inevitable impurity elements. Specifically, the oxygen content in the molten steel is measured before the converter is tapped, and the amount of RE-Si-Fe composite deoxidizer and silicon-manganese alloy added is determined based on the oxygen content. The amount of RE-Si-Fe composite deoxidizer added during the converter tapping process can be, for example, 0.4kg / t 钢 、0.45kg / t 钢 , 0.5kg / t 钢 、0.55kg / t 钢 , 0.6kg / t 钢 、0.65kg / t 钢 , 0.7kg / t钢 , 0.75 kg / t 钢 , 0.8 kg / t 钢 , 0.85 kg / t 钢 , 0.9 kg / t 钢 , 0.95 kg / t 钢 , 1.0 kg / t 钢 , 1.05 kg / t 钢 , 1.1 kg / t 钢 , 1.3 kg / t 钢 , 1.5 kg / t 钢 , 1.75 kg / t 钢 , 2.0 kg / t 钢 , 2.25 kg / t 钢 , 2.5 kg / t 钢 , 2.75 kg / t 钢 , 3.0 kg / t 钢 , 3.25 kg / t 钢 , 3.5 kg / t 钢 , 3.75 kg / t 钢 , 4.0 kg / t 钢 , 4.25 kg / t 钢 , 4.4 kg / t 钢 , 4.5 kg / t

[0023] Preferably, in the step S2, the RE-Si-Fe composite deoxidizer or the RE-Si-Fe composite deoxidizer and the silicon-manganese alloy are added when the tapping amount of the converter steel liquid is 1 / 4 to 1 / 3.

[0024] Preferably, in the step S2, a low lance position (150 mm ± 50 mm) and a high oxygen supply intensity (oxygen supply intensity is 3.0 m 3 / (min·t 钢) above) can ensure the dephosphorization effect and avoid temperature fluctuation caused by carbon-oxygen reaction; the temperature during the dephosphorization period of the converter blowing is controlled at 1300-1350°C, which can obtain a good dephosphorization effect and maintain good slag fluidity and composition uniformity; the slag basicity during the dephosphorization period of the converter blowing is regulated to 1.8-2.2, which can save lime consumption and reduce production cost while ensuring the dephosphorization rate; the FeO content of the converter end-point slag is controlled to be >20wt%, and the basicity is 4-6, so that the phosphorus content in the molten steel is stably controlled to be below 0.002wt%. Specifically, the temperature during the dephosphorization period of the converter blowing can be controlled at, for example, any one of 1300°C, 1305°C, 1310°C, 1315°C, 1320°C, 1325°C, 1330°C, 1335°C, 1340°C, 1345°C, 1350°C, or a range between any two of them; the slag basicity during the dephosphorization period of the converter blowing can be, for example, any one of 1.8, 1.9, 2.0, 2.1, 2.2, or a range between any two of them; and the converter end-point slag basicity can be, for example, any one of 4, 4.5, 5, 5.5, 6, or a range between any two of them.

[0025] Preferably, in the step S2, the slag-blocking tapping is adopted during the converter tapping process, and the amount of slag per ton of molten steel is controlled to be not more than 5kg / t 钢 , to avoid the influence of large amount of slag on the cleanliness of the molten steel.

[0026] Preferably, in the step S3, small-particle lime 2.1-4.2kg / t 钢 is added to the top slag, and 0.5-1.67kg / t 钢 of a modified agent containing 50-60wt% Al and 40-50wt% CaO is further added to modify the top slag, so as to realize the high cleanliness condition of SiO2≤10wt%, CaO / Al2O3=1.2-1.5, and (MnO+FeO)≤2wt% in the top slag of the ladle, to avoid the consumption of rare earth elements in the RE-Si-Fe composite deoxidizer due to the quality fluctuation of the top slag and the molten steel, and to realize the precise control of the retention amount of rare earth in the steel. Specifically, the addition amount of the small-particle lime can be, for example, any one of 2.1kg / t 钢 , 2.25kg / t 钢 , 2.5kg / t 钢 , 2.75kg / t 钢 , 3.0kg / t 钢 , 3.25kg / t 钢 , 3.5kg / t 钢 , 3.75kg / t 钢 , 4.0kg / t 钢 , 4.2kg / t 钢 , or a range between any two of them; and the addition amount of the modified agent can be, for example, 0.5kg / t 钢, 0.75 kg / t 钢 , 1.0 kg / t 钢 , 1.25 kg / t 钢 , 1.5 kg / t 钢 , 1.67 kg / t 钢 , any one of or a range between any two of 10 wt%, 9.5 wt%, 9 wt%, 8.5 wt%, 8 wt%, 7.5 wt%, 7 wt%, 6.5 wt%, 6 wt%, 5.5 wt%, 5 wt%, etc.; CaO / Al2O3 in the top slag of the ladle after the modification can be, for example, a range between any one of or any two of 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, 1.5; (MnO+FeO) in the top slag of the ladle after the modification can be, for example, a range between any one of or any two of 2 wt%, 1.75 wt%, 1.5 wt%, 1.25 wt%, 1 wt%, 0.75 wt%, 0.5 wt%, etc.; the oxygen content in the molten steel can be, for example, a range between any one of or any two of 550 ppm, 540 ppm, 530 ppm, 520 ppm, 510 ppm, 500 ppm, 490 ppm, 480 ppm, 470 ppm, 460 ppm, 450 ppm, 440 ppm, 430 ppm, 420 ppm, 410 ppm, 400 ppm, etc.

