WO2021052426A1 - 一种薄规格高耐蚀钢及其生产方法 - Google Patents

一种薄规格高耐蚀钢及其生产方法 Download PDF

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WO2021052426A1
WO2021052426A1 PCT/CN2020/115953 CN2020115953W WO2021052426A1 WO 2021052426 A1 WO2021052426 A1 WO 2021052426A1 CN 2020115953 W CN2020115953 W CN 2020115953W WO 2021052426 A1 WO2021052426 A1 WO 2021052426A1
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steel
strip
corrosion
thin
rolling
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PCT/CN2020/115953
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French (fr)
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吴建春
方园
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宝山钢铁股份有限公司
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Priority to JP2022517465A priority Critical patent/JP7395719B2/ja
Priority to DE112020004425.4T priority patent/DE112020004425T5/de
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    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
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    • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • 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
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    • C21D2211/00—Microstructure comprising significant phases
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Definitions

  • the invention belongs to a high corrosion resistant steel product, and specifically relates to a thin gauge high corrosion resistant steel and a production method thereof.
  • tin (Sn) and copper (Cu) are typical residual elements or harmful elements in steel. It is very difficult and very expensive to fully remove Sn and Cu during the steelmaking process. Once the steel contains Sn , Cu, basically can not be completely eliminated, only by diluting molten steel to reduce the content of Sn, Cu, these all cause the increase in the smelting cost of steel products.
  • Traditional thin strip steel is mostly produced by continuous rolling of cast billets with a thickness of 70-200mm through multiple passes.
  • the traditional hot rolling process is: continuous casting + billet reheating and heat preservation + rough rolling + finishing rolling + cooling + Coiling, that is, firstly obtain a cast slab with a thickness of about 200mm through continuous casting. After reheating and holding the cast slab, rough rolling and finishing rolling are performed to obtain a steel strip with a thickness generally greater than 2mm, and finally the steel strip is processed Laminar cooling and coiling complete the entire hot rolling production process. If you want to produce steel strips with a thickness of less than 1.5mm (inclusive), the difficulty is relatively large, and the hot-rolled steel strips are usually subjected to subsequent cold rolling and annealing to complete. In addition, the long process flow, high energy consumption, many units and equipment, and high capital construction costs result in high production costs.
  • the thin slab continuous casting and rolling process is: continuous casting + slab heat preservation and soaking + hot continuous rolling + cooling + coiling.
  • the main difference between this process and the traditional process is that the thickness of the cast slab in the thin slab process is greatly reduced to 50-90mm. Because the cast slab is thin, the cast slab only needs to undergo 1 to 2 passes of rough rolling (the thickness of the cast slab is 70-90mm When the thickness of the cast slab is 50mm, the thickness of the continuous casting slab in the traditional process must be repeatedly rolled to reduce the thickness to the required specifications before the finishing rolling; and the thin slab casting process Without cooling, the billet directly enters the soaking furnace for soaking and heat preservation, or a small amount of temperature compensation, so the thin slab process greatly shortens the process flow, reduces energy consumption, reduces investment, and reduces production costs.
  • ESP all-headless thin slab continuous casting and rolling process
  • the flame cutting of slab and the heating furnace for heat preservation and soaking and slab transition are eliminated, and the length of the entire production line is greatly shortened to about 190 meters.
  • the thickness of the slab casted by the continuous casting machine is 90-110mm, and the width is 1100-1600mm.
  • the continuous casting slab passes through a section of induction heating roller table to keep the slab warm and soak, and then enters the rough rolling one by one. , Finish rolling, layer cooling, and coiling processes to obtain hot-rolled plates.
  • this process can obtain the thinnest hot-rolled plate with a thickness of 0.8mm, which expands the specification range of the hot-rolled plate.
  • its single production line output can reach 2.2 million tons/year.
  • the process has been rapidly developed and promoted.
  • the shorter process flow than thin slab continuous casting and rolling is the thin strip continuous casting and rolling process.
  • the thin strip continuous casting technology is a cutting-edge technology in the field of metallurgy and materials research. Its appearance has brought a revolution to the steel industry. It changes the production process of steel strip in the traditional metallurgical industry, integrating continuous casting, rolling, and even heat treatment into a whole, so that the produced thin strip will be formed into thin steel strip at one time after one online hot rolling.
  • the production process is simplified and the production cycle is shortened.
  • the length of the process line is only about 50m; the equipment investment is also reduced, and the product cost is significantly reduced. It is a low-carbon and environmentally friendly hot-rolled thin strip production process.
  • the twin-roll thin strip continuous casting process is a main form of the thin strip continuous casting process, and it is also the world's only industrialized thin strip continuous casting process.
  • the typical process flow of twin-roll thin strip continuous casting is shown in Figure 1.
  • the molten steel in the ladle 1 is directly poured into one by two through the ladle nozzle 2, the tundish 3, the immersion nozzle 4 and the distributor 5
  • the molten steel solidifies on the rotating circumferential surfaces of the crystallizing rollers 8a, 8b to form a solidified shell and gradually grow, and then the two A 1-5mm thick cast strip 11 is formed at the smallest gap (nip point) of the crystallizing roll.
  • the cast strip is fed into the rolling mill 13 through the guide plate 9 and guided to the pinch roll 12 to be rolled into a thin strip of 0.7-2.5mm, and then passed through the cooling device 14 is cooled, after being cut by the flying shear device 16, it is finally sent to the coiler 19 to be wound into a roll.
  • Thin-gauge high corrosion resistance steel is increasingly used in some areas that require high corrosion resistance, such as the transformation of green leather cars in the train manufacturing industry.
  • the market for the transformation of green leather cars is very large.
  • the corrosion resistance of steel puts forward more stringent requirements, which requires the corrosion resistance of steel to be doubled on the basis of traditional atmospheric corrosion resistant steel.
  • stainless steel should not be used, considering that the product requires good bending and forming properties; product thickness specification: 1.0-2.0mm.
  • the present invention proposes that the use of thin strip continuous casting technology to produce this kind of high corrosion resistance steel has certain advantages.
  • the successful development of this thin gauge high corrosion resistance steel product will give the train manufacturing industry a lighter, greener, It offers broad prospects in terms of reducing energy consumption and high corrosion resistance comparable to stainless steel.
  • Thin strip continuous casting is used to produce thin-gauge high corrosion-resistant steel. Due to the thinner thickness, the thin strip continuous casting process has strong manufacturing and cost advantages.
  • the specifications and characteristic thicknesses of the products supplied with high corrosion resistant steel after post-treatment are 1.0mm, 1.1mm, 1.2mm, 1.25mm, 1.4mm, 1.5mm, 1.6mm, 1.8mm and 2.0mm, etc. Due to the thinner product thickness, If it is difficult to use the traditional continuous casting + hot continuous rolling production line to produce, it is generally produced by the hot continuous rolling process and then cold rolling. This production process increases the production cost of thin gauge high corrosion resistant steel. .
  • thin strip continuous casting due to its own rapid solidification process characteristics, thin strip continuous casting generally has the problems of uneven structure, low elongation, high yield ratio, and poor formability.
  • the cast strip has austenite crystals. The grains have obvious non-uniformity, which will cause the final product structure obtained after austenite transformation to be uneven, resulting in unstable product properties, especially forming properties. Therefore, the use of thin strip continuous casting production lines to produce high corrosion-resistant steel products also has certain difficulties and challenges, and requires breakthroughs in composition and technology.
  • the above-mentioned high-strength corrosion-resistant steels all adopt the microalloying route, and all contain Nb, V, Ti, Mo and other alloying elements in the composition system, and they are all produced by the traditional hot rolling process.
  • the traditional hot rolling process is: continuous casting + billet reheating and heat preservation + rough rolling + finishing rolling + cooling + coiling, that is, first a cast billet with a thickness of about 200mm is obtained through continuous casting, and then the billet is reheated and insulated Then, rough rolling and finishing rolling are performed to obtain a steel strip with a thickness generally greater than 2mm. Finally, the steel strip is laminar cooling and coiling to complete the entire hot rolling production process.
  • Corrosion-resistant steel contains a relatively high content of easily segregated elements such as copper, which improves the corrosion resistance of the steel strip.
  • the traditional process is likely to cause macro-segregation of copper and other elements due to the slow solidification and cooling rate of the cast slab, resulting in various Anisotropy and macroscopic cracks appear, and the yield rate is low.
  • Corrosion-resistant steel has the characteristics of easy segregation in the traditional process, so in the composition design of the traditional process to produce high-strength corrosion-resistant steel, the amount of copper added is in the range of 0.2-0.55%, and the lower limit is usually taken in actual production. , The amount of chromium added is in the range of 0.2-1.25, which is generally low. As a result, the corrosion resistance of the steel strip is not high.
  • the thin slab continuous casting and rolling process is: continuous casting + slab heat preservation and soaking + hot continuous rolling + cooling + coiling.
  • the main difference between this process and the traditional process is that the thickness of the cast slab in the thin slab process is greatly reduced to 50-90mm.
  • the cast slab is thin, the cast slab only needs to undergo 1 to 2 passes of rough rolling (the thickness of the cast slab is 70-90mm When the thickness of the cast slab is 50mm, the thickness of the continuous casting slab in the traditional process must be repeatedly rolled to reduce the thickness to the required specifications before the finish rolling; and the thin slab casting process is not necessary to go through rough rolling (when the thickness of the cast slab is 50mm). Without cooling, the slab directly enters the soaking furnace for soaking and heat preservation, or a small amount of temperature compensation.
  • the thin slab process greatly shortens the process flow, reduces energy consumption, reduces investment, and reduces production costs; in addition, the thin slab process
  • the speed of solidification and cooling of the cast slab is accelerated, which can reduce the macro-segregation of elements to a certain extent, thereby reducing product defects and increasing the yield. It is precisely because of this that the composition of the microalloy high-strength corrosion-resistant steel produced by the thin slab process is appropriately designed
  • the content range of phosphorus and copper, which are the elements to improve corrosion resistance, is relaxed, which is beneficial for improving the corrosion resistance of steel.
  • Chinese patent CN200610123458.1 discloses a method for producing 700MPa grade high-strength corrosion-resistant steel based on thin slab continuous casting and rolling process using Ti microalloying process.
  • the chemical composition of the method for manufacturing corrosion-resistant steel plate 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 is Fe and unavoidable impurities.
  • the yield strength of the steel plate is ⁇ 700MPa, the tensile strength is ⁇ 775MPa, and the elongation is ⁇ 21%.
  • phosphorus is controlled in accordance with impurity elements, and the content is less than or equal to 0.04%, which is more relaxed than the traditional process of less than or equal to 0.025%.
  • Chinese patent CN200610035800.2 discloses a method for producing 700MPa grade VN microalloyed corrosion-resistant steel based on the thin slab continuous casting and rolling process.
  • the chemical composition of the corrosion-resistant steel plate produced by the method 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 balance is Fe and unavoidable impurities.
