A hot-rolled carbon wire rod for 1860MPa grade stranded wire and a manufacturing method thereof

Abstract

The invention relates to a hot-rolled carbon wire rod for 1860MPa grade stranded wire and a manufacturing method thereof. After a wire rod is spun into a wire rod at a spinning temperature of ≥890°C using a wire rod rolled with a eutectoid carbon chemical composition, the wire rod is subjected to an online molten salt strong isothermal treatment to cool the wire rod at a cooling rate of ≥35°C / s, enter a pearlite phase region from an austenite state, promote the formation of a sorbite phase transformation and perform isothermal tempering, promote the melting and spheroidization of part of cementite sheets, and finally undergo slow cooling on a roller to produce a hot-rolled carbon wire rod having a microstructure including a mixed structure of tempered sorbite with a volume percentage of ≥94% and the rest being tempered ferrite and quasi-spheroidized carbides. The hot-rolled carbon wire rod can simplify the material composition, further reduce the material cost, achieve high strength and plasticity matching, reach a tensile strength of 1250-1300MPa, and a cross-sectional shrinkage of 38%-43%, thereby improving the uniformity of the same turn. The wire rod can be used for manufacturing 1860MPa grade stranded wire and can reduce the risk of wire breakage during drawing.

Description

Technical Field

[0001] The invention belongs to the technical field of hot-rolled wire rods, and in particular relates to a hot-rolled carbon wire rod for 1860MPa grade stranded wire and a manufacturing method thereof. Background Art

[0002] As the mainstream grade of steel strand, 1860MPa grade steel strand is widely used in construction, highway and bridge systems. It is made of hot-rolled wire rods as raw materials and twisted into braided ropes through cold drawing. Due to the large reduction rate of deep drawing, the performance and cost of hot-rolled wire rods directly affect the grade, yield rate and cost of strands. In the prior art, hot-rolled wire rods for 1860MPa grade steel strands usually use 82B composition, combined with the post-rolling Stelmor air-cooled line to produce fine lamellar pearlite steel, but for 82B wire rods with a diameter of 10.5~13.0mm, the tensile strength can only reach 1060~1180MPa, and the surface reduction rate is not less than 25%. The hot-rolled wire rods for 1860MPa grade steel strands with lower manufacturing cost, better tensile strength, surface reduction rate and drawing performance still have the following technical difficulties:

[0003] 1. For the purpose of improving the tensile strength of the product, strengthening elements such as Cr, V, and B are further added to refine the austenite grains or reduce the pearlite transformation temperature, so as to refine the pearlite lamellae and increase the sorbite content that is beneficial to the drawing performance during the air-cooling phase transformation process. For example, patent CN112301287B discloses a wire rod for prestressed steel strands and a production method thereof, which adopts a C-Si-Mn-Cr-V-Al composition design, combines low-temperature spinning and post-rolling Stelmor fast cooling + slow cooling process to obtain a wire rod mainly composed of sorbite and a small amount of pearlite, which can be used to manufacture prestressed steel strands with a tensile strength of ≥1860MPa. However, the lower spinning temperature brings greater pressure to the rolling line load, and there is a risk of carbon precipitation. The addition of alloy elements will increase the material cost. Omitting alloys or reducing the alloy content for the purpose of reducing material costs will affect the grains and phase transformation temperature, resulting in a significant loss of strength.

[0004] Second, since the material is hypereutectoid steel with high C and Mn contents, it is difficult to reduce the segregation of the ingot by high-temperature diffusion. In the process of controlling the phase change of the wire rod structure in the Stelmor air cooling line, it is often difficult to control the formation of network carbon. Therefore, in the prior art, the fan air volume and roller speed of the wire rod entering the Stelmor cooling line are increased to increase the cooling speed before the phase change. However, on the one hand, the maximum cooling capacity of air cooling is limited, which can only reach about 10℃ / s at most. The time for the wire rod to pass through the network carbide is still relatively long. Affected by segregation, the formation and Precipitation will not only deteriorate the uniformity of the organization, but also be significantly detrimental to the plasticity of the wire rod, which will cause wire breakage in the subsequent deep drawing process; on the other hand, the increase in the air volume of the fan will further increase the uncontrollable influence of wind speed and wind temperature, and expand the temperature difference between the windward side and the leeward side of the wire rod, causing some positions to form hard and brittle bainite or martensite organizations that are not conducive to drawing at a faster cooling rate, and the distribution of troostite or pearlite content from the edge to the core has a large difference, resulting in a decrease in the uniformity of the organization in the same circle and an increase in the fluctuation of mechanical properties, which will cause breakage in the drawing process.

[0005] 3. In order to maximize the content of fine pearlite or troostite in the wire rod that is beneficial to drawing, the pearlite lamellae will be refined by reducing the pearlite transformation temperature in combination with elements such as Cr. The cooling rate during the phase transformation process is reduced by turning off the fan and keeping warm, and the phase transformation time is extended to obtain a troostitized structure. However, on the one hand, the cooling rate of the wire rod before the phase transformation is low, and it is difficult to obtain a large degree of supercooling, which increases the spacing between the pearlite lamellae. The time spent in the phase transformation temperature range during continuous cooling is limited, which will lead to a decrease in the troostite content, an increase in ferrite, and a loss of the strength and drawing performance of the wire rod. The residual austenite will also increase the risk of precipitation of abnormal structures during the subsequent cooling process. On the other hand, the minimum cooling rate of the wire rod is limited, and it is still in a continuous cooling process. The coarser cementite lamellae will increase the difficulty of softening. The phase transformation temperature is low, and it is already in a low temperature state after the phase transformation. The thermal power is insufficient, which will make the obtained troostite or pearlite structure have higher organizational stress and dislocation density, and greater resistance to plastic deformation, and thus a higher risk of wire breakage during the manufacture of stranded wire. Summary of the invention

[0006] The present invention aims to solve at least one of the above-mentioned technical problems to a certain extent. The present invention provides a hot-rolled carbon wire rod for 1860MPa grade stranded wire and a manufacturing method thereof, which can simplify the material composition, further reduce the material cost, achieve high strength and plasticity matching, improve the uniformity of the same turn, and be used for the manufacture of 1860MPa grade stranded wire, which can reduce the risk of wire breakage in the downstream wire drawing process.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A method for manufacturing a hot-rolled carbon wire rod for 1860MPa grade stranded wire, the manufacturing method comprising:

