A high carbon steel wire rod with a diameter of ≤6.5 mm and excellent bending ability and a production method thereof

Abstract

A high carbon steel wire rod with a diameter of ≤6.5mm and excellent bending ability, the chemical composition and wt% of which are: under the existing components in the field of this steel type, it is: P≤0.012wt%, S≤0.009wt%, Cu≤0.095wt%; production method: heating the ingot after smelting and pouring into a billet; rolling; spinning; cooling; bundling and packaging after air cooling to room temperature. The present invention provides a kind of wire rod with uniform and stable performance after 15 days of aging under the premise of ensuring mechanical properties, wire rod segregation ≤2.0 level, no obvious softening zone in the cross section, pearlite volume proportion in the metallographic structure is not less than 80%; elongation ≥9.0%, surface reduction ≥35.0%, strength circle difference ≤65MPa, cross-section microhardness extreme difference ≤15%, repeated bending times ≥18.0 times, bending wire breakage during deep processing is less than 0.5 times / kiloton.

Description

Technical Field

[0001] The present invention relates to a wire rod and a production method, in particular to a high-carbon steel wire rod with a diameter of ≤6.5mm and excellent bending ability, which is suitable for any steel type with a component composition in the technical field, i.e., a tensile strength of not less than 980MPa and above. Background Art

[0002] High carbon wire rods are mostly drawn materials, which need to be drawn and heat treated during use. Taking cord steel as an example, its downstream deep processing procedures include more than twenty drawing and heat treatment processes in total.

[0003] In order to ensure the surface quality of the wire rod during the drawing process, the iron oxide scale on the surface of the wire rod needs to be removed before continuous cold drawing. With the increasingly stringent requirements of society for energy conservation and environmental protection, the traditional pickling process has been gradually eliminated and replaced by mechanical descaling, which mainly includes two processes: belt grinding and repeated bending. For large-sized wire rods (>6.5mm), due to the large diameter of the wire rod, it is impossible to be bent repeatedly. At present, the belt grinding process is mostly used; however, for small-sized wire rods, that is, those with a diameter of ≤6.5mm, for economic considerations, the more cost-effective repeated bending process is currently used to remove the surface iron oxide scale. During the repeated bending process of the wire rod, the iron oxide scale on the surface of the wire rod is peeled off from the matrix, making it suitable for subsequent drawing. In this process, the wire rod is only subjected to bending and is not subjected to drawing deformation. In this process, manual welding is required after the wire rod breaks, which will increase the risk of material breakage in the subsequent processing process, generate unnecessary manual labor, and cause some material waste.

[0004] However, such fractures cannot be completely avoided in actual operation. The current wire breakage rate is about 5.0 to 10.0 times / kt, and the wire breakage rate increases significantly with the increase of wire rod carbon equivalent. Although the wire rod fractures in the process of bending and dephosphorization have various forms, they are all caused by the low and uneven plasticity of the wire rod.

[0005] After searching:

[0006] The document with Chinese patent publication number CN101208445 discloses "A high-strength wire with excellent wire drawing performance and its manufacturing method". It is obtained by directly quenching the hard steel wire with a determined composition with molten salt after hot rolling, or quenching it with molten salt or lead after austenitization, wherein pearlite is the main body, and the average area ratio of the non-pearlite structure composed of primary ferrite, pseudo-pearlite or bainite in the cross section is less than 5%, or in the part from the surface to a depth of 100μm, the average area ratio of the non-pearlite structure is less than 10%. The document emphasizes an offline quenching process, and the microstructure includes pearlite, primary ferrite, pseudo-pearlite or bainite, etc. This patent introduces a conventional Stelmor controlled cooling process, the structure is mainly pearlite and ferrite, there is no abnormal structure such as martensite, the uniformity is good, and it has excellent bending ability. The two inventions are significantly inconsistent.

[0007] The document with Chinese patent publication number CN101331243 discloses "A high-strength wire with excellent wire drawing properties and a method for manufacturing the same". Although the document can obtain a wire with excellent wire drawing processability, good production efficiency, high yield rate and low cost, the patent does not stipulate the specific cooling control method of the wire rod, and focuses more on the drawability of the wire rod, which is significantly different from the emphasis on the cooling control process of the wire rod in this patent.

