WO2013135098A1 - 一种薄带连铸700MPa级高强耐候钢制造方法 - Google Patents

一种薄带连铸700MPa级高强耐候钢制造方法 Download PDF

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WO2013135098A1
WO2013135098A1 PCT/CN2013/000154 CN2013000154W WO2013135098A1 WO 2013135098 A1 WO2013135098 A1 WO 2013135098A1 CN 2013000154 W CN2013000154 W CN 2013000154W WO 2013135098 A1 WO2013135098 A1 WO 2013135098A1
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strip
steel
hot rolling
strength
manufacturing
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PCT/CN2013/000154
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English (en)
French (fr)
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方园
王秀芳
于艳
吴建春
张丰
何伟
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宝山钢铁股份有限公司
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Priority to JP2014561267A priority Critical patent/JP5893770B2/ja
Priority to KR1020147024160A priority patent/KR20140117654A/ko
Priority to US14/372,678 priority patent/US9987669B2/en
Priority to DE112013000841.6T priority patent/DE112013000841B4/de
Publication of WO2013135098A1 publication Critical patent/WO2013135098A1/zh

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B1/24—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process
    • B21B1/26—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length in a continuous or semi-continuous process by hot-rolling, e.g. Steckel hot mill
    • 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
    • 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
    • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment 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
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0421—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the working steps
    • C21D8/0426—Hot rolling
    • 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
    • C21D9/52—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for wires; for strips ; for rods of unlimited length
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
    • 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
    • C22C38/12—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
    • C22C38/16—Ferrous alloys, e.g. steel alloys containing copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B21B2001/225—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length by hot-rolling
    • 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
    • B22D11/06—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars
    • B22D11/0622—Continuous casting of metals, i.e. casting in indefinite lengths into moulds with travelling walls, e.g. with rolls, plates, belts, caterpillars formed by two casting wheels
    • 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
    • C21D2211/002—Bainite
    • 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

Definitions

  • the invention relates to a thin strip continuous casting process, in particular to a method for manufacturing a 700 MPa high-strength weathering steel for thin strip continuous casting, the yield strength of the steel strip is ⁇ 700 MP a , the tensile strength is ⁇ 780 MPa, the elongation is ⁇ 18%, and the bending performance is 180°. Qualified, with a small, uniform hooked bainite and acicular ferrite structure, resulting in good strength and elongation matching. Background technique
  • Weathering steel or weather-resistant steel refers to a low-alloy structural steel with a protective rust layer that is resistant to atmospheric corrosion and can be used to manufacture steel structures such as vehicles, bridges, towers, and containers. Compared with plain carbon steel, weathering steel has better corrosion resistance in the atmosphere. Compared with stainless steel, weathering steel has only a small amount of alloying elements, such as phosphorus, copper, chromium, nickel, molybdenum, niobium, vanadium, titanium, etc., the total amount of alloying elements is only a few percent, not like stainless steel, reaching 100 More than a dozen, so the price is relatively low.
  • alloying elements such as phosphorus, copper, chromium, nickel, molybdenum, niobium, vanadium, titanium, etc.
  • 700MPa strength grade atmospheric corrosion resistant steels mostly use Nb, V, Ti, Mo composite microalloying technology, through fine grain strengthening. And precipitation strengthening to improve the overall mechanical properties of atmospheric corrosion resistant steel.
  • Chinese Patent No. 200610030713.8 discloses an atmospheric corrosion resistant steel with a yield strength of 700 MPa and a manufacturing method thereof.
  • the chemical composition of the method for producing an atmospheric corrosion resistant steel sheet is: C 0.05-0.1%, Si ⁇ 0, 5%, Mn 0.8-1.6% , P ⁇ 0.02%, S ⁇ 0.01%, Al 0.01-0.05%, Cr 0.4-0.8%, Ni 0.12-0.4%, Cu 0.2-0.55%, Ca 0.001-0.006%, N 0.001-0.006%, Containing at least two of Nb ⁇ 0.07%, Ti ⁇ 0.18%, Mo ⁇ 0.35%, the rest being Fe and unconfirmed Avoid impurities.
  • the yield strength of the steel plate is ⁇ 700 ⁇ ?, the tensile strength is ⁇ 750 MPa, and the elongation is ⁇ 15%.
  • Chinese patent 201010246778.2 discloses a non-tempered high-strength weathering steel with a low-cost yield strength of 700 MPa and a manufacturing method thereof.
  • the chemical composition of the method for manufacturing a weather-resistant steel sheet is: C 0.05-0.1%, Si ⁇ 0.15%, Mn 1.5-2 %, P ⁇ 0.015%, S ⁇ 0.01%, Cr 0.3-0.8%, Ni 0.15-0.4%, Cu 0.2-0.4%, Nb 0.02-0.08%, Ti ⁇ 0.09-0.15%, N ⁇ 0.005%, the remainder Fe and inevitable impurities.
  • the yield strength of the steel plate is ⁇ 700 MPa, the tensile strength is ⁇ 800 MPa, and the elongation is ⁇ 18%.
  • Chinese patent 200610125125.2 discloses an ultra-high strength atmospheric corrosion resistant steel.
  • the chemical composition of the method for producing an atmospheric corrosion resistant steel sheet is: C 0.01-0.07%, Si 0.25-0.5%, Mn 1.6-2, P ⁇ 0.018%, S ⁇ 0.008%, Al ⁇ 0.035%, Cr 0.4-0.75%, Ni 0.25-0.6%, Cu 0.2-0.5%, Nb 0.03-0.08%, Ti ⁇ 0.02%, Mo 0.1-0.4%, B 0.0005- 0.003, the rest For Fe and inevitable impurities.
  • the yield strength of the steel plate is ⁇ 700 MPa, the tensile strength is ⁇ 750 MPa, and the elongation is ⁇ 10%.
  • the above-mentioned 700MPa strength grade high-strength and atmospheric corrosion-resistant steel adopts a microalloying route, and contains Nb, V, Ti, Mo and other alloying elements in the component system, and both are produced by a conventional hot rolling process.
  • the traditional hot rolling process is: continuous casting + slab reheating + rough rolling + finishing rolling + cooling + coiling, that is, firstly, a slab having a thickness of about 200 mm is obtained by continuous casting, and the slab is reheated and kept warm. Then, rough rolling and finish rolling are performed to obtain a steel strip having a thickness of generally more than 2 mm, and finally the laminar cooling and coiling of the steel strip is completed to complete the entire hot rolling production process.
  • the atmospheric corrosion resistant steel contains a high content of easily segregated elements such as phosphorus and copper which improve the atmospheric corrosion resistance of the steel strip.
  • the traditional process is easy to cause macro segregation of elements such as phosphorus and copper due to the slow solidification cooling speed of the cast slab. As a result, the anisotropy of the slab and the occurrence of macroscopic cracks result in a low success rate.
  • the weather resistance of atmospheric corrosion resistant steel mainly depends on the interaction of phosphorus and copper. Due to its easy segregation characteristics in traditional processes, it is often not added in the design of components for producing high-strength and atmospheric corrosion-resistant steel by conventional techniques. Phosphorus, its content is controlled according to the level of impurity elements, usually ⁇ 0.025%; The amount of copper added is in the range of 0.2-0.55%, and the lower limit is usually taken in actual production. As a result, the weather resistance of the steel strip is not high.
  • the rolling temperature of finishing rolling is usually lower than 950 °C, and the finishing rolling temperature is 850 °.
  • rolling at a lower temperature coupled with an increase in the amount of deformation with the rolling process, leads to a significant increase in the strength of the steel strip, which also significantly increases the difficulty and consumption of hot rolling.
  • the thin slab continuous casting and rolling process is: continuous casting + slab insulation heat + hot rolling + cooling + coiling.
  • the main difference between this process and the traditional process is: The thickness of the slab in the thin slab process is greatly reduced, which is 50-90mm. Because the slab is thin, the slab is only roughed by 1-2 passes (the slab thickness is 70-90mm).
  • the continuous casting of the conventional process has to be repeatedly rolled to reduce the required specifications before finishing rolling; and the casting of the thin slab process
  • the billet is directly cooled into the soaking furnace for uniform heat preservation, or a small amount of temperature is not cooled. Therefore, the thin slab process greatly shortens the process flow, reduces energy consumption, reduces investment, and reduces production cost;
  • the solidification cooling speed of the slab is accelerated, which can reduce the macro segregation of the element to a certain extent, thereby reducing the product defects and improving the finished product rate. It is also because of this that the composition design of the micro-alloy high-strength and atmospheric corrosion-resistant steel is produced by the thin slab process.
  • the range of contents of the elements phosphorus and copper which improve the corrosion resistance is appropriately relaxed, which is advantageous for improving the weather resistance of the steel.
  • Chinese patent 200610123458.1 discloses a method for producing 700MPa grade high-strength weathering steel by Ti microalloying process based on thin slab continuous casting and rolling process.
  • the chemical composition of the method for manufacturing weathering steel sheet is: C 0.03-0.07%, Si 0.3-0.5 %, Mn 1.2-1.5, P ⁇ 0.04%, S ⁇ 0.008%, Al 0.025-0.05%, Cr 0.3-0.7%, Ni 0.15-0.35%, Cu 0.2-0.5%, Ti 0.08-0.14%, N ⁇ 0.008%, the balance being Fe and unavoidable impurities.
  • the yield strength of the steel plate is > 700 MPa
  • the tensile strength is ⁇ 775 MPa
  • the elongation is ⁇ 21%.
  • phosphorus is controlled according to the impurity element, the content is ⁇ 0.04%, which is relaxed compared with ⁇ 0.025% of the conventional process.
  • Chinese patent 200610035800.2 discloses a method for producing 700MPa grade VN microalloyed atmospheric corrosion resistant steel based on thin slab continuous casting and rolling process.
