Ferritic stainless steel having excellent ductility and method for manufacturing same

Abstract

Ferritic stainless steel having a high degree of ductility and a method for manufacturing the ferritic stainless steel are provided. The stainless steel includes, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities, wherein the ferritic stainless steel includes 3.5×10 6 or fewer particles of an independent Ti(CN) precipitate per square millimeter (mm 2 ) of ferrite matrix.

1 . Ferritic stainless steel comprising, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities,
 wherein the ferritic stainless steel comprises 3.5×10 6  or fewer particles of an independent Ti(CN) precipitate per square millimeter (mm 2 ) of ferrite matrix.   
     
     
         2 . Ferritic stainless steel comprising, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities,
 wherein the ferritic stainless steel comprises an independent Ti(CN) precipitate and a dependent Ti(CN) precipitate formed using a TiN inclusion as precipitation nuclei, and the ferritic stainless steel has a P within a range of 60% or less, the P being defined by Formula 1 below:
     P (%)={ N   S /( N   S   +N   C )}×100   [Formula 1]
 
   where N S  refers to the number of independent Ti(CN) precipitate particles per unit area (mm 2 ), and N C  refers to the number of dependent Ti(CN) precipitate particles per unit area (mm 2 ).   
     
     
         3 . The ferritic stainless steel of  claim 2 , wherein the P is 58% or less. 
     
     
         4 . The ferritic stainless steel of  claim 1 , wherein the independent Ti(CN) precipitate has a particle diameter of 0.01 μm or greater. 
     
     
         5 . The ferritic stainless steel of  claim 1 , wherein the independent Ti(CN) precipitate has an average particle diameter of 0.15 μm or less. 
     
     
         6 . The ferritic stainless steel of  claim 2 , wherein the TiN inclusion has an average particle diameter of 2 μm or greater. 
     
     
         7 . The ferritic stainless steel of  claim 1 , wherein the ferritic stainless steel has an elongation of 34% or greater. 
     
     
         8 . A method for manufacturing ferritic stainless steel, the method comprising casting molten steel as a slab, the molten steel comprising, by wt %, C: 0.005% to 0.1%, Si: 0.01% to 2.0%, Mn: 0.01% to 1.5%, P: 0.05% or less, S: 0.005% or less, Cr: 10% to 30%, Ti: 0.005% to 0.5%, Al: 0.01% to 0.15%, N: 0.005% to 0.03%, and the balance of Fe and inevitable impurities,
 wherein in the casting of the molten steel, the slab is cooled at an average cooling rate of 5° C./sec or less (excluding 0° C./sec) within a temperature range of 1100° C. to 1200° C. based on a surface temperature of the slab.   
     
     
         9 . The method of  claim 8 , wherein in the casting of the molten steel, the slab is cooled at an average cooling rate of 5° C./sec or less (excluding 0° C./sec) within a temperature range of 1000° C. to 1250° C. based on the surface temperature of the slab. 
     
     
         10 . The method of  claim 8 , wherein after the casting of the molten steel, the method further comprises:
 reheating the slab;   obtaining hot-rolled steel by performing a hot rolling process on the reheated slab; and   performing a hot band annealing process on the hot-rolled steel within a temperature range of 450° C. to 1080° C. for 60 minutes or less.   
     
     
         11 . The ferritic stainless steel of  claim 2 , wherein the independent Ti(CN) precipitate has a particle diameter of 0.01 μm or greater. 
     
     
         12 . The ferritic stainless steel of  claim 2 , wherein the independent Ti(CN) precipitate has an average particle diameter of 0.15 μm or less. 
     
     
         13 . The ferritic stainless steel of  claim 2 , wherein the ferritic stainless steel has an elongation of 34% or greater.