Silicomanganese killed high carbon steel and method of control of inclusions thereof

Abstract

The application discloses a kind of silicon manganese calm high-carbon steel and its inclusion control method, converter low-carbon, high-oxygen tapping, deoxidation alloying when tapping 15%, using the strong oxidizing property of molten steel, first weak deoxidation alloy is added, Al, Ti brought in by alloy is all oxidized, finally low-titanium low-aluminum ferrosilicon final deoxidation alloying is added, after deoxidation alloying, acidic synthetic slag is added, then silicon carbide, low-alkalinity synthetic slag is added to form slag.Then it is transported to LF refining, after adjusting the composition and temperature of molten steel to reach the standard, it is treated by RH vacuum degassing and inclusion removal, and then continuous casting is carried out.The content of alumina, titanium oxide in refractory, synthetic slag, tundish covering agent, mold powder and the content of aluminum and titanium in alloy are strictly controlled.The application is extremely beneficial to control high-melting-point inclusions such as alumina, magnesium aluminate spinel and titanium oxide, and molten steel with extremely low brittle inclusion content is obtained, which is used for casting high-quality billet and producing high-machining-performance wire rod.

Description

Technical Field

[0001] This invention relates to a method for controlling inclusions in silicon-manganese killed high-carbon steel, belonging to the technical field of steelmaking. Background Technology

[0002] Silicon-manganese steel is an alloy composed of manganese, silicon, iron, and small amounts of carbon and other elements. It is a widely used and produced ferroalloy. According to the degree of deoxidation and casting process, it is classified as: a. rimmed steel, b. semi-killed steel, c. killed steel, and d. special killed steel.

[0003] There is still very little research in the industry on the control of inclusions in the manufacturing process of silicon-manganese killed high-carbon steel, which comprehensively studies the deoxidation alloying and slag-making processes, alloys, refractory materials, and slag-making auxiliary materials.

[0004] The inventors discovered through research that some existing patents describe processes for controlling inclusions. For example, patent CN 113249542 A, entitled "A Smelting Process for Improving the Purity and Plasticity of Inclusions in Spring Steel," discloses a process of first dehydrogenating and denitrogenating the steel with RH, followed by heating with LF to allow the slag to fully react, controlling the plasticity of inclusions, and then directly casting the steel using soft blowing for at least 60 minutes. The resulting spring steel has a total oxygen content of 0.0010%, a hydrogen content ≤0.00015%, a nitrogen content ≤0.0030%, and an Al2O3 content in the non-metallic inclusions that is not higher than 15% and whose composition is located in the low melting point region, making it easy to deform. However, this patented process is not suitable for high-strength silicon-manganese killed high-carbon steel. This method mainly considers the control of inclusion plasticity, but it does not fully account for the problem of brittle inclusions introduced by refractory materials, alloys, and auxiliary materials, and it does not reduce the titanium content in the spring steel. Therefore, it does not significantly improve the fatigue fracture problem of spring steel caused by brittle inclusions.

[0005] Patent CN 112296287 A, entitled "A Method for Controlling Inclusions in High-Carbon Steel," discloses a method that involves feeding magnesium-containing cored wire into the tundish during continuous casting. The magnesium vapor generated after entering the molten steel reacts with oxygen in the steel to form a large number of dispersed, micron-sized magnesium oxide or magnesium-aluminum spinel particles. This alters the precipitation sequence of inclusions during continuous casting, reducing the quantity and size of aluminum-containing inclusions and mitigating the harmful effects of brittle inclusions on the drawing process and wire breakage. While this process changes the precipitated phases of inclusions inside the billet during continuous casting of high-carbon steel, it cannot reduce the aluminum and titanium elements in the steel. Due to the presence of a large amount of magnesium oxide inclusions and a certain amount of aluminum, brittle magnesium-aluminum spinel inclusions are easily produced, failing to truly improve the brittle inclusion content problem in high-carbon steel and severely impacting the processing performance of wire rod. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention discloses a method for controlling inclusions in silicon-manganese killed high-carbon steel, the specific technical solution of which is as follows:

[0007] A silicon-manganese killed high-carbon steel, wherein the chemical composition of the silicon-manganese killed high-carbon steel, in addition to alloying elements, includes the following chemical composition by mass percentage: C: 0.50-1.05%, P≤0.012%, S≤0.005%, Alt≤0.0008%, Ti≤0.0005%, N≤0.0035%, T0≤0.0012%, with the remainder being Fe and other unavoidable impurities.

[0008] Furthermore, the inclusions in the silicon-manganese killed high-carbon steel include silicate inclusions, with an average mass content of Al2O3 in inclusions larger than 1 μm ≤ 5%, and brittle inclusions of alumina, titanium oxide, and magnesium aluminum spinel ≤ 5 μm in size, and a total number density of brittle inclusions larger than 1 μm ≤ 0.00035 inclusions / mm. 2 .

[0009] Furthermore, the wire rods made of silicon-manganese killed high-carbon steel, when subjected to ultra-high cycle fatigue tests under loads of 600-800MPa, exhibit a fatigue life of ≥1.5 million cycles; when drawing steel cord or diamond wire with a diameter ≥0.05mm from silicon-manganese killed high-carbon steel, the frequency of wire breakage caused by inclusions is ≤1.5 times / ton; and cable steel made of silicon-manganese killed high-carbon steel, during torsion testing, exhibits no fracture caused by inclusions after ≥25 torsion cycles.

[0010] A method for controlling inclusions in silicon-manganese killed high-carbon steel, produced according to the process flow of hot metal pretreatment—converter smelting—LF refining—RH vacuum—large billet continuous casting—bill rolling—Stelmo air cooling, specifically including the following steps:

[0011] Step 1: Hot metal pretreatment, KR deep desulfurization treatment, to obtain hot metal with S content ≤0.0015%;

[0012] Step 2: Converter smelting. The desulfurized molten iron and scrap steel are added to the converter for smelting. The converter adopts double slag operation. The final C content of the converter is 0.040-0.075%, O content is 0.030-0.065%, Al≤0.0002%, and Ti≤0.0003%. Steel is tapped after smelting.

