CN115261735B

CN115261735B - Wire rod for prestressed steel strand and production process thereof

Info

Publication number: CN115261735B
Application number: CN202211178999.XA
Authority: CN
Inventors: 屈小波; 王淼; 刘荣
Original assignee: Lianfeng Steel Zhangjiagang Co Ltd
Current assignee: Lianfeng Steel Zhangjiagang Co Ltd
Priority date: 2022-09-27
Filing date: 2022-09-27
Publication date: 2022-12-06
Anticipated expiration: 2042-09-27
Also published as: CN115261735A

Abstract

The invention relates to a wire rod for a prestressed steel strand and a production process thereof, wherein Mn/Si =0.81-0.87 is adopted to increase the stability of cementite and inhibit the coarsening of cementite; the Nb and V, ti synergistically strengthen the fine grain effect by Ce-Cu composite refined lamella spacing; trace B reduces decarburization sensitivity; the rare earth La reduces residual elements; the process comprises the working procedures of converter smelting, LF refining, VD vacuum, continuous casting, heating, high-pressure water descaling, rolling, spinning and stelmor line cooling, wherein low-carbon ferroboron is added after the VD vacuum is broken, a titanium wire is fed, and the processes of fast cooling, slow cooling and air cooling are adopted to control inclusions, macroscopic structure quality, oxide scale thickness and composition and hypereutectoid structure, realize narrow component control, improve mechanical stripping performance, improve drawing performance, reduce wire breaking rate, improve sorbite conversion rate, reduce inter-lamellar space, ensure complete and straight lamella and improve comprehensive mechanical performance.

Description

Wire rod for prestressed steel strand and production process thereof

Technical Field

The invention belongs to the technical field of prestressed steel strands, and particularly relates to a wire rod for a prestressed steel strand and a production process thereof.

Background

The prestressed steel strand is stranded by a plurality of medium and high strength steel wires and is used for eliminating stress, prestressed concrete members, bridges and the like, the steel strand is a key bearing member in a prestressed structure, and along with the improvement of application requirements of a large-span structure, severe environment working conditions, structural service life and the like, the requirements on high strength, plasticity, low relaxation performance and high yield strength of the steel wires are higher. The existing wire rod for the prestressed steel strand still has the following problems:

(1) Residual elements and inclusions: the residual elements cause the second type of temper brittleness of the structural steel by inward grain boundary segregation and are influenced seriously under the action of silicon and manganese, the strip-shaped sulfide and silicate inclusions with larger sizes become strips after rolling, the obdurability is obviously reduced, and the steel is anisotropic, wherein the steel comprises Al ₂ O ₃ 、MgO·Al ₂ O ₃ And high-melting point calcium aluminate and other invariant impurities are easy to deposit in the submerged nozzle to cause nozzle blockage, surface defects are generated, the fluctuation of the tensile strength is large, the face shrinkage rate is reduced, brittle fracture is easy to cause in the drawing or stranding process, and fine brittle inclusion particles are easy to cause dynamic fatigue performance reduction and increase the wire breakage rate.

(2) Macrostructure: carbon, sulfur, phosphorus and partial alloy elements are easy to segregate in the solidification process, the center segregation of a casting blank leads a C curve to move to the right, the solidification shrinkage rate of the casting blank is high, the center of the casting blank is easy to loosen, the surface of the casting blank in a high-temperature brittle zone is cracked under the pulling speed condition, the critical cooling speed is reduced, a wire rod is easy to generate a bright and white martensite layer, the martensite with high hardness and low plasticity cannot cooperatively deform to cause drawing fracture, the center is loosened, the high temperature of edge heating leads to oxidation decarburization and netlike cementite, the plasticity is reduced, the plasticity rheology is discontinuous, the product stability is influenced, stress concentration is easy to generate, and the center fracture of a steel wire is caused.

(3) Oxide scale thickness and composition: the surface scale causes insufficient pressure in a lubrication area during drawing, partial lubrication failure and surface transverse crack, the thickness of the scale thickness pin wire rod is small due to low spinning temperature, the proportion of FeO in the scale is low, and the scale pollution is greatly removed by acid washing.

(4) Hypereutectoid organization: the temperature difference between the surface of the rolled wire rod and the core part is large, the internal compactness and the core part permeability are insufficient, austenite grains are large, and the performance of the whole wire rod is not uniform, so that the anisotropy is caused; the roll speed is not changed, so that the temperature of a lap joint area is not uniform, the thickness of a decarburized layer is increased, martensite and grain boundary cementite coexist or the cooling speed is too low, bainite transformation occurs to reduce strength and toughness, the sorbite conversion rate of a wire rod is low, the sorbite content is not uniform, the drawing performance is unstable, the tensile performance is reduced, the content of hard and brittle phase pearlite is high, cementite in incomplete pearlite lamella and coarse pearlite is thick, the lamella structure is few or the lamella is bent, the brittleness is increased, the comprehensive mechanical property is reduced, and sharp or uneven stress fracture is generated in the multi-pass drawing process.

Disclosure of Invention

The invention aims to solve at least one of the technical problems to a certain extent, and provides a wire rod for a prestressed steel strand and a production process thereof.

The technical scheme adopted by the invention for solving the technical problem is as follows:

a wire rod for a prestressed steel strand comprises the following components in percentage by mass: c:0.89-0.93%, si:0.69-0.78%, mn:0.56-0.63%, P: less than or equal to 0.015%, S: less than or equal to 0.01 percent, cr:0.32-0.37%, ni:0.12 to 0.19%, mo:0.02 to 0.08%, cu:0.01-0.015%, al:0.04-0.06%, ti:0.01-0.015%, V:0.03-0.039%, nb:0.015-0.02%, B: 0.0015-0.003%, ce:0.0015-0.003%, la:0.0015-0.003%, sn: less than or equal to 0.015 percent, sb: less than or equal to 0.01 percent, as: less than or equal to 0.015 percent, O: less than or equal to 0.0012 percent, N:0.008-0.015% and the balance of Fe and inevitable impurities.

Above-mentioned wire rod for prestressed steel strand, further, mn/Si =0.81-0.87 in the component, the inclusion come-up of being convenient for can improve austenite grain size, strengthen the grain boundary diffusion, control the pearlite and grow up, guarantee that the lamella is complete straight, avoid Mn/Si to hang down and increase cementite lamella balling rate, avoid Mn/Si too high can influence the distribution of transition interface atom concentration, cause incomplete pearlite lamella and cementite to coarsen.

The wire rod for the prestressed steel strand is characterized in that the total decarburized layer (ferrite + transition layer depth) of the wire rod is less than or equal to 1.2% of the nominal diameter of the wire rod, and the mechanical property of the wire rod is as follows: the tensile strength is 2145-2250MPa, the yield strength is 1965-2180MPa, the elongation is more than or equal to 29%, the reduction of area is more than or equal to 45%, the impact energy Akv is more than or equal to 82J, and the wire rod has uniform metallographic structure, stable chemical components and high sorbite conversion rate.

The wire rod for the prestressed steel strand comprises the following components by design:

(1) C content determination: c is an important element influencing wear resistance, the strength of steel can be obviously improved through solid solution strengthening and precipitation strengthening, but the decarburization tendency is increased due to the fact that C is too high, so that brittle pre-eutectoid net-shaped carbides are increased, the net-shaped carbides are easily formed, the connectivity among grain boundaries is reduced, the fatigue performance is influenced, meanwhile, grain boundary cementite is precipitated along the grain boundaries to form cracks, and the center segregation, the ductility and toughness and the crack sensitivity performance of the steel are adversely influenced, and the content range of C is determined to be 0.89-0.93%.

(2) Determination of contents of Si, mn, cr and Mo: si is reinforced ferrite, so that a CCT curve can be shifted to the right, a finer pearlite structure can be obtained at the same cooling speed to improve the strength, mn is promoted to be distributed to a cementite phase, the spheroidization of cementite is slowed down, the stability of the cementite is increased, the coarsening of the cementite is inhibited, and abnormal ferrite of a crystal boundary can be caused by overhigh Si; the Si content of the invention is determined to be 0.69-0.78%; mn is used as a deoxidizing element in the steelmaking process, austenite can be stabilized, the molten ferrite has a solid solution strengthening effect and can improve hardenability, but the MnS strip is caused by excessively high content of the Mn element to cause serious center segregation of steel, the residual austenite is increased due to coarse grains during quenching, and martensite is more likely to appear in a high Mn and Cr core part; the range of the Mn content of the present invention is determined as Mn:0.56-0.63%; cr is a carbide forming element, cr dissolved into austenite during heating can reduce the content of proeutectoid ferrite in the structure, so that the structure of a wire rod on an air cooling roller is fully transformed, the structural stress and the thermal stress are reduced, the sorbite content is increased to improve the comprehensive performance, the tendency of steel stone desertification and decarburization can be reduced, meanwhile, the plasticity and toughness of steel are improved by refining grains, the drawing is facilitated, but the Cr content is too high to be combined with carbon in the steel, large carbide is easily formed, and the plasticity is reduced; the range of the Cr content is determined to be 0.32-0.37%; mo can prevent temper brittleness, improve fatigue performance and improve quenching property; the range of Mo content in the present invention is defined as 0.02 to 0.08%.

(3) Determination of Ni, cu and Ce contents: ni can shift the CCT curve to the right to improve hardenability, can enlarge an austenite region, homogenize an austenite structure, reduce transformation temperature, increase the number of sorbite in the structure, and improve the solubility of Cu in austenite to improve copper brittleness, thereby strengthening a matrix, but Ni is too high to form a NiS network structure on a grain boundary to generate hot brittleness; the range of the Ni content is determined to be 0.12-0.19%; cu can improve the strength of steel through solid solution strengthening, but too high Cu can cause precipitated phase coarsening, and the Cu content range is determined to be 0.01-0.015 percent; ce can promote Cu dispersion and improve dislocation strengthening, ce-Cu compounding can refine lamella spacing, promote NbC precipitation and strengthen fine grain effect, and MnS is included by Ce ₂ O ₃ 、Ce ₂ O ₂ S and the like can reduce the size of the inclusions, but the grain size is increased by excessively high Ce, and the content of Ce in the invention is determined to be 0.0015-0.003%.

