WO2021078111A1 - Acier à haute ténacité ayant une bonne ductilité et son procédé de fabrication - Google Patents

Acier à haute ténacité ayant une bonne ductilité et son procédé de fabrication Download PDF

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WO2021078111A1
WO2021078111A1 PCT/CN2020/122085 CN2020122085W WO2021078111A1 WO 2021078111 A1 WO2021078111 A1 WO 2021078111A1 CN 2020122085 W CN2020122085 W CN 2020122085W WO 2021078111 A1 WO2021078111 A1 WO 2021078111A1
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strength steel
steel
excellent ductility
manufacturing
strength
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Chinese (zh)
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陈孟
钟勇
汪水泽
李旭飞
王利
毛新平
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宝山钢铁股份有限公司
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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
    • 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
    • C21D1/26—Methods of annealing
    • 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
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    • 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
    • C21D8/0236—Cold rolling
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    • 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
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
    • 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
    • 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
    • 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
    • C22C38/12—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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
    • 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
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with 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
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese
    • 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
    • C21D2211/001—Austenite
    • 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
    • C21D2211/008—Martensite

Definitions

  • the invention relates to a kind of steel and a manufacturing method thereof, in particular to a high-strength steel and a manufacturing method thereof.
  • Advanced high-strength steel is the most comprehensively competitive body lightweight material at present by increasing the strength of the steel plate to reduce the thickness of the steel plate while maintaining excellent formability. It is also the focus of steel mills and OEMs.
  • TRIP steel is composed of ferrite, bainite and retained austenite. This phase structure limits the further improvement of its strength. Using martensite instead of bainite as the main strengthening phase can continue to increase Strength of TRIP steel.
  • the main factors that determine its ductility are the shape, volume fraction and stability of retained austenite in the steel. The stability of retained austenite is closely related to its size and carbon content.
  • the existing advanced high-strength steels are mostly based on the composition of carbon-manganese steel, adding more alloy elements such as Cr, Mo, Nb, Ti, B, etc., which not only increases the material cost, but also improves the steelmaking
  • the manufacturability of hot rolling and cold rolling brings difficulties.
  • the publication number is CN106574342A
  • the publication date is April 19, 2017,
  • the Chinese patent document entitled "High-strength steel sheet and its manufacturing method, and high-strength galvanized steel sheet manufacturing method" discloses a high-strength steel sheet.
  • the manufacturing method is as follows: heating a slab satisfying the composition conditions to 1100-1300°C, finishing rolling outlet temperature 800-1000°C, average coiling temperature 450-700°C, after pickling
  • the steel plate is kept at 450°C ⁇ Ac1 temperature for 900 ⁇ 36000s, cold rolling is performed at a reduction rate of 30% or more, the steel plate is heated to 820 ⁇ 950°C for the first annealing, and then the average cooling rate up to 500°C is 15°C/
  • cool to below Ms temperature and then heat to 740 ⁇ 840°C for the second annealing, cool to 150 ⁇ 350°C at a cooling rate of 1 ⁇ 15°C/s, and then heat to 350 ⁇ 550°C for more than 10s .
  • heating and rolling are required, and two annealing treatments are adopted, the production process is cumbersome, and the manufacturing cost increases. Therefore, its application in the automotive field is greatly restricted.
  • the publication number is CN104245971A
  • the publication date is December 24, 2014
  • the Chinese patent document titled "High-strength cold-rolled steel sheet and method for producing the same” discloses a high-strength cold-rolled steel sheet.
  • its composition is: C: 0.1% to 0.3%, Si: 0.4% to 1.0%, Mn: 2.0% to 3.0%, Cr ⁇ 0.6%, Si+0.8Al+Cr :1.0% ⁇ 1.8%, Al:0.2% ⁇ 0.8%, Nb ⁇ 0.1%, Mo ⁇ 0.3%, Ti ⁇ 0.2%, V ⁇ 0.1%, Cu ⁇ 0.5%, Ni ⁇ 0.5%, S ⁇ 0.01%, P ⁇ 0.02%, N ⁇ 0.02%, B ⁇ 0.005%, Ca ⁇ 0.005%, Mg ⁇ 0.005%, REM ⁇ 0.005%, and the balance is Fe and unavoidable impurities.
