Hot-rolled wire rod and method for improving its plastic deformation capacity

Abstract

This application belongs to the field of cold heading steel rolling technology, specifically relating to a hot-rolled wire rod and a method for improving its plastic deformation capacity. The method includes the following steps: S1, obtaining a first steel billet, and shot-blasting the first steel billet to obtain a second steel billet; S2, preheating, heating and holding the second steel billet to obtain a third steel billet; S3, subjecting the third steel billet to first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing and coiling to obtain a first hot-rolled wire rod; S4, placing the first hot-rolled wire rod into the Steyrmo cooling transport line for cooling to obtain a hot-rolled wire rod. This application achieves microstructure control of hot-rolled wire rod through composition optimization and process adjustment, realizing the transformation from coarse grains and high bainite content to fine grains and uniform "ferrite + pearlite", significantly improving the plastic deformation capacity of hot-rolled wire rod, adapting to the downstream "one-shear two-draw" process requirements, and greatly improving production efficiency and product qualification rate.

Description

Technical Field

[0001] This application belongs to the field of cold heading steel rolling technology, specifically relating to a hot-rolled wire rod and a method for improving its plastic deformation capacity. Background Technology

[0002] SCM435 hot-rolled wire rod is an ideal material for producing high-strength bolts, nuts, screws, and other standard parts. Its advantages are particularly evident in manufacturing high-strength and ultra-high-strength fasteners of grades 10.9 to 12.9. Hot-rolled wire rod requires further drawing to produce fasteners of different specifications, typically employing a "annealing-rough drawing-annealing-fine drawing" process (two annealing and two drawing steps), resulting in high production costs. To reduce production costs, downstream customers are currently seeking to cut the first annealing step and directly implement a rough drawing process (one annealing and two drawing steps) to save costs. However, existing SCM435 hot-rolled wire rods have poor plasticity in certain areas (tensile strength ≥900MPa, elongation ≤20%, and reduction of area ≤40%), making it difficult to match the customers' "two drawing and one annealing" process requirements. When customers skip the first annealing process, SCM435 hot-rolled wire rod is prone to cracking, wire breakage, and other defects during the drawing process. This not only reduces production efficiency but also leads to a decline in product qualification rate, thereby increasing the customer's actual production costs and quality risks.

[0003] Existing SCM435 hot-rolled wire rods are difficult to adapt to downstream "two-draw-one-retard" processes. The core problem lies not only in insufficient macroscopic properties but also in microstructural defects caused by the mismatch between composition and process. Existing SCM435 steel has a pearlite lamellar spacing of approximately 150-180 nm, resulting in significant dislocation movement resistance and a matrix hardness of approximately 280-300 HV. Its critical cooling rate for bainite phase transformation is approximately 12℃ / s. Thermo-Calc thermodynamic calculations show that under conventional hot-rolling cooling processes, the cooling rate is approximately 10-14℃ / s, easily leading to the formation of 15%-30% bainite. The hardness difference between bainite and pearlite causes stress concentration within the microstructure, making it prone to cracking at the two-phase interface during drawing. Furthermore, the existing process uses an inlet temperature of 900±15℃ for the sizing mill and a wire drawing temperature of 840±15℃. During this temperature range, austenite grains typically grow to 50-70μm, resulting in fewer pearlite nucleation sites and poor phase transformation uniformity, which may lead to the formation of martensite islands in localized areas, further deteriorating the material's plasticity. Therefore, simply optimizing the macroscopic composition or process parameters cannot solve the fundamental problem. There is an urgent need to provide a new method for preparing hot-rolled wire rod that can improve the plastic deformation capacity of the wire rod by synergistically controlling the microstructure through composition and process to reduce strength and increase elongation. Summary of the Invention

[0004] To solve the above-mentioned technical problems, this application provides a method for improving the plastic deformation capacity of hot-rolled wire rod, comprising the following steps: S1, obtaining a first steel billet, and shot-blasting the first steel billet to obtain a second steel billet, wherein the composition of the first steel billet includes: C: 0.29-0.32wt%, Cr: 1.30-1.50wt%; S2, preheating, heating and holding the second steel billet to obtain a third steel billet; S3, subjecting the third steel billet to a first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing and coiling to obtain a first hot-rolled wire rod. Wherein, the initial rolling temperature of the roughing mill is 1000-1100℃, the initial rolling temperature of the finishing mill is 900-1000℃, the initial rolling temperature of the reducing mill is 840-900℃, and the wire drawing temperature is 800-825℃; S4, the first hot-rolled wire rod is placed into the Steyrmo cooling transport line for cooling to obtain hot-rolled wire rod, wherein the Steyrmo cooling transport line has 11 sets of relatively independent roller tracks, and the roller tracks are marked along the transport direction, and are sequentially numbered 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and 11;

[0005] The cooling conditions for the Steyrmo cooling transport line are as follows:

[0006] The conveying speed of roller conveyor No. 1 is 0.15-0.16 m / s.

[0007] The conveying speed of the No. 2 roller conveyor is 0.16-0.17 m / s.

[0008] The conveying speed of the No. 3 roller conveyor is 0.17-0.18 m / s.

[0009] The conveying speed of the No. 4 roller conveyor is 0.18-0.19 m / s.

[0010] The conveying speed of the No. 5 roller conveyor is 0.19-0.20 m / s.

[0011] The conveying speed of roller conveyor No. 6 is 0.21-0.22 m / s.

[0012] The conveying speed of the No. 7 roller conveyor is 0.23-0.24 m / s.

[0013] The conveying speed of the No. 8 roller conveyor is 0.25-0.26 m / s.

[0014] The conveying speed of roller conveyor No. 9 is 0.27-0.28 m / s.

[0015] The conveying speed of roller conveyor No. 10 is 0.32-0.33 m / s.

[0016] The conveying speed of roller conveyor No. 11 is 0.38-0.39 m / s;

[0017] Each set of independent roller conveyors is equipped with two heat insulation covers, marked along the transport direction:

[0018] The heat insulation covers of roller conveyor No. 1 are designated as 1A and 1B, respectively.

[0019] The heat insulation covers of roller conveyor No. 2 are designated as 2A and 2B, respectively.

[0020] The heat insulation covers for roller conveyor No. 3 are designated as 3A and 3B, respectively.

[0021] The heat insulation covers for roller conveyor No. 4 are designated as 4A and 4B, respectively.

[0022] The heat insulation covers for roller conveyor No. 5 are designated as 5A and 5B, respectively.

[0023] The heat insulation covers for roller conveyor No. 6 are designated as 6A and 6B, respectively.

[0024] The heat insulation covers for roller conveyor No. 7 are designated as 7A and 7B, respectively.

[0025] The heat insulation covers for roller conveyor No. 8 are designated as 8A and 8B, respectively.

[0026] The heat insulation covers for roller conveyor No. 9 are designated as 9A and 9B, respectively.

