WO2023274223A1 - 一种含钛超低碳钢的制备方法 - Google Patents

一种含钛超低碳钢的制备方法 Download PDF

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WO2023274223A1
WO2023274223A1 PCT/CN2022/101860 CN2022101860W WO2023274223A1 WO 2023274223 A1 WO2023274223 A1 WO 2023274223A1 CN 2022101860 W CN2022101860 W CN 2022101860W WO 2023274223 A1 WO2023274223 A1 WO 2023274223A1
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titanium
steel
low carbon
containing ultra
molten steel
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PCT/CN2022/101860
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English (en)
French (fr)
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胡汉涛
吴雄
陈兆平
马志刚
张志强
职建军
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宝山钢铁股份有限公司
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Priority to DE112022003281.2T priority Critical patent/DE112022003281T5/de
Publication of WO2023274223A1 publication Critical patent/WO2023274223A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/10—Handling in a vacuum
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/0006—Adding metallic additives
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/06—Deoxidising, e.g. killing
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
    • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
    • C21C7/04—Removing impurities by adding a treating agent
    • C21C7/068—Decarburising
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C33/00—Making ferrous alloys
    • C22C33/04—Making ferrous alloys by melting
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/005—Ferrous alloys, e.g. steel alloys containing rare earths, i.e. Sc, Y, Lanthanides
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium

Definitions

  • the invention belongs to the field of metallurgical steelmaking technology, and in particular relates to a preparation method of titanium-containing ultra-low carbon steel.
  • Adding rare earth to titanium-containing ultra-low carbon steel greatly increases the frequency of nozzle nodulation during continuous casting. At this time, even if the total oxygen in the steel can be controlled to be lower than 18ppm or even lower, corresponding to the extremely low level of the total amount of inclusions in the steel, nozzle nodulation still occurs frequently.
  • Al deoxidation products Al 2 O 3
  • REM rare earth metals
  • the publication number CN1218839A emphasizes that after the decarburization of molten steel is completed, Ti is used for deoxidation, alloying, and CaSi alloy or CaSi-REM alloy is added to control the final oxide inclusion composition to be Ti 2 O 3 -CaO or REM oxide-Al 2 O 3 Composite inclusions, containing a small amount of SiO 2 or MnO, wherein the mass percentage of CaO+REM oxides is in the interval [5, 50], so as to obtain a steel plate with improved surface corrosion rate; the theoretical basis of this technology: residual oxide-based inclusions in steel In a specific composition range, the nozzle will not be blocked, and the inclusions can be finely dispersed (proposed by the inventor), so as to manufacture a steel plate with good surface properties; the comparative patent emphasizes the technological effect of its invention, which is due to the controlled addition of deoxidizing Ti content (Ti/Al ratio), the amount of Ca or REM added, so that the composition of the final inclusion is an oxide containing Ti, Ca/REM
  • the object of the present invention is to provide a preparation method of titanium-containing ultra-low carbon steel, by modifying the aluminum deoxidized substance Al 2 O 3 in the steel with rare earth, suppressing its harm and controlling the refining process at the same time
  • the oxygen content and the purity of rare earth metals in molten steel eliminate the influence of rare earth addition on continuous casting and pouring, so that rare earth treated titanium-containing ultra-low carbon steel can be pouring in a straight line, thereby effectively improving the performance of deoxidized inclusions in steel and solving the problem of molten steel It can reduce the incidence of cold rolling defects caused by Al 2 O 3 and improve the product quality of titanium-containing ultra-low carbon steel.
  • the present invention adopts the following technical solutions:
  • the invention provides a preparation method of titanium-containing ultra-low carbon steel, which includes molten iron pretreatment, primary smelting in a converter, vacuum refining, continuous casting, hot rolling, pickling and cold rolling;
  • the free oxygen content in the molten steel is 100-350ppm
  • the circulation time of the molten steel is ⁇ 3min
  • the steel Liquid circulation time ⁇ 2min, the final oxide Re 2 O 3 ⁇ Al 2 O 3 is formed in the molten steel, and the vacuum refining is completed.
  • the rare earth is Ce or La
  • REM is the mass of rare earth added
  • the unit is kg
  • T.O is the total oxygen in the steel
  • the unit is ppm;
  • the content of impurities other than rare earth elements in the rare earth is less than 0.1wt%, wherein the total oxygen T.O is less than 100ppm, and the N content is less than or equal to 30ppm.
  • the oxide Re 2 O 3 ⁇ Al 2 O 3 in the molten steel is Ce 2 O 3 ⁇ Al 2 O 3 or La2O 3 ⁇ Al 2 O 3 .
  • the circulation time of the molten steel is 3-10 min.
  • the circulating time of the molten steel is 2-10 minutes.
  • the vacuum refining device used in the vacuum refining process is a RH vacuum circulation degassing refining furnace (RH furnace) or a vacuum decarburization furnace (VD furnace) or a vacuum oxygen blowing decarburization furnace (VOD furnace).
  • RH furnace RH vacuum circulation degassing refining furnace
  • VD furnace vacuum decarburization furnace
  • VOD furnace vacuum oxygen blowing decarburization furnace
  • Adopt KR desulfurization after desulfurization, remove 70% ⁇ 80%, such as 3/4 of the top slag of molten iron;
  • the S content in the molten iron after desulfurization treatment is ⁇ 20ppm.
  • the free oxygen content in the molten steel is ⁇ 600ppm;
  • ultra-low carbon steel means that the mass percentage of finished carbon in steel is ⁇ 0.005%.
  • the titanium-containing ultra-low carbon steel comprises the following components by mass percentage: C ⁇ 0.005%, Si ⁇ 0.05%, Mn: 0.05-0.3%, Al: 0.04-0.15%, Ti: 0.04-0.1% , P ⁇ 0.05%, S ⁇ 0.02%, N ⁇ 0.003%, the balance is Fe and unavoidable impurities, and the content of Al is greater than that of Ti.
