CN118639122A - 15.9-Grade annealing-free hot-rolled high-carbon cold heading steel wire rod and manufacturing method thereof - Google Patents

Abstract

The invention relates to a 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod and a manufacturing method thereof, wherein hot-rolled wire-laying is designed to be wire rod based on high C-Si-Mn-Al-Cr components, then on-line salt bath strong tempering is carried out, the front molten salt circulation is controlled to be larger than the rear molten salt circulation, so that the wire rod is cooled to a pearlite area at a cooling speed of more than or equal to 38 ℃/s to carry out isothermal phase transition, the wire rod is controlled to form a sorbite structure and a pearlite structure and promote tempering softening, finally the wire rod is slowly cooled by a roller way, so that the cold heading steel wire rod mainly comprising tempered pearlite, a small amount of tempered sorbite, ferrite and fused pearlite structure can be manufactured, the material cost can be reduced by utilizing the high-carbon components, abnormal structure is avoided, wire rod structure regulation and strong plastic energy matching are realized, the tensile strength is between 1165MPa, the section shrinkage is 47% -52%, the wire rod is suitable for the efficient green manufacturing of 15.9-grade fastener annealing, the method is favorable for reducing the risk of cold processing cracking, and the yield is improved.

Description

15.9-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 15.9-grade annealing-free hot-rolled high-carbon cold-heading steel wire rod and a manufacturing method thereof.

Background

At present, the cold forging steel for 8.8-12.9-level fasteners is more in application, generally adopts low-carbon, medium-carbon and alloying component combination design, is often used for manufacturing various fasteners such as screws, bolts, nuts, self-tapping screws, wallboard nails and the like in view of the excellent room-temperature cold processing performance of the cold forging steel, and provides application requirements for fasteners with higher strength grades, such as the cold forging steel for 15.9-level fasteners with tensile strength more than or equal to 1500MPa and yield ratio more than or equal to 0.9. Cold-heading steel for fasteners of higher strength grades is often increased in strength grade by adding a large amount of high hardenability elements, for example:

The patent CN114058974B discloses a 15.9 grade corrosion-resistant high strength bolt steel, a production method and a heat treatment method thereof, based on the component design of medium C-Si-Mn-Cr-Mo-V-Nb-Ti-B-Ni-Cu-Al, excellent bar rolling is carried out after square billet rolling is combined, a hot rolled state structure of pearlite and ferrite is obtained by slow cooling on a cooling bed, then the hot rolled state structure is regulated and controlled to be tempered sorbite and dispersed and separated fine carbide through the thermomechanical treatment and the high-frequency tempering heat treatment, and 15.9 grade fasteners are processed through the procedures of annealing, drawing, warm forging, heat treatment and plating, but in order to realize the production of the 15.9 grade fasteners with lower cost, greener and high efficiency, the following problems and technical difficulties still exist:

(1) In order to realize the high-strength performance grade of the 15.9-grade fastener by quenching and tempering heat treatment after cold heading, a large amount of strong hardenability such as Mn, cr, mo and the like and microalloy components such as V, ti, nb and the like are added into steel, but the problems that the risk of abnormal structure is increased and the plastic lifting difficulty is increased when controlled cooling after rolling is caused by high hardenability are simultaneously brought, and the problems that the brittle failure in the wire rod manufacturing process and the cracking risk in the fastener processing process are caused by abnormal structure precipitation are solved:

A case is that a blank or a bar with larger diameter is obtained by forging or rolling steel, so that martensite or bainite hard brittle phases are avoided in the post-rolling Steyr wire-controlled cooling process of high-speed wire manufacture, and further, coil collection brittle failure and yield are caused to be adversely affected, the coil rod with smaller diameter is difficult to directly obtain through rolling under the process, the method is suitable for manufacturing fasteners with larger specifications, and the difficulty is larger or the working procedures are more for manufacturing the fasteners with smaller specifications.

The other condition is that the steel adopts low-temperature rolling and heat-preserving cooling to obtain a pearlite with larger lamellar spacing and ferrite soft phase structure with larger lamellar spacing so as to reduce the risk of abnormal structure precipitation and improve the plasticity of the wire rod, but the formed pearlite structure has larger stress and dislocation density, the improvement on the plasticity of the wire rod is limited, the strength and drawing performance of the wire rod can be excessively deteriorated due to the increase of soft phase composition, the strength is required to be increased through larger reduction ratio, so as to meet the strength requirement before tempering, the loss of plasticity in the process is larger, the risks of drawing wire breakage and cold heading cracking are further increased, the hot rolled state structure of pearlite and ferrite is further regulated and controlled by the high-frequency tempering heat treatment, the hot rolled state structure of the pearlite and ferrite is required to be further heat treated after being cooled to the austenitizing temperature, the problems of more procedures, high energy consumption and high cost and influence on the production efficiency are caused, the low-grade user also needs to further anneal the raw material after forming the wire rod to improve the deformation performance, and the energy consumption, the cost and the efficiency pressure are caused to the fastener.

(2) Besides the increase of the process difficulty and the process flow, the addition of a large amount of high-hardenability elements and microalloy components also brings about the problem of remarkable increase of the steel raw material cost, and the high-carbon steel with lower price is limited by the cold control capability of the post-rolling stelmor cooling line, and is insufficient for meeting the requirement of the 15.9-grade annealing-free hot-rolled cold heading steel wire rod, because:

The existing high-carbon steel for drawing manufacture mainly improves drawing performance by improving sorbite content in a structure, prolongs the inoculation time of a wire rod in a sorbite phase region by combining a heat preservation or low-speed cooling process after spinning, increases sorbite content in the structure, and also reduces the risk of occurrence of abnormal bainite or martensite structure by avoiding air volume difference and overlarge temperature difference on the surface of the wire rod caused by air cooling strength increase after spinning, but the overlow cooling speed can cause longer time of stay of the high-temperature wire rod after spinning in a secondary cementite precipitation region to form higher-level reticular carbide, seriously deteriorates the plasticity and toughness of the wire rod, cannot save an annealing procedure and is difficult to eliminate reticular carbide residues in annealing treatment, thereby causing cracking risk in a cold heading process.

In order to reduce the risk of net carbon precipitation in the wire laying stage caused by low-temperature wire laying, the wire laying temperature is properly increased, meanwhile, the wire laying is limited to reduce the risk of hard and brittle abnormal tissue precipitation, a heat preservation process is adopted after wire laying is performed, the online time of the wire rod is prolonged, the heat preservation cooling rate is low, the online time is not too long to influence the production efficiency, the wire laying temperature cannot be too high, the larger supercooling degree is difficult to obtain, the spacing between sorbite sheets is larger, the drawing performance is unfavorable, the matrix strength is difficult to regulate and control, the heat preservation cooling rate is relatively low, the wire rod is still in a continuous cooling state, the wire rod is in a low-temperature state after undergoing sorbite phase transition, softening difficulty is also increased, the dislocation density of the final sorbite tissue is higher, the wire rod plasticity is difficult to be improved, annealing processing is difficult to be avoided, and the cracking risk in the cold heading process is also aggravated.

