Fe Base, Ni 27, Cr 22, Mo 7, Cu 1
High Performance Alloys stocks and
produces this grade in the following forms: Bar, wire, sheet, plate, coil, fasteners and forgings.
Overview
INCOLOY® alloy 27-7MO (UNS S31277)
is an advanced 7% molybdenum
super-austenitic stainless steel offering corrosion
resistance in most environments superior to 6%
molybdenum super-austenitic stainless steels. In
many environments alloy 27-7MO offers resistance
approaching that of much more highly alloyed materials
such as INCONEL alloys 625, 22, and C-276.
Alloy 27-7MO products typically contain 27%
nickel, 22% chromium, 7.2% molybdenum, and 0.34%
nitrogen. Its limiting chemical composition is presented
in Table 1. The alloy's content of nickel and nitrogen
produce a stable austenitic structure. By virtue of its
content of molybdenum, chromium, and nitrogen, alloy
27-7MO offers excellent resistance to pitting and
crevice corrosion. The nickel, nitrogen, and
molybdenum provide resistance to reducing media
while a high content of chromium offers resistance to
oxidizing media. Alloy 27-7MO performs well in mixed
acid environments, especially those containing
oxidizing and reducing acids. The alloy's contents of
nickel and nitrogen result in resistance to stress
corrosion cracking and attack by caustic media. Alloy
27-7MO offers excellent resistance to corrosion in
seawater and brine. It also resists stress corrosion
cracking in all concentrations of sodium chloride up to
saturation at the boiling point. It is resistant to the
aggressive media encountered in air pollution control
systems such as flue gas desulfurization equipment for
high-sulfur coal-fired electric power utilities.
Applications for INCOLOY alloy 27-7MO are
found in the pollution control, power, marine, chemical
processing, pulp and paper and oil and gas industries.
The alloy offers a unique combination of corrosion
resistance, high strength and ease of fabrication at an
economical price. Alloy 27-7MO is available in
standard product forms including plate, sheet, rod, bar,
wire rod, pipe, tube, and forging stock.
Corrosion Resistance
Pitting Resistance Equivalency Number - A means of comparing the corrosion resistance of alloys is by their Pitting
Resistance Equivalency Number or 'PREN'. Alloys exhibiting higher PREN values are generally found to be more resistant to
localized corrosion than those with lower PREN values. The PREN can be calculated by several different equations based
upon the chemical composition of the alloys. Some equations are applicable to stainless steels while others are better applied
to nickel-based alloys. The equation used here is generally accepted as being applicable to a wide range of alloy compositions.
When comparing alloys by their PREN it is absolutely necessary that the same equation be used for all materials to be
compared. Comparing alloys by PRENs generated from different equations will give erroneous results. For more information
on the use of PRENs to compare the corrosion resistance of materials, refer to the Special Metals publication, “High
Performance Alloys for Resistance to Aqueous Corrosion” or visit the Special Metals website, www.specialmetals.com.
PRENs for alloy 27-7MO and similar materials are seen in Table 5. Based on these values of PREN, alloy 27-7MO would
be predicted to offer significantly better corrosion resistance than alloy 25-6MO (and similar grades of super-austenitic
Resistance to Corrosion by Seawater
Nickel-chromium alloys and austenitic and super-austenitic
stainless steels containing molybdenum are well known for
their resistance to corrosion in seawater and marine
environments. A test program conducted at the LaQue
Center for Corrosion Technology in Wrightsville Beach,
North Carolina (a laboratory well known for marine
corrosion testing) produced data showing that INCOLOY
alloy 27-7MO offers corrosion-resistance superior to many
of the corrosion-resistant alloys commonly used in marine
service. Samples of sheet to which Teflon crevice devices
were attached were exposed to flowing natural seawater at
Applications
Applications for INCOLOY alloy 27-7MO are
found in the pollution control, power, marine, chemical
processing, pulp and paper and oil and gas industries.
The alloy offers a unique combination of corrosion
resistance, high strength and ease of fabrication at an
economical price. Alloy 27-7MO is available in
standard product forms including plate, sheet, rod, bar,
Chemistry
Chemical Requirements |
|
Ni |
Cr |
Mo |
Mn |
C |
Si |
Cu |
Fe |
Max |
26.0 |
20.5 |
6.5 |
3.00 |
0.02 |
0.5 |
1.5 |
Bal. |
Min |
28.0 |
23.0 |
8.00 |
|
|
|
0.5 |
|
Tensile Data
Mechanical Property Requirements |
|
Ultimate Tensile |
Yield Strength (0.2% OS) |
Elong. |
R/A |
Hardness |
Min |
120 KSi |
60 KSi |
50 |
|
Rb 95 |
Max |
|
|
|
|
|
Min |
827 MPa |
414 MPa |
|
|
|
Max |
|
|
|
|
|
Specifications
Form |
Standard |
Metal Type |
UNS S31277 |
Bar |
ASTM A
479/ASME SA 479 |
Wire |
ASTM A
479/ASME SA 479 |
Sheet |
ASTM A 240/ASME SA 240 |
Plate |
ASTM A 240/ASME SA 240 |
Tube |
ASTM A 213/ASME SA 213 (Tube),
ASTM A 249/ASME SA 249 |
Pipe |
ASTM A 312/ASME
SA 312 |
Fitting |
ASTM A182 |
Forging |
ASTM A
479/ASME SA 479, ASTM A182 |
Weld Wire |
|
Weld Electrode |
|
ASME CODE |
Allowable design stresses for ASME Boiler and Pressure
Vessel Code construction are defined in ASME Code Case 2458. |
Din |
|
Machinability RATING: 27% of B-1112
TYPICAL STOCK REMOVAL RATE: 45 surface feet/minute with high speed tools, 125 surface feet/minute with carbide.
Machining Guide |
Operation |
Tool Type |
Speed SFPM |
Feed Inch Per Rev. |
Depth in Cut Inch |
Cut Type |
Turning |
WC |
68 88 |
.009-.016 .006-.009 |
.050-.100 .011-.015 |
Rough Finish |
HSS |
18 21 |
.007-.011 .003-.008 |
.025-.045 .008-.011 |
Rough Finish |
Facing |
WC |
68 88 |
.009-.016 .006-.009 |
.040-.075 .011-.015 |
Rough Finish |
HSS |
18 21 |
.007-.011 .003-.008 |
.025-.045 .008-.011 |
Rough Finish |
Boring |
WC |
42 53 |
.009-.016 .006-.009 |
.043-.060 .012-.015 |
Rough Finish |
Drilling |
HSS |
18 25 |
.003-.007 .002-.004 |
--- --- |
Rough Finish |
Reaming |
HSS |
25 35 |
.006-.010 --- |
--- .012-.015 |
Rough Finish |
Shaping |
WC |
20 30 |
--- .005-.010 |
.060-.090 .018-.025 |
Rough Finish |
HSS |
13 15 |
--- .005-.010 |
.050-.080 .018-.025 |
Rough Finish |
Milling |
HSS |
15 25 |
1/2-1 IPM |
.100-.200 in. cut |
Rough Finish |
INCOLOY® is a registered trademark of Special Metals Corporation