STAINLESS STEEL POWDER FOR PRODUCING DUPLEX SINTERED STAINLESS STEEL

• US 20190309399A1
• Filed: 12/01/2017
• Published: 10/10/2019
• Est. Priority Date: 12/07/2016
• Status: Active Application

• Current Assignee: Hoganas AB (H. Intressenter AB)
• Original Assignee: Hoganas AB (H. Intressenter AB)
• Inventors: Badwe, Sunil
• Application Number:
  US16/467,267
• Publication Number:
  US 20190309399A1
• Time in Patent Office: Days
• CPC Class Codes: B22F 2009/0828 with water
• CPC Class Codes: B22F 2301/058 Magnesium
• CPC Class Codes: B22F 2301/10 Copper
• CPC Class Codes: B22F 2301/15 Nickel or cobalt
• CPC Class Codes: B22F 2304/10 Micron size particles, i.e. above 1 micrometer up to 500 micrometer
• CPC Class Codes: B22F 9/082 atomising using a fluid using centrifugal force B22F9/10
• CPC Class Codes: C22C 33/0271 with only C, Mn, Si, P, S, As as alloying elements, e.g. carbon steel
• CPC Class Codes: C22C 33/0285 with Cr, Co, or Ni having a minimum content higher than 5%
• CPC Class Codes: C22C 38/001 containing N
• CPC Class Codes: C22C 38/002 containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• CPC Class Codes: C22C 38/02 containing silicon
• CPC Class Codes: C22C 38/04 containing manganese
• CPC Class Codes: C22C 38/08 containing nickel C22C38/105 takes precedence
• CPC Class Codes: C22C 38/12 containing tungsten, tantalum, molybdenum, vanadium, or niobium
• CPC Class Codes: C22C 38/34 with more than 1.5% by weight of silicon
• CPC Class Codes: C22C 38/42 with copper
• CPC Class Codes: C22C 38/44 with molybdenum or tungsten

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.

Claims

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.