Material to UNS S (and the other specifications listed in our technical datasheet) is described as a 6% Mo super austenitic stainless steel.
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The steel combines moderate mechanical strength (typically over 300 MPa yield strength) and high ductility with excellent corrosion resistance in seawater and a variety of industrial environments. Typically the alloy has a PREn (Pitting Resistance Equivalent) of 42-44 which ensures that the resistance to pitting corrosion is high. In addition, the steel provides good resistance to crevice corrosion. Ambient and sub-zero temperature notch ductility is very good. These attributes mean that this high molybdenum stainless steel can be used successfully as an alternative to 300 series austenitic stainless steels (such as type 316) in applications where higher mechanical strength and/or enhanced resistance to pitting and crevice corrosion is required.
This alloy possesses a lower yield strength than that of duplex stainless steel (and much lower than that of super duplex steel) and pitting resistance which is comparable to super duplex stainless steel (such as UNS S / S).
Commercial applications for this engineering material include:
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Welding
Annealing
Hot Working
Cold Working
Hardening
Applications
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&#;.
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 0.20 Carbon, C 0.010The physical properties of stainless steel grade 254 SMO&#; are tabulated below.
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Properties Metric Imperial Density 8 g/cm3 0.289 lb/in3The following table shows mechanical properties of stainless steel grade 254 SMO&#;.
Properties Metric Imperial Tensile strength 680 MPa psi Yield strength 300 MPa psi Modulus of elasticity 195 GPa ksi Shear modulus 75 GPa ksi Poisson&#;s ratio 0.30 0.30 Elongation at break 50 % 50 % Hardness, Brinell 210 210The 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.°FOther 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 A814Stainless 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 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 of this material should be performed at -°C (-°F), which should be followed by a water quench.
Forging, upsetting and other operations relating to this material can be performed at 982 - °C ( - °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 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.
Stainless steel grade 254 SMO&#; does not respond to heat treatment. Hardening is possible only through cold reduction.
Stainless steel grade 254 SMO&#; is used in the following areas:
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