[0027] Preferably, the deoxidation rate in the converter tapping process is ≥93% when the process of the present application is used. Further preferably, the deoxidation rate in the converter tapping process is ≥94% when the process of the present application is used.

[0028] The technical solutions of the present application are further described below in connection with specific examples.

[0029] Example 1 The process of the present application was used to produce Q235B steel billets (the silicon content of Q235B steel is 0.25 wt%, which belongs to the case of silicon content ≥0.020 wt%), a 150 t volume converter was used, and the following steps were included: S1, hot metal desulfurization pretreatment: hot metal slagging rate is above 95%, and the sulfur content of the hot metal is controlled to be <0.0010 wt%; S2, after pretreatment, the hot metal is added to the converter for smelting, and after the converter blowing starts, a low lance position (165 mm) and an oxygen supply intensity of 3.5 m 3 / (min·t 钢), the actual control range of the converter dephosphorization temperature is 1310~1335℃, and the slag basicity is controlled to 2.1 during the converter dephosphorization period, achieving a good dephosphorization effect. The dephosphorization product floats into the slag, and maintains good slag fluidity and uniform composition. The dephosphorization effect reaches more than 90%, and the temperature fluctuation is controlled stably; the FeO content in the converter terminal slag is 24wt%, the basicity is 5.8, and the phosphorus content in the final molten steel reaches a high cleanliness control level of 0.012wt%. During the converter tapping process, a slide plate is used to block the slag, and the slag discharge amount is 2.6kg / t 钢 This prevents the impact of P and other components in the molten steel on the cleanliness of the molten steel caused by large slag discharge. When the converter tapping rate reaches 1 / 3, a RE-Si-Fe composite deoxidizer (comprising, by mass percentage, 33wt% rare earth La, 54wt% silicon, with the balance being Fe and unavoidable impurities) and a silicon-manganese alloy (25wt% silicon, 65wt% manganese, 10wt% iron) are added. The converter tapping rate is 165 tons, and the oxygen content of the molten steel is 611ppm. Based on the oxygen content, the amounts of RE-Si-Fe composite deoxidizer and silicon-manganese alloy added are 128kg and 455kg, respectively. S3. After tapping, add 3.6kg / t of small-grained white ash to the top slag 钢 , then add 1.55kg / t 钢 The top slag is modified with a modifier containing 52wt% Al and 48wt% CaO to achieve the conditions of SiO2 of 6.8wt%, CaO / Al2O3=1.4, (MnO+FeO) of 1.1wt% in the ladle top slag, and oxygen in the molten steel ≤650ppm.

[0030] In this embodiment, the oxygen content of the steel tapped from the converter is 611 ppm, the oxygen content in the subsequent refining process is 32.6 ppm, and the deoxidation rate is 94.66%.

[0031] The rare earth content in the production process of this embodiment was tested. The rare earth content in the steel was: the La+Ce content of the refined in-situ steel sample was 19ppm, and the La+Ce content of the tundish steel sample was 18ppm, achieving stable control of the rare earth content in the steel.

