A 460mpa grade thick and wide steel plate having good low temperature toughness and a method for manufacturing the same

Abstract

The application provides a 460MPa-grade thick and wide steel plate with good low-temperature toughness and a manufacturing method thereof, and the steps are as follows: molten iron pretreatment, converter smelting, LF treatment, RH vacuum treatment, continuous casting, slow cooling of the casting blank, heating, rolling and cooling, slow cooling of the steel plate, finishing, inspection, and ultrasonic flaw detection; the components and contents of the steel plate are as follows: C: 0.04-0.07%, Si: 0.10-0.35%, Mn: 1.60-1.70%, P: ≤0.015%, S: ≤0.003%, Al: 0.015-0.035%, Nb: 0.030-0.045%, Ni: 0.20-0.35%, Ti: 0.008-0.025%, Cr: 0.20-0.35%, and the balance is Fe. The thick and wide steel plate produced by the method has good low-temperature toughness and can be widely used in engineering machinery, ocean platforms and the like in extremely cold regions.

Description

Technical Field

[0001] This invention belongs to the technical field of continuous casting billet production of medium and thick plates, specifically relating to a 460MPa grade steel plate with good low-temperature toughness and a thickness and width, and its manufacturing method. Background Technology

[0002] With the global energy shortage in recent years, resource development in some marine and extremely cold regions has intensified, leading to increased demand for medium and thick plates with wide and thick specifications and low-temperature resistance. Currently, thick 460MPa grade steel plates have problems such as poor low-temperature resistance, poor weldability, small width, and watermark defects on the surface. There is an urgent need to develop a 460MPa grade steel plate with good low-temperature toughness, wide and thick specifications, easy weldability, and good surface quality.

[0003] Compared with document 1, the patent "A 460MPa grade high toughness extra-thick plate and its manufacturing method" (publication number: CN114686776B) has the characteristics of large thickness and low alloy cost. However, the production process adopts offline normalizing + weak water cooling, which has the disadvantages of increased process cost and long production delivery time. The low temperature impact performance of the steel plate can only meet the requirements of -40℃, and the impact performance data of -60℃ is not mentioned, which cannot meet the service requirements of extremely cold regions.

[0004] Comparative document 2, patent "A method for producing high-strength and tough thick steel plates" (publication number: CN112342350A), uses TMCP + tempering to produce a 460MPa high-strength and tough thick steel plate. The online quenching method places high demands on water-cooling equipment, and the tempering process increases costs and extends production lead time. The produced steel plate only meets the -40℃ impact requirement and cannot meet the service requirements in extremely cold regions.

[0005] Compared with document 3, the patent "A 460MPa grade steel plate for service in extremely cold regions and its preparation method" (publication number: CN115181908A) shows that although the steel plate invented by this patent has the characteristics of good core impact toughness and easy welding, the thickest steel plate is only 100mm, the low temperature resistance meets the requirement of -40℃, and the surface of the thick steel plate is prone to defects such as watermarks because it is not specially used for dephosphorization water during rolling, which cannot meet the service requirements of thick steel plates in extremely cold regions. Summary of the Invention

[0006] The technical problem to be solved by this invention is to provide a 460MPa grade steel plate with good low-temperature toughness and thickness. This invention also provides a method for producing this 460MPa grade steel plate with good low-temperature toughness and thickness. Through reasonable composition, smelting control, and controlled rolling and cooling processes, an 80-120mm thick steel plate is produced, with a longitudinal impact energy ≥220J at -60℃, CEV≤0.42, Pcm≤0.18, good weldability, yield strength ratio ≤0.83, good seismic performance, and good surface quality, with no watermarks or mottling defects on the steel plate surface.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a 460MPa grade steel plate with good low-temperature toughness and a thickness and width, wherein the chemical composition and mass percentage of the steel plate are: C: 0.04-0.07%, Si: 0.10-0.35%, Mn: 1.60-1.70%, P≤0.015%, S≤0.003%, Al: 0.015-0.035%, Nb: 0.030-0.04%. 5%, Ni: 0.20-0.35%, Ti: 0.008-0.025%, Cr: 0.20-0.35%, balance is Fe and unavoidable impurities, CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.42, CEpcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.18.

[0008] This invention employs a low-carbon (C) design to ensure the toughness and weldability of the steel plate. Microalloying elements Nb and Ti are added, along with alloying element Cr to guarantee strength, and alloying element Ni to ensure low-temperature toughness. This compositional design ensures that the invented steel plate possesses excellent strength, toughness, low-temperature resistance, and weldability.

