A method for producing 65Mn thin strip steel based on twin-roll casting and rolling

Abstract

This invention belongs to the field of steel smelting and production technology, and relates to a method for producing 65Mn thin strip steel based on twin-roll casting. The production process of this invention includes: converter or electric furnace smelting, vacuum treatment (VD), slag removal after VD vacuum breaking, LF refining to adjust composition and control the slag system and inclusions after slag removal, strong oxygen blowing before tapping in the LF process to further improve inclusions, and by controlling the fluctuation range of molten steel composition and slag system, controlling the oxygen content in the tundish and roller brush parameters during casting, and synergistically controlling the oxide content of the casting rolls, stable casting of 65Mn thin strip steel is achieved, improving the segregation of the billet and strip, reducing production costs, and increasing production efficiency.

Description

Technical Field

[0001] This invention belongs to the field of steel smelting and production technology, and relates to a method for producing 65Mn thin strip steel based on twin-roll casting and rolling. Background Technology

[0002] Traditionally hot-rolled 65Mn, a typical high-carbon structural steel, is widely used in saw blades, springs, and other fields due to its excellent strength and elasticity. However, its "high carbon and high manganese" composition also presents significant challenges in production, mainly in the continuous casting and rolling processes.

[0003] Because traditional 65Mn steel has a high carbon and manganese content, it is prone to center segregation in the cast billet during production, which is one of the most critical quality issues. During solidification, elements such as C and Mn accumulate in the center of the billet, leading to uneven microstructure. Severe center segregation significantly reduces the plasticity of the steel and is a major cause of fracture during subsequent drawing or machining.

[0004] To mitigate the tendency for center segregation in 65Mn steel, dynamic light reduction and end-of-line electromagnetic stirring techniques are commonly used when casting molten steel into billets. After heating in a furnace, the billets undergo continuous multi-stand rolling. Traditional processes for producing this steel grade involve numerous steps and a long production flow. Compared to traditional methods, the twin-roll casting process features rapid and sub-rapid solidification during continuous casting, avoiding elemental segregation. This significantly reduces the thickness of the hot-rolled plates produced. Furthermore, the shorter production line and protective atmosphere result in no decarburized layer on the steel plate surface. It also reduces the number of cold rolling and annealing processes in subsequent production, lowering production costs and increasing efficiency.

[0005] However, this steel grade has a high carbon content, resulting in 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, the casting strip has many liquid cores during casting, easily causing white lines, "snake-egg" patterns, and strip breakage, leading to production instability. 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, 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, the inventors discovered that changes in carbon content and the Mn / Si ratio can easily cause abrupt changes in heat transfer and strip shape. All these factors contribute to casting instability, making stable and continuous production of 65Mn thin strip steel impossible using twin-roll casting. The production of 65Mn using the twin-roll casting process requires high standards for molten steel quality, stability, and smelting. Summary of the Invention

[0006] To address this problem, this invention proposes a method for producing 65Mn thin strip steel based on twin-roll casting. This method overcomes at least some of the shortcomings of existing technologies, solves the problem of stable casting and rolling of 65Mn thin strip steel, improves the stability of 65Mn thin strip forming, achieves continuous twin-roll casting production of 65Mn thin strip steel, reduces production costs, and increases yield.

[0007] Specifically, the technical solution adopted in this invention is as follows:

[0008] According to a first aspect of the present invention, a method for producing 65Mn thin strip steel based on twin-roll casting and rolling is proposed.

[0009] The chemical composition of the 65Mn thin strip steel, by mass percentage, is as follows: 0.62%≤C≤0.72%, 0.27%≤Si≤0.33%, 0.95%≤Mn≤1.05%, 0.02%≤Cr≤0.03%, P≤0.02%, S≤0.003%, 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;

[0010] The method includes the following steps:

[0011] (1) Converter / electric furnace smelting:

[0012] The free oxygen content in the initial molten steel is controlled at 500~800ppm, the final temperature is ≥1650℃, and S≤0.0150%;

[0013] (2) VD vacuum treatment:

[0014] During the smelting process, the basicity of VD slag formation is controlled at 2.5~3.5, wherein the initial molten steel is vacuum treated in a VD vacuum furnace for more than 25 minutes, and the duration of vacuum degree <67Pa is not less than 10 minutes.