[0013] According to the alloy composition requirements of the steel grade, one or more of the following are added for deoxidation and alloying: metallic manganese, carbon powder, ferrochrome, and ferrovanadium. After more than 70% of the steel has been tapped, low-titanium and low-aluminum ferrosilicon is added for final deoxidation, followed by the addition of carbon powder. After all the carbon powder has been added, synthetic slag is added to form slag. The basicity of the refined slag (CaO / SiO2) is 0.45-0.75, and the T.Fe+MnO content in the slag is 3.5-6.5%. The bottom blowing is turned on for more than 5 minutes, then the slag is skimmed off, and silicon carbide, synthetic slag, and lime are added to form slag. Finally, the basicity of the ladle slag (CaO / SiO2) is 0.9-1.2, the MgO content is 5-10%, and the T.Fe+MnO content in the slag is ≤3.0%. Then it is transported to LF refining.

[0014] Step 3: LF refining. During the refining process, the bottom blowing and stirring are turned on. According to the composition and temperature of the molten steel entering the station, one or more alloys of metallic manganese, carbon powder, ferrochrome, and ferrovanadium are added, and the temperature is increased by electricity. After the composition and temperature of the molten steel are controlled to meet the standards, it is transported to RH treatment.

[0015] Step 4: RH vacuum treatment, RH vacuum degassing treatment, treatment time ≥15 minutes, then break the vacuum and tap the steel, soft blowing for more than 5 minutes, shut down bottom blowing and calm for more than 10 minutes, then transport to continuous casting for pouring;

[0016] Step 5: Continuous casting of large billets, with protective pouring;

[0017] Step 6: Billet rolling;

[0018] Step 7: Stello air cooling.

[0019] Furthermore, in step 1, the initial composition of the molten iron, by mass percentage, includes: C: 4.1-4.5%, Si: 0.20-0.65%, Mn: 0.2-0.5%, P≤0.15%, S≤0.045%, Ti≤0.08%, as well as Fe and other unavoidable impurity components, at a temperature of 1380-1450℃.

[0020] Furthermore, in step 2, the scrap steel used in the converter has Al≤0.06%, Ti≤0.02%, P≤0.025%, S≤0.015%, with the remainder being Fe and other unavoidable components.

[0021] Furthermore, in step 2, during the converter double-slag smelting, the steel temperature is 1390-1470℃ during the first slag dumping, the Ti content in the steel is ≤0.0008%, the P content is ≤0.025%, and the TiO2 content in the slag is ≥1.0%; the converter final temperature is ≥1620℃, the P content is ≤0.013%, and the TiO2 content in the slag is ≤0.5% before tapping the steel, using a sliding plate to block the slag, and leaving ≥2 tons of steel.

[0022] Furthermore, in step 2, during the stage of adding alloy carbon powder at the converter tapping, the bottom blowing rate of the ladle is 500-800 NL / min. The bottom blowing rate is changed to 800-1000 NL / min for the first addition of synthetic slag. After the slag removal is completed, the bottom blowing rate of the ladle for re-slag formation is controlled at 300-500 NL / min.

[0023] Furthermore, in step 2, the basicity of the synthesized slag is CaO / SiO2=0.6-0.8, MgO content is 7-12%, Al2O3 content is ≤1.0%, TiO2 content is ≤0.25%, and the remainder is CaO, SiO2 and other unavoidable impurity components; the lime contains CaO content ≥95%, Al2O3 content ≤1.0%, and other unavoidable components.

[0024] Furthermore, in step 3, the bottom blowing flow rate of the ladle is 400-600 NL / min when adding alloys and carbon powder during LF refining, 200-400 NL / min during the heating operation, and 150-250 NL / min during other operations.

[0025] Furthermore, in step 4, the RH inlet is evacuated, three water ring pumps and two steam pumps are turned on, and two steam pumps are turned off. The vacuum chamber pressure is controlled at ≥10 mbar, and the boosted gas flow rate is controlled at 80-120 Nm. 3 / h.

[0026] Furthermore, in step 5, large square billets are continuously cast with a cross-section of 260-380mm × 360-480mm. The continuous casting process is protected during pouring. The main components of the continuous casting low-alkalinity, low-alumina tundish covering agent include: CaO: 35-45%, SiO2: 40-50%, CaF2: 2-5%, Al2O3≤2%, MgO: 3-6%, and other unavoidable components.

[0027] The electromagnetic stirring current of the crystallizer is 400-600A, the frequency is 5-7Hz, the continuous casting speed is controlled at 0.5-0.7m / min, and the reduction is 15-35mm, resulting in a billet with a C segregation index of 0.95-1.05, free from central porosity and crack defects.

[0028] Further, in step 6, the large square billet obtained in step 5 is placed into a heating furnace and heated to 1180-1250℃, then cut into small square billets of 140mm×140mm, and then inspected and ground, with an average grinding depth ≥1.0mm. A coating layer with a thickness of 1.0-2.5mm is sprayed onto the surface of the ground small square billet, and then it is heated and rolled in a heating furnace. The small square billet is heated to a temperature of 1100-1160℃, and the initial rolling temperature is controlled at 960-1020℃.

[0029] Furthermore, in step 7, the rolled wire rod obtained in the rolling process is subjected to temperature-controlled air cooling. The wire drawing temperature of the air cooling line is controlled at 860-930℃. The air volume of the Stellmore air cooling line fan is adjusted according to the steel composition to obtain silicon-manganese killed high carbon steel wire rod with a C segregation index of 0.96-1.04, a sorbitization rate of ≥97%, and no surface defects.

