A high basicity high oxygen blowing molten steel smelting method for a twin roll strip high carbon steel

Abstract

The present application belongs to the technical field of steel smelting production, and relates to a high-alkalinity strong oxygen blowing molten steel smelting method for double-roller thin strip high-carbon steel. The smelting process of the present application comprises: converter or electric furnace smelting, VD vacuum treatment, LF refining adjustment of components and regulation of inclusions; control of molten steel component fluctuation range, so that the maximum size of molten steel inclusions is not more than 15 microns, and the number of inclusions below 5 microns accounts for more than 98%. The method of the present application can realize multi-furnace continuous casting of thin strip high-carbon steel.

Description

Technical Field

[0001] This invention belongs to the field of iron and steel smelting and production technology, and relates to a method for smelting high-basicity, strongly oxygen-blown molten steel in double-roll thin strip. Background Technology

[0002] High-carbon steel possesses high strength, hardness, and good wear resistance. Traditional production processes for this steel grade are lengthy and involve numerous steps. Compared to traditional methods, the twin-roll casting and rolling process significantly reduces the thickness of hot-rolled high-carbon steel plates, thus minimizing the need for subsequent cold rolling and annealing processes.

[0003] However, this steel grade has a high carbon content and a large solid-liquid phase region during solidification. Furthermore, due to the strong cooling capacity of twin-roll casting, it undergoes rapid or sub-rapid solidification, amplifying the unevenness of heat transfer and solidification in the transverse direction of the rolls. Currently, when casting this product, there are many liquid cores in the casting strip, which easily leads to white lines, broken strips, or cracks in the cast product, resulting in product rejection. This is mainly related to the fluidity of the molten steel, the wettability between the molten steel and the casting rolls, the uniformity of heat transfer in the molten steel, and the uniformity of the solidified billet shell. During casting, poor meniscus formation in the molten pool, uneven heat transfer and solidification in the transverse direction, and insufficient lubrication between the billet shell and the casting rolls easily cause a series of problems such as molten pool fluctuations, roll gap fluctuations, and thickness fluctuations. In addition, fluctuations in the steel composition and inclusion type in the continuous casting furnace during the casting process, especially large changes in carbon content and Mn / Si ratio, can easily cause abrupt changes in heat transfer and plate shape, resulting in casting instability and making continuous production of thin strip high-carbon steel impossible. The production of high-carbon steel using twin-roll casting and rolling processes requires high standards for molten steel quality, stability, and smelting techniques. Summary of the Invention

[0004] To address this problem, this invention proposes a method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strips. This method overcomes at least some of the shortcomings of existing technologies, solves the problems of high smelting costs, high difficulty, and low success rate, and improves the stability of strip formation and the continuity of continuous casting.

[0005] Specifically, the technical solution adopted in this invention is as follows:

[0006] According to a first aspect of the present invention, a method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip is provided, wherein the chemical composition of the twin-roll thin strip high-carbon steel, by mass percentage, is: 0.505% ≤ C ≤ 0.545%, 0.21% ≤ Si ≤ 0.26%, 0.6% ≤ Mn ≤ 0.75%, 0.01% ≤ Cr ≤ 0.03%, P ≤ 0.02%, S ≤ 0.005%, Al ≤ 0.003%, 0.0005% ≤ B ≤ 0.001%, 0.001% ≤ Ca ≤ 0.002%, N ≤ 0.005%, with the balance being Fe and other unavoidable impurities. The method includes the following steps:

[0007] (1) Converter / electric furnace smelting:

[0008] The free oxygen content in the initial molten steel is controlled at 500~800ppm, the final temperature is ≥1650℃, and S≤0.0120%;

[0009] (2) VD vacuum treatment:

[0010] The primary steel is subjected to vacuum treatment in a VD vacuum furnace for more than 25 minutes, wherein the vacuum degree is <67Pa and the duration is controlled to be no less than 10 minutes.

[0011] (3) LF Refining:

[0012] The obtained molten steel is transported to the LF furnace for refining, and low-nitrogen carbon raisers and alloys are added to adjust the composition, controlling the Mn / Si ratio to be 2.4~3.5.

[0013] After the components are matched, lime or synthetic slag is added for slag conditioning, and the slag is ionized by electricity. The basicity of the LF furnace slag is adjusted and controlled to 2.0~2.7.

