Lean duplex stainless steel and method of manufacturing the same

Abstract

A lean duplex stainless steel and a method of manufacturing the same are disclosed. A lean duplex stainless steel according to an embodiment of the present invention comprises, by weight percent, 0.05 to 0.1% of carbon (C), 2.0 to 4.0% of silicon (Si), 4.0 to 8.0% of manganese (Mn), 13.0 to 15.0% of chromium (Cr), 0.05 to 0.15% of nitrogen (N), with the remainder being iron (Fe) and other unavoidable impurities. Therefore, it is possible to minimize the manufacturing costs by minimizing or excluding the alloy components of Cr, Ni, Mo, and the like. in the component system of the duplex stainless steel, to secure an elongation of 30% or more and to secure a corrosion resistance level of 400 series general steel.

1 . A lean duplex stainless steel comprising:
 by weight percent, 0.05 to 0.1% of carbon (C), 2.0 to 4.0% of silicon (Si), 4.0 to 8.0% of manganese (Mn), 13.0 to 15.0% of chromium (Cr), 0.05 to 0.15% of nitrogen (N), with the remainder being iron (Fe) and other unavoidable impurities.   
     
     
         2 . The lean duplex stainless steel according to  claim 1 , wherein the ferrite fraction(FF(%)) according to the following formula (1) is 60 to 80%, and modified Md30(MM(° C.)) according to the following formula (2) is 110° C. or less.
   FF(%)=398−146*C+9.07*Si-0.58*Mn-22.5*Cr-416N   (1)
 
   MM(° C. )=551−[462*(C+N)/(1−0.01*FF)]−9.2*Si-8.1*Mn-13.7*Cr   (2)
 
 
     
     
         3 . The lean duplex stainless steel according to  claim 1 , wherein the stainless steel comprises 13.5 to 14.5% of chromium (Cr). 
     
     
         4 . The lean duplex stainless steel according to  claim 1 , wherein the stainless steel has a Cr equivalent of 13.0 to 16.0 according to the following formula (3).
   Cr equivalent=Cr+0.48Si+1.5Mo   (3)
   
     
     
         5 . The lean duplex stainless steel according to  claim 1 , wherein the stainless steel comprises 0.05% or less of nickel (Ni). 
     
     
         6 . The lean duplex stainless steel according to  claim 1 , wherein the stainless steel has a Ni equivalent of 5.0 or less according to the following formula (4).
   Ni equivalent=Ni+18N+30C+0.1Mn-0.01Mn 2    (4)
   
     
     
         7 . The lean duplex stainless steel according to  claim 1 , wherein the elongation of the stainless steel is 30% or more. 
     
     
         8 . A method of manufacturing a lean duplex stainless steel comprising:
 a step of hot rolling a lean duplex stainless steel slab comprising, by weight percent, 0.05 to 0.1% of carbon (C), 2.0 to 4.0% of silicon (Si), 4.0 to 8.0% of manganese (Mn), 13.0 to 15.0% of chromium (Cr), 0.05 to 0.15% of nitrogen (N), with the remainder being iron (Fe) and other unavoidable impurities;   a step of annealing the hot-rolled steel sheet at a temperature of 1,050 to 1,150° C.; and   a step of water-cooling.   
     
     
         9 . The lean duplex stainless steel according to  claim 8 , wherein the hot-rolled steel sheet is annealed for 10 to 60 minutes.