600Mpa-grade steel plate for heavy icebreaker and preparation method of 600Mpa-grade steel plate

Abstract

The invention discloses a 600Mpa-grade steel plate for a heavy icebreaker and a preparation method of the 600Mpa-grade steel plate, and relates to the technical field of metallurgy, and the 600Mpa-grade steel plate comprises the following chemical components in percentage by mass: 0.03 to 0.08 percent of C, 0.10 to 0.50 percent of Si, 1.20 to 1.90 percent of Mn, less than or equal to 0.020 percent of P, less than or equal to 0.0020 percent of S, 0.020 to 0.050 percent of V, 0.50 to 1.70 percent of Ni, 0.20 to 0.70 percent of Cr, 0.010 to 0.040 percent of Nb, 0.010 to 0.050 percent of Alt, 0.003 to 0.030 percent of Ti, 0.0005 to 0.0040 percent of Ca, less than or equal to 0.0050 percent of N and the balance of Fe and inevitable impurities. The yield strength of the prepared steel plate ranges from 500 MPa to 600 MPa, the tensile strength ranges from 600 MPa to 690 MPa, the V-shaped transverse impact mean value is 200 J or above, and the near surface NDTT temperature is minus 60 DEG C or below.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and particularly to a 600Mpa grade steel plate for heavy icebreakers and a preparation method thereof. Background Art

[0002] Although China had the ability to develop 600Mpa grade civil steel in the early stage, systematic research on low-temperature application performance was not carried out. Key data such as low-temperature toughness fracture performance, crack arrest performance, fatigue performance, and corrosion and wear performance were not fully grasped, and accurate evaluation of its low-temperature adaptability could not be made, which restricted its use in polar ship equipment. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a 600Mpa grade steel plate for heavy icebreakers and a preparation method thereof.

[0004] To solve the above technical problems, the technical solution of the present invention is as follows: A 600Mpa grade steel plate for heavy icebreakers, the chemical composition and mass percentage thereof are: C: 0.03 - 0.08%, Si: 0.10 - 0.50%, Mn: 1.20 - 1.90%, P: ≤0.020%, S: ≤0.0020%, V: 0.020 - 0.050%, Ni: 0.50 - 1.70%, Cr: 0.20 - 0.70%, Nb: 0.010 - 0.040%, Alt: 0.010 - 0.050%, Ti: 0.003 - 0.030%, Ca: 0.0005 - 0.0040%, N: ≤0.0050%, and the rest is Fe and inevitable impurities.

[0005] As a preferred scheme of the 600Mpa grade steel plate for heavy icebreakers of the present invention, wherein: the thickness of the steel plate is less than or equal to 80mm.

[0006] As a preferred scheme of the 600Mpa grade steel plate for heavy icebreakers of the present invention, wherein: the yield strength of the steel plate is greater than or equal to 500MPa, and the tensile strength is greater than or equal to 600MPa.

[0007] The present invention also provides a preparation method of a 600Mpa grade steel plate for heavy icebreakers, including: Smelting: Pretreat the hot metal for desulfurization, then carry out converter smelting, and carry out LF refining and RH vacuum treatment after tapping from the converter; Continuous casting: Control the target temperature of the tundish to be 15 - 25°C higher than the liquidus temperature; Heating: Heat the billet after continuous casting, control the soaking temperature at 1130 - 1230°C, the soaking time > 64 min, the overall heating time at 11 - 20 min / cm, and the tapping temperature at 1130 - 1200°C; Rolling: Adopt a two-stage controlled rolling process for rolling.

[0008] As a preferred embodiment of the method for preparing a 600 Mpa grade steel plate for heavy icebreakers according to the present invention, wherein: the LF refining includes: carrying out refining treatment with white slag, and the white slag holding time is greater than or equal to 20 min.

[0009] As a preferred embodiment of the method for preparing a 600 Mpa grade steel plate for heavy icebreakers according to the present invention, wherein: the RH vacuum treatment includes: controlling the RH vacuum treatment holding time to be greater than or equal to 15 min, and feeding 110 - 130 m seamless calcium wire after the vacuum treatment.

