Stainless steel powder for producing duplex sintered stainless steel

Abstract

A method for producing a stainless steel powder by water atomization including the steps of providing a molten metal of having a chemical composition, subjecting a stream of the molten metal to water atomization, recovering the obtained stainless steel powder. A sintered duplex stainless steel, wherein the steel has a composition, wherein the microstructure of the sintered duplex stainless steel is characterized by austenite phase precipitated in ferrite phase.

1 . A method for producing a stainless steel powder by water atomization comprising the steps of:
 providing a molten metal of having a chemical composition comprising:
 C, in an amount up to 0.1 wt. % of C, 
 1.5-3 wt. % of Si, 
 Mn, in an amount up to 0.5 wt. % of Mn, 
 20-27 wt. % of Cr, 
 3-8 wt. % of Ni, 
 1-6 wt. % of Mo, 
 W, in an amount up to 3 wt. % of W, 
 N, in an amount up to 0.1 wt. % N, 
 Cu, in an amount up to 4 wt. % of Cu, 
 P, in an amount up to 0.04 wt. % of P, 
 S, in an amount up to 0.04 wt. % of S, 
 unavoidable impurities up to 0.8 wt. %, 
 optionally one or more of up to 0.004 wt. % B, up to 1 wt. % Nb, up to 0.5 wt. % Hf, up to 1 wt. % Ti, up to 1 wt. % Co, 
 rest Fe, 
   subjecting a stream of the molten metal to water atomization,   recovering the obtained stainless steel powder, wherein the powder has at least 99.5% ferritic structure and wherein the powder is configured for an austenitic phase to precipitate out during a sintering cycle.   
     
     
         2 . The method according to  claim 1  wherein the molten metal has a composition comprising:
 C, in an amount up to 0.03 wt. % of C, 
 1.5-2.5 wt. % of Si, 
 Mn, in an amount up to 0.3 wt. % of Mn, 
 24-26 wt. % of Cr, 
 5-7 wt. % of Ni, 
 1-1.5 wt. % of Mo, 
 1-1.5 wt. % of W, 
 N, in an amount up to 0.06 wt. % N, 
 1-3 wt. % of Cu, 
 P, in an amount up to 0.02 wt. % of P, 
 S, in an amount up to 0.015 wt. % of S, 
 unavoidable impurities up to 0.8 wt. %, 
 optionally one or more of up to 0.004 wt. % B, up to 1 wt. % Nb, up to 0.5 wt. % Hf, up to 1 wt. % Ti, up to 1 wt. % Co, 
 rest Fe. 
 
     
     
         3 . The method according to  claim 1 , wherein the average particle size of the obtained stainless steel powder is between 53 microns and 18 microns such that at least 80% of the particles are less than 53 microns and at most 20% of the particles are less than 18 microns. 
     
     
         4 . The method according to  claim 1  wherein the average particle size of the obtained stainless steel powder is between 26 microns and 5 microns such that at least 80% of the particles are less than 26 microns and at most 20% of the particles are less than 5 microns. 
     
     
         5 . The method according to  claim 1 , wherein the average particle size of the obtained stainless steel powder is between 150 microns and 26 microns such that at least 80% of the particles are less than 150 microns and at most 20% of the particles are less than 26 microns. 
     
     
         6 . A method for producing a stainless steel powder by water atomization comprising the steps of:
 providing a molten metal of having a chemical composition comprising:
 C, in an amount up to 0.1 wt. % of C, 
 0.5-3 wt. % of Si, 
 Mn, in an amount up to 0.5 wt. % of Mn, 
 20-27 wt. % of Cr, 
 4-7 wt. % of Ni, 
 1-6 wt. % of Mo, 
 W, in an amount up to 3 wt. % of W, 
 N, in an amount up to 0.1 wt. % N, 
 1-3 wt. % of Cu, 
 P, in an amount up to 0.04 wt. % of P, 
 S, in an amount up to 0.04 wt. % of S, 
 unavoidable impurities up to 0.8 wt. %, 
 optionally one or more of up to 0.004 wt. % B, up to 1 wt. % Nb, up to 0.5 wt. % Hf, up to 1 wt. % Ti, up to 1 wt. % Co, 
 rest Fe, 
   subjecting a stream of the molten metal to water atomization,   recovering the obtained stainless steel powder, wherein the powder has at least 99.5% ferritic structure and wherein the powder is configured for an austenitic phase to precipitate out during a sintering cycle.   
     
