CN116397162A - Marine high-strength steel plate with excellent low-temperature ductility and manufacturing method thereof - Google Patents

Marine high-strength steel plate with excellent low-temperature ductility and manufacturing method thereof Download PDF

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CN116397162A
CN116397162A CN202310283229.XA CN202310283229A CN116397162A CN 116397162 A CN116397162 A CN 116397162A CN 202310283229 A CN202310283229 A CN 202310283229A CN 116397162 A CN116397162 A CN 116397162A
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temperature
equal
steel
cooling
continuous casting
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CN116397162B (en
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李广龙
严玲
王�华
韩鹏
张鹏
李博雍
齐祥羽
李黎明
肖青松
应传涛
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Angang Steel Co Ltd
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Angang Steel Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/12—Accessories for subsequent treating or working cast stock in situ
    • B22D11/1206—Accessories for subsequent treating or working cast stock in situ for plastic shaping of strands
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/18—Controlling or regulating processes or operations for pouring
    • B22D11/181—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level
    • B22D11/182—Controlling or regulating processes or operations for pouring responsive to molten metal level or slag level by measuring temperature
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B22—CASTING; POWDER METALLURGY
    • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
    • B22D11/16—Controlling or regulating processes or operations
    • B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
    • B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
    • C21D8/0226—Hot rolling
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/009—Pearlite

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

The invention relates to a marine high-strength steel plate with excellent low-temperature ductility and a manufacturing method thereof, wherein the steel plate comprises the chemical components of 0.020-0.080% of C, 0.10-0.50% of Si, 0.80-1.20% of Mn, 0.005-0.050% of Nb, 0.020-0.055% of V, 0.10-0.40% of Cu, 0.0100-0.0140% of N, 0.40-1.00% of Ni, 0.40-0.80% of Cr, less than or equal to 0.008% of P, less than or equal to 0.003% of S, and the balance of Fe and impurities; the strength, toughness and ductility of the steel are improved through chemical composition design; the continuous casting adopts a process of high superheat degree and strong secondary cooling water, the columnar crystal proportion of the continuous casting blank is controlled to be more than 96 percent, the internal stress caused by strong cooling is reduced through a stacking slow cooling process, and the grain size is controlled at the same time; the two-stage controlled rolling is adopted, and the rolled steel plate adopts the mode of 'accelerated cooling, high reddening temperature and high stacking temperature', so that the internal stress and the precipitated phase distribution of the finished steel plate are controlled, and the finished steel plate has excellent low-temperature ductility and comprehensive performance.

Description

Marine high-strength steel plate with excellent low-temperature ductility and manufacturing method thereof
Technical Field
The invention relates to the technical field of production of marine steel plates, in particular to a marine high-strength steel plate with excellent low-temperature ductility and a manufacturing method thereof.
Background
In recent years, polar vessels gradually progress from low-grade ice region reinforcement to high-grade ice region reinforcement with self-breaking performance, and the demand for new commercial icebreakers such as polar oil tankers, polar LPG (liquefied petroleum gas carrier), polar container ships and the like with ice breaking capability has rapidly increased. The hull structure of polar ships, especially heavy icebreaker, usually adopts special steel, especially the hull steel of position below the ice layer contact line requires the highest, and this part hull bears the repeated striking of ice layer, can cause disastrous results such as structural failure, goods leakage, environmental pollution, casualties when serious, therefore this part hull steel needs to possess comprehensive properties such as sufficient intensity, low temperature toughness, collision resistance.
The key indicator for evaluating the impact resistance is the ductility of steel, and the better the ductility of steel, the more energy is absorbed when the steel is impacted, and the better the impact resistance. In the case of steel for ships in service in an ice environment, excellent low-temperature ductility is required since it is in service in a low-temperature environment for a long period of time.
The patent application with the application number 201810320311.4 discloses an EH 40-grade ship plate steel with high ductility and a preparation method thereof, wherein the steel comprises the following chemical components: 0.04 to 0.08 percent of C, 0.04 to 0.16 percent of Si, 0.90 to 1.20 percent of Mn, 0.03 to 0.04 percent of Nb, 0.01 to 0.02 percent of Ti, 0.02 to 0.04 percent of Als, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, and the balance of iron and unavoidable impurities; the steel billet with the thickness of 120-140 mm is adopted to obtain the finished ship plate steel through the processes of heating, heat preservation, rough rolling, finish rolling, cooling and the like, the yield strength of the finished ship plate steel is 475-530 MPa, the tensile strength of the finished ship plate steel is 540-609 MPa, the elongation after breaking is 31.4-35.7%, and the impact energy at the temperature of minus 40 ℃ is 231-274J. The cooling process adopts water cooling, air cooling and water cooling three-section cooling, the process is complex, the impact power evaluation temperature is only-40 ℃, the impact power evaluation temperature is far lower than the service temperature of the ice area ship, the elongation after break is the elongation after break at room temperature, and the use requirement of the ice area ship can not be met.