[0010] As a preferred embodiment of the method for preparing a 600 Mpa grade steel plate for heavy icebreakers according to the present invention, wherein: the RH vacuum treatment further includes: controlling the N content in the molten steel after the RH vacuum treatment to be less than or equal to 40 ppm, and the H content to be less than or equal to 1.5 ppm.

[0011] As a preferred embodiment of the method for preparing a 600 Mpa grade steel plate for heavy icebreakers according to the present invention, wherein: the two-stage controlled rolling process includes rough rolling and finish rolling; The rough rolling includes: controlling the pre-rolling heating temperature at 1130°C - 1230°C, the rough rolling starting temperature at 1030 - 1130°C, and the thickness h1 of the intermediate billet after rough rolling satisfies: 2.0h ≤ h1 ≤ 3.5h, where h is the thickness of the finished steel; The finish rolling includes: controlling the finish rolling starting temperature at 700 - 790°C, and the finish rolling ending temperature at 700 - 790°C.

[0012] As a preferred embodiment of the method for preparing a 600 Mpa grade steel plate for heavy icebreakers according to the present invention, wherein: the total number of passes in the finish rolling is less than or equal to 9 passes.

[0013] As a preferred embodiment of the method for preparing a 600 Mpa grade steel plate for heavy icebreakers according to the present invention, wherein: after the rolling using the two-stage controlled rolling process, it further includes: Cool the rolled piece, and control the red-return temperature at 300 - 430°C.

[0014] The beneficial effects of the present invention are: (1) By optimizing the chemical composition of the steel plate and adopting the controlled rolling and controlled cooling process, a medium-temperature transformation structure is obtained. Through technical means such as tissue strengthening and grain refinement, the strength and toughness of the steel plate and excellent mechanical properties are ensured. The yield strength of the prepared steel plate is 500 MPa to 600 Mpa, the tensile strength is 600 Mpa to 690 MPa, the average V-notch transverse impact is above 200 J, and the near-surface NDTT temperature is below -60 °C.

[0015] (2) The present invention performs two-stage controlled rolling on the heated slab. The first stage is rolling in the recrystallization zone, and the rolling temperature is controlled in the range above the recrystallization critical temperature, which is 1030 - 1130 °C. The average single-pass reduction rate is ≥15%, and the cumulative reduction rate is 40% - 50%. Through large reduction rate deformation, the austenite at the 1 / 4 and 1 / 2 thickness positions of the steel plate is recrystallized, and the austenite grains are refined. The starting rolling temperature range of the second stage is 700 - 790 °C, and the finishing rolling temperature is 700 °C - 790 °C to increase the effective area of the austenite grain boundary and provide more nucleation points for the transformation of austenite, achieving the effect of grain refinement.

[0016] (3) After the steel plate rolling is completed, the present invention performs ACC cooling on the steel plate, and the return red temperature is controlled between 300 - 430 °C, which can avoid the growth of internal grains of the steel plate after rolling, affect the impact toughness, and ensure that the steel plate has good strength and toughness. Specific Embodiments

[0017] To make the content of the present invention easier to be clearly understood, the following further detailed description of the present invention is made according to specific embodiments.

[0018] This application provides a 600 Mpa grade steel plate for heavy icebreakers, and its chemical composition and mass percentage are: C: 0.03 - 0.08%, Si: 0.10 - 0.50%, Mn: 1.20 - 1.90%, P: ≤0.020%, S: ≤0.0020%, V: 0.020 - 0.050%, Ni: 0.50 - 1.70%, Cr: 0.20 - 0.70%, Nb: 0.010 - 0.040%, Alt: 0.010 - 0.050%, Ti: 0.003 - 0.030%, Ca: 0.0005 - 0.0040%, N: ≤0.0050%, and the rest is Fe and inevitable impurities.

[0019] The structure of the above steel plate is mainly fine lath bainite, and there is also a small amount of ferrite and pearlite, which can ensure excellent low-temperature toughness while having high strength.