  • the microstructure (vol%) is: retained austenite 5%-20%, bainite + bainite ferrite + tempered martensite ⁇ 80%, polygonal ferrite ⁇ 10%, martensite -Austenite composition ⁇ 20%. It should be pointed out that because the steel components involved in the technical solution need to add a certain amount of Cr and Mo, although its tensile strength is ⁇ 980MPa, the elongation is only about 14%, which is very important for the cost and forming of steel for automotive parts. The sexual advantage is not obvious.
  • One of the objectives of the present invention is to provide a high-strength steel with excellent ductility.
  • the high-strength steel adopts a simple composition design and makes full use of the influence law of C, Si and Mn on the phase transformation of the material to ensure the Strength and ductility.
  • the present invention proposes a high-strength steel with excellent ductility, the mass percentage of chemical elements is:
  • the balance is Fe and other unavoidable impurities.
  • C In the high-strength steel with excellent ductility of the present invention, the solubility of C in austenite is much higher than its solubility in ferrite, which can prolong the incubation period before austenite transformation and reduce Ms temperature.
  • C is also the most basic solid solution strengthening element in steel. However, an excessively high mass percentage of C will reduce the weldability of the steel.
  • the mass percentage of C in the steel exceeds 0.25%, more twins are prone to appear after quenching, which increases crack sensitivity. Based on this, in the high-strength steel with excellent ductility according to the present invention, the mass percentage of C is controlled at 0.15-0.25 wt%.
  • Si In the high-strength steel with excellent ductility described in the present invention, the solubility of Si in carbides is extremely small, and the formation of cementite is strongly inhibited during the partitioning process, and carbon is concentrated in retained austenite. Improve the stability of retained austenite. However, if the mass percentage of Si is too high, it will reduce the high-temperature plasticity of the steel and increase the incidence of hot rolling defects. At the same time, when the mass percentage of Si is high, stable oxides will be formed on the surface of the steel sheet, reducing the wettability of the steel sheet. Based on this, the mass percentage of Si in the high-strength steel with excellent ductility according to the present invention is controlled at 1.00 to 2.00 wt%.
  • Mn In the high-strength steel with excellent ductility described in the present invention, Mn can expand the austenite phase region, reduce Ac3, Ms and Mf points, improve the stability of austenite and the hardenability of steel, and reduce critical transformation The speed is beneficial to the preservation of retained austenite to room temperature. At the same time, Mn can also play a solid solution strengthening effect in steel. However, if the mass percentage of Mn is too high, it will aggravate the tendency of grain coarsening, reduce the plasticity and toughness of steel, and deteriorate corrosion resistance and welding performance. However, if the mass percentage of Mn is too low, the segregation will cause ferrite and pearlite banded structures to be produced at low cooling rates. Based on this, the mass percentage of Mn in the high-strength steel with excellent ductility according to the present invention is controlled to be 1.50 to 3.00 wt%.
  • Al In the high-strength steel with excellent ductility of the present invention, when Al exists in a solid solution state, it can increase the stacking fault energy, inhibit the precipitation of cementite and the transformation of ⁇ to martensite, and improve the stability of austenite .
  • Al, C and N form fine and dispersed insoluble points, which can refine grains, but the strengthening effect of Al is weaker than that of Si, and the ability to stabilize austenite is also weaker than that of Si.
  • the mass percentage of Al is too high to easily form a large number of oxide inclusions, which is not conducive to steelmaking and continuous casting. Therefore, the mass percentage of Al in the high-strength steel with excellent ductility according to the present invention is controlled to be 0.03 to 0.06 wt%.
  • the mass percentage of each chemical element satisfies at least one of the following items:
  • the high-strength steel with excellent ductility according to the present invention also contains at least one of the following elements:
  • the aforementioned Cr, Mo, Nb, Ti, V, and B can further improve the performance of the high-strength steel according to the present invention.
  • Cr and Mo can improve the hardenability of steel and adjust the strength of steel, but Cr will be enriched on the surface of the steel plate, which affects the welding performance, and the higher mass percentage of Mo leads to the increase of the cold-rolled deformation resistance of the steel.