[0008] The document with Chinese patent publication number CN101649416, which involves "a high carbon steel wire rod with a tensile strength of more than 1200MPa and a surface shrinkage of more than 35% and its preparation process", contains basic components such as C, Si, Mn, Cr and V, as well as optional components such as Ni, Cu, Al, B, Ti, Nb and Mo; its preparation process includes: smelting, casting, rolling and controlled cooling processes in sequence, the rolling temperature of the rolling process is controlled between 1000 and 1100°C, the wire drawing temperature is 870 to 930°C, the controlled cooling process adopts Stelmor controlled cooling, rapid cooling is adopted before and in the early stage of phase change, and slow cooling is adopted in the late stage of phase change. Although the high carbon steel wire rod has excellent mechanical properties, less alloying elements, and low cost, its preparation process is only a small adjustment to the existing high carbon steel wire rod production process, and it will hardly increase any production cost. This patent provides a "fast cooling + slow cooling" process idea, which is a typical cooling control method. In order to avoid excessively high coiling temperature, affecting subsequent shearing and bundling processes, and to ensure the thickness of the iron oxide scale, this patent proposes the "fast cooling + slow cooling + fast cooling" idea, and quantifies the specific cooling rate. In addition, in order to avoid uneven internal structure of the wire rod caused by temperature changes during the cooling process, combined with the wire environment, the specific numerical upper limit of the change process is emphasized to improve the bending ability of the material. There are obvious differences between the two inventions.

[0009] The document with Chinese patent publication number CN101921897 discloses a method for reducing carbon segregation inside high carbon steel. The production process adopted is: steelmaking → refining → continuous casting → heating in heating furnace → continuous rolling, which is characterized in that: when heating in heating furnace, the heating time is ≤1.5 hours, the soaking time is ≥2.0 hours, the total time is ≤3.5 hours, the furnace temperature is 1150℃~1250℃, the rolling temperature is 1100℃~1250℃, and the final rolling temperature is ≥900℃. The patent mainly emphasizes the temperature and time control during heating and soaking, and achieves the effect of promoting carbon diffusion and thus reducing the low effect. The controlled cooling process is not described, while this patent mainly adjusts the controlled cooling process to reduce the unevenness of its cross section, thereby achieving the effect of improving the bending ability. There is a significant difference between the two.

[0010] The document with Chinese patent publication number CN102019296 discloses "A method for controlled cooling of high carbon steel wire rod after rolling", which includes controlled cooling on a roller after spinning, wherein the cooling roller is concave, a water trough is arranged in the concave part, and the roller is wrapped in a water trough containing water, and the wire rod enters the water trough for controlled cooling after spinning, and the wire rod after exiting the water trough is air-cooled to room temperature. Although the document makes the controlled cooling process after rolling of high carbon steel wire rod increase the troostitization rate of high carbon steel wire rod from 80% to 85% of the air cooling process to more than 95%, there is a problem of causing martensite to appear inside the material, which is obviously different from the traditional Stelmor process adjustment of the present invention.

[0011] The document with Chinese patent publication number CN102216482 discloses "A high carbon steel wire with excellent processability". It contains 0.6-1.1 mass% C, 0.1-0.5 mass% Si, 0.2-0.6 mass% Mn, 0.004-0.015 mass% S, 0.02 mass% or more and less than 0.05 mass% Cr, and the remainder, which contains inevitable impurities and Fe that limit P to less than 0.02 mass% and Al to less than 0.003 mass%; the wire has a pearlite structure on the surface, and the crystal plane of the ferrite in the pearlite structure has a {110} plane with a concentration of more than 1.2 in the cross section of the wire at the periphery. This document emphasizes the internal orientation of the material, and does not focus on the controlled cooling process, which is significantly different from the content of the present invention.

[0012] The document with Chinese patent publication number CN102312169 discloses "A high-strength low-alloy high-carbon steel wire rod and its production method". Its composition is [C]: 0.86% to 1.0%, [Si]: 0.1% to 2.0%, [Mn]: 0.3% to 1.0%, [Cr]: 0.1% to 1.0%, [P] ≤ 0.020%, [S] ≤ 0.015%, and the inevitable impurities are not higher than 0.1%. Production method: 1) Hot metal desulfurization pretreatment: control the sulfur content below 0.005%; 2) Converter smelting: phosphorus content in steel ≤ 0.010%, converter terminal molten steel temperature 1570-1680℃; 3) LF refining: temperature 1550-1620℃; 4) Continuous casting: use low superheat pouring process system, the superheat of molten steel in the tundish is not more than 25℃, and the size of the ingot is (200-400mm)*(300-500mm); 5) Continuous rolling and wire rolling: wire rod diameter 5.5-8mm, wire rod phase change process supercooling 50-75℃. Its tensile strength is not less than 1300Mpa, and the surface reduction index is not less than 35%, which meets the user's drawing requirements. This document mainly focuses on process control in steelmaking. It is significantly different from the present invention's focus on adjusting the controlled cooling process to reduce the unevenness of its cross section, thereby achieving the effect of improving bending ability.

