High carbon steel wire rod and method for producing the same

Abstract

The application discloses a high-carbon steel wire rod and a production method thereof. In the production method, the heating rate of a preheating section is 10-15 DEG C / min, the heating rate of a heating section is 30-40 DEG C / min, and the heating rate from the heating section to a soaking section is 20-30 DEG C / min; the water cooling before finish rolling comprises two-stage water cooling with water flow being 500-550 L / min and 120-180 L / min in sequence; the water cooling after finish rolling comprises four-stage water cooling with water flow being 900-1000 L / min, 600-700 L / min, 200-400 L / min and 30-60 L / min in sequence; and in Stelmor cooling, when the temperature is equal to or greater than 850 DEG C, if a hardening factor F is less than or equal to 8, the cooling speed is controlled to be 20-28 DEG C / s, if 8

Description

Technical Field

[0001] This application belongs to the field of steel production and manufacturing technology, specifically relating to a method for producing high-carbon steel wire rod, and also to a high-carbon steel wire rod prepared based on the said production method. Background Technology

[0002] Various steel wire products made from wire rod are widely used in many aspects of society, such as automobiles, communication cables, bridges, and engineering machinery. Therefore, the performance requirements for wire rod are very strict, such as the surface quality of the wire rod.

[0003] During the heating, hot rolling, and cooling processes, the surface of wire rod undergoes a chemical reaction upon contact with air, forming an oxide scale, which is typically gray or bluish-gray. High-carbon steel wire rod has a relatively low silicon content, and the oxide scale formed on its surface is mainly composed of FeO and Fe3O4.

[0004] During the production process, the oxide scale formed on the surface of the wire rod can blister and burst during subsequent cooling, coiling, and transportation. This bursting results in residual oxide scale on the wire rod surface, which is difficult for downstream customers to remove mechanically during descaling. Furthermore, the bursting oxide scale forms a thick layer on tooling and the ground, and may even float in the air, seriously impacting environmental hygiene and human health.

[0005] Therefore, how to reduce the blistering and cracking of oxide scale on the surface of high-carbon steel wire rod is one of the important issues in the field of steel production technology. Summary of the Invention

[0006] The purpose of this application is to provide a method for producing high-carbon steel wire rod, and the high-carbon steel wire rod prepared by the method.

[0007] To achieve the above objectives, one embodiment provides a method for producing high-carbon steel wire rod, wherein a billet is sequentially processed through a heating process, a hot rolling process, and a Stellmore cooling process to prepare the wire rod. The chemical composition of the billet, by mass percentage, includes: C 0.50~0.96%, Mn 0.30~0.60%, Si 0.10~0.90%, wherein the hardening factor F = 10×C + 1.5×(Mn+V) + 0.5×Si + 2.5×Cr + 0.3×Ni + 3×Mo + 2×Nb;

[0008] The heating process includes a preheating section, a heating section, and a homogenizing section performed sequentially. The heating rate of the preheating section is 10~15℃ / min, the heating rate of the heating section is 30~40℃ / min, and the heating rate from the heating section to the homogenizing section is 20~30℃ / min. The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing rolling, pre-finishing water cooling, finishing rolling, post-finishing water cooling, and wire drawing in sequence. The high-pressure water used for descaling has a pressure of 26-28 MPa and a flow rate of 280-350 L / min. The pre-finishing water cooling includes two stages with flow rates of 500-550 L / min and 120-180 L / min, respectively. Water cooling is performed during finishing rolling at a pressure of (0.3F-0.6F) MPa and a flow rate of 80-120 L / min. The post-finishing water cooling includes four stages with flow rates of 900-1000 L / min, 600-700 L / min, 200-400 L / min, and 30-60 L / min, respectively. In the Stellmore cooling process, when the temperature is ≥850℃, if F≤8, the cooling rate is controlled at 20~28℃ / s; if 8<F≤12, the cooling rate is controlled at 18~22℃ / s; and if F>12, the cooling rate is controlled at 16~20℃ / s.

[0009] As a further improvement to one embodiment, the chemical composition of the high-carbon steel, by mass percentage, includes: C 0.60~0.96%, Mn 0.30~0.60%, Si 0.10~0.80%, P≤0.02%, S≤0.015%, with the remainder being Fe and unavoidable impurities; Alternatively, the chemical composition of the high-carbon steel, by mass percentage, includes: C 0.50~0.90%, Mn 0.30~0.60%, Si 0.10~0.90%, Cr≤1.00%, Ni≤1.50%, Mo≤0.80%, V≤0.50%, Nb≤0.10%, P≤0.02%, S≤0.015%, with the remainder being Fe and unavoidable impurities.

[0010] As a further improvement to one embodiment, in the heating process, if F≤8, the temperature of the heat spreader is controlled at 1220~1280℃; if 8<F≤12, the temperature of the heat spreader is controlled at 1180~1240℃; if F>12, the temperature of the heat spreader is controlled at 1160~1220℃; the heat spreader time is ≤10min.

[0011] As a further improvement to one embodiment, in the heating process, the temperature of the heating section is ≤1000℃.

[0012] As a further improvement to one embodiment, the thickness of the decarburized layer on the surface of the billet after the heating process is controlled to be 200~320μm, and the thickness of the oxide scale is controlled to be 100~150μm.

[0013] As a further improvement to one embodiment, in the water cooling after finishing rolling, the water pressure of the first two stages of water cooling is 6~7 bar, and the water pressure of the last two stages of water cooling is 3~4 bar.

[0014] As a further improvement to one embodiment, in the water cooling after finishing rolling, when the ambient temperature is 20~45℃, the cooling water temperature is 10~15℃; when the ambient temperature is <20℃, the cooling water temperature is 15~25℃.

[0015] As a further improvement to one embodiment, when the diameter d of the wire rod satisfies 5mm≤d≤10mm, the temperature difference between the core and the surface of the wire rod after finishing rolling and water cooling is controlled to be ≤30℃; when d satisfies 10mm<d≤14mm, the temperature difference between the core and the surface of the wire rod after finishing rolling and water cooling is controlled to be ≤50℃.

[0016] As a further improvement to one implementation method, if F≤8, the spinning temperature is controlled at 900~930℃; if 8<F≤12, the spinning temperature is controlled at 890~920℃; if F>12, the spinning temperature is controlled at 870~910℃.

[0017] As a further improvement to one implementation method, the spinning speed is controlled to be ≤100m / s.

[0018] As a further improvement to one embodiment, the Steyrmo cooling process employs a Steyrmo cooling line, which comprises 12 cooling sections, each equipped with 2 fans, each fan having a maximum airflow of 180,000 m³ / s. 3 / h; When F≤8, if the diameter d of the wire rod satisfies 5mm≤d≤10mm, then the first 9 fans are turned on and the corresponding insulation covers are opened. The air volume of fans 1-4 is 85-100% of the maximum air volume, the air volume of fans 5-6 is 50-70% of the maximum air volume, and the air volume of fans 7-9 is 10-40% of the maximum air volume. If the diameter d of the wire rod satisfies 10mm<d≤14mm, then the first 12 fans are turned on and the corresponding insulation covers are opened. The air volume of each fan is 30-100% of the maximum air volume. In the cooling section where the fans are turned off, the corresponding insulation covers are all closed, and the cooling rate of the wire rod is controlled at 3-5℃ / s. When 8 < F ≤ 12, if the diameter d of the wire rod satisfies 5 mm ≤ d ≤ 10 mm, then turn on the first 6 to 8 fans and open the corresponding insulation covers. Among them, the air volume of the 1 to 4 fans is 80 to 95% of the maximum air volume, the air volume of the 5 to 6 fans is 50 to 70% of the maximum air volume, and the air volume of the 7 to 8 fans is 0 to 20% of the maximum air volume. If the diameter d of the wire rod satisfies 10 mm < d ≤ 14 mm, then turn on the first 12 fans and open the corresponding insulation covers. The air volume of each fan is 20 to 95% of the maximum air volume. The insulation covers corresponding to the cooling sections where the fans are turned off are all closed, and the cooling rate of the wire rod is controlled at 2 to 4℃ / s. When F > 12, if the diameter d of the wire rod satisfies 5mm ≤ d ≤ 10mm, then turn on the first 6 to 7 fans and open the corresponding insulation covers. Among them, the air volume of the first 4 fans is 80 to 90% of the maximum air volume, the air volume of the 5 to 6 fans is 40 to 60% of the maximum air volume, and the air volume of the 7 fans is 0 to 20% of the maximum air volume. If the diameter d of the wire rod satisfies 10mm < d ≤ 14mm, then turn on the first 10 fans and open the corresponding insulation covers. The air volume of each fan is 20 to 90% of the maximum air volume. The insulation covers corresponding to the cooling sections where the fans are turned off are all closed, and the cooling rate of the wire rod is controlled at 2 to 3℃ / s.