[0032] The inclusion situation of the production process of this embodiment was detected, as shown in Table 1: Table 1 Size and number of inclusions in steel The main differences between the technical solution before the improvement of the present invention and the present embodiment in the production of Q235B steel square billets are: Aluminum iron (containing aluminum 40%) and silicon manganese alloy (silicon 25wt%-manganese 65wt%-iron 10wt%) are added in the converter tapping process, the converter tapping amount is 163 tons, the oxygen content of the molten steel is 605ppm respectively, and the adding amount of aluminum iron and silicon manganese alloy is determined according to the oxygen content, which is 160kg and 500kg respectively; 200 meters of calcium wire is fed in the last 5 minutes of the LF refining process. The oxygen content of the converter tapping is 605ppm, the in-situ oxygen content of the subsequent process refining is 58.9ppm, and the deoxidization rate is 90.25%. The inclusions in the production process are detected, as shown in Table 2: Table 2 Size and number of inclusions in steel From the above results, it can be seen that the improved technical solution of the embodiment has better deoxidization rate and effect. And the total number and size of inclusions of the embodiment are obviously improved compared with the improved technical solution, which shows that after the embodiment is executed, rare earth can be stably retained in the steel, and at the same time, the rare earth element plays a role in refining the deoxidization products in the steel, reducing the probability of generating large-sized inclusions in the steel, providing a new path for developing high-cleanliness, low-cost and high-value-added rare earth steel products.

[0033] The cost generated by the improved technical solution before execution is (0.16t*(9000 yuan / t 铝铁 ) / 163t 钢 +(0.50t*(6200 yuan / t 硅锰 ) / 163t 钢 , the manufacturing cost is 27.82 yuan / t 钢 , and the calcium treatment operation is needed to modify the deoxidization product Al2O3, which costs (200m*0.45kg / m*8900 yuan / t 钙线 ) / 163=4.91 yuan / t 钢 , and takes 5 minutes / ton of steel, the total cost is 32.73 yuan / t 钢 , while the cost generated by the execution of the embodiment process is (0.128t*(8500 yuan / t RE-Si-Fe复合脱氧剂 ) / 165t 钢 +(0.455t*(6200 yuan / t 硅锰 ) / 165t 钢 , the manufacturing cost is 23.69 yuan / t 钢 , the calcium treatment production cost and treatment time are saved, which has obvious cost advantage and advantage of improving production rate.

[0034] Example 2 The present application is used to produce a 20# steel billet (the silicon content of the 20# steel is 0.30wt%, which belongs to the case of the silicon content being greater than or equal to 0.020wt%), and a 150t volume converter is used, including the following steps: S1, hot metal desulfurization pretreatment: the hot metal slagging rate is greater than 95%, and the sulfur content of the hot metal is controlled to be less than 0.0010wt%; S2, after the pretreated hot metal is added to the converter for smelting, a low lance position (155mm) and an oxygen supply intensity of 3.7m 3 / (min·t 钢 ) are used after the converter blowing starts, the actual control range of the temperature during the converter blowing dephosphorization period is 1315~1332℃, the slag basicity during the converter blowing dephosphorization period is controlled to be 2.2, a good dephosphorization effect is obtained, the dephosphorization product floats to the slag, and good slag fluidity and composition uniformity are maintained, the dephosphorization effect is more than 92%, and the temperature fluctuation is stably controlled; the FeO content in the converter end slag is 21wt%, the basicity is 5.5, and the phosphorus content in the final molten steel reaches a high cleanliness control level of 0.013wt%. A sliding plate slag stopping is used during the converter tapping process, the amount of slag is 2.4kg / t 钢 , and the influence of the P and other components in the molten steel on the cleanliness of the molten steel caused by the large amount of slag is avoided. When the converter molten steel tapping amount reaches 1 / 4, RE-Si-Fe composite deoxidizer (including: rare earth La 30wt%, silicon 55wt%, and the balance of Fe and unavoidable impurity elements) and silicon-manganese alloy (silicon 25wt%-manganese 65wt%-iron 10wt%) are added, the converter tapping amount is 157 tons, the oxygen content of the molten steel is 812ppm, and the addition amounts of the RE-Si-Fe composite deoxidizer and the silicon-manganese alloy are 148kg and 565kg respectively according to the oxygen content; S3, after the tapping is completed, 3.3kg / t 钢 of small particle white ash is added to the top slag, and 1.52kg / t 钢 of a modified agent containing Al 54wt% and CaO 46wt% is further added for top slag modification, so that the SiO2 in the ladle top slag is 6.5wt%, the CaO / Al2O3 is 1.32, the (MnO+FeO) is 0.9wt%, and the oxygen in the molten steel is less than or equal to 850ppm.

