FERRITIC STAINLESS STEEL HAVING EXCELLENT RIDGING PROPERTY AND EXCELLENT SURFACE QUALITY AND METHOD OF MANUFACTURING THE SAME

1 . A ferritic stainless steel having excellent ridging properties and excellent surface quality comprising, by wt %, 0.005 to 0.1% of carbon (C), 0.01 to 2.0% of silicon (Si), 0.01 to 1.5% of manganese (Mn), 0.05% or less of phosphorus (P), 0.005% or less of sulfur (S), 10 to 30% of chromium (Cr), 0.005 to 0.1% of nitrogen (N), 0.005 to 0.2% of aluminum (Al), and the remainder of iron (Fe) and other impurities,

wherein a γ max value represented by Formula 1 below is in the range of 20% to less than 50%,

420×C+470×N+10×Mn+180−11.5×Cr−11.5×Si−52.0×Al  (1)

wherein C, N, Mn, Cr, Si, and Al refer to amounts of respective elements (wt %).

2 . The ferritic stainless steel according to claim 1 , wherein the stainless steel has a surface microgroove area ratio of 2.0% or less.

3 . The ferritic stainless steel according to claim 1 , wherein the stainless steel has a ridging height of 12 μm or less.

4 . The ferritic stainless steel according to claim 1 , wherein the stainless steel has an r-bar value of 1.2 or greater.

5 . A method of manufacturing a ferritic stainless steel having excellent ridging properties and excellent surface quality, the method comprising:

preparing a slab comprising, by wt %, 0.005 to 0.1% of carbon (C), 0.01 to 2.0% of silicon (Si), 0.01 to 1.5% of manganese (Mn), 0.05% or less of phosphorus (P), 0.005% or less of sulfur (S), 10 to 30% of chromium (Cr), 0.005 to 0.1% of nitrogen (N), 0.005 to 0.2% of aluminum (Al), and the remainder of iron (Fe) and other impurities and having a γ max value represented by Formula 1 below and satisfying 20% to less than 50%;

hot rolling the slab by reheating;

coiling the hot rolled steel sheet; and

cold rolling the coiled hot rolled steel sheet before conducting hot annealing:

420×C+470×N+10×Mn+180−11.5×Cr−11.5×Si−52.0×Al  (1)

wherein C, N, Mn, Cr, Si, and Al refer to amounts of respective elements (wt %).

6 . The method according to claim 5 , wherein a coiling temperature is 750° C. or higher in the coiling of the hot rolled steel sheet.

7 . The method according to claim 5 , wherein the cold rolling is performed by asymmetric cold rolling.

8 . The method according to claim 5 , wherein the cold rolling or the asymmetric cold rolling is performed with a reduction ratio of 30% or more.

9 . The method according to claim 7 , wherein the asymmetric cold rolling is performed under rolling conditions of a speed ratio between upper and lower rolling rolls (V h /V l ) of 1.25 or greater and a rolling shape factor (l/d) of 1.7 or greater.

wherein

V h : speed of fast roll,

V l : speed of slow roll,

rolling shape factor: l/d=2√{square root over (r(h 0 −h))}/(h 0 +h),

l: length to which contact arc between roll and steel sheet in rolling roll bite is projected,

d: average thickness of the steel sheet, d=(h 0 +h)/2,

r: radius of rolling roll,

h 0 : initial thickness of steel sheet, and

h: final thickness of steel sheet.

10 . The method according to claim 9 , wherein a height of a stainless steel prepared by performing hot annealing, secondary cold rolling, and cold annealing after the asymmetric cold rolling is 10 μm or less.

11 . The method according to claim 5 , further comprising hot annealing after the cold rolling.

12 . The method according to claim 11 , wherein the hot annealing is performed in a temperature range of 550 to 950° C. for 60 minutes or less.

13 . The method according to claim 11 , wherein an average aspect ratio of a structure of a thickness center of a cross-section of the hot annealed steel sheet is 4.0 or less after the hot annealing.