The patent application with the application number 201910970390.8 discloses an EH420 grade ship plate steel with high ductility and a production method thereof, wherein the steel comprises the following chemical components: 0.08 to 0.13 percent of C, 0.10 to 0.25 percent of Si, 1.0 to 1.4 percent of Mn, 0.01 to 0.03 percent of Nb, 0.02 to 0.04 percent of Ti, 0.02 to 0.040 percent of Als, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, and the balance of iron and unavoidable impurities. The production process comprises the steps of continuous casting, heating, rolling and cooling, wherein the yield strength of the steel plate is 462-515 MPa, the tensile strength is 551-623 MPa, the elongation after breaking is 28.4-31.8%, and the impact energy at minus 40 ℃ is 243-295J. In the cooling procedure, the front section adopts ultra-fast cooling, the rear section adopts laminar cooling, the process is also complex, and the evaluation temperatures of impact energy and elongation after break are higher than the service temperature of the actual ice ship, so that the use requirement cannot be met.
The patent application with the application number 201810320314.8 discloses a high-ductility FH500 grade ship plate steel and a preparation method thereof, wherein the steel comprises the following chemical components: 0.04 to 0.08 percent of C, 0.04 to 0.16 percent of Si, 1.2 to 1.4 percent of Mn, 0.03 to 0.04 percent of Nb, 0.01 to 0.02 percent of Ti, 0.02 to 0.04 percent of Als, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, and the balance of Fe and unavoidable impurities; the steel plate is manufactured by adopting the processes of heating, heat preservation, rough rolling, finish rolling, cooling and the like of a steel billet with the thickness of 120-140 mm, the yield strength of the finished steel plate is 541-597 MPa, the tensile strength of the finished steel plate is 622-686 MPa, the elongation after breaking is 30.5-31.5%, and the impact energy at minus 60 ℃ is 187-216J. The cooling process adopts water cooling-air cooling-water cooling three-section cooling, the process is complex, the elongation after break is room temperature elongation after break, and the use requirement of the ship in the ice area cannot be met.
The patent application with the application number of 202110051756.9 discloses a high-strength and high-toughness EH36 ship plate marine steel plate and a production method thereof, wherein the steel comprises the following chemical components: 0.09 to 0.13 percent of C, 0.20 to 0.35 percent of Si, 1.30 to 1.40 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, 0.040 to 0.050 percent of Als, 0.025 to 0.035 percent of Nb, 0.020 to 0.030 percent of V, 0.005 to 0.012 percent of Ti, and the balance of Fe and unavoidable impurities; the final steel plate is obtained through multi-mechanism strengthening and toughening coupling tissue regulation and control and smelting-continuous casting and heat treatment integrated production technology, and the yield strength, the tensile strength and the impact performance of the finished steel plate are high. However, the technological process comprises normalizing treatment, so that the process complexity is increased, the elongation after break is room temperature elongation after break and the value is not high, and the anti-collision requirement of the steel for the ship cannot be met.
In summary, the production of the high ductility steel sheet for ship at present mainly has the following problems: 1) The low-temperature toughness of the steel plate is insufficient, and the use requirement cannot be met. 2) The low-temperature ductility of the steel plate is insufficient, and the service requirement of an ice area of a ship is affected. 3) The production process of the steel plate is complex.
Disclosure of Invention
The invention provides a marine high-strength steel plate with excellent low-temperature ductility and a manufacturing method thereof, wherein the strength, toughness and ductility of the steel are improved through chemical composition design; the continuous casting adopts a process of high superheat degree and strong secondary cooling water, the columnar crystal proportion of the continuous casting blank is controlled to be more than 96 percent, the internal stress caused by strong cooling is reduced through a stacking slow cooling process, and the grain size is controlled at the same time; the two-stage controlled rolling is adopted, and the rolled steel plate adopts the mode of 'accelerated cooling, high reddening temperature and high stacking temperature', so that the internal stress and the precipitated phase distribution of the finished steel plate are controlled, and the finished steel plate has excellent low-temperature ductility and comprehensive performance.
