WO2024002207A1 - 一种490MPa级心部高疲劳强度的厚钢板及其制造方法 - Google Patents

一种490MPa级心部高疲劳强度的厚钢板及其制造方法 Download PDF

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WO2024002207A1
WO2024002207A1 PCT/CN2023/103582 CN2023103582W WO2024002207A1 WO 2024002207 A1 WO2024002207 A1 WO 2024002207A1 CN 2023103582 W CN2023103582 W CN 2023103582W WO 2024002207 A1 WO2024002207 A1 WO 2024002207A1
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steel plate
inclusions
thick steel
temperature
core
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PCT/CN2023/103582
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English (en)
French (fr)
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芦晓辉
高珊
张才毅
施青
梅峰
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宝山钢铁股份有限公司
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Publication of WO2024002207A1 publication Critical patent/WO2024002207A1/zh

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    • 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
    • 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
    • B22D11/10—Supplying or treating molten metal
    • B22D11/11—Treating the molten metal
    • B22D11/114—Treating the molten metal by using agitating or vibrating means
    • B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • 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
    • 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
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • 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
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel
    • 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
    • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
    • 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
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
    • 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum

Definitions

  • the invention belongs to the field of material technology, and particularly relates to a thick steel plate with excellent 490MPa core fatigue strength and a manufacturing method thereof.
  • Thick steel plates are important structural materials for large structures, equipment and facilities such as high-rise buildings, ocean development, crude oil spherical tanks, oil and gas pipelines, ships and warships.
  • the current inspection standards often refer to the performance at 1/4 of the thickness of the steel plate, which has less constraints on the core performance. Therefore, for thick steel plates, especially in harsh service environments with high requirements on toughness, fatigue performance, etc., it is very necessary to improve the comprehensive mechanical properties of the central part.
  • Patent Document 1 discloses a 460MPa grade hot-rolled automobile structural steel plate with good fatigue properties and a manufacturing method. Its chemical element composition and its weight percentage are C: 0.03 ⁇ 0.06%, Mn: 1.0 ⁇ 1.2%, and Nb: 0.025 ⁇ 0.035%, Ti: 0.025 ⁇ 0.035%, Si: ⁇ 0.10%, S: ⁇ 0.005%, P: ⁇ 0.015%, N: ⁇ 40ppm, Als: 0.025 ⁇ 0.050%, the balance is iron and inevitable impurities .
  • Nb-Ti micro-alloying technology is used to fix S and N in the steel with trace amounts of Ti (S ⁇ 0.005%, N ⁇ 40ppm), reduce the inclusion of MnS in the steel, and give full play to the fine graining effect of Nb and Ti.
  • the invention adopts rolling, laminar flow, and coiling processes to produce, with a thickness of 1.0 to 3.0 mm, a yield strength of 460 to 560 MPa, and a tensile strength of 500 to 640 MPa.
  • the automobile girder steel with a thickness of 2.0-7.0mm produced by this invention has mechanical properties reaching ReL ⁇ 480MPa, Rm ⁇ 600MPa, A ⁇ 20%, and the weight of the parts is reduced by 17%.
  • the thickness of this steel type is 2.0-7.0mm, and the mechanical properties are ReL ⁇ 480MPa, Rm ⁇ 600MPa, A ⁇ 20%; this automobile beam steel not only has good fatigue properties, but also has excellent formability.
  • Patent Document 3 discloses a large thickness quenched and tempered FO460 ship steel plate and its manufacturing method. Its chemical element content is C: 0.06 ⁇ 0.10%; Si: 0.05 ⁇ 0.14%; Mn: 1.40 ⁇ 1.80%; S: ⁇ 0.002%; P: ⁇ 0.008%; Als: 0.015% ⁇ 0.045%; N: 0.003% ⁇ 0.015%; Nb: 0.01 ⁇ 0.04%; Cu: 0.16 ⁇ 0.35%; Ni: 0.30 ⁇ 0.60%; Cr: 0.15 ⁇ 0.30%; Ti: 0.008 ⁇ 0.014%; the balance is Fe and inevitable impurities.
  • the steel plate of this invention has a thickness of 60 to 100mm, a yield strength of ⁇ 460MPa, and a tensile strength of ⁇ 570MPa, which can meet the technical requirements of marine steel plates in harsh and harsh marine environments.
  • Patent Document 4 discloses a quenched and tempered steel plate for building structures with a yield strength of 420 MPa and a production method thereof.
  • the composition design is based on the Fe-Mn-C system and is subjected to Nb and Ti micro-alloying treatment.
  • the steel plate material is The chemical composition percentages are: C: 0.13 ⁇ 0.18%, Si: 0.20 ⁇ 0.50%, Mn: 1.40 ⁇ 1.70%, P: ⁇ 0.015%, S: ⁇ 0.005%, Cr: ⁇ 0.30%, Mo: ⁇ 0.30% , Ni: ⁇ 0.30%, Cu: ⁇ 0.30%, Al: 0.020 ⁇ 0.050%, V: ⁇ 0.015%, Nb: 0.025 ⁇ 0.050%, Ti: 0.010-0.020%, N: ⁇ 0.006%, the rest is Fe and unavoidable impurity elements.
  • the production process is: the smelting raw materials are sequentially subjected to converter smelting, refining outside the furnace, and RH furnace refining to obtain molten steel with higher purity, pouring the molten steel into 370mm ⁇ 450mm billets, and then using reasonable billet heating, rolling, online direct quenching and Tempering heat treatment technology has been used to obtain a steel plate material with a yield strength of 420MPa suitable for large-scale steel structure construction projects such as high-rise buildings, long-span stadiums, airports, convention and exhibition centers, and industrial plants.
  • the thickness of this Fangming steel is 50-100mm
  • the yield strength ReL is 410-540MPa
  • the tensile strength Rm is 530-680MPa.
  • Patent document 1 CN107641760B
  • Patent document 2 CN109161795A
  • Patent document 3 CN113174535A
  • Patent Document 4 CN112981235A
  • Patent Documents 1 and 2 disclose automobile steels with good fatigue properties, the thickness specifications are only 1-7 mm, and their technical methods are not suitable for manufacturing thick steel plates.
