CN110791709A

CN110791709A - Structural steel wire rod and method for improving cutting performance of structural steel wire rod

Info

Publication number: CN110791709A
Application number: CN201911099178.5A
Authority: CN
Inventors: 胡娟; 李成良; 黄德智; 周楠; 谢杰智; 雷中钰; 敖永明; 农之江; 刘金源; 刘春林
Original assignee: Shaogang Songshan Co Ltd Guangdong
Current assignee: SGIS Songshan Co Ltd; Shaogang Songshan Co Ltd Guangdong
Priority date: 2019-11-11
Filing date: 2019-11-11
Publication date: 2020-02-14
Anticipated expiration: 2039-11-11
Also published as: CN110791709B

Abstract

A structural steel wire and a method for improving the cutting performance of the structural steel wire belong to the field of steel smelting. The composition of the structural steel wire rod is as follows: 0.42 to 0.48% of C, 0.15 to 0.35% of Si, 0.6 to 0.9% of Mn, 0.030% or less of P, 0.012 to 0.028% of S, Ni: 0.003-0.2%, Cr: 0.02 to 0.2%, Cu: 0.02-0.3 percent of Ni and Cr, and less than or equal to 0.35 percent of Ni and Cr; controlling the Mn/S to be 20-40; the class A inclusion grade is 1.0-3.0 grade; and Als: 0.010-0.035%, and the balance of Fe and inevitable impurities. The structural steel wire rod has good cutting performance.

Description

Structural steel wire rod and method for improving cutting performance of structural steel wire rod

Technical Field

The application relates to the field of steel smelting, in particular to a structural steel wire and a method for improving the cutting performance of the structural steel wire.

Background

Structural steel wire is often required to be properly processed in applications to meet specific size and shape requirements. However, the conventional structural steel wire rod has poor cutting workability, which often causes problems such as damage to a tool during cutting, low efficiency, and increased machining cost. In response to these problems with structural steel wire, some attempts have been made in the prior art to address the above dilemma.

For example, patent No. CN201810458364 is a control method for improving the machinability of high-sulfur free-cutting steel, and discloses a way to improve the machinability of the free-cutting steel by obtaining ideal spindle-shaped sulfides, wherein S is 0.25% to 0.50%, and Mn/S is not less than 4.0, so that sufficient MnS can be formed. The invention can greatly improve the cutting performance of the wire rod and is mainly used for products with higher requirements on the cutting performance. However, the high-sulfur free-cutting steel disclosed in this patent is difficult to produce and is not suitable for application to structural steel wire rods having mainly mechanical properties and secondarily cutting properties.

The invention patent with the patent number of CN201710122704 is a preparation method of a graphitized free-cutting steel high-speed wire rod, and discloses a preparation method of graphitized annealing, wherein isothermal treatment of 620-Ac 1 is mainly adopted, isothermal time is 3-6 hours, the structure after annealing mainly comprises graphite and ferrite grains, the graphite is in a nearly spherical shape and is uniformly distributed, the average diameter is about 5 mu m, and the average diameter of the ferrite grains is about 20 mu m. However, the process not only requires heat treatment equipment, but also has a long production period, and is not suitable for industrial mass production.

Disclosure of Invention

The application provides a method for improving the cutting performance of a structural steel wire rod, which can improve the cutting performance of the structural steel wire rod and has good mechanical performance.

The embodiment of the application is realized as follows:

in a first aspect, the present examples provide a structural steel wire rod having a class a inclusion rating of 1.0 to 3.0.

The chemical components of the structural steel wire rod are as follows, C is 0.42-0.48%, Si is 0.15-0.35%, Mn is 0.6-0.9%, P is less than 0.030%, S is 0.012-0.028%, Ni: 0.003-0.2%, Cr: 0.02 to 0.2%, Cu: 0.02-0.3 percent of Ni and Cr, and less than or equal to 0.35 percent of Ni and Cr; the value of Mn/S is 20-40, Als:

0.010-0.035%, and the balance of Fe and inevitable impurities.