  • the yield strength of the steel plate is ⁇ 700MPa, the tensile strength is ⁇ 785MPa, and the elongation is ⁇ 21%.
  • phosphorus is controlled in accordance with the elements that improve corrosion resistance, with a content of 0.07-0.15%; the content of copper is 0.25-0.6%, and its lower limit and upper limit are respectively higher than the lower limit of 0.2% and the lower limit of copper content in the traditional process.
  • the upper limit is 0.55%.
  • the thin slab process has the above advantages in the production of microalloyed high-strength corrosion-resistant steel, some problems in the traditional process still exist in the thin slab process.
  • the microalloying elements cannot be maintained during the hot rolling process.
  • the solid solution, analyzed by the generating part leads to an increase in the strength of the steel, thereby increasing the rolling load, increasing energy consumption and roll consumption, so that the thickness specifications of the high-strength corrosion-resistant steel hot-rolled products can be economically and practically produced, and the thickness specifications are not too thin. ⁇ 1.5mm, see Chinese patents CN200610123458.1, CN200610035800.2 and CN200710031548.2.
  • Chinese patent CN1633509A mentions a method for producing copper-containing carbon steel products produced by thin strip continuous casting.
  • the patent emphasizes the need to perform annealing, tempering and other heat treatment processes for this strip steel in the range of 400-700°C to make the copper element in the Precipitation or recrystallization in the strip.
  • trace element B is added to the composition of the present invention, and the content of Cr is obviously increased, which has obvious distinguishing characteristics, and at the same time, the subsequent treatment process is completely different.
  • the manufacturing method of high-copper low-alloy thin strip mentioned in the US patent US2008264525/CN200580009354.1 has the technical feature of cooling the strip steel in a non-oxidizing atmosphere to below 1080°C before entering the rolling mill In order to prevent the occurrence of "hot brittleness" of the strip.
  • trace element B is added in the present invention, and the content of Cr is obviously increased, and the subsequent processing method of the strip steel after the strip is taken out is also different.
  • the microstructure of the hot-rolled strip is bainite + acicular ferrite.
  • the patent believes that the alloying elements mainly in the solid solution state in the cast strip inhibit the recrystallization of austenite after hot rolling. Even if the reduction rate reaches 40%, the recrystallization of austenite is very limited.
  • the hot rolling reduction rate of 20-40% does not recrystallize the austenite, the hardenability of the coarse austenite can be maintained after hot rolling, so as to obtain the room temperature of bainite + acicular ferrite organization.
  • the temperature range used for hot rolling is not given in the patent, but in articles related to these patents (CRKillmore, etc. Development of Ultra-Thin Cast Strip Products by the Process. AIS Tech, Indianapolis, Indiana, USA, May 7-10, 2007), reported that the hot rolling temperature used was 950°C.
  • the thin strip continuous casting low-carbon microalloy steel products produced by this method have high strength.
  • the yield strength can reach 650MPa and the tensile strength can reach 750MPa, but the main problem is the extension of the product.
  • the rate is not high ( ⁇ 6% or ⁇ 10%).
  • the main reason for the low elongation is that the austenite grain size of the cast strip obtained through the thin strip continuous casting process is not uniform, ranging from tens of microns to 700 to 800 microns.
  • After the thin strip continuous casting process generally only 1-2 stand rolling mills, its hot rolling reduction rate is usually difficult to exceed 50%, and the effect of grain refinement through deformation is very small.
  • austenite is not refined through recrystallization It is difficult to effectively improve the structure of bulk grains and uneven austenite after hot rolling.
  • the structure of bainite + acicular ferrite produced by the transformation of austenite with uneven size is also very uneven, so The elongation is not high.
  • Cisar Patent 02825466.X proposes another method for producing microalloyed steel thin strip with a thickness of 1-6mm by using the thin strip continuous casting and rolling process.
  • the composition system of the microalloy steel used in this 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 to 1.5%, Ni: 0.01 to 0.5%, Mo: ⁇ 0.5%, N: 0.003 to 0.012%, the balance is Fe and unavoidable impurities.
  • the hot rolling of the cast strip is in the range of 1150-(Ar1-100)°C, 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%.
  • This method designs an on-line heating system after the thin strip continuous casting and rolling mill.
  • the heating temperature range is 670 to 1150°C.
  • the purpose is to make the cast strip completely recrystallize after being kept warm for a period of time after hot rolling in the different phase zone. Make the steel belt get better strong plastic matching.
  • the purpose of the present invention is to provide a thin-gauge high-corrosion-resistant steel and its production method, which fully utilizes scrap steel as a raw material to reduce the cost of molten steel, and can further reduce the production process cost and improve product performance, especially the corrosion resistance of the product through continuous thin strip casting. performance.
  • the yield strength of the high corrosion-resistant steel reaches more than 350MPa, the tensile strength reaches more than 480MPa, and the elongation reaches more than 26%; the relative corrosion rate is less than or equal to 25%.
  • the invention utilizes the residual Sn, Cu and other elements in the scrap steel to smelt molten steel, and selectively adds Cr, Ni and other alloying elements and B elements to the steel; during the smelting process, the basicity of the slag and the type of inclusions in the steel are controlled And the melting point, the free oxygen content in the molten steel, and the acid-soluble aluminum Als content; then double-roll thin strip continuous casting is carried out to cast a 1.5-3mm thick strip.
  • the strip After the strip exits the crystal roll, it directly enters a non-oxidizing In the lower airtight chamber of the atmosphere, and enter the on-line rolling mill for hot rolling under airtight conditions; the rolled steel strip adopts gas atomization cooling method to cool the strip steel, and the gas atomization cooling method can effectively reduce the surface of the strip steel.
  • the thickness of the oxide scale improves the temperature uniformity of the strip and improves the surface quality of the strip.
  • the final produced steel coils can be used after pickling-leveling, or they can be used after pickling-hot-dip galvanizing.
  • the thin-gauge high-corrosion-resistant steel of the present invention has the following chemical composition weight percentages as follows: C: 0.02-0.06%, Si: 0.1-0.5%, Mn: 0.4-1.7%, P ⁇ 0.02%, Cr: 4.0-6.0%, Ni: 1.0-3.0%, S ⁇ 0.007%, N: 0.004-0.010%, Als ⁇ 0.001%, B: 0.001-0.006%, total oxygen [O] T : 0.007-0.020%, The balance is Fe and unavoidable impurities, and at the same time meets:
  • the high corrosion-resistant steel of the present invention has a yield strength of ⁇ 350MPa, a tensile strength of ⁇ 480MPa, an elongation rate of ⁇ 26%, and a relative corrosion rate of ⁇ 25%.
  • the microstructure of the high corrosion-resistant steel of the present invention is a mixed microstructure of acicular ferrite+pearlite.
  • the average corrosion rate of the high corrosion resistant steel of the present invention is less than 0.1250 mg/cm 2 ⁇ h.
  • the yield ratio of the high corrosion resistant steel of the present invention is ⁇ 0.75.
  • C is the most economical and basic strengthening element in steel. It improves the strength of steel through solid solution strengthening and precipitation strengthening. C is an essential element for the precipitation of cementite during austenite transformation. Therefore, the level of C content determines the strength level of steel to a large extent, that is, a higher C content corresponds to a higher strength level.
  • the interstitial solid solution and precipitation of C have great harm to the plasticity and toughness of steel, and the excessively high C content is detrimental to the welding performance, so the C content cannot be too high, and the strength of the steel can be compensated by adding alloy elements appropriately .
  • casting in the peritectic reaction zone is prone to slab surface cracks, and breakout accidents may occur in severe cases.
  • Si plays a solid solution strengthening effect in steel, and the addition of Si to steel can improve steel purity and deoxidation, but excessive Si content will lead to deterioration of weldability and toughness of the welding heat-affected zone. Therefore, the range of Si content used in the present invention is 0.1-0.5%.
  • Mn is one of the cheapest alloying elements. It can improve the hardenability of steel and has a considerable solid solubility in steel. It can improve the strength of steel through solid solution strengthening, and at the same time, it can basically improve the plasticity and toughness of steel. No damage, it is the most important strengthening element to increase the strength of steel, and it can also play a role in deoxidizing steel. However, excessive Mn content will cause deterioration of weldability and toughness of the welding heat-affected zone. Therefore, the range of Mn content used in the present invention is 0.4-1.7%.
  • P High content of P is easy to segregate in grain boundaries, increase the cold brittleness of steel, deteriorate welding performance, reduce plasticity, and deteriorate cold bending performance.
  • the solidification and cooling rate of the cast strip is extremely fast, which can effectively inhibit the segregation of P, thereby effectively avoiding the disadvantages of P and giving full play to the advantages of P. Therefore, in the present invention, a higher P content than the traditional production process is adopted, the content of P element is appropriately relaxed, and the dephosphorization process is eliminated in the steelmaking process. In actual operation, there is no need to deliberately perform the dephosphorization process, and no additional process is required. Add phosphorus, the range of P content is less than 0.02%.
  • S Under normal circumstances, S is a harmful element in steel, causing steel to produce hot brittleness, reducing the ductility and toughness of steel, and causing cracks during rolling. S also reduces welding performance and corrosion resistance. Therefore, in the present invention, S is also controlled as an impurity element, and its content range is ⁇ 0.007%; in some embodiments, the S content is ⁇ 0.067%. And, Mn/S ⁇ 250. In some embodiments, Mn/S>250.
  • N Similar to the C element, the N element can improve the strength of the steel through interstitial solid solution.
  • the present invention uses the effect of N and B in the steel to generate the precipitated phase of BN, which requires a certain amount of N in the steel.
  • the interstitial solid solution of N has great harm to the plasticity and toughness of steel.
  • the existence of free N will increase the yield ratio of steel, so the N content cannot be too high.
  • the range of N content used in the present invention is 0.004-0.010%.
  • Cr not only is the element that improves the hardenability of steel, but Cr is the main alloying element in stainless steel, which can significantly improve the corrosion resistance of steel. If its content is too high, it will seriously deteriorate the welding performance. The content of Cr is limited in the present invention. At 4.0-6.0%.
  • Ni can improve the hardenability and significantly improve the low temperature toughness of steel. It is a beneficial element to improve the corrosion resistance and toughness of steel. At the same time, Ni can counteract the adverse effect of Cr on welding performance. Ni can also effectively prevent the heat of Cu. brittle. The present invention limits the Ni content to 1.0-3.0%.
  • Nb In the thin strip continuous casting process, due to its unique rapid solidification and rapid cooling characteristics, the added alloying element Nb can mainly exist in the steel strip in a solid solution state. Even if the steel strip is cooled to room temperature, it is almost impossible to observe To the precipitation of Nb.
  • the Nb element dissolved in steel can play a role of solid solution strengthening.
  • the content of Nb designed in the present invention ranges from 0.01% to 0.08%.
