510Mpa-grade steel plate for icebreaker in extremely cold environment and manufacturing method of 510Mpa-grade steel plate

Abstract

The invention discloses a 510Mpa-grade steel plate for an ice breaker in an extremely cold environment. The 510Mpa-grade steel plate comprises the following chemical components in percentage by weight: 0.03 to 0.08 percent of C, 0.10 to 0.50 percent of Si, 1.00 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, 0.30 to 1.50 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 method has the advantages that the yield strength of the steel plate is larger than or equal to 390 MPa, the tensile strength is larger than or equal to 510 MPa, the average impact energy of base metal at-60 DEG C is larger than or equal to 220 J, the near-surface NDTT temperature is smaller than or equal to-60 DEG C, and the mechanical property is good.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and particularly relates to a 510Mpa grade steel plate for icebreakers in extremely cold environments and a manufacturing method thereof. Background Art

[0002] At present, in the research and application technology of high-strength steel for icebreakers in extremely cold environments, the EH36 steel has not been mass-applied to the main hull structure, and the application technology foundation is relatively weak. At the same time, the strength of the EH36 steel is relatively low and cannot meet the construction requirements of icebreakers with higher icebreaking grades. Although the development ability of 500MPa grade civil steel is available at present, the systematic research on low-temperature application performance has not been carried out, and the key data such as low-temperature toughness fracture performance, crack arrest performance, fatigue performance, and corrosion and wear performance have not been comprehensively mastered, making it impossible to accurately evaluate its low-temperature adaptability, which restricts its use in polar ship equipment. Summary of the Invention

[0003] The purpose of the invention is to solve the problem of poor performance of existing high-strength steel, and provides a 510Mpa grade steel plate for icebreakers in extremely cold environments. By adopting the double processes of controlled rolling and controlled cooling, the microstructure and grain size in the plate thickness direction are controlled to obtain a low-temperature steel plate with excellent low-temperature toughness, large thickness and high strength, and the application range is wider.

[0004] In order to achieve the above purpose, the invention adopts the following technical scheme: A 510Mpa grade steel plate for icebreakers in extremely cold environments, the chemical components and their weight percentages are as follows: C: 0.03 - 0.08%, Si: 0.10 - 0.50%, Mn: 1.00 - 1.90%, P: ≤0.020%, S: ≤0.0020%, V: 0.020 - 0.050%, Ni: 0.30 - 1.50%, 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 unavoidable impurities.

[0005] Further, the structure of the steel plate is mainly fine lath bainite, and also contains a small amount of ferrite and pearlite, so as to have both high strength and excellent low-temperature toughness.

[0006] Further, the thickness of the steel plate is ≤80mm.

[0007] Further, the yield strength of the steel plate is 390 MPa to 500 MPa, the tensile strength is 510 MPa to 600 MPa, the average V-notch transverse impact is above 220 J, and the near-surface NDTT temperature is below -60°C.

[0008] To further achieve the object of the present invention, a manufacturing method of a 510 Mpa grade steel plate for icebreakers in extremely cold environments is also provided, including hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling and stacking cooling, specifically including: (1) Steelmaking and continuous casting process: First, desulfurize the hot metal pretreatment; then carry out converter smelting, adopt the high-blow and low-draw method to dephosphorize, the bottom nozzle is clean and without defects, and the converter tapping has slag; LF refining adopts white slag operation, the white slag holding time ≥ 20 min, control the target basicity; the RH vacuum treatment holding time ≥ 15 min, feed 110 - 130 m of seamless calcium wire after vacuum treatment; use a five-hole nozzle for continuous casting, the tundish target temperature is 15 - 25°C higher than the liquidus temperature, the casting speed is stable, and use a carbon-free covering agent; (2) Rolling process: Adopt a two-stage controlled rolling and controlled cooling process for rolling; adopt a controlled rolling and controlled cooling process, the pre-rolling heating temperature is 1150°C - 1230°C, the rough rolling starting temperature is 1050 - 1130°C, rough roll into an intermediate billet with a finished thickness of 2.0h ≤ thickness ≤ 3.3h, the finish rolling starting temperature is 700 - 780°C, the finish rolling final rolling temperature is 700 - 780°C, to increase the effective area of austenite grain boundaries, provide more nucleation points for austenite transformation, and achieve the effect of refining grains.

