HIGH MOLYBDENUM DUPLEX STAINLESS STEEL
Disclosed herein are duplex stainless steel alloys comprising 40 wt %-60 wt % ferrite and 60 wt %-40 wt % austenite and methods of formation thereof, the alloys including or consisting essentially of from 10 wt % to 20 wt % chromium (Cr); from 7 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); less than 0.05 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. The duplex stainless steel alloy may include cast or wrought steel, or it may be in powder form.
1 . A duplex stainless steel alloy, comprising:
from 10 wt % to 20 wt % chromium (Cr);
from 7 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);
less than 0.05 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
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
,
and
(
i
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 3<Ni eq <20 and 16<Cr eq <36, respectively; or
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
+
(
30
×
wt
.
%
N
)
,
and
(
ii
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 4<Ni eq <15 and 16<Cr eq <36, 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 1.25 wt % to 3.5 wt % copper (Cu);
from 0.1 wt % to 0.3 wt % nitrogen (N);
from 0.0005 wt % to 0.045 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 7 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);
less than 0.05 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
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
,
and
(
i
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 3<Ni eq <20 and 16<Cr eq <36, respectively; or
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
+
(
30
×
wt
.
%
N
)
,
and
(
ii
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 4<Ni eq <15 and 16<Cr eq <36, 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 1.25 wt % to 3.5 wt % copper (Cu);
from 0.1 wt % to 0.3 wt % nitrogen (N);
from 0.0005 wt % to 0.045 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 7 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);
less than 0.05 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
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
,
and
(
i
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 3<Ni eq <20 and 16<Cr eq <36, respectively; or
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
+
(
30
×
wt
.
%
N
)
,
and
(
ii
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 4<Ni eq <15 and 16<Cr eq <36, 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);
less than 0.05 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
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
,
and
(
i
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 3<Ni eq <20 and 16<Cr eq <36, respectively; or
nickel
equivalent
(
Ni
eq
)
=
wt
.
%
Ni
+
(
30
×
wt
.
%
C
)
+
(
0.5
×
wt
.
%
Mn
)
+
(
30
×
wt
.
%
N
)
,
and
(
ii
)
chromium
equivalent
(
Cr
eq
)
=
wt
.
%
Cr
+
wt
.
%
Mo
+
(
1.5
×
wt
.
%
Si
)
+
(
0.5
×
wt
.
%
Nb
)
,
Ni eq and Cr eq having values of 4<Ni eq <15 and 16<Cr eq <36, 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.