Method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it

Abstract

Disclosed is a method for manufacturing ferritic stainless steel slabs with equiaxed grain structures and the ferritic stainless steel manufactured by it, which control concentration of alumina inclusions in molten steel to maximize an available TiN generation effect serving as a non-uniform nucleating site of ferrite when solidifying it, thereby improving equiaxed crystal ratio, the method comprising the steps of: performing oxygen decarburization reaction by blowing oxygen from the upper part of the molten steel in a vacuum oxygen decarburization ladle; injecting Al in the molten steel to which the oxygen decarburization reaction is made for Cr 2 O 3 reduction; making composite deoxidation by injecting deoxidizer in the molten steel into which the Al is injected for the Cr 2 O 3 reduction; making alloying process by injecting alloying metal in the molten steel; first judging for judging whether Al concentration is in the range of a setting value by analyzing the Al concentration in the molten steel; if the Al concentration satisfies the setting value, stirring it using inert gas and second judging for judging whether alumina inclusion concentration in the final molten steel corresponds to a target value; and if the alumina inclusion concentration satisfies the target value, continuously casting the molten steel.

1 . A method for manufacturing ferritic stainless steel slabs with equiaxed grain structures comprising the steps of:
 performing oxygen decarburization reaction by blowing oxygen from the upper part of the molten steel in a vacuum oxygen decarburization ladle;   injecting Al in the molten steel to which the oxygen decarburization reaction is made for Cr 2 O 3  reduction;   making composite deoxidation by injecting deoxidizer in the molten steel into which the Al is injected for the Cr 2 O 3  reduction;   making alloying process by injecting alloying metal in the molten steel;   first judging for judging whether Al concentration is in the range of a setting value by analyzing the Al concentration in the molten steel;   if the Al concentration satisfies the setting value, stirring it using inert gas and second judging for judging whether alumina inclusion concentration in the final molten steel corresponds to a target value; and   if the alumina inclusion concentration satisfies the target value, continuously casting the molten steel.   
   
   
       2 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein in the composite deoxidating step, the deoxidizer is Si and Mn. 
   
   
       3 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein in the allyoing step, the alloying metal is Ti. 
   
   
       4 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 3 , wherein the Ti is with 0.2˜0.4% by mass. 
   
   
       5 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein in the continuous casting step, the alumina inclusion concentration in the molten steel satisfies the following condition;
   [Al] alumina <70 ppm   (where, [Al] alumina =[Al] total −[Al] dissolved ).   
   
   
       6 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein in the continuous casting step, the component of the molten steel satisfies the following condition;
   [Si]+[Mn]=0.5˜1.0%,   however, % is % by mass.   
   
   
       7 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein that the final composition of a refined slag in the vacuum oxygen decarburization refining ladle satisfies the following condition;
   1.2≦(% CaO)/(% Al 2 O 3 )≦1.4     4≦(% TiO 2 )/(% SiO 2 )≦6   however, % is % by mass.   
   
   
       8 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein the molten steel is 80˜85 ton. 
   
   
       9 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein the setting value of Al concentration in the first judging step is 0.05˜0.12% by mass. 
   
   
       10 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 9 , wherein if the Al concentration is less than 0.05% by mass, it further comprises the step of additionally injecting Al. 
   
   
       11 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 10 , wherein the Al of 30˜40 kg relative to the molten steel of 80˜85 ton is injected. 
   
   
       12 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 9 , wherein if the Al concentration is 0.12% by mass or more, it further comprises the step of additionally injecting quicklime. 
   
   
       13 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 12 , wherein the quicklime of 250˜300 kg relative to the molten steel of 80˜85 ton is injected. 
   
   
       14 . The method for manufacturing ferritic stainless steel slabs with equiaxed grain structures as claimed in  claim 1 , wherein the target value of the alumina inclusion concentration in the second judging step is 70 ppm or less. 
   
   
       15 . A ferritic stainless steel with equiaxed grain structures manufactured according to the method as claimed in  claim 1  to  claim 14 , wherein the alumina inclusion concentration is 70 ppm or less and the equiaxed crystal ratio is 40% or more.