Marine steel plate with excellent low-temperature impact toughness and production method thereof

Abstract

The invention discloses an offshore steel plate with excellent low-temperature impact toughness and a production method thereof. The steel plate comprises the following chemical components in percentage by mass: 0.10%-0.18% of C, 0.15%-0.50% of Si, 1.00%-1.50% of Mn, less than or equal to 0.010% of P, less than or equal to 0.005% of S, 0.50%-1.50% of Cr, 0.50%-1.50% of Ni, 0.020%-0.060% of V, 0.10%-0.50% of Mo, 0.020%-0.050% of Nb, 0.015%-0.050% of Ti, 0.020%-0.050% of Al and the balance of Fe and inevitable impurities. The production method comprises the procedures of steelmaking, continuous casting, heating rolling and heat treatment. The yield strength of the steel plate is larger than or equal to 700 MPa, the tensile strength is larger than or equal to 900 MPa, the ductility is larger than or equal to 20%, the transverse V-shaped impact energy at the temperature of-60 DEG C is larger than or equal to 100 J, and obdurability matching is good

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of metallurgy, and particularly relates to a sea-use steel plate with excellent low-temperature impact toughness and a production method thereof. BACKGROUND

[0002] With the rapid development of social technology, the consumption of various resources on the earth is rapidly increasing, and countries pay more and more attention to the development of ocean and polar regions. China also vigorously develops key equipment technologies for developing marine resources, and has built multiple scientific research stations in the Antarctic and the Arctic. High-strength steel plates with excellent ultra-low-temperature impact toughness are generally used as key components of large marine steel structures such as offshore platforms, oil drilling platforms, self-elevating offshore platform legs, and wind power installation ships. With the deepening of the working sea area, the use temperature is lower, and at the same time, the steel structure of these key parts needs to withstand harsh service environments such as sea waves, ocean currents, and atmospheric corrosion. Therefore, it must have high strength, ultra-low-temperature toughness, fatigue resistance, lamellar tear resistance, and good weldability. Steel materials that can withstand ultra-low-temperature toughness above-60 DEG C still restrict the development of China's marine equipment manufacturing. The development of high-strength steel with ultra-low-temperature toughness has important social significance and economic value for the development of China's marine engineering and polar scientific research.

[0003] At present, the production of ultra-low-temperature series steel plates in China mainly includes nickel series and high manganese steel series. However, although these series of steel have good low-temperature impact toughness, the production cost is extremely high, which is not conducive to mass production and use. Therefore, there is an urgent need for sea-use steel plates with low production cost, simple production process, and-60 DEG C low-temperature impact resistance. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a 10-50mm-thick sea-use steel plate with ultra-low-temperature toughness and a production method thereof. To solve the above problems, the chemical composition is designed reasonably as the basis, and through the control of each production process of steelmaking, continuous casting, rolling, and heat treatment, a sea-use steel plate with excellent low-temperature impact toughness is obtained.

[0005] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a sea-use steel plate with excellent low-temperature impact toughness, the chemical composition and mass percentage of the steel plate are as follows: C: 0.10-0.18%, Si: 0.15-0.50%, Mn: 1.00-1.50%, P≤0.010%, S≤0.005%, Cr: 0.50-1.50%, Ni: 0.50-1.50%, V: 0.020-0.060%, Mo: 0.10-0.50%, Nb: 0.020-0.050%, Ti: 0.015-0.050%, Al: 0.020-0.050%, and the rest is Fe and inevitable impurities.

[0006] The steel plate has a thickness of 10-50 mm.

[0007] The steel plate has a yield strength of ≥700 MPa, a tensile strength of ≥900 MPa, an elongation of ≥20%, and a transverse V-type impact energy at -60 ℃ of ≥100 J, and has high strength, good toughness and uniform structure.

[0008] Another object of the present application is to provide a production method of the offshore steel plate with excellent low-temperature impact toughness, which comprises the steps of steelmaking, continuous casting, heating rolling and heat treatment; the heating rolling step has a two-stage rough rolling temperature of 850-910 ℃, adopts large reduction rolling, ensures three passes each with a reduction rate of ≥20%, and has a finish rolling temperature of 800-860 ℃.

[0009] In the steelmaking step, the qualified molten steel from the preliminary smelting furnace is sent to the LF refining furnace, complete deoxidation is required in the LF refining process, the white slag retention time is ≥20 min, the total refining time is ≥60 min, after the LF refining is qualified, the molten steel is sent to the VD furnace for vacuum degassing treatment, the high vacuum degree is ≤66.7 Pa, the high vacuum retention time is ≥18 min, after the vacuum is finished, calcium wire is fed at 2-3 m / t of molten steel to perform spheroidization treatment on the inclusions, and then soft blowing is performed for 10-15 min to promote the spheroidization and floating of the inclusions.