[0013] The document with Chinese patent publication number CN102352469 discloses "An ultra-high strength vanadium-titanium composite microalloyed high carbon steel wire rod and its preparation method". The wire rod is made by vanadium-titanium composite microalloying process, and contains basic components such as C, Si, Mn, P, S, V, Ti, Cr, Cu, Ni, O, N, and optional components such as Al, Ca, B, Mg; its preparation method includes circuit smelting, refining, continuous casting, rolling and cooling steps in sequence. The diameter of the wire rod of the present invention is 11-15mm, the tensile strength Rm is 1330-1410MPa, the average is 1380MPa, and the cross-sectional shrinkage rate Z ≥ 32%. The tensile strength of 15.2mm prestressed steel strand produced by the low-alloy high-carbon steel wire rod of the present invention is above 2140MPa, the tensile strength of 15.2mm galvanized steel strand is above 1960MPa, and the tensile strength of 7mm galvanized steel wire is above 1860MPa. This document mainly describes the steelmaking process control of a large-size high-strength wire rod.

[0014] The document with Chinese patent publication number CN102409228 discloses "A high-strength high-carbon steel wire rod and its production method". Its composition is: [C] 0.85% to 0.90%, [Si] 0.1% to 1.0%, [Mn] 0.3% to 1.0%, [P] ≤ 0.015%, [S] ≤ 0.010%, [Ti] ≤ 0.0010%, and the rest is iron. Its production method: 1) Smelting: Pre-treatment of molten iron controls sulfur to less than 0.005%, converter inlet [Ti] ≤ 0.040%, converter smelting end point phosphorus content ≤ 0.010%; converter end point molten steel temperature 1570-1680 ℃; refining process temperature 1530-1625 ℃, time 20-50 minutes; 2) Continuous casting: large square billet continuous casting, tundish molten steel superheat is not more than 30 ℃; 3) Continuous rolling and wire rolling: wire rod diameter 5.5-8.0mm, wire drawing temperature 870-910 ℃, wire rod sorbite transformation process temperature controlled at 640-600 ℃, transformation time controlled at 7-12 seconds, wire rod sorbite transformation process average supercooling 60-80 ℃. The tensile strength of the wire rod in the document reaches 1200MPa-1300MPa, and the shrinkage index is not less than 30%. The document focuses on the control of steelmaking process.

[0015] The document with Chinese patent publication number CN102492814 discloses "A straight-draw wire for high-carbon steel filaments and its manufacturing method". The original wire rod of the straight-draw wire has a carbon content of 0.69-0.73wt%, a tensile strength of 900-960MPa, a surface shrinkage of 35-44%, and a size of non-deformed inclusions less than 15μm. It can be directly drawn from Φ5.5mm to Φ0.9-2.0mm; its manufacturing method includes electric furnace smelting, refining outside the furnace, continuous casting of small square billets, high-speed wire-controlled rolling and Stelmor wire-controlled cooling processes in sequence. In the Stelmor wire-controlled cooling process, the phase change is ensured to be carried out at 600-680℃, and the temperature difference between the coil overlap point and other positions does not exceed 50℃. The straight-drawn wire in this document fully meets the use requirements of straight-drawn materials for high-carbon steel filaments. The intermediate drawing heat treatment step can be omitted in the process of processing high-carbon steel filaments such as steel cord, tire bead wire, and hose wire. It has the advantages of saving energy, reducing pollution, and lowering costs. Its preparation process is simple and controllable, meeting the requirements of large-scale industrial production. However, it is significantly different from the present invention which emphasizes a controlled cooling method for small-sized high-carbon wire rods. This method can improve the uniformity of the wire rod cross-section structure, thereby having excellent bending ability and greatly reducing the bending breakage rate during deep processing.