  • the chemical composition of the method for producing atmospheric corrosion resistant steel sheet is: C ⁇ 0.08%, Si 0.25-0.75 %, Mn 0.8-2, P ⁇ 0.07-0.15%, S ⁇ 0.04%, Cr 0.3-1.25%, Ni ⁇ 0.65%, Cu 0.25-0.6%, V 0.05-0.2%, N 0.015-0.03%, the remainder Fe and inevitable impurities.
  • the yield strength of the steel plate is ⁇ 700MPa, the tensile strength is ⁇ 785MPa, and the elongation is ⁇ 21%.
  • phosphorus is controlled according to elements that improve corrosion resistance, the content is 0.07-0.15%; the content of copper is 0.25-0.6%, and the lower and upper limits are respectively higher than the lower limit of 0.2% of the copper content of the conventional process and The upper limit is 0.55%.
  • the thin slab process has the above advantages in the production of microalloyed high-strength and atmospheric corrosion resistant steels, some problems in the conventional process production still exist in the thin slab process, for example: microalloying elements cannot be maintained during hot rolling.
  • the analysis of the generating part leads to an increase in the strength of the steel, thereby increasing the rolling load, increasing the energy consumption and the roll consumption, so that the thickness specification of the high-strength weathering steel hot-rolled product which can be economically and practically produced cannot be too thin, thickness For ⁇ 1.5 mm, see patents 200610123458.1, 200610035800.2 and 200710031548.2.
  • Thin strip continuous casting technology is a cutting-edge technology in the field of metallurgy and materials research. Its emergence has brought a revolution to the steel industry. It has changed the production process of steel strips in the traditional metallurgical industry, which will be continuously cast and rolled. Even the heat treatment is integrated into one, so that the thin strip produced by the hot strip is formed into a thin steel strip at one time, which greatly simplifies the production process and shortens the production cycle. The length of the process line is only about 50m. Equipment investment has also decreased, and product costs have decreased significantly.
  • the twin-roll strip casting process is one of the main forms of the thin strip continuous casting process, and it is also the only thin strip continuous casting process in the world that realizes industrialization.
  • the molten steel is introduced from the ladle through the long nozzle, the tundish and the immersion nozzle into a molten pool of a pair of relatively rotating and internally water-cooled crystallization rolls and side seals.
  • a solidified shell is formed on the roll surface, and the solidified shells are gathered together at the nip between the crystallizing rolls to form a cast strip which is pulled downward from the nip.
  • the casting belt is conveyed to the roller table by the swinging guide and the pinch roller, and then passed through the on-line hot rolling mill, spray cooling, flying shears to the coiler, and the production of the thin strip continuous casting product is completed.
  • Thin strip continuous casting eliminates the complicated process of slab heating, multi-pass repeated hot rolling, and direct hot rolling of the thin casting belt, and the production cost is greatly reduced.
  • the thickness of the cast strip for continuous casting of thin strip is usually l-5mm. It is hot rolled to the desired thickness of the product, usually l-3mm. The production of thin gauge products does not need to be cold rolled.
  • the low-carbon microalloyed steel is produced by the thin strip continuous casting process, and the alloying elements such as Nb, V, Ti, Mo, etc. are mainly in a solid solution state during the hot rolling process, so the strength of the steel strip is relatively low, thereby
  • the single-stand hot rolling reduction rate can be as high as 30-50%, and the steel strip thinning efficiency is high.
  • the thin strip continuous casting process produces low carbon microalloyed steel, and the high temperature cast strip is directly hot rolled.
  • the added alloying elements such as Nb, V, Ti, Mo are mainly in a solid solution state, which can improve the utilization ratio of the alloy. Therefore, the problem of precipitation of alloying elements during the cooling process of the conventional process slab is overcome, and the alloy element is not sufficiently remelted when the slab is reheated, thereby reducing the utilization factor of the alloy elements.
  • atmospheric corrosion resistant steel is a special type of product that requires better strong plasticity matching. Even for higher strength grades, it is required to have a high elongation at the same time, otherwise it is difficult to meet the forming process. Process requirements.
  • the products containing microalloying elements such as Nb, V, Ti, Wo, etc. produced by the strip casting process may retain the coarse austenite of the cast strip due to the inhibition of microalloying elements on the recrystallization of austenite after hot rolling.
  • the inhomogeneity of the bulk crystal grains, the final product structure obtained by the non-uniform coarse austenite transformation is also very uneven, resulting in a low elongation of the product.
  • the international patents WO 2008137898, WO 2008137899, WO 2008137900, and Chinese patents 200880023157.9, 200880023167.2, 200880023586.6 disclose a method of producing a microalloyed steel strip having a thickness of 0.3-3 mm by a strip casting process.
  • the chemical composition of the method is C ⁇ 0.25%, Mn 0.20-2.0%, Si 0.05-0.50%, Al ⁇ 0.01%, and further includes Nb 0.01-0.20%, V 0.01-0.20%, Mo 0.05-0.50% At least one of them.
  • the microstructure of the hot rolled strip is bainite + acicular ferrite.
  • the patent inhibits the recrystallization of austenite after hot rolling by adding alloying elements, maintains the austenite grain coarseness of thin strip continuous casting to improve the hardenability, and obtains the room temperature structure of bainite + acicular ferrite. .
  • the temperature range used for hot rolling is not given in the patent, but in the articles related to these patents (CR Killmore, etc. Development of Ultra-Thin Cast Strip Products by the CASTRIP® Process. AIS Tech, Indianapolis, Indiana, USA, May 7-10, 2007) reported a hot rolling temperature of 950. C.
  • the thin-belt continuous casting low-carbon microalloyed steel products produced by this method have high strength. Within the above composition system, the strength can reach 650 MPa and the tensile strength can reach 750 MPa, but the main problem is the product. The elongation is not high. The main reasons for the low elongation are:
  • the cast strip obtained by the strip casting process has a large austenite grain size and is very uneven, as small as several tens of micrometers, as large as seven or eight hundred micrometers or even millimeters. .
  • the hot rolling rate of the strip casting process usually does not exceed 50%, and the effect of refining the grains by deformation is very small.
  • the austenite grains are not refined by recrystallization, the coarse uneven austenite will not It is effectively improved after hot rolling, and the bainite + acicular ferrite structure produced by the coarse austenite transformation is also uneven, so the elongation is not high.
  • Cipheral Patent No. 02825466.X proposes another method for producing a microalloyed steel strip having a thickness of l-6 mm by a strip casting process.
  • the composition system of the microalloyed steel used in the method is C 0.02-0.20%, Mn 0.1-1.6%, Si 0.02-2.0%, Al ⁇ 0.05%, S ⁇ 0.03%, P ⁇ 0.1%, Cr 0.01-1.5%, Ni 0.01-0.5%, Mo ⁇ 0.5%, N 0.003-0.012%, Ti ⁇ 0.03%, V ⁇ 0.10%, Nb ⁇ 0.035%, B ⁇ 0.005%, the balance being Fe and unavoidable impurities.
  • the hot rolling of the cast strip is in the range of 1150-(Arl-100) ° ⁇ , corresponding to the austenite zone, the austenitic ferrite two-phase zone, or the ferrite zone for hot rolling, the hot rolling reduction rate is 15 -80%.
  • the in-line heating system is designed.
  • the heating temperature range is 670-1150 °C.
  • the purpose is to make the casting strip completely recrystallize after being heated for a period of time after hot rolling in different phase zones. Thereby the steel strip is better matched to the strong plasticity.
  • composition is 0.048%, Mn 0.73%, Si 0.28%, Cr 0.07%, Ni 0.07 %, Cu 0.18%, Ti 0.01%, Mo 0.02%, S 0.002%, P 0.008%, Al 0.005%, N 0.0065% steel strip yield strength is 260 MPa, tensile strength 365 MPa, elongation is 28%.
  • using this method for production requires an in-line heating system to be added during the design of the line, and because of the length of the heating, depending on the belt speed and the length of the furnace, the furnace must be of sufficient length to ensure uniform heating. This not only increases the investment cost, but also significantly increases the floor space of the strip casting and rolling line, which reduces the advantages of the line.
  • the object of the present invention is to provide a method for manufacturing a 700MPa grade high-strength weathering steel for thin strip continuous casting.
  • austenite on-line recrystallization after hot rolling of the cast strip can be realized without increasing production equipment.
  • Austenite grains and improved austenite grain size uniformity so that the product obtains a more uniform distribution of small-sized bainite and acicular ferrite structure, thereby having high strength and elongation.
  • a thin strip continuous casting method for manufacturing 700MPa grade high-strength weathering steel comprising the following steps:
  • the chemical composition weight percentage is: C 0.03-0.1%, Si ⁇ 0.4%, Mn 0.75-2.0%, P 0.07-0.22%, S ⁇ 0.01%, N ⁇ 0.012%, Cu 0.25-0.8%, and further, at least one of Nb, V, Ti, Mo, Nb 0.01-0.1%, V 0.01-0.1%, Ti 0.01-0.1%, Mo 0.1-0.5%, the balance being Fe and unavoidable impurities;
  • cooling the hot strip is 10-80 ° C / s;
  • the hot rolled strip is taken up, and the coiling temperature is 500-650 ° C ; the microstructure of the finally obtained steel strip is mainly composed of uniform bainite and acicular ferrite.
  • the content of Nb, V, and Ti is in the range of 0.01 to 0.05%, and the content of Mo is in the range of 0.1 to 0.25% by weight.
  • step 2) the casting belt cooling rate is greater than 30 ° C / s.
  • the hot rolling temperature is 1100-1250 ° C, or 1150-1250 ° (:.
  • step 3 the hot rolling reduction ratio is 30-50%.
  • step 4 the hot strip cooling rate is 30-80 ° C / s.
  • step 5 the coiling temperature is 500-600 °C.
  • microalloying elements bismuth, vanadium, titanium and molybdenum in low carbon steel plays a major role in two aspects:
  • the first is to exert its solid solution strengthening effect and improve the strength of the steel strip
  • the second is to drag the austenite grain boundary by the solute atoms to inhibit the austenite grain growth to a certain extent, thereby refining the austenite grains and promoting austenite recrystallization.