[0027] The heat insulation covers for roller conveyor No. 10 are designated as 10A and 10B, respectively.

[0028] The heat insulation covers of roller conveyor No. 11 are designated as 11A and 11B, respectively.

[0029] The insulation cover has two states: open and closed. The insulation covers 1A and 1B of roller conveyor No. 1 are open, all insulation covers of roller conveyors No. 2 to No. 11 are closed, and all fans are turned off.

[0030] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S1, the thickness of the iron oxide scale removed by shot blasting is ≥0.5mm, and the composition of the first steel billet further includes: Mn: 0.60-0.90wt%, Si: 0.15-0.35wt%, Mo: 0.15-0.25wt%, Ni≤0.20wt%, Cu≤0.20wt%, Al: 0.005-0.035wt%, P≤0.015wt%, S≤0.010wt%, [O]≤0.0030wt%, [N]≤0.0070wt%, with the balance being Fe and unavoidable impurities.

[0031] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S2, the preheating temperature is 780-880℃, the heating rate is ≤5℃ / min, the holding temperature is 1150-1200℃, the holding time is 40-60min, and the total heating time of the preheating, heating and holding is 90-150min.

[0032] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S3, the initial rolling temperature of the roughing mill is 1000-1050℃, the roughing mill consists of 6-8 passes, the reduction rate of the first pass of the roughing mill is 15%-20%, the reduction rate of the second pass of the roughing mill is 20%-25%, and the reduction rate of subsequent passes of the roughing mill gradually increases to 25%-35%.

[0033] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S3, the pressure of the first descaling is 20-22 MPa, and the pressure of the second descaling is 18-20 MPa after the first pass of the rough rolling.

[0034] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S3, the reduction rate of subsequent passes of the roughing mill is gradually increased to 30%-35%.

[0035] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S3, the initial rolling temperature of the finishing mill is 930-990℃, the initial rolling temperature of the reducing mill is 860-900℃, and the wire drawing temperature is 805-825℃.

[0036] As a preferred embodiment of the method for improving the plastic deformation capacity of hot-rolled wire rod as described in this application, in step S3, the reducing mill rolls for a total of 3-4 passes, the reduction rate of a single pass of the reducing mill is 10%-15%, the total reduction rate of the reducing mill is 30%-60%, and the specification of the first hot-rolled wire rod is φ6-10mm.

[0037] This application also provides a hot-rolled wire rod, which is prepared by the above-described method for improving the plastic deformation capacity of hot-rolled wire rod.

[0038] As a preferred embodiment of the hot-rolled wire rod described in this application, the microstructure of the hot-rolled wire rod is: ferrite + pearlite accounting for more than 95%, bainite accounting for less than 5%, the grain size of the hot-rolled wire rod is ≤30μm, and the Cr content of the hot-rolled wire rod is... 23The C6 content is ≥0.40wt%, the hardness of the hot-rolled wire rod is ≤260HV, the yield strength of the hot-rolled wire rod is ≤600MPa, the tensile strength of the hot-rolled wire rod is ≤800MPa, the yield strength ratio of the hot-rolled wire rod is ≤75%, the elongation of the hot-rolled wire rod is ≥20%, and the reduction of area of ​​the hot-rolled wire rod is ≥45%.

[0039] The beneficial effects of this application are as follows:

[0040] This application achieves microstructure control of hot-rolled wire rod through synergistic composition optimization and process adjustment, significantly improving the plastic deformation capacity of hot-rolled wire rod. Specifically, the beneficial effects are as follows: the carbon content is reduced from the current 0.33-0.38 wt% to 0.29-0.32 wt%, lowering the pearlite phase transformation temperature range from 680-720℃ to 650-690℃. This adjustment not only reduces the carbon atom diffusion rate, increasing the pearlite lamellar spacing to 250-300 nm and reducing dislocation slip resistance, thus lowering the matrix hardness from 260-290 HV to 240-260 HV, but also reduces the critical cooling rate of bainite phase transformation to 10℃ / s; the chromium content is increased from the current 0.90-1.20 wt% to 1.30-1.50 wt%, and as a strong carbide-forming element, it can form Cr with C. 23C6 carbide content was increased by approximately 0.3 wt%. This carbide preferentially precipitates at grain boundaries and forms a pinning effect, effectively inhibiting austenite grain growth during hot rolling heating and rolling processes. Furthermore, Cr extends the pearlite phase transformation incubation period, ensuring a sufficiently uniform pearlite phase transformation process. Based on this composition, the reduction sizing inlet temperature was reduced from 900±15℃ to 840-900℃. This temperature falls within the dynamic recrystallization range of the optimized composition for austenite. At this temperature, reduction sizing rolling achieves a dynamic recrystallization fraction of over 90% for austenite, refining the grains to 20-30 μm. The refined austenite grains increase the pearlite nucleation density, laying the microstructure foundation for a uniform phase transformation. Then, on one hand, the wire drawing temperature was reduced from 840±15℃ to 800-825℃; on the other hand, the initial cooling rate was increased to 5-8℃ / s through the design of the Steyrmore cooling transport line with "1A-1B insulation cover open, 2A-11B insulation cover closed". This cooling rate rapidly reduces the wire rod temperature from the drawing temperature to the pearlitic transformation range of 650-690℃. This avoids high-temperature holding that could lead to austenite grain growth, providing more grain boundary nucleation sites for ferrite and promoting the formation of fine-grained ferrite. Furthermore, because the cooling rate is below the critical cooling rate for bainitic transformation, it precisely falls within the pearlitic transformation region of the CCT curve of the optimized composition of the hot-rolled wire rod, ensuring a sufficiently uniform pearlitic transformation. Ultimately, this results in a two-phase microstructure of "fine-grained ferrite + uniform pearlite," with grain size refined from 55-60μm to 20-30μm, a key guarantee for improving the plasticity of hot-rolled wire rod. In addition, shot blasting before the billet enters the furnace and two high-pressure water descaling processes optimize surface quality, preventing stress concentration at defects during drawing and twisting that could cause cracking and wire breakage, further ensuring the continuity of plastic deformation. Through the aforementioned synergistic combination of composition and process, the microstructure of hot-rolled wire rod is transformed from coarse-grained, high-bainite composition to fine-grained, uniform "ferrite + pearlite" composition. This results in a "ferrite + pearlite" content exceeding 95% in the finished hot-rolled wire rod, achieving stable performance indicators such as hardness ≤260HV, yield strength ≤600MPa, tensile strength ≤800MPa, yield ratio ≤75%, elongation ≥20%, and reduction of area ≥45%, thus meeting the requirements of downstream "one annealing, two drawing" processes. In practical applications, this method can help downstream customers reduce one annealing step, significantly lowering energy and time costs; simultaneously, the improved plasticity reduces the wire breakage rate during drawing, greatly improving production efficiency and product qualification rate. Furthermore, this process requires no additional complex equipment, demonstrating strong potential for large-scale application. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0042] Figure 1 Images showing the microstructure of the hot-rolled wire rod prepared in Example 1 of this application;

[0043] Figure 2 This is a microstructure image of the hot-rolled wire rod prepared in Comparative Example 1 of this application.

