254 SMO is a super austenitic stainless steel developed by Western European steel producers in the 1980s by combining the properties of two austenitic stainless steels such as alloy 20 and 25.
Its an alloy of chromium-nickel-molybdenum-copper-nitrogen, created to overcome the limitations of alloys such as 309 and 310, offering equal or improved corrosion resistance. 254 SMo is, however, a type of stainless steel with a higher alloys content, making it more expensive as well as featuring a higher resistance to corrosion in comparison with conventional austenitic stainless steels. It also has excellent pitting corrosion resistance and high mechanical strength.
Chemical Composition of 254 SMO:
C (Carbon) 0.020 max
Mn (Manganese) 2.00 max
P (Phosphorus) 0.040 max
Si (Silicon) 1.00 max
S (Sulphur) 0.030 max
Cr (Chromium) 20.0-22.0
Mo (Molybdenum) 6.00-6.50
Ni (Nickel) 17.0-19.0
N(Nitrogen) 0.18-0.25
Cu (Copper) 0.50-0.80
The difference between 254 SMO and other austenitic alloys is due to the presence of the higher number nitrogen and molybdenum elements contained in the alloy. This results in providing increased resistance to pitting and crevice corrosion, higher mechanical strength and resistance to stress corrosion cracking.
From a mechanical point, 254 SMO can be tempered using three methods, namely solution annealing, low temperature annealing, and solution annealing plus low-temperature ageing. In terms of welding, 254 SMO is much easier to weld than other high-alloy austenitic stainless steels, while special techniques such as post-weld heat treatment may be used to increase its corrosion resistance.
In conclusion, 254 SMO is a premium grade, super austenitic stainless steel created in the 1980s which combines the properties of alloy 20 and 25, offering clients a vastly improved corrosion resistance at a higher price. Its combination of elements and the addition of nitrogen and molybdenum, as well as its medium-high mechanical strength, makes it an ideal choice for industrial applications, such as petrochemical, pharmaceutical, food and marine industries.