In a second aspect, the present examples provide a method of improving machinability of a structural steel wire rod. The method includes controlling a rolling temperature of a billet according to a target diameter of the wire rod to obtain a structural steel wire rod having a class a inclusion grade of 1.0 to 3.0.

The chemical components of the steel billet comprise the following components: 0.42 to 0.48% of C, 0.15 to 0.35% of Si, 0.6 to 0.9% of Mn, 0.030% or less of P, 0.012 to 0.028% of S, Ni: 0.003-0.2%, Cr: 0.02 to 0.2%, Cu: 0.02-0.3 percent of Ni and Cr, and less than or equal to 0.35 percent of Ni and Cr; the value of Mn/S is 20-40, Als: 0.010-0.035%, and the balance of Fe and inevitable impurities.

The rolling schedule for rolling the billet is as follows:

when the diameter of the wire rod is more than or equal to 5.5mm and less than or equal to 10mm, the initial rolling temperature is 950 ℃ to 1100 ℃, and the final rolling temperature is 780 ℃ to 840 ℃. When the diameter of the wire rod is more than 10mm and less than or equal to 15mm, the initial rolling temperature is 950 ℃ to 1100 ℃, and the final rolling temperature is 800 ℃ to 860 ℃. When the diameter of the wire rod is more than 15mm and less than or equal to 20mm, the initial rolling temperature is 950 ℃ to 1100 ℃, and the final rolling temperature is 820 ℃ to 880 ℃.

Has the advantages that:

in order to improve the cutting performance of the structural steel wire rod and obtain proper chip breaking, and simultaneously have mechanical performance so as to meet the requirements of cutting processing and application to the field of household appliances such as refrigerators, air conditioners and the like as mechanical parts, the chemical composition of the structural steel is selected and controlled in the application example, and the structural steel wire rod mainly relates to S (sulfur), Ni + Cr (manganese + chromium); Mn/S (manganese/sulfur), A-type inclusion grade and the like, and inclusion control.

In addition, the scheme also has the following characteristics:

the S content is controlled to be 0.012-0.028%, the reduced manganese-sulfur ratio (Mn/S is controlled to be 20-40) is controlled, and the grade of A-type inclusions (GB/T10561A method is adopted) is improved to 1.0-3.0 grade from below 1.0. Because the A-type inclusion component is strip MnS formed by combining Mn and S, the continuity of a matrix can be blocked during turning, so that chip breaking is facilitated, and the cutting performance is improved.

2. By reasonably controlling the smelting process, the narrow-range control of S, Mn content is realized, and the components are ensured to meet the target requirements.

3. In addition, the initial rolling temperature is fixed, and different final rolling temperatures are determined through a large number of tests. Particularly, according to wire rods with different diameters, the initial rolling temperature is 950-1100 ℃, the final rolling temperature is 780-880 ℃, so that the final structure of the wire rods is a uniform pearlite + ferrite structure from the center to the surface, and the wire rods with proper cutting performance and hardness and good plasticity are obtained.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present application and therefore should not be considered as limiting the scope, and it will be apparent to those skilled in the art that other related drawings can be obtained from the drawings without inventive effort.

FIG. 1 is a diagram showing the morphology of A fine inclusions in a conventional structural steel wire rod;

FIG. 2 is a morphology chart of A fine inclusions of a structural steel wire rod obtained based on an embodiment of the present application;

FIG. 3 is a cut (chip) profile of the structural steel wire rod of FIG. 1;

fig. 4 is a cut (chip) profile of the structural steel wire rod of fig. 2.

Detailed Description

Embodiments of the present application will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present application and should not be construed as limiting the scope of the present application. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

In order to achieve a balance between mechanical properties and machinability, the inventors propose a structural steel with a new chemical composition in the examples of the present application. The structural steel may be fabricated for use in a variety of configurations and shapes, such as round steel, wire, and the like. In the examples, the structural steel is exemplarily illustrated in the form of a wire.

