HIGH MOLYBDENUM DUPLEX STAINLESS STEEL

1 . A duplex stainless steel alloy, comprising:

from 10 wt % to 20 wt % chromium (Cr);

from 6 wt % to 13 wt % molybdenum (Mo);

from 0.5 wt % to 6.5 wt % nickel (Ni);

from 2.25 wt % to 12 wt % manganese (Mn);

from 0.05 wt % to 5 wt % copper (Cu);

from 0.05 wt % to 0.4 wt % nitrogen (N);

from 0.05 wt % to 0.35 wt % carbon (C);

from 0.01 wt % to 3.5 wt % cobalt (Co);

less than 2 wt % silicon (Si);

less than 2 wt % tungsten (W); and

iron (Fe) balance,

wherein the stainless steel alloy comprises 40 wt %-60 wt % ferrite and 60 wt %-40 wt % austenite, and has a nickel equivalent and a chromium equivalent,

wherein the nickel equivalent and the chromium equivalent are defined as one of

(i) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn), and chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 7<Ni eq <20 and 21<Cr eq <38, respectively; or

(ii) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn)+(30×wt % N), and

chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 10<Ni eq <18 and 21<Cr eq <27, respectively.

2 . The composition of claim 1 , comprising

from 12 wt % to 17 wt % chromium (Cr);

from 7.25 wt % to 11 wt % molybdenum (Mo);

from 0.75 wt % to 5 wt % nickel (Ni);

from 2.5 wt % to 8 wt % manganese (Mn);

from 1.75 wt % to 3.5 wt % copper (Cu);

from 0.1 wt % to 0.3 wt % nitrogen (N);

from 0.075 wt % to 0.2 wt % carbon (C);

from 0.01 wt % to 3 wt % cobalt (Co);

less than 1.5 wt % silicon (Si);

less than 1.5 wt % tungsten (W); and

iron (Fe) balance.

3 . The duplex stainless steel alloy of claim 1 , wherein the stainless steel alloy comprises cast steel.

4 . The duplex stainless steel alloy of claim 1 , wherein the stainless steel alloy comprises wrought steel.

5 . The duplex stainless steel of claim 1 , wherein the stainless steel alloy has a yield strength of at least 70 ksi.

6 . The duplex stainless steel of claim 1 , wherein the stainless steel alloy has an ultimate tensile strength of at least 115 ksi.

7 . The duplex stainless steel of claim 1 , wherein the stainless steel alloy has an elongation>30%.

8 . The duplex stainless steel of claim 1 , wherein the stainless steel alloy has a reduction of area>50%.

9 . The duplex stainless steel of claim 1 , wherein the stainless steel alloy has a pitting resistance equivalent number value of at least 30.

10 . A duplex stainless steel alloy powder for additive manufacturing, comprising:

from 10 wt % to 20 wt % chromium (Cr);

from 6 wt % to 13 wt % molybdenum (Mo);

from 0.5 wt % to 6.5 wt % nickel (Ni);

from 2.25 wt % to 12 wt % manganese (Mn);

from 0.05 wt % to 5 wt % copper (Cu);

from 0.05 wt % to 0.4 wt % nitrogen (N);

from 0.05 wt % to 0.35 wt % carbon (C);

from 0.01 wt % to 3.5 wt % cobalt (Co);

less than 2 wt % silicon (Si);

less than 2 wt % tungsten (W); and

iron (Fe) balance,

wherein the stainless steel alloy comprises 40 wt %-60 wt % ferrite and 60 wt %-40 wt % austenite, and has a nickel equivalent and a chromium equivalent,

wherein the nickel equivalent and the chromium equivalent are defined as one of

(i) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn), and chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 7<Ni eq <20 and 21<Cr eq <38, respectively; or

(ii) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn)+(30×wt % N), and

chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 10<Ni eq <18 and 21<Cr eq <27, respectively and

wherein the powder comprises a plurality of spherical particulates having a mean particle size selected from a range of 15-53 microns or 45-103 microns.