[0009] This invention also discloses a 460MPa grade steel plate with good low-temperature toughness and a thickness and width, and its manufacturing method. The production steps of the manufacturing method include hot metal pretreatment, converter smelting, LF+RH double refining treatment, continuous casting, heating, rolling, and cooling. In the manufacturing method of the aforementioned 460MPa grade steel plate with good low-temperature toughness and thickness, as a preferred embodiment, the desulfurization of molten iron (KR) is S≤0.007%, the converter adopts a double-slag process, and the tapping P≤0.012% and S≤0.005% are achieved; argon blowing is carried out throughout the LF refining process, and aluminum granules or aluminum wire are used for deoxidation, with white slag holding time ≥20min and final slag basicity ≥3.0; the vacuum degree in the RH furnace is ≤100Pa, the pressure holding time is ≥12min, calcium treatment is performed before tapping, and static argon blowing time after wire feeding is ≥12min, with final H≤0.00015%; the superheat during continuous casting is controlled to ≤20℃, and a secondary cooling system is used. Electromagnetic stirring and light pressure at the end of solidification are used to maintain a constant casting speed during the casting process, and the cooling time of the billet after it is removed from the production line is ≥24h. In the above-mentioned manufacturing method of 460MPa grade steel plate with good low-temperature toughness and thick and wide specifications, as a preferred embodiment, the heating adopts a multi-stage heating method. The temperature of the first heating stage is 900-1000℃, the temperature of the second heating stage is 1100-1180℃, the temperature of the third heating stage is 1180-1260℃, and the temperature of the soaking stage is 1220-1250℃. The total heating time of the billet in the heating furnace is 328-520min. Preferably, after the billet is heated, it is subjected to high-pressure water descaling treatment.

[0010] In this invention, a multi-stage heating method is used to limit the heating temperature and heating time, which on the one hand ensures that the billet is heated evenly and thoroughly, and on the other hand prevents the austenite grains from growing excessively.

[0011] In the manufacturing method of the above-mentioned 460MPa grade steel plate with good low-temperature toughness and thickness, as a preferred embodiment, a two-stage controlled rolling process is adopted. The roughing rolling start temperature is 1020-1100℃, the rolling speed is ≤1.5m / s, and after the steel plate is widened, the longitudinal rolling single-pass reduction is at least 3 passes with a reduction of ≥30mm. The final pass of the roughing rolling is used to remove phosphorus. After the roughing rolling is completed, the plate is first passed through the finishing mill without phosphorus and then waited for the temperature in front of the finishing mill. The finishing rolling start temperature is 800-830℃. The first and last passes of the finishing rolling are used to remove phosphorus. The phosphorus removal pressure is 25MPa. The final rolling temperature is 770-800℃, and the intermediate billet is 130-190mm.

[0012] This invention defines rough rolling as recrystallization rolling, limits the initial rolling temperature and rolling speed, and ensures that the single-pass reduction in longitudinal rolling after widening is at least 3 passes with a reduction of ≥30mm. This high-temperature, low-speed, high-reduction rolling strategy fully refines the austenite grains, laying the foundation for the strong and tough microstructure of thick steel plates. By defining finish rolling as non-recrystallization rolling, limiting the finish rolling temperature and cumulative reduction rate during the finish rolling stage, the entire finish rolling stage is ensured to be rolled in the non-recrystallization zone to avoid mixed crystals. This promotes the formation of numerous deformation bands, twins, and dislocations within the austenite grains, creating conditions for ferrite phase deformation nuclei, thus improving the strength and toughness of the steel plate. Controlling the thickness of the intermediate slab allows for a reasonable distribution of the reduction in rough and finish rolling, improving the uniformity of the microstructure in the thickness direction of thick steel plates, which is beneficial for low-temperature impact performance. Finally, controlling the descaling water pressure and its operation during rough and finish rolling ensures complete removal of the iron oxide scale generated on the surface of thick steel plates.

[0013] In the manufacturing method of the above-mentioned 460MPa grade steel plate with good low-temperature toughness and thickness, as a preferred embodiment, the water cooling adopts a three-pass reciprocating cooling process, with a water volume of 90-100m³ / h, 19 sets of cooling water are turned on, the roller speed is 0.6-0.8m / s, the water ratio is 2.3, the first pass reddening temperature is 680-710℃, the second pass reddening temperature is 550-580℃, and the third pass reddening temperature is 410-460℃; after hot straightening, the steel plate is slowly cooled in a slow cooling pit or stacked for slow cooling, with a slow cooling time of ≥48h.