[0014] (4) Twin-roll thin strip continuous casting:

[0015] The qualified molten steel obtained in steps (1) to (4) is continuously cast through two counter-rotating casting rolls. The molten steel is cooled by the casting rolls under the protection of inert gas to form a casting strip. The casting speed is 40 to 60 m / min.

[0016] The obtained cast strip is rolled and coiled to form hot-rolled steel coils or directly coiled to form cast strip steel coils.

[0017] According to the present invention, the high-basicity strong oxygen blowing molten steel smelting method for high-carbon steel with double-roll thin strip is preferably used in step (1) for smelting in the primary smelting furnace, converter, and electric furnace using ordinary scrap steel.

[0018] According to the present invention, the high basicity strong oxygen blowing molten steel smelting method of high carbon steel of twin-roll thin strip is preferably, in step (1), the free oxygen content of the molten steel smelted in the converter is controlled to be 500~700ppm, the final temperature is ≥1630℃, and S≤0.0100%.

[0019] According to the present invention, the high basicity strong oxygen blowing molten steel smelting method of high carbon steel of double roll thin strip is preferably, in step (1), the free oxygen content of the molten steel smelted in the electric furnace is controlled to be 600~800ppm, the final temperature is ≥1650℃, and S≤0.0120%.

[0020] According to the present invention, in the method for smelting high-basicity strong oxygen blowing molten steel of high-carbon steel with double roll thin strip, preferably, in step (2), the basicity of VD slag formation during the smelting process is controlled to be 2.3~3.3; 400~600 kg of slag-forming lime and 100~200 kg of fluorite are added to the molten steel provided by the converter.

[0021] According to the present invention, the high basicity strong oxygen blowing molten steel smelting method of high carbon steel of double roll thin strip is preferably, in step (2), the basicity of VD slag formation in the smelting process is controlled to be 2.3~3.3; 700~1000 kg of slag-forming lime and 250~400 kg of fluorite are added to the molten steel provided by the electric furnace.

[0022] According to the present invention, in the method for smelting high-basicity strong oxygen blowing molten steel of high-carbon steel with twin rolls, preferably, in step (3), the carbon content is controlled to be 0.51~0.54% and the Mn / Si ratio is controlled to be 2.8~3.3.

[0023] According to the present invention, in the method for smelting high-basicity strong oxygen blowing molten steel of high carbon steel by double-roll thin strip, preferably, in step (3), after the steel liquid composition of the LF process is hit, the power is continued to be applied to raise the temperature, and the oxygen blowing operation is carried out after the temperature reaches 1640~1660℃.

[0024] In the method for smelting high-basicity, strongly oxygen-blown molten steel for high-carbon strip using twin-roller smelting according to the present invention, preferably, in step (3), the basicity of the final slag is controlled to be 1.8 to 2.5.

[0025] According to the twin-roller method for smelting high-basicity, high-oxygen-blown molten steel for thin strip according to the present invention, preferably, in step (3), a strong oxygen blowing operation is performed before the LF refining and tapping, with an oxygen blowing intensity of 10~12 m. 3 / min, oxygen blowing rate is 120~150m³ 3 .

[0026] In the method for smelting high-basicity, strong oxygen-blown molten steel for high-carbon strip using twin-roll thin strip according to the present invention, preferably, the bottom blowing argon gas in the ladle is reduced to 70~150L / min before LF oxygen blowing.

[0027] According to the present invention, the method for smelting high-basicity, strongly oxygen-blown molten steel of high-carbon strip using twin-roll thin strip steel is preferably carried out by adding 3-5 kg ​​of ferroboron after oxygen blowing and continuing to heat the molten steel to 1665-1675°C. Calcium carbide is added during the energizing process at a rate of 0.5-1.0 kg / min. After the energizing process ends, calcium wire feeding is performed at a rate of 80-100 m and a feeding speed of 2.5-3 m / s.

[0028] In the method for smelting high-basicity, strongly oxygen-blown molten steel for high-carbon strip using twin-roller smelting according to the present invention, preferably, soft stirring is performed after wire feeding, and the soft stirring time is controlled to be not less than 5 minutes.

[0029] According to the present invention, the high-basicity strong oxygen blowing molten steel smelting method for high-carbon steel of twin-roll thin strip is preferably used to control the inclusions in the molten steel by oxygen blowing and wire feeding. The inclusions in the molten steel are high-SiO2, MnO and CaO inclusions, and the Al2O3 content in the inclusions is controlled to be below 15%wt.

