On-line tempering Soxhlet type 10.9-grade non-quenched and tempered cold heading steel wire rod and manufacturing method thereof

Abstract

The invention provides an online tempering Soxhlet type 10.9-grade non-quenched and tempered cold heading steel wire rod and a manufacturing method thereof, and belongs to the technical field of steel smelting, the hot rolling wire rod comprises the following chemical components in percentage by mass: 0.27-0.33% of C, 0.10-0.30% of Si, 0.9-1.2% of Mn, 0.10-0.30% of Cr, less than or equal to 0.015% of P, less than or equal to 0.015% of S, 0.0010-0.0040% of B, 0.02-0.06% of Ti, 0.02-0.06% of Al, less than or equal to 0.0045% of N and the balance of Fe and inevitable impurities, and Ti / N is greater than or equal to 3.4; and the microscopic structure is a tempered sorbite structure. A C-Mn component design is adopted, on-line salt bath quenching and heat preservation gallery on-line annealing are carried out, the plasticity of the wire rod is remarkably improved, meanwhile, by adding B, the grain boundary is strengthened, the whole material obtains high-strength plasticity, and follow-up straight pulling and large-deformation cold heading are ensured.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel smelting, and particularly relates to an on-line tempering sorbite type 10.9-grade non-quenched and tempered cold heading steel wire rod and a manufacturing method thereof. BACKGROUND

[0002] In modern industrial production, the cold heading steel wire rod as a key master batch for manufacturing fasteners has a decisive influence on the quality and production efficiency of the fasteners. Especially in the current rapid development of the automobile and mechanical manufacturing industries, the demand for 10.9-grade high-strength fasteners is increasing, which also promotes the continuous improvement of the performance requirements of the cold heading steel wire rod. In the traditional production of 10.9-grade fasteners, the cold heading steel wire rod needs to be drawn for multiple times, spheroidized annealed, cold headed and formed, and quenched and tempered so as to reach the corresponding performance grade. Although spheroidizing annealing can improve the plasticity of the wire rod and reduce the risk of cold heading cracking, both the quenching and tempering and the spheroidizing annealing have problems of high energy consumption, high cost and low efficiency, which are not conducive to the demand for low-carbon, green and sustainable development.

[0003] From the material composition system, carbon component system materials need alloying treatment to improve the strength of the rod to meet the production needs of high-strength fasteners. However, alloying not only brings the increase of material cost, but also generally needs spheroidizing annealing treatment before drawing, which has high overall cost and long production cycle. For example, CN115874105A, a production method of high fatigue life fastener SCM435 cold heading steel, adds 0.95% Cr and 0.18% Mo elements in the component design, which has high overall alloy cost and needs spheroidizing annealing and quenching and tempering treatment in the processing process. Patent CN115386802B discloses a non-quenched and tempered steel for 10.9 grade large size wind power bolt and a production method thereof, which adopts high Mn C-Si-Mn-Cr-Mo-Nb-Ti-B-Al multi-alloying component design, and obtains full granular bainite (upper bainite structure) through low temperature rolling and strong air cooling. Patent CN117265362A discloses a production method of non-quenched and tempered rod for 10.9 grade high plasticity standard parts, which adopts C-Si-Mn-Cr-V component design and slow cooling process after low temperature wire drawing, and obtains fine sorbite / troostite and ferrite structure, so as to achieve tensile strength of 800 MPa and reduction of area ≥52%. Patent CN116904877A discloses a cold-drawn steel wire for 10.9 grade non-quenched U-shaped bolt and a manufacturing method thereof, which adopts C-Si-Mn-Cr-Nb component design and water bath cooling process after low temperature wire drawing, and obtains ferrite + sorbite structure, so as to achieve tensile strength greater than 800 MPa and reduction of area greater than 55%. The initial strength of the rod is low, and it needs to be deformed by large drawing to improve the strength by cold deformation strengthening, so as to improve the strength grade of the non-quenched fastener. However, the poor plasticity of the rod makes the cold heading cracking risk extremely high, and the rod can only be used for U-shaped bolts, long rod bolts and the like, so the overall application is limited. CN117265408 A, a non-annealing cold heading steel and a manufacturing method thereof and a fastener obtained by the method, contains Al, Cr, Mo, B and other elements in the rod, and the metallographic structure is ferrite + degenerated pearlite. Although the rod is drawn without annealing, the rod needs to be quenched and tempered to ensure the final strength performance of the fastener, which increases the overall cost and causes problems such as poor straightness of the bolt after quenching and tempering and decarburization.

