CN118639128B - 13.9-Grade annealing-free hot-rolled cold heading steel wire rod and manufacturing method thereof - Google Patents

Abstract

The invention relates to a 13.9-grade annealing-free hot rolled cold heading steel wire rod and a manufacturing method thereof, wherein the wire rod is subjected to online salt bath isothermal control after being rolled and spun into a wire rod based on high-C Ti and Mo-containing chemical components, so that the wire rod is firstly subjected to front-stage molten salt, the wire rod is cooled to a sorbite phase region at a cooling speed of more than or equal to 43 ℃/s to carry out isothermal transformation, the austenite part is promoted to be transformed into a sorbite tissue, the wire rod is then subjected to rear-stage molten salt heating isothermal, the unconverted austenite is transformed into a pearlite tissue, the transformation of the sorbite tissue, the pearlite tissue and carbide into a spheroidized tissue is promoted, and finally, the wire rod is slowly cooled by a roller way to prepare the cold heading steel wire rod with microstructures including tempered pearlite, tempered sorbite, ferrite and quasi-spheroidized carbide, so that the wire rod tissue regulation and strong plastic energy matching are realized, the tensile strength is 1080-1130MPa, and the section shrinkage is 51-11356%, and the wire rod is suitable for 13.9-grade ultra-high-strength fastening bolt annealing-free efficient green manufacturing.

Description

13.9-Grade annealing-free hot-rolled 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 13.9-grade annealing-free hot-rolled cold-heading steel wire rod and a manufacturing method thereof.

Background

The bolt fastening is used as an important connection mode of industrial equipment, is widely applied to the fields of automobile industry, mechanical equipment, buildings and the like, the cold heading steel is used as a base material of the bolt, plays a vital role in the performance of the bolt, and along with the development of application fields such as new energy automobiles and the like, the requirements and the requirements of the cold heading steel wire rod are continuously improved. At present, the research and development of cold heading steel wire rods for 13.9-grade ultra-high strength fasteners is mainly focused on the medium carbon steel base, and the strength grade is improved by improving the alloy content, adding micro-alloy elements and regulating and controlling the wire rod structure to be a structure containing part of bainite, martensite or all bainite, for example: the 13.9-grade and 14.9-grade delayed fracture-resistant high-strength wire rods for fasteners and the manufacturing method thereof disclosed in the patent CN104046903B adopt the component design of medium C-Si-Mn-Cr-Mo-V-Nb-B-Al, and are combined with low-temperature wire-laying, siteur slow cooling or quick-before-slow cooling to obtain a structure with bainite as a main component, but on one hand, the obtained wire rods have insufficient plasticity, and a spheroidizing annealing process is also needed before a drawing or cold heading process of bolt manufacture to improve cold deformation performance, so that the problems of more bolt manufacturing processes, high energy consumption and emission and low efficiency are brought, and therefore, in order to meet the development requirements of the automobile industry in the direction of light weight and cleaning, the 13.9-grade annealing-free hot-rolled cold-rolled steel wire rods are required to realize the efficient green manufacture of ultra-strength fastener bolts; on the other hand, the reinforced alloy and microalloy in the wire rod have more components, the material cost is increased, meanwhile, the bainite structure is used as a hard and brittle phase, the brittle fracture risk of the wire rod is increased, the wire rod is easy to break in the processes of collecting coils in a steel mill, transporting coils to downstream in the steel mill, and paying off the coils by downstream users, so that the waste of raw materials and the reduction of the yield are caused, and the application of the cold heading steel wire rod is limited.

Although some annealing-free cold heading steel wire rods are developed at present, the annealing-free cold heading steel wire rods are mainly concentrated on the cold heading steel wire rods for 8.8-10.9-level fasteners, and technical difficulties and reasons that the annealing procedure requirements are omitted in 13.9-level fastener processing are difficult to meet include:

(1) In order to meet the requirement that the performance grade of a 13.9-grade fastener can be achieved after annealing-free, drawing, cold heading and hardening and tempering processes, a higher-strength component system is required, the plastic lifting difficulty of the cold heading steel wire rod is increased, more deformation-induced ferrite and coarse lamellar pearlite are obtained through low-temperature wire spinning and slow cooling after rolling, the annealing-free cold heading steel production design for improving the wire rod plasticity can cause excessive degradation of the wire rod strength, the wire rod strength is required to be improved through drawing and cold heading with large reduction ratio, the plastic loss is further increased in the process, meanwhile, the pearlite structure contains larger tissue stress and dislocation density, the plastic improving effect is limited, the wire rod plasticity is insufficient, and the drawing wire breakage risk and cold heading cracking risk are aggravated or the final performance grade cannot be achieved through hardening and tempering.

(2) Carbon element is used as an element which can improve strength and is more economical in steel, and replaces reinforced alloy or micro-alloy element to be beneficial to reducing material cost, but on one hand, as the carbon content is increased, the precipitation risk of secondary cementite is increased, when a low-temperature wire laying and stelmor slow cooling process is adopted, the time of a precipitation temperature interval of the secondary cementite is longer, so that reticular carbide in the steel tends to be continuous and coarsened, the continuity of a matrix is damaged, the brittleness of the material is increased, the strength, particularly toughness, of the wire rod bearing load is reduced, the cracking risk is further increased, the temperature of a bainite phase region is increased due to the increase of the carbon content, the uneven distribution of air volume on the surface of the wire rod is increased under the condition that the stelmor air cooling speed is increased, the temperature difference of the wire rod and the risk of precipitation of bainite even martensite abnormal structures are increased, the plasticity and the yield of the wire rod are obviously reduced, and the mechanical fluctuation of the wire rod is increased, and the production and use are not beneficial; on the other hand, the existing wire rod with high carbon content mainly comprises a sorbite structure with high proportion, and the strength of the wire rod is improved, and the wire rod is in a low-temperature state after the sorbite structure is inoculated in the continuous slow cooling phase transition process due to the limited cold control capability of the stelmor air cooling line, so that the dislocation density of the obtained sorbite structure is higher, the plasticity of the final wire rod is insufficient, and the improvement of the plasticity by the increase of pearlite or ferrite structure is limited, so that the performance of the final wire rod is difficult to meet the performance grade requirements after drawing cold heading and tempering.

(3) Compared with V, nb, ti is used as a microalloy element capable of improving the plastic toughness performance of the wire rod through fine crystal strengthening and precipitation strengthening, a stronger hydrogen trap is formed while strengthening a matrix, and the hydrogen embrittlement resistance of the steel can be further improved, but in order to improve the plasticity of the cold heading steel wire rod through low-temperature wire laying and heat preservation slow cooling, the temperature in the rolling stage is lower so as to lead to the precipitation of deformed austenite, the microalloy in the rolling stage is not beneficial to precipitation strengthening, and meanwhile, under the continuous slow cooling after rolling, the time of a precipitation phase temperature interval is still shorter, so that fewer or coarsening of nanoscale precipitates are caused, the waste of alloy is caused, and even the performance of a final product is reduced.

