Method for fiberizing MnS inclusions in free-cutting steel and free-cutting steel
By heating and performing multi-pass precision rolling on free-cutting steel, adjusting the pass interval time and deformation rate, the fiberization of MnS inclusions is achieved, solving the problem of the difficulty in refining the size of MnS inclusions in the existing technology, and improving the cutting performance and service life of free-cutting steel.
Patent Information
- Application Number
- CN202510949321.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-07-10
- Publication Date
- 2025-11-18
AI Technical Summary
While existing technologies can reduce the production cost of free-cutting steel, they are unable to effectively refine the size of MnS inclusions, which affects the mechanical and cutting properties of the material.
After heat treatment of free-cutting steel, six passes of precision rolling are performed in the high relative plasticity region of MnS inclusions. The pass interval time is adjusted to 0.1s-0.4s, and combined with appropriate deformation rate and temperature range, the MnS inclusions are fiberized.
While reducing production costs, the MnS inclusions are made to form a uniform and fine dispersion, which improves the cutting performance of free-cutting steel and extends its service life.
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Figure CN120967113A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application relates to the technical field of steel smelting, in particular to a method for fiberizing MnS inclusions in free-cutting steel and free-cutting steel. BACKGROUND
[0002] As a main structural material, the MnS inclusions in free-cutting steel have a significant influence on the mechanical properties of the material, so it is of great significance to improve the size of the MnS inclusions.
[0003] The method for controlling the MnS inclusions usually includes reducing the S content in the molten steel through LF refining furnace to reduce the MnS content, or adding high-melting-point oxide inclusions to induce the nucleation of MnS on the inclusions to accelerate the precipitation of the MnS inclusions and increase the nucleation rate, so as to refine the size of the MnS inclusions, but the above method increases the production cost of the free-cutting steel.
[0004] Therefore, it is urgent to provide a method for refining the MnS inclusions, which can reduce the production cost of the free-cutting steel. SUMMARY
[0005] The application provides a method for fiberizing MnS inclusions in free-cutting steel and free-cutting steel, which can form uniform and small dispersions of the MnS inclusions in the free-cutting steel under the premise of reducing the production cost, thereby improving the cutting performance of the free-cutting steel and prolonging the service life of the free-cutting steel.
[0006] In a first aspect, the application provides a method for fiberizing MnS inclusions in free-cutting steel, which comprises: heating the free-cutting steel to obtain heated free-cutting steel, wherein the temperature of the heated free-cutting steel is 1015-1025 DEG C; and performing 6-pass finishing rolling on the heated free-cutting steel to obtain finished free-cutting steel, wherein the interpass time of the 6-pass finishing rolling is 0.1-0.4 s.
[0007] In some embodiments, the method further comprises: performing heat preservation treatment on the heated free-cutting steel, wherein the heat preservation treatment time is 10-20 min.
[0008] In some embodiments, the heating treatment has a temperature rising rate of 8-12 DEG C / s.
[0009] In some embodiments, the 6-pass finishing rolling has a deformation rate of 15-25 s -1 -25 s -1 .
[0010] In some embodiments, the 6-pass finish rolling process includes a 1st pass finish rolling process, a 2nd pass finish rolling process, a 3rd pass finish rolling process, a 4th pass finish rolling process, a 5th pass finish rolling process, and a 6th pass finish rolling process.
[0011] In some embodiments, the temperature of the 6-pass finish rolling process is 955-1020℃.
[0012] In some embodiments, the temperature of the 1st-2nd pass finish rolling process is greater than the temperature of the 3rd-6th pass finish rolling process.
[0013] In some embodiments, the temperature of the 1st pass finish rolling process is 1010-1020℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0014] In some embodiments, the temperature of the 2nd pass finish rolling process is 1010-1020℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0015] In some embodiments, the temperature of the 3rd pass finish rolling process is 955-980℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0016] In some embodiments, the temperature of the 4th pass finish rolling process is 955-980℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0017] In some embodiments, the temperature of the 5th pass finish rolling process is 955-980℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0018] In some embodiments, the temperature of the 6th pass finish rolling process is 955-980℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0019] In some embodiments, the temperature of the 6th pass finish rolling process is 955-980℃, and the amount of deformation of the free-cutting steel is less than or equal to 30%.