[0019] As a further improvement to one embodiment, in the Stellmore cooling process, if F≤8, the side wind speed of the control roller is: middle wind speed = 1.6~1.8, and the cooling rate of the edge overlap point of the wire rod is: the cooling rate of the middle non-overlap point of the wire rod = 1.08~1.12; if 8<F≤12, the side wind speed of the control roller is: middle wind speed = 1.4~1.6, and the cooling rate of the edge overlap point of the wire rod is: the cooling rate of the middle non-overlap point of the wire rod = 1.05~1.10; if F>12, the side wind speed of the control roller is: middle wind speed = 1.3~1.5, and the cooling rate of the edge overlap point of the wire rod is: the cooling rate of the middle non-overlap point of the wire rod = 1.02~1.06.

[0020] As a further improvement to one embodiment, in the Stellmore cooling process, supplementary air is provided at the inlet section of the Stellmore cooling line, with a wind speed of 15~20m / s and a supplementary air temperature of 20~30℃.

[0021] As a further improvement to one embodiment, in the Steilmo cooling process, CO2 or N2 is sprayed onto the surface of the wire rod in the first two cooling sections of the Steilmo cooling line, with a spray flow rate of 5~10m / s and a spray gas temperature of 200~350℃.

[0022] As a further improvement to one embodiment, the production method further includes transporting the coiled wire obtained after the Stellmore cooling process by hanging it on a C-hook, and controlling the cooling rate of the wire surface to be ≤5℃ / s when the wire surface temperature is ≥150℃.

[0023] To achieve the above objectives, one embodiment provides a high-carbon steel wire rod, which is prepared using the aforementioned high-carbon steel wire rod production method.

[0024] Compared with the prior art, the beneficial effects of this application are as follows: On the one hand, by designing the temperature and cooling regime in the heating, hot rolling and Stellmore cooling processes, the temperature difference between the core and surface of the rolled piece can be controlled during the production process, thereby reducing the stress difference between the rolled piece surface and the oxide scale, reducing the degree of decarburization on the surface of the wire rod during the cooling process, thereby reducing the blistering and cracking of the oxide scale on the surface of the high carbon steel wire rod, and improving the surface quality of the high carbon steel wire rod. On the other hand, based on different hardening factors and wire rod diameters, by controlling the cooling rate of the Stellmore cooling line above 850°C, the thickness and structure of the oxide scale generated above 850°C can be controlled. This maintains the oxide scale with an inner layer of FeO and an outer layer of Fe3O4 in a certain proportion of phase structure, and the FeO layer contains Fe3O4 precipitates, reducing the gas barrier effect of the oxide scale surface. This allows gases such as CO and N2 formed at the interface to escape in an orderly manner instead of accumulating and expanding to form explosions. It can also prevent the expansion coefficient of Fe oxides from changing too much during the cooling process, thereby reducing the occurrence of oxide scale explosions.

[0025] In summary, by controlling the composition, thickness, and structure of the iron oxide scale on the surface of the wire rod, the iron oxide scale on the surface of the wire rod is made to have a clear color, reducing the cracking and generation of the scale, and greatly improving the mechanical peeling performance of the iron oxide scale. The wire rod is suitable for mechanical peeling to remove the iron oxide scale on its surface, with excellent peeling effect, greatly reducing the pickling process, and making it more energy-saving and environmentally friendly. Furthermore, the wire rod itself has excellent structure and properties, combined with its good mechanical peeling performance, making the wire rod more suitable for drawing or other subsequent deep processing, which can greatly increase the production speed of wire rod deep processing and improve the production efficiency of steel wire products. Attached Figure Description

[0026] Figure 1 This is a photograph of the wire rod of Embodiment 1 of this application; Figure 2 This is a microstructure diagram of the oxide scale of the wire rod in Example 1 of this application; Figure 3 This is a photograph of the wire rod in Embodiment 2 of this application; Figure 4 This is a microstructure diagram of the oxide scale of the wire rod in Example 2 of this application; Figure 5 This is a photograph of the wire rod of Embodiment 3 of this application; Figure 6 This is a microstructure image of the oxide scale on the wire rod of Example 3 of this application; Figure 7 This is a photograph of the wire rod in proportion to the specifications of this application. Detailed Implementation

[0027] One embodiment of this application provides a method for producing high-carbon steel wire rod, in which a billet is sequentially subjected to a heating process, a hot rolling process, and a Stellmore cooling process to prepare it into wire rod. Furthermore, one embodiment also provides high-carbon steel wire rod prepared based on this production method.

[0028] The chemical composition of the billet, by weight percentage, includes: C 0.50~0.96%, Mn 0.30~0.60%, and Si 0.10~0.90%. Correspondingly, the prepared high-carbon steel wire rod also includes, by weight percentage, C 0.50~0.96%, Mn 0.30~0.60%, and Si 0.10~0.90%. That is, the production method involves the production of high-carbon steel wire rod with a C content of 0.50~0.96% by weight.

[0029] In a preferred embodiment, the chemical composition of the high-carbon steel, by mass percentage, includes: C 0.60~0.96%, Mn 0.30~0.60%, Si 0.10~0.80%, P≤0.02%, S≤0.015%, with the remainder being Fe and unavoidable impurities.

[0030] In another preferred embodiment, the chemical composition of the high-carbon steel, by mass percentage, comprises: C 0.50~0.90%, Mn 0.30~0.60%, Si 0.10~0.90%, Cr≤1.00%, Ni≤1.50%, Mo≤0.80%, V≤0.50%, Nb≤0.10%, P≤0.02%, S≤0.015%, with the remainder being Fe and unavoidable impurities.

[0031] The hardening factor F is defined as: F = 10 × C + 1.5 × (Mn + V) + 0.5 × Si + 2.5 × Cr + 0.3 × Ni + 3 × Mo + 2 × Nb. The hardening factor F characterizes the stability of supercooled austenite and the degree of delay in pearlite phase transformation in steel under Stellmore cooling conditions.

[0032] In the formula, C, Mn, Si, Cr, Ni, Mo, V, and Nb represent the mass percentages of the corresponding elements. For example, if the mass percentage of C is 0.60%, then the mass percentage of C is 0.60, and C is substituted into 0.60 for calculation. If the element content is 0, then 0 is substituted into the formula for calculation.

[0033] Research has found that when the temperature rises (F), the microstructure of the steel becomes more sensitive, and hard phase structures such as bainite and martensite will form at low cooling rates, which is not conducive to subsequent processing of the steel. On the other hand, a lower temperature rise (F) will greatly limit the improvement of the strength and plasticity of the steel.

[0034] The heating process, hot rolling process, and Stellmore cooling process of a preferred embodiment of this application will be described in turn below.

[0035] (1) Heating process The billet is heated in a heating furnace. The heating process includes a preheating section, a heating section, and a soaking section, which are performed sequentially.

[0036] The heating rate of the preheating section is 10~15℃ / min, the heating rate of the heating section is 30~40℃ / min, and the heating rate from the heating section to the soaking section is 20~30℃ / min.

[0037] By controlling the heating rate of the preheating section, heating section, and heating section to homogenization section, the thermal stress on the surface and core of the billet can be reduced, decarburization and oxidation loss can be reduced, thereby inhibiting excessive decarburization on the billet surface, reducing the amount of oxide scale and CO and CO2 gas generated at the interface between oxide scale and billet matrix, reducing blistering and nucleation on the wire rod surface, and thus reducing oxide scale cracking.

[0038] Preferably, the thickness of the decarburized layer on the surface of the billet after the heating process is controlled to be 200~320μm, and the thickness of the oxide scale is controlled to be 100~150μm.

[0039] In this heating process, the temperature of the soaking zone is 1160~1280℃, which can effectively control the degree of decarburization of the billet and ensure uniform heating of the billet.

[0040] Preferably, the temperature of the soaking zone is controlled according to the different hardening factors F. Specifically, if F≤8, the temperature of the soaking zone is controlled at 1220~1280℃; if 8<F≤12, the temperature of the soaking zone is controlled at 1180~1240℃; and if F>12, the temperature of the soaking zone is controlled at 1160~1220℃.

[0041] Preferably, the soaking time is ≤10 min. By controlling the heating time of the soaking section, excessive decarburization on the billet surface can be suppressed, the amount of oxide scale and CO and CO2 gas generated at the interface between the oxide scale and the billet matrix can be reduced, the blistering and nucleation of wire rod surface can be reduced, and thus the oxide scale cracking can be reduced.