[0010] In the continuous casting step, the slab is cast by a slab continuous casting machine to a thickness of 200-300 mm, the molten steel superheat is controlled at 15-25 ℃ during casting, the pulling speed is controlled at 0.80-0.90 m / min, and the secondary cooling water is reasonably controlled to ensure good internal quality of the cast slab.

[0011] In the heating rolling step, the continuous casting slab is heated in a continuous furnace, the slab charging temperature is ≥300 ℃, the temperature in the holding stage is controlled at 1220-1280 ℃, and the total heating time is ≥8 min / cm according to the thickness of the slab.

[0012] In the heat treatment step, the quenching temperature is 850-910 ℃, the heating time is 60-120 min, the tempering temperature is 650-700 ℃, the total heating time is 100-150 min, and then the steel plate is obtained after air cooling to room temperature.

[0013] The design concept of this invention is as follows: This invention employs a medium-carbon alloy with appropriate chemical composition design. Through suitable chemical composition design, the required performance is achieved while keeping the alloy content as low as possible. During steelmaking, the alloy composition is precisely controlled through LF refining. During VD (vacuum distillation), the vacuum degree and holding time are controlled. After vacuum treatment, calcium treatment and a reasonable soft blowing process are used to ensure the purity of the molten steel, laying a good foundation for the quality of the subsequent steel plates. Then, a large-thickness continuous casting billet is cast using continuous casting. By controlling the superheat and casting speed, segregation during the solidification process of the continuous casting billet is reduced, ensuring the internal quality of the steel plate. During rolling, a high-reduction rolling process is used to further improve the internal quality of the steel plate. After rolling, a reasonable heat treatment process is applied, ultimately producing 10-50mm thick marine steel plates with excellent ultra-low temperature toughness. These plates possess good strength and toughness, making them promising for applications in ultra-low temperature environments, especially in cold polar regions at sea.

[0014] The roles of each chemical component and its content in this invention are as follows: C: 0.10~0.18%. Carbon has a significant impact on various properties of steel, especially the strength and hardness of steel plates. Too low a carbon content will result in low strength of steel and increase the difficulty of smelting. High carbon content can significantly improve the hardness and strength of steel. This invention designs this content according to the required strength requirements.

[0015] Si: 0.15-0.50%. Silicon is the main reducing agent and deoxidizer in the steelmaking process. Killed steel contains a certain amount of silicon. Silicon can improve the elastic limit, yield strength and tensile strength of steel.

[0016] Mn: 1.00~1.50%. Manganese alloys are inexpensive and are also good deoxidizers and desulfurizers. They can increase the toughness, strength, and hardness of steel, improve the hardenability of steel, and improve the hot working performance of steel. Considering the influence of various factors, the manganese content in this invention was determined.

[0017] Phosphorus content ≤ 0.010% is generally considered a harmful element in steel, increasing its cold brittleness, reducing its plasticity, and worsening its weldability. Therefore, phosphorus content should be reduced as much as possible while keeping costs under control.

[0018] Sulfur is a harmful element in steel, with a content of ≤0.005%. It increases the hot brittleness of steel and reduces its ductility and toughness. However, sulfur can increase the machinability of steel. Unless there are special requirements, the sulfur content in steel should be reduced as much as possible.

[0019] Cr: 0.50-1.50%. Chromium is an important element for improving the hardenability of steel and can improve the uniformity of steel plate properties. Adding a certain amount of chromium can improve the ballistic performance of steel plates. However, if too much chromium is added, it will form a low-melting-point Cr-Mn composite oxide with manganese, which will cause surface cracks during hot working. The chromium content of this invention was determined based on the results of multiple experiments.

[0020] Ni: 0.50~1.50%. Nickel can improve the strength of steel, and also enhance its plasticity and toughness, especially its low-temperature toughness. However, it is relatively expensive and is a rare precious metal.

[0021] V: 0.020~0.060%, V: 0.020~0.050%. Vanadium is a good deoxidizer in steel, which can refine grains and improve the strength and toughness of steel. The carbides formed by vanadium and carbon can improve the resistance to hydrogen corrosion under high temperature and high pressure.