[0009] The wire rod is produced by rolling according to the chemical composition of the hot-rolled carbon wire rod, and the chemical composition and mass percentage of the hot-rolled carbon wire rod include: C: 0.76%~0.79%, Si: 0.45%~0.55%, Mn: 0.45%~0.68%, P≤0.014%, S≤0.014%, and the rest are Fe and unavoidable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥890°C, it is subjected to an online molten salt strong isothermal treatment, so that the wire rod is cooled at a cooling rate of ≥35°C / s, and enters the pearlite phase region from the austenite state, promotes the formation of troostite phase transformation and isothermal tempering, promotes the melting and spheroidization of part of the cementite sheets, and finally is slowly cooled through a roller to produce a hot-rolled carbon wire rod with a microstructure including tempered troostite with a volume percentage of ≥94%, and the rest is a mixed structure composed of tempered ferrite and quasi-spheroidized carbides.

[0010] The chemical composition and mass percentage design basis of the above hot rolled carbon wire rod include:

[0011] (1) Carbon: As an effective strengthening element, C is cheaper than other alloying elements. It can increase the volume fraction of cementite strengthening phase in tempered troostite structure and improve the tensile strength of wire rod. However, too high C content will increase the central segregation, decarburization and precipitation tendency of network cementite during the solidification process of the alloy, making the cementite sheet thicker, which is not conducive to rapid tempering softening, and thus reducing the uniformity of the same circle and the plasticity of the wire rod. Therefore, in order to take into account the high strength of 1860MPa grade stranded wire, reduce the difficulty of controlling the uniformity of the same circle and consider the material cost, it is chosen to appropriately reduce the carbon content to reduce the component segregation, which is more conducive to the online molten salt strong isothermal refinement of cementite sheets to improve the strengthening effect and compensate for the strength loss. At the same time, the troostite peak precipitation temperature can be adjusted to make the pearlite phase region temperature higher, which can promote the melting and spheroidization of some cementite sheets with more thermal power. Therefore, the mass percentage of C is controlled to be 0.76%~0.79%.

[0012] (2) Silicon: The Si element is often used as a deoxidizer during the smelting process. It can improve the strength of the wire rod through solid solution strengthening, which is beneficial to obtaining a finer troostite structure. At the same time, it can inhibit the coarsening of cementite and accelerate the diffusion rate of carbon, which is beneficial to promote the melting and spheroidization of some cementite sheets. However, too high silicon will increase the decarburization tendency, prolong the phase transformation time, and cause the toughness to decrease, which is not conducive to the deep cold drawing of stranded wire manufacturing. Therefore, on the basis of reducing the C and Mn contents, in order to improve the strength of the wire rod and reduce the difficulty of tempering softening, the Si content is appropriately increased, and the mass percentage of Si is controlled to be 0.45%~0.55%.

[0013] (3) Manganese: Mn can be added as a deoxidizer during the steelmaking process. As an austenite stabilizing element, it can increase the strength of steel, reduce the phase transition temperature, improve the hardenability of wire rod, and then form a troostite structure with fine interlayer spacing to improve the matrix strength. However, when the Mn content is too high, it will increase the central alloy element segregation of the steel billet, increase the risk of abnormal structure precipitation and material cost, and reduce the diffusion activity of carbon. It is not conducive to promoting the melting and spheroidization of some cementite sheets during isothermal tempering, and reduce the drawing performance of wire rod. Therefore, in order to take into account the high strength-plasticity combination and uniformity of the hot-rolled carbon wire rod and the low material cost, it is chosen to appropriately reduce the Mn content, and the mass percentage of Mn is controlled to be 0.45%~0.68%.

[0014] (4) Phosphorus and sulfur: P and S are impurity elements. The lower the better. Therefore, P is controlled to be ≤ 0.014% and S is ≤ 0.014%.

[0015] The hot-rolled carbon wire rod adopts C-Mn-Si high-carbon carbon composition without adding Cr, V, B and other alloys, which can simplify the composition and appropriately reduce the C and Mn contents, which can not only further reduce the material cost compared with the existing 82B wire rod, but also reduce the component segregation, and then with a reasonable Si content, the sorbite phase transformation precipitation temperature is regulated to be higher, and the carbon diffusion rate is accelerated, which provides favorable conditions for promoting the rapid melting and spheroidization of cementite sheets. Furthermore, the above-mentioned manufacturing method selects a higher spinning temperature to ensure that the wire rod is in a high-temperature austenitized state to prevent the precipitation of net carbon in the spinning stage, and then directly adopts online molten salt strong isothermal treatment:

[0016] 1. Compared with the limited cooling capacity of the Stelmor air cooling line, the online molten salt strong isothermal treatment can use the high heat exchange capacity of the molten salt to promote the wire rod to cool down at a faster rate. On the one hand, it can cooperate with C and Mn to reduce the influence of segregation, quickly skip the network carbide precipitation range of 700~800℃, avoid the network carbon of high carbon steel is difficult to suppress and weaken its strengthening effect, deteriorate the uniformity and plasticity of the organization, and improve the matrix strength of C. On the other hand, compared with the existing use of elements such as Cr to make the wire rod obtain a refined troostite structure at a lower phase transformation temperature, the online molten salt strong isothermal treatment can make the wire rod quickly enter the pearlite phase region from the high temperature austenite state, provide a large degree of supercooling, and then make the wire rod form a structure dominated by troostite structure with fine lamellar spacing, making up for the strength loss caused by C, Mn content and simplified composition.