  • the titanium-containing ultra-low carbon steel comprises the following components by mass percentage: C ⁇ 0.0018%, Si ⁇ 0.03%, Mn: 0.07-0.15%, Al: 0.04-0.07%, Ti: 0.04-0.06%, P ⁇ 0.015%, S ⁇ 0.005%, N ⁇ 0.003%, the balance is Fe and unavoidable impurities, wherein the content of Al is greater than that of Ti.
  • the present invention finds that in the late stage of refining after deoxidation treatment, rare earth (Ce or La) is added to the molten steel, and the deoxidation product Al2O3 that does not exclude the molten steel reacts as follows:
  • n in the above formula are 11, 1, and 0; correspondingly, as the amount of rare earth added increases, the resulting reaction products are Re 2 O 3 ⁇ 11Al 2 O 3 (also known as ⁇ Al 2 O 3 ) , Re 2 O 3 ⁇ Al 2 O 3 (Ce 2 O 3 ⁇ Al 2 O 3 or La2O 3 ⁇ Al 2 O 3 ) and Re 2 O 3 ; the Ce in the product Re 2 O 3 ⁇ Al 2 O 3 2 O 3 ⁇ Al 2 O 3 is in liquid phase at 1600°C molten steel temperature, and in solid phase, the edges are smooth without obvious sharp angles, and the hardness is close to that of steel matrix.
  • the Al 2 O 3 crystals produced by conventional aluminum deoxidized steels belong to the ⁇ crystal form, which is a hexagonal crystal structure. It is a solid phase at the temperature of the molten steel, with sharp edges and a Mohs hardness of 9, which is much larger than other common materials.
  • the probability of mechanical damage to the steel plate matrix by the inclusions Re 2 O 3 ⁇ Al 2 O 3 in the titanium-containing ultra-low carbon steel of the present invention Greatly reduced, thereby reducing the degree of damage to the steel plate matrix and improving the surface quality of the finished product;
  • the typical inclusions in the cold-rolled finished product produced by the process of the present invention (the main component is confirmed to be Re 2 O 3 Al 2 O 3 ) are shown in Figure 3,
  • the single deoxidation product Al 2 O 3 in the cold-rolled finished product produced by the conventional process is given, as shown in Fig. 2 .
  • the composite inclusions produced under the control of the present invention have relatively smooth edges without obvious edges and corners, and the inclusions of the present invention tend to extend along the rolling direction after rolling, and have better plasticity.
  • titanium-containing ultra-low carbon steel causes nodules and is difficult to cast is that on the one hand, Ti in molten steel improves the wettability of the interface between the Al 2 O 3 surface layer and molten steel, thereby reducing the Al
  • the formation of the nodule position promotes the aggravation of nodulation.
  • test results conducted by the inventors show that: when the titanium-containing ultra-low carbon steel is smelted, when rare earth is added to the aluminum-deoxidized steel, the nozzle nodulation tends to intensify, and the crystallizer liquid level fluctuation rate increases, which seriously affects the continuous casting process
  • the forward movement reduces the proportion of qualified slabs and deteriorates the quality of finished products.
  • O/C mass ratio ⁇ 2.0 it is believed that oxygen in molten steel must ensure a sufficient excess (O/C mass ratio ⁇ 2.0) to maintain a high vacuum decarburization rate.
  • the present invention found that the initial oxygen-carbon mass ratio of vacuum decarburization in actual production is greater than 1.25, preferably greater than 1.27, for example greater than 1.3, and the carbon in molten steel can be reduced to below 10ppm within 17min.
  • the mass ratio of oxygen to carbon is less than 2.15, preferably less than 2.1, such as less than 2.0, so as to ensure that the oxygen content in the molten steel at the end of decarburization is less than 350ppm.
  • the vacuum refining decarburization treatment of the present invention makes the carbon in the molten steel below the required value of the finished product.
  • the free oxygen O in the molten steel is in the range of 100-350ppm; Decarburization time, the lower the free oxygen, the greater the decarburization time extension value; if the free oxygen after decarburization is higher than 350ppm, there are more deoxidized products in molten steel, the content of Al 2 O 3 in ladle slag is higher, and the crystallizer liquid level Volatility increased significantly.
  • the pure circulation time of the molten steel after aluminum addition and deoxidation is required to be ⁇ 3 minutes, so as to ensure that the deoxidation product Al2O3 in the steel fully floats up to the top slag of the ladle, so that most of the generated inclusions float up to the ladle top slag.
  • the composition of molten steel is adjusted to the target range, and the composition of oxide inclusions in the steel is controlled.
  • the circulation time of molten steel is ⁇ 2min, so that the number of residual inclusions in the molten steel is as small as possible.
  • Requirements about rare earth in the present invention 1) total oxygen T.O ⁇ 100ppm, which belongs to harmful components and will pollute molten steel, the lower the content, the better, so as to ensure the smooth flow of molten steel continuous casting; 2) N content ⁇ 30ppm, Control the content of titanium nitride in the finished product to be at a low level; 3) Other impurities in the rare earth except rare earth elements contain ⁇ 0.1wt%; achieve pouring straight, improve the performance of oxide inclusions, and reduce the titanium content of ultra-low carbon steel cold rolling The purpose of steel defects.
  • the preparation method of titanium-containing ultra-low carbon steel provided by the present invention effectively improves the performance of deoxidized inclusions in the steel, solves the problem of the casting of molten steel, reduces the incidence of cold rolling defects caused by Al 2 O 3 , and improves
  • the product quality of titanium-containing ultra-low carbon steel specifically includes the following beneficial effects:
  • the cold-rolling defect rate caused by Al 2 O 3 is lower than 0.05%, which is more than 90% lower than the conventional rare earth-free treatment process;
  • composition of oxide inclusions in steel changes from pure Al 2 O 3 to Re 2 O 3 Al 2 O 3 ;
  • the ratio of slab to steel is about 35% on average, which is better than the conventional rare earth-free treatment process (about 37% on average);
  • the vacuum refining time is less than 27 minutes, which is equivalent to the conventional rare earth-free treatment process
  • the consumption of titanium is lower than 0.7kg/t steel, which is equivalent to the conventional rare earth-free treatment process, and about 0.5kg/t steel less than the previous treatment process of adding titanium rare earth.