In order to achieve the above purpose, the invention is realized by adopting the following technical scheme:
the marine high-strength steel plate with excellent low-temperature ductility comprises, by weight, 0.020% -0.080% of C, 0.10% -0.50% of Si, 0.80% -1.20% of Mn, 0.005% -0.050% of Nb, 0.020% -0.055% of V, 0.10% -0.40% of Cu, 0.0100% -0.0140% of N, 0.40% -1.00% of Ni, 0.40% -0.80% of Cr, less than or equal to 0.008% of P, less than or equal to 0.003% of S, and the balance of Fe and unavoidable impurities; the metallographic structure of the steel plate is an ultrafine equiaxed ferrite+pearlite structure, wherein the ferrite size is less than or equal to 10.0 mu m, and the ferrite ratio is more than or equal to 85 percent in terms of area ratio; the ferrite matrix is dispersed with (Nb, V) (C, N) precipitated phase with the size less than or equal to 20.0nm.
A manufacturing approach of the marine high-strength steel plate with excellent low-temperature ductility, including smelting, continuous casting, heating, rolling and cooling technological process; the method comprises the following steps:
(1) Smelting; smelting steel according to the set chemical composition;
(2) Continuous casting; continuously casting the molten steel obtained in the step (1) to obtain a continuous casting blank, controlling the superheat degree of a tundish to be 40-65 ℃ in the continuous casting process, protecting and casting in the whole process, and controlling the specific water quantity of secondary cooling water to be more than or equal to 0.50m 3 And/t, so that the columnar crystal proportion in the continuous casting billet is more than 96.0 percent; adopting a soft reduction process for casting blanks at the end of continuous casting, wherein the reduction is 6.0-10.0mm, then carrying out stacking slow cooling on the continuous casting blanks, wherein the stacking starting temperature is 950-1050 ℃, and the stacking time is more than or equal to 40h;
(3) Heating; heating the continuous casting blank obtained in the step (3) to 1120-1200 ℃; the heating time below 600 ℃ is controlled to be 0.30-0.50 min/mm by adopting a sectional heating mode; heating time is controlled to be 0.20-0.40 min/mm at 600-1000 ℃; heating time above 1000 ℃ is controlled to be 0.10-0.20 min/mm; the heat preservation time is 0.5-2.0 h;
(4) Rolling; performing two-stage controlled rolling on the continuous casting blank; the first-stage rolling adopts a high-temperature rapid rolling mode, the continuous casting billet is directly rolled after being discharged from a furnace and descaled, the average rolling reduction of the first two times is more than or equal to 50mm, the roller speed is 30-50 r/min, the rolling reduction of the other passes is 20-40%, and the final rolling temperature is above 1000 ℃; the cooling speed of the intermediate blank is 2.0-10.0 ℃/s; the initial rolling temperature of the two-stage rolling is 830-900 ℃, the pass reduction rate is 20-30%, and the final rolling temperature is 780-820 ℃;
(5) Cooling; the rolled steel plate is cooled in an accelerated way, the cooling temperature is 750-800 ℃, the cooling speed is 10-25 ℃/s, and the reddening temperature is 620-680 ℃; and stacking and slowly cooling the steel plates after accelerated cooling, wherein the stacking temperature is more than or equal to 500 ℃, and the stacking time is more than or equal to 24 hours.
Further, in the step (1), the smelting process specifically includes:
a) Adjusting the content of C, si, mn, P, S element to a set range during converter smelting;
b) When the molten steel is refined, the content of other alloy elements is adjusted to be within a set range;
c) RH treatment is carried out on refined molten steel, the RH treatment time is more than or equal to 40min, nitrogen is blown in the whole process during RH treatment, the final N content of the steel is ensured to be within a set range, and meanwhile, the content of [ H ] in the steel is controlled to be less than or equal to 2.0ppm and the content of [ O ] in the steel is controlled to be less than or equal to 18ppm.
In the step (4), the thickness of the intermediate blank is 2.0-2.5 times that of the finished steel plate, and a water spray cooling mode is adopted.
