A method for producing steel fibered wire rod

Abstract

The application provides a steel fiber wire rod production method, and belongs to the technical field of metallurgy, which comprises six processes of smelting, continuous casting, heating, sectional controlled rolling, gradient controlled cooling after wire drawing, and surface regulation and control.The chemical composition of the wire rod is as follows in terms of mass percentage: C: 0.12-0.18%, Si: ≤0.12%, Mn: 0.4-0.55%, P: ≤0.035%, S: ≤0.035%, Nb: 0.01-0.03%, V: 0.02-0.04%, and the rest is Fe and inevitable impurities, the smelting contains calcium treatment and RH vacuum refining, the continuous casting uses electromagnetic stirring, the heating is three-stage temperature control, the sectional controlled rolling contains asynchronous rolling, the wire drawing is followed by three-stage gradient cooling, and the surface is regulated and controlled through a weak reducing atmosphere and online shot blasting.The steel fiber wire rod production method provided by the application realizes accurate matching of strength and plasticity, reduces the wire breakage rate and production cost, and guarantees the stability of the product.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical technology, and more specifically, relates to a method for producing steel fiber wire rod. Background Technology

[0002] As a reinforcing material for concrete, steel fibers can significantly improve the tensile strength, flexural strength, impact toughness, and crack resistance of concrete. Their production and processing methods mainly include wire cutting, melting and drawing, and milling. Among these, wire cutting has become the mainstream production process due to its advantages such as high production efficiency, good fiber dimensional uniformity, and stable mechanical properties. Wire cutting requires hot-rolled wire rods to be cold-drawn multiple times and then cut into steel fibers. This places extremely high demands on the comprehensive performance of the wire rods: on the one hand, they need sufficient strength to ensure that the final steel fibers reach the target strength level; on the other hand, they need excellent plasticity to adapt to the large deformation drawing process. Simultaneously, the content and morphology of inclusions must be controlled, and surface quality optimized to reduce the risk of wire breakage during drawing and cutting.

[0003] Patent 201710304551.0 discloses a "hot-rolled wire rod for ultra-low carbon steel fiber and its production method". It adopts an ultra-low carbon composition of C≤0.010% and adds Ti element to achieve fine grain strengthening. The tensile strength of the wire rod is only 310-360MPa. Although the elongation after fracture is relatively high (≥50.0%), the strength is low. This means that the amount of drawing deformation needs to be greatly increased to meet the requirements of 1300MPa level steel fiber. This not only increases the processing cost, but also significantly increases the probability of wire breakage.

[0004] Patent 202411392801.7 discloses a "production method of hot-rolled wire rod for low-carbon alloy steel fiber". By adding multiple alloying elements such as Cr, Ti, and B, the tensile strength of the wire rod can reach 550-600MPa. However, the large amount of alloying elements added significantly increases the production cost, and its wire drawing temperature is relatively low (760-790℃), which easily leads to excessively fine pearlite lamellae, reduced plasticity, and insufficient toughness during the drawing process.

[0005] Therefore, developing a method for producing steel fiber wire rods that achieves a precise match between strength and plasticity has become a pressing technical problem to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a method for producing steel fiber wire rod, which aims to solve the problem of poor matching between wire rod strength and plasticity in existing wire rod production technology. Either the strength is too low, resulting in large drawing deformation and high wire breakage rate, or the strength is too high, resulting in insufficient plasticity and poor toughness.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: a method for producing steel fiber wire rod, including smelting, continuous casting, heating, segmented controlled rolling, wire stripping gradient controlled cooling, and surface conditioning processes. The chemical composition of the wire rod, by mass percentage, is: C: 0.12-0.18%, Si: ≤0.12%, Mn: 0.4-0.55%, P: ≤0.035%, S: ≤0.035%, Nb: 0.01-0.03%, V: 0.02-0.04%, with the remainder being Fe and unavoidable impurities.

[0008] In one possible implementation, the mass ratio of Nb to V in the chemical composition of the wire rod is 1:2 to 1:3, and the total mass percentage of Nb and V is ≤0.06%.

[0009] In one possible implementation, the smelting process includes the following steps:

[0010] Converter smelting: blast furnace molten iron is fed into a converter for smelting, and the oxygen supply intensity, carbon content, phosphorus content and tapping temperature at the end of smelting are controlled to obtain crude steel that meets the requirements of subsequent refining.

[0011] Inclusion morphology control: During or after the tapping process in the converter, calcium treatment is performed on the molten steel to transform hard and brittle inclusions in the molten steel into spherical inclusions.

[0012] LF furnace refining: The molten steel after the inclusion morphology has been adjusted is sent into the LF furnace, slag-forming agent is added to adjust the slag basicity, the temperature is raised and held, and the molten steel is dephosphorized, desulfurized and its composition is finely adjusted.

[0013] RH furnace refining: The molten steel refined in the LF furnace is sent to the RH furnace for vacuum treatment, and gases and inclusions in the molten steel are removed through decarburization and circulation operation.