[0044] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0045] The technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0046] This application provides a method for improving the plastic deformation capacity of hot-rolled wire rod, comprising the following steps:

[0047] S1. Obtain a first steel billet and perform shot blasting on the first steel billet to obtain a second steel billet;

[0048] The composition of the first steel billet is as follows: C: 0.29-0.32wt%, Cr: 1.30-1.50wt%, Mn: 0.60-0.90wt%, Si: 0.15-0.35wt%, Mo: 0.15-0.25wt%, Ni≤0.20wt%, Cu≤0.20wt%, Al: 0.005-0.035wt%, P≤0.015wt%, S≤0.010wt%, [O]≤0.0030wt%, [N]≤0.0070wt%, with the balance being Fe and unavoidable impurities;

[0049] The thickness of the iron oxide scale removed by the shot blasting treatment is ≥0.5mm;

[0050] Specifically, the content of C is any one of 0.29wt%, 0.30wt%, 0.31wt%, 0.32wt%, or a range between two of them, and the content of Cr is any one of 1.30wt%, 1.40wt%, 1.50wt%, or a range between two of them.

[0051] S2. The second steel billet is preheated, heated, and held at the temperature to obtain the third steel billet;

[0052] In step S2, the preheating temperature is 780-880℃, the heating rate is ≤5℃ / min, the holding temperature is 1150-1200℃, the holding time is 40-60min, and the total heating time of the preheating, heating and holding is 90-150min.

[0053] Specifically, the insulation temperature is any one of 1150℃, 1160℃, 1170℃, 1180℃, 1190℃, 1200℃ or a range between two of them;

[0054] S3. The third steel billet undergoes a first descaling, rough rolling, a second descaling, finishing mill rolling, reducing sizing mill rolling, wire drawing, and coiling to obtain a first hot-rolled wire rod. The starting rolling temperature of the rough rolling is 1000-1100℃, the starting rolling temperature of the finishing mill rolling is 900-1000℃, the starting rolling temperature of the reducing sizing mill rolling is 840-900℃, and the wire drawing temperature is 800-825℃.

[0055] The first dephosphorization pressure is 20-22 MPa, and the second dephosphorization is carried out after the first pass of the rough rolling, with a pressure of 18-20 MPa.

[0056] Specifically, the initial rolling temperature of the roughing mill is any one or a range between 1000℃, 1010℃, 1020℃, 1030℃, 1040℃, 1050℃, 1060℃, 1070℃, 1080℃, 1090℃, and 1100℃, and the initial rolling temperature of the finishing mill is 900℃, 910℃, 920℃, 930℃, 940℃, 950℃, 960℃, and 970℃. The temperature range is any one of 980℃, 990℃, 1000℃ or between two of them; the initial rolling temperature of the reducing mill is any one of 840℃, 850℃, 860℃, 870℃, 880℃, 890℃, 900℃ or between two of them; and the wire drawing temperature is any one of 800℃, 805℃, 810℃, 815℃, 820℃, 825℃ or between two of them.

[0057] S4. The first hot-rolled wire rod is placed into the Steyrmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The Steyrmo cooling conveyor line is equipped with 11 relatively independent roller tracks. The roller tracks are marked along the conveying direction and are numbered 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 in sequence.

[0058] The cooling conditions for the Steyrmo cooling transport line are as follows:

[0059] The conveying speed of roller conveyor No. 1 is 0.15-0.16 m / s.

[0060] The conveying speed of the No. 2 roller conveyor is 0.16-0.17 m / s.

[0061] The conveying speed of the No. 3 roller conveyor is 0.17-0.18 m / s.

[0062] The conveying speed of the No. 4 roller conveyor is 0.18-0.19 m / s.

[0063] The conveying speed of the No. 5 roller conveyor is 0.19-0.20 m / s.

[0064] The conveying speed of roller conveyor No. 6 is 0.21-0.22 m / s.

[0065] The conveying speed of the No. 7 roller conveyor is 0.23-0.24 m / s.

[0066] The conveying speed of the No. 8 roller conveyor is 0.25-0.26 m / s.

[0067] The conveying speed of roller conveyor No. 9 is 0.27-0.28 m / s.

[0068] The conveying speed of roller conveyor No. 10 is 0.32-0.33 m / s.

[0069] The conveying speed of roller conveyor No. 11 is 0.38-0.39 m / s;

[0070] Each set of independent roller conveyors is equipped with two heat insulation covers, marked along the transport direction:

[0071] The heat insulation covers of roller conveyor No. 1 are designated as 1A and 1B, respectively.

[0072] The heat insulation covers of roller conveyor No. 2 are designated as 2A and 2B, respectively.

[0073] The heat insulation covers for roller conveyor No. 3 are designated as 3A and 3B, respectively.

[0074] The heat insulation covers for roller conveyor No. 4 are designated as 4A and 4B, respectively.

[0075] The heat insulation covers for roller conveyor No. 5 are designated as 5A and 5B, respectively.

[0076] The heat insulation covers for roller conveyor No. 6 are designated as 6A and 6B, respectively.

[0077] The heat insulation covers for roller conveyor No. 7 are designated as 7A and 7B, respectively.

[0078] The heat insulation covers for roller conveyor No. 8 are designated as 8A and 8B, respectively.

[0079] The heat insulation covers for roller conveyor No. 9 are designated as 9A and 9B, respectively.

[0080] The heat insulation covers for roller conveyor No. 10 are designated as 10A and 10B, respectively.

[0081] The heat insulation covers of roller conveyor No. 11 are designated as 11A and 11B, respectively.

[0082] The insulation cover has two states: open and closed. The insulation covers 1A and 1B of roller conveyor No. 1 are open, all insulation covers of roller conveyors No. 2 to No. 11 are closed, and all fans are turned off.

[0083] The technical solution of this application will be further described below with reference to specific embodiments.

[0084] Example 1

[0085] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0086] Step S1: Obtain the first steel billet and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.6 mm. The composition of the first steel billet is as follows: C: 0.30 wt%, Cr: 1.40 wt%, Mn: 0.75 wt%, Si: 0.20 wt%, Mo: 0.20 wt%, Ni: 0.12 wt%, Cu: 0.12 wt%, Al: 0.030 wt%, P: 0.010 wt%, S: 0.008 wt%, [O]: 0.0020 wt%, [N]: 0.0050 wt%, with the balance being Fe and unavoidable impurities.

[0087] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 830℃, the heating rate is 4℃ / min, the holding temperature is 1180℃, the holding time is 55min, and the total heating time is 130min.