[0004] Based on the deficiencies of the prior art, a high-strength plastic rod is developed to meet the production requirements of 10.9 grade high-strength fasteners, and an online tempering sorbite type cold heading steel rod and a production method thereof are developed to become the key problems to be solved in the current fastener manufacturing field. The present application aims to overcome the problems in the prior art through innovative component design and unique production process, and realize the green, efficient and low-cost production of 10.9 grade high-strength fasteners. SUMMARY

[0005] To solve the technical problems in the background art, the application provides an online tempering sorbite type 10.9 grade non-quenched and tempered cold upsetting steel wire rod and a manufacturing method thereof.

[0006] To achieve the above-mentioned purposes, the application adopts the following technical scheme: an online tempering sorbite type 10.9 grade non-quenched and tempered cold upsetting steel wire rod, the chemical composition and mass percentage of the hot-rolled wire rod include: C: 0.27-0.33%, Si: 0.10-0.30%, Mn: 0.9-1.2%, Cr: 0.10-0.30%, P≤0.015%, S≤0.015%, B: 0.0010-0.0040%, Ti: 0.02-0.06%, Al: 0.02-0.06%, N≤0.0045%, the rest is Fe and inevitable impurities, and Ti / N≥3.4; and the microstructure is a tempering sorbite structure.

[0007] The chemical composition and mass percentage of the above-mentioned hot-rolled wire rod are designed according to the following: (1) Carbon: C is added as a main strengthening element, which is lower in cost than other alloy elements, effectively plays a solid solution strengthening role, and ensures the strength and hardenability of the steel. However, with the increase of the carbon content, the plasticity of the steel will decrease, and the decarburization sensitivity and carbide coarsening risk of medium and high carbon steel will increase. Therefore, in order to ensure the high strength and plasticity deformation ability of the 10.9 grade non-quenched fastener, the mass percentage of C is controlled to be 0.27%-0.33%.

[0008] (2) Silicon: a small amount of Si exists in ferrite at room temperature, which can strengthen the strength of ferrite, but excessive Si will reduce the plasticity of the wire rod. However, adding a small amount of Si can appropriately deoxidize, improve the final deoxidization effect of Al element, and be beneficial to improving the oxidation inclusions in the steel. Therefore, the mass percentage of Si is controlled to be 0.10%-0.30%.

[0009] (3) Manganese: Mn is a main solid solution strengthening element, which can effectively improve the strength of the wire rod, effectively increase the grain boundary area, provide more interfaces for carbide spheroidization, and indirectly reduce the tempering temperature; at the same time, Mn can expand the austenite phase region, delay the pearlite transformation, and promote the martensite transformation, but excessive content will increase the spheroidization difficulty. Therefore, in order to balance the strength and plasticity of the steel, the mass percentage of Mn is controlled to be 0.9%-1.2%.

[0010] (4) Chromium: Cr element is a ferrite forming element, which can improve the hardenability of the steel, strengthen the strength of the body-centered cubic matrix, significantly promote the dispersion of carbides, reduce the atomic diffusion distance required for spheroidization, reduce the annealing temperature by 50-100℃, and shorten the tempering time by 20%-30%. Therefore, 0.10%-0.30% of Cr is added.

[0011] (5) Titanium: Forming fine titanium nitride (TiN) as spheroidization core, reducing carbon diffusion activation energy, indirectly reducing tempering temperature. At the same time, avoiding N and B combination, improving the hardenability effect of B element. But excessive Ti element will form micron-sized large particle TiN, resulting in a substantial reduction in fatigue and low temperature impact performance, so the mass percentage of Ti is controlled at 0.02 - 0.06%.

[0012] (6) Aluminum: Al is an effective deoxidizer, Al can reduce the formation of cementite (Fe3C), improve ferrite stability, and achieve grain refinement. At the same time, the solid solution strengthening effect of Al element is significant, which can improve the strength of steel. But too high Al can reduce the toughness of the material, so the mass percentage of Al is controlled at 0.02 - 0.06%.

[0013] (7) Boron: B element can improve the hardenability, which is beneficial to accelerate the transformation of austenite to martensite, and can also strengthen the grain boundary and inhibit the segregation of P and S elements at the grain boundary, thereby improving the fatigue performance of the material. However, excessive boron is prone to cause thermal embrittlement, so the mass percentage of B is controlled at 0.0010 - 0.0040%.