[0042] Preferably, the temperature of the heating section is controlled to be ≤1000℃. This can reduce the oxidation loss of the billet under oxygen-rich conditions.

[0043] In one embodiment, the fuel for the heating furnace is a mixture of coke oven gas and blast furnace gas, in which the volume percentage of coke oven gas is 15-25%. The excess air coefficient is 1.10-1.13, and the oxygen enrichment is 25-30%. This improves thermal efficiency.

[0044] The chemical composition of the mixed gas, by volume percentage, includes: H2 22-27%, CH4 8-12%, CO 18-22%, N2 34-38%, CO2 6-10%, with the balance being C2H2 and C2H4. This composition of the mixed gas can reduce decarburization and oxidation loss of the billet.

[0045] (2) Hot rolling process The billet that has undergone the heating process is then hot-rolled.

[0046] The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing, pre-finishing water cooling, finishing, post-finishing water cooling, and wire drawing. Correspondingly, the high-speed wire rod rolling production line is equipped with a descaling device, a roughing mill, an intermediate rolling mill, a pre-finishing mill, two pre-finishing water tanks, a finishing mill, four post-finishing water tanks, and a wire drawing machine.

[0047] The finishing mill is also equipped with water-cooled guides.

[0048] The high-pressure water used for descaling has a pressure of 26~28MPa and a flow rate of 280~350L / min, which means the descaling device has a water pressure of 26~28MPa and a flow rate of 280~350L / min.

[0049] The pre-finishing water cooling system comprises two sections with water flow rates of 500-550 L / min and 120-180 L / min, respectively. That is, the water flow rates of the two pre-finishing water tanks are 500-550 L / min and 120-180 L / min, respectively.

[0050] Water cooling is performed during the finishing rolling process, with a water pressure of (0.3F~0.6F) MPa and a water flow rate of 80~120 L / min. That is, the water pressure of the water-cooled guides in the finishing rolling mill is (0.3F~0.6F) MPa, and the water flow rate is 80~120 L / min.

[0051] The post-finishing water cooling system comprises four stages with water flow rates of 900~1000 L / min, 600~700 L / min, 200~400 L / min, and 30~60 L / min, respectively. That is, the water flow rates of the four post-finishing water tanks are 900~1000 L / min, 600~700 L / min, 200~400 L / min, and 30~60 L / min, respectively.

[0052] In this way, by designing the water cooling pressure and flow rate for descaling, pre-finishing water cooling, water cooling during finishing rolling, and post-finishing water cooling, it is possible to avoid excessive temperature gradients in the wire rod during water cooling, thereby reducing the large stress generated in the core and surface of the wire rod, and thus reducing the possibility of the oxide scale formed on the surface of the wire rod peeling off and cracking due to excessive stress.

[0053] Preferably, the oxide scale removal rate on the surface of the billet after descaling is controlled to be ≥99.7%.

[0054] Preferably, during descaling, the angle between the high-pressure water jet used for descaling and the upper or lower surface of the billet is controlled to be 30-45°. That is, the angle between the descaling nozzle of the descaling device and the upper or lower surface of the billet is controlled to be 30-45°. This avoids the situation where the angle is too small, resulting in insufficient pressure from the high-pressure water impacting the billet surface; and it also avoids the situation where the angle is too large, resulting in excessive pressure of the high-pressure water flow in the direction perpendicular to the upper surface of the billet, thus preventing any impact on the scale removal effect.

[0055] Preferably, during rough rolling and intermediate rolling, the surface temperature difference between the corner and center of the billet is controlled to be ≤20℃, so as to effectively reduce the stress increase caused by the uneven temperature between the corner and center of the billet, reduce the stress difference between the corner and center of the billet, thereby reducing the stress between the oxide scale formed on the surface of the billet and the substrate, and increasing the bonding force between the oxide scale and the substrate.

[0056] Preferably, during roughing and intermediate rolling, when water cooling the rolls, water is flushed into the roll grooves, avoiding flushing water onto the billet surface. This reduces the temperature difference between the billet core and surface, effectively reducing the stress increase caused by uneven temperature between the billet core and surface, reducing the stress difference between the corners and center of the billet, thereby reducing the stress between the oxide scale formed on the billet surface and the matrix, increasing the bonding force between the oxide scale and the matrix, and controlling the austenite grain size difference between the core and surface to ≤5μm.

[0057] The water pressure for the pre-finishing water cooling system is 6-10 bar. That is, the pipeline pressure for both pre-finishing water tanks is 6-10 bar. Each pre-finishing water tank is controlled by a separate water valve to avoid mutual interference.

[0058] In the pre-finishing water cooling process, the distance between the two water cooling sections is 15-20m. That is, the distance between the two pre-finishing water tanks is 15-20m. The rolled piece is transported between the two pre-finishing water tanks via roller conveyors. This allows the surface of the rolled piece to reheat, ensuring that the temperature difference between the core and the surface of the rolled piece is ≤30℃ when it enters the next pre-finishing water tank.

[0059] Preferably, in the water cooling after finishing rolling, the water pressure of the first two stages of water cooling is controlled at 6-7 bar, and the water pressure of the last two stages is controlled at 3-4 bar. That is, the water pressure of the first two water tanks after finishing rolling is 6-7 bar, and the water pressure of the last two water tanks after finishing rolling is 3-4 bar. In this way, by controlling the water pressure of each stage of water cooling after finishing rolling, the cooling rate and temperature distribution of the rolled piece surface can be effectively adjusted, reducing the increase in surface stress caused by excessive temperature drop, and providing a surface foundation for the formation of a uniform and dense iron oxide layer on the surface during subsequent cooling.

[0060] Preferably, in the water cooling after finishing rolling, when the ambient temperature is 20~45℃, the cooling water temperature is 10~15℃; when the ambient temperature is <20℃, the cooling water temperature is 15~25℃.

[0061] Preferably, when the diameter d of the wire rod satisfies 5mm ≤ d ≤ 10mm, the temperature difference between the core and surface of the wire rod after finishing rolling and water cooling is controlled to be ≤ 30℃; when d satisfies 10mm < d ≤ 14mm, the temperature difference between the core and surface of the wire rod after finishing rolling and water cooling is controlled to be ≤ 50℃. In this way, by reducing the temperature difference between the core and surface of the wire rod, surface stress is reduced, thereby reducing the stress difference between the oxide scale and the substrate, and reducing the probability of oxide scale cracking and falling off.

[0062] Specifically, in the water cooling process after finishing milling, the distance between the four water cooling sections is ≥20m, and the distance between the fourth water cooling section and the wire drawing machine is ≥40m. That is, the distance between the four water tanks after finishing milling is ≥20m, and the distance between the fourth water tank and the wire drawing machine is ≥40m. This allows the surface of the wire rod to reheat during transport between the water tanks after finishing milling and during transport to the wire drawing machine, effectively reducing the temperature difference between the wire rod surface and the core. This, in turn, reduces the large stress difference between the core and the surface of the wire rod, thereby reducing the possibility of the oxide scale forming on the wire rod surface peeling off and cracking due to excessive stress.

[0063] It is understandable that the four water cooling sections after finishing mill are arranged sequentially from finishing mill to wire drawing machine, with the fourth water cooling section being the one closest to the wire drawing machine. Correspondingly, the four water tanks after finishing mill are arranged sequentially from finishing mill to wire drawing machine, with the fourth water tank being the one closest to the wire drawing machine.

[0064] Optionally, during wire drawing, if F ≤ 8, the wire drawing temperature is controlled at 900~930℃; if 8 < F ≤ 12, the wire drawing temperature is controlled at 890~920℃; if F > 12, the wire drawing temperature is controlled at 870~910℃. Thus, by controlling the wire drawing temperature according to the different ranges of the hardening factor F, not only can the formation temperature of the initial oxide scale on the wire rod surface be controlled, but the microstructure and properties of the wire rod can also be adjusted.

[0065] Preferably, the spinning speed is controlled to be ≤100m / s.

[0066] (3) Stellmore cooling process The wire rods produced by the hot rolling process are transported to the Steyrmo cooling line for cooling after leaving the wire spinning machine.

[0067] When the temperature is ≥850℃, if F≤8, the cooling rate should be controlled at 20~28℃ / s; if 8<F≤12, the cooling rate should be controlled at 18~22℃ / s; if F>12, the cooling rate should be controlled at 16~20℃ / s.

[0068] Thus, based on different hardening factors and wire rod diameters, by controlling the cooling rate of the Stellmore cooling line above 850°C, the thickness and structure of the oxide scale generated above 850°C can be controlled. This maintains the oxide scale with an inner layer of FeO and an outer layer of Fe3O4 in a certain proportion, and the FeO layer contains Fe3O4 precipitates. This reduces the gas barrier effect of the oxide scale surface, allowing gases such as CO and N2 formed at the interface to escape in an orderly manner instead of accumulating and expanding to cause explosions. It also prevents the expansion coefficient of Fe oxides from changing too much during the cooling process, thereby reducing the occurrence of oxide scale explosions.