  • V In the thin strip continuous casting process, V is similar to Nb, but the effect is weaker than that of Nb, and it mainly exists in the steel strip in a solid solution state. Even if the steel strip is cooled to room temperature, almost no precipitation of V is observed. The V element dissolved in steel can play a role of solid solution strengthening.
  • the content range of V used in the present invention is 0.01-0.08%.
  • Cu It mainly plays a role of solid solution and precipitation strengthening in steel. Because Cu is an element that is easy to segregate, the Cu content is generally strictly controlled in the traditional process. Using the rapid solidification effect of thin strip continuous casting, the present invention increases the upper limit of Cu to 0.60%. The increase of Cu content can, to a certain extent, realize the effective use of copper in scrap steel or inferior mineral resources (high copper ore), promote the recycling of steel, reduce production costs, and achieve the purpose of sustainable development. In some embodiments, when contained, the Cu content may range from 0.1% to 0.6%.
  • Sn element is also one of the main participating elements in scrap steel. It is recognized as a harmful element in steel. Because Sn is an element that is easy to segregate, a small amount of Sn will be enriched at the grain boundary, resulting in cracks and other defects. In the traditional process, the content of Sn element is strictly controlled. Due to the characteristics of rapid solidification of thin strip continuous casting, the segregation of elements in the dendrites is greatly reduced, which can greatly increase the amount of solid solution of the elements. Therefore, under the conditions of the thin strip continuous casting process, the range of Sn elements can be expanded, so it can greatly Reduce steelmaking costs.
  • Figure 2 is the relationship between the Sn element and the average heat flux. It can be seen from Fig.
  • FIG. 3 shows the relationship between Sn content and surface roughness. Because the cracks on the surface of the cast strip are usually produced at the uneven wrinkles on the surface of the cast strip, the surface roughness is used to characterize the occurrence of surface cracks. If the roughness is large, the probability of occurrence of cracks is high. It can be seen from Fig. 3 that the increase of Sn content does not adversely affect the surface quality of the cast strip under the conditions of rapid solidification. From the results of Fig. 2 and Fig. 3, it can be seen that Sn has no adverse effect on the solidification and surface quality of the cast strip. Therefore, in the present invention, the requirements for Sn content can be further relaxed, and the design Sn content range is 0.005-0.04%.
  • B The significant effect of B in steel is: a very small amount of boron can double the hardenability of steel, and B can preferentially precipitate coarse BN particles in high-temperature austenite, thereby inhibiting the precipitation of fine AlN and weakening the fineness
  • the pinning effect of AlN on the grain boundary improves the growth ability of the grains, thereby coarsening and homogenizing the austenite grains, which is conducive to the recrystallization after rolling. After the austenite grains are coarsened and homogenized, there is also It is beneficial to improve the yield ratio of the product and improve the forming performance of the product; in addition, the combination of B and N can effectively prevent the appearance of the low melting point phase B 2 O 3 at the grain boundary.
  • B is a lively and easily segregated element, which is easy to segregate in the grain boundary.
  • the B content is generally controlled very strictly, generally around 0.001-0.003%; while in the thin strip continuous casting process, solidification and cooling The speed is faster, which can effectively inhibit the segregation of B and solid-solve more B content, so the B content can be appropriately relaxed; it can also be controlled by a reasonable process to generate coarse BN particles, inhibit the precipitation of fine AlN, and achieve nitrogen fixation effect.
  • the method for producing thin-gauge high-corrosion-resistant steel of the present invention includes the following steps:
  • the MnO/SiO 2 (mass ratio) in the -SiO 2 -Al 2 O 3 ternary inclusions is controlled to be 0.5-2, preferably 1 to 1.8;
  • the free oxygen [O] Free content in the molten steel is: 0.0005 to 0.005% ;In the composition of molten steel, Mn/S ⁇ 250;
  • the continuous casting adopts double-roll thin strip continuous casting to form a 1.5-3mm thick cast strip at the smallest gap between the two crystallizing rolls; the diameter of the crystallizing roll is between 500-1500mm, preferably 800mm; the inside of the crystallizing roll is cooled by water.
  • the casting speed of the machine is 60-150m/min; the continuous casting flow adopts a two-stage molten steel distribution flow system, that is, the tundish + flow distributor;
  • the temperature of the casting belt is between 1420 and 1480 °C, and it enters the lower closed chamber directly.
  • the lower closed chamber is filled with non-oxidizing gas.
  • the oxygen concentration in the lower closed chamber is controlled at ⁇ 5%.
  • the casting belt at the exit of the lower closed chamber The temperature is 1150-1300°C;
  • the cast strip is sent to the rolling mill via pinch rolls in the lower enclosed chamber and rolled into a strip steel with a thickness of 0.8-2.5mm.
  • the rolling temperature is 1100-1250°C and the hot rolling reduction rate is controlled to 10-50%. Hot rolling is preferred.
  • the reduction rate is 30-50%, and the thickness of the strip after rolling is 0.8-2.5mm, preferably 1.0-1.8mm;
  • the cooling rate of gas atomization cooling is 20-100°C/s
  • the cooled hot-rolled steel strip is directly coiled into a coil, and the coiling temperature is 600-700°C.
  • the steel coil is used as an acid flat coil after pickling and flattening, or used as a galvanized sheet after pickling and hot-dip galvanizing.
  • the smelting raw material can be 100% scrap steel without pre-screening, and the molten steel smelting adopts electric furnace steelmaking; or, the smelting adopts converter steelmaking, and the scrap steel is added to the converter at a ratio of more than 20wt% of the smelting raw material, and No need to pre-screen; then enter LF furnace, VD/VOD furnace or RH furnace for refining.
  • the non-oxidizing gas is N 2 , Ar, or CO 2 gas obtained by sublimation of dry ice.
  • the gas-water ratio of the gas atomization cooling is 15:1-10:1, the air pressure is 0.5-0.8 MPa, and the water pressure is 1.0-1.5 MPa.
  • the air-water ratio refers to the flow ratio of compressed air and water, and the unit of flow is m 3 /h.
  • the coiling adopts a double coiler form, or a Carrousel coiling form to ensure continuous production of strip steel.
  • the cooled hot-rolled steel strip is directly coiled into a coil after being cut by a cutting head to remove the poor quality head, and the coiling temperature is 600-700°C.
  • MnO-SiO 2 -Al 2 O 3 ternary inclusions In order to improve the castability of thin strip continuous casting molten steel, it is necessary to obtain low melting point MnO-SiO 2 -Al 2 O 3 ternary inclusions, as shown in the shaded area in Figure 4, MnO-SiO 2 -Al 2 O 3 ternary inclusions
  • the MnO/SiO 2 (mass ratio) in the product is controlled to be 0.5-2, preferably 1 to 1.8.
  • oxygen (O) in the steel is an essential element for the formation of oxidized inclusions.
  • the present invention requires the formation of low melting point ternary inclusions of MnO-SiO 2 -Al 2 O 3 ,
  • the required free oxygen [O] Free range in molten steel is: 0.0005-0.005%.
  • the temperature of the casting belt is at 1420-1480°C, and it enters the lower closed chamber directly.
  • the oxygen concentration in the lower closed chamber is controlled at ⁇ 5%.
  • the anti-oxidation protection of the casting belt in the lower closed chamber reaches the entrance of the rolling mill, and the lower is closed.
  • the temperature of the cast strip at the outlet of the chamber is between 1150-1300°C.
  • thermodynamic equations of boron and nitrogen, aluminum and nitrogen in ⁇ -Fe in steel are as follows:
  • the initial precipitation temperature of BN in steel is about 1280°C, and the precipitation of BN tends to be balanced at 980°C, while the precipitation of AlN has just begun (the precipitation temperature of AlN is about 980°C).
  • the precipitation of BN has priority over AlN.
  • the invention completes the combination of B and N in the lower closed chamber to generate coarse BN particles, thereby inhibiting the precipitation of fine AlN, weakening the pinning effect of fine AlN on grain boundaries, improving the growth ability of grains, and thereby coarsening austenite
  • the grains make the austenite grains more uniform, which is beneficial to effectively reduce the yield ratio of the product and improve the product performance; in addition, the combination of B and N can effectively prevent the appearance of the low melting point phase B 2 O 3 at the grain boundary.
  • the raw material can be 100% scrap steel without pre-screening, which greatly reduces the production cost.
  • converter steelmaking to provide molten steel requires manufacturers to have the conditions to provide molten iron. Under normal circumstances, blast furnace ironmaking or non-blast furnace ironmaking equipment is required, which belongs to the current long-process steel production mode. However, today with increasingly rich scrap steel resources, the country is advocating to increase the converter scrap ratio, so as to achieve the purpose of energy saving, consumption reduction and cost reduction.
  • the average level of converter scrap ratio in the past was about 8%. Now and in the future, the target of converter scrap ratio It is 15-25%.
  • the scrap ratio of the converter of the present invention can reach more than 20%.
  • Scrap steel As the main raw material.
  • Traditional processes such as die casting or thick plate continuous casting have a solidification and cooling rate of only 10 -1 -10°C/s. These residual elements in the scrap will solidify Grain boundary segregation occurs during the process, which deteriorates the performance and quality of the steel. In severe cases, cracks and fractures occur directly. Therefore, in the traditional process, these harmful elements must be strictly controlled.
  • some pre-screening is required.
  • some special treatments are required in the steelmaking process, such as adding some concentrates for dilution, etc., which undoubtedly increase the cost of production operations. Due to the need to control the composition of steel, there are certain quality requirements for the used scrap raw materials.
  • the scrap steel needs to be pre-screened and classified.
  • some domestic electric furnace steel plants will choose to add refined materials such as purchased sponge iron and iron carbide to the raw material composition to dilute the harmful elements that are difficult to remove in the scrap and improve the quality of molten steel.
  • Some domestic steel mills that have both blast furnaces and electric furnaces use self-produced molten iron into the electric furnace as raw materials to improve the production efficiency of the electric furnace, thereby greatly shortening the tapping time of the electric furnace, and the hot metal blending ratio in the electric furnace can reach 30-50% .
  • twin-roll thin strip continuous casting technology is a typical sub-rapid solidification process.
  • the solidification cooling rate is as high as 10 2 -10 4 °C/s.
  • Some harmful residual elements in the scrap such as Cu, Sn, P, etc., can be maximized
  • the ground solid dissolves into the steel matrix without producing grain boundary segregation, so 100% all scrap steel smelting can be realized without pre-screening, which greatly reduces the cost of raw materials.
  • These residual elements can also play a role of solid solution strengthening, thereby producing ultra-thin hot-rolled strip steel with excellent properties. Realize the comprehensive utilization of low-quality scrap steel resources, which has the effect of "turning harm into profit” and "waste utilization" for these harmful residual elements in the scrap steel.
  • the rolled steel strip adopts gas atomization cooling method:
  • the strip steel after rolling adopts gas atomization cooling method to cool the strip steel.
  • the gas atomization cooling method can effectively reduce the thickness of the oxide scale on the surface of the strip and improve the strip steel. Temperature uniformity improves the surface quality of strip steel.