  • Fig. 1 is the schematic flow sheet of the preparation method of the titanium-containing ultra-low carbon steel of some embodiments of the present invention
  • Figure 2 is a schematic diagram of typical inclusions in cold-rolled finished steel under conventional processes
  • Fig. 3 is a schematic diagram of typical inclusions in the cold-rolled finished steel of the present invention.
  • Fig. 4 is a schematic diagram of crystallizer liquid level fluctuation coincidence rate
  • Figure 5 is a schematic diagram of the ratio of billet to steel.
  • the preparation method of titanium-containing ultra-low carbon steel provided by the present invention includes molten iron pretreatment, primary smelting in converter, vacuum refining, continuous casting, hot rolling, pickling and cold rolling; decarburization in vacuum refining
  • the free oxygen content in the molten steel is 100-350ppm, and then add Al for deoxidation treatment, the molten steel circulation time is ⁇ 3min; then add other alloys and rare earths to the molten steel, the molten steel circulation time is ⁇ 2min, and the final molten steel
  • the oxide Re 2 O 3 ⁇ Al 2 O 3 is formed in the process, and the vacuum refining is completed.
  • Other alloys added in vacuum refining are determined according to the composition of the specific finished steel product.
  • other alloys may include but not limited to one or more of alloying elements such as Mn, Nb, V, and B.
  • the molten iron is desulfurized by KR. After desulfurization, 3/4 of the top slag of the molten iron is removed; the S content in the molten iron after desulfurization is ⁇ 20ppm.
  • the converter adopts top-bottom combined blowing to ensure the strength of the bottom blowing.
  • the free oxygen content in the molten steel is ⁇ 600ppm;
  • the free oxygen O in the molten steel is between 100 and 350 ppm, and in some embodiments, the free oxygen O is between 100 and 300 ppm.
  • the applicable steel type is titanium-containing ultra-low-carbon steel products
  • this type of titanium-containing ultra-low-carbon steel includes the following components by mass percentage: C ⁇ 0.005%, Si ⁇ 0.05%, Mn: 0.05 ⁇ 0.3%, Al: 0.04 ⁇ 0.15%, Ti: 0.04 ⁇ 0.1%, P ⁇ 0.05%, S ⁇ 0.02%, N ⁇ 0.003%, the balance is Fe and unavoidable impurities
  • the content of Al is greater than that of Ti, so as to ensure that the final deoxidation of the molten steel is controlled by Al in the molten steel before the rare earth is added.
  • the preparation method of the titanium-containing ultra-low carbon steel of the present invention is further introduced in conjunction with specific examples below; wherein the following components of the titanium-containing ultra-low carbon steel in the embodiments are: C ⁇ 0.0018%, Si ⁇ 0.03%, Mn: 0.07 ⁇ 0.15%, Al: 0.04 ⁇ 0.07%, Ti: 0.04 ⁇ 0.06%, P ⁇ 0.015%, S ⁇ 0.005%, N ⁇ 0.003%, the balance is Fe and unavoidable impurities, the content of Al Greater than Ti content;
  • the process path adopted in this embodiment is molten iron pretreatment (hot metal desulfurization, dephosphorization) ⁇ converter primary smelting (converter top-bottom combined blowing smelting, tapping) ⁇ ladle top slag modification ⁇ vacuum refining (decarburization, deoxidation, alloying chemical and rare earth treatment) ⁇ continuous casting ⁇ hot rolling ⁇ pickling ⁇ cold rolling;
  • the coincidence rate of ⁇ 5mm of liquid level fluctuation in the crystallizer is 94.2%, and the coincidence rate of ⁇ 5mm of liquid level fluctuation is 36%; 40%, and the steel defect rate caused by Al 2 O 3 is 0.02%.
  • Table 1 and table 2 are other situations of applying the program example of the present invention in actual production, contrast I group adopting titanium pre-deoxidation rare earth treatment and contrast II group adopting the situation comparison of conventional non-rare earth treatment;
  • contrast I group comparativative examples 1 ⁇ 6
  • process molten iron pretreatment (desulfurization, dephosphorization) ⁇ primary smelting (converter top-bottom blowing smelting, tapping) ⁇ ladle top slag modification ⁇ vacuum refining (decarburization, titanium pre-deoxidation, Al deoxidation, alloying and rare earth treatment) ⁇ continuous casting ⁇ hot rolling ⁇ pickling ⁇ cold rolling
  • comparison group II comparativative examples 7 to 12) process: molten iron pretreatment (desulfurization, dephosphorization) ⁇ primary smelting (converter top and bottom combined blowing smelting, tapping) ⁇ Ladle top slag modification ⁇ vacuum refining (decarburization, Al deoxidation, alloying) ⁇ continuous
  • the crystallizer liquid level fluctuates The coincidence rates of ⁇ 5mm and ⁇ 3mm are >92% and >32%, respectively, which are superior to the conventional rare earth-free treatment process;
  • the oxide inclusion composition of the titanium-containing ultra-low carbon steel of the present invention is transformed from pure Al 2 O 3 to Re 2 O 3 Al 2 O 3 ;
  • the titanium-containing ultra-low carbon steel of the present invention has an average ratio of slab to steel of about 35%, which is better than the conventional rare earth-free treatment process (average about 37%);
  • the vacuum refining time is less than 27min, which is different from the conventional non- The rare earth treatment process is equivalent;
  • the titanium consumption is equivalent to the conventional rare earth-free treatment process, which is about 0.5kg/t steel less than the previous rare earth treatment process with titanium addition.
