Wire rod for spring steel with high fatigue life, wire and manufacturing method therefor

Abstract

A wire rod for spring steel and a wire made therefrom. The wire rod for spring steel contains, in addition to Fe and inevitable impurities, the following chemical elements in percentage by mass: C: 0.52-0.60%, Si: 1.60-1.80%, Mn: 0.50-0.70%, Cr: 0.60-0.80%, V: 0.05-0.09%, Ce: 0.002-0.005%, Y: 0.006-0.009%, and 0<Al≤0.002%. The wire rod for spring steel has good strength and toughness and good fatigue performance.

Description

A high fatigue life spring steel wire rod, wire rod and its manufacturing method Technical Field

[0001] This disclosure relates to a wire rod, a wire, and a method for manufacturing the same, and more particularly to a wire rod, a wire, and a method for manufacturing the same for spring steel. Background Technology

[0002] Springs, as important mechanical components, are widely used in transportation, machinery manufacturing, and the automotive industry. Springs operate cyclically under alternating stresses such as bending and torsion, therefore requiring high tensile strength, ductility, and fatigue life. Fatigue life is a key performance indicator for spring steel.

[0003] The mechanical properties, surface quality, and purity of the steel all affect the fatigue life of a spring. Improving the strength and hardness of the material, ensuring that the surface of the spring steel is free of obvious defects, and reducing the number and size of hard inclusions in the steel are all beneficial to improving the fatigue life of spring steel.

[0004] For example, Chinese patent document CN117344212A, published on January 5, 2024, entitled "A Spring Steel and its Manufacturing Method," discloses a high fatigue life spring steel and its manufacturing method. The spring steel's chemical composition percentages are: C: 0.52-0.58%, Si: 1.40-1.60%, Mn: 0.45-0.85%, Cr: 0.40-0.80%, Al: 0.001-0.003%, O: 0.0015-0.0035%, Ca: ≤0.0005%, N: ≤0.0055%, Ti: ≤0.0005%, P: ≤0.012%, S: ≤0.008%, with the balance being Fe and unavoidable impurity elements. No rare earth elements or microalloying elements are added to this spring steel. After heat treatment, the tensile strength of spring steel is above 1900MPa, the reduction of area is ≥45%, and the fatigue life is ≥20 million cycles.

[0005] For example, Chinese patent document CN107747060A, published on November 12, 2017, entitled "Production Method of High-Strength, High-Fatigue-Life Spring Steel," discloses a method for producing high-strength, high-fatigue-life spring steel. The elemental composition of the wire rod includes C: 0.51%–0.59%, Si: 1.40%–1.60%, Mn: 0.50%–0.80%, P≤0.012%, S≤0.010%, Cr: 0.50–0.80%, Nb≤0.02%, Ti≤0.005%, Al≤0.005%, with the balance being Fe and unavoidable impurity elements. This spring steel is not subjected to subsequent quenching and tempering heat treatment. Summary of the Invention

[0006] One of the objectives of this disclosure is to provide a high fatigue life spring steel wire rod. This wire rod is optimized and modified by utilizing appropriate amounts of rare earth elements Y and Ce, while simultaneously reducing and refining the number and size of hard inclusions, thereby giving the spring steel wire rod excellent strength and toughness.

[0007] To achieve the above objectives, this disclosure provides a spring steel wire rod that, in addition to Fe and unavoidable impurities, contains the following chemical elements in the following mass percentages:

[0008] C: 0.52~0.60%, Si: 1.60~1.80%, Mn: 0.50~0.70%, Cr: 0.60%~0.80%, V: 0.05~0.09%, Ce: 0.002%~0.005%, Y: 0.006~0.009%, Al≤0.0020%.

[0009] Preferably, in the spring steel wire rod of this disclosure, the mass percentage content of its chemical elements is as follows:

[0010] C: 0.52–0.60%, Si: 1.60–1.80%, Mn: 0.50–0.70%, Cr: 0.60%–0.80%, V: 0.05–0.09%, Ce: 0.002%–0.005%, Y: 0.006–0.009%, Al ≤ 0.0020%; balance Fe and unavoidable impurities.