[0017] 2. Compared with the Stelmore air cooling line, which causes the decrease of uniformity in the same circle or the formation of abnormal structure due to the uncontrollable strong air volume and insufficient phase transformation, when the wire rod undergoes the online molten salt strong isothermal treatment, the molten salt can effectively reduce the temperature difference between different positions in the same circle of the wire rod and the edge to the core of the cross section by covering the surface of the wire rod and rapid heat exchange. On the one hand, it can control the wire rod to enter the pearlite phase area, so that the austenite structure from the edge to the core of the wire rod is evenly transformed into the troostite structure, improve the uniformity of content distribution, and avoid the wire rod entering the bainite or martensite phase area to produce abnormal structure that is unfavorable for drawing; on the other hand, the temperature of the wire rod and the molten salt can be kept consistent for a longer phase transformation treatment, which promotes the full transformation of the troostite structure of the wire rod like fine sheet interlayer spacing, and avoids the residual austenite from forming abnormal martensite structure during the subsequent roller slow cooling process, thereby improving the uniformity in the same circle and reducing the fluctuation of mechanical properties and the risk of wire breakage in deep drawing.

[0018] 3. Compared with the Stelmore air cooling line, which has limited cooling capacity and insufficient phase transformation or insufficient plasticity during continuous cooling, the above manufacturing method can maintain the wire rod in the pearlite phase region through online molten salt strong isothermal treatment, and carry out isothermal treatment for a longer time instead of continuous cooling. On the one hand, the austenite structure is continuously transformed into the troostite structure with fine lamellar spacing, which can increase the troostite structure content and thus improve the strength, compensating for the adverse effect of increasing Si content on prolonging the phase transformation time. On the other hand, the temperature of the pearlite phase region is relatively high under the composition design, and is higher than the temperature of the bainite phase region, which can provide more thermal power. During the long-term isothermal tempering of the wire rod, some cementite sheets are melted and spheroidized, thereby forming tempered troostite with better plasticity. A small amount of tempered ferrite and quasi-carbide are evenly distributed on the plastic matrix, reducing the organizational stress and dislocation density. Finally, it is slowly cooled through a roller, and the high temperature state of the wire rod after it comes out of the salt bath is used to slowly cool it. The softening and spheroidization effects of the later stage of the online molten salt strong isothermal treatment are continued to regulate the wire rod organization and strength and plasticity matching. Finally, on the basis of further reducing material costs compared to 82B wire rod, the strength and plasticity of the wire rod and the uniformity of the same turn are further improved, thereby reducing the risk of wire breakage in the downstream wire drawing process.

[0019] Selecting lower residual oxygen content in the heating furnace, soaking temperature in the heating furnace and time in the furnace before rolling can reduce the risk of decarburization in the furnace after the Si content of the high-carbon steel billet is increased, and promote composition homogenization. In a preferred embodiment, before rolling, the residual oxygen content in the heating furnace is controlled to be ≤1.5%, the soaking temperature in the heating furnace is ≤1100°C, and the time in the furnace is ≤4h.

[0020] After the billet is heated, an appropriate descaling water pressure is selected. The descaling water can be used to remove the oxide scale on the surface of the billet to prevent the oxide scale from being rolled into the wire rod and affecting the surface quality and organizational uniformity of the wire rod. In a preferred embodiment, the descaling water pressure after passing through the heating furnace before rolling is 15~18MPa.

[0021] Since the spinning temperature is relatively high, a higher rolling temperature can be selected to reduce the rolling line load and wear, and improve the rolling speed and efficiency. In a preferred embodiment, during the rolling, the initial rolling temperature is controlled to be 1050~1075℃, and the initial rolling reduction is 23%~30%.

[0022] Appropriate rolling temperature and reduction can be further selected to promote dynamic recrystallization during the final rolling process and refine the grains. In a preferred embodiment, during the rolling, the final rolling temperature is ≥910°C and the final rolling reduction is 30%~35%.

[0023] In a preferred embodiment, the molten salt temperature of the online molten salt strong isothermal treatment is 538~585℃, and the treatment time is 450~750s. The lower the molten salt temperature, the greater the degree of supercooling can be formed, the interlamellar spacing of the formed troostite structure is finer, the proportion of tempered troostite increases, and the proportion of tempered ferrite decreases, which can improve the strength of the wire rod matrix. However, if the molten salt temperature is too low, it is not conducive to promoting the melting and spheroidization of cementite sheets, resulting in a decrease in the plasticity of the wire rod, and even the appearance of bainite structure, which significantly loses the plasticity of the wire rod. On the contrary, the higher the molten salt temperature, the more thermal power can be provided, which is beneficial to the tempering of the troostite structure and the melting and spheroidization of the cementite sheets into quasi-spheroidized carbides, thereby increasing the plasticity of the wire rod. However, if the molten salt temperature is too high, it will be detrimental to the troostite structure sheets. The layer refinement is unfavorable, and even a pearlite structure with coarse interlamellar spacing is produced, the proportion of tempered ferrite increases, and even the cooling rate of the wire rod decreases, which is not conducive to suppressing the network carbon and leads to a decrease in the strength and plasticity of the wire rod; the longer the treatment time, the better the softening effect of the wire rod in high-temperature isothermal treatment, and the plasticity of the wire rod increases. However, if the treatment time is too long, it will affect the production efficiency of the wire rod and lose the strength of the wire rod. On the contrary, the shorter the treatment time, the lower the spheroidization and softening effects, the plasticity of the wire rod decreases, and the strength increases. However, if the treatment time is too short, the wire rod is not softened, resulting in insufficient plasticity, or the strength decreases or abnormal structure is caused due to insufficient phase transformation of the troostite. Therefore, the molten salt temperature and treatment time of the online molten salt intensive isothermal treatment can be further controlled to regulate the strength and plasticity matching of the wire rod.

[0024] In a preferred embodiment, the online molten salt intensive isothermal treatment is divided into a front-stage treatment and a back-stage treatment. The treatment time of the front-stage treatment is ≥40s, the molten salt circulation rate is 460~660t / h, the molten salt temperature rise is ≤10°C, and the cooling rate of the wire rod from the high-temperature austenite state of spinning into the pearlite phase region is relatively fast. A higher molten salt circulation rate is used to control the molten salt temperature rise, which can inhibit the formation of network carbon and form a structure dominated by a troostite structure with fine lamellar spacing, thereby improving the matrix strength.