  • the titanium-containing ultra-low carbon steel produced by the present invention has the same vacuum refining time as the titanium consumption and conventional rare earth-free treatment, and can ensure that the continuous casting process goes smoothly and greatly reduces the occurrence of cold rolling defects caused by Al 2 O 3 rate (reduction > 90%), significantly improving the product quality of titanium-containing ultra-low carbon steel;
  • the preparation method of titanium-containing ultra-low carbon steel of the present invention effectively improves the performance of deoxidized inclusions in the steel, solves the problem of continuous casting of molten steel, and reduces the amount of Al 2 O 3
  • the occurrence rate of cold-rolling defects caused by it is suitable for improving the quality of titanium-containing ultra-low carbon steel cold-rolled products, and has the value of popularization and application in steelmaking plants.

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Abstract

本发明公开了一种含钛超低碳钢的制备方法，包括铁水预处理、转炉初炼、真空精炼、连铸、热轧、酸洗和冷轧；真空精炼脱碳结束后，钢液中自由氧含量为100～350ppm，然后加Al进行脱氧处理后，钢液循环时间≥3min；再向钢液中加入其他合金和稀土元素调整钢液成分至成品规格后，钢液循环时间≥2min，最终钢液中生成氧化物Re 2O 3·Al 2O 3，真空精炼结束。该方法能有效改善钢中脱氧夹杂物的性能，解决钢液的浇铸顺行问题，降低Al 2O 3所引起的冷轧缺陷的发生率，改善含钛超低碳钢的产品质量。

Description

一种含钛超低碳钢的制备方法 技术领域
本发明属于冶金炼钢工艺领域，尤其涉及一种含钛超低碳钢的制备方法。
背景技术
超低碳钢冶炼时，一般地用铝对钢液终脱氧，脱氧产物以α-Al 2O 3相存在于钢中，其中α-Al 2O 3夹杂的硬度远大于钢，在后续冷轧或其他形式加工时，Al 2O 3夹杂损伤钢的基体，成为裂纹的发源地或诱因，损害钢品质；在中国专利CN109402321B和公开号WO2021036974A1中提出，在钢中添加稀土可有效减少Al 2O 3夹杂所造成的缺陷。
在含钛超低碳钢冶炼时，钢中钛常常造成水口结瘤，连铸结晶器液面波动幅度加大，结晶器保护渣卷入钢液形成缺陷的风险增加，甚至水口内壁结冷钢，导致连铸机拉速下降甚至浇注中止。普遍的观点认为，减少钢中脱氧产物Al 2O 3含量是解决含钛超低碳钢水口结瘤的有效方法。
对含钛超低碳钢添加稀土，连铸时水口结瘤发生频率大大增加。此时，即便将钢中总氧可以控制至低于18ppm甚至更低，对应钢中夹杂物总量已达到极低水平，仍频繁发生水口结瘤。
为此，对含钛超低碳钢，降低Al脱氧产物(Al 2O 3)对冷轧钢质的危害，需控制钢中氧化物夹杂的特性，且保证冶炼时浇注过程的稳定性。
中国专利CN1678761B，强调向Al脱氧钢中加入稀土金属(REM)，加入量为质量比REM/T.O＝0.05-0.5(最终氧化物中稀土类氧化物占比0.5-15％)，从而减少钢中相邻Al 2O 3颗粒之间FeO或FeO·Al 2O 3的数量，抑制Al 2O 3颗粒的团聚，最终能够提高成品质量；该技术的理论基础：钢中相邻Al 2O 3颗粒之间存在FeO 或FeO·Al 2O 3(发明人提出)，二者在钢液中呈液态，致使钢中Al 2O 3夹杂团聚成大尺寸颗粒，这些大尺寸夹杂物颗粒是后续成品质量恶化的重要原因。
公开号CN1218839A强调钢液脱碳完成后，依次使用Ti脱氧，合金化，加入CaSi合金或CaSi-REM合金，控制最终氧化物夹杂组成为Ti 2O 3-CaO或REM氧化物-Al 2O 3的复合夹杂，含少量SiO 2或MnO，其中CaO+REM氧化物质量百分比位于区间[5，50]，从而获得改善表面锈蚀率的钢板；该技术的理论依据：钢中残留的氧化物系夹杂物在特定组成范围内不会造成水口堵塞，而且可以是夹杂物微细分散化(发明人提出)，从而制造表面性能良好的钢板；对比专利强调其发明的工艺效果，是由于控制加入脱氧用的Ti含量(Ti/Al比值)，加入的Ca或REM量，使其满足最终夹杂物的组成为含Ti、Ca/REM和Al的氧化物。