[0014] This invention employs a three-stage cooling method to ensure uniform cooling along the thickness of thick steel plates, rationally control the proportion of microstructures, reduce the amount of pearlite and martensite, and ensure that a composite microstructure of bainite can be obtained in steel plates of different thicknesses or in different locations on the same steel plate, which is beneficial to the low-temperature impact performance of thick steel plates. After hot straightening, the steel plates are moved into a slow cooling pit or stacked for slow cooling for ≥48 hours to ensure the phase transformation process is fully carried out and to improve the microstructure uniformity of thick steel plates.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The 460MPa grade steel plate with good low-temperature toughness and thick and wide specifications produced by the present invention not only has good strength, but also has excellent low-temperature impact performance, with yield strength ≥465MPa, tensile strength 580-606MPa, longitudinal impact energy at 1 / 4 position -50℃ ≥280J, longitudinal impact energy at 1 / 4 position -60℃ ≥220J, and longitudinal impact energy at 1 / 2 position -50℃ ≥150J; CEV≤0.42, Pcm≤0.18, and good weldability.

[0016] 2. The low-temperature toughness steel plate with a thickness and width of 460MPa produced by this invention has good seismic performance and a yield strength ratio ≤0.83.

[0017] 3. The invention produces 460MPa steel plates with good low-temperature toughness and a width of up to 3350mm, reducing the number of welding operations for downstream customers and improving production efficiency.

[0018] 4. The low-temperature toughness steel plate with a thickness and width of 460MPa produced by this invention has a uniform internal structure and good internal quality. The flaw detection of the steel plate meets the TI grade requirements of NB / T47013-2015 standard.

[0019] 5. The low-temperature toughness steel plate with a thickness and width of 460MPa produced by this invention has good surface quality, and the steel plate surface is free of watermarks or mottling defects. Attached Figure Description

[0020] Figure 1 Example 1: Typical microstructure of a 1 / 4 section of a 460MPa grade steel plate with good low-temperature toughness.

[0021] Figure 2 Example 1: Typical microstructure of a 1 / 2 thick and wide 460MPa grade steel plate with good low-temperature toughness.

[0022] Figure 3 Example 1: Surface condition of a 460MPa grade steel plate with good low-temperature toughness and thickness.

[0023] Figure 4 Comparison 1: Surface condition of a 460MPa grade steel plate with good low-temperature toughness and thickness. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments.

[0025] The specific embodiments of the present invention provide a 460MPa grade steel plate with good low-temperature toughness and a thickness and width, and its manufacturing method. The production steps of the manufacturing method are as follows: hot metal pretreatment, converter smelting, LF+RH double refining treatment, and continuous casting: hot metal KR desulfurization S≤0.007%, converter adopts double slag process, steel tapping P≤0.012%, S≤0.005%; LF refining is carried out with argon blowing throughout the process, aluminum particles or aluminum wire are used for deoxidation, white slag holding time≥20min, final slag basicity≥3.0; RH furnace vacuum degree≤100Pa, holding time≥12min, calcium treatment before tapping, static argon blowing time after wire feeding≥12min, final H≤0.00015%; the superheat control during continuous casting is ≤20℃, secondary cooling electromagnetic stirring and light pressure at the end of solidification are adopted, constant casting speed is maintained during casting, and the billet cooling time after leaving the line is ≥24h. Example 1: A 460MPa grade steel plate with good low-temperature toughness and a thickness of 80mm is provided. The chemical composition and mass percentage of the steel plate are as follows: C: 0.07%, Si: 0.10%, Mn: 1.65%, P: 0.015%, S: 0.002%, Al: 0.018%, Nb: 0.035%, Ni: 0.25%, Ti: 0.012%, Cr: 0.25%, H: 0.0001%, with the balance being Fe and unavoidable impurities. CEV=0.41, Pcm=0.18.

[0026] The production steps and process parameters of steel plates are as follows: 1. Smelting: In the smelting steps, the molten iron is pretreated, smelted in a converter, and double-refined by LF+RH. The continuous casting is then cast into 328mm continuous casting billets according to the above method.

[0027] 2. Heating: The temperature of the first heating stage is 900℃, the temperature of the second heating stage is 1150℃, the temperature of the third heating stage is 1200℃, and the temperature of the soaking stage is 1220℃. The total heating time of the billet in the heating furnace is 328 minutes. After the billet is heated, it undergoes high-pressure water descaling treatment.