[0030] Furthermore, the low-carbon carbon raiser added during converter tapping and LF refining has an N content of ≤0.025%, with the remainder being C and unavoidable impurity elements;

[0031] The content of Mn in metallic manganese is ≥99%, Al content is ≤0.0035%, Ti content is ≤0.0015%, P content is ≤0.008%, S content is ≤0.004%, and the remainder is iron and unavoidable impurity elements;

[0032] The silicon carbide contains ≥98% SiC, ≤0.0065% Al, ≤0.0055% Ti, and other unavoidable impurity elements.

[0033] Low-titanium, low-aluminum ferrosilicon contains 75-80% Si, ≤0.005% Al, ≤0.002% Ti, ≤0.01% P, and ≤0.005% S, with the remainder being iron and unavoidable impurity elements.

[0034] Ferrochrome contains 55-60% Cr, ≤1.5% C, ≤0.015% P, ≤0.0065% Al, ≤0.0025% Ti, with the remainder being iron and unavoidable impurity elements.

[0035] Ferrovanadium contains 45-50% V, ≤0.012% P, ≤0.005% Al, ≤0.003% Ti, and the remainder is iron and unavoidable impurity elements.

[0036] Furthermore, the bottom bricks, molten pool bricks, and ladle mouth bricks of the ladle are all made of magnesia bricks, in which the Al2O3 content is ≤2.5%, the C content is ≤8%, and the remainder is MgO and other unavoidable components; the slag line bricks and permeable bricks of the ladle are made of magnesia-zirconium-carbon bricks, in which the ZrO2 content is 10-15%, the Al2O3 content is ≤1.5%, the C content is ≤5%, and the remainder is MgO and other unavoidable components; in the bottom bricks, molten pool bricks, ladle mouth bricks, and slag line bricks of the ladle, the proportion of magnesia sand particles >5mm exceeds 80%, and the density is 2.8-3.5g / cm³. 3 Flexural strength 38-42MPa, porosity ≤10%.

[0037] Furthermore, in step 4, the refractory material used for the impregnation tube and bottom tank of the RH vacuum furnace is magnesia-chrome ultra-low carbon brick, wherein the C content is ≤1.5%, MgO: 80-90%, Cr2O3: 5-10%, magnesium aluminum spinel: 4-6%, and other unavoidable impurity components; the proportion of magnesia sand particles with a size of 5-25mm in the magnesia-chrome ultra-low carbon brick exceeds 75%, and the density is 3.2-3.8g / cm³. 3 Flexural strength 43-48MPa, porosity ≤8%.

[0038] Furthermore, step 5 involves using a container to collect the diversion sand in the impact zone of the tundish during the initial pouring of the main ladle, then pouring the diversion sand out, and then pouring normally.

[0039] The large-scale pouring sand is made of chromium silicate, containing 50-60% SiO2, 25-35% Cr2O3, ≤3.5% Al2O3, and other unavoidable impurities.

[0040] The long nozzle of the ladle used in the continuous casting process is made of corundum, with Al2O3 ≥ 96% and small amounts of other unavoidable components, and a density of 3.2-3.6 g / cm³. 3 The porosity is ≤12%, and the inner wall of the long nozzle is coated with a MgSiO3 coating with a thickness of ≥5mm. It is baked for >3.5 hours before use at a temperature of ≥1400℃.

[0041] The inner wall of the intermediate ladle is coated with a magnesium coating, wherein the magnesium coating contains ≥90% MgO, ≤2% Al2O3, and other unavoidable components, and the magnesium coating has a density of 2.6-3.0 g / cm³ after drying. 3 ;

[0042] The tundish retaining wall is a magnesium-zirconium-carbon retaining wall, wherein MgO: 80-90%, ZrO2: 5-15%, Al2O3 ≤3%, ZrO2 content ≥10% at the slag line position, and other unavoidable components, with a density of 2.8-3.2 g / cm³. 3 Porosity ≤13%;

[0043] The upper and lower water inlets and the immersion water inlet of the intermediate tundish are all made of magnesium carbonaceous material. In the magnesium carbonaceous water inlet, MgO: 80-90%, C≤10%, Al2O3≤1.5%, and other unavoidable components.

[0044] The tundish flow control plug rod body is made of magnesium-carbon material, with MgO: 80-90%, C≤15%, Al2O3≤3%, and other unavoidable components; the slag line position and rod head are made of magnesium-zirconium-carbon, with MgO: 80-85%, ZrO2: 10-15%, Al2O3≤1.5%, and other unavoidable components.

[0045] The principle of the smelting process of this invention is as follows:

[0046] This invention reduces the sulfur content in the KR and converter to a low level, avoiding the strong slag-metal reaction during desulfurization in the LF refining process, which leads to the formation of large inclusions in the molten steel that are difficult to remove. Low-Ti molten iron and scrap steel are used for smelting, and a double-slag smelting process is employed in the converter. Early slag removal removes most of the alumina and titanium oxide-containing slag, and the use of sliding plate slag blocking and steel retention effectively avoids problems such as Al, Ti, and P reversion caused by slag removal, further preventing the precipitation of brittle inclusions such as alumina, titanium oxide, and titanium nitride during continuous casting.