文献Investigating the influence of Ti and P on the clogging of ULC steels in the continuous casting process(C.Bernhard等InSteelCon 2011 Proceedings)揭示，在严格控制二次氧化条件下，加入钢中的钛能够提高氧化铝和钢液间润湿性，同时可以提高Al 2O 3基耐火材料与钢液的润湿性，这就会降低传热界面阻力；由于钢液与浸入式水口的导热速率增加，因此会产生由于温度低造成的结瘤。
在公开号WO2021036974A1中，发明人提出含钛超低碳钢冶炼时，真空(RH、VD或VOD)脱碳结束先后向钢液中加入Ti和Al进行脱氧，随后向钢液中加入稀土，能有效解决含钛超低碳钢稀土处理连铸浇注顺行问题；实际生产中，先行加入的钛与钢液中自由氧的反应产物上浮至钢包顶渣并被其吸收，致使钛消耗量增加0.5kg/t钢；此外，先行加Ti预脱氧将延长真空处理时间5min以上；即含钛超低碳钢稀土处理时采用先行加钛预脱氧操作，增加了产品的原料成本，延长了精炼周期，增加了冶炼过程热量负荷。
鉴于上述情况，业界亟待研发一种新的含钛超低碳钢的制备方法，能够有效改善钢中脱氧夹杂物的性能，解决钢液的浇铸顺行问题，降低Al 2O 3所引起的冷轧缺陷的发生率，改善含钛超低碳钢的产品质量。
发明内容
针对现有技术中存在的上述缺陷，本发明的目的是提供一种含钛超低碳钢的制备方法，通过稀土改性钢中的铝脱氧物Al 2O 3，抑制其危害，同时控制精炼过程钢液中氧含量和稀土金属纯度，消除稀土加入对连铸浇注顺行的影响，使得稀土处理含钛超低碳钢浇注顺行，从而有效改善钢中脱氧夹杂物的性能，解决钢液的浇铸顺行问题，降低Al 2O 3所引起的冷轧缺陷的发生率，改善含钛超低碳钢的产品质量。
为实现上述目的，本发明采用如下技术方案：
本发明提供了一种含钛超低碳钢的制备方法，包括铁水预处理、转炉初炼、真空精炼、连铸、热轧、酸洗和冷轧；
所述真空精炼中，脱碳结束后，钢液中自由氧含量为100～350ppm，然后加Al进行脱氧处理后，钢液循环时间≥3min；再向钢液中加入其他合金和稀土后，钢液循环时间≥2min，最终钢液中生成氧化物Re 2O 3·Al 2O 3，真空精炼结束。
优选地，所述真空精炼过程中：
所述脱碳处理前，调整所述钢液中自由氧含量，满足质量比O/C＝1.25～2.15，优选O/C＝1.27～2.1，例如O/C＝1.3～2.0；和/或
所述稀土为Ce或La，添加量按质量比REM/T.O＝0.7～3.0，REM为稀土加入质量，单位kg，T.O为钢中总氧，单位ppm；和/或
所述稀土中除稀土元素外的其他杂质含量＜0.1wt％，其中总氧T.O＜100ppm，N含量≤30ppm。
优选地，所述钢液中氧化物Re 2O 3·Al 2O 3为Ce 2O 3·Al 2O 3或La2O 3·Al 2O 3。
在一个或多个实施方案中，加Al进行脱氧处理后，钢液循环时间为3-10min。
在一个或多个实施方案中，向钢液中加入其他合金和稀土后，钢液循环时间为2-10min。
优选地，所述真空精炼过程中所用的真空精炼装置为RH真空循环脱气精炼炉(RH炉)或真空脱碳炉(VD炉)或真空吹氧脱碳炉(VOD炉)。
优选地，所述铁水预处理中：
采用KR脱硫，脱硫后，扒除70％～80％、例如3/4的铁水包顶渣；和/或
脱硫处理后的铁水中S含量≤20ppm。
优选地，所述转炉初炼过程中：
采用顶底复合吹炼，停吹时，钢液中游离氧含量≤600ppm；和/或
出钢过程中，出钢量达到1/6～1/4、例如1/5时，向钢包中加入石灰1.6～3kg/t钢，出钢量达到4/5以上、例如9/10时，向钢包中加入铝渣1.0～1.4kg/t钢；和/或
出钢结束后，调整钢包顶渣成分为：CaO＝40～50wt％，FeO+MnO≤7.0wt％。
本发明中，超低碳钢是指钢中成品碳的质量百分比≤0.005％。
优选地，所述含钛超低碳钢包含按质量百分比计的如下成分：C≤0.005％、Si≤0.05％，Mn：0.05～0.3％，Al：0.04～0.15％、Ti：0.04～0.1％、P≤0.05％，S≤0.02％、N≤0.003％，余量为Fe和不可避免的杂质，且Al的含量大于Ti的含量。
在一个或多个实施方案中，所述含钛超低碳钢包含按质量百分比计的如下成分：C≤0.0018％、Si≤0.03％、Mn：0.07～0.15％、Al：0.04～0.07％、Ti：0.04～0.06％、P≤0.015％、S≤0.005％、N≤0.003％，余量为Fe和不可避免的杂质，其中Al的含量大于Ti的含量。
本发明发现脱氧处理后的精炼后期，加入稀土(Ce或La)至钢液中，与未排除钢液的脱氧产物Al 2O 3发生如下反应：
2[Re]+(Al 2O 3)＝(Re 2O 3·n Al 2O 3)+2[Al]   (1)
上式中的n的可能取值为11、1、0；与之对应，随着稀土加入量增加，生成的反应产物依次为Re 2O 3·11Al 2O 3(又称βAl 2O 3)、Re 2O 3·Al 2O 3(Ce 2O 3·Al 2O 3或La2O 3·Al 2O 3)和Re 2O 3；其中生成物Re 2O 3·Al 2O 3中的Ce 2O 3·Al 2O 3在1600℃钢液温度下呈液相，固相时边缘光滑无明显锐角，硬度与钢基体的接近。而常规铝脱氧钢种生成的Al 2O 3晶体属于α晶型，为六方晶系结构，钢液温度下呈固相，边缘锐利，莫氏硬度为9级，远大于其他常见材料。在冷轧和后续冷加工时，与原始单一组分的Al 2O 3夹杂相比，本发明的含钛超低碳钢中夹杂物Re 2O 3·Al 2O 3对钢板基体机械损伤的几率大大降低，从而减轻对钢板基体的损伤程度，改善成品 表面质量；本发明工艺生产的冷轧成品中典型夹杂物(主要组分确认为Re 2O 3·Al 2O 3)示于图3，同时给出了常规工艺生产的冷轧成品中单一脱氧产物Al 2O 3，如图2所示。与单一Al 2O 3相比，本发明控制生成的复合夹杂物，边缘相对光滑无明显棱角，经轧制本发明的夹杂物有沿轧制方向延展的趋势，塑性较好。