  • the gas-water ratio of gas atomization cooling is 15:1 ⁇ 10:1, the air pressure is 0.5 ⁇ 0.8MPa, and the water pressure is 1.0 ⁇ 1.5MPa. After the gas is atomized, high-pressure water mist is sprayed on the surface of the steel strip. On the one hand, it can reduce the temperature of the steel strip.
  • the water mist will form a dense gas film covering the surface of the steel strip, which can prevent the strip from being oxidized. It can effectively control the growth of oxide scale on the surface of hot-rolled steel strip.
  • This cooling method can avoid the problems caused by traditional spraying or laminar cooling, make the surface temperature of the strip drop uniformly, improve the uniformity of the strip temperature, and achieve the effect of homogenizing the internal microstructure; at the same time, the uniform cooling can improve the strip The shape quality and performance stability of the steel; effectively reduce the thickness of the oxide scale on the surface of the strip.
  • the cooling rate of gas atomization cooling is in the range of 20-100°C/s.
  • the present invention uses thin strip continuous casting technology to produce corrosion-resistant steel containing tin (Sn), copper (Cu)/tin (Sn), copper (Cu), and boron (B). There have been no reports so far.
  • Sn tin
  • Cu copper
  • Cu copper
  • B boron
  • the present invention eliminates the need for complex processes such as slab heating and multi-pass repeated hot rolling. Through double-roll thin strip continuous casting + one online hot rolling process, the production process is shorter, the efficiency is higher, and the investment cost of the production line is reduced. The production cost is greatly reduced.
  • the present invention omits many complicated intermediate steps in the production of corrosion-resistant steel by the traditional process. Compared with the traditional production process, the energy consumption and CO 2 emission of production are greatly reduced, and it is a green and environmentally friendly product.
  • the present invention adopts the thin strip continuous casting process to produce hot-rolled thin-gauge corrosion-resistant steel.
  • the corrosion resistance is greatly improved, which can be comparable to stainless steel, and can be achieved in traditional corrosion resistance.
  • the corrosion of steel is doubled; meanwhile, the thickness of the cast strip itself is relatively thin.
  • the production of thin gauge products does not require cold rolling, and is directly supplied to the market for use in the thin gauge hot-rolled plate.
  • the purpose of goods delivery and the purpose of "cooling in the hot zone" can significantly improve the cost-effectiveness of the plate and strip.
  • the present invention adopts the addition of a small amount of boron element to preferentially precipitate coarse BN particles in high-temperature austenite, thereby inhibiting the precipitation of fine AlN, weakening the pinning effect of fine AlN on grain boundaries, improving the growth ability of grains, and thus Refining and homogenizing the austenite grains is conducive to improving the yield ratio and formability of the product.
  • the smelting of the present invention adopts electric furnace steel smelting, and the raw materials smelted can be smelted with 100% scrap steel in a true sense without pre-screening, which greatly reduces the cost of raw materials; if the smelting is through converter steel smelting, scrap accounts for 20% of the raw materials
  • the above ratio is added to the converter without pre-screening, which maximizes the scrap ratio of the converter and greatly reduces the smelting cost and energy consumption.
  • the present invention uses scrap steel containing Cu and Sn to "turn harm into benefits" for Cu and Sn in the steel, and realize the full use of existing scrap steel or low-quality low-quality mineral resources (high tin ore, high copper ore) Utilize, promote the recycling of scrap steel, reduce production costs, and realize the sustainable development of the steel industry.
  • the present invention adopts the strip steel gas atomization cooling method after rolling, which can avoid the problems caused by traditional spraying or laminar cooling, make the surface temperature of the strip uniformly drop, improve the uniformity of the strip temperature, and achieve uniform internal microcosmic The effect of the structure; at the same time, uniform cooling can improve the shape quality and performance stability of the strip; effectively reduce the thickness of the oxide scale on the surface of the strip.
  • the precipitation of alloying elements occurs during the cooling process of the traditional slab.
  • the utilization of alloying elements is often reduced due to insufficient re-dissolution of the alloy elements.
  • the high-temperature cast strip is directly hot-rolled, and the added alloy elements mainly exist in a solid solution state, which can improve the alloy utilization rate.
  • the present invention uses a hot-rolled steel strip Carrousel coiler, which effectively shortens the length of the production line; at the same time, co-coiling can greatly improve the control accuracy of the coiling temperature and improve the stability of product performance.
  • the most obvious feature of the present invention which is different from the existing thin strip continuous casting technology is the diameter of the crystallizing roll and its corresponding flow distribution method.
  • the technical feature of EUROSTRIP is ⁇ 1500mm large diameter crystallizing roller, large crystallizing roller, large molten steel capacity in molten pool, easy flow distribution, high cost of crystallizing roller manufacturing and operation and maintenance.
  • the technical feature of CASTRIP is the ⁇ 500mm small diameter crystallizing roller, the crystallizing roller is small, the molten steel volume is small, and the flow distribution is very difficult, but the cost of manufacturing and operation and maintenance of the casting machine is low.
  • CASTRIP adopts a three-stage molten steel distribution flow system (tundish + transition bag + flow distributor).
  • the use of a three-stage flow distribution system directly leads to an increase in the cost of refractory materials; more importantly, the three-stage flow distribution system makes the path of molten steel flow longer and the temperature drop of molten steel is also greater.
  • the tapping temperature needs to be greatly increased. The increase in the tapping temperature will cause problems such as increased steelmaking costs, increased energy consumption, and shortened life of refractory materials.
  • the molten steel flowing out of the distributor forms different distribution patterns along the roller surface and the two end surfaces, and flows in two paths without interfering with each other. Due to the use of a two-stage flow distribution system, compared with a three-stage flow system, the cost of refractory materials is greatly reduced; the shortening of the molten steel flow path reduces the temperature drop of the molten steel, which can lower the tapping temperature, compared with the three-stage flow system , The tapping temperature can be reduced by 30-50°C.
  • the lowering of the tapping temperature can effectively reduce the cost of steelmaking, save energy and extend the life of refractory materials.
  • the invention is matched with a crystallizing roller with a roller diameter of ⁇ 800mm and adopts a two-stage molten steel distribution system, which not only realizes the requirement of stable molten steel distribution, but also realizes the goals of simple structure, convenient operation and low processing cost.
  • Figure 1 is a schematic diagram of the process layout of the twin-roll thin strip continuous casting process
  • Figure 2 is a schematic diagram of the relationship between Sn content and average heat flux
  • Figure 3 is a schematic diagram of the relationship between the Sn content and the surface roughness of the cast strip
  • Figure 4 is a ternary phase diagram of MnO-SiO 2 -Al 2 O 3 (shaded area: low melting point area);
  • Figure 5 is a schematic diagram of the thermodynamic curves of the precipitation of BN and AlN.
  • the molten steel designed in accordance with the chemical composition of the present invention is directly poured in a large ladle through the ladle nozzle 2, the tundish 3, the immersion nozzle 4 and the distributor 5, which can rotate relatively quickly and quickly
  • the molten steel solidifies on the rotating circumferential surfaces of the crystallizing rollers 8a, 8b, and then forms a solidified shell and gradually grows on the two crystallizing rollers.
  • a 1.5-3mm thick cast belt 11 is formed at the smallest gap (nip point); the crystal roll of the present invention has a diameter of 500-1500mm, and the inside is cooled by water.
  • the casting speed of the casting machine ranges from 60-150m/min.
  • the temperature of the casting belt 11 is 1420-1480°C, and it directly enters the lower closed chamber 10, and the lower closed chamber 10 is protected by inert gas to protect the strip from oxidation.
  • the atmosphere for the anti-oxidation protection can be N 2 , Ar, or other non-oxidizing gases, such as CO 2 gas obtained by sublimation of dry ice.
  • the oxygen concentration in the lower closed chamber 10 is controlled to be less than 5%.
  • the lower airtight chamber 10 protects the cast strip 11 from oxidation to the entrance of the rolling mill 13.
  • the temperature of the cast strip at the outlet of the lower closed chamber 10 is between 1150-1300°C.
  • the cast strip is sent to the hot rolling mill 13 through the swing guide plate 9, the pinch roll 12, and the roller table 15.
  • a gas atomization rapid cooling device 14 Cooling is carried out by means of gas atomization cooling to improve the uniformity of strip temperature.
  • the cutting head falls into the flying shear pit 18 along the flying shear guide plate 17, and the hot-rolled strip after the cutting head enters the coiler 19 for coiling.
  • the steel coil is removed from the coiler, it is naturally cooled to room temperature.
  • the final produced steel coils can be used after pickling-leveling, or they can be used after pickling-hot-dip galvanizing.
  • Examples are used to further illustrate the method of the present invention.
  • the chemical composition of the embodiment of the present invention is shown in Table 2, and the balance of the composition is Fe and other unavoidable impurities.
  • the process parameters are shown in Table 3, and the mechanical properties of the finally obtained hot-rolled strip are shown in Table 4.
  • the high corrosion resistant steel produced by the thin strip continuous casting process technology according to the steel grade composition design range provided by the present invention has a yield strength ⁇ 350MPa, tensile strength ⁇ 480MPa, elongation ⁇ 26%, and a low yield strength ratio. Below 0.8, the cold working bending performance is qualified.
  • the comparison results of corrosion resistance also show that the relative corrosion rate of the invention steel is ⁇ 25.