[0088] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 21 MPa, the roughing temperature is 1040℃, and the roughing process consists of 7 passes. The reduction rate in the first pass is 16%, the reduction rate in the second pass is 24%, and the reduction rate in subsequent passes gradually increases to 33%. The second descaling is performed after the first pass of the roughing process, with a pressure of 19 MPa. The finishing mill rolling temperature is 960℃, the reducing mill rolling temperature is 875℃, and the reducing mill rolling process consists of 3 passes. The reduction rate in a single pass is 14%, the total reduction rate is 42%, and the wire drawing temperature is 815℃. The first hot-rolled wire rod has a diameter of φ8mm.

[0089] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; open 1A and 1B, close 2A to 11B, and turn off all fans.

[0090] Please see Figure 1 , Figure 1 The image shows the microstructure of the hot-rolled wire rod prepared in Example 1 of this application. It can be seen that the ferrite + pearlite ratio in the microstructure of the hot-rolled wire rod prepared in Example 1 is 96.5%, the grain size is 27 μm, and the content of fine bainite phase interspersed is 3.5%. Cr 23 The C6 carbide content is 0.47wt%, the hardness of the hot-rolled wire rod is 250HV, the yield strength is 590MPa, the tensile strength is 788MPa, the yield strength ratio is 74.9%, the elongation is 24%, and the reduction of area is 47.5%.

[0091] Example 2

[0092] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0093] Step S1: Obtain the first steel billet, and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.5 mm. The composition of the first steel billet is as follows: C: 0.29 wt%, Cr: 1.30 wt%, Mn: 0.60 wt%, Si: 0.15 wt%, Mo: 0.15 wt%, Ni: 0.10 wt%, Cu: 0.10 wt%, Al: 0.005 wt%, P: 0.012 wt%, S: 0.006 wt%, [O]: 0.0025 wt%, [N]: 0.0060 wt%, with the balance being Fe and unavoidable impurities.

[0094] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 780℃, the heating rate is 4℃ / min, the holding temperature is 1150℃, the holding time is 40min, and the total heating time is 90min.

[0095] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing sizing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 20 MPa, the roughing temperature is 1000℃, and the roughing process consists of 6 passes. The reduction rate in the first pass is 15%, the reduction rate in the second pass is 20%, and the reduction rate in subsequent passes gradually increases to 25%. The second descaling is performed after the first pass of the roughing process, with a pressure of 18 MPa. The finishing mill rolling temperature is 900℃, the reducing sizing mill rolling temperature is 840℃, and the reducing sizing mill rolling consists of 3 passes. The reduction rate in a single pass is 10%, the total reduction rate is 30%, and the wire drawing temperature is 800℃. The first hot-rolled wire rod has a diameter of φ9 mm.

[0096] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; open 1A and 1B, close 2A to 11B, and turn off all fans.

[0097] The hot-rolled wire rod prepared in Example 2 had a ferrite + pearlite ratio of 95%, a grain size of 29 μm, a bainite phase of 5%, and Cr... 23The C6 carbide content is 0.40wt%, the hardness of the hot-rolled wire rod is 245HV, the yield strength is 580, the tensile strength of the hot-rolled wire rod is 785MPa, the yield strength ratio is 73.9%, the elongation is 22%, and the reduction of area is 46%.

[0098] Example 3

[0099] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0100] Step S1: Obtain the first steel billet, and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.7 mm. The composition of the first steel billet is as follows: C: 0.32 wt%, Cr: 1.50 wt%, Mn: 0.90 wt%, Si: 0.35 wt%, Mo: 0.25 wt%, Ni: 0.20 wt%, Cu: 0.20 wt%, Al: 0.035 wt%, P: 0.010 wt%, S: 0.008 wt%, [O]: 0.0022 wt%, [N]: 0.0055 wt%, with the balance being Fe and unavoidable impurities.

[0101] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 880℃, the heating rate is 5℃ / min, the holding temperature is 1200℃, the holding time is 60min, and the total heating time is 150min.

[0102] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 22 MPa, the roughing temperature is 1100℃, and the roughing process consists of 8 passes. The reduction rate in the first pass is 18%, the reduction rate in the second pass is 25%, and the reduction rate in subsequent passes gradually increases to 35%. The second descaling is performed after the first pass of the roughing process. The second descaling pressure is 20 MPa, the finishing mill temperature is 1000℃, the reducing mill temperature is 900℃, and the reducing mill rolling process consists of 4 passes. The reduction rate in a single pass is 15%, the total reduction rate is 60%, and the wire drawing temperature is 825℃. The first hot-rolled wire rod has a diameter of φ6.5 mm.

[0103] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; open 1A and 1B, close 2A to 11B, and turn off all fans.

[0104] The hot-rolled wire rod prepared in Example 3 had a ferrite + pearlite ratio of 97%, a grain size of 23 μm, a bainite phase of 3%, and Cr... 23 The C6 carbide content is 0.54wt%, the hardness of the hot-rolled wire rod is 255HV, the yield strength is 600MPa, the tensile strength of the hot-rolled wire rod is 800MPa, the yield strength ratio is 75.0%, the elongation is 24%, and the reduction of area is 48%.

[0105] Comparative Example 1

[0106] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0107] Step S1: Obtain the first steel billet, wherein the composition of the first steel billet is: C: 0.37wt%, Cr: 0.95wt%, Mn: 0.72wt%, Si: 0.28wt%, Mo: 0.21wt%, Ni: 0.16wt%, Cu: 0.14wt%, Al: 0.025wt%, P: 0.018wt%, S: 0.014wt%, [O]: 0.0035wt%, [N]: 0.0085wt%, with the balance being Fe and unavoidable impurities;

[0108] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 920℃, the heating rate is 7℃ / min, the holding temperature is 1230℃, the holding time is 30min, and the total heating time is 80min.

[0109] Step S3: The third steel billet undergoes first descaling, roughing, finishing mill rolling, sizing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 15 MPa, the initial rolling temperature of the roughing mill is 1040℃, and the roughing mill has 7 passes. The reduction rate of the first pass is 16%, the reduction rate of the second pass is 24%, and the reduction rate of subsequent passes gradually increases to 33%. The initial rolling temperature of the finishing mill is 960℃, the initial rolling temperature of the sizing mill is 920℃, and the sizing mill has 3 passes. The reduction rate of a single pass is 14%, the total reduction rate is 42%, and the wire drawing temperature is 860℃. The specification of the first hot-rolled wire rod is φ8mm.

[0110] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; shut down 1A to 11B and all fans.