(4) Determination of Al, ti, V and Nb contents: al is a deoxidizing and nitrogen-fixing agent in steel making, can refine steel grains and improve low-temperature toughness, and the range of the Al content is determined to be 0.04-0.06%; the microalloy element Ti can prevent austenite grains from growing and refining at high temperature, and can improve the problem of surface cracks of a continuous casting billet in a high-temperature brittle zone under the high-pulling-speed condition of alloy steel with rare earth elements, but the Ti content is determined to be 0.01-0.015 percent, and the TiN inclusion with edge angles can destroy the continuity of a matrix and easily generate stress concentration to become a crack source when the Ti content is too high; v can form V (C/N) to influence the structure and the performance of steel, precipitates in ferrite of austenite grain boundary, can inhibit recrystallization of austenite and prevent grain growth in the rolling process, plays a role in strengthening dispersion, reduces phase transformation point, improves the strength and the toughness of steel, but over high V can increase the cold brittleness of steel, and leads to the increase of cold crack sensitivity; the V content range of the invention is determined to be 0.03-0.039%; nb and V, ti cooperate to have dispersion strengthening effect, nb (C, N) has small size, and blocks the growth of high-temperature austenite grains, so that the grains after rolling are refined, the spacing between pearlite pieces can be reduced, the tensile strength and the toughness are improved, but the high effect of Nb is saturated; the Nb content of the invention is determined to be 0.015 to 0.02%.

(5) B content determination: trace B is melted into austenite in the form of interstitial atoms and can be adsorbed on austenite grain boundaries to reduce grain boundary energy, block carbon atom diffusion channels to improve hardenability, reduce decarburization sensitivity and improve the ductile-brittle transition temperature tendency of steel, but over high B can cause BN inclusion to influence the purity of molten steel; the range of the B content of the present invention is determined to be 0.0015 to 0.003%.

(6) Determination of P, S content: p seriously causes segregation during solidification in steel, P is dissolved in ferrite to cause the grains to be distorted and large, and cold brittleness is increased, and the range of the P content is determined to be less than or equal to 0.015 percent; the S element can be combined with the Mn element to form hard and brittle MnS, so that the cutting processability of steel is improved, but the excessive S content can cause hot brittleness of steel, reduce the ductility and toughness of the steel and increase the center segregation of the steel; the range of the S content of the invention is determined to be less than or equal to 0.01 percent.

(7) Determination of La, sb, sn and As content: la can change irregular silicate and aluminate into oxides or sulfides of spherical rare earth lanthanum, adsorb MnS to improve tensile strength and hardness, can obviously reduce residual elements of Sb, sn and As to improve grain boundary segregation and temper brittleness, and improve the problem of surface cracks of continuous casting billets in high-temperature brittle zones of alloy steel under the condition of high drawing speed, but the anisotropy is influenced by excessive inclusion amount due to excessive La, and the content range of La is determined to be 0.0015-0.003%; sb, sn and As are subjected to grain boundary segregation from the interior of the crystal to cause the second type of temper brittleness of structural steel and aggravate the influence under the action of silicon and manganese, and the method controls the Sn: less than or equal to 0.015 percent, sb: less than or equal to 0.01%, as: less than or equal to 0.015 percent.

The production process of the wire rod for the prestressed steel strand comprises the following steps:

s1, smelting in a converter: pre-desulfurizing a steelmaking raw material by using 120tKR molten iron, smelting by using a top-bottom combined blowing converter and a double-slag converter to obtain molten steel, controlling S to be less than or equal to 0.0045%, adopting 1.2-2kg/t of lime of the molten steel, 1.2-1.4kg/t of dolomite of the molten steel and 0.15-0.2kg/t of fluorite slag material by using a double-slag method, controlling the alkalinity to be 2.7-3.1, keeping better fluidity, controlling the end point phosphorus content to be less than or equal to 0.008%, avoiding intragranular segregation of phosphorus in the crystallization process, controlling the end point carbon content of tapping to be 0.22-0.28%, ensuring the carbon-remaining hit rate by high carbon drawing, avoiding the carbon content from causing larger aluminum loss, avoiding the process control from being influenced by overhigh carbon, controlling the ultralow temperature to be 1580-1610 ℃, and avoiding the return phosphorus caused by overhigh temperature;

adding 75-92kg of aluminum cakes into 90-110t of molten steel in each furnace when tapping 1/5-1/3, and quickly deoxidizing;

adding 440-490kg of silicomanganese alloy (FeMn 64Si 18), 180-220kg of low-carbon ferrosilicon (FeSi 75-A) and 60-90kg of silicon calcium barium iron (FeBa 12CaSi 40) when tapping 2/5-1/2, and performing deoxidation and slagging pre-refining, wherein the addition of barium does not easily cause splashing, can increase the activity of MnO and improve the modification effect of Ca;

390-430kg of cleaning promoter (CaO53.5%, siO) is added when tapping 2/3-3/4 ₂ 3.5％，Al ₂ O ₃ 34.3 percent of MgO 8.5 percent) and 170-200kg of lime, ensures the fluidity of the slag, controls the slag amount, increases the contact area of the slag, converts alumina into calcium aluminate and manganese sulfide into spherical calcium sulfide to cover calcium magnesium aluminosilicate, promotes the floating of steel inclusions and gas, inhibits the silicon return and the total MnS content of the molten steel, and ensures that the slag system is positionedIn the low melting point area, high melting point inclusions are avoided, and the fatigue life is prolonged;

s2, LF refining: feeding the molten steel in the step S1 into an LF (ladle furnace) station, refining by precipitation deoxidation and diffusion deoxidation, adding 1-1.5kg of wollastonite, 0.15-0.2kg of aluminum wire and 0.05-0.1kg of rare earth lanthanum into each ton of steel, precipitating and deoxidizing to produce white slag, and absorbing Al-containing wollastonite with low oxygen potential and low melting point ₂ O ₃ Spherical CaO-SiO as deoxidation inclusion-producing inclusions ₂ -Al ₂ O ₃ The irregular silicate and aluminate are changed into oxide or sulfide of spherical rare earth lanthanum, and the La and MnS react to produce dispersed La with small size ₂ O ₂ S or La ₂ S ₃ Further absorbing MnS, remarkably reducing residual elements of Sb, sn and As to improve grain boundary segregation and temper brittleness, effectively controlling cluster-shaped alumina inclusions, improving B-type inclusions, improving the fluidity of molten steel, reducing the damage of nozzle nodulation and brittle inclusions to a matrix in the casting process, improving fatigue cracks, tensile strength and hardness, controlling the viscosity and fluidity of slag, controlling the alkalinity of the slag to be 2.2-2.6, playing roles of deoxidation and desulfurization, improving the speed and capacity of absorbing the impurities, ensuring that the white slag time is not less than 20min, ensuring that the smelting time is not less than 40min, sufficiently removing the oxygen content in the molten steel in the white slag time, ensuring that the alloy components are accurately controlled in a proper smelting period, sufficiently floating and removing the impurities, and adding 0.5-0.85kg/t of CaC of molten steel ₂ Diffusion deoxidation, caC ₂ Creating deep deoxidation condition, avoiding N absorption of molten steel, avoiding increasing brittle inclusion due to overhigh alkalinity, ensuring purity of molten steel and finishing point [ O ]]≤160ppm；

The argon flow in the early stage of LF refining is 300-330NL/min, and the argon is properly increased and stirred to melt slag as soon as possible and promote deoxidation and alloying;

low-carbon ferrochrome (FeCr69C 1.0), low-aluminum ferrovanadium (FeV 50-C) and ferrocolumbium (FeNb 50-B) are used in the middle of LF refining, the argon flow is 150-180NL/min, the argon strength such as argon is kept for component adjustment, alloy melting is accelerated, the yield is improved, target components are controlled, element fluctuation is reduced, and narrow component control is realized;

the argon flow in the later stage of LF refining is 50-80NL/min, the rolling oxidation of molten steel is avoided, and the argon flow is controlled to be 0.8-1.1Feeding magnesium wire of 0.3-0.7m/t molten steel at m/s speed, feeding cerium wire of 0.5-0.8m/t molten steel at 1.4-1.6m/s speed, passing through Ce ₂ O ₃ 、Ce ₂ O ₂ S and the like further replace long-strip MnS and are modified into dispersed spherical Ce with small size ₂ S ₃ MgS system and MgS-MnS system inclusions are included, the tensile strength, the yield strength and the toughness are improved, the inclusion morphology is controlled, the drawing performance is improved, and the wire breakage rate is reduced;

s3, VD vacuum: carrying out VD vacuum degassing treatment on the molten steel VD station in the step S2, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is not less than 20min, slagging and deoxidation are ensured to remove impurities, the soft argon blowing time is not less than 35min, the argon flow is 17-25NL/min, the denitrification power is enhanced, non-metallic impurities are enabled to float sufficiently, the cold crack sensitivity is reduced, 0.08-0.11kg/t of molten steel low-carbon ferroboron (FeB16C0.1) is added after breaking the space, the molten steel low-carbon ferroboron can be adsorbed on austenite grain boundaries to reduce the grain boundary energy, a carbon atom diffusion channel is blocked to improve the hardenability and reduce the decarburization sensitivity, a 0.2-0.4m/t of titanium wire is fed at the speed of 0.7-1m/S, and the problems of continuous casting billet surface cracks of a high-temperature brittle zone under the high drawing speed condition of the alloy steel are effectively improved by improving the purity of the molten steel, reducing the yield fluctuation of titanium, refining grains by trace Ti and rare earth elements;

s4, continuous casting: the molten steel in the step S3 is cast in an eight-machine eight-strand continuous casting machine in a whole-process protection manner, the alkaline tundish prevents the molten steel from being secondarily oxidized by using carbonized rice hulls and a neutral covering agent, oxygen is prevented from being added, the temperature of the molten steel in the tundish is 1495-1545 ℃, the superheat degree is controlled to be 10-25 ℃, the phenomenon that the melting of protective slag in a crystallizer is influenced and the billet shell is not uniform due to overhigh superheat degree or overhigh fluctuation is avoided, the phenomenon that the nozzle nodulation is caused by an undersized tundish is avoided, the stability of the drawing speed is favorably ensured, and the carbon segregation is improved;