Further, the normal temperature tensile properties of the finished steel sheet are: the yield strength is more than 420MPa, the tensile strength is more than 530MPa, and the elongation after fracture is more than 33.0%; the tensile properties at-20 ℃ are: the yield strength is above 460MPa, the tensile strength is above 570MPa, and the elongation after fracture is above 31.0%; impact energy at 80 ℃ below zero is more than 200J, ductile-brittle transition temperature FATT is less than-75 ℃, and non-plastic transition temperature NDTT is less than or equal to-75 ℃.
Compared with the prior art, the invention has the beneficial effects that:
1) The chemical components adopt a low-carbon design, so that the carbon equivalent of the steel is reduced, and the low-temperature toughness and the ductility of the steel are improved; adding Nb, V, N and other microalloy elements which are easy to form spherical precipitated phases, and improving the strength, toughness and ductility of the steel through precipitation strengthening and fine grain strengthening; elements such as Al, ti and the like which are easy to form a polyhedral precipitated phase are eliminated, and Si, mn and other elements are adopted for refining for deoxidization;
2) The continuous casting adopts a process of high superheat degree and strong secondary cooling water, the columnar crystal proportion of the continuous casting blank is controlled to be more than 96 percent, the internal stress caused by the strong cooling is reduced in a stacking slow cooling mode, and the grain size is controlled at the same time;
3) Adopting two-stage controlled rolling, preparing for fine grain control of a final steel plate by a high-temperature rapid rolling mode and a mode of rapidly cooling an intermediate blank when the temperature is to be reached;
4) The method comprises the steps that the rolled steel plate adopts an accelerated cooling mode, a high reddening temperature mode and a high stacking temperature mode to control the internal stress and precipitated phase distribution of the final steel plate; the metallographic structure of the finished steel plate is an ultrafine equiaxed ferrite and pearlite structure, the ferrite size is less than or equal to 10.0 mu m, the ferrite proportion is more than or equal to 85 percent, the ferrite matrix is dispersed and distributed with (Nb, V) (C, N) to separate out phases, and the size of the separated phases is less than or equal to 20.0nm;
5) The finished steel plate has excellent low-temperature ductility and comprehensive performance, and the normal-temperature tensile property is as follows: the yield strength is more than 420MPa, the tensile strength is more than 530MPa, and the elongation after fracture is more than 33.0%; the tensile properties at-20 ℃ are: the yield strength is above 460MPa, the tensile strength is above 570MPa, and the elongation after fracture is above 31.0%; in addition, the impact energy at the temperature of minus 80 ℃ is more than 200J, the FATT is less than minus 75 ℃, and the NDTT is less than or equal to minus 75 ℃.
Detailed Description
The chemical components of the marine high-strength steel plate with excellent low-temperature ductility comprise, by weight, 0.020% -0.080% of C, 0.10% -0.50% of Si, 0.80% -1.20% of Mn, 0.005% -0.050% of Nb, 0.020% -0.055% of V, 0.10% -0.40% of Cu, 0.0100% -0.0140% of N, 0.40% -1.00% of Ni, 0.40% -0.80% of Cr, less than or equal to 0.008% of P, less than or equal to 0.003% of S, and the balance of Fe and unavoidable impurities; the metallographic structure of the steel plate is an ultrafine equiaxed ferrite+pearlite structure, wherein the ferrite size is less than or equal to 10.0 mu m, and the ferrite ratio is more than or equal to 85 percent in terms of area ratio; the ferrite matrix is dispersed with (Nb, V) (C, N) precipitated phase with the size less than or equal to 20.0nm.
