Alloy 2507 (UNS S32750) is a super duplex stainless steel with 25% chromium, 4% molybdenum, and 7% nickel designed for demanding applications which require exceptional strength and corrosion resistance, such as chemical process, petrochemical, and seawater equipment. The steel has excellent resistance to chloride stress corrosion cracking, high thermal conductivity, and a low coefficient of thermal expansion. The high chromium, molybdenum, and nitrogen levels provide excellent resistance to pitting, crevice, and general corrosion.
Specs:
2507 (UNS S32750)
A 25Cr Duplex Stainless Steel
General Properties
Applications
Standards
Corrosion Resistance
Chemical Analysis
Mechanical Properties
Physical Properties
Processing
Welding
General
Properties
Alloy 2507 is a super duplex stainless steel
with 25% chromium, 4% molybdenum, and 7% nickel
designed for demanding applications which require
exceptional strength and corrosion resistance,
such as chemical process, petrochemical, and seawater
equipment. The steel has excellent resistance
to chloride stress corrosion cracking, high thermal
conductivity and a low coefficient of thermal
expansion. The high chromium, molybdenum, and
nitrogen levels provide excellent resistance to
pitting, crevice, and general corrosion.
The impact strength is also high. Alloy 2507 is not recommended for applications which require long exposures to temperatures above 570°F because of the risk of a reduction in toughness.
Standards
ASTM/ASME .......... A240 - UNS S32750
EURONORM............ 1.4410 - X2 Cr Ni MoN 25.7.4
AFNOR.................... Z3 CN 25.06 Az
Corrosion
Resistance
General Corrosion
The high chromium and molybdenum content of
2507 makes it extremely resistant to uniform corrosion
by organic acids like formic and acetic acid.
2507 also provides excellent resistance to
inorganic acids, especially those containing chlorides.
In dilute sulfuric acid contaminated with chloride ions, 2507 has better corrosion resistance than 904L, which is a highly alloyed austenitic steel grade specially designed to resist pure sulfuric acid.
Stainless steel of type 316L (2.5%Mo) cannot be used in hydrochloric acid due to the risk of localized and uniform corrosion. However, 2507 can be used in dilute hydrochloric acid. Pitting need not be a risk in the zone below the borderline in this figure, but crevices must be avoided.
Isocorrosion curves, 0.1 mm/year, in sulfuric
acid
with an addition of 2000 ppm chloride ions
Isocorrosion curves, 0.1 mm/year, in hydrochloric
acid.
Broken line curve represents the boiling point
Critical Pitting Temperature (CPT) range for
various alloys in 1M NACl
Critical Crevice Corrosion Temperature (CCT)
for various alloys in 10% FeCl3
Intergranural Corrosion
2507’s low carbon content greatly lowers
the risk of carbide precipitation at the grain
boundaries during heat treatment; therefore, the
alloy is highly resistant to carbide-related intergranular
corrosion.
Stress Corrosion Cracking
The duplex structure of 2507 provides excellent
resistance to chloride stress corrosion cracking
(SCC). Because of its higher alloy content,
2507 is superior to 2205 in corrosion resistance
and strength. 2507 is especially useful in
offshore oil and gas applications and in wells
with either naturally high brine levels or where
brine has been injected to enhance recovery.
Pitting Corrosion
Different testing methods can be used to establish
the pitting resistance of steels in chloride-containing
solutions. The data above were measured by an
electrochemical technique based on ASTM G 61.
The critical pitting temperatures (CPT) of several
high-performance steels in a 1M sodium chloride
solution were determined. The results illustrate
the excellent resistance of 2507 to pitting
corrosion. The normal data spread for each grade
is indicated by the dark gray portion of the bar.
Crevice Corrosion
The presence of crevices, almost unavoidable in
practical constructions and operations, makes
stainless steels more susceptable to corrosion
in chloride enviroments. 2507 is highly resistant
to crevice corrosion. The critical crevice corrosion
temperatures of 2507 and several other high-performance
stainless steels are shown above.
Chemical
Analysis
Typical values (Weight %)
C | Cr | Ni | Mo | N | Others |
0.020 | 25 | 7 | 4.0 | .27 | S=0.001 |
PREN = [Cr%] + 3.3 [Mo%] + 16 [N%] ≥ 40 |
Mechanical
Properties
Mechanical and Physical Properties
2507 combines high tensile and impact strength
with a low coefficient of thermal expansion and
high thermal conductivity. These properties are
suitable for many structural and mechanical components.