  • Example 1 0.026 0.22 1.35 0.008 0.005 0.0078 0.0093 0.0009 4.8 1.9 0.36
  • Example 2 0.047 0.10 0.90 0.013 0.003 0.0065 0.0110 0.0005 5.0 2.3 0.23 0.005 0.001
  • Example 3 0.057 0.33 1.28 0.015 0.004 0.0059 0.0150 0.0006 5.2 3.0 0.10 0.033 0.004
  • Example 4 0.020 0.27 1.10 0.013 0.004 0.0087 0.0130 0.0007 4.3 2.6
  • Example 5 0.026 0.43 0.65 0.009 0.002 0.0052 0.0120 0.0008 4.0 1.9 0.46 0.015 0.003
  • Example 6 0.048 0.41 0.67 0.012 0.002 0.0046 0.0070 0.0005 5.2 1.0 0.53
  • Example 7 0.056 0.19 0.85 0.015 0.003 0.0040 0.0100 0.0008 6.0 1.2
  • Example 10 0.060 0.44 0.40 0.020 0.001 0.0055 0.0125 0.0004 5.5 2.2 To 0.018 0.006
  • Example 11 0.038 0.50 0.65 0.010 0.002 0.0091 0.0090 0.0005 4.5 2.7 0.49 0.007 0.003
  • Example 12 0.042 0.27 1.70 0.012 0.0067 0.0084 0.0118 0.0003 5.7 1.7 0.34
  • Example 13 0.028 0.46 1.37 0.008 0.004 0.0048 0.0132 0.0006 4.5 2.9
  • Example 14 0.033 0.28 1.40 0.017 0.003 0.0064 0.0075 0.0005 5.7 1.8 0.28 0.029 0.004
  • Example 12 0.1068 21.79
  • Example 13 0.1143 23.32
  • Example 14 0.1194 24.36

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Abstract

一种薄规格高耐蚀钢及其生产方法，其利用废钢中残余的Sn、Cu等元素进行钢水冶炼，并有选择地添加Cr、Ni、B元素；冶炼过程中控制渣的碱度、钢中夹杂物类型、熔点、钢水中的游离氧含量及酸溶铝Als含量；然后采用双辊薄带连铸浇铸出带钢（11），经下密闭室（10）进入在线轧机（13）进行热轧；轧后冷却采用气雾化冷却方式对带钢（11）进行冷却，可有效减小表面氧化皮厚度、改善温度均匀性及提高表面质量。

Description

一种薄规格高耐蚀钢及其生产方法 技术领域
本发明属于高耐蚀钢产品，具体涉及一种薄规格高耐蚀钢及其生产方法。
背景技术
近年来，由于废钢的连续循环利用，废钢资源越来越多，电价也持续降低，国内基于废钢的短流程电炉炼钢日益兴起，导致钢中的Sn、Cu等残余元素的含量逐渐升高，钢中的Sn、Cu是易偏析元素，容易富集在晶界导致裂纹等缺陷发生，因此在传统的工艺中Sn、Cu元素的含量是被严格控制的，在普通结构用钢中，对Sn、Cu的含量均有明确的要求：Sn(wt％)≤0.005％；Cu(wt％)≤0.2％。
在传统钢铁生产流程中，锡(Sn)、铜(Cu)是钢中典型的残余元素或有害元素，炼钢过程中要充分地去除Sn、Cu非常困难而且也是非常昂贵，一旦钢中含有Sn、Cu，基本是无法彻底消除的，只能通过稀释钢水来降低Sn、Cu的含量，这些都造成钢铁产品冶炼成本的升高。
因此，如果能对钢(特别是废钢)中Sn、Cu等残余元素做到合理利用，“化害为利”，将对整个冶金界产生积极的影响；可以实现对现有废钢或低品质劣质矿资源(高锡矿、高铜矿)的有效利用，促进钢的循环利用，降低生产成本，实现钢铁业可持续发展。
传统的薄带钢大都是由厚达70-200mm的铸坯经过多道次连续轧制生产出来的，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1.5mm(含)的钢带，则难度相对较大，通常要对热轧钢带进行后续冷轧以及退火来完成。且工艺流程长、能耗高、机组设备多、基建成本高，导致生产成本较高。
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。但薄板坯连铸连轧由于较快的冷速会导致钢材强度提高，屈强比提高，从而增加轧制载荷，使得可经济地生产热轧产品的厚度规格也不可能太薄，一般为≥1.5mm，见专利CN200610123458.1，CN200610035800.2以及CN200710031548.2，且这些专利均未涉及元素Sn和Cu。
近年来兴起的一种全无头薄板坯连铸连轧工艺(简称：ESP)，是在上述半无头薄板坯连铸连轧工艺的基础上发展起来的一种改进工艺，ESP实现了板坯连铸的无头轧制，取消了板坯火焰切割和起保温均热、板坯过渡作用的加热炉，整条产线长度大大缩短到190米左右。连铸机连铸出来的板坯厚度在90-110mm，宽度在1100-1600mm，连铸出来的板坯通过一段感应加热辊道对板坯起到保温均热的作用，然后再依次进入粗轧、精轧、层冷、卷取工序得到热轧板。这种工艺由于实现了无头轧制，可以得到最薄0.8mm厚度的热轧板，拓展了热轧板的规格范围，再加上其单条产线产量可达220万吨/年规模。目前该工艺得到了快速发展和推广，目前世界上已有多条ESP产线在运营生产。
比薄板坯连铸连轧更短的工艺流程是薄带连铸连轧工艺，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，缩短了生产周期，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，是一种低碳环保的热轧薄带生产工艺。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。
双辊薄带连铸典型的工艺流程如图1所示，大包1中的熔融钢水通过大包长水口2、中间包3、浸入式水口4以及布流器5直接浇注在一个由两个相对转动并能够快速冷却的结晶辊8a、8b和侧封装置6a、6b围成的熔池7中，钢水在结晶辊8a、8b旋转的周向表面凝固形成凝固壳并逐渐生长，进而在两结晶辊辊缝隙最小处(nip 点)形成1-5mm厚的铸带11，铸带经由导板9导向夹送辊12送入轧机13中轧制成0.7-2.5mm的薄带，随后经过冷却装置14冷却，经飞剪装置16切头后，最后送入卷取机19卷取成卷。
薄规格的高耐蚀钢被越来越多地应用在一些需要高耐蚀的领域，比如列车制造行业中绿皮车的车厢改造，绿皮车的车厢改造用钢市场用量很大，对钢的耐腐蚀性能提出了比较严苛的要求，它要求钢的耐腐蚀性能在传统耐大气腐蚀钢的基础上再提升一倍。且对成本也有一定要求。针对这样一个庞大的市场需求，没有现成的钢种可以拿来直接对应和使用，必须要开发一种全新的钢种。为了成本考虑，不宜采用不锈钢，考虑到该产品要求具备良好的弯曲和成形性能；产品厚度规格：1.0-2.0mm。本发明提出，采用薄带连铸工艺来生产这种高耐蚀钢，具备一定的优势，这种薄规格的高耐蚀钢产品的成功开发，将给列车制造行业在轻量化、绿色化、降低能耗、高耐蚀媲美不锈钢等方面提供了广阔前景。
采用薄带连铸来生产薄规格高耐蚀钢，由于厚度较薄，薄带连铸工艺具有较强的制造和成本优势。高耐蚀钢经后处理后供货的产品规格特征厚度为1.0mm、1.1mm、1.2mm、1.25mm、1.4mm、1.5mm、1.6mm、1.8mm和2.0mm等，由于产品厚度较薄，假如采用传统的连铸+热连轧产线进行生产比较困难，一般采用先热连轧工艺生产，然后进行冷轧的方式来生产，这样的生产流程增加了薄规格高耐蚀钢的生产成本。
热轧带钢作为薄规格热轧板或者“以热代冷”产品使用时，对带钢表面质量要求很高。一般要求带钢表面氧化皮的厚度越薄越好，这就需要在铸带后续的各个阶段控制氧化铁皮的生成，如在双辊薄带连铸工艺中，在结晶辊直至轧机入口均采用密闭室装置防止铸带氧化，在密闭室装置内如美国专利US6920912添加氢气以及在美国专利US20060182989中控制氧气含量小于5％，均可以控制铸带表面的氧化皮厚度。但是在轧机至卷取这段输送过程如何控制氧化皮的厚度很少有关专利涉及，尤其是在采用层流冷却或喷淋冷却对带钢进行冷却的过程中，高温的带钢与冷却水接触，铸带表面的氧化皮厚度增长很快。同时，高温的带钢与冷却水接触还会带来很多问题：其一，会在带钢表面形成水斑(锈斑)，影响表面质量；其二，层流冷却或喷淋冷却用的冷却水容易造成带钢表面局部冷却不均匀，造成带钢内部微观组织的不均匀，从而造成带钢性能的不均匀，影响产品质量；其三，带钢表面局部冷 却不均匀，会造成板形的恶化，影响板形质量。
但是，薄带连铸由于其本身的快速凝固工艺特性，生产的钢种普遍存在组织不均匀、延伸率偏低、屈强比偏高、成型性不好的问题；同时铸带奥氏体晶粒具有明显不均匀性，会导致奥氏体相变后所获得的最终产品组织也不均匀，从而导致产品的性能特别是成形性能不稳定。因此采用薄带连铸生产线来生产高耐蚀钢产品，同样具有一定难度和挑战，需要在成分和工艺上有突破。
目前国内外已就耐蚀钢及其制造方法申请了多项专利，其中450MPa及其以上强度级别的耐蚀钢，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蚀钢的综合力学性能，具体专利成分和性能见表1。
表1：耐蚀钢的专利对比(wt％)
Figure PCTCN2020115953-appb-000001
Figure PCTCN2020115953-appb-000002
上述高强耐蚀钢，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。上述专利也有提及钢中添加硼(B)元素，比如专利CN200610125125.2和US6315946，但公开的发明内容中没有涉及硼(B)元素添加后具体的工艺控制方法，而且添加的量也比较少。
利用传统工艺生产微合金高强耐蚀钢，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)耐蚀钢中含有较高含量的提高钢带耐蚀性能的铜等易偏析元素，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纹，成材率较低。
(3)耐蚀钢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蚀钢的成分设计中，铜的添加量在0.2-0.55％的范围，实际生产中通常取下限，铬的添加量在0.2-1.25的范围，普遍较低。其结果造成钢带的耐蚀性不高。
(4)这些耐腐蚀钢的耐腐蚀性能无法实现本发明钢的耐腐蚀性能要求，即在传统耐腐蚀钢的基础上再提升一倍。
(5)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，导致钢材组织晶粒细小，屈强比提高，成型性能差，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高强耐蚀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。