Disclosure of Invention

The invention aims to solve at least one of the technical problems to a certain extent, and provides a 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod and a manufacturing method thereof, which can utilize high-carbon components to reduce material cost, avoid abnormal tissues, realize wire rod tissue regulation and control and strong plastic energy matching, remarkably improve wire rod plasticity, simplify the manufacturing method, are suitable for high-efficiency green manufacturing of a 15.9-grade fastener without an annealing process, and are beneficial to reducing cold working cracking risk and improving yield.

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

the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod comprises the following chemical components in percentage by mass: c:0.82% -0.86%, si:0.30% -0.45%, mn:0.22% -0.42%, al:0.10% -0.30%, cr: 0.15-0.35%, P not more than 0.015%, S not more than 0.015%, and the balance Fe and unavoidable impurities, wherein the microstructure comprises 74-80% by volume of tempered pearlite, 14-20% by volume of tempered sorbite, and the balance ferrite and fused pearlite.

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 used as the element with the most economic and effective solid solution strengthening and precipitation strengthening effects and is the main added element for ensuring the matrix strength and high hardenability of steel, but the decarburization sensitivity and the risk of reticular distribution of cementite along the grain boundary are increased, the content of the element C is too high, the cementite sheet layer is thicker, the difficulty of fusing and tempering softening of the cementite is increased, and the matrix structure is not beneficial to regulation and control, so that the mass percentage of C is controlled to be 0.82% -0.86% in order to ensure the cold deformation performance of the cold heading steel wire rod and meet the final performance grade requirement of a 15.9-grade fastener.

(2) Silicon: the main deoxidizing element in the Si element steel can be dissolved in austenite to improve the strength of the steel, can inhibit coarsening of crystal grains in the early stage of strong tempering in an online salt bath, is beneficial to the nucleation and tempering softening of sorbite, but excessive silicon can increase nonmetallic inclusion and impurity element segregation, improves the diffusion of carbon in the steel, aggravates the decarburization of the steel, obviously increases the cold heading deformation resistance, and is unfavorable for cold heading and cold extrusion, so that the mass percentage of Si is controlled to be 0.30% -0.45%.

(3) Manganese: mn element is often added into steel as a deoxidizer in the smelting process and used as a solid solution strengthening element to improve the strength and hardenability of the steel, but the excessive Mn content can aggravate segregation in the solidification process of a steel billet, reduce the activity of carbon to reduce the diffusion speed of the carbon, increase the spheroidizing tempering softening difficulty and the control difficulty of a controlled cooling structure, cause deformation resistance, and the excessive Mn can also bring about the increase of material cost, so that the mass percentage of Mn is controlled to be 0.22% -0.42%.

(4) Aluminum: the Al element is used as a deoxidizer in the smelting process, so that the non-metal inclusion quantity in steel can be reduced, a tiny precipitated phase is formed during hot rolling, the coarsening of cementite is restrained, the thickness of the cementite sheet is thinned, the fusing of the cementite sheet at high temperature through on-line salt bath strong tempering is further facilitated, the impact toughness of the steel is improved, the cold embrittlement tendency is reduced, the graphitization of the steel is promoted due to the fact that the Al content is too high, the decarburization risk is increased, and therefore the mass percentage of the Al is controlled to be 0.22% -0.42%.

(5) Chromium: cr element is used as a solid solution strengthening element, the hardenability of the material can be strongly improved, matrix phase composition can be regulated, fine dispersed carbide particles are separated out through on-line salt bath strong tempering, the strength of the material is improved, but the Cr content is too high, the tempering brittleness tendency and the low-temperature tissue risk of steel can be increased, the plasticity lifting difficulty is increased, the separation and coarsening of Cr can obviously deteriorate the wire rod plastic-strengthening performance, and therefore the mass percentage of Cr is controlled to be 0.15% -0.35%.

(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.

In a preferred embodiment, the lamellar spacing of the tempered pearlite is 165-205 nm, the lamellar spacing of the tempered sorbite is 90-130 nm, the volume percentage of ferrite is less than or equal to 5%, the smaller the lamellar spacing of the tempered pearlite and the tempered sorbite is, the strength and plasticity of the wire rod are increased, the proportion of the tempered pearlite is increased, the lamellar spacing is increased, the ferrite content is increased, and the strength and plasticity of the wire rod are reduced.

The cold heading steel wire rod adopts the high C-Si-Mn-Al-Cr component design, uses lower-priced carbon elements to replace the addition of strong hardenability elements and microalloy elements, has lower Mn and Cr alloy content, does not contain noble value Mo, ti, nb, V, B and other elements, ensures that a component system can meet the requirement that the performance grade of a 15.9-grade fastener can be achieved after drawing, cold heading and tempering, reduces the material cost, provides the matrix strength by matching tempered pearlite and tempered sorbite in a microstructure, has thicker lamellar spacing of the pearlite structure than sorbite, has higher plasticity than sorbite and better strength than ferrite, can keep the moderate strength characteristic of the pearlite after tempering, fusing and converting the pearlite into tempered pearlite and fused pearlite to spheroidized structure, further reduces the tissue stress and dislocation density, further improves the plasticity, ensures that the tempered pearlite occupies larger area, the soft phase ferrite structure with little incomparable avoidance is accompanied, the excessive loss of the strength of the wire rod is avoided, the sorbite structure is finer than the lamellar spacing of the pearlite structure, the plasticity is better than the bainite and martensite hard brittle phase structure, after the transformation from tempering to spheroidizing structure to tempering sorbite, the characteristic of higher strength of sorbite can be kept, the dislocation density of the sorbite group is further reduced, the plasticity is improved, the drawing hardening is effectively reduced, the excessive degradation of the strength of the wire rod can be avoided compared with the existing hot rolled wire rod structure with pearlite+ferrite, the obviously improved plastic toughness performance is realized, the adverse influence of a high carbon component system on the plasticity and cold deformation performance of the wire rod is compensated, the yield can be further improved, the wire rod with smaller specification is rapidly and directly obtained through rolling, the manufacturing difficulty of the small-size fastener is reduced, and the 15.9-grade fastener is manufactured by cold heading under the annealing-free process, so that the cracking risk is reduced.

In the preferred embodiment, the mesh carbide of the cold heading steel wire rod is 0 grade, so that uncontrollable deterioration factors caused by the mesh carbide can be eliminated, the strengthening effect of carbon elements is improved, and the cracking risk is reduced.