[0011] Preferably, in the spring steel wire rod of this disclosure, the mass percentage content of each chemical element also satisfies: (Ce+Y) / (O+S)≥1.00, where the symbol of each element is replaced by the value before the percentage sign of the corresponding element mass percentage content.

[0012] Preferably, the unavoidable impurities in the spring steel wire rod of this disclosure include N, P, S, O and Ti, and N≤0.0050%, P≤0.008%, S≤0.008%, O≤0.0020%, and Ti≤0.0010%.

[0013] Preferably, the microstructure of the spring steel wire rod disclosed herein is pearlite + ferrite.

[0014] Preferably, in the spring steel wire rod of this disclosure, the detection area is 1000 mm² in the direction parallel to the longitudinal axis of the wire rod. 2 Within this range, the number of inclusions with a width of 5–15 μm does not exceed 20.

[0015] Preferably, in the spring steel wire rod of this disclosure, the width of the inclusions is <15μm and the length is ≤50μm.

[0016] Another object of this disclosure is to provide a wire that has a high fatigue life after being subjected to a quenching and tempering heat treatment process from the aforementioned wire rod.

[0017] To achieve the above objectives, this disclosure provides a wire made from the aforementioned spring steel wire rod.

[0018] Preferably, the microstructure of the wire disclosed herein is tempered sorbite.

[0019] Preferably, the wire disclosed herein has a tensile strength ≥2000MPa, a reduction of area ≥45%, and a fatigue life exceeding 20 million cycles.

[0020] Another object of this disclosure is to provide a method for manufacturing spring steel wire rod. This method employs a reasonable rolling process to obtain a spring steel wire rod with good strength and toughness and a high fatigue life.

[0021] To achieve the above objectives, this disclosure provides a method for manufacturing wire rod for spring steel, comprising the following steps:

[0022] Smelting and continuous casting;

[0023] Initial rolling and billet preparation;

[0024] High-speed wire rod controlled rolling: heating temperature is 950~1050℃, initial rolling temperature is 930~1000℃, sizing temperature is 890~910℃, and wire drawing temperature is 860~890℃;

[0025] Stelmore fan cooling.

[0026] Preferably, in the method for manufacturing spring steel wire rod of this disclosure, during the cooling process of the Stellmore fan, the air volume of each fan section is controlled as follows: the air volume of F1-F3 fans is 10-30%, the air volume of F4-F6 fans is 0-10%, and the air volume of F7-F14 fans is 0%.

[0027] Preferably, in the initial rolling and billet preparation step of the spring steel wire rod disclosed herein, the rolling temperature is 1050–1200°C.

[0028] Another object of this disclosure is to provide a method for manufacturing a wire. This method employs a quenching and tempering heat treatment process to obtain a wire with high fatigue life and mechanical properties.

[0029] To achieve the above objectives, this disclosure provides a method for manufacturing wire, comprising the steps of:

[0030] Smelting and continuous casting;

[0031] Initial rolling and billet preparation;

[0032] High-speed wire rod controlled rolling: heating temperature is 950~1050℃, initial rolling temperature is 930~1000℃, sizing temperature is 890~910℃, and wire drawing temperature is 860~890℃;

[0033] Stelmore fan cooling;

[0034] Peeling and pulling;

[0035] Quenching and tempering heat treatment: Quenching temperature is 860~920℃, followed by oil cooling; tempering temperature is 400~450℃, followed by air cooling.

[0036] Preferably, in the stripping process of the wire manufacturing method disclosed herein, a full stripping process is used to treat the oxide scale and decarburized layer on the surface of the wire rod to remove the oxide scale and decarburized layer on the surface of the wire rod.

[0037] The spring steel wire rod, wire rod, and manufacturing method disclosed herein have the following advantages and beneficial effects compared to the prior art:

[0038] The spring steel wire rod disclosed herein is optimized and modified by using appropriate amounts of rare earth elements Y and Ce, while strictly controlling the content of impurity elements, reducing and refining the number and size of hard inclusions, so that the spring steel wire rod has good strength and toughness.

[0039] In some embodiments, the width of the inclusions in the spring steel of this disclosure is <15μm and the length is ≤50μm.

[0040] The wire disclosed herein has a high fatigue life. In some embodiments, the tensile strength of the wire disclosed herein is ≥2000MPa, the reduction of area is ≥45%, and the fatigue life exceeds 20 million cycles. Detailed Implementation

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0042] In this paper, tensile strength and reduction of area were determined according to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Test method at room temperature".