[0014] (8) Nitrogen: N element can cause aging embrittlement, and free nitrogen (solid solution state) can interact with dislocations, resulting in room temperature brittleness (blue brittleness phenomenon). Therefore, it is necessary to reduce the nitrogen content as much as possible, and form TiN with Ti to avoid combination with B, so as to reduce the effective B content. However, considering the cost factor, the mass percentage of nitrogen is controlled at N≤0.0045%.

[0015] (9) Phosphorus and sulfur: P and S elements are impurity elements, which are prone to segregate at the grain boundary, increase the cold and hot brittleness of steel, and reduce the plasticity of the material. Therefore, the mass percentage of P and S is controlled at P, S≤0.015%.

[0016] The above cold heading steel wire rod adopts C-Mn composition design basis, C as the main additive element instead of Cr, Mo, Ni and other strong hardenability elements, which can significantly reduce the cost of the material and ensure that the performance grade of 10.9 level fastener can be reached after cold working. Combined with austenite forming elements Mn, B to expand the austenite phase region, Cr to inhibit ferrite precipitation, the hardenability of the material is greatly improved. And the combination of Cr, Mn and Ti elements greatly reduces the tempering temperature and time, providing a design basis for online tempering.

[0017] The cold heading steel wire rod converts martensite to tempered sorbite after tempering, the dislocation density is greatly reduced, the deformation resistance is greatly weakened, spherical cementite is precipitated and uniformly distributed on the plastic matrix, the organizational stress is further reduced and improved, there is no martensite, upper bainite and other organizations that are not conducive to cold heading, and the online tempering temperature and time can be adjusted to realize the matching of high strength and plasticity of the wire rod.

[0018] The application also relates to a manufacturing method of an online tempering sorbite type 10.9 grade non-tempered cold upsetting steel wire rod, which comprises the following steps in sequence: (1) smelting of molten steel: smelting raw materials are subjected to KR desulfurization, converter smelting, LF refining and vacuum degassing in sequence, S≤0.008% after KR desulfurization, P≤0.010% when the converter is tapped, slag is added when the converter is tapped, the slag is used for removing inclusions and deoxidizing alloying during the LF refining process, aluminum blocks and titanium-iron cored wires are added in sequence after the formation of a reducing slag, and the molten steel is allowed to stand for more than 25 minutes after the vacuum degassing is completed; (2) preparation of a blank: the molten steel meeting the element composition design is cast into a billet, and the billet is subjected to skinning treatment and magnetic powder detection; (3) heating of the billet: the billet is uniformly sprayed with an anti-decarburization coating before being put into a furnace, and the heating section and the soaking section are heated at a temperature of 1100-1200 ℃, so that the structure is re-heated to completely austenitize the structure and fully diffuse and homogenize carbon and manganese; (4) wire rod rolling: the finish rolling temperature is controlled to be 820-850 ℃, the reducing rolling temperature is controlled to be 790-820 ℃, rolling is performed in the austenite-ferrite phase region, the total deformation amount of temperature-controlled rolling is 90%-120%, and the wire rod drawing temperature is controlled to be 770-810 ℃; (5) cooling of the wire rod: the wire rod after drawing is cooled in a QM online salt bath within 7s, the temperature of the salt bath molten salt is 300-310 ℃, the cooling speed is greater than 50 ℃ / s, the wire rod is uniformly cooled in the QM salt bath tank, the cooling time is ≥20s, the wire rod does not appear reverse temperature after being taken out of the salt bath tank, and the coil is collected on a Stelmor roller within 20s, and the coil temperature is ≥280 ℃; (6) the wire rod after being collected is heated in an online heat preservation corridor heating area within 30s, the temperature of the heat preservation corridor heating area is controlled to be 500-520 ℃, the wire rod slowly runs in the heat preservation corridor heating area for 60-80 min, so that the wire rod is uniformly heated in the heating area, the subsequent coil slowly runs in the heat preservation corridor cooling area, is cooled to below 300 ℃ within 20-30 min, is taken out of the heat preservation corridor for air cooling, sampling detection and packaging.

[0019] Preferably, in the molten steel smelting, alloys are added when the converter is tapped, and the alloys are low-carbon manganese iron and low-carbon chromium iron for adjusting the content of Mn and Cr in the molten steel.

[0020] Preferably, in the preparation of the blank, the molten steel is cast into a billet by a continuous casting machine, the superheat of the molten steel is controlled to be 10-25 ℃, the billet is cast by the continuous casting tundish under the whole-process argon protection, and the argon sealing pressure is 1.1-1.3 atm.

