TI- AND NB-ADDED FERRITIC STAINLESS STEEL EXCELLENT IN LOW-TEMPERATURE TOUGHNESS OF WELDS
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)