In light of the foregoing, the composition of the structural steel is as follows: 0.42 to 0.48% of C, 0.15 to 0.35% of Si, 0.6 to 0.9% of Mn, 0.030% or less of P, 0.012 to 0.028% of S, Ni: 0.003-0.2%, Cr: 0.02 to 0.2%, Cu: 0.02-0.3 percent of Ni and Cr, and less than or equal to 0.35 percent of Ni and Cr; controlling the Mn/S to be 20-40; and Als: 0.010-0.035%, and the balance of Fe and inevitable impurities. And the class A inclusion grade is 1.0-3.0.

Illustratively, the content of C may also be 0.43%, 0.44%, 0.45%, 0.46% or 0.47%. The silicon content may also be 0.15%, 0.20%, 0.25% or 0.30%. The manganese content may also be 0.65%, 0.70%, 0.75%, 0.80% or 0.85%. The content of phosphorus may also be 0.015%, 0.020% or 0.025%. The sulfur content may also be 0.015%, 0.020%, or 0.025%. The nickel content may also be 0.005%, 0.010%, 0.015% or 0.020%. The chromium content may also be 0.05%, 0.10% or 0.15%. The copper content may also be 0.04%, 0.06%, 0.08% or 0.10%. The total amount of nickel and chromium may also be 0.05%, 0.10%, 0.15%, 0.20% or 0.25%. The manganese/sulfur ratio may also be 25, 28, 30, 32, 35 or 38. The class a inclusions are rated, for example, 1.0, 1.5, 2.0, 2.5, or 3.0.

Wherein the chemical in the structural steel may be appropriately selected within the above range. For avoiding redundancy, for the structural steel in the above example, specific components thereof may also be defined as follows. For example, the S content ranges from 0.020% to 0.025%, and the S content can be selected from 0.015%, 0.020% and 0.025%. The Mn/S ratio ranges from 25 to 35, 28 to 30. The Mn/S ratio can also be selected from 25, 28, 30 and 35. The grade range of the A-type inclusion is 1.5-2.5, and the grade of the A-type inclusion can be 1.5, 2.0 and 2.5. Ni + Cr is in the range of 0.10-0.15%, and Ni + Cr is 0.10-0.15%.

In particular, the diameter of the structural steel wire rod may be Φ 5.5mm to 10 mm; phi 10.1 mm-15 mm; phi 15.1 mm-20 mm.

Thus, the chemical composition of the structural steel is clarified, and in order to obtain the structural steel having the composition, the example also provides a smelting process thereof, which is advantageous for those skilled in the art to implement the scheme of the present application.

The smelting process mainly comprises three steps, and mainly relates to converter primary smelting and secondary refining outside a furnace (including LF refining furnace refining and RH furnace refining). In addition, in order to obtain various specific steel products, the smelted molten steel is poured to obtain a billet, and different rolling modes are selected according to different use requirements to obtain steel products with specific specifications, such as wire rods.

Step S1 is as follows.

Smelting the molten iron without desulfurization pretreatment by using a converter, and sequentially carrying out deoxidation alloying treatment and slag charge addition in the tapping process of the converter.

The deoxidation of the molten steel is to add deoxidation elements into the steel, so that the deoxidation elements react with oxygen to generate deoxidation products which are insoluble in the molten steel. Since the deoxidized product is insoluble in molten steel, it floats from the molten steel into slag, i.e., the removed oxygen is removed in the form of inclusions. The oxygen content in the steel can reach the requirement through the deoxidation operation. The alloying of the molten steel means that the operation of adding ferroalloy or metal into the steel is alloying in order to adjust the content of the alloy elements in the steel to reach the component range of the steel specification.

The deoxidation alloying treatment can be realized by adding aluminum iron and then adding alloy elements including carbon and manganese during tapping. In an alternative embodiment, the amount of aluminum and iron is 1.5-2.5 kg/t, or 1.6kg/t, or 1.7kg/t, or 1.8kg/t, or 2.0kg/t, 2.1kg/t, or 2.2kg/t, or 2.4 kg/t.