[0014] In one possible implementation, the calcium treatment involves adding a silicon-calcium alloy in 2 to 3 batches of molten steel at a ratio of 0.8 to 1.2 kg / t, with a 3-minute interval between each batch; after the calcium treatment, the molten steel is left to stand in the ladle for 5 to 8 minutes.

[0015] In one possible implementation, the continuous casting process employs electromagnetic stirring in the crystallizer, with a stirring current of 280–320 A and a frequency of 3–5 Hz; the superheat of the molten steel in the continuous casting process is controlled at 20–25 °C, the casting speed is 2.0–2.2 m / min, and the secondary cooling water volume is 0.7–0.9 L / kg.

[0016] In one possible implementation, the heating process employs a pusher-type heating furnace to heat the steel billet in three stages, including:

[0017] In the preheating section, the steel billet is gradually heated to 800-850℃ and held for 20-25 minutes;

[0018] In the heating section, the steel billet is heated to 950–980℃ and stabilized for 30–40 minutes.

[0019] In the soaking zone, the steel billet is heated to 990–1010℃ and held for 60–80 minutes.

[0020] In one possible implementation, the heating rate of the heating section is 5–8 °C / min.

[0021] In one possible implementation, the segmented controlled rolling process includes:

[0022] Roughing and intermediate rolling, initial rolling temperature 970–990℃, total reduction rate 75–80%;

[0023] Pre-finishing rolling, with an inlet temperature of 920–940℃, a total reduction of 40–45%, and an asynchronous rolling mode with an upper and lower roll speed ratio of 1.05–1.1;

[0024] Finishing rolling: inlet temperature 890–910℃, total reduction 50–55%, and final rolling speed 10–12 m / s.

[0025] In one possible implementation, the coiling gradient cooling process employs a Stellmore cooling line to perform three-stage continuous cooling on the coiled wire, with a coiling temperature of 860–880°C. The three-stage continuous cooling process includes, in sequence:

[0026] The initial cooling is slow, with a wind speed of 2-3 m / s, a cooling rate of 0.8-1.2℃ / s, and a cooling time of 8-10 s;

[0027] The intermediate isothermal transition has an isothermal temperature of 820–840℃ and an isothermal time of 12–15 seconds.

[0028] The rear section is air-cooled with a wind speed of 3-4 m / s and a cooling rate of 1.5-2.0℃ / s. After cooling to 550-580℃, it is allowed to cool naturally.

[0029] In one possible implementation, the surface conditioning process includes furnace atmosphere control and online shot blasting of wire rods;

[0030] The atmosphere control of the heating furnace is to introduce natural gas and air into the heating furnace at a mixing ratio of 1:1.05 to 1:1.1 to maintain a weak reducing atmosphere. The oxygen content in the heating furnace is ≤3%. The atmosphere control is carried out throughout the entire heating process.

[0031] The online shot blasting treatment of the wire rod is carried out when the wire rod temperature drops to 600-650℃, with a shot blasting intensity of 0.15-0.20MPa and a shot blasting time of 3-5s.

[0032] The beneficial effects of the steel fiber wire rod production method provided by this invention are as follows: Compared with the prior art, the steel fiber wire rod production method of this invention, by precisely controlling the C content (0.12-0.18%) and the composite ratio of Nb and V (1:2-1:3, total ≤0.06%), combined with a three-stage heating, segmented controlled rolling and gradient controlled cooling process, makes the wire rod microstructure a uniform ferrite / pearlite, which not only ensures that the tensile strength meets the target requirements of steel fiber, but also has excellent plasticity. It avoids the problems of "low strength leading to large drawing deformation and high wire breakage rate" or "high strength but insufficient plasticity and poor toughness" in the prior art, and significantly improves the drawing adaptability. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The image shows the microstructure of the wire rod in the embodiment. Detailed Implementation

[0035] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0036] The present invention provides a method for producing steel fiber wire rod. This method includes smelting, continuous casting, heating, segmented controlled rolling, gradient controlled cooling during wire drawing, and surface conditioning processes.

[0037] In production, the chemical composition of wire rod directly determines the stability of subsequent smelting, continuous casting, rolling, and other processes, as well as the performance of the final product. In existing technologies, for example, patent 201710304551.0 discloses a "hot-rolled wire rod for ultra-low carbon steel fiber and its production method," which uses an ultra-low carbon composition (C≤0.010%). While this composition exhibits excellent plasticity, its basic strength is insufficient, requiring a large amount of Ti (0.05~0.12%) to refine the grains, leading to increased alloy costs. Another example is patent 202411392801.7, which discloses a "production method for hot-rolled wire rod for low-carbon alloy steel fiber," adding multiple alloys such as Cr, Ti, and B. While this improves strength, the alloy system is complex, making raw material procurement and proportioning difficult, resulting in higher production costs.