[0030] According to the present invention, in the method for smelting high-basicity strong oxygen blowing molten steel of high carbon steel by twin-roll thin strip, preferably, in step (3), the maximum size of the inclusions in the molten steel obtained after inclusion modification and removal does not exceed 15μm, and the number of inclusions below 5μm accounts for more than 98%.

[0031] In the method for smelting high-basicity, strongly oxygen-blown molten steel for high-carbon strip according to the present invention, preferably, the content of (SiO2+MnO+CaO) component in the inclusions is ≥80%wt.

[0032] According to the present invention, the high basicity strong oxygen blowing molten steel smelting method of high carbon steel of twin-roll thin strip is preferably carried out in step (4) by transporting the qualified molten steel to the ladle turret for casting; the molten steel flows into the molten pool through the tundish and transition ladle, and the molten pool level is controlled by the casting speed and the opening of the tundish slide plate.

[0033] According to a second aspect of the invention, a twin-roll thin strip high carbon steel is provided, which is produced using a method having one or more of the aforementioned features.

[0034] Beneficial technical effects

[0035] Compared with traditional and existing technologies, the features and beneficial technical effects of the present invention include at least the following:

[0036] 1) This invention reduces the production difficulty of thin strip high carbon steel, thereby greatly improving the production efficiency, hit rate and stability of thin strip high carbon steel.

[0037] 2) The thickness of the billet was reduced, and the solidification rate of molten steel was fast and sub-fast, which solved the element segregation defect of high carbon steel. Attached Figure Description

[0038] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings of the embodiments will be briefly described below. Obviously, the drawings described below only relate to some embodiments of the present invention and are not intended to limit the present invention.

[0039] Figure 1 This is a schematic diagram of the oxide interface between molten steel and the casting rolls in the twin-roll continuous casting of high-carbon steel thin strip.

[0040] Figure 2 A comparison of the elemental C and Mn distributions in high-carbon steel strip produced by twin-roll thin strip casting and conventional processes (this invention, conventional process). Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0042] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0043] The principle of the smelting process of this invention is as follows:

[0044] C: Carbon has a significant impact on the strength, hardness, plasticity, and microstructure of steel, and also greatly affects the heat transfer during the solidification process of molten steel, especially in the rapid and sub-rapid solidification of twin-roll thin strip casting. Considering product performance requirements, smelting difficulty and success rate, and production stability, the carbon content of this invention is controlled within the range of 0.51~0.54%wt. The aim is to meet performance requirements while reducing compositional fluctuations, solving the problem of sudden changes in heat transfer between molten steel and roll surface caused by abrupt changes in composition between continuous casting furnaces, improving the casting stability and billet solidification uniformity of high-carbon steel produced by twin-roll thin strip casting and rolling, and ensuring a certain process window to guarantee the success rate.

[0045] Si and Mn: Silicon has a significant solid solution strengthening effect and exists in molten steel in a solid solution state. Silicon can change the quantity, size, and morphology of carbides precipitated during tempering and increase the tempering temperature of steel. However, if the silicon content is too high, it will increase the brittleness of the steel. Manganese is an effective alloying element to improve hardenability. It has a solid solution strengthening effect when dissolved in ferrite and can also improve the heat treatment performance of steel. However, if the manganese content is too high, the toughness will decrease.

[0046] The inventors discovered through research that the Mn / Si ratio has a significant impact on the strip shape during the twin-roll casting process. If the Mn / Si ratio is too high or too low, the strip shape stability during the casting process is poor. Therefore, the silicon content range of this invention is 0.21~0.26%wt, the manganese content range is 0.6~0.75%wt, and the Mn / Si ratio control range is 2.3~3.6, preferably 2.8~3.3.

[0047] Trace element control: Adding boron to molten steel can effectively reduce the surface tension of molten steel and improve the wettability between molten steel and the surface of the casting roll. However, excessive boron content can easily cause cracks on the plate surface. Therefore, the boron content range of this invention is 5~10 ppm.

[0048] By controlling the content of preferred alloying elements, product performance requirements can be met, while ensuring casting and rolling stability and production continuity.