  • Nb, Ti, V elements can form fine carbides with C to promote structure refinement, but the formation of such fine carbides is not conducive to the enrichment of C into retained austenite and the stabilization of retained austenite .
  • the main function of B is to improve the hardenability of steel.
  • B is easy to segregate at the austenite grain boundary and delay the transformation of austenite to ferrite. Adding a small amount to the steel can play a significant role. The quality of B Too high a percentage will increase the strength of the steel, which is not conducive to good shaping. Therefore, the mass percentage of B can be controlled at B ⁇ 0.001%.
  • the addition of the above-mentioned elements will increase the cost of the material. Considering the performance and cost control comprehensively, in the technical solution of the present invention, at least one of the above-mentioned elements can be preferably added.
  • each chemical element satisfies at least one of the following items:
  • Mo ⁇ 0.25wt% preferably, Mo ⁇ 0.20wt%
  • V ⁇ 0.02wt% preferably, V ⁇ 0.01wt%.
  • P, S, and N are impurities.
  • P can play a solid solution strengthening effect and inhibit the formation of carbides, it is beneficial to improve the stability of retained austenite.
  • the mass percentage of P is too high, it will weaken The grain boundary increases the brittleness of the material and deteriorates the welding performance, that is, the positive effect of P is weaker than its negative effect. Therefore, it is preferable to control the mass percentage of P to P ⁇ 0.015wt%.
  • N too high mass percentage of N will bring difficulties to steelmaking and continuous casting, and is not conducive to the control of inclusions. Therefore, it is preferable to control the mass percentage of N to N ⁇ 0.008wt%.
  • the microstructure is 30% to 50% ferrite + 40% to 60% martensite + retained austenite.
  • grains of 10 ⁇ m or less account for 80% or more, and grains of 5 ⁇ m or less account for 50% or more of ferrite.
  • the average grain size of the retained austenite is less than or equal to 2 ⁇ m; and/or the average C content in the retained austenite is more than or equal to 1.1 wt%. In some embodiments, the average grain size of retained austenite is in the range of 0.3-2 ⁇ m. In some embodiments, the average C content in the retained austenite is 1.1 wt% to 1.5 wt%, such as 1.1 wt% to 1.3 wt%.
  • the yield strength is 550-850MPa
  • the tensile strength is 900-1100MPa
  • the uniform elongation (UEL) is ⁇ 13%
  • the elongation at break (TEL) It is 18%-28%.
  • the uniform elongation is 13-19%.
  • another object of the present invention is to provide the above-mentioned manufacturing method of high-strength steel with excellent ductility.
  • the manufacturing method adopts a thin slab continuous casting process combined with a pickling or pickling process to obtain excellent ductility after continuous annealing.
  • the manufacturing method is simple to produce, and the obtained high-strength steel has a significantly improved elongation under the same strength condition.
  • the present invention proposes the above-mentioned manufacturing method of high-strength steel with excellent ductility, which includes the following steps:
  • the thickness of the slab at the exit end of the continuous casting is controlled to be 52-60mm, preferably 55-60mm;
  • Continuous annealing annealing at 800 ⁇ 920°C, slowly cooling to 680 ⁇ 750°C at a cooling rate of 3 ⁇ 10°C/s to obtain a certain proportion of ferrite; then quickly cooling to 220 ⁇ 320°C, cooling The speed is 50-1000°C/s to partially transform austenite into martensite; then it is heated to 360-460°C for 100-500s, and finally cooled to room temperature.
  • step (1) adopts thin slab continuous casting, the rough rolling process can be omitted, and the deformation of hot rolling can be reduced, thereby ensuring that the subsequent steps (4) and step ( 5) The performance of the steel plate.
  • step (1) adopts thin slab continuous casting, it can make full use of the heat of the slab and reduce the energy consumption required for heating, thereby obtaining a more uniform ferrite or ferrite + pearlite structure, which is beneficial to the step 5) Maintain a certain amount of fine-grained ferrite in the microstructure of the finished product to improve the uniformity of the structure.
  • step (3) controlling the thickness of the scale on the surface of the steel strip after hot rolling to be ⁇ 5 ⁇ m, and the (FeO+Fe 3 O 4 ) in the scale on the surface of the steel strip after the hot rolling is ⁇ 40wt%, which can be beneficial to the subsequent steps
  • the progress of (4) has an important influence on the performance of the steel sheet obtained after continuous annealing.