[0016] The document with Chinese patent publication number CN102644029 discloses "a microalloyed cord steel wire rod with large strain drawing performance". Its chemical composition and mass percentage are: C is 0.65-0.85%, Si is 0.15-0.25%, Mn is 0.48-0.58%, P≤0.015%, S≤0.020%, Ti≤0.0010%, Al≤0.0050%, O≤0.0030%, N≤0.0060%; the microalloying elements are two or three of Cr 0.1-0.50%, V 0.05-0.20% and Co 0.10-0.50%. The cord steel wire rod produced by the present invention has a tensile strength of 1150-1250MPa, a cross-sectional shrinkage of 39-45%, and a GBC grade of A or B. After being treated with sorbitization, it can be continuously drawn to a true strain of 4.92, and the tensile strength of the steel cord filaments reaches 3500-4000MPa, the number of fracture torsion is 60-70, and the wire breakage rate is 1.5-2.1 times / ton. The document has the characteristics of significantly reducing production costs, improving strength, and having large strain drawing performance, and the drawability is particularly emphasized, but it is significantly different from the bending ability emphasized by the present invention.

[0017] The document with Chinese patent publication number CN102791900 discloses "A high carbon steel wire with excellent wire drawing processability and fatigue properties after wire drawing". The document appropriately adjusts the chemical composition and sets the area ratio of pearlite structure to more than 90%. In the pearlite structure of 2000μm2, the number of BN compounds with an equivalent circle diameter of more than 100nm and less than 1000nm is less than 100 (including 0), and the number of BN compounds with an equivalent circle diameter of more than 1000nm is less than 10 (including 0). This is different from the problem that the present invention is intended to solve.

[0018] Chinese patent publication number CN102953005 discloses a high carbon low alloy steel wire rod for producing fine steel wire and its manufacturing method. The chemical composition weight percentage of the wire rod is: C 0.87% to 1.1%, Si 0.1% to 1.0%, Mn 0.3% to 1.2%, Cr0.1% to 1.0%, P≤0.015%, S≤0.010%, Ti≤0.0010%, N≤0.0050%; the total aluminum content in the steel is 0.0005% to 0.0020%, the total oxygen content is 0.0010% to 0.0030%, and the rest is iron and unavoidable impurities. The manufacturing method mainly includes deoxidation and alloying after the converter furnace, the residual aluminum and titanium content of the ferrosilicon and ferromanganese used is ≤0.03%, and the addition amount is 1.5-2.5kg / t and 3.5-4.5kg / t respectively; deoxidation and alloying during the refining process, the residual aluminum and titanium content of the ferrosilicon and ferromanganese used is ≤0.03%, and the addition amount of ferrosilicon and ferromanganese during the refining process is 0.5-1.0kg / t and 0.4-0.9kg / t respectively; the aluminum content of the molten steel is controlled at 0.0002%-0.0015% and the total oxygen content is controlled at 0.0020%-0.0040% during the refining process. The tensile strength of the wire rod in the document is 80-150Mpa higher than that of the ordinary 80 grade, the surface reduction index is not less than 35%, no network cementite structure is found, and not less than 90% of the oxide inclusions have the characteristics of an aspect ratio greater than 3 along the rolling direction, which meets the drawing needs of users. However, this invention emphasizes a controlled cooling method for small-sized high-carbon wire rods, by which the uniformity of the wire rod cross-section structure can be improved, thereby having excellent bending ability and significantly reducing the bending wire breakage rate during deep processing.

[0019] The document with Chinese patent publication number CN103409682 discloses "A method for producing ultra-fine steel wire from high-carbon carbon steel wire". It includes the following steps: selecting high-carbon carbon steel wire with a C content of 0.60-1.20% and a Mn content of 0.20-0.45%; removing the iron scale on the surface of the high-carbon carbon steel wire, and then performing 7-15 initial continuous drawing, omitting the intermediate annealing process, to obtain a semi-finished steel wire; then performing heat treatment and quenching; and finally performing 15-25 continuous drawing to obtain an ultra-fine steel wire. The present invention first obtains a wire with lower strength and hardness than conventional wires through a heating furnace process, a high-temperature rolling process and a delayed rapid cooling process during the wire production process. This relatively soft high-carbon steel wire has excellent performance during cold processing, which can not only increase the drawing speed, but also omit the annealing process during the drawing process due to low internal stress, effectively improving the production efficiency of the steel wire, reducing the production cost, and ensuring the strength performance index of the steel wire. However, the problem solved by the present invention is significantly different from that solved by the present invention.