[0021] Preferably, in the billet heating stage, the heating is carried out by using a heat exchange step-by-step heating furnace, the temperature of the preheating section of the heating furnace is controlled to be ≤680℃, and the total heating time is controlled to be 110-160 min; after the billet is heated, high-pressure water is used to remove phosphorus, the phosphorus removal pressure is ≥21 MPa, and after the phosphorus removal, rolling is carried out.

[0022] Preferably, in the wire rod cooling stage, the roller way speed of the Stelmor cooling line is 0.5-0.8 m / s.

[0023] Preferably, the mechanical properties of the obtained non-quenched cold-upset steel wire rod are as follows: yield strength 790-820 MPa, tensile strength 880-910 MPa, elongation 26-29%, reduction of area 74-77%, and room temperature Kv2 impact energy 88-103 J.

[0024] Preferably, after the obtained non-quenched cold-upset steel wire rod is drawn with a reduction of area of 26-33%, the yield strength of the steel wire is 930-980 MPa, the tensile strength is 1042-1078 MPa, the elongation is ≥19%, the reduction of area is ≥66%, and the room temperature Kv2 impact energy is 59-75 J.

[0025] Compared with the prior art, the advantages and positive effects of the present application are as follows: the C-Mn component design is adopted, and the cold-upset steel wire rod is quenched and annealed in an online salt bath and an online annealing holding corridor, the microstructure is tempered sorbite, compared with upper bainite or ferrite + tempered martensite, the plasticity of the wire rod is significantly improved, meanwhile, the addition of B strengthens the grain boundary, the material as a whole obtains high strength and plasticity, and the subsequent direct drawing and large deformation cold-upset are ensured; the mechanical properties of the obtained non-quenched cold-upset steel wire rod are as follows: yield strength 790-820 MPa, tensile strength 880-910 MPa, elongation 26-29%, reduction of area 74-77%, and room temperature Kv2 impact energy 88-103 J; after the obtained non-quenched cold-upset steel wire rod is drawn with a reduction of area of 26-33%, the yield strength of the steel wire is 930-980 MPa, the tensile strength is 1042-1078 MPa, the elongation is ≥19%, the reduction of area is ≥66%, and the room temperature Kv2 impact energy is 59-75 J. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is the tempered sorbite microstructure of the wire rod in Example 1 of the present application.

[0027] Figure 2 It is the tempered sorbite microstructure of the wire rod in Example 2 of the present application.

[0028] Figure 3 It is the tempered sorbite microstructure of the wire rod in Example 3 of the present application.

[0029] Figure 4 Microstructure of upper bainite of the wire rod in the present application comparative example 1.

[0030] Figure 5 Microstructure of sorbite + pearlite + ferrite of the wire rod in the present application comparative example 2. DETAILED DESCRIPTION

[0031] In order to enable persons skilled in the art to more clearly understand the above-mentioned objects, features and advantages of the present application, the present application will be further described below through examples. It should be noted that the examples of the present application and the features in the examples can be combined with each other without conflict.

[0032] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other ways different from those described herein, therefore, the present application is not limited to the specific examples disclosed in the following description. Example 1

[0033] The present example provides a manufacturing method for an online tempering sorbite type 10.9 grade non-quenched and tempered cold upsetting steel wire rod, the online tempering sorbite type 10.9 grade non-quenched and tempered cold upsetting steel wire rod contains the following elements and weight percentages: C: 0.30%, Si: 0.15%, Mn: 0.98%, P: ≤0.012%, S: ≤0.010%, Cr: 0.15%, Ti: 0.04%, Al: 0.04%, B: 0.0025%, N ≤0.0028%, and the balance is Fe and unavoidable impurity elements. The wire diameter is 13.0 mm, and the process flow is as follows: (1) Molten steel smelting: the main raw materials are sequentially subjected to KR desulfurization, converter smelting, LF + RH external refining, S ≤0.008% after KR desulfurization, P ≤0.010% at the time of converter tapping, slag is added at the time of converter tapping, the slag is used for removing inclusions and deoxidizing alloying during refining, low-carbon ferromanganese and low-carbon chromium iron are added at the time of converter tapping to adjust the content of Mn and Cr in the molten steel, aluminum blocks and titanium-iron cored wires are sequentially added before tapping at the LF refining, after RH refining, the molten steel is placed for 28 minutes, and then cast into a continuous casting billet, the molten steel is cast into a continuous casting billet using 15℃ high superheat argon protection, and the billet is slowly cooled and then subjected to surface treatment.