  • a uniform austenite structure or austenite + ferrite structure can be formed by controlling the annealing temperature; then slowly cool to 660-750°C at a cooling rate of 3-10°C/s, Preferably 680-750°C to further adjust the content of ferrite in the structure and improve the shaping of the material; then cool to 220-320 at a rate of 50-1000°C/s, preferably 50-600°C, more preferably 50-100°C °C (that is, between Ms and Mf temperature), at this time, austenite is partially transformed into martensite to ensure that the steel has higher strength; then heat to 360 ⁇ 460°C and keep for 100 ⁇ 500s, such as 100- 300s, the carbon is partitioned between martensite and austenite to form a certain amount of carbon-rich retained austenite, which is kept stable to room temperature. Due to the TRIP effect, the work hardening ability and formability of the steel can be significantly improved, and the ductility can be obtained. High-stre
  • the high-strength steel in this case adopts high-carbon, high-manganese design and ferrite grain refinement
  • the nucleation point of the reverse phase transformation of austenite increases while the size is further refined.
  • the average grain size of the retained austenite that is stably maintained to room temperature can be ⁇ 2 ⁇ m; the average C content in the retained austenite is ⁇ 1.1wt%.
  • the martensite formed by rapid cooling basically does not decompose during the partitioning process to ensure the content of martensite in the structure, thereby ensuring the strength of the steel.
  • step (1) the continuous casting drawing speed is controlled to be 2-5 m/min.
  • step (2) the slab is heated to 1200-1250°C.
  • step (3) the finishing rolling temperature is controlled to be 860 to 930°C, and the coiling temperature is to be 450 to 600°C.
  • step (4) when the pickling + cold rolling step is adopted, the deformation is controlled to be 30% to 70%.
  • step (5) the volume content of hydrogen in the reducing atmosphere in the continuous annealing furnace is controlled to 10-15%.
  • step (5) the continuous annealing process is controlled to satisfy at least one of the following items:
  • Annealing temperature is 820 ⁇ 870°C
  • the volume content of hydrogen in the reducing atmosphere in the continuous annealing furnace is controlled to 10-15%.
  • the high-strength steel with excellent ductility and its manufacturing method according to the present invention have the following advantages and beneficial effects:
  • the high-strength steel of the present invention is based on carbon-silicon-manganese steel without adding any expensive alloy elements, and by optimizing the ratio of carbon-silicon-manganese, a high-strength cold-rolled steel sheet with excellent ductility is obtained.
  • the manufacturing method of the present invention has a simple production process, and the obtained high-strength steel can significantly increase its elongation under the same strength conditions. It will have a good application prospect in automobile safety structural parts, and is particularly suitable for manufacturing complex shapes, Vehicle structural parts and safety parts that require high formability, such as A/B pillars, longitudinal beams, door anti-collision bars, bumpers, etc.
  • Fig. 1 is a microstructure photograph of the high-strength steel of Example 12.
  • Fig. 2 is an EBSD photograph of the phase composition of the high-strength steel of Example 12.
  • the high-strength steel with excellent ductility of Examples 1-36 was prepared by the following steps:
  • Hot rolling The thickness of the oxide scale on the surface of the steel strip after hot rolling is ⁇ 5 ⁇ m, and the (FeO+Fe 3 O 4 ) in the oxide scale on the surface of the strip after hot rolling is ⁇ 40wt%, and the final rolling temperature is controlled at 860 ⁇ 930°C , The coiling temperature is 450 ⁇ 600°C.
  • Continuous annealing annealing at 800 ⁇ 920°C, slowly cooling to 660 ⁇ 750°C at a cooling rate of 3 ⁇ 10°C/s to obtain a certain proportion of ferrite; then quickly cooling to 220 ⁇ 320°C, cooling The speed is 50-1000°C/s to partially transform austenite into martensite; then it is heated to 360-460°C for 100-500s, and finally cooled to room temperature.
  • the volume content of hydrogen in the reducing atmosphere in the continuous annealing furnace is controlled to 10-15%.