     
         7 . A sintered duplex stainless steel, wherein the steel has a composition of:
 C, in an amount up to 0.1 wt. % of C,   1.5-3 wt. % of Si,   Mn, in an amount up to 0.5 wt. % of Mn,   20-27 wt. % of Cr,   3-8 wt. % of Ni,   1-6 wt. % of Mo,   W, in an amount up to 3 wt. % of W,   N, in an amount up to 0.1 wt. % N,   Cu, in an amount up to 4 wt. % of Cu,   P, in an amount up to 0.04 wt. % of P,   S, in an amount up to 0.04 wt. % of S,   unavoidable impurities up to 0.8 wt. %,   optionally one or more of up to 0.004 wt. % B, up to 1 wt. % Nb, up to 0.5 wt. % Hf, up to 1 wt. % Ti, up to 1 wt. % Co,   rest Fe,   wherein the microstructure of the sintered duplex stainless steel is characterized by austenite phase precipitated in ferrite phase.   
     
     
         8 . The sintered duplex stainless steel according to  claim 7 , wherein the steel has a composition of:
 C, in an amount up to 0.03 wt. % of C,   1.5-2.5 wt. % of Si,   Mn, in an amount up to 0.3 wt. % of Mn,   24-26 wt. % of Cr,   5-7 wt. % of Ni,   1-1.5 wt. % of Mo,   1-1.5 wt. % of W,   N, in an amount up to 0.06 wt. % N,   1-3 wt. % of Cu,   P, in an amount up to 0.02 wt. % of P,   S, in an amount up to 0.015 wt. % of S,   unavoidable impurities up to 0.8 wt. %,   optionally one or more of up to 0.004 wt. % B, up to 1 wt. % Nb, up to 0.5 wt. % Hf, up to 1 wt. % Ti, up to 1 wt. % Co,   rest Fe.   
     
     
         9 . The sintered duplex stainless steel according to  claim 7 , wherein the Ni equivalent (Nieq) is such that 5<Nieq<11 and the Cr equivalent (Creq) is such that 27<Creq<38, and wherein Creq and Nieq are calculated according to the formulas:
   Creq=Cr+2Si+1.5Mo+0.75W     Nieq=Ni+0.5Mn+0.3Cu+25N+30C and,   wherein Cr, Ni, etc. are the level of each element in the alloy in weight %.   
     
     
         10 . The sintered duplex stainless steel according to  claim 7 , wherein the pitting resistance equivalent number (PREN) is 28<PREN<33 and wherein PREN is calculated according to the formula:
   PREN=Cr+3.3Mo+16N and,   wherein Cr, Mo and N are the level of each element in the alloy in weight %.   
     
     
         11 . The sintered duplex stainless steel according to  claim 7 , wherein the microstructure of the sintered duplex stainless steel contains 30-70% austenite. 
     
     
         12 . The sintered duplex stainless steel according to  claim 7 , wherein the microstructure is characterized by being free from sigma phases and nitrides. 
     
     
         13 . A sintered duplex stainless steel, wherein the steel has a composition of:
 C, in an amount up to 0.1 wt. % of C,   0.5-3 wt. % of Si,   Mn, in an amount up to 0.5 wt. % of Mn,   20-27 wt. % of Cr,   4-7 wt. % of Ni,   1-6 wt. % of Mo,   W, in an amount up to 3 wt. % of W,   N, in an amount up to 0.1 wt. % N,   1-3 wt. % of Cu,   P, in an amount up to 0.04 wt. % of P,   S, in an amount up to 0.04 wt. % of S,   unavoidable impurities up to 0.8 wt. %,   optionally one or more of up to 0.004 wt. % B, up to 1 wt. % Nb, up to 0.5 wt. % Hf, up to 1 wt. % Ti, up to 1 wt. % Co,   rest Fe,   wherein the microstructure of the sintered duplex stainless steel is characterized by austenite phase precipitated in ferrite phase.