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254SMO F44 UNS S31254 1.4547 Super Stainless Steel

254SMO F44 UNS S31254 1.4547 Super Stainless Steel

254SMO F44 UNS S31254 1.4547 Super Stainless Steel

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254SMO F44 UNS S31254 1.4547 Super Stainless Steel

Chemical Composition


%
 Ni
 		Cr Mo
 Cu N C Mn
 		Si P S

17.50-18.50 19.50-20.50 6.0-6.50 0.50-1.0 0.18-0.22 Max 0.02 Max 1.0 Max 0.80 Max 0.03 Max 0.01


Physical properties


■Characteristic



Tensile strength
Rm N/mm²
Yiield Strength (0.2％ offset)
Rp0.2N/mm²
Density
Elongation
A5 ％
Melting point
(℃)
650
 300
 8.0g/cm³
 35
 1320-1390

Features


Due to its high content of molybdenum and chromium and nitrogen, it has a high resistance to corrosion and crevice corrosion resistance, has good corrosion resistance. The addition of copper improves the corrosion resistance in certain acids. In addition, due to its high
nickel content and high chromium and molybdenum content, 254SMO has excellent resistance to stress corrosion cracking.

1, Extensive field trials and extensive experience have shown that even at slightly higher temperatures, 254SMO has high crevice corrosion resistance in seawater, and only a few types of stainless steel have this property.

2, The corrosion resistance of 254SMO in acidic solutions and oxidizing halide solutions such as paper bleaching can be compared with nickel-based alloys and titanium alloys with the highest corrosion resistance.

3, Since 254SMO has a high nitrogen content, its mechanical strength is higher than other types of austenitic stainless steel. In addition, 254SMO also has high ductility and impact strength as well as good weldability.

4, The high molybdenum content of 254SMO allows it to have a higher oxidation rate when returned, resulting in a rougher surface than normal stainless steel after pickling. But this has no adverse effect on the corrosion resistance of the steel.

Metallographic Structure


254SMO is a face-centered cubic crystal structure. In order to obtain an austenitic structure, 254SMO is generally annealed at a temperature of 1150 to 1200 degrees Celsius. In some cases, the center of the material may have traces of the metallic intermediate phase. However, in general, they have no adverse effect on impact strength and corrosion resistance. When placed in the range of 600-1000 degrees Celsius, these phases may precipitate on the grain boundaries.


Corrosion Resistance


The 254SMO has a very low carbon content, which means that the risk of carbide precipitation due to heating is small. The steel can pass the Strauss intergranular corrosion test even after sensitization for one hour at 600-1000 degrees Celsius. However, due to the high alloy content of the steel. It is possible for the metal intermediate phase to precipitate on the grain boundaries within the above temperature range. These deposits may pose a risk of intergranular corrosion in the heat affected zone. Therefore, soldering can be performed without intergranular corrosion. However, in hot concentrated nitric acid, these deposits may cause intergranular corrosion in the heat affected zone. Ordinary stainless steels containing solutions such as nitrides, bromides or iodide ions are immediately corroded by localized corrosion in the form of pitting, crevice or stress corrosion cracking. However, in some cases, the presence of a halide accelerates uniform corrosion. This is especially the case in the presence of halides in non-oxidizing acids. In pure sulfuric acid, 254SMO has much greater corrosion resistance than 316 normal stainless steel. However, the 254SMO has a slightly weaker corrosion resistance than the 904L (N08904) type stainless steel at high concentrations. Among the sulfuric acid containing chloride ions, 254SMO has the greatest corrosion resistance. 316 normal stainless steel cannot be used in hydrochloric acid due to local corrosion and uniform corrosion, but 254 SMO can be used in diluted hydrochloric acid at normal temperature. There is no need to worry about pitting corrosion in the following areas of the boundary line. But we must try to avoid the existence of gaps. In fluorosilicic acid (H2SiF4) and hydrofluoric acid (HF), the corrosion resistance range of ordinary stainless steel is very limited, while 254SMO can be applied in a wide range of concentrations and temperatures.

Applications


254SMO alloy is a versatile material that can be used in many industrial applications:

1, Petroleum and petrochemical equipment, Such as bellows in petrochemical equipment.
2, Pulp and paper bleaching equipment, such as pulp digester, bleaching equipment, barrels and pressure rollers for filter scrubbers, etc.
3, Power plant flue gas desulfurization device, the main use parts are: tower body of the absorption tower, flue, door panel, internal parts,     sprinkler system, etc.
4, Offshore systems or seawater treatments, such as thin-walled condensing pipes that are cooled by seawater in power plants,  
   desalination plants, and even in equipment where seawater may not flow.
5, Desalination industry.
6, Heat exchangers, especially in heat exchangers with chloride ion working conditions.