[0038] In this invention, the chemical composition of the wire rod, by mass percentage, is as follows: C: 0.12–0.18%, Si: ≤0.12%, Mn: 0.4–0.55%, P: ≤0.035%, S: ≤0.035%, Nb: 0.01–0.03%, V: 0.02–0.04%, with the remainder being Fe and unavoidable impurities. The mass ratio of Nb to V in the wire rod's chemical composition is 1:2 to 1:3, and the total mass percentage of Nb and V is ≤0.06%.

[0039] In applications, carbon (C) is a core element affecting the strength and ductility of steel. Too low a C content (e.g., ≤0.01%) leads to insufficient pearlite content, resulting in low basic strength of the wire rod; too high a C content (e.g., >0.2%) causes thicker pearlite lamellars, increased hardness, and a significant decrease in ductility, making the wire rod prone to brittle fracture during drawing. Therefore, the C content needs to be controlled between 0.12% and 0.18% to balance the basic strength provided by pearlite with the ductility provided by ferrite.

[0040] Si is a deoxidizing element, but excessive Si will increase the brittleness of steel and reduce the plasticity and drawing properties of wire rod. In particular, wire rod is prone to cracking during cold working. Therefore, the Si content is limited to ≤0.12%.

[0041] Mn can strengthen ferrite through solid solution, improve the hardness and strength of pearlite, and enhance the hot workability of steel. However, excessive Mn can increase the hardenability of steel and easily form a hard and brittle structure during cooling. Therefore, the Mn content should be controlled between 0.4% and 0.55% to achieve a balance between strength enhancement and plasticity retention.

[0042] P and S are harmful impurities in steel. P easily causes cold brittleness in steel, while S easily forms low-melting-point sulfides such as FeS, which can cause hot brittleness in steel during hot working. Both can significantly reduce the toughness and drawing performance of wire rod. Therefore, it is necessary to strictly control the P content to ≤0.035% and the S content to ≤0.035%.

[0043] Both Nb and V are microalloying elements that enhance wire rod strength through grain refinement and precipitation strengthening. Nb(C,N) formed during heating inhibits austenite grain growth, thus achieving grain refinement. V(C,N) precipitated during cooling produces precipitation strengthening, increasing wire rod strength. Adding either Nb or V alone is insufficient to simultaneously achieve both strengthening and plasticity. Combining them can have a synergistic effect, but an improper ratio can lead to over-strengthening and decreased plasticity. Furthermore, excessively high total content increases production costs and introduces more inclusions. Therefore, the mass ratio of Nb to V is limited to 1:2 to 1:3, with a total mass ≤0.06%.

[0044] The wire rod with the chemical composition provided by the present invention has a microstructure mainly composed of uniform ferrite and pearlite, without abnormal structures such as Widmanstätten or martensite.

[0045] In the method of the present invention, the smelting process includes converter smelting, inclusion morphology control, LF furnace refining, and RH furnace refining steps.

[0046] In converter smelting, molten iron from the blast furnace is fed into a converter for smelting. The oxygen supply intensity, carbon and phosphorus content at the smelting endpoint, and tapping temperature are controlled to obtain rough steel that meets the requirements of subsequent refining. Specifically, the molten iron from the blast furnace is fed into a top-and-bottom blown converter, and after pretreatment, the sulfur content is ≤0.015%; the oxygen supply intensity is controlled at 3.0–3.5 mg / L. 3 / (t The process employs a "high carbon content and low oxygen consumption" method, controlling the carbon content at the smelting endpoint to 0.06-0.08%, the phosphorus content to ≤0.018%, and the tapping temperature to 1640-1660℃. During the tapping process, lime, fluorite, and other slag-forming agents are added to initially adjust the slag basicity to 1.2-1.5.

[0047] Inclusion morphology control involves calcium treatment of the rough steel during or after tapping in the converter, which transforms hard and brittle inclusions in the steel into spherical inclusions.

[0048] The reason for controlling the morphology of inclusions is that inclusions such as Al2O3 and SiO2 in molten steel are hard and brittle phases, which are prone to cutting the matrix during drawing, leading to wire breakage. Therefore, calcium treatment is needed to transform them into spherical calcium aluminate inclusions, reducing the stress concentration effect. The specific operation of this step is as follows: Select a silicon-calcium alloy with a Ca content ≥30%, and add it to the roughing steel in 2-3 batches at a ratio of 0.8-1.2 kg / t of molten steel, with an interval of 3 minutes between each batch to ensure uniform distribution and full reaction of calcium. After calcium treatment, let the roughing steel stand in the ladle for 5-8 minutes to allow the generated spherical inclusions to float and separate fully, avoiding the accumulation of inclusions in the molten steel.

[0049] After calcium treatment, the conversion rate of hard and brittle inclusions in molten steel is ≥90%, the proportion of spherical inclusions is ≥85%, and the size of inclusions is ≤5μm, thus avoiding wire breakage caused by inclusions during the drawing process.

