254SMO characteristics/comparison grade/corrosion resistance
254SMO alloy characteristics:
The high molybdenum content and high chromium and nitrogen content give 254SMO excellent resistance to pitting corrosion and crevice corrosion. The addition of copper improves corrosion resistance in certain acids. In addition, due to its higher nickel content and high
The chromium and molybdenum content make 254SMO have good resistance to stress corrosion cracking.
1. A large number of field experiments and extensive use experience show that even at slightly higher temperatures, 254SMO has high crevice corrosion resistance in seawater. Only a few types of stainless steel have this performance.
The corrosion resistance of 2.254SMO in acidic solutions and oxidizing halide solutions required for paper bleaching production is comparable to the most corrosion-resistant nickel-based alloys and titanium alloys.
3. Because 254SMO has a higher nitrogen content, its mechanical strength is higher than other types of austenitic stainless steel. In addition, 254SMO has high ductility and impact strength as well as good weldability.
The high molybdenum content of 4.254SMO enables it to have a higher oxidation rate during annealing, resulting in a rougher surface than ordinary stainless steel after pickling. But this has no adverse effect on the corrosion resistance of the steel.
Metallographic structure of 254SMO:
254SMO has a face-centered cubic lattice structure. In order to obtain an austenitic structure, 254SMO is generally annealed at a temperature of 1150-1200 degrees Celsius. In some cases, there may be traces of metallic intermediate phases (χ and α phases) in the center of the material. But in general, they have no adverse effects on impact strength and corrosion resistance. These phases may precipitate at grain boundaries when placed in the range of 600-1000 degrees Celsius.
Corrosion resistance of 254SMO:
The carbon content of 254SMO is very low, which means that the risk of carbide precipitation due to heating is very small. The steel can pass the Strauss Test ASTMA262 Procedure E even after one hour of sensitization treatment at 600-1000 degrees Celsius. However, due to the high alloy content of this steel. Within the above temperature range, the metallic intermediate phase may precipitate on the grain boundaries. These precipitates do not put the steel at risk of intergranular corrosion when used in corrosive media. Therefore welding can be performed without intercrystalline corrosion.
However, in hot concentrated nitric acid, these precipitates may cause intergranular corrosion in the heat affected zone. In solutions containing ions such as chloride, bromide or iodide, ordinary stainless steels will immediately suffer from localized corrosion in the form of pitting corrosion, crevice corrosion or stress corrosion cracking. In some cases, however, uniform corrosion can be accelerated by the presence of halides. This is especially true when halides are present in non-oxidizing acids.
In pure sulfuric acid, 254SMO has much greater corrosion resistance than 316 ordinary stainless steel. However, compared with 904L (NO8904) stainless steel at high concentrations, the corrosion resistance of 254SMO is slightly weaker. Among sulfuric acids containing chloride ions, 254SMO has the greatest corrosion resistance. Due to the possibility of local corrosion and uniform corrosion, 316 ordinary stainless steel cannot be used in hydrochloric acid, but 254SMO can be used in dilute hydrochloric acid at normal temperatures. There is no need to worry about pitting corrosion in areas below the boundary line. But efforts must be made 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 used in a fairly wide range of concentration and temperature.
254SMO application fields:
254SMO alloy is a versatile material that can be used in many industrial fields:
1. Petroleum and petrochemical equipment, such as bellows in petrochemical equipment.
2. Pulp and paper bleaching equipment, such as pulp digesters, bleaching equipment, barrels and pressure rollers for filter washers, etc.
3. The main parts used in power plant flue gas desulfurization equipment are: the tower body of the absorption tower, the flue, the baffle plate, the internal parts, the spray system, etc.
4. Offshore systems or seawater treatment, such as thin-walled condensation pipes cooled by seawater in power plants, seawater desalination equipment, and can be applied even in equipment where seawater may not flow.
5. Desalination industry, such as salt production or desalination equipment.
6. Heat exchangers, especially heat exchangers in working environments with chloride ions.
