CN118497622B

CN118497622B - 12.9-Grade annealing-free hot-rolled high-carbon cold heading steel wire rod and manufacturing method thereof

Info

Publication number: CN118497622B
Application number: CN202410969479.3A
Authority: CN
Inventors: 彭梦都; 时彤彤; 于同仁; 王晓兰
Original assignee: Jiangsu Yonggang Group Co Ltd
Current assignee: Jiangsu Yonggang Group Co Ltd
Priority date: 2024-07-19
Filing date: 2024-07-19
Publication date: 2024-10-01
Anticipated expiration: 2044-07-19
Also published as: CN118497622A

Abstract

The invention relates to a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod and a manufacturing method thereof, wherein low hardenability and hypoeutectoid high-carbon chemical component rolling spinning with high C-Si-Mn are adopted to form the wire rod, then on-line molten salt pearlite temperature control treatment is carried out, so that the wire rod is cooled to a pearlite phase region at a cooling speed of more than or equal to 34 ℃/s for transformation, meanwhile, the pearlite formed by isothermal promotion of phase transformation is softened at a high temperature to form quasi-spheroidized carbide, finally, the quasi-spheroidized carbide is slowly cooled by a roller way, and finally, the cold heading steel wire rod with a microstructure comprising 87-92% of tempered pearlite and the rest ferrite and quasi-spheroidized carbide is manufactured, so that the material cost can be reduced, the manufacturing procedure can be simplified, the tensile strength is 1110-1160 MPa, the section shrinkage rate is 51-56%, and the netlike, the netlike carbide is 0 grade, and the wire rod is used for manufacturing 12.9-grade annealing-free high-strength fastener bolts and other application fields, and the risks of drawing and cold heading cracking are reduced.

Description

12.9-Grade annealing-free hot-rolled high-carbon cold heading steel wire rod and manufacturing method thereof

Technical Field

The invention belongs to the technical field of hot-rolled cold-heading steel wire rods, and particularly relates to a 12.9-grade annealing-free hot-rolled high-carbon cold-heading steel wire rod and a manufacturing method thereof.

Background

With the continuous development of the new energy automobile field, the development of the cold heading steel wire rod for the 12.9-grade ultra-high strength fastener needs to sequentially carry out multiple spheroidizing annealing, drawing, cold heading, tempering and other processes on the hot rolled wire rod to reach a final performance grade, wherein the spheroidizing annealing process is carried out for 4-7 hours at the temperature of 750-780 ℃, the aim is to soften a structure to improve the drawing and cold heading performance, reduce the drawing broken wire and cold heading cracking risk of the wire rod, but simultaneously bring the problems of more processes, high manufacturing cost, high energy consumption, high emission and the like, and because of the annealing-free requirement of the green production of the cold heading steel wire rod for the 12.9-grade ultra-high strength fastener, the design of the raw material hot rolled wire rod, particularly the material plasticity, has higher requirements.

The existing hot-rolled cold heading steel wire rod for simplifying annealing and even manufacturing a 12.9-grade fastener without annealing generally adopts medium and low carbon steel, then alloy components such as Cr, mo, B, ti and the like for improving the hardenability or strength of the steel are added, and the wire rod with ferrite and pearlite metallographic structure is obtained under the stelmor air cooling process after rolling and spinning, so that the ferrite proportion in the structure is increased to improve the plasticity of the wire rod, for example: the invention discloses an annealing-free cold heading steel and a manufacturing method thereof as well as a fastener obtained by the annealing-free cold heading steel, wherein the annealing-free cold heading steel adopts the component design of medium C-Si-Mn-Al-Cr-Mo-B-Mg, and combines a heat preservation slow cooling process after spinning by low-temperature rolling to obtain most ferrite and little degenerated pearlite structure, so that Rm is less than or equal to 650MPa, and the area shrinkage is more than or equal to 53 percent; on the other hand, the addition of Cr, ti, B and other alloy components leads to high hardenability of the wire rod, bainite, martensite and other brittle and harmful tissues which are unfavorable for drawing are easy to separate out in the controlled cooling process after rolling, the cracking risk of the wire rod is increased in the drawing and cold heading processes, meanwhile, the design thought of increasing the ferrite proportion in the tissues and improving the plasticity of the wire rod can lead to obvious loss of the wire rod strength, the wire rod is required to be drawn with high reduction rate in the drawing manufacturing process, so that the wire rod strength can be quenched and tempered to reach 12.9 grade after being improved, the plastic loss in the process is high, and the risk of wire breakage or cracking is also caused, so that part of cold heading steel wire rods for ultra-high strength fasteners are selected on the basis of the high hardenability components, a small amount of bainite in the tissues is reserved, so that the proper strength of a matrix is maintained, but the dislocation density of the bainite is high, the plastic hinge is poor, the wire rod is easy to break in the wire rod coiling, transportation or downstream paying-off processes, the wire rod yield is limited, and the production window is narrower; although the 12.9-grade annealing-free hot-rolled complex-phase cold heading steel wire rod and the manufacturing method thereof disclosed in the patent CN118166189A adopt the medium C-Si-Mn-Cr component design, and combine molten salt ultra-fast quenching after spinning, online molten salt heating tempering and roller way slow cooling to obtain a complex-phase structure of tempered bainite, tempered martensite and quasi-spheroidized carbide, the tensile strength is 1012-1063 MPa, the reduction of area is 55% -59%, and the problem of brittle phase can be effectively improved, but two times of salt bath control are needed, and the process is not simplified enough.

The carbon element is the most basic element in steel and is also a more economic strengthening element compared with other elements, and the tensile strength of the steel can be improved along with the increase of the carbon content, so that the hot-rolled cold heading steel wire rod is manufactured by using a carbon steel grade which contains no Cr, ti, B and other alloy components, is used for the annealing-free high-efficiency green manufacturing of the 12.9-grade fastener, has important significance for reducing the cost of the steel, but the existing high-carbon hot-rolled wire rod is difficult to meet the technical difficulty and cause of the annealing-free cold heading manufacturing of the 12.9-grade fastener, and is characterized in that:

(1) With the increase of the carbon content in steel, the segregation of molten steel in the solidification process is increased, the length and the highest cooling capacity of a stelmor air cooling line are limited, the lower middle carbon cold heading steel wire rod is easier to break wires and crack in the stelmor air cooling process after rolling, and because the time in a secondary carbide precipitation interval is longer, carbide precipitates into netlike secondary cementite which is netlike carbide along grain boundaries, the existence of the netlike carbide weakens the connection among grains, the non-uniformity of chemical components in the steel is increased, the utilization rate of carbon elements is reduced, the mechanical property of the steel is reduced, particularly the plastic toughness can be reduced sharply, the wire breakage and cracking risks are easy to occur due to uneven stress or insufficient plasticity when the material is subjected to annealing-free drawing or cold heading, and in order to avoid the netlike carbide precipitation when the wire laying temperature of the high carbon hot rolling wire rod is lower, or the grade of net carbon precipitated in an air cooling section after spinning is reduced, a medium-high Wen Tusi and stelmor rapid cooling process is adopted in the existing high-carbon hot rolled wire rod, but on one hand, the rolling temperature of the wire rod under the medium-high Wen Tu wire is higher, the rolling time is longer, austenite grains are easy to be coarse, the matrix strength and certain toughness of the cold heading steel wire rod for maintaining a 12.9-grade fastener under the condition of reducing or omitting alloy components are not good, on the other hand, the air cooling strength is further improved, the air volume difference between the air receiving surface and the leeward surface of the wire rod is increased, the fluctuation of mechanical properties of the wire rod is increased due to the increase of the temperature difference of the wire rod, the risk of precipitation of bainite and martensite abnormal phases is also increased, meanwhile, the inoculation time of diffusion type net carbon of the wire rod after spinning is still longer, the net carbon precipitation quantity is reduced, the grade is still higher, the wire rod productivity is affected, and the wire breakage or cracking risk of subsequent processing is caused.

(2) The existing high-carbon hot rolled wire rod for drawing processing mainly improves supercooling degree by increasing the wire rod cooling speed of an air cooling process after spinning, promotes the phase transition of a sorbite structure with smaller lamellar spacing, improves the strength of the wire rod by increasing the sorbite content in the structure and improving the sorbite rate so as to achieve the ultrahigh strength of a drawn product, but loses the plasticity of the wire rod to a certain extent, meanwhile, the carbon content is increased, the spheroidization trend of carbide is slow, the time of the wire rod passing through the sorbite phase transition temperature interval in the continuous cooling process is shorter, the obtained hot rolled wire rod is higher in tissue stress and dislocation density, cannot be softened at low temperature, and finally leads to great stress concentration of a matrix, the plasticity of the wire rod is insufficient, carbide is easy to be broken or microcracked in drawing cold heading, the ferrite content in the structure is increased by reducing the cold speed, the strength of the wire rod is lost, the improvement of the plasticity of the wire rod is limited, and the problem of network carbon is also unfavorable for improving, and the annealing-free cold heading requirement of a 12.9-level fastener is difficult to meet.

Disclosure of Invention

The invention aims to solve at least one of the technical problems to a certain extent, and provides a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod and a manufacturing method thereof, which can reduce material cost, simplify manufacturing procedures, realize hot-rolled high-carbon cold heading steel wire rod tissue regulation and strong plasticity matching, are used for annealing-free high-efficiency green manufacturing of 12.9-grade high-strength cold heading steel fasteners, and can reduce cracking risks in drawing and cold heading processing processes.

The technical scheme adopted for solving the technical problems is as follows:

The 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod comprises the following chemical components in percentage by mass: c:0.65% -0.70%, si:0.15% -0.35%, mn:0.45% -0.55%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, and the balance is Fe and unavoidable impurities; the microstructure of the alloy comprises 87-92% by volume of tempered pearlite, and the balance of ferrite and quasi-spheroidized carbide.

The design basis of the chemical components and the mass percentage of the cold heading steel wire rod comprises:

(1) Carbon: the element C is the most basic and more economical strengthening element compared with other elements in steel, exists in the steel in a gap solid solution or carbide mode, obviously improves the tensile strength of the steel along with the increase of the carbon content on the basis of not adding Cr, mo, B, ti and other alloy components for improving the hardenability or strength of the steel, reduces the plasticity and toughness, increases the decarburization risk and the network distribution risk of cementite along the pearlite grain boundary, and simultaneously thickens tissue sheets, influences the carbide spheroidization trend, and further influences the quasi-spheroidization carbide content generated during the high-temperature softening of the pearlite, so that the final performance grade of a 12.9-grade fastener can be achieved through tempering in order to ensure that the cold heading steel wire rod is free from annealing, simultaneously, the control of the network carbide and the formation difficulty of the quasi-spheroidization carbide can be reduced, the cold deformation performance of the cold heading steel wire rod is considered, and the mass percentage of C is controlled to be 0.65% -0.70%.

(2) Silicon: si element is a better deoxidizing element in steel smelting, and can be dissolved in ferrite in a solid solution way, so that the stability of supercooled austenite and the critical transition temperature of steel are improved in hypoeutectoid steel, but excessive silicon can easily generate bainitic structures due to the improvement of the hardenability of the steel, the plasticity and impact toughness of the steel are reduced, and the cold heading forming difficulty is increased, so that the mass percentage of Si is controlled to be 0.15% -0.35%.

(3) Manganese: mn element is a good deoxidizer and desulfurizer in the steelmaking process, mainly exists in a substitution and solid solution mode in steel, can improve the strength and wear resistance of the steel, but the excessive Mn content can aggravate segregation in the solidification process of a steel billet, so that the uniformity of the steel is poor, a bainite structure is easy to generate due to the improvement of the hardenability of the steel, and carbide spheroidization is easy to generate due to the reduction of the activity of carbon, so that the mass percentage of Mn is controlled to be 0.45% -0.55%.

(4) Phosphorus, sulfur: the lower the P element and the S element are, the better, so that the P is less than or equal to 0.015 percent and the S is less than or equal to 0.015 percent.

On the basis of the design of the low-cost and low-hardenability sub-eutectoid high-carbon chemical components, the high-carbon wire rod subjected to hot rolling and cooling is abandoned from a traditional microstructure consisting of sorbite and ferrite, the microstructure of the cold heading steel wire rod contains most tempered pearlite and a small amount of unavoidable ferrite, the tempered pearlite has the strength characteristics equivalent to pearlite, the matrix strength is provided, the high-carbon components are combined to compensate the strength loss under the alloy components such as Cr, ti and B, the wire rod hardenability is lower, the nucleation rate of bainite or martensite in the wire rod is inhibited in the cooling process after rolling, the pearlite has better plasticity and toughness than sorbite with finer lamellar spacing, the stress of the pearlite structure can be further eliminated, the density of the pearlite dislocation and the concentration of the matrix stress are reduced, the plasticity and toughness of the pearlite structure are obviously improved, the microstructure also contains a small amount of quasi-carbide formed by the pearlite temperature softening, the quasi-carbide on the high-carbon wire rod is obviously improved along with the high-toughness, the high-quality of the high-carbon alloy is obviously matched with the high-temperature deformation resistance of the cold-spheroidized steel wire rod, and the high-temperature-toughness is obviously improved along with the high-toughness of the cold-spheroidized steel, and the high-temperature-toughness is obviously matched with the high-toughness, and the high-toughness of the cold-toughness-spheroidized steel, and the cold-finished product is more obviously, and the high-quality, and the quality-oriented plastic fastener is reduced, and has the high-quality compared with the quality steel.