Disclosure of Invention

The invention aims to solve at least one of the technical problems to a certain extent, and provides a 13.9-grade annealing-free hot-rolled cold heading steel wire rod and a manufacturing method thereof, which can reduce alloy consumption, play C, ti roles, realize wire rod tissue regulation and strong plastic energy matching, are suitable for the annealing-free high-efficiency green manufacturing of 13.9-grade ultrahigh-strength fastener bolts, are beneficial to reducing the risks of drawing broken wires and cold heading cracking, and improve the yield.

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

A13.9-grade annealing-free hot-rolled cold heading steel wire rod comprises the following chemical components in percentage by mass: c:0.72% -0.77%, si:0.10% -0.30%, mn:0.30% -0.50%, ti: 0.010% -0.030%, mo: 0.10-0.30%, P not more than 0.015%, S not more than 0.015%, and the balance Fe and unavoidable impurities, wherein the microstructure comprises a mixed structure composed of 46-52% by volume of tempered pearlite, 40-49% by volume of tempered sorbite, 2-5% by volume of ferrite and the balance 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 C element is a main strengthening element of the invention, is cheaper than other elements in steel, mainly exists in a carbide form, is favorable for providing the matrix strength of the material through solid solution strengthening and precipitation strengthening, determines the final hardness and strength of the finished bolt after tempering, but increases the decarburization risk and the risk of netlike distribution of cementite along a grain boundary, and has higher content, higher temperature in a bainite phase region and adverse structure regulation, so that the quality percentage of C is controlled to be 0.75% -0.79% in order to meet the final performance grade requirement of 13.9-grade fasteners, and the cold heading performance and the convenience of structure regulation are both considered.

(2) Silicon: si element is often added into steel as a deoxidizer in the smelting process, the strength of the wire rod can be improved through solid solution strengthening, the coarsening of the wire rod through the grains of molten salt at the front section is restrained, but excessive silicon can increase the risks of nonmetallic inclusion and decarburization, so that the elongation, the area shrinkage and the toughness of the steel are reduced, and the cold heading forming performance is deteriorated, so that the mass percentage of Si is controlled to be 0.10% -0.30%.

(3) Manganese: mn element is often added into steel as deoxidizer in smelting process, carbide can be formed, strength and hardenability of the steel are further improved through precipitation strengthening and solid solution strengthening, but too high Mn content can aggravate segregation in the solidification process of steel billet, so that uniformity of the steel is poor, grain coarsening tendency in the heating process of material is increased, workability and plasticity of the steel are deteriorated, and too high Mn can bring about increase of material cost, so that mass percentage of Mn is controlled to be 0.30% -0.50%.

(4) Titanium: the Ti element can refine grains through a strain-induced precipitation mechanism in the high-temperature rolling process, plays a role in fine grain strengthening, reduces the work hardening rate of steel, improves the cold workability of steel, and meanwhile, the dispersive precipitation phase of Ti can improve the strength and hydrogen embrittlement resistance of a finished bolt, but the excessive content of Ti can cause cost increase, coarse carbide and inclusion are easy to form and plasticity is also reduced, so that the mass percentage of Ti is controlled to be 0.010% -0.030% based on the role of Ti and the material cost.

(5) Molybdenum: the Mo element can strongly improve the hardenability and inhibit coarsening of a precipitated phase of the material, maximally exert the strengthening effect of the precipitated phase, improve the tempering stability of steel, form hydrogen traps by combining molybdenum cutting with carbon, and improve the delayed fracture resistance of the material, but has extremely high cost, can promote decarburization and easily form ferrite phase or brittle phase, and lower toughness, so that the mass percentage of Mo is controlled to be 0.10% -0.30% based on the action of Mo and the material cost.

(6) 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.

The cold heading steel wire rod adopts the design of high C chemical components containing Ti and Mo, the Mn content is relatively low, alloy components such as Cr, V, nb, B and the like are not added, the material cost can be relatively reduced, meanwhile, the microstructure of the cold heading steel wire rod is mainly composed of tempered pearlite and tempered sorbite, contains a small amount of ferrite and quasi-spheroidized carbide, compared with the microstructure of sorbite sheets, the layer spacing and plasticity are better, after the pearlite structure is converted into tempered pearlite through tempering, the structure stress and dislocation density are further reduced, the layer spacing and the strength of the sorbite structure are finer than those of the pearlite sheets, the dislocation density is lower than that of the microstructure of the sorbite, after the sorbite structure is converted into tempered sorbite through tempering, the dislocation density is further reduced, and the carbide is further converted into phase spheroidized structure, so compared with the existing cold heading steel wire rod mainly composed of bainite and containing bainite, the microstructure mainly composed of the pearlite and the tempered sorbite, the strength characteristics of pearlite and the sorbite are reserved, the reinforcing effect of the high C component is matched, the diffusion-out phase and the diffusion-out phase toughness of the steel wire rod is not obviously improved, but the solid solution hardening strength of the phase is improved.

Compared with the existing high-carbon steel wire rod mainly containing sorbite, the cold heading steel wire rod has the advantages that pearlite and sorbite are used for regulating the plasticity of the wire rod, after tempering state regulation, the plasticity of the cold heading steel wire rod is further improved due to the reduction of the structural stress and dislocation density, the cold heading steel wire rod is more suitable for drawing and cold heading manufacturing under the bolt annealing-free process, and compared with the existing annealing-free wire rod with the increased ferrite content for improving the plasticity, the cold heading steel wire rod only contains a small amount of ferrite structure, excessive loss of the strength of the wire rod is avoided, and further the strength and plasticity matching of the wire rod are guaranteed.

In a preferred embodiment, the lamellar spacing of the tempered pearlite is 155-180 nm, the lamellar spacing of the tempered sorbite is 80-115 nm, and the greater the lamellar spacing of the tempered pearlite and the tempered sorbite, the strength of the cold heading steel wire rod is reduced and the plasticity is increased.

In the preferred embodiment, the mesh carbide grade of the cold heading steel wire rod is 0 grade, so that the mesh carbide can be effectively eliminated, the deterioration of the mesh carbide on the wire rod performance is avoided, the utilization of carbon elements is improved, and the cold heading steel wire rod is more suitable for drawing cold heading.

In a preferred embodiment, the diameter of the cold heading steel wire rod is 14.0-22.0 mm, the tensile strength is 1080-630 MPa, the area reduction rate is 51% -56%, the cold heading steel wire rod avoids excessive loss of the tensile strength, the area reduction rate is obviously improved, and the drawing broken wire and the cold heading cracking risk can be effectively reduced without a spheroidizing annealing process.