  • Patent Documents 3 and 4 disclose two manufacturing methods of large-thickness steel plates, they do not mention the fatigue properties of the steel plates.
  • an object of the present invention is to provide a thick steel plate with excellent core fatigue strength of 490 MPa level and a manufacturing method thereof.
  • the thickness of the steel plate of the present invention is 60-100mm, the yield strength is ⁇ 490MPa, the tensile strength is ⁇ 600MPa, and the fatigue strength in the center of the plate thickness is ⁇ 340MPa. It has excellent core fatigue performance, and the strength, toughness and fatigue performance of the steel plate are further improved.
  • the comprehensive mechanical properties of the central part are excellent, which can solve the problems of uneven cross-sectional chemical composition distribution, internal segregation and brittle zone in the center that cause premature damage in high-strength steel for large components. It is especially suitable for toughness and fatigue. Application fields with higher performance requirements.
  • the present invention proposes a thick steel plate with a 490MPa core and high fatigue strength.
  • the chemical composition of the thick steel plate includes:
  • One or both of B: 0.0005-0.0009% and Mo: 0.15-0.25% can be added to the thick steel plate.
  • the microstructure is quasi-polygonal ferrite (QF) + lath bainite (BF) + pearlite (P), where In terms of area percentage, the QF phase ratio is 30-60%, the BF phase ratio is 40-70%, and the P phase ratio is 0.1-3%, which can further ensure that the steel has good strength and toughness.
  • the strength, toughness and fatigue performance of the steel plate can be further effectively improved.
  • the oxide inclusions are mainly Ce 2 O 3 +Al 2 O 3, Ce 2 O 3, Al 2 O 3 and each of them.
  • Core composite inclusions in which the proportion of Ce 2 O 3 + Al 2 O 3 and the composite inclusions with it as the core is more than 90%, and the proportion of Ce 2 O 3 and the composite inclusions with it as the core is 1-10%, the proportion of Al 2 O 3 and its core composite inclusions is less than 1%.
  • the inclusion density is 100-500/mm 2 , in which the proportion of 0.2-2 ⁇ m inclusions is more than 95%, and >2-5 ⁇ m inclusions
  • the number of inclusions is below 5%, the number of inclusions >5-10 ⁇ m is below 0.01%, and there are no inclusions larger than 10 ⁇ m.
  • the present invention also provides a method for manufacturing a thick steel plate with high fatigue strength at the core of 490MPa level.
  • the steps are preferably:
  • the opening rolling temperature in the first stage is not lower than 1063°C, the reduction in a single pass is ⁇ 20mm, and the reduction in the last two passes is ⁇ 40mm; the opening rolling temperature in the second stage is not higher than 943°C. °C, the reduction rate of the first two passes is greater than 15%, the reduction rate of the remaining rolling passes is controlled at 8-10%, and the final rolling temperature is 821-843°C. Rapid cooling after final rolling, the cooling rate is 0.5 ⁇ 5°C/s, and the red return temperature is controlled not to be higher than 430°C;
  • the tempering temperature is between 611 and 631°C.
  • the furnace time is: (product thickness/mm ⁇ 1.5)min. After reaching the temperature, the continuous holding time is not less than (product thickness/mm ⁇ 0.9). min. After tempering, air cool to room temperature.
  • the steel plate of the invention has a thickness of 60 to 100 mm, a yield strength of ⁇ 490MPa, a tensile strength of ⁇ 600MPa, and a fatigue strength of the central part of the plate thickness of ⁇ 340MPa. It has excellent core fatigue performance and can be used for steel plate cores in construction, engineering machinery, marine engineering, etc. Supports and components that have certain requirements for fatigue performance.
  • the invention has the advantages of simple manufacturing process and can be implemented in various metallurgical enterprises.
  • a thick steel plate with high fatigue strength at the core of 490 MPa level and a manufacturing method thereof are provided.
  • the chemical composition of the thick steel plate includes: C: 0.045-0.076%, Si : 0.19 ⁇ 0.31%, Mn: 0.95 ⁇ 1.13%, P: ⁇ 0.008%, S: ⁇ 0.002%, Als: 0.010 ⁇ 0.040%, Nb: 0.014 ⁇ 0.038%, V: 0.025-0.041%, Ti: 0.011 ⁇ 0.022%, Ni: 1.35 ⁇ 1.55%, Ce: 0.020-0.040%, Fe and other inevitable impurities.
  • C and Mn are very effective elements in improving the strength of steel.
  • the carbon content increases, the tensile strength and yield strength of the steel increase, but the elongation and impact toughness decrease, and the welding heat-affected zone of the steel also undergoes hardening, leading to the occurrence of welding cold cracks.
  • Mn content increases, the strength of steel increases significantly, while the impact transition temperature hardly changes.
  • Mn is also an element that expands the austenite zone. Increased Mn content can improve the stability of austenite, reduce the critical cooling rate, strengthen ferrite, significantly improve hardenability, and at the same time slow down the rate of tissue decomposition and transformation during the tempering process after quenching. Slow and improve the stability of the tempered structure.
  • C and Mn elements are elements that are easily segregated in the center of the slab and cause central segregation. Therefore, the present invention controls C and Mn at low levels (C: 0.045 ⁇ 0.076%, Mn: 0.95 ⁇ 1.13%), uses other alloy elements to balance the strength and toughness of the steel plate, and reduces the adverse effects of central segregation on core performance. .
  • Si element can increase the solid solution hardness and strength in steel. It can not only increase the hardenability of steel, but also increase the tempering resistance of quenched steel, allowing the steel to be tempered at higher temperatures, thus improving the toughness and resistance of the steel. Delayed fracture performance; Si can significantly improve the elastic limit, yield strength and yield ratio of steel. Excessive Si content will cause the thermal conductivity of steel to deteriorate, and cracks or crack defects will easily appear on the surface of steel ingots and billets.
  • the Si content of the steel of the present invention is designed to be 0.19-0.31%.
  • P and S are impurity elements in steel and are elements that are prone to segregation. They can form severe segregation and inclusions in parts of the steel, reducing plasticity and toughness.
  • the steel of the present invention strictly controls the sulfur and phosphorus content levels, that is, P ⁇ 0.008% and S ⁇ 0.002%.
  • Al is the main deoxidizing element in steel.
  • Al has a high melting point.
