Duplex Stainless Steel Having Excellent Corrosion Resistance with Low Nickel

Abstract

Disclosed is duplex stainless steel that containes relatively low content of Ni, and limits constituents of Cr—Mo—Mn—N to make volume fraction of α and γ have about 50:50, thereby minimizing incidence of a edge crack to enhance a production yield and decrease a processing load, in which the alloy constituents includes Cr of 19.5˜22.5%. Mo of 0.5-2.5%, Ni if 1.0-3.0%, Mn of 1.5-4.5%, N of 0.15-0.25%, Fe and unavoidable elements, and a constitution range of the alloy constituents are adjusted to make a CPt higher than 20° C. depending on the constitution range of the alloy constituents. Thus, the contents of Cr, Mo and Ni is decreased and the content of Mn is increased a little, so that a production cost thereof is reduced; the corrosion resistance is secured to be better than the STS 304 steel and the 316L steel; the incidence of the edge cract is decreased while being hot-rolled, thereby decreasing a load on the following process; and the surface defective is decreased, thereby improving a production yield.

1 . (canceled) 
     
     
         2 . (canceled) 
     
     
         3 . A duplex stainless steel having excellent corrosion resistance with low Ni, having alloy constituents comprising Cr ranging from 19.5 wt% to 22.5 wt%, Mo ranging from 0.5 wt% to 2.5 wt%, Ni ranging from  1 .Owt% to 3.0 wt%, Mn ranging from 1.5 wt% to 4.5 wt%, N ranging from 0.15 wt% to 0.25 wt%, Fe and unavoidable elements, wherein a critical pitting temperature of the duplex stainless steel is calculated as a function of constitution ranges of Cr, Mo, Mn, and N in the alloy constituents, and the constitution ranges of the alloy constituents are adjusted to have the critical pitting temperature of 20° C. or more. 
     
     
         4 . The duplex stainless steel according to  claim 3 , further including C of 0.03 wt% or less P of 0.03 wt% or less, and Si of 2 wt% or less. 
     
     
         5 . The duplex stainless steel according to  claim 3 , wherein the critical pitting temperature of the duplex stainless steel is calculated by:
   CPT=CONST+2.65Cr+11.71Mo−1.3Mn+64.58N, and   wherein CPT is the critical pitting temperature in ° C and CONST is a constant for calculating the critical pitting temperature in C.   
     
     
         6 . The duplex stainless steel according to  claim 5 , wherein the constant, CONST, is a negative constant. 
     
     
         7 . The duplex stainless steel according to  claim 6 , wherein the negative constant is −50.47. 
     
     
         8 . The duplex stainless steel according to  claim 7 , wherein the constitution ranges of the alloy constituents are adjusted to have the critical pitting temperature of 25° C. or more. 
     
     
         9 . The duplex stainless steel according to  claim 3 , wherein the constitution ranges of the alloy constituents are adjusted to have the critical pitting temperature of 25° C. or more. 
     
     
         10 . A method for forming duplex stainless steel having excellent corrosion resistance with low Ni, having alloy constituents including Cr ranging from 19.5 wt% to 22.5wt%, Mo ranging from 0.5 wt% to 2.5 wt%, Ni ranging from 1.0wt% to 3.0 wt%, Mn ranging from 1.5 wt% to 4.5 wt%, N ranging from 0.15 wt% to 0.25 wt%, Fe and unavoidable elements, the method comprising:
 calculating a critical pitting temperature of the duplex stainless steel as a function of constitution ranges of Cr, Mo, Mn, and N in the alloy constituents, and adjusting the constitution ranges of the alloy constituents to have the critical pitting temperature of  20  C or more.   
     
     
         11 . The method according to  claim 10 , further comprising:
 adding C of 0.03 wt% or less, P of 0.03 wt% or less, and Si of 2 wt% or less to form the duplex stainless steel.   
     
     
         12 . The method according to  claim 10 , wherein the calculating the critical pitting temperature of the duplex stainless steel comprises calculating the critical pitting temperature of the duplex stainless steel using:
   CPT=CONST+2.65Cr+11.71Mo−1.3Mn+64.58N, and   wherein CPT is the critical pitting temperature in ° C and CONST is a constant for calculating the critical pitting temperature in ° C.   
     
     
         13 . The method according to  claim 12 , wherein the constant, CONST, is a negative constant. 
     
     
         14 . The method according to  claim 13 , wherein the constant, CONST, is - 50 . 47 . 
     
     
         15 . The method according to  claim 14 , wherein the adjusting the constitution ranges of the alloy constituents comprises adjusting the constitution ranges of the alloy constituents to have the critical pitting temperature of  25  C or more. 
     
     
         16 . The method according to  claim 10 , wherein the constitution ranges of the alloy constituents are adjusted to have the critical pitting temperature of  25  C or more.