electromagnetic stirring of a crystallizer, electromagnetic stirring of a secondary cooling zone and electromagnetic stirring of the tail end are adopted; the electromagnetic stirring parameters of the crystallizer are 200-300A of current and 3-4Hz of frequency, so that molten steel in a casting blank forcibly flows, the temperature of a liquid core is promoted to be uniform, columnar crystals on the wall of the crystallizer are broken, the molten steel compensation and the formation of isometric crystals are facilitated, the liquid level of the crystallizer is ensured to be stable, subcutaneous inclusion is avoided, and the central segregation and the porosity are improved; the electromagnetic stirring parameters of the secondary cooling zone are 150-200A of current and 10-12Hz of frequency, and columnar crystals in the two-phase zone are crushed to prevent the bridging phenomenon of dendrites; the tail end electromagnetic stirring parameters are 500-600A of current and 6-8Hz of frequency, solute elements gathered in a two-phase region at the solidification tail end are reduced, the solute elements are uniformly dispersed, and center segregation is reduced;

the secondary cooling specific water flow is 0.72-0.87L/kg, surface cracks caused by overlarge secondary cooling specific water amount are avoided, segregation or porosity caused by precipitation of solute elements caused by undersize secondary cooling specific water amount is avoided, the drawing speed is 1.3-1.7m/min, center segregation and porosity are improved, columnar crystals are prevented from developing due to overhigh drawing speed, the segregation is aggravated due to unfavorable formation of isometric crystals and the casting blank is cracked, the influence on yield and blank shell uniformity caused by overlow drawing speed is avoided, depression and corner cracks are generated at the weak position, the solidification end reduction is 7-9mm, enriched solute among dendrites is kept in situ and does not move towards the center, center segregation and porosity are improved, the ingot is cut by a straightener and a fixed ruler and then enters a pit for slow cooling, the casting blank pit entry temperature is controlled to be not less than 630 ℃, the slow cooling time is not less than 42h, the pit exit temperature is not more than 205 ℃, the slow cooling and heat preservation effects are improved, the cooling speed is reduced to improve carbon segregation, 165mm is obtained, the carbon segregation is within 1.01, the casting blank is prevented from being straightened, the carbon segregation index is not more than 890.78, and the ingot is formed in the subsequent ingot rolling process, the ingot is generally formed by the segregation and the segregation-grade inclusions of an average shrinkage porosity of an ingot, and the ingot is not more than 0.78, and the segregation-grade of the ingot.

S5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating section I is controlled to be 790-850 ℃, the time of the heating section I is 0.5-1.2h, the temperature of a heating section II is 1060-1120 ℃, the time of the heating section II is 0.8-1.4h, the temperature of a soaking section is 1150-1190 ℃, and the time of the soaking section is 1.2-2h, improving the diffusion degree of central carbon of the casting blank by adopting two-section heating and one-section soaking, reducing the net carbon of a core part of a wire rod and ensuring the initial rolling temperature, avoiding the conditions of decarburization and coarse grains and weakening the nucleation caused by excessive high-temperature diffusion, avoiding the influence of the low temperature on the solid solution of alloy elements, and obtaining a steel blank, wherein the temperature difference of the head, the middle and the tail of the steel blank is less than or equal to 30 ℃;

s6, high-pressure water descaling: when the descaling water pressure is more than or equal to 20MPa, descalingThe speed of the roller way is less than or equal to 0.8m/s, and the striking force of the nozzle is more than or equal to 0.8N/mm ² Removing the scale on the surface of the billet steel to avoid hindering the growth of an FeO layer in subsequent rolling;

s7, rolling: the steel billet which is processed by the step S6 enters a rolling line and is subjected to 6 times of rough rolling, 6 times of middle rolling, 10 times of finish rolling and 4 times of sizing reduction rolling to form a wire rod, at least 2 sections of water penetrating boxes are arranged in the direction from the middle rolling to the finish rolling, at least 3 sections of water penetrating boxes are arranged between the finish rolling and the sizing reduction, at least 2 sections of water penetrating boxes are arranged between the sizing reduction and the spinning, and a temperature equalizing guide groove is arranged between adjacent water penetrating boxes and is used for cooling without water spraying and recovering the rolling temperature, so that the temperature of the wire rod is uniform after leaving the water boxes, the temperature difference between the surface of the wire rod and a core part is reduced, the reliability of rolling temperature control is ensured, crystal grains are finer, and the section structure is more uniform;

the 6-pass rough rolling adopts a horizontal and vertical alternating rough rolling unit, the initial rolling temperature is controlled to be 1060-1090 ℃, the phenomenon that the original crystal grains are coarse due to high-temperature initial rolling is avoided, the rough rolling cooling speed is 3.5-5.5 ℃/s, the deformation rate of two passes before the rough rolling is less than or equal to 16%, the deformation rate of not less than two passes after the rough rolling is 25% -28%, the internal defects of the billet are eliminated through large reduction, and the internal compactness is improved;

the 6-pass intermediate rolling adopts a horizontal and vertical alternative intermediate rolling unit, the intermediate rolling cooling speed is 7-9 ℃/s, and sub-crystals are formed in austenite grains, so that fine ferrite grains are formed in the phase change process, the deformation rate of each pass of the intermediate rolling is 18-37%, the deformation rate of not less than 2 passes of the subsequent passes of the intermediate rolling is not less than 34%, the improvement of the permeability of a core part is facilitated, the uniformity of the structure is ensured, and the anisotropy is reduced;

the 10-pass finish rolling adopts a top-crossing 45-degree finish rolling unit, the temperature of the finish rolling unit is 925-950 ℃, the rapid temperature rise of a wire rod caused by deformation after high-speed finish rolling is reduced, the diameter reduction and sizing are reduced, the low-temperature high-speed temperature control rolling is carried out, the deformation rate of each pass of the finish rolling is 12% -18%, the low-temperature large reduction of a finish rolling area is increased, the austenite recrystallization area is controlled to carry out a large amount of thermal deformation, micro-alloy elements are separated out at the austenite grain boundary, the austenite grain boundary is pinned to obtain more fine austenite grains, and the non-recrystallization area is controlled to carry out hot rolling deformation;

4-pass reducing and sizing adopts a MORGEN sixth generation reducing and sizing machine set, the temperature of reducing and sizing is 905-915 ℃, the reduction of two passes after reducing and sizing is 3-4mm, the size and the size precision of original austenite grains are controlled, further, the wire rod grains are refined, the evenness and the strip passing performance are uniform, the microalloy element V/Nb/Ti can be separated out on a high-density defect under the strain induction action, and fine ferrite grains are formed in the phase change process of gamma phase to alpha phase;

s8, spinning: clamping the tail of a wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 18-22%, avoiding surface defects caused by thermal stress, setting the lead quantity of a spinning machine to be 8-11%, feeding and spinning into the spinning machine to be the wire rod, setting the spinning temperature to be 875-895 ℃, and setting the spinning speed to be 28-36m/s, avoiding that the thickness of a decarburized layer is increased due to overhigh spinning temperature, and avoiding that the thickness of an oxide skin is reduced due to overlow spinning temperature to be not beneficial to shelling treatment;

s9, stelmor line cooling: the wire rod enters a stelmor line, the speed of a roller way at the initial stage is set to be 0.14-0.18m/s, the speed of a subsequent roller way is increased by 0.02-0.03m/s, the wire rod is uniformly distributed on the roller way in a scattered manner, overlapping areas are staggered, the temperature change uniformity and the sorbite conversion rate of each position are improved, and therefore mechanical property fluctuation is reduced, the surface shrinkage rate is improved, and the sorbite structure is fully transformed in the cooling control process without martensite abnormal structures;

the wire rod enters the heat preservation cover at a cooling speed of 3.6-4.3 ℃/s, the wire rod is rapidly cooled to improve the phase change power, inhibit the precipitation of a pro-eutectoid cementite structure and improve the tensile strength and the section shrinkage rate, on one hand, the phenomenon that the cold speed is too low to increase the thickness of a decarburized layer is avoided, trace B is melted into austenite in a form of interstitial atoms and can be adsorbed on an austenite grain boundary to reduce the grain boundary energy, the strengthening and precipitation effects of V microalloy are fully exerted to improve the pearlite strength, on the other hand, the hardening is stronger due to the fact that the wire rod contains higher elements such as Si, cr and the like, the right shift range of a C curve of phase change cooling is higher, the phenomenon that the cold speed is too high to cause a martensite structure and a net carbide in a core part and the coexistence of martensite and grain boundary cementite is avoided, so that the performance is reduced;

controlling the temperature of the cover to 592-613 ℃, reducing the air volume of a fan, completing phase change at 525-542 ℃ in the cover at a cooling speed of 0.9-1.6 ℃/s, balancing the air cooling speed and phase change heat energy to prolong the phase change time, slowing down the diffusion speed of C, reducing the pearlite interlamellar spacing and the lamellar thickness of cementite by Ce-Cu, increasing the number of sorbite, promoting Mn diffusion by Si to slow down the spheroidization of the cementite, increasing the stability of the cementite, inhibiting the coarsening of the cementite, ensuring the complete and flat lamella, avoiding the tensile property reduction caused by the pearlite structure and the thick short rod-shaped cementite due to overhigh cooling speed, avoiding the bainite transformation caused by too low cooling speed to reduce the strength and toughness, simultaneously controlling the thickness of the iron scale to be more than 13 mu m by fast cooling and delayed cooling, controlling the proportion of FeO in the iron scale to be more than 68%, having large internal pressure stress of the oxide layer and better mechanical stripping performance, and being capable of replacing the acid washing mode which seriously pollutes the environment to remove the iron scale;

the covering temperature is more than or equal to 425 ℃, air cooling is carried out at the speed of 1.8-2.7 ℃/s after covering, the influence on the mechanical property caused by larger temperature stress due to overhigh cooling speed is avoided, the steel strand wire rod is obtained, the wire rod structure is pearlite and sorbite with the volume fraction accounting for 88-94%, the interval between pearlite lamella is less than 160nm, the interval between cementite lamella is less than 90nm, the plastic deformation resistance is large, the strength and the toughness of the sorbite are improved, no martensite structure exists, the net shape of carbide is less than or equal to 1.0 grade, the grain size is more than or equal to 8 grade, the comprehensive mechanical property is ensured, and the steel strand wire rod is suitable for drawing production.