[0015] (3) LF Refining:

[0016] After being vacuum treated by VD, the molten steel is transferred to LF, where fluorite is added to adjust the slag, and after heating and slag melting, the slag is removed.

[0017] After slag removal, the slag is transferred to the LF furnace for carbonization. Following carbonization, a low-nitrogen carbonizer is added, controlling the C content to 0.63-0.68%. Then, 400-800 kg of lime, 0-150 kg of fluorite, 0-150 kg of quartz sand, and 500-1500 kg of synthetic slag are added, and the slag is electrolytically treated, controlling the Mn / Si ratio to 2.8-3.7. The basicity of the LF slag is controlled to 1.0-1.5.

[0018] (4) Twin-roll thin strip continuous casting:

[0019] The qualified molten steel obtained in steps (1) to (3) is continuously cast through an intermediate ladle, a transition ladle and 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 with a thickness of 1.5~2.5mm. The casting and rolling speed is 40~60m / min.

[0020] The resulting cast strip is rolled or coiled to form hot-rolled steel coils or directly coiled to form cast strip steel coils.

[0021] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to the present invention, 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 ≥1650℃, and S≤0.0100%.

[0022] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to the present invention, 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 ≥1670℃, and S≤0.0150%.

[0023] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to the present invention, preferably, in step (2), 400~600kg of slag-forming lime and 100~180kg of fluorite are added to the molten steel provided by the converter.

[0024] According to the method for producing 65Mn thin strip steel based on twin-roll casting according to the present invention, preferably, in step (2), 700~1000 kg of slag-forming lime and 200~350 kg of fluorite are added to the molten steel supplied by the electric furnace.

[0025] According to the method of producing 65Mn thin strip steel based on twin roll casting according to the present invention, preferably, in step (3), after the VD is broken, it is transferred to LF, 50~100kg of fluorite is added, and the temperature is raised to 1600~1620℃ and then transferred to the slag removal position for slag removal operation, and the slag removal rate is not less than 80%.

[0026] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to the present invention, preferably, in step (3), the basicity of LF slag is adjusted and controlled to be 1.0~1.25; during the process, the alloy composition is adjusted and the Mn / Si ratio is controlled to be 3.0~3.5.

[0027] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to the present invention, 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 to 1620~1640℃ to maintain the slag-gold reaction, and the reaction time is controlled to be not less than 25min; during the process, the bottom blowing argon gas of the ladle is adjusted to 80~200L / min, and the slag surface fluctuates.

[0028] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling of the present invention, preferably, a strong oxygen blowing operation is performed after the slag-gold reaction time is satisfied to increase the free oxygen potential of the molten steel, and the oxygen blowing intensity is 10~12m. 3 / min, oxygen blowing rate is 120~150m³ 3 .

[0029] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling of the present invention, preferably, after oxygen blowing, the temperature of the molten steel is raised to 1660~1670℃ by continuing to heat the molten steel; 3~5kg of ferroboron is added and calcium wire feeding is performed to modify the inclusions, wherein the wire feeding amount is 80~120m and the wire feeding speed is 2.5~3m / s;

[0030] After feeding the silk, perform soft mixing, and control the soft mixing time to be no less than 8 minutes.

[0031] Slag replacement, oxygen blowing, and wire feeding are used to control inclusions in molten steel. The inclusions in the molten steel are high-SiO2 and MnO inclusions, and the Al2O3 content in the inclusions is controlled to be below 10%wt.

[0032] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling of the present invention, preferably, the maximum size of the endogenous inclusions in the molten steel obtained after inclusion modification and inclusion removal does not exceed 15μm, and the number of inclusions smaller than 5μm accounts for more than 98%.

[0033] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling of the present invention, preferably, the content of (SiO2+MnO+CaO) component in the inclusions is ≥80%wt.

[0034] According to the method for producing 65Mn thin strip steel based on twin-roll casting according to the present invention, preferably, in step (4), the qualified molten steel obtained is transported to the ladle tumbler 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.

[0035] According to the method for producing 65Mn thin strip steel based on twin-roll casting according to the present invention, preferably, in step (4), the casting process adopts tundish auxiliary heating technology to control the tundish temperature at 1600±5℃.