The added slag can be selected from lime and synthetic slag. Corresponding to the dosage of the aluminum and the iron, the dosage of the lime can be selected to be 3.0 plus or minus 0.3Kg/t, and the dosage of the synthetic slag is selected to be 2.5 plus or minus 0.25 Kg/t. The lime and the synthetic slag have stronger desulfurization and dephosphorization effects and can reduce gas and impurities in molten steel.

Step S2 is as follows.

And the molten steel enters an LF refining furnace for slagging operation to control refining slag.

The slagging operation is, for example, to add lime and low-alkalinity slag into the LF refining furnace to control the alkalinity of the refining slag. Corresponding to a specific alternative example, the lime is used in an amount of 2.0 +/-0.2 Kg/t, the low-alkalinity slag is used in an amount of 4.5 +/-0.45 Kg/t, and the alkalinity of the refining slag is 1.5-3.0 (or 1.6, or 1.7, or 1.9, or 2.1, or 2.3, or 2.5, or 2.7, or 2.9).

In addition, the sulfur content in the molten steel is monitored in the refining process of the LF refining furnace, when the sulfur content deviates from a target value (namely a molten steel smelting component target value), the sulfur content is adjusted by adding ferro-sulphur or a ferro-sulphur wire, and the sulfur is gradually adjusted to the internal control target value +/-0.003 percent of the steel grade requirement by using the ferro-sulphur or the ferro-sulphur wire.

Step S3 is as follows.

And refining the steel tapped from the LF refining furnace in an RH furnace.

And when the steel discharged from the LF refining furnace enters the RH furnace, supplementing aluminum wires in the RH furnace according to the Als content at the refining end point in the LF refining furnace, and supplementing the aluminum wires by the RH furnace according to the Als content at the LF end point until the Als content is controlled to be + 0.015%. An RH furnace is used to accomplish vacuum melting, and in an example, a refining method in the RH furnace includes: adding high-alumina slag in the vacuum refining, adding a pure calcium wire after the vacuum refining is finished, and carrying out soft blowing.

As an alternative specific example, the vacuum refining conditions are that the vacuum degree is less than 0.266KPa, the vacuum treatment time is 18 to 21 minutes (or 19 minutes, or 20 minutes), the dosage of the high-alumina slag is 0.8 to 1.2Kg/t (or 0.9Kg/t, or 1.0Kg/t, or 1.1Kg/t), the dosage of the pure calcium wire is 0.02 to 0.05Kg (or 0.03Kg, or 0.04KG), and the soft blowing time is 10 to 15 minutes (or 11 minutes, or 12 minutes, or 13 minutes, or 14 minutes).

As described above, the molten steel that has been subjected to RH furnace smelting can be subsequently cast and rolled. The rolling process is selected to achieve specific performance requirements. The rolling conditions are, for example:

the heating temperature is 1000 ℃ to 1200 ℃, for example 1050 ℃, 1075 ℃, 1100 ℃, 1108 ℃, 1110 ℃, 1120 ℃, 1136 ℃, 1147 ℃, 1150 ℃, 1163 ℃ or 1178 ℃.

The initial rolling temperature is 950 ℃ to 1100 ℃, for example, 959 ℃, 961 ℃, 968 ℃, 970 ℃, 986 ℃, 992 ℃, 1000 ℃, 1030 ℃, 1058 ℃, 1069 ℃, 1075 ℃, 1083 ℃ or 1099 ℃.

The finishing temperature is 780 to 880 ℃ and is, for example, 784 ℃, 789 ℃, 793 ℃, 800 ℃, 812 ℃, 819 ℃, 822 ℃, 825 ℃, 830 ℃, 837 ℃, 845 ℃, 856 ℃ or 860 ℃.

The spinning temperature is 850 to 910 ℃, for example 854 ℃, 860 ℃, 868 ℃, 873 ℃, 874 ℃, 880 ℃, 896 ℃ or 900 ℃.

