Duplex stainless steel having excellent corrosion resistance and method for manufacturing the same

Abstract

The present invention relates to a duplex stainless steel, and to a duplex stainless steel having excellent corrosion resistance and a method of manufacturing the same.

What is claimed is: 
     
         1 . A duplex stainless steel having excellent corrosion resistance, wherein a surface portion of the steel includes an austenite structure having an area fraction of 85% or more, and an interior of the steel includes ferrite and austenite. 
     
     
         2 . The duplex stainless steel of  claim 1 , wherein the surface portion is up to ⅓ of a steel thickness. 
     
     
         3 . The duplex stainless steel of  claim 1 , wherein the content of nitrogen, included in the surface portion, is 0.4 wt % to 1.0 wt %. 
     
     
         4 . The duplex stainless steel of  claim 1 , wherein the interior of the steel includes an austenite structure having an area fraction of 40% to 60% and a ferrite structure having an area fraction of 40% to 60%. 
     
     
         5 . The duplex stainless steel of  claim 1 , wherein a composition of the steel includes carbon (C): 0.01 wt % to 0.10 wt %, silicon (Si): 0.5 wt % to 1.5 wt %, manganese (Mn): 1.0 wt % to 5.0 wt %, phosphorus (P): 0.03 wt % or less, sulfur (S): 0.02% wt % or less, chromium (Cr): 19.0 wt % to 23.0 wt %, nickel (Ni): 0.5 wt % to 6.5 wt %, molybdenum (Mo): 3.5 wt % or less, copper (Cu): 0.1 wt % to 1.5 wt %, nitrogen (N): 0.1 wt % to 0.3 wt %, and a balance of iron (Fe) and inevitable impurities. 
     
     
         6 . A method of manufacturing a duplex stainless steel having excellent corrosion resistance, comprising:
 preparing a duplex stainless steel; and   bright annealing heat treating the duplex stainless steel in a reducing atmosphere at a temperature within a range of 1000° C. to 1200° C. for 10 seconds or more to 30 minutes or less.   
     
     
         7 . The method of  claim 6 , wherein a dew point temperature of the reducing atmosphere is −20° C. to −80° C. 
     
     
         8 . The method of  claim 6 , wherein, in an atmosphere gas of the reducing atmosphere, a ratio of nitrogen (N 2 ) to hydrogen (H 2 ) is 1:3 or more. 
     
     
         9 . The method of  claim 8 , wherein the atmosphere gas is 100% nitrogen (N 2 ).