Compared with the prior art, the invention has the beneficial effects that:

(1) Optimizing component design: by Mn/Si =0.81-0.87, the grain boundary diffusion is enhanced, the growth of pearlite is controlled, the completeness and flatness of a lamella are ensured, the stability of cementite is increased, and the coarsening of the cementite is inhibited; by the Ce-Cu composite refined lamella spacing, the NbC precipitation is promoted, and the Nb and V, ti cooperate to strengthen the fine grain effect; trace B reduces decarburization sensitivity; the rare earth La reduces residual elements of Sb, sn and As, improves grain boundary segregation and temper brittleness and improves fracture.

(2) Controlling the inclusion: the converter smelting adopts a pre-desulfurization and double-slag method to control S, P, high carbon-pulling ensures the hit rate of retained carbon, tapping, slag fluidity is ensured, the amount of discharged slag is controlled, the total amount of silicon and MnS in molten steel is inhibited, so that the slag system is in a low-melting-point area, and high-melting-point inclusions are avoided; LF refining absorbs deoxidation impurities through wollastonite with low oxygen potential and low melting point, and changes irregular silicate and aluminate into spherical rare earth lanthanum oxide orSulfide further adsorbing MnS, caC ₂ Creating a deep deoxidation condition, improving the fluidity of molten steel, and modifying inclusions by a magnesium feeding line and a cerium feeding line, realizing narrow component control, reducing the damage of nozzle nodulation and brittle inclusions to a matrix in the casting process, wherein A, B, C and D type inclusions are both less than or equal to 0.5 grade, DS type inclusions are less than or equal to 1.0 grade, improving the drawing performance and reducing the wire breakage rate.

(3) Controlling the quality of the hypo-tissue: controlling superheat degree to ensure the stability of drawing speed and improve carbon segregation, reducing solute elements accumulated in a two-phase region at the solidification tail end by adopting crystallizer electromagnetic stirring, secondary cooling region electromagnetic stirring and tail end electromagnetic stirring, improving central segregation and looseness by adopting proper secondary cooling specific water flow and drawing speed, and avoiding the central fracture of steel wires, wherein the central segregation, shrinkage cavity and corner cracks are all less than or equal to 0.5 grade.

(4) Controlling the thickness and composition of the oxide skin: the carbon diffusion degree of the center of a casting blank is improved by heating two sections and soaking one section, scale on the surface of the steel blank is removed by high-pressure water descaling, the condition that the growth of an FeO layer is hindered in subsequent rolling is avoided, the condition that the thickness of the scale is reduced due to too low spinning temperature is avoided, the thickness of the scale is controlled to be more than 13 mu m by fast cooling and delayed cooling, the proportion of FeO in the scale is more than 68%, the internal compressive stress of the scale is large, the mechanical stripping performance is improved, and the pickling pollution is avoided.

(5) Control of hypereutectoid organization: after VD vacuum breaking, adding low-carbon ferroboron and feeding titanium wires to reduce yield fluctuation, and refining grains by using trace Ti and rare earth elements; the temperature difference between the surface of the wire rod and a core part is reduced, the permeability of the core part is improved, the crystal grains are finer, the section structure is more uniform, and the anisotropy is reduced through 6-pass rough rolling, 6-pass intermediate rolling, 10-pass finish rolling and 4-pass reducing and sizing rolling; the stelmor line is accelerated by a roller way, is rapidly cooled by 3.6-4.3 ℃/s + slowly cooled by 0.9-1.6 ℃/s + air cooled by 1.8-2.7 ℃/s, contains 88-94% of pearlite and sorbite by volume fraction, has pearlite lamella spacing less than 160nm, cementite lamella spacing less than 90nm, has no martensite structure, has a carbide net shape less than or equal to 1.0 grade and a grain size more than or equal to 8 grade, improves comprehensive mechanical properties, avoids fracture, and is suitable for drawing production.

Detailed Description

The following detailed description of embodiments of the invention is intended to be illustrative, and is not to be construed as limiting the invention.

Example 1:

the invention relates to a better implementation mode of a wire rod for a prestressed steel strand, which has the specification of phi 12.5mm and comprises the following components in percentage by mass: c:0.90%, si:0.71%, mn:0.58%, P:0.008%, S:0.005%, cr:0.34%, ni:0.17%, mo:0.04%, cu:0.012%, al:0.045%, ti:0.013%, V:0.034%, nb:0.018%, B: 0.002%, ce:0.0025%, la:0.002%, sn:0.0012%, sb:0.009%, as:0.009%, O:0.001%, N:0.009%, the balance being Fe and inevitable impurities; mn/Si =0.82.

The production process of the wire rod for the prestressed steel strand comprises the following steps of:

s1, smelting in a converter: pre-desulfurizing a steelmaking raw material by using 120tKR molten iron, smelting by using a top-bottom combined blowing converter and a double-slag method converter to obtain molten steel, controlling S to be less than or equal to 0.0045%, adopting 1.8kg/t of molten steel lime, 1.4kg/t of molten steel dolomite and 0.17kg/t of fluorite slag charge by using the double-slag method, controlling the alkalinity to be 2.95, controlling the end-point phosphorus content to be less than or equal to 0.008%, and controlling the tapping temperature to be 1590% when the end-point carbon content of tapping is 0.25%;

95t of molten steel in each furnace, and 85kg of aluminum cakes are added when 1/5 of steel is tapped; when tapping at 2/5, adding 430kg of silicon-manganese alloy (FeMn 64Si 18), 190kg of low-carbon silicon-iron (FeSi 75-A) and 80kg of silicon-calcium-barium-iron (FeBa 12CaSi 40) for deoxidation and slagging pre-refining; 415kg of a cleaning promoter (CaO53.5%, siO) was added at the time of tapping 2/3 ₂ 3.5％，Al ₂ O ₃ 34.3%, mgO 8.5%) and 190kg lime;

s2, LF refining: feeding the molten steel in the step S1 into an LF (ladle furnace) station, performing precipitation deoxidation and diffusion deoxidation refining, adding 1.5kg of wollastonite, 0.18kg of aluminum wire and 0.09kg of rare earth lanthanum into each ton of steel, performing precipitation deoxidation to prepare white slag, controlling the slag alkalinity to be 2.6, the white slag time to be 25min, smelting the slag to be 50min, and adding 0.7kg/t of CaC of molten steel ₂ Diffusion deoxidation is carried out, end point [ O ]]≤160ppm；

The argon flow in the early stage of LF refining is 320NL/min; low-carbon ferrochrome (FeCr69C1.0), low-aluminum ferrovanadium (FeV 50-C) and ferrocolumbium (FeNb 50-B) are used in the middle stage of LF refining, and the argon flow is 160NL/min; feeding a magnesium wire of 0.4m/t molten steel and a cerium wire of 0.6m/t molten steel at the speed of 1.5m/s into an argon flow rate of 75NL/min in the later stage of LF refining;

s3, VD vacuum: carrying out VD vacuum degassing treatment on the molten steel VD station in the step S2, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 40min, the argon flow is 20NL/min, 0.09kg/t of molten steel low-carbon ferroboron (FeB16C0.1) is added after the vacuum breaking, and a 0.3m/t titanium wire is fed at the speed of 0.8 m/S;

s4, continuous casting: the molten steel in the step S3 is cast in an eight-machine eight-strand continuous casting machine in a whole-process protection mode, the alkaline tundish uses carbonized rice hulls and a neutral covering agent, the temperature of the molten steel in the tundish is 1520 ℃, and the superheat degree is controlled to be 10-25 ℃;

electromagnetic stirring of a crystallizer, electromagnetic stirring of a secondary cooling zone and electromagnetic stirring of the tail end are adopted; electromagnetic stirring parameters of the crystallizer are current 200A and frequency 34Hz; the electromagnetic stirring parameters of the secondary cooling zone are 150A of current and 10Hz of frequency; the electromagnetic stirring parameters at the tail end are current 600A and frequency 8Hz; and the secondary cooling specific water flow is 0.84L/kg, the pulling speed is 1.5m/min, the casting blank is straightened by a straightening machine, cut to length and then put into a pit for slow cooling in time, the pit-entering temperature of the casting blank is controlled to be 640 ℃, the slow cooling time is 48 hours, and the pit-outlet temperature is controlled to be 200 ℃, so that the 165mm casting blank.

S5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating section I is controlled to be 820 ℃, the heating time of the heating section I is 0.8h, the temperature of a heating section II is 1090 ℃, the heating time of the heating section II is 1.3h, the temperature of a soaking section is 1160 ℃, and the soaking time is 1.5h, so as to obtain a steel blank, wherein the temperature difference of the head, the middle and the tail of the steel blank is less than or equal to 30 ℃;

s6, high-pressure water descaling: under the conditions that the descaling water pressure is 22MPa, the speed of a descaling roller way is 0.75m/s, and the striking force of a nozzle is 0.82N/mm ² Removing the scale on the surface of the billet steel to avoid hindering the growth of an FeO layer in subsequent rolling;

s7, rolling: the steel billet passing through the step S6 is subjected to 6-pass rough rolling, 6-pass intermediate rolling, 10-pass finish rolling and 4-pass reduced diameter rolling to form a wire rod, a 1# water penetrating box and a 2# water penetrating box are arranged in the direction from the intermediate rolling to the finish rolling, 3#, 4# and 5# water penetrating boxes are arranged between the finish rolling and the reduced diameter, 6#, 7# and 8# water penetrating boxes are arranged between the reduced diameter and the spinning, and a uniform temperature guide groove is arranged between adjacent water penetrating boxes;

adopting a horizontal and vertical alternating rough rolling unit for 6-pass rough rolling, controlling the initial rolling temperature to be 1070 ℃ and the rough rolling cooling speed to be 4.5 ℃/s; 6-pass intermediate rolling adopts a horizontal and vertical alternating intermediate rolling unit, and the cooling speed of the intermediate rolling is 8 ℃/s; adopting a top crossing 45-degree finishing mill group for 10-time finish rolling, and putting the steel plate into a finishing mill at the temperature of 940 ℃; reducing and sizing 4 times by adopting a MORGEN sixth generation reducing and sizing machine set, and reducing and sizing the temperature to 910 ℃;

s8, spinning: clamping the tail part of the wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 19%, setting the lead quantity of a laying head to be 10%, feeding and laying wires into the laying head to be the wire rod, setting the laying temperature to be 880 ℃, and setting the laying speed to be 29m/s;

s9, stelmor line cooling: the wire rod enters into a stelmor line, the speed of the roller way at the initial section is set to be 0.17m/s, and the speed of the subsequent roller way is increased progressively at the speed of 0.025 m/s; the wire rod enters the heat preservation cover at the cooling speed of 3.9 ℃/s; controlling the temperature of the cover to be 610 ℃, and finishing the phase change of 530 ℃ in the cover at a cooling speed of 1.2 ℃/s in the cover; the cover discharging temperature is 430 ℃, and the finished product is obtained by air cooling at the speed of 2.2 ℃/s after the cover discharging.