Preferably, the lamellar spacing of the tempered pearlite is 160-200 nm, the volume percentage of ferrite is 6% -11%, the smaller the lamellar spacing of the tempered pearlite is, the smaller the ferrite content is, the strength of the cold heading steel wire rod is increased, the plasticity is reduced, the larger the lamellar spacing of the tempered pearlite is, the larger the quasi-spheroidized carbide content is, the strength of the cold heading steel wire rod is reduced, the plasticity is increased, and the lamellar spacing of the tempered pearlite, the ratio of ferrite to the quasi-spheroidized carbide can be further controlled to further regulate and control the strong plastic matching of the cold heading steel wire rod.

Preferably, the mesh carbide of the cold heading steel wire rod is 0 grade, and the utilization rate of C element in steel and the uniformity of chemical components can be increased along with the reduction of the mesh carbide grade, so that the tissue stress is further reduced, the mechanical property of the steel is improved, and particularly the impact property and plasticity are improved, and the wire rod cracking caused by the coarse mesh carbide in the cold heading drawing process is avoided.

Preferably, the diameter of the cold heading steel wire rod is 14.0-22.0 mm, the tensile strength Rm is 1110-1160 MPa, the reduction of area Z is 51% -56%, compared with a cold heading steel wire rod with middle and low carbon, the cold heading steel wire rod has a certain tensile strength, meanwhile, compared with a cold heading steel wire rod with a carbon steel wire rod with high carbon, the cold heading steel wire rod has obviously improved plasticity and is higher in reduction of area, so that the risks of wire breakage during drawing and cold heading cracking can be reduced under annealing-free treatment, and the production application of 12.9-level fasteners is met.

The application of the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod comprises the following steps: the method is used for manufacturing the 12.9-grade fastener through drawing, cold heading and hardening and tempering processes without a spheroidizing annealing process.

The manufacturing method of the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod comprises the following steps: and rolling the wire rod according to the chemical components of the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, spinning the wire rod into the wire rod according to the spinning temperature of more than or equal to 900 ℃, performing online molten salt pearlite temperature control treatment to enable the wire rod to be cooled to a pearlite area at a cooling speed of more than or equal to 34 ℃/s, simultaneously performing isothermal promotion on pearlite formed by phase transformation to soften at a high temperature to form quasi-spheroidized carbide, and finally performing roller way slow cooling to obtain the cold heading steel wire rod with microstructure comprising 87-92% of tempered pearlite by volume percent, and the balance being ferrite and quasi-spheroidized carbide.

According to the manufacturing method, on the basis of the hypoeutectoid high-carbon chemical components with low hardenability, through proper wire-laying temperature, the wire rod is prevented from forming net-shaped carbide on a grain boundary and austenitizing tissues at the excessively low wire-laying temperature, meanwhile, the wire rod is directly subjected to online molten salt pearlite temperature control treatment through a salt bath after wire-laying, on one hand, compared with the air cooling, water cooling and other modes, the rapid heat exchange capacity of molten salt can be utilized, the wire rod can be rapidly cooled from the wire-laying temperature in a very rapid cooling mode, the precipitation interval of secondary cementite can be skipped, the wire rod can rapidly reach a high-temperature pearlite area, and therefore, carbide precipitation along the austenitic grain boundary is prevented, and net-shaped carbide is prevented from being formed on the hypoeutectoid high-carbon steel wire rod in the cooling process.

On the other hand, the wire rod can be fully contacted with molten salt to ensure uniform cooling, compared with air cooling, the problem of temperature difference between the air-receiving surface and the air-receiving surface of the wire rod is avoided, so that uniform phase transformation is generated, fluctuation of mechanical properties of the same circle is reduced, low hardenability of the combined components is realized, abnormal phases of bainite and martensite are avoided to be separated out after temperature control, a long-time high-temperature isothermal state can be maintained after the temperature of the wire rod reaches a high-temperature pearlite phase region compared with air cooling, high-temperature austenite in the wire rod structure is enabled to be fully inoculated into the pearlite structure, the pearlite is formed into a mixed structure consisting of main ferrite and small amount of ferrite structure, so that strong plastic matching of materials is ensured, meanwhile, the pearlite formed by the high-temperature transformation is enabled to be softened at high temperature in a temperature control process continuously, quasi-spheroidized carbide is formed, tissue stress is eliminated, and dislocation density of the structure is further regulated and controlled, and controlled for two times.

Preferably, when the billet is heated before rolling, the soaking temperature of the billet is controlled to be less than or equal to 1080 ℃, the soaking time is controlled to be less than or equal to 1.5 hours, the uniform diffusion of components in the steel can be promoted by utilizing high temperature, meanwhile, the low-temperature soaking is controlled to reduce decarburization risk, decarburization caused by overhigh soaking temperature and overlong uniform time is avoided, the soaking temperature is preferably 1030-1080 ℃, the soaking time is 1-1.5 hours, and the total heating time is 4-5 hours.

Preferably, during rolling, the initial rolling temperature is controlled to be 1020-1060 ℃, the initial rolling deformation is controlled to be 26-34%, and the online molten salt pearlite temperature control treatment stage can effectively improve the net carbon problem, so that the initial rolling temperature is lower than that of the prior art, the capability of a rolling line in the rolling process can be reasonably utilized, the billet columnar crystals can be broken by using the lower initial rolling temperature and the larger initial rolling deformation as much as possible, preparation is made for refining grains, and the problem that the final rolling reduction is difficult to distribute larger due to the overlarge initial rolling deformation is avoided.

Preferably, during rolling, the finishing temperature is controlled to be 930-975 ℃, the finishing reduction is controlled to be 28-37%, on the basis of avoiding the follow-up wire-laying temperature from being too low, the quantity of deformed austenite recrystallization is promoted to be increased along with the reduction of the finishing temperature and the increase of the finishing reduction, dynamic recrystallization is generated as much as possible, the grain size is reduced, the grains of the wire rod after rolling are greatly thinned, meanwhile, certain plasticity is lost due to strengthening effects such as solution and the like, the fine grain strengthening can have better strengthening and toughening effects on the final wire rod, meanwhile, carbides precipitated along grain boundaries are distributed on larger grain boundaries, the improvement of net-shaped carbides is facilitated, and the accumulated dislocation density structure can increase nucleation rate, so that the transformation of carbides to spheroidized tissues in the follow-up online molten salt pearlite temperature control treatment process is facilitated.

Preferably, the spinning temperature is 900-945 ℃, the spinning temperature is further controlled, the temperature can be matched with the temperature in the rolling process, meanwhile, the coarsening of crystal grains and the Wittig body tissue caused by overhigh temperature are avoided, and conditions are created for pearlite phase transformation nucleation.