  • Al in steel can form AlN with N, and AlN can hinder the growth of high-temperature austenite and refine the grains.
  • the Als content of the steel of the present invention is controlled to be 0.010-0.040%.
  • Nb and Ti are two strong carbide and nitride forming elements. They have a strong affinity with nitrogen and carbon and can form extremely stable carbonitrides with them.
  • the distribution of the dispersed Nb carbonitride second phase particles along the austenite grain boundary can greatly increase the coarsening temperature of the original austenite grains.
  • the carbonitride precipitates can serve as the nucleation core of austenite grains, and in the non-recrystallization temperature range, the dispersed carbonitride precipitates of Nb can effectively pin the austenite grain boundaries and prevent austenite grains from forming.
  • the bulk grains further grow, thereby refining the ferrite grains and achieving the purpose of improving strength and impact toughness; Ti nitrides can effectively pin the austenite grain boundaries and help control the austenite grain boundaries. Grows up and greatly improves the low temperature toughness of the welding heat affected zone. Therefore, through the micro-combination of Nb and Ti The fine grain strengthening and precipitation strengthening effects of gold element can make the steel plate obtain excellent strength and toughness.
  • the Nb content of the steel of the present invention is designed to be 0.014-0.038%, and the Ti content is designed to be 0.011-0.022%.
  • V is a very strong carbide-forming element that can improve the strength of steel through fine-grain strengthening, precipitation strengthening and solid solution strengthening.
  • the mass percentage of V is less than 0.1%, as the V content increases, the ductile-brittle transition temperature of the steel decreases.
  • the mass percentage of V exceeds 0.1%, the V content increases and the ductile-brittle transition temperature increases instead.
  • adding a small amount of V can significantly reduce the effects of these two elements on grain growth and increase the ductile-brittle transition temperature.
  • V and Nb are added in combination, it can not only increase the strength of the steel but also improve the toughness of the steel.
  • the content of V element in the present invention is 0.025-0.041%.
  • Ni in steel can strengthen the ferrite matrix, inhibit coarse proeutectoid ferrite, significantly improve the toughness of steel, reduce the ductile-brittle transition temperature of steel, and improve the low-temperature impact toughness of steel.
  • the content of Ni is designed to be 1.35-1.55%.
  • Ce is a rare earth element that has a strong affinity with oxygen and sulfur, and has a purifying and obvious deterioration effect in steel.
  • Solid solution in steel can be enriched in the grain boundaries through the diffusion mechanism, reducing the segregation of inclusion elements at the grain boundaries. As a result, the grain boundaries are strengthened and the properties related to the grain boundaries are improved, such as low-temperature brittleness, toughness, etc.
  • the amount of Ce added in the present invention is 0.020-0.040%.
  • Mo element in steel The main role of Mo element in steel is solid solution strengthening.
  • a small amount of Mo can form refractory carbides, which hinders the growth of austenite grains during heating, refines the product structure, and improves strength, hardness and wear resistance.
  • Mo can improve the hardenability, reduce or eliminate the temper brittleness caused by other alloy elements, which is greatly beneficial to the toughness of steel, improve tempering stability, and effectively eliminate or reduce the residual stress in the steel.
  • too high Mo will quickly During the cooling and welding cooling processes, coarse martensite is easily obtained, which reduces the low-temperature toughness of the base material and deteriorates the welding performance. Therefore, the present invention preferably controls the Mo content to 0.15 to 0.25%.
  • B is an element that strongly improves hardenability.
  • the addition of B can effectively inhibit the nucleation and growth of proeutectoid ferrite. Due to the non-equilibrium segregation of B on the austenite grain boundaries, the ⁇ - ⁇ phase is strongly inhibited.
  • the B content in the present invention is preferably 0.0005 to 0.0009%.
  • the oxide inclusions are mainly Ce 2 O 3 +Al 2 O 3, Ce 2 O 3, Al 2 O 3 and composites with each of them as the core.
  • the inclusion density is 100-500/mm 2 , in which the proportion of 0.2-2 ⁇ m inclusions is more than 95%, and >2-5 ⁇ m inclusions
  • the number of inclusions is below 5%, the number of inclusions >5-10 ⁇ m is below 0.01%, and there are no inclusions larger than 10 ⁇ m.
  • the control of the inclusion type has the effect of refining the grains and promoting the bainite phase transformation; the miniaturization control of the inclusion size has the effect of refining the grains, promoting the bainite phase transformation and improving the strength and toughness of the steel plate. energy and fatigue strength.
  • high-density fine inclusions can serve as heterogeneous nucleation points for ferrite during the cooling process of the steel plate, promoting the formation of ferrite, thus refining the grains and promoting bainite transformation.
  • a method for manufacturing a thick steel plate with high fatigue strength at the core of 490 MPa is provided.
  • the steps preferably include:
  • the opening rolling temperature in the first stage is not lower than 1063°C, the reduction in a single pass is ⁇ 20mm, and the reduction in the last two passes is ⁇ 40mm; the opening rolling temperature in the second stage is not higher than 943°C. °C, the reduction rate of the first two passes is greater than 15%, the reduction rate of the remaining rolling passes is controlled at 8-10%, and the final rolling temperature is 821-843°C. Rapid cooling after final rolling, the cooling rate is 0.5 ⁇ 5°C/s, and the red return temperature is controlled not to be higher than 430°C;
  • the tempering temperature is between 611 and 631°C.
  • the furnace time is: (product thickness/mm ⁇ 1.5)min. After reaching the temperature, the continuous holding time is not less than (product thickness/mm ⁇ 0.9). min. After tempering, air cool to room temperature.
  • Controlling the continuous casting speed, using two-stage electromagnetic stirring, and controlling the dynamic light reduction interval and the total reduction amount are within the above-mentioned scope of the present invention, which can minimize defects such as center segregation of the slab.
  • Controlling the slab heating temperature and the furnace discharge temperature within the above-mentioned range of the present invention can further ensure that the steel of the present invention forms sufficient austenitization.
  • two-stage rolling is used to change the pass reduction, rather than a simple large-reduction, few-pass rolling process.
  • This can nucleate the recrystallized grains and ferrite in the two stages.