[0034] (2) Billet preparation: the molten steel meeting the element composition design is cast into a steel billet, and the steel billet is subjected to skinning treatment + magnetic powder detection.

[0035] (3) Billet heating: the steel billet is uniformly sprayed with anti-decarburization coating before entering the furnace, and is heated in a heat exchange step-by-step heating furnace, the temperature in the preheating section is controlled at 680°C, the temperature in the heating section and the soaking section after entering the furnace is heated at 1130-1180°C, and the temperature is kept for 140 min before leaving the furnace, so as to reheat the structure to make the structure fully austenitized, and carbon, manganese and the like are fully diffused and uniform.

[0036] (4) Wire rod rolling: the temperature in the finishing rolling is controlled at 830°C, the temperature in the reducing sizing rolling is controlled at 810°C, rolling is performed in the austenite-ferrite phase region, the total deformation amount of the temperature-controlled rolling is 110%, and the wire rod drawing temperature is controlled at 790°C.

[0037] (5) Wire rod cooling: the wire rod after drawing is cooled in a QM online salt bath within 6s, the temperature of the salt bath molten salt is 305°C, the cooling speed is greater than 50°C / s, the wire rod is uniformly cooled in the QM salt bath tank, the cooling time is 25s, the wire rod does not appear reverse temperature after leaving the salt bath tank, and the coil temperature is 285°C after the wire rod is collected on the Stelmor roller within 16s.

[0038] (6) The wire rod after coiling is slowly run in an online heat preservation corridor heating area within 26s, the temperature in the heat preservation corridor heating area is controlled at 510°C, the wire rod slowly runs in the heat preservation corridor heating area for 70 min to ensure that the wire rod is uniformly heated in the heating area, and the subsequent coil slowly runs in the heat preservation corridor cooling area, and is cooled to below 300°C within 25 min, and then is air cooled, sampled, and packaged.

[0039] The yield strength of the obtained hot-rolled wire rod is 799 MPa, the tensile strength is 902 MPa, the elongation is 28%, the reduction of area is 76%, and the room temperature KV2 impact energy is 95 J. After 28% area reduction wire drawing, the yield strength of the steel wire is 971 MPa, the tensile strength is 1061 MPa, the elongation is 21%, the reduction of area is 68%, the room temperature KV2 impact energy is 68 J, and the structure is tempered sorbite. The specific structure is shown in Figure 1 . Example 2

[0040] The embodiment provides a manufacturing method of an online tempered sorbite type 10.9 grade non-quenched and tempered cold upsetting steel wire rod, the online tempered sorbite type 10.9 grade non-quenched and tempered cold upsetting steel wire rod contains the following elements and the weight percentage is as follows: C: 0.31%, Si: 0.13%, Mn: 1.02%, P: ≤0.013%, S: ≤0.009%, Cr: 0.16%, Ti: 0.04%, Al: 0.04%, B: 0.0028%, N ≤0.0031%, and the balance is Fe and inevitable impurity elements. The wire diameter is 12.0 mm, and the process flow is as follows: (1) Steel smelting: the main raw materials successively pass through KR desulfurization, converter smelting, LF+RH external refining, S≤0.008% after KR desulfurization, P≤0.010% when the converter is tapped, slag is added when the converter is tapped, the slag is used to remove inclusions and deoxidize alloying during refining, low-carbon ferromanganese and low-carbon ferrochrome are added when the converter is tapped to adjust the content of Mn and Cr in the molten steel, aluminum blocks and titanium-iron cored wires are successively added before tapping in the LF refining, the molten steel is kept for 27 minutes after the RH refining is completed, and then is sent to a continuous casting machine for casting, the molten steel is cast into a continuous casting billet by using 24℃ high superheat and argon protection throughout the casting process, and the billet is slowly cooled after the billet is slowly cooled for surface treatment.

[0041] (2) Billet preparation: the molten steel meeting the element composition design is cast into a steel billet, and the steel billet is subjected to skinning treatment and magnetic powder detection.

[0042] (3) Billet heating: the steel billet is uniformly sprayed with anti-decarburization coating before entering the furnace, is heated by using a heat exchange step-by-step heating furnace, the temperature in the preheating section is controlled at 650℃, the temperature in the heating section and the soaking section after entering the furnace is controlled at 1135-1184℃, and the billet is kept for 145 minutes before being taken out of the furnace, so as to reheat the structure to make the structure completely austenitized and carbon and manganese fully diffuse and uniform.