  • the finer the austenite grain size the higher the dislocation density generated during deformation, and the greater the deformation storage energy, thereby increasing the recrystallization driving force and promoting the recrystallization process; and the recrystallized core is mainly in the original large-angle grain boundary.
  • the finer the grain size the larger the grain boundary area
  • the easier the recrystallization nucleation thereby facilitating the recrystallization process.
  • Shape variable Control the hot rolling reduction ratio (shape variable) to promote austenite recrystallization in an appropriate range.
  • Deformation is the basis of recrystallization. It is the driving force of recrystallization. The source of deformation energy is stored. Since recrystallization must occur after a certain driving force has to be exceeded, recrystallization will occur only after a certain amount of deformation. The larger the deformation, the larger the deformation storage energy, and the larger the deformation storage energy, the greater the recrystallization nucleation and growth rate, and the recrystallization can be started and completed quickly enough even at lower temperatures. Moreover, the increase of the shape variable also reduces the grain size after austenite recrystallization, because the recrystallization nucleation rate increases exponentially with the increase of the deformation storage energy.
  • C is the most economical and basic strengthening element in steel. It enhances the strength of steel by solid solution strengthening and precipitation strengthening. C is an indispensable element for the precipitation of cementite during austenite transformation. Therefore, the level of C content largely determines the strength level of steel, that is, the higher C content corresponds to a higher strength level.
  • the solution solid solution and precipitation of C have a great hazard to the plasticity and toughness of steel, and the excessive C content is unfavorable for the splicing performance, the C content cannot be too high, and the strength of the steel is appropriately added by alloying elements. make up. Therefore, the C content used in the present invention ranges from 0.03 to 0.1%.
  • Si acts as a solid solution strengthening in steel, and the addition of Si to the steel improves the purity and deoxidation of the steel. However, if the Si content is too high, the weldability and the toughness of the weld heat affected zone deteriorate. Therefore, the Si content used in the present invention is in the range of ⁇ 0.4%.
  • Mn is one of the cheapest alloying elements. It can improve the hardenability of steel, has a considerable solid solubility in steel, and improves the strength of steel through solid solution strengthening. At the same time, the plasticity and toughness of steel are basically No damage, it is the most important strengthening element to increase the strength of steel under the condition of reducing C content. However, if the Mn content is too high, the weldability and the toughness of the heat affected zone are deteriorated. Therefore, the Mn content used in the present invention ranges from 0.75 to 2.0%.
  • P can significantly improve the atmospheric corrosion resistance of steel, and can significantly refine austenite grains.
  • high content of P tends to segregate at the grain boundary, increase the cold brittleness of the steel, deteriorate the splicing performance, reduce the plasticity, and deteriorate the cold bending performance. Therefore, in the atmospheric corrosion resistant steel produced by the conventional process, P is mostly used as an impurity. The element is controlled and the content is very low.
  • the solidification and cooling rate of the cast strip is extremely fast, which can effectively suppress the segregation of P, thereby effectively avoiding the disadvantage of P, giving full play to the advantages of P, thereby improving the atmospheric corrosion resistance of steel, and Refinement of austenite grains promotes austenite recrystallization. Therefore, in the present invention, the P content of the atmospheric corrosion resistant steel produced by a conventional process is higher, ranging from 0.07 to 0.22%.
  • S Under normal conditions, S is also a harmful element in steel, which causes hot brittleness of steel, reduces ductility and toughness of steel, and causes cracks during rolling. S also reduces weldability and corrosion resistance. Therefore, in the present invention, S is controlled as an impurity element, and its content is in the range of ⁇ 0.01%.
  • Cu is a key element for improving the atmospheric corrosion resistance of steel, and it is more effective in combination with P. Cu can also exert solid solution strengthening to increase the strength of steel, but has no weldability. negative effect. However, Cu is an easily segregated element and is liable to cause hot brittleness in hot working of steel. Therefore, in the atmospheric corrosion resistant steel produced by the conventional process, the Cu content generally does not exceed 0.6%.
  • the solidification and cooling rate of the cast strip is extremely fast, which can effectively inhibit the segregation of Cu, thereby effectively avoiding the disadvantage of Cu and giving full play to the advantages of Cu. Therefore, in the present invention, the C content of the atmospheric corrosion resistant steel produced by the conventional process is higher, and the range is 0.25-0.8%.
  • Nb is the strongest alloying element to inhibit austenite recrystallization after hot rolling.
  • Nb is generally added, one for strengthening, and the other is to suppress recrystallization of austenite after hot rolling to achieve the purpose of deforming and refining austenite grains.
  • Nb can effectively prevent the migration of the large-angle grain boundary and the sub-grain boundary by the solute atom drag mechanism and the precipitated second phase particle pinning mechanism of the carbonitride, thereby significantly preventing the recrystallization process, wherein the second phase particle The effect of preventing recrystallization is more pronounced.
  • the added alloying element Nb can be mainly present in the solid solution state in the steel strip, even if the steel strip is cooled to room temperature, it is almost observed. Less than the precipitation of Nb. Therefore, although the Nb element can effectively inhibit austenite recrystallization, it is very difficult to prevent recrystallization by merely acting on the solute atoms without exerting the second phase particle, for example, at a high deformation temperature. When the shape variable is large, even if Nb is added, austenite recrystallizes.
  • the Nb element dissolved in steel can drag the austenite grain boundary through the solute atom, and inhibit the austenite grain growth to a certain extent, thereby refining the austenite grain, from this point
  • Nb is advantageous for promoting recrystallization after austenitic hot rolling.
  • the invention not only needs to exert the solid solution strengthening effect of Nb to improve the strength of the steel, but also minimizes the inhibition effect of Nb on recrystallization, and the content thereof is designed to be 0.01-0.1%.
  • the Nb content ranges from 0.01 to 0.05%, and the steel strip can have a superior strength and plastic ratio.
  • V Of the four microalloying elements commonly used in Nb, V, Ti, and Mo, V has the weakest inhibitory effect on austenite recrystallization. In the recrystallization controlled rolling steel, V is usually added, which can not only strengthen the effect, but also suppress the recrystallization relatively small, and achieve the purpose of recrystallizing and refining the austenite grains.
  • V is also mainly present in the steel strip in a solid solution state, and even if the steel strip is cooled to room temperature, almost no precipitation of V is observed. Therefore, the inhibition of austenite recrystallization by element V The effect is very limited.
  • V is an ideal alloying element in the case where the solid solution strengthening action of the alloying element is used to increase the strength of the steel, and the alloying element is required to suppress the recrystallization, which is most in accordance with the concept of the present invention.
  • the V element dissolved in steel can drag the austenite grain boundary through the solute atom, and inhibit the austenite grain growth to a certain extent, thereby refining the austenite grain, from this point speak,
  • V is advantageous for promoting recrystallization after austenitic hot rolling.
  • the content of V in the present invention ranges from 0.01 to 0.1%.
  • the V content ranges from 0.01 to 0.05%, and the steel strip can have a superior strength and plastic ratio.
  • Ti Among the four microalloying elements commonly used in Nb, V, Ti and Mo, Ti has a lower inhibitory effect on austenite recrystallization than Nb, but higher than Mo and V. In this regard, Ti is disadvantageous in promoting austenite recrystallization. However, Ti has an outstanding advantage, its solid solubility is very low, it can form a relatively stable second phase point TiN of about lOnm at high temperature, which can prevent austenite grain coarsening during soaking. This serves to promote recrystallization. Therefore, in the recrystallization controlled rolling steel, a trace amount of Ti is usually added to refine austenite grains and promote austenite recrystallization.
  • Ti is mainly present in the solid steel strip in a solid solution state, and if the steel strip is cooled to room temperature, a little precipitation of Ti may be observed. Therefore, the inhibition of austenite recrystallization by Ti element is limited.
  • the Ti element dissolved in steel can drag the austenite grain boundary through the solute atom, inhibiting the austenite grain growth to a certain extent, thereby refining the austenite grain, from this point It is advantageous to promote recrystallization after austenitic hot rolling.
  • the invention not only needs to exert the strengthening effect of Ti to increase the strength of the steel, but also minimizes the inhibition effect of Ti on recrystallization, and the designed content ranges from 0.01 to 0.1%.
  • the Ti content ranges from 0.01 to 0.05%, and the steel strip can have a superior strength and plastic ratio.
  • Mo Among the four microalloying elements commonly used in Nb, V, Ti and Mo, the inhibition of austenite recrystallization by Mo is relatively weak, only higher than V.
  • Mo is also mainly present in the steel strip in a solid solution state, and even if the steel strip is cooled to room temperature, almost no precipitation of Mo is observed. Therefore, the inhibition of austenite recrystallization by Mo element is very limited.
  • the Mo element dissolved in steel can drag the austenite grain boundary through the solute atom, inhibiting the austenite grain growth to a certain extent, thereby refining the austenite grain, from this point speak, It is advantageous for promoting austenite recrystallization.
  • the present invention employs a Mo content ranging from 0.1 to 0.5%.
  • the Mo content ranges from 0.1 to 0.25%, and the steel strip can have a superior strength and plastic ratio.
  • the N element can increase the strength of the steel by the gap solid solution.
  • the gap solid solution of N has a great hazard to the plasticity and toughness of the steel, so the N content cannot be too high.
  • the N content used in the present invention is in the range of ⁇ 0.012%.
  • the strip casting that is, the molten steel is introduced into a molten pool formed by a pair of relatively rotating and internally water-cooled crystallization rolls and side seal plates, and after rapid solidification, a cast strip having a thickness of l-5 mm is directly cast.
  • the cast strip is cooled, and the cast strip is continuously cast from the crystallization roll, and then passed through a sealed chamber to be cooled in a sealed chamber.
  • the casting belt is cooled by air cooling, and the pressure, flow rate and gas nozzle position of the cooling gas can be adjusted and controlled.
  • the cooling gas may be an inert gas such as argon gas, nitrogen gas or helium gas, or a mixed gas of several gases.
  • the control of the cooling rate of the cast strip is achieved by controlling the type of cooling gas, pressure, flow rate, and the distance between the nozzle and the cast strip.