[0043] In this paper, fatigue life was determined according to GB / T 16947-2009 "Specification for Fatigue Testing of Helical Springs".

[0044] In this paper, the microstructure, number of inclusions, and size of inclusions in wire rods and wires were determined using metallographic microscopy or scanning electron microscopy.

[0045] As is commonly used in this field, Steyrmo fans refer to a series of fan devices arranged on the Steyrmo controlled cooling line for forced air cooling of high-temperature rolled wire rods to precisely control their cooling rate and microstructure transformation. These fans are divided into several groups (such as F1-F14) along the length of the cooling line, and by independently adjusting the airflow of each group of fans, precise temperature control can be achieved for different cooling stages.

[0046] The design principles of each chemical element in the spring steel wire rod disclosed herein are as follows:

[0047] C: In the spring steel wire rod disclosed herein, carbon (C) is an essential element for improving the strength of spring steel, and its content directly determines the strength of the product. Simultaneously, C can increase the content of pearlite and sorbite in the microstructure, refine the lamellar structure, and improve the hardenability of the steel. When the mass percentage of C in the wire rod is too low, the strength of the spring steel cannot be guaranteed, and it is also detrimental to the precipitation of carbides from microalloying elements. When the mass percentage of C in the wire rod is too high, it will lead to a decrease in plasticity and toughness, reducing the processing performance and fatigue life of the spring. Therefore, in the spring steel wire rod disclosed herein, the mass percentage of C is controlled between 0.52% and 0.60%.

[0048] Si: In the spring steel wire rod disclosed herein, Si can improve the elastic limit and resistance to spring reduction of the spring steel material, thus optimizing spring performance. Simultaneously, Si can also play a role in solid solution strengthening, increasing the strength of the steel. Si is also commonly added to steel as a deoxidizer during the smelting process. However, when the mass percentage content of Si in the wire rod is too high, it not only affects the forming performance of the spring but also promotes the diffusion of carbon in the steel, exacerbating decarburization; in severe cases of complete decarburization, it can also lead to a decrease in the fatigue performance of the spring. Therefore, in order to maximize the beneficial effects of Si, the mass percentage content of Si in the spring steel wire rod disclosed herein is controlled between 1.60% and 1.80%.

[0049] Mn: In the spring steel wire rod disclosed herein, Mn can play a role in solid solution strengthening and can also improve the strength and hardenability of the material. Mn is also often added as a deoxidizer during the steelmaking process, and can also form MnS with the harmful element S in the steel, reducing the harm caused by S. However, when the mass percentage content of Mn in the wire rod is too high, it is easy to cause segregation problems in the steel, and it also leads to a tendency for coarse grains. Therefore, in the spring steel wire rod disclosed herein, the mass percentage content of Mn is controlled between 0.50% and 0.70%.

[0050] Cr: In the spring steel wire rod disclosed herein, Cr element is beneficial for improving the hardenability of spring steel. At the same time, an appropriate amount of Cr element can refine the microstructure after tempering, improve the strength and plasticity of the material, and increase its tempering stability. However, when the mass percentage content of Cr element in the wire rod is too high, coarse carbides will form, reducing the plasticity and toughness of the material. Therefore, in the spring steel wire rod disclosed herein, the mass percentage content of Cr element is controlled between 0.60% and 0.80%.

[0051] V: In the spring steel wire rod disclosed herein, vanadium (V), as the most commonly used microalloying element in steel, can combine with carbon (C) to form fine, dispersed carbides, which can inhibit the growth of austenite grains and thus refine the grain size. Simultaneously, vanadium also plays a role in precipitation strengthening, increasing the strength of the steel without reducing its ductility and toughness. However, when the mass percentage of vanadium in the wire rod is too high, it leads to the aggregation of large amounts of carbides and the formation of large-sized precipitates. Therefore, in the spring steel wire rod disclosed herein, the mass percentage of vanadium is controlled between 0.05% and 0.09%.