The manufacturing method of the marine high-strength steel plate with excellent low-temperature ductility comprises the technical processes of smelting, continuous casting, heating, rolling and cooling; the method comprises the following steps:
(1) Smelting; smelting steel according to the set chemical composition;
(2) Continuous casting; continuously casting the molten steel obtained in the step (1) to obtain a continuous casting blank, controlling the superheat degree of a tundish to be 40-65 ℃ in the continuous casting process, protecting and casting in the whole process, and controlling the specific water quantity of secondary cooling water to be more than or equal to 0.50m 3 And/t, so that the columnar crystal proportion in the continuous casting billet is more than 96.0 percent; adopting a soft reduction process for casting blanks at the end of continuous casting, wherein the reduction is 6.0-10.0mm, then carrying out stacking slow cooling on the continuous casting blanks, wherein the stacking starting temperature is 950-1050 ℃, and the stacking time is more than or equal to 40h;
(3) Heating; heating the continuous casting blank obtained in the step (3) to 1120-1200 ℃; the heating time below 600 ℃ is controlled to be 0.30-0.50 min/mm by adopting a sectional heating mode; heating time is controlled to be 0.20-0.40 min/mm at 600-1000 ℃; heating time above 1000 ℃ is controlled to be 0.10-0.20 min/mm; the heat preservation time is 0.5-2.0 h;
(4) Rolling; performing two-stage controlled rolling on the continuous casting blank; the first-stage rolling adopts a high-temperature rapid rolling mode, the continuous casting billet is directly rolled after being discharged from a furnace and descaled, the average rolling reduction of the first two times is more than or equal to 50mm, the roller speed is 30-50 r/min, the rolling reduction of the other passes is 20-40%, and the final rolling temperature is above 1000 ℃; the cooling speed of the intermediate blank is 2.0-10.0 ℃/s; the initial rolling temperature of the two-stage rolling is 830-900 ℃, the pass reduction rate is 20-30%, and the final rolling temperature is 780-820 ℃;
(5) Cooling; the rolled steel plate is cooled in an accelerated way, the cooling temperature is 750-800 ℃, the cooling speed is 10-25 ℃/s, and the reddening temperature is 620-680 ℃; and stacking and slowly cooling the steel plates after accelerated cooling, wherein the stacking temperature is more than or equal to 500 ℃, and the stacking time is more than or equal to 24 hours.
Further, in the step (1), the smelting process specifically includes:
a) Adjusting the content of C, si, mn, P, S element to a set range during converter smelting;
b) When the molten steel is refined, the content of other alloy elements is adjusted to be within a set range;
c) RH treatment is carried out on refined molten steel, the RH treatment time is more than or equal to 40min, nitrogen is blown in the whole process during RH treatment, the final N content of the steel is ensured to be within a set range, and meanwhile, the content of [ H ] in the steel is controlled to be less than or equal to 2.0ppm and the content of [ O ] in the steel is controlled to be less than or equal to 18ppm.
In the step (4), the thickness of the intermediate blank is 2.0-2.5 times that of the finished steel plate, and a water spray cooling mode is adopted.
Further, the normal temperature tensile properties of the finished steel sheet are: the yield strength is more than 420MPa, the tensile strength is more than 530MPa, and the elongation after fracture is more than 33.0%; the tensile properties at-20 ℃ are: the yield strength is above 460MPa, the tensile strength is above 570MPa, and the elongation after fracture is above 31.0%; impact energy at 80 ℃ below zero is more than 200J, ductile-brittle transition temperature FATT is less than-75 ℃, and non-plastic transition temperature NDTT is less than or equal to-75 ℃.
The marine high-strength steel plate with excellent low-temperature ductility has the following chemical components in steel:
c: the basic strengthening elements in the steel are main elements for ensuring the strength and the hardness in the steel; when the C content is low, the amount of carbide and the like produced is reduced, and the effect of refining grains during rolling is affected. When the C content is higher, the cementite content in the steel increases, which has adverse effects on the low-temperature toughness and ductility of the steel sheet. The invention controls the content range of C to be 0.020-0.080% by comprehensively considering factors such as cost, performance and the like.
Si: the essential elements for steelmaking deoxidization have strong solid solution capacity in steel, can improve the elastic limit and yield strength of the steel, but have adverse effects on the low-temperature toughness and surface quality of the steel when the Si content is too high. The invention controls the content range of Si to be 0.10-0.50%.
Mn: a substitutional solid solution is formed in the steel, and can be dissolved in a large amount in the Fe matrix. The transformation of ferrite and pearlite in the steel can be delayed, the hardenability of the steel is greatly increased, the brittle transformation temperature of the steel is reduced, and the impact toughness is improved; however, too high a Mn content tends to form segregation in the steel, adversely affecting both the plasticity and toughness of the steel. After comprehensive consideration, the Mn content is controlled to be 0.80-1.20%.
Nb: grain refinement elements, carbon and nitride particles of undissolved Nb are distributed on an austenite grain boundary during heating, so that the growth of austenite grains of the steel during heating can be prevented; can effectively delay the recrystallization of deformed austenite, prevent austenite grains from growing, refine ferrite grains, improve the plasticity and impact toughness of steel and reduce the brittle transition temperature of steel. The invention controls the content range of Nb to be 0.005-0.050%.
V: the strong carbide forming element has small influence on austenite recrystallization, and a large amount of carbon and nitride of V are precipitated at low temperature, so that the method has obvious precipitation strengthening and tissue refining effects, and the plasticity and toughness of the steel are improved. The content range of V is controlled to be 0.020% -0.055%.