[0036] According to the method for producing 65Mn thin strip steel based on twin-roll casting according to the present invention, preferably, in step (4), the molten steel in the tundish is subjected to constant oxygen and oxygen blowing operations intermittently during the casting process; the roller brush speed is controlled at 400±10rpm, and the torque gradually increases from 0 to 200±10N•m within 30 minutes after casting begins; when the molten steel in the tundish needs oxygen blowing and after oxygen blowing, the roller brush speed is gradually reduced to 380±10rpm, and the torque is adjusted from 200±10N•m during normal casting to 170±10N•m.

[0037] According to the method for producing 65Mn thin strip steel based on twin-roll casting and rolling of the present invention, preferably, the oxygen blowing amount in each tundish is ≥5m³. 3 The oxygen blowing pressure is 0.4~0.6MPa.

[0038] According to a second aspect of the invention, a 65Mn thin strip steel is provided, which is produced using a method having one or more of the aforementioned features.

[0039] Beneficial technical effects

[0040] Compared with traditional and existing technologies, the features and beneficial technical effects of the present invention include at least the following:

[0041] 1) This invention reduces the thickness of the billet and achieves rapid and sub-rapid solidification of molten steel, thus solving the elemental segregation defect in 65Mn steel.

[0042] 2) This invention reduces the production difficulty of 65Mn steel, shortens the production process, and reduces production costs; it is a green and environmentally friendly product and provides a new product selection solution. Attached Figure Description

[0043] 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.

[0044] 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 thin strip 65Mn steel. Detailed Implementation

[0045] 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.

[0046] 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.

[0047] The principle of the smelting process of this invention is as follows:

[0048] C: Carbon has a significant impact on the strength, hardness, plasticity and microstructure of steel, and also has a significant impact on the heat transfer during the solidification process of molten steel. This impact is particularly important in twin-roll thin strip continuous casting with rapid and sub-rapid solidification. Considering product performance requirements, smelting difficulty and hit rate, and production stability, the carbon content of this invention is controlled within the range of 0.63~0.68%wt.

[0049] 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.

[0050] The inventors discovered that the Mn / Si ratio has a significant impact on the strip shape during twin-roll casting. Within the process range, a higher Mn / Si ratio results in higher strip shape stability during casting. Therefore, the silicon content range of this invention is 0.27~0.33%wt, the manganese content range is 0.95~1.05%wt, and the Mn / Si ratio control range is 2.8~3.7, preferably 3.0~3.5.

[0051] 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.

[0052] By controlling the content of preferred alloying elements, product performance requirements can be met, while ensuring casting and rolling stability and production continuity.

[0053] Oxide control:

[0054] During the solidification process of molten steel casting rolls, oxides are generated and continuously accumulate on the surface of the casting rolls. These oxides (SiO2, MnO, CaO, Al2O3, FeO) in turn affect the interface between molten steel and casting rolls, affecting heat transfer and lubrication between the billet shell and the casting rolls.

[0055] a) The composition of molten steel affects the composition and melting point of the oxides formed. The composition of oxides can be controlled by adjusting the content of Mn, Si, and dissolved oxygen in the molten steel. LF (Left-Left) slag removal and replacement operations can modify inclusions and oxides in the molten steel.

[0056] b) By controlling the free oxygen content of the molten steel in the tundish and by controlling the torque and speed of the roller brushes, the solidification process of the twin-roll thin strip 65Mn steel is controlled, thereby controlling the oxide deposits (deposition film) on the surface of the twin-roll continuous casting rolls. The SiO2 and MnO deposited on the roll surface can improve the heat transfer and lubrication between the billet shell and the casting rolls, improve the performance of the casting strip, and enhance the casting stability.

[0057] 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.

[0058] The technical solution of the present invention will be further described in detail below through specific embodiments.

[0059] Example 1

[0060] This embodiment uses a converter smelting process to produce thin strip 65Mn steel. The specific process flow is as follows:

[0061] Step 1: VD treatment of molten steel in converter

[0062] The steel was smelted in a converter, with a final oxygen content of 556 ppm, a final carbon content of 0.045% wt, and a sulfur content of 0.0083% wt. The remaining components of the molten steel were Fe and unavoidable residual elements and impurities. The molten steel was then transferred to a VD vacuum furnace for vacuum treatment for 31 minutes. During the vacuum treatment, a silicon-manganese deoxidizer was added sequentially for deoxidation, followed by the addition of lime and fluorite for desulfurization. The amount of slag-forming lime added was 454 kg, and the amount of fluorite added was 105 kg. After vacuum furnace treatment, molten steel with an sulfur content of 0.0021% wt and a VD final slag basicity of 2.85 was obtained.