[0111] Please see Figure 2 , Figure 2 The image shows the microstructure of the hot-rolled wire rod prepared in Comparative Example 1 of this application. It can be seen that the ferrite + pearlite ratio in the microstructure of the hot-rolled wire rod prepared in Comparative Example 1 is 68%, the grain size is 58 μm, the bainite phase content is 32%, and the Cr content is... 23 The C6 carbide content is 0.13wt%, the hardness of the hot-rolled wire rod is 295HV, the yield strength is 730MPa, the tensile strength is 915MPa, the yield ratio is 79.8%, the elongation is 12%, and the reduction of area is 35%.

[0112] Comparative Example 2

[0113] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0114] Step S1: Obtain the first steel billet, and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.5 mm. The composition of the first steel billet is as follows: C: 0.36 wt%, Cr: 0.90 wt%, Mn: 0.75 wt%, Si: 0.20 wt%, Mo: 0.20 wt%, Ni: 0.12 wt%, Cu: 0.12 wt%, Al: 0.030 wt%, P: 0.010 wt%, S: 0.008 wt%, [O]: 0.0020 wt%, [N]: 0.0050 wt%, with the balance being Fe and unavoidable impurities.

[0115] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 780℃, the heating rate is 4℃ / min, the holding temperature is 1150℃, the holding time is 40min, and the total heating time is 90min.

[0116] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing sizing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 20 MPa, the roughing temperature is 1000℃, and the roughing process consists of 6 passes. The reduction rate in the first pass is 15%, the reduction rate in the second pass is 20%, and the reduction rate in subsequent passes gradually increases to 25%. The second descaling is performed after the first pass of the roughing process, with a pressure of 18 MPa. The finishing mill rolling temperature is 900℃, the reducing sizing mill rolling temperature is 840℃, and the reducing sizing mill rolling consists of 3 passes. The reduction rate in a single pass is 10%, the total reduction rate is 30%, and the wire drawing temperature is 800℃. The first hot-rolled wire rod has a diameter of φ9 mm.

[0117] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; open 1A and 1B, close 2A to 11B, and turn off all fans.

[0118] The hot-rolled wire rod prepared in Comparative Example 2 had a ferrite + pearlite ratio of 75%, a grain size of 48 μm, a bainite phase of 25%, and Cr... 23 The C6 carbide content is 0.11 wt%, the hardness of the hot-rolled wire rod is 285 HV, the yield strength is 700 MPa, the tensile strength of the hot-rolled wire rod is 890 MPa, the yield strength ratio is 78.7%, the elongation is 13%, and the reduction of area is 38%.

[0119] Comparative Example 3

[0120] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0121] Step S1: Obtain the first steel billet, wherein the composition of the first steel billet is: C: 0.32wt%, Cr: 1.50wt%, Mn: 0.90wt%, Si: 0.35wt%, Mo: 0.25wt%, Ni: 0.20wt%, Cu: 0.20wt%, Al: 0.035wt%, P: 0.010wt%, S: 0.008wt%, [O]: 0.0022wt%, [N]: 0.0055wt%, with the balance being Fe and unavoidable impurities;

[0122] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 900℃, the heating rate is 6℃ / min, the holding temperature is 1250℃, the holding time is 30min, and the total heating time is 70min.

[0123] Step S3: The third steel billet undergoes first descaling, roughing, finishing mill rolling, sizing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 12 MPa, the initial rolling temperature of the roughing mill is 1150℃, and the roughing mill has 8 passes. The reduction rate of the first pass is 18%, the reduction rate of the second pass is 25%, and the reduction rate of subsequent passes gradually increases to 35%. The initial rolling temperature of the finishing mill is 1050℃, the initial rolling temperature of the sizing mill is 920℃, and the sizing mill has 4 passes. The reduction rate of a single pass is 15%, the total reduction rate is 60%, and the wire drawing temperature is 860℃. The specification of the first hot-rolled wire rod is φ6.5mm.

[0124] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; shut down 1A to 11B and all fans.

[0125] The hot-rolled wire rod prepared in Comparative Example 3 had a ferrite + pearlite ratio of 82%, a grain size of 42 μm, and a bainite phase of 18%. Cr 23 The hot-rolled wire rod has a C6 carbide content of 0.52 wt%, a hardness of 275 HV, a yield strength of 670 MPa, a tensile strength of 855 MPa, a yield-to-tensile ratio of 78.4%, an elongation of 16%, and a reduction of area of ​​38%.

[0126] Comparative Example 4

[0127] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0128] Step S1: Obtain the first steel billet, wherein the composition of the first steel billet is: C: 0.32wt%, Cr: 1.50wt%, Mn: 0.90wt%, Si: 0.35wt%, Mo: 0.25wt%, Ni: 0.20wt%, Cu: 0.20wt%, Al: 0.035wt%, P: 0.010wt%, S: 0.008wt%, [O]: 0.0022wt%, [N]: 0.0055wt%, with the balance being Fe and unavoidable impurities;

[0129] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 880℃, the heating rate is 5℃ / min, the holding temperature is 1200℃, the holding time is 60min, and the total heating time is 150min.

[0130] Step S3: The third steel billet undergoes a first descaling, roughing, finishing mill rolling, sizing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 22 MPa, the initial rolling temperature of the roughing mill is 1100℃, and the roughing mill has 8 passes. The reduction rate of the first pass is 18%, the reduction rate of the second pass is 25%, and the reduction rate of subsequent passes gradually increases to 35%. The initial rolling temperature of the finishing mill is 1000℃, the initial rolling temperature of the sizing mill is 900℃, and the sizing mill has 4 passes. The reduction rate of a single pass is 15%, the total reduction rate is 60%, and the wire drawing temperature is 825℃. The specification of the first hot-rolled wire rod is φ6.5mm.

[0131] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; open 1A and 1B, close 2A to 11B, and turn off all fans.

[0132] The hot-rolled wire rod prepared in Comparative Example 4 had a ferrite + pearlite ratio of 96%, a grain size of 25 μm, a bainite phase of 4%, and Cr... 23 The hot-rolled wire rod has a C6 carbide content of 0.53 wt%, a hardness of 240 HV, a yield strength of 590 MPa, a tensile strength of 785 MPa, a yield-to-tensile ratio of 75.2%, an elongation of 22%, and a reduction of area of ​​46%.

[0133] Comparative Example 5

[0134] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0135] Step S1: Obtain the first steel billet, and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.7 mm. The composition of the first steel billet is as follows: C: 0.32 wt%, Cr: 1.50 wt%, Mn: 0.90 wt%, Si: 0.35 wt%, Mo: 0.25 wt%, Ni: 0.20 wt%, Cu: 0.20 wt%, Al: 0.035 wt%, P: 0.010 wt%, S: 0.008 wt%, [O]: 0.0022 wt%, [N]: 0.0055 wt%, with the balance being Fe and unavoidable impurities.

[0136] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 880℃, the heating rate is 5℃ / min, the holding temperature is 1200℃, the holding time is 60min, and the total heating time is 150min.