Example 2:

the invention relates to a better implementation mode of a wire rod for a prestressed steel strand, which has the specification of phi 12.5mm and comprises the following components in percentage by mass: c:0.92%, si:0.73%, mn:0.63%, P:0.01%, S:0.008%, cr:0.36%, ni:0.18%, mo:0.06%, cu:0.013%, al:0.05%, ti:0.014%, V:0.036%, nb:0.016%, B: 0.0019%, ce:0.0023%, la:0.0022%, sn:0.007%, sb:0.009%, as:0.008%, O:0.001%, N:0.013%, the balance of Fe and inevitable impurities; mn/Si =0.85.

s1, smelting in a converter: pre-desulfurizing the steelmaking raw materials by using 120tKR molten iron, smelting by using a top-bottom combined blowing converter and a double-slag converter to obtain molten steel, controlling S to be less than or equal to 0.0045%, adopting 1.7kg/t of lime of the molten steel, 1.2kg/t of dolomite of the molten steel and 0.19kg/t of fluorite slag charge by using a double-slag method, controlling the alkalinity to be 2.8, controlling the end-point phosphorus content to be less than or equal to 0.008%, and controlling the tapping temperature to be 1580-1610 ℃ when the end-point carbon content of tapping is 0.26%;

adding 90kg of aluminum cakes when the molten steel in each furnace is 97t and tapping is 1/5; when tapping for 2/5, 480kg of silicon-manganese alloy (FeMn 64Si 18), 210kg of low-carbon silicon-iron (FeSi 75-A) and 75kg of silicon-calcium-barium-iron (FeBa 12CaSi 40) are added for deoxidation and slagging pre-refining; 400kg of a cleaning promoter (CaO53.5%, siO) was added at the time of tapping 2/3 ₂ 3.5％，Al ₂ O ₃ 34.3%, mgO 8.5%) and 195kg lime;

s2, LF refining: feeding the molten steel in the step S1 into an LF (ladle furnace) station, performing precipitation deoxidation and diffusion deoxidation refining, adding 1.2kg of wollastonite, 0.19kg of aluminum wire and 0.07kg of rare earth lanthanum into each ton of steel, performing precipitation deoxidation to prepare white slag, controlling the slag alkalinity to be 2.4, the white slag time to be 25min, smelting the slag to be 50min, and adding 0.77kg/t of CaC of molten steel ₂ Diffusion deoxidation is carried out, end point [ O ]]≤160ppm；

The argon flow in the early stage of LF refining is 305NL/min; low-carbon ferrochrome (FeCr69C 1.0), low-aluminum ferrovanadium (FeV 50-C) and ferrocolumbium (FeNb 50-B) are used in the middle stage of LF refining, and the argon flow is 170NL/min; feeding argon flow 65NL/min at the later stage of LF refining into a magnesium wire of 0.4m/t molten steel at the speed of 0.9m/s and a cerium wire of 0.7m/t molten steel at the speed of 1.5 m/s;

s3, VD vacuum: carrying out VD vacuum degassing treatment on the molten steel VD station in the step S2, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 40min, the argon flow is 19NL/min, 0.1kg/t of molten steel low-carbon ferroboron (FeB16C0.1) is added after the vacuum breaking, and a 0.26m/t titanium wire is fed at the speed of 0.8 m/S;

s4, continuous casting: the molten steel in the step S3 is cast in an eight-machine eight-strand continuous casting machine in a whole-process protection manner, the alkaline tundish uses carbonized rice hulls and a neutral covering agent, the temperature of the molten steel in the tundish is 1540 ℃, and the superheat degree is controlled to be 10-25 ℃;

adopting crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring and tail end electromagnetic stirring; electromagnetic stirring parameters of the crystallizer are 300A of current and 3Hz of frequency; the electromagnetic stirring parameters of the secondary cooling zone are current 200A and frequency 12Hz; the electromagnetic stirring parameters at the tail end are 500A of current and 6Hz of frequency; and the secondary cooling specific water flow is 0.77L/kg, the pulling speed is 1.4m/min, the casting blank is straightened by a straightening machine, cut to length and then put into a pit in time for slow cooling, the pit-entering temperature of the casting blank is controlled to be 640 ℃, the slow cooling time is 48h, and the pit-leaving temperature is controlled to be 200 ℃, so that the 165mm casting blank is obtained.

S5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating section I is controlled to be 815 ℃, the time of the heating section I is 1h, the temperature of a heating section II is 1070 ℃, the time of the heating section II is 1h, the temperature of a soaking section is 1190 ℃, and the time of the soaking section is 1.4h, so as to obtain a steel blank, wherein the temperature difference between the head, the middle and the tail of the steel blank is less than or equal to 30 ℃;

adopting a horizontal and vertical alternating rough rolling unit for 6-pass rough rolling, controlling the initial rolling temperature to be 1070 ℃ and the rough rolling cooling speed to be 4.5 ℃/s; 6-pass intermediate rolling adopts a horizontal and vertical alternating intermediate rolling unit, and the intermediate rolling cooling speed is 8.2 ℃/s; adopting a top-crossing 45-degree finishing mill group for 10-time finish rolling, and putting the steel plate into a finishing mill at the temperature of 936 ℃; reducing and sizing 4 times by adopting a MORGEN sixth generation reducing and sizing machine set, wherein the reducing and sizing temperature is 909 ℃;

s8, spinning: clamping the tail part of the wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 20%, setting the lead quantity of a laying head to be 9%, feeding and laying wires into the laying head to be the wire rod, setting the laying temperature to be 887 ℃, and setting the laying speed to be 32m/s;

s9, stelmor line cooling: the wire rod enters a stelmor line, the speed of the roller way in the initial section is set to be 0.17m/s, and the speed of the subsequent roller way is increased progressively by 0.021 m/s; the wire rod enters the heat preservation cover at the cooling speed of 4.2 ℃/s; controlling the temperature of the cover to be 607 ℃, and finishing the phase change of 531 ℃ in the cover at the cooling speed of 1.3 ℃/s; the cover discharging temperature is 430 ℃, and the finished product is obtained after air cooling at the speed of 2.1 ℃/s after cover discharging.

Example 3:

the invention relates to a better implementation mode of a wire rod for a prestressed steel strand, which has the specification of phi 12.5mm and comprises the following components in percentage by mass: c:0.91%, si:0.76%, mn:0.63%, P:0.009%, S:0.009%, cr:0.35%, ni:0.16%, mo:0.06%, cu:0.017%, al:0.045%, ti:0.018%, V:0.033%, nb:0.018%, B: 0.0018%, ce:0.0022%, la:0.0027%, sn:0.012%, sb:0.007%, as:0.011%, O:0.0011%, N:0.009%, and the balance of Fe and inevitable impurities; mn/Si =0.83.

s1, smelting in a converter: pre-desulfurizing a steelmaking raw material by using 120tKR molten iron, smelting by using a top-bottom combined blowing converter and a double-slag method converter to obtain molten steel, controlling S to be less than or equal to 0.0045%, adopting 1.4kg/t of molten steel lime, 1.2kg/t of molten steel dolomite and 0.16kg/t of fluorite slag, controlling the alkalinity to be 2.75, controlling the end-point phosphorus content to be less than or equal to 0.008%, and controlling the tapping temperature to be 1590% when the end-point carbon content of tapping is 0.27%;

102t of molten steel in each furnace, and 91kg of aluminum cakes are added when 1/3 of steel is tapped; adding 475kg of silicon-manganese alloy (FeMn 64Si 18), 195kg of low-carbon ferrosilicon (FeSi 75-A) and 85kg of silicon-calcium-barium-iron (FeBa 12CaSi 40) when tapping 1/2 of steel, and carrying out deoxidation and slagging pre-refining; 415kg of a cleaning promoter (CaO53.5%, siO) was added at the time of tapping 2/3 ₂ 3.5％，Al ₂ O ₃ 34.3%, mgO 8.5%) and 178kg lime;

s2, LF refining: feeding the molten steel in the step S1 into an LF (ladle furnace) station, performing precipitation deoxidation and diffusion deoxidation refining, adding 1-1.5kg of wollastonite, 0.15-0.2kg of aluminum wire and 0.05-0.1kg of rare earth lanthanum into each ton of steel, performing precipitation deoxidation to produce white slag, controlling the slag alkalinity to be 2.2-2.6, controlling the white slag time to be 25min, performing smelting for 50min, and adding 0.5-0.85kg/t of CaC of the molten steel ₂ Diffusion deoxidation is carried out, end point [ O ]]≤160ppm；

The argon flow in the early stage of LF refining is 320NL/min; low-carbon ferrochrome (FeCr69C 1.0), low-aluminum ferrovanadium (FeV 50-C) and ferrocolumbium (FeNb 50-B) are used in the middle stage of LF refining, and the argon flow is 150NL/min; feeding a magnesium wire of 0.6m/t molten steel and a cerium wire of 0.7m/t molten steel at the speed of 1.6m/s into an argon flow rate of 80NL/min in the later stage of LF refining;

s3, VD vacuum: carrying out VD vacuum degassing treatment on the molten steel VD station in the step S2, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 40min, the argon flow is 17-25NL/min, 0.08-0.11kg/t of molten steel low-carbon ferroboron (FeB16C0.1) is added after the vacuum breaking, and a 0.2-0.4m/t titanium wire is fed at the speed of 0.7-1 m/S;

s4, continuous casting: the molten steel in the step S3 is cast in an eight-machine eight-strand continuous casting machine in a whole-process protection manner, the alkaline tundish uses carbonized rice hulls and a neutral covering agent, the temperature of the molten steel in the tundish is 1530 ℃, and the superheat degree is controlled to be 10-25 ℃;

adopting crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring and tail end electromagnetic stirring; the electromagnetic stirring parameters of the crystallizer are 300A of current and 3Hz of frequency; the electromagnetic stirring parameters of the secondary cooling zone are current 200A and frequency 12Hz; the electromagnetic stirring parameters at the tail end are current 600A and frequency 8Hz; and the secondary cooling specific water flow is 0.86L/kg, the pulling speed is 1.65m/min, the casting blank is straightened by a straightening machine, cut to length and then put into a pit for slow cooling in time, the pit-entering temperature of the casting blank is controlled to be 640 ℃, the slow cooling time is 48 hours, and the pit-outlet temperature is controlled to be 200 ℃, so that the 165mm casting blank.