In a preferred embodiment, the diameter of the cold heading steel wire rod is 12.0-26.0 mm, the tensile strength is 1115-1165 MPa, the area reduction rate is 47% -52%, the cold heading steel wire rod has higher tensile strength and remarkably increased area reduction rate, and the performance grade of the 15.9-grade fastener can be achieved through drawing, cold heading and quenching and tempering heat treatment under the condition that an annealing process is omitted.

A manufacturing method of a 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod comprises the following steps:

The 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is rolled to produce a wire rod according to the chemical composition, the wire rod is subjected to on-line salt bath strong tempering after being subjected to wire spinning according to the wire spinning temperature of more than or equal to 960 ℃, the front end molten salt circulation amount of the on-line salt bath strong tempering is controlled to be larger than the rear end molten salt circulation amount, the wire rod is cooled to a pearlite phase area at a cooling speed of more than or equal to 38 ℃/s to carry out isothermal phase transformation, the wire rod is controlled to form a sorbite structure and a pearlite structure, the sorbite structure and the pearlite structure are promoted to be tempered and softened, and finally, the cold heading steel wire rod is slowly cooled by a roller way, wherein the microstructure comprises 74-80% by volume of tempered pearlite, 14-20% by volume of tempered sorbite, and the balance of mixed structure consisting of ferrite and fused pearlite.

According to the manufacturing method, the wire rod is austenitized at a higher wire-laying temperature, secondary cementite is prevented from being precipitated in the wire-laying stage, compared with slow cooling modes such as heat preservation and cooling, on-line salt bath strong tempering is directly carried out after wire laying, the wire rod cooling can be controlled at a cooling rate which is obviously higher than the upper limit of the air cooling intensity of 10 ℃/s by utilizing the high heat exchange capacity of molten salt, on one hand, the precipitation temperature interval of the secondary cementite and the tertiary cementite can be skipped rapidly, the generation of netlike carbide is avoided, the deterioration of the mechanical property, particularly the plasticity and toughness of the high-carbon steel wire rod is avoided, and the utilization rate of carbon is improved; on the other hand, the remarkable increase of the cooling speed breaks the limit that the wire laying temperature cannot be improved due to overlong online time, higher wire laying temperature can be adopted, the front end molten salt circulation quantity is matched with the rear end to be larger to form larger supercooling degree, the wire rod rapidly enters a pearlite area to carry out isothermal diffusion phase transformation, the austenitic structure of the wire rod is controlled to form a sorbite structure with finer lamellar spacing, the wire rod can pass through the molten salt when passing through the molten salt, the molten salt is uniformly coated on the surface of the wire rod, the problems of air quantity difference and temperature difference of an air receiving surface and a leeward surface of the wire rod under a strong air cooling process do not exist, and the wire rod can be prevented from entering a bainite phase area to generate a bainite abnormal structure.

The circulation amount of molten salt at the rear end of the online salt bath strong tempering is smaller than that at the front end, the supercooling degree can be properly reduced, unconverted high-temperature austenite is controlled to enter a pearlite area for isothermal transformation, so that the phase transformation regulation and control of the sorbite and the pearlite can be realized in the online salt bath strong tempering process, the process is simplified, meanwhile, the temperature of the wire rod can be kept consistent with that of the molten salt due to the high heat exchange effect, the wire rod is not subjected to continuous cooling in the existing heat preservation treatment, the wire rod is still in a high-temperature state after the phase transformation is finished, the sorbite is promoted to be transformed into tempered sorbite along with the high-temperature isothermal process for a longer time, the dislocation density is reduced, the thickness of a sheet layer of Al refined cementite is matched, the pearlite sheet layer is promoted to be fused into fused pearlite, the pearlite is transformed into spheroidized tissue stress and dislocation density are reduced, the precipitation coarsening of Cr is avoided, and the matrix strong plastic property is regulated.

The coil rod is subjected to the on-line salt bath strong tempering and then is subjected to the tissue full phase transformation, so that abnormal tissue is avoided in a roller way slow cooling stage, the coil rod is in a high-temperature state after the on-line salt bath strong tempering treatment, the softening effect of the high-temperature state of the coil rod can be continued by using low-speed cooling by utilizing the roller way slow cooling, the tissue softening and the plasticity promotion are further promoted, compared with the direct prolonging of the on-line salt bath strong tempering time, the energy consumption can be saved, finally, the tempered pearlite, a small amount of tempered sorbite, ferrite and fused pearlite tissue, the non-bainite and martensite tissue are obtained, the tissue regulation and the strong plasticity matching are realized, the coil is smoothly collected, the brittle fracture is avoided, the finished material is improved, the coil rod can be transported to the downstream unreeling and drawing without reheating and heat treatment or annealing in the prior art, the manufacturing process flow of the coil rod and the fastener can be simplified, and the emission is efficiently reduced.

In a preferred embodiment, during rolling, the temperature of a heating furnace is controlled to be less than or equal to 1155 ℃ before rolling, the soaking time is 3-4 h, the furnace time is less than or equal to 6h, the higher heating furnace temperature and the longer soaking time are selected to promote the uniform components of the steel billet, the high-temperature rolling can be quickly performed, and meanwhile the risk of burning loss and decarburization on the surface of the steel billet caused by overlong furnace time is avoided.

Because the limitation of the existing low-temperature wire laying on the low-temperature rolling requirement is broken, in a preferred embodiment, during rolling, high-temperature rolling is adopted, the initial rolling temperature is controlled to 1085-1125 ℃, the initial rolling reduction is controlled to 33% -38%, the higher initial rolling temperature is selected to reduce the deformation resistance of a billet and the abrasion to a rolling mill, the rolling speed is improved, the interface bonding strength is improved by matching with the larger initial rolling reduction, and the original austenite grains are thinned.

In a preferred embodiment, during rolling, the finishing temperature is controlled to be less than or equal to 1000 ℃, the finishing rolling reduction is 32% -42%, austenite grains are prevented from being coarse due to overlarge finishing temperature, the nucleation rate is increased by matching with larger finishing rolling reduction, dynamic recrystallization is promoted, and local stress concentration in a local area is prevented from being aggravated.