[0137] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 12 MPa, the roughing temperature is 1150℃, and the roughing process consists of 8 passes. The reduction rate in the first pass is 18%, the reduction rate in the second pass is 25%, and the reduction rate in subsequent passes gradually increases to 35%. The second descaling is performed after the first pass of the roughing process, with a pressure of 20 MPa. The finishing mill rolling temperature is 1050℃, the reducing mill rolling temperature is 920℃, and the reducing mill rolling process consists of 4 passes. The reduction rate in a single pass is 15%, the total reduction rate is 60%, and the wire drawing temperature is 860℃. The first hot-rolled wire rod has a diameter of φ6.5 mm.

[0138] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; shut down 1A to 11B and all fans.

[0139] The hot-rolled wire rod prepared in Comparative Example 5 had a ferrite + pearlite ratio of 85%, a grain size of 40 μm, a bainite phase of 15%, and Cr... 23 The hot-rolled wire rod has a C6 carbide content of 0.52 wt%, a hardness of 270 HV, a yield strength of 650 MPa, a tensile strength of 830 MPa, a yield-to-tensile ratio of 78.3%, an elongation of 18%, and a reduction of area of ​​40%.

[0140] Comparative Example 6

[0141] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0142] Step S1: Obtain the first steel billet, and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.7 mm. The composition of the first steel billet is as follows: C: 0.32 wt%, Cr: 1.50 wt%, Mn: 0.90 wt%, Si: 0.35 wt%, Mo: 0.25 wt%, Ni: 0.20 wt%, Cu: 0.20 wt%, Al: 0.035 wt%, P: 0.010 wt%, S: 0.008 wt%, [O]: 0.0022 wt%, [N]: 0.0055 wt%, with the balance being Fe and unavoidable impurities.

[0143] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 880℃, the heating rate is 5℃ / min, the holding temperature is 1200℃, the holding time is 60min, and the total heating time is 150min.

[0144] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 22 MPa, the roughing temperature is 1100℃, and the roughing process consists of 8 passes. The reduction rate in the first pass is 18%, the reduction rate in the second pass is 25%, and the reduction rate in subsequent passes gradually increases to 35%. The second descaling is performed after the first pass of the roughing process. The second descaling pressure is 20 MPa, the finishing mill temperature is 1000℃, the reducing mill temperature is 900℃, and the reducing mill rolling process consists of 4 passes. The reduction rate in a single pass is 15%, the total reduction rate is 60%, and the wire drawing temperature is 825℃. The first hot-rolled wire rod has a diameter of φ6.5 mm.

[0145] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; shut down 1A to 11B and all fans.

[0146] The hot-rolled wire rod prepared in Comparative Example 6 had a ferrite + pearlite ratio of 90%, a grain size of 40 μm, a bainite phase of 3%, and Cr... 23 The C6 carbide content is 0.53wt%, the hardness of the hot-rolled wire rod is 250HV, the yield strength is 595MPa, the tensile strength is 782MPa, the yield ratio is 76.1%, the elongation is 19%, and the reduction of area is 40%.

[0147] Comparative Example 7

[0148] A method for improving the plastic deformation capacity of hot-rolled wire rod, the specific preparation steps of which are as follows:

[0149] Step S1: Obtain the first steel billet, and perform shot blasting on the first steel billet to obtain the second steel billet. The thickness of the iron oxide scale removed by shot blasting is 0.7 mm. The composition of the first steel billet is as follows: C: 0.32 wt%, Cr: 1.50 wt%, Mn: 0.90 wt%, Si: 0.35 wt%, Mo: 0.25 wt%, Ni: 0.20 wt%, Cu: 0.20 wt%, Al: 0.035 wt%, P: 0.010 wt%, S: 0.008 wt%, [O]: 0.0022 wt%, [N]: 0.0055 wt%, with the balance being Fe and unavoidable impurities.

[0150] Step S2: The second steel billet is preheated, heated and held at the temperature to obtain the third steel billet. The preheating temperature is 880℃, the heating rate is 5℃ / min, the holding temperature is 1200℃, the holding time is 60min, and the total heating time is 150min.

[0151] Step S3: The third steel billet undergoes first descaling, rough rolling, second descaling, finishing mill rolling, reducing mill rolling, wire drawing, and coiling to obtain the first hot-rolled wire rod. The first descaling pressure is 22 MPa, the roughing temperature is 1100℃, and the roughing process consists of 8 passes. The reduction rate in the first pass is 18%, the reduction rate in the second pass is 25%, and the reduction rate in subsequent passes gradually increases to 35%. The second descaling is performed after the first pass of the roughing process. The second descaling pressure is 20 MPa, the finishing mill temperature is 1000℃, the reducing mill temperature is 900℃, and the reducing mill rolling process consists of 4 passes. The reduction rate in a single pass is 15%, the total reduction rate is 60%, and the wire drawing temperature is 825℃. The first hot-rolled wire rod has a diameter of φ6.5 mm.

[0152] Step S4: Place the first hot-rolled wire rod into the Stellmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The roller speeds are as follows: No. 1: 0.15m / s, No. 2: 0.16m / s, No. 3: 0.17m / s, No. 4: 0.18m / s, No. 5: 0.19m / s, No. 6: 0.21m / s, No. 7: 0.23m / s, No. 8: 0.25m / s, No. 9: 0.27m / s, No. 10: 0.32m / s, No. 11: 0.38m / s; open 1A and 1B, close 2A to 11B, and turn on fan No. 1.

[0153] The hot-rolled wire rod prepared in Comparative Example 7 had a ferrite + pearlite ratio of 88%, a grain size of 25 μm, and a bainite phase of 12%. Cr 23 The hot-rolled wire rod has a C6 carbide content of 0.53 wt%, a hardness of 270 HV, a yield strength of 670 MPa, a tensile strength of 855 MPa, a yield-to-tensile ratio of 78.4%, an elongation of 18%, and a reduction of area of ​​41%.