[0020] The document with Chinese patent publication number CN104651724 discloses "A wire rod for prestressed steel strand and its production method". It includes converter smelting, LF furnace refining, continuous casting, heating and controlled rolling and controlled cooling processes. The weight ratio of the chemical composition of the ingot in the continuous casting process is: C 0.78%-0.82%, Si 0.20%-0.25%, Mn 0.75%-0.80%, Cr0.20%-0.25%, P≤0.012%, S≤0.010%, V 0.02%-0.03%; the controlled rolling and controlled cooling process includes rolling, wire laying, cooling and coiling processes; in the rolling process, the starting rolling temperature is 1000±15℃, and the finishing rolling temperature is 920℃-950℃; in the wire laying process, the wire laying temperature is 860℃-880℃. This document, based on optimizing and controlling the chemical composition, improves the sorbitization rate of the wire rod, reduces the spacing between sorbitan layers, avoids the generation of undesirable structures, and achieves the characteristics of high strength, high plasticity and low range of the wire rod, meets the use requirements of unbroken wire at high drawing speed, increases the drawing speed, reduces the wire breakage rate, and thus improves the production efficiency to some extent. However, the problem that this document focuses on solving is significantly different from that of the present invention.

[0021] The document with Chinese patent publication number CN113684423 relates to a high carbon steel wire rod. The wire rod has a diameter of 5.0-6.5 mm and includes the following components in percentage by mass: C 0.60-0.64%, Si 0.15-0.25%, Mn 0.40-0.50%, P≤0.018%, S≤0.015%, Al 0.025-0.055%, and B 0.0020-0.0045%. The document optimizes the composition of SWRH62A, adds aluminum and boron elements, and forms fine AlN by combining aluminum elements with nitrogen in steel, thereby achieving the effect of fine grain strengthening; adds an appropriate amount of boron elements to improve the hardenability of steel; and designs reasonable steelmaking and rolling processes to effectively improve the strength and plasticity of the wire rod. However, this invention emphasizes a controlled cooling method for small-sized high-carbon wire rods, by which the uniformity of the wire rod cross-section structure can be improved, thereby having excellent bending ability and significantly reducing the bending wire breakage rate during deep processing. Summary of the invention

[0022] The present invention aims to overcome the shortcomings of the prior art and provide a method for producing a steel product while ensuring the mechanical properties of the steel product.

[0023] After 15 days of aging, the performance is uniform and stable, the wire rod segregation is ≤2.0 level, there is no obvious softening zone in the cross section, the metallographic structure is mainly ferrite and pearlite, of which the volume proportion of pearlite is not less than 80%; the elongation is ≥9.0%, the surface reduction rate is ≥35.0%, the strength difference is ≤65MPa, the microhardness extreme difference of the cross section is ≤15%, the number of repeated bending times is ≥18.0 times, and the wire breakage during deep processing is less than 0.5 times / thousand tons. The high carbon steel wire rod with a diameter of ≤6.5mm and the production method have excellent bending ability.

[0024] Measures to achieve the above objectives:

[0025] A high carbon steel wire rod with a diameter of ≤6.5 mm and excellent bending ability, under the existing components in the field of this steel grade, it is: P≤0.012wt%, S≤0.009wt%, Cu≤0.095wt%; the carbon equivalent is controlled as follows:

[0026] CE=(C+Mn / 6)≥0.75;

[0027] The segregation degree of steel is as follows:

[0028] When CE=(C+Mn / 6)≥0.75% to <0.85%, the segregation requirement is ≤1.16;

[0029] When CE=(C+Mn / 6)≥0.85% to <0.95%, the segregation requirement is ≤1.12;

[0030] When CE=(C+Mn / 6)≥0.95%, the segregation requirement is ≤1.08;

[0031] Metallographic structure: the volume proportion of pearlite is not less than 80%, the volume proportion of ferrite is 0-20%.

[0032] A method for producing a high carbon steel wire rod with a diameter of ≤6.5 mm and excellent bending ability, comprising the following steps:

[0033] 1) After smelting and pouring into billets, heat the billets and control the billet heating temperature at 1100-1250°C.

[0034] ≤28℃, furnace pressure maintained at 32~42MPa, reducing atmosphere in the furnace: O2<1.15%, CO<2.70%; furnace time 120~180min;

[0035] 2) Rolling on high-speed wire: control the starting rolling temperature at 930-1050°C, the finishing rolling inlet temperature at 850-920°C; the reducing and sizing mill inlet temperature at 860-930°C;

[0036] 3) Spinning silk, controlling the spinning temperature at 850-940° C.;

[0037] 4) Cooling in Stelmore air cooling line:

[0038] A. In the front section, when the surface temperature of the wire rod is not less than 650℃, the cooling speed of the wire rod is controlled at 8~12℃ / s.