The manufacturing method of the 13.9-grade annealing-free hot-rolled cold heading steel wire rod comprises the following steps:

And (3) rolling the 13.9-grade annealing-free hot-rolled cold heading steel wire rod according to the chemical composition control to produce a wire rod, wherein the wire rod is subjected to on-line salt bath isothermal control after being subjected to wire spinning according to the wire spinning temperature of more than or equal to 930 ℃ to enable the wire rod to pass through a front-stage molten salt, the wire rod is subjected to isothermal transformation from cooling speed of more than or equal to 43 ℃/s to a sorbite phase region to promote the transformation of a high-temperature austenite part into a sorbite structure, the wire rod is subjected to subsequent-stage molten salt heating isothermal to enable the unconverted high-temperature to be transformed into the pearlite structure, meanwhile, the transformation of the sorbite structure, the pearlite structure and carbide into a spheroidized structure is promoted, and finally, the wire rod is subjected to roller way slow cooling to be manufactured into the cold heading steel wire rod with a mixed structure comprising 46-52% tempered pearlite by volume percentage, 40-49% tempered sorbite by volume percentage 2-5% ferrite by volume percentage and the balance standard spheroidized carbide.

According to the manufacturing method, the chemical component design of high C containing Ti and Mo is combined with an online salt bath isothermal control technology, so that the problem that Ti is difficult to separate out and continuously refine grains due to the fact that the rolling temperature is too low is avoided, meanwhile, compared with a Steyr forced air cooling forced cooling process, a precipitation temperature interval of secondary cementite can be skipped rapidly at a higher cooling speed, the deterioration influence of reticular carbide on the wire rod is effectively eliminated, a larger supercooling degree is formed, the wire rod is cooled rapidly to a sorbite phase region to carry out isothermal transformation, a high-temperature austenitic structure part after wire rod wire spinning is promoted to be transformed into a sorbite structure with finer sheet spacing, matrix strength and plasticity are provided, preparation is made for controlling the tempered sorbite proportion in the structure, and since the wire rod passes through the fused salt, the surface of the wire rod can be covered, the fused salt has high heat exchange capacity, uniform heat exchange of the wire rod and the temperature difference between the wire rod and the fused salt is avoided, and the risk of bainite or abnormal structure due to overlarge temperature difference is avoided.

Compared with the heat preservation slow cooling or delay cooling process after the low Wen Tu wire, the temperature of the rear molten salt is higher than that of the front molten salt, after the wire rod passing through the front molten salt is heated and isothermal through the rear molten salt, the wire rod can reach a pearlite phase temperature change interval, unconverted high-temperature austenite in the tissue is converted into pearlite or a small amount of unavoidable ferrite tissue, isothermal treatment is carried out by keeping the temperature of the wire rod and the temperature of the rear molten salt consistent at the same time without continuous cooling, isothermal time of the wire rod at a higher temperature is prolonged, the conversion of sorbite and pearlite tissue to spheroidized tissue is promoted, the tissue stress and dislocation density are reduced, the conversion into tempered sorbite and tempered pearlite tissue is carried out, carbide is converted to spheroidized tissue, on the basis of coarsening of a precipitation phase is restrained by Mo, tiC precipitates are dispersed and precipitated on crystal boundaries and crystal grains in a large amount, the strengthening effect of the dispersed precipitation phase is maximally exerted, further strengthening property of the wire rod is realized, under the slow cooling effect of a roller way, the high upsetting effect of the wire rod after passing through the rear molten salt is utilized, the wire rod is further improved, the excessive cooling effect of the spheroidized tissue is further promoted, and the excessive cooling effect of the wire rod is further improved.

In a preferred embodiment, during controlled rolling, the heating temperature of the steel billet is controlled to be less than or equal to 1120 ℃ before rolling, the soaking time is 2-3 h, the sufficient dissolution and homogenization of alloy elements in the steel are promoted, and the risks of energy waste, burning loss, coarsening of original grains and decarburization caused by the excessively high heating temperature and the long soaking time of the steel billet are avoided.

In a preferred embodiment, during controlled rolling, the initial rolling temperature is controlled to be 1055-1100 ℃, the initial rolling reduction is 30% -45%, and the precipitation temperature of Ti is higher than Nb and V, and because the direct salt bath after spinning can quickly enter a sorbite phase region for isothermal transformation, the limitation of low-temperature spinning on cold heading steel wire rod production is broken, the controlled rolling stage can induce a large amount of Ti-containing precipitation phases to diffuse and precipitate pinning grain boundaries through high-temperature rolling, the original austenite is refined by using larger initial rolling reduction, and further the effect of refining grains is finally achieved, so that the slow precipitation of Ti, the too low rolling speed, the increase of rolling mill abrasion and the influence on production efficiency caused by the too low initial rolling temperature are avoided.

In a preferred embodiment, during the controlled rolling, the final rolling temperature is 940-980 ℃, the final rolling reduction is 20% -33%, the reduction of nano-grade precipitates caused by the excessively low final rolling temperature is avoided, the Ti-containing precipitated phase is utilized to continuously refine grains, and the matrix is strengthened, so that cracks are not easy to initiate and propagate in the drawing or cold heading process.

In a preferred embodiment, the temperature of the molten salt at the front stage is 460-490 ℃, the treatment time is 20-40 s, the lower the temperature of the molten salt at the front stage, the longer the treatment time, and the higher the cooling rate, the more the coil rod is converted into sorbite, the finer the inter-layer distance of the sorbite, the more the tempered sorbite accounts for in the obtained microstructure, the higher the strength of the coil rod, the lower the plasticity, but the risk of precipitation of a bainite abnormal structure is caused due to the excessively low temperature, the longer the time, the tempered pearlite content in the structure is affected, the adverse to the plasticity of the coil rod, the lower the temperature of the molten salt at the front stage, the thicker the inter-layer distance of the coil rod, the lower the coil rod strength, and the plasticity, but the excessively high temperature of the molten salt at the front stage, the excessively short the treatment time, the adverse to the transformation of the austenite structure into the sorbite structure, the excessive loss of the strength of the coil rod, the excessive temperature of the sorbite, the increased the spheroidization difficulty and even the precipitation risk of the network carbide, and the further control of the temperature and the treatment time at the front stage, the temperature and the treatment time are controlled to provide the strength of the austenite structure and the inter-layer distance of the sorbite, and the plastic structure.

In a preferred embodiment, the molten salt circulation amount of the front-stage molten salt is 600-800 t/h, the molten salt temperature rise is less than or equal to 8 ℃, the molten salt temperature rise is controlled by using the larger molten salt circulation amount, the isothermal temperature precision of the wire rod passing through the front-stage molten salt is maintained, and the occurrence of bainite abnormal structure is avoided.