[0035] The oxygen content of the converter tapping in the present embodiment is 812ppm, the in-place oxygen content of the subsequent process refining is 24.7ppm, and the deoxidation rate is 96.96%.

[0036] The rare earth content in the production process of the present embodiment is detected, and the rare earth content in the steel is: the La+Ce content of the refining in-place steel sample is 16ppm, and the La+Ce content of the tundish steel sample is 14ppm, so that the rare earth content in the steel is stably controlled.

[0037] The inclusion situation of the production process of the embodiment is detected, as shown in Table 3: Table 3 Size and quantity of inclusions in steel The difference between the production of the 20# steel billet using the technical solution before the improvement of the application and the embodiment mainly lies in that: Aluminum iron (containing aluminum 40%) and silicon manganese alloy (silicon 25wt%-manganese 65wt%-iron 10wt%) are added in the converter tapping process, the tapping amount of the converter is 155 tons, and the oxygen content of the molten steel is 797ppm, respectively. The addition amount of aluminum iron and silicon manganese alloy is determined according to the oxygen content, which is 197kg and 575kg, respectively. The wire feeding process is adopted at the end of the LF refining process for 6 minutes to feed 270 meters of calcium wire. The oxygen content of the converter tapping is 797ppm, and the in-situ oxygen content of the subsequent refining process is 70.5ppm, and the deoxidation rate is 91.15%. The inclusion situation of the production process is detected, as shown in Table 4: Table 4 Size and quantity of inclusions in steel From the above results, it can be seen that the embodiment has better deoxidation rate and effect than the improved technical solution. The total inclusion quantity and size of the embodiment are obviously improved compared with the improved technical solution, which shows that the rare earth can be stably retained in the steel after the embodiment is executed, and the rare earth element plays a role in refining the deoxidation products in the steel, reducing the probability of generating large-size inclusions in the steel, and providing a new path for developing high-cleanliness, low-cost and high-value-added rare earth steel products.

[0038] The cost generated by the improved technical solution before execution is (0.197t*(9000 yuan / t 铝铁 )+(0.575t*(6200 yuan / t 硅锰 )) / 155t 钢 , the production cost is 34.4 yuan / t 钢 , and the calcium treatment operation is required to modify the deoxidation product Al2O3, which generates a cost of (270m*0.45kg / m*8900 yuan / t 钙线 ) / 155=6.97 yuan / t 钢 , and the time is 6 minutes / ton of steel, and the total cost is 41.37 yuan / t 钢 , while the cost generated by the execution of the embodiment is (0.148t*(8500 yuan / t RE-Si-Fe复合脱氧剂 )+(0.565t*(6200 yuan / t 硅锰 )) / 157t 钢 , the production cost is 22.31 yuan / t 钢 , the calcium treatment production cost and treatment time are saved, and there is obvious cost advantage and advantage of improving production rate.

[0039] Example 3 A certain low-alloy high-strength steel (the composition of the low-alloy high-strength steel is shown in Table 5, and the silicon content is 0.05wt%, which belongs to the case of silicon content <0.020wt%) is produced by hot continuous rolling by using the process of the present application, a 240t volume converter is used, Table 5 Composition of low-alloy high-strength steel (wt%) comprising the following steps: S1, hot metal desulfurization pretreatment: hot metal slagging rate is more than 95%, and the sulfur content of hot metal is controlled to be <0.0010wt%; S2, after pretreatment, the hot metal is added to the converter for smelting, low gun position (170mm) is used after converter blowing, and oxygen supply intensity is 3.7m 3 / (min·t 钢 ), the actual control range of the temperature during the converter blowing dephosphorization period is 1315~1338℃, the slag basicity during the converter blowing dephosphorization period is controlled to be 2.25, good dephosphorization effect is obtained, the dephosphorization product floats to the slag, and good slag fluidity and composition uniformity are maintained, the dephosphorization effect is more than 93%, and the temperature fluctuation is stable; the FeO content in the converter end slag is 21wt%, the basicity is 5.4, and the phosphorus content in the final molten steel reaches the high cleanliness control level of 0.011wt%. During the converter tapping process, the slide plate is used to block the slag tapping, the amount of slag is 2.1kg / t 钢 , which avoids the influence of P and other components in the molten steel on the cleanliness of the molten steel caused by large amount of slag. When the converter molten steel tapping amount reaches 1 / 4, the RE-Si-Fe composite deoxidizer (including: rare earth La 40wt%, silicon 40wt%, and the balance of Fe and unavoidable impurity elements) is added, the converter tapping amount is 247 tons, the oxygen content of the molten steel is 719ppm, and the amount of the RE-Si-Fe composite deoxidizer is determined according to the oxygen content, which is 955kg; S3, after the tapping is completed, 3.2kg / t 钢 of small particle lime is added to the top slag, and 1.52kg / t 钢 of modified agent containing Al 52wt% and CaO 48wt% is further added for top slag modification, so that the SiO2 in the ladle top slag is 6.6wt%, the CaO / Al2O3 is 1.5, the (MnO+FeO) is 1.05wt%, and the oxygen in the molten steel is ≤750ppm.