Cu: the method can improve the stability of austenite in steel, increase the hardenability of the steel, and improve the strength, plasticity and low-temperature toughness of the steel when added in proper amount, but the hot brittleness of the steel is deteriorated and hot cracks are easily generated when the Cu content is too high. The invention controls the content range of Cu to be 0.10-0.40%.
N: the invention is an important strengthening and toughening element, and the addition of N element is beneficial to promoting the mass formation of V (C, N), thereby refining the crystal grains and improving the plasticity and toughness of the steel. The nitrogen-containing steel not only eliminates the cost increase caused by degassing and refining nitrogen removal in the steelmaking process, but also can fully play the role of micro-alloying elements by nitrogen increase in the steel, saves the consumption of alloying elements, and further greatly reduces the production cost. The invention controls the content range of N to be 0.0100% -0.0140%.
Ni: the method has no adverse effect on the hardening property and toughness of a welding heat affected zone of steel, can improve the plasticity and low-temperature toughness of the steel, can reduce the hot cracking tendency caused by high Cu content by adding Ni, and comprehensively considers the factors such as cost, performance and the like, and the content range of Ni is controlled to be 0.40-1.00%.
Cr: can increase the hardenability of steel and improve the toughness of steel. The addition of a small amount of Cr can also effectively delay the initial corrosion of the steel plate. The invention controls the content range of Cr to be 0.40-0.80% by comprehensively considering the factors such as cost, performance and the like.
The invention relates to a manufacturing method of a marine high-strength steel plate with excellent low-temperature ductility, which comprises the technical processes of smelting, continuous casting, heating, rolling and the like, and the design principle is as follows:
(1) Smelting steel according to the chemical components, specifically:
a) During converter smelting, adjusting the content of C, si, mn, P, S and other elements to control the content within the limit range of the invention, and adding other alloy components according to the requirements for smelting;
b) When the molten steel is refined, the content of other alloy elements is adjusted to be within the limit of the invention;
c) RH treatment is carried out on refined molten steel, the RH treatment time is more than or equal to 40min, nitrogen is blown in the whole process during RH treatment, the final N content of the steel is ensured to be within the limit range of the invention, and meanwhile, the content of [ H ] in the steel is controlled to be less than or equal to 2.0ppm and the content of [ O ] in the steel is controlled to be less than or equal to 18ppm.
(2) Continuously casting the molten steel obtained in the step (1) to obtain a continuous casting blank, controlling the superheat degree of a tundish to be 40-65 ℃ for controlling the columnar crystal content in the continuous casting blank, and protecting casting in the whole process, wherein the specific water content of secondary cooling water is more than or equal to 0.50m 3 And/t, the columnar crystal proportion of the continuous casting billet is more than 96.0 percent. And after continuous casting, adopting a soft reduction process for the casting blank, wherein the reduction is 6.0-10.0mm, so that the grains of the continuous casting blank are primarily crushed.
In order to reduce the internal stress of the cooled continuous casting billet, the grain size is controlled, the continuous casting billet is stacked and slowly cooled, the stacking start temperature is 950-1050 ℃, and the stacking time is more than or equal to 40h.
(3) Heating the continuous casting blank to 1120-1200 ℃; a sectional heating process is adopted, and the heating time below 600 ℃ is controlled to be 0.30-0.50 min/mm; heating time is controlled to be 0.20-0.40 min/mm at 600-1000 ℃; heating time above 1000 ℃ is controlled to be 0.10-0.20 min/mm; the heat preservation time is 0.5-2.0 h.
(4) Rolling the continuous casting blank into a hot rolled steel plate through two-stage controlled rolling, wherein in order to fully break austenite grains and prepare for subsequent grain refinement, the one-stage rolling is performed in a high-temperature rapid rolling mode, the continuous casting blank is directly rolled after being discharged from a furnace and descaled, the average rolling reduction of the first two times is more than or equal to 50mm, the roller speed is 30-50 r/min, the rolling reduction of the other passes is 20-40%, and the final rolling temperature is above 1000 ℃.
The thickness of the intermediate blank is 2.0-2.5 times of the thickness of the finished steel plate. In order to inhibit the growth of grains of the intermediate blank, the intermediate blank is cooled by spraying water at a cooling speed of 2.0-10.0 ℃/s.
