SMO 254 Material (UNS S31254)

SMO 254 material is a very high end austenitic stainless steel. It is designed with a combination of impact toughness resistance to chloride stress corrosion cracking, and pitting and crevice corrosion with strength that is twice that of the stainless steel 300 series.

When comparing SMO 254 to super duplex stainless steels, it is non-magnetic, potentially more straightforward to weld and has a wider operating temperature range. Although it contains a variety of alloying elements, SMO 254 still has good processing properties and can be formed and processed by conventional processing methods -such as forging, rolling, machining, etc.

What is the difference between SMO 254 and SS316?

SMO 254 Stainless steels have better corrosion resistance against sulphuric acid or chlorid content environments comparing with 304, 316 and 904 grade steels. 304 and 316 conventional stainless steels can be sensitive against stress corrosion cracking at 80-100⁰C.

Chemical composition

SMO 254

Chromium (Cr): The content is about 19.5% - 20.5%. Chromium can form a dense oxide film on the steel surface to improve the corrosion resistance of the material.

Nickel (Ni): The content is about 17.5% - 18.5%. Nickel can improve the toughness and corrosion resistance of steel, making it have good performance in various environments.

Molybdenum (Mo): The content is about 6% - 6.5%. Molybdenum can significantly enhance the corrosion resistance of steel in reducing media, especially the corrosion resistance to chloride ions.

SS316

Chromium (Cr): Contains approximately 16% - 18%, providing basic corrosion resistance.

Nickel (Ni): The content is about 10% - 14%, which gives the material good toughness and weldability.

Molybdenum (Mo): The content is about 2% - 3%, which enhances the corrosion resistance of the material in certain corrosive environments.

Corrosion resistance

SMO 254 stainless steel is known for its exceptional corrosion resistance in harsh environments, such as seawater and acidic solutions. It has higher resistance to pitting and crevice corrosion than 316 stainless steel. 316 stainless steel also offers good corrosion resistance, but not as high as 254 SMO, especially in chloride-containing environments.

Weldability

SMO 254

Smo254 has good weldability, but due to its high alloy content, the welding process requires strict control of welding parameters and processes.

SS316

Welding characteristics: SS316 has good weldability and is a stainless steel material that is easy to weld. Although SS316 has good weldability, it is also necessary to pay attention to controlling welding parameters during the welding process to avoid welding defects.

What is the difference between 254 and 6Mo alloy?

SMO 254 has extremely good resistance to pitting, crevice corrosion and stress corrosion cracking. It also has good tolerance to various corrosive media such as acids, alkalis, salts, etc., and has a low corrosion rate in acidic media such as sulfuric acid and phosphoric acid and some alkaline environments.

6MO is similar to SMO 254. 6MO also has excellent corrosion resistance, especially in media containing chloride ions. Its resistance to pitting and crevice corrosion is outstanding, and it can maintain the integrity of the material in harsh corrosive environments.

In some specific chemical media, the corrosion resistance of 6MO may be slightly different from that of SMO 254 due to different specific components, but in general, the two have similar corrosion resistance.

Is duplex better than stainless steel?

In comparison to austenitic stainless steels, duplex stainless steels are nearly twice as strong. They also offer better resistance to localised corrosion, particularly pitting, crevice corrosion, and stress corrosion cracking. In addition, they are more ductile and tougher than ferritic stainless steel.

The ferritic steels are magnetic and the austenitic steels are non-magnetic. They have different metallurgic micro structures. The duplex steels have both ferritic and austenitic phases in the metallurgic micro structure and have the best of both ferritic and austenitic steel grades together.

SMO 254 Material

Chemical Composition

The chemical composition of SMO 254 is characterized by the precise ratio of various alloying elements.

Chromium

The content is about 19.5 - 20.5%. Chromium is a key element in the formation of a passive film in stainless steel, which can improve the oxidation resistance and corrosion resistance of steel, allowing it to form a dense chromium oxide protective film under different environments to prevent further corrosion.

Nickel

The content is about 17.5 - 18.5%. Nickel can expand the austenite phase region, make the steel have a stable austenite structure, improve the toughness, weldability and cold working performance of the steel, and enhance the corrosion resistance of the steel in non-oxidizing acid and alkali solutions.

Mechanical Properties

SMO 254 has high strength and good toughness. Its tensile strength is usually ≥650MPa, yield strength ≥300MPa, and elongation ≥35%. This allows it to maintain structural stability under high pressure and stress, and is not prone to breakage or deformation. It is suitable for various engineering applications that require strength and toughness.

Fabrication and Other Properties of SMO 254

Welding

Welding  of stainless steel grade 254 SMO requires filler material without which it results in poor strength properties. Filler metals such as AWS A5.14 ERNiCrMo-3, and alloy 625 are recommended. Electrodes used in the process, have to match with AWS A5.11 ENiCrMo-12.

Annealing

Annealing of this material should be performed at 1149-1204℃ (2100-2200°F), which should be followed by a water quench.

Hot Working

Forging, upsetting and other operations relating to this material can be performed at 982 - 1149℃ (1800 - 2100°F). It is recommended that temperatures do not exceed this range as it would result in scaling and reduction in the workability of the material. To re-attain maximum corrosion resistant properties, it is advisable to perform post-process annealing.

Cold Working

Cold working can be carried out using all the traditional methods; however the process would be tough due to its high work hardening rate. The result will provide the material with increased strength and toughness.

Hardening

Stainless steel grade 254 SMO™ does not respond