[0028] 3. Rolling: A two-stage controlled rolling process is adopted. The roughing rolling temperature is 1020℃ and the rolling speed is 1.5m / s. After the steel plate is widened, there are 4 longitudinal rolling passes with reductions of 25mm, 30mm, 31mm and 35mm respectively. The last pass of the roughing rolling is used to remove phosphorus. After the roughing rolling is completed, it is first passed through the finishing mill to remove phosphorus, and then it is placed in front of the finishing mill to wait for the temperature. The starting temperature of the finishing rolling is 830℃. The first and last passes of the finishing rolling are used to remove phosphorus. The dephosphorization pressure is 25Mpa. The final rolling temperature is 800℃ and the intermediate billet is 130mm.

[0029] 4. Cooling: A three-pass reciprocating cooling process is adopted, with a water flow rate of 90 m³ / h, 19 sets of cooling water activated, a roller speed of 0.8 m / s, and a water ratio of 2.3. The first pass reddening temperature is 695℃, the second pass reddening temperature is 580℃, and the third pass reddening temperature is 460℃. After hot straightening, the products are placed in a slow cooling pit or stacked for slow cooling, with a slow cooling time of ≥48 hours.

[0030] The steel plate obtained in this embodiment has a yield strength of 470 MPa, a tensile strength of 580 Pa, a longitudinal impact energy of 310 J at -50°C at 1 / 4 of its thickness, 295 J at -60°C at 1 / 4 of its thickness, and a longitudinal impact energy ≥185 J at -50°C at 1 / 2 of its thickness. The yield strength ratio is 0.81, and the flaw detection results of the steel plate meet the TI grade requirements of the NB / T47013-2015 standard. The surface quality of the steel plate is good, with no watermarks or mottling defects.

[0031] Example 2: A 90mm thick 460MPa grade steel plate with good low-temperature toughness and good width and thickness. The chemical composition and mass percentage of the steel plate are as follows: C: 0.06%, Si: 0.30%, Mn: 1.60%, P: 0.013%, S: 0.002%, Al: 0.035%, Nb: 0.045%, Ni: 0.20%, Ti: 0.025%, Cr: 0.20%, H: 0.00015%, with the balance being Fe and unavoidable impurities. CEV=0.38, Pcm=0.16.

[0032] The production steps and process parameters of steel plates are as follows: 1. Smelting: In the smelting steps, the molten iron is pretreated, smelted in a converter, and double-refined by LF+RH. The continuous casting is then cast into 328mm continuous casting billets according to the above method.

[0033] 2. Heating: The temperature of the first heating stage is 950℃, the temperature of the second heating stage is 1100℃, the temperature of the third heating stage is 1180℃, and the temperature of the soaking stage is 1220℃. The total heating time of the billet in the heating furnace is 394 minutes. After the billet is heated, it undergoes high-pressure water descaling treatment.

[0034] 3. Rolling: A two-stage controlled rolling process is adopted. The roughing rolling temperature is 1050℃ and the rolling speed is 1.2m / s. After the steel plate is widened, there are 4 longitudinal rolling passes with reductions of 24mm, 30mm, 30mm and 32mm respectively. After the roughing rolling is completed, the plate is first passed through the finishing mill to remove phosphorus water, and then it is placed in front of the finishing mill to wait for the temperature. The finishing rolling temperature is 805℃. The first and last passes of the finishing rolling remove phosphorus water with a dephosphorization pressure of 25Mpa. The final rolling temperature is 780℃ and the intermediate billet is 150mm.

[0035] 4. Cooling: A three-pass reciprocating cooling process is adopted, with a water flow rate of 90 m³ / h, 19 sets of cooling water activated, roller speed of 0.8 m / s, water ratio of 2.3, first pass reddening temperature of 710℃, second pass reddening temperature of 575℃, and third pass reddening temperature of 440℃. After hot straightening, the products are placed in a slow cooling pit or stacked for slow cooling, with a slow cooling time of ≥48 hours.

[0036] The steel plate obtained in this embodiment has a yield strength of 485 MPa, a tensile strength of 606 Pa, a longitudinal impact energy of 285 J at -50°C at 1 / 4 of its thickness, 260 J at -60°C at 1 / 4 of its thickness, and a longitudinal impact energy ≥180 J at -50°C at 1 / 2 of its thickness. The yield strength ratio is 0.80, and the flaw detection results of the steel plate meet the TI grade requirements of NB / T47013-2015 standard. The surface quality of the steel plate is good, with no watermarks or mottling defects.