[0022] Mo: 0.10-0.50%. Molybdenum significantly improves strength, plasticity, and low-temperature impact toughness. This is because when Mo dissolves in ferrite and austenite, it significantly improves the hardenability of steel. Moreover, molybdenum can significantly increase the recrystallization temperature of steel. Molybdenum can also improve the strength and toughness of steel. It is also a relatively expensive metal.

[0023] Nb: 0.020~0.050%. Niobium can promote the grain refinement of the microstructure of steel plates, while improving strength and toughness. During the rolling process, it can effectively refine the microstructure by inhibiting austenite recrystallization, and improve the hardenability of steel through precipitation strengthening, reduce the overheating sensitivity of steel, and improve welding performance.

[0024] Ti: 0.015~0.050%. Titanium can refine grains in steel. The TiC carbide formed with carbon is extremely stable, which can inhibit grain growth and effectively prevent the precipitation of grain boundary carbides. The carbides formed by titanium remain stable at high temperatures, so that titanium-containing steel still has good mechanical properties in high-temperature environments.

[0025] Al: 0.020~0.050%. Aluminum is a commonly used deoxidizer in steel and an essential alloy for killed steel. Adding a small amount of aluminum to steel can refine the grains, improve impact toughness, and also provide oxidation and corrosion resistance. Excessive aluminum content affects the hot working performance, weldability, and machinability of steel.

[0026] The beneficial effects of adopting the above technical solution are as follows: 1. This invention optimizes the chemical composition design, using medium carbon and suitable alloy components to ensure the strength of the steel plate, laying the foundation for improving the overall uniformity of the steel plate's structure and performance requirements. 2. This invention reduces endogenous non-metallic inclusions in molten steel by employing LF refining, large slab continuous casting machine, VD vacuum furnace, calcium treatment, and soft blowing processes, thereby improving the purity of the molten steel and the internal quality of the steel plate. 3. This invention, through reasonable heating rolling and heat treatment processes, enables the steel plate to possess good strength and good ultra-low temperature impact toughness, meeting users' requirements for ultra-low temperature and ultra-high strength of steel plates, and has broad application prospects. 4. The steel plates produced by this invention have a thickness specification of 10-50mm, a yield strength ≥700MPa, a tensile strength ≥900MPa, an elongation ≥20%, and a transverse impact energy ≥100J at -60℃, exhibiting good strength and toughness matching. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. Example 1

[0028] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 20mm. Its chemical composition and mass percentage are as follows: C: 0.16%, Si: 0.50%, Mn: 1.46%, P: 0.010%, S: 0.004%, Cr: 0.78%, Ni: 0.90%, V: 0.056%, Mo: 0.30%, Nb: 0.043%, Ti: 0.028%, Al: 0.020%, with the remainder being Fe and unavoidable impurities.

[0029] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is held for 31 minutes, and the total refining time is 76 minutes. After the molten steel is qualified after LF furnace refining, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 32 Pa and the high vacuum holding time is 22 minutes. After the vacuum is completed, 3 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 11 minutes to promote the spheroidization and flotation of inclusions.

[0030] (2) Continuous casting process: The slab is cast into a 245mm thick slab using a large slab continuous casting machine. During the casting process, the molten steel is superheated to 22℃ and the casting speed is controlled at 0.81m / min. At the same time, the amount of secondary cooling water is reasonably controlled to ensure that the slab has good internal quality.

[0031] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 300℃, the holding stage temperature is 1280℃, the total heating time is 267min, and large reduction rolling is adopted. The two-stage rolling temperature is 864℃, there are three passes, each with a reduction rate of 22%, and the final rolling temperature is 853℃.

[0032] (4) Heat treatment process: Quenching temperature 870℃, total heating time 80min, tempering temperature 680℃, total heating time 120min, and then air cooling to room temperature to obtain the steel plate.

[0033] The resulting steel plate has a yield strength of 770 MPa, a tensile strength of 986 MPa, an elongation of 22%, and an average transverse V-shaped impact energy of 137 J at -60℃. It exhibits good strength and toughness matching and excellent performance. Example 2

[0034] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 15mm and its chemical composition and mass percentage are as follows: C: 0.18%, Si: 0.15%, Mn: 1.23%, P: 0.008%, S: 0.003%, Cr: 1.50%, Ni: 1.50%, V: 0.028%, Mo: 0.42%, Nb: 0.037%, Ti: 0.015%, Al: 0.043%, with the remainder being Fe and unavoidable impurities.