The roller table speed is 0.30m/s to 1.20m/s, for example 0.4m/s, 0.5m/s, 0.6m/s, 0.7m/s, 0.8m/s, 0.9m/s, 10.0m/s or 1.1 m/s.

Or the rolling conditions are as follows: the heating temperature is 1050-1150 ℃, the initial rolling temperature is 970-1030 ℃, the final rolling temperature is 780-880 ℃, the spinning temperature is 860-880 ℃, and the roller speed is 0.70-1.10 m/s.

Generally, according to the different structural steel wire rods to be manufactured, different choices can be made for the rolling method, so that the final structure of the wire rod is a uniform pearlite + ferrite structure from the center to the surface, and the wire rod with proper machinability and hardness and good plasticity can be obtained. For example, table 1 below gives an exemplary correspondence of the gauge of a wire rod to the rolling conditions. And as a principle, the finishing rolling temperature is set in different ranges according to the diameter, and the larger the diameter of the wire rod is, the smaller the cooling speed under the same cooling condition is. Therefore, the cooling speed can be increased by increasing the finish rolling temperature, and the reduction of the cooling speed caused by the increase of the diameter is compensated, so that the performance of the wire rod is ensured, and the stable cutting performance is facilitated.

TABLE 1 Rolling temperature control

Therefore, based on the process method, a product with the performance meeting the requirements can be obtained on the basis of the existing steel smelting process. Practice shows that the grade of A fine inclusions of the Shaao steel S45C product (wire rod) can be improved from below 1.0 to 1.0-3.0 by implementing the process, and the A fine inclusions are MnS and are connected in light gray short strips, and the comparison of the A fine inclusions in a specific example can be seen in figures 1 and 2. The chip morphology of the product before the process in the application example is in a slender spiral shape as shown in figure 3; the chip form of the product after the process in the present application example is C-chip or short spiral chip, as shown in fig. 4. For band-shaped chip wrapped workpieces (shown in fig. 3), the machined surface quality of the workpiece and the tool life are affected. The chips after the process is implemented are smooth to flow out and not easy to wind on a workpiece, and the sharpening frequency can be reduced by 50 percent, namely the product cutting performance after the process is implemented in the application example is superior to the cutting performance of a wire rod without the process in the application example.

Example 1

The structural steel wire rod has the following chemical composition.

0.45 percent of C, 0.2 percent of Si, 0.7 percent of Mn, 0.023 percent of P, 0.026 percent of S, 0.011 percent of Ni, 0.038 percent of Cr, 0.060 percent of Cu, and less than or equal to 0.049 percent of Ni and Cr; 20-40 parts of Mn/S; als of 0.016 percent and class A inclusion grade (GB/T10561A method adopted) of 1.5.

The smelting method comprises the following steps:

molten iron is not subjected to desulfurization pretreatment, molten steel is deoxidized and alloyed by converter tapping, 2.0kg/t of aluminum and iron is added in the tapping, alloy elements such as C, Mn are added to adjust the components of the molten steel to the lower limit of the range, and finally 3.0kg/t of slag material lime and 2.5kg/t of synthetic slag are added.

2.0kg/t lime and 4.5kg/t low-alkalinity slag are added into the LF refining furnace, the composition of the refining slag is controlled, and the alkalinity of the refining slag is 2.0. And the LF refining furnace gradually adjusts sulfur to the required internal control target value +/-0.003 percent of the steel grade by using ferro-sulfur or ferro-sulfur wires according to the process sample.

And feeding the aluminum wire by the RH furnace according to the Als content at the LF end point until the Als content is controlled to be +0.015 percent. And (3) carrying out vacuum treatment on the molten steel for 18-21 minutes under the vacuum degree of less than 0.266KPa, and adding 1.0kg/t of high-alumina slag. After the vacuum treatment, 0.04kg of pure calcium wire is fed, and the soft blowing time is controlled according to 10-15 minutes.