[0052] Ce: In the spring steel wire rod disclosed herein, Ce, as a rare earth element, is added to the steel to alter the morphology of inclusions. Appropriate addition of Ce can refine the microstructure, thereby improving the strength and plasticity of the spring steel. However, when the mass percentage of Ce in the wire rod is too high, it leads to coarsening of the microstructure and a decrease in mechanical properties. Therefore, in the spring steel wire rod disclosed herein, the mass percentage of Ce is controlled between 0.002% and 0.005%.

[0053] Y: In the spring steel wire rod disclosed herein, element Y, as a rare earth element, is added to the steel. It readily segregates at grain boundaries, reducing the content of impurity elements at these boundaries, purifying the molten steel and grain boundaries, and improving both intragranular strength and grain boundary strength. Element Y can also effectively improve the toughness and plasticity of the material, making large rare earth composite inclusions easier to float during refining, while retaining smaller inclusions in the molten steel, making them easier to break down during subsequent processing and improving inclusion size. Therefore, in the spring steel wire rod disclosed herein, the mass percentage of element Y is controlled between 0.006% and 0.009%.

[0054] Al: In the spring steel wire rod disclosed herein, Al is the most effective deoxidizing element in steel. However, during the smelting process, Al easily forms alumina-like inclusions that are not easily deformable. Large, brittle inclusions are one of the main factors causing abnormal fractures in spring steel, affecting the fatigue life of the material. Therefore, in order to effectively and stably control the alumina-like hard inclusions in the steel and reduce the occurrence of large, hard inclusions, the Al content in the spring steel wire rod disclosed herein should be reduced as much as possible, and the mass percentage of Al should be controlled to Al ≤ 0.0020%.

[0055] In the spring steel wire rod disclosed herein, N, P, S, O, and Ti are all unavoidable impurity elements. Among them, P and S, as impurity elements, will cause segregation at the austenite grain boundaries, leading to embrittlement of the steel. To obtain steel with better quality and performance, and to avoid excessive inclusion size and quantity, the content of impurity elements should be minimized. Furthermore, in the spring steel wire rod disclosed herein, N will form nitrides with microalloying elements in the steel, especially with Ti and Al, forming brittle inclusions, which adversely affect the drawing process and the fatigue life of the springs. Therefore, in the spring steel wire rod disclosed herein, the mass percentage content of the aforementioned impurity elements is preferably controlled as follows: N ≤ 0.0050%, P ≤ 0.008%, S ≤ 0.008%, O ≤ 0.0020%, and Ti ≤ 0.0010%.

[0056] The method for manufacturing spring steel wire rod disclosed herein includes the following steps: smelting and continuous casting; initial rolling; high-speed wire rod controlled rolling: heating temperature of 950–1050°C, initial rolling temperature of 930–1000°C, sizing temperature of 890–910°C, and wire drawing temperature of 860–890°C; and Stelmore fan cooling.

[0057] In some implementations, smelting is carried out in an electric furnace or converter, followed by ladle refining using LF ladle refining and VD vacuum degassing to allow the refining slag to fully react with inclusions in the steel.

[0058] In some implementations, the VD vacuum degassing treatment time is more than 30 minutes to ensure that gaseous elements in the molten steel are completely removed.

[0059] In some implementations, billet segregation is controlled by adjusting the casting speed and light reduction process. Specifically, the superheating temperature during continuous casting can be controlled at 25–30°C, the light reduction can be controlled at 20–25 mm, and the casting speed can be controlled at 0.6–0.8 m / min.

[0060] In some implementations, the heating and holding time in the high-speed wire rod controlled rolling process is controlled to be 1 to 2 hours to ensure uniform heating of the billet.

[0061] The following will further explain and illustrate the spring steel wire rods, wires and their manufacturing methods with reference to specific embodiments. However, such explanation and illustration do not constitute an undue limitation on the technical solutions of this disclosure.

[0062] Examples 1-5 and Comparative Examples 1-2

[0063] The wire rods of Examples 1-5 and Comparative Examples 1-2 were all prepared using the following steps:

[0064] (1) Smelting and continuous casting: Smelting is carried out in an electric furnace or converter, followed by ladle refining using LF ladle refining and VD vacuum degassing treatment to ensure that the refining slag reacts fully with the inclusions in the steel. The molten steel is cast into large square billets with a cross-sectional dimension of 320mm×425mm using a continuous casting machine, and argon gas is used for protection during the casting process.