[0037] Example 3: A 100mm thick 460MPa grade steel plate with good low-temperature toughness and a wide and thick specification. The chemical composition and mass percentage of the steel plate are as follows: C: 0.05%, Si: 0.35%, Mn: 1.70%, P: 0.013%, S: 0.003%, Al: 0.020%, Nb: 0.035%, Ni: 0.30%, Ti: 0.008%, Cr: 0.35%, H: 0.00015%, with the balance being Fe and unavoidable impurities. CEV=0.42, Pcm=0.17.

[0038] The production steps and process parameters of steel plates are as follows: 1. Smelting: In the smelting steps, the molten iron is pretreated, smelted in a converter, and double-refined by LF+RH. The continuous casting is then cast into 400mm continuous casting billets according to the above method.

[0039] 2. Heating: The temperature of the first heating stage is 1000℃, the temperature of the second heating stage is 1180℃, the temperature of the third heating stage is 1240℃, and the temperature of the soaking stage is 1230℃. The total heating time of the billet in the heating furnace is 480 minutes. After the billet is heated, it undergoes high-pressure water descaling treatment.

[0040] 3. Rolling: A two-stage controlled rolling process is adopted. The roughing rolling temperature is 1080℃ and the rolling speed is 1.2m / s. After the steel plate is widened, there are 4 longitudinal rolling passes with reductions of 30mm, 32mm, 35mm and 40mm respectively. The last pass of the roughing rolling is used to remove phosphorus. After the roughing rolling is completed, it is first passed through the finishing mill to remove phosphorus, and then it is placed in front of the finishing mill to wait for the temperature. The starting temperature of the finishing rolling is 810℃. The first and last passes of the finishing rolling are used to remove phosphorus. The dephosphorization pressure is 25Mpa. The final rolling temperature is 775℃ and the intermediate billet is 160mm.

[0041] 4. Cooling: A three-pass reciprocating cooling process is adopted, with a water flow rate of 100 m³ / h, 19 sets of cooling water activated, a roller speed of 0.6 m / s, and a water ratio of 2.3. The first pass reddening temperature is 680℃, the second pass reddening temperature is 560℃, and the third pass reddening temperature is 420℃. After hot straightening, the products are placed in a slow cooling pit or stacked for slow cooling, with a slow cooling time of ≥48 hours.

[0042] The steel plate obtained in this embodiment has a yield strength of 465 MPa, a tensile strength of 560 Pa, a longitudinal impact energy of 290 J at -50°C at 1 / 4 of its thickness, 220 J at -60°C at 1 / 4 of its thickness, and a longitudinal impact energy ≥155 J at -50°C at 1 / 2 of its thickness. The yield strength ratio is 0.83, and the flaw detection results of the steel plate meet the TI grade requirements of the NB / T47013-2015 standard. The surface quality of the steel plate is good, with no watermarks or mottling defects.

[0043] Example 4: A 460MPa grade steel plate with good low-temperature toughness and a thickness of 120mm has the following chemical composition and mass percentage: C: 0.04%, Si: 0.35%, Mn: 1.65%, P: 0.012%, S: 0.002%, Al: 0.025%, Nb: 0.030%, Ni: 0.35%, Ti: 0.020%, Cr: 0.30%, H: 0.00012%, with the balance being Fe and unavoidable impurities. CEV=0.40, Pcm=0.16.

[0044] The production steps and process parameters of steel plates are as follows: 1. Smelting: In the smelting steps, the molten iron is pretreated, smelted in a converter, and double-refined by LF+RH. The continuous casting is then cast into 400mm continuous casting billets according to the above method.

[0045] 2. Heating: The temperature of the first heating stage is 1000℃, the temperature of the second heating stage is 1170℃, the temperature of the third heating stage is 1260℃, and the temperature of the soaking stage is 1250℃. The total heating time of the billet in the heating furnace is 520 minutes. After the billet is heated, it undergoes high-pressure water descaling treatment.

[0046] 3. Rolling: A two-stage controlled rolling process is adopted. The roughing rolling temperature is 1100℃ and the rolling speed is 1.0m / s. After the steel plate is widened, there are 4 longitudinal rolling passes with reductions of 26mm, 31mm, 32mm and 35mm respectively. After the roughing rolling is completed, the plate is first passed through the finishing mill to remove phosphorus water, and then it is placed in front of the finishing mill to wait for the temperature. The finishing rolling temperature is 800℃. The first and last passes of the finishing rolling remove phosphorus water with a dephosphorization pressure of 25Mpa. The final rolling temperature is 770℃ and the intermediate billet is 190mm.