[0039] The speed range is greater than 1 and less than or equal to 1.05;

[0040] B. In the middle section, when the surface temperature of the wire rod is between 380 and 650°C, adjust the fan air volume to ensure that the wire rod cooling speed is between 2 and 4°C / s, the roller speed range is less than 1 and ≥0.96, and the air volume is kept continuously and stably output;

[0041] The maximum absolute air volume difference between adjacent distributed fans is controlled as follows:

[0042] When the ambient temperature of the inhaled air is lower than 5°C, the maximum absolute air volume difference between adjacent fans shall not exceed 40,000m 3 / h control;

[0043] When the ambient temperature of the inhaled air is not less than 5°C, the maximum absolute air volume difference between adjacent fans is

[0044] The value shall not exceed 60000m 3 / h control;

[0045] C. In the rear section, when the surface temperature of the wire rod is ≤380℃, all the Stelmor insulation covers are opened to ensure that the cooling speed of the wire rod is controlled at 6~9℃ / s;

[0046] 5) After the wire rods are air-cooled to room temperature, they are bundled and packaged.

[0047] Preferably: the heating temperature of the casting is between 1155 and 1215°C, the cross-sectional temperature difference is ≤23°C, and the time in the furnace is 150 to 170 minutes.

[0048] Preferably, the starting rolling temperature is between 946 and 1035°C, the finishing rolling inlet temperature is between 872 and 910°C, and the sizing mill inlet temperature is between 885 and 915°C.

[0049] Preferably, the spinning temperature is between 885 and 920°C.

[0050] Functions and mechanisms of the components and main processes in the present invention

[0051] The reason why the present invention controls CE=(C+Mn / 6)≥0.75 is that the present invention is mainly aimed at a high-carbon steel wire rod, and the carbon equivalent here is an explanation of high carbon.

[0052] The reason why the present invention controls copper, that is, Cu≤0.095wt%, is that Cu will segregate at the grain boundaries of the material, significantly increasing the brittleness of the material, and requires strict control, so the required range is determined to be: Cu≤0.095wt%.

[0053] The phosphorus of the present invention, that is, P≤0.012wt% and S≤0.009wt%, is because they are harmful elements and need to be strictly controlled. If they exceed the limit, the bending performance will be significantly reduced.

[0054] The reason why the present invention controls the heating temperature of the casting billet to be 1100-1250°C, the cross-sectional temperature difference ≤28°C, and the furnace time to be 120-180min is that the heating temperature and time are mainly to ensure that the alloy elements in the material are completely dissolved.

[0055] The reason why the present invention controls the starting rolling temperature at 930-1050°C, the finishing rolling entrance temperature at 850-920°C, and the sizing mill entrance temperature at 860-930°C is that the temperature ranges of these points are key control points in the wire rolling process, mainly to ensure that the material size matches the stability, and then ensure that the material has a suitable spinning temperature.

[0056] The reason why the spinning temperature of the present invention is 850-940° C. is that based on the existing component system, under the existing controlled cooling line conditions, it can ensure that the material has sufficient phase change conditions to obtain the ideal tissue type and quantitative requirements.

[0057] The present invention is based on the Stelmor air cooling line:

[0058] A. In the front area, that is, when the surface temperature of the wire rod is not lower than 650℃, the cooling speed of the wire rod is controlled at 8-12℃ / s, the roller speed range is greater than 1 to ≤1.05, the fan is in high-power on state, to ensure that the cooling speed of the wire rod is 8-12℃ / s, the roller speed adopts acceleration mode, and the acceleration roller speed range is ≤1.05.

[0059] B. In the middle section, when the surface temperature of the wire rod is between 380 and 650°C, the fan air volume is adjusted to ensure that the wire rod cooling speed is 2 to 4°C / s. The roller speed range is less than 1 to ≥0.96, and the air volume is kept continuously and stably output; the maximum absolute air volume difference between adjacent fans is controlled as follows:

[0060] When the ambient temperature of the inhaled air is lower than 5°C, the maximum absolute air volume difference between adjacent distributed fans shall be controlled to not exceed 40,000 m3 / h;

[0061] When the ambient temperature of the inhaled air is not less than 5°C, the maximum absolute air volume difference between adjacent distributed fans shall be controlled to not exceed 60,000 m3 / h;