[0063] Step Two: Slag Removal Operation

[0064] The molten steel treated by VD vacuum is transferred to the LF furnace for top slag adjustment before slag removal. During the slag adjustment operation, 85 kg of fluorite is added and the temperature is raised to 1620℃ to ensure good fluidity of the top slag. The slag is then transferred to the slag removal position for slag removal operation, with a slag removal rate of 85~90%.

[0065] Step 3: LF Refining Process

[0066] After slag removal, the molten steel is transferred to the LF furnace for refining. After the molten steel arrives at the station, 152 kg of lime is added, the temperature is raised for 2.5 min by electricity, and after slag formation, the bottom blowing argon gas is increased to 410 L / min. Low nitrogen carbonizing agent is added to increase carbon, and alloy is added to adjust the composition.

[0067] The carbon content is 0.654%, and the Mn / Si ratio is controlled at 3.27.

[0068] After the components are matched, add 355 kg of lime and 850 kg of synthetic slag for slag conditioning, and then turn on the electricity to slag-melt. Adjust the basicity of the LF slag to 1.23. After slag-melting, reduce the bottom blowing argon gas of the ladle to 175 L / min and maintain the slag-metal reaction for 25.5 min.

[0069] After the slag-gold reaction lasted 25.5 minutes, the temperature was increased by electricity. Once the temperature reached 1646℃, oxygen blowing was performed at an intensity of 10-12 m / s. 3 / min, oxygen blowing rate is 120~150m³ 3 ;

[0070] After oxygen blowing, add 5 kg of ferroborone, turn on the power to raise the temperature of the molten steel to 1672℃; after the power is turned off, feed calcium wire at a rate of 110 m and a speed of 2.5 m / s; after feeding the wire, perform soft stirring for 5 minutes.

[0071] Step 4: Twin-roll continuous casting

[0072] 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 40~43m / min.

[0073] Molten steel in the pool forms a strip on the surface of the casting roll, with the strip thickness controlled between 1.85 and 2.0 mm. The strip is then rolled into a coil after a single pass to achieve the target thickness.

[0074] Step 5: Stabilize Casting and Rolling Control

[0075] During the initial pouring and normal pouring processes, the rotation speed of the twin roller brush was set to 400±10 rpm, and the torque gradually increased from 0 to 220±10 N•m within 25 minutes of the initial pouring.

[0076] Step Six: Oxygenation of Intermediate Batch

[0077] Oxygen content in the molten steel is intermittently checked during the casting process. When the oxygen content test result shows a free oxygen content <30ppm, oxygen blowing is immediately performed in the tundish, with a single blowing volume of not less than 5m³. Oxygen blowing is also required in the tundish when the twin-roll casting signal frequently shows white lines with an intensity >2.5, with a single blowing volume of not less than 5m³. The oxygen blowing pressure is set to 0.4~0.6MPa.

[0078] Step 7: Adjusting the roller brush parameters

[0079] When oxygen blowing is required for molten steel in the tundish and after oxygen blowing, the roller brush parameters are actively adjusted: the roller brush speed is gradually reduced to 380±10rpm, and the torque is adjusted from 220±10N•m during normal casting to 175±10N•m.

[0080] 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 65Mn steel, and successfully achieving stable production of twin-roll thin strip 65Mn steel, completing the whole furnace casting.

[0081] Example 2

[0082] 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.

[0083] Step 1: Electric furnace steelmaking

[0084] This embodiment employs an electric arc furnace (EAF)-VD furnace-LF furnace smelting process. The EAF smelting process controls the final oxygen content to 783 ppm, the final carbon content to 0.0346% wt, and the sulfur content to 0.0124% wt. Compared to converter smelting, EAF smelting results in a wider range of final oxygen content, a slightly lower range of final carbon content, and a relatively higher sulfur content. The remaining components in the molten steel are Fe and unavoidable residual elements and impurities. Subsequent processes after EAF smelting, such as VD vacuum treatment and LF refining, are the same as in Example 1, but the treatment requirements differ depending on the characteristics of the EAF molten steel.