Preferably, when the online molten salt pearlite is subjected to temperature control treatment, the temperature control temperature is controlled to be 570-620 ℃, the treatment time is 500-750 s, the higher the temperature control temperature is, the larger the lamellar spacing of tempered pearlite is, the proeutectoid ferrite is increased, the proportion of tempered pearlite in a tissue is reduced, the strength of a wire rod is reduced, and the plasticity is increased; the lower the temperature control temperature is, the smaller the interlayer spacing of the tempered pearlite is, the smaller the ferrite ratio in the structure is, the strength of the wire rod is increased, the plasticity is reduced, but the lower the temperature control temperature is, the bainitic structure is formed, and the brittleness of the wire rod is obviously increased; the longer the treatment time is, the better the high-temperature softening effect of pearlite is, the more the content of quasi-spheroidized carbide is, the strength of the wire rod is reduced, the plasticity is improved, but the longer the treatment time is, the energy consumption is increased, the production efficiency is reduced, and the strength and the plasticity of the wire rod are reduced due to the fact that the quasi-spheroidized carbide is combined and grown up; the shorter the treatment time is, the higher the tissue stress and dislocation density are, the content of quasi-spheroidized carbide is reduced, the strength of the wire rod is increased, and the plasticity is reduced, so that the temperature control temperature and the treatment time of the online molten salt pearlite temperature control treatment can be further controlled, and the wire rod tissue and the strength and plasticity performance can be regulated.

Preferably, the cooling speed of the wire rod from the wire spinning temperature to the high-temperature pearlite area is high, the circulating amount of molten salt is controlled to be 480-680 t/h during the online molten salt pearlite temperature control treatment, the temperature rise of the molten salt is less than or equal to 7 ℃, the temperature rise of the molten salt can be controlled through the large circulating amount of the molten salt, the temperature control temperature precision is improved, and the uniform phase change of the wire rod tissue is promoted.

Preferably, the speed of a roller way of the wire rod passing through molten salt is 18-30 m/min, and the processing time control of the wire rod and the temperature control temperature can be met at the speed of the roller way, so that the production rhythm is further regulated and controlled.

Preferably, when the roller way is slowly cooled, the wire rods are conveyed to pass through the inside of the heat insulation cover at the roller way speed of less than or equal to 0.6m/s, so that the wire rods are slowly cooled at the cooling speed of 0.55-0.85 ℃/s until the wire rods are collected, the roller way speed and the wire rod cooling speed can be further controlled to prolong the time of the wire rods in a high-temperature state, the high-temperature softening is promoted to form quasi-spheroidized carbide, and meanwhile, the influence of the too low cooling speed on the production efficiency is avoided.

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

(1) Aiming at the current situation that the development of the cold heading steel wire rod for the existing 12.9 ultra-high strength fastener has higher requirements on the design of the cold heading steel wire rod, cr, ti, B and other alloy elements are added on low and medium carbon to improve the hardenability of the wire rod, and the cracking risk is improved in the drawing and cold heading processing processes, the hot-rolled cold heading steel wire rod disclosed by the invention adopts the design of the hypoeutectoid high-carbon chemical components with low hardenability, so that the material cost can be effectively reduced, the limit of the application of the hypoeutectoid high-carbon steel on the cold heading steel can be broken, the combined cold heading steel wire rod comprises the mixed structure regulation and control of mainly tempered pearlite, a small amount of ferrite and quasi-spheroidized carbide, the structural stress and dislocation density of the wire rod can be obviously reduced on the basis of certain strength, the wire rod plasticity is improved, the cold heading steel wire rod product after hot rolling cooling can reach the tensile strength of-1160 MPa, the shrinkage rate of 51% -56%, the netlike, and the netlike can be used for manufacturing 12.9-level annealing-free high-strength fasteners, and the like, and the cold heading steel wire rod has good application prospects in the drawing and cracking processes.

(2) The manufacturing method of the invention combines the design of the hypoeutectoid high carbon chemical components with low hardenability with the online molten salt pearlite temperature control and roller way slow cooling technology, regulates and controls the structure of the hot rolled wire rod, and obviously improves the problem of net carbon by controlling the wire rod after hot rolling spinning to quickly skip the secondary cementite precipitation interval, and then carries out long-time isothermal transformation in the high-temperature pearlite phase area to form a mixed structure composed of pearlite and ferrite, thereby ensuring the strong plasticity matching of the material, and continuously softening the pearlite formed by the high-temperature transformation at high temperature in the temperature control process to form quasi-spheroidized carbide, regulating and controlling the structure of the hot rolled wire rod to a tempering state without martensite and bainite structures, simultaneously only needing one molten salt treatment, simplifying the manufacturing procedure, and successfully preparing the 12.9-grade annealing-free hot rolled high carbon cold heading steel wire rod with good industrial applicability.

(3) The manufacturing method can improve the net carbon through online molten salt pearlite temperature control, further control low-temperature soaking and rolling, can reduce decarburization risk, enable dynamic recrystallization to refine grains as much as possible, improve the strength and the toughness of the wire rod through fine grain strengthening, further improve the softening effect of the wire rod through roller way slow cooling, is more suitable for drawing cold heading processing, and has good industrial adaptability.

Drawings

The foregoing and/or additional aspects and advantages of the invention will become apparent and may be better understood from the following description of embodiments taken in conjunction with the accompanying drawings in which:

FIG. 1 is a metallographic structure diagram of example 1 of the present invention;

FIG. 2 is a metallographic structure diagram of example 2of the present invention;

FIG. 3 is a metallographic structure diagram of example 3 of the present invention;

FIG. 4 is a metallographic structure of comparative example 6 of the present invention.

Detailed Description

The embodiments described below are exemplary only and are not intended to limit the description of the features and characteristics of the invention, in order to set forth the best mode of carrying out the invention, intended to illustrate it and to enable those skilled in the art to practice it, without any limitation to its scope, which is defined solely by the claims appended hereto.

Example 1:

the invention relates to a preferred embodiment of a manufacturing method of a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which comprises the following chemical components in percentage by mass: c:0.69%, si:0.26%, mn:0.45%, P:0.015%, S:0.013%, the balance of Fe and unavoidable impurities; the manufacturing method comprises the following steps of low-temperature heating, low-temperature rolling, spinning, online molten salt pearlite temperature control, roller way slow cooling and coil collecting, and specifically comprises the following steps of:

the low-temperature heating procedure is used for heating a billet with the specification of 220mm multiplied by 220mm into a high-temperature billet with rolling plasticity through a heating furnace, the heating furnace is sequentially heated according to a preheating section, a heating section and a soaking section, and decarburization risks are reduced through low-temperature soaking, and the method comprises the following steps of: the soaking temperature of the steel billet is controlled to be 1080 ℃, the soaking time is 1h, and the total heating time is 4h.