[0049] Oxide Control: During the solidification process of molten steel on the surface of the casting roll, oxides are generated and continuously accumulate on the roll surface. These oxides (SiO2, MnO, CaO, Al2O3, Fe2O3) in turn affect the interface between the molten steel and the casting roll, impacting heat transfer and lubrication between the billet and the roll. The composition of the molten steel affects the composition and melting point of the formed oxides. The composition of the oxides can be controlled by adjusting the Mn, Si, and dissolved oxygen content in the molten steel. The strong oxygen blowing operation before tapping in LF can generate a large number of fine, low-melting-point SiMn oxides. The SiO2 and MnO deposited on the roll surface during the casting process can improve heat transfer and lubrication between the billet and the casting roll, improve the performance of the casting strip, and enhance casting stability.

[0050] Macro-segregation control: For high-carbon steel with a carbon content ≥0.45%wt, traditional processes, due to their slow cooling rate (typically 0.1-10℃ / s), provide ample time for the diffusion and redistribution of solute elements, especially carbon, leading to severe macroscopic segregation problems. In contrast, the cooling rate of twin-roll thin strip casting and rolling is significantly higher than that of traditional processes, reaching 10℃ / s. 2 -10 4 At ℃ / s, the molten steel is instantly cooled, and the solidification structure is mainly composed of fine columnar crystals, rather than the traditional coarse equiaxed crystals, thus suppressing and resolving the segregation problem. The control of oxides on the roll surface improves the heat transfer between the billet shell and the casting roll, further suppressing macroscopic segregation.

[0051] The following are embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention. All other embodiments that can be obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0052] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0053] Example 1

[0054] This embodiment uses a converter smelting process to produce thin strip high-carbon steel. The specific process flow is as follows:

[0055] Step 1: VD treatment of molten steel in converter

[0056] The steel was smelted in a converter, with a final oxygen content of 570 ppm. The final composition of the converter-smelted steel consisted of 0.046% wt carbon, 0.0089% wt sulfur, 0.0124% wt phosphorus, 0.002% wt silicon, and 0.065% wt manganese, with the balance being feine oxide and unavoidable residual elements and impurities. The molten steel was then transferred to a VD vacuum furnace for vacuum treatment for 30 minutes. During the vacuum treatment, ferrosilicon deoxidizing alloys were added sequentially for deoxidation and alloying, with 325 kg of ferrosilicon alloy and 800 kg of ferromanganese alloy added. Then, lime and fluorite were added for desulfurization, with 460 kg of slag-forming lime and 120 kg of fluorite added. After vacuum furnace treatment, the steel had an sulfur content of 0.0025% wt, and the VD final slag basicity was 2.8.

[0057] Step Two: LF Refining Process

[0058] The molten steel treated by VD vacuum was transferred to the LF furnace for refining. After the molten steel arrived at the station, it was heated by electricity for 2 minutes. After slag formation, the bottom blowing argon gas was increased to a flow rate of 450 L / min. 630 kg of low-nitrogen carbon raiser was added to increase the carbon content to 0.534%. Alloys were added to adjust the composition, with 250 kg of ferromanganese alloy and 45 kg of ferrosilicon alloy added. The Mn content in the molten steel was 0.735% wt, the Si content was 0.2348% wt, and the Mn / Si ratio was controlled at 3.13.

[0059] After the components are matched, 80 kg of synthetic slag is added for slag conditioning, and the slag is energized to adjust the basicity of the LF furnace slag to 2.5.

[0060] After powering on and heating up to 1650℃, oxygen blowing is performed at an intensity of 11m. 3 / min, oxygen blowing rate 125m 3 Before oxygen blowing, reduce the argon gas flow rate at the bottom of the ladle to 80 L / min.

[0061] After oxygen blowing, add 5 kg of ferroboron and continue to heat the molten steel to 1672℃. After the power is turned off, feed calcium wire at a rate of 100 m and a speed of 2.5 m / s. After feeding the wire, perform soft stirring for 7.5 min.

[0062] Step 3: Twin-roll continuous casting

[0063] The refined molten steel was hoisted to the turret for casting. The tundish temperature was controlled at 1600±5℃ using tundish auxiliary heating technology, while the casting speed was controlled within the range of 40~42m / min. When 60 tons of molten steel remained in the turret ladle, a sample was taken for analysis. The chemical composition of the steel, by mass percentage, was: C: 0.528%, Si: 0.228%, Mn: 0.73%, Cr: 0.024%, P: 0.0134%, S: 0.0030%, Al: 0.0025%, B: 0.0008%, Ca: 0.0015%, N: 0.0015%, with the balance being Fe and other unavoidable impurities.