In a preferred embodiment, the temperature of the rear-stage molten salt is 525-570 ℃, the treatment time is 300-600 s, the higher the temperature of the rear-stage molten salt and the longer the treatment time are, the larger the pearlite sheet spacing of the unconverted high-temperature austenite transformation is, the ferrite content is increased, the transformation from the sorbite, pearlite structure and carbide to the spheroidized structure is facilitated, the obvious toughening and spheroidizing effects are realized, the lower the wire rod strength and the plasticity are improved, but the higher the temperature of the rear-stage molten salt is, the overlarge layer spacing of the precipitated pearlite and the overlarge ferrite ratio can cause overlarge strength loss, the overlong treatment time is, the risks of coarsening of precipitates of Ti and aggregation and agglomeration growth of quasi-spheroidized carbide are caused, the obvious loss of the strong plastic performance is caused, and conversely, the lower the treatment time of the rear-stage molten salt is, the ferrite content is reduced, the tempered pearlite sheet spacing is reduced, the transformation from the carbide to the tissue is unfavorable, the toughening and spheroidization softening effects are weaker, the wire rod strength is improved, the plasticity is reduced, the temperature and the treatment time of the rear-stage molten salt can be further controlled, and the plastic structure of the wire rod can be further regulated and softened, and the plastic structure is properly matched.

In a preferred embodiment, the molten salt circulation amount of the rear-stage molten salt is 150-250 t/h, the molten salt temperature rise is less than or equal to 5 ℃, the molten salt temperature rise can be controlled by using a relatively smaller molten salt circulation amount, the isothermal treatment temperature precision of the rear-stage molten salt is maintained, and the molten salt circulation energy consumption is reduced.

In a preferred embodiment, the roller way slow cooling control wire rod is slowly cooled at a cooling speed of 0.3-0.8 ℃/s, then the wire rod is collected, and the preferable collection temperature is below 350 ℃, so that further annealing of the wire rod tissue and further spheroidization of carbide can be further promoted, and the softening effect of the wire rod is improved.

In the preferred embodiment, the roller way is slowly cooled by adopting the heat preservation cover to be closed, or the heat preservation cover is closed and hot air above the salt bath which is isothermally controlled by the online salt bath is simultaneously input into the heat preservation cover, so that air heat energy which is isothermally controlled by the online salt bath can be recycled, the influence on production efficiency caused by too low roller way speed due to low-speed cooling is avoided, the energy consumption is further reduced, and the yield is improved.

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

(1) Aiming at the current situation that the cold heading steel wire rod for the existing 13.9-grade ultrahigh-strength fastener is required to be subjected to spheroidizing annealing, has high energy consumption and emission and limited application, the invention adopts the design of high C chemical components containing Ti and Mo, has relatively low Mn content, does not add Cr, V, nb, B and other alloy components, does not contain bainite and martensite hard and brittle phase structures, has a microstructure type of mixed structures consisting of tempered pearlite, tempered sorbite as a main component, a small amount of ferrite and quasi-spheroidized carbide, and has the advantages of regulating and controlling the wire rod structure stress and dislocation density by using the tempered state structure, obviously improving the wire rod plasticity, reaching the product tensile strength Rm of 1080-630 MPa and the section shrinkage Z of 51% -56%, being used for manufacturing 13.9-grade annealing-free high-strength fastener bolts and other application fields, being beneficial to reducing the risk of wire breakage during drawing and cold heading, improving the yield, reducing the waste of raw materials, realizing the efficient green manufacturing of the ultrahigh-strength fastener bolts, being beneficial to adapting to the continuous development of the automobile industry towards the light and clean directions, and having good market application prospects.

(2) Aiming at the current situation that the existing cold heading steel wire rod is limited by a Steyr air cooling line and is difficult to meet the 13.9-grade annealing-free wire rod manufacturing, the manufacturing method is based on the combination of high C Ti-containing and Mo chemical components and an online salt bath isothermal control technology, the structure performance of the hot rolled wire rod is regulated and controlled, the isothermal transformation is firstly carried out on a sorbite phase region by using a front-stage molten salt to control the high Wen Tusi wire rod to carry out isothermal transformation at a larger supercooling degree and a quicker cooling speed, the deterioration influence of reticular carbide on the wire rod performance is effectively improved, the matrix strength and plasticity are provided, the transformation of unconverted austenite tissue to pearlite, the transformation of sorbite, the pearlite tissue and carbide to a spheroidized tissue are promoted by using a rear-stage molten salt, the matrix tissue is softened, the further toughening of the wire rod tissue and the further spheroidization of the carbide are promoted by using slow cooling, the softening effect of the wire rod is improved, the strength and the plasticity matching of the wire rod is realized, the effect of C, ti can be effectively exerted, the yield is improved, and the industrial adaptability is good.

(3) The manufacturing method breaks the limit of low-temperature wire laying on the manufacturing of cold heading steel wire rods, a large amount of Ti-containing precipitated phases are induced to diffuse and precipitate pinning grain boundaries through high-temperature rolling, the Ti-containing precipitated phases are utilized to continuously refine grains, the Mo is utilized to inhibit coarsening of the material precipitated phases, the strengthening effect of the precipitated phases is exerted to the maximum extent, and the strength and hydrogen embrittlement resistance of finished bolts can be improved.

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 2 of the present invention;

FIG. 3 is a metallographic structure of example 3 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 13.9-grade annealing-free hot-rolled cold heading steel wire rod manufacturing method of the invention comprises the following chemical components in percentage by mass: c:0.72%, si:0.3%, mn:0.45%, ti:0.013%, mo: 0.21%, P:0.014%, S:0.011%, and the balance of Fe and unavoidable impurities, and the manufacturing method comprises the following steps of rolling control, spinning, on-line salt bath isothermal control, roller way slow cooling and coil collection, and specifically:

The controlled rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote the full dissolution and homogenization of alloy elements in the steel and avoid burning loss and decarburization risks, rolling the steel billets which are discharged from the heating furnace into wires with the diameter of 20mm through a rolling line after heating the steel billets with high temperature reaching rolling plasticity, inducing Ti-containing precipitated phases to be dispersed and precipitated in a large amount to form pinning grain boundaries through high temperature rolling, and finally playing a role of refining grains, and the concrete steps are as follows: the billet heating temperature is controlled to 1100 ℃, the soaking time is controlled to 2.5h, the initial rolling temperature is 1080 ℃, the initial rolling reduction is 36%, the finishing rolling temperature is 960 ℃, and the finishing rolling reduction is 25%.

The wire rod that the silk process was used for going out the pass line is the wire rod through the silk machine that spouts, and the wire rod spreads on the roll table along the roll table and carries, through appropriate silk temperature that spouts, avoids the wire rod to separate out netted carbide at the silk stage, continues the grain refining effect, creates the advantage for forming great supercooling degree and sorbite nucleation, and is specific: the laying temperature was controlled to 940 ℃.