The initial rolling temperature of the two-stage rolling is 830-900 ℃, the pass reduction rate is 20-30%, and the final rolling temperature is 780-820 ℃, so that the crystal grains are fully deformed, and the crystal grain size is further reduced.
(5) In order to keep fine grains after rolling and prevent the grains from growing, the rolled steel plate is accelerated cooled, the cooling temperature is 750-800 ℃, the cooling speed is 10-25 ℃/s, and the reddening temperature is 620-680 ℃.
In order to release the internal stress formed in the rolling-cooling process of the steel plate and further form fine precipitated phases, stacking and slow cooling are carried out on the steel plate after accelerated cooling, wherein the stacking temperature is more than or equal to 500 ℃, and the stacking time is more than or equal to 24 hours.
The following examples are given by way of illustration of detailed embodiments and specific procedures based on the technical scheme of the present invention, but the scope of the present invention is not limited to the following examples.
[ example ]
Smelting according to the chemical composition range of the invention, and carrying out continuous casting, heating, rolling and cooling on the obtained molten steel to obtain a finished steel plate, wherein the chemical composition of the steel in each embodiment is shown in table 1, the smelting and heating process parameters are shown in table 2, the rolling process parameters are shown in table 3, and the cooling process parameters are shown in table 4.
TABLE 1 chemical composition (wt%) of example steels
Examples C Si Mn Nb V Cu N Ni Cr P S
1 0.033 0.46 1.16 0.036 0.024 0.24 0.0134 0.42 0.76 0.007 0.003
2 0.076 0.14 1.02 0.014 0.052 0.36 0.0136 0.53 0.43 0.006 0.002
3 0.059 0.32 0.94 0.019 0.048 0.18 0.0116 0.48 0.63 0.003 0.001
4 0.044 0.42 1.08 0.022 0.043 0.12 0.0103 0.56 0.58 0.005 0.002
5 0.039 0.38 1.06 0.031 0.034 0.26 0.0118 0.77 0.72 0.004 0.001
6 0.048 0.26 1.11 0.026 0.028 0.32 0.0126 0.88 0.49 0.002 0.003
7 0.051 0.22 1.14 0.018 0.046 0.38 0.0139 0.94 0.52 0.006 0.002
8 0.062 0.19 0.99 0.021 0.038 0.16 0.0122 0.66 0.69 0.005 0.003
9 0.068 0.42 0.91 0.047 0.022 0.28 0.0108 0.83 0.66 0.003 0.001
10 0.072 0.16 0.97 0.042 0.043 0.34 0.0112 0.96 0.54 0.004 0.002
11 0.024 0.36 0.83 0.007 0.054 0.39 0.0129 0.98 0.47 0.002 0.001
Table 2 smelting and heating process parameters for steels of various examples
Figure BDA0004138735990000081
TABLE 3 Rolling Process parameters for example steels
Figure BDA0004138735990000091
Table 4 cooling process parameters for the steels of each example
Examples Cooling temperature/°c Cooling rate/°c/s Temperature of redback/. Degree.C Stacking temperature/°c Stacking time/h
1 753 23 634 564 33
2 774 14 673 579 39
3 766 19 646 583 30
4 764 18 658 554 37
5 758 22 638 569 31
6 792 17 668 573 32
7 769 24 651 581 27
8 783 16 636 559 29
9 796 15 664 562 34
10 789 12 676 589 28
11 758 22 629 563 29
Conventional structural performance tests were performed on the finished steel sheet of each example, and the results are shown in table 5.
TABLE 5 conventional mechanical Properties of the steels of examples
Figure BDA0004138735990000101
The low-temperature properties of the steel sheets obtained in each example were examined, and the results are shown in Table 6.
TABLE 6 Low temperature Properties of the steels of examples
Figure BDA0004138735990000111
The foregoing is only a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art, who is within the scope of the present invention, should make equivalent substitutions or modifications according to the technical scheme of the present invention and the inventive concept thereof, and should be covered by the scope of the present invention.

