What Is 1.4547 ​​​​​​​Stainless Steel?

What is 1.4547 stainless steel?

1.4547 stainless steel, commonly known as 254 SMO or UNS S31254, is a high-performance super austenitic stainless steel with exceptional resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride environments. With its high molybdenum and nitrogen content, combined with significant chromium and nickel, it offers performance that bridges the gap between standard austenitic grades and more expensive nickel-based alloys. It is widely used in seawater handling, chemical processing, and pollution control equipment where conventional stainless steels are inadequate.

 

1.4547 Stainless Steel Equivalent Materials

Standard	Equivalent Grade
EN (Europe)	1.4547
ASTM/AISI (USA)	254 SMO, UNS S31254
Common Name	254 SMO, 6% Moly

 

1.4547 Stainless Steel Chemical Composition

Element	C	Si	Mn	P	S	Cr	Ni	Mo	N	Cu
Content (%)	≤ 0.02	≤ 0.8	≤ 1.0	≤ 0.03	≤ 0.01	19.5 - 20.5	17.5 - 18.5	6.0 - 6.5	0.18 - 0.22	0.5 - 1.0

 

1.4547 Stainless Steel Mechanical Properties

Property	Yield Strength (Rp0.2)	Tensile Strength (Rm)	Elongation (A)	Hardness (HB)
Typical Value	≥ 300 MPa	650 - 850 MPa	≥ 35%	≤ 250

 

Key Characteristics and Applications of 1.4547 / 254 SMO

Exceptional Pitting and Crevice Corrosion Resistance: With a PREN (Pitting Resistance Equivalent Number) typically > 40, it offers outstanding resistance in aggressive chloride environments, including seawater and hypochlorite solutions.

Excellent Stress Corrosion Cracking (SCC) Resistance: Performs well under tensile stress in corrosive environments where standard austenitic grades like 316L would fail.

High Strength: Provides higher yield strength than standard austenitic grades (300 MPa vs. 200 MPa), allowing for lighter designs.

Good Weldability and Formability: Can be welded using common techniques with matching high-alloy filler materials, maintaining good corrosion resistance in the weld zone.

 

254 SMO Stainless Steel Applications:

Seawater Systems: Heat exchangers, piping, pumps, and valves in desalination plants, offshore platforms, and marine applications.

Chemical Processing: Equipment for handling aggressive acids, chlorides, and oxidizing media, particularly in bleach plants and pulp processing.

Pollution Control: FGD (Flue Gas Desulfurization) systems, scrubbers, and ducting in power plants.

Oil & Gas: Offshore topside equipment, seawater injection systems, and process piping.

Pulp & Paper: Bleaching equipment, digesters, and handling systems for chlorine dioxide environments.

Pharmaceutical: High-purity equipment requiring exceptional corrosion resistance.

 

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How does 254 SMO (1.4547 ) compare to 316L (1.4404) and 6% Moly alloys?
254 SMO offers dramatically superior corrosion resistance compared to 316L, with PREN > 40 vs. 316L's 24-26. It can withstand seawater temperatures up to 40-50°C, while 316L is limited to ambient temperatures in seawater. It offers excellent resistance to stress corrosion cracking, where 316L is susceptible. Compared to other 6% moly super austenitic alloys, 254 SMO is one of the most widely used and proven grades, offering a well-established balance of properties. It bridges the performance gap between standard stainless steels and more expensive nickel-based alloys like C-276, offering a cost-effective solution for severe chloride environments.

 

What are the welding considerations for 254 SMO stainless steel?
Welding 254 SMO requires careful control to maintain corrosion resistance. Recommended practices include using matching or over-alloyed filler metals (such as Alloy 625 or 276 type fillers) to ensure the weld zone maintains corrosion resistance comparable to the base metal. Controlling heat input (typically 0.5-1.5 kJ/mm) is important to avoid excessive grain growth and precipitation of detrimental phases. Proper shielding gas (argon-based with nitrogen addition) helps maintain nitrogen content in the weld metal. Post-weld cleaning is essential to preserve corrosion resistance in the weld zone, and pickling/passivation is recommended to restore the passive layer.

 

What is the maximum service temperature for 254 SMO in chloride environments?
For continuous immersion in seawater or other chloride-containing environments, 254 SMO offers excellent performance up to approximately 40-50°C (104-122°F). Above this temperature, the risk of pitting and crevice corrosion increases, and higher-alloyed materials (such as higher 6% Mo grades or nickel-based alloys) may be required. For non-immersed applications or where chlorides are not present, 254 SMO can be used at higher temperatures up to about 300°C, but care must be taken to avoid prolonged exposure to temperatures above 300°C due to potential embrittlement concerns.

 

Looking for a Reliable Supplier of 1.4547 / 254 SMO Stainless Steel?
GNEE Steel supplies premium super austenitic 254 SMO (1.4547 /UNS S31254) stainless steel in plate, pipe, bar, fitting, and flange forms for the most demanding corrosive and marine applications. We provide full material traceability and certification (EN 10204 3.1) to ensure optimal performance. If you have any requirements, please feel free to contact us.