[0043] (4) Wire rod rolling: the finish rolling temperature is controlled at 827℃, the reducing diameter rolling temperature is controlled at 807℃, the wire rod is rolled in the austenite-ferrite phase region, the total deformation amount of the temperature-controlled rolling is 120%, and the wire rod laying temperature is controlled at 785℃.

[0044] (5) Wire rod cooling: the wire rod after laying is put into a QM online salt bath extreme cooling within 6s, the temperature of the salt bath molten salt is 307℃, the cooling speed is greater than 50℃ / s, the wire rod is uniformly cooled in the QM salt bath tank, the cooling time is 25s, the wire rod does not appear reverse temperature after being taken out of the salt bath tank, and the coil temperature is 284℃ after the wire rod is collected by a Stelmor roller within 16s.

[0045] (6) The wire rod after being collected is put into an online heat preservation corridor heating section within 25s, the temperature of the heat preservation corridor heating section is controlled at 505℃, the wire rod slowly runs in the heat preservation corridor heating section for 70 minutes to ensure that the wire rod is uniformly heated in the heating section, and the subsequent coil slowly runs in the heat preservation corridor cooling section, is cooled to below 300℃ within 25 minutes, and is taken out of the heat preservation corridor for air cooling, sampling detection and packaging.

[0046] The obtained hot-rolled wire rod has a yield strength of 805MPa, a tensile strength of 906MPa, an elongation of 28%, a reduction of area of 76%, and a room temperature KV2 impact energy of 98J. After 29% area reduction wire drawing, the steel wire has a yield strength of 966MPa, a tensile strength of 1059MPa, an elongation of 22%, a reduction of area of 68%, a room temperature KV2 impact energy of 70J, and a structure of tempered sorbite, and the specific structure is shown inFigure 2 . Example 3

[0047] The present example provides a manufacturing method for an online tempering sorbite type 10.9 grade non-quenched and tempered cold-upset steel wire rod, the online tempering sorbite type 10.9 grade non-quenched and tempered cold-upset steel wire rod containing the following elements and weight percentages: C: 0.32%, Si: 0.16%, Mn: 1.05%, P: ≤0.012%, S: ≤0.008%, Cr: 0.18%, Ti: 0.04%, Al: 0.04%, B: 0.0024%, N ≤0.0038%, and the balance being Fe and inevitable impurity elements. The wire rod has a diameter of 15.0 mm, and the process flow is as follows: (1) Molten steel smelting: the main raw materials are sequentially subjected to KR desulfurization, converter smelting, LF+RH external refining, S ≤0.008% after KR desulfurization, P ≤0.010% at the time of converter tapping, slag is added at the time of converter tapping, the slag is used for removing inclusions and deoxidizing alloying during refining, low-carbon ferromanganese and low-carbon ferrochrome are added at the time of converter tapping to adjust the content of Mn and Cr in the molten steel, aluminum blocks and titanium-iron cored wires are sequentially added before tapping at the LF refining, the molten steel is cast into a continuous casting billet after the molten steel is kept for 26 minutes after the RH refining is completed, the molten steel is cast into a continuous casting billet using 15 ℃ high superheat and argon protection throughout the process, and the billet is slowly cooled before surface treatment.

[0048] (2) Billet preparation: the molten steel meeting the element composition design is cast into a steel billet, and the steel billet is subjected to skinning treatment + magnetic powder detection.

[0049] (3) Billet heating: the steel billet is uniformly sprayed with anti-decarburization coating before entering the furnace, a heat exchange step-type heating furnace is used for heating, the temperature of the preheating section is controlled at 660 ℃, the heating section and the soaking section are heated at a temperature of 1140-1188 ℃ after entering the furnace, and the billet is taken out after being kept for 150 minutes, so that the structure is re-heated to completely austenitize the structure and fully diffuse carbon and manganese.

[0050] (4) Wire rod rolling: the temperature of finish rolling is controlled at 833 ℃, the temperature of reducing diameter rolling is controlled at 801 ℃, rolling is performed in the austenite-ferrite phase region, the total deformation amount of temperature-controlled rolling is 90%, and the wire rod temperature is controlled at 790 ℃.

[0051] (5) Wire rod cooling: the wire rod after wire drawing is cooled in a QM online salt bath within 6 seconds, the temperature of the salt bath molten salt is 304 ℃, the cooling speed is greater than 50 ℃ / s, the wire rod is uniformly cooled in the QM salt bath tank, the cooling time is 25 seconds, the wire rod does not appear reverse temperature after being taken out of the salt bath tank, and the wire rod is collected through a Stelmor roller within 16 seconds, and the coil temperature is 288 ℃.