[0025] In a preferred embodiment, the molten salt circulation rate of the post-stage treatment is 150~280t / h, and the molten salt temperature rise is ≤3°C. The post-stage treatment can promote the untransformed residual austenite to continue to transform into a troostite structure with fine lamellar spacing, promote the formed troostite structure with fine lamellar spacing to undergo long-term isothermal tempering, and promote the melting and spheroidization of some cementite sheets. At the same time, a higher molten salt circulation rate is adopted than in the whole process. The post-stage treatment can accurately control the temperature and reduce production energy consumption by appropriately reducing the molten salt circulation rate.

[0026] In a preferred embodiment, the roller slow cooling controls the wire rod to be cooled to below 300°C at a slow cooling rate of 0.52-0.75°C / s for coiling, which can promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod.

[0027] Since the slow cooling rate of the roller slow cooling is relatively high, in a preferred embodiment, the roller slow cooling adopts a heat preservation cover to be closed, which can increase the roller speed and make the wire rod quickly come off the line, thereby improving production efficiency, or the heat preservation cover is not closed tightly and hot air from the salt bath tank of online molten salt strong isothermal treatment is blown to the conveying roller of the wire rod, which can control the slow cooling speed of the wire rod and blow away the molten salt on the surface of the wire rod at the same time.

[0028] A hot-rolled carbon wire rod for 1860 MPa grade stranded wire, wherein the hot-rolled carbon wire rod is manufactured by any one of the above-mentioned methods for manufacturing the hot-rolled carbon wire rod for 1860 MPa grade stranded wire.

[0029] The above-mentioned hot-rolled carbon wire rod adopts a carbon component with reduced C and Mn content, and the material cost is low. At the same time, the microstructure is mainly tempered troostite, containing a small amount of tempered ferrite and quasi-spheroidized carbide. The interlamellar spacing of troostite is finer than that of pearlite, and the strength is higher. After troostite is tempered and the cementite sheets are melted and spheroidized to transform into tempered troostite and quasi-spheroidized carbides, the organizational stress and dislocation density decrease, and the plasticity is further improved. The tempered troostite content is high, which can make up for the strength loss caused by reducing the C and Mn content and not adding other alloy components. At the same time, it does not contain abnormal tissues such as martensite and bainite. The toughened mixed tissue can make the wire rod have better plasticity and drawing properties than the existing pearlite stranded wire steel wire rod, so that when it is used to manufacture 1860MPa grade stranded wire, the risk of wire breakage during drawing and stranding can be reduced.

[0030] Smaller tempered troostite interlamellar spacing can make the wire rod stronger, but too small interlamellar spacing is accompanied by a decrease in the molten salt temperature, which is not conducive to controlling isothermal tempering softening. In a preferred embodiment, the interlamellar spacing of the tempered troostite is 90-130 nm.

[0031] In a preferred embodiment, the network carbide level of the hot-rolled carbon wire rod is level 0, which can avoid the adverse effects of the network carbide on the uniformity and plasticity of the wire rod and reduce the risk of wire breakage.

[0032] Since the uniformity of the structure from the edge to the core of the wire rod is improved and no abnormal structure is contained, the fluctuation of the mechanical properties is reduced accordingly. In a preferred embodiment, the mechanical property difference of the hot-rolled carbon wire rod is ≤32MPa.

[0033] In a preferred embodiment, the hot-rolled carbon wire rod has a diameter of 10~15mm, a tensile strength of 1250~1300MPa, and a cross-sectional reduction rate of 38%~43%. The smaller wire rod diameter allows the wire rod to quickly reach the target diameter of the stranded wire during drawing. The higher tensile strength can reduce the number of drawing passes in the process of manufacturing 1860MPa stranded wire and quickly reach the corresponding strength grade. The higher cross-sectional reduction rate enables the wire rod to have better drawing performance and can reduce the risk of wire breakage during drawing and stranding.

[0034] Compared with the prior art, the beneficial effects of the present invention are at least:

[0035] (1) In view of the high cost of existing 82B and other eutectoid steel wire rod materials, it is often difficult to control the formation of network carbon during the phase transformation process of the Stelmor air-cooled line, resulting in a decrease in the plasticity of the wire rod and poor uniformity in the same coil, which increases the risk of wire breakage in the downstream wire drawing process. The manufacturing method of the present invention adopts the eutectoid carbon chemical composition design combined with the online molten salt strong isothermal technology process design to control the wire rod to quickly skip the network carbon interval from the high-temperature austenite state to the pearlite phase region, inhibit the formation of network carbon and form a structure dominated by a fine lamellar spacing troostite structure, compensate for the strength loss caused by reducing the C and Mn content and not adding other alloy components, and at the same time promote the formation of a fine lamellar spacing troostite structure for a long time isothermal tempering, promote the melting and spheroidization of some cementite sheets, and finally improve the tempering softening effect of the wire rod through slow cooling on a roller, so as to adjust the strength and plasticity matching of the wire rod, achieve high strength and plasticity matching, improve the uniformity in the same coil, and have good industrial adaptability.

[0036] (2) In view of the current situation that the hot-rolled wire rod for 1860MPa grade stranded wire steel has high material cost, insufficient strength and plasticity, and large fluctuations in mechanical properties, the hot-rolled carbon wire rod of the present invention can simplify the composition and appropriately reduce the C and Mn contents, further reducing the material cost and the influence of segregation. The microstructure type is a mixed structure composed of a high content of tempered troostite, a small amount of tempered ferrite, and quasi-spheroidized carbides, which can improve the strengthening effect of the carbon element and inhibit the precipitation of network carbides. It does not contain abnormal structures, and the stress and dislocation density of the structure are reduced by regulating the tempering state, so as to achieve high strength and plasticity matching of the wire rod, and achieve a tensile strength of 1250~1300MPa, a cross-sectional shrinkage rate of 38%~43%, and a mechanical property circle difference of ≤32MPa. It is used for the manufacture of 1860MPa grade stranded wire, which can reduce the risk of wire breakage in the downstream wire drawing process and has good market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0038] Figure 1 is a metallographic structure diagram of Example 1 of the present invention;

[0039] Figure 2 is the metallographic structure diagram of Example 2 of the present invention;

[0040] Figure 3 It is the metallographic structure diagram of Example 3 of the present invention. DETAILED DESCRIPTION