S5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating section I is controlled to be 840 ℃, the time of the heating section I is controlled to be 1h, the temperature of a heating section II is 1080 ℃, the time of the heating section II is 1.2h, the temperature of a soaking section is 1150 ℃, and the time of the soaking section is 1.4h, so as to obtain a steel blank, wherein the temperature difference between the head, the middle and the tail of the steel blank is less than or equal to 30 ℃;

adopting a horizontal and vertical alternating rough rolling unit for 6-pass rough rolling, controlling the initial rolling temperature to be 1080 ℃ and the rough rolling cooling speed to be 4.1 ℃/s; 6-pass intermediate rolling adopts a horizontal and vertical alternating intermediate rolling unit, and the cooling speed of the intermediate rolling is 8.4 ℃/s; adopting a top-crossing 45-degree finishing mill group for 10-time finish rolling, and feeding the steel plate into a finishing mill at the temperature of 934 ℃; reducing and sizing for 4 times by adopting a MORGEN sixth generation reducing and sizing machine set, and reducing and sizing at the temperature of 912 ℃;

s8, spinning: clamping the tail part of the wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 21%, setting the lead quantity of a spinning machine to be 10%, feeding and spinning by the spinning machine to be the wire rod, setting the spinning temperature to be 891 ℃ and the spinning speed to be 29m/s;

s9, stelmor line cooling: the wire rod enters a stelmor line, the speed of the roller way at the initial stage is set to be 0.17m/s, and the speed of the subsequent roller way is increased progressively at the speed of 0.024 m/s; the wire rod enters the heat preservation cover at the cooling speed of 4 ℃/s; controlling the temperature of the shield to be 598 ℃, and finishing the phase change of 539 ℃ in the shield at the cooling speed of 1.1 ℃/s; the cover discharging temperature is 430 ℃, and the finished product is obtained by air cooling at the speed of 1.9 ℃/s after cover discharging.

Example 4:

the invention relates to a better implementation mode of a wire rod for a prestressed steel strand, which has the specification of phi 12.5mm and comprises the following components in percentage by mass: c:0.89%, si:0.74%, mn:0.61%, P:0.01%, S:0.008%, cr:0.33%, ni:0.13%, mo:0.04%, cu:0.014%, al:0.053%, ti:0.015%, V:0.033%, nb:0.019%, B: 0.021%, ce:0.017%, la:0.019%, sn:0.009%, sb:0.007%, as:0.009%, O:0.0009%, N:0.0014%, the balance being Fe and unavoidable impurities; mn/Si =0.82.

s1, smelting in a converter: pre-desulfurizing a steelmaking raw material by using 120tKR molten iron, smelting by using a top-bottom combined blowing converter and a double-slag method converter to obtain molten steel, controlling S to be less than or equal to 0.0045%, adopting 1.8kg/t of molten steel lime, 1.3kg/t of molten steel dolomite and 0.19kg/t of fluorite slag, controlling the alkalinity to be 3.06, the end-point phosphorus content to be less than or equal to 0.008%, and controlling the tapping temperature to be 1602 ℃ when the end-point carbon content of tapping is 0.25%;

adding 81kg of aluminum cakes when tapping 1/3 of 107t of molten steel in each furnace; when tapping 1/2, 480kg of silicon-manganese alloy (FeMn 64Si 18), 192kg of low-carbon silicon-iron (FeSi 75-A) and 77kg of silicon-calcium-barium-iron (FeBa 12CaSi 40) are added for deoxidation and slagging pre-refining; 415kg of a cleaning promoter (CaO53.5%, siO) was added at the time of tapping 3/4 ₂ 3.5％，Al ₂ O ₃ 34.3%, mgO 8.5%) and 188kg lime;

s2, LF refining: feeding the molten steel in the step S1 into an LF (ladle furnace) station, performing precipitation deoxidation and diffusion deoxidation refining, adding 1.3kg of wollastonite, 0.19kg of aluminum wire and 0.07kg of rare earth lanthanum into each ton of steel, performing precipitation deoxidation to prepare white slag, controlling the slag alkalinity to be 2.5, the white slag time to be 25min, smelting the slag to be 50min, and adding 0.64kg/t of CaC of molten steel ₂ Diffusion deoxidation is carried out, end point [ O ]]≤160ppm；

The argon flow in the early stage of LF refining is 320NL/min; low-carbon ferrochrome (FeCr69C 1.0), low-aluminum ferrovanadium (FeV 50-C) and ferrocolumbium (FeNb 50-B) are used in the middle stage of LF refining, and the argon flow is 160NL/min; feeding a magnesium wire of 0.6m/t molten steel and a cerium wire of 0.8m/t molten steel at the speed of 1.5m/s into an argon flow rate of 55NL/min in the later stage of LF refining;

s3, VD vacuum: carrying out VD vacuum degassing treatment on the molten steel VD station in the step S2, wherein the ultimate vacuum degree is less than or equal to 68Pa, the pressure maintaining time is 25min, the soft argon blowing time is 40min, the argon flow is 22NL/min, 0.09kg/t of molten steel low-carbon ferroboron (FeB16C0.1) is added after the vacuum breaking, and a 0.35m/t titanium wire is fed at the speed of 0.9 m/S;

s4, continuous casting: the molten steel in the step S3 is cast in an eight-machine eight-strand continuous casting machine in a whole-process protection mode, the alkaline tundish uses carbonized rice hulls and a neutral covering agent, the temperature of the molten steel in the tundish is 1498 ℃, and the superheat degree is controlled to be 10-25 ℃;

electromagnetic stirring of a crystallizer, electromagnetic stirring of a secondary cooling zone and electromagnetic stirring of the tail end are adopted; electromagnetic stirring parameters of the crystallizer are current 200A and frequency 3Hz; the electromagnetic stirring parameters of the secondary cooling zone are 150A of current and 11Hz of frequency; the electromagnetic stirring parameters at the tail end are 550A of current and 7Hz of frequency; and (3) straightening by a straightening machine, cutting to length, then timely putting the cast blank into a pit for slow cooling, controlling the temperature of the cast blank in the pit to be 640 ℃, the slow cooling time to be 48h and the temperature of the cast blank out of the pit to be 200 ℃, and obtaining the 165mm/165mm cast blank, wherein the flow rate of the secondary cooling water is 0.75L/kg, the pulling speed is 1.4 m/min.

S5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating section I is controlled to be 810 ℃, the heating time of the heating section I is 1.1h, the temperature of a heating section II is 1110 ℃, the heating time of the heating section II is 0.9h, the temperature of a soaking section is 1180 ℃, and the soaking time is 1.4h, so as to obtain a steel blank, wherein the temperature difference of the head, the middle and the tail of the steel blank is less than or equal to 30 ℃;

s7, rolling: the steel billet passing through the step S6 is subjected to 6-pass rough rolling, 6-pass intermediate rolling, 10-pass fine rolling and 4-pass reduced diameter rolling to form a wire rod, a 1# water penetrating box and a 2# water penetrating box are arranged in the direction from the intermediate rolling to the fine rolling, 3#, 4# and 5# water penetrating boxes are arranged between the fine rolling and the reduced diameter rolling, 6#, 7# and 8# water penetrating boxes are arranged between the reduced diameter rolling and spinning, and a uniform temperature guide groove is arranged between adjacent water penetrating boxes;

adopting a horizontal and vertical alternating rough rolling unit for 6-pass rough rolling, controlling the initial rolling temperature to be 1040 ℃, and controlling the rough rolling cooling speed to be 4.9 ℃/s; 6-pass intermediate rolling adopts a horizontal and vertical alternating intermediate rolling unit, and the cooling speed of the intermediate rolling is 8.6 ℃/s; adopting a top-crossing 45-degree finishing mill group for 10-pass finish rolling, and putting the steel plate into a finishing mill at the temperature of 944 ℃; reducing and sizing 4 times by adopting a MORGEN sixth generation reducing and sizing machine set, wherein the reducing and sizing temperature is 914 ℃;

s8, spinning: clamping the tail part of the wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 21%, setting the lead quantity of a spinning machine to be 9%, feeding and spinning the wire rod into the spinning machine, setting the spinning temperature to be 882 ℃ and the spinning speed to be 34m/s;

s9, stelmor line cooling: the wire rod enters into a stelmor line, the speed of the roller way at the initial section is set to be 0.17m/s, and the speed of the subsequent roller way is increased progressively at the speed of 0.026 m/s; the wire rod enters the heat preservation cover at the cooling speed of 4.3 ℃/s; controlling the temperature of the cover to be 611 ℃, and completing phase change of 533 ℃ in the cover at a cooling speed of 1.4 ℃/s; the cover discharging temperature is 430 ℃, and the finished product is obtained by air cooling at the speed of 2.3 ℃/s after the cover discharging.

Comparative example 1:

a wire rod for a prestressed steel strand, which has the specification of phi 12.5mm, comprises the following components in percentage by mass: c:0.85%, si:0.32%, mn:0.8%, P:0.02%, S:0.02%, cr:0.2%, cu:0.15%, al:0.15%, O:0.004%, N:0.007% and the balance of Fe and inevitable impurities; mn/Si =2.5.