[0020] This application also provides a preparation method for a 600 Mpa grade steel plate for heavy icebreakers, including: Smelting: Pretreat the hot metal for desulfurization, then carry out converter smelting, and perform LF refining and RH vacuum treatment after tapping from the converter.

[0021] Specifically, during converter smelting, the high-blow and low-draw method is used for dephosphorization, requiring that the lower nozzle is clean and free of defects, and slagging occurs during tapping from the converter. After tapping from the converter, LF refining is carried out. LF refining is carried out with white slag for refining treatment, and the holding time of the white slag is greater than or equal to 20 min, and the target basicity is controlled. After LF refining, RH vacuum treatment is carried out, and the holding time of RH vacuum treatment is controlled to be greater than or equal to 15 min, and seamless calcium wire of 110 - 130 m is fed after vacuum treatment.

[0022] It should be noted that the molten steel after vacuum treatment needs to meet the following conditions: the N content is less than or equal to 40 ppm, and the H content is less than or equal to 1.5 ppm.

[0023] Continuous casting: Five-hole nozzles are used for continuous casting, and the target temperature of the tundish is controlled to be 15 - 25 °C higher than the liquidus temperature, the drawing speed is stable, and carbon-free covering agents are used.

[0024] Heating: The steel billet with a thickness of 320 - 460 mm obtained by continuous casting pouring is heated, the soaking temperature is controlled at 1130 - 1230 °C, the soaking time > 64 min, the overall heating time is 11 - 20 min / cm, and the tapping temperature is 1130 - 1200 °C.

[0025] Rolling: Two-stage controlled rolling process is used for rolling.

[0026] Specifically, the heated billet is subjected to two-stage controlled rolling. The first stage is rolling in the recrystallization zone, that is, rough rolling. The rolling temperature is controlled in the range above the recrystallization critical temperature, which is 1030 - 1130 °C. The average single-pass reduction rate ≥ 15%, and the cumulative reduction rate is 40% - 50%. The purpose is to recrystallize the austenite at the 1 / 4 and 1 / 2 thickness positions of the steel plate through large reduction rate deformation and refine the austenite grains. The subsequent intermediate billet is kept at temperature.

[0027] It should be noted that the thickness h1 of the intermediate billet after rough rolling satisfies: 2.0h ≤ h1 ≤ 3.5h, where h is the thickness of the finished steel.

[0028] The second stage is rolling in the non-recrystallization zone. The starting rolling temperature range of the second stage is 700 - 790 °C, and the finishing rolling temperature is 700 °C - 790 °C to increase the effective area of the austenite grain boundary and provide more nucleation points for the transformation of austenite, achieving the effect of grain refinement.

[0029] In this embodiment, the total number of finishing rolling passes is less than or equal to 9 passes.

[0030] After rolling, the steel plate enters the ACC cooling process, and the return red temperature is controlled between 300 and 430 °C, which can prevent the internal grains of the steel plate from growing after rolling, affecting the impact toughness, and ensuring that the steel plate has good strength and toughness.

[0031] The thickness of the steel plate prepared by the above preparation method is ≤80 mm, the yield strength is between 500 MPa and 600 MPa, the tensile strength is between 600 MPa and 690 MPa, the average V-notch transverse impact is above 200 J, and the near-surface NDTT temperature is above -60 °C.

[0032] The following is a further illustration through specific examples.

[0033] Table 1 shows the chemical compositions and mass percentages of the 600 MPa grade steel plates for heavy icebreakers in Examples 1 to 4.

[0034]

[0035] Table 1 Table 2 shows the numerical values of various parameters in the preparation method of the 600 MPa grade steel plates for heavy icebreakers provided in Examples 1 to 4.

[0036]

[0037] Table 2 Table 3 shows the conventional mechanical properties of the 600 MPa grade steel plates for heavy icebreakers prepared in Examples 1 to 4.

[0038]

[0039] Table 3 Table 4 shows the NDTT test data of the 600 MPa grade steel plates for heavy icebreakers prepared in Examples 1 to 4.