[0041] The embodiments described below with reference to the accompanying drawings are exemplary and are only for illustration and do not limit the description of the features and characteristics of the present invention, so as to propose the best way to implement the present invention, and are intended to be used to explain the present invention and are sufficient to enable those skilled in the art to implement the present invention, but cannot be understood as any limitation on the scope of the present invention, which is limited only by the appended claims; the organization and performance testing of the hot-rolled wire rods obtained in the following embodiments and comparative examples include: the tensile test is carried out using "GB-T 228.1-2021 Metallic Material Tensile Test Part 1: Room Temperature Test Method" to obtain the tensile strength and cross-sectional reduction rate; the organization test is carried out according to the metal microstructure detection method of GB / T13298 standard; the mechanical property same circle difference test method: take 2 circles of wire rod 5m away from the end of the coil, take the overlap area position as the base point, divide each circle of wire rod into 8 sections on average, take 1 tensile specimen on each section, and the strength extreme difference of the tensile specimen after the tensile test is the mechanical property same circle difference. Embodiment 1:

[0042] A preferred embodiment of the method for manufacturing the hot-rolled carbon wire rod for 1860MPa grade stranded wire of the present invention, the chemical composition and mass percentage of the hot-rolled carbon wire rod include: C: 0.77%, Si: 0.53%, Mn: 0.68%, P: 0.014%, S: 0.014%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt strong isothermal → roller slow cooling → coiling, specifically:

[0043] The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled and plastic, reduce the risk of decarburization of the steel billet in the furnace, remove the surface oxide scale of the steel billet through high-pressure descaling water after leaving the heating furnace, and send it to the rolling line. The rolling line rolls the steel billet into a wire with a diameter specification of 15mm. The appropriate rolling temperature and reduction amount are selected to promote dynamic recrystallization in the final rolling process and refine the grains. Specifically: the heating furnace is heated up in sequence according to preheating, heating, and soaking, and the residual oxygen content in the heating furnace is controlled to be ≤1.4 %, the heating furnace soaking temperature is 1100℃, the furnace time is 4h, the descaling water pressure is 18MPa, the initial rolling temperature is 1075℃, the initial rolling reduction is 23%, the final rolling temperature is 925℃, and the final rolling reduction is 30%; the wire-spinning process is used to convert the wire rod coming out of the rolling line into wire rods through the wire-spinning mechanism, and the wire rods are spread on the roller and transported along the roller. The higher wire-spinning temperature ensures that the wire rod is in a high-temperature austenitized state and prevents the precipitation of network carbon, providing favorable conditions for obtaining sorbite nucleation. Specifically: the wire-spinning temperature is controlled to be 905℃.

[0044] The online molten salt strong isothermal process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 35°C / s, and quickly passes through the network carbon interval from the high-temperature austenite state to the pearlite phase area, inhibiting the formation of network carbon and forming a structure dominated by a fine lamellar spacing sorbite structure, and then conveyed by a roller through the second stage salt bath tank for back-end treatment, promoting the untransformed residual austenite to continue to transform into a fine lamellar spacing sorbite structure. The formed fine lamellar spacing troostite structure is promoted to undergo long-term isothermal tempering, which causes some cementite sheets to melt and spheroidize, so as to regulate the strength-plasticity matching of the wire rod. Specifically, the molten salt temperature of the front-end treatment and the back-end treatment is 585°C, the treatment time of the front-end treatment is 45s, the molten salt circulation volume is 460t / h, and the molten salt temperature rise is ≤10°C; the treatment time of the back-end treatment is 510s, the molten salt circulation volume is 240t / h, and the molten salt temperature rise is ≤3°C, that is, the online molten salt strong isothermal treatment time is 555s.

[0045] The roller slow cooling process adopts closing the heat preservation cover, and the wire rod coming out of the second salt bath tank is transported into the heat preservation cover by the conveying roller for slow cooling treatment, so as to promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod. Specifically, the wire rod is controlled to be cooled to 295°C at a slow cooling rate of 0.75°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the hot-rolled carbon wire rod product is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 1 shown.

[0046] Comparative Example 1:

[0047] A method for manufacturing hot-rolled carbon wire rod, the difference between the manufacturing method and embodiment 1 is that: the manufacturing method is manufactured according to the process flow of rolling → spinning → Stelmor strong air cooling → roller slow cooling, specifically: the heating furnace is controlled to have a soaking temperature of 1075°C, the furnace time is 4.5h, the initial rolling temperature is 1035°C, the final rolling temperature is 900°C, and the spinning temperature is 875°C; the Stelmor strong air cooling adopts an air volume of 200,000 m per fan 3 / h, open 1~7# fans at 80%, cool the wire rod to 600℃ at a cooling rate of 7.5℃ / s, and slow cool the roller by closing the fan and covering with a heat preservation cover, cool the wire rod to 295℃ at a cooling rate of 1.1℃ / s. After coming off the line, the hot-rolled carbon wire rod is obtained.

[0048] Comparative Example 2:

[0049] A method for manufacturing a hot-rolled carbon wire rod, which differs from Example 1 in that: the heating furnace soaking temperature is controlled to be 1075°C, the furnace time is 4.5h, the initial rolling temperature is 1035°C, the final rolling temperature is 900°C, the spinning temperature is 875°C, the wire rod is cooled at a cooling rate of 30°C / s during online molten salt intensive isothermal treatment, and a hot-rolled carbon wire rod finished product is obtained after going offline. Embodiment 2:

[0050] A preferred embodiment of the method for manufacturing the hot-rolled carbon wire rod for 1860MPa grade stranded wire of the present invention, the chemical composition and mass percentage of the hot-rolled carbon wire rod include: C: 0.76%, Si: 0.55%, Mn: 0.65%, P: 0.012%, S: 0.012%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt strong isothermal → roller slow cooling → coiling, specifically:

[0051] The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled and plastic, reduce the risk of decarburization of the steel billet in the furnace, remove the surface oxide scale of the steel billet through high-pressure descaling water after leaving the heating furnace, and send it to the rolling line. The rolling line rolls the steel billet into a wire with a diameter specification of 14mm. The appropriate rolling temperature and reduction amount are selected to promote dynamic recrystallization in the final rolling process and refine the grains. Specifically: the heating furnace is heated up in sequence according to preheating, heating, and soaking, and the residual oxygen content in the heating furnace is controlled to be ≤1.5 %, the heating furnace soaking temperature is 1090℃, the furnace time is 4h, the descaling water pressure is 17MPa, the initial rolling temperature is 1070℃, the initial rolling reduction is 25%, the final rolling temperature is 920℃, and the final rolling reduction is 32%; the wire-spinning process is used to convert the wire rod coming out of the rolling line into wire rods through the wire-spinning mechanism, and the wire rods are spread on the roller and transported along the roller. The higher wire-spinning temperature ensures that the wire rod is in a high-temperature austenitized state and prevents the precipitation of network carbon, providing favorable conditions for obtaining sorbite nucleation. Specifically: the wire-spinning temperature is controlled to be 900℃.