[0065] (2) Initial rolling: The large square billet obtained by continuous casting is subjected to initial rolling after high-temperature diffusion. The rolling temperature is 1050~1200℃ and it is rolled into a small square billet of 142mm×142mm. The small square billet is tested for surface defects by magnetic particle testing or ultrasonic testing. Then it is subjected to finishing treatment such as grinding with a grinding wheel and waits to enter the heating furnace for high-speed wire rod finishing rolling.

[0066] (3) High-speed wire rod controlled rolling: The heating temperature is controlled at 950~1050℃, the initial rolling temperature is 930~1000℃, the sizing temperature is 890~910℃, and the wire drawing temperature is 860~890℃. The resulting wire rod has a specification of Φ5.5-10mm.

[0067] (4) Steilmo fan cooling: After the wire rod is rolled, it enters the Steilmo air cooling line for controlled cooling. The air volume of each fan is controlled as follows: the air volume of F1-F3 fans is 10-30%, the air volume of F4-F6 fans is 0-10%, and the air volume of F7-F14 fans is 0%.

[0068] The wires of Examples 1-5 and Comparative Examples 1-2 were obtained from the wire rods obtained in the various embodiments and comparative examples through the following steps:

[0069] (5) Peeling and drawing: The surface of the wire rod is treated by a full peeling process to remove the surface oxide scale and decarburized layer. Then the wire rod is drawn in multiple passes to produce semi-finished steel wire.

[0070] (6) Quenching and tempering heat treatment: The drawn spring steel wire is subjected to quenching and tempering heat treatment. The quenching temperature is 860~920℃, followed by oil cooling. The tempering temperature is 400~450℃, followed by air cooling.

[0071] Tables 1-1 and 1-2 list the mass percentages of each chemical element in the wire rods of Examples 1-5 and Comparative Examples 1-2.

[0072] Table 1-1.

[0073] (wt%, balance Fe and other unavoidable impurities other than N, P, S, O and Ti)

[0074] Table 1-2.

[0075] (The balance consists of Fe and other unavoidable impurities besides N, P, S, O, and Ti.)

[0076] Tables 2-1, 2-2, and 2-3 list the specific process parameters for the wire rods and coils of Examples 1-5 and Comparative Examples 1-2.

[0077] Table 2-1.

[0078] Table 2-2.

[0079] Table 2-3.

[0080] Samples were taken from the wire rods of Examples 1-5 and Comparative Examples 1-2, and the microstructure of each example and comparative example was observed using a metallographic microscope. The results of the microstructure observation are listed in Table 3 below.

[0081] Table 3 lists the microstructure observation results of the wire rods in Examples 1-5 and Comparative Examples 1-2.

[0082] Table 3.

[0083] As can be seen from Table 3 above, the microstructure of the wire rods in Examples 1-5 is pearlite + ferrite, and the width of the inclusions is less than 15 μm and the length is less than or equal to 50 μm.

[0084] Samples of steel wires (wires) from Examples 1-5 and Comparative Examples 1-2 were taken and their microstructures were observed using a metallographic microscope (model Axio plan2) and a scanning electron microscope (model EVO MA25). The results of the microstructure observations are listed in Table 4 below.

[0085] Table 4 lists the microstructure observation results of the steel wires in Examples 1-5 and Comparative Examples 1-2.

[0086] Table 4.

[0087] As can be seen from Table 4 above, the microstructure of the steel wires in Examples 1-5 is tempered sorbite.

[0088] In addition, the steel wires from Examples 1-5 and Comparative Examples 1-2 were sampled again and subjected to relevant mechanical property tests. The results of the mechanical property tests are listed in Table 5. The relevant mechanical property test methods are as follows:

[0089] Tensile test: Under room temperature conditions, the tensile strength and reduction of area of ​​each example and comparative example were determined according to GB / T 228.1-2010 "Metallic materials - Tensile testing - Part 1: Test method at room temperature".

[0090] Fatigue life test: After making springs of the same model from the steel wires of each embodiment and the comparative example, fatigue life test was carried out in accordance with GB / T 16947-2009 "Specification for Fatigue Test of Helical Springs".

[0091] Table 5 lists the relevant mechanical property test results of the steel wires in Examples 1-5 and Comparative Examples 1-2.