  • Grain superposition refinement Furthermore, by setting and controlling the opening rolling temperature in the first stage to not be lower than 1063°C, combined with the single-pass reduction, the rolling pressure can be effectively transmitted to the center of the slab, fully refining the austenite grains; controlling the second stage.
  • the opening rolling temperature in the second stage is not higher than 943°C, the reduction rate of the first two passes is limited to be greater than 15%, the reduction rate of the remaining rolling passes is 8 to 10%, and the final rolling temperature is 821 to 843°C. It can be further adjusted.
  • the superposition and refinement of crystal grains and ferrite nucleation grains further improves the toughness of the steel plate and indirectly gives enough time to reduce center segregation and center porosity.
  • Cooling after rolling by controlling the cooling rate and controlling the red temperature to no higher than 430°C, can further ensure that the steel plate obtains a quasi-polygonal ferrite + lath bainite + pearlite structure, and obtains a proportion that meets the requirements. Obtain excellent basic performance and fatigue performance.
  • the steel components with different compositions shown in Table 1 are used to obtain thick steel plates according to the process shown in Table 2.
  • Fatigue strength is based on GB/T3075 "Axial Force Control Method for Fatigue Testing of Metal Materials”. Samples are taken from the center, specimens with the same nominal size are clamped on the axial force fatigue testing machine, and constant amplitude cyclic stress is applied, with a stress ratio of 0.1 , the applied force is along the longitudinal axis of the specimen and passes through the axis of the cross-section of the specimen. The test continues until the specimen fails or until more than 10 7 cycles are exceeded. The maximum stress when the specimen does not fail is Fatigue strength of materials.
  • Yield strength and tensile strength are measured at room temperature of 25°C. According to the GB/T228.1-2010 standard "Tensile Test of Metal Materials Part 1: Room Temperature Test Method", axial tension is applied to the tensile specimen and a certain Stretch at a tensile speed. The maximum stress before the sample yields and the force drops for the first time is the yield strength. The stress corresponding to the maximum tensile force before the material breaks is the tensile strength.
  • each phase of the microstructure is to grind the metallographic sample flat with 1000X sandpaper, and after polishing, use 4% nitric acid alcohol for etching, and use a metallographic microscope to take metallographic photos.
  • QF quasi-polygonal ferrite
  • the morphological characteristics of lath bainite (BF) and pearlite (P) were calibrated for each phase area, and the area and phase ratio were calculated for the calibrated areas.