In a preferred embodiment, the temperature of the molten salt for on-line salt bath strong tempering is 590-625 ℃, the treatment time is 490-740 s, the finer the interlayer spacing of the phase-transformed sorbite and pearlite structure is, the higher the matrix strength is, the plasticity is reduced, the softening of the molten salt for fusing and converting into a tempering state is facilitated, but the lower the molten salt temperature is, the proportion of tempered sorbite is increased, the plastic lifting of the wire rod is unfavorable, even the abnormal bainite structure is generated, the wire rod brittleness is obviously increased, otherwise, the higher the molten salt temperature is, the larger the interlayer spacing of the phase-transformed sorbite and pearlite structure is, the higher the proportion of ferrite is, the matrix strength is reduced, the plasticity is increased, more thermal power can be provided for the matrix softening, but the higher the molten salt temperature is difficult to form a larger supercooling degree, the sorbite with finer interlayer spacing is unfavorable for forming the network carbon and the restraint of network carbon, and more ferrite is generated, so that the matrix strength and drawing performance are reduced; the longer the treatment time is, the better the tempering softening effect after the phase transformation is finished is, the lower the tissue stress and dislocation density of tempered sorbite and tempered pearlite are, the strength of the wire rod is reduced, the plasticity is increased, but the longer the treatment time is, the risk that the strength of the wire rod is lost due to excessive tempering softening and precipitation coarsening of Cr are obviously reduced, otherwise, the shorter the treatment time is, the worse the tempering softening effect is, the strength of the wire rod is increased, the plasticity is reduced, the sorbite and pearlite obtained after the treatment time is too short cannot be softened, the dislocation density is higher, the risks of drawing broken wire and cold heading cracking are easily caused by stress concentration and drawing hardening, and the adverse effects on the annealing process, even the strength loss even abnormal tissue are caused due to insufficient phase transformation are avoided, so that the temperature and the treatment time of molten salt of on-line salt bath strong tempering can be further controlled, and the tempering sorbite ratio, the sheet spacing and the softening effect are regulated.

In a preferred embodiment, the front-end molten salt circulation amount of the on-line strong tempering of the salt bath is 600-900 t/h, the temperature rise of the front-end molten salt is controlled to be less than or equal to 10 ℃, a molten salt circulation pipeline can be arranged at the front end close to the salt bath to control the front-end molten salt circulation amount, the larger front-end molten salt circulation amount is selected to control the molten salt temperature rise, the treatment precision is improved, the wire rod can enter a phase region to carry out isothermal diffusion phase transformation at a larger supercooling degree, a small amount of austenitic tissues are promoted to be converted into sorbite tissues with finer lamellar spacing, and the tempered sorbite duty ratio is regulated.

In a preferred embodiment, the circulation amount of the rear-end molten salt in the on-line strong tempering is 200-400 t/h, the temperature rise of the rear-end molten salt is controlled to be less than or equal to 5 ℃, a molten salt circulation pipeline can be arranged at the rear end close to a salt bath to control the circulation amount of the rear-end molten salt, the control supercooling degree of the rear-end molten salt with smaller circulation amount is preferred to be lower, the temperature precision is further controlled, and unconverted high-temperature austenite enters a pearlite phase region to carry out isothermal phase transformation and tempering softening, and the matrix strength-plasticity performance is regulated and controlled.

In the preferred embodiment, the roller way slow cooling adopts a closed heat preservation cover, the wire rod is controlled to be cooled at the cooling speed of 0.2-0.5 ℃/s, the slow cooling time is more than or equal to 500s, the wire rod subjected to on-line salt bath strong tempering treatment can be controlled to be slowly cooled along the roller way in the heat preservation cover by utilizing the lower cooling speed, and the softening of tempered pearlite and tempered sorbite is further promoted, and the matrix strength and plasticity performance is regulated and controlled.

In the preferred embodiment, the roller way slow cooling adopts that hot air above the salt bath in the on-line salt bath strong tempering is led into the heat insulation cover, so that hot air heat energy in the on-line salt bath strong tempering process can be recycled, the cooling speed of the wire rod is reduced for the roller way slow cooling heat insulation, and the energy consumption can be saved.

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

(1) Aiming at the current situation that the cold heading steel for the fastener with higher strength grade usually has high material cost, increased abnormal structure risk and insufficient plasticity due to the fact that a large amount of high hardenability elements are added to improve the strength grade of the cold heading steel, the cold heading steel wire rod disclosed by the invention has the advantages that the content of Mn and Cr alloy is lower through the component design of high C-Si-Mn-Al-Cr, the material cost is reduced, elements such as a noble price Mo, ti, nb, V, B and the like are not contained, a microstructure does not contain bainite or martensite hard and brittle phases, tempered pearlite is mainly, a small amount of tempered pearlite, ferrite and fused pearlite structure are adopted, the tissue stress and dislocation density are further reduced, the plasticity of the wire rod is remarkably improved, the adverse influence of a high-carbon component system on the plasticity and cold deformation performance of the wire rod is overcome, the strong plasticity is matched, the yield is further improved, the drawing hardening is reduced, the tensile strength is up to 1115 MPa, the section shrinkage is 47% -52%, and the application prospect of the fastener with the heat treatment grade of 15.9 is achieved under the condition of saving annealing working procedures.

(2) Aiming at the problems that the existing manufacturing process is difficult to directly obtain small-specification wire rods, the yield is low, the plasticity is insufficient or the working procedure is too much due to the fact that the existing manufacturing process is controlled by abnormal tissue, the manufacturing method is characterized in that through the high C-Si-Mn-Al-Cr component design and the combination of the online salt bath strong tempering and roller way slow cooling technology, the higher wire-laying temperature is selected to improve the supercooling degree of the wire rods in the subsequent online salt bath strong tempering treatment, the stay time in a network carbon area is effectively shortened, uncontrollable deterioration factors of the network carbide are eliminated, the strengthening effect of carbon elements is improved, the high-speed heat exchange capacity of molten salt is utilized, the wire rods are controlled to carry out isothermal diffusion phase transformation to form sorbite, the front end molten salt circulation volume is larger than the rear end molten salt circulation volume, the rear end supercooling degree is enabled to be lower, unconverted high-temperature austenite is controlled to enter the pearlite area to carry out isothermal phase transformation, after the phase transformation is completed, the matrix is further softened in the subsequent long-time high-temperature isothermal process, the matrix is slowly cooled by the roller way, the matrix is matched with strong plasticity, the brittle coiling is avoided, the brittle coiling is improved, the material is no longer, the need to be reheated or annealed, the thermal treatment or annealed is simplified, the steel wire rod can be manufactured with good cold 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 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 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod manufacturing method comprises the following chemical components in percentage by mass: c:0.84%, si:0.45%, mn:0.22%, al:0.29%, cr:0.27%, P:0.014%, S:0.013%, and the balance of Fe and unavoidable impurities, wherein the manufacturing method comprises the steps of high-temperature rolling, wire laying, on-line strong tempering in salt bath, roller way slow cooling and coil collecting, and specifically comprises the following steps:

The high-temperature rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote homogenization of steel billet components, avoid burning loss and decarburization risk, roll 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 the high-temperature rolling plasticity, improve rolling speed, reduce deformation resistance of the steel billets and abrasion to the rolling line by adopting the high-temperature rolling, refine original austenite grains by matching with larger reduction, and is specific: the heating furnace adopts the preheating, heating and soaking procedures with sequential heating, the temperature of the heating furnace is controlled to 1150 ℃, the soaking time is controlled to 3h, the furnace time is controlled to 5.5h, the initial rolling temperature is 1115 ℃, the initial rolling reduction is 34%, the final rolling temperature is 995 ℃, and the final rolling reduction is 35%.