[0047] 4. Cooling: A three-pass reciprocating cooling process is adopted, with a water flow rate of 100 m³ / h, 19 sets of cooling water are turned on, the roller speed is 0.6 m / s, the water ratio is 2.3, the first pass reddening temperature is 690℃, the second pass reddening temperature is 580℃, and the third pass reddening temperature is 410℃. After hot straightening, the parts are placed in a slow cooling pit or stacked for slow cooling, with a slow cooling time of ≥48 hours.

[0048] The steel plate obtained in this embodiment has a yield strength of 465 MPa, a tensile strength of 567 Pa, a longitudinal impact energy of 280 J at -50°C at 1 / 4 of its thickness, 230 J at -60°C at 1 / 4 of its thickness, and a longitudinal impact energy ≥150 J at -50°C at 1 / 2 of its thickness. The yield strength ratio is 0.82, and the flaw detection results of the steel plate meet the TI grade requirements of the NB / T47013-2015 standard. The surface quality of the steel plate is good, with no watermarks or mottling defects.

[0049] Comparative Example 1: A 460MPa grade steel plate with good low-temperature toughness and a thickness of 80mm. The chemical composition and mass percentage of the steel plate are as follows: C: 0.07%, Si: 0.20%, Mn: 1.65%, P: 0.015%, S: 0.002%, Al: 0.018%, Nb: 0.035%, Ni: 0.25%, Ti: 0.012%, Cr: 0.25%, H: 0.0001%, with the balance being Fe and unavoidable impurities. CEV=0.41, Pcm=0.18.

[0050] The production steps and process parameters of steel plates are as follows: 1. Smelting: In the smelting steps, the molten iron is pretreated, smelted in a converter, and double-refined by LF+RH. The continuous casting is then cast into 328mm continuous casting billets according to the above method.

[0051] 2. Heating: The temperature of the first heating stage is 900℃, the temperature of the second heating stage is 1150℃, the temperature of the third heating stage is 1200℃, and the temperature of the soaking stage is 1220℃. The total heating time of the billet in the heating furnace is 328 minutes. After the billet is heated, it undergoes high-pressure water descaling treatment.

[0052] 3. Rolling: A two-stage controlled rolling process is adopted. The roughing rolling temperature is 1020℃. After the steel plate is widened, there are three longitudinal rolling passes with reductions of 18mm, 20mm and 25mm respectively. The finishing rolling temperature is 800℃ and the intermediate slab is 180mm.

[0053] 4. Cooling: A three-pass reciprocating cooling process is adopted, with a water flow rate of 90 m³ / h, 19 sets of cooling water activated, a roller speed of 0.8 m / s, and a water ratio of 2.3. The first pass reddening temperature is 695℃, the second pass reddening temperature is 580℃, and the third pass reddening temperature is 460℃. After hot straightening, the products are placed in a slow cooling pit or stacked for slow cooling, with a slow cooling time of ≥48 hours.

[0054] The steel plate obtained in this embodiment has a yield strength of 465 MPa, a tensile strength of 550 Pa, a longitudinal impact energy of 156 J at -50°C at 1 / 4 of its thickness, 115 J at -60°C at 1 / 4 of its thickness, and 47 J at -50°C at 1 / 2 of its thickness. The yield strength ratio is 0.85. The flaw detection results of the steel plate do not meet the TI grade requirements of the NB / T47013-2015 standard. Watermark defects are present on the surface of the steel plate.

[0055] Comparative Example 2: A 460MPa grade steel plate with good low-temperature toughness and a thickness of 120mm was used. The chemical composition and mass percentage of the steel plate were as follows: C: 0.04%, Si: 0.35%, Mn: 1.65%, P: 0.012%, S: 0.002%, Al: 0.025%, Nb: 0.030%, Ni: 0.35%, Ti: 0.020%, Cr: 0.30%, H: 0.00012%, with the balance being Fe and unavoidable impurities. CEV=0.40, Pcm=0.16.

[0056] The production steps and process parameters of steel plates are as follows: 1. Smelting: In the smelting steps, the molten iron is pretreated, smelted in a converter, and double-refined by LF+RH. The continuous casting is then cast into 400mm continuous casting billets according to the above method.