[0040] The oxygen content of the converter tapping in this example is 729ppm, the in-situ oxygen content of the subsequent process refining is 23.8ppm, and the deoxidation rate is 96.74%.

[0041] The rare earth content in the production process of the embodiment is detected, and the rare earth content in the steel is as follows: the La+Ce content of the on-site steel sample in the refining is 24 ppm, and the La+Ce content of the tundish steel sample is 22 ppm, so that the stable control of the rare earth content in the steel is realized.

[0042] The inclusion situation in the production process of the embodiment is detected, as shown in Table 6: Table 6 Size and quantity of inclusions in steel The difference between the low-alloy high-strength steel hot continuous rolling production using the technical solution before the improvement of the application and the embodiment mainly lies in that: Al-Fe (containing 40% Al) is added in the converter tapping process, the converter tapping amount is 245 tons, and the oxygen content of the molten steel is 693 ppm. According to the oxygen content, the addition amount of Al-Fe is 1105 kg. The wire feeding process is adopted at the end of the LF refining process for 6 minutes to feed 350 meters of calcium wire. The oxygen content of the converter tapping is 693 ppm, the oxygen content of the on-site refining in the subsequent process is 60.6 ppm, and the deoxidation rate is 91.25%. The inclusion situation in the production process is detected, as shown in Table 7: Table 7 Size and quantity of inclusions in steel As can be seen from the above results, the embodiment has better deoxidation rate and effect than the improved technical solution. The total inclusion quantity and size of the embodiment are obviously improved compared with the improved technical solution, which shows that the rare earth can be stably retained in the steel after the embodiment is executed, and the rare earth element plays a role in refining the deoxidation products in the steel, reducing the probability of generating large-size inclusions in the steel, and providing a new path for developing high-cleanliness, low-cost and high-value rare earth steel products.

[0043] The cost generated by the improved technical solution before execution is (1.105t*(9000 yuan / t 铝铁 ) / 245t 钢 , the production cost is 40.6 yuan / t 钢 , and the calcium treatment operation is required to modify the deoxidation product Al2O3, which generates a cost of (350m*0.45kg / m*8900 yuan / t 钙线 ) / 245=5.72 yuan / t 钢 , and the time is 8 minutes / ton of steel, and the total cost is 46.32 yuan / t 钢 , and the cost generated by the process of the embodiment is (0.955t*(8500 yuan / t RE-Si-Fe复合脱氧剂 ) / 247t 钢 , the production cost is 32.9 yuan / t 钢 , the calcium treatment production cost and treatment time are saved, and there is obvious cost advantage and advantage of improving production rate.

[0044] Comparative Example 1 The difference from Example 2 is that in 7 of the 156 continuously produced 20# steel heats, the lance position (205-215 mm) is used after the start of the converter blowing, the actual control range of the converter blowing dephosphorization temperature is 1338-1355°C, the converter blowing dephosphorization temperature is controlled to 1.1-1.45 slag basicity, the dephosphorization effect is only 81-85%, and the phosphorus content in the final molten steel reaches 0.032-0.055wt%. On-site 1-2 point blowing is taken to remedy, causing serious over-oxidation of the molten steel, and the oxygen content in the converter end-point steel reaches 1050-1215ppm; the high oxygen potential of the molten steel increases the amount of RE-Si-Fe composite deoxidizer to 170-187kg, and the deoxidation rate decreases to 83.4-89.1%.