[0020] In some embodiments, the grain size rating of the MnS inclusions in the free-cutting steel is less than or equal to 2.
[0021] The embodiment of the application realizes the fibration of MnS by heating the free-cutting steel to 1015-1025 DEG C, and performing 6-pass finishing rolling treatment in the high relative plasticity region of MnS inclusions; by adjusting the pass interval time of the 6-pass finishing rolling treatment to 0.1-0.4s, the pass interval time will affect the softening degree of the structure, when the pass interval time is within the above range, the matrix structure is softened, the deformation process is easier, meanwhile, the temperature reduction of the free-cutting steel during the 6-pass finishing rolling treatment is smaller, so that the MnS inclusions can keep a certain relative plasticity during the finishing rolling process, the free-cutting steel is subjected to multi-pass rapid finishing rolling deformation in a proper temperature range, and the size of the MnS inclusions is further refined. The above method does not need to increase the refining process or increase the alloy, so that the MnS inclusions in the free-cutting steel can be formed to be uniform and fine dispersion, not only the cutting performance of the free-cutting steel is improved, but also the service life of the free-cutting steel is prolonged. BRIEF DESCRIPTION OF DRAWINGS
[0022] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are included to provide a description of the preferred embodiments and are not intended to limit the scope of the present application. Moreover, the same reference numerals in the different figures denote the same or similar components.
[0023] Figure 1 The morphology of the MnS inclusions in the free-cutting steel in Example 1 is shown in the figure. Figure 2 The morphology of the MnS inclusions in the free-cutting steel in Example 2 is shown in the figure. Figure 3 The morphology of the MnS inclusions in the free-cutting steel in Example 3 is shown in the figure. Figure 4 The morphology of the MnS inclusions in the free-cutting steel in Comparative Example 1 is shown in the figure.
[0024] Figures 1-4 The scale in the figure is uniform 100 microns. DETAILED DESCRIPTION
[0025] Hereinafter, the embodiments of the present application will be described with reference to the accompanying drawings. It is to be understood, however, that these descriptions are merely exemplary and are intended to limit the scope of the present application.
[0026] 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 application belongs; the terminology used in the specification herein is for describing particular embodiments only and is not intended to be limiting of the application; the use herein of terms such as "comprise", "have" and "include" and any variation thereof, is intended to cover the nature of a disclosure, but is not intended to exclude or to otherwise exclude additional features, elements or steps.
[0027] Reference to an "embodiment" in this application means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of one another. As will be apparent to those of ordinary skill in the art, embodiments described in this application can be combined with one another.
[0028] In the description of the embodiments of the application, the term "and / or" is merely an association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone.
[0029] In the description of the embodiments of the application, the term "a plurality of" means more than two (including two).
[0030] In the related art, by adding passivated magnesium balls, passivated silicon-calcium composite balls or passivated magnesium-calcium composite balls in the RH vacuum refining process, and controlling the corresponding vacuum degree, MgO and CaS are generated as the nucleation core of MnS, which can improve the morphology and size of MnS inclusions during solidification. By adjusting the Ti / Al ratio to control the size of its oxide, the precipitation size of MnS inclusions can be controlled, thereby realizing the control of MnS inclusions. In addition, the refinement of MnS inclusions can also be realized through the control of multiple steps such as hot metal pretreatment, converter smelting, LF refining furnace, RH refining furnace, continuous casting, step heating, hot continuous rolling, and controlled cooling after rolling, but the internal principle is still to reduce the S content through the refining process to control the size of MnS inclusions.
[0031] In summary, whether it is through high-melting-point oxides to induce MnS precipitation or through external refining to reduce the S content to refine the size of MnS inclusions, it is necessary to add alloys during smelting.
[0032] Therefore, the application provides a method for fiberizing MnS inclusions in free-cutting steel, comprising: The free-cutting steel is subjected to heating treatment to obtain heated free-cutting steel, and the temperature of the heated free-cutting steel is 1015-1025℃. The heated free-cutting steel is subjected to 6-pass finish rolling treatment to obtain finished free-cutting steel, and the interpass time of the 6-pass finish rolling treatment is 0.1-0.4s.