After the molten steel was poured, rolling treatment was performed under the following conditions.

The heating temperature is 1000 ℃, the initial rolling temperature is 960 ℃, the final rolling temperature is 800 ℃, the spinning temperature is 900 ℃ and the roller speed is 0.50 m/s.

Other examples and comparative examples of the present application were conducted in the same manner as in example 1, and are mainly different in the chemical composition constitution of the steel and are shown in Table 2.

The chemical composition of the structural steel in each example is as follows in table 2.

The effect of properties of structural steel wire rods (e.g., wire rods) obtained based on the data of table 2 above, a number of examples are given in table 3 below.

TABLE 3 comparison of wire rod Properties

In the properties of the wire rod shown in table 3, the mechanical properties of the wire rod used as a steel wire rod are well reflected in the brinell strength, tensile strength and reduction of area.

The morphology of the class a inclusions of the structural steel wire rod of example 1 is shown in fig. 2; the morphology of the type a inclusions of the structural steel wire rod of comparative example 1 is shown in fig. 1.

The practical feedback shows that the cutting performance of the Shao steel S45C product is obviously improved. Before the solution in the examples of the present application was carried out (i.e., the wire rod article prepared without the solution provided by the present application), the chip morphology of the wire rod product was elongated helical. In contrast, the cutting chip form of the wire rod product after the embodiment of the present application is implemented is C-chip or short spiral chip. Wherein the chip morphology of the product of example 1 is shown in FIG. 4, and the chip morphology of the product of comparative example is shown in FIG. 3.

According to the feedback of a user, the strip-shaped cutting scraps can be wound on the workpiece, so that the machining surface quality of the workpiece and the service life of a cutter are influenced, the cutting scraps after the method is implemented flow out smoothly and are not easy to be wound on the workpiece, the sharpening frequency can be reduced by 50%, and the cutting performance of the implemented wire rod product is superior to that before the method is implemented.

The foregoing is illustrative of the present application and is not to be construed as limiting thereof, as numerous modifications and variations will be apparent to those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A structural steel wire rod is characterized in that the grade of A-type inclusions of the structural steel wire rod is 1.0-3.0 grade;

the structural steel wire comprises the following chemical components of 0.42-0.48% of C, 0.15-0.35% of Si, 0.6-0.9% of Mn, less than 0.030% of P, 0.012-0.028% of S, Ni: 0.003-0.2%, Cr: 0.02 to 0.2%, Cu: 0.02-0.3 percent of Ni and Cr, and less than or equal to 0.35 percent of Ni and Cr; the value of Mn/S is 20-40, Als: 0.010-0.035%, and the balance of Fe and inevitable impurities.

2. The structural steel wire rod according to claim 1, wherein in the structural steel wire rod, the S content is 0.020% to 0.025%;

alternatively, the Mn/S ratio is from 25 to 35; or a Mn/S ratio of 28 to 30;

or the class A inclusion is 1.5-2.5;

alternatively, the Ni + Cr content is 0.10% to 0.15%.

3. The structural steel wire rod according to claim 1, wherein a diameter of the structural steel wire rod is 5.5mm or more and 10mm or less; or the diameter of the structural steel wire rod is more than 10mm and less than or equal to 15 mm; or the diameter of the structural steel wire rod is more than 15mm and less than or equal to 20 mm.

4. A method for improving the machinability of a structural steel wire rod is characterized in that the rolling temperature of a billet is controlled according to the target diameter of the wire rod to obtain the structural steel wire rod with class A inclusion grade from 1.0 grade to 3.0 grade;

the chemical components of the steel billet comprise the following components: 0.42 to 0.48% of C, 0.15 to 0.35% of Si, 0.6 to 0.9% of Mn, 0.030% or less of P, 0.012 to 0.028% of S, Ni: 0.003-0.2%, Cr: 0.02 to 0.2%, Cu: 0.02-0.3 percent of Ni and Cr, and less than or equal to 0.35 percent of Ni and Cr; the value of Mn/S is 20-40, Als: 0.010% -0.035%, the rest is composed of Fe and unavoidable impurity;