[0092] Table 5.

[0093] As can be seen from Table 5 above, the tensile strength of the steel wires in Examples 1-5 is all above 2000MPa, the reduction of area is all above 45%, and the fatigue life is all above 20 million cycles. They have good strength and toughness and can meet the needs of springs used in automotive and other parts with high fatigue life requirements.

[0094] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0095] It should also be noted that the embodiments listed above are merely specific embodiments of this disclosure. Obviously, this disclosure is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in this disclosure, and should all fall within the protection scope of this disclosure.

Claims

1. A spring steel wire rod containing Fe and unavoidable impurities, characterized in that, The wire rod also contains the following chemical elements in the following mass percentages: C: 0.52~0.60%, Si: 1.60~1.80%, Mn: 0.50~0.70%, Cr: 0.60%~0.80%, V: 0.05~0.09%, Ce: 0.002%~0.005%, Y: 0.006~0.009%, Al≤0.0020%.

2. The spring steel wire rod as described in claim 1, characterized in that, The chemical element mass percentage content of the wire rod is: C: 0.52–0.60%, Si: 1.60–1.80%, Mn: 0.50–0.70%, Cr: 0.60%–0.80%, V: 0.05–0.09%, Ce: 0.002%–0.005%, Y: 0.006–0.009%, Al ≤ 0.0020%; balance Fe and unavoidable impurities.

3. The spring steel wire rod as described in claim 1 or 2, characterized in that, The mass percentage content of each chemical element also satisfies: (Ce+Y) / (O+S)≥1.00, where the element symbols are replaced with the values ​​before the percentage signs of the corresponding element mass percentage content.

4. The spring steel wire rod as described in claim 1 or 2, characterized in that, Unavoidable impurities include N, P, S, O, and Ti, with N ≤ 0.0050%, P ≤ 0.008%, S ≤ 0.008%, O ≤ 0.0020%, and Ti ≤ 0.0010%.

5. The spring steel wire rod as described in claim 1 or 2, characterized in that, The microstructure of the wire rod is pearlite + ferrite.

6. The spring steel wire rod as described in claim 1 or 2, characterized in that, The width of the inclusions in the wire rod is <15μm and the length is ≤50μm; preferably, the detection area is 1000mm² in the direction parallel to the longitudinal axis of the wire rod. 2 Within this range, the number of inclusions with a width of 5–15 μm does not exceed 20.

7. A wire made from spring steel wire rod according to any one of claims 1-6.

8. The wire as described in claim 7, characterized in that, The microstructure of the wire is tempered sorbite.

9. The wire as described in claim 7, characterized in that, The wire has a tensile strength ≥2000MPa, a reduction of area ≥45%, and a fatigue life exceeding 20 million cycles.

10. A method for manufacturing spring steel wire rod according to any one of claims 1-6, characterized in that, The method includes the following steps: Smelting and continuous casting; Initial rolling and billet preparation; High-speed wire rod controlled rolling: heating temperature is 950~1050℃, initial rolling temperature is 930~1000℃, sizing temperature is 890~910℃, and wire drawing temperature is 860~890℃; Stelmore fan cooling.

11. The method as described in claim 10, characterized in that, During the cooling process of the Stellmore fan, the air volume of each fan section is controlled as follows: F1-F3 fans have an air volume of 10-30%, F4-F6 fans have an air volume of 0-10%, and F7-F14 fans have an air volume of 0%.

12. The method as described in claim 10, characterized in that, In the initial rolling process, the rolling temperature is 1050–1200℃.

13. A method for manufacturing the wire according to any one of claims 7-9, characterized in that, The method includes the following steps: Smelting and continuous casting; Initial rolling and billet preparation; High-speed wire rod controlled rolling: heating temperature is 950~1050℃, initial rolling temperature is 930~1000℃, sizing temperature is 890~910℃, and wire drawing temperature is 860~890℃; Stelmore fan cooling; Peeling and pulling; Quenching and tempering heat treatment: Quenching temperature is 860~920℃, followed by oil cooling; tempering temperature is 400~450℃, followed by air cooling.

14. The method as described in claim 13, characterized in that, In the peeling process, a full peeling process is used to treat the oxide scale and decarburized layer on the surface of the wire rod.

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