[0062] The reason why the difference in the fan air volume change is limited is that the softening zone (pearlite and grain boundary ferrite) in the microstructure of the longitudinal section of the high-carbon wire rod is a typical structural inhomogeneity and the main structural reason for the wire rod fracture. There is a strong correspondence between the difference in microstructure and its cooling control process. At present, Stelmor air cooling is mostly used for cooling the wire rod. Since the temperature measured during the cooling control process of the wire rod is the surface temperature, and there is a certain amount of heat storage inside the wire rod, when the fan air volume changes too much during the structural transformation stage, the wire rod will return to the surface from the core, and the part of the pearlite that has been transformed in the surface area of ​​the wire rod will be reheated to above Ac1 (below Ac3), and the pearlite will be transformed into austenite, and a small amount of ferrite will be precipitated at the grain boundary, resulting in the formation of a softening zone inside the wire rod. Moreover, when the external temperature is lower, the influence of the fan air volume change on the structure is greater, and it should be more strictly controlled. Based on the above reasons, when the external ambient temperature is lower than 5℃, the maximum absolute air volume difference between adjacent distributed fans is controlled to be ≤40000m3 / h; when the external ambient temperature is not lower than 5℃, the maximum absolute air volume difference between adjacent distributed fans is ≤60000m3 / h.

[0063] C. In the rear area, that is, when the surface temperature of the wire rod is ≤380℃, all the Stelmor insulation covers are opened to ensure that the cooling speed of the wire rod is controlled at 6-9℃ / s; rapid cooling in the rear section of controlled cooling is to avoid excessively thick oxide scale caused by excessively high coiling temperature of the wire rod and strength reduction caused by self-tempering.

[0064] The present invention provides a high-carbon steel wire rod with a diameter of ≤6.5 mm and excellent bending ability, and a production method thereof, which has the advantages of ensuring the mechanical properties of the produced steel grade, uniform and stable performance after 15 days of aging, wire rod segregation ≤2.0 level, no obvious softening zone in the cross section, metallographic structure mainly composed of ferrite and pearlite, wherein the volume proportion of pearlite is not less than 80%; elongation ≥9.0%, surface reduction ≥35.0%, strength circle difference ≤65MPa, cross-sectional microhardness extreme difference ≤15%, repeated bending times ≥18.0 times, and bending breakage in the deep processing process is less than 0.5 times / kiloton. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 The metallographic structure diagram of the bending fracture microstructure of the cord steel of the present invention;

[0066] Figure 2 The metallographic structure diagram of the softening zone of the present invention at X100;

[0067] Figure 3 The metallographic structure diagram of the conventional region of the present invention at X100;

[0068] Figure 4 The organization diagram of the softening belt of the present invention is scanned at X 5000;

[0069] Figure 5 The tissue diagram of the conventional area softening strip of the present invention was scanned at X 5000. DETAILED DESCRIPTION

[0070] The present invention is described in detail below:

[0071] Table 1 is a list of chemical components of various embodiments and comparative examples of the present invention;

[0072] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0073] Table 3 is a list of the performance test results of various embodiments of the present invention and comparative examples.

[0074] Each embodiment of the present invention is produced according to the following steps:

[0075] 1) After smelting and pouring into billets, heat the billets and control the billet heating temperature at 1100-1250°C.

[0076] ≤28℃, furnace pressure maintained at 32~42MPa, reducing atmosphere in the furnace: O2<1.15%, CO<2.70%; furnace time 120~180min;

[0077] 2) Rolling on high-speed wire: control the starting rolling temperature at 930-1050°C, the finishing rolling inlet temperature at 850-920°C; the reducing and sizing mill inlet temperature at 860-930°C;

[0078] 3) Spinning silk, controlling the spinning temperature at 850-940° C.;

[0079] 4) Cooling in Stelmore air cooling line:

[0080] A. In the front section, when the surface temperature of the wire rod is not less than 650℃, the fan is turned on at maximum power, the wire rod cooling speed is controlled at 8~12℃ / s, and the roller speed range is greater than 1 to ≤1.05;

[0081] B. In the middle section, when the surface temperature of the wire rod is between 380 and 650°C, the fan air volume is adjusted to ensure that the wire rod cooling speed is 2 to 4°C / s. The roller speed is reduced, and the roller speed range is less than 1 to ≥0.96;

[0082] And the air volume is kept continuously and stably output; the maximum absolute air volume difference between adjacent distributed fans is controlled as follows:

[0083] When the ambient temperature of the inhaled air is lower than 5°C, the maximum absolute air volume difference between adjacent fans shall not exceed 40,000m 3 / h control;

[0084] When the ambient temperature of the inhaled air is not less than 5°C, the maximum absolute air volume difference between adjacent fans shall not exceed 60,000m 3 / h control;

[0085] D. In the rear section, when the surface temperature of the wire rod is ≤380℃, all the Stelmor insulation covers are opened to ensure that the cooling speed of the wire rod is controlled at 6~9℃ / s;

[0086] 5) After the wire rods are air-cooled to room temperature, they are bundled and packaged.