[0052] (6) The coiled wire rod is fed into the on-line holding gallery heating zone at 25 s, the temperature of the holding gallery heating zone is controlled at 506 ℃, the wire rod slowly runs in the holding gallery heating zone for 70 min to ensure the wire rod is uniformly heated, and then the subsequent coiled wire rod slowly runs in the holding gallery cooling zone, and is cooled to below 300 ℃ within 25 min, and then is taken out of the holding gallery for air cooling, sampling detection, and packaging.

[0053] The obtained hot-rolled wire rod has a yield strength of 798 MPa, a tensile strength of 901 MPa, an elongation of 27%, a reduction of area of 75%, and a room temperature KV2 impact energy of 95 J. After 30% area reduction wire drawing, the steel wire has a yield strength of 959 MPa, a tensile strength of 1051 MPa, an elongation of 20%, a reduction of area of 68%, and a room temperature KV2 impact energy of 68 J, and the microstructure is tempered sorbite, and the specific microstructure is shown in Figure 3 .

[0054] Comparative Example 1 A method for manufacturing an on-line tempered sorbite type 10.9 grade non-quenched and tempered cold heading steel wire rod, which is different from that of Example 3 in that the temperature of the on-line molten salt quenching is controlled at 480 ℃, and the quenching treatment time is controlled at 60 s. The coiled wire rod is fed into the on-line holding gallery within 25 s, the temperature of the holding gallery heating zone is controlled at 506 ℃, the wire rod slowly runs in the holding gallery heating zone for 70 min to ensure the wire rod is uniformly heated, and then the subsequent coiled wire rod slowly runs in the holding gallery cooling zone, and is cooled to below 300 ℃ within 25 min, and then is taken out of the holding gallery for air cooling, sampling detection, and packaging.

[0055] In comparison with Example 3, the microstructure of the wire rod of Comparative Example 1 is lower bainite, the tensile strength is greater than 980 MPa, and the reduction of area is less than 65%, which is difficult to be drawn and cold headed. The specific microstructure is shown in FIG. 2. Figure 4 .

[0056] Comparative Example 2 A method for manufacturing an on-line tempered sorbite type 10.9 grade non-quenched and tempered cold heading steel wire rod, which is different from that of Example 3 in that the temperature of the on-line molten salt quenching is controlled at 580 ℃, and the quenching treatment time is controlled at 60 s. The coiled wire rod is fed into the on-line holding gallery within 25 s, the temperature of the holding gallery heating zone is controlled at 506 ℃, the wire rod slowly runs in the holding gallery heating zone for 70 min to ensure the wire rod is uniformly heated, and then the subsequent coiled wire rod slowly runs in the holding gallery cooling zone, and is cooled to below 300 ℃ within 25 min, and then is taken out of the holding gallery for air cooling, sampling detection, and packaging.

[0057] In comparison with Example 3, the wire rod of Comparative Example 2 has a structure of sorbite + pearlite + ferrite, the tensile strength is 680-720 MPa, the reduction of area is 68%-73%, and after 30% reduction of diameter by drawing, it is difficult to reach the requirement that the tensile strength of the finished wire is greater than 1000 MPa. The specific structure is shown in the following table. Figure 5 .

[0058] The above description is only the preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical content to equivalent embodiments applied to other fields, but any simple modification, equivalent change and modification of the above embodiments made according to the technical essence of the present application without departing from the technical solution content of the present application still belongs to the protection scope of the present application technical solution.

Claims

1. An on-line tempered sorbite type 10.9 grade non-quenched and tempered cold-upset steel wire rod, characterized in that, The hot-rolled wire rod has the following chemical components and mass percentages: C: 0.27-0.33%, Si: 0.10-0.30%, Mn: 0.9-1.2%, Cr: 0.10-0.30%, P≤0.015%, S≤0.015%, B: 0.0010-0.0040%, Ti: 0.02-0.06%, Al: 0.02-0.06%, N≤0.0045%, and the rest is Fe and inevitable impurities, and Ti / N≥3.4; and the microstructure is tempered sorbite.

