FERRALIUM® alloy 255 (UNS S32550)


Cr 25.5, Ni 5.5, Mo 3.4 C 0.04, Mn 1.5, Si 1.0, Fe bal, N 0.175, S 0.030, Cu 2.00, P 0.040

 

Overview

Alloy 255 is finding many cost effective applications in the chemical, marine, metallurgical, municipal sanitation, plastics, oil and gas, petrochemical, pollution control, wet phosphoric acid, paper making and metalworking industries.

Called "super" because it is more alloyed than ordinary stainless steels and has superior corrosion resistance, alloy 255 is being used in areas where conventional stainless' are inadequate or, at best marginal. One good example s in the paper industry which was hit with an epidemic of corrosion problems when environmental laws forced recycling of process liquids In closed systems, chemicals such as chlorides can build up to highly corrosive concentrations over time. Paper makers have found that ordinary stainless equipment, which had previously given good service, was no longer adequate for many applications.

Duplex alloy with a high strength to weight ratio, with superior abrasion and cavitation resistance. Resistance to chloride SCC, as well as crevice corrosion and pitting. Good ductility with a high fatigue strength in marine applications. Twice the yield strength of Alloy 20, and stronger than Duplex 2205. An excellent 40°C critical pitting temperature (ASTM G48-Method A), twice that of Alloy 2205.

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

Characteristics

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

Is Stronger Than Most Competitive Alloys

Alloy

UNS

Typical Tensile
(ksi)

Typical Yeild
(ksi)

Typical Elongation
(%)

Alloy 255

S32550

126

98

30

316L

S31603

81

42

50

NiCu400

N04400

78

31

50

20Cb-3

N08020

92

47

39

2205 Duplex

S31803

112

75

32

 

Alloy Comparison

Chemistry

Alloy 316SS

Alloy 2205

Alloy 255

CR

17

22

25.3

NI

10

5

6

MO

2

3

3

CU

--

--

2

N

--

0.15

0.22

 

Applications

Alloy 255 is a cost effective alternative to materials such as the nickel alloys, 20 type alloys, brass and bronze. Marine environments have long been the domain of admiralty bronze. Alloy 255 is replacing admiralty bronze, and the nickel alloys, in offshore platforms, deck hardware, rudders and shafting.

Alloy 255 is also making inroads in "borderline" corrosion applications where the nickel alloys and high performance alloys have been used but may not have been absolutely necessary. In some instances, it has even been used to replace high performance Ni-Cr-Mo-F-Cu alloys in the phosphoric acid industry.

Valves, pumps, shafts, marine environments, Applications in down-hole, waste water, polycarbonate production, and demineralized water production.

Fluid Flow Applications

Process

Temperature

Corrodant

Prior Material

Caffeine Production

95 °C

Cholrides

316

Waste Odor Removal

Ambient

Cholrides

--

Wet Process Phos Acid

180 °F

H 2 SO 4
Solids

317L
316L

Sour Gas Downhole
Instruments

Up to 350 °F

H 2 S Chlorides

316, 410
Nitronic 50

Waste Water Treatment

150-300 °F

Mixed Acids
Chlorides

316 FRP

Polycarbonate Production 250-300 °F Ambient 2205
Demineralize Water Ambient Chlorides PVC, Carbon
Steel, Stainless
Gold Mine Oxygen Lance
and Vent
217 °F H 2 SO 4
Chlorides
316, C-276
600, TI

 

Chemistry

The alloy's high critical pitting temperature and high critical crevice temperature provide more resistance to pitting and crevice corrosion than lesser alloyed materials. The alloy's very high yield strength combined with good ductility allows lower wall thicknesses in process equipment.

 

Chemical Requirements

Ni

Cr

Mo

Mn

C

Si

Fe

Max

6.5

27.0

3.9

1.50

0.04

1.00

Bal

Min

4.5

24.0

2.9


Tensile Data

Mechanical Property Requirements

Ultimate Tensile

Yield Strength (0.2% OS)

Elong.

R/A

HardnessBrinell

Min

110 KSi

80 KSi

15%

Max

297

Min

760 MPa

550 MPa

Max


Specifications

Form

Standard

Metal Type

UNS S32550

Bar

ASTM A479

Wire

Sheet

ASTM A240

Plate

ASTM A240

Fitting

 

Forging

 

Weld Wire

 

Weld Electrode
E2553

Din

1.4507

 

 

Machining

MACHINING DATA
Carbide tools are suggested
for rates better than 50% of Type 304.
Machining Type Suggested starting rates are:
Single Point turning : Roughing - 0.15" depth, 0.015"/rev feed -175 SFM
Finishing - 0.025" depth, 0.007"/rev feed - 200 SFM
Drilling : 1/4" Dia hole - 0.004"/rev feed - 60 SFM
1/2" Dia hole - 0.007"/rev feed - 60 SFM
3/4" Dia hole - 0.010"/rev feed - 60 SFM
Reaming : Feed - same as drilling - 100 SFM
Side and Slot Milling : Roughing - 0.25" depth - 0.007"/tooth feed - 125SFM
Finishing - 0.050" depth - 0.009"/tooth feed - 140SFM
These rates are for carbide tools,
Type C-2 for roughing, drilling and reaming.
Type C-3 for finishing.

Other Technical Data

Elongation Comparison

elongation Comparison

elongation

Alloy 316SS Alloy 2205 Ferralium Alloy 255

 

40

25

15

Hardness Comparison

Wear Resistance

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

Hardness

RB80

RC21

RC28

Critical Pitting Temperature Comparison
Critical Pitting Temperature

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

Degree C ASTM
G48-Method A
0 20 40
Pitting Potential - MV Comparison
Temperature

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

50 °C 60 370 No Pitting
60 °C No Test No Test 110
60 °C No Test No Test 170
Critical Crevice Comparison
Critical Crevice Temperature

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

Degree C ASTM
G48-Method B
(10% FE CL 6H 0)
-2.5 17.5 22.5
C Ring Stress Cracking Comparison
C Ring Stress Cracking

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

80 Degree C Stressed to 100% Yield Strength, H2S
0.125 Bar, Sour Brine with 46,000 MG/L Chloride
Cracks Fine Cracks No Cracks
PREN No. Comparison
Resistance to Localized Corrosion

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

PREN No. CR + 3.3(MO) + 16(N) 23.6 34.5 40
Corrosion Rates Comparison
Corrosion Rates MPY

Alloy 316SS

Alloy 2205

Ferralium Alloy 255

10% Sulfuric Boiling 855 206 40
65% Nitric Boiling 11 21 5
       

 

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