[0050] LF furnace refining involves feeding molten steel, after inclusion morphology control, into an LF furnace, adding slag-forming agents to adjust slag basicity, raising and holding the temperature to dephosphorize, desulfurize, and fine-tune the composition of the molten steel. Specifically, calcium-treated molten steel is fed into the LF furnace, and slag-forming agents such as lime and bauxite are added to adjust the slag basicity to 1.8–2.2, forming reducing slag. Submerged arc heating is used to raise the temperature of the molten steel to 1650–1670℃ and hold it for 30–40 minutes. During this time, argon gas stirring (stirring intensity 0.3–0.5 m / s) promotes the steel-slag reaction, achieving dephosphorization (final phosphorus ≤ 0.035%) and desulfurization (final sulfur ≤ 0.035%). Based on ICP-OES test results, alloys such as ferromanganese, ferroniobium, and ferrovanadium are added for composition fine-tuning to ensure that the content of each element meets the above-mentioned requirements for the chemical composition of the wire rod.

[0051] RH furnace refining involves sending molten steel refined in an LF furnace into an RH furnace for vacuum treatment. Through decarburization and circulation, gases and inclusions are removed from the molten steel. RH furnace vacuum treatment effectively removes gases such as H and N, as well as fine inclusions, improving the cleanliness of the steel and preventing gas bubbles from forming in the wire rod. The specific operation of RH furnace refining is as follows: molten steel refined in an LF furnace is sent into an RH furnace for vacuum treatment, with the vacuum level controlled at ≤67 Pa for 15–20 min; circulating argon gas is used for stirring, with an argon flow rate of 150–200 L / min to promote the flotation and removal of H and N gases and fine inclusions in the molten steel; after treatment, the molten steel is allowed to stand in the RH furnace for 5–10 min to further improve its cleanliness.

[0052] In the method of this invention, the continuous casting process adopts an arc-shaped continuous casting machine, and the crystallizer is a copper-plated crystallizer; the tundish adopts an integral nozzle to avoid uneven steel flow caused by nozzle nodules; the crystallizer is protected with a special protective slag for medium carbon steel, with a melting point of 1200-1250℃ and a viscosity of 0.8-1.2 Pa·s, to ensure that the protective slag evenly covers the surface of the molten steel and prevents secondary oxidation.

[0053] The process parameters for continuous casting include: controlling the superheat of molten steel at 20–25°C, adjusting it in real time through tundish temperature monitoring to avoid fluctuations in superheat; maintaining a stable casting speed of 2.0–2.2 m / min, using a constant casting speed control mode to reduce the impact of casting speed fluctuations on billet quality; using water mist cooling for secondary cooling, with a water volume controlled at 0.7–0.9 L / kg, and dividing the cooling zone into fan-shaped sections 1 (strong cooling zone), 2–3 (medium cooling zone), and 4–5 (weak cooling zone) from the crystallizer outlet to ensure a uniform decrease in billet surface temperature; and using electromagnetic stirring in the crystallizer with a stirring current of 280–320 A and a frequency of 3–5 Hz, employing an alternating stirring mode to promote molten steel mixing and grain refinement.

[0054] During continuous casting, the superheat of molten steel directly affects the grain size of the billet. Excessive superheat (>25℃) will result in coarse austenite grains, making it difficult to refine them during subsequent rolling. Insufficient superheat (<20℃) will increase the resistance to the flow of molten steel, making it easy to produce defects such as incomplete filling and slag inclusions.

[0055] Too fast a casting speed will lead to faster solidification of the billet, severe component segregation, and easy cracking; too slow a casting speed will reduce production efficiency and increase energy consumption.

[0056] Excessive secondary cooling water volume can cause a sudden change in the surface temperature gradient of the billet, resulting in cracks; insufficient volume will cause the center temperature of the billet to be too high, prolonging the solidification time and exacerbating component segregation.

[0057] Electromagnetic stirring in the crystallizer can break up the solidified shell, promote uniform mixing of molten steel, reduce component segregation, refine the grain size of the billet, and improve the uniformity of the billet structure.

[0058] In the method of the present invention, the continuous casting process uses a pusher-type heating furnace to heat the steel billet in three stages, including a preheating stage, a heating stage, and a soaking stage.

[0059] In application, the pusher-type heating furnace is divided into three zones: preheating zone, heating zone, and soaking zone. The temperature and atmosphere of each zone are independently controlled. Natural gas is used for heating inside the furnace, and the excess air coefficient is controlled between 1.05 and 1.1.

[0060] The preheating section gradually raises the temperature of the steel billet to 800-850℃ and holds it for 20-25 minutes, with the heating rate controlled at 3-5℃ / min to avoid thermal stress caused by rapid heating of the steel billet.

[0061] The heating section involves raising the preheated steel billet to 950–980°C at a rate of 5–8°C / min and holding it at that temperature for 30–40 minutes to ensure that the surface and core temperatures of the steel billet gradually approach each other, thus initiating the austenitization transformation.