[0069] In this embodiment, the high-carbon steel wire rod has a relatively low Si content, and the oxide scale structure on the surface of the wire rod consists of FeO and Fe3O4 from the matrix outwards.

[0070] Because different Fe oxides have significantly different coefficients of thermal expansion relative to the matrix at different temperatures.

[0071] For example, at 900℃, the coefficient of thermal expansion of FeO is 17.5 × 10⁻⁶. -6 At ℃, the coefficient of thermal expansion of Fe3O4 is 15×10⁻⁶. -6 At ℃, the coefficient of thermal expansion of Fe2SiO4 is 12×10⁻⁶. -6 / ℃.

[0072] When the temperature drops to 600℃, the coefficient of thermal expansion of FeO decreases to 12.6 × 10⁻⁶. -6 At ℃, the coefficient of thermal expansion of Fe3O4 remains 15×10⁻⁶. -6 At ℃, the coefficient of thermal expansion of Fe2SiO4 decreases to 10.5 × 10⁻⁶. -6 / ℃.

[0073] When the temperature drops further to 400℃, the coefficient of thermal expansion of FeO decreases to 11.0×10⁻⁶. -6 At / ℃, Fe3O4 decreased to 14.2×10 -6 At / ℃, Fe2SiO4 decreased to 9.8×10 -6 / ℃.

[0074] Studies have revealed that cooling rate significantly affects the formation and expansion behavior of Fe oxides. On one hand, cooling rate directly influences the phase composition of iron oxide scale. When cooling from 650℃ to below 350℃, the Fe3O4 content increases and the proportion of FeO layer thickness in the iron oxide scale decreases as the cooling rate decreases. Conversely, the higher the cooling rate, the greater the proportion of FeO layer thickness in the iron oxide scale, and the greater the decrease in the coefficient of thermal expansion of FeO with decreasing temperature (from 17.5 × 10⁻⁶ at 900℃). -6 / °C drops to 400°C at 11.0×10 -6The volume shrinkage is relatively significant, so the higher the FeO content in the oxide scale, the more prominent the interfacial stress caused by the expansion difference between the layers of the iron oxide scale during cooling. On the other hand, the cooling rate also affects the eutectoid transformation behavior of FeO: FeO is thermodynamically unstable below 570℃, and in the "nose temperature" range of 350~550℃, proeutectoid Fe3O4 precipitation and eutectoid reaction (FeO→Fe+Fe3O4) will occur. This eutectoid transformation is accompanied by a volume expansion of about 3~5%. If the cooling rate is not properly controlled, it will lead to a violent eutectoid reaction in local areas of the wire rod, which will cause stress concentration inside the oxide scale and aggravate the cracking and peeling of the oxide scale.

[0075] The Stellmore cooling line comprises 12 cooling sections, each equipped with two fans. Each fan has a maximum airflow of 180,000 m³ / s. 3 / h.

[0076] When F≤8, if the diameter d of the wire rod satisfies 5mm≤d≤10mm, then the first 9 fans are turned on and the corresponding insulation covers are opened. The airflow of fans 1-4 is 85-100% of the maximum airflow, the airflow of fans 5-6 is 50-70% of the maximum airflow, and the airflow of fans 7-9 is 10-40% of the maximum airflow. If the diameter d of the wire rod satisfies 10mm<d≤14mm, then the first 12 fans are turned on and the corresponding insulation covers are opened. The airflow of each fan is 30-100% of the maximum airflow. In the cooling section where the fans are off, the corresponding insulation covers are all closed, controlling the cooling rate of the wire rod to 3-5℃ / s.

[0077] When 8 < F ≤ 12, if the diameter d of the wire rod satisfies 5mm ≤ d ≤ 10mm, then the first 6 to 8 fans are turned on, and the corresponding insulation covers are opened. Among them, the air volume of fans 1 to 4 is 80 to 95% of the maximum air volume, the air volume of fans 5 to 6 is 50 to 70% of the maximum air volume, and the air volume of fans 7 to 8 is 0 to 20% of the maximum air volume. If the diameter d of the wire rod satisfies 10mm < d ≤ 14mm, then the first 12 fans are turned on, and the corresponding insulation covers are opened. The air volume of each fan is 20 to 95% of the maximum air volume. In the cooling section where the fans are turned off, the corresponding insulation covers are all closed, and the cooling rate of the wire rod is controlled at 2 to 4℃ / s.

[0078] When F > 12, if the diameter d of the wire rod satisfies 5mm ≤ d ≤ 10mm, then the first 6-7 fans are turned on, and the corresponding insulation covers are opened. The airflow of fans 1-4 is 80-90% of the maximum airflow, fans 5-6 are 40-60% of the maximum airflow, and fans 7 are 0-20% of the maximum airflow. If the diameter d of the wire rod satisfies 10mm < d ≤ 14mm, then the first 10 fans are turned on, and the corresponding insulation covers are opened. The airflow of each fan is 20-90% of the maximum airflow. In the cooling section where the fans are off, the corresponding insulation covers are all closed, controlling the cooling rate of the wire rod to 2-3℃ / s.

[0079] Thus, based on different hardening factors and wire rod diameters, by controlling the opening and closing of fans and insulation covers at different locations on the Steyrmore cooling line, as well as the fan airflow, the surface cooling rate of the wire rod at different locations on the Steyrmore cooling line can be controlled. This not only controls the thickness and structure of the oxide scale formed above 850℃, but also controls the residence time of the oxide scale on the wire rod surface in the temperature range of 660~850℃. This maintains the oxide scale with an inner layer of FeO and an outer layer of Fe3O4 in a certain proportion, and the FeO layer contains Fe3O4 precipitates, reducing the gas barrier effect of the oxide scale surface. This allows gases such as CO and N2 formed at the interface to escape in an orderly manner rather than accumulating and expanding to cause explosions. It also prevents the expansion coefficient of Fe oxide from changing too much during the cooling process, thereby reducing the occurrence of oxide scale explosions.

[0080] Optionally, if F≤8, the edge wind speed of the control roller is controlled as follows: the middle wind speed = 1.6~1.8, and the cooling rate of the edge overlap point of the wire rod is controlled as follows: the cooling rate of the middle non-overlap point of the wire rod = 1.08~1.12; if 8<F≤12, the edge wind speed of the control roller is controlled as follows: the middle wind speed = 1.4~1.6, and the cooling rate of the edge overlap point of the wire rod is controlled as follows: the cooling rate of the middle non-overlap point of the wire rod = 1.05~1.10; if F>12, the edge wind speed of the control roller is controlled as follows: the middle wind speed = 1.3~1.5, and the cooling rate of the edge overlap point of the wire rod is controlled as follows: the cooling rate of the middle non-overlap point of the wire rod = 1.02~1.06. Adjusting the wind speed ratio between the edge and middle of the roller conveyor, as well as the cooling speed ratio between the overlapping points at the edge and the non-overlapping points at the middle, based on the hardening factor, can minimize the temperature gradient within the same coil of wire rod, resulting in a more uniform temperature distribution. This reduces the difference in the expansion coefficients of the wire rod matrix and the oxide scale caused by temperature differences, thereby reducing the possibility of oxide scale cracking.

[0081] The ratio of the edge wind speed to the center wind speed on the roller conveyor can be adjusted by changing the direction of the fan opening and the direction of the baffles inside the fan. An anemometer is installed on the Stellmore cooling line to measure the edge and center wind speeds of the roller conveyor.

[0082] In one embodiment, makeup air is supplied at the inlet section of the Stellmore cooling line at a velocity of 15-20 m / s and a temperature of 20-30°C. This prevents the oxide scale from rapidly thickening and forming a dense two-layer structure due to excessively high surface temperatures at the inlet section of the wire rod, thus reducing stress increase caused by excessive differences in the coefficients of thermal expansion due to rapid oxide scale growth.

[0083] Correspondingly, an air supply device is installed at the inlet section of the Stellmore cooling line to blow air onto the surface of the wire rod.

[0084] The entrance section of the Stellmore cooling line is located between the spinning machine and the first cooling section. The length of the entrance section is 2-3 meters.

[0085] In one embodiment, CO2 or N2 is sprayed onto the surface of the wire rod in the first two cooling sections of the Stellmore cooling line at a flow rate of 5-10 m / s and a gas temperature of 200-350°C. This reduces the O2 concentration on the wire rod surface, decreases the reaction rate between C and O, reduces the amount of CO and other gases generated between the wire rod substrate and the oxide layer, and reduces blistering and cracking of the oxide scale caused by gases generated from the reaction between the substrate and O2.