[0033] The embodiment of the application realizes the fibration of MnS by heating the free-cutting steel to 1015-1025 DEG C and performing 6-pass finishing rolling treatment in the high relative plasticity region of MnS inclusions; by adjusting the inter-pass gap time of the 6-pass finishing rolling treatment to 0.1-0.4 s, the inter-pass gap time will affect the softening degree of the structure, when the inter-pass gap time is within the above range, the matrix structure is softened, the deformation process is easier, meanwhile, the temperature of the free-cutting steel can be reduced to a smaller extent during the 6-pass finishing rolling treatment, so that the MnS inclusions can maintain a certain relative plasticity during the finishing rolling process, the free-cutting steel is subjected to multi-pass rapid finishing rolling deformation in a proper temperature range, and the size of the MnS inclusions is further refined. The above method does not need to increase the refining process or add alloys, so that the MnS inclusions in the free-cutting steel can be formed to be uniform and fine dispersion, not only the cutting performance of the free-cutting steel is improved, but also the service life of the free-cutting steel is prolonged.
[0034] In some embodiments, the method further comprises: performing a holding treatment on the heated free-cutting steel, and the holding treatment time can be 10-20 min, for example, can be 10 min, 12 min, 14 min, 16 min, 18 min, 20 min, or a range composed of any two of the above values. The holding treatment time within the above range can soften the matrix structure of the free-cutting steel and further refine the size of the MnS inclusions.
[0035] In some embodiments, the heating rate of the heating treatment can be 8-12 DEG C / s, for example, can be 8 DEG C / s, 9 DEG C / s, 10 DEG C / s, 11 DEG C / s, 12 DEG C / s, or a range composed of any two of the above values.
[0036] The heating rate of the heating treatment affects the matrix thermal history and the size of austenite grains, and the size of austenite grains affects the rheological behavior of the matrix structure, and the heating rate of the heating treatment within the above range can further adjust the relative plasticity of the MnS inclusions within a proper range.
[0037] In some embodiments, the deformation rate of the 6-pass finishing rolling treatment can be 15 s -1 -25 s -1 , for example, can be 15 s -1 , 17 s -1 , 19 s -1 , 21 s -1 , 23 s -1 , 25 s -1 , or a range composed of any two of the above values.
[0038] The deformation rate in the finish rolling process refers to the degree of deformation of the metal material per unit time in the rolling process, and reflects the speed of deformation of the metal material. The specific definition is: deformation rate = deformation amount / (deformation time x average height of the rolled piece contacting the roller), unit: s -1 .
[0039] The deformation rate of the finish rolling process is within the above range, and the interpass gap time can be adjusted within a suitable range, so as to change the temperature of the 6-pass finish rolling process, and realize the deformation of the MnS inclusions in different relative plasticity temperature ranges.
[0040] In some embodiments, the 6-pass finish rolling process can include a first-pass finish rolling process, a second-pass finish rolling process, a third-pass finish rolling process, a fourth-pass finish rolling process, a fifth-pass finish rolling process, and a sixth-pass finish rolling process.
[0041] In some embodiments, the deformation rate of the first-pass finish rolling process is 15s -1 -16s -1 , the deformation rate of the second-pass finish rolling process is 17s -1 -18s -1 , the deformation rate of the third-pass finish rolling process is 19s -1 -20s -1 , the deformation rate of the fourth-pass finish rolling process is 21 -1 -22s -1 , the deformation rate of the fifth-pass finish rolling process is 23s -1 -24s -1 , and the deformation rate of the sixth-pass finish rolling process is 25s -1 .
[0042] The deformation rate from the first-pass finish rolling process to the sixth-pass finish rolling process is within the above range, that is, the deformation rate gradually increases, which is beneficial to the constant temperature of free-cutting steel, so as to better adjust the relative plasticity of the MnS inclusions.
[0043] In some embodiments, the temperature of the 6-pass finish rolling process can be 955℃-1020℃, for example, it can be 955℃, 960℃, 965℃, 970℃, 980℃, 990℃, 1000℃, 1010℃, 1020℃, or a range composed of any two of the above values.
[0044] In some embodiments, the temperature of the first-pass and second-pass finish rolling process is greater than the temperature of the third-pass to sixth-pass finish rolling process.