[0062] The soaking zone involves raising the temperature of the preheated steel billet to 990–1010℃ and holding it at that temperature for 60–80 minutes. During this period, the temperature inside the furnace is monitored (every 10 minutes) to ensure that the temperature difference between the inside and outside of the steel billet is ≤30℃, so that austenitization is complete and the grains are uniform.

[0063] In applications, pusher-type heating furnaces are characterized by their large heating capacity, but their heating uniformity is easily affected by temperature gradients. If a single heating temperature or an excessively fast heating rate is used, it can lead to an excessive temperature difference between the inside and outside of the steel billet, generating thermal stress and even causing cracks.

[0064] The preheating section is used to gradually increase the temperature of the billet, reduce the temperature difference between the billet and the furnace, and avoid thermal shock. The heating section is used to raise the temperature of the billet to the austenitizing temperature to ensure that the billet is fully austenitized. The soaking section is used to eliminate the temperature difference between the inside and outside of the billet and the non-uniformity of the microstructure, so that the austenite grains grow uniformly.

[0065] Excessively high heating temperature (>1010℃) will result in coarse austenite grains, making it difficult to refine them during subsequent rolling and easily forming a mixed-grain structure; excessively low heating temperature (<990℃) will result in incomplete austenitization, affecting plastic deformation and microstructure control during the rolling process.

[0066] If the heating rate in the heating section is too fast (>8℃ / min), it will exacerbate the temperature difference between the inside and outside of the steel billet and generate thermal stress; if it is too slow (<5℃ / min), it will reduce production efficiency and increase energy consumption.

[0067] In the method of the present invention, the segmented controlled rolling process includes roughing and intermediate rolling, pre-finishing rolling, and finishing rolling.

[0068] In the roughing and intermediate rolling processes, seven horizontally arranged short-stress rolling mills (roughing mills) and eight horizontally arranged short-stress rolling mills (intermediate mills) are configured, each with independent drive. The rolls are made of high-speed steel. The process parameters for roughing and intermediate rolling are as follows: initial rolling temperature 970–990℃, controlled by monitoring the furnace exit temperature and maintaining the roller table temperature; total reduction rate 75–80%, single-pass reduction rate controlled at 15–20% to avoid excessive reduction rate leading to surface cracking of the billet; rolling speed gradually increasing, with the roughing mill exit speed at 1.5–2.0 m / s and the intermediate mill exit speed at 4.0–5.0 m / s; high-pressure water descaling is performed before roughing and after intermediate rolling, with a water pressure of 18–20 MPa and a water flow velocity of 30–35 m / s to remove iron oxide scale from the billet surface.

[0069] The pre-finishing rolling process is equipped with four cantilever rolling mills arranged alternately in a horizontal and vertical configuration. Each mill is driven independently and uses an asynchronous rolling mode. The process parameters are as follows: inlet temperature 920-940℃, controlled by a two-stage cooling water tank between the intermediate and pre-finishing mills, with a cooling water volume of 50-60 m³ / h; total reduction rate 40-45%, single-pass reduction rate 10-12%; upper and lower roll speed ratio 1.05-1.1, with the upper roll speed higher than the lower roll, thereby generating shear deformation to refine the grains; exit speed 7.0-8.0 m / s.

[0070] The finishing rolling process utilizes an 8-stand, 45° cantilevered rolling mill with collective drive. The rolls are coated with tungsten carbide to improve wear resistance and dimensional accuracy. Process parameters are as follows: inlet temperature 890–910℃, controlled by a cooling water tank between the pre-finishing and finishing mills, with a cooling water flow rate of 70–80 m³ / h; total reduction rate 50–55%, single-pass reduction rate 8–10% to ensure uniform deformation; final rolling speed 10–12 m / s, adjusted by mill speed. A laser diameter gauge is installed at the finishing mill exit to monitor the wire rod diameter in real time, controlling dimensional tolerances within ±0.1 mm to ensure uniform wire rod specifications.

[0071] In this invention, the core of segmented controlled rolling is to achieve gradual refinement of austenite grains by controlling the temperature and reduction rate at different stages, thereby improving the strength of the wire rod by combining fine grain strengthening, while maintaining good plasticity.

[0072] The roughing and intermediate rolling stages need to be carried out at relatively high temperatures to utilize the good plasticity of the billet to achieve a large reduction rate deformation, breaking down the coarse austenite grains and laying the foundation for subsequent refinement. If the initial rolling temperature is too high (>990℃), it will cause austenite grain growth, while if it is too low (<970℃), it will increase the rolling force and easily produce rolling cracks.

[0073] During the pre-finishing rolling stage, the temperature needs to be reduced and asynchronous rolling should be adopted. Asynchronous rolling generates shear deformation through the speed difference between the upper and lower rolls, which further refines the grains. At the same time, the reduction rate should be controlled to avoid excessive deformation that leads to a decrease in plasticity.

