Stainless steel powder for producing duplex sintered stainless steel

Abstract

Embodiments of the present invention may provide a new stainless steel powder suitable for manufacturing of duplex sintered stainless steels. Embodiments of the present invention may also relate to a method for producing the stainless steel powder, the duplex sintered stainless steel as well as methods for producing the duplex sintered stainless steel.

1 . A stainless steel powder comprising:
 up to 0.1% of C,   0.5-3% of Si,   up to 0.5% of Mn,   20-27% of Cr,   3-8% of Ni,   1-6% of Mo,   up to 3% of W,   up to 0.1% N,   up to 4% of Cu,   up to 0.04% of P,   up to 0.04% of S,   unavoidable impurities up to 0.8%,   optionally one or more of up to 0.004% B, up to 1% Nb, up to 0.5% Hf, up to 1% Ti, up to 1% Co, rest Fe.   
     
     
         2 . A stainless steel powder according to  claim 1  comprising:
 up to 0.06% of C, 
 1-3% of Si, 
 up to 0.3% of Mn, 
 23-27% of Cr, 
 4-7% of Ni, 
 1-3% of Mo, 
 0.8-1.5% of W, 
 up to 0.07% N, 
 1-3% of Cu, 
 up to 0.03% of P, 
 up to 0.03% of S, 
 unavoidable impurities up to 0.8%, 
 optionally one or more of up to 0.004% B, up to 1% Nb, up to 0.5% Hf, up to 1% Ti, up to 1% Co, rest Fe. 
 
     
     
         3 . A stainless steel powder according to  claim 1  comprising:
 up to 0.03% of C, 
 1.5-2.5% of Si, 
 up to 0.3% of Mn, 
 24-26% of Cr, 
 5-7% of Ni, 
 1-1.5% of Mo, 
 1-1.5% of W, 
 up to 0.06% N, 
 1-3% of Cu, 
 up to 0.02% of P, 
 up to 0.015% of S, 
 unavoidable impurities up to 0.8%, 
 optionally one or more of up to 0.004% B, up to 1% Nb, up to 0.5% Hf, up to 1% Ti, up to 1% Co, rest Fe. 
 
     
     
         4 . A stainless steel powder according to  claim 1  wherein the stainless steel powder is ferritic. 
     
     
         5 . A stainless steel powder according to  claim 1  wherein the stainless steel powder is produced by water atomization. 
     
     
         6 . A stainless steel powder according to  claim 1  wherein the stainless steel powder is produced by gas atomization. 
     
     
         7 . A stainless steel powder according to  claim 1  wherein the particle size of the 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. 
     
     
         8 . A stainless steel powder according to  claim 1  wherein the particle size of the 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. 
     
     
         9 . A stainless steel powder according to  claim 1  wherein the particle size of the 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. 
     
     
         10 . A stainless steel powder according to  claim 1  wherein the powder is a prealloyed powder. 
     
     
         11 . A method for producing a stainless steel powder by water atomization comprising the steps of:
 providing a molten metal of having a chemical composition corresponding to the chemical composition of the stainless steel powder according to  claim 1 ,   subjecting a stream of the molten metal to water atomization,   recovery of the obtained stainless steel powder.   
     
     
         12 . A sintered duplex stainless steel having a chemical composition according to  claim 1  and wherein the microstructure of the sintered duplex stainless steel is characterized by austenite phase precipitated in ferrite phase. 
     
     
         13 . A sintered duplex stainless steel according to  claim 12  wherein the Ni equivalent (Ni eq ) is such that 5<Ni eq <11 and the Cr equivalent (Cr eq ) is such that 27<Cr eq <38 and wherein Cr eq  and Ni eq  are calculated according to the formulas:
   Cr eq =Cr+2Si+1.5Mo+0.75W 
   Ni eq =Ni+0.5Mn+0.3Cu+25N+30C and, 
 wherein Cr, Ni, etc. are the level of each element in the alloy in weight %. 
 
     
     
         14 . A sintered duplex stainless steel according to  claim 12  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 %. 
 
     
     
         15 . A sintered duplex stainless steel according to  claim 12  wherein the microstructure of the sintered duplex stainless steel contains 30-70% austenite. 
     
     
         16 . A sintered duplex stainless steel according to  claim 12  wherein the microstructure is characterized by being free from sigma phases and nitrides. 
     
     
         17 . A method for producing a duplex sintered stainless steel comprising the steps of:
 providing a stainless steel powder according to according to  claim 1 ,   optionally mixing the stainless steel powder with a lubricant and optionally other additives,   subjecting the stainless steel powder or the mixture to a consolidation process forming a green component,   subjecting the compacted green component to a sintering step in an inert or reducing atmosphere or in vacuum at a temperature between 1150° C. to 1450° C., preferably at a temperature between 1275° C. to 1400° C. for a period of time of 5 minutes to 120 minutes,   subjecting the sintered component to a cooling step down to ambient temperature.   
     
     
         18 . A method for producing a duplex sintered stainless according to  claim 17  wherein the consolidation process includes:
 uniaxial compaction at a compaction pressure of up to 900 MPa in a die to form a green component, 
 ejecting the obtained compacted green component from the die.