  • the fatigue strength of the embodiments of the present invention is above 340MPa, which is significantly higher than that of the comparative example, and has good heart fatigue. performance.
  • the steel plate of the present invention is a 60-100mm thick steel plate with a yield strength of ⁇ 490MPa, a tensile strength of ⁇ 600MPa, and a fatigue strength of ⁇ 340MPa at the center of the plate thickness. It can be used for supports and components that have certain requirements for the fatigue performance of the core of steel plates in construction, engineering machinery, and marine engineering.
  • the invention has the advantages of simple manufacturing process and can be implemented in various metallurgical enterprises.

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Abstract

本发明提供一种490MPa级心部高疲劳强度的厚钢板及其制造方法，以质量百分数计，所述厚钢板的化学成分包含：C：0.045～0.076％，Si：0.19～0.31％，Mn：0.95～1.13％，P：≤0.008％，S：≤0.002％，Als：0.010～0.040％，Nb：0.014～0.038％，V：0.025-0.041％，Ti：0.011～0.022％，Ni：1.35～1.55％，Ce：0.020-0.040％，Fe和其他不可避免的杂质。该厚钢板具有优异的心部疲劳性能，可用于建筑、工程机械、海洋工程等对钢板心部疲劳性能有一定需求的支撑件、构件。

Description

一种490MPa级心部高疲劳强度的厚钢板及其制造方法 技术领域
本发明属于材料技术领域，特别涉及到一种490MPa级心部疲劳强度优异的厚钢板及其制造方法。
背景技术
随着现今经济发展和装备设计、制造能力的不断进步，对大型构件用高强度钢需求越来越多，而且其主体结构用材正向高强度、高韧化、大厚度方向不断发展。厚钢板是高层建筑、海洋开发、原油球罐、油气管线、船舶军舰等大型结构、设备、设施等重要的结构材料。
目前厚钢板通常采用大厚度铸坯轧制而成，但绝大部分连铸坯受其凝固特性以及现有冶炼设备、工艺的限制，铸坯截面化学成分分布不均、内部偏析、疏松、缩孔等缺陷严重，都会对钢板强度、韧性、疲劳性能等指标造成较大影响。尤其是铸坯的中心偏析，其会在轧制过程中“遗传”给钢板，造成钢板厚度中心部位组织异常、探伤不合，并在下一步加工工序或者使用过程中由于心部出现脆性区和提前开始损坏，影响钢结构构件的安全性，再加上现行检验标准往往以钢板厚度1/4处性能为代表，对心部性能约束较少。因此，针对厚钢板，尤其是在一些对韧性、疲劳性能等有较高要求恶劣服役环境，如何改善中心部位的综合力学性能就显得十分必要。
专利文献1公开了一种460MPa级具有良好的疲劳性能的热轧汽车结构钢板及制造方法，其化学元素成分及其重量百分比为C：0.03～0.06％、Mn：1.0～1.2％、Nb：0.025～0.035％、Ti：0.025～0.035％、Si：＜0.10％、S：≤0.005％、P：≤0.015％、N：≤40ppm、Als：0.025～0.050％，余量为铁和不可避免的杂质。在短流程采用Nb-Ti微合金化技术，利用微量Ti固定钢中的S、N(S≤0.005％、N≤40ppm)，减少钢中MnS的夹杂，充分发挥Nb、Ti的细晶作用，获得细小的F+P，得到较高强度的同时，改善钢种的疲劳性能。该发明采用轧制、层流、卷取工艺生产，厚度为1.0～3.0mm，钢的屈服强度在460～560MPa，抗拉强度500～640MPa。
专利文献2中公开了一种具有良好疲劳性能和成型性能的高强汽车大梁钢及其制造方法，该钢的化学成分及重量百分比如下：C：0.04～0.07％，Si：0.05～0.15％，Mn：1.3～1.6％，P：≤0.013％，S：≤0.004％，Nb：0.02～0.04％，Ti：≤0.002％，N：≤0.004％，Alt：0.010～0.030％，O：≤0.002％，且Ti/O＜2，其余为Fe及不可避免的杂质。该发明生产出来的厚度2.0～7.0mm的汽车大梁钢，力学性能达到了ReL≥480MPa，Rm≥600MPa，A≥20％，零件减重17％，该钢种厚度2.0～7.0mm，力学性能ReL≥480MPa，Rm≥600MPa，A≥20％；该汽车大梁钢不但具有良好的疲劳性能，还具有极佳的成型性能。
专利文献3中公开了一种大厚度调质态FO460船舶用钢板及其制造方法，其化学元素含量C：0.06～0.10％；Si：0.05～0.14％；Mn：1.40～1.80％；S：≤0.002％；P：≤0.008％；Als：0.015％～0.045％；N：0.003％～0.015％；Nb：0.01～0.04％；Cu：0.16～0.35％；Ni：0.30～0.60％；Cr：0.15～0.30％；Ti：0.008～0.014％；余量为Fe和不可避免的杂质。该发明钢板厚度60～100mm，屈服强度≥460MPa，抗拉强度≥570MPa，可满足海洋恶劣、苛刻环境对船用钢板的技术要求。
专利文献4中公开了一种屈服强度420MPa级的调质型建筑结构用钢板及其生产方法，其在Fe-Mn-C系基础上进行Nb、Ti微合金化处理的成分设计，钢板材料的化学成分百分比分别为：C：0.13～0.18％，Si：0.20～0.50％，Mn：1.40～1.70％，P：≤0.015％，S：≤0.005％，Cr：≤0.30％，Mo：≤0.30％，Ni：≤0.30％，Cu：≤0.30％，Al：0.020～0.050％，V：≤0.015％，Nb：0.025～0.050％，Ti：0.010-0.020％，N：≤0.006％，其余为Fe及不可避免的杂质元素。生产过程为：冶炼原料依次进行转炉冶炼、炉外精炼、RH炉精炼以获得纯净度较高的钢水，将钢水浇注成370mm～450mm钢坯，然后采用合理的钢坯加热、轧制、在线直接淬火以及回火热处理技术，获得一种适用于高层建筑、大跨度体育场馆、机场、会展中心及工业厂房等大型钢结构建筑工程用的屈服强度420MPa级的钢板材料。该方明钢种厚度为50～100mm，屈服强度ReL为410-540MPa，抗拉强度Rm为530～680MPa。
