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UNS S31254 ,1.4547 , 254SMO ,X1CrNiMoCuN 20-18-7

Material No.

EN symbol X1CrNiMoCuN 20-18-7

Z1 CNDU 20.18.06AZ





UNS S31254 is an austenitic grade in which the additions of chromium, molybdenum and nitrogen give
high resistance to pitting in sea water. This alloy has a mean Pitting Resistance Equivalent Number (‚PREN‘
= Cr+3.3Mo+16N) of 43.8. Tests indicate high resistance to crevice-corrosion attack in seawater and to
stress corrosion cracking in hot concentrated sodium chloride.Compared with CrNiMo 17 12 2.5 steels, it
shows superior corrosion resistance in many acids at similar concentrations and its yield strength is approximately
50% higher. Good weldability using Ni-Cr-Mo consumables. Quench annealing and short periods
within the 600-1000°C range avoids the possiblen development of deleterious sigma phase, which may
embrittle and impair corrosion resistance.
The steel is mainly characterized by the following properties:
*Excellent resistance to pitting and crevice corrosion
*High resistance to general corrosion
*High resistance to stress corrosion cracking
*Higher strength than conventional austenitic stainless steels
*Good weldability

Chemical composition (%)





Mechanical Properties:

GradeTensile StrengthYield Strength 0.2%Elongation -% in  50 mm (min.)HardnessHardness
ksi (min.)Offset ksi (min.)(Brinell) MAX(Rockwell B) MAX

Convert ksi to Mpa Formula:  ksi/0.1450377

Heat Treatment 
The tubes are delivered in heat treated condition. If additional heat treatment is needed due to further processing the following is recommended.

Solution Annealing
1150–1200°C (2100–2190°F), quenching in water. Thin-walled tubes min. 1130°C (2060°F), quenching in air/water.

Welding filler for welded pipe & tube

*The weldability of  254 SMO is good. Welding should be undertaken without preheating, and if correctly performed there will be no need for any subsequent heat treatment. Suitable methods of fusion welding are manual metal-arc welding with covered electrodes and gas-shielded arc welding, mainly by means of the TIG and MIG methods.

*Since the material is intended for use under severe corrosive conditions, welding must be carried out with care and followed by thorough cleaning to ensure that the weld metal and the heat-affected zone maintain the best possible corrosion properties.

In common with all austenitic stainless steels, 254 SMO has low thermal conductivity and high thermal expansion. For this reason, welding should be carefully planned in advance so that distortion of the welded joint can be minimized. If, despite these precautions, it is believed that residual stresses may impair the function of the weldment, it is recommended that the entire structure be solution annealed. See under Heat treatment.

*Welding wire and covered electrodes AWS ENiCrMo-3/EN number Ni 6625 are recommended as filler metal. These filler metals are overalloyed in order to compensate for microsegregation of molybdenum and thereby producing a weld with good corrosion resistance. Dilution from parent material into the weld metal should be kept as low as possible to secure good corrosion resistance. AWS ENiCrMo-3/EN number Ni 6625  is also suitable for welding joints between 254 SMO and nickel alloys, other stainless steels or carbon steels.


Main fields of application(depending on the specific conditions of use)

254 SMO is used in the following applications:

-Equipment for handling of seawater, such as, seawater cooling, cooling water pipes, ballast water systems, firefighting systems etc.
-Hydraulic and instrumention tubing
-Equipment in pulp bleaching plants
-Components in gas cleaning systems
-Tanks and pipelines for chemicals with high halide contents