[0074] The finishing rolling stage needs to be carried out at a relatively low temperature. Through a combination of high reduction rate deformation and rapid cooling, the transformation of austenite to ferrite / pearlite is achieved, refining the transformation microstructure and improving the strength and hardness of the wire rod. If the inlet temperature is too high (>910℃), it will result in coarse grains after transformation, while if it is too low (<890℃), it will increase the rolling difficulty and affect dimensional accuracy.

[0075] In the method of this invention, during the gradient cooling process of wire drawing, a wire drawing machine with grooved pinch rollers is used. The pressure of the pinch rollers is controlled at 0.3–0.5 MPa to avoid indentations on the surface of the wire rod during pinching. The wire drawing temperature is 860–880°C, and is adjusted in real time by temperature detection between the finishing mill exit and the wire drawing machine. If the temperature is too high, the water volume in the cooling water tank is increased; if the temperature is too low, the cooling water volume is reduced or the roller table insulation device is activated.

[0076] The Stellmore cooling line is used to cool the coils after spinning. In practice, the Stellmore cooling line is divided into three sections: the front section (sections 1-3), the middle section (sections 4-6), and the rear section (sections 7-9). The wind speed and the state of the insulation cover are independently controlled in each section to continuously cool the coils after spinning in three sections.

[0077] The initial slow cooling process involves closing the insulation cover, controlling the wind speed at 2–3 m / s, the cooling rate at 0.8–1.2℃ / s, and the cooling time at 8–10 s, thereby reducing the wire rod temperature from 860–880℃ to 820–840℃.

[0078] The mid-section isothermal transition is switched to open insulation cover, with wind speed controlled at 0.5-1.0 m / s, maintaining isothermal temperature at 820-840℃, and insulation time at 12-15s to ensure uniform transformation of pearlite, with pearlite lamellar spacing controlled at 0.2-0.3 μm.

[0079] The rear air-cooling section involves closing the insulation cover, increasing the air velocity to 3-4 m / s, and the cooling rate to 1.5-2.0℃ / s, cooling the wire rod temperature to 550-580℃, and then allowing it to cool naturally to room temperature.

[0080] In this process, the spinning temperature is a key parameter for controlling the pearlite transformation. If it is too high (>880℃), the pearlite transformation time will be prolonged, the lamellars will be coarse, and the strength will be insufficient; if it is too low (<860℃), the transformation speed will be too fast, the pearlite lamellars will be too fine, and the plasticity will decrease.

[0081] If the cooling rate of low carbon steel is too fast (>2.0℃ / s), Widmanstätten structure is easily generated, while if it is too slow (<0.8℃ / s), pearlite grains will become coarse. Therefore, gradient cooling and segmented control of the cooling rate are required.

[0082] The purpose of the initial slow cooling is to reduce the temperature difference between the surface and the core of the wire rod to avoid thermal stress; the middle isothermal transformation ensures uniform nucleation and growth of pearlite, forming a uniform pearlite structure; the subsequent air cooling is to rapidly cool to the pearlite transformation termination temperature, fix the structure morphology, and prevent abnormal structures from being generated in subsequent transformations.

[0083] The method of this invention also includes a surface conditioning process. In application, an excessively strong oxidizing atmosphere in the heating furnace can cause a thick and hard Fe2O3 iron oxide scale to form on the surface of the wire rod. During cold drawing, this scale can easily scratch the steel wire or cause the iron oxide scale to be pressed into the matrix, leading to wire breakage. After wire drawing, the surface of the wire rod may have a small amount of iron oxide scale or minor defects (such as scratches or burrs). Therefore, a surface conditioning process is required during the heating process and after the wire drawing gradient controlled cooling process.

[0084] Specifically, the surface conditioning process includes furnace atmosphere control and online shot blasting of wire rods. Furnace atmosphere control involves introducing natural gas and air into the furnace at a mixing ratio of 1:1.05 to 1:1.1 to maintain a weakly reducing atmosphere. The oxygen content in the furnace is ≤3%, and this atmosphere control is maintained throughout the entire heating process. This furnace atmosphere control creates a weakly reducing atmosphere within the furnace, reducing the formation of iron oxide scale and ensuring that the scale is primarily composed of easily detachable FeO.

[0085] The online shot blasting of the wire rod is carried out between the outlet of the Stellmore cooling line and the coil collecting device using a centrifugal shot blasting machine. The shot material is high-carbon steel shot with a diameter of 0.2–0.3 mm. The shot blasting is performed when the wire rod temperature drops to 600–650℃, at which point the iron oxide scale has a weaker bond with the substrate and is easier to remove. The shot blasting intensity is 0.15–0.20 MPa, the shot blasting time is 3–5 seconds, the shot flow rate is 50–60 kg / min, and the shot blasting angle is 45° to ensure uniform shot blasting on the wire rod surface. After shot blasting, high-pressure air purging (pressure 0.6–0.8 MPa) is used to remove residual shot and iron oxide scale powder from the wire rod surface.