[0064] Step 4: Casting and Rolling

[0065] Molten steel in the pool forms a strip of a certain thickness on the surface of the casting roll, with the thickness controlled between 1.8 and 2.0 mm. The strip is then rolled into a coil after a single pass to achieve the target thickness.

[0066] The second furnace followed the same process. The final oxygen content in the converter was 610 ppm, the final carbon content was 0.041% wt, and the sulfur content was 0.0080% wt. The vacuum decomposition (VD) treatment time was 30 min. During the process, 330 kg of ferrosilicon alloy, 850 kg of ferromanganese alloy, 478 kg of slag-forming lime, and 105 kg of fluorite were added. After vacuum furnace treatment, molten steel with an sulfur content of 0.0022% wt and a VD final slag basicity of 2.83 were obtained.

[0067] LF underwent carbonization and alloying adjustments, with the addition of 620 kg of low-nitrogen carbonizer, 260 kg of ferromanganese alloy, and 40 kg of ferrosilicon alloy, resulting in a carbon content of 0.530% and a Mn / Si ratio controlled at 3.18. After oxygen blowing, 4 kg of ferroboron was added, and the tapping temperature was 1666℃.

[0068] During the casting process, molten steel samples were taken from the tundish for testing and analysis. The chemical composition of the steel, by mass percentage, was: C: 0.526%, Si: 0.23%, Mn: 0.72%, Cr: 0.024%, P: 0.0128%, S: 0.0025%, Al: 0.0024%, B: 0.0007%, Ca: 0.0017%, N: 0.0015%, with the balance being Fe and other unavoidable impurities.

[0069] Through the above process, the deposition state of inclusions in molten steel and oxides on the surface of the casting rolls was effectively controlled, meeting the requirements for stable casting of thin strip high-carbon steel. This successfully achieved continuous and stable production of twin-roll thin strip high-carbon steel, completing two consecutive heats. The main chemical composition of the oxides on the roll surface is shown in Table 1.

[0070] Table 1. Chemical composition of roller surface oxides (%)

[0071] The remaining amount in Table 1 is for impurities.

[0072] By controlling the oxide on the roll surface, the heat transfer between the billet shell and the casting roll was improved, and the cooling rate was increased from 1700℃ / s to 2500℃ / s, thereby improving the stability and quality of twin-roll thin strip high-carbon steel casting and rolling.

[0073] Compared with traditional products, the segregation problem of twin-roll thin strip casting and rolling of high-carbon steel is solved, such as... Figure 2 As shown, the C and Mn elements in the upper twin-roll thin strip high-carbon steel are more evenly distributed, while the C and Mn elements in the lower traditional process high-carbon steel show obvious segregation.

[0074] Example 2

[0075] This embodiment uses an electric furnace smelting process to produce thin strip high-carbon steel. Compared with Embodiment 1, this embodiment uses a different smelting process path in steelmaking.

[0076] Step 1: Electric furnace steelmaking

[0077] This embodiment employs an electric arc furnace (EAF)-VD furnace-LF furnace smelting process. In EAF smelting, the final oxygen content is controlled at 720 ppm and 770 ppm. The final carbon content in the molten steel composition is 0.038% wt and 0.035% wt, sulfur content is 0.0110% wt and 0.0120% wt, Si content is 0.002% wt and 0.001% wt, and Mn content is 0.060% wt and 0.062% wt. The balance is Fe and unavoidable residual elements and impurities. Compared to converter smelting, EAF smelting results in a higher range of final oxygen content, a slightly lower range of final carbon content, and a relatively higher sulfur content. The subsequent VD vacuum treatment and LF refining processes after EAF smelting are the same as in Example 1, but the specific characteristics of EAF molten steel necessitate different treatment requirements.

[0078] Step 2: VD and LF processing

[0079] Molten steel smelted in an electric arc furnace is treated in a VD vacuum furnace. The molten steel from the electric arc furnace has a high gas content and high sulfur content, and the treatment time is long, resulting in a large amount of lime consumption. The treatment time is 35 min and 36 min. During the process, 300 kg and 330 kg of ferrosilicon alloy, 720 kg and 700 kg of ferromanganese alloy, 780 kg and 800 kg of slag-forming lime, and 280 kg and 300 kg of fluorite are added. After vacuum furnace treatment, molten steel with an S content of 0.0020%wt and 0.0019%wt is obtained, and the VD final slag basicity is 3.02 and 3.10.