[0085] Step 2: VD Processing

[0086] Molten steel smelted in an electric arc furnace is treated in a vacuum furnace (VD). The molten steel from the electric arc furnace has a high gas content and high sulfur content, and the treatment time is long with a large amount of lime consumption. The treatment time is 37 minutes, and the amount of lime added for slag formation is 770 kg, and the amount of fluorite added is 230 kg. After vacuum furnace treatment, molten steel with an S content of 0.0020%wt is obtained, and the basicity of the final VD slag is 3.02.

[0087] Step 3: Slag Removal

[0088] The molten steel treated by VD vacuum is transferred to the LF furnace for slag removal pretreatment. 80 kg of fluorite is added and the temperature is raised to 1613℃ and 1610℃. After completion, it is hoisted to the slag removal position for slag removal operation. The slag removal rate is 85~90%.

[0089] Step 4: LF Refining Process

[0090] After slag removal, the molten steel is transported back to the LF furnace for refining. When the molten steel arrives at the station, 120 kg of lime is added, and the temperature is raised for 2.5 min by electricity. After slag formation, the bottom blowing argon gas is increased to 380 L / min. Low-nitrogen carbonizer is added to increase carbon content, and alloy is added to adjust the composition.

[0091] The carbon content is 0.655%wt, and the Mn / Si ratio is controlled at 3.3.

[0092] After the components are in place, add 340 kg of lime and 710 kg of synthetic slag for slag conditioning, and then turn on the slag to make it slag. Adjust the basicity of the LF slag to 1.20. The slag-gold reaction time is 25 min, and the bottom blowing argon gas is adjusted to 110 L / min during the process.

[0093] After a slag-gold reaction time of 25 minutes, electricity was applied to raise the temperature. Once the temperature reached 1640℃, oxygen blowing was initiated at an intensity of 10-12 m / s. 3 / min, oxygen blowing rate 125m 3 ;

[0094] After oxygen blowing, add 4 kg of ferroborone, turn on the power to raise the temperature of the molten steel to 1670℃; 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 5 minutes.

[0095] Step 5: Twin-roll continuous casting

[0096] 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 38~40m / min.

[0097] Molten steel in the pool forms a strip on the surface of the casting roll, with the strip thickness controlled between 1.85 and 2.0 mm. The strip is then rolled into a coil after a single pass to achieve the target thickness.

[0098] Step Six: Stabilizing Casting and Rolling Control

[0099] During the initial pouring and normal pouring processes, the rotation speed of the twin roller brush was set to 400±10 rpm, and the torque gradually increased from 0 to 220±10 N•m within 25 minutes of the initial pouring.

[0100] Step 7: Oxygenation of the intermediate bag

[0101] Oxygen content in the molten steel is intermittently checked during the casting process. When the oxygen content test result shows a free oxygen content <30ppm, oxygen blowing is immediately performed in the tundish, with a single blowing volume of not less than 5m³. Oxygen blowing is also required in the tundish when the twin-roll casting signal frequently shows white lines with an intensity >2.5, with a single blowing volume of not less than 5m³. The oxygen blowing pressure is set to 0.4~0.6MPa.

[0102] Step 8: Adjusting the roller brush parameters

[0103] When oxygen blowing is required for molten steel in the tundish and after oxygen blowing, the roller brush parameters are actively adjusted: the roller brush speed is gradually reduced to 380±10rpm, and the torque is adjusted from 220±10N•m during normal casting to 175±10N•m.

[0104] Through the above process, the deposition state of inclusions in the molten steel and oxides on the surface of the casting rolls was effectively controlled, meeting the requirements for stable casting of thin-strip 65Mn steel. Stable production of twin-roll thin-strip 65Mn steel was successfully achieved, completing the whole-furnace casting of molten steel in the electric arc furnace process. The electric arc furnace smelting process provides another feasible smelting route for the production of thin-strip 65Mn steel, expanding the applicability of this method.

[0105] 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 producing 65Mn thin strip steel based on twin-roll casting and rolling, characterized in that, The chemical composition of the 65Mn thin strip steel, by mass percentage, is as follows: 0.62%≤C≤0.72%, 0.27%≤Si≤0.33%, 0.95%≤Mn≤1.05%, 0.02%≤Cr≤0.03%, P≤0.02%, S≤0.003%, 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≤0.0150%; (2) VD vacuum treatment: During the smelting process, the basicity of VD slag formation is controlled at 2.5~3.5, wherein the initial molten steel is vacuum treated in a VD vacuum furnace for more than 25 minutes, and the duration of vacuum degree <67Pa is not less than 10 minutes. (3) LF Refining: After being vacuum treated by VD, the molten steel is transferred to LF, where fluorite is added to adjust the slag, and after heating and slag melting, the slag is removed. After slag removal, the slag is transferred to the LF furnace for carbonization. Following carbonization, a low-nitrogen carbonizer is added, controlling the C content to 0.63-0.68%. Then, 400-800 kg of lime, 0-150 kg of fluorite, 0-150 kg of quartz sand, and 500-1500 kg of synthetic slag are added, and the slag is electrolytically treated, controlling the Mn / Si ratio to 2.8-3.