The low, ambient, and elevated temperature mechanical
properties of 2507 sheet and plate are shown
below. All of the test data shown are for samples
in the annealed and quenched condition.
2507 is not recommended for applications which require long exposures to temperatures in excess of 570°F because of the increased risk of a reduction in toughness. The data listed here are typical for wrought products and should not be regarded as a maximum or minimum value unless specifically stated.
Mechanical Properties
0.2% Offset Yield Strength 0.2%, ksi | 80 min. |
Ultimate Tensile Strength, ksi | 116 min. |
0.1% Offset Yield Strength 0.2%, ksi | 91 min. |
Elongation in 2 inches, % | 15 min. |
Hardness Rockwell C | 32 max. |
Impact Energy, ft.-lbs. | 74 min. |
Low Temperature Impact Properties
Temperature °F
|
RT | 34 | -4 | -40 |
Ft.-lbs. | 162 | 162 | 155 | 140 |
Temperature °F | -76 | -112 | -148 | -320 |
Ft.-lbs. | 110 | 44 | 30 | 7 |
Elevated Temperature Tensile Properties
Temperature °F
|
68 | 212 | 302 | 392 | 482 |
0.2% Offset Yield Strength, ksi | 80 | 65 | 61 | 58 | 55 |
Ultimate Tensile Strength, ksi | 116 | 101 | 98 | 95 | 94 |
Density | lb/in3 | 0.28 |
Modulus of Elasticity | psi x 106 | 29 |
Coefficient
of Thermal Expansion 68-212°F/°F |
x10-6/°F | 7.2 |
Thermal Conductivity | Btu/h ft °F | 8.7 |
Heat Capacity | Btu/lb/°F | 0.12 |
Electrical Resistivity | W-in x 10-6 | 31.5 |
Processing
Hot forming
2507 should be hot worked between 1875°F
and 2250°F. This should be followed by a solution
anneal at 1925°F minimum and a rapid air or
water quench.
Cold Forming
Most of the common stainless steel forming methods
can be used for cold working 2507. The alloy
has a higher yield strength and lower ductility
than the austenitic steels so fabricators may
find that higher forming forces, increased radius
of bending, and increased allowance for springback
are necessary. Deep drawing, stretch forming,
and similar processes are more difficult to perform
on 2507 than on an austenitic stainless steel.
When forming requires more than 10% cold deformation,
a solution anneal and quench are recommended.
Heat Treatment
2507 should be solution annealed and quenched
after either hot or cold forming. Solution annealing
should be done at a minimum of 1925°F. Annealing
should be followed immediately by a rapid air
or water quench. To obtain maximum corrosion resistance,
heat treated products should be pickled and rinsed.
Welding
2507 possesses good weldability and
can be joined to itself or other materials by
shielded metal arc welding (SMAW), gas tungsten
arc welding (GTAW), plasma arc welding (PAW),
flux cored wire (FCW), or submerged arc welding
(SAW). 2507/P100 filler metal is suggested when
welding 2507 because it will produce the appropriate
duplex weld structure.
Preheating of 2507 is not necessary except
to prevent condensation on cold metal. The interpass
weld temperature should not exceed 300°F or
the weld integrity can be adversely affected.
The root should be shielded with argon or 90%
N2/10% H2 purging gas for
maximum corrosion resistance. The latter provides
better corrosion resistance.
If welding is to be done on only one surface and
post-weld cleaning is not possible, GTAW is suggested
for root passes. GTAW or PAW should not be done
without a filler metal unless post-weld cleanup
is possible. A heat input of 5-38 kJ/in. should
be used for SMAW or GTAW. A heat input of about
50kJ/in. can be used for SAW.
NOTE
2205 Code Plus Two and 254 SMO are registered trademarks of Outokumpu Stainless, Inc.
This technical data and information represents our best knowledge at the time of printing. However, it may be subject to some slight variations due to our ongoing research program on corrosion resistant grades.
We, therefore, suggest that information be verified at time of inquiry or order. Furthermore, in service, real conditions are specific for each application. The data presented here is only for the purpose of description and may only be considered as guarantees when our Company has given formal written approval.
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