[0035] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is maintained for 26 minutes, and the total refining time is 70 minutes. After the molten steel is qualified after refining in LF furnace, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 50 Pa and the high vacuum maintenance time is 23 minutes. After the vacuum is completed, 2.8 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 13 minutes to promote the spheroidization and flotation of inclusions.

[0036] (2) Continuous casting process: The slab is cast into a 255mm thick slab using a large slab continuous casting machine. During the casting process, the molten steel is superheated to 17℃ and the casting speed is controlled at 0.87m / min. At the same time, the amount of secondary cooling water is reasonably controlled to ensure that the slab has good internal quality.

[0037] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 325℃, the holding stage temperature is 1260℃, the total heating time is 273min, and large reduction rolling is adopted. The two-stage rolling temperature is 900℃, there are three passes, each with a reduction rate of 24%, and the final rolling temperature is 816℃.

[0038] (4) Heat treatment process: Quenching temperature 880℃, total heating time 60min, tempering temperature 700℃, total heating time 110min, and then air cooling to room temperature to obtain the steel plate.

[0039] The resulting steel plate has a yield strength of 760 MPa, a tensile strength of 980 MPa, an elongation of 21%, and an average transverse V-shaped impact energy of 100 J at -60℃. It exhibits good strength-toughness matching and excellent performance. Example 3

[0040] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 40mm. Its chemical composition and mass percentage are as follows: C: 0.14%, Si: 0.48%, Mn: 1.17%, P: 0.009%, S: 0.002%, Cr: 1.32%, Ni: 0.85%, V: 0.060%, Mo: 0.28%, Nb: 0.031%, Ti: 0.036%, Al: 0.035%, with the remainder being Fe and unavoidable impurities.

[0041] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is maintained for 28 minutes, and the total refining time is 75 minutes. After the molten steel is qualified after LF furnace refining, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 66.7 Pa and the high vacuum maintenance time is 19 minutes. After the vacuum is completed, 2.5 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 10 minutes to promote the spheroidization and flotation of inclusions.

[0042] (2) Continuous casting process: The slab is cast into a 275mm thick slab using a large slab continuous casting machine. During the casting process, the molten steel is superheated to 19℃ and the casting speed is controlled at 0.90m / min. At the same time, the amount of secondary cooling water is reasonably controlled to ensure that the slab has good internal quality.

[0043] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 335℃, the holding stage temperature is 1230℃, the total heating time is 243min, and large reduction rolling is adopted. The two-stage rolling temperature is 910℃, there are three passes, each with a reduction rate of 24%, and the final rolling temperature is 816℃.

[0044] (4) Heat treatment process: Quenching temperature 850℃, total heating time 120min, tempering temperature 670℃, total heating time 140min, and then air cooling to room temperature to obtain the steel plate.

[0045] The resulting steel plate has a yield strength of 750 MPa, a tensile strength of 921 MPa, an elongation of 20%, and an average transverse V-shaped impact energy of 150 J at -60℃. It exhibits good strength and toughness matching and excellent performance. Example 4

[0046] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 30mm and its chemical composition and mass percentage are as follows: C: 0.17%, Si: 0.22%, Mn: 1.06%, P: 0.007%, S: 0.005%, Cr: 0.85%, Ni: 1.30%, V: 0.025%, Mo: 0.10%, Nb: 0.015%, Ti: 0.050%, Al: 0.038%, with the remainder being Fe and unavoidable impurities.

[0047] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is maintained for 23 minutes, and the total refining time is 78 minutes. After the molten steel is qualified after refining in LF furnace, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 31 Pa and the high vacuum maintenance time is 18 minutes. After the vacuum is completed, 2.6 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 12 minutes to promote the spheroidization and flotation of inclusions.

[0048] (2) Continuous casting process: The slab is cast into a 300mm thick slab using a large slab continuous casting machine. During the casting process, the molten steel is superheated to 15℃ and the casting speed is controlled at 0.86m / min. At the same time, the amount of secondary cooling water is reasonably controlled to ensure that the slab has good internal quality.

[0049] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 385℃, the holding stage temperature is 1240℃, the total heating time is 223min, and large reduction rolling is adopted. The two-stage rolling temperature is 863℃, there are three passes, each with a reduction rate of 23%, and the final rolling temperature is 830℃.

[0050] (4) Heat treatment process: Quenching temperature 900℃, total heating time 100min, tempering temperature 690℃, total heating time 135min, and then air cooling to room temperature to obtain the steel plate.