现有技术
专利文献
专利文献1：CN107641760B
专利文献2：CN109161795A
专利文献3：CN113174535A
专利文献4：CN112981235A
发明内容
发明要解决的技术问题
上述专利文献1和2中虽然公开了具有良好的疲劳性能汽车用钢，但厚度规格仅为1-7mm，其技术方法也不适用于厚钢板制造。专利文献3和4中虽然公开了两种大厚度钢板制造方法，但未提及钢板疲劳性能。
鉴于上述现有技术，本发明的目的在于提供一种490MPa级心部疲劳强度优异的厚钢板及其制造方法。本发明的钢板厚度60～100mm，屈服强度≥490MPa，抗拉强度≥600MPa，而且板厚中心部位疲劳强度≥340MPa，具有优良的心部疲劳性能，其钢板强度、韧性、疲劳性能得到进一步提升，尤其是中心部位的综合力学性能优异，可解决大型构件用高强度钢中出现的截面化学成分分布不均、内部偏析及心部出现脆性区引发提前开始损坏的问题，尤其适用于对韧性、疲劳性能等有较高要求的应用领域。
解决技术问题的手段
为了实现上述目的，本发明提出一种490MPa级心部高疲劳强度的厚钢板，以质量百分数计，所述厚钢板的化学成分包含：
C：0.045～0.076％，Si：0.19～0.31％，Mn：0.95～1.13％，P：≤0.008％，S：≤0.002％，Als：0.010～0.040％，Nb：0.014～0.038％，V：0.025-0.041％，Ti：0.011～0.022％，Ni：1.35～1.55％，Ce：0.020-0.040％，Fe和其他不可避免的杂质。
所述厚钢板中可以添加B：0.0005～0.0009％，Mo：0.15～0.25％中的一种或两种。
进一步地，在本发明所述的心部疲劳性能优异的厚钢板中，通过使其微观组织为准多边形铁素体(QF)+板条贝氏体(BF)+珠光体(P)，其中以面积百分比计，QF相比例在30-60％，BF相比例在40-70％，P相比例在0.1-3％，由此可以进一步保证钢材具有良好的强韧性能。
进一步地，在本发明所述的心部疲劳性能优异的厚钢板中，通过使其平均晶粒尺寸为8-12μm，由此可进一步有效提升钢板强韧性能和疲劳性能。
进一步地，在本发明所述的心部疲劳性能优异的厚钢板，其氧化物类夹杂物主要为Ce2O3+Al2O3、Ce2O3、Al2O3以及各自以其为核心的复合夹杂物，其中Ce2O3+Al2O3及以其为核心的复合夹杂物的数量比例为90％以上，Ce2O3及以其为核心的复合夹杂物的数量比例为1-10％，Al2O3及以其为核心的复合夹杂物的数量比例为1％以下。
进一步地，在本发明所述的心部疲劳性能优异的厚钢板，其夹杂物密度为100-500个/mm2，其中0.2-2μm夹杂物的数量比例在95％以上，>2～5μm夹杂物的数量比例在5％以下，>5-10μm夹杂物的数量比例在0.01％以下，不存在大于10μm的夹杂物。
本发明还提供一种490MPa级心部高疲劳强度的厚钢板的制造方法，其步骤优选为：
1)进行铁水脱硫，并控制铁水中S≤0.002％；
2)真空处理时间≥21min；连铸拉速0.5-1.0m/min；采用两段式电磁搅拌，其电流参数分别为420A、455A；动态轻压下固相率0.35～0.70，压下量为6-10mm；
3)常规连铸成坯并对铸坯加热，控制加热温度在1201～1245℃，出炉温度不低于1180℃；
4)采用两阶段式轧制，第一阶段开轧温度不低于1063℃，单道次压下量≥20mm，最后两道次压下量≥40mm；第二阶段开轧温度不高于943℃，前两道次压下率大于15％，其余轧制道次压下率控制在8～10％，终轧温度在821～843℃。终轧后快速冷却，冷却速度为0.5～5℃/s，控制返红温度不高于430℃；
5)进行工业炉回火热处理，回火温度在611～631℃，在炉时间为：(产品厚度/mm×1.5)min，到温后持续保温时间不低于(产品厚度/mm×0.9)min。回火结束后空冷至室温。
发明效果
本发明钢板厚度60～100mm，屈服强度≥490MPa，抗拉强度≥600MPa，而且板厚中心部位疲劳强度≥340MPa，具有优良的心部疲劳性能，可用于建筑、工程机械、海洋工程等对钢板心部疲劳性能有一定需求的支撑件、构件。本发明具有制造工序简单等优点，在各冶金企业均可实施。
具体实施方式
下文将结合具体实施方式和实施例，具体阐述本发明，但本领域技术人员应理解，这些具体实施方式和实施例是用于说明本发明，而非限制本发明。
在整个说明书中，除非另有特别说明，本文使用的术语应理解为如本领域中通常所使用的含义。因此，除非另有定义，本文使用的所有技术和科学术语具有与本发明所属领域技术人员的一般理解相同的含义。若存在矛盾，本说明书优先。
本发明提供以下的技术方案以获得上述效果：
根据本发明一种典型的实施方式，提供一种490MPa级心部高疲劳强度的厚钢板及其制造方法，以质量百分数计，所述厚钢板的化学成分包含：C：0.045～0.076％，Si：0.19～0.31％，Mn：0.95～1.13％，P：≤0.008％，S：≤0.002％，Als：0.010～0.040％，Nb：0.014～ 0.038％，V：0.025-0.041％，Ti：0.011～0.022％，Ni：1.35～1.55％，Ce：0.020-0.040％，Fe和其他不可避免的杂质。
所述厚钢板中可以添加B：0.0005～0.0009％，Mo：0.15～0.25％中的一种或两种。
本发明对于各个化学成分的控制原理如下：
C、Mn是提高钢材强度非常有效的元素。一方面，碳含量的增加钢的抗拉强度和屈服强度随之提高，但延伸率和冲击韧性下降，而且钢材的焊接热影响区还会出现淬硬现象，导致焊接冷裂纹的产生。随着Mn含量的增加，钢的强度明显增加，而冲击转变温度几乎不发生变化。Mn也是扩大奥氏体区元素，Mn含量增加可提高奥氏体稳定性，降低临界冷却速度，强化铁素体，显著提高淬透性，同时可使淬火后回火过程中组织分解转变速度减慢，提高回火组织稳定性。而另一方面，C、Mn元素又是铸坯中心极易偏聚、引发中心偏析的元素。因此，本发明将C、Mn控制在较低的水平(C：0.045～0.076％，Mn：0.95～1.13％)，采用其他合金元素平衡钢板强度、韧性，减轻中心偏析对心部性能的不利影响。
Si元素可以提高钢中固溶体硬度和强度，不仅可以增加钢的淬透性，而且还可以增加淬火钢的抗回火性，使钢能在较高温度下回火，从而改善钢的韧性和耐延迟断裂性能；Si能显著提高钢的弹性极限、屈服强度和屈强比。Si含量过高会使钢的导热性变差，钢锭、钢坯表面易出现开裂或裂纹缺陷。本发明钢的Si含量设计为0.19～0.31％。