11 . The powder of claim 10 , wherein the composition comprises:

from 12 wt % to 17 wt % chromium (Cr);

from 7.25 wt % to 11 wt % molybdenum (Mo);

from 0.75 wt % to 5 wt % nickel (Ni);

from 2.5 wt % to 8 wt % manganese (Mn);

from 1.75 wt % to 3.5 wt % copper (Cu);

from 0.1 wt % to 0.3 wt % nitrogen (N);

from 0.075 wt % to 0.2 wt % carbon (C);

from 0.01 wt % to 3 wt % cobalt (Co);

less than 1.5 wt % silicon (Si);

less than 1.5 wt % tungsten (W); and

iron (Fe) balance.

12 . A method for forming a duplex stainless steel alloy, the method comprising the steps of:

melting a mixture of elements to form a molten metal alloy comprising

from 10 wt % to 20 wt % chromium (Cr);

from 6 wt % to 13 wt % molybdenum (Mo);

from 0.5 wt % to 6.5 wt % nickel (Ni);

from 2.25 wt % to 12 wt % manganese (Mn);

from 0.05 wt % to 5 wt % copper (Cu);

from 0.05 wt % to 0.4 wt % nitrogen (N);

from 0.05 wt % to 0.35 wt % carbon (C);

from 0.01 wt % to 3.5 wt % cobalt (Co);

less than 2 wt % silicon (Si);

less than 2 wt % tungsten (W); and

iron (Fe) balance,

wherein the stainless steel alloy comprises 40 wt %-60 wt % ferrite and 60 wt %-40 wt % austenite, and has a nickel equivalent and a chromium equivalent,

wherein the nickel equivalent and the chromium equivalent are defined as one of

(i) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn), and chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 7<Ni eq <20 and 21<Cr eq <38, respectively; or

(ii) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn)+(30×wt % N), and

chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 10<Ni eq <18 and 21<Cr eq <27, respectively; and

quenching the molten metal alloy to solidify the metal alloy.

13 . The method of claim 12 , further comprising:

forging the solidified metal alloy.

14 . The method of claim 13 , further comprising:

heat treating the forged metal alloy.

15 . A method for forming a duplex stainless steel alloy powder comprising a composition of

from 10 wt % to 20 wt % chromium (Cr);

from 6 wt % to 13 wt % molybdenum (Mo);

from 0.5 wt % to 6.5 wt % nickel (Ni);

from 2.25 wt % to 12 wt % manganese (Mn);

from 0.05 wt % to 5 wt % copper (Cu);

from 0.05 wt % to 0.4 wt % nitrogen (N);

from 0.05 wt % to 0.35 wt % carbon (C);

from 0.01 wt % to 3.5 wt % cobalt (Co);

less than 2 wt % silicon (Si);

less than 2 wt % tungsten (W); and

iron (Fe) balance,

wherein the stainless steel alloy comprises 40 wt %-60 wt % ferrite and 60 wt %-40 wt % austenite, and has a nickel equivalent and a chromium equivalent,

wherein the nickel equivalent and the chromium equivalent are defined as one of

(i) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn), and chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 7<Ni eq <20 and 21<Cr eq <38, respectively; or

(ii) nickel equivalent (Ni eq )=wt % Ni+(30×wt % C)+(0.5×wt % Mn)+(30×wt % N), and

chromium equivalent (Cr eq )=wt % Cr+wt % Mo+(1.5×wt % Si)+(0.5×wt % Nb), Ni eq and Cr eq having values of 10<Ni eq <18 and 21<Cr eq <27, respectively and

wherein the powder comprises a plurality of spherical particulates having a mean particle size selected from a range of 15-53 microns or 45-103 microns,

the method comprising the steps of:

melting charge material comprising the composition to form a molten metal bath;

generating a molten metal stream from the molten metal bath;

atomizing the molten metal stream to form a plurality of metal droplets; and

cooling the metal droplets, wherein the metal droplets solidify to form the powder.

16 . The method of claim 15 , wherein the charge material is melted in an atmosphere comprising air, an inert gas, or vacuum.

17 . The method of claim 15 , wherein the molten metal stream is atomized in a high-pressure gas comprising at least one of argon, nitrogen, or helium.