A method for producing a high-strength free-cutting steel

Abstract

The application discloses a production method of high-strength free-cutting steel, which comprises the following steps: controlling the chemical components of the free-cuting steel as follows: C 0.45-0.50%; Si 0.10-0.40%; Mn 0.70-1.10%; P≤0.07%; S 0.15-0.25%, and the rest is Fe and inevitable inclusions; and optimizing and controlling production process parameters, including converter tapping temperature, LF furnace refining in-place temperature, off-site temperature, refining time, continuous casting speed and rolling temperature, so that the high-strength free-cutting steel with a tensile strength of greater than or equal to 766 MPa can be obtained, and the performance of the free-cutting steel can be further improved and the use range of the free-cutting steel can be widened.

Description

Technical Field

[0001] This invention belongs to the field of metal materials technology, and specifically relates to a method for producing high-strength free-cutting steel. Background Technology

[0002] Free-cutting steel is made by adding appropriate amounts of free-cutting elements such as S, P, Pb, SeTe, Ca, and Bi to high-quality carbon steel, giving it excellent cutting performance. my country needs at least 120,000 tons of free-cutting steel every year, mainly for use in the automated machine tool processing industry and the automotive parts industry.

[0003] The applicant has developed a Y45S20 free-cutting steel that meets mechanical performance and requirement standards (see patent document CN102433516A, hereinafter referred to as Document 1). Its chemical composition and percentage content are: C 0.45–0.50%; Si 0.10–0.40%; Mn 0.70–1.10%; P ≤ 0.07%; S 0.15–0.25%, with the remainder being Fe and unavoidable inclusions. The maximum tensile strength of this Y45S20 free-cutting steel can reach 720 MPa. With increasingly prominent requirements for high-speed cutting of steel and product surface finish, coupled with demands for weight reduction and increased equipment performance, free-cutting steel must simultaneously balance the contradictory aspects of cutting performance and mechanical properties. Therefore, there is a need to further improve the strength of the Y45S20 free-cutting steel produced in Document 1 to further enhance its performance and expand its application range. Summary of the Invention

[0004] To address the problems existing in the prior art, one aspect of the present invention provides a method for producing high-strength free-cutting steel, wherein the tensile strength of the high-strength free-cutting steel satisfies: tensile strength ≥ 766 MPa;

[0005] The chemical composition of the high-strength free-cutting steel, by mass percentage, is: C 0.45–0.50%; Si 0.10–0.40%; Mn 0.70–1.10%; P ≤ 0.07%; S 0.15–0.25%, with the remainder being Fe and unavoidable inclusions;

[0006] The production method includes the following technological steps: converter smelting, LF refining, continuous casting, and rolling; wherein:

[0007] In the converter smelting process, the converter tapping temperature is controlled at 1670℃~1685℃, and the carbon content of the converter tapping steel is 0.06~0.12%.

[0008] In the LF refining process, the LF furnace refining temperature is controlled at 1600-1610℃, the refining temperature at 1620-1630℃, the refining time is 60-70 min, and the soft blowing time is 10-15 min.

[0009] In the continuous casting process, the temperature of the upper stage of the continuous casting station is controlled at 1540-1590℃, the superheat is 20-30℃, and the casting speed is 0.2-0.3m / min to obtain the continuous casting billet;

[0010] In the rolling process, the continuously cast billet is first rolled into a billet through a first rolling process, and then the billet is rolled into the high-strength free-cutting steel through a second rolling process; wherein the initial rolling temperature of the first rolling process is 1200-1220℃ and the final rolling temperature is 880-920℃, and the initial rolling temperature of the second rolling process is 1200-1220℃ and the final rolling temperature is 900-930℃.

[0011] In some embodiments, the chemical composition of the high-strength free-cutting steel, by mass percentage, is: C 0.46–0.47%; Si 0.24–0.25%; Mn 0.91–0.93%; P 0.028–0.031%; S 0.19–0.21%, with the remainder being Fe and unavoidable inclusions.

[0012] In some embodiments, the phosphorus content of the converter steel is controlled to be ≤0.025% in the converter smelting process.

[0013] In some embodiments, the soft blowing time in the LF refining process is also controlled to be 10-15 min, and the soft blowing flow rate is 50-90 Nl / min.

[0014] In some embodiments, the cross-section of the continuously cast billet is 280mm × 380mm in the continuous casting process.

[0015] In some embodiments, the billet has dimensions of 152mm × 152mm in the rolling process.

[0016] In some embodiments, the high-strength free-cutting steel is a round steel bar with a diameter of φ32mm.

[0017] In another aspect, the present invention provides a high-strength free-cutting steel obtained by the above-described production method.