The online salt bath isothermal control adopts two sections of salt baths with built-in fused salt, wire rods after spinning are conveyed through a roller way to pass through the first section of salt baths, namely front section fused salt, are rapidly cooled to the fused salt temperature of the front section fused salt, so that the wire rods are cooled at a cooling speed of 46 ℃/s, the high Wen Tusi wire rods are controlled to rapidly skip a precipitation temperature interval of secondary cementite, isothermal phase transformation is carried out in a sorbite phase area at a larger supercooling degree and a faster cooling speed, the transformation of a high-temperature austenite part into sorbite tissues is promoted, matrix strength and plasticity are provided, the wire rods passing through the front section fused salt pass through a second section of salt baths, namely rear section fused salt, are heated and isothermal, the unconverted high-temperature austenite is transformed into pearlite tissues, and the transformation of the sorbite tissues, the pearlite tissues and carbides to spheroidized tissues are promoted at the same time, and matrix tissues are softened, so that the strength and the plasticity of the wire rods are ensured to be matched, and the following conditions are specific: the temperature of the molten salt at the front section is 460 ℃, the treatment time is 40s, the circulating amount of the molten salt is 800t/h, and the temperature rise of the molten salt is less than or equal to 8 ℃; the temperature of the molten salt at the later stage is 525 ℃, the treatment time is 300s, the circulating amount of the molten salt is 180t/h, and the temperature rise of the molten salt is less than or equal to 5 ℃.

The roller way slow cooling procedure adopts the heat preservation cover to close, uses the roller way to carry the wire rod that comes out from the second section salt bath to get into the heat preservation cover, carries into the heat preservation cover with the steam that two sections salt bath top produced as hot-blast simultaneously in, carries out slow cooling treatment, and the slow cooling promotes the further toughening of wire rod tissue and the further spheroidization of carbide, and is specific: slowly cooling the wire rod at a cooling speed of 0.3 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting and coiling the wire rods into coils through a coil collecting drum, the coil collecting temperature is 320 ℃, and the cold heading steel wire rod finished products are obtained after packaging and warehouse entering, and the metallographic structure diagram is shown in figure 1.

Comparative example 1:

The manufacturing method of the wire rod is different from the manufacturing method of the embodiment 1 in that the manufacturing method is manufactured according to the process flow of controlled rolling, low-temperature spinning, stelmor heat preservation slow cooling and coil collecting, and specifically comprises the following steps: the billet heating temperature is controlled to 1050 ℃, the soaking time is controlled to 3h, the initial rolling temperature is 1030 ℃, the final rolling temperature is 910 ℃, the spinning temperature is 890 ℃, the stelmor heat preservation slow cooling adopts to close all fans and heat preservation covers, the roller way is used for conveying the wire rods, the wire rods finish phase change in the covers at the cooling speed of 1.2 ℃/s, and the finished wire rod products are obtained after coil collection and coil discharging.

Comparative example 2:

The manufacturing method of the wire rod is different from the manufacturing method of the embodiment 1 in that the manufacturing method is manufactured according to the process flow of rolling control, spinning, stelmor quick cooling, roller way slow cooling and coil collecting, specifically: the step of Steyr quick cooling is to start a 1-7 # fan according to 35% so as to cool the wire rod to 680 ℃ at a cooling speed of 3.5 ℃/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 1.3 ℃/s, and the finished wire rod product is obtained after coil collection and coil off-line.

Comparative example 3:

the manufacturing method of the wire rod is different from the manufacturing method of the embodiment 1 in that the manufacturing method is manufactured according to the process flow of controlled rolling, low-temperature wire laying, steyr rapid cooling and roller way slow cooling, specifically: the billet heating temperature is controlled to 1075 ℃, the soaking time is controlled to 3 hours, the initial rolling temperature is 150 ℃, the final rolling temperature is 930 ℃, the spinning temperature is 910 ℃, the stelmor rapid cooling is realized by starting a 1-6 # fan according to 80 percent, the wire rod is cooled to 710 ℃ according to the cooling speed of 7.4 ℃/s, the roller way slow cooling is realized by closing all fans and a heat preservation cover, the wire rod is subjected to phase change in the cover at the cooling speed of 0.9 ℃/s, and the finished wire rod product is obtained after the wire rod is taken off line.

The wire rods obtained in example 1 and comparative examples 1 to 3 were subjected to structure and performance detection: 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 comparative results of the tissue properties of wire rods from different manufacturing methods

As can be seen from the comparison result of the example 1 and the comparative example 1, based on the design of the chemical composition of high C Ti and Mo, compared with the low Wen Tu wire and slow cooling process, the method is unfavorable for inducing Ti to precipitate refined grains in the rolling stage, and is characterized in that pearlite+ferrite soft phase structure is obtained, but the precipitation temperature interval of secondary cementite is longer, so that the reticular carbide in steel tends to be continuous and coarsened, the continuity of matrix is destroyed, the brittleness of the material is increased, the improvement of the plasticity of the wire rod is limited, the method is combined with the online salt bath isothermal control technology, the isothermal transformation is carried out in the sorbite phase region by using the front-stage molten salt at a higher supercooling degree and a faster cooling speed, the deterioration influence of reticular carbide on the performance of the wire rod is effectively improved, the strength and plasticity of the matrix are provided, the transformation of the non-transformed austenite structure to pearlite structure is promoted by using the rear-stage molten salt, the matrix structure is softened, the further spheroidization of the wire rod structure and the further spheroidization of the carbide are promoted by slow cooling, the effect of C, ti can be effectively exerted, the performance of the hot rolled wire rod structure is improved, and the performance is regulated.

As can be seen from the comparison result of the embodiment 1 and the comparative example 2, compared with the improvement of the air cooling intensity after spinning, the improvement of the net carbon grade is limited, the obtained sorbite sheets have larger spacing and smaller content, the wire rod is in a low temperature state after the sorbite tissue is inoculated in the continuous slow cooling phase transition process, the dislocation density of the obtained sorbite tissue is higher, the final wire rod plasticity is insufficient, and the invention uses the tempering state tissue to regulate the wire rod tissue stress and dislocation density, so that the wire rod plasticity can be remarkably improved.

As can be seen from the comparison result of the embodiment 1 and the comparative example 3, compared with the air cooling strength after spinning is further improved, the bainite structure appears, the bainite structure as a hard brittle phase increases the brittle fracture risk of the wire rod, the coil is easy to break in the processes of collecting coils in a steel mill, transporting the coils to the downstream in the steel mill, and paying off the coils by downstream users, so that the waste of raw materials and the reduction of the yield are caused.

Example 2:

The 13.9-grade annealing-free hot-rolled cold heading steel wire rod manufacturing method of the invention comprises the following chemical components in percentage by mass: c:0.75%, si:0.1%, mn:0.3%, ti:0.023%, mo: 0.3%, P:0.01%, S:0.012 percent of Fe and unavoidable impurities, and the manufacturing method comprises the following steps of rolling control, spinning, on-line salt bath isothermal control, roller way slow cooling and coil collection, and the specific steps are as follows:

The controlled rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote the full dissolution and homogenization of alloy elements in the steel and avoid burning loss and decarburization risks, rolling the steel billets which are discharged from the heating furnace into wires with the diameter of 16mm through a rolling line after heating the steel billets with high temperature reaching rolling plasticity, inducing Ti-containing precipitated phases to be dispersed and precipitated in a large amount to form pinning grain boundaries through high temperature rolling, and finally playing a role of refining grains, and the concrete steps are as follows: the billet heating temperature is controlled to 1110 ℃, the soaking time is 2.5h, the initial rolling temperature is 1090 ℃, the initial rolling reduction is 40%, the finishing rolling temperature is 970 ℃, and the finishing rolling reduction is 29%.