The low-temperature rolling procedure is used for rolling a billet which is discharged from a heating furnace into a wire rod with the diameter specification of 18mm through a rolling line, crushing columnar crystals of the billet as far as possible through low-temperature blooming and larger blooming deformation, preparing for refining the crystal grains, carrying out dynamic recrystallization to refine the crystal grains as far as possible through low-temperature finish rolling and larger finish rolling reduction, providing favorable conditions for converting carbide into spheroidized structures, and simultaneously avoiding the risk of net carbon precipitation when the temperature of spinning is too low and spinning is caused by too low temperature, and particularly: the initial rolling temperature is controlled to 1060 ℃, the initial rolling deformation is 32%, the final rolling temperature is 975 ℃, and the final rolling reduction is 31%.

The wire rod that the wire rod process of laying wire is used for going out the pass line, and the wire rod is the wire rod through the wire rod mechanism of laying wire, and the wire rod spreads on the roll table and follows the roll table and carry, through suitable wire outlet temperature, avoids the wire rod to form netted carbide and austenitizing the structure on the grain boundary under the low wire outlet temperature, avoids the high temperature to arouse the grain coarsening, creates the condition for pearlite phase transition nucleation, and is specific: the laying temperature was controlled to 945 ℃.

The online molten salt pearlite temperature control adopts a section of salt bath tank with molten salt arranged therein, wire rods after spinning pass through the salt bath tank through a roller way, and are rapidly cooled to the molten salt temperature to perform online molten salt pearlite temperature control treatment, so that the wire rods are cooled to a high-temperature pearlite area at a cooling speed of 36 ℃/s to be transformed, a mixed structure consisting of pearlite and ferrite is formed based on high-carbon component design, so that the material strong plasticity is ensured to be matched, the pearlite formed by isothermal promotion phase transformation is softened at a high temperature at the same time, and quasi-spheroidized carbide is formed, so that the wire rod tissue performance is regulated and controlled, and the following specific: the temperature is controlled to be 605 ℃, the treatment time is 500s, the circulation amount of molten salt is controlled to be 630t/h, the temperature rise of the molten salt is less than or equal to 7 ℃, and the roller way speed of the wire rod passing through the molten salt is 30m/min.

The roller way slow cooling procedure carries the wire rod that comes out from the salt bath into the heat preservation cover with the roller way and carries out slow cooling treatment, promotes carbide spheroidization, further improves the wire rod and softens the effect, and is specific: conveying the wire rod through the inside of the heat preservation cover at the roller speed of 0.55m/s, and slowly cooling the wire rod to 365 ℃ at the cooling speed of 0.75 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting and coiling the wire rods into coils through the coil collecting drum, and obtaining cold heading steel wire rod finished products after packaging and warehousing, and a metallographic structure diagram of the cold heading steel wire rod finished products is shown in figure 1.

Comparative example 1:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 1 in that: the manufacturing method comprises the following steps of heating, rolling, spinning, steyr quick cooling, roller way slow cooling and coil collecting, and specifically comprises the following steps of: the soaking temperature of the steel billet in the heating process is 1110 ℃; the initial rolling temperature of the rolling process is 1100 ℃, the final rolling temperature is 1010 ℃, and the wire laying process controls the wire laying temperature to be 980 ℃; the step of Steyr quick cooling is to start a 1-6 # fan according to 95% so as to cool the wire rod to 605 ℃ according to a cooling speed of 9.6 ℃/s, the step of slow cooling on a roller way is to close all fans and a heat insulation cover so as to enable the wire rod to finish phase change in the cover at a cooling speed of 1.5 ℃/s, and the finished wire rod product is obtained after coil collection and coil off-line.

Comparative example 2:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 1 in that: the manufacturing method comprises the following steps of heating, rolling, spinning, steyr quick cooling, roller way slow cooling and coil collecting, and specifically comprises the following steps of: the soaking temperature of the steel billet in the heating process is 995 ℃; the initial rolling temperature of the rolling process is 980 ℃, the final rolling temperature is 890 ℃, and the wire laying process controls the wire laying temperature to be 860 ℃; the step of Steyr quick cooling is to start a 1-7 # fan according to 100% so as to cool the wire rod to 570 ℃ at a cooling speed of 10.3 ℃/s, the step of slow cooling on the roller way is to close all fans and a heat preservation cover so as to enable the wire rod to finish phase change in the cover at a cooling speed of 1.2 ℃/s, and the finished wire rod product is obtained after coil collection and coil off-line.

Example 2:

The invention relates to a preferred embodiment of a manufacturing method of a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which comprises the following chemical components in percentage by mass: c:0.65%, si:0.35%, mn:0.52%, P:0.014%, S:0.01% of Fe and the balance of unavoidable impurities; the manufacturing method comprises the following steps of low-temperature heating, low-temperature rolling, spinning, online molten salt pearlite temperature control, roller way slow cooling and coil collecting, and specifically comprises the following steps of:

The low-temperature heating procedure is used for heating a billet with the specification of 220mm multiplied by 220mm into a high-temperature billet with rolling plasticity through a heating furnace, the heating furnace is sequentially heated according to a preheating section, a heating section and a soaking section, and decarburization risks are reduced through low-temperature soaking, and the method comprises the following steps of: the soaking temperature of the steel billet is controlled to 1040 ℃, the soaking time is 1.2h, and the total heating time is 4.5h.

The low-temperature rolling procedure is used for rolling a billet which is discharged from a heating furnace into a wire rod with the diameter specification of 14mm through a rolling line, crushing columnar crystals of the billet as far as possible through low-temperature blooming and larger blooming deformation, preparing for refining the crystal grains, carrying out dynamic recrystallization to refine the crystal grains as far as possible through low-temperature finish rolling and larger finish rolling reduction, providing favorable conditions for converting carbide into spheroidized structures, and simultaneously avoiding the risk of net carbon precipitation when the temperature of spinning is too low and spinning is caused by too low temperature, and particularly: the initial rolling temperature is controlled to be 1032 ℃, the initial rolling deformation is controlled to be 34%, the final rolling temperature is controlled to be 945 ℃, and the final rolling reduction is controlled to be 37%.

The wire rod that the wire rod process of laying wire is used for going out the pass line, and the wire rod is the wire rod through the wire rod mechanism of laying wire, and the wire rod spreads on the roll table and follows the roll table and carry, through suitable wire outlet temperature, avoids the wire rod to form netted carbide and austenitizing the structure on the grain boundary under the low wire outlet temperature, avoids the high temperature to arouse the grain coarsening, creates the condition for pearlite phase transition nucleation, and is specific: the laying temperature was controlled to 920 ℃.