[0080] The molten steel treated by VD vacuum is transferred to the LF furnace for refining. After the molten steel arrives at the station, it is heated by electricity for 2-3 minutes. After slag formation, the bottom blowing argon gas is increased to a flow rate of 430L / min and 400L / min. 600kg and 585kg of low nitrogen carbonizing agent are added to increase carbon, and 40kg of ferromanganese alloy is added to adjust the composition.

[0081] The carbon content is 0.530%wt and 0.525%wt, and the Mn / Si ratio is controlled at 3.22 and 3.28.

[0082] After the components are matched, add 100-120 kg of synthetic slag for slag conditioning, and then apply electricity to the slag to adjust the basicity of the LF furnace slag to 2.65 or 2.70.

[0083] After powering on and heating up to 1640℃, oxygen blowing is performed at an intensity of 10m. 3 / min, oxygen blowing rate 120m 3 After oxygen blowing, add 4.3 kg of ferroboron and continue to heat the molten steel to 1670℃ and 1665℃ respectively. After the power is turned off, feed calcium wire at a rate of 100 m and a speed of 2.5 m / s. After feeding the wire, perform soft stirring for 8 minutes.

[0084] Step 3: Twin-roll continuous casting

[0085] The refined molten steel is hoisted to the rotary table for casting. The tundish temperature is controlled at 1600±5℃ using tundish auxiliary heating technology, while the casting speed is controlled within the range of 40~42m / min.

[0086] During the casting process, molten steel samples were taken from the tundish for testing and analysis. The chemical composition of the steel, expressed as a percentage by mass, is shown in Table 2 below.

[0087] Table 2 Chemical composition (%) of the steel in the examples

[0088] The balance consists of Fe and other unavoidable impurities.

[0089] Step 4: Casting and Rolling

[0090] Molten steel in the pool forms a strip of a certain thickness on the surface of the casting roll, with the thickness controlled between 1.8 and 2.0 mm. The strip is then rolled into a coil after a single pass to achieve the target thickness.

[0091] By adopting the smelting process path of electric arc furnace-VD furnace-LF furnace, the deposition state of oxides on the surface of the casting rolls can also be effectively controlled (see Table 3), meeting the requirements for stable casting of thin strip high-carbon steel, and completing two consecutive heats of thin strip high-carbon steel casting in electric arc furnace. The electric arc furnace smelting process provides another feasible smelting path for the production of thin strip high-carbon steel, expanding the applicability of this method.

[0092] The main chemical composition of the roller surface oxides collected after the electric furnace production process is completed is shown in Table 3.

[0093] Table 3 Chemical composition of roller surface oxides (%)

[0094] The remaining amount in Table 3 represents impurities.

[0095] In the two path embodiments described above, molten steel samples from the tundish were used for inclusion analysis, with a sample scanning area of ​​100 mm². 2 The size and quantity of inclusions are shown in Table 4. The inclusions are mainly small inclusions smaller than 5 μm. The composition analysis of the inclusions is shown in Table 5. The main components of the inclusions are SiO2-MnO-CaO-Al2O3.

[0096] Table 4. Statistics on the size and quantity of inclusions (pieces / mm) 2 )

[0097] Table 5. Main components of inclusions (%)

[0098] The balance consists of some sulfides and MgO.

[0099] The above description is only a specific embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for smelting high-basicity, strongly oxygen-blown molten steel in a double-roller thin strip, characterized in that, The chemical composition of the twin-roll thin strip high-carbon steel, by mass percentage, is: 0.505%≤C≤0.545%, 0.21%≤Si≤0.26%, 0.6%≤Mn≤0.75%, 0.01%≤Cr≤0.03%, P≤0.02%, S≤0.005%, Al≤0.003%, 0.0005%≤B≤0.001%, 0.001%≤Ca≤0.002%, N≤0.005%, with the balance being Fe and other unavoidable impurities. The method includes the following steps: (1) Converter / electric furnace smelting: The free oxygen content in the initial molten steel is controlled at 500~800ppm, the final temperature is ≥1650℃, and S≤0.0120%; (2) VD vacuum treatment: The primary steel is subjected to vacuum treatment in a VD vacuum furnace for more than 25 minutes, wherein the vacuum degree is <67Pa and the duration is controlled to be no less than 10 minutes. (3) LF Refining: The obtained molten steel is transported to the LF furnace for refining, and low-nitrogen carbon raisers and alloys are added to adjust the composition, controlling the Mn / Si ratio to be 2.4~3.