  • the cast strip is hot rolled on-line and the controlled rolling temperature is 1050-1250 °C.
  • the purpose is to achieve complete recrystallization of austenite after hot rolling and to refine austenite grains.
  • Nb, V, Ti, Mo microalloying elements are added.
  • the addition of alloying elements has a certain inhibitory effect on austenite recrystallization, although in the thin strip continuous casting process This inhibition is lowered, but hot rolling is performed at less than 1050 ° C, and it is difficult to completely recrystallize austenite.
  • hot rolling at a temperature higher than 1250 ° C makes the hot rolling process difficult to control due to the low strength of the strip.
  • the present invention selects a rolling temperature range of 1050-1250 °C.
  • the hot rolling temperature ranges from 1 100 to 1250 ° C, or from 1 150 to 1250 ° C.
  • the hot rolling reduction ratio is controlled to be 20-50%.
  • the increase in hot rolling reduction promotes austenite recrystallization and refines austenite grains.
  • the preferred hot rolling reduction ratio is 30-50%.
  • Controlling hot rolling deformation rate > 20s The increase in deformation rate promotes austenite recrystallization.
  • the preferred deformation rate range is > 30s—.
  • the thickness of the steel strip after hot rolling ranges from 0.5 to 3.0 mm.
  • the hot strip is cooled, and the hot strip is cooled by means of aerosol cooling, laminar cooling or spray cooling.
  • the flow rate of the cooling water, the flow rate, and the position of the water outlet can be adjusted to control the cooling rate of the hot strip. Control the cooling rate of the hot strip to 10-80 ° C / s, cooling hot rolling Bring to the required coiling temperature.
  • the cooling rate is one of the important factors affecting the actual starting temperature of the austenite transformation. The higher the cooling rate, the lower the actual starting temperature of the austenite transformation, and the smaller the microstructure size obtained after the phase transformation. It is advantageous to improve the toughness of the steel strip, and the preferred cooling rate ranges from 30 to 80 ° C / s.
  • the hot rolled strip is taken up, and the coiling temperature of the hot rolled strip is controlled to be 500-650 ° C so that the hot rolled strip has the structural characteristics of bainite plus acicular ferrite.
  • the coiling temperature ranges from 500 to 600 °C.
  • the most fundamental difference between the present invention and the aforementioned prior patents is that the austenite on-line recrystallization after hot rolling is controlled by using different composition ranges and process routes to produce a small and uniform bainite plus needle shape.
  • the weathering steel strip of the ferrite structure thus has good strength and elongation matching.
  • the invention adopts the thin strip continuous casting process to exert the characteristics of short process, low energy consumption, high efficiency, simple process, etc., and greatly reduces the production cost of the microalloy high-strength and thin gauge weather-resistant steel with a thickness of 0.5-3 mm. .
  • the invention effectively suppresses the segregation of P and Cu by adopting the thin strip continuous casting process and the cooling rate control of the casting strip, and the upper limit of the Cu content of the microalloy high-strength and atmospheric corrosion resistant steel is 0.55% of the conventional process and the thin slab
  • the 0.6% of the process is increased to 0.8%
  • the upper limit of the P content is increased from 0.02% of the conventional process and 0.15% of the thin slab process to 0.22%.
  • the present invention is improved by?
  • the Cu content improves the atmospheric corrosion resistance of the steel, and the precious metals Cr and Ni are not added, further reducing the production cost.
  • the invention realizes the austenite on-line recrystallization after hot rolling by controlling the amount of microalloying elements added, the hot rolling temperature, the hot rolling reduction rate and the hot rolling deformation rate, so that the steel strip obtains uniform bainite and acicular ferrite. Body tissue with good strong plasticity matching.
  • the chemical composition design of the present invention contains P and Cu to improve the atmospheric corrosion resistance of the steel. In essence, it corresponds to the production of different steel grades.
  • Chinese patent 02825466.X controls the recrystallization of austenite after hot rolling by increasing on-line heating System implemented.
  • the present invention controls the recrystallization of austenite after hot rolling by controlling the amount of microalloying elements added, the hot rolling temperature, the hot rolling reduction ratio, and the hot rolling deformation rate.