[0047] This converter breaks away from the traditional high-carbon steelmaking process of tapping high-carbon steel, adopting a low-carbon, high-oxygen tapping method. The molten steel has a high oxygen content. During tapping, metallic manganese, carbon powder, ferrochrome, ferrovanadium, and other deoxidizing alloys are first added for alloying. The high oxygen content oxidizes and removes elements such as Al and Ti introduced into the alloy. Then, low-titanium, low-aluminum ferrosilicon is added for final deoxidation and alloying. Finally, the remaining carbon powder is added. After alloying, low-basicity synthetic slag is added, controlling the slag basicity below 0.75. The slag contains a certain amount of Ti, Fe, and MnO. With large-scale bottom blowing and stirring, the acidic, weakly oxidizing slag easily oxidizes and removes Al and Ti from the molten steel. Combined with slag skimming, the Al and Ti content is further reduced. Finally, lime, synthetic slag, and silicon carbide are added to create a low-basicity slag system, while controlling the slag's oxidizing properties and MgO content to reduce the subsequent erosion of the ladle refractory materials by the low-basicity slag.

[0048] The LF refining process involves heating and adjusting the steel composition, but low-to-medium bottom blowing is used throughout to avoid problems such as excessive slag entrainment caused by large-scale bottom blowing agitation. Once the steel composition and temperature meet the standards, it is transported to the RH vacuum treatment process. The RH treatment process does not employ conventional deep vacuum treatment; two fewer steam pumps are used, and a low to medium boost gas flow rate is employed. This allows the molten steel to undergo degassing and inclusion removal at a lower circulation throughput under higher vacuum chamber pressure. This modified process avoids the problem of excessive refractory erosion caused by high-throughput steel circulation in conventional processes, while efficiently removing inclusions originally present in the molten steel.

[0049] Furthermore, the entire smelting process utilizes high-quality ladle refractories, tundish refractories, refractories for the three main continuous casting components, high-quality alloys, and slag-forming materials to reduce the erosion intensity of the refractories and minimize the introduction of alumina, titanium oxide, metallic aluminum, and metallic titanium from the refractories, alloys, and auxiliary materials, thus reducing the problem of excessive foreign brittle inclusions. Comprehensive control of the quality of refractories, alloys, and auxiliary materials, combined with improvements in smelting technology, results in steel with low brittle inclusion content.

[0050] The continuous casting process utilizes protective casting techniques and employs electromagnetic stirring and reduction control technologies to obtain high-quality billets with low segregation indices. The design and improvement of processes such as billet preparation, grinding, and Stellmore air cooling in the rolling process yield high-carbon steel wire rods with low segregation indices, uniform microstructure, and high surface quality. Combined with brittle inclusion control technology, high-performance silicon-manganese killed high-carbon steel is comprehensively obtained.

[0051] The beneficial effects of this invention are:

[0052] (1) This invention breaks with conventional traditional processes. The silicon-manganese killed high carbon steel adopts a converter low carbon and high oxygen tapping process. During the tapping process, metal manganese, carbon powder, ferrochrome and other deoxidation alloys are added first. The strong oxidizing property of molten steel is used to oxidize all the Al and Ti brought in by the weak deoxidation alloy. Finally, low titanium and low aluminum silicon ferrosilicon are added for final deoxidation alloying. This avoids the traditional process of first adding silicon alloy for deoxidation, removing oxygen in molten steel to an extremely low level, and then adding metal manganese and other alloys. When the oxygen content is low, it is not easy to remove harmful impurity elements such as Al and Ti brought in by the weak deoxidation alloying elements.

[0053] (2) After the deoxidation and alloying of the converter steel is completed, low-basicity synthetic slag is added to control the slag basicity below 0.75. At the same time, the slag contains a certain amount of Ti, Fe and MnO. Bottom blowing and stirring are turned on. The acidic and weakly oxidizing slag is very easy to oxidize and remove Al and Ti from the molten steel. Combined with the slag removal operation, the Al and Ti content is further reduced. Finally, lime, synthetic slag and silicon carbide are added to create a low-basicity slag system. At the same time, the oxidizing property and MgO content of the slag are controlled to reduce the subsequent corrosion of the ladle refractory materials by the low-basicity slag.

[0054] (3) The RH treatment process does not use conventional deep vacuum treatment process, two fewer steam pumps are turned on, and medium and low gas flow rate is used to degas and remove inclusions in the molten steel under higher vacuum chamber pressure and with lower circulation throughput. This process method can avoid the problem of large amount of refractory corrosion caused by high-throughput circulation of molten steel in conventional process, and at the same time, it can efficiently remove the inclusions that originally existed in the molten steel.

[0055] (4) The entire smelting process uses high-quality refractory materials for ladles, tundishes, continuous casting, and other components, as well as high-quality alloys and slag-forming materials to reduce the erosion intensity of the refractory materials and minimize the introduction of alumina, titanium oxide, metallic aluminum, and metallic titanium by the refractory materials, alloys, and auxiliary materials, thus reducing the problem of excessive foreign brittle inclusions. Comprehensive control of the quality of refractory materials, alloys, and auxiliary materials, combined with improvements in smelting technology, comprehensively obtains molten steel with low brittle inclusion content.

[0056] This invention is extremely advantageous for controlling high-melting-point inclusions such as alumina, magnesium aluminum spinel, and titanium oxide, resulting in molten steel with extremely low brittle inclusion content, which can be used to cast high-quality billets and produce wire rods with high machinability. Attached Figure Description

[0057] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0058] The application of the present invention will be further illustrated below with reference to specific embodiments.

[0059] Example:

[0060] The production process of high-strength spring steel is as follows: hot metal pretreatment—converter smelting—LF refining—RH vacuum—large billet continuous casting—bill rolling—Stelmore air cooling—finished wire rod. Besides alloying elements, impurity elements include P≤0.012%, S≤0.005%, Alt≤0.0008%, Ti≤0.0005%, N≤0.0035%, and TO≤0.0012%, with the remainder being Fe and other unavoidable impurities.

[0061] The application of this invention is illustrated using spring steel, tire bead steel, cord steel, and cable steel as examples.