[0045] Comparative Example 2 The difference from Example 1 is that in 9 of the 163 continuously produced Q235B steel heats, the top slag is not modified according to the method of the application, and the composition of the top slag in the final ladle is controlled in the range of SiO2 10.5-13.8wt%, CaO / Al2O3 1.05-1.15, and (MnO+FeO) 2.8-3.3wt%. The excessively high (MnO+FeO) in the top slag of the ladle continuously returns oxygen to the inside of the molten steel due to slag-steel dynamic balance during the subsequent refining and continuous casting process, causing deterioration of the cleanliness of the molten steel and reaction with rare earth in the steel, resulting in consumption of rare earth, leading to low overall retention of rare earth in the steel and large fluctuation range.

[0046] By sampling the finished steel plate and performing inclusion rating detection, the detection results show that the size and number of oxide inclusions in the steel have significantly increased (Table 8).

[0047] Table 8 Size and Number of Inclusions in Steel Comparative Example 3 The only difference from Example 1 is that Si-Fe alloy (Si content 55wt%) is used instead of RE-Si-Fe composite deoxidizer.

[0048] Because the reducing property of Si is relatively poor compared to rare earth La and Ce, it cannot achieve deep deoxidation of the molten steel. The detection results of the in-situ oxygen content of the 14 produced Q235B steel refining show (Table 9) that the average activity oxygen content in the molten steel is 76.2ppm, and the average deoxidation rate is only 87.4%, which cannot meet the production requirements of high-quality steel products.

[0049] Table 9 Deoxidation Rate Statistics The detection of the inclusion situation of the execution of the process production process, because of not using rare earth to modify the refinement of inclusions, and the oxygen content control of the steel is higher, the detection statistical result shows (table 10), there are a large number of large size inclusions in the steel, which cannot meet the development requirements of high quality products.

[0050] Table 10 Inclusion size and quantity in steel Comparative example 4 The difference from example 1 is only that La-Fe alloy (La content is 35wt%) is used instead of RE-Si-Fe composite deoxidizer.

[0051] In 150t volume converter, 2 batches of Q235B steel are produced by using rare earth iron alloy deoxidation, because there is no Si element in La-Fe alloy, and the Fe element in it has no deoxidation effect, therefore, the oxygen in the steel is removed by La reaction, resulting in a large amount of La-Fe alloy (table 11), which leads to the accumulation of rare earth compounds produced in the molten steel on the surface of the stopper and the inner wall of the nozzle, and the nozzle and stopper produce serious flocculation phenomenon during casting in the two trial production processes, resulting in the production accident of continuous casting casting interruption, the ladle is left with 86 tons and 73 tons of steel respectively. And because of the large amount of La-Fe alloy, the final deoxidation cost is (1.56 tons * 30000 yuan / t RE-Fe合金 ) / 158 tons=296.2 yuan / t 钢 And (1.495 tons * 30000 yuan / t RE-Fe合金 ) / 162 tons=276.9 yuan / t 钢 The production cost is increased seriously.

[0052] Comparative example 5 The difference from example 1 is that the composition of RE-Si-Fe composite deoxidizer is different from that of example 1, which includes: rare earth La 45wt%, silicon 52wt%, the rest is Fe and inevitable impurity elements.

[0053] The RE-Si-Fe composite deoxidizer with the content of La being 45wt% is used for the converter tapping deoxidation test. Because the proportion of La element is high, close to the composition and properties of traditional flint, self-ignition occurs many times during transportation and storage, which has serious safety hazards. The RE-Si-Fe composite deoxidizer (La content is 45wt%) is used for deoxidation of 6 heats of Q235B steel in a 150t volume converter. During the tapping process of the converter, the RE-Si-Fe composite deoxidizer (La content is 45wt%) burns fiercely above the molten steel, which cannot effectively sink into the molten steel to play a deoxidation reaction. The detection results of the in-place oxygen content of the 6 heats of Q235B steel produced show (Table 10) that the average activity oxygen content in the molten steel is 191ppm, and the average deoxidation rate is only 70.4%, which cannot meet the requirements of deoxidation effect in the normal production process.

[0054] Table 10 Deoxidation rate statistics Comparative example 6 The difference from example 1 is that the composition of the RE-Si-Fe composite deoxidizer is different from that of example 1. In mass percent, it includes: La 25wt%, Si 72wt%, and the balance is Fe and unavoidable impurity elements.