The wire rod that the silk process was used for going out the pass line is the wire rod through the silk machine that spouts, and the wire rod spreads on the roll table along the roll table and carries, through appropriate silk temperature that spouts, avoids the wire rod to separate out netted carbide at the silk stage, continues the grain refining effect, creates the advantage for forming great supercooling degree and sorbite nucleation, and is specific: the laying temperature was controlled to 950 ℃.

The online salt bath isothermal control adopts two sections of salt baths with built-in fused salt, wire rods after spinning are conveyed through a roller way to pass through the first section of salt baths, namely front section fused salt, are rapidly cooled to the fused salt temperature of the front section fused salt, so that the wire rods are cooled at a cooling speed of 45 ℃/s, the high Wen Tusi wire rods are controlled to rapidly skip a precipitation temperature interval of secondary cementite, isothermal phase transformation is carried out in a sorbite phase area at a larger supercooling degree and a faster cooling speed, the transformation of a high-temperature austenite part into sorbite tissues is promoted, matrix strength and plasticity are provided, the wire rods passing through the front section fused salt pass through a second section of salt baths, namely rear section fused salt, are heated and isothermal, the unconverted high-temperature austenite is transformed into pearlite tissues, and the transformation of the sorbite tissues, the pearlite tissues and carbides to spheroidized tissues are promoted at the same time, and matrix tissues are softened, so that the strength and the plasticity of the wire rods are ensured to be matched, and the following conditions are specific: the temperature of the molten salt at the front section is 475 ℃, the treatment time is 25s, the circulating amount of the molten salt is 700t/h, and the temperature rise of the molten salt is less than or equal to 8 ℃; the temperature of the molten salt at the later stage is 536 ℃, the treatment time is 500s, the circulating amount of the molten salt is 150t/h, and the temperature rise of the molten salt is less than or equal to 5 ℃.

The roller way slow cooling procedure adopts the heat preservation cover to close, uses the roller way to carry the wire rod that comes out from the second section salt bath to get into the heat preservation cover, carries into the heat preservation cover with the steam that two sections salt bath top produced as hot-blast simultaneously in, carries out slow cooling treatment, and the slow cooling promotes the further toughening of wire rod tissue and the further spheroidization of carbide, and is specific: slowly cooling the wire rod at a cooling speed of 0.4 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting the coil rod into coils through a coil collecting drum, the coil collecting temperature is 335 ℃, and the cold heading steel coil rod finished product is obtained after packaging and warehousing, and the metallographic structure diagram is shown in figure 2.

Comparative example 4:

A method for manufacturing a wire rod, which differs from example 2 in that: the heating temperature of the steel billet is controlled to 1070 ℃, the soaking time is controlled to 3h, the initial rolling temperature is 1040 ℃, the final rolling temperature is 920 ℃, the spinning temperature is 900 ℃, the coiled wire after spinning passes through the front-stage molten salt, the coiled wire is controlled to be cooled at a cooling speed of 40 ℃/s, and the coiled wire finished product is obtained after coiling and off-line.

Comparative example 5:

A method for manufacturing a wire rod, which differs from example 2 in that: the wire rod after spinning passes through a front-stage molten salt, the wire rod is controlled to be cooled at a cooling speed of 48 ℃/s, the temperature of the front-stage molten salt is 455 ℃, the treatment time is 45s, the circulating quantity of the molten salt is 850t/h, and the finished wire rod is obtained after coil collection and coil discharging.

Comparative example 6:

A method for manufacturing a wire rod, which differs from example 2 in that: and (3) cooling the wire rod subjected to spinning at a cooling speed of 44 ℃ per second through a front-section molten salt, wherein the temperature of the front-section molten salt is 495 ℃, the treatment time is 15s, and a finished wire rod product is obtained after coil collection and coil discharging.

Example 3:

The 13.9-grade annealing-free hot-rolled cold heading steel wire rod manufacturing method of the invention comprises the following chemical components in percentage by mass: c:0.77%, si:0.15%, mn:0.5%, ti:0.01%, mo: 0.25%, P:0.013%, S:0.012 percent of Fe and unavoidable impurities, and the manufacturing method comprises the following steps of rolling control, spinning, on-line salt bath isothermal control, roller way slow cooling and coil collection, and the specific steps are as follows:

The controlled rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote the full dissolution and homogenization of alloy elements in the steel and avoid burning loss and decarburization risks, rolling the steel billets which are discharged from the heating furnace into wires with the diameter of 22mm through a rolling line after heating the steel billets with high temperature reaching rolling plasticity, inducing Ti-containing precipitated phases to be dispersed and precipitated in a large amount to form pinning grain boundaries through high temperature rolling, and finally playing a role of refining grains, and the concrete steps are as follows: the billet heating temperature is controlled to 1085 ℃, the soaking time is 3 hours, the initial rolling temperature is 1055 ℃, the initial rolling reduction is 30%, the finishing temperature is 940 ℃, and the finishing rolling reduction is 20%.

The wire rod that the silk process was used for going out the pass line is the wire rod through the silk machine that spouts, and the wire rod spreads on the roll table along the roll table and carries, through appropriate silk temperature that spouts, avoids the wire rod to separate out netted carbide at the silk stage, continues the grain refining effect, creates the advantage for forming great supercooling degree and sorbite nucleation, and is specific: the laying temperature was controlled to 930 ℃.

The online salt bath isothermal control adopts two sections of salt baths with built-in fused salt, wire rods after spinning are conveyed through a roller way to pass through the first section of salt baths, namely front section fused salt, are rapidly cooled to the fused salt temperature of the front section fused salt, so that the wire rods are cooled at a cooling speed of 43 ℃/s, the high Wen Tusi wire rods are controlled to rapidly skip a precipitation temperature interval of secondary cementite, isothermal phase transformation is carried out in a sorbite phase area at a larger supercooling degree and a faster cooling speed, the transformation of a high-temperature austenite part into sorbite tissues is promoted, matrix strength and plasticity are provided, the wire rods passing through the front section fused salt pass through a second section of salt baths, namely rear section fused salt, are heated and isothermal, the unconverted high-temperature austenite is transformed into pearlite tissues, and the transformation of the sorbite tissues, the pearlite tissues and carbides to spheroidized tissues are promoted at the same time, and matrix tissues are softened, so that the strength and the plasticity of the wire rods are ensured to be matched, and the following conditions are specific: the temperature of the molten salt at the front section is 490 ℃, the treatment time is 20s, the circulating amount of the molten salt is 600t/h, and the temperature rise of the molten salt is less than or equal to 8 ℃; the temperature of the molten salt at the later stage is 570 ℃, the treatment time is 400s, the circulating amount of the molten salt is 250t/h, and the temperature rise of the molten salt is less than or equal to 5 ℃.