2. A process for the production of an on-line tempered sorbite type 10.9 grade non- quenched and tempered cold heading steel wire rod, characterized in that, The method comprises the following steps in sequence: (1) Steel smelting: the smelting raw materials are sequentially subjected to KR desulfurization, converter smelting, LF refining, and vacuum degassing, S≤0.008% after KR desulfurization, P≤0.010% when the converter is tapped, and slag is added when the converter is tapped, the slag is used for removing inclusions and deoxidizing alloying during LF refining, and aluminum blocks and titanium-iron cored wires are sequentially added after the formation of reducing slag in the LF refining process, and the molten steel is statically placed for more than 25 minutes after vacuum degassing; (2) Billet preparation: the molten steel meeting the element component design is cast into a steel billet, and the steel billet is subjected to skinning treatment and magnetic powder detection; (3) Billet heating: the steel billet is uniformly sprayed with an anti-decarburization coating before being put into the furnace, and the heating section and the soaking section are heated at a temperature of 1100-1200 ℃, so as to reheat the structure, completely austenitize the structure, and fully diffuse and uniformly distribute carbon and manganese; (4) Wire rod rolling: the finish rolling temperature is controlled to be 820-850 ℃, the reducing diameter rolling temperature is controlled to be 790-820 ℃, rolling is performed in the austenite-ferrite phase region, the total deformation amount of temperature-controlled rolling is 90%-120%, and the wire rod drawing temperature is controlled to be 770-810 ℃; (5) Wire rod cooling: the wire rod after drawing is put into a QM online salt bath extreme cooling within 7s, the temperature of the salt bath molten salt is 300-310 ℃, the cooling speed is greater than 50 ℃ / s, the wire rod is uniformly cooled in the QM salt bath tank, the cooling time is greater than or equal to 20s, the wire rod does not appear reverse temperature after being taken out of the salt bath tank, and the wire rod is collected on a Stelmor roller within 20s, and the coil temperature is greater than or equal to 280 ℃; (6) The wire rod after being collected is put into an online heat preservation corridor heating area within 30s, the temperature of the heat preservation corridor heating area is controlled to be 500-520 ℃, the wire rod slowly runs in the heat preservation corridor heating area for 60-80 min, so as to ensure that the wire rod is uniformly heated in the heating area, the subsequent coil slowly runs in the heat preservation corridor cooling area, and is cooled to below 300 ℃ within 20-30 min, and then is taken out of the heat preservation corridor to be air cooled, sampled and detected, and packed.

3. A process for the production of on-line tempered sorbite type 10.9 grade non- quenched and tempered cold-upset steel wire rod as claimed in claim 2, wherein: In the steel smelting, an alloy is added when the converter is tapped, and the alloy is low-carbon ferromanganese and low-carbon ferrochrome to adjust the content of Mn and Cr in the molten steel.

4. The method for manufacturing online tempered sorbitic grade 10.9 non-quenched and tempered cold heading steel wire rod according to claim 2, characterized in that: In the billet preparation stage, the molten steel is cast into a steel billet by a continuous casting machine, the superheat degree of the molten steel is controlled to be 10-25 ℃, and the continuous casting tundish is used to cast the steel billet under the whole-process argon protection, and the argon sealing pressure is 1.1-1.3 atm.

5. The method for manufacturing online tempered sorbitic grade 10.9 non-quenched and tempered cold heading steel wire rod according to claim 2, characterized in that: In the billet heating stage, the billet is heated in a heat exchange step-by-step heating furnace, the temperature of the preheating section of the heating furnace is controlled to be ≤680℃, and the total heating time is controlled to be 110-160 min; after the billet is heated, high-pressure water is used to remove phosphorus, the pressure is ≥21 MPa, and then the billet is rolled.

6. The method for manufacturing online tempered sorbitic grade 10.9 non-quenched and tempered cold heading steel wire rod according to claim 2, characterized in that: In the wire rod cooling stage, the roller way speed of the Stelmor cooling line is 0.5-0.8 m / s.

7. The process of producing an online tempering sorbite type 10.9 grade non- quenched and tempered cold-upset steel wire rod as claimed in claim 2, wherein, The mechanical properties of the obtained non-tempered cold-upsetting steel wire rod are as follows: yield strength 790-820 MPa, tensile strength 880-910 MPa, elongation 26-29%, reduction of area 74-77%, and room temperature Kv2 impact energy 88-103 J.

8. The process of producing an on-line tempered sorbite type 10.9 grade non- quenched and tempered cold-upset steel wire rod as claimed in claim 7, wherein, After the wire rod is drawn with a reduction of 26-33%, the yield strength of the obtained steel wire is 930-980 MPa, the tensile strength is 1042-1078 MPa, the elongation is ≥19%, the reduction of area is ≥66%, and the room temperature Kv2 impact energy is 59-75 J.

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