[0086] Correspondingly, the first two cooling sections of the Steilmo cooling line are equipped with side-blowing devices for spraying CO2 or N2 onto the surface of the wire rod.

[0087] In one embodiment, the production method of the high-carbon steel wire rod further includes transporting the wire rod obtained after the Stellmore cooling process by hanging it on a C-hook and controlling the cooling rate of the wire rod surface to be ≤5℃ / s when the surface temperature is ≥150℃. This effectively avoids the reduction in oxide scale adhesion caused by excessively rapid cooling during transportation and rapid changes in the oxide scale expansion coefficient, thereby improving the adhesion between the oxide scale and the substrate.

[0088] Furthermore, the wire rod obtained by the production method of this embodiment is a high-carbon steel wire rod, which has excellent microstructure and properties, and its surface iron oxide scale has good mechanical peeling properties. This wire rod is suitable for mechanical peeling and can be better suited for drawing or other subsequent deep processing.

[0089] In one embodiment, the wire rod has a tensile strength of 980~1280MPa and a reduction of area of ​​35~58%.

[0090] In a preferred embodiment, regarding the oxide scale structure of the wire rod, the thickness ratio of the FeO layer to the Fe3O4 layer in the iron oxide scale is 3 to 5, and the proportion of Fe3O4 generated by the co-deposition reaction in the FeO layer is 5 to 10%.

[0091] Studies have shown that due to the high cooling rate used in the cooling process of high carbon steel, the oxide scale on its surface exhibits a two-layer structure. The layer closer to the substrate is the FeO layer, while the outer layer closer to the outside is the Fe3O4 layer. Fe3O4 generated by the eutectoid reaction also exists in the FeO layer. By controlling the cooling rate, different amounts of Fe3O4 precipitates can be obtained.

[0092] In summary, compared with the prior art, the beneficial effects of this application are as follows: On the one hand, by designing the temperature and cooling regime in the heating, hot rolling and Stellmore cooling processes, the temperature difference between the core and surface of the rolled piece can be controlled during the production process, thereby reducing the stress difference between the rolled piece surface and the oxide scale, reducing the degree of decarburization on the surface of the wire rod during the cooling process, thereby reducing the blistering and cracking of the oxide scale on the surface of the high carbon steel wire rod, and improving the surface quality of the high carbon steel wire rod. On the other hand, based on different hardening factors and wire rod diameters, by controlling the cooling rate of the Stellmore cooling line above 850°C, the thickness and structure of the oxide scale generated above 850°C can be controlled. This maintains the oxide scale with an inner layer of FeO and an outer layer of Fe3O4 in a certain proportion of phase structure, and the FeO layer contains Fe3O4 precipitates, reducing the gas barrier effect of the oxide scale surface. This allows gases such as CO and N2 formed at the interface to escape in an orderly manner instead of accumulating and expanding to form explosions. It can also prevent the expansion coefficient of Fe oxides from changing too much during the cooling process, thereby reducing the occurrence of oxide scale explosions.

[0093] In summary, by controlling the composition, thickness, and structure of the iron oxide scale on the surface of the wire rod, the iron oxide scale on the surface of the wire rod is made to have a clear color, reducing the cracking and generation of the scale, and greatly improving the mechanical peeling performance of the iron oxide scale. The wire rod is suitable for mechanical peeling to remove the iron oxide scale on its surface, with excellent peeling effect, greatly reducing the pickling process, and making it more energy-saving and environmentally friendly. Furthermore, the wire rod itself has excellent structure and properties, combined with its good mechanical peeling performance, making the wire rod more suitable for drawing or other subsequent deep processing, which can greatly increase the production speed of wire rod deep processing and improve the production efficiency of steel wire products.

[0094] The technical solution of this application will be further described below through Examples 1-3 and comparative examples.

[0095] Example 1 This embodiment provides a method for producing high-carbon steel wire rod with a diameter of 8mm.

[0096] The billet comprises, by mass percentage: C 0.65%, Mn 0.45%, Si 0.25%, P 0.015%, S 0.010%, with the remainder being Fe and unavoidable impurities. The hardening factor F = 7.30.

[0097] (1) Heating process The billet is heated in a heating furnace. The heating process includes a preheating section, a heating section, and a soaking section, which are performed sequentially.

[0098] The preheating section has a heating rate of 12℃ / min, the heating section has a heating rate of 35℃ / min, the temperature in the heating section does not exceed 1000℃, the heating rate from the heating section to the soaking section is 25℃ / min, the soaking section temperature is 1250℃, and the soaking section time is 8 minutes. After the heating process, the thickness of the decarburized layer on the surface of the billet is 280μm, and the oxide scale thickness is 120μm.

[0099] The heating furnace is fueled by a mixture of coke oven gas and blast furnace gas, with coke oven gas accounting for 20% of the volume. The excess air coefficient is 1.12, and the oxygen enrichment is 28%.

[0100] The chemical composition of the mixed gas, by volume percentage, includes: H2 25%, CH4 10%, CO 20%, N2 36%, CO 28%, with the balance being C2H2 and C2H4.

[0101] (2) Hot rolling process The billet that has undergone the heating process is then hot-rolled.

[0102] The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing, pre-finishing water cooling, finishing, post-finishing water cooling, and wire drawing. Correspondingly, the high-speed wire rod rolling production line is equipped with a descaling unit, a roughing mill, an intermediate mill, a pre-finishing mill, two pre-finishing water tanks, a finishing mill, four post-finishing water tanks, and a wire drawing machine. The finishing mill also includes water-cooling guides.

[0103] The high-pressure water used for descaling has a pressure of 27 MPa and a flow rate of 320 L / min. The angle between the high-pressure water jet and the upper or lower surface of the billet is 38°. After descaling, the oxide scale removal rate on the billet surface reaches 99.8%.

[0104] During roughing and intermediate rolling, the surface temperature difference between the corners and the center of the billet is controlled at 15°C. During roughing and intermediate rolling, when water cooling the rolls, water is flushed into the roll grooves, but water is avoided from flushing onto the surface of the billet. The austenite grain size difference between the core and the surface is controlled at 4μm.

[0105] The pre-finishing water cooling system consists of two sections with water flow rates of 525 L / min and 150 L / min respectively, and the distance between the two sections is 18 m. The water pressure of the pre-finishing water cooling system is 8 bar. Thus, when the rolled piece enters the pre-finishing water tank, the temperature difference between the core and the surface is 25 °C.

[0106] During the finishing rolling process, the water pressure for water cooling is 3.5 MPa, and the water flow rate is 120 L / min.

[0107] The water cooling system after finishing rolling consists of four stages with water flow rates of 950 L / min, 650 L / min, 300 L / min, and 45 L / min, respectively. The distance between each stage is 25 m, and the distance from the fourth stage to the wire drawing stage is 50 m. The water pressure for the first two stages is 6.5 bar, and for the latter two stages it is 3.5 bar. The ambient temperature is 30°C, the cooling water temperature is 12°C, and the temperature difference between the core and surface of the wire rod after finishing rolling and water cooling is 25°C.

[0108] During the spinning process, the spinning temperature is 915℃ and the spinning speed is 85m / s.

[0109] (3) Stellmore cooling process The wire rods produced by the hot rolling process are transported to the Steyrmo cooling line for cooling after leaving the wire spinning machine.

[0110] The Stellmore cooling line comprises 12 cooling sections, each equipped with two fans. Each fan has a maximum airflow of 180,000 m³ / s. 3 / h.

[0111] When the temperature is ≥850℃, the cooling rate is controlled at 24℃ / s. By adjusting the opening direction of the fan and the direction of the baffle inside the fan, the wind speed at the edge of the roller conveyor is 1.7 times that at the middle, and the cooling rate at the edge overlap point of the wire rod is 1.1 times that at the non-overlap point of the wire rod.

[0112] Turn on the first 9 fans and open the corresponding insulation covers. The air volume of fans 1-4 is 95% of the maximum air volume, the air volume of fans 5-6 is 60% of the maximum air volume, and the air volume of fans 7-9 is 25% of the maximum air volume. When the fans are turned off, the corresponding insulation covers are closed. The cooling rate of the coil is controlled at 4℃ / s.

[0113] Makeup air is supplied at the inlet section of the Stellmore cooling line at a velocity of 18 m / s and a temperature of 25°C. The length of the inlet section is 2.5 m.

[0114] In the first two cooling sections of the Stellmore cooling line, CO2 is sprayed onto the surface of the wire rod at a flow rate of 8 m / s and a gas temperature of 280°C.