The online molten salt pearlite temperature control adopts a section of salt bath tank with molten salt arranged therein, wire rods after spinning pass through the salt bath tank through a roller way, and are rapidly cooled to the molten salt temperature to perform online molten salt pearlite temperature control treatment, so that the wire rods are cooled to a high-temperature pearlite area at a cooling speed of 37 ℃/s to be transformed, a mixed structure consisting of pearlite and ferrite is formed based on high-carbon component design, so that the material strong plasticity is ensured to be matched, the pearlite formed by isothermal promotion phase transformation is softened at a high temperature at the same time, and quasi-spheroidized carbide is formed, so that the wire rod tissue performance is regulated and controlled, and the following specific: the temperature is controlled to be 570 ℃, the treatment time is 559s, the circulation amount of molten salt is controlled to be 680t/h, the temperature rise of the molten salt is less than or equal to 7 ℃, and the roller way speed of the wire rod passing through the molten salt is 26m/min.

The roller way slow cooling procedure carries the wire rod that comes out from the salt bath into the heat preservation cover with the roller way and carries out slow cooling treatment, promotes carbide spheroidization, further improves the wire rod and softens the effect, and is specific: conveying the wire rod through the inside of the heat preservation cover at the roller speed of 0.45m/s, and slowly cooling the wire rod to 352 ℃ at the cooling speed of 0.55 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting and coiling the wire rods into coils through the coil collecting drum, and obtaining cold heading steel wire rod finished products after packaging and warehousing, and a metallographic structure diagram of the cold heading steel wire rod finished products is shown in figure 2.

Comparative example 3:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 2 in that: the soaking temperature is 1088 ℃, the blooming temperature is 1082 ℃, the blooming deformation is 39%, the finishing temperature is 992 ℃, the finishing rolling reduction is 22%, the wire laying temperature is 960 ℃, and the finished product of the wire rod is obtained after coil collecting and off-line.

Comparative example 4:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 2 in that: the wire rod is cooled by a salt bath at a cooling speed of 30 ℃/s, the temperature is 635 ℃, and the finished wire rod is obtained after coil collection and off-line.

Comparative example 5:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 2 in that: the wire rod is cooled by a salt bath at a cooling speed of 36 ℃/s, the temperature is controlled to be 560 ℃, and the finished wire rod is obtained after coil collection and off-line.

Comparative example 6:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 2 in that: the wire rod is cooled by a salt bath at a cooling speed of 45 ℃/s, the temperature is controlled to be 350 ℃, the molten salt circulation quantity is 730t/h, and the finished wire rod product is obtained after coil collection and off-line.

Example 3:

The invention relates to a preferred embodiment of a manufacturing method of a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which comprises the following chemical components in percentage by mass: c:0.68%, si:0.32%, mn:0.48%, P:0.015%, S:0.015% of Fe and the balance of unavoidable impurities; the manufacturing method comprises the following steps of low-temperature heating, low-temperature rolling, spinning, online molten salt pearlite temperature control, roller way slow cooling and coil collecting, and specifically comprises the following steps of:

The low-temperature heating procedure is used for heating a billet with the specification of 220mm multiplied by 220mm into a high-temperature billet with rolling plasticity through a heating furnace, the heating furnace is sequentially heated according to a preheating section, a heating section and a soaking section, and decarburization risks are reduced through low-temperature soaking, and the method comprises the following steps of: the soaking temperature of the billet is controlled to 1030 ℃, the soaking time is 1.2h, and the total heating time is 4.5h.

The low-temperature rolling procedure is used for rolling a billet which is discharged from a heating furnace into a wire rod with the diameter specification of 20mm through a rolling line, crushing columnar crystals of the billet as far as possible through low-temperature blooming and larger blooming deformation, preparing for refining the crystal grains, carrying out dynamic recrystallization to refine the crystal grains as far as possible through low-temperature finish rolling and larger finish rolling reduction, providing favorable conditions for converting carbide into spheroidized structures, and simultaneously avoiding the risk of net carbon precipitation when the temperature of spinning is too low and spinning is caused by too low temperature, and particularly: the initial rolling temperature is controlled to be 1020 ℃, the initial rolling deformation is controlled to be 28%, the final rolling temperature is controlled to be 930 ℃, and the final rolling reduction is controlled to be 35%.

The wire rod that the wire rod process of laying wire is used for going out the pass line, and the wire rod is the wire rod through the wire rod mechanism of laying wire, and the wire rod spreads on the roll table and follows the roll table and carry, through suitable wire outlet temperature, avoids the wire rod to form netted carbide and austenitizing the structure on the grain boundary under the low wire outlet temperature, avoids the high temperature to arouse the grain coarsening, creates the condition for pearlite phase transition nucleation, and is specific: the laying temperature was controlled to 900 ℃.

The online molten salt pearlite temperature control adopts a section of salt bath tank with molten salt arranged therein, wire rods after spinning pass through the salt bath tank through a roller way, and are rapidly cooled to the molten salt temperature to perform online molten salt pearlite temperature control treatment, so that the wire rods are cooled to a high-temperature pearlite area at a cooling speed of 34 ℃/s to be transformed, a mixed structure consisting of pearlite and ferrite is formed based on high-carbon component design, so that the material strong plasticity is ensured to be matched, the pearlite formed by isothermal promotion phase transformation is softened at a high temperature at the same time, and quasi-spheroidized carbide is formed, so that the wire rod tissue performance is regulated and controlled, and the following specific: the temperature is controlled to be 587 ℃, the treatment time is 750s, the circulation quantity of molten salt is controlled to be 480t/h, the temperature rise of the molten salt is less than or equal to 7 ℃, and the roller way speed of the wire rod passing through the molten salt is 18m/min.

The roller way slow cooling procedure carries the wire rod that comes out from the salt bath into the heat preservation cover with the roller way and carries out slow cooling treatment, promotes carbide spheroidization, further improves the wire rod and softens the effect, and is specific: conveying the wire rod through the inside of the heat preservation cover at the roller speed of 0.5m/s, and slowly cooling the wire rod to 360 ℃ at the cooling speed of 0.62 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting and coiling the wire rods into coils through the coil collecting drum, and obtaining cold heading steel wire rod finished products after packaging and warehousing, and a metallographic structure diagram of the cold heading steel wire rod finished products is shown in figure 3.

Comparative example 7:

a method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 3 in that: the processing time is 800s, the roller way speed of the wire rod passing through the fused salt is 15m/min, and the finished wire rod product is obtained after coil collection and coil discharging.

Comparative example 8:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 3 in that: the processing time is 910s, the roller speed of the wire rod passing through the fused salt is 13m/min, and the finished wire rod product is obtained after coil collection and coil discharging.