[0051] The resulting steel plate has a yield strength of 755 MPa, a tensile strength of 930 MPa, an elongation of 21%, and an average transverse V-shaped impact energy of 128 J at -60℃. It exhibits good strength-toughness matching and excellent performance. Example 5

[0052] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 50mm and its chemical composition and mass percentage are as follows: C: 0.12%, Si: 0.31%, Mn: 1.00%, P: 0.006%, S: 0.003%, Cr: 0.50%, Ni: 1.05%, V: 0.035%, Mo: 0.32%, Nb: 0.050%, Ti: 0.044%, Al: 0.050%, with the remainder being Fe and unavoidable impurities.

[0053] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is maintained for 29 minutes, and the total refining time is 60 minutes. After the molten steel is qualified after refining in LF furnace, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 36 Pa and the high vacuum maintenance time is 23 minutes. After the vacuum is completed, 2.0 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 15 minutes to promote the spheroidization and flotation of inclusions.

[0054] (2) Continuous casting process: The 200mm thick slab is cast by a large slab continuous casting machine. During the casting process, the molten steel is superheated to 25℃ and the casting speed is controlled at 0.88m / min. At the same time, the amount of secondary cooling water is reasonably controlled so that the slab has good internal quality.

[0055] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 350℃, the holding stage temperature is 1220℃, the total heating time is 234min, and large reduction rolling is adopted. The two-stage rolling temperature is 850℃, there are three passes, each with a reduction rate of 21%, and the final rolling temperature is 800℃.

[0056] (4) Heat treatment process: Quenching temperature 860℃, total heating time 110min, tempering temperature 650℃, total heating time 150min, and then air cooling to room temperature to obtain the steel plate.

[0057] The resulting steel plate has a yield strength of 785 MPa, a tensile strength of 985 MPa, an elongation of 23%, and an average transverse V-shaped impact energy of 145 J at -60℃. It exhibits good strength-toughness matching and excellent performance. Example 6

[0058] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 35mm and its chemical composition and mass percentage are as follows: C: 0.13%, Si: 0.39%, Mn: 1.50%, P: 0.008%, S: 0.004%, Cr: 0.95%, Ni: 0.95%, V: 0.042%, Mo: 0.50%, Nb: 0.020%, Ti: 0.028%, Al: 0.045%, with the remainder being Fe and unavoidable impurities.

[0059] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is maintained for 36 minutes, and the total refining time is 68 minutes. After the molten steel is qualified after refining in LF furnace, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 28 Pa and the high vacuum maintenance time is 20 minutes. After the vacuum is completed, 2.3 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 14 minutes to promote the spheroidization and flotation of inclusions.

[0060] (2) Continuous casting process: The slab is cast into a 285mm thick slab using a large slab continuous casting machine. During the casting process, the molten steel is superheated to 20℃ and the casting speed is controlled at 0.84m / min. At the same time, the amount of secondary cooling water is reasonably controlled to ensure that the slab has good internal quality.

[0061] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 356℃, the holding stage temperature is 1275℃, the total heating time is 265min, and large reduction rolling is adopted. The two-stage rolling temperature is 890℃, there are three passes, each with a reduction rate of 23%, and the final rolling temperature is 844℃.

[0062] (4) Heat treatment process: Quenching temperature 910℃, total heating time 75min, tempering temperature 685℃, total heating time 130min, and then air cooling to room temperature to obtain the steel plate.

[0063] The resulting steel plate has a yield strength of 715 MPa, a tensile strength of 945 MPa, an elongation of 22%, and an average transverse V-shaped impact energy of 122 J at -60℃. It exhibits good strength and toughness matching and excellent performance. Example 7

[0064] The marine steel plate with excellent low-temperature impact toughness produced in this embodiment has a thickness of 10 mm and its chemical composition and mass percentage are as follows: C: 0.10%, Si: 0.28%, Mn: 1.35%, P: 0.009%, S: 0.003%, Cr: 1.00%, Ni: 0.50%, V: 0.020%, Mo: 0.15%, Nb: 0.025%, Ti: 0.019%, Al: 0.028%, with the remainder being Fe and unavoidable impurities.

[0065] The production method of marine steel plates with excellent low-temperature impact toughness in this embodiment includes steelmaking, continuous casting, hot rolling, and heat treatment processes. The specific process steps are as follows: (1) Steelmaking process: The qualified molten steel after primary refining furnace is sent to LF refining furnace. During the refining process in LF furnace, deoxidation is complete, white slag is maintained for 33 minutes, and the total refining time is 65 minutes. After the molten steel is qualified after LF furnace refining, the molten steel is sent to VD furnace for vacuum degassing treatment. The high vacuum degree is 35 Pa and the high vacuum maintenance time is 23 minutes. After the vacuum is completed, 2.7 m / t of calcium wire is fed into the molten steel, and then soft blowing is performed for 13 minutes to promote the spheroidization and flotation of inclusions.