[0062] The chemical composition (mass percentage) of spring steel 55SiCr is as follows: C: 0.50-0.75%, Si: 1.45-1.55%, Mn: 0.55-0.70%, Cr: 0.55-0.65%, V: 0.15-0.25%;

[0063] The chemical composition (mass percentage) of the C82DA bead is as follows: C: 0.75-0.85%, Si: 0.15-0.35%, Mn: 0.50-0.65%.

[0064] Chemical composition (mass percentage) of 97A cord: C: 0.95-1.05%, Si: 0.15-0.30%, Mn: 0.35-0.45%;

[0065] The chemical composition (mass percentage) of cable steel 87B is as follows: C: 0.85-0.90%, Si: 0.45-0.60%, Mn: 0.70-0.85%, Cr: 0.20-0.35%, V: 0.02-0.05%;

[0066] Step 1: KR molten iron pretreatment

[0067] The initial composition of the molten iron, by mass percentage, includes: C: 4.1-4.5%, Si: 0.20-0.65%, Mn: 0.2-0.5%, P≤0.15%, S≤0.045%, Ti≤0.08%, as well as Fe and other unavoidable impurities, at a temperature of 1380-1450℃. The molten iron is then transported to the KR processing station for deep desulfurization treatment to obtain low-sulfur molten iron, which is then added to the converter for smelting.

[0068] Table 1 Main parameters of KR desulfurized molten iron

[0069]

[0070] Step 2: Converter smelting

[0071] The desulfurized molten iron and scrap steel are mixed into the converter for smelting. The scrap steel used in the converter has Al≤0.06%, Ti≤0.02%, P≤0.025%, S≤0.015%, and the remainder is Fe and other unavoidable components.

[0072] In the converter double-slag smelting, during the first slag dumping, the temperature of the molten steel, the Ti and P content in the molten steel, and the TiO2 content in the slag are controlled. At the end of the converter, the temperature, P content, C content, and O content are well controlled, and Al ≤ 0.0002%, Ti ≤ 0.0003%, and TiO2 content in the slag ≤ 0.5%. Slag is blocked by a sliding plate when tapping steel, and steel is retained during the operation.

[0073] Table 2. Main parameters for the first slag removal in the converter.

[0074]

[0075] Table 3 Main parameters of converter endpoint

[0076]

[0077] According to the alloy composition requirements of spring steel, tire bead steel, cord steel, and cable steel, one or more of the following are added for deoxidation and alloying during the converter tapping process: metallic manganese, carbon powder, ferrochrome, and ferrovanadium. After more than 70% of the steel has been tapped, low-titanium and low-aluminum ferrosilicon is added for final deoxidation, followed by carbon powder. After all the carbon powder is added, synthetic slag is added to form slag. The basicity and oxidizing properties of the refining slag are controlled, and bottom blowing is activated for stirring. Then, the slag is skimmed off. After skimming, silicon carbide, synthetic slag, and lime are added to form slag. The basicity, MgO content (%), and T.Fe+MnO content in the ladle slag are controlled, and then the slag is transported to the LF refining plant. During the stage of adding alloy carbon powder during converter tapping, the bottom blowing rate of the ladle is 500-800 NL / min. After the first addition of synthetic slag, the bottom blowing rate is changed to 800-1000 NL / min. After skimming, the bottom blowing rate of the ladle is controlled at 300-500 NL / min for slag formation.

[0078] The basicity of the synthetic slag is CaO / SiO2=0.6-0.8, MgO content is 7-12%, Al2O3 content is ≤1.0%, TiO2 content is ≤0.25%, and the remainder is CaO, SiO2 and other unavoidable impurities; the lime contains CaO content ≥95%, Al2O3 content ≤1.0%, and other unavoidable components.

[0079] Table 4. Main parameters of the converter tapping process

[0080]

[0081] Step 3: LF Refining

[0082] During the LF refining process, a small bottom blowing agitation is initiated. Based on the composition and temperature of the molten steel entering the station, one or more alloys from metallic manganese, carbon powder, ferrochrome, and ferrovanadium are added, and the temperature is increased by electricity. When adding alloys and carbon powder during LF refining, the bottom blowing flow rate of the ladle is 400-600 NL / min. During the heating operation, the ladle flow rate is 200-400 NL / min. During other operations, the bottom blowing flow rate is 150-250 NL / min. After the composition and temperature of the molten steel are controlled to meet the standards, it is transported to RH treatment.

[0083] Table 5. Main parameters of LF refining

[0084]

[0085] Step 4: RH vacuum treatment

[0086] The RH system is evacuated upon entry, with three water ring pumps and two steam pumps turned on, and two steam pumps turned off. The vacuum chamber pressure, gas flow rate, processing time, soft blowing time, and settling time are controlled. After processing, the gas is transported to the continuous casting station for pouring.

[0087] Table 6 Main parameters of RH vacuum treatment

[0088]

[0089] Step 5: Continuous casting of large billets

[0090] Large square billets were continuously cast. 55SiCr was cast with a 320mm × 420mm cross-section, C82DA with a 260mm × 360mm cross-section, 97A with a 380mm × 480mm cross-section, and 87B with a 350mm × 450mm cross-section. The entire casting process was protected during continuous casting. By controlling process parameters such as the crystallizer stirring current and frequency, casting speed, and reduction, billets with low carbon segregation index were obtained. Two low-magnification samples were taken from each heat for inspection, and no central porosity or crack defects were found.

[0091] When pouring from the ladle, a container is used to collect the diverting sand in the impact zone of the tundish. The diverting sand is then poured out, and normal pouring proceeds. The diverting sand is made of chromium silicate, containing 50-60% SiO2, 25-35% Cr2O3, ≤3.5% Al2O3, and other unavoidable impurities. The main components of the continuous casting low-basicity, low-alumina tundish covering agent include: 35-45% CaO, 40-50% SiO2, 2-5% CaF2, ≤2% Al2O3, 3-6% MgO, and other unavoidable components.