[0055] Because the proportion of La element in La-Si-Fe alloy is low, it cannot effectively play the effect of strong deoxidation reaction and the role of spheroidizing and refining inclusions in steel. The La-Si-Fe alloy (La content is 25wt%, Si content is 72wt%) is used for deoxidation of 3 heats of Q235B steel in a 150t volume converter. The detection results of the in-place oxygen content of the 3 heats of Q235B steel produced show (Table 11) that the average activity oxygen content in the molten steel is 132ppm, and the average deoxidation rate is only 79.7%, which cannot meet the requirements of deoxidation effect in the normal production process.

[0056] Table 11 Deoxidation rate statistics The inclusions in the production process are detected. Because the proportion of rare earth is low, the modification and refinement of inclusions in steel by rare earth cannot be effectively played. At the same time, because the oxygen content in steel is high due to low deoxidation rate, the detection statistical results show (Table 12) that there are a large number of large size inclusions in the steel, which cannot meet the development requirements of high quality products.

[0057] Table 12 Size and number of inclusions in steel The above merely describes the preferred embodiments of the present application, and is not intended to limit the patent scope of the present application. Any equivalent structural variations or direct / indirect applications in other related technical fields based on the content of the present application description are included in the patent protection scope of the present application.

Claims

1. A process for smelting molten steel using a RE-Si-Fe composite deoxidizer, characterized in that: The steps include: S1, molten iron desulfurization pretreatment; S2. The pretreated molten iron is added to the converter for smelting. After the converter blowing begins, a low lance position and high oxygen supply intensity are adopted; the converter blowing and dephosphorization period temperature is controlled at 1300-1350° C., and the slag basicity is adjusted to 1.8-2.2; the FeO content of the converter end slag is controlled to be greater than 20wt% and the basicity is 4-6, so that the phosphorus content in the molten steel is stably controlled below 0.002wt%; a RE-Si-Fe composite deoxidizer is added during the converter tapping process, wherein the RE-Si-Fe composite deoxidizer comprises, by mass percentage, 30-40wt% of rare earth, 40-55wt% of silicon, and the balance being Fe and unavoidable impurity elements; S3. After tapping is completed, the ladle top slag is modified to achieve the conditions of SiO2≤10wt%, CaO / Al2O3=1.2~1.5, and (MnO+FeO)≤2wt% in the ladle top slag; The deoxidation rate of the converter steel-making process is ≥93%.

2. The process for smelting molten steel using a RE-Si-Fe composite deoxidizer according to claim 1, characterized in that: In step S1, the molten iron slag rate is above 95%, and the sulfur content of the molten iron is controlled to be less than 0.0010 wt%.

3. The process for smelting molten steel using a RE-Si-Fe composite deoxidizer according to claim 1, wherein: In step S2, according to the silicon content requirement of the steel grade, RE-Si-Fe composite deoxidizer or RE-Si-Fe composite deoxidizer and silicon alloy are added during the converter tapping process, specifically: When the silicon content of the steel grade is required to be less than 0.2wt%, add 1.4~5.3kg / t during the converter tapping process. 钢 RE-Si-Fe composite deoxidizer; When the silicon content of steel is required to be ≥0.2wt%, add 0.4~1.1kg / t during the converter tapping process. 钢 RE-Si-Fe composite deoxidizer and 1.3~4.4kg / t 钢 of silicon alloy.

4. The process for smelting molten steel using a RE-Si-Fe composite deoxidizer according to claim 3, characterized in that: The silicon alloy is a silicon-manganese alloy, which includes: 25-35wt% silicon, 55-65wt% manganese, and the balance being Fe and inevitable impurity elements.

5. The process for smelting molten steel using a RE-Si-Fe composite deoxidizer according to claim 3, characterized in that: In the step S2, when the tapping amount of the converter molten steel reaches 1 / 4 to 1 / 3, the RE-Si-Fe composite deoxidizer or the RE-Si-Fe composite deoxidizer and the silicon alloy are added.

6. The process for smelting molten steel using a RE-Si-Fe composite deoxidizer according to claim 1, characterized in that: In step S2, slag blocking is used during the converter tapping process, and the amount of slag is controlled to be no more than 5kg / t 钢 .

7. The process for smelting molten steel using a RE-Si-Fe composite deoxidizer according to claim 1, characterized in that: In step S3, 2.1-4.2 kg / t of small-grained white ash is added to the top slag. 钢 , then add 0.5~1.67kg / t 钢 The top slag is modified by using a modifier containing 50~60wt% Al and 40~50wt% CaO.

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