本发明认为，含钛超低碳钢造成水口易结瘤、难以浇注的原因在于：一方面钢液中的Ti提高了Al 2O 3表层与钢液之间界面的润湿性，从而降低Al 2O 3夹杂物的大小，而氧化铝夹杂物颗粒越小，越容易结瘤；其二更好的润湿性使得结瘤物与耐材间传热效果更佳，从而造成冷钢在结瘤位置的形成，促使结瘤程度加重。
本发明人进行的试验结果表明：含钛超低碳钢冶炼时，当向铝脱氧钢中加入稀土后，水口结瘤呈现加剧趋势，结晶器液面波动率加大，严重影响了连铸过程的顺行，降低了合格板坯的比例，恶化了成品质量。
经本发明多次试验发现，含钛超低碳钢真空精炼时，控制脱碳终点钢液氧含量，保证加入的稀土纯净度尤其是氧含量，可以有效抑制钢液中Ti对钢液中Al 2O 3表面润湿性的影响，进而改善连铸过程中水口结瘤，保证结晶器液面平稳和连铸过程的顺行。图4和图5分别为本发明冶炼含钛超低碳钢的结晶器液面波动率和铸坯改钢比例。采用本发明技术后，结晶器液面波动幅度最小。
本发明中在真空精炼脱碳处理前，控制钢液中自由氧含量，使得钢液中O、C质量比满足O/C＝1.25～2.15，优选O/C＝1.27～2.1，例如O/C＝1.3～2.0；其中氧碳质量比大于1.25、优选大于1.27、例如大于1.3，用以保证脱去钢液中碳所需的最低氧量。传统意义上，认为钢液中氧必须保证足够过剩量(O/C质量比≥2.0)，以维持较高的真空脱碳速率。本发明研究发现，实际生产中真空脱碳初始氧碳质量比大于1.25、优选大于1.27、例如大于1.3，能够在17min以内将钢液中碳降至10ppm以下。氧碳质量比小于2.15、优选小于2.1、例如小于2.0，以保证脱碳终点钢液中氧含量小于350ppm。
本发明真空精炼脱碳处理，使得钢液中碳位于成品要求值以下，真空处理脱碳结束时，钢液中自由氧O位于100～350ppm区间；若脱碳结束自由氧低于100ppm，将延长脱碳时间，自由氧越低，脱碳时间延长值越大；若脱碳结束自由 氧高于350ppm，钢液中脱氧产物较多，钢包渣中Al 2O 3含量较高，结晶器液面波动显著增大。
本发明真空精炼脱碳处理后，关于加铝脱氧后钢液的纯循环时间，要求≥3min，以保证钢中脱氧产物Al 2O 3充分上浮至钢包顶渣，使得大部分生成的夹杂物上浮至钢包顶渣。
本发明真空精炼处理后期(脱氧后)加入其他合金和稀土(特指Ce或La)后，调整钢液成分至目标范围，控制钢中氧化物夹杂的组成，加入稀土后，钢液循环时间≥2min，使得钢液中残留地夹杂物数量尽可能少。
本发明中关于稀土的要求：1)总氧T.O＜100ppm，属于有害组分，会污染钢液，含量越低越好，以保证钢液连铸浇注的顺行；2)N含量≤30ppm，控制成品中氮化钛含量处于较低水平；3)稀土中除稀土元素以外的其他杂质含＜0.1wt％；达到浇注顺行，改善氧化物类夹杂性能，降低含钛超低碳钢冷轧钢质缺陷的目的。
本发明中关于稀土的加入量：其上限确定为稀土加入质量(kg)与钢液中总氧T.O(ppm)比REM/T.O＝3.0，当稀土加入量超过一定值后，钢液中Al 2O 3可被全部还原，钢液中的氧全部以Re 2O 3形式存在，存在2种可能的不良后果：1)生成单一稀土氧化物Re 2O 3，比重大，不易上浮；2)钢中游离态Re含量急剧上升，与耐材反应，污染钢液，严重情况下会导致塞棒或水口熔损，致使浇铸异常或终断。稀土加入量的下限确定为REM/T.O＝0.70，稀土加入量过低，钢中存在不稳定的Re 2O 3·11Al 2O 3(βAl 2O 3)，甚至单一的Al 2O 3，随着温度的降低，中低温下不稳定的βAl 2O 3分解，发生共析反应：
Re 2O 3·11Al 2O 3(S)→Al 2O 3(S4)+Re 2O 3·Al 2O 3(S)   (2)
生成两个稳定固相Al 2O 3(S4)和Ce(La) 2O 3·Al 2O 3；这些残存于钢中的单一Al 2O 3，降低了稀土对Al 2O 3夹杂的改性效果，无法充分体现冷轧产品质量提高的冶金效果。
本发明所提供的含钛超低碳钢的制备方法，有效改善钢中脱氧夹杂物的性能，解决钢液的浇铸顺行问题，降低Al 2O 3所引起的冷轧缺陷的发生率，改善含钛超低碳钢的产品质量，具体包括以下几点有益效果：
1、结晶器液面波动±5mm和±3mm符合率分别＞92％和＞32％，优于常规无稀土处理工艺；
2、Al 2O 3所引起的冷轧缺陷率低于0.05％，与常规无稀土处理工艺相比降低幅度＞90％；
3、钢中的氧化物夹杂组成由单纯的Al 2O 3转变为Re 2O 3·Al 2O 3；
4、铸坯改钢比例平均约35％，优于常规无稀土处理工艺(平均约37％)；
5、真空精炼时间小于27min，与常规无稀土处理工艺相当；
6、钛消耗量低于0.7kg/t钢，与常规无稀土处理工艺相当，较先行加钛稀土处理工艺约减少0.5kg/t钢。
附图说明
通过阅读参照以下附图对非限制性实施例所作的详细描述，本发明的其它特征、目的和优点将会变得更明显：
图1为本发明的一些实施方案的含钛超低碳钢的制备方法的流程示意图；