如果采用薄板坯连铸连轧工艺生产微合金高强耐腐蚀钢，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腐蚀钢的成分设计适当放宽了提高耐蚀性的元素磷、铜的含量范围，这对于提高钢的耐蚀性能是有利的。
中国专利CN200610123458.1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级高强耐腐蚀钢的方法，该方法制造耐腐蚀钢板的化学成分为：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％，余量为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CN200610035800.2公开了一种基于薄板坯连铸连轧工艺生产700MPa级V-N微合金化耐腐蚀钢的方法，该方法制造耐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％，余量为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腐蚀钢热轧产品的厚度规格也不可能太薄，为≥1.5mm，见中国专利CN200610123458.1，CN200610035800.2以及CN200710031548.2。
中国专利CN1633509A提到了一种薄带连铸所生产含铜碳钢产品的方法，该专利强调要对这种的带钢在400-700℃范围内进行退火、回火等热处理工序使铜元素在带钢中沉淀或再结晶。与本发明相对比，本发明成份中添加了微量元素B，Cr的含量明显增加，具有明显区别特征，同时后续处理工艺完全不一样。
美国专利US2008264525/CN200580009354.1中提到的一种高铜低合金薄带的制造方法，其技术特点是，在进入轧机前对所述的带钢在非氧化气氛中实施冷却至低于1080℃以防止带钢发生“热脆”现象。与本发明相比，本发明中添加了微量元素B，且Cr的含量明显增加，对带钢出带后的后续处理方法也有所不同。
国际专利WO 2008137898、WO 2008137899、WO 2008137900，以及中国专利CN200880023157.9、CN200880023167.2、CN200880023586.6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。专利认为，铸带中主要以固熔态存在的合金元素抑制了热轧后奥氏体的再结晶，即使压下率达到40％，奥氏体的再结晶也非常有限。由于20-40％的热轧压下率均没有使奥氏体发生再结晶，使得粗大奥氏体的淬透性在热轧后得以保持，从而获得贝氏体+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
Figure PCTCN2020115953-appb-000003
Process.AIS Tech,Indianapolis,Indiana,USA,May 7-10,2007)，报导了所采用的热轧温度为950℃。
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，屈服强度可达到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(≤6％或者≤10％)。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，奥氏体晶粒尺寸不均匀，小到几十微米，大到七八百微米。而薄带连铸工艺后一般只跟1-2机架轧机，其热轧压下率通常很难超过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，不均匀的奥氏体组织很难在热轧后得到有效改善，由尺寸不均匀的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1-6mm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％，余量为Fe和不可避免的杂质。铸带的热轧在1150-(Ar1-100)℃范围内，对应奥氏体区、奥氏体铁素体两相区、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***，加热温度范围是670-1150℃，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。利用这种方法进行生产，需要在产线设计时增加在线加热***，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。
发明内容
本发明的目的在于提供一种薄规格高耐蚀钢及其生产方法，充分利用废钢作为原料降低钢水成本，通过薄带连铸可以进一步降低生产工序成本以及提高产品性能，特别是产品的耐腐蚀性能。所述高耐蚀钢的屈服强度达到350MPa以上，抗拉强度达到480MPa以上，延伸率达到26％以上；相对腐蚀率≤25％。
为达到上述目的，本发明的技术方案是：
本发明利用废钢中残余的Sn、Cu等元素进行钢水的冶炼，并在钢中有选择地添加Cr、Ni等合金元素和B元素；冶炼过程中通过控制渣的碱度、钢中夹杂物类型及熔点、钢水中的游离氧含量、酸溶铝Als含量；然后进行双辊薄带连铸浇铸出1.5-3mm厚的带钢，在带钢出结晶辊后，直接进入到一个有非氧化性气氛的下密闭室中，并在密闭情况下进入到在线轧机进行热轧；轧制后的带钢采用气雾化冷却方 式对带钢进行冷却，气雾化冷却方式可以有效减小带钢表面氧化皮厚度，改善带钢温度均匀性，提高带钢表面质量。最后生产的钢卷可以经过酸洗-平整后使用，也可以经过酸洗-热镀锌后使用。
具体的，本发明所述的一种薄规格高耐蚀钢，其化学成分重量百分比为：C：0.02-0.06％，Si：0.1-0.5％，Mn：0.4-1.7％，P≤0.02％，Cr：4.0-6.0％，Ni：1.0-3.0％，S≤0.007％，N：0.004-0.010％，Als<0.001％，B：0.001-0.006％，总氧[O] T：0.007-0.020％，余量为Fe和不可避免杂质，且同时满足：
含有Cu：0.1-0.6％和Sn：0.005-0.04％中的一种或两种元素；
Mn/S≥250。
本发明所述高耐蚀钢的屈服强度≥350MPa，抗拉强度≥480MPa，延伸率≥26％，相对腐蚀率≤25％。
本发明所述高耐蚀钢的显微组织为针状铁素体+珠光体混合微观组织。
优选地，本发明所述高耐蚀钢的平均腐蚀速率小于0.1250mg/cm 2·h。
优选地，本发明所述高耐蚀钢的屈强比≤0.75。
在本发明所述高耐蚀钢的化学成分设计中：
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含量对焊接性能不利，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。同时，对常规板坯连铸来说，在包晶反应区浇铸易产生铸坯表面裂纹，严重时会发生漏钢事故。对薄带连铸来说也同样如此，在包晶反应区浇铸铸带坯易发生表面裂纹，严重时会发生断带。因此，Fe-C合金的薄带连铸同样需要避开包晶反应区。故本发明采用的C含量范围是0.02-0.06％。
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0.1-0.5％。
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， 是提高钢的强度最主要的强化元素，还可以在钢中起到脱氧的作用。但Mn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Mn含量范围是0.4-1.7％。
P：高含量的P容易在晶界偏析，增加钢的冷脆性，使焊接性能变坏，降低塑性，使冷弯性能变坏。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。故在本发明中，采用较传统工艺生产时高的P含量，适当放宽P元素的含量，炼钢工序中取消脱磷工序，在实际操作中，不需要刻意进行脱磷工序，也不需要额外添加磷，P含量的范围≤0.02％。
S：在通常情况下S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也作为杂质元素来控制，其含量范围是≤0.007％；在一些实施方案中，S含量≤0.067％。且，Mn/S≥250。在一些实施方案中，Mn/S＞250。
Als：为控制钢中的夹杂物，本发明要求不能用Al脱氧，耐材的使用中，也应尽量避免Al的额外引入，严格控制酸溶铝Als的含量：<0.001％。
N：与C元素类似，N元素可通过间隙固溶提高钢的强度，本发明要利用钢中的N跟B作用生成BN的析出相，需要钢中有一定的N含量。但是，N的间隙固溶对钢的塑性和韧性有较大危害，自由N的存在会提高钢的屈强比，因此N含量也不能过高。本发明采用的N含量范围是0.004-0.010％。
Cr：不仅是提高钢的淬透性的元素，而且Cr是不锈钢中的主要合金元素，可以显著提高钢的耐蚀性能，其含量太高就会严重恶化焊接性能，本发明中将Cr含量限定在4.0-6.0％。
Ni：能提高淬透性，显著改善钢材的低温韧性，是提高钢的耐蚀性和强韧性的有利元素，同时，Ni可以对冲Cr对焊接性能的不利影响，Ni还能有效阻止Cu的热脆。本发明将Ni含量限定在1.0-3.0％。
Nb：在薄带连铸工艺中，由于其独特的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。固溶于钢中的Nb元素，可以起到固溶强化的作用。本发明设计Nb的含量范围是0.01-0.08％。
V：在薄带连铸工艺中，V和Nb类似，但作用弱于Nb，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，固溶于钢中的V元素，可以起到固溶强化的作用。本发明采用V的含量范围是0.01-0.08％。
Cu：在钢中主要起固溶和沉淀强化作用，由于Cu是易偏析元素，传统工艺流程中一般对Cu含量有较严格的控制。运用薄带连铸的快速凝固效应，本发明将Cu的上限提高到0.60％。Cu含量的提高，在一定意义上可以实现废钢或劣质矿资源(高铜矿)中铜的有效利用，促进钢的循环利用，降低生产成本，实现可持续发展的目的。在一些实施方案中，含有时，Cu含量范围可为0.1-0.6％。
Sn：Sn元素也是废钢中的主要参与元素之一，它被公认为钢中的有害元素，因为Sn是易偏析元素，少量的Sn就会在晶界富集，导致是裂纹等缺陷发生，因此在传统的工艺中Sn元素的含量是被严格控制的。薄带连铸由于快速凝固的特点，元素在枝晶间的偏析大大减小，可以大大提高元素的固溶量，因此在薄带连铸工艺条件下，Sn元素的范围可以扩大，因此可以大大降低炼钢成本。图2是Sn元素与平均热流密度的关系。由图2可见，当Sn加入量小于0.04％时，对热流密度的影响不大，即对薄带凝固过程没有影响。图3是Sn含量与表面粗糙度的关系。因为铸带表面的裂纹通常都是在铸带表面凹凸不平的皱褶处产生，用表面粗糙度来表征表面裂纹发生情况。如果粗糙度大，则裂纹发生的概率高。由图3可知，Sn含量的增加，在快速凝固条件下并没有对铸带的表面质量产生不良的影响。由图2和图3的结果可知，Sn没有对铸带的凝固和表面质量产生不良影响。故在本发明中，对Sn含量的要求可进一步放宽，设计Sn的含量范围在0.005-0.04％。