[0009] Further, in the heating process, the soaking temperature of the steel billet with a thickness of 320 - 460 mm obtained in continuous casting is 1150 - 1230°C, the soaking time > 64 min, the overall heating time is 11 - 20 min / cm, and the tapping temperature is 1150 - 1210°C.

[0010] Further, in the rolling process, the heated billet is subjected to two-stage controlled rolling. 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 1050 - 1130°C, the average single-pass reduction rate ≥ 15%, and the cumulative reduction rate is 40% - 50%. The purpose is to recrystallize austenite at the 1 / 4 and 1 / 2 thickness positions of the steel plate through large reduction rate deformation and refine austenite grains.

[0011] Further, in the rolling process, after rolling, the steel plate enters ACC cooling, adopts large water volume for accelerated cooling, and the return red temperature is controlled at 330 - 450°C, and then stacks and cools to avoid grain growth inside the rolled steel plate, affecting the impact toughness, and ensure that the steel plate has good strength and toughness.

[0012] Further, after the vacuum treatment, N ≤ 40 ppm and H ≤ 1.5 ppm.

[0013] Further, in the rolling process, the total number of finish rolling passes does not exceed 9.

[0014] In the technical solution of the present invention, by adopting the controlled rolling and controlled cooling process, a medium-temperature transformation structure can be obtained, and the strength and toughness matching of the steel plate and excellent mechanical properties are ensured through various means such as tissue strengthening and grain refinement. Description of the Drawings

[0015] Figure 1 It is the steel chemical composition and its weight percentage table for Examples 1 to 4 of this embodiment; Figure 2 It is the parameter table of the steel preparation method for Examples 1 to 4 of this embodiment; Figure 3 It is the conventional mechanical property table of the steel for Examples 1 to 4 of this embodiment; Figure 4 It is the NDT test result table of the steel for Examples 1 to 4 of this embodiment. Detailed Embodiments Example 1

[0016] To make the present invention clearer and more understandable, a 510 Mpa grade steel plate for icebreakers in extremely cold environments and its manufacturing method are further described below. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0017] See Figure 1 , a 510 Mpa grade steel plate for icebreakers in extremely cold environments, whose chemical composition and weight percentage are: C: 0.045%, Si: 0.26%, Mn: 1.75%, P: ≤ 0.020%, S: ≤ 0.0020%, V: 0.038%, Ni: 0.87%, Cr: 0.40%, Nb: 0.031%, Alt: 0.035%, Ti: 0.012%, Ca: 0.0005 - 0.0040%, N: ≤ 0.0050%, and the rest is Fe and inevitable impurities.

[0018] The manufacturing method of the above-mentioned 510 Mpa grade steel plate for icebreakers in extremely cold environments includes hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling and stacking cooling.

[0019] See Figure 2, wherein, the heating temperature is 1170°C, the rough rolling temperature is 1100°C, the thickness of the intermediate billet is 60 mm. In the finish rolling stage, the starting rolling temperature of the second stage is 770°C, and the finishing rolling temperature is 780°C, so as to increase the effective area of austenite grain boundaries, provide more nucleation sites for the transformation of austenite, and achieve the effect of grain refinement. After rolling, the steel plate enters ACC cooling, and the recrystallization temperature is controlled at 440°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.

[0020] See Figure 3 and Figure 4 , the yield strength of the steel plate manufactured by the method of this embodiment is 472 MPa, the tensile strength is 587 MPa, the elongation is 31.0%, and the V-notch impact test data and NDT test results are shown in the table. Example 2

[0021] See Figure 1 , a 510 Mpa grade steel plate for icebreakers in extremely cold environments, the chemical composition and its weight percentage are as follows: C: 0.055%, Si: 0.20%, Mn: 1.62%, P: ≤0.020%, S: ≤0.0020%, V: 0.030%, Ni: 0.80%, Cr: 0.22%, Nb: 0.024%, Alt: 0.021%, Ti: 0.022%, Ca: 0.0005 - 0.0040%, N: ≤0.0050%, and the rest are Fe and unavoidable impurities.