[0052] The online molten salt strong isothermal process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 36°C / s, and quickly passes through the network carbon interval from the high-temperature austenite state to the pearlite phase area, inhibiting the formation of network carbon and forming a structure dominated by a fine lamellar spacing sorbite structure, and then conveyed by a roller through the second stage salt bath tank for back-end treatment, promoting the untransformed residual austenite to continue to transform into a fine lamellar spacing sorbite structure. The formed fine lamellar spacing troostite structure is promoted to undergo long-term isothermal tempering, which causes some cementite sheets to melt and spheroidize, so as to regulate the strength-plasticity matching of the wire rod. Specifically: the molten salt temperature of the front-end treatment and the back-end treatment is 567°C, the treatment time of the front-end treatment is 50s, the molten salt circulation volume is 500t / h, and the molten salt temperature rise is ≤10°C; the treatment time of the back-end treatment is 560s, the molten salt circulation volume is 200t / h, and the molten salt temperature rise is ≤3°C, that is, the online molten salt strong isothermal treatment time is 610s.

[0053] The roller slow cooling process adopts closing the heat preservation cover, and the wire rod coming out of the second salt bath tank is transported into the heat preservation cover by the conveying roller for slow cooling treatment, so as to promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod. Specifically, the wire rod is controlled to be cooled to 280°C at a slow cooling rate of 0.65°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the hot-rolled carbon wire rod product is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 2 shown.

[0054] Comparative Example 3:

[0055] A method for manufacturing a hot-rolled carbon wire rod, the manufacturing method of which differs from that of Example 2 in that: during the online molten salt intensive isothermal treatment, the molten salt temperature of the front-end treatment and the back-end treatment is 590°C, the wire rod is cooled at a cooling rate of 34°C / s, and a hot-rolled carbon wire rod finished product is obtained after going offline.

[0056] Comparative Example 4:

[0057] A method for manufacturing a hot-rolled carbon wire rod, the manufacturing method of which differs from Example 2 in that: during the online molten salt intensive isothermal treatment, the molten salt temperature of the front-end treatment and the back-end treatment is 520°C, the wire rod is cooled at a cooling rate of 39°C / s, and the hot-rolled carbon wire rod finished product is obtained after going offline. Embodiment 3:

[0058] A preferred embodiment of the method for manufacturing the hot-rolled carbon wire rod for 1860MPa grade stranded wire of the present invention, the chemical composition and mass percentage of the hot-rolled carbon wire rod include: C: 0.78%, Si: 0.49%, Mn: 0.45%, P: 0.012%, S: 0.014%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt strong isothermal → roller slow cooling → coiling, specifically:

[0059] The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled and plastic, reduce the risk of decarburization of the steel billet in the furnace, remove the surface oxide scale of the steel billet through high-pressure descaling water after leaving the heating furnace, and send it to the rolling line. The rolling line rolls the steel billet into a wire with a diameter specification of 10mm. The appropriate rolling temperature and reduction amount are selected to promote dynamic recrystallization in the final rolling process and refine the grains. Specifically: the heating furnace is heated up in sequence according to preheating, heating, and soaking, and the residual oxygen content in the heating furnace is controlled to be ≤1.3 %, the heating furnace soaking temperature is 1080℃, the furnace time is 3h, the descaling water pressure is 15MPa, the initial rolling temperature is 1060℃, the initial rolling reduction is 30%, the final rolling temperature is 915℃, and the final rolling reduction is 35%; the wire-spinning process is used to convert the wire rods leaving the rolling line into wire rods through the wire-spinning mechanism, and the wire rods are spread on the roller and transported along the roller. The higher wire-spinning temperature ensures that the wire rods are in a high-temperature austenitized state and prevents the precipitation of network carbon, providing favorable conditions for obtaining sorbite nucleation. Specifically: the wire-spinning temperature is controlled to be 895℃.

[0060] The online molten salt strong isothermal process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 37°C / s, and quickly passes through the network carbon interval from the high-temperature austenite state to the pearlite phase area, inhibiting the formation of network carbon and forming a structure dominated by a fine lamellar spacing sorbite structure, and then conveyed by a roller through the second stage salt bath tank for back-end treatment, promoting the untransformed residual austenite to continue to transform into a fine lamellar spacing sorbite structure. The formed fine lamellar spacing troostite structure is promoted to undergo long-term isothermal tempering, which causes some cementite sheets to melt and spheroidize, so as to regulate the strength-plasticity matching of the wire rod. Specifically, the molten salt temperature of the front-end treatment and the back-end treatment is 549°C, the treatment time of the front-end treatment is 55s, the molten salt circulation volume is 590t / h, and the molten salt temperature rise is ≤10°C; the treatment time of the back-end treatment is 695s, the molten salt circulation volume is 150t / h, and the molten salt temperature rise is ≤3°C, that is, the online molten salt strong isothermal treatment time is 750s.

[0061] The roller slow cooling process uses an insulation cover that is not closed tightly, and the wire rod coming out of the second salt bath tank is transported by a conveying roller for slow cooling treatment. The hot air above the two salt bath tanks with a temperature of more than 230°C is blown to the conveying roller of the wire rod to promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod. Specifically: the wire rod is controlled to be cooled to 290°C at a slow cooling rate of 0.6°C / s; the coiling process is used to coil the wire rod into a coil through a coiling drum, and the hot-rolled carbon wire rod product is obtained after packaging and storage. Its metallographic structure diagram is as follows Figure 3 shown.