[0040]

[0041] Table 4 As can be seen from the above tables, the yield strengths of the steel plates prepared in the above examples are all between 500 MPa and 600 MPa, the tensile strengths are all between 600 MPa and 690 MPa, the average V-notch transverse impact is above 200 J, and the near-surface NDTT temperature is below -60 °C.

[0042] In addition to the above examples, the present invention may have other embodiments; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A 600Mpa grade steel plate for heavy icebreakers, characterized in that: Its chemical composition and mass percentage are as follows: C: 0.03 - 0.08%, Si: 0.10 - 0.50%, Mn: 1.20 - 1.90%, P: ≤0.020%, S: ≤0.0020%, V: 0.020 - 0.050%, Ni: 0.50 - 1.70%, Cr: 0.20 - 0.70%, Nb: 0.010 - 0.040%, Alt: 0.010 - 0.050%, Ti: 0.003 - 0.030%, Ca: 0.0005 - 0.0040%, N: ≤0.0050%, and the rest is Fe and inevitable impurities.

2. The 600Mpa grade steel plate for heavy icebreakers according to claim 1, characterized in that: The thickness of the steel plate is less than or equal to 80 mm.

3. The 600Mpa grade steel plate for heavy icebreakers according to claim 1, characterized in that: The yield strength of the steel plate is greater than or equal to 500 MPa, and the tensile strength is greater than or equal to 600 MPa.

4. A preparation method of a 600Mpa grade steel plate for a heavy icebreaker according to any one of claims 1 to 3, characterized in that: It includes: Smelting: Pretreat the hot metal for desulfurization, then carry out converter smelting, and perform LF refining and RH vacuum treatment after tapping from the converter. Continuous casting: Control the target temperature of the tundish to be 15 - 25 °C higher than the liquidus temperature. Heating: Heat the continuously cast billet, control the soaking temperature at 1130 - 1230 °C, the soaking time > 64 min, the overall heating time at 11 - 20 min / cm, and the tapping temperature at 1130 - 1200 °C. Rolling: Adopt a two-stage controlled rolling process for rolling.

5. The preparation method of the 600Mpa grade steel plate for heavy icebreakers according to claim 4, characterized in that: The LF refining includes: Carry out refining treatment with white slag, and the white slag holding time is greater than or equal to 20 min.

6. The preparation method of the 600Mpa grade steel plate for heavy icebreakers according to claim 4, characterized in that: The RH vacuum treatment includes: Control the holding time of the RH vacuum treatment to be greater than or equal to 15 min, and feed 110 - 130 m seamless calcium wire after the vacuum treatment.

7. The preparation method of the 600Mpa grade steel plate for heavy icebreakers according to claim 4, characterized in that: The RH vacuum treatment also includes: Control the N content in the molten steel after the RH vacuum treatment to be less than or equal to 40 ppm, and the H content to be less than or equal to 1.5 ppm.

8. The preparation method of the 600Mpa grade steel plate for heavy icebreakers according to claim 4, characterized in that: The two-stage controlled rolling process includes rough rolling and finish rolling. The rough rolling includes: Control the pre-rolling heating temperature at 1130 °C - 1230 °C, the rough rolling starting temperature at 1030 - 1130 °C, and the thickness h1 of the intermediate billet after rough rolling satisfies: 2.0h ≤ h1 ≤ 3.5h, where h is the thickness of the finished steel. The finish rolling includes: Control the finish rolling starting temperature at 700 - 790 °C, and the finish rolling final temperature at 700 - 790 °C.

9. The preparation method of the 600Mpa grade steel plate for heavy icebreakers according to claim 8, characterized in that: The total number of passes in the finish rolling is less than or equal to 9 passes.

10. The preparation method of the 600Mpa grade steel plate for heavy icebreakers according to claim 4, characterized in that: After adopting the two-stage controlled rolling process for rolling, it also includes: Cool the rolled piece, and control the return red temperature at 300 - 430 °C.

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