High-grade duplex stainless steel with much suppressed formation of intermetallic phases and having an excellent corrosion resistance, embrittlement resistance castability and hot workability

Abstract

Formation of intermetallic phases such as sigma (σ) and khi (χ) shows detrimental effects on the corrosion and mechanical properties of high-grade duplex stainless steel. The present invention provides high-grade duplex stainless steel with much suppressed formation of intermetallic phases, of which the chemical composition consists essentially, on a weight basis, of: Cr: 21.0%˜38.0%, Ni: 3.0%˜12.0%, Mo: 1.5%˜6.5%, W: 6.5% or less, Si: 3.0% or less, Mn: 8.0% or less, N: 0.2%˜0.7%, C: 0.1% or less, at least one element selected from the group consisting of Ba: 0.0001˜0.6% and one or more elements of Mischmetal (MM) and Y: 0.0001˜1.0% in total, and a balance of Fe and incidental impurities. The pitting resistance equivalent has a value of 40≦PREW≦67 defined by the following formula (1): PREW=wt. % Cr+3.3(wt. % Mo+0.5 wt. % W)+30 wt. % N  ((1) The present high-grade duplex stainless steel exhibits an excellent corrosion resistance, embrittlement resistance, castability and hot workability.

1 . High-grade duplex stainless steel with high corrosion resistance, embrittlement resistance, castability and hot workability which suppresses formation of intermetallic phases, consisting essentially of 21.0 to 38.0% of Cr, 3.0, to 12.0% of Ni, 1.5 to 6.5% of Mo, 0 to 6.5% of W, 3.0% or less of Si, 8.0% or less of Mn, 0.2 to 0.7% of N, 0.1% or less of C, 0.0001 to 0.6% of Ba, and a balance of Fe and incidental impurities on a weight basis, a pitting resistance equivalent (PREW) defined by following formula {circle over (1)} satisfying 40≦PREW≦67:  
         PREW=wt % Cr+3.3(wt % Mo+0.5wt % W)+30 wt % N  {circle over (1)} 
     
     
         2 . The high-grade duplex stainless steel of  claim 1 , further containing 0.0001 to 1.0% of mischmetal (MM) and/or Y in total.  
     
     
         3 . The high-grade duplex stainless steel of  claim 2 , wherein Ba is added within the range of 0.001 to 0.2%.  
     
     
         4 . High-grade duplex stainless steel with high corrosion resistance, embrittlement resistance, castability and hot workability which suppresses formation of intermetallic phases, consisting essentially of 21.0 to 38.0% of Cr, 3.0 to 12.0% of Ni, 1.5 to 6.5% of Mo, 0 to 6.5% of W, 3.0% or less of Si, 8.0% or less of Mn, 0.2 to 0.7% of N, 0.1 % or less of C, 0.0001 to 1.0% of MM and/or Y in total, and a balance of Fe and incidental impurities on a weight basis, a pitting resistance equivalent (PREW) defined by following formula {circle over (1)} satisfying 40≦PREW≦67:  
         PREW=wt % Cr+3.3 (wt % Mo+0.5 w1 % W)+3 Owt % N  {circle over (1)} 
     
     
         5 . The high-grade duplex stainless steel of one of  claims 2  to  4 , wherein a value of [MM and/or Y+Al]·[O+S] which is an equation of solubility products of MM and/or Y, and Al, O and S of steel ranges from 0.001×10 −5  to 30000×10 −5 [%] 2 .  
     
     
         6 . The high-grade duplex stainless steel of  claim 5 , wherein, in the case of a cast product, the value of the equation of the solubility products ranges from 1×10 −5  to 5000×10 −5 [%] 2 .  
     
     
         7 . The high-grade duplex stainless steel of  claim 5 , wherein, in the case of a hot working product, the value of the equation of the solubility products ranges from 0.1×10 −5  to 2000×10 −5 [%] 2 .  
     
     
         8 . The high-grade duplex stainless steel of one of  claims 2  to  4 , wherein a total amount of MM and/or Y ranges from 0.01 to 0.6%.  
     
     
         9 . The high-grade duplex stainless steel of  claim 8 , wherein the total amount of MM and/or Y ranges from 0.2 to 0.5%.  
     
     
         10 . The high-grade duplex stainless steel of one of  claims 1  to  4 , further containing at least one element selected from the group consisting of 0.5% or less of Ca, 0.5% or less of Mg, 1.0% or less of Al, 0.5% or less of Ta, 0.5% or less of Nb, 1.5% or less of Ti, 1.0% or less of Zr, 1.0% or less of Sn and 1.0% or less of In.  
     
     
         11 . The high-grade duplex stainless steel of one of  claims 1  to  4 , further containing 0.1% or less of B.  
     
     
         12 . The high grade duplex stainless steel of one of  claims 1  to  4 , further containing one or more among 3.0% or less of Cu and 3.0% or less of Co.  
     
     
         13 . The high-grade duplex stainless steel of one of  claims 1  to  4 , wherein a value of [PREW(γ)−PREW(α)] which is a corrosion resistance balance of austenitic phase and ferritic phase ranges from −5 to 10.  
     
     
         14 . The high-grade duplex stainless steel of one of  claims 1  to  4 , wherein a volume fraction of ferritic phase ranges from 20 to 70%, and a volume fraction of austenitic phase ranges from 30 to 80% on a volume basis.  
     
     
         15 . The high-grade duplex stainless steel of  claim 10 , further containing 0.1% or less of B.  
     
     
         16 . The high grade duplex stainless steel of  claim 10 , further containing one or more among 3.0% or less of Cu and 3.0% or less of Co.  
     
     
         17 . The high grade duplex stainless steel of  claim 11 , further containing one or more among 3.0% or less of Cu and 3.0% or less of Co.