What is Stainless Steel 254 SMO?
Stainless Steel 254 SMO is a high-alloy austenitic chromium-nickel-molybdenum stainless steel developed for use in seawater, pulp and paper industry, brackish water and other aggressive chloride-bearing media. The specific levels of Cr, Ni, Mo, and N in this “super austenitic” chemical makeup allow 31254 to combine impact toughness resistance to corrosion cracking, with pitting and crevice corrosion resistance. The result is strength of nearly twice that of 300 series stainless steels.
UNS S31254 is often referred to as a “6% Moly” grade due to the molybdenum content; the 6% Moly family has the ability to withstand high temperatures and maintain strength under volatile conditions. This grade has surpassed its original intent and overlapped into many industries proving useful owing to its high level of molybdenum amount other elements, which allows 31254 to be used successfully in various applications such as flue gas desulfurization and chemical environments. In some applications it has even been found to be a more cost effective substitute for high nickel and titanium alloys.
Properties and Processing Characteristics of Stainless Steel 254 SMO
- Excellent resistance to pitting and crevice corrosion, PRE = ≥42.5*. (*The PRE is defined as, in weight-%, PRE = %Cr + 3.3 x %Mo + 16 x %N)
- High resistance to general corrosion
- High resistance to stress corrosion cracking
- Higher strength than conventional austenitic stainless steels
- Good weldability
Chemical Properties of Stainless Steel 254 SMO
|254 SMO||0.02 max||min: 19.5||1.00 max||min: 6.0||min: 0.18||min: 17.5||0.03 max||0.80 max||1.01 max|
|max:20.0||max: 6.5||max: 0.20||max: 18.0|
Mechanical Properties of Stainless Steel 254 SMO
|Grade||Tensile Strength ksi (MPa) min||Yield Strength 0.2% Offset ksi (MPa) min||Elongation – % in 50 mm (min.)||Hardness|
|(Brinell) MAX||(Rockwell B) MAX|
|254 SMO Sheet & Strip||100 (690)||45 (310)||35||223||96|
|254 SMO Plate||95 (655)||45 (310)||35||223||96|
Physical Properties of Stainless Steel 254 SMO
|Grade||Stainless Steel 254 SMO|
|Modulus of Elasticity||195 GPa|
|Linear Expansion at 68 to 212°F(20 to 100°C)||16.5 X10^-6/°C|
|Thermal Conductivity||14 w/m°C|
|Thermal Capacity||500 J/kg°C|
|Electrical Resistivity||0.85 μΩm|
Applications of Stainless Steel 254 SMO Plates, Pipes, Fasteners & Forgings
- 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
- Heat exchangers
Fabrication Data & Other Properties of Stainless Steel 254 SMO
Avoid abrasion against copper/copper alloys or other similar metals which, if present in metallic form, can cause cracks during subsequent welding, hot processing or heat treatment.
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.
The excellent formability of 254 SMO permits cold bending to very tight bending radii. Annealing is not normally necessary after cold bending.
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 1149-1204°C (2100-2200°F), which should be followed by a water quench.
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 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.
This is a highly alloyed material and the recommended forging temperature range is 2370/1920ºF (1300/1050ºC), followed by a solution anneal at 2100ºF (1150ºC) minimum temperature.
Corrosion Resistant Properties of Stainless Steel 254 SMO
- Excellent resistance to pitting and crevice corrosion due to its high chromium, molybdenum, and nitrogen content
- Has a very low carbon content, which means there is very little risk of carbide precipitation during heating
- Possesses very good resistance in water containing chlorides, therefore, it is suitable for use in seawater as it can be exposed to it for prolonged periods without suffering from crevice corrosion