The wire rod of rolling line is used for going out to the silk process, is the wire rod through the silk machine of spouting, and the wire rod spreads on the roll table and follows the roll table and carry, selects higher silk temperature of spouting for use, is used for improving the supercooling degree of wire rod in the strong tempering of online salt bath later, and effectively shortens the dwell time in net carbon region, and is specific: the laying temperature was controlled to 970 ℃.

The online salt bath strong tempering adopts a salt bath tank with molten salt arranged therein, wire rods after spinning are conveyed through the salt bath tank by a roller way, are rapidly cooled to the molten salt temperature, the front-end molten salt circulation amount of the salt bath tank is controlled to be larger than the rear-end molten salt circulation amount, the wire rods are cooled to a pearlite phase region at a cooling speed of 39 ℃/s to carry out isothermal phase transformation, a precipitation temperature interval of secondary cementite is rapidly passed, a network carbon deterioration phase caused by overhigh carbon element is eliminated, the use value of the carbon element is improved, simultaneously, a larger supercooling degree is formed by using a larger front-end molten salt circulation amount, a small amount of austenitic tissue is promoted to be converted into a sorbite tissue with finer lamellar spacing, the supercooling degree is properly reduced by using a smaller rear-end molten salt circulation amount, unconverted high-temperature austenite is controlled to enter the pearlite phase region to carry out isothermal phase transformation to form a pearlite tissue, and meanwhile, the tempering softening of the sorbite tissue and the pearlite tissue is promoted, and the following characteristics are promoted: controlling the molten salt temperature to 615 ℃, the treatment time to 565s, the front molten salt circulation amount to 700t/h, the front molten salt temperature rise to less than or equal to 10 ℃, the rear molten salt circulation amount to 250t/h, and the rear molten salt temperature rise to less than or equal to 5 ℃.

The roller way slow cooling procedure adopts to close the heat preservation cover, the wire rod coming out of the salt bath is conveyed by the roller way to enter the heat preservation cover, hot air above the salt bath is led into the heat preservation cover for slow cooling treatment, and further softening of wire rod tissues is promoted, specifically: the wire rod is controlled to be cooled at a cooling speed of 0.4 ℃/s, the slow cooling time is 680s, and the wire rod is cooled to 343 ℃; 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:

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, spinning and stelmor heat preservation slow cooling, specifically: the temperature of a heating furnace is controlled to 1090 ℃, the soaking time is controlled to 4 hours, the furnace time is 6 hours, the initial rolling temperature is 1050 ℃, the final rolling temperature is 950 ℃, the spinning temperature is 920 ℃, the Steyr heat preservation slow cooling adopts the steps of closing all fans and heat preservation covers, conveying wire rods by using a roller way, finishing phase change of the wire rods in the covers at a cooling speed of 1.5 ℃/s, and obtaining finished wire rod products after the wire rods are taken off line.

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 low-temperature rolling, low-temperature spinning, stelmor air cooling and heat preservation slow cooling, specifically: the low-temperature rolling control heating furnace temperature is 1010 ℃, soaking time is 5h, furnace time is 6.5h, initial rolling temperature is 980 ℃, finishing rolling temperature is 880 ℃, wire laying temperature of low-temperature wire laying is 850 ℃, the Steyr air cooling is to start a 1-7 # fan according to 10%, so that a wire rod is cooled to 690 ℃ at a cooling speed of 2.3 ℃/s, and the heat preservation slow cooling is to close all fans and heat preservation covers, so that the wire rod completes phase change in the covers at a cooling speed of 0.9 ℃/s, and a wire rod finished product is obtained after the wire rod is taken 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 rolling, spinning, stelmor quick cooling and roller way slow cooling, specifically: the temperature of a heating furnace is controlled to be 1080 ℃, the soaking time is controlled to be 4.5h, the furnace time is 6h, the initial rolling temperature is 1040 ℃, the final rolling temperature is 940 ℃, the spinning temperature is 910 ℃, the Steyr rapid cooling is realized by starting a1-6 # fan according to 45 percent, the wire rod is cooled to 680 ℃ according to the cooling speed of 4.5 ℃/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 is obtained after the wire rod is taken off.

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 embodiment 1 and the comparative example 1, compared with the method limited by lower heat preservation cooling speed, inadvisable on-line time to influence production efficiency, the wire laying temperature cannot be too high, the sorbite structure can be obtained under heat preservation cooling, but the mesh carbide grade is higher, the wire rod is in a low-temperature state after undergoing the sorbite phase transition, the dislocation density is higher, the plasticity of the wire rod is difficult to promote, the method can reduce the material cost by utilizing high carbon components, and the method can eliminate uncontrollable deterioration factors of the mesh carbide, promote the strengthening effect of carbon elements, realize tempering softening in the isothermal process of long-time high temperature, and can improve the yield and reduce the drawing hardening.

As can be seen from the comparison results of the example 1 and the comparative example 2, compared with the case of low-temperature rolling and wire laying, although the grains are refined, the method is limited in that the method is used for reducing the precipitation risk of hard and brittle abnormal tissues, the improvement of the netlike carbide is limited, meanwhile, the formed pearlite tissue is larger in stress and dislocation density, the improvement of the plasticity of the wire rod is limited, the strength and drawing performance of the wire rod can be excessively deteriorated due to the increase of the soft phase composition, the wire rod is controlled to perform isothermal diffusion phase transformation to form sorbite, and the strengthening effect of carbon elements is improved to provide matrix strength by matching with tempered pearlite and tempered sorbite in a microstructure, so that the matrix strong plasticity matching is regulated.

As can be seen from the comparison result of the embodiment 1 and the comparative example 3, compared with the method for accelerating the cooling speed and aggravating the abnormal tissue precipitation risk and further causing the coil collecting brittle failure and the adverse effect of the yield, the invention avoids the occurrence of the bainite abnormal tissue caused by the entering of the coil rod into the bainite phase region, has no bainite and martensite tissues, has obviously improved plastic toughness performance, compensates the adverse effect of a high-carbon component system on the plasticity and the cold deformation performance of the coil rod, further can improve the yield, rapidly and directly obtain the wire rod with smaller specification by rolling, and reduces the manufacturing difficulty of the small-specification fastener.