[0057] 2. Heating: The temperature of the first heating stage is 1000℃, the temperature of the second heating stage is 1170℃, the temperature of the third heating stage is 1260℃, and the temperature of the soaking stage is 1250℃. The total heating time of the billet in the heating furnace is 520 minutes. After the billet is heated, it undergoes high-pressure water descaling treatment.

[0058] 3. Rolling: A two-stage controlled rolling process is adopted. The roughing rolling temperature is 1100℃ and the rolling speed is 1.0m / s. After the steel plate is widened, there are 4 longitudinal rolling passes with reductions of 26mm, 31mm, 32mm and 35mm respectively. After the roughing rolling is completed, the plate is first passed through the finishing mill to remove phosphorus water, and then it is placed in front of the finishing mill to wait for the temperature. The finishing rolling temperature is 800℃. The first and last passes of the finishing rolling remove phosphorus water with a dephosphorization pressure of 25Mpa. The final rolling temperature is 770℃ and the intermediate billet is 190mm.

[0059] 4. Cooling: A single-pass water cooling process is adopted, with a water flow rate of 100 m³ / h, and 19 sets of cooling water are turned on, achieving a red-hot temperature of 420℃. After hot straightening, the products are slowly cooled in a slow-cooling pit or stacked for slow cooling, with a slow-cooling time of ≥48 hours.

[0060] The steel plate obtained in this embodiment has a yield strength of 470 MPa, a tensile strength of 556 Pa, a longitudinal impact energy of 86 J at -50°C at 1 / 4 of its thickness, a longitudinal impact energy of 46 J at -60°C at 1 / 4 of its thickness, and a longitudinal impact energy of ≥21 J at -50°C at 1 / 2 of its thickness. The yield strength ratio is 0.85.

[0061] Figure 1 , Figure 2 It can be seen that the microstructure of the steel plate is mainly bainite, which is dense and interwoven. The precipitated relative dislocations have a pinning effect, which gives the steel plate good low-temperature toughness at the 1 / 4 and 1 / 2 thickness positions. Figure 4 In comparison Figure 3 It has obvious watermark-like defects. Figure 3 The surface quality is good.

[0062] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A 460MPa grade steel plate with good low-temperature toughness and a thickness and width, characterized in that: The composition includes the following components in the indicated mass percentages: C: 0.04-0.07%, Si: 0.10-0.35%, Mn: 1.60-1.70%, P≤0.015%, S≤0.003%, Al: 0.015-0.035%, Nb: 0.030-0.045%, Ni: 0.20-0.35%, Ti: 0.008-0.025%, Cr: 0.20-0.35%, with the balance being Fe and unavoidable impurities. CEV=C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15≤0.42, CEpcm=C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B≤0.18; The steel plate is manufactured through the following steps: (1) Smelting: Hot metal pretreatment → converter smelting → LF furnace treatment → RH vacuum treatment → continuous casting; The desulfurization of molten iron (KR) is S≤0.007%, the converter adopts a double-slag process, and the tapping P≤0.012% and S≤0.005% are achieved. The LF refining process involves argon blowing throughout, deoxidation is performed using aluminum granules or aluminum wire, the white slag holding time is ≥20 min, and the final slag basicity is ≥3.

0. The RH furnace vacuum degree is ≤100 Pa, the pressure holding time is ≥12 min, calcium treatment is performed before tapping, and the static argon blowing time after wire feeding is ≥12 min, with a final H≤0.00015%. The superheat during continuous casting is controlled to ≤20℃, and secondary cooling electromagnetic stirring and light pressure reduction at the end of solidification are adopted. A constant casting speed is maintained during casting, and the billet cooling time after exiting the line is ≥24 h. (2) Heating: A multi-stage heating method is adopted. The temperature of the first heating stage is 900-1000℃, the temperature of the second heating stage is 1100-1180℃, the temperature of the third heating stage is 1180-1260℃, and the temperature of the soaking stage is 1220-1250℃. The total heating time of the billet in the heating furnace is 328-520 min. After the billet is heated, it is subjected to high-pressure water descaling treatment. (3) Rolling: A two-stage controlled rolling process is adopted. The initial rolling temperature of the roughing rolling is 1020-1100℃, the rolling speed is ≤1.5m / s, and the reduction of the longitudinal rolling single pass after the steel plate is widened is at least 3 passes with a reduction of ≥30mm. The last pass of the roughing rolling is dephosphorized. After the roughing rolling is completed, the plate is first passed through the finishing mill to remove the phosphorus, and then it is placed in front of the finishing mill to wait for the temperature. The initial rolling temperature of the finishing rolling is 800-830℃. The first and last passes of the finishing rolling are dephosphorized. The dephosphorization pressure is 25MPa. The final rolling temperature is 770-800℃, and the intermediate billet is 130-190mm. (4) Cooling: A three-pass reciprocating cooling process is adopted, with a water volume of 90-100 m³ / h, 19 sets of cooling water are turned on, the roller speed is 0.6-0.8 m / s, the water ratio is 2.3, the first reddening temperature is 680-710℃, the second reddening temperature is 550-580℃, and the third reddening temperature is 410-460℃. (5) Slow cooling: After hot straightening, the product is slow cooled in a slow cooling pit or stacked for slow cooling. The slow cooling time is ≥48h.