图2为常规工艺下冷轧成品钢中的典型夹杂物示意图；
图3为本发明冷轧成品钢中的典型夹杂物示意图；
图4为结晶器液面波动符合率示意图；
图5为铸坯改钢比例示意图。
具体实施方式
为了能更好地理解本发明的上述技术方案，下面结合实施例进一步说明本发明的技术方案。
结合图1所示，本发明所提供的含钛超低碳钢的制备方法，包括铁水预处理、转炉初炼、真空精炼、连铸、热轧、酸洗和冷轧；在真空精炼脱碳结束后，钢液中自由氧含量为100～350ppm，然后加Al进行脱氧处理后，钢液循环时间≥3min；再向钢液中加入其他合金和稀土，钢液循环时间≥2min，最终钢液中生成氧化物 Re 2O 3·Al 2O 3，真空精炼结束。真空精炼中加入的其他合金根据具体钢成品成分确定，例如其他合金可以包括但不限于Mn、Nb、V、B等合金元素中的一种或多种。
在铁水预处理中：铁水采用KR脱硫，脱硫后，扒除3/4的铁水包顶渣；其中脱硫处理后的铁水中S含量≤20ppm。
在转炉初炼过程中：转炉采用顶底复合吹炼，保证底吹强度，停吹时，钢液中游离氧含量≤600ppm；在转炉出钢过程中，出钢量达到1/5时，向钢包中加入石灰1.6～3kg/t钢，出钢量达到9/10时，向钢包中加入铝渣1.0～1.4kg/t钢。在一些实施方案中，转炉初炼出钢结束后，进行钢包顶渣改质，调整钢包顶渣成分为：CaO＝40～50wt％，FeO+MnO≤7.0wt％，钢包顶渣改质结束后，进行真空精炼。
在真空精炼过程中：真空精炼前期，调整钢液中自由氧含量，满足质量比O/C＝1.25～2.15、优选O/C＝1.27～2.1，在一些实施方案中O/C＝1.3～2.0；之后在脱碳处理结束，钢液中自由氧O处于100～350ppm之间，在一些实施方案中自由氧O处于100～300ppm之间，之后加Al进行脱氧处理后，钢液继续循环时间≥3min；在真空精炼后期，加入其他合金元素和稀土(包含稀土元素Ce或La)，调整钢液成分和温度至规格范围内，钢液循环时间≥2min，最终钢液中生成氧化物Re 2O 3·Al 2O 3(比如Ce 2O 3·Al 2O 3或La 2O 3·Al 2O 3)，真空精炼结束；其中稀土的添加量按质量比REM/T.O＝0.7～3.0，稀土REM质量，单位kg，钢中总氧T.O，单位ppm，所添加的稀土中除稀土元素外的其他杂质含量＜0.1wt％，其中总氧T.O＜100ppm，N含量≤30ppm。
上述含钛超低碳钢的制备方法中，适用的钢种为含钛超低碳钢类产品，此类含钛超低碳钢包括按质量百分比计的如下成分：C≤0.005％、Si≤0.05％，Mn：0.05～0.3％，Al：0.04～0.15％、Ti：0.04～0.1％、P≤0.05％，S≤0.02％、N≤0.003％，余量为Fe和不可避免的杂质，且Al的含量大于Ti的含量，以保证稀土加入前钢液的终脱氧受钢液中Al所控制。其中在浇铸过程中：结晶器液面波动±5mm的符合率＞92％；结晶器液面波动±3mm的符合率＞32％。
下面结合具体的例子对本发明的含钛超低碳钢的制备方法进一步介绍；其中实施例中含钛超低碳钢按质量百分比计的以下组分为：C≤0.0018％、Si≤0.03％、Mn：0.07～0.15％、Al：0.04～0.07％、Ti：0.04～0.06％、P≤0.015％、S≤0.005％、N≤0.003％，余量为Fe和不可避免的杂质，其中Al的含量大于Ti的含量；
实施例1
本实施例所采用的工艺路径为铁水预处理(铁水脱硫、脱磷)→转炉初炼(转炉顶底复吹冶炼、出钢)→钢包顶渣改质→真空精炼(脱碳、脱氧、合金化和稀土处理)→连铸→热轧→酸洗→冷轧；
本实施例为本发明冶炼的典型炉次：采用KR脱硫，脱硫后，扒除3/4的铁水包顶渣，脱硫处理后的铁水中S含量为15ppm；转炉初炼过程中，采用顶底复合吹炼，转炉吹炼结束，钢水中C＝220ppm、O＝580ppm，挡渣出钢，出钢初期(出钢量达到1/5时)加入石灰2.2kg/t钢，末期(出钢量达到9/10时)加入铝渣1.1kg/t钢；真空精炼处理前钢包顶渣成分FeO+MnO＝6.50wt％、CaO：42wt％，渣厚110mm；真空精炼处理前期(脱碳处理前)，调整钢液中自由氧含量，使得钢液中质量比O/C＝1.27；真空精炼脱碳结束，钢液中自由氧O：320ppm；之后加入Al进行脱碳处理后，钢液继续循环4.5min；真空精炼后期，加入其他合金元素和稀土，稀土为CeLa合金(Ce∶La质量比为2∶1)，稀土中除稀土元素外的其他杂质含量＜0.1wt％，其中总氧T.O＜100ppm，N含量≤30ppm，调整钢液成份至规格范围，稀土加入后，钢液循环5min，精炼结束，连铸，随后热轧、酸洗和冷轧，其中REM/T.O＝1.2；
工艺效果：本实施例连铸过程中，结晶器液面波动±5mm的符合率为94.2％，液面波动±5mm的符合率为36％；本实施例冷轧钢的铸坯改钢比例为40％，Al 2O 3所致的钢质缺陷率为0.02％。
表1和表2为实际生产中应用本发明方案例的其他情况、对比I组采用钛预脱氧稀土处理以及对比II组采用常规无稀土处理的情况对比；其中对比I组(对比例1～6)工艺：铁水预处理(脱硫、脱磷)→初炼(转炉顶底复吹冶炼、出钢)→钢包顶渣改质→真空精炼(脱碳、钛预脱氧、Al脱氧、合金化和稀土处理)→连铸→热轧→酸洗→冷轧；对比II组(对比例7～12)工艺：铁水预处理(脱硫、脱磷) →初炼(转炉顶底复吹冶炼、出钢)→钢包顶渣改质→真空精炼(脱碳、Al脱氧、合金化)→连铸→热轧→酸洗→冷轧。实施例2～6、对比I组和对比II组与实施例1的工艺参数区别如表1所示。