B：B在钢中的显著作用是：极微量的硼就可以使钢的淬透性成倍增加，B可以在高温奥氏体中优先析出粗大的BN颗粒从而抑制细小AlN的析出，减弱细小AlN对晶界的钉扎作用，提高晶粒的生长能力，从而粗化和均匀化奥氏体晶粒，有利于轧制后的再结晶，奥氏体晶粒粗化均匀化以后，也有利于产品屈强比的改善，提高产品的成形性能；另外B与N的结合可以有效防止晶界低熔点相B 2O 3的出现。
B是活泼易偏析元素，容易在晶界偏聚，传统工艺生产含B钢时，B含量一般控制的非常严格，一般在0.001-0.003％左右；而在薄带连铸工艺中，凝固和冷却速率较快，可有效抑制B的偏析，固溶更多的B含量，因此B的含量可以适当放宽；还可以通过合理的工艺控制生成粗大的BN颗粒，抑制细小的AlN析出，起到固氮 的作用。还有研究表明，B在和Nb、V复合添加时，会得到更好的效果，会减小C原子的偏聚倾向，避免了晶界Fe 23(C,B) 6的析出，因此可以添加更多的B。故在本发明中，采用较传统工艺更高的B含量，范围是0.001-0.006％。
本发明所述的薄规格高耐蚀钢的生产方法，其包括如下步骤：
a)冶炼
按照上述化学成分要求进行冶炼，炼钢过程造渣的碱度a＝CaO/SiO 2(质量比)控制在a<1.5，优选a<1.2，或a＝0.7-1.0；钢水中获得低熔点MnO-SiO 2-Al 2O 3三元夹杂物中的MnO/SiO 2(质量比)控制在0.5～2，优选为1～1.8；钢水中的自由氧[O] Free含量为：0.0005-0.005％；钢水成分中，Mn/S≥250；
b)连铸
连铸采用双辊薄带连铸，在两结晶辊辊缝隙最小处形成1.5-3mm厚的铸带；结晶辊直径在500-1500mm之间，优选直径为800mm；结晶辊内部通水冷却，铸机的浇铸速度为60-150m/min；连铸布流采用两级钢水分配布流***，即中间包+布流器；
c)下密闭室保护
铸带出结晶辊后，铸带温度在1420-1480℃，直接进入到下密闭室内，下密闭室内通非氧化性气体，下密闭室内的氧浓度控制在<5％，下密闭室出口铸带温度为1150-1300℃；
d)在线热轧
铸带在下密闭室内经夹送辊送至轧机，轧制成0.8-2.5mm厚度的带钢，轧制温度为1100-1250℃，控制热轧压下率为10-50％，优选热轧压下率30-50％，轧后带钢厚度为0.8-2.5mm，优选厚度为1.0-1.8mm；
e)带钢轧后冷却
对轧后带钢进行冷却，采用气雾化冷却方式对带钢进行冷却，气雾化冷却的冷却速率为20-100℃/s；
f)带钢卷取
冷却后的热轧带钢直接进行卷取成卷，卷取温度为600-700℃。
进一步，还包括步骤g)后续处理，钢卷经过酸洗-平整后作为酸平卷使用，或经过酸洗-热镀锌后作为镀锌板使用。
优选的，步骤a)中，冶炼原料可选用100％全废钢，无需预筛选，钢水冶炼采用电炉炼钢；或者，冶炼采用转炉炼钢，废钢按占冶炼原料20wt％以上的比例加入转炉，且无需预筛选；然后再进入LF炉、VD/VOD炉或RH炉精炼。
优选的，步骤c)中，所述非氧化性气体为N 2、Ar、或干冰升华得到的CO 2气体。
优选的，步骤e)中，所述气雾化冷却的气水比为15：1～10：1，气压0.5～0.8MPa，水压1.0～1.5MPa。气水比指压缩空气和水的流量比，流量的单位为m 3/h。
优选的，步骤f)中，卷取采用双卷取机形式，也可以采用卡罗塞尔卷取形式，保证带钢的连续生产。
优选的，步骤f)中，冷却后的热轧带钢经切头剪切除质量较差的头部后，直接进行卷取成卷，卷取温度为600-700℃。
在本发明所述生产方法中：
为提高薄带连铸钢水的可浇铸性，炼钢过程造渣的碱度a＝CaO/SiO 2控制在a<1.5，优选a<1.2，或a＝0.7-1.0。
为提高薄带连铸钢水的可浇铸性，需要获得低熔点MnO-SiO 2-Al 2O 3三元夹杂物，如图4的阴影区域，MnO-SiO 2-Al 2O 3三元夹杂物中的MnO/SiO 2(质量比)控制在0.5～2，优选在1～1.8。
为提高薄带连铸钢水的可浇铸性，钢中的氧(O)是形成氧化夹杂物的必要元素，本发明需要形成低熔点的MnO-SiO 2-Al 2O 3的三元夹杂物，要求钢水中的自由氧[O] Free范围为：0.0005-0.005％。
为提高薄带连铸钢水的可浇铸性，上述成分中，Mn和S的控制须满足如下关系式：Mn/S≥250。
铸带出结晶辊后铸带温度在1420-1480℃，直接进入到下密闭室内，下密闭室内的氧浓度控制在<5％，下密闭室对铸带的防氧化保护到轧机入口，下密闭室出口铸带的温度在1150-1300℃。
铸带在下密闭过程中涉及到的BN析出相的理论基础：
钢中硼与氮、铝和氮在γ-Fe中的热力学方程如下：
BN＝B+N；Log[B][N]＝-13970/T+5.24    (1)
AlN＝Al+N；Log[Al][N]＝-6770/T+1.03    (2)
如图5所示，钢中BN的开始析出温度在1280℃左右，980℃时BN的析出趋于平衡，而此时AlN的析出才刚刚开始(AlN的析出温度在980℃左右)，从热力学上讲，BN的析出要优先于AlN。本发明在下密闭室内完成B与N的结合，生成粗大的BN颗粒，从而抑制了细小的AlN析出，减弱细小AlN对晶界的钉扎作用，提高晶粒的生长能力，从而粗化奥氏体晶粒，使奥氏体晶粒更加均匀，有利于有效降低产品的屈强比，改善产品性能；另外B与N的结合可以有效防止晶界低熔点相B 2O 3的出现。
原料可选用100％全废钢无需预筛选，大大降低生产成本。
现代钢铁生产企业为节省投资成本与生产成本，积极对现有生产工艺流程进行技术革新。针对现有热带钢生产工艺流程长、设备多且复杂的问题，许多生产厂家将连铸连轧技术与传统工艺紧密结合，以满足连铸连轧工艺的需求。
采用转炉炼钢提供钢水，则需要生产厂家具备有提供铁水的条件，一般情况下，需要有高炉炼铁或者非高炉炼铁设备，属于目前长流程钢铁生产模式。但是，在废钢资源日益丰富的今天，国家正在倡导提高转炉废钢比，从而可以达到节能降耗、降成本的目的，以前转炉废钢比的平均水平在8％左右，现在和今后转炉废钢比的目标是15-25％。本发明转炉废钢比已经可以达到20％以上。
采用电炉炼钢提供钢水，则以废钢为主要原料，传统工艺比如模铸或者厚板连铸，其凝固冷却速度仅有10 -1-10℃/s，废钢中的这些残余元素，会在凝固过程中发生晶界偏析，恶化钢的性能和质量，严重时直接发生开裂、断裂现象，所以在传统工艺中，要对这些有害元素严加控制，在废钢原料的选择上，需要进行一些预筛选，以及在炼钢过程中需要进行一些特殊处理，比如添加一些精料进行稀释等等，这无疑增加了生产作业成本。由于需要控制钢的成分，对采用的废钢原料有一定的质量要求，一般情况下，需要对废钢进行预筛选分类。有些国内电炉钢厂为了提高生产效率，会在原料组成里选择添加精料如外购海绵铁、碳化铁等来稀释废钢中难以脱除的有害元素，提高钢水的质量。有些国内同时拥有高炉和电炉的钢厂利用自产铁水兑入到电炉中作为电炉原料来提高电炉的生产效率，从而大大缩短电炉的出钢时间，电炉中的铁水勾兑比可达到30～50％。
而采用双辊薄带连铸技术，是典型的亚快速凝固过程，凝固冷却速度高达10 2-10 4℃/s，废钢中的一些有害残余元素，比如Cu、Sn、P等，可以最大限度地固 溶到钢的基体中而不产生晶界偏析，因此可以实现100％全废钢冶炼，无需进行预筛选，大大降低原料成本。这些残余元素还可以起到固溶强化的作用，从而生产出性能优良的超薄热轧带钢。实现劣质废钢资源的生产综合利用，对废钢中的这些有害残余元素起到“化害为利”，“废物利用”的效果。
轧制后的带钢采用气雾化冷却方式：
对在线热轧后的带钢进行轧后冷却，轧制后的带钢采用气雾化冷却方式对带钢进行冷却，气雾化冷却方式可以有效减小带钢表面氧化皮厚度，改善带钢温度均匀性，提高带钢表面质量。气雾化冷却的气水比为15：1～10：1，气压0.5～0.8MPa，水压1.0～1.5MPa。气雾化后形成高压水雾喷射在钢带表面，一方面起到了降低钢带温度的作用，另一方面水雾会形成致密的气膜包覆在带钢表面，起到带钢防氧化的作用，从而有效控制了热轧带钢表面氧化皮的生长。该种冷却方式可以避免传统喷淋或者层流冷却带来的问题，使带钢表面温度均匀下降，提高带钢温度均匀性，从而达到均匀化内部微观组织的效果；同时冷却均匀，可以提高带钢的板形质量和性能稳定性；有效减少带钢表面的氧化皮厚度。气雾化冷却的冷却速率范围为20-100℃/s。
本发明的主要优点：
本发明利用薄带连铸技术生产含锡(Sn)、铜(Cu)/含锡(Sn)、铜(Cu)、硼(B)的耐蚀钢，迄今为止尚未见报导，归纳优点如下：
1.本发明省去了板坯加热、多道次反复热轧等复杂过程，通过双辊薄带连铸+一道次在线热轧工序，生产流程更短、效率更高，产线投资成本和生产成本大幅降低。
2.本发明省去了传统工艺生产耐蚀钢中诸多复杂的中间步骤，与传统生产工艺相比，生产的能耗和CO 2排放大幅度降低，是一种绿色环保的产品。
3.本发明采用薄带连铸工艺生产热轧薄规格耐蚀钢，通过提高Cr的含量，且不存在Cr的偏析问题，耐蚀性能大大提高，可以与不锈钢相媲美，可以实现在传统耐腐蚀钢的基础上再提升一倍；同时铸带厚度本身较薄，通过在线热轧至期望产品厚度，薄规格产品的生产不需要经过冷轧，直接供给市场使用，达到薄规格热轧板供货的目的以及“以热带冷”目的，可以显著提高板带材的性价比。
4.本发明采用添加微量的硼元素，在高温奥氏体中优先析出粗大的BN颗粒从 而抑制细小AlN的析出，减弱细小AlN对晶界的钉扎作用，提高晶粒的生长能力，从而粗化、均匀化奥氏体晶粒，有利于改善产品的屈强比和成形性能。
5.本发明冶炼采用通过电炉炼钢，冶炼的原料可以从真正意义上实现100％全废钢冶炼，无需进行预筛选，大大降低原料成本；如果冶炼通过转炉炼钢，废钢按占冶炼原料20％以上的比例加入转炉，且无需预筛选，最大限度提高转炉废钢比，大大降低冶炼成本和能耗。
6.本发明利用含Cu、Sn的废钢，对钢中的Cu、Sn做到“化害为利”，实现对现有废钢或低品质劣质矿资源(高锡矿、高铜矿)的充分利用，促进废钢的循环利用，降低生产成本，实现钢铁业可持续发展。
7.本发明采用轧后带钢气雾化冷却方式，可以避免传统喷淋或者层流冷却带来的问题，使带钢表面温度均匀下降，提高带钢温度均匀性，从而达到均匀化内部微观组织的效果；同时冷却均匀，可以提高带钢的板形质量和性能稳定性；有效减少带钢表面的氧化皮厚度。
8.传统工艺板坯冷却过程中发生合金元素析出，板坯再加热时往往会由于合金元素回溶不充分而降低合金元素利用率。本发明薄带连铸工艺中，高温铸带直接热轧，所添加的合金元素主要以固溶态存在，可提高合金利用率。
9.本发明选用热轧钢带卡罗塞尔卷取机，有效缩短产线长度；同时同位卷取可以大大提高卷取温度的控制精度，提高产品性能的稳定性。
10.本发明区别于现有薄带连铸技术最明显的一个特征就是结晶辊的辊径及其相对应的布流方式。EUROSTRIP技术特征就是Φ1500mm大辊径结晶辊，结晶辊大、熔池钢水容量大，布流容易，结晶辊制造及运维成本高。CASTRIP技术特征就是Φ500mm小辊径结晶辊，结晶辊小、熔池钢水容量小，布流非常困难，但铸机设备制造与运维成本低。CASTRIP为解决小熔池的均匀布流问题，采用三级钢水分配布流***(中间包+过渡包+布流器)。由于采用了三级布流***，会直接导致耐材成本增加；更为主要的是，三级布流***使钢水流动的路径变长，钢水的温降也较大，为了满足熔池钢液的温度，出钢温度需要大大提高。出钢温度的提高，会导致炼钢成本增加、能耗增加以及耐材寿命缩短等问题。