The roller way slow cooling procedure is closed by adopting a heat preservation cover, the wire rods coming out of the second section salt bath are conveyed by the roller way to enter the heat preservation cover, slow cooling treatment is carried out, the slow cooling promotes further toughening of the wire rod tissue and further spheroidization of carbide, and the method is characterized in that: slowly cooling the wire rod at a cooling speed of 0.8 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting the coil rod into coils through a coil collecting drum, the coil collecting temperature is 340 ℃, and the cold heading steel coil rod finished product is obtained after packaging and warehousing, and the metallographic structure diagram is shown in figure 3.

Comparative example 7:

A method for manufacturing a wire rod, which differs from example 3 in that: the temperature of the molten salt at the later stage is 585 ℃, the treatment time is 610s, and the finished product of the wire rod is obtained after coil collection and off-line.

Comparative example 8:

a method for manufacturing a wire rod, which differs from example 3 in that: the processing time is 700s, and the finished product of the wire rod is obtained after coil collecting and off-line.

Comparative example 9:

a method for manufacturing a wire rod, which differs from example 3 in that: the temperature of the molten salt at the later stage is 520 ℃, the treatment time is 250s, and the finished product of the wire rod is obtained after coil collection and offline.

Example 4:

The 13.9-grade annealing-free hot-rolled cold heading steel wire rod manufacturing method of the invention comprises the following chemical components in percentage by mass: c:0.73%, si:0.22%, mn:0.38%, ti:0.03%, mo: 0.1%, P:0.015%, S:0.015 percent of Fe and unavoidable impurities, and the manufacturing method comprises the following steps of rolling control, spinning, on-line salt bath isothermal control, roller way slow cooling and coil collection, and the specific steps are as follows:

The controlled rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote the full dissolution and homogenization of alloy elements in the steel and avoid burning loss and decarburization risks, rolling the steel billets which are discharged from the heating furnace into wires with the diameter of 14mm through a rolling line after heating the steel billets with high temperature reaching rolling plasticity, inducing Ti-containing precipitated phases to be dispersed and precipitated in a large amount to form pinning grain boundaries through high temperature rolling, and finally playing a role of refining grains, and the concrete steps are as follows: the billet heating temperature is controlled to 1120 ℃, the soaking time is controlled to 2 hours, the initial rolling temperature is 1100 ℃, the initial rolling reduction is 45%, the final rolling temperature is 980 ℃, and the final rolling reduction is 33%.

The wire rod that the silk process was used for going out the pass line is the wire rod through the silk machine that spouts, and the wire rod spreads on the roll table along the roll table and carries, through appropriate silk temperature that spouts, avoids the wire rod to separate out netted carbide at the silk stage, continues the grain refining effect, creates the advantage for forming great supercooling degree and sorbite nucleation, and is specific: the laying temperature was controlled to 960 ℃.

The online salt bath isothermal control adopts two sections of salt baths with built-in fused salt, wire rods after spinning are conveyed through a roller way to pass through the first section of salt baths, namely front section fused salt, are rapidly cooled to the fused salt temperature of the front section fused salt, so that the wire rods are cooled at a cooling speed of 46 ℃/s, the high Wen Tusi wire rods are controlled to rapidly skip a precipitation temperature interval of secondary cementite, isothermal phase transformation is carried out in a sorbite phase area at a larger supercooling degree and a faster cooling speed, the transformation of a high-temperature austenite part into sorbite tissues is promoted, matrix strength and plasticity are provided, the wire rods passing through the front section fused salt pass through a second section of salt baths, namely rear section fused salt, are heated and isothermal, the unconverted high-temperature austenite is transformed into pearlite tissues, and the transformation of the sorbite tissues, the pearlite tissues and carbides to spheroidized tissues are promoted at the same time, and matrix tissues are softened, so that the strength and the plasticity of the wire rods are ensured to be matched, and the following conditions are specific: the temperature of the molten salt at the front section is 482 ℃, the treatment time is 30s, the circulating amount of the molten salt is 760t/h, and the temperature rise of the molten salt is less than or equal to 8 ℃; the temperature of the molten salt at the later stage is 552 ℃, the treatment time is 600s, the circulating amount of the molten salt is 200t/h, and the temperature rise of the molten salt is less than or equal to 5 ℃.

The roller way slow cooling procedure is closed by adopting a heat preservation cover, the wire rods coming out of the second section salt bath are conveyed by the roller way to enter the heat preservation cover, slow cooling treatment is carried out, the slow cooling promotes further toughening of the wire rod tissue and further spheroidization of carbide, and the method is characterized in that: slowly cooling the wire rod at a cooling speed of 0.6 ℃/s until the wire rod is collected; the coil collecting procedure is used for collecting the coil rod into coils through a coil collecting drum, the coil collecting temperature is 315 ℃, and the cold heading steel coil rod finished product is obtained after packaging and warehousing.

Comparative example 10:

The manufacturing method of the wire rod is different from the manufacturing method of the embodiment 4 in that the manufacturing method is manufactured according to the process flow of rolling control, spinning, on-line salt bath isothermal control, air cooling and coil collecting, and specifically comprises the following steps: the air cooling process adopts a heat preservation cover to be opened, a roller way is used for conveying the wire rods coming out of the second section of salt bath, the wire rods are controlled to be cooled at a speed of 1.8 ℃/s, and the finished wire rod products are obtained after coil collection and coil discharging.

The wire rods obtained in examples 2 to 4 and comparative examples 4 to 10 were subjected to structure and performance detection: 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 2 below:

TABLE 2 comparison of the composition of the steel wire rods with the properties of the wire rod structure of the manufacturing method

As can be seen from the results of examples 1-4, the invention can reach the tensile strength Rm of 1080-630 MPa and the area reduction rate Z of 51-56%, is used for manufacturing 13.9-grade annealing-free high-strength fastener bolts and other application fields, realizes the efficient green manufacturing of the ultra-high-strength fastener bolts, and has good market application prospects.

As can be seen from the comparison of the results of example 2 and comparative example 4, the use of low-temperature wire laying causes too low rolling temperature to cause Ti to be difficult to precipitate out and continuously refine grains, and is disadvantageous in forming a large supercooling degree to control sorbite formation; as can be seen from the comparison result between the example 2 and the comparative example 5, the lower the temperature of the molten salt at the front stage, the longer the treatment time and the higher the cooling rate, the more the wire rod is converted into sorbite, the finer the inter-layer distance between the sorbite sheets, the more the tempered sorbite is occupied in the obtained microstructure, the strength of the wire rod is increased, the plasticity is reduced, but the longer the treatment time, the content of tempered pearlite in the tissue is affected, and the plasticity of the wire rod is unfavorable; as can be seen from the comparison between the example 2 and the comparative example 6, the too high temperature and the too short treatment time of the former molten salt are detrimental to transformation from the austenitic structure to the sorbite structure, and cause excessive loss of strength of the wire rod, and too large spacing between sorbite sheets increases the difficulty of spheroidization and even the risk of precipitation of network carbide.

