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Stainless Steel Grade 254 SMO (UNS S31254)

Time:[9/6/2013]   Hits:5768

Stainless steel grade 254 SMO™ is a very high end austenitic stainless steel. It is designed with a combination of impact toughness resistance to chloride stress corrosion cracking, and pitting and crevice corrosion with strength that is twice that of the stainless steel 300 series.

For certain applications, grade 254 SMO™ has been reported to be a cost-effective substitute for high nickel and titanium alloys. It is known to possess excellent workability as well.

The following sections will discuss in detail about stainless steel grade 254 SMO™.

Chemical Composition
The chemical composition of stainless steel grade 254 SMO™ is outlined in the following table.

Element Content (%)
Iron, Fe 55.69
Chromium, Cr 20
Nickel, Ni 18
Molybdenum, Mo 6.1
Nitrogen, N 0.2
Carbon, C 0.01



Physical Properties
The physical properties of stainless steel grade 254 SMO™ are tabulated below.

Properties Metric Imperial
Density 8 g/cm3 0.289 lb/in3



Mechanical Properties
The following table shows mechanical properties of stainless steel grade 254 SMO™.

Properties Metric Imperial
Tensile strength 680 MPa 98600 psi
Yield strength 300 MPa 43500 psi
Modulus of elasticity 195 GPa 28300 ksi
Shear modulus 75 GPa 10900 ksi
Poisson's ratio 0.3 0.3
Elongation at break 50% 50%
Hardness, Brinell 210 210



Thermal Properties
The thermal properties of stainless steel grade 254 SMO™ are tabulated below.

Properties Metric Imperial
Thermal expansion co-efficient (@20-100°C/68-212°F) 16.5 µm/m°C 9.17 µin/in°F
Thermal conductivity 14 W/mK 97.2 BTU in/hr.ft².°F



Other Designations
Other designations that are equivalent to stainless steel grade 254 SMO™ include the following.

ASTM A813 ASTM A469 ASTM A269 ASTM A240 ASTM A182 (F44)
ASTM A814 ASTM A312 ASTM A249


Fabrication and Heat Treatment
Machinability
Stainless steel grade 254 SMO™ is quite tough to machine due to the extremely high work hardening rate and lack of sulfur content; however using sharp tools, overpowered machine tools, positive feeds, good amount of lubrication, and slow speeds tend to provide good machining results.

Welding
Welding of stainless steel grade 254 SMO™ requires filler material without which it results in poor strength properties. Filler metals such as AWS A5.14 ERNiCrMo-3, and alloy 625 are recommended. Electrodes used in the process, have to match with AWS A5.11 ENiCrMo-12.

Annealing
Annealing of this material should be performed at 1149-1204°C (2100-2200°F), which should be followed by a water quench.

Hot Working
Forging, upsetting and other operations relating to this material can be performed at 982 - 1149°C (1800 - 2100°F). It is recommended that temperatures do not exceed this range as it would result in scaling and reduction in the workability of the material. To re-attain maximum corrosion resistant properties, it is advisable to perform post-process annealing.

Cold Working
Cold working can be carried out using all the traditional methods; however the process would be tough due to its high work hardening rate. The result will provide the material with increased strength and toughness.

Hardening
Stainless steel grade 254 SMO™ does not respond to heat treatment. Hardening is possible only through cold reduction.

Applications
Stainless steel grade 254 SMO™ is used in the following areas:
Saltwater handling
Tall oil distillation columns
Flue gas desulfurization scrubbers
Components used in petroleum production
Food processing equipment
Process equipment in chemical industry
Bleaching equipment in the pulp and paper industry
Flue-gas cleaning
Desalination
Heat exchangers