Comparative example 9:

a method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 3 in that: the processing time is 458s, the roller speed of the wire rod passing through the fused salt is 30m/min, and the finished wire rod product is obtained after coil collection and coil discharging.

Example 4:

The invention relates to a preferred embodiment of a manufacturing method of a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which comprises the following chemical components in percentage by mass: c:0.7%, si:0.15%, mn:0.55%, P:0.014%, S:0.013%, the balance of Fe and unavoidable impurities; the manufacturing method comprises the following steps of low-temperature heating, low-temperature rolling, spinning, online molten salt pearlite temperature control, roller way slow cooling and coil collecting, and specifically comprises the following steps of:

the low-temperature heating procedure is used for heating a billet with the specification of 220mm multiplied by 220mm into a high-temperature billet with rolling plasticity through a heating furnace, the heating furnace is sequentially heated according to a preheating section, a heating section and a soaking section, and decarburization risks are reduced through low-temperature soaking, and the method comprises the following steps of: the soaking temperature of the steel billet is controlled to be 1050 ℃, the soaking time is 1.5h, and the total heating time is 5h.

The low-temperature rolling procedure is used for rolling a billet which is discharged from a heating furnace into a wire rod with the diameter specification of 22mm through a rolling line, crushing columnar crystals of the billet as far as possible through low-temperature blooming and larger blooming deformation, preparing for refining the crystal grains, carrying out dynamic recrystallization to refine the crystal grains as far as possible through low-temperature finish rolling and larger finish rolling reduction, providing favorable conditions for converting carbide into spheroidized structures, and simultaneously avoiding the risk of net carbon precipitation when the temperature of spinning is too low and spinning is caused by too low temperature, and particularly: the initial rolling temperature is controlled to 1045 ℃, the initial rolling deformation is 26%, the final rolling temperature is 965 ℃, and the final rolling reduction is 28%.

The wire rod that the wire rod process of laying wire is used for going out the pass line, and the wire rod is the wire rod through the wire rod mechanism of laying wire, and the wire rod spreads on the roll table and follows the roll table and carry, through suitable wire outlet temperature, avoids the wire rod to form netted carbide and austenitizing the structure on the grain boundary under the low wire outlet temperature, avoids the high temperature to arouse the grain coarsening, creates the condition for pearlite phase transition nucleation, and is specific: the laying temperature was controlled to 938 ℃.

The online molten salt pearlite temperature control adopts a section of salt bath tank with molten salt arranged therein, wire rods after spinning pass through the salt bath tank through a roller way, and are rapidly cooled to the molten salt temperature to perform online molten salt pearlite temperature control treatment, so that the wire rods are cooled to a high-temperature pearlite area at a cooling speed of 35 ℃/s to be transformed, a mixed structure consisting of pearlite and ferrite is formed based on high-carbon component design, so that the material strong plasticity is ensured to be matched, the pearlite formed by isothermal promotion phase transformation is softened at a high temperature at the same time, and quasi-spheroidized carbide is formed, so that the wire rod tissue performance is regulated and controlled, and the following specific: the temperature is controlled to be 620 ℃, the treatment time is 625s, the circulation quantity of molten salt is controlled to be 520t/h, the temperature rise of the molten salt is less than or equal to 7 ℃, and the roller way speed of the wire rod passing through the molten salt is 22m/min.

The roller way slow cooling procedure carries the wire rod that comes out from the salt bath into the heat preservation cover with the roller way and carries out slow cooling treatment, promotes carbide spheroidization, further improves the wire rod and softens the effect, and is specific: conveying the wire rod through the inside of the heat preservation cover at the roller speed of 0.6m/s, and slowly cooling the wire rod to 371 ℃ at the cooling speed of 0.8 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting and winding the coil rod into coils through the coil collecting drum, and obtaining a cold heading steel coil rod finished product after packaging and warehousing.

Comparative example 10:

A method for manufacturing a hot rolled high carbon steel wire rod, which differs from example 4 in that: the manufacturing method comprises the following steps of low-temperature heating, low-temperature rolling, spinning, online molten salt pearlite temperature control, air cooling and coil collecting, and specifically comprises the following steps of: the air cooling process adopts the steps of opening a heat preservation cover, conveying the wire rods from a salt bath tank by a roller way at the roller way speed of 0.85m/s, cooling the wire rods at the cooling speed of 2.2 ℃/s until the wire rods are collected and the wire rods are taken off the line after the collection of the wire rods.

The wire rods obtained in the above examples and comparative examples were subjected to tissue and performance testing: tensile testing was performed using the metal material tensile test section 1 of GB-T228.1-2021: room temperature test method, to obtain tensile strength and reduction of area, and to perform tissue detection according to the metal microstructure detection method of GB/T13298 standard, the comparison results obtained are shown in table 1 below:

TABLE 1 comparison of the composition of the steel wire rods of the different Cold heading and the properties of the wire rod structure of the manufacturing method

As can be seen from the comparison result of the example 1 and the comparative example 1, compared with the pearlite and ferrite structure obtained by the high-temperature wire laying and air cooling rapid cooling process, the invention is accompanied by higher-grade reticular carbide defects, the invention adjusts and controls the hot rolled wire rod structure by combining the design of the hypoeutectoid high-carbon chemical components with low hardenability and the online fused salt pearlite temperature control and roller way slow cooling technology, and controls the wire rod after the hot rolling wire laying to carry out ultra-rapid cooling by controlling the online fused salt pearlite temperature control, thereby rapidly skipping the secondary cementite precipitation interval, obviously improving the reticular carbide problem, leading the reticular carbide to reach 0 grade, and simultaneously leading the comparison result of the example 1, the comparative example 2 to be accompanied by higher-grade reticular carbide defects compared with the sorbite and ferrite structure obtained by the low Wen Tusi and air cooling rapid cooling process, on the basis of effectively improving the net carbon problem, the invention also utilizes the direct salt bath after spinning to carry out long-time isothermal transformation in a high-temperature pearlite area to form a mixed structure composed of most pearlite and a small amount of ferrite, and utilizes the pearlite formed by high-temperature transformation to continuously soften at high temperature in the temperature control process to form quasi-spheroidized carbide, regulate and control the hot rolled wire rod structure to a tempering state, can obviously reduce the structure stress and dislocation density, improve the wire rod plasticity, and the cold heading steel wire rod product after hot rolling and cooling can reach the tensile strength of 1110-1160 MPa and the section shrinkage of 51-56 percent, thereby being used for the application fields of manufacturing 12.9-grade annealing-free high-strength fastener bolts and the like, being capable of reducing the cracking risk in the drawing and cold heading processes and having good application prospect.