  • the chemical composition design of the present invention contains P and Cu, which are substantially corresponding to the production of different steel grades.
  • the invention has the beneficial effects - the reasonable composition design in the production process of the strip casting, the reasonable cooling rate control of the casting belt, the reasonable hot rolling temperature, the hot rolling reduction rate, the hot rolling deformation rate design, without increasing
  • the austenite is recrystallized after hot rolling of the cast strip containing microalloying elements, and an atmospheric corrosion resistant steel strip with uniform bainite and acicular ferrite structure is produced, which has good strength. Matches the elongation.
  • Figure 1 is a schematic view of the process of thin strip continuous casting. detailed description
  • the molten steel in the bale 1 is poured through the long nozzle 2, the tundish 3 and the submerged nozzle 4 into two relatively rotating water-cooling crystallization rolls 5a, 5b and
  • the molten pool 7 formed by the side sealing plates 6a, 6b is cooled by a water-cooling crystallization roll to form a l-5 mm cast strip 1 1, and the cast strip is controlled by a secondary cooling device 8 in the closed chamber 10 to control the cooling rate thereof, and the oscillating guide is passed.
  • the pinch roll 12 feeds the cast strip to the hot rolling mill 13, and after hot rolling, forms a hot rolled strip of 0.5-3 mm, passes through the cooling device 14 three times, and then the hot rolled strip enters the coiler 15. After the steel coil was removed from the coiler, it was naturally cooled to room temperature.
  • the molten steel of the embodiment of the present invention is obtained by smelting in an electric furnace, and the specific chemical composition is shown in Table 1.
  • Table 1 The thickness of the cast strip obtained after continuous casting of the strip, the rate of casting strip, the hot rolling temperature, the hot rolling reduction ratio, the hot rolling deformation rate, the thickness of the hot rolled strip, the cooling rate of the hot strip, the coiling temperature, and the like, and The tensile properties and bending properties of the hot rolled strip after cooling to room temperature are shown in Table 2.
  • the yield strength of the steel strip of the present invention is ⁇ 700 MPa, and the tensile strength ⁇ 780MPa, elongation ⁇ 18%, 180° bending performance, excellent excellent plasticity matching.
  • Table 1 Chemical composition of molten steel in the examples (wt.%)

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Abstract

一种薄带连铸700MPa级髙强耐候钢制造方法，其包括如下步骤：1）在双辊连铸机中铸造厚度为1-5mm的铸带，其化学成分重量百分比为：C 0.03-0.1%，Si≤0.4%，Mn0.75-2.0%，P 0.07-0.22%，S≤0.01%，N≤0.012%，Cu 0.25-0.8%，此外，还包含Nb、V、Ti、Mo中一种以上，Nb 0.01-0.1%，V 0.01-0.1%，Ti 0.01-0.1%，Mo 0.1-0.5%，其余为Fe和不可避免杂质；2）对铸带进行冷却，冷却速率大于20℃/s； 3）对铸带进行热轧，热轧温度1050-1250℃；压下率为20-50%，形变速率>20s-1；热轧后发生奥氏体在线再结晶，热轧带厚度为0.5-3.0mm； 4）冷却，冷却速率为10-80℃/s；5）卷取，卷取温度500-650℃。获得的钢带显微组织主要由分布均匀的贝氏体和针状铁素体构成。

Description

一种薄带连铸 700MPa级髙强耐候钢制造方法
技术领域
本发明涉及薄带连铸工艺， 特别涉及一种薄带连铸 700MPa级高强耐 候钢制造方法， 钢带的屈服强度≥700MPa， 抗拉强度≥780MPa， 延伸率≥ 18%, 180°弯曲性能合格， 具有尺寸细小的、 均勾的贝氏体加针状铁素体 组织， 从而具有良好的强度和延伸率匹配。 背景技术
耐候钢或称耐大气腐蚀钢， 是指具有保护锈层耐大气腐蚀， 可用于制 造车辆、 桥梁、 塔架、 集装箱等钢结构的低合金结构钢。 与普碳钢相比， 耐候钢在大气中具有更优良的抗蚀性能。 与不锈钢相比， 耐候钢只有微量 的合金元素， 诸如磷、 铜、 铬、 镍、 钼、 铌、 钒、 钛等， 合金元素总量仅 占百分之几， 而不像不锈钢那样， 达到百分之十几， 因此价格较为低廉。
近年来使用较多的耐大气腐蚀钢有 295MPa级的 09CuPTiRE、345MPa 级的 09CuPCrNi以及 450MPa级的 Q450NQR1。随着国民经济的发展对车 辆减重、 提速、 增加货运量、 延长使用寿命和降低物流成本等方面的要求 不断提高， 上述钢种很难满足要求， 开发高强度、 高耐蚀性、 低成本的耐 大气腐蚀钢具有重要的实用价值和经济意义。
目前国内外已就高强度耐大气腐蚀钢及其制造方法申请了多项专利， 其中 700MPa强度级别的耐大气腐蚀钢， 大都采用 Nb、 V、 Ti、 Mo复合 微合金化技术， 通过细晶强化和沉淀强化来提高耐大气腐蚀钢的综合力学 性能。
中国专利 200610030713.8公开了一种屈服强度 700MPa级耐大气腐蚀 钢及其制造方法，该方法制造耐大气腐蚀钢板的化学成分为： C 0.05-0.1%, Si < 0,5%， Mn 0.8-1.6%, P≤ 0.02%, S < 0.01%, Al 0.01-0.05%, Cr 0.4-0.8%, Ni 0.12-0.4%, Cu0.2-0.55%, Ca 0.001-0.006%, N 0.001-0.006%, 此外还 包含 Nb≤ 0.07%， Ti< 0.18%, Mo≤ 0.35%中至少两种， 其余为 Fe和不可 确认本 避免的杂质。 钢板的屈服强度≥ 700^ ? ， 抗拉强度≥750 MPa， 延伸率≥ 15%。
中国专利 201010246778.2公开了一种低成本屈服强度 700MPa级非调 质处理高强耐候钢及其制造方法， 该方法制造耐候钢板的化学成分为： C 0.05-0.1%, Si < 0.15%, Mn 1.5-2%, P < 0.015%, S < 0.01%, Cr 0.3-0.8%, Ni 0.15-0.4%, Cu 0.2-0.4%, Nb 0.02-0.08%, Ti< 0.09-0.15%, N < 0.005%, 其余为 Fe和不可避免的杂质。 钢板的屈服强度 ≥ 700MPa, 抗拉强度 ≥ 800MPa, 延伸率 ≥ 18%。
中国专利 200610125125.2公开了一种特高强度耐大气腐蚀钢，该方法 制造耐大气腐蚀钢板的化学成分为： C 0.01-0.07%, Si 0.25-0.5%, Mn 1.6-2, P < 0.018%, S < 0.008%, Al < 0.035%, Cr 0.4-0.75%, Ni 0.25-0.6%, Cu 0.2-0.5%, Nb 0.03-0.08%, Ti < 0.02%, Mo 0.1-0.4%, B 0.0005- 0.003， 其 余为 Fe 和不可避免的杂质。 钢板的屈服强度 ≥ 700MPa, 抗拉强度 ≥ 750MPa， 延伸率 ≥ 10%。
上述 700MPa强度级别的高强耐大气腐蚀钢，均采用了微合金化路线， 在成分体系中均含有 Nb， V， Ti, Mo等合金元素， 并且均采用传统热轧 工艺生产。 传统热轧工艺流程是： 连铸 +铸坯再加热保温 +粗轧 +精轧 + 冷却 +卷取， 即首先通过连铸得到厚度为 200mm左右的铸坯， 对铸坯进 行再加热并保温后， 再进行粗轧和精轧， 得到厚度一般大于 2mm的钢带， 最后对钢带进行层流冷却和卷取， 完成整个热轧生产过程。 如果要生产厚 度小于 2mm 的钢带， 一般要对热轧钢带继续进行冷轧以及后续退火来完 成。 利用传统工艺生产微合金高强耐大气腐蚀钢， 存在的主要问题有：