2. The manufacturing method of a 460MPa grade steel plate with good low-temperature toughness and a thickness and width as described in claim 1, characterized in that: Includes the following steps: (1) Smelting: Hot metal pretreatment → converter smelting → LF furnace treatment → RH vacuum treatment → continuous casting; The desulfurization of molten iron (KR) is S≤0.007%, the converter adopts a double-slag process, and the tapping P≤0.012% and S≤0.005% are achieved. The LF refining process involves argon blowing throughout, deoxidation is performed using aluminum granules or aluminum wire, the white slag holding time is ≥20 min, and the final slag basicity is ≥3.

0. The RH furnace vacuum degree is ≤100 Pa, the pressure holding time is ≥12 min, calcium treatment is performed before tapping, and the static argon blowing time after wire feeding is ≥12 min, with a final H≤0.00015%. The superheat during continuous casting is controlled to ≤20℃, and secondary cooling electromagnetic stirring and light pressure reduction at the end of solidification are adopted. A constant casting speed is maintained during casting, and the billet cooling time after exiting the line is ≥24 h. (2) Heating: A multi-stage heating method is adopted. The temperature of the first heating stage is 900-1000℃, the temperature of the second heating stage is 1100-1180℃, the temperature of the third heating stage is 1180-1260℃, and the temperature of the soaking stage is 1220-1250℃. The total heating time of the billet in the heating furnace is 328-520 min. After the billet is heated, it is subjected to high-pressure water descaling treatment. (3) Rolling: A two-stage controlled rolling process is adopted. The initial rolling temperature of the roughing rolling is 1020-1100℃, the rolling speed is ≤1.5m / s, and the reduction of the longitudinal rolling single pass after the steel plate is widened is at least 3 passes with a reduction of ≥30mm. The last pass of the roughing rolling is dephosphorized. After the roughing rolling is completed, the plate is first passed through the finishing mill to remove the phosphorus, and then it is placed in front of the finishing mill to wait for the temperature. The initial rolling temperature of the finishing rolling is 800-830℃. The first and last passes of the finishing rolling are dephosphorized. The dephosphorization pressure is 25MPa. The final rolling temperature is 770-800℃, and the intermediate billet is 130-190mm. (4) Cooling: A three-pass reciprocating cooling process is adopted, with a water volume of 90-100 m³ / h, 19 sets of cooling water are turned on, the roller speed is 0.6-0.8 m / s, the water ratio is 2.3, the first reddening temperature is 680-710℃, the second reddening temperature is 550-580℃, and the third reddening temperature is 410-460℃. (5) Slow cooling: After hot straightening, the product is slow cooled in a slow cooling pit or stacked for slow cooling. The slow cooling time is ≥48h.

3. The manufacturing method according to claim 2, characterized in that: The finished steel plate has a yield strength ≥465MPa, a tensile strength of 560-606Pa, a longitudinal impact energy of ≥280J at -50℃ at 1 / 4 of the thickness, a longitudinal impact energy of ≥220J at -60℃ at 1 / 4 of the thickness, and a longitudinal impact energy of ≥150J at -50℃ at 1 / 2 of the thickness.

4. The manufacturing method according to claim 2, characterized in that: The yield strength ratio of the steel plate is ≤0.

83.

5. The manufacturing method according to claim 2, characterized in that: The steel plate has a specification of (80-120)*3350mm.

6. The manufacturing method according to claim 2, characterized in that: The flaw detection results of the steel plate meet the TI level requirements of the NB / T47013-2015 standard.

7. The manufacturing method according to claim 2, characterized in that: The steel plate surface is free of watermarks or mottled defects.

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