[0087] Table 1 Chemical composition list of various embodiments and comparative examples of the present invention (wt%)

[0088]

[0089]

[0090] Table 2 List of main process parameters of various embodiments of the present invention and comparative examples

[0091]

[0092] Table 2 Stelmore air cooling line cooling

[0093]

[0094]

[0095] Table 3 List of mechanical properties test results of various embodiments of the present invention and comparative examples

[0096]

[0097] Description: Examples 1 to 10 all use high carbon steel grades with a carbon equivalent of not less than 0.77%. Combined with the rolling process required by the present invention, the resulting wire rod has uniform and stable performance after 15 days of aging, the wire rod segregation is ≤2.0 level, the metallographic structure is mainly ferrite and pearlite, of which the volume proportion of pearlite is not less than 80%; the elongation is ≥9.0%, the area reduction is ≥35.0%, the strength difference is ≤65MPa, the cross-sectional microhardness extreme difference is ≤15%, the number of repeated bendings is ≥18.0 times, and the bending breakage during the deep processing process is less than 0.5 times / kiloton.

[0098] In Comparative Example 1, within the same range of chemical composition, due to excessively high temperature control during rolling, the toughness and bending ability of the wire rod are low, and the rough breaking rate reaches 0.97 times / kiloton; in Comparative Example 2, within the same range of chemical composition, due to the large difference in the maximum absolute air volume of adjacent fans during the controlled cooling process, the bending ability of the wire rod is significantly reduced, and the rough breaking rate reaches 2.11 times / kiloton.

[0099] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A high carbon steel wire rod with a diameter of ≤6.5 mm and excellent bending ability, under the existing components in the field of this steel grade, characterized by: P≤0.012wt%, S≤0.009wt%, Cu≤0.095wt%; carbon equivalent is controlled as follows: CE=(C+Mn / 6)≥0.75; The segregation degree of steel is as follows: When CE=(C+Mn / 6)≥0.75% to <0.85%, the segregation requirement is ≤1.16; When CE=(C+Mn / 6)≥0.85% to <0.95%, the segregation requirement is ≤1.12; When CE=(C+Mn / 6)≥0.95%, the segregation requirement is ≤1.08; Metallographic structure: pearlite volume proportion is not less than 80%, ferrite volume proportion: 0~20%; Production method: 1) After smelting and casting, the ingot is heated, and the heating temperature of the ingot is controlled at 1100~1250℃, the cross-section temperature difference is ≤28℃, the furnace pressure is maintained at 32~42MPa, and the reducing atmosphere in the furnace is: O2<1.15%, CO<2.70%; the furnace time is 120~180min; 2) Rolling on high-speed wire: control the starting rolling temperature at 930-948°C, the finishing rolling inlet temperature at 850-872°C; the reducing and sizing mill inlet temperature at 860-882°C; 3) Spinning, controlling the spinning temperature at 850-876°C; 4) Cooling in Stelmore air cooling line: A. In the front section, when the surface temperature of the wire rod is not less than 650℃, the wire rod cooling speed is controlled at 8~9.98℃ / s, and the roller speed range is greater than 1 to ≤1.05; B. In the middle section, when the surface temperature of the wire rod is between 380 and 650°C, adjust the fan air volume to ensure that the wire rod cooling speed is between 3.07 and 4°C / s, and the roller speed range is less than 1 to ≥0.96; and the air volume is kept continuously and stably output; the maximum absolute air volume difference between adjacent fans is controlled as follows: When the ambient temperature of the inhaled air is lower than 5°C, the maximum absolute air volume difference between adjacent fans is No more than 40000m 3 / h control; When the ambient temperature of the inhaled air is not less than 5°C, the maximum absolute air volume difference between adjacent fans shall not exceed 60,000m 3 / h control; C. In the rear section, when the surface temperature of the wire rod is ≤380℃, all the Stelmor insulation covers are opened to ensure that the cooling speed of the wire rod is controlled at 6~6.98℃ / s; 5) After the wire rods are air-cooled to room temperature, they are bundled and packaged.

Images