[0062] Comparative Example 5:

[0063] A method for manufacturing a hot-rolled carbon wire rod, which differs from Example 3 in that during online molten salt strong isothermal treatment, the processing time of the front-end treatment is 55s, and the processing time of the back-end treatment is 795s, that is, the online molten salt strong isothermal treatment time is 850s, and the hot-rolled carbon wire rod finished product is obtained after going offline.

[0064] Comparative Example 6:

[0065] A method for manufacturing a hot-rolled carbon wire rod, the manufacturing method of which differs from Example 3 in that: during online molten salt strong isothermal treatment, the processing time of the front-end treatment is 55s, and the processing time of the back-end treatment is 345s, that is, the online molten salt strong isothermal treatment time is 400s, and the hot-rolled carbon wire rod finished product is obtained after going offline. Embodiment 4:

[0066] A preferred embodiment of the method for manufacturing the hot-rolled carbon wire rod for 1860MPa grade stranded wire of the present invention, the chemical composition and mass percentage of the hot-rolled carbon wire rod include: C: 0.79%, Si: 0.45%, Mn: 0.52%, P: 0.014%, S: 0.013%, and the rest is Fe and unavoidable impurities; the manufacturing method is manufactured according to the process flow of rolling → spinning → online molten salt strong isothermal → roller slow cooling → coiling, specifically:

[0067] The rolling process is used to heat the steel billet with a specification of 220mm×220mm through a heating furnace to achieve a high-temperature steel billet that can be rolled and plastic, reduce the risk of decarburization of the steel billet in the furnace, remove the surface oxide scale of the steel billet through high-pressure descaling water after leaving the heating furnace, and send it to the rolling line. The rolling line rolls the steel billet into a wire with a diameter specification of 12mm. The appropriate rolling temperature and reduction amount are selected to promote dynamic recrystallization in the final rolling process and refine the grains. Specifically: the heating furnace is heated up in sequence according to preheating, heating, and soaking, and the residual oxygen content in the heating furnace is controlled to be ≤1.3% The heating furnace has an average heating temperature of 1075°C, a furnace time of 3.5h, a descaling water pressure of 16MPa, an initial rolling temperature of 1050°C, an initial rolling reduction of 28%, a final rolling temperature of 910°C, and a final rolling reduction of 34%; the spinning process is used to convert the wire rods coming out of the rolling line into wire rods through a spinning mechanism, and the wire rods are spread on the rollers and transported along the rollers. The higher spinning temperature ensures that the wire rods are in a high-temperature austenitized state and prevents the precipitation of network carbon, providing favorable conditions for obtaining sorbite nucleation. Specifically, the spinning temperature is controlled to be 890°C.

[0068] The online molten salt strong isothermal process adopts a two-stage salt bath tank with molten salt inside. The wire rod after spinning is conveyed by a roller through the first stage salt bath tank for front-end treatment, so that the wire rod is cooled at a cooling rate of 38°C / s, and quickly passes through the network carbon interval from the high-temperature austenite state to the pearlite phase area, inhibiting the formation of network carbon and forming a structure dominated by a fine lamellar spacing sorbite structure, and then conveyed by a roller through the second stage salt bath tank for back-end treatment, promoting the untransformed residual austenite to continue to transform into a fine lamellar spacing sorbite structure. The formed fine lamellar spacing troostite structure is promoted to undergo long-term isothermal tempering, which causes some cementite sheets to melt and spheroidize, so as to regulate the strength-plasticity matching of the wire rod. Specifically, the molten salt temperature of the front-end treatment and the back-end treatment is 538°C, the treatment time of the front-end treatment is 40s, the molten salt circulation volume is 660t / h, and the molten salt temperature rise is ≤10°C; the treatment time of the back-end treatment is 410s, the molten salt circulation volume is 280t / h, and the molten salt temperature rise is ≤3°C, that is, the online molten salt strong isothermal treatment time is 450s.

[0069] The roller slow cooling process uses an insulation cover that is not closed tightly, and the wire rod coming out of the second salt bath tank is transported by a conveyor roller for slow cooling treatment. Hot air with a temperature of more than 230°C above the two salt bath tanks is blown to the conveyor roller of the wire rod to promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod. Specifically: the wire rod is controlled to be cooled to 292°C at a slow cooling rate of 0.52°C / s; the coiling process is used to coil the wire rod into a coil by a coiling drum, and the hot-rolled carbon wire rod product is obtained after packaging and storage.

[0070] Comparative Example 7:

[0071] A method for manufacturing a hot-rolled carbon wire rod, which differs from Example 4 in that: the method is manufactured according to the process flow of rolling → spinning → online molten salt strong isothermal → air cooling, the air cooling adopts the heat preservation cover to open, and the wire rod coming out of the second salt bath tank is transported by a conveyor roller for air cooling treatment, and the wire rod is controlled to be cooled at a slow cooling rate of 2.1°C / s; after coming off the line, the hot-rolled carbon wire rod finished product is obtained.

[0072] The hot rolled carbon wire rods obtained in the above examples 1 to 4 and comparative examples 1 to 7 were subjected to microstructure and performance tests, and the comparative results obtained are shown in Table 1 below:

[0073] Table 1. Comparison of microstructure and performance of hot rolled carbon wire rods with different compositions and manufacturing methods

[0074]

[0075] From the comparison results of Example 1 and Comparative Example 1, it can be seen that compared with the phase transformation process of the Stelmor air-cooled wire, it is difficult to control the formation of network carbon, the pearlite lamellar spacing is large and the content is low, the organizational stress and dislocation density are high, resulting in insufficient strength and plasticity of the wire rod, poor uniformity in the same circle, and an increased risk of wire breakage in the downstream wire drawing process. The present invention adopts the eutectoid carbon chemical composition design combined with the online molten salt strong isothermal technology process design to control the wire rod to quickly skip the network carbon interval from the high-temperature austenite state to enter the pearlite phase region, inhibit the formation of network carbon and form a structure dominated by a troostite structure with fine lamellar spacing, which can To compensate for the strength loss caused by reducing the C and Mn contents and not adding other alloy components, the strength of the wire rod is improved. At the same time, after a long period of isothermal tempering, some cementite sheets can be melted and spheroidized to regulate the strength-plasticity matching of the wire rod, achieve high strength and plasticity matching, and improve the uniformity of the same turn. It can be seen from the results of Examples 1 to 4 that the preferred performance of the present invention can reach a tensile strength of 1250 to 1300 MPa, a cross-sectional shrinkage rate of 38% to 43%, and a mechanical property same-turn difference of ≤32 MPa. It is used for the manufacture of 1860 MPa-grade stranded wire, and can reduce the risk of wire breakage in the downstream wire drawing process.