As can be seen from the comparison result of the example 2 and the comparative example 3, compared with the case of high temperature soaking and rolling, the coarsening of the rolled crystal grains is unfavorable for the transition of carbide to spheroidized structure in the subsequent online molten salt pearlite temperature control treatment process, the low temperature soaking and rolling are further controlled, the decarburization risk can be reduced, dynamic recrystallization refinement of crystal grains can be generated as much as possible, and the plastic toughness performance of the wire rod is improved by fine grain strengthening.

As can be seen from the comparison results of examples 1 to 4 and comparative example 4, the higher the temperature control temperature is, the larger the lamellar spacing of tempered pearlite is, the more proeutectoid ferrite is increased, the tempered pearlite ratio in the structure is reduced, the strength of the wire rod is reduced, the plasticity is increased, but the larger the temperature control temperature is, the larger the strength loss of the cold forging steel wire rod is caused; as can be seen from the comparison results of examples 1 to 4 and comparative example 5, the lower the temperature control temperature is, the smaller the interlayer spacing of tempered pearlite sheets is, the smaller the ferrite ratio in the structure is, the strength of the wire rod is increased, the plasticity is reduced, but the lower the temperature control temperature is, the larger the plastic loss of the cold heading steel wire rod is caused; and as can be seen from the results of comparative example 6, a bainitic structure appears at a temperature that is too low, and the coil brittleness is significantly increased.

As can be seen from the comparison results of examples 1 to 4 and comparative example 7, the longer the treatment time is, the better the high-temperature softening effect of pearlite is, the more the content of quasi-spheroidized carbide is, the strength of the wire rod is reduced, the plasticity is increased, but the longer the treatment time is, the larger the strength loss of the cold heading steel wire rod is caused; as can be seen from the comparison between examples 1 to 4 and comparative example 8, the further increase of the treatment time also resulted in a decrease in the strength and plasticity of the wire rod due to the growth of the quasi-spheroidized carbides in combination with each other; as can be seen from the comparison results of examples 1-4 and comparative example 9, the shorter the treatment time, the higher the tissue stress and dislocation density, the lower the content of quasi-spheroidized carbide, the higher the strength of the wire rod and the lower the plasticity, so the temperature control temperature and the treatment time of the online molten salt pearlite temperature control treatment can be further improved, and the wire rod tissue and the strength and plasticity performance can be regulated.

As can be seen from the comparison results of examples 1-4 and comparative example 10, the softening effect is weakened compared with that of the molten salt after air cooling, the roller way slow cooling is further adopted after the online molten salt pearlite temperature control treatment, the roller way speed and the wire rod cooling speed are controlled, the time of the wire rod in a high temperature state is further prolonged, the high temperature softening can be continuously promoted to form quasi-spheroidized carbide, and the method has good industrial adaptability.

The above list of detailed descriptions is only specific to practical embodiments of the present invention, and they are not intended to limit the scope of the present invention, and all equivalent embodiments or modifications that do not depart from the spirit of the present invention should be included in the scope of the present invention.

Claims

1. The 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized by comprising the following chemical components in percentage by mass: c:0.65% -0.70%, si:0.15% -0.35%, mn:0.45% -0.55%, P is less than or equal to 0.015%, S is less than or equal to 0.015%, and the balance is Fe and unavoidable impurities; the microstructure comprises 87-92% by volume of tempered pearlite, and the balance of ferrite and quasi-spheroidized carbide;

The manufacturing method comprises the following steps: rolling the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod according to chemical components to produce a wire rod, spinning the wire rod into the wire rod according to a spinning temperature of 900-945 ℃, performing online molten salt pearlite temperature control treatment to enable the wire rod to be transformed into a pearlite phase region by cooling at a cooling speed of more than or equal to 34 ℃/s, simultaneously performing isothermal promotion on pearlite formed by phase transformation to soften at a high temperature to form quasi-spheroidized carbide, and finally performing roller way slow cooling to prepare the cold heading steel wire rod with microstructure comprising tempered pearlite, ferrite and quasi-spheroidized carbide; and during the online molten salt pearlite temperature control treatment, the temperature control temperature is controlled to be 570-620 ℃, the treatment time is 500-750 s, and during the roller way slow cooling, the wire rods are conveyed to pass through the inside of the heat preservation cover at the roller way speed of less than or equal to 0.6m/s, so that the wire rods are slowly cooled at the cooling speed of 0.55-0.85 ℃/s until the wire rods are collected.

2. The 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod according to claim 1, wherein the lamellar spacing of the tempered pearlite is 160-200 nm, the ferrite accounts for 6-11% by volume, and the net carbide of the cold heading steel wire rod is grade 0.

3. The 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod according to claim 1, wherein the diameter of the cold heading steel wire rod is 14.0-22.0 mm, the tensile strength is 1110-1160 mpa, and the reduction of area is 51% -56%.

4. The manufacturing method of the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized by comprising the following steps of: the method comprises the steps of according to claim 1, carrying out chemical component rolling production on a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, carrying out on-line molten salt pearlite temperature control treatment after the wire rod is spun into the wire rod according to the spinning temperature of 900-945 ℃, enabling the wire rod to be cooled to a pearlite phase area at a cooling speed of more than or equal to 34 ℃ per second, simultaneously carrying out isothermal promotion on the pearlite formed by phase transformation to be softened at a high temperature, forming quasi-spheroidized carbide, and finally carrying out roller way slow cooling to obtain the cold heading steel wire rod with a microstructure comprising 87-92% of tempered pearlite and the balance of ferrite and quasi-spheroidized carbide, wherein the temperature control temperature is 570-620 ℃ during on-line molten salt pearlite temperature control treatment, and the treatment time is 500-750 s, and during roller way slow cooling, conveying the wire rod to the inside of a heat preservation cover at a roller way speed of less than or equal to 0.6m/s, and enabling the wire rod to be slowly cooled at a cooling speed of 0.55-0.85 ℃ per second until coil is collected.

5. The method for manufacturing the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which is characterized in that when the steel billet is heated before rolling, the soaking temperature of the steel billet is controlled to be less than or equal to 1080 ℃ and the soaking time is controlled to be less than or equal to 1.5h.

6. The method for manufacturing a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod according to claim 4, wherein the initial rolling temperature is controlled to be 1020-1060 ℃ and the initial rolling deformation is controlled to be 26-34%.

7. The method for manufacturing a 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod according to claim 6, wherein the rolling is performed at a finish rolling temperature of 930-975 ℃ and a finish rolling reduction of 28-37%.

8. The manufacturing method of the 12.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized in that the circulating amount of molten salt is controlled to be 480-680 t/h during the online molten salt pearlite temperature control treatment, the temperature rise of the molten salt is less than or equal to 7 ℃, and the roller way speed of the wire rod passing through the molten salt is 18-30 m/min.