[0045] The embodiments of the present application utilize the relative plasticity difference between MnS inclusions and austenite, first large deformation occurs in the low relative plasticity region, which promotes the fragmentation of coarse MnS inclusions, then deformation occurs in the high plasticity region at low temperature, which promotes the fiberization of MnS inclusions, and fine MnS inclusions are formed. Thus, the hardness change of the matrix material under different temperature conditions and the sensitivity of the relative plasticity of MnS inclusions to temperature are utilized to realize the regulation of the morphology of MnS inclusions.
[0046] It should be noted that the "low relative plasticity region" refers to the temperature interval in which the relative plasticity of MnS is relatively low, and the "high plasticity region" refers to the temperature interval in which the relative plasticity of MnS is relatively high.
[0047] In some embodiments, the temperature of the first pass finishing treatment can be 1010-1020℃, and the deformation of the free-cutting steel is less than or equal to 30%, for example, it can be 10%, 15%, 20%, 25%, 30%, or a range composed of any two of the above values.
[0048] The deformation of the free-cutting steel is a reflection of the plastic deformation degree of the free-cutting steel during the pass rolling, and the deformation = (thickness before rolling-thickness after rolling) / thickness before rolling x 100%.
[0049] In some embodiments, the temperature of the second pass finishing treatment can be 1010-1020℃, and the deformation of the free-cutting steel is less than or equal to 30%, for example, it can be 10%, 15%, 20%, 25%, 30%, or a range composed of any two of the above values.
[0050] It should be noted that in the general rolling process, the temperature of the workpiece will decrease, but in the rapid finishing deformation process of the embodiments of the present application, the deformation rate is fast, the pass interval time is short, and the temperature of the workpiece can remain unchanged.
[0051] The embodiments of the present application can make the free-cutting steel deform greatly in the low relative plasticity region by multi-pass rapid finishing of the free-cutting steel at high temperature, which promotes the fragmentation of coarse MnS inclusions.
[0052] In some embodiments, the temperature of the third pass finishing treatment can be 955-980℃, and the deformation of the free-cutting steel is less than or equal to 30%, for example, it can be 10%, 15%, 20%, 25%, 30%, or a range composed of any two of the above values.
[0053] In some embodiments, the temperature of the fourth pass finishing treatment can be 955-980℃, and the deformation of the free-cutting steel is less than or equal to 30%, for example, it can be 10%, 15%, 20%, 25%, 30%, or a range composed of any two of the above values.
[0054] In some embodiments, the 5th pass finishing temperature can be 955-980℃, and the deformation of the free-cutting steel is less than or equal to 30%, for example, can be 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of the above.
[0055] In some embodiments, the 6th pass finishing temperature can be 955-980℃, and the deformation of the free-cutting steel is less than or equal to 30%, for example, can be 10%, 15%, 20%, 25%, 30%, or a range consisting of any two of the above.
[0056] The rest of the preparation process in the embodiments of the present application except for the finishing treatment can refer to the preparation process of a conventional free-cutting steel.
[0057] The present application provides a free-cutting steel prepared by the above method, wherein, based on the total mass of the free-cutting steel being 100%, the free-cutting steel comprises the following mass contents of components: C < 0.09%, Si < 0.15%, Mn < 1.05%, P < 0.09%, S: 0.26%-0.35%, and the balance being Fe and unavoidable impurities.
[0058] In some embodiments, the free-cutting steel can be a Y1215 free-cutting steel workpiece.
[0059] The method for fiberizing MnS inclusions in the free-cutting steel of the embodiments of the present application is suitable for the finishing process of rod wire.
[0060] In some embodiments, the grain size grade of the MnS inclusions in the free-cutting steel is less than or equal to grade 2.
[0061] The grain size grade of the MnS inclusions is determined according to GB / T 10561-2023 "Determination of Non-metallic Inclusion Content in Steel".
[0062] Embodiments The following embodiments more specifically describe the content of the present application, which are only used for illustrative description, and various modifications and changes within the scope of the content of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are commercially available.
