Ferritic stainless steel having improved surface characteristics and method for manufacturing same

Abstract

Disclosed are a ferrite-based stainless steel having improved surface characteristics and a method for manufacturing same. The ferrite-based stainless steel according to the present invention includes, in percent by weight (wt %), 0.001 to 0.05% of C, 0.001 to 0.05% of N, 0.1 to 1.0% of Si, 0.1 to 1.0% of Mn, 12.0 to 22.0% of Cr, 0.01 to 1.0% of Ti, 0.01 to 1.0% of Nb, and the remainder of Fe and unavoidable impurities, wherein micro flaws having a length of 100 μm or more are distributed at a density of 5 pieces/mm2 or less.

1 . A ferrite-based stainless steel having improved surface characteristics comprising, in percent by weight (wt %), 0.001 to 0.05% of C, 0.001 to 0.05% of N, 0.1 to 1.0% of Si, 0.1 to 1.0% of Mn, 12.0 to 22.0% of Cr, 0.01 to 1.0% of Ti, 0.01 to 1.0% of Nb, and the remainder of Fe and unavoidable impurities,
 wherein micro flaws having a length of 100 μm or more are distributed at a density of 5 pieces/mm 2  or less.   
     
     
         2 . The ferrite-based stainless steel according to  claim 1 , further comprising at least one of 0.01 to 2.0% of Mo, 0.10% or less (excluding 0) of Al, 1.0% or less (excluding 0) of Cu, 0.01 to 0.3% of V, 0.01 to 0.3% of Zr, and 0.0010 to 0.0100% of B. 
     
     
         3 . The ferrite-based stainless steel according to  claim 1 , wherein an area rate of micro flaws is 2% or less. 
     
     
         4 . The ferrite-based stainless steel according to  claim 1 , wherein an area rate of micro flaws is 1.6% or less, and
 micro flaws having a length of 100 μm or more are distributed at a density of 2 pieces/mm 2  or less.   
     
     
         5 . The ferrite-based stainless steel according to  claim 1 , wherein a distinctness of reflected image is 90 or more in a rolling direction (L direction) and a direction (C direction) perpendicular to the rolling direction, respectively. 
     
     
         6 . The ferrite-based stainless steel according to  claim 5 , wherein a deviation of distinctness of reflected image between the L direction and the C direction is 5 or less. 
     
     
         7 . A method for manufacturing a ferrite-based stainless steel having improved surface characteristics, the method comprising:
 hot rolling a slab comprising, in percent by weight (wt %), 0.001 to 0.05% of C, 0.001 to 0.05% of N, 0.1 to 1.0% of Si, 0.1 to 1.0% of Mn, 12.0 to 22.0% of Cr, 0.01 to 1.0% of Ti, 0.01 to 1.0% of Nb, and the remainder of Fe and unavoidable impurities and hot annealing the hot-rolled steel sheet;   cold rolling and cold annealing the hot-rolled, annealed steel sheet twice or more by controlling a roll diameter to 70 mm or less;   bright annealing the cold-rolled, annealed steel sheet; and   skin pass rolling the bright-annealed steel sheet,   wherein surface polishing treatment is introduced after hot annealing or after primary cold rolling.   
     
     
         8 . The method according to  claim 7 , wherein the ferrite-based stainless steel further comprises at least one of 0.01 to 2.0% of Mo, 0.10% or less (excluding 0) of Al, 1.0% or less (excluding 0) of Cu, 0.01 to 0.3% of V, 0.01 to 0.3% of Zr, and 0.0010 to 0.0100% of B. 
     
     
         9 . The method according to  claim 7 , wherein the cold rolling comprises:
 primary cold rolling performed at a reduction ratio of 40% or more; and   secondary cold rolling performed at a reduction ratio of 40% or more,   wherein a total reduction ratio is 80% or more.   
     
     
         10 . The method according to  claim 9 , wherein the cold rolling further comprising tertiary cold rolling performed at a reduction ratio of 40% or more. 
     
     
         11 . The method according to  claim 7 , wherein a re-heating temperature is from 1050 to 1280° C., and a final rolling temperature is from 800 to 950° C. during the hot rolling. 
     
     
         12 . The method according to  claim 7 , wherein the surface polishing treatment is performed by removing the surface layer by 7 μm or more using a polishing belt having a roughness of #70 mesh or more. 
     
     
         13 . The method according to  claim 12 , wherein the surface polishing treatment is performed once or twice. 
     
     
         14 . The method according to  claim 7 , wherein the cold annealing is performed at a temperature of 850 to 1,100° C. 
     
     
         15 . The method according to  claim 7 , wherein the bright annealing is performed at a temperature of 850 to 1,100° C. 
     
     
         16 . The method according to  claim 7 , wherein the skin pass rolling is performed using a work roll having an average roughness of #600 or more. 
     
     
         17 . The method according to  claim 16 , wherein the skin pass rolling is performed twice to five times. 
     
     
         18 . The method according to  claim 16 , wherein micro flaws having a length of 100 μm or more are distributed at a density of 5 pieces/mm 2  or less. 
     
     
         19 . The method according to  claim 7 , wherein a distinctness of reflected image is 90 or more in a rolling direction (L direction) and a direction (C direction) perpendicular to the rolling direction, respectively. 
     
     
         20 . The method according to  claim 19 , wherein a deviation of distinctness of reflected image between the L direction and the C direction is 5 or less.