[0022] The manufacturing method of the above-mentioned 510 Mpa grade steel plate for icebreakers in extremely cold environments includes hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling and stacking cooling.

[0023] See Figure 2 , wherein, the heating temperature is 1210°C, the rough rolling temperature is 1080°C, the thickness of the intermediate billet is 110 mm. In the finish rolling stage, the starting rolling temperature of the second stage is 764°C, and the finishing rolling temperature is 775°C, so as to increase the effective area of austenite grain boundaries, provide more nucleation sites for the transformation of austenite, and achieve the effect of grain refinement. After rolling, the steel plate enters ACC cooling, and the recrystallization temperature is controlled at 420°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.

[0024] See Figure 3 and Figure 4 , the yield strength of the steel plate manufactured by the method of this embodiment is 460 MPa, the tensile strength is 571 MPa, the elongation is 30.5%, and the V-notch impact test data and NDT test results are shown in the table. Example 3

[0025] SeeFigure 1 , a 510Mpa grade steel plate for icebreakers in extremely cold environments, with its chemical composition and weight percentages as follows: C: 0.065%, Si: 0.27%, Mn: 1.51%, P: ≤0.020%, S: ≤0.0020%, V: 0.025%, Ni: 0.77%, Cr: 0.34%, Nb: 0.035%, Alt: 0.030%, Ti: 0.017%, Ca: 0.0005 - 0.0040%, N: ≤0.0050%, and the rest being Fe and unavoidable impurities.

[0026] The manufacturing method of the above 510Mpa grade steel plate for icebreakers in extremely cold environments includes hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and stacking cooling.

[0027] See Figure 2 , among which, the heating temperature is 1200°C, the rough rolling temperature is 1110°C, the thickness of the intermediate billet is 190mm. In the finish rolling stage, the starting rolling temperature of the second stage is 730°C, and the finishing rolling temperature is 760°C, so as to increase the effective area of austenite grain boundaries, provide more nucleation sites for the transformation of austenite, and achieve the effect of refining grains. After rolling, the steel plate enters ACC cooling, and the return red temperature is controlled at 400°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.

[0028] See Figure 3 and Figure 4 , the steel plate manufactured by the method of this embodiment has a yield strength of 441MPa, a tensile strength of 553MPa, an elongation rate of 29.7%, and the V-notch impact test data and NDT test results are shown in the table. Example 4

[0029] See Figure 1 , a 510Mpa grade steel plate for icebreakers in extremely cold environments, with its chemical composition and weight percentages as follows: C: 0.075%, Si: 0.21%, Mn: 1.40%, P: ≤0.020%, S: ≤0.0020%, V: 0.028%, Ni: 0.70%, Cr: 0.30%, Nb: 0.028%, Alt: 0.022%, Ti: 0.010%, Ca: 0.0005 - 0.0040%, N: ≤0.0050%, and the rest being Fe and unavoidable impurities.

[0030] The manufacturing method of the above 510Mpa grade steel plate for icebreakers in extremely cold environments includes hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling, and stacking cooling.

[0031] See Figure 2, wherein, the heating temperature is 1220°C, the rough rolling temperature is 1120°C, the thickness of the intermediate billet is 210 mm. In the finish rolling stage, the starting rolling temperature of the second stage is 740°C, and the finishing rolling temperature is 755°C, so as to increase the effective area of austenite grain boundaries, provide more nucleation sites for the transformation of austenite, and achieve the effect of refining grains. After rolling, the steel plate enters ACC cooling, and the return red temperature is controlled at 360°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.

[0032] See Figure 3 and Figure 4 , the yield strength of the steel plate manufactured by the method of this embodiment is 427 MPa, the tensile strength is 537 MPa, the elongation is 28.4%, and the V-notch impact test data and NDT test results are shown in the table.

[0033] In summary, the yield strength of the steel plate manufactured by the method of the present invention is ≥390 MPa, the tensile strength is ≥510 MPa, the average impact energy of the base metal at -60°C is above 220 J, and the near-surface NDTT temperature is below -60°C. The present invention adopts the controlled rolling and controlled cooling process to obtain the medium-temperature transformation structure, and then realizes the strength and toughness matching of the steel plate through various means such as tissue strengthening and grain refinement, making it have excellent mechanical properties.