[0115] The coiled wire obtained after the Stellmore cooling process is transported by hanging it on a C-hook, and the cooling rate of the coil surface is controlled at 3℃ / s when the surface temperature of the coil is ≥150℃.

[0116] See Figure 1 The wire rod surface is free of oxide scale cracking defects, and the oxide scale is well bonded to the substrate.

[0117] Regarding the oxide scale structure, the oxide scale structure of the wire rod was observed using scanning electron microscopy, and its microstructure was captured as follows: Figure 2 As shown, the layer closest to the substrate is an FeO layer with a thickness of 11.712 μm, while the outermost layer closest to the outside is an Fe3O4 layer with a thickness of 2.788 μm. The thickness ratio of the FeO layer to the Fe3O4 layer is 4.2. Based on the microstructure diagram, the area of ​​the FeO layer and the Fe3O4 generated by the eutectoid reaction within it was calculated. The arrow indicates Fe3O4, and the proportion of Fe3O4 generated by the eutectoid reaction in the FeO layer was measured to be 7.5%.

[0118] In terms of mechanical properties, referring to GB / T 228.1-2021, the tensile strength and reduction of area of ​​the wire rod were tested using a tensile testing machine. The tensile strength of the wire rod was measured to be 988 MPa and the reduction of area was 56%.

[0119] Example 2 This embodiment provides a method for producing high-carbon steel wire rod with a diameter of 12mm.

[0120] The billet comprises, by mass percentage: C 0.85%, Mn 0.50%, Si 0.55%, P 0.018%, S 0.012%, with the remainder being Fe and unavoidable impurities. The hardening factor F = 9.525.

[0121] (1) Heating process The billet is heated in a heating furnace. The heating process includes a preheating section, a heating section, and a soaking section, which are performed sequentially.

[0122] The heating rate in the preheating section is 13℃ / min, the heating rate in the heating section is 38℃ / min, the temperature in the heating section does not exceed 1000℃, the heating rate from the heating section to the soaking section is 28℃ / min, the temperature in the soaking section is 1210℃, and the soaking time is 9 minutes. The thickness of the decarburized layer on the surface of the billet after the heating process is 300μm, and the oxide scale thickness is 135μm.

[0123] The heating furnace is fueled by a mixture of coke oven gas and blast furnace gas, with coke oven gas accounting for 22% of the volume. The excess air coefficient is 1.11, and the oxygen enrichment is 27%.

[0124] The chemical composition of the mixed gas, by volume percentage, includes: H2 24%, CH4 9%, CO 19%, N2 37%, CO2 8%, with the balance being C2H2 and C2H4.

[0125] (2) Hot rolling process The billet that has undergone the heating process is then hot-rolled.

[0126] The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing, pre-finishing water cooling, finishing, post-finishing water cooling, and wire drawing. Correspondingly, the high-speed wire rod rolling production line is equipped with a descaling unit, a roughing mill, an intermediate mill, a pre-finishing mill, two pre-finishing water tanks, a finishing mill, four post-finishing water tanks, and a wire drawing machine. The finishing mill also includes water-cooling guides.

[0127] The high-pressure water used for descaling has a pressure of 27.5 MPa and a flow rate of 340 L / min. The angle between the high-pressure water jet and the upper or lower surface of the billet is 42°. After descaling, the oxide scale removal rate on the billet surface reaches 99.8%.

[0128] During roughing and intermediate rolling, the surface temperature difference between the corners and the center of the billet is controlled at 18°C. During roughing and intermediate rolling, when water cooling the rolls, water is flushed into the roll grooves, but water is avoided from flushing onto the surface of the billet. The austenite grain size difference between the core and the surface is controlled at 4.5 μm.

[0129] The pre-finishing water cooling system consists of two sections with water flow rates of 540 L / min and 160 L / min respectively, and the distance between the two sections is 19 m. The water pressure of the pre-finishing water cooling system is 9 bar. Thus, when the rolled piece enters the pre-finishing water tank, the temperature difference between the core and the surface is 28 °C.

[0130] During the finishing rolling process, the water pressure for water cooling is 4.5 MPa, and the water flow rate is 150 L / min.

[0131] The water cooling system after finishing rolling consists of four stages with water flow rates of 980 L / min, 680 L / min, 350 L / min, and 50 L / min, respectively. The distance between each stage is 22 m, and the distance from the fourth stage to the wire drawing stage is 45 m. The water pressure in the first two stages is 6.8 bar, and the water pressure in the latter two stages is 3.8 bar. The ambient temperature is 25℃, the cooling water temperature is 13℃, and the temperature difference between the core and surface of the wire rod after finishing rolling and water cooling is 45℃.

[0132] During the spinning process, the spinning temperature is 905℃ and the spinning speed is 92m / s.

[0133] (3) Stellmore cooling process The wire rods produced by the hot rolling process are transported to the Steyrmo cooling line for cooling after leaving the wire spinning machine.

[0134] The Stellmore cooling line comprises 12 cooling sections, each equipped with two fans. Each fan has a maximum airflow of 180,000 m³ / s. 3 / h.

[0135] When the temperature is ≥850℃, the cooling rate is controlled at 20℃ / s. By adjusting the opening direction of the fan and the direction of the baffle inside the fan, the wind speed at the edge of the roller conveyor is 1.5: the wind speed at the middle is 1.5, and the cooling rate at the edge overlap point of the wire rod is 1.08: the cooling rate at the middle non-overlap point of the wire rod.

[0136] Turn on the first 12 fans and open the corresponding insulation covers. The air volume of fans 1-4 is 90% of the maximum air volume, the air volume of fans 5-6 is 60% of the maximum air volume, the air volume of fans 7-8 is 15% of the maximum air volume, and the air volume of fans 9-12 is 40% of the maximum air volume. When the fans are turned off, the corresponding insulation covers are closed. The cooling rate of the coil is controlled at 3℃ / s.

[0137] Makeup air is supplied at the inlet section of the Stellmore cooling line at a velocity of 19 m / s and a temperature of 22°C. The length of the inlet section is 2.8 m.

[0138] In the first two cooling sections of the Stellmore cooling line, N2 is sprayed onto the surface of the wire rod at a flow rate of 9 m / s and a gas temperature of 320°C.

[0139] The coiled wire obtained after the Stellmore cooling process is transported by hanging it on a C-hook, and the cooling rate of the coil surface is controlled at 4℃ / s when the surface temperature of the coil is ≥150℃.

[0140] See Figure 3 The wire rod surface is free of oxide scale cracking defects, and the oxide scale is well bonded to the substrate.

[0141] Regarding the oxide scale structure, the oxide scale structure of the wire rod was observed using scanning electron microscopy, and its microstructure was captured as follows: Figure 4 As shown, the layer closest to the substrate is an FeO layer with a thickness of 11.212 μm, while the outermost layer closest to the outside is an Fe3O4 layer with a thickness of 3.114 μm. The thickness ratio of the FeO layer to the Fe3O4 layer is 3.6. Based on the microstructure diagram, the area of ​​the FeO layer and the Fe3O4 generated by the eutectoid reaction within it was calculated. The arrow indicates Fe3O4, and the proportion of Fe3O4 generated by the eutectoid reaction in the FeO layer was measured to be 8.2%.

[0142] In terms of mechanical properties, referring to GB / T 228.1-2021, the tensile strength and reduction of area of ​​the wire rod were tested using a tensile testing machine. The tensile strength of the wire rod was measured to be 1203 MPa and the reduction of area was 37%.

[0143] Example 3 This embodiment provides a method for producing high-carbon steel wire rod with a diameter of 12mm.

[0144] The billet comprises, by weight percentage: C 0.85%, Mn 0.55%, Si 0.65%, Cr 0.70%, Ni 0.80%, Mo 0.40%, V 0.15%, Nb 0.05%, P 0.012%, S 0.008%, with the remainder being Fe and unavoidable impurities. The hardening factor F = 13.165.

[0145] (1) Heating process The billet is heated in a heating furnace. The heating process includes a preheating section, a heating section, and a soaking section, which are performed sequentially.

[0146] The preheating section has a heating rate of 11℃ / min, the heating section has a heating rate of 36℃ / min, the temperature in the heating section does not exceed 1000℃, the heating rate from the heating section to the soaking section is 26℃ / min, the soaking section temperature is 1180℃, and the soaking section time is 6 minutes. After the heating process, the surface decarburized layer thickness of the billet is 220μm, and the oxide scale thickness is 105μm.

[0147] The heating furnace is fueled by a mixture of coke oven gas and blast furnace gas, with coke oven gas accounting for 23% of the volume. The excess air coefficient is 1.10, and the oxygen enrichment is 29%.