[0092] Table 7 Main parameters of continuous casting process

[0093]

[0094] Step 6: Billet rolling

[0095] The large billet obtained in step 5 is placed into a heating furnace, the heating temperature is controlled and kept warm, and then it is cut into 140mm×140mm small billets. After flaw detection and grinding, a coating is sprayed on the surface of the ground small billet, and then it is heated and rolled in a heating furnace. The heating temperature and rolling temperature of the small billet are controlled to obtain high-quality wire rod.

[0096] Table 8 Main parameters of the billet rolling process

[0097]

[0098] Step 7: Stello air cooling

[0099] The rolled wire rods obtained in the rolling process are subjected to temperature-controlled air cooling. The wire drawing temperature of the air cooling line is controlled, and the airflow of the Stelmore air cooling line fan is adjusted according to the steel composition to obtain wire rods with low carbon segregation index and high sorbitization rate. Five coils of wire rod are selected from each heat for surface inspection, and no surface defects are found. Six coils of wire rod are taken from each heat, and two samples are taken from each coil to measure segregation and sorbite.

[0100] Table 8 Main process parameters for air cooling

[0101]

[0102] The requirements for alloys and refractory materials used in the smelting and continuous casting stages are as follows:

[0103] (1) Alloy requirements

[0104] The low-carbon carburizing agent added during converter tapping and LF refining has a nitrogen content of ≤0.025%, with the remainder being carbon and unavoidable impurity elements;

[0105] The content of Mn in metallic manganese is ≥99%, Al content is ≤0.0035%, Ti content is ≤0.0015%, P content is ≤0.008%, S content is ≤0.004%, and the remainder is iron and unavoidable impurity elements;

[0106] The silicon carbide contains ≥98% SiC, ≤0.0065% Al, ≤0.0055% Ti, and other unavoidable impurity elements.

[0107] Low-titanium, low-aluminum ferrosilicon contains 75-80% Si, ≤0.005% Al, ≤0.002% Ti, ≤0.01% P, and ≤0.005% S, with the remainder being iron and unavoidable impurity elements.

[0108] Ferrochrome contains 55-60% Cr, ≤1.5% C, ≤0.015% P, ≤0.0065% Al, ≤0.0025% Ti, with the remainder being iron and unavoidable impurity elements.

[0109] Ferrovanadium contains 45-50% V, ≤0.012% P, ≤0.005% Al, ≤0.003% Ti, and the remainder is iron and unavoidable impurity elements.

[0110] (2) Requirements for refractory materials

[0111] The bottom bricks, molten pool bricks, and ladle mouth bricks of the ladle are all made of magnesia bricks. In these magnesia bricks, the Al2O3 content is ≤2.5%, the C content is ≤8%, and the remainder is MgO and other unavoidable components. The slag line bricks and permeable bricks of the ladle are made of magnesia-zirconium-carbon bricks. In these magnesia-zirconium-carbon bricks, the ZrO2 content is 10-15%, the Al2O3 content is ≤1.5%, the C content is ≤5%, and the remainder is MgO and other unavoidable components. In the bottom bricks, molten pool bricks, ladle mouth bricks, and slag line bricks of the ladle, the proportion of magnesia sand particles >5mm exceeds 80%, and the density is 2.8-3.5g / cm³. 3 Flexural strength 38-42MPa, porosity ≤10%.

[0112] The impregnation tubes and bottom tanks of the RH vacuum furnace are made of magnesia-chrome ultra-low carbon bricks, with a C content ≤1.5%, MgO: 80-90%, Cr2O3: 5-10%, magnesia-alumina spinel: 4-6%, and other unavoidable impurities. The magnesia-chrome ultra-low carbon bricks contain over 75% magnesia with a particle size of 5-25mm, and a density of 3.2-3.8 g / cm³. 3 Flexural strength 43-48MPa, porosity ≤8%.

[0113] The long nozzle of the ladle used in the continuous casting process is made of corundum, with Al2O3 ≥ 96% and small amounts of other unavoidable components, and a density of 3.2-3.6 g / cm³. 3 The porosity is ≤12%, and the inner wall of the long nozzle is coated with a MgSiO3 coating with a thickness of ≥5mm. It is baked for >3.5 hours before use at a temperature of ≥1400℃.

[0114] The inner wall of the intermediate ladle is coated with a magnesium coating, wherein the magnesium coating contains ≥90% MgO, ≤2% Al2O3, and other unavoidable components, and the magnesium coating has a density of 2.6-3.0 g / cm³ after drying. 3 ;

[0115] The tundish retaining wall is a magnesium-zirconium-carbon retaining wall, wherein MgO: 80-90%, ZrO2: 5-15%, Al2O3≤3%, ZrO2 content ≥10% at the slag line position, and other unavoidable components, with a density of 2.8-3.2 g / cm³. 3 Porosity ≤13%;

[0116] The upper and lower water inlets and the immersion water inlet of the intermediate tundish are all made of magnesium carbonaceous material. In the magnesium carbonaceous water inlet, MgO: 80-90%, C≤10%, Al2O3≤1.5%, and other unavoidable components.

[0117] The tundish flow control plug rod body is made of magnesium-carbon material, with MgO: 80-90%, C≤15%, Al2O3≤3%, and other unavoidable components; the slag line position and rod head are made of magnesium-zirconium-carbon, with MgO: 80-85%, ZrO2: 10-15%, Al2O3≤1.5%, and other unavoidable components.