the rolling schedule for rolling the billet is as follows:

when the diameter of the wire rod is more than or equal to 5.5mm and less than or equal to 10mm, the initial rolling temperature is 950 ℃ to 1100 ℃, and the final rolling temperature is 780 ℃ to 840 ℃;

when the diameter of the wire rod is more than 10mm and less than or equal to 15mm, the initial rolling temperature is 950 ℃ to 1100 ℃, and the final rolling temperature is 800 ℃ to 860 ℃;

when the diameter of the wire rod is more than 15mm and less than or equal to 20mm, the initial rolling temperature is 950 ℃ to 1100 ℃, and the final rolling temperature is 820 ℃ to 880 ℃.

5. The method for improving the machinability of a structural steel wire according to claim 4, wherein, in the rolling step, the heating temperature is 1000 ℃ to 1200 ℃, the initial rolling temperature is 950 ℃ to 1100 ℃, the final rolling temperature is 780 ℃ to 880 ℃, the spinning temperature is 850 ℃ to 910 ℃, and the roller speed is 0.30m/s to 1.20 m/s.

6. The method for improving the machinability of the structural steel wire rod according to claim 4, wherein, in the rolling step, the heating temperature is 1050 ℃ to 1150 ℃, the starting temperature is 970 ℃ to 1030 ℃, the finishing temperature is 780 ℃ to 880 ℃, the spinning temperature is 860 ℃ to 880 ℃, and the roller table speed is 0.70m/s to 1.10 m/s.

7. The method of improving machinability of a structural steel wire according to claim 4, wherein the billet is manufactured by the following method:

smelting molten iron which is not subjected to desulfurization pretreatment by a converter, and sequentially carrying out deoxidation alloying treatment and slag charge addition in the converter tapping process, wherein the deoxidation alloying method comprises the steps of firstly adding aluminum iron and then adding alloy elements comprising carbon and manganese during tapping, and the added slag charge is lime and synthetic slag;

the molten steel enters an LF refining furnace, and slagging operation is carried out to control refining slag, wherein the slagging operation comprises adding lime and low-alkalinity slag to control the alkalinity of the refining slag;

and (3) tapping from an LF refining furnace, adding high-alumina slag into an RH furnace for vacuum refining, adding a pure calcium wire after the vacuum refining is finished, and performing soft blowing.

8. The method for improving the machinability of a structural steel wire according to claim 7, wherein the aluminum iron is added before tapping, and the amount of the aluminum iron is 1.5 to 2.5 kg/t.

Or in the tapping process, the dosage of lime is 3.0 plus or minus 0.3Kg/t, and the dosage of synthetic slag is 2.5 plus or minus 0.25Kg/t

Or in the LF refining furnace process, the dosage of the added lime is 2.0 +/-0.2 Kg/t, the dosage of the low-alkalinity slag is 4.5 +/-0.45 Kg/t, and the alkalinity of the refining slag is 1.5-3.0.

9. The method for improving the machinability of a structural steel wire rod according to claim 7, wherein the sulfur content in the molten steel is monitored during the refining process of the LF refining furnace, and when the sulfur content deviates from a target value, the content of elemental sulfur is adjusted by adding ferrosulfur or a ferrosulfur wire;

or when the steel discharged from the LF refining furnace enters the RH furnace, supplementing aluminum wires in the RH furnace according to the Als content at the refining end point in the LF refining furnace.

10. The method for improving the machinability of a structural steel wire according to claim 8 or 9, wherein the vacuum refining is performed under the conditions of a vacuum degree of less than 0.266KPa, a vacuum treatment time of 18 to 21 minutes, a use amount of the high-alumina slag of 0.8 to 1.2Kg/t, a use amount of the pure calcium wire of 0.02 to 0.05Kg/t, and a soft blowing time of 10 to 15 minutes.