The production process of the wire rod for the prestressed steel strand is different from that of the embodiment 1 in that:

s1, smelting in a converter: the carbon content at the steel end point is 0.19%, 107t of molten steel in each furnace is added with 190kg of aluminum cakes, 200kg of silicon-manganese alloy (FeMn 64Si 18), 110kg of ferrochrome (FeCr69C 4.0) and 300kg of lime in turn when tapping;

s2, LF refining: feeding the molten steel in the step S1 into an LF (ladle furnace) station, adding 0.9kg of lime and 1.5kg of aluminum beans into each ton of steel to prepare white slag, controlling the slag alkalinity to be 3.2, controlling the white slag time to be 25min, and controlling the smelting time to be 50min; the argon flow in the early stage of LF refining is 180NL/min; high-carbon ferromanganese (FeMn68C7.0) is used in the middle stage of LF refining, and the argon flow is 300NL/min; feeding 1.5m/t molten steel calcium-silicon wire with argon flow of 150NL/min at the later stage of LF refining at the speed of 1 m/s;

s3, VD vacuum: no low-carbon ferroboron (FeB16C0.1) is added, and no titanium wire is fed;

s4, continuous casting: the temperature of molten steel in the tundish is 1590 ℃, and the superheat degree is controlled to be 30-45 ℃; adopting crystallizer electromagnetic stirring, secondary cooling zone electromagnetic stirring and tail end electromagnetic stirring; the electromagnetic stirring parameters of the crystallizer are 400A of current and 5Hz of frequency; the electromagnetic stirring parameters of the secondary cooling zone are 180A of current and 10Hz of frequency; the electromagnetic stirring parameters at the tail end are 300A of current and 4Hz of frequency; the secondary cooling specific water flow is 0.95L/kg, and the drawing speed is 2.2m/min.

S5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating section I is controlled to be 860 ℃, the time of the heating section I is controlled to be 1.5h, the temperature of a heating section II is controlled to be 1190 ℃, the time of the heating section II is controlled to be 1.5h, the temperature of a soaking section is 1250 ℃, and the time of the soaking section is controlled to be 1h, so that a steel blank is obtained;

s6, high-pressure water descaling: under the conditions that the descaling water pressure is 18MPa, the speed of a descaling roller way is 0.9m/s, and the striking force of a nozzle is 0.65N/mm ² Removing scale on the surface of the billet;

s7, rolling: the steel billet passing through the step S6 is subjected to 6-pass rough rolling, 6-pass intermediate rolling, 10-pass finish rolling and 4-pass reduced diameter rolling to form a wire rod, a 1# water penetrating box and a 2# water penetrating box are arranged in the direction from the intermediate rolling to the finish rolling, 3#, 4# and 5# water penetrating boxes are arranged between the finish rolling and the reduced diameter, 6#, 7# and 8# water penetrating boxes are arranged between the reduced diameter and the spinning, and no temperature equalizing guide groove is arranged between adjacent water penetrating boxes;

adopting a horizontal and vertical alternating rough rolling unit for 6-pass rough rolling, controlling the initial rolling temperature to be 1170 ℃, and controlling the rough rolling cooling speed to be 6 ℃/s; 6-pass intermediate rolling adopts a horizontal and vertical alternating intermediate rolling unit, and the cooling speed of the intermediate rolling is 6 ℃/s; adopting a top crossing 45-degree finishing mill group for 10-time finish rolling, and putting the steel plate into a finishing mill at the temperature of 980 ℃; 4-pass reducing and sizing by adopting a MORGEN sixth generation reducing and sizing machine set, wherein the reducing and sizing temperature is 860 ℃;

s8, spinning: clamping the tail part of the wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 29%, setting the lead quantity of a laying head to be 5%, feeding and laying wires into the laying head to be the wire rod, setting the laying temperature to be 835 ℃, and setting the laying speed to be 25m/s;

s9, stelmor line cooling: the wire rod enters a stelmor line, the speed of an initial roller way is set to be 0.17m/s, and the speed of a subsequent roller way is set to be 0.24m/s; the wire rod enters the heat-preserving cover at the cooling speed of 12.5 ℃/s; controlling the temperature of the shield to be 670 ℃, and finishing the phase change of 605 ℃ in the shield at the cooling speed of 2.5 ℃/s in the shield; the cover discharging temperature is 520 ℃, and the finished product is obtained by air cooling at the speed of 6 ℃/s after the cover discharging.

The casting blanks of examples 1 to 4 and comparative example 1 were tested for inclusion components according to GB/T10561, and the results are shown in Table 1 below;

TABLE 1

As can be seen from Table 1, the converter smelting adopts a pre-desulfurization and double-slag method to control S, P, high carbon-pulling ensures the carbon-remaining hit rate, tapping, slag fluidity, slag amount control, and the total amount of silicon and MnS return of molten steel is inhibited, so that a slag system is in a low-melting-point area, and high-melting-point inclusions are avoided; in LF refining, the deoxidation impurities are absorbed by wollastonite with low oxygen potential and low melting point, the irregular silicate and aluminate are changed into oxides or sulfides of spherical rare earth lanthanum, and MnS and CaC are further adsorbed ₂ Creating a deep deoxidation condition, improving the fluidity of molten steel, and modifying inclusions by a magnesium feeding line and a cerium feeding line, realizing narrow component control, reducing the damage of nozzle nodulation and brittle inclusions to a matrix in the casting process, wherein A, B, C and D type inclusions are both less than or equal to 0.5 grade, DS type inclusions are less than or equal to 1.0 grade, improving the drawing performance and reducing the wire breakage rate.

The cast slabs of examples 1 to 4 and comparative example 1 were subjected to the macrostructure and defect pickling test of steel according to the standard GB/T226, and rated according to the standard GB/T1979, the results of which are shown in Table 2 below;

TABLE 2

As can be seen from Table 2, the superheat degree is controlled to ensure the pulling speed stability and improve the carbon segregation, the crystallizer electromagnetic stirring, the secondary cooling zone electromagnetic stirring and the tail end electromagnetic stirring are adopted to reduce the solute elements accumulated in the two-phase zone at the solidification tail end, the proper secondary cooling specific water flow and the pulling speed are adopted to improve the central segregation and the porosity, the central porosity, the general porosity, the ingot type segregation, the shrinkage cavity and the corner cracks are all less than or equal to 0.5 grade, and the central fracture of the steel wire is avoided.

Comparative example 2:

a wire rod for prestressed steel strands is different from the wire rod in embodiment 4 in that:

s5, heating: putting the casting blank into a three-section stepping heating furnace, wherein the temperature of a heating I section is controlled to be 860 ℃, the time of the heating I section is controlled to be 1.5h, the temperature of a heating II section is controlled to be 1020 ℃, the time of the heating II section is controlled to be 1.5h, the temperature of a soaking section is 1140 ℃, and the time of the soaking section is 1h, so as to obtain a steel blank;

s6, high-pressure water descaling: under the conditions that the descaling water pressure is 19MPa, the speed of a descaling roller way is 0.9m/s, and the striking force of a nozzle is 0.7N/mm ² Removing scale on the surface of the billet;

adopting a horizontal and vertical alternating rough rolling unit for 6-pass rough rolling, controlling the initial rolling temperature to be 1100 ℃ and the rough rolling cooling speed to be 2.5 ℃/s; 6-pass intermediate rolling adopts a horizontal and vertical alternative intermediate rolling unit, and the cooling speed of the intermediate rolling is 10 ℃/s; adopting a top crossing 45-degree finishing mill group for 10-time finish rolling, and putting the steel plate into a finishing mill at the temperature of 960 ℃; reducing and sizing 4 times by adopting a MORGEN sixth generation reducing and sizing machine set, wherein the reducing and sizing temperature is 935 ℃;

s8, spinning: clamping the tail part of the wire rod by adopting a pinch roll, setting the torque parameter of the pinch roll before spinning to be 29%, setting the lead quantity of a spinning machine to be 5%, feeding and spinning the wire rod into the spinning machine, setting the spinning temperature to be 905 ℃ and the spinning speed to be 25m/s;

s9, stelmor line cooling: the wire rod enters a stelmor line, the speed of a roller way at the initial section is set to be 0.14m/s, and the speed of a subsequent roller way is set to be 0.18m/s; the wire rod enters the heat-preserving cover at the cooling speed of 2.5 ℃/s; controlling the temperature of the cover to be 620 ℃, and finishing the phase change of 593 ℃ in the cover at the cooling speed of 0.7 ℃/s; the cover discharging temperature is 410 ℃, and the finished product is obtained by air cooling at the speed of 6 ℃/s after the cover discharging.

The rolling reduction and the reduced rolling reduction of each pass of examples 1 to 4 and comparative examples 1 to 2 are shown in Table 3 below;

TABLE 3

As can be seen from Table 3, the rolling process of the invention adopts 6-pass rough rolling, 6-pass intermediate rolling, 10-pass finish rolling and 4-pass reducing and sizing rolling; temperature equalizing guide grooves are respectively arranged between the middle rolling and the finish rolling, between the finish rolling and the reducing diameter, and between the reducing diameter and the spinning water tank; the rough rolling cooling speed is 3.5-5.5 ℃/s, the deformation rate of two passes before rough rolling is less than or equal to 16%, and the deformation rate of not less than two passes after rough rolling is 25-28%; the cold speed of the medium rolling is 7-9 ℃/s, the deformation rate of each pass of the medium rolling is 18-37%, and the deformation rate of not less than 2 passes of the subsequent passes of the medium rolling is not less than 34%; the deformation rate of each pass of finish rolling is 12-18 percent; the rolling reduction of two times after diameter reduction is 3-4mm.

The bars of examples 1 to 4 and comparative examples 1 to 2 were subjected to a tensile test according to test standard GB/T228.1, to a Charpy pendulum impact test according to standard GB/T229 and to a grain size test according to GB/T6394, the results of which are given in Table 4 below:

TABLE 4

The carbon diffusion degree of the center of a casting blank is improved by heating two sections and soaking one section, scale on the surface of the steel blank is removed by high-pressure water descaling, the condition that the growth of an FeO layer is hindered in subsequent rolling is avoided, the condition that the thickness of the scale is reduced due to too low spinning temperature is avoided, the thickness of the scale is controlled to be more than 13 mu m by fast cooling and delayed cooling, the proportion of FeO in the scale is more than 68%, the internal compressive stress of the scale is large, the mechanical stripping performance is improved, and the pickling pollution is avoided.