[0066] (2) Continuous casting process: The slab is cast into a 265mm thick slab using a large slab continuous casting machine. During the casting process, the molten steel is superheated to 18℃ and the casting speed is controlled at 0.83m / min. At the same time, the amount of secondary cooling water is reasonably controlled to ensure that the slab has good internal quality.

[0067] (3) Heating and rolling process: The continuous casting billet is heated in a continuous furnace. The billet loading temperature is 410℃, the holding stage temperature is 1255℃, the total heating time is 236min, and large reduction rolling is adopted. The two-stage rolling temperature is 870℃, there are three passes, each with a reduction rate of 22%, and the final rolling temperature is 835℃.

[0068] (4) Heat treatment process: Quenching temperature 890℃, total heating time 65min, tempering temperature 660℃, total heating time 100min, and then air cooling to room temperature to obtain the steel plate.

[0069] The resulting steel plate has a yield strength of 700 MPa, a tensile strength of 975 MPa, an elongation of 25%, and an average transverse V-shaped impact energy of 180 J at -60℃. It exhibits good strength-toughness matching and excellent performance.

[0070] The above embodiments are only used to illustrate and not limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention without departing from the spirit and scope of the present invention. Any modifications or partial substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A marine steel plate with excellent low-temperature impact toughness, characterized in that, The chemical composition and mass percentage of the steel plate are as follows: C: 0.10-0.18%, Si: 0.15-0.50%, Mn: 1.00-1.50%, P≤0.010%, S≤0.005%, Cr: 0.50-1.50%, Ni: 0.50-1.50%, V: 0.020-0.060%, Mo: 0.10-0.50%, Nb: 0.020-0.050%, Ti: 0.015-0.050%, Al: 0.020-0.050%, with the remainder being Fe and unavoidable impurities.

2. The marine steel plate with excellent low-temperature impact toughness according to claim 1, characterized in that, The thickness of the steel plate is 10-50 mm.

3. A marine steel plate with excellent low-temperature impact toughness according to claim 1 or 2, characterized in that, The steel plate has a yield strength ≥700MPa, tensile strength ≥900MPa, elongation ≥20%, and transverse V-shaped impact energy ≥100J at -60℃.

4. A method for producing marine steel plates with excellent low-temperature impact toughness according to any one of claims 1-3, characterized in that, The method includes steelmaking, continuous casting, heated rolling and heat treatment processes; the heated rolling process has a two-stage initial rolling temperature of 850-910℃, adopts high reduction rolling, ensures that there are three passes with a reduction rate of ≥20% per pass, and a final rolling temperature of 800-860℃.

5. The method for producing marine steel plates with excellent low-temperature impact toughness according to claim 4, characterized in that, In the steelmaking process, the molten steel that has passed the primary refining furnace is sent to the LF refining furnace. During the LF refining process, complete deoxidation is required, the white slag holding time is ≥20min, and the total refining time is ≥60min. After passing the LF refining, the molten steel is sent to the VD furnace for vacuum degassing treatment. When the high vacuum degree is ≤66.7Pa, the high vacuum holding time is ≥18min. After the vacuum is completed, 2-3m / t of calcium wire is fed into the molten steel to spheroidize the inclusions, and then soft blowing is performed for 10-15min.

6. The method for producing marine steel plates with excellent low-temperature impact toughness according to claim 4, characterized in that, The continuous casting process involves casting slabs with a thickness of 200-300 mm using a slab continuous casting machine. During the casting process, the superheat of the molten steel is controlled at 15-25°C, and the casting speed is controlled at 0.80-0.90 m / min.

7. A method for producing marine steel plates with excellent low-temperature impact toughness according to any one of claims 4-6, characterized in that, The heating and rolling process involves heating the continuously cast billet in a continuous furnace. The billet loading temperature is ≥300℃, and the holding temperature is controlled at 1220~1280℃. The total heating time is ≥8min / cm depending on the billet thickness.

8. A method for producing marine steel plates with excellent low-temperature impact toughness according to any one of claims 4-6, characterized in that, The heat treatment process involves a quenching temperature of 850–910°C, a heating time of 60–120 min, a tempering temperature of 650–700°C, and a total heating time of 100–150 min. The steel plate is then obtained by air cooling to room temperature.