Twin-roll strip caster, method for manufacturing thin duplex stainless steel sheet using the same and thin duplex stainless steel sheet

Abstract

Provided are a twin-roll strip caster, a method for manufacturing a duplex stainless steel sheet using the same, and a thin duplex stainless steel sheet. The twin-roll strip caster includes a pair of casting rolls rotating in opposite directions, an edge dam installed such that a molten steel pool is formed on respective sides of the casting rolls, and a meniscus shield provided to cover the molten steel pool such that a contact between the molten steel pool and air is blocked, wherein hills and valleys are alternately arranged on surfaces of the cast rolls in circumferential directions thereof and a hill area in edge sections thereof is higher than that in centers sections thereof. Since cast rolls in which a hill area ratio of edge sections is higher than that of center sections are used, a thin stainless steel sheet with improved edge quality may be provided.

What is claimed is: 
     
         1 . A twin-roll strip caster comprising:
 a pair of casting rolls rotating in opposite directions;   an edge dam installed such that a molten steel pool is formed on respective sides of the pair of casting rolls; and   a meniscus shield provided to cover the molten steel pool such that a contact between the molten steel pool and air is blocked,   wherein hills and valleys are alternately arranged on surfaces of the pair of cast rolls in circumferential directions thereof and a hill area ratio (an area ratio of hills) in edge sections thereof is higher than that in centers sections thereof.   
     
     
         2 . The twin-roll strip caster of  claim 1 , wherein the hill area ratio is constant in the center section and is continuously increased in the edge section in a direction away from a boundary between the edge section and the center section. 
     
     
         3 . The twin-roll strip caster of  claim 1 , wherein the hill area ratio in the center section is in a range of about 10-40% and the hill area ratio in the edge section increases up to 70%. 
     
     
         4 . The twin-roll strip caster of  claim 1 , wherein the edge sections have a width of 50-200 mm from one ends of the pair of casting rolls. 
     
     
         5 . The twin-roll strip caster of  claim 1 , wherein a gas discharge index G of the center section has a value of 80-130, the gas discharge index G of the edge section continuously decreases to a range of at least 50-70 from a boundary of the center section, and G=width (W) of valley depth (d)/pitch (p). 
     
     
         6 . A method for manufacturing a thin duplex stainless steel sheet, the method comprising:
 forming a cast strip by pouring molten steel between a pair of cast rolls rotating in opposite directions; and   manufacturing a hot rolled strip by rolling the cast strip in a rolling mill,   wherein hills and valleys are alternately arranged on surfaces of the pair of cast rolls in circumferential directions thereof and a hill area ratio (an area ratio of hills) in edge sections thereof is higher than that in centers sections thereof.   
     
     
         7 . The method of  claim 6 , wherein the reduction ratio is in a range of 15-60%. 
     
     
         8 . The method of  claim 6 , further comprising annealing the hot rolled strip,
 wherein the annealing temperature is in a range of 1,000-1,250° C.   
     
     
         9 . A thin duplex stainless steel sheet manufactured by the method as set forth in  claim 6 . 
     
     
         10 . The duplex stainless steel sheet of  claim 9 , wherein the thin duplex stainless steel sheet comprises, by weight: 0.1% or less carbon (C) (exclusive of 0%), 0.2-3.0% silicon (Si), 1.0-4.0% manganese (Mn), 19.0-23.0% chromium (Cr), 0.3-2.5% nickel (Ni), 0.15-0.3% nitrogen (N), 0.3-2.5% copper (Cu), a balance of iron (Fe), and inevitable impurities. 
     
     
         11 . The duplex stainless steel sheet of  claim 9 , wherein the thin duplex stainless steel sheet may has an elongation of 25-55% in a direction perpendicular to the rolling direction and a yield strength of 350-700 MPa. 
     
     
         12 . The duplex stainless steel sheet of  claim 9 , wherein the thin duplex stainless steel sheet has a recrystallized grain size of about 4-9 μm and a necking-down width of 10 mm or less.