[0148] The chemical composition of the mixed gas, by volume percentage, includes: H2 26%, CH4 11%, CO 20%, N2 35%, CO 26%, with the balance being C2H2 and C2H4.

[0149] (2) Hot rolling process The billet that has undergone the heating process is then hot-rolled.

[0150] The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing, pre-finishing water cooling, finishing, post-finishing water cooling, and wire drawing. Correspondingly, the high-speed wire rod rolling production line is equipped with a descaling unit, a roughing mill, an intermediate mill, a pre-finishing mill, two pre-finishing water tanks, a finishing mill, four post-finishing water tanks, and a wire drawing machine. The finishing mill also includes water-cooling guides.

[0151] The high-pressure water used for descaling has a pressure of 28 MPa and a flow rate of 330 L / min. The angle between the high-pressure water jet and the upper or lower surface of the billet is 40°. After descaling, the oxide scale removal rate on the billet surface reaches 99.8%.

[0152] During roughing and intermediate rolling, the surface temperature difference between the corners and the center of the billet is controlled at 16°C. During roughing and intermediate rolling, when water cooling the rolls, water is flushed into the roll grooves, but water is avoided from flushing onto the surface of the billet, and the austenite grain size difference between the core and the surface is controlled at 4.8 μm.

[0153] The pre-finishing water cooling system consists of two sections with water flow rates of 545 L / min and 170 L / min respectively, and the distance between the two sections is 20 m. The water pressure of the pre-finishing water cooling system is 10 bar. Thus, when the rolled piece enters the pre-finishing water tank, the temperature difference between the core and the surface is 26 °C.

[0154] During the finishing rolling process, the water pressure for water cooling is 5.5 MPa, and the water flow rate is 180 L / min.

[0155] The water cooling system after finishing rolling consists of four stages with water flow rates of 960 L / min, 660 L / min, 280 L / min, and 55 L / min, respectively. The distance between each stage is 23 m, and the distance from the fourth stage to the wire drawing stage is 55 m. The water pressure in the first two stages is 6.8 bar, and the water pressure in the latter two stages is 3.6 bar. The ambient temperature is 35℃, the cooling water temperature is 11℃, and the temperature difference between the core and surface of the wire rod after finishing rolling and water cooling is 42℃.

[0156] During the spinning process, the spinning temperature is 885℃ and the spinning speed is 95m / s.

[0157] (3) Stellmore cooling process The wire rods produced by the hot rolling process are transported to the Steyrmo cooling line for cooling after leaving the wire spinning machine.

[0158] The Stellmore cooling line comprises 12 cooling sections, each equipped with two fans. Each fan has a maximum airflow of 180,000 m³ / s. 3 / h.

[0159] When the temperature is ≥850℃, the cooling rate is controlled at 18℃ / s. By adjusting the opening direction of the fan and the direction of the baffle inside the fan, the wind speed at the edge of the roller conveyor is 1.4 times that at the middle, and the cooling rate at the edge overlap point of the wire rod is 1.04 times that at the non-overlap point of the wire rod.

[0160] Turn on the first 10 fans and open the corresponding insulation covers. The air volume of fans 1-4 is 85% of the maximum air volume, the air volume of fans 5-6 is 50% of the maximum air volume, the air volume of fans 7-8 is 15% of the maximum air volume, and the air volume of fans 9-10 is 30% of the maximum air volume. When the fans are turned off, the corresponding insulation covers are closed. The cooling rate of the coil is controlled at 2.5℃ / s.

[0161] Makeup air is supplied at the inlet section of the Stellmore cooling line at a velocity of 20 m / s and a temperature of 20°C. The length of the inlet section is 3.0 m.

[0162] In the first two cooling sections of the Stellmore cooling line, N2 is sprayed onto the surface of the wire rod at a flow rate of 10 m / s and a gas temperature of 350°C.

[0163] The coiled wire obtained after the Stellmore cooling process is transported by hanging it on a C-hook, and the cooling rate of the coil surface is controlled at 2.5℃ / s when the surface temperature of the coil is ≥150℃.

[0164] See Figure 5 The wire rod surface is free of oxide scale cracking defects, and the oxide scale is well bonded to the substrate.

[0165] Regarding the oxide scale structure, the oxide scale structure of the wire rod was observed using scanning electron microscopy, and its microstructure was captured as follows: Figure 6 As shown, the layer closest to the substrate is an FeO layer with a thickness of 11.002 μm, while the outermost layer closest to the outside is an Fe3O4 layer with a thickness of 3.429 μm. The thickness ratio of the FeO layer to the Fe3O4 layer is 3.2. Based on the microstructure diagram, the area of ​​the FeO layer and the Fe3O4 generated by the eutectoid reaction within it was calculated. The arrow indicates Fe3O4, and the proportion of Fe3O4 generated by the eutectoid reaction in the FeO layer was measured to be 9.5%.

[0166] In terms of mechanical properties, referring to GB / T 228.1-2021, the tensile strength and reduction of area of ​​the wire rod were tested using a tensile testing machine. The tensile strength of the wire rod was measured to be 1275 MPa and the reduction of area was 36%.

[0167] Comparative Example This comparative example provides a method for producing high-carbon steel wire rod with a diameter of 6.5 mm.

[0168] The billet comprises, by mass percentage: C 0.85%, Mn 0.50%, Si 0.55%, P 0.018%, S 0.012%, with the remainder being Fe and unavoidable impurities. The hardening factor F = 9.525.

[0169] (1) Heating process The billet is heated in a heating furnace. The heating process includes a preheating section, a heating section, and a soaking section, which are performed sequentially.

[0170] The preheating section has a heating rate of 16℃ / min, the heating section has a heating rate of 40℃ / min, the heating section temperature is 1050℃, the soaking section temperature is 1290℃, and the soaking section time is 15min. After the heating process, the thickness of the decarburized layer on the surface of the billet is 450μm, and the oxide scale thickness is 200μm.

[0171] The heating furnace atmosphere uses pure blast furnace gas, with an excess air coefficient of 1.20 and an oxygen enrichment of 35%.

[0172] (2) Hot rolling process The billet that has undergone the heating process is then hot-rolled.

[0173] The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing, pre-finishing water cooling, finishing, post-finishing water cooling, and wire drawing. Correspondingly, the high-speed wire rod rolling production line is equipped with a descaling unit, a roughing mill, an intermediate mill, a pre-finishing mill, two pre-finishing water tanks, a finishing mill, four post-finishing water tanks, and a wire drawing machine. The finishing mill also includes water-cooling guides.

[0174] The pressure of the high-pressure water used for descaling is 28 MPa, and the water flow rate is 340 L / min. The angle between the high-pressure water jet used for descaling and the upper or lower surface of the billet is 55°.

[0175] During rough rolling and intermediate rolling, the surface temperature difference between the corners and the center of the billet is controlled at 32℃, and the austenite grain size difference between the core and the surface reaches 10μm.

[0176] The pre-finishing water cooling system consists of two sections with a water flow rate of 580 L / min each, and the distance between the two sections is 20 m. The water pressure in the pre-finishing water cooling system is 10 bar. When the rolled piece enters the pre-finishing water tank, the temperature difference between the core and the surface is 45 °C.

[0177] During the finishing rolling process, the water pressure for water cooling is 8.0 MPa, and the water flow rate is 190 L / min.

[0178] The finishing mill water cooling system uses a three-stage water cooling system with a water flow rate of 970 L / min for each stage. The distance between the three stages is 23 m, and the distance between the fourth stage and the wire drawing stage is 55 m. The water pressure in the first two stages is 8 bar, and the water temperature is 22℃. After finishing mill water cooling, the temperature difference between the core and surface of the wire rod is 48℃.

[0179] During the spinning process, the spinning temperature is 930℃ and the spinning speed is 90m / s.

[0180] (3) Stellmore cooling process The wire rods produced by the hot rolling process are transported to the Steyrmo cooling line for cooling after leaving the wire spinning machine.

[0181] The Stellmore cooling line comprises 12 cooling sections, each equipped with two fans. Each fan has a maximum airflow of 180,000 m³ / s. 3 / h.

[0182] When the temperature is ≥850℃, the cooling rate is 16℃ / s. The wind speed at the edge of the roller conveyor is 1.2 times that at the middle. The cooling rate at the edge overlap of the wire rod is 1.22 times that at the middle non-overlapping point of the wire rod.

[0183] Turn on the first 7 fans and open the corresponding insulation covers. The airflow rates of the 7 fans are 99%, 99%, 90%, 90%, 85%, 85%, and 80%, respectively. All insulation covers are open. No make-up air is supplied to the inlet section of the Stellmore cooling line, and CO2 or N2 is not sprayed onto the surface of the wire rods in the first two cooling sections.