Claims

1. A method for controlling inclusions in silicon-manganese killed high-carbon steel, characterized in that, In addition to alloying elements, the chemical composition of silicon-manganese killed high-carbon steel includes the following chemical components by mass percentage: C: 0.50%~1.05%, P≤0.012%, S≤0.005%, Alt≤0.0008%, Ti≤0.0005%, N≤0.0035%, TO≤0.0012%, with the remainder being Fe and other unavoidable impurities. The production process follows a flow of hot metal pretreatment—converter smelting—LF refining—RH vacuum—large billet continuous casting—bill rolling—Stelmo air cooling, specifically including the following steps: Step 1: Iron pretreatment. The initial composition of the molten iron, by mass percentage, includes C: 4.1%–4.5%, Si: 0.20%–0.65%, Mn: 0.2%–0.5%, P≤0.15%, S≤0.045%, Ti≤0.08%, as well as Fe and other unavoidable impurities. The temperature is 1380–1450℃. KR deep desulfurization treatment is performed to obtain molten iron with S content ≤0.0015%. Step 2: Converter smelting. Desulfurized molten iron and scrap steel are added to the converter for smelting. The scrap steel used in the converter has Al ≤ 0.06%, Ti ≤ 0.02%, P ≤ 0.025%, S ≤ 0.015%, with the remainder being Fe and other unavoidable components. The converter uses double-slag smelting. During the first slag removal, the molten steel temperature is 1390-1470℃, with Ti content ≤ 0.0008% and P content ≤ 0.025% in the molten steel, and TiO2 content in the slag ≥ 1.0%. The final converter temperature is ≥ 1620℃, with P content ≤ 0.013% and TiO2 content in the slag ≤ 0.5% before tapping. Slag is blocked using a sliding plate, leaving ≥ 2 tons of steel. The final converter temperature is C content 0.040%~0.075%, O content 0.030%~0.065%, Al ≤ 0.0002%, and Ti ≤ 0.0003%. Smelting is then completed, and the steel is tapped. According to the alloy composition requirements of the steel grade, one or more of the following are added for deoxidation and alloying: metallic manganese, carbon powder, ferrochrome, and ferrovanadium. After more than 70% of the steel has been tapped, low-titanium and low-aluminum ferrosilicon is added for final deoxidation, followed by the addition of carbon powder. After all the carbon powder has been added, synthetic slag is added to form slag. The basicity of the refined slag (CaO / SiO2) is 0.45-0.75, and the T.Fe+MnO content in the slag is 3.5% to 6.5%. The bottom blowing is turned on for more than 5 minutes, then the slag is skimmed off, and silicon carbide, synthetic slag, and lime are added to form slag. Finally, the basicity of the ladle slag (CaO / SiO2) is 0.9-1.2, the MgO content is 5% to 10%, and the T.Fe+MnO content in the slag is ≤3.0%. The slag is then transported to the LF refining plant. During the stage of adding alloy carbon powder during converter tapping, the bottom blowing rate of the ladle is 500-800 NL / min. The bottom blowing rate is changed to 800-1000 NL / min for the first addition of synthetic slag. After the slag removal is completed, the bottom blowing rate of the ladle for re-slag formation is controlled at 300-500 NL / min. The basicity of the synthesis residue is CaO / SiO2 = 0.6-0.8, MgO content is 7%-12%, Al2O3 content is ≤1.0%, TiO2 content is ≤0.25%, and the remainder is CaO, SiO2 and other unavoidable impurities. Step 3: LF refining. During the refining process, the bottom blowing and stirring are turned on. According to the composition and temperature of the molten steel entering the station, one or more alloys of metallic manganese, carbon powder, ferrochrome, and ferrovanadium are added, and the temperature is increased by electricity. After the composition and temperature of the molten steel are controlled to meet the standards, it is transported to RH treatment. Step 4: RH vacuum treatment, RH vacuum degassing treatment, treatment time ≥15 minutes, then break the vacuum and tap the steel, soft blowing for more than 5 minutes, shut down bottom blowing and calm for more than 10 minutes, then transport to continuous casting for pouring; Step 5: Continuous casting of large billets, protective pouring; when pouring from the ladle, use a container to collect the diversion sand in the impact zone of the tundish, pour out the diversion sand, and then pour normally; The casting sand used for large-scale pouring is chromium-silica casting sand, which contains 50%–60% SiO2, 25%–35% Cr2O3, ≤3.5% Al2O3, and other unavoidable impurities. Step 6: Billet rolling; Step 7: Stello air cooling.

2. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 2, the lime contains ≥95% CaO, ≤1.0% Al2O3, and other unavoidable components.

3. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 3, the bottom blowing flow rate of the ladle is 400-600 NL / min when adding alloys and carbon powder during LF refining, 200-400 NL / min during the heating operation, and 150-250 NL / min during other operations.

4. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 4, the RH inlet station is evacuated, three water ring pumps and two steam pumps are turned on, and two steam pumps are turned off. The vacuum chamber pressure is controlled at ≥10 mbar, and the booster gas flow rate is controlled at 80-120 Nm³. 3 / h.

5. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 5, large square billets are continuously cast with a cross-section of 260-380mm × 360-480mm. The continuous casting process is protected during pouring. The main components of the continuous casting low-alkalinity, low-alumina tundish covering agent include: CaO: 35%-45%, SiO2: 40%-50%, CaF2: 2%-5%, Al2O3≤2%, MgO: 3%-6%, and other unavoidable components. The electromagnetic stirring current in the crystallizer is 400-600A, the frequency is 5-7Hz, the continuous casting speed is controlled at 0.5-0.7m / min, and the reduction is 15-35mm, resulting in a billet with a C segregation index of 0.95-1.05, free from central porosity and crack defects.

6. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 6, the large square billet obtained in step 5 is placed in a heating furnace and heated to 1180-1250℃. It is then cut into small square billets of 140mm×140mm, inspected and ground, with an average grinding depth ≥1.0mm. A coating layer with a thickness of 1.0~2.5mm is sprayed onto the surface of the ground small square billet. Then, it is heated and rolled in a heating furnace. The small square billet is heated to a temperature of 1100-1160℃, and the initial rolling temperature is controlled at 960-1020℃.

7. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 7, the rolled wire rod obtained in the rolling process is subjected to temperature-controlled air cooling. The wire drawing temperature of the air cooling line is controlled at 860-930℃. The air volume of the Stelmo air cooling line fan is adjusted according to the steel composition to obtain silicon-manganese killed high carbon steel wire rod with a C segregation index of 0.96-1.04, a sorbitization rate of ≥97%, and no surface defects.

8. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, The low-carbon carburizing agent added during converter tapping and LF refining has a nitrogen content of ≤0.025%, with the remainder being carbon and unavoidable impurity elements; The content of Mn in metallic manganese is ≥99%, Al content is ≤0.0035%, Ti content is ≤0.0015%, P content is ≤0.008%, S content is ≤0.004%, and the remainder is iron and unavoidable impurity elements; Silicon carbide contains ≥98% SiC, ≤0.0065% Al, ≤0.0055% Ti, and other unavoidable impurity elements; Low-titanium, low-aluminum ferrosilicon contains 75%–80% Si, ≤0.005% Al, ≤0.002% Ti, ≤0.01% P, and ≤0.005% S, with the remainder being iron and unavoidable impurity elements. Ferrochrome contains 55%–60% Cr, ≤1.5% C, ≤0.015% P, ≤0.0065% Al, ≤0.0025% Ti, with the remainder being iron and unavoidable impurity elements. Ferrovanadium contains 45%–50% V, ≤0.012% P, ≤0.005% Al, ≤0.003% Ti, with the remainder being iron and unavoidable impurity elements.

9. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, The bottom bricks, molten pool bricks, and ladle mouth bricks of the ladle are all made of magnesia bricks. In these magnesia bricks, the Al2O3 content is ≤2.5%, the C content is ≤8%, and the remainder is MgO and other unavoidable components. The slag line bricks and permeable bricks of the ladle are made of magnesia-zirconium-carbon bricks. In these magnesia-zirconium-carbon bricks, the ZrO2 content is 10%–15%, the Al2O3 content is ≤1.5%, the C content is ≤5%, and the remainder is MgO and other unavoidable components. In the bottom bricks, molten pool bricks, ladle mouth bricks, and slag line bricks of the ladle, the proportion of magnesia sand particles >5mm exceeds 80%, and the density is 2.8–3.5 g / cm³. 3 Flexural strength 38-42MPa, porosity ≤10%.

10. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, In step 4, the refractory material used for the impregnation tube and bottom tank of the RH vacuum furnace is magnesia-chrome ultra-low carbon brick, wherein the C content is ≤1.5%, MgO: 80%~90%, Cr2O3: 5%~10%, magnesium aluminum spinel: 4%~6%, and other unavoidable impurities; the proportion of magnesia sand particles with a size of 5~25mm in the magnesia-chrome ultra-low carbon brick exceeds 75%, and the density is 3.2~3.8g / cm³. 3 Flexural strength 43-48MPa, porosity ≤8%.

11. The method for controlling inclusions in silicon-manganese killed high-carbon steel according to claim 1, characterized in that, The long nozzle of the ladle used in the continuous casting process is made of corundum, with Al2O3 ≥ 96% and small amounts of other unavoidable components, and a density of 3.2–3.6 g / cm³. 3 The porosity is ≤12%, and the inner wall of the long nozzle is coated with MgSiO3 coating with a thickness of ≥5mm. It is baked for >3.5 hours before use at a temperature of ≥1400℃. The inner wall of the intermediate ladle is coated with a magnesium coating, wherein the magnesium coating contains ≥90% MgO, ≤2% Al2O3, and other unavoidable components, and the magnesium coating has a density of 2.6–3.0 g / cm³ after drying. 3 ; The tundish retaining wall is a magnesium-zirconium-carbon retaining wall, wherein MgO: 80%–90%, ZrO2: 5%–15%, Al2O3 ≤ 3%, ZrO2 content ≥ 10% at the slag line position, and other unavoidable components, with a density of 2.8–3.2 g / cm³. 3 Porosity ≤13%; The upper and lower water inlets and the immersion water inlet of the intermediate tundish are all made of magnesium carbonaceous material. In the magnesium carbonaceous water inlet, MgO: 80%~90%, C≤10%, Al2O3≤1.5%, and other unavoidable components. The tundish flow control plug rod body is made of magnesium-carbon material, with MgO: 80%~90%, C≤15%, Al2O3≤3%, and other unavoidable components; the slag line position and rod head are made of magnesium-zirconium-carbon, with MgO: 80%~85%, ZrO2: 10%~15%, Al2O3≤1.5%, and other unavoidable components.

12. A silicon-manganese killed high-carbon steel prepared by the method for controlling inclusions in silicon-manganese killed high-carbon steel according to any one of claims 1-11, characterized in that, The inclusions in the silicon-manganese killed high-carbon steel include silicate inclusions, with an average Al2O3 content of ≤5% in inclusions larger than 1 μm, and brittle inclusions of alumina, titanium oxide, and magnesium aluminum spinel ≤5 μm in size, with a total number density of brittle inclusions larger than 1 μm ≤0.00035 inclusions / mm. 2 .

13. The silicon-manganese killed high-carbon steel according to claim 12, characterized in that, Silicon manganese killed high carbon steel wire rod, when subjected to ultra-high cycle fatigue tests under loads of 600-800MPa, exhibits a fatigue life ≥1.5 million cycles. When drawing steel cord or diamond wire with a diameter ≥0.05mm from silicon manganese killed high carbon steel, the frequency of wire breakage caused by inclusions is ≤1.5 times / ton. Cable steel made from silicon manganese killed high carbon steel, during torsion testing, exhibits no fracture caused by inclusions after ≥25 torsion cycles.

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