SUPER DUPLEX FERRALIUM 255 / S32550
FERRINOX® 255 (UNS S32550) is a stainless steel containing 25.5% chromium, 6% nickel with significant additions of molybdenum, copper and nitrogen and a PREn (pitting resistance equivalent) of ≥40.0. The copper content of 1.6% is particularly beneficial in promoting optimum resistance to corrosion in acidic environments. The chemical composition and mechanical properties conform to the requirements of UNS S32550, 1.4507 and several oil & gas industry specifications. The microstructure is carefully controlled with a phase balance close to 50:50 austenite and ferrite with complete freedom from grain boundary carbides, sigma phase and other deleterious precipitates. Hardness is kept to a level which satisfies the requirements of NACE MR01-75 for sour service.
It should be stressed that, although the above standards form the basis for FERRINOX® 255 supply, a consistent, optimised property combination is only achieved by the targeting of a much tighter composition window and detailed knowledge, gained from long term, volume supply, of metal processing techniques and heat treatment regimes. Rigorous testing carried out on all production batches, such as ASTM G-48A at 500C to demonstrate very high pitting resistance and notch ductility testing at minus 460C to confirm sub-zero suitability, also guarantees the absence of phases potentially deleterious to ductility, corrosion resistance and weldability.
FERRINOX® 255 (UNS S32550) is categorised as a super duplex (austenitic/ferritic) stainless steel. This high performance alloy combines high mechanical strength (typically up to over 600 MPa yield strength) and good ductility with outstanding corrosion resistance to marine environments and a wide, diverse range of industrial media. These attributes result in the widespread specification of FERRINOX® 255 as an alternative to 300 series stainless steel (such as type 316), standard 22% Cr duplex steel, precipitation hardening stainless steels (typical 17/4PH) and the alloy can in some instances obviate the need to choose a much higher cost nickel based alloy
The highly attractive combination of attributes provided by FERRINOX® 255 has led to many years of successful application in Defence, Oil & Gas production, Chemicals processing, Pollution Control (FGD), Pulp & Paper Production, Architecture and Nuclear Engineering.
Chemical Requirements |
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Ni |
Cr |
Mo |
Mn |
C |
Si |
Fe |
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Max |
6.5 |
27.0 |
3.9 |
1.50 |
0.04 |
1.00 |
Bal |
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Min |
4.5 |
24.0 |
2.9 |
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Principal Features of Alloy 255 Compared To 300 Series Austenitic Stainless Steels
- Superior Corrosion Resistance
- Pitting
- Crevice Corrosion
- Chloride Stress Corrosion Cracking
- General Corrosion In Many Environments
- Good Ductility
- High Strength-To-Weight Ratio
- High Fatigue Strength In Marine Environments
- Superior Abrasion and Cavitation Erosion Resistance
- High Mechanical Strength - (over twice the yield strength of austenitic stainless steels)
- Good Fabricability
Physical Properties
- Density 0.282 lb/in
- Specific Gravity 7.81
- Thermal Expansion
- Coefficient (68° to 600°F) 6.7X10^-6 in/in/°F
- Thermal Conductivity (68°F) 105 Btu/sqr ft/hr/°F/in
- Electrical Resisitivity (68°F) 473 Ohms/cir mil ft
- Dynamic Modulus of Elasticity 30.5x10^6 psi
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Is Stronger Than Most Competitive Alloys
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Alloy |
UNS |
Typical Tensile |
Typical Yeild |
Typical Elongation |
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Alloy 255 |
S32550 |
126 |
98 |
30 |
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316L |
S31603 |
81 |
42 |
50 |
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NiCu400 |
N04400 |
78 |
31 |
50 |
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20Cb-3 |
N08020 |
92 |
47 |
39 |
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2205 Duplex |
S31803 |
112 |
75 |
32 |
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Alloy Comparison
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Chemistry |
Alloy 316SS |
Alloy 2205 |
Alloy 255 |
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CR |
17 |
22 |
25.3 |
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NI |
10 |
5 |
6 |
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MO |
2 |
3 |
3 |
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CU |
-- |
-- |
2 |
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N |
-- |
0.15 |
0.22 |
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Fluid Flow Applications
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Process |
Temperature |
Corrodant |
Prior Material |
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Caffeine Production |
95 °C |
Cholrides |
316 |
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Waste Odor Removal |
Ambient |
Cholrides |
-- |
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Wet Process Phos Acid |
180 °F |
H 2 SO 4
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317L
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Sour Gas Downhole
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Up to 350 °F |
H 2 S Chlorides |
316, 410
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Waste Water Treatment |
150-300 °F |
Mixed Acids
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316 FRP |
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Polycarbonate Production |
250-300 °F |
Ambient |
2205 |
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Demineralize Water |
Ambient |
Chlorides |
PVC, Carbon
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Gold Mine Oxygen Lance
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217 °F |
H 2 SO 4
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316, C-276
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Mechanical Property Requirements |
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Ultimate Tensile
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Yield Strength (0.2% OS)
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Elong. |
R/A
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HardnessBrinell |
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Min |
110 KSi |
80 KSi |
15% |
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Max |
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297 |
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Min |
760 MPa |
550 MPa |
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Max |
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Form |
Standard |
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Metal Type |
UNS S32550
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Bar |
ASTM A479
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Wire |
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Sheet |
ASTM A240
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Plate |
ASTM A240
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Fitting |
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Forging |
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Weld Wire
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Weld Electrode
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E2553 |
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Din |
1.4507 |
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Carbide tools are suggested
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Machining Type |
Suggested starting rates are: |
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Single Point turning : |
Roughing - 0.15" depth, 0.015"/rev feed -175 SFM
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Drilling : |
1/4" Dia hole - 0.004"/rev feed - 60 SFM
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Reaming : |
Feed - same as drilling - 100 SFM |
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Side and Slot Milling : |
Roughing - 0.25" depth - 0.007"/tooth feed - 125SFM
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These rates are for carbide tools,
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