[0184] The coiled wire obtained after the Stellmore cooling process is transported by hanging it on a C-hook, and the cooling rate of the coil surface is ≥5℃ / s.

[0185] See Figure 7 The oxide scale on the surface of the wire rod was severely cracked. Therefore, it was impossible to observe the oxide scale structure of the wire rod.

[0186] In terms of mechanical properties, referring to GB / T 228.1-2021, the tensile strength and reduction of area of ​​the wire rod were tested using a tensile testing machine. The tensile strength of the wire rod was measured to be 1220 MPa and the reduction of area was 40%.

[0187] It should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

[0188] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing high-carbon steel wire rod, comprising sequentially processing a billet through a heating process, a hot rolling process, and a Stellmore cooling process to produce wire rod, characterized in that, The chemical composition of the billet, by mass percentage, includes: C 0.50~0.96%, Mn 0.30~0.60%, Si 0.10~0.90%, wherein the hardening factor F = 10×C + 1.5×(Mn+V) + 0.5×Si + 2.5×Cr + 0.3×Ni + 3×Mo + 2×Nb; The heating process includes a preheating section, a heating section, and a homogenizing section performed sequentially. The heating rate of the preheating section is 10~15℃ / min, the heating rate of the heating section is 30~40℃ / min, and the heating rate from the heating section to the homogenizing section is 20~30℃ / min. The hot rolling process includes descaling, roughing, intermediate rolling, pre-finishing rolling, pre-finishing water cooling, finishing rolling, post-finishing water cooling, and wire drawing in sequence. The high-pressure water used for descaling has a pressure of 26-28 MPa and a flow rate of 280-350 L / min. The pre-finishing water cooling includes two stages with flow rates of 500-550 L / min and 120-180 L / min, respectively. Water cooling is performed during finishing rolling at a pressure of (0.3F-0.6F) MPa and a flow rate of 80-120 L / min. The post-finishing water cooling includes four stages with flow rates of 900-1000 L / min, 600-700 L / min, 200-400 L / min, and 30-60 L / min, respectively. In the Stellmore cooling process, when the temperature is ≥850℃, if F≤8, the cooling rate is controlled at 20~28℃ / s; if 8<F≤12, the cooling rate is controlled at 18~22℃ / s; and if F>12, the cooling rate is controlled at 16~20℃ / s.

2. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, The chemical composition of the high-carbon steel, by mass percentage, includes: C 0.60~0.96%, Mn 0.30~0.60%, Si 0.10~0.80%, P≤0.02%, S≤0.015%, with the remainder being Fe and unavoidable impurities; Alternatively, the chemical composition of the high-carbon steel, by mass percentage, includes: C 0.50~0.90%, Mn 0.30~0.60%, Si 0.10~0.90%, Cr≤1.00%, Ni≤1.50%, Mo≤0.80%, V≤0.50%, Nb≤0.10%, P≤0.02%, S≤0.015%, with the remainder being Fe and unavoidable impurities.

3. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the heating process, if F≤8, the temperature of the heat spreader is controlled at 1220~1280℃; if 8<F≤12, the temperature of the heat spreader is controlled at 1180~1240℃; if F>12, the temperature of the heat spreader is controlled at 1160~1220℃; the heat spreader time is ≤10min.

4. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the heating process, the temperature of the heating section is ≤1000℃.

5. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, The thickness of the decarburized layer on the surface of the billet after the heating process is controlled to be 200~320μm, and the thickness of the oxide scale is controlled to be 100~150μm.

6. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the water cooling process after finishing rolling, the water pressure of the first two stages of water cooling is 6~7 bar, and the water pressure of the last two stages of water cooling is 3~4 bar.

7. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the water cooling process after finishing rolling, when the ambient temperature is 20~45℃, the cooling water temperature is 10~15℃; when the ambient temperature is <20℃, the cooling water temperature is 15~25℃.

8. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, When the diameter d of the wire rod meets the condition of 5mm≤d≤10mm, the temperature difference between the core and the surface of the wire rod after finishing and water cooling is controlled to be ≤30℃; when d meets the condition of 10mm<d≤14mm, the temperature difference between the core and the surface of the wire rod after finishing and water cooling is controlled to be ≤50℃.

9. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, If F≤8, the spinning temperature is controlled at 900~930℃; if 8<F≤12, the spinning temperature is controlled at 890~920℃; if F>12, the spinning temperature is controlled at 870~910℃.

10. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, Control the silk-spinning speed to ≤100m / s.

11. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, The Steilmo cooling process utilizes the Steilmo cooling line, which comprises 12 cooling sections, each equipped with 2 fans, each fan having a maximum airflow of 180,000 m³ / s. 3 / h; When F≤8, if the diameter d of the wire rod satisfies 5mm≤d≤10mm, then the first 9 fans are turned on and the corresponding insulation covers are opened. The air volume of fans 1-4 is 85-100% of the maximum air volume, the air volume of fans 5-6 is 50-70% of the maximum air volume, and the air volume of fans 7-9 is 10-40% of the maximum air volume. If the diameter d of the wire rod satisfies 10mm<d≤14mm, then the first 12 fans are turned on and the corresponding insulation covers are opened. The air volume of each fan is 30-100% of the maximum air volume. In the cooling section where the fans are turned off, the corresponding insulation covers are all closed, and the cooling rate of the wire rod is controlled at 3-5℃ / s. When 8 < F ≤ 12, if the diameter d of the wire rod satisfies 5 mm ≤ d ≤ 10 mm, then turn on the first 6 to 8 fans and open the corresponding insulation covers. Among them, the air volume of the 1 to 4 fans is 80 to 95% of the maximum air volume, the air volume of the 5 to 6 fans is 50 to 70% of the maximum air volume, and the air volume of the 7 to 8 fans is 0 to 20% of the maximum air volume. If the diameter d of the wire rod satisfies 10 mm < d ≤ 14 mm, then turn on the first 12 fans and open the corresponding insulation covers. The air volume of each fan is 20 to 95% of the maximum air volume. The insulation covers corresponding to the cooling sections where the fans are turned off are all closed, and the cooling rate of the wire rod is controlled at 2 to 4℃ / s. When F > 12, if the diameter d of the wire rod satisfies 5mm ≤ d ≤ 10mm, then turn on the first 6 to 7 fans and open the corresponding insulation covers. Among them, the air volume of the first 4 fans is 80 to 90% of the maximum air volume, the air volume of the 5 to 6 fans is 40 to 60% of the maximum air volume, and the air volume of the 7 fans is 0 to 20% of the maximum air volume. If the diameter d of the wire rod satisfies 10mm < d ≤ 14mm, then turn on the first 10 fans and open the corresponding insulation covers. The air volume of each fan is 20 to 90% of the maximum air volume. The insulation covers corresponding to the cooling sections where the fans are turned off are all closed, and the cooling rate of the wire rod is controlled at 2 to 3℃ / s.

12. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the Stellmore cooling process, if F≤8, the side air velocity of the roller conveyor is controlled as follows: the middle air velocity = 1.6~1.8, and the cooling rate at the edge overlap point of the wire rod is controlled as follows: the cooling rate at the middle non-overlap point of the wire rod is controlled as follows: 1.08~1.12; if 8<F≤12, the side air velocity of the roller conveyor is controlled as follows: the middle air velocity = 1.4~1.6, and the cooling rate at the edge overlap point of the wire rod is controlled as follows: the cooling rate at the middle non-overlap point of the wire rod is controlled as follows: 1.05~1.10; if F>12, the side air velocity of the roller conveyor is controlled as follows: the middle air velocity = 1.3~1.5, and the cooling rate at the edge overlap point of the wire rod is controlled as follows: the cooling rate at the middle non-overlap point of the wire rod is controlled as follows: 1.02~1.

06.

13. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the Stellmore cooling process, makeup air is supplied at the inlet section of the Stellmore cooling line at a wind speed of 15-20 m / s and a makeup air temperature of 20-30°C.

14. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, In the Steilmo cooling process, CO2 or N2 is sprayed onto the surface of the wire rod in the first two cooling sections of the Steilmo cooling line at a flow rate of 5-10 m / s and a gas temperature of 200-350°C.

15. The method for producing high-carbon steel wire rod according to claim 1, characterized in that, The production method also includes transporting the coiled wire obtained after the Stellmore cooling process by hanging it on a C-hook, and controlling the cooling rate of the wire surface to be ≤5℃ / s when the surface temperature of the wire is ≥150℃.

16. A high-carbon steel wire rod, characterized in that, The wire rod is prepared by the production method described in any one of claims 1 to 15.

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