  • control parameters can be further controlled to satisfy at least one of the following items:
  • Annealing temperature is 820 ⁇ 870°C
  • the volume content of hydrogen in the reducing atmosphere in the continuous annealing furnace is controlled to 10-15%.
  • the comparative examples 1-3 were manufactured using conventional processes.
  • Table 1 lists the mass percentage ratios of the chemical elements of the high-strength steel with excellent ductility of Examples 1-36 and the comparative steel of Comparative Examples 1-3.
  • Table 2-1 and Table 2-2 list the specific process parameters of the high-strength steel with excellent ductility in Examples 1-36 and the comparative steel in Comparative Examples 1-3.
  • Table 3 lists the mechanical performance test results of the high-strength steel with excellent ductility in Examples 1-36 and the comparative steel in Comparative Examples 1-3.
  • the high-strength steel with excellent ductility in Examples 1-36 of this case guarantees its strength and has excellent ductility surface. Its yield strength is 550-850 MPa, and its tensile strength is 900-1100 MPa. The rate is ⁇ 13%, and the elongation at break is 18%-28%.
  • the microstructure of the high-strength steel with excellent ductility in Examples 1-36 of this case is 30% to 50% ferrite + 40% to 60% martensite + retained austenite
  • the grains below 10 ⁇ m account for more than 80%
  • the grains below 5 ⁇ m account for more than 50%
  • the average grain size of retained austenite is ⁇ 2 ⁇ m
  • retained austenite The average C content in the body is ⁇ 1.1wt%.
  • the high-strength steel with excellent ductility in each embodiment of this case has a certain amount of fine-grained ferrite and good microstructure uniformity, so that the high-strength steel of each embodiment can be used in high-strength steels. At the same time, it has excellent ductility.
  • Fig. 1 is a photo of the microstructure of the high-strength steel of Example 12.
  • Fig. 2 is an EBSD photograph of the phase composition of the high-strength steel of Example 12.
  • the microstructure of the high-strength steel of Example 12 is 30% to 50% ferrite + 40% to 60% martensite + retained austenite.
  • the grains below 10 ⁇ m account for more than 80%
  • the grains below 5 ⁇ m account for more than 50%
  • the average grain size of retained austenite is ⁇ 2 ⁇ m
  • the average C content in retained austenite is ⁇ 1.1 wt%.
  • the high-strength steel of the present invention is based on carbon-silicon-manganese steel without adding any expensive alloying elements. By optimizing the ratio of carbon-silicon-manganese, high-strength cold-rolled steel with excellent ductility is obtained. Steel plate.
  • the manufacturing method of the present invention has a simple production process, and the obtained high-strength steel can significantly increase its elongation under the same strength conditions. It will have a good application prospect in automobile safety structural parts, and is particularly suitable for manufacturing complex shapes, Vehicle structural parts and safety parts that require high formability, such as A/B pillars, longitudinal beams, door anti-collision bars, bumpers, etc.

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Abstract

Est ici décrit un acier à haute ténacité ayant une bonne ductilité, les éléments chimiques de celui-ci, en pourcentages en masse, étant : 0,15 à 0,25 % en poids de C, 1,00 à 2,00 % en poids de Si, 1,50 à 3,00 % en poids de Mn, et 0,03 à 0,06 % en poids d'Al, le reste étant du Fe et les inévitables impuretés. Est en outre décrit un procédé de fabrication de l'acier, le procédé comprenant les étapes suivantes : (1) fusion et coulée continue d'une ébauche de tôle mince, l'épaisseur d'une ébauche de tôle au niveau d'une extrémité de sortie de coulée continue étant contrôlée pour aller de 55 à 60 mm ; (2) chauffage ; (3) laminage à chaud, une calamine oxydée sur la surface d'une bande d'acier laminée à chaud ayant une épaisseur ≤ 5 μm, et la teneur en (FeO + Fe3O4) dans la calamine oxydée sur la surface la bande d'acier laminée à chaud étant ≤ 40 % en poids ; (4) décapage à l'acide ou décapage à l'acide et laminage à froid ; et (5) recuit continu.
PCT/CN2020/122085 2019-10-21 2020-10-20 Acier à haute ténacité ayant une bonne ductilité et son procédé de fabrication WO2021078111A1 (fr)

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