[0034] In addition to the above embodiments, the present invention may also have other implementation manners. Any technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention.

Claims

1. A 510Mpa grade steel plate for icebreaker in extremely cold environment, characterized in that: Its chemical composition and weight percentage are as follows: C: 0.03 - 0.08%, Si: 0.10 - 0.50%, Mn: 1.00 - 1.90%, P: ≤0.020%, S: ≤0.0020%, V: 0.020 - 0.050%, Ni: 0.30 - 1.50%, 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 unavoidable impurities.

2. The 510Mpa grade steel plate for icebreaker in extremely cold environment according to claim 1, characterized in that: The microstructure of the steel plate is mainly fine lath bainite, and also contains a small amount of ferrite and pearlite.

3. The 510Mpa grade steel plate for icebreaker in extremely cold environment according to claim 1 or 2, characterized in that: The thickness of the steel plate is ≤80mm.

4. The 510Mpa grade steel plate for icebreaker in extremely cold environment according to claim 1, characterized in that: The yield strength of the steel plate is 390MPa - 500MPa, the tensile strength is 510MPa - 600MPa, the average value of V-shaped transverse impact is above 220J, and the near-surface NDTT temperature is below -60°C.

5. A manufacturing method of the 510Mpa grade steel plate for icebreaker in extremely cold environment as claimed in claim 1, including hot metal pretreatment, converter smelting, LF refining, RH refining, continuous casting, heating, rolling and stacking cooling, characterized in that: (1) Steelmaking and continuous casting process: First, perform hot metal pretreatment for desulfurization; then carry out converter smelting, adopt the high-blowing and low-drawing method for dephosphorization, the bottom nozzle is clean and without defects, and slag is discharged during converter tapping; LF refining adopts white slag operation, the white slag holding time ≥20min, and the target basicity is controlled; the RH vacuum treatment holding time ≥15min, and 110 - 130m of seamless calcium wire is fed after vacuum treatment; continuous casting uses a five-hole nozzle, the tundish target temperature is 15 - 25°C higher than the liquidus temperature, the casting speed is stable, and a carbon-free covering agent is adopted; (2) Rolling process: Adopt a two-stage controlled rolling and controlled cooling process for rolling; adopt the controlled rolling and controlled cooling process, the pre-rolling heating temperature is 1150°C - 1230°C, the rough rolling starting temperature is 1050 - 1130°C, the rough rolling produces an intermediate billet with a finished thickness of 2.0h ≤ thickness ≤ 3.3h, the finish rolling starting temperature is 700 - 780°C, and the finish rolling final temperature is 700 - 780°C, so as to increase the effective area of austenite grain boundaries and provide more nucleation points for austenite transformation, achieving the effect of grain refinement.

6. The manufacturing method of the 510Mpa grade steel plate for icebreaker in extremely cold environment according to claim 5, characterized in that: In the heating process, the soaking temperature of the steel slab with a thickness of 320 - 460 mm obtained in continuous casting pouring is 1150 - 1230°C, the soaking time is > 64 min, the overall heating time is 11 - 20 min / cm, and the tapping temperature is 1150 - 1210°C.

7. The manufacturing method of the 510 Mpa grade steel plate for icebreaking ships in extremely cold environments according to claim 5, characterized in that: In the rolling process, two-stage controlled rolling is performed 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 1050 - 1130°C. The average single-pass reduction rate is ≥ 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.

8. The manufacturing method of the 510 Mpa grade steel plate for icebreaking ships in extremely cold environments according to claim 5, characterized in that: In the rolling process, after rolling, the steel plate enters ACC cooling, and accelerated cooling is carried out with a large amount of water. The return red temperature is controlled at 330 - 450°C, and then stacking cooling is performed.

9. The manufacturing method of the 510 Mpa grade steel plate for icebreaking ships in extremely cold environments according to claim 5, characterized in that: After the vacuum treatment, N ≤ 40 ppm and H ≤ 1.5 ppm.

10. The manufacturing method of the 510 Mpa grade steel plate for icebreaking ships in extremely cold environments according to claim 5, characterized in that: In the rolling process, the total number of finishing passes does not exceed 9.

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