[0063] Embodiment 1 The Y1215 free-cutting steel workpiece is heated to 1020°C at a heating rate of 10°C / s on a thermal simulation testing machine, and then is subjected to 6 passes of finish rolling treatment, and the pass interval time of the 6 passes of finish rolling treatment is 0.1s; The deformation rate of the first pass of finish rolling treatment is 15s -1 The deformation of the free-cutting steel is 18%. The deformation rate of the second pass of finish rolling treatment is 17s -1 The deformation of the free-cutting steel is 20%. The deformation rate of the third pass of finish rolling treatment is 19s -1 The deformation of the free-cutting steel is 22%. The deformation rate of the fourth pass of finish rolling treatment is 21s -1 The deformation of the free-cutting steel is 23%. The deformation rate of the fifth pass of finish rolling treatment is 23s -1 The deformation of the free-cutting steel is 20%. The deformation rate of the sixth pass of finish rolling treatment is 25s -1 The deformation of the free-cutting steel is 10%. The MnS inclusions are fiberized, and the MnS inclusions in the obtained free-cutting steel are as shown in Figure 1 The grain size grade of the MnS inclusions is grade 2.
[0064] Example 2 The Y1215 free-cutting steel workpiece is heated to 1020°C at a heating rate of 10°C / s on a thermal simulation testing machine, and then is subjected to 6 passes of finish rolling treatment, and the pass interval time of the 6 passes of finish rolling treatment is 0.2s; The deformation rate of the first pass of finish rolling treatment is 15s -1 The deformation of the free-cutting steel is 18%. The deformation rate of the second pass of finish rolling treatment is 17s -1 The deformation of the free-cutting steel is 20%. The deformation rate of the third pass of finish rolling treatment is 19s -1 The deformation of the free-cutting steel is 22%. The deformation rate of the fourth pass of finish rolling treatment is 21s -1 The deformation of the free-cutting steel is 23%. The deformation rate of the fifth pass of finish rolling treatment is 23s -1 The deformation of the free-cutting steel is 20%. The deformation rate of the sixth pass of finish rolling treatment is 25s -1 The deformation of the free-cutting steel is 10%. The MnS inclusions in the free-cutting steel obtained after the fiberization of the MnS inclusions are shown in FIG. 3. Figure 2 As shown in FIG. 3, the grain size level of the MnS inclusions is level 2.
[0065] Example 3 The Y1215 free-cutting steel workpiece was heated to 1020°C at a heating rate of 10°C / s on a thermal simulation testing machine, and was kept for 30 min, and then was subjected to 6-pass finish rolling treatment, and the interpass time of the 6-pass finish rolling treatment was 0.4 s. The deformation rate of the first-pass finish rolling treatment was 15 s -1 , and the deformation amount of the free-cutting steel was 18%. The deformation rate of the second-pass finish rolling treatment was 17 s -1 , and the deformation amount of the free-cutting steel was 20%. The deformation rate of the third-pass finish rolling treatment was 19 s -1 , and the deformation amount of the free-cutting steel was 22%. The deformation rate of the fourth-pass finish rolling treatment was 21 s -1 , and the deformation amount of the free-cutting steel was 23%. The deformation rate of the fifth-pass finish rolling treatment was 23 s -1 , and the deformation amount of the free-cutting steel was 20%. The deformation rate of the sixth-pass finish rolling treatment was 25 s -1 , and the deformation amount of the free-cutting steel was 10%. The MnS inclusions in the free-cutting steel obtained after the fiberization of the MnS inclusions are shown in FIG. 3. Figure 3 As shown in FIG. 3, the grain size level of the MnS inclusions is level 2.
[0066] Comparative Example 1 The Y1215 free-cutting steel workpiece was heated to 1010°C at a heating rate of 10°C / s on a thermal simulation testing machine, and was kept for 20 min, and then was subjected to 6-pass finish rolling treatment, and the interpass time of the 6-pass finish rolling treatment was 0.8 s. The deformation rate of the first-pass finish rolling treatment was 15 s -1 , and the deformation amount of the free-cutting steel was 18%. The deformation rate of the second-pass finish rolling treatment was 15 s -1 , and the deformation amount of the free-cutting steel was 20%. The deformation rate of the third-pass finish rolling treatment was 15 s -1 , and the deformation amount of the free-cutting steel was 22%. The deformation rate of the fourth-pass finish rolling treatment was 15 s -1 , and the deformation amount of the free-cutting steel was 23%. The deformation rate of the fifth-pass finish rolling treatment was 15 s -1, the deformation of the free-cutting steel is 20%; The deformation rate of the sixth pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 10%; The fiberization of the MnS inclusions is completed, and the MnS inclusions in the obtained free-cutting steel are as shown in Figure 4 The grain size grade of the MnS inclusions is 3.5.