Claims (5)

1. The marine high-strength steel plate with excellent low-temperature ductility is characterized in that the steel plate comprises, by weight, 0.020% -0.080% of C, 0.10% -0.50% of Si, 0.80% -1.20% of Mn, 0.005% -0.050% of Nb, 0.020% -0.055% of V, 0.10% -0.40% of Cu, 0.0100% -0.0140% of N, 0.40% -1.00% of Ni, 0.40% -0.80% of Cr, less than or equal to 0.008% of P, less than or equal to 0.003% of S, and the balance of Fe and unavoidable impurities; the metallographic structure of the steel plate is an ultrafine equiaxed ferrite+pearlite structure, wherein the ferrite size is less than or equal to 10.0 mu m, and the ferrite ratio is more than or equal to 85 percent in terms of area ratio; the ferrite matrix is dispersed with (Nb, V) (C, N) precipitated phase with the size less than or equal to 20.0nm.
2. The method for manufacturing a high strength steel sheet for a ship excellent in low temperature ductility according to claim 1, comprising the steps of smelting, continuous casting, heating, rolling and cooling; the method comprises the following steps:
(1) Smelting; smelting steel according to the set chemical composition;
(2) Continuous casting; continuously casting the molten steel obtained in the step (1) to obtain a continuous casting blank, controlling the superheat degree of a tundish to be 40-65 ℃ in the continuous casting process, protecting and casting in the whole process, and controlling the specific water quantity of secondary cooling water to be more than or equal to 0.50m 3 And/t, so that the columnar crystal proportion in the continuous casting billet is more than 96.0 percent; adopting a soft reduction process for casting blanks at the end of continuous casting, wherein the reduction is 6.0-10.0mm, then carrying out stacking slow cooling on the continuous casting blanks, wherein the stacking starting temperature is 950-1050 ℃, and the stacking time is more than or equal to 40h;
(3) Heating; heating the continuous casting blank obtained in the step (3) to 1120-1200 ℃; the heating time below 600 ℃ is controlled to be 0.30-0.50 min/mm by adopting a sectional heating mode; heating time is controlled to be 0.20-0.40 min/mm at 600-1000 ℃; heating time above 1000 ℃ is controlled to be 0.10-0.20 min/mm; the heat preservation time is 0.5-2.0 h;
(4) Rolling; performing two-stage controlled rolling on the continuous casting blank; the first-stage rolling adopts a high-temperature rapid rolling mode, the continuous casting billet is directly rolled after being discharged from a furnace and descaled, the average rolling reduction of the first two times is more than or equal to 50mm, the roller speed is 30-50 r/min, the rolling reduction of the other passes is 20-40%, and the final rolling temperature is above 1000 ℃; the cooling speed of the intermediate blank is 2.0-10.0 ℃/s; the initial rolling temperature of the two-stage rolling is 830-900 ℃, the pass reduction rate is 20-30%, and the final rolling temperature is 780-820 ℃;
(5) Cooling; the rolled steel plate is cooled in an accelerated way, the cooling temperature is 750-800 ℃, the cooling speed is 10-25 ℃/s, and the reddening temperature is 620-680 ℃; and stacking and slowly cooling the steel plates after accelerated cooling, wherein the stacking temperature is more than or equal to 500 ℃, and the stacking time is more than or equal to 24 hours.
3. The method for manufacturing a high strength steel sheet for a ship excellent in low-temperature ductility according to claim 2, wherein in the step (1), the smelting process is specifically:
a) Adjusting the content of C, si, mn, P, S element to a set range during converter smelting;
b) When the molten steel is refined, the content of other alloy elements is adjusted to be within a set range;
c) RH treatment is carried out on refined molten steel, the RH treatment time is more than or equal to 40min, nitrogen is blown in the whole process during RH treatment, the final N content of the steel is ensured to be within a set range, and meanwhile, the content of [ H ] in the steel is controlled to be less than or equal to 2.0ppm and the content of [ O ] in the steel is controlled to be less than or equal to 18ppm.
4. The method for producing a high strength steel sheet for a ship excellent in low temperature ductility according to claim 2, wherein in the step (4), the thickness of the intermediate slab is 2.0 to 2.5 times the thickness of the finished steel sheet, and water spray cooling is employed.
5. The method for manufacturing a high strength steel sheet for a ship excellent in low-temperature ductility according to claim 2, wherein the normal-temperature tensile properties of the finished steel sheet are: the yield strength is more than 420MPa, the tensile strength is more than 530MPa, and the elongation after fracture is more than 33.0%; the tensile properties at-20 ℃ are: the yield strength is above 460MPa, the tensile strength is above 570MPa, and the elongation after fracture is above 31.0%; impact energy at 80 ℃ below zero is more than 200J, ductile-brittle transition temperature FATT is less than-75 ℃, and non-plastic transition temperature NDTT is less than or equal to-75 ℃.
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