7. The basicity of the LF slag is controlled to 1.0-1.

5. (4) Twin-roll thin strip continuous casting: The qualified molten steel obtained in steps (1) to (3) is continuously cast through an intermediate ladle, a transition ladle and 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 with a thickness of 1.5~2.5mm. The casting and rolling speed is 40~60m / min. The resulting cast strip is rolled or coiled to form hot-rolled steel coils or directly coiled to form cast strip steel coils.

2. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (1), the free oxygen content of the molten steel smelted in the converter is controlled at 500~700ppm, the final temperature is ≥1650℃, and S≤0.0100%.

3. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling 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 at 600~800ppm, the final temperature is ≥1670℃, and S≤0.0150%.

4. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (2), 400-600 kg of slag-forming lime and 100-180 kg of fluorite are added to the molten steel supplied by the converter.

5. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (2), 700-1000 kg of slag-forming lime and 200-350 kg of fluorite are added to the molten steel supplied by the electric furnace.

6. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (3), after the VD is broken, it is transferred to the LF, 50~100kg of fluorite is added, and the temperature is raised to 1600~1620℃ before being transferred to the slag removal position for slag removal operation. The slag removal rate is not less than 80%.

7. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (3), the basicity of the LF slag is adjusted to 1.0~1.25; during the process, the alloy composition is adjusted to control the Mn / Si ratio to 3.0~3.

5.

8. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling 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 turned on to raise the temperature to 1620~1640℃ to maintain the slag-gold reaction, and the reaction time is controlled to be no less than 25min; during the process, the bottom blowing argon gas of the ladle is adjusted to 80~200L / min, and the slag surface fluctuates.

9. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 8, characterized in that: After the slag-metal reaction time is satisfied, a strong oxygen blowing operation is performed to increase the free oxygen potential of the molten steel. The oxygen blowing intensity is 10~12m. 3 / min, oxygen blowing rate is 120~150m³ 3 .

10. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 9, characterized in that: After oxygen blowing, continue to heat the molten steel to 1660~1670℃; add 3~5kg of ferroboron and perform calcium wire feeding to modify the inclusions, wherein the wire feeding amount is 80~120m and the wire feeding speed is 2.5~3m / s; After feeding the silk, perform soft mixing, and control the soft mixing time to be no less than 8 minutes. Slag replacement, oxygen blowing, and wire feeding are used to control inclusions in molten steel. The inclusions in the molten steel are high-SiO2 and MnO inclusions, and the Al2O3 content in the inclusions is controlled to be below 10%wt.

11. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 10, characterized in that: The maximum size of the endogenous inclusions in the molten steel after inclusion modification and removal does not exceed 15μm, and the number of inclusions smaller than 5μm accounts for more than 98%.

12. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 11, characterized in that: The content of (SiO2+MnO+CaO) component in the inclusion is ≥80%wt.

13. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling 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.

14. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (4), the casting process uses tundish auxiliary heating technology to control the tundish temperature at 1600±5℃.

15. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 1, characterized in that: In step (4), oxygen is intermittently applied to the molten steel in the tundish during the casting process; the roller brush speed is controlled at 400±10 rpm, and the torque gradually increases from 0 to 200±10 N•m within 30 minutes of casting; when oxygen is needed for the molten steel in the tundish and after oxygen blowing, the roller brush speed gradually decreases to 380±10 rpm, and the torque is adjusted from 200±10 N•m during normal casting to 170±10 N•m.

16. The method for producing 65Mn thin strip steel based on twin-roll casting and rolling according to claim 15, characterized in that: Oxygen blowing volume of ≥5m³ per tundish 3 The oxygen blowing pressure is 0.4~0.6MPa.

17. A 65Mn thin strip steel, characterized in that, The 65Mn thin strip steel is produced using the method described in any one of claims 1 to 16.

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