[0086] The present invention provides a method for producing steel fiber wire rod. Compared with the prior art, by precisely controlling the C content (0.12-0.18%) and the composite ratio of Nb and V (1:2-1:3, total ≤0.06%), and combining it with a three-stage heating, segmented controlled rolling and gradient controlled cooling process, the microstructure of the wire rod is made into uniform ferrite / pearlite. This ensures that the tensile strength meets the target requirements of steel fiber and also has excellent plasticity. It avoids the problems of "low strength leading to large drawing deformation and high wire breakage rate" or "high strength but insufficient plasticity and poor toughness" in the prior art, and the drawing adaptability is significantly improved.

[0087] This method uses only two microalloying elements, Nb and V, for synergistic strengthening, without the need to add multiple high-priced alloys such as Cr, Ti, and B. Moreover, the total content of microalloys is ≤0.06%. Compared with existing multi-alloy system schemes, the raw material procurement and proportioning costs are lower, while reducing the risk of inclusions introduced by excessive alloys.

[0088] The smelting process of this method transforms hard and brittle inclusions into spherical shapes through calcium treatment, and combines it with vacuum degassing and impurity removal in an RH furnace to reduce the cutting of the matrix by gases and inclusions; surface control (weak reducing atmosphere) reduces the formation of iron oxide scale and efficiently removes residual defects, avoiding scratches or iron oxide scale pressing in during drawing, and further reducing the probability of wire breakage.

[0089] Example

[0090] I. Chemical composition of wire rod (mass percentage)

[0091] C: 0.15%, Si: 0.10%, Mn: 0.48%, P: 0.030%, S: 0.028%, Nb: 0.02%, V: 0.04% (Nb to V mass ratio 1:2, total content 0.06%), the remainder being Fe and unavoidable impurities.

[0092] II. Process Implementation Parameters

[0093] 1. Smelting process

[0094] Converter smelting: oxygen supply intensity 3.2m 3 / (t (min), the final carbon content of the smelting process is 0.07% and the phosphorus content is 0.016%, and the tapping temperature is 1650℃;

[0095] Inclusion morphology control: Select a silicon-calcium alloy containing ≥30% Ca, add it in two batches at a ratio of 1.0 kg / t molten steel, with an interval of 3 min, and let the ladle stand for 6 min;

[0096] LF furnace refining: slag basicity 2.0, temperature raised to 1660℃, held for 35 min, argon stirring intensity 0.4 m / s, to complete dephosphorization, desulfurization and composition fine-tuning;

[0097] RH furnace refining: vacuum degree ≤67Pa, processing time 18min, circulating argon flow rate 180L / min, and settling time 8min after processing.

[0098] 2. Continuous casting process

[0099] The crystallizer has an electromagnetic stirring current of 300A and a frequency of 4Hz; a steel superheat of 22℃; a casting speed of 2.1m / min; a secondary cooling water volume of 0.8L / kg; and a protective slag melting point of 1230℃ and a viscosity of 1.0Pa·s.

[0100] 3. Heating process (three-stage heating in a pusher-type heating furnace)

[0101] Preheating section: Heat to 830℃, hold for 22 minutes, heating rate 4℃ / min;

[0102] Heating section: Heat to 960℃, hold for 35 minutes, heating rate 6℃ / min;

[0103] Heat soaking section: Heat to 1000℃ and hold for 70 minutes, with the temperature difference between the inside and outside of the billet ≤30℃.

[0104] 4. Segmented controlled rolling process

[0105] Roughing and intermediate rolling: initial rolling temperature 980℃, total reduction rate 78%, single-pass reduction rate 18%, high-pressure water descaling pressure 19MPa;

[0106] Pre-finishing rolling: inlet temperature 930℃, total reduction rate 42%, upper and lower roll speed ratio 1.08, exit speed 7.5m / s;

[0107] Finishing rolling: inlet temperature 900℃, total reduction rate 52%, final rolling speed 11m / s, wire rod diameter tolerance ±0.1mm.

[0108] 5. Gradient cooling process for spinning silk.

[0109] The spinning temperature is 870℃, and it uses a three-stage cooling system with a Steyrmo cooling line.

[0110] Front-end slow cooling: air velocity 2.5m / s, cooling rate 1.0℃ / s, cooling time 9s;

[0111] Mid-section isothermal transition: isothermal temperature 830℃, holding time 13s;

[0112] Rear-stage air cooling: air velocity 3.5m / s, cooling rate 1.8℃ / s, cooled to 560℃ and then naturally cooled.

[0113] 6. Surface conditioning process

[0114] The natural gas to air mixing ratio in the heating furnace is 1:1.08, and the oxygen content is 2.2%. When the wire rod temperature drops to 620℃, online shot blasting is performed with a shot blasting intensity of 0.18MPa, a time of 4s, and a shot diameter of 0.25mm. Afterwards, it is purged with 0.7MPa high-pressure air.

