V-n microalloyed steel and method for producing v-n microalloyed and surface-crack-free continuous casting blank

Abstract

Disclosed are a V-N microalloyed steel and a method for producing a V-N microalloyed and surface-crack-free continuous casting blank. The V-N microalloyed steel is composed of the following chemical components by mass percentage: 0.09%-0.13% of C, 0.1%-0.4% of Si, 1.0%-3.0% of Mn, less than or equal to 0.05% of P, less than or equal to 0.05% of S, 0.1%-0.4% of V, 0.011%-0.2% of N and the balance of Fe and unavoidable impurity elements. A continuous casting blank is subjected to component control according to the chemical components of the V-N microalloyed steel; and the production method therefor comprises converter smelting, LF refining and continuous casting steps in sequence. According to the present invention, by means of reasonable component design and smelting and continuous casting processes, the thermoplasticity of the continuous casting blank is improved, so that a high-temperature brittle region is prevented in a casting blank straightening region of the continuous casting blank or the thermoplasticity is good enough such that no surface crack appears, the casting blank is good in terms of surface quality and does not need to be cleaned, and the production efficiency is improved.

1 . A V-N microalloyed steel, characterized in that the V-N microalloyed steel consists of the following chemical components by mass percentage: C: 0.09˜0.13%, Si: 0.1˜0.4%, Mn: 1.0˜3.0%, P: ≤0.05%, S: ≤0.05%, V: 0.1˜0.4%, N: 0.011˜0.2%, and the balance of Fe and unavoidable impurity elements. 
     
     
         2 . A production method for V-N microalloyed surface-crack-free continuous casting blanks, characterized in that the casting blanks are produced according to the chemical components of the V-N microalloyed steel according to  claim 1 ; the method includes the following processes in sequence: converter smelting, LF refining and continuous casting. 
     
     
         3 . The production method according to  claim 2 , characterized in that a cross-sectional specification of the continuous casting blanks is (150-350) mm*(1250-2400) mm. 
     
     
         4 . The production method according to  claim 2 , characterized in that in the converter smelting process, a molten iron proportion is controlled between 88.0wt %˜91.0wt %, a top-bottom combined blowing mode is used throughout entire process, and nitrogen gas is blown first and then argon gas is blown later during blowing process, wherein an argon-blowing time shall not be less than 3 minutes;
 the blowing process adopts a one blow to end blowing mode without reblowing process; 
 a C content at smelting endpoint is controlled between 0.09˜0.13 wt %, and a tapping temperature is between 1625˜1645° C. 
 
     
     
         5 . The production method according to  claim 4 , characterized in that LF refining is performed after tapping, and the refining is without vacuum degassing. 
     
     
         6 . The production method according to  claim 5 , characterized in that in the continuous casting process, a weak water cooling mode is adopted in continuous casting; in the continuous casting process, protective casting is adopted, water port is closed immediately while large ladle alarms at the end of casting, reopening the water port is strictly prohibited after the water port is closed, an intermediate ladle is covered with alkaline covering agent, and a crystallizer uses low-carbon steel protective slag;
 a specific amount of water in the continuous casting process is 0.7˜1.25 L/kg;   a superheat degree of molten steel is 10˜25° C.;   further preferably, a casting speed during continuous casting process is 1.0˜1.3 m/minute.   
     
     
         7 . The production method according to  claim 4 , characterized in that deoxidation alloying is carried out during tapping process in the converter smelting process, while slag filtrating is also carried out;
 a specific operation method of the deoxidation alloying is as follows: during tapping process, a silicon containing substance is selected for deoxidation with an addition amount of 3.5˜4.0 kg/ton of steel; and silicon manganese and vanadium nitrogen alloys are selected for alloying, wherein an addition amount of the vanadium nitrogen alloy is 1˜2 kg/ton of steel;   the slag filtrating is carried out using a substance containing CaO with an addition amount of 3.5˜4.0 kg/ton of steel, and the substance containing CaO needs to be added before molten steel reaches 3/4.   
     
     
         8 . The production method according to  claim 5 , characterized in that in the LF refining process, in an early stage of LF refining, an argon-blowing amount for argon-blowing stirring is 400˜1000 L/minute, an argon-blowing stirring time is 3˜4 minutes, a silicon containing substance should be used for deoxidation, and the components are fine-tuned under the condition of argon-blowing stirring. 
     
     
         9 . The production method according to  claim 8 , characterized in that in the LF refining process, at the end of LF refining, an argon-blowing amount for argon-blowing stirring is 100˜200 L/minute, and a time of argon-blowing stirring is ≥5 minutes; a total refining time is controlled within 40˜50 minutes, and N content obtained is 100˜2000 ppm. 
     
     
         10 . The production method according to  claim 6 , characterized in that in the continuous casting process, a specific distribution of water volume in the continuous casting process is as follows: a water volume in inner and outer arcs of a wide-side foot-roller of the casting blank accounts for about 8.0˜10.0% of the total water volume, a water volume in a narrow-side foot-roller accounts for 3.4˜4.5% of the total water volume, and a water volume in inner and outer arcs of a second zone of a vertical bending section accounts for 11.0˜15.9% of the total water volume, a water volume in inner and outer arcs of a third zone accounts for 13.0˜15.9% of the total water volume, a water volume in inner and outer arcs of a fourth zone accounts for 12.0˜13.0% of the total water volume, a water volume in inner and outer arcs of a fifth zone of arc section 1 accounts for 8.5˜9.5% of the total water volume, a water volume in inner and outer arcs of a sixth zone corresponding to arc sections 2 and 3 accounts for 12.0˜14.0% of the total water volume, a water volume in inner and outer arcs of a seventh zone of sections 4˜5 accounts for 8.0˜11.5% of the total water volume, a water volume in inner and outer arcs of a eighth zone of straightening section 6, section 7 and section 8 accounts for 8.0˜11.5% of the total water volume, and a remaining water volume is allocated to a horizontal section.