[0018] The advantages of this invention are as follows: By optimizing and controlling production process parameters, including converter tapping temperature, LF furnace refining placement temperature, departure temperature, refining time, continuous casting speed, and rolling temperature, this invention can significantly improve the tensile strength of free-cutting steel compared to the aforementioned Reference 1, satisfying the requirement of tensile strength ≥ 766 MPa. Therefore, the method of this invention can further improve the performance of free-cutting steel and broaden its application range. Detailed Implementation

[0019] The present invention will be described in detail below through specific embodiments. These embodiments are intended to help understand the present invention and are not intended to limit the scope of the present invention.

[0020] Example: High-strength free-cutting steel

[0021] In this example, two heats of free-cutting steel (Y45S20) were produced on a trial basis. The specific process parameters were controlled as follows:

[0022] 1) Converter smelting

[0023] The carbon content, phosphorus content, and tapping temperature of the molten steel at the converter's final stage are shown in Table 1 below.

[0024] Table 1

[0025] 1# 1670 0.06 0.018 2# 1685 0.08 0.023

[0026] 2) LF Refining

[0027] The specific parameters for the LF refining process are shown in Table 2 below.

[0028] Table 2

[0029]

[0030] 3) Continuous casting

[0031] In continuous casting production, the cross-section of the continuously cast billet is 280mm×380mm. The superheat and casting speed are controlled as shown in Table 3 below. Table 4 shows the composition and percentage content of the continuously cast billet of free-cutting steel.

[0032] Table 3

[0033] 1# 1585 20 0.2 2# 1545 30 0.3

[0034] Table 4

[0035] 1# 0.46 0.24 0.91 0.031 0.21 2# 0.47 0.25 0.93 0.028 0.19

[0036] 4) Rolling

[0037] 4.1) First rolling process

[0038] The soaking zone temperature of the walking beam furnace is approximately 1210℃, and the heating time in the furnace is 2.5 hours. The initial rolling temperature and final rolling temperature of the continuously cast billet are shown in Table 5 below, and a billet with a specification of 152mm×152mm is obtained by rolling.

[0039] Table 5

[0040] 1# 1200 880 2# 1220 920

[0041] 4.2) Second rolling process

[0042] The 152mm×152mm billet obtained in step 4.1) was further rolled into φ32mm steel. The initial rolling temperature and final rolling temperature are shown in Table 6 below.

[0043] Table 6

[0044] 1# 1200 900 2# 1220 930

[0045] 5) Mechanical property testing

[0046] The mechanical properties of the free-cutting steel produced above were tested, and the results are shown in Table 7 below. As can be seen from Table 7, the rolled finished steel fully meets the standard requirements, and the tensile strength is above 766 MPa, significantly higher than the tensile strength of the free-cutting steel produced in Reference 1. Furthermore, the surface quality and tolerances of the finished product also meet the user's requirements, and the user has reported good results.

[0047] Table 7

[0048]

[0049]

[0050] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing high-strength free-cutting steel, characterized in that, The tensile strength of the high-strength free-cutting steel meets the following requirement: tensile strength ≥ 766 MPa; The chemical composition of the high-strength free-cutting steel, by mass percentage, is: C 0.46–0.47%; Si 0.24–0.25%; Mn 0.91–0.93%; P 0.028–0.031%; S 0.19–0.21%, with the remainder being Fe and unavoidable inclusions; The production method includes the following technological steps: converter smelting, LF refining, continuous casting, and rolling; wherein: In the aforementioned converter smelting process, the converter tapping temperature is controlled at 1670℃~1685℃, and the carbon content of the converter tapping steel is 0.06~0.12%; In the LF refining process, the LF furnace refining temperature is controlled at 1600-1610℃, the refining temperature at 1620-1630℃, the refining time is 60-70 min, and the soft blowing time is 10-15 min. In the continuous casting process, the temperature of the upper stage of the continuous casting station is controlled at 1540-1590℃, the superheat is 20-30℃, and the casting speed is 0.2-0.3 m / min to obtain a continuous casting billet with a cross-section of 280mm×380mm. In the rolling process, the continuously cast billet is first rolled into a billet through a first rolling process, and then the billet is rolled into the high-strength free-cutting steel through a second rolling process; wherein the initial rolling temperature of the first rolling process is 1200-1220℃ and the final rolling temperature is 880-920℃, and the initial rolling temperature of the second rolling process is 1200-1220℃ and the final rolling temperature is 900-930℃; wherein the billet has a specification of 152mm×152mm, and the high-strength free-cutting steel is a round bar with a diameter of φ32mm.

2. The production method according to claim 1, characterized in that, In the converter smelting process, the phosphorus content of the steel tapped from the converter is controlled to be ≤0.025%.

3. The production method according to claim 1 or 2, characterized in that, In the LF refining process, the soft blowing flow rate is also controlled to be 50-90 NL / min.

4. A high-strength free-cutting steel, obtained by the production method according to any one of claims 1-3.

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