11.本发明结晶辊直径在500-1500mm优选Φ800mm辊径的结晶辊，采用两级钢水分配布流***(中间包+布流器)。从布流器流出的钢水，沿辊面和两个端面 形成不同的布流模式，且分两路流动，互不干扰。由于采用了两级布流***，相比三级布流***，耐材成本大幅度降低；钢水流动路径的缩短，使钢水温降减小，可以降低出钢温度，相比三级布流***，出钢温度可降低30-50℃。出钢温度的降低，可有效降低炼钢成本、节约能耗以及延长耐材寿命。本发明配合优选Φ800mm辊径的结晶辊，采用两级钢水分配布流***，既实现了钢水稳定布流的要求，又实现了结构简单、操作方便、加工成本低的目标。
附图说明
图1为双辊薄带连铸工艺的工艺布置示意图；
图2为Sn含量与平均热流密度的关系示意图；
图3为Sn含量与铸带表面粗糙度的关系示意图；
图4为MnO-SiO 2-Al 2O 3三元相图(阴影区域：低熔点区)；
图5为BN、AlN析出的热力学曲线示意图。
具体实施方式
下面用实施例对本发明作进一步阐述，但这些实施例绝非对本发明有任何限制。本领域技术人员在本说明书的启示下对本发明实施中所作的任何变动都将落在本发明权利要求保护范围内。
参加图1，将符合本发明化学成分设计的钢水经大包1，通过大包长水口2、中间包3、浸入式水口4以及布流器5直接浇注在一个由两个相对转动并能够快速冷却的结晶辊8a、8b和侧封板装置6a、6b围成的熔池7中，钢水在结晶辊8a、8b旋转的周向表面凝固，进而形成凝固壳并逐渐生长随后在两结晶辊辊缝隙最小处(nip点)形成1.5-3mm厚的铸带11；本发明所述的结晶辊直径在500-1500mm之间，内部通水冷却。根据铸带厚度不同，铸机的浇铸速度范围介于60-150m/min。
在铸带11出结晶辊8a、8b后，铸带温度在1420-1480℃，直接进入到下密闭室10内，下密闭室10通惰性气体保护带钢，实现对带钢的防氧化保护，防氧化保护的气氛可以是N 2，也可以是Ar，也可以是其他非氧化性气体，比如干冰升华得到的CO 2气体等，下密闭室10内的氧浓度控制在<5％。下密闭室10对铸带11的防氧化保护到轧机13入口。下密闭室10出口铸带的温度在1150-1300℃。然后通 过摆动导板9、夹送辊12、辊道15将铸带送至热轧机13，热轧后形成0.8-2.5mm的热轧带，轧制后的带钢使用气雾化快速冷却装置14以气雾化冷却方式进行冷却，改善带钢温度均匀性。经飞剪装置16切头之后，切头沿着飞剪导板17掉入飞剪坑18中，切头后的热轧带进入卷取机19进行卷取。将钢卷从卷取机上取下后，自然冷却至室温。最后生产的钢卷可以经过酸洗-平整后使用，也可以经过酸洗-热镀锌后使用。
通过实施例来进一步阐述本发明的方法。本发明实施例化学成分如表2所示，其成分余量为Fe和其它不可避免杂质。经本发明的制造方法，工艺参数见表3，最终获得热轧带的力学性能见表4。
对实施例钢进行耐腐蚀性能测试：以普通碳钢Q345B及传统耐大气腐蚀钢SPA-H为对比样品，按耐蚀钢周期浸润腐蚀试验方法(TB/T2375-93)进行72h的周期浸润循环腐蚀实验。通过计算样品单位面积腐蚀失重量求得平均腐蚀速率，进而求得钢种的相对腐蚀率。测试结果见表5。
综上所述，利用薄带连铸工艺技术按本发明提供的钢种成分设计范围生产的高耐蚀钢，屈服强度≥350MPa，抗拉强度≥480MPa，延伸率≥26％，屈强比低于0.8，冷加工折弯性能合格。耐腐蚀性能对比结果亦表明发明钢种的相对腐蚀率≤25。
表2：实施例钢的化学成分(wt.％)
  C Si Mn P S N O Als Cr Ni Cu Sn B
实施例1 0.026 0.22 1.35 0.008 0.005 0.0078 0.0093 0.0009 4.8 1.9 0.36   0.003
实施例2 0.047 0.10 0.90 0.013 0.003 0.0065 0.0110 0.0005 5.0 2.3 0.23 0.005 0.001
实施例3 0.057 0.33 1.28 0.015 0.004 0.0059 0.0150 0.0006 5.2 3.0 0.10 0.033 0.004
实施例4 0.020 0.27 1.10 0.013 0.004 0.0087 0.0130 0.0007 4.3 2.6   0.040 0.006
实施例5 0.026 0.43 0.65 0.009 0.002 0.0052 0.0120 0.0008 4.0 1.9 0.46 0.015 0.003
实施例6 0.048 0.41 0.67 0.012 0.002 0.0046 0.0070 0.0005 5.2 1.0 0.53   0.005
实施例7 0.056 0.19 0.85 0.015 0.003 0.0040 0.0100 0.0008 6.0 1.2 0.16 0.038 0.003
实施例8 0.037 0.38 1.00 0.014 0.004 0.0100 0.0085 0.0003 4.3 1.6 0.60 0.014 0.002
实施例9 0.045 0.35 0.84 0.018 0.003 0.0074 0.0200 0.0006 5.6 2.5 0.43 0.026 0.004
实施例10 0.060 0.44 0.40 0.020 0.001 0.0055 0.0125 0.0004 5.5 2.2   0.018 0.006
实施例11 0.038 0.50 0.65 0.010 0.002 0.0091 0.0090 0.0005 4.5 2.7 0.49 0.007 0.003
实施例12 0.042 0.27 1.70 0.012 0.0067 0.0084 0.0118 0.0003 5.7 1.7 0.34   0.002
实施例13 0.028 0.46 1.37 0.008 0.004 0.0048 0.0132 0.0006 4.5 2.9   0.033 0.005
实施例14 0.033 0.28 1.40 0.017 0.003 0.0064 0.0075 0.0005 5.7 1.8 0.28 0.029 0.004
表3：实施例的工艺参数
Figure PCTCN2020115953-appb-000004
表4：实施例钢的产品力学性能
Figure PCTCN2020115953-appb-000005
Figure PCTCN2020115953-appb-000006
表5：实施例钢的耐大气腐蚀性能测试结果
  平均腐蚀速率(mg/cm 2·h) 相对腐蚀率(％)
Q345B 0.4902 100
SPA-H 0.2148 43.82
实施例1 0.1152 23.50
实施例2 0.1178 24.03
实施例3 0.1038 21.18
实施例4 0.1156 23.58
实施例5 0.1202 24.52
实施例6 0.1087 22.17
实施例7 0.1161 23.68
实施例8 0.1126 22.97
实施例9 0.1218 24.85
实施例10 0.1169 23.85
实施例11 0.1187 24.21
实施例12 0.1068 21.79
实施例13 0.1143 23.32
实施例14 0.1194 24.36

Claims (12)

  1. 一种薄规格高耐蚀钢，其化学成分重量百分比为：C：0.02-0.06％，Si：0.1-0.5％，Mn：0.4-1.7％，P≤0.02％，Cr：4.0-6.0％，Ni：1.0-3.0％，S≤0.007％，N：0.004-0.010％，Als<0.001％，B：0.001-0.006％，总氧[O] T：0.007-0.020％，余量为Fe和不可避免杂质，且同时满足：
    含有Cu：0.1-0.6％和Sn：0.005-0.04％中的一种或两种元素；
    Mn/S≥250。
  2. 如权利要求1所述的薄规格高耐蚀钢，其特征在于，所述高耐蚀钢的屈服强度≥350MPa，抗拉强度≥480MPa，延伸率≥26％，相对腐蚀率≤25％。
  3. 如权利要求1所述的薄规格高耐蚀钢，其特征在于，所述高耐蚀钢的平均腐蚀速率小于0.1250mg/cm 2·h。
  4. 如权利要求1所述的薄规格高耐蚀钢，其特征在于，所述高耐蚀钢的屈强比≤0.75。
  5. 如权利要求1或2所述的薄规格高耐蚀钢，其特征在于，所述高耐蚀钢的显微组织为针状铁素体+珠光体混合微观组织。
  6. 如权利要求1-5中任一项所述的薄规格高耐蚀钢的生产方法，其特征是，包括如下步骤：
    a)冶炼
    按照权利要求1所述化学成分要求进行冶炼，炼钢过程造渣的碱度a＝CaO/SiO 2控制在a<1.5，优选a<1.2，或a＝0.7-1.0；钢水中获得低熔点MnO-SiO 2-Al 2O 3三元夹杂物中的MnO/SiO 2控制在0.5～2，优选为1～1.8；钢水中的自由氧[O] Free含量为：0.0005-0.005％；钢水成分中，Mn/S≥250；
    b)连铸
    连铸采用双辊薄带连铸，在两结晶辊辊缝隙最小处形成1.5-3mm厚的铸带；结晶辊直径在500-1500mm之间，优选直径为800mm；结晶辊内部通水冷却，铸机的浇铸速度为60-150m/min；连铸布流采用两级钢水分配布流***，即中间包+布流器；
    c)下密闭室保护
    铸带出结晶辊后，铸带温度在1420-1480℃，直接进入到下密闭室内，下密闭室内通非氧化性气体，下密闭室内的氧浓度控制在<5％，下密闭室出口铸带温度为1150-1300℃；
    d)在线热轧
    铸带在下密闭室内经夹送辊送至轧机，轧制成0.8-2.5mm厚度的带钢，轧制温度为1100-1250℃，控制热轧压下率为10-50％，优选热轧压下率30-50％，轧后带钢厚度为0.8-2.5mm，优选厚度为1.0-1.8mm；
    e)带钢轧后冷却
    对轧后带钢进行冷却，采用气雾化冷却方式对带钢进行冷却，气雾化冷却的冷却速率为20-100℃/s；
    f)带钢卷取
    冷却后的热轧带钢直接进行卷取成卷，卷取温度为600-700℃。
  7. 如权利要求6所述的薄规格高耐蚀钢的生产方法，其特征是，还包括步骤g)后续处理，钢卷经过酸洗-平整后作为酸平卷使用，或经过酸洗-热镀锌后作为镀锌板使用。
  8. 如权利要求6所述的薄规格高耐蚀钢的生产方法，其特征是，步骤a)中，冶炼原料为100％全废钢，无需预筛选，钢水冶炼采用电炉炼钢；或者，冶炼采用转炉炼钢，废钢按占冶炼原料20％以上的比例加入转炉，且无需预筛选；然后再进入LF炉、VD/VOD炉或RH炉精炼。
  9. 如权利要求6所述的薄规格高耐蚀钢的生产方法，其特征是，步骤c)中，所述非氧化性气体为N 2、Ar、或干冰升华得到的CO 2气体。
  10. 如权利要求6所述的薄规格高耐蚀钢的生产方法，其特征是，步骤e)中，所述气雾化冷却的气水流量比为15：1～10：1，气压0.5～0.8MPa，水压1.0～1.5MPa，流量单位为m 3/h。
  11. 如权利要求6所述的薄规格高耐蚀钢的生产方法，其特征是，步骤f)中，卷取采用双卷取机形式，也可以采用卡罗塞尔卷取形式，保证带钢的连续生产。
  12. 如权利要求6所述的薄规格高耐蚀钢的生产方法，其特征是，步骤f)中，冷却后的热轧带钢经切头剪切除质量较差的头部后，直接进行卷取成卷，卷取温度为600-700℃。
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