As can be seen from the comparison result between the example 3 and the comparative example 7, the higher the temperature of the molten salt at the rear stage and the longer the treatment time, the larger the interlayer spacing of pearlite sheets in the unconverted high-temperature austenite transformation is, the more ferrite content is increased, the transformation from sorbite, pearlite structure and carbide to spheroidized structure is facilitated, and the toughening and spheroidization effects are more obvious; as can be seen from the comparison of the results of example 3 and comparative example 8, the treatment time is too long, and there is a risk that the Ti precipitates coarsen and the quasi-spheroidized carbides aggregate and grow up, which will result in a significant loss of the strength and plasticity properties; as can be seen from the comparison between example 3 and comparative example 9, the lower the temperature of the molten salt at the latter stage, the shorter the treatment time, which is unfavorable for transformation of carbide into spheroidized structure, the weaker the toughening and spheroidizing softening effects, the higher the strength of wire rod and the lower the plasticity.

As can be seen from the comparison result of the embodiment 4 and the comparative example 10, under the action of the roller way slow cooling, the high-temperature waste heat after the wire rod passes out of the molten salt at the rear section can promote the further toughening of the wire rod tissue and the further spheroidization of carbide under the continuous slow cooling, and the softening effect of the wire rod is improved.

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 (9)

1. The 13.9-grade annealing-free hot-rolled cold heading steel wire rod is characterized by comprising the following chemical components in percentage by mass: c:0.72% -0.77%, si:0.10% -0.30%, mn:0.30% -0.50%, ti: 0.010% -0.030%, mo: 0.10-0.30%, P less than or equal to 0.015%, S less than or equal to 0.015%, and the balance of Fe and unavoidable impurities, wherein the microstructure comprises mixed structures composed of 46-52% by volume of tempered pearlite, 40-49% by volume of tempered sorbite, 2-5% by volume of ferrite and the balance of quasi-spheroidized carbide;

The manufacturing method comprises the following steps: the wire rod is produced by controlled rolling according to the chemical components of the 13.9-grade annealing-free hot rolled cold heading steel wire rod, the wire rod is subjected to on-line salt bath isothermal control after being spun into the wire rod according to the spinning temperature of more than or equal to 930 ℃, the wire rod is firstly subjected to isothermal phase transformation from a former molten salt to a sorbite phase region at a cooling speed of more than or equal to 43 ℃ per second, the austenite part is promoted to be transformed into a sorbite structure, the wire rod is further subjected to isothermal heating through a latter molten salt, the unconverted austenite is transformed into a pearlite structure, the transformation of the sorbite structure, the pearlite structure and carbide into a spheroidized structure is promoted, and finally, the cold heading steel wire rod with a microstructure comprising a mixed structure consisting of tempered pearlite, tempered sorbite, ferrite and quasi-spheroidized carbide is manufactured through roller way slow cooling, wherein the temperature of the former molten salt is 460-490 ℃, and the treatment time is 20-40 s; the temperature of the rear molten salt is 525-570 ℃, and the treatment time is 300-600 s.

2. The 13.9 grade annealing-free hot rolled cold heading steel wire rod of claim 1, wherein the lamellar spacing of the tempered pearlite is 155-180 nm, the lamellar spacing of the tempered sorbite is 80-115 nm, and the mesh carbide grade of the cold heading steel wire rod is 0 grade.

3. The 13.9-grade annealing-free hot rolled cold heading steel wire rod according to claim 1 or 2, wherein the diameter of the cold heading steel wire rod is 14.0-22.0 mm, the tensile strength is 1080-1130 mpa, and the reduction of area is 51% -56%.

4. The manufacturing method of the 13.9-grade annealing-free hot-rolled 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 composition controlled rolling on a 13.9-grade annealing-free hot rolled cold heading steel wire rod to produce a wire rod, carrying out on-line salt bath isothermal control after the wire rod is spun into the wire rod according to the spinning temperature of more than or equal to 930 ℃, enabling the wire rod to pass through a front-stage molten salt, reducing the temperature of the wire rod to a sorbite phase region at a cooling speed of more than or equal to 43 ℃/s, carrying out isothermal transformation on the wire rod, promoting the austenite to be partially transformed into a sorbite structure, carrying out subsequent-stage molten salt heating isothermal on the wire rod, enabling the unconverted austenite to be transformed into the pearlite structure, promoting the transformation of the sorbite structure, the pearlite structure and carbide to be transformed into a spheroidized structure, and finally carrying out roller way slow cooling to prepare the cold heading steel wire rod with a mixed structure comprising 46-52% tempered pearlite, 40-49% tempered sorbite, 2-5% tempered pearlite and balance quasi-spheroidized carbide; the temperature of the molten salt at the front section is 460-490 ℃, and the treatment time is 20-40 s; the temperature of the rear molten salt is 525-570 ℃, and the treatment time is 300-600 s.

5. The method for manufacturing the 13.9-grade annealing-free hot-rolled cold heading steel wire rod, which is characterized in that during controlled rolling, the heating temperature of a steel billet is controlled to be less than or equal to 1120 ℃ and the soaking time is 2-3 h.

6. The method for manufacturing a 13.9-grade annealing-free hot rolled cold heading steel wire rod according to claim 4, wherein during the controlled rolling, a blooming temperature is controlled to be 1055-1100 ℃, a blooming rolling reduction is controlled to be 30% -45%, a finishing temperature is controlled to be 940-980 ℃, and a finishing rolling reduction is controlled to be 20% -33%.

7. The manufacturing method of the 13.9-grade annealing-free hot rolled cold heading steel wire rod, which is characterized in that the molten salt circulation amount of the front-stage molten salt is 600-800 t/h, the molten salt temperature rise is less than or equal to 8 ℃, the molten salt circulation amount of the rear-stage molten salt is 150-250 t/h, and the molten salt temperature rise is less than or equal to 5 ℃.

8. The method for manufacturing a 13.9-grade annealing-free hot rolled cold heading steel wire rod according to claim 4, characterized in that the roller way slow cooling control wire rod is slowly cooled at a cooling speed of 0.3-0.8 ℃/s.

9. The method for manufacturing the 13.9-grade annealing-free hot rolled cold heading steel wire rod according to claim 8, wherein the roller way slow cooling is closed by adopting a heat preservation cover, or the heat preservation cover is closed, and hot air above a salt bath which is controlled by online salt bath isothermal is simultaneously input into the heat preservation cover.