P、S是钢中的杂质元素，也是易于偏析的元素，可在钢的局部形成严重偏析、夹杂物，降低塑性及韧性。本发明钢，在冶金质量方面严格控制了硫、磷含量水平，即P≤0.008％，S≤0.002％。
Al是钢中的主要脱氧元素，另外，Al的熔点较高，在生产中，钢中Al可与N形成AlN，而AlN可阻碍高温奥氏体长大，起到细化晶粒的作用。本发明钢的Als含量控制为0.010～0.040％。
Nb、Ti是两种强烈的碳化物和氮化物形成元素，与氮、碳有极强的亲合力，可与之形成极其稳定的碳氮化物。弥散分布的Nb的碳氮化物第二相质点沿奥氏体晶界的分布，可大大提高原始奥氏体晶粒粗化温度，在轧制过程中的奥氏体再结晶温度区域内，Nb的碳氮化析出物可以作为奥氏体晶粒的形核核心，而在非再结晶温度范围内，弥散分布的Nb的碳氮化析出物可以有效钉扎奥氏体晶界，阻止奥氏体晶粒进一步长大，从而细化铁素体晶粒，达到提高强度和冲击韧性的目的；Ti的氮化物能有效地钉扎奥氏体晶界，有助于控制奥氏体晶粒的长大，大大改善焊接热影响区的低温韧性。因此，通过Nb、Ti微合 金元素的细晶强化和沉淀强化作用，可以使钢板获得优良的强韧性。本发明钢Nb含量设计为0.014～0.038％，Ti含量设计为0.011～0.022％。
V是一种相当强烈的碳化物形成元素，它可以通过细晶强化、沉淀强化和固溶强化来提高钢材的强度。此外在钢中，当V的质量百分数低于0.1％时，随着V含量的增加，钢的韧脆转变温度降低。当V的质量百分数超过0.1％时，V含量增加，韧脆转变温度反而升高。在含Si、Mn的钢中，加入少量的V就可以明显减轻这两种元素对晶粒长大和提高韧脆转变温度的影响。V与Nb复合添加时，既能提高钢的强度又能改善钢的韧性。本发明V元素含量0.025-0.041％。
Ni在钢中能强化铁素体基体，抑制粗大的先共析铁素体，显著改善钢材的韧性，降低钢材的韧脆转变温度，提高钢的低温冲击韧性。本发明将Ni的含量设计为1.35～1.55％。
Ce是稀土元素的一种，和氧、硫有很强的亲和力，在钢中有净化和明显的变质作用。固溶在钢中可以通过扩散机制富集于晶界，减少夹杂元素在晶界的偏聚，结果强化了晶界，改善了与晶界相关的性能，如低温脆性、韧性等。本发明Ce添加量为0.020-0.040％。
Mo元素在钢中的主要作用是固溶强化，少量Mo可以形成难熔碳化物，阻碍加热时奥氏体晶粒长大，细化产品组织，提高强度、硬度和耐磨性。Mo可以提高淬透性，减轻或消除其他合金元素所导致的回火脆性而大大有利于钢的韧性，提高回火稳定性，有效消除或降低钢中的残余应力，但过高的Mo在快速冷却和焊接冷却过程中极易获得粗大马氏体，降低基材低温韧性和恶化焊接性能，因此，本发明优选将Mo含量控制为0.15～0.25％。
B是强烈提高淬透性的元素，B的加入，可有效的抑制先共析铁素体的形核及生长，由于B在奥氏体晶界上的非平衡偏析，强烈抑制γ-α相变，促使奥氏体在淬火时形成细小的低碳马氏体，从而提高钢的屈服强度和抗拉强度，本发明的B含量优选为0.0005～0.0009％。
在本发明所述的心部疲劳性能优异的厚钢板，其氧化物类夹杂物主要为Ce2O3+Al2O3、Ce2O3、Al2O3以及各自以其为核心的复合夹杂物，其中Ce2O3+Al2O3及以其为核心的复合夹杂物的数量比例为90％以上，Ce2O3及以其为核心的复合夹杂物的数量比例为1-10％，Al2O3及以其为核心的复合夹杂物的数量比例为1％以下。
进一步地，在本发明所述的心部疲劳性能优异的厚钢板，其夹杂物密度为100-500个/mm2，其中0.2-2μm夹杂物的数量比例在95％以上，>2～5μm夹杂物的数量比例在5％以下，>5-10μm夹杂物的数量比例在0.01％以下，不存在大于10μm的夹杂物。
在上述技术方案中，夹杂物类型的控制具有细化晶粒、促进贝氏体相变的作用；夹杂物尺寸的微细化控制具有细化晶粒、促进贝氏体相变、提高钢板强韧性能和疲劳强度的作用。具体地，高密度的微细夹杂物在钢板冷却过程中，可以作为铁素体的异质形核点，促进铁素体生成，从而细化晶粒、促进贝氏体相变。
根据本发明另一实施方式，提供一种490MPa级心部高疲劳强度的厚钢板的制造方法，其步骤优选包括：
1)进行铁水脱硫，并控制铁水中S≤0.002％；
2)真空处理时间≥21min；连铸拉速0.5-1.0m/min；采用两段式电磁搅拌，其电流参数分别为420A、455A；动态轻压下固相率0.35～0.70，压下量为6-10mm；
3)常规连铸成坯并对铸坯加热，控制加热温度在1201～1245℃，出炉温度不低于1180℃；
4)采用两阶段式轧制，第一阶段开轧温度不低于1063℃，单道次压下量≥20mm，最后两道次压下量≥40mm；第二阶段开轧温度不高于943℃，前两道次压下率大于15％，其余轧制道次压下率控制在8～10％，终轧温度在821～843℃。终轧后快速冷却，冷却速度为0.5～5℃/s，控制返红温度不高于430℃；
5)进行工业炉回火热处理，回火温度在611～631℃，在炉时间为：(产品厚度/mm×1.5)min，到温后持续保温时间不低于(产品厚度/mm×0.9)min。回火结束后空冷至室温。
本发明的制造方法设计要点和理由如下：
控制连铸拉速、采用两段式电磁搅拌、控制动态轻压下区间及总压下量在上述本发明范围内，可以最大程度的改善铸坯中心偏析等缺陷。
控制铸坯加热温度、出炉温度在上述本发明范围内，可以进一步保证本发明钢形成足够的奥氏体化。
本发明中，采用两阶段式轧制，变换道次压下量，而非单纯的大压下、少道次轧制工艺，由此可以对两个阶段的再结晶晶粒、铁素体形核晶粒叠加细化。进一步，通过设置控制第一阶段开轧温度不低于1063℃，配合单道次压下量，可以有效的将轧制压力传导到铸坯中心部位，充分细化奥氏体晶粒；控制第二阶段开轧温度不高于943℃、限定前两道次压下率大于15％，其余轧制道次压下率在8～10％、终轧温度在821～843℃，可进一步对再结晶晶粒、铁素体形核晶粒叠加细化，进一步提升钢板韧性，并间接给予足够的时间减轻中心偏析、中心疏松。
轧后进行冷却，通过控制冷却速度及将返红温度控制不高于430℃，可进一步保证钢板获得准多边形铁素体+板条贝氏体+珠光体组织，并获得满足要求的比例，以获得优异的基础性能及疲劳性能。
控制回火温度在611～631℃，过低的回火加热温度会造成本发明钢回火时部分元素析出不充分，导致钢板强度不足，韧性不良；过高的温度会导致本方面钢强度下降。同时，由于钢板进入工业炉回火时，会引起炉温降低。因此，必须通过控制足够的回火到温后持续保温时间不低于(产品厚度/mm×0.9)min，以使钢板回火时元素析出、扩散充分，且内应力消除充分，从而获得优良的综合性能。
通过采用本发明的化学成分、制造方法进行冶炼、轧制、冷却及回火工艺参数，可以制造满足本发明要求的钢板。
下面结合实施例和对比例及实验数据对本发明做进一步详细说明。
实施例