[0154] As can be seen from the above examples and comparative examples: Example 1, combined with Comparative Example 1, shows that using existing components (C: 0.37wt%, Cr: 0.95wt%) and conventional processes (preheating to 920℃, heating rate 7℃ / min, sizing and rolling at 920℃, wire drawing at 860℃, and closing all insulation covers), the high C content results in a small pearlite lamellar spacing (150-180nm), and the low Cr content results in a small Cr content. 23 The low C6 content fails to effectively suppress grain growth, and the high spinning temperature leads to cooling rates fluctuating to 10-14℃ / s (exceeding the critical cooling rate for bainite), resulting in the formation of a large amount of bainite. This ultimately leads to high yield strength and tensile strength, but low elongation and reduction of area, and poor plastic deformation capacity. Example 2, combined with Comparative Example 2, shows that optimizing the process without adjusting the C and Cr content results in lower Cr content. 23The C6 carbide content remains low, grain refinement is limited, bainite content increases, yield strength and tensile strength are high, and elongation and reduction of area are low. Example 3, combined with Comparative Example 3, shows that optimizing only the composition without optimizing the process and without shot blasting and second descaling treatments leads to grain coarsening and a high bainite content due to high-temperature rolling and surface defects, resulting in high yield strength and tensile strength, but low elongation and reduction of area. Example 3, combined with Comparative Example 4, shows that the absence of shot blasting and second descaling treatments results in poor surface quality, defects forming high stress concentration zones that induce crack initiation, and gaps at the interface between the iron oxide scale and the matrix. Disruption of the microstructure continuity hinders the transmission of plastic deformation, thereby deteriorating the plasticity of the wire rod. Although the microstructure parameters are close to those of Example 3, the yield strength, tensile strength, elongation, and reduction of area are slightly worse than those of Example 3. Example 3, combined with Comparative Example 5, shows that even with optimized composition but not optimized process, high-temperature rolling still leads to grain coarsening, improper cooling rate resulting in a higher proportion of bainite, higher yield strength and tensile strength, and lower elongation and reduction of area. Example 3, combined with Comparative Example 6, shows that when all insulation covers are closed, the wire rod is kept at high temperature in the No. 1 roller table area, and the cooling rate is slower, lower than the 5-8℃ / s in Example 3. The precise cooling range resulted in a longer holding time in the austenitic transformation zone of the wire rod, leading to grain coarsening. The final grain size increased from 23 μm in Example 3 to 40 μm. The slower cooling rate also caused grain coarsening, reducing yield strength, tensile strength, elongation, and rate of reduction. Example 3, combined with Comparative Example 7, showed that turning on the No. 1 roller fan increased the initial cooling rate from 5-8℃ / s in Example 3 to 12-15℃ / s, exceeding the 10℃ / s critical cooling rate for bainitic transformation of the optimized billet (C: 0.29-0.32wt%, Cr: 1.30-1.50wt%). This causes the wire rod to rapidly enter the bainitic phase transformation range and disrupts the gradient temperature field of "slow cooling in the front section and heat preservation in the back section," forming a temperature difference gradient between the surface and the core, which exacerbates the uneven phase transformation. Ultimately, the proportion of bainitic structure increases from 3% in Example 3 to 12%. The higher bainitic content results in higher yield strength and tensile strength, but lower elongation and reduction of area. Examples 1-3 combined with Comparative Examples 1-7 show that changing the composition and process can reduce the tensile strength of hot-rolled wire rod. The core lies in the synergistic effect of "composition regulation of microstructure formation basis + process optimization of microstructure evolution process," which reduces the resistance to dislocation movement inside the material. In terms of composition, the C content is reduced from the current 0.33-0.38% to 0.29-0.32%, increasing the pearlite lamellar spacing from 150-180 nm to 250-300 nm, reducing interfacial resistance during dislocation slip, and simultaneously reducing the carbon atom solid solution strengthening effect; the Cr content is increased from 0.90-1.20% to 1.20-1.50%, promoting Cr... 23C6 carbide precipitation inhibits austenite grain growth through grain boundary pinning effect, and refined grains reduce the obstruction on dislocation movement paths. In terms of process, the sizing rolling temperature is reduced to 840-900℃, which is within the dynamic recrystallization range of austenite, further refining the grains. The wire drawing temperature is reduced to 800-825℃, combined with the precise controlled cooling of the Steyrmo line ("1A / 1B open, 2A-11B closed, fan off") (cooling rate 5-8℃ / s), to avoid the formation of high-hardness bainite, and finally form a low-resistance structure mainly composed of "fine-grained ferrite + uniform pearlite", so that the tensile strength is stably reduced to below 800MPa.

[0155] This application achieves microstructure control of hot-rolled wire rod through synergistic composition optimization and process adjustment, significantly improving the plastic deformation capacity of hot-rolled wire rod. Specifically, the beneficial effects are as follows: the carbon content is reduced from the current 0.33-0.38 wt% to 0.29-0.32 wt%, lowering the pearlite phase transformation temperature range from 680-720℃ to 650-690℃. This adjustment not only reduces the carbon atom diffusion rate, increasing the pearlite lamellar spacing to 250-300 nm and reducing dislocation slip resistance, thus lowering the matrix hardness from 260-290 HV to 240-260 HV, but also reduces the critical cooling rate of bainite phase transformation to 10℃ / s; the chromium content is increased from the current 0.90-1.20 wt% to 1.30-1.50 wt%, and as a strong carbide-forming element, it can form Cr with C. 23C6 carbide content was increased by approximately 0.3 wt%. This carbide preferentially precipitates at grain boundaries and forms a pinning effect, effectively inhibiting austenite grain growth during hot rolling heating and rolling processes. Furthermore, Cr extends the pearlite phase transformation incubation period, ensuring a sufficiently uniform pearlite phase transformation process. Based on this composition, the reduction sizing inlet temperature was reduced from 900±15℃ to 840-900℃. This temperature falls within the dynamic recrystallization range of the optimized composition for austenite. At this temperature, reduction sizing rolling achieves a dynamic recrystallization fraction of over 90% for austenite, refining the grains to 20-30 μm. The refined austenite grains increase the pearlite nucleation density, laying the microstructure foundation for a uniform phase transformation. Then, on one hand, the wire drawing temperature was reduced from 840±15℃ to 800-825℃; on the other hand, the initial cooling rate was increased to 5-8℃ / s through the design of the Steyrmore cooling transport line with "1A-1B insulation cover open, 2A-11B insulation cover closed". This cooling rate rapidly reduces the wire rod temperature from the drawing temperature to the pearlitic transformation range of 650-690℃. This avoids high-temperature holding that could lead to austenite grain growth, providing more grain boundary nucleation sites for ferrite and promoting the formation of fine-grained ferrite. Furthermore, because the cooling rate is below the critical cooling rate for bainitic transformation, it precisely falls within the pearlitic transformation region of the CCT curve of the optimized composition of the hot-rolled wire rod, ensuring a sufficiently uniform pearlitic transformation. Ultimately, this results in a two-phase microstructure of "fine-grained ferrite + uniform pearlite," with grain size refined from 55-60μm to 20-30μm, a key guarantee for improving the plasticity of hot-rolled wire rod. In addition, shot blasting before the billet enters the furnace and two high-pressure water descaling processes optimize surface quality, preventing stress concentration at defects during drawing and twisting that could cause cracking and wire breakage, further ensuring the continuity of plastic deformation. Through the aforementioned synergistic combination of composition and process, the microstructure of hot-rolled wire rod is transformed from coarse-grained, high-bainite composition to fine-grained, uniform "ferrite + pearlite" composition. This results in a "ferrite + pearlite" content exceeding 95% in the finished hot-rolled wire rod, achieving stable performance indicators such as hardness ≤260HV, yield strength ≤600MPa, tensile strength ≤800MPa, yield ratio ≤75%, elongation ≥20%, and reduction of area ≥45%, thus meeting the requirements of downstream "one annealing, two drawing" processes. In practical applications, this method can help downstream customers reduce one annealing step, significantly lowering energy and time costs; simultaneously, the improved plasticity reduces the wire breakage rate during drawing, greatly improving production efficiency and product qualification rate. Furthermore, this process requires no additional complex equipment, demonstrating strong potential for large-scale application.