结合表1、表2所示，与先行加钛与脱氧稀土处理和常规无稀土处理工艺相比，采用本发明的含钛超低碳钢的制备方法在连铸过程中，结晶器液面波动±5mm和±3mm符合率分别＞92％和＞32％，优于常规无稀土处理工艺；本发明的含钛超低碳钢的氧化物夹杂组成由单纯的Al 2O 3转变为Re 2O 3·Al 2O 3；本发明的含钛超低碳钢，铸坯改钢比例平均约35％，优于常规无稀土处理工艺(平均约37％)；真空精炼时间小于27min，与常规无稀土处理工艺相当；钛消耗量与常规无稀土处理工艺相当，较先行加钛稀土处理工艺约减少0.5kg/t钢。采用本发明生成的含钛超低碳钢，真空精炼时间与钛消耗量和常规无稀土处理相当，且能保证连铸浇注过程顺行，大幅度降低Al 2O 3所引起的冷轧缺陷发生率(降低幅度＞90％)，显著改善含钛超低碳钢的产品质量；
因此，本发明的含钛超低碳钢的制备方法，有效改善钢中脱氧夹杂物的性能，解决钢液的连铸浇注过程顺行问题，降低了冷轧成品钢质种Al 2O 3所引起的冷轧缺陷的发生率，适用于含钛超低碳钢冷轧产品质量改善，在炼钢厂具有推广应用价值。
表1
Figure PCTCN2022101860-appb-000001
Figure PCTCN2022101860-appb-000002
表2
Figure PCTCN2022101860-appb-000003
Figure PCTCN2022101860-appb-000004
本技术领域中的普通技术人员应当认识到，以上的实施例仅是用来说明本发明，而并非用作为对本发明的限定，只要在本发明的实质精神范围内，对以上所述实施例的变化、变型都将落在本发明的权利要求书范围内。

Claims (12)

  1. 一种含钛超低碳钢的制备方法，其特征在于，包括铁水预处理、转炉初炼、真空精炼、连铸、热轧、酸洗和冷轧；
    所述真空精炼中，脱碳结束后，钢液中自由氧含量为100～350ppm，然后加Al进行脱氧处理后，钢液循环时间≥3min；再向钢液中加入其他合金和稀土后，钢液循环时间≥2min，最终钢液中生成氧化物Re 2O 3·Al 2O 3，真空精炼结束。
  2. 根据权利要求1所述的含钛超低碳钢的制备方法，其特征在于，所述真空精炼过程中：
    所述脱碳处理前，调整所述钢液中自由氧含量，满足质量比O/C＝1.25～2.15，例如O/C＝1.3～2.0；和/或
    所述稀土为Ce或La，添加量按质量比REM/T.O＝0.7～3.0，REM为稀土加入质量，单位kg，T.O为钢中总氧，单位ppm；和/或
    所述稀土中除稀土元素外的其他杂质含量＜0.1wt％，其中总氧T.O＜100ppm，N含量≤30ppm。
  3. 根据权利要求2所述的含钛超低碳钢的制备方法，其特征在于，所述氧化物Re 2O 3·Al 2O 3为Ce 2O 3·Al 2O 3或La 2O 3·Al 2O 3。
  4. 根据权利要求2所述的含钛超低碳钢的制备方法，其特征在于，所述真空精炼过程中所用的真空精炼装置为RH炉或VD炉或VOD炉。
  5. 根据权利要求1所述的含钛超低碳钢的制备方法，其特征在于，所述铁水预处理中：
    采用KR脱硫，脱硫后，扒除70％～80％、例如3/4的铁水包顶渣；和/或
    脱硫处理后的铁水中S含量≤20ppm。
  6. 根据权利要求1所述的含钛超低碳钢的制备方法，其特征在于，所述转炉初炼过程中：
    采用顶底复合吹炼，停吹时，钢液中游离氧含量≤600ppm；和/或
    出钢过程中，出钢量达到1/6～1/4、例如1/5时，向钢包中加入石灰1.6～3kg/t钢，出钢量达到4/5以上、例如9/10时，向钢包中加入铝渣1.0～1.4kg/t钢；和/或
    出钢结束后，调整钢包顶渣成分为：CaO＝40～50wt％，FeO+MnO≤7.0wt％。
  7. 根据权利要求1-6任一项所述的含钛超低碳钢的制备方法，其特征在于，所述含钛超低碳钢包含按质量百分比计的如下成分：C≤0.005％、Si≤0.05％，Mn：0.05～0.3％，Al：0.04～0.15％、Ti：0.04～0.1％、P≤0.05％，S≤0.02％、N≤0.003％，余量为Fe和不可避免的杂质，且Al的含量大于Ti的含量。
  8. 根据权利要求1-6任一项所述的含钛超低碳钢的制备方法，其特征在于，所述含钛超低碳钢包含按质量百分比计的如下成分：C≤0.0018％、Si≤0.03％、Mn：0.07～0.15％、Al：0.04～0.07％、Ti：0.04～0.06％、P≤0.015％、S≤0.005％、N≤0.003％，余量为Fe和不可避免的杂质，其中Al的含量大于Ti的含量。
  9. 根据权利要求1-6任一项所述的含钛超低碳钢的制备方法，其特征在于，加Al进行脱氧处理后，钢液循环时间为3-10min；和/或向钢液中加入其他合金和稀土后，钢液循环时间为2-10min。
  10. 根据权利要求1-6任一项所述的含钛超低碳钢的制备方法，其特征在于，所述连铸过程中，结晶器液面波动±5mm符合率分别＞92％，和/或结晶器液面波动±3mm符合率＞32％。
  11. 根据权利要求1-6任一项所述的含钛超低碳钢的制备方法，其特征在于，所述冷轧过程中，Al 2O 3所引起的冷轧缺陷率低于0.05％。
  12. 根据权利要求1-6任一项所述的含钛超低碳钢的制备方法，其特征在于，所述制备方法的钛消耗量低于0.7kg/t钢。
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