[0067] Comparative Example 2 The Y1215 free-cutting steel workpiece is heated to 1020℃ at a heating rate of 10℃ / s on a thermal simulation testing machine, and then subjected to six pass finishing treatments, and the interpass interval time of the six pass finishing treatments is 0.1s; The deformation rate of the first pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 18%; The deformation rate of the second pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 20%; The deformation rate of the third pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 22%; The deformation rate of the fourth pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 23%; The deformation rate of the fifth pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 20%; The deformation rate of the sixth pass finishing treatment is 15s -1 , the deformation of the free-cutting steel is 10%; The fiberization of the MnS inclusions is completed, and the grain size grade of the MnS inclusions is 3.5.
[0068] Test Part The grain size grade of the MnS inclusions is determined according to GB / T 10561-2023 "Determination of Non-metallic Inclusion Content in Steel".
[0069] From the above examples and comparative examples, it can be seen that the method for fiberizing the MnS inclusions in the free-cutting steel of the present application can make the MnS inclusions in the free-cutting steel form uniform and fine dispersion under the premise of reducing production cost, not only improving the cutting performance of the free-cutting steel, but also prolonging the service life of the free-cutting steel.
[0070] The above embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some or all of the technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and the specification of the present application. In particular, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.
Claims
1. A method for fiberizing MnS inclusions in free-cutting steel, characterized in that, include: Free-cutting steel is heated to obtain heated free-cutting steel, wherein the temperature of the heated free-cutting steel is 1015℃-1025℃. The heated free-cutting steel is subjected to a 6-pass finishing rolling process to obtain finished free-cutting steel. The interval between the 6 passes of the finishing rolling process is 0.1s-0.4s.
2. The method according to claim 1, characterized in that, The method further includes: subjecting the heated free-cutting steel to a heat-holding treatment for 10-20 minutes; and / or, The heating rate of the heat treatment is 8℃ / s-12℃ / s.
3. The method according to claim 1, characterized in that, The deformation rate of the six-pass finishing rolling process is 15s. -1 -25s -1 .
4. The method according to claim 1, characterized in that, The six-pass finishing rolling process includes the first, second, third, fourth, fifth, and sixth finishing rolling processes.
5. The method according to claim 4, characterized in that, The temperature for the six-pass finishing rolling process is 955℃-1020℃; and / or, The temperature of the first and second finishing rolling passes is higher than the temperature of the third to sixth finishing rolling passes.
6. The method according to claim 4, characterized in that, The temperature of the first finishing rolling process is 1010℃-1020℃, and the deformation of the free-cutting steel is less than or equal to 30%; and / or, The temperature of the second finishing rolling process is 1010℃-1020℃, and the deformation of the free-cutting steel is less than or equal to 30%.
7. The method according to claim 4, characterized in that, The temperature of the third finishing rolling process is 955℃-980℃, and the deformation of the free-cutting steel is less than or equal to 30%; and / or, The temperature of the fourth finishing rolling process is 955℃-980℃, and the deformation of the free-cutting steel is less than or equal to 30%.
8. The method according to claim 4, characterized in that, The fifth finishing rolling temperature is 955℃-980℃, and the deformation of the free-cutting steel is less than or equal to 30%; and / or, The sixth finishing rolling temperature is 955℃-980℃, and the deformation of the free-cutting steel is less than or equal to 30%.
9. A free-cutting steel, characterized in that, Prepared by the method according to any one of claims 1-8, the free-cutting steel comprises, by weight 100%, the following components: C < 0.09%, Si < 0.15%, Mn < 1.05%, P < 0.09%, S: 0.26%-0.35%, with the balance being Fe and unavoidable impurities.
10. The free-cutting steel according to claim 9, characterized in that, The grain size grade of MnS inclusions in the free-cutting steel is less than or equal to grade 2.