[0115] III. Implementation Results

[0116] The steel fiber wire rod produced in this embodiment, combined with the attached... Figure 1 It is evident that the microstructure of the wire rod is uniformly distributed ferrite / pearlite (without abnormal structures such as Widmanstätten or martensite); mechanical tests show that its tensile strength reaches 580 MPa and its elongation after fracture is 32%; the wire breakage rate during drawing is ≤0.3%, achieving a precise match between strength and plasticity, thus reducing production costs and processing risks.

[0117] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing steel fiber wire rod, characterized in that, The process includes smelting, continuous casting, heating, segmented controlled rolling, wire drawing gradient controlled cooling, and surface conditioning. The chemical composition of the wire rod, by mass percentage, is: C: 0.12-0.18%, Si: ≤0.12%, Mn: 0.4-0.55%, P: ≤0.035%, S: ≤0.035%, Nb: 0.01-0.03%, V: 0.02-0.04%, with the remainder being Fe and unavoidable impurities. The chemical composition of the wire rod has a Nb to V mass ratio of 1:2 to 1:3, and the total mass percentage of Nb and V is ≤0.06%. in, The smelting process includes the following steps: Converter smelting: blast furnace molten iron is fed into a converter for smelting, and the oxygen supply intensity, carbon content, phosphorus content and tapping temperature at the end of smelting are controlled to obtain crude steel that meets the requirements of subsequent refining. Inclusion morphology control: During or after the tapping process in the converter, calcium treatment is performed on the molten steel to transform hard and brittle inclusions in the molten steel into spherical inclusions. LF furnace refining: The molten steel after the inclusion morphology has been adjusted is sent into the LF furnace, slag-forming agent is added to adjust the slag basicity, the temperature is raised and held, and the molten steel is dephosphorized, desulfurized and its composition is finely adjusted. RH furnace refining: The molten steel refined in the LF furnace is sent to the RH furnace for vacuum treatment. Gases and inclusions in the molten steel are removed through decarburization and circulation operations. The segmented controlled rolling process includes: Roughing and intermediate rolling, initial rolling temperature 970–990℃, total reduction rate 75–80%; Pre-finishing rolling, with an inlet temperature of 920–940℃, a total reduction of 40–45%, and an asynchronous rolling mode with an upper and lower roll speed ratio of 1.05–1.1; Finishing rolling: inlet temperature 890-910℃, total reduction 50-55%, final rolling speed 10-12m / s; The coiling gradient cooling process employs a Stellmore cooling line to perform three-stage continuous cooling on the coiled wire after coiling, with a coiling temperature of 860–880°C. The three-stage continuous cooling process includes: The initial cooling is slow, with a wind speed of 2-3 m / s, a cooling rate of 0.8-1.2℃ / s, and a cooling time of 8-10 s; The intermediate isothermal transition has an isothermal temperature of 820–840℃ and an isothermal time of 12–15 seconds. The rear section is air-cooled with a wind speed of 3-4 m / s and a cooling rate of 1.5-2.0℃ / s. After cooling to 550-580℃, it is allowed to cool naturally.

2. The method for producing steel fiber wire rod as described in claim 1, characterized in that, The calcium treatment involves adding a silicon-calcium alloy to the molten steel in 2-3 batches at a ratio of 0.8-1.2 kg / t, with a 3-minute interval between each batch. After the calcium treatment, the molten steel is left to stand in the ladle for 5-8 minutes.

3. The method for producing steel fiber wire rod as described in claim 1, characterized in that, The continuous casting process employs electromagnetic stirring in the crystallizer, with a stirring current of 280–320 A and a frequency of 3–5 Hz. The superheat of the molten steel in the continuous casting process is controlled at 20–25 °C, the casting speed is 2.0–2.2 m / min, and the secondary cooling water volume is 0.7–0.9 L / kg.

4. The method for producing steel fiber wire rod as described in claim 1, characterized in that, The heating process employs a pusher-type heating furnace to heat the steel billet in three stages, including: In the preheating section, the steel billet is gradually heated to 800-850℃ and held for 20-25 minutes; In the heating section, the steel billet is heated to 950–980℃ and stabilized for 30–40 minutes. In the soaking zone, the steel billet is heated to 990–1010℃ and held for 60–80 minutes.

5. A method for producing steel fiber wire rod as described in claim 4, characterized in that, The heating rate of the heating section is 5–8 °C / min.

6. The method for producing steel fiber wire rod as described in claim 1, characterized in that, The surface conditioning process includes furnace atmosphere control and online shot blasting of wire rods; The atmosphere control of the heating furnace is to introduce natural gas and air into the heating furnace at a mixing ratio of 1:1.05 to 1:1.1 to maintain a weak reducing atmosphere. The oxygen content in the heating furnace is ≤3%. The atmosphere control is carried out throughout the entire heating process. The online shot blasting treatment of the wire rod is carried out when the wire rod temperature drops to 600-650℃, with a shot blasting intensity of 0.15-0.20MPa and a shot blasting time of 3-5s.

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