( 1 ) 工艺流程长、 能耗高、 机组设备多、 基建成本高， 导致生产成 本高。
( 2 )耐大气腐蚀钢中含有较高含量的提高钢带耐大气腐蚀性能的磷、 铜等易偏析元素， 传统工艺由于铸坯凝固冷却速度慢， 容易造成磷、 铜等 元素的宏观偏析，从而导致铸坯的各向异性和出现宏观裂紋，成才率较低。
( 3 ) 耐大气腐蚀钢的耐侯性主要取决于磷和铜的共同作用， 由于其 在传统工艺中存在易偏析特征， 因此在利用传统工艺生产高强耐大气腐蚀 钢的成分设计中， 往往不添加磷， 其含量按照杂质元素水平来控制， 通常 < 0.025%； 铜的添加量在 0.2-0.55%的范围， 实际生产中通常取下限。其结 果造成钢带的耐侯性不高。
( 4)传统工艺中， 由于微合金元素在热轧过程中不能保持为固溶体， 发生部分析出， 导致钢材强度提高， 因此会显著增加轧制载荷， 增加能耗 和辊耗， 对装备的损伤较大， 从而就限制了可经济地和实际地生产髙强耐 候钢热轧产品的厚度范围，通常是≥2mm。对传统热轧产品继续进行冷轧， 可进一步降低钢带厚度， 然而热轧钢带的高强度导致冷轧也存在困难。 一 是高的冷轧载荷对装备的要求较高， 损伤较大； 二是热轧产品中由合金元 素析出的第二相， 使冷轧后钢带的再结晶退火温度显著增加。
( 5 ) 传统工艺中， 生产含有微合金元素的高强产品时， 通常是利用 形变细化奥氏体晶粒原理， 因此精轧的开轧温度通常低于 950°C， 终轧温 度在 850°C左右， 在较低温度下进行轧制， 再加上随轧制过程进行形变量 的增加， 会导致钢带强度显著增加， 这也会显著增加热轧难度和消耗。
如果采用薄板坯连铸连轧工艺生产微合金高强耐候钢，可在一定程度 上克服传统工艺的缺点。 薄板坯连铸连轧工艺流程是： 连铸 +铸坯保温均 热 +热连轧 +冷却 +卷取。 该工艺与传统工艺的主要区别是： 薄板坯工艺 的铸坯厚度大大减薄， 为 50-90mm， 由于铸坯薄， 铸坯只要经过 1-2道次 粗轧（铸坯厚度为 70-90mm时）或者不需要经过粗轧（铸坯厚度为 50mm 时） ， 而传统工艺的连铸坯要经过反复多道次轧制， 才能减薄到精轧前所 需规格；而且薄板坯工艺的铸坯不经冷却，直接进入均热炉进行均热保温， 或者少量补温， 因此薄板坯工艺大大缩短了工艺流程， 降低了能耗， 减少 了投资，从而降低了生产成本；另外薄板坯工艺的铸坯凝固冷却速度加快， 可在一定程度上减少元素宏观偏析，从而减少了产品缺陷，提高了成材率， 也正是因为这点， 利用薄板坯工艺生产微合金高强耐大气腐蚀钢的成分设 计适当放宽了提高耐腐蚀性的元素磷、 铜的含量范围， 这对于提高钢的耐 候性能是有利的。
中国专利 200610123458.1 公开了一种基于薄板坯连铸连轧流程采用 Ti微合金化工艺生产 700MPa级高强耐候钢的方法， 该方法制造耐候钢板 的化学成分为： C 0.03-0.07%, Si 0.3-0.5%, Mn 1.2-1.5 , P < 0.04%, S < 0.008%, Al 0.025-0.05%, Cr 0.3-0.7%, Ni 0.15-0.35%, Cu 0.2-0.5%, Ti 0.08-0.14%, N < 0.008%, 其余为 Fe和不可避免的杂质。 钢板的屈服强度 > 700MPa, 抗拉强度 ≥ 775MPa， 延伸率 ≥21%。 在该专利中， 磷是按照 杂质元素来控制的， 含量≤ 0.04%， 较传统工艺的≤ 0.025%， 有所放宽。
中国专利 200610035800.2 公开了一种基于薄板坯连铸连轧工艺生产 700MPa级 V-N微合金化耐大气腐蚀钢的方法， 该方法制造耐大气腐蚀钢 板的化学成分为： C < 0.08%, Si 0.25-0.75%, Mn 0.8-2 , P < 0.07-0.15%, S ≤ 0.04%, Cr 0.3-1.25%, Ni <0.65%, Cu 0.25-0.6%, V 0.05-0.2%, N 0.015-0.03%, 其余为 Fe和不可避免的杂质。 钢板的屈服强度 ≥ 700MPa， 抗拉强度 ≥ 785MPa， 延伸率 ≥21 %。 在该专利中， 磷是按照提高耐腐蚀 性的元素来控制的， 含量为 0.07-0.15%; 铜的含量为 0.25-0.6%， 其下限 和上限分别高于传统工艺的铜含量下限 0.2%和上限 0.55%。
虽然薄板坯工艺在生产微合金高强耐大气腐蚀钢上存在如上优势，但 传统工艺生产中存在的某些问题， 在薄板坯工艺中仍然存在， 例如： 微合 金元素在热轧过程中也不能保持为固溶体， 发生部分析出， 导致钢材强度 提高， 从而增加轧制载荷， 增加能耗和辊耗， 使得可经济地和实际地生产 高强耐候钢热轧产品的厚度规格也不可能太薄， 厚度为≥1.5mm， 见专利 200610123458.1 , 200610035800.2以及 200710031548.2。
薄带连铸技术是冶金及材料研究领域内的一项前沿技术， 它的出现为 钢铁工业带来一场革命， 它改变了传统治金工业中钢带的生产过程， 将连 续铸造、 轧制、 甚至热处理等整合为一体， 使生产的薄带坯经过一道次在 线热轧就一次性形成薄钢带， 大大简化了生产工序， 縮短了生产周期， 其 工艺线长度仅 50m左右。 设备投资也相应减少， 产品成本显著降低。
双辊薄带连铸工艺是薄带连铸工艺的一种主要形式， 也是世界上唯一 实现产业化的一种薄带连铸工艺。 在双辊薄带连铸过程中， 镕融钢水从钢 包经过长水口、 中间包和浸入式水口， 被引入到一对相对旋转且内部水冷 的结晶辊和侧封板形成的熔池之内， 在移动的辊面上形成凝固壳， 凝固壳 在结晶辊之间的辊隙处聚集在一起， 形成从辊隙向下拉出的铸带。 之后通 过摆动导板、 夹送辊将铸带输送至辊道， 再经过在线热轧机， 喷淋冷却， 飞剪直至卷取机， 完成薄带连铸产品的生产。
利用薄带连铸技术生产微合金高强耐大气腐蚀钢， 迄今为止尚未见报 导， 其可能存在的优点如下：
( 1 ) 薄带连铸省去了板坯加热、 多道次反复热轧等复杂过程， 对薄 铸带直接进行一道次在线热轧， 生产成本大幅降低。
( 2 ) 薄带连铸的铸带厚度通常在 l-5mm， 通过在线热轧至期望产品 厚度， 通常在 l-3mm， 薄规格产品的生产不需要经过冷轧。
( 3 ) 薄带连铸工艺生产低碳微合金钢， 所添加的 Nb、 V、 Ti、 Mo 等合金元素， 在热轧过程中主要以固溶态存在， 因此钢带强度相对较低， 从而使单机架热轧压下率可高达 30-50%， 钢带减薄效率高。
( 4 ) 薄带连铸工艺生产低碳微合金钢， 高温铸带直接热轧， 所添加 的 Nb、 V、 Ti、 Mo等合金元素主要以固溶态存在， 可提高合金利用率。 从而克服传统工艺板坯冷却过程中发生合金元素析出， 板坯再加热时合金 元素回溶不充分而降低合金元素利用率的问题。
但是， 耐大气腐蚀钢是一类比较特殊的产品， 要求其具有较好的强塑 性匹配， 即使是对于较高强度级别的产品， 也要求其同时具有较高的延伸 率， 否则难以满足成形加工工艺的要求。 而利用薄带连铸工艺生产的含有 Nb、 V、 Ti、 Wo 等微合金元素的产品， 可能由于微合金元素对热轧后奥 氏体再结晶的抑制作用， 而保留其铸带粗大奥氏体晶粒的不均匀性， 由这 种不均匀的粗大奥氏体相变后所获得的最终产品组织也很不均匀， 从而导 致产品的延伸率不高。
国际专利 WO 2008137898、 WO 2008137899、 WO 2008137900, 以及 中国专利 200880023157.9、 200880023167.2、 200880023586.6公开了一种 利用薄带连铸连轧工艺生产厚度在 0.3-3mm的微合金钢薄带的方法。该方 法采用的化学成分为 C < 0.25%, Mn 0.20-2.0%, Si 0.05-0.50%, Al < 0.01%, 此外， 还包含 Nb 0.01-0.20%， V 0.01-0.20%, Mo 0.05-0.50%中至少一种。 在热轧压下率为 20-40%， 卷取温度≤700 工艺条件下， 热轧带的显微组 织为贝氏体 +针状铁素体。 该专利通过添加合金元素抑制奥氏体热轧后发 生再结晶， 保持薄带连铸奥氏体晶粒粗大特征以提高淬透性， 从而获得了 贝氏体 +针状铁素体的室温组织。在专利中没有给出热轧所采用的温度范 围， 但在与这些专利相关的文章中 ( C.R. Killmore, etc. Development of Ultra-Thin Cast Strip Products by the CASTRIP® Process. AIS Tech, Indianapolis, Indiana, USA, May 7-10, 2007) ， 报导了所采用的热轧温度为 950。C。
利用这种方法生产的薄带连铸低碳微合金钢产品， 强度较高， 在以上 成分体系范围内， 威服强度可达到 650MPa， 抗拉强度可达到 750MPa， 但 最主要的问题是产品的延伸率不高。 导致延伸率不高主要原因是： 通过薄 带连铸工艺获得的铸带， 奥氏体晶粒尺寸粗大， 且非常不均勾， 小到几十 微米， 大到七八百微米甚至毫米量级。 而薄带连铸工艺热轧压卜率通常不 超过 50%， 通过形变细化晶粒的效果非常小， 如果不通过再结晶细化奥氏 体晶粒， 粗大的不均匀奥氏体不会在热轧后得到有效改善， 由尺寸粗大的 不均匀奥氏体相变后产生的贝氏体 +针状铁素体组织也很不均勾， 因此延 伸率不高。
为了改善薄带连铸微合金钢的强塑性匹配， 中国专利 02825466.X提 出了另外一种利用薄带连铸连轧工艺生产厚度在 l-6mm 的微合金钢薄带 的方法。该方法所采用的微合金钢成分体系为 C 0.02-0.20%, Mn 0.1-1.6%, Si 0.02-2.0%, Al < 0.05%, S < 0.03%, P < 0.1%, Cr 0.01-1.5%, Ni 0.01-0.5%, Mo < 0.5%, N 0.003-0.012%, Ti <0.03%, V <0.10%, Nb <0.035%, B <0.005%, 其余为 Fe和不可避免的杂质。 铸带的热轧在 1150- ( Arl-100) °〇范围内， 对应奥氏体区， 奧氏体铁素体两相区， 或者铁素体区进行热轧， 热轧压下率为 15-80%。 该方法在薄带连铸连轧机组后， 设计了在线加热 系统， 加热温度范围是 670-1150°C，目的是使得铸带在不同相区热轧后， 保温一段时间后发生完全再结晶， 从而使钢带获得较好的强塑性匹配。
利用这种方法来生产薄带连铸低碳微合金钢产品， 的确可以使钢带获 得良好的强塑性匹配， 例如成分为 C 0.048%, Mn 0.73%, Si 0.28%, Cr 0.07%, Ni 0.07%, Cu 0.18%, Ti 0.01%, Mo 0.02%, S 0.002%, P 0.008%, Al 0.005%, N 0.0065%的钢带屈服强度为 260MPa， 抗拉强度 365MPa， 延 伸率为 28%。 但利用这种方法进行生产， 需要在产线设计时增加在线加热 系统， 而且由于加热时间的长短， 取决于带速和加热炉长度， 加热炉必须 有足够长度， 才能保证加热均匀性。 这不仅增加了投资成本， 也会显著增 加薄带连铸连轧产线的占地面积， 降低了该产线的优势。
综上所述， 利用薄带连铸工艺生产具有较好的强塑性匹配的微合金高 强耐大气腐蚀钢， 由于铸带厚度薄， 不能通过形变方式细化奥氏体晶粒， 至关重要的是如何通过再结晶细化奥氏体晶粒， 使产品获得细小均勾的显 微组织， 从而具有较好的强塑性匹配。 发明内容
