Method for preparing titanium-containing ultra-low-carbon steel

Abstract

Disclosed is a method for preparing a titanium-containing ultra-low-carbon steel, comprising molten iron pretreatment, converter primary smelting, vacuum refining, continuous casting, hot rolling, pickling, and cold rolling. After vacuum refining decarbonization is finished, the content of free oxygen in molten steel is 100-350 ppm; after Al is then added for deoxidation treatment, the circulation time of the molten steel is greater than or equal to 3 min; after other alloys and rare earth elements are then added to the molten steel to adjust the components of the molten steel to the specifications of a finished product, the circulation time of the molten steel is greater than or equal to 2 min; and finally, an oxide Re 2 O 3 ·Al 2 O 3 is generated in the molten steel, and the vacuum refining is finished. The method can effectively improve the properties of a deoxidation inclusion in steel, solve the problem of smooth running of casting of the molten steel, reduce the incidence of cold rolling defects caused by Al 2 O 3 , and improve the product quality of the titanium-containing ultra-low-carbon steel.

1 . A method for preparing a titanium-containing ultra-low-carbon steel,
 comprising hot metal pretreatment, primary converter refining, vacuum refining, continuous casting, hot rolling, pickling and cold rolling;   wherein in the vacuum refining, after decarburization is completed, a free oxygen content in molten steel is 100 to 350 ppm; then Al is added for deoxidization treatment, after which a circulation time of the molten steel is ≥3 min; then additional alloying and rare earth components are added to the molten steel, after which a circulation time of the molten steel is ≥2 min, wherein an oxide of Re 2 O 3 · Al 2 O 3  is finally generated in the molten steel; and the vacuum refining is completed.   
     
     
         2 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein in the vacuum refining,
 before the decarburization treatment, the free oxygen content in the molten steel is adjusted to satisfy a mass ratio O/C=1.25 to 2.15; and/or   the rare earth component comprises Ce or La, and is added in an amount based on a mass ratio REM/T.O=0.7 to 3.0, wherein REM represents a mass of the rare earth component added in kg, and T.O represents a total oxygen amount in the steel in ppm; and/or   a content of impurities other than rare earth element(s) in the rare earth component is <0.1 wt %, wherein a total oxygen amount T.O is <100 ppm, and a N content is ≤30 ppm.   
     
     
         3 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 2 , wherein the oxide of Re 2 O 3 ·Al 2 O 3  is Ce 2 O 3 ·Al 2 O 3  or La 2 O 3 ·Al 2 O 3 . 
     
     
         4 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 2 , wherein a vacuum refining device used for the vacuum refining is an RH furnace or a VD furnace or a VOD furnace. 
     
     
         5 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein in the hot metal pretreatment,
 KR desulfurization is adopted, after which 70% to 80%, of a hot metal ladle top slag is removed; and/or   a S content in the hot metal after the desulfurization is ≤20 ppm.   
     
     
         6 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein in the primary converter refining,
 a top-bottom combined blowing process is adopted, wherein when blowing is stopped, the free oxygen content in the molten steel is ≤600 ppm; and/or   during tapping, when a tapping amount reaches 1/6 to 1/4, lime is added to a steel ladle in an amount of 1.6 to 3 kg/t steel; and when the tapping amount reaches 4/5 or more, aluminum slag is added to the steel ladle in an amount of 1.0 to 1.4 kg/t steel; and/or   after the tapping is completed, a composition of a steel ladle top slag is adjusted to: CaO=40 to 50 wt %, FeO+MnO≤7.0 wt %.   
     
     
         7 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein the titanium-containing ultra-low-carbon steel comprises the following components in mass percentage: C≤0.005%, Si≤0.05%, Mn: 0.05 to 0.3%, Al: 0.04 to 0.15%, Ti: 0.04 to 0.1%, P≤0.05%, S≤0.02%, N≤0.003%, and a balance of Fe and unavoidable impurities, wherein an Al content is greater than a Ti content. 
     
     
         8 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein the titanium-containing ultra-low-carbon steel comprises the following components in mass percentage: C<0.0018%, Si≤0.03%, Mn: 0.07 to 0.15%, Al: 0.04 to 0.07%, Ti: 0.04 to 0.06%, P≤0.015%, S≤0.005%, N≤0.003%, and a balance of Fe and unavoidable impurities, wherein an Al content is greater than a Ti content. 
     
     
         9 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein after Al is added for deoxidization treatment, the circulation time of the molten steel is 3 to 10 min; and/or after the additional alloying and rare earth components are added to the molten steel, the circulation time of the molten steel is 2 to 10 min. 
     
     
         10 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein during the continuous casting, a pass rate of the mold liquid level fluctuation within ±5 mm is >92%; and/or a pass rate of the mold liquid level fluctuation within ±3 mm is >32%. 
     
     
         11 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein during the cold rolling, a cold rolling defect rate caused by Al 2 O 3  is less than 0.05%. 
     
     
         12 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 1 , wherein a titanium consumption in said method is less than 0.7 kg/t steel. 
     
     
         13 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 2 , wherein in the vacuum refining, before the decarburization treatment, the free oxygen content in the molten steel is adjusted to satisfy a mass ratio O/C=1.3 to 2.0. 
     
     
         14 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 5 , wherein in the hot metal pretreatment, KR desulfurization is adopted, after which 3/4 of a hot metal ladle top slag is removed. 
     
     
         15 . The method for preparing a titanium-containing ultra-low-carbon steel according to  claim 6 , wherein in the primary converter refining, during tapping, when a tapping amount reaches 1/5, lime is added to a steel ladle in an amount of 1.6 to 3 kg/t steel; and when the tapping amount reaches 9/10, aluminum slag is added to the steel ladle in an amount of 1.0 to 1.4 kg/t steel.