By Mn/Si =0.81-0.87, the grain boundary diffusion is enhanced, the growth of pearlite is controlled, the completeness and flatness of a lamella are ensured, the stability of cementite is increased, and the coarsening of the cementite is inhibited; by the Ce-Cu composite refined lamella spacing, the NbC precipitation is promoted, and the Nb and V, ti cooperate to strengthen the fine grain effect; trace B reduces decarburization sensitivity; the rare earth La reduces residual elements of Sb, sn and As, improves grain boundary segregation and temper brittleness and improves fracture.

Control of hypereutectoid organization: after VD vacuum breaking, adding low-carbon ferroboron and feeding titanium wires to reduce yield fluctuation, and refining grains by using trace Ti and rare earth elements; the temperature difference between the surface of the wire rod and a core part is reduced, the permeability of the core part is improved, the crystal grains are finer, the section structure is more uniform, and the anisotropy is reduced through 6-pass rough rolling, 6-pass intermediate rolling, 10-pass finish rolling and 4-pass reducing and sizing rolling; the stelmor line is accelerated by a roller way, is rapidly cooled by 3.6-4.3 ℃/s + slowly cooled by 0.9-1.6 ℃/s + air cooled by 1.8-2.7 ℃/s, contains 88-94% of pearlite and sorbite by volume fraction, has pearlite lamella spacing less than 160nm, cementite lamella spacing less than 90nm, has no martensite structure, has a carbide net shape less than or equal to 1.0 grade and a grain size more than or equal to 8 grade, improves comprehensive mechanical properties, avoids fracture, and is suitable for drawing production.

The above-listed detailed description is only a specific description of a possible embodiment of the present invention, and they are not intended to limit the scope of the present invention, and equivalent embodiments or modifications made without departing from the technical spirit of the present invention should be included in the scope of the present invention.

Claims

1. The wire rod for the prestressed steel strand is characterized by comprising the following components in percentage by mass: c:0.89-0.93%, si:0.69 to 0.78%, mn:0.56-0.63%, P: less than or equal to 0.015 percent, S: less than or equal to 0.01 percent, cr:0.32-0.37%, ni:0.12 to 0.19%, mo:0.02-0.08%, cu:0.01-0.015%, al:0.04-0.06%, ti:0.01-0.015%, V:0.03-0.039%, nb:0.015-0.02%, B: 0.0015-0.003%, ce:0.0015-0.003%, la:0.0015-0.003%, sn: less than or equal to 0.015 percent, sb: less than or equal to 0.01 percent, as: less than or equal to 0.015 percent, O: less than or equal to 0.0012 percent, N:0.008-0.015% and the balance of Fe and inevitable impurities; mn/Si =0.81-0.87;

the production process of the wire rod for the prestressed steel strand comprises the working procedures of converter smelting, LF refining, VD vacuum, continuous casting, heating, high-pressure water descaling, rolling, spinning and stelmor line cooling;

adding aluminum cakes, silicon-manganese alloy, low-carbon ferrosilicon, silicon-calcium-barium-iron, a cleaning promoter and lime during tapping in the converter smelting process;

the LF refining process adopts wollastonite, aluminum wires and rare earth lanthanum to precipitate and deoxidize; by using CaC ₂ Carrying out diffusion deoxidation; feeding a magnesium wire and a cerium wire in the later stage of LF refining;

after the VD vacuum process is broken, adding low-carbon ferroboron and feeding a titanium wire;

the continuous casting process controls the superheat degree to be 10-25 ℃;

the rolling process controls the initial rolling temperature to be 1060-1090 ℃ and the temperature of finishing mill to be 925-950 ℃;

the spinning temperature of the spinning procedure is 875-895 ℃;

the speed of a roller way in the initial stage of the stelmor line cooling process is set to be 0.14-0.18m/s, the speed of a subsequent roller way is increased gradually at the speed of 0.02-0.03m/s, the wire rod enters a heat-insulating cover at the cooling speed of 3.6-4.3 ℃/s, the temperature of the cover entering is 592-613 ℃, the phase change of 525-542 ℃ in the cover is completed at the cooling speed of 0.9-1.6 ℃/s in the cover, the temperature of the cover leaving is not less than 425 ℃, and the cover leaving is air-cooled at the speed of 1.8-2.7 ℃/s.

2. The wire rod for the prestressed steel strand as claimed in claim 1, wherein the total decarburized layer of the wire rod is not more than 1.2% of the nominal diameter of the wire rod, the wire rod structure is pearlite and sorbite, the sorbite has a volume fraction of 88-94% in the wire rod structure, the pearlite lamellar spacing is less than 160nm, the cementite lamellar spacing is less than 90nm, the carbide network is not more than 1.0 grade, the grain size is not less than 8 grade, and the wire rod has mechanical properties: the tensile strength is 2145-2250MPa, the yield strength is 1965-2180MPa, the elongation is more than or equal to 29%, the reduction of area is more than or equal to 45%, and the impact energy Akv is more than or equal to 82J.

3. The wire rod for the prestressed steel strand as claimed in claim 1, wherein the converter smelting process comprises KR molten iron pre-desulfurization, top-bottom combined blowing and converter smelting by a double slag method, wherein S is controlled to be less than or equal to 0.0045%, the double slag method adopts lime, dolomite and fluorite slag-making materials, the alkalinity is controlled to be 2.7-3.1, the end-point phosphorus content is less than or equal to 0.008%, the end-point carbon content of steel is 0.22-0.28%, and the tapping temperature is 1580-1610 ℃;

adding 75-92kg of aluminum cakes when 90-110t of molten steel in each furnace and 1/5-1/3 of steel are tapped; when tapping is carried out for 2/5-1/2, 440-490kg of silicon-manganese alloy, 180-220kg of low-carbon ferrosilicon and 60-90kg of silicon-calcium-barium-iron are added; 390-430kg of cleaning promoter and 170-200kg of lime are added when tapping is carried out at 2/3-3/4, and the cleaning promoter comprises CaO, siO and Al ₂ O ₃ 、MgO。

4. The wire rod for the prestressed steel strand as claimed in claim 1, wherein the LF refining process comprises adding wollastonite in an amount of 1-1.5kg, aluminum wire in an amount of 0.15-0.2kg and rare earth lanthanum in an amount of 0.05-0.1kg per ton to produce white slag by precipitation and deoxidation, controlling the slag basicity to be 2.2-2.6, the white slag time to be not less than 20min, the smelting time to be not less than 40min, and adding CaC containing molten steel in an amount of 0.5-0.85kg/t ₂ Diffusion deoxidation is carried out, end point [ O ]]≤160ppm；

The argon flow in the early stage of LF refining is 300-330NL/min; the argon flow in the middle stage of LF refining is 150-180NL/min, and low-carbon ferrochrome, low-aluminum ferrovanadium and ferrocolumbium are used for component adjustment; the argon flow in the later stage of LF refining is 50-80NL/min, and the magnesium wire of 0.3-0.7m/t molten steel is fed at the speed of 0.8-1.1m/s, and the cerium wire of 0.5-0.8m/t molten steel is fed at the speed of 1.4-1.6 m/s.

5. The wire rod for the prestressed steel strand according to claim 1, wherein the argon flow in the VD vacuum process is 17-25NL/min, 0.08-0.11kg/t of molten steel low-carbon ferroboron is added after the vacuum breaking, and 0.2-0.4m/t of titanium wire is fed at a speed of 0.7-1 m/s.

6. The wire rod for the prestressed steel strand as recited in claim 1, wherein the electromagnetic stirring parameters of the crystallizer in the continuous casting process are current of 200-300A and frequency of 3-4Hz; the electromagnetic stirring parameters of the secondary cooling zone are 150-200A of current and 10-12Hz of frequency; the electromagnetic stirring parameters at the tail end are 500-600A of current and 6-8Hz of frequency; the secondary cooling specific water flow is 0.72-0.87L/kg; the pulling speed is 1.3-1.7m/min; the reduction amount of the solidification tail end is 7-9mm, the temperature of a casting blank entering a pit is more than or equal to 630 ℃, the slow cooling time is more than or equal to 42h, and the temperature of a casting blank leaving the pit is less than or equal to 205 ℃.

7. The wire rod for the prestressed steel strand as claimed in claim 1, wherein in the heating step, the temperature of the heating section I is controlled to be 790-850 ℃, the time of the heating section I is 0.5-1.2h, the temperature of the heating section II is controlled to be 1060-1120 ℃, the time of the heating section II is 0.8-1.4h, the temperature of the soaking section is 1150-1190 ℃, and the time of the soaking section is 1.2-2h; the descaling water pressure of the high-pressure water descaling procedure is more than or equal to 20MPa, the speed of a descaling roller way is less than or equal to 0.8m/s, and the nozzle hitting power is more than or equal to 0.8N/mm ² 。

8. The wire rod for the prestressed steel strand as claimed in claim 1, wherein the rolling process comprises 6-pass rough rolling, 6-pass intermediate rolling, 10-pass finish rolling and 4-pass reducing and sizing rolling; temperature equalizing guide grooves are respectively arranged between the middle rolling and the finish rolling, between the finish rolling and the reducing diameter, and between the reducing diameter and the spinning water tank; the rough rolling cooling speed is 3.5-5.5 ℃/s, the deformation rate of two passes before rough rolling is less than or equal to 16%, and the deformation rate of not less than two passes after rough rolling is 25-28%; the cold speed of the medium rolling is 7-9 ℃/s, the deformation rate of each pass of the medium rolling is 18-37%, and the deformation rate of not less than 2 passes of the subsequent passes of the medium rolling is not less than 34%; the deformation rate of each pass of finish rolling is 12-18 percent; the rolling reduction of two passes after sizing is 3-4mm.

9. The wire rod for prestressed steel strands as recited in claim 1, wherein said spinning process sets the torque parameter of pinch rolls before spinning to 18-22% and the spinning speed to 28-36m/s.