本发明的目的在于提供一种薄带连铸 700MPa 级高强耐候钢制造方 法， 通过合理的成分和工艺设计， 在不增加生产装备情况下， 实现铸带热 轧后奥氏体在线再结晶， 细化奧氏体晶粒并改善奥氏体晶粒尺寸均勾性， 使产品获得分布更加均匀的尺寸细小的贝氏体加针状铁素体组织， 从而同 时具有较高的强度和延伸率。
为达到 h述目的， 本发明的技术方案是：
一种薄带连铸 700MPa级高强耐候钢制造方法， 其包括如下步骤：
1) 在双辊连铸机中铸造厚度为 l-5mm的铸带，其化学成分重量百分比 为： C 0.03-0.1%, Si≤ 0.4%, Mn 0.75-2.0%, P 0.07-0.22%, S < 0.01%, N < 0.012%, Cu 0.25-0.8%, 此外， 还包含 Nb、 V、 Ti、 Mo中至少 一种， Nb 0.01-0.1%, V 0.01-0.1%, Ti 0.01-0.1%, Mo 0.1-0.5%, 其 余为 Fe和不可避免的杂质；
2) 对铸带进行冷却， 冷却速率大于 20°C/s;
3) 对铸带进行热轧， 热轧温度 1050-1250°C， 压下率 20-50%， 形变速 率> 20 ； 热轧后钢带的厚度为 0.5-3.0mm; 钢带热轧后发生奥氏体 在线再结晶；
4) 对热轧带进行冷却， 冷却速率为 10- 80°C/s;
5) 对热轧带进行卷取， 卷取温度 500- 650°C ; 最终获得钢带的显微组 织主要由均匀的贝氏体和针状铁素体构成。
进一步， 步骤 1 ) 中， Nb、 V、 Ti 的含量范围均为 0.01-0.05%， Mo 的含量范围为 0.1-0.25%， 以重量百分比计。
步骤 2 ) 中， 铸带冷却速率大于 30°C/s。
步骤 3 ) 中， 热轧温度为 1100-1250°C， 或为 1150-1250° (：。
步骤 3 ) 中， 热轧压下率为 30-50%。 步骤 4) 中， 热轧带冷却速率为 30-80°C/s。
步骤 5 ) 中， 卷取温度为 500- 600°C。
本发明的技术构思如下：
( 1 ) 在低碳钢中适量添加微合金元素铌、 钒、 钛、 钼， 主要发挥两 方面作用：
其一是发挥其固溶强化作用， 提高钢带强度；
其二是通过溶质原子拖曳奥氏体晶界， 在一定程度上抑制奥氏体晶粒 长大，从而细化奥氏体晶粒，促进奥氏体再结晶。奥氏体晶粒尺寸越细小， 形变时产生的位错密度越高， 形变储存能将越大， 从而增大再结晶驱动力 而促进再结晶过程的进行； 而且再结晶核心主要在原大角晶界处或其附近 形核的， 因此晶粒尺寸越细 （晶界面积越大） ， 再结晶形核越容易， 从而 促进再结晶过程的进行。
( 2 ) 利用薄带连铸工艺中铸带的快速凝固和快速冷却特性， 并适当 控制铸带的冷却速率， 可有效控制磷、 铜的偏析， 从而实现在低碳钢中添 加较高含量的提高钢带耐大气腐蚀性能的磷、 铜元素。
( 3 ) 适当提高在奥氏体区的热轧温度 （形变再结晶温度） ， 促进奥 氏体再结晶。 再结晶形核率和长大速率均随形变温度的升高而呈指数型关 系的增长 （雍岐龙著， 微合金钢一物理和力学冶金） ， 温度越髙， 越容易 发生再结晶。
( 4) 控制热轧压下率 （形变量） 在合适的范围内， 促进奥氏体再结 晶。形变是发生再结晶的基础，是再结晶的驱动力一一形变储存能的来源， 由于必须超过一定的驱动力之后才会发生再结晶， 故只有超过一定的形变 量之后才会发生再结晶。 形变量越大， 形变储存能越大， 而形变储存能越 大， 再结晶形核和长大速率均越大， 即使在较低温度下也能足够迅速地开 始和完成再结晶。 而且， 形变量增大， 还会减小奥氏体再结晶后的晶粒尺 寸， 这是因为再结晶形核率随形变储存能的升高而呈指数型关系的增长
(雍岐龙著， 微合金钢一物理和力学冶金） ， 因此有利于获得更加细小的 奥氏体相变的产物， 对提高钢带的强塑性都是有利的。
( 5 ) 控制形变速率在合适的范围内， 促进奥氏体再结晶。 增大形变 速率， 将增大形变储存能， 从而增大再结晶驱动力， 促进再结晶过程的进 行。
在本发明的化学成分设计中：
C: C 是钢中最经济、 最基本的强化元素， 通过固溶强化和析出强化 来提高钢的强度。 C是奥氏体转变过程中析出渗碳体必不可少的元素， 因 此 C含量的高低在很大程度上决定钢的强度级别，即较高的 C含量对应较 高的强度级别。但是， 由于 C的间隙固溶和析出对钢的塑性和韧性有较大 危害， 而且， 过高的 C含量对悍接性能不利， 因此 C含量不能过高， 钢的 强度通过适当添加合金元素来弥补。 故本发明采用的 C 含量范围是 0.03-0.1%。
Si: Si在钢中起固溶强化作用，且钢中加 Si能提高钢质纯净度和脱氧， 但 Si 含量过高会导致可焊性和焊接热影响区韧性恶化。 故本发明采用的 Si含量范围是 ≤0.4%。
Mn: Mn是价格最便宜的合金元素之一， 它能提高钢的淬透性， 在钢 中具有相当大的固溶度， 通过固溶强化提高钢的强度， 同时对钢的塑性和 韧性基本无损害， 是在降低 C 含量情况下提高钢的强度最主要的强化元 素。 但 Mn含量过高会导致可焊性和悍接热影响区韧性恶化。 故本发明采 用的 Mn含量范围是 0.75-2.0%。
P: P可显著提高钢的耐大气腐蚀性能， 并且能显著细化奥氏体晶粒。 但高含量的 P容易在晶界偏析， 增加钢的冷脆性， 使悍接性能变坏， 降低 塑性， 使冷弯性能变坏 因此目前在传统工艺生产的耐大气腐蚀钢中， P 大多作为杂质元素来控制， 含量很低。
在薄带连铸工艺中， 铸带的凝固和冷却速率极快， 可有效抑制 P的偏 析， 从而可有效避免 P的劣势， 充分发挥 P的优势， 从而提高钢的耐大气 腐蚀性能， 并通过细化奥氏体晶粒促进奥氏体再结晶。 故在本发明中， 采 用较传统工艺生产的耐大气腐蚀钢更高的 P含量， 范围是 0.07-0.22%。
S: 在通常情况下 S也是钢中有害元素， 使钢产生热脆性， 降低钢的 延展性和韧性， 在轧制时造成裂纹。 S还会降低焊接性能和耐腐蚀性。 故 在本发明中， S是作为杂质元素来控制， 其含量范围是 ≤0.01%。
Cu: Cu是提高钢的耐大气腐蚀性能的关键元素， 与 P配合使用效果 更为显著。 Cu 还能发挥固溶强化作用提高钢的强度， 而对焊接性能没有 不利的影响。 但 Cu是易偏析元素， 容易引起钢材热加工时的热脆。 因此 目前在传统工艺生产的耐大气腐蚀钢中， Cu含量一般不超过 0.6%。
在薄带连铸工艺中， 铸带的凝固和冷却速率极快， 可有效抑制 Cu的 偏析， 从而可有效避免 Cu的劣势， 充分发挥 Cu的优势。 故在本发明中， 采用较传统工艺生产的耐大气腐蚀钢更高的 C含量， 范围是 0.25-0.8%。
Nb: 在常用的 Nb、 V、 Ti、 Mo 四种微合金元素中， Nb是最强的抑 制热轧后奥氏体再结晶的合金元素。 在传统控制轧制用的微合金钢中， 一 般都添加 Nb， 一是起到强化的作用， 二是抑制热轧后奥氏体发生再结晶， 实现形变细化奥氏体晶粒的目的。 Nb 可通过溶质原子拖曳机制， 以及所 析出的碳氮化铌第二相质点钉扎机制而有效地阻止大角晶界及亚晶界的 迁移， 从而显著地阻止再结晶过程， 其中第二相质点阻止再结晶的作用更 为显著。
在薄带连铸丁艺中， 由于其独特的钢带快速凝固和快速冷却特性， 可 以使添加的合金元素 Nb主要以固溶态存在于钢带中， 即使钢带冷却到室 温， 也几乎观察不到 Nb的析出。 因此， 尽管 Nb元素可有效地抑制奥氏 体再结晶， 但仅靠溶质原子而不发挥第二相质点的作用来阻止再结晶， 在 很多情况下是非常困难的， 例如在形变温度较高、 形变量较大的情况下， 即使添加 Nb元素， 奥氏体也会发生再结晶。
另一方面， 固溶于钢中的 Nb元素， 可通过溶质原子拖曳奥氏体晶界， 在一定程度上抑制奥氏体晶粒长大，从而细化奥氏体晶粒，从这一点上讲， Nb对于促进奥氏体热轧后再结晶是有利的。
本发明既要发挥 Nb的固溶强化作用提高钢的强度，又要尽量降低 Nb 对再结晶的抑制作用， 设计其含量范围是 0.01-0.1%。 优选的， Nb的含量 范围是 0.01-0.05%， 钢带可具有更优的强度和塑性配比。
V： 在常用的 Nb、 V、 Ti、 Mo 四种微合金元素中， V对奥氏体再结 晶的抑制作用最弱。 在再结晶控轧钢中， 通常是添加 V， 既可以起到强化 作用， 同时对再结晶的抑制作用相对来说又比较小， 实现再结晶细化奥氏 体晶粒的目的。
在薄带连铸工艺中， V也主要以固溶态存在于钢带中， 即使钢带冷却 到室温， 也几乎观察不到 V的析出。 因此， V元素对奥氏体再结晶的抑制 作用非常有限。 在既要发挥合金元素的固溶强化作用提高钢的强度， 又要 降低合金元素对再结晶抑制作用的情况下， V是比较理想的合金元素， 最 为符合本发明的构思。
另一方面， 固溶于钢中的 V元素， 可通过溶质原子拖曳奥氏体晶界， 在一定程度上抑制奥氏体晶粒长大，从而细化奥氏体晶粒，从这一点上讲，
V对于促进奥氏体热轧后再结晶是有利的。
本发明采用 V 的含量范围是 0.01-0.1%。 优选的， V 的含量范围是 0.01-0.05%, 钢带可具有更优的强度和塑性配比。
Ti: 在常用的 Nb、 V、 Ti、 Mo四种微合金元素中， Ti对奥氏体再结 晶的抑制作用次于 Nb， 但高于 Mo、 V。 从这一点上讲， Ti对促进奥氏体 再结晶是不利的。 但 Ti 有一个突出的优点， 它的固溶度很低， 它可以在 高温下形成相当稳定的尺寸约为 lOnm左右的第二相质点 TiN， 可阻止均 热时奥氏体晶粒粗化， 由此起到促进再结晶的作用。 因此， 在再结晶控轧 钢中， 通常添加微量 Ti， 细化奥氏体晶粒， 促进奥氏体再结晶。
在薄带连铸工艺中， Ti主要以固溶态存在于热态钢带中， 如果钢带冷 却到室温， 可能观察到少许 Ti的析出。 因此， Ti元素对奥氏体再结晶的 抑制作用是有限的。
另一方面， 固溶于钢中的 Ti元素， 可通过溶质原子拖曳奥氏体晶界， 在一定程度上抑制奥氏体晶粒长大，从而细化奥氏体晶粒，从这一点上讲， 对于促进奥氏体热轧后再结晶是有利的。
本发明既要发挥 Ti的强化作用提高钢的强度， 又要尽量降低 Ti对再 结晶的抑制作用， 设计其含量范围是 0.01-0.1%。 优选的， Ti 的含量范围 是 0.01-0.05%， 钢带可具有更优的强度和塑性配比。
Mo: 在常用的 Nb、 V、 Ti、 Mo四种微合金元素中， Mo对奥氏体再 结晶的抑制作用相对来说也是较弱的， 仅高于 V。
在薄带连铸工艺中， Mo也主要以固溶态存在于钢带中， _即使钢带冷 却到室温， 也几乎观察不到 Mo的析出。 因此， Mo元素对奥氏体再结晶 的抑制作用非常有限。
另一方面， 固溶于钢中的 Mo元素，可通过溶质原子拖曳奥氏体晶界， 在一定程度上抑制奥氏体晶粒长大，从而细化奥氏体晶粒，从这一点上讲， 对于促进奥氏体再结晶是有利的。
本发明采用 Mo的含量范围是 0.1 -0.5%。 优选的， Mo的含量范围是 0.1-0.25%, 钢带可具有更优的强度和塑性配比。
N: 与 C元素类似， N元素可通过间隙固溶提高钢的强度， 但是， N 的间隙固溶对钢的塑性和韧性有较大危害， 因此 N含量不能过高。本发明 采用的 N含量范围是 ≤ 0.012%。
在本发明制造工艺中：
薄带连铸， 即钢水被引入到一对相对旋转且内部水冷的结晶辊和侧封 板形成的熔池之内， 经过快速凝固后直接浇铸出厚度为 l-5mm的铸带。
