Ti- and nb-added ferritic stainless steel excellent in low-temperature toughness of welds

Abstract

A Ti, Nb-added ferritic stainless steel with excellent low-temperature toughness of weld zone according to an embodiment of present disclosure includes, in percent (%) by weight of the entire composition, C: 0.004 to 0.015%, N: 0.004 to 0.015%, Si: 0.01 to 0.7%, Mn: 0.01 to 0.7%, P: 0.0001 to 0.04%, S: 0.0001 to 0.005%, Cr: 10 to 30%, Al: 0.005 to 0.04%, Ti: 0.1 to 0.5%, Nb: 0.1 to 0.6%, Ca: 0.0001 to 0.003%, the remainder of iron (Fe) and other inevitable impurities, satisfies the following equation (1), and Al—Ca—Ti—Mg—O-based oxide and Ti—Nb—C—N carbonitride containing the oxide have an average diameter of 3 to 10 μm and a distribution density of 4/mm 2 or more. {(Ti+0.5*Nb)*(C+N)}/Al>0.25  (1)

1 . A Ti, Nb-added ferritic stainless steel with excellent low-temperature toughness of weld zone comprising, in percent (%) by weight of the entire composition, C: 0.004 to 0.015%, N: 0.004 to 0.015%, Si: 0.01 to 0.7%, Mn: 0.01 to 0.7%, P: 0.0001 to 0.04%, S: 0.0001 to 0.005%, Cr: 10 to 30%, Al: 0.005 to 0.04%, Ti: 0.1 to 0.5%, Nb: 0.1 to 0.6%, Ca: 0.0001 to 0.003%, the remainder of iron (Fe) and other inevitable impurities, and
 satisfying the following equation (1),   Al—Ca—Ti—Mg—O-based oxide and Ti—Nb—C—N carbonitride containing the oxide have an average diameter of 3 to 10 μm and a distribution density of 4/mm 2  or more:
   {(Ti+0.5*Nb)*(C+N)}/Al>0.25  (1)
 
   (Here, Ti, Nb, C, N, and Al mean the content (% by weight) of each element).   
     
     
         2 . The ferritic stainless steel of  claim 1 , wherein the distribution density is 4/mm 2  or more and 15/mm 2  or less. 
     
     
         3 . The ferritic stainless steel of  claim 1 , further comprising: any one or more selected from the group consisting of Mo: 0.1 to 2.0%, Ni: 0.1 to 2.0% and Cu: 0.1 to 2.0%. 
     
     
         4 . The ferritic stainless steel of  claim 1 , wherein the Al—Ca—Ti—Mg—O-based oxide satisfies the following equations (2) to (4):
   %(TiO 2 )+%(CaO)+%(Al 2 O 3 )≥80  (2)
 
   {%(TiO 2 )+%(CaO)}/{%(TiO 2 )+%(CaO)+%(Al 2 O 3 )}≥0.3  (3)
 
   0.3≤%(CaO)/%(TiO 2 )≤0.8.  (4)
 
 
     
     
         5 . The ferritic stainless steel of  claim 1 , wherein the Ti—Nb—C—N carbonitride has the Al—Ca—Ti—Mg—O-based oxide as a nucleus and is formed to surround the Al—Ca—Ti—Mg—O-based oxide. 
     
     
         6 . The ferritic stainless steel of  claim 1 , wherein the average grain size of the solidified structure of the weld zone is less than 150 μm. 
     
     
         7 . The ferritic stainless steel of  claim 1 , wherein an impact energy of the weld zone is 90 J/cm 2  or more at −30° C. 
     
     
         8 . The ferritic stainless steel of  claim 1 , wherein a DBTT of the weld zone is −25° C. or less:
   {(Ti+0.5*Nb)*(C+N)}/Al≥0.25.  (1)