5. After the components are matched, lime or synthetic slag is added for slag conditioning, and the slag is ionized by electricity. The basicity of the LF furnace slag is adjusted and controlled to 2.0~2.

7. (4) Twin-roll thin strip continuous casting: The qualified molten steel obtained in steps (1) to (4) is continuously cast through two counter-rotating casting rolls. The molten steel is cooled by the casting rolls under the protection of inert gas to form a casting strip. The casting speed is 40 to 60 m / min. The obtained cast strip is rolled and coiled to form hot-rolled steel coils or directly coiled to form cast strip steel coils.

2. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (1), ordinary scrap steel is used in the primary smelting furnace, converter, and electric furnace smelting.

3. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (1), the free oxygen content of the molten steel smelted in the converter is controlled to be 500~700ppm, the final temperature is ≥1630℃, and S≤0.0100%.

4. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (1), the free oxygen content of the molten steel smelted in the electric furnace is controlled to be 600~800ppm, the final temperature is ≥1650℃, and S≤0.0120%.

5. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (2), the basicity of VD slag formation during the smelting process is controlled to be 2.3~3.3; 400~600kg of slag-forming lime and 100~200kg of fluorite are added to the molten steel supplied by the converter.

6. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (2), the basicity of VD slag formation during the smelting process is controlled at 2.3~3.3; 700~1000 kg of slag-forming lime and 250~400 kg of fluorite are added to the molten steel supplied by the electric furnace.

7. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (3), the carbon content is controlled to be 0.51~0.54%, and the Mn / Si ratio is controlled to be 2.8~3.

3.

8. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (3), after the molten steel composition of the LF process is hit, the power is continued to be applied to raise the temperature. After the temperature reaches 1640~1660℃, the oxygen blowing operation is carried out.

9. The method for smelting high-basicity, strongly oxygen-blown molten steel for double-roll thin strip according to claim 1, characterized in that: In step (3), the alkalinity of the final residue is controlled to be 1.8~2.

5.

10. The method for smelting high-basicity, strongly oxygen-blown molten steel for double-roll thin strip according to claim 1, characterized in that: In step (3), a strong oxygen blowing operation is performed before the LF refining process, with an oxygen blowing intensity of 10~12m. 3 / min, oxygen blowing rate is 120~150m³ 3 .

11. The method for smelting high-basicity, strongly oxygen-blown molten steel for double-roll thin strip according to claim 10, characterized in that: Before LF oxygen blowing, reduce the bottom argon gas flow rate of the ladle to 70~150L / min.

12. The method for smelting high-basicity, strongly oxygen-blown molten steel for double-roll thin strip according to claim 10, characterized in that: After oxygen blowing, add 3-5 kg ​​of ferroboron and continue to heat the molten steel to 1665-1675℃. During the heating process, add calcium carbide at a rate of 0.5-1.0 kg / min. After the heating is finished, feed calcium wire at a rate of 80-100 m and a feeding speed of 2.5-3 m / s.

13. The method for smelting high-basicity, strongly oxygen-blown molten steel for double-roll thin strip according to claim 12, characterized in that: After feeding the silk, perform soft mixing, and control the soft mixing time to be no less than 5 minutes.

14. The method for smelting high-basicity, strongly oxygen-blown molten steel for double-roll thin strip according to claim 12, characterized in that: Oxygen blowing and wire feeding are used to control inclusions in molten steel. The inclusions in the molten steel are high-SiO2, MnO, and CaO inclusions, and the Al2O3 content in the inclusions is controlled to be below 15%wt.

15. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (3), the maximum size of inclusions in the molten steel obtained after inclusion modification and removal does not exceed 15 μm, and the number of inclusions below 5 μm accounts for more than 98%.

16. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 15, characterized in that: The content of (SiO2+MnO+CaO) component in the inclusion is ≥80%wt.

17. The method for smelting high-basicity, strongly oxygen-blown molten steel in twin-roll thin strip according to claim 1, characterized in that: In step (4), the qualified molten steel is transported to the ladle turret for casting; the molten steel flows into the molten pool through the tundish and transition ladle, and the molten pool level is controlled by the casting speed and the opening of the tundish slide plate.

18. A type of double-roll thin strip high-carbon steel, characterized in that, The twin-roll thin strip high-carbon steel is produced using the method described in any one of claims 1 to 17.

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