铸带冷却， 铸带从结晶辊连铸出来后， 经过密闭室， 在密闭室内进行 冷却。 为了快速降低铸带温度， 以防止奥氏体晶粒在高温下长大过快， 更 重要的是控制 P、 Cu的偏析， 控制铸带的冷却速率大于 20°C/s， 优选的冷 却速率是大于 30°C/s。 铸带冷却采用气冷方式， 冷却气体的压力、 流量和 气喷嘴位置可以调节和控制。 冷却气体可以是氩气、 氮气、 氦气等惰性气 体， 或者是几种气体的混和气体。通过控制冷却气体的类型、压力、流量， 以及喷嘴到铸带之间的距离等， 实现对铸带冷却速率的控制。
铸带在线热轧， 控制轧制温度为 1050-1250°C， 目的是实现热轧后奥 氏体发生完全再结晶， 细化奥氏体晶粒。 在本发明的化学成分设计中， 添 加了 Nb、 V、 Ti、 Mo微合金元素， 如前所述， 合金元素的添加对奥氏体 再结晶有一定的抑制作用， 尽管在薄带连铸工艺下这种抑制作用会降低， 但在低于 1050°C下进行热轧， 很难发生奥氏体完全再结晶。 而在高于 1250°C下进行热轧， 由于带钢强度低， 使得热轧过程很难控制。 因此本发 明选择 1050-1250°C轧制温度范围。优选的，热轧温度范围是 1 100-1250°C， 或者是 1 150-1250°C。 控制热轧压下率为 20-50%， 热轧压下量增加会促进 奥氏体再结晶， 细化奥氏体晶粒， 优选的热轧压下率范围是 30-50%。 控 制热轧形变速率 > 20s— 形变速率增加会促进奥氏体再结晶，优选的形变 速率范围是 > 30s— '。 热轧后钢带的厚度范围是 0.5-3.0mm。
热轧带冷却， 采用气雾冷却、 层流冷却或者喷淋冷却等方式对热轧带 进行冷却。 冷却水的流量、 流速， 以及出水口位置等可以调节， 从而实现 对热轧带冷却速率的控制。控制热轧带的冷却速率为 10-80°C/s， 冷却热轧 带到所需要的卷取温度。 冷却速率是影响奥氏体相变实际开始温度的重要 因素之一， 冷却速率越大， 奥氏体相变实际开始温度越低， 这样相变后所 获得的组织晶粒尺寸也就越细小， 对提高钢带的强韧性都是有利的， 优选 的冷却速率范围是 30-80°C /s。
热轧带卷取， 控制热轧带的卷取温度为 500-650°C， 以使热轧带具有 贝氏体加针状铁素体的组织特征。 优选的， 卷取温度范围是 500-600°C。
本发明与前述现有专利的最根本不同在于，采用不同的成分范围和工 艺技术路线，控制实现热轧后奥氏体在线再结晶，生产出具有尺寸细小的、 均匀的贝氏体加针状铁素体组织的耐候钢带， 从而具有良好的强度和延伸 率匹配。
与现有利用传统工艺和薄板坯工艺制造高强耐大气腐蚀钢的专利相 比， 本发明的优点在于：
( 1 ) 本发明通过采用薄带连铸工艺， 发挥其流程短、 能耗低、 效率 高、 工艺简单等特点， 大幅度降低 0.5-3mm厚度的微合金高强薄规格耐大 气腐蚀钢的生产成本。
( 2 ) 本发明通过采用薄带连铸工艺， 并配合铸带冷却速率控制， 有 效抑制 P、 Cu的偏析， 将微合金高强耐大气腐蚀钢 Cu含量的上限由传统 工艺的 0.55%和薄板坯工艺的 0.6%提高到 0.8%， 将 P含量的上限由传统 工艺的 0.02%和薄板坯工艺的 0.15%提高到 0.22%。
( 3 ) 本发明通过提高？、 Cu含量来提高钢的耐大气腐蚀性能， 没有 添加贵金属 Cr、 Ni， 进一步降低生产成本。
与现有利用薄带连铸工艺生产微合金高强钢的中国专利 200880023157.9、 200880023167.2 , 200880023586.6 相比， 本发明的不同 之处在于： 中国专利 200880023157.9. 200880023167.2、 200880023586.6 通过添加微合金元素抑制奥氏体热轧后的再结晶， 使钢带获得贝氏体加针 状铁素体组织， 由尺寸粗大的不均匀奥氏体相变后产生的贝氏体 +针状铁 素体组织也很不均匀， 因此延伸率较低。 本发明通过控制微合金元素添加 量、 热轧温度、 热轧压下率、 热轧形变速率， 实现热轧后奥氏体在线再结 晶，使钢带获得均匀的贝氏体加针状铁素体组织，具有良好的强塑性匹配。 另外， 本发明化学成分设计中含有 P、 Cu, 以提髙钢的耐大气腐蚀性能， 实质上是对应不同钢种的生产。
与现有利用薄带连铸工艺生产微合金钢的中国专利 02825466.X相比， 本发明的不同之处在于： 中国专利 02825466.X控制热轧后奥氏体发生再 结晶是通过增加在线加热系统实现的。 本发明控制热轧后奥氏体发生再结 晶是通过控制微合金元素添加量、 热轧温度、 热轧压下率、 热轧形变速率 实现的。 另外， 本发明化学成分设计中含有 P、 Cu, 实质上是对应不同钢 种的生产。
本发明的有益效果- 本发明通过薄带连铸生产过程中合理的成分设计， 合理的铸带冷却速 率控制， 合理的热轧温度、 热轧压下率、 热轧形变速率设计， 在不增加生 产装备情况下， 控制实现含有微合金元素的铸带热轧后奥氏体在线再结 晶， 生产出具有均匀的贝氏体加针状铁素体组织的耐大气腐蚀钢带， 具有 良好的强度和延伸率匹配。 附图说明
图 1为薄带连铸工艺过程示意图。 具体实施方式
参见图 1， 本发明的薄带连铸工艺过程， 大包 1中的钢水经过长水口 2、 中间包 3和浸入式水口 4， 浇入到由两个相对旋转的水冷结晶辊 5a、 5b和侧封板 6a、 6b形成的熔池 7内， 经过水冷结晶辊的冷却形成 l-5mm 铸带 1 1， 铸带经过在密闭室 10内的二次冷却装置 8控制其冷却速率， 通 过摆动导板 9、 夹送辊 12将铸带送至热轧机 13， 热轧后形成 0.5-3mm的 热轧带， 再经三次冷却装置 14， 之后热轧带进入卷取机 15。 将钢卷从卷 取机上取下后， 自然冷却至室温。
本发明实施例的钢水均釆用电炉冶炼得到，具体化学成分如表 1所示。 薄带连铸后得到的铸带厚度， 铸带 却速率， 热轧温度， 热轧压下率， 热 轧形变速率， 热轧带厚度， 热轧带冷却速率， 卷取温度等工艺参数， 以及 热轧带冷却到室温后的拉伸性能和弯曲性能见表 2。
从表 2 可以看出， 本发明钢带的屈服强度≥ 700MPa , 抗拉强度≥ 780MPa, 延伸率≥ 18%， 180°弯曲性能合格， 具有优良的强塑性匹配。 表 1 实施例的钢水化学成分 （wt.% )
Figure imgf000017_0001
表 2 实施例的工艺参数及产品性能
铸带 热轧 热轧 热轧 热轧带
实 铸带 热轧 卷取 屈服 抗拉 延伸 180°弯曲 冷却 压下 形变 带厚 冷却
施 厚度 温度 温度 强度 强度 弯心直径 速率 率 速率 度 速率
例 mm 。C MPa MPa % a=带厚
"C/s % S"1 mm 。C/s
1 4.5 25 1236 35 33 2.9 79 500 735 813 1 8 合格
2 1 .1 30 1098 50 46 0.6 23 618 708 788 22 合格
3 3.3 36 1057 25 38 2.5 25 600 712 789 21 合格
4 2.2 24 1212 35 40 1.4 36 580 716 798 21 合格
5 2.8 28 1 168 40 35 1 .7 14 650 703 782 23 合格
6 2.4 24 1245 30 28 1.7 52 535 722 806 20 合格
7 5.0 23 1250 48 3 1 2.6 43 630 710 790 19 合格
8 1.0 42 1 150 50 76 0.5 32 640 715 803 20 合格

Claims

1. 一种薄带连铸 700MPa级高强耐候钢制造方法， 其包括如下步骤：
1) 在双辊连铸机中铸造厚度为 l-5mm的铸带，其化学成分重量百分比 为： C 0.03-0.1%, Si < 0.4%, Mn 0.75-2.0%, P 0.07-0.22%, S < 0.01%, N < 0.012%, Cu 0.25-0.8%, 此外， 还包含 Nb、 V、 Ti、 Mo中至少 —种， Nb 0.01-0.1%, V 0.01-0.1%, Ti 0.01-0.1%, Mo 0.1-0.5%, 其 余为 Fe和不可避免的杂质；
2) 对铸带进行冷却， 冷却速率大于 20°C/s;
3) 对铸带进行热轧， 热轧温度 1050-1250°C， 压下率 20-50%， 形变速 率〉 。 ； 热轧后钢带的厚度为 0.5-3.0mm; 钢带热轧后发生奥氏体 在线再结晶；
4) 对热轧带进行冷却， 冷却速率为 10-80°C/s;
5) 对热轧带进行卷取， 卷取温度为 500-650°C ;
最终获得钢带的显微组织主要由分布均匀的贝氏体和针状铁素体构 成。
2. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法，其特征 是： 所述步骤 1 ) 中， Nb、 V、 Ti的含量范围均为 0.01-0.05%， 以重量 百分比计。
3. 如权利要求 1或 2所述的薄带连铸 700MPa级高强耐候钢制造方法，其 特征是： 所述步骤 1 ) 中， Mo的含量为 0.1- 0.25%， 以重量百分比计。
4. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法，其特征 是： 所述步骤 2 ) 中， 铸带冷却速率大于 30°C/s。
5. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法，其特征 是： 所述步骤 3 ) 中， 热轧温度为 1 100-1250°C。
6. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法，其特征 是： 所述步骤 3 ) 中， 热轧温度为 1 150-1250°C。
7. 如权利要求 1或 5所述的薄带连铸 700MPa级高强耐候钢制造方法，其 特征是： 所述步骤 3 ) 中， 热轧压下率为 30-50%。
8. 如权利要求 1或 5或 7所述的薄带连铸 700MPa级高强耐候钢制造方法， 其特征是： 所述步骤 3 ) 中， 热轧形变速率 > 30s—
9. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法，其特征 是： 所述步骤 4 ) 中， 热轧带冷却速率为 30-80°C/s。
10.如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法，其特征 是： 所述步骤 5 ) 中， 卷取温度为 500-600° (：。
1 1. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法， 其特 征是： 所述钢带的厚度小于 3mm。
12. 如权利要求 1所述的薄带连铸 700MPa级高强耐候钢制造方法， 其特 征是： 所述钢带的厚度小于 2mm。
13. 如权利要求 1所述的薄带连铸 700MPa级髙强耐候钢制造方法， 其特 征是： 所述钢带的厚度小于 l mm。
14. 如权利要求 1或 1 1所述的薄带连铸 700MPa级高强耐候钢制造方法， 其特征是：所述钢带的屈服强度至少为 700MPa、抗拉强度至少为 780MPa、 延伸率至少为 18%。
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