[0076] From the comparison results of Example 1 and Comparative Example 2, it can be seen that a higher spinning temperature not only ensures that the wire rod is in a high-temperature austenitized state to prevent the precipitation of carbon in the spinning stage, which is beneficial to the formation of a larger degree of supercooling to form troostite with finer interlamellar spacing, but also can reduce the restriction on the rolling temperature, thereby reducing the rolling line load and wear, and improving the rolling speed and efficiency.

[0077] From the comparison results of Example 2 and Comparative Example 3, it can be seen that the higher the molten salt temperature of the online molten salt intensive isothermal treatment, the more thermal power it can provide, which is beneficial to the tempering of the troostite structure and the melting and spheroidization of the cementite sheets into quasi-spheroidized carbides, thereby increasing the plasticity of the wire rod. However, if the molten salt temperature is too high, it is not conducive to the refinement of the troostite structure lamellae, and may even produce pearlite structure with coarse lamella spacing, resulting in a decrease in the strength of the wire rod.

[0078] From the comparison results of Example 2 and Comparative Example 4, it can be seen that the lower the molten salt temperature of the online molten salt strong isothermal treatment, the greater the degree of supercooling can be formed, the interlamellar spacing of the formed troostite structure is finer, the proportion of tempered troostite increases, and the proportion of tempered ferrite decreases, which can improve the strength of the wire rod matrix. However, if the molten salt temperature is too low, it is not conducive to promoting the melting and spheroidization of cementite sheets, resulting in a decrease in the plasticity of the wire rod.

[0079] From the comparison results of Example 3 and Comparative Example 5, it can be seen that the longer the treatment time of the online molten salt intensive isothermal treatment, the better the softening effect of the wire rod in the high-temperature isothermal treatment, and the plasticity of the wire rod increases, but if the treatment time is too long, it will affect the production efficiency of the wire rod and lose the strength of the wire rod; from the comparison results of Example 3 and Comparative Example 6, it can be seen that if the treatment time of the online molten salt intensive isothermal treatment is too short, the wire rod is not softened, resulting in insufficient plasticity.

[0080] From the comparison results of Example 4 and Comparative Example 7, it can be seen that slow cooling on the roller can promote further toughening of the wire rod structure and improve the tempering and softening effect of the wire rod. At the same time, the slow cooling rate is relatively high, which can increase the roller speed to make the wire rod go off the line quickly and improve production efficiency.

[0081] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. All equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for manufacturing a hot-rolled carbon wire rod for 1860MPa grade stranded wire, characterized in that: The manufacturing method thereof comprises: The wire rod is produced by rolling according to the chemical composition of the hot-rolled carbon wire rod, wherein the chemical composition and mass percentage of the hot-rolled carbon wire rod include: C: 0.76%~0.79%, Si: 0.45%~0.55%, Mn: 0.45%~0.68%, P≤0.014%, S≤0.014%, and the rest are Fe and unavoidable impurities; after the wire rod is spun into a wire rod at a spinning temperature of ≥890°C, it is subjected to an online molten salt strong isothermal treatment to make the wire rod ≥3 The temperature is lowered at a cooling rate of 5°C / s from the austenite state into the pearlite phase region, the troostite phase transformation is promoted and isothermal tempering is performed, the melting and spheroidization of some cementite sheets are promoted, and finally, the hot-rolled carbon wire rod is made into a mixed structure consisting of tempered troostite with a volume percentage of ≥94% and the rest of tempered ferrite and quasi-spheroidized carbides. The molten salt temperature of the online molten salt strong isothermal treatment is 538~585°C, and the treatment time is 450~750s.

2. The method for manufacturing the hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 1, characterized in that: Before the rolling, the residual oxygen content in the heating furnace is controlled to be ≤1.5%, the soaking temperature of the heating furnace is ≤1100°C, the time in the furnace is ≤4h, and the descaling water pressure after passing through the heating furnace is 15-18MPa.

3. The method for manufacturing the hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 1, characterized in that: During the rolling, the initial rolling temperature is controlled to be 1050-1075° C., the initial rolling reduction is 23%-30%, the final rolling temperature is ≥910° C., and the final rolling reduction is 30%-35%.

4. The method for manufacturing the hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 1, characterized in that: The online molten salt strong isothermal treatment is divided into a front-end treatment and a back-end treatment. The treatment time of the front-end treatment is ≥40s, the molten salt circulation volume is 460~660t / h, and the molten salt temperature rise is ≤10°C.

5. The method for manufacturing the hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 4, characterized in that: The molten salt circulation rate of the latter stage treatment is 150-280 t / h, and the molten salt temperature rise is ≤3°C.

6. The method for manufacturing the hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 1, characterized in that: The roller slow cooling controls the wire rod to be cooled to below 300° C. at a slow cooling rate of 0.52-0.75° C. / s for coiling.

7. A hot-rolled carbon wire rod for 1860MPa grade stranded wire, characterized in that: The hot-rolled carbon wire rod is manufactured by the method for manufacturing hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to any one of claims 1 to 6.

8. The hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 7, characterized in that: The interlamellar spacing of the tempered bainite is 90-130 nm, the network carbide grade of the hot-rolled carbon wire rod is grade 0, and the mechanical property difference is ≤32 MPa.

9. The hot-rolled carbon wire rod for 1860 MPa grade stranded wire according to claim 7, characterized in that: The hot-rolled carbon wire rod has a diameter of 10-15 mm, a tensile strength of 1250-1300 MPa, and a cross-sectional shrinkage of 38%-43%.

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