[0156] The above description is only a preferred embodiment of this application and does not limit the patent scope of this application. All equivalent structural transformations made using the content of this application's specification under the inventive concept of this application, or direct / indirect applications in other related technical fields, are included within the patent protection scope of this application.

Claims

1. A method for improving the plastic deformation capacity of hot-rolled wire rod, characterized in that, Includes the following steps: S1. Obtain a first steel billet, and perform shot blasting on the first steel billet to obtain a second steel billet. The composition of the first steel billet is as follows: C: 0.29-0.32wt%, Cr: 1.30-1.40wt%, Mn: 0.60-0.90wt%, Si: 0.15-0.35wt%, Mo: 0.15-0.25wt%, Ni≤0.20wt%, Cu≤0.20wt%, Al: 0.005-0.035wt%, P≤0.015wt%, S≤0.010wt%, [O]≤0.0030wt%, [N]≤0.0070wt%, with the balance being Fe and unavoidable impurities. S2. The second steel billet is preheated, heated, and held at the temperature to obtain the third steel billet; The insulation temperature is 1150-1200℃; S3. The third steel billet undergoes a first descaling, rough rolling, a second descaling, finishing mill rolling, reducing sizing mill rolling, wire drawing, and coiling to obtain a first hot-rolled wire rod. The starting rolling temperature for the rough rolling is 1000-1100℃, the starting rolling temperature for the finishing mill rolling is 900-1000℃, the starting rolling temperature for the reducing sizing mill rolling is 840-900℃, and the wire drawing temperature is 805-825℃. S4. The first hot-rolled wire rod is placed into the Steyrmo cooling conveyor line for cooling to obtain hot-rolled wire rod. The Steyrmo cooling conveyor line is equipped with 11 relatively independent roller tracks. The roller tracks are marked along the conveying direction and are numbered 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11 in sequence. The cooling conditions for the Steyrmo cooling transport line are as follows: The conveying speed of roller conveyor No. 1 is 0.15-0.16 m / s. The conveying speed of the No. 2 roller conveyor is 0.16-0.17 m / s. The conveying speed of the No. 3 roller conveyor is 0.17-0.18 m / s. The conveying speed of the No. 4 roller conveyor is 0.18-0.19 m / s. The conveying speed of roller conveyor No. 5 is 0.19-0.20 m / s. The conveying speed of roller conveyor No. 6 is 0.21-0.22 m / s. The conveying speed of the No. 7 roller conveyor is 0.23-0.24 m / s. The conveying speed of the No. 8 roller conveyor is 0.25-0.26 m / s. The conveying speed of roller conveyor No. 9 is 0.27-0.28 m / s. The conveying speed of roller conveyor No. 10 is 0.32-0.33 m / s. The conveying speed of roller conveyor No. 11 is 0.38-0.39 m / s; Each set of independent roller conveyors is equipped with two heat insulation covers, marked along the transport direction: The heat insulation covers of roller conveyor No. 1 are designated as 1A and 1B, respectively. The heat insulation covers of roller conveyor No. 2 are designated as 2A and 2B, respectively. The heat insulation covers of roller conveyor No. 3 are designated as 3A and 3B, respectively. The heat insulation covers for roller conveyor No. 4 are designated as 4A and 4B, respectively. The heat insulation covers for roller conveyor No. 5 are designated as 5A and 5B, respectively. The heat insulation covers for roller conveyor No. 6 are designated as 6A and 6B, respectively. The heat insulation covers for roller conveyor No. 7 are designated as 7A and 7B, respectively. The heat insulation covers for roller conveyor No. 8 are designated as 8A and 8B, respectively. The heat insulation covers for roller conveyor No. 9 are designated as 9A and 9B, respectively. The heat insulation covers for roller conveyor No. 10 are designated as 10A and 10B, respectively. The heat insulation covers of roller conveyor No. 11 are designated as 11A and 11B, respectively. The insulation cover has two states: open and closed. The insulation covers 1A and 1B of roller conveyor 1 are open, all insulation covers of roller conveyor 2 to roller conveyor 11 are closed, and all fans are turned off. The microstructure of the hot-rolled wire rod is: ferrite + pearlite accounting for more than 95%, bainite accounting for less than 5%, the grain size of the hot-rolled wire rod is ≤30μm, and the Cr content of the hot-rolled wire rod is... 23 The C6 content is ≥0.40wt%, the yield strength of the hot-rolled wire rod is ≤600MPa, the tensile strength of the hot-rolled wire rod is ≤800MPa, and the yield strength ratio of the hot-rolled wire rod is ≤75%.

2. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 1, characterized in that, In step S1, the thickness of the iron oxide scale removed by the shot blasting is ≥0.5mm.

3. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 1, characterized in that, In step S2, the preheating temperature is 780-880℃, the heating rate is ≤5℃ / min, the holding time is 40-60min, and the total heating time of preheating, heating and holding is 90-150min.

4. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 1, characterized in that, In step S3, the initial rolling temperature of the roughing mill is 1000-1050℃, the roughing mill consists of 6-8 passes, the reduction rate of the first pass of the roughing mill is 15%-20%, the reduction rate of the second pass of the roughing mill is 20%-25%, and the reduction rate of the subsequent passes of the roughing mill gradually increases to 25%-35%.

5. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 1, characterized in that, In step S3, the pressure of the first descaling is 20-22 MPa, and the pressure of the second descaling is 18-20 MPa after the first pass of the rough rolling.

6. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 4, characterized in that, In step S3, the reduction rate of subsequent passes in the roughing mill is gradually increased to 30%-35%.

7. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 1, characterized in that, In step S3, the starting rolling temperature of the finishing mill is 930-990℃, the starting rolling temperature of the reducing mill is 860-900℃, and the wire drawing temperature is 805-825℃.

8. The method for improving the plastic deformation capacity of hot-rolled wire rod according to claim 1, characterized in that, In step S3, the reducing mill rolls 3-4 passes in total. The reduction rate of a single pass of the reducing mill is 10%-15%, and the total reduction rate of the reducing mill is 30%-60%. The specification of the first hot-rolled wire rod is φ6-10mm.

9. A hot-rolled wire rod, characterized in that, It is prepared by the method for improving the plastic deformation capacity of hot-rolled wire rod as described in any one of claims 1-8.

10. A hot-rolled wire rod according to claim 9, characterized in that, The hot-rolled wire rod has a hardness ≤260HV, an elongation ≥20%, and a section shrinkage ≥45%.

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