将表1中所示的不同成分的钢成分按表2所示的工艺得到厚钢板。
表1本发明各实施例及对比例的化学组分及质量百分数含量
实施例1～实施例8及对比例的具体工艺参数如表2所示：
表2本发明各实施例及对比例的主要工艺参数

实施例1～8钢板的综合性能检测结果如下表所示。
疲劳强度根据GB/T3075《金属材料疲劳试验轴向力控制方法》，对中心部位取样，将公称尺寸相同的试样装夹在轴向力疲劳试验机上，并施加等幅循环应力，应力比0.1，施加的力沿着试样的纵轴方向并通过试样横截面的轴心，试验一直持续到试样失效或者直到超过107循环周次，试样不发生断裂失效时的最大应力即为材料的疲劳强度。
屈服强度和抗拉强度在室温25℃条件下，根据GB/T228.1-2010标准《金属材料拉伸试验第1部分：室温试验方法》，对拉伸试样施加轴向拉力，并按一定的拉伸速度进行拉伸，试样发生屈服而力首次下降前的最大应力为屈服强度，材料发生断裂前最大拉伸力对应的应力为抗拉强度。
夹杂物的类型、比例及密度测试方法为利用扫描电镜(SEM)及其附属能谱仪(EDS)，对磨削、抛光后的材料20mm2以上的面积进行扫描，根据夹杂物与钢铁机体衬度不同识别夹杂物，并利用能谱仪对夹杂物进行成分分析，判定夹杂物尺寸及类型，统计夹杂物数量，计算其比例。
微观组织各相的测定是对金相试样进行1000X砂纸磨平，并经过抛光后，采用4％硝酸酒精进行腐蚀，采用金相显微镜拍摄金相照片，根据准多边形铁素体(QF)、板条贝氏体(BF)、珠光体(P)的形貌特征进行各相区域标定，对标定的区域分别计算面积及相比例。
表3本发明各实施例性能检测结果
表4本发明各实施例夹杂物检测结果
表5本发明各相的检测结果

由上表可知，本发明各实施例中均获得了本发明范围内的夹杂物及微晶组织，本发明实施例的疲劳强度均在340MPa以上，明显高于对比例，具有良好的心部疲劳性能。
本发明钢板是一种屈服强度≥490MPa，抗拉强度≥600MPa，板厚中心部位疲劳强度≥340MPa的60～100mm厚钢板。可用于建筑、工程机械、海洋工程等对钢板心部疲劳性能有一定需求的支撑件、构件。本发明具有制造工序简单等优点，在各冶金企业均可实施。
此外，本案中各技术特征的组合方式并不限于具体实施方式及实施例中所记载的组合方式，本案记载的所有技术特征可以以任何方式进行自由组合或结合，除非相互之间产生矛盾。本领域的技术人员从本发明公开的内容直接导出或联想到的所有变形，均应属于本发明的保护范围。

Claims (14)

  1. 一种490MPa级心部高疲劳强度的厚钢板，其特征在于，以质量百分数计，所述钢板的化学成分包含：
    C：0.045～0.076％，Si：0.19～0.31％，Mn：0.95～1.13％，P：≤0.008％，S：≤0.002％，Als：0.010～0.040％，Nb：0.014～0.038％，V：0.025-0.041％，Ti：0.011～0.022％，Ni：1.35～1.55％，Ce：0.020-0.040％，Fe和其他不可避免的杂质。
  2. 如权利要求1所述的厚钢板，其特征在于，所述钢板进一步含有B：0.0005～0.0009％，Mo：0.15～0.25％中的一种或两种。
  3. 一种490MPa级心部高疲劳强度的厚钢板，其特征在于，以质量百分数计，所述钢板的化学成分为：
    C：0.045～0.076％，Si：0.19～0.31％，Mn：0.95～1.13％，P：≤0.008％，S：≤0.002％，Als：0.010～0.040％，Nb：0.014～0.038％，V：0.025-0.041％，Ti：0.011～0.022％，Ni：1.35～1.55％，Ce：0.020-0.040％，以及可选地含有B：0.0005～0.0009％，Mo：0.15～0.25％中的一种或两种，余量为Fe和其他不可避免的杂质。
  4. 如权利要求1～3中任一项所述的厚钢板，其特征在于，所述钢板中，V：0.032-0.041％。
  5. 如权利要求1～3中任一项所述的厚钢板，其特征在于，以面积百分比计，所述钢板的微观组织由30-60％的准多边形铁素体、40-70％的板条贝氏体以及0.1-3％的珠光体构成。
  6. 如权利要求5所述的厚钢板，其特征在于，所述钢板的微观组织的平均晶粒尺寸为8-12μm。
  7. 如权利要求1～3中任一项所述的厚钢板，其特征在于，所述钢板中包含氧化物类夹杂物，其中氧化物类夹杂物主要为Ce2O3+Al2O3、Ce2O3、Al2O3以及各自以其为核心的复合夹杂物，Ce2O3+Al2O3及以其为核心的复合夹杂物的数量比例为90％以上，Ce2O3及以其为核心的复合夹杂物的数量比例为1-10％，Al2O3及以其为核心的复合夹杂物的数量比例为1％以下。
  8. 如权利要求7所述的厚钢板，其特征在于，所述夹杂物的密度为100-500个/mm2，其中0.2-2μm夹杂物的数量比例在95％以上，大于2μm且5μm以下的夹杂物的数量比例在5％以下，大于5μm且10μm以下的夹杂物的数量比例在0.01％以下，不存在大于10μm的夹杂物。
  9. 如权利要求1～8中任一项所述的厚钢板，其特征在于，所述钢板的屈服强度≥490MPa，抗拉强度≥600MPa。
  10. 如权利要求1～8中任一项所述的厚钢板，其特征在于，所述钢板的厚度为60～100mm，板厚中心部位疲劳强度≥340MPa。
  11. 一种490MPa级心部高疲劳强度的厚钢板的制造方法，其包括：
    1)根据权利要求1～4中任一项所示的化学成分进行冶炼、铁水脱硫，并控制铁水中S≤0.002％；
    2)真空处理时间≥21min；连铸拉速0.5-1.0m/min；采用两段式电磁搅拌；动态轻压下固相率0.35～0.70，压下量为6-10mm；
    3)连铸成坯并对铸坯加热；
    4)采用两阶段式轧制；
    5)进行回火热处理，回火温度在611～631℃，在炉时间为：(产品厚度/mm×1.5)min，到温后持续保温时间不低于(产品厚度/mm×0.9)min；回火结束后空冷至室温。
  12. 如权利要求11所述的制造方法，其特征在于，所述步骤3)中，控制加热温度在1201～1245℃，出炉温度不低于1180℃。
  13. 如权利要求11或12所述的制造方法，其特征在于，所述步骤4)中，第一阶段开轧温度不低于1063℃；第二阶段开轧温度不高于943℃，终轧温度在821～843℃；终轧后以0.5～5℃/s的速度冷却，控制返红温度不高于430℃。
  14. 如权利要求13所述的制造方法，其特征在于，所述步骤4)中，第一阶段开轧中，单道次压下量≥20mm，最后两道次压下量≥40mm；第二阶段开轧中，前两道次压下率大于15％，其余轧制道次压下率控制在8～10％。
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