Example 2:

The 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod manufacturing method comprises the following chemical components in percentage by mass: c:0.82%, si:0.3%, mn:0.31%, al:0.1%, cr:0.32%, P:0.015%, S:0.013%, and the balance of Fe and unavoidable impurities, wherein the manufacturing method comprises the steps of high-temperature rolling, wire laying, on-line strong tempering in salt bath, roller way slow cooling and coil collecting, and specifically comprises the following steps:

The high-temperature rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote homogenization of steel billet components, avoid burning loss and decarburization risk, roll the steel billets which are discharged from the heating furnace into wires with the diameter of 12mm through a rolling line after heating the steel billets with the high-temperature rolling plasticity, improve rolling speed, reduce deformation resistance of the steel billets and abrasion to the rolling line by adopting the high-temperature rolling, refine original austenite grains by matching with larger reduction, and is specific: the heating furnace adopts the preheating, heating and soaking procedures with sequential heating, the temperature of the heating furnace is controlled to 1140 ℃, the soaking time is 3 hours, the initial rolling temperature is 1080 ℃, the initial rolling reduction is 38%, the final rolling temperature is 985 ℃ and the final rolling reduction is 42%.

The wire rod of rolling line is used for going out to the silk process, is the wire rod through the silk machine of spouting, and the wire rod spreads on the roll table and follows the roll table and carry, selects higher silk temperature of spouting for use, is used for improving the supercooling degree of wire rod in the strong tempering of online salt bath later, and effectively shortens the dwell time in net carbon region, and is specific: the laying temperature was controlled to 960 ℃.

The online salt bath strong tempering adopts a salt bath tank with molten salt arranged therein, wire rods after spinning are conveyed through the salt bath tank by a roller way, are rapidly cooled to the molten salt temperature, the front-end molten salt circulation amount of the salt bath tank is controlled to be larger than the rear-end molten salt circulation amount, the wire rods are cooled to a pearlite phase region at a cooling speed of 41 ℃ per second to carry out isothermal phase transformation, a precipitation temperature interval of secondary cementite is rapidly passed, a network carbon deterioration phase caused by overhigh carbon element is eliminated, the use value of the carbon element is improved, simultaneously, a larger supercooling degree is formed by using a larger front-end molten salt circulation amount, a small amount of austenitic tissue is promoted to be converted into a sorbite tissue with finer lamellar spacing, the supercooling degree is properly reduced by using a smaller rear-end molten salt circulation amount, unconverted high-temperature austenite is controlled to enter the pearlite phase region to carry out isothermal phase transformation to form a pearlite tissue, and meanwhile, the tempering softening of the sorbite tissue and the pearlite tissue is promoted, and the following characteristics are promoted: the molten salt temperature is controlled to 590 ℃, the treatment time is 740s, the front molten salt circulation amount is 900t/h, the front molten salt temperature rise is less than or equal to 10 ℃, the rear molten salt circulation amount is 400t/h, and the rear molten salt temperature rise is less than or equal to 5 ℃.

The roller way slow cooling procedure adopts to close the heat preservation cover, the wire rod coming out of the salt bath is conveyed by the roller way to enter the heat preservation cover, hot air above the salt bath is led into the heat preservation cover for slow cooling treatment, and further softening of wire rod tissues is promoted, specifically: controlling the wire rod to be cooled at a cooling speed of 0.2 ℃/s, wherein the slow cooling time is 990s, and the wire rod is cooled to 392 ℃; 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 4:

The manufacturing method of the wire rod is different from that of the embodiment 2 in that the temperature of a heating furnace is controlled to 1090 ℃, the soaking time is controlled to 4 hours, the furnace time is controlled to 6 hours, the initial rolling temperature is 1050 ℃, the final rolling temperature is 950 ℃, the wire-throwing temperature is 920 ℃, the online salt bath strong tempering control wire rod is cooled to a pearlitic phase region at a cooling speed of 35 ℃/s for isothermal phase change, and the wire rod finished product is obtained after the wire rod is taken off line.

Comparative example 5:

The manufacturing method of the wire rod is different from the manufacturing method of the embodiment 2 in that the online salt bath strong tempering control wire rod is cooled to a pearlite area at a cooling speed of 35 ℃/s for isothermal phase transition, the molten salt temperature is 630 ℃, the roller way slow cooling procedure control wire rod is cooled at a cooling speed of 0.2 ℃/s, the slow cooling time is 1200s, and the wire rod is cooled to 390 ℃; and obtaining a finished product of the wire rod after off-line.

Comparative example 6:

the manufacturing method of the wire rod is different from the manufacturing method of the embodiment 2 in that the online salt bath strong tempering control wire rod is cooled to a pearlite area at a cooling speed of 44 ℃/s to perform isothermal phase change, the molten salt temperature is 560 ℃, and a wire rod finished product is obtained after the wire rod is taken off line.

Example 3:

The 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod manufacturing method comprises the following chemical components in percentage by mass: c:0.83%, si:0.4%, mn:0.37%, al:0.18%, cr:0.15%, P:0.012%, S:0.015 percent of Fe and unavoidable impurities, and the manufacturing method comprises the following steps of high-temperature rolling, wire laying, on-line strong tempering in salt bath, roller way slow cooling and coil collecting, and the specific steps are as follows:

The high-temperature rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote homogenization of steel billet components, avoid burning loss and decarburization risk, roll the steel billets which are discharged from the heating furnace into wires with the diameter of 18mm through a rolling line after heating the steel billets with the high-temperature rolling plasticity, improve rolling speed, reduce deformation resistance of the steel billets and abrasion to the rolling line by adopting the high-temperature rolling, refine original austenite grains by matching with larger reduction, and is specific: the heating furnace adopts the preheating, heating and soaking procedures with sequential heating, the temperature of the heating furnace is controlled to 1145 ℃, the soaking time is controlled to 3.5h, the initial rolling temperature is 1095 ℃, the initial rolling reduction is 36%, the finishing rolling temperature is 990 ℃, and the finishing rolling reduction is 40%.

The wire rod of rolling line is used for going out to the silk process, is the wire rod through the silk machine of spouting, and the wire rod spreads on the roll table and follows the roll table and carry, selects higher silk temperature of spouting for use, is used for improving the supercooling degree of wire rod in the strong tempering of online salt bath later, and effectively shortens the dwell time in net carbon region, and is specific: the laying temperature was controlled to 965 ℃.

The online salt bath strong tempering adopts a salt bath tank with molten salt arranged therein, wire rods after spinning are conveyed through the salt bath tank by a roller way, are rapidly cooled to the molten salt temperature, the front-end molten salt circulation amount of the salt bath tank is controlled to be larger than the rear-end molten salt circulation amount, the wire rods are cooled to a pearlite phase region at a cooling speed of 40 ℃/s to carry out isothermal phase transformation, a precipitation temperature interval of secondary cementite is rapidly passed, a network carbon deterioration phase caused by overhigh carbon element is eliminated, the use value of the carbon element is improved, simultaneously, a larger supercooling degree is formed by using a larger front-end molten salt circulation amount, a small amount of austenitic tissue is promoted to be converted into a sorbite tissue with finer lamellar spacing, the supercooling degree is properly reduced by using a smaller rear-end molten salt circulation amount, unconverted high-temperature austenite is controlled to enter the pearlite phase region to carry out isothermal phase transformation to form a pearlite tissue, and meanwhile, the tempering softening of the sorbite tissue and the pearlite tissue is promoted, and the following characteristics are promoted: the molten salt temperature is controlled to be 600 ℃, the treatment time is 650s, the front molten salt circulation amount is 800t/h, the front molten salt temperature rise is less than or equal to 10 ℃, the rear molten salt circulation amount is 300t/h, and the rear molten salt temperature rise is less than or equal to 5 ℃.

The roller way slow cooling procedure adopts to close the heat preservation cover, the wire rod coming out of the salt bath is conveyed by the roller way to enter the heat preservation cover, hot air above the salt bath is led into the heat preservation cover for slow cooling treatment, and further softening of wire rod tissues is promoted, specifically: controlling the wire rod to be cooled at a cooling speed of 0.3 ℃/s, wherein the slow cooling time is 790s, and the wire rod is cooled to 363 ℃; 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:

The manufacturing method of the wire rod is different from the manufacturing method of the embodiment 3 in that the processing time of the on-line salt bath strong tempering is 400s, and the finished wire rod product is obtained after off-line.

Comparative example 8:

The manufacturing method of the wire rod is different from the manufacturing method of the embodiment 3 in that the processing time of the on-line salt bath strong tempering is 780s, and the finished wire rod product is obtained after the wire rod is taken off.

Example 4:

The 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod manufacturing method comprises the following chemical components in percentage by mass: c:0.86%, si:0.43%, mn:0.42%, al:0.3%, cr:0.35%, P:0.014%, S:0.012 percent of Fe and unavoidable impurities, and the manufacturing method comprises the following steps of high-temperature rolling, wire laying, on-line strong tempering in salt bath, roller way slow cooling and coil collecting, and the specific steps are as follows:

The high-temperature rolling is used for heating steel billets with the specification of 220mm multiplied by 220mm through a heating furnace to promote homogenization of steel billet components, avoid burning loss and decarburization risk, roll the steel billets which are discharged from the heating furnace into wires with the diameter of 26mm through a rolling line after heating the steel billets with the high-temperature rolling plasticity, improve rolling speed, reduce deformation resistance of the steel billets and abrasion to the rolling line by adopting the high-temperature rolling, refine original austenite grains by matching with larger reduction, and is specific: the heating furnace adopts the preheating, heating and soaking procedures with sequential heating, the temperature of the heating furnace is controlled to be 1155 ℃, the soaking time is controlled to be 4 hours, the initial rolling temperature is 1125 ℃, the initial rolling reduction is 33%, the final rolling temperature is 1000 ℃, and the final rolling reduction is 32%.

The wire rod of rolling line is used for going out to the silk process, is the wire rod through the silk machine of spouting, and the wire rod spreads on the roll table and follows the roll table and carry, selects higher silk temperature of spouting for use, is used for improving the supercooling degree of wire rod in the strong tempering of online salt bath later, and effectively shortens the dwell time in net carbon region, and is specific: the laying temperature was controlled at 975 ℃.

The online salt bath strong tempering adopts a salt bath tank with molten salt arranged therein, wire rods after spinning are conveyed through the salt bath tank by a roller way, are rapidly cooled to the molten salt temperature, the front-end molten salt circulation amount of the salt bath tank is controlled to be larger than the rear-end molten salt circulation amount, the wire rods are cooled to a pearlite phase region at a cooling speed of 38 ℃/s to carry out isothermal phase transformation, a precipitation temperature interval of secondary cementite is rapidly passed, a network carbon deterioration phase caused by overhigh carbon element is eliminated, the use value of the carbon element is improved, simultaneously, a larger supercooling degree is formed by using a larger front-end molten salt circulation amount, a small amount of austenitic tissue is promoted to be converted into a sorbite tissue with finer lamellar spacing, the supercooling degree is properly reduced by using a smaller rear-end molten salt circulation amount, unconverted high-temperature austenite is controlled to enter the pearlite phase region to carry out isothermal phase transformation to form a pearlite tissue, and meanwhile, the tempering softening of the sorbite tissue and the pearlite tissue is promoted, and the following characteristics are promoted: the molten salt temperature is controlled to be 625 ℃, the treatment time is 490s, the front molten salt circulation amount is 600t/h, the front molten salt temperature rise is less than or equal to 10 ℃, the rear molten salt circulation amount is 200t/h, and the rear molten salt temperature rise is less than or equal to 5 ℃.

The roller way slow cooling procedure adopts a closed heat preservation cover, the roller way is used for conveying the wire rods coming out of the salt bath into the heat preservation cover, slow cooling treatment is carried out, further softening of wire rod tissues is promoted, and the method is specific: the wire rod is controlled to be cooled at a cooling speed of 0.5 ℃/s, the slow cooling time is 500s, and the wire rod is cooled to 375 ℃; 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 9:

the manufacturing method of the wire rod is different from the manufacturing method of the embodiment 4 in that the circulation amount of the front molten salt of the on-line salt bath strong tempering is 450t/h, the circulation amount of the rear molten salt is 450t/h, and the finished wire rod product is obtained after the wire rod is taken off.

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 high-temperature rolling, spinning, on-line salt bath strong tempering, air cooling and coil collecting, specifically: the heat preservation cover is opened in the air cooling, the wire rods coming out of the salt bath are conveyed by the roller way to be subjected to air cooling, the wire rods are controlled to be cooled for 125 seconds at the cooling speed of 2 ℃/s, and the wire rods are cooled to 375 ℃, and the finished wire rod products are obtained after the wire rods are taken off line.

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 cold heading steel wire rod disclosed by the invention has the advantages that through the design of high C-Si-Mn-Al-Cr components, a microstructure does not contain bainite or martensite hard and brittle phases, tempered pearlite is mainly used, a small amount of tempered sorbite, ferrite and fused pearlite are used, the tensile strength of 1115-1165 MPa and the area reduction rate of 47% -52% can be achieved, the performance grade of a 15.9-grade fastener can be achieved through direct drawing, cold heading and tempering heat treatment under the condition that an annealing process is omitted, and the cold heading steel wire rod has good market application prospect.

As can be seen from the comparison result of the embodiment 2 and the comparative example 4, the higher spinning temperature is selected to improve the supercooling degree of the wire rod in the subsequent on-line salt bath strong tempering treatment, the high-speed heat exchange capability of molten salt is utilized to control the wire rod to carry out isothermal diffusion phase transformation to form sorbite, and uncontrollable degradation factors of the reticular carbide can be eliminated; as can be seen from the comparison result of example 2 and comparative example 5, the higher the molten salt temperature is, the larger the spacing between the sorbite and pearlite sheets formed by phase transformation is, the higher the ferrite ratio is, and more thermal power can be provided for softening the matrix, but the higher the molten salt temperature is, the larger supercooling degree is difficult to form, and the defects of forming the sorbite with finer spacing between the sheets and inhibiting the network carbon are overcome, so that the strength and the drawing performance of the matrix are reduced; as is apparent from the comparison between the example 2 and the comparative example 6, the lower the molten salt temperature, the finer the spacing between the sorbite and pearlite structure sheets formed by the phase transformation, the higher the matrix strength and the lower the plasticity, but the lower the molten salt temperature, the higher the tempered sorbite ratio and the adverse effect on the plasticity improvement of the wire rod.

As can be seen from the comparison result of the example 3 and the comparative example 7, the sorbite and the pearlite obtained after too short treatment time can not be softened, the dislocation density is higher, the plasticity is unfavorable, and the risks of drawing broken wire and cold heading cracking are easily caused by stress concentration and drawing hardening; as can be seen from the comparison between the results of example 3 and comparative example 8, the longer the treatment time, the better the tempering softening effect after the phase transformation is completed, the lower the structural stress and dislocation density of tempered sorbite and tempered pearlite are, the strength of the wire rod is reduced, the plasticity is increased, but the longer the treatment time is, the strength of the wire rod is lost due to excessive tempering softening, and the precipitation roughening of Cr can obviously reduce the strength and plasticity performance.

As can be seen from the comparison result of the embodiment 4 and the comparative example 9, the front end molten salt circulation amount is consistent with the rear end molten salt circulation amount, the formed sorbite structure is smaller, the interlayer spacing is thicker, and the structure regulation and control are unfavorable, and the phase change regulation and control of sorbite and pearlite can be realized in an online salt bath strong tempering process by further controlling the molten salt circulation amount difference of the front end and the rear end, so that the process is simplified; as can be seen from the comparison of the results of example 4 and comparative example 10, the softening effect of the wire rod at high temperature can be continued by low-speed cooling using the roller way slow cooling, further promoting tissue softening and plastic promotion.

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, for example: the billet can be obtained by sequentially carrying out converter smelting, refining and continuous casting procedures on steel-making raw materials; controlling the front-end molten salt circulation amount and the rear-end molten salt circulation amount: the device and the process for online heat treatment of high-speed wire based on energy recycling as disclosed in patent CN116287664B can be adopted, wherein the circulating position of a quick cooling tank or an isothermal tank is designed, and a molten salt circulating pipeline and a temperature detection device are respectively arranged at the front end and the rear end of a salt bath for online strong tempering of the salt bath along the conveying direction so as to respectively control the circulating amount of the molten salt at the front end, the circulating amount of the molten salt at the rear end and the temperature rise of the molten salt, so that equivalent embodiments or changes which do not depart from the spirit of the present invention are included in the protection scope of the present invention.

Claims (10)

1. The 15.9-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:0.82% -0.86%, si:0.30% -0.45%, mn:0.22% -0.42%, al:0.10% -0.30%, cr: 0.15-0.35%, P not more than 0.015%, S not more than 0.015%, and the balance Fe and unavoidable impurities, wherein the microstructure comprises 74-80% by volume of tempered pearlite, 14-20% by volume of tempered sorbite, and the balance ferrite and fused pearlite.

2. The 15.9-grade annealing-free hot-rolled high-carbon cold-heading steel wire rod according to claim 1, wherein the lamellar spacing of tempered pearlite is 165-205 nm, the lamellar spacing of tempered sorbite is 90-130 nm, the volume percentage of ferrite is less than or equal to 5%, and the net-shaped carbide of the cold-heading steel wire rod is grade 0.

3. The 15.9-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 12.0-26.0 mm, the tensile strength is 1115-1165 mpa, and the reduction of area is 47% -52%.

4. The manufacturing method of the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized by comprising the following steps of:

The 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is rolled to produce a wire rod according to chemical components, the wire rod is subjected to on-line salt bath strong tempering after being spun into the wire rod according to the spinning temperature of more than or equal to 960 ℃, the front molten salt circulation amount of the on-line salt bath strong tempering is controlled to be larger than the rear molten salt circulation amount, the wire rod is cooled to a pearlite area at a cooling speed of more than or equal to 38 ℃/s to carry out isothermal transformation, the wire rod is controlled to form a sorbite structure and a pearlite structure, the sorbite structure and the pearlite structure are promoted to be tempered and softened, and finally, the wire rod is subjected to roller way slow cooling to prepare the cold heading steel wire rod of which the microstructure comprises 74-80% by volume of tempered pearlite, 14-20% by volume of tempered sorbite and the balance ferrite and fused pearlite.

5. The manufacturing method of the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized in that the temperature of a heating furnace is controlled to be less than or equal to 1155 ℃ before rolling, the soaking time is 3-4 h, and the furnace time is less than or equal to 6h.

6. The method for manufacturing the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which is characterized in that high-temperature rolling is adopted during rolling, the initial rolling temperature is controlled to be 1085-1125 ℃, the initial rolling reduction is controlled to be 33-38%, the final rolling temperature is less than or equal to 1000 ℃, and the final rolling reduction is controlled to be 32-42%.

7. The method for manufacturing the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod according to any one of claims 4-6, wherein the molten salt temperature of the on-line salt bath strong tempering is 590-625 ℃, and the treatment time is 490-740 s.

8. The manufacturing method of the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized in that the front-end molten salt circulation amount of the online salt bath strong tempering is 600-900 t/h, the front-end molten salt temperature rise is controlled to be less than or equal to 10 ℃, the rear-end molten salt circulation amount is controlled to be 200-400 t/h, and the rear-end molten salt temperature rise is controlled to be less than or equal to 5 ℃.

9. The manufacturing method of the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod is characterized in that the roller way slow cooling is performed by closing a heat preservation cover, the wire rod is controlled to be cooled at a cooling speed of 0.2-0.5 ℃/s, and the slow cooling time is more than or equal to 500s.

10. The method for manufacturing the 15.9-grade annealing-free hot-rolled high-carbon cold heading steel wire rod, which is characterized in that the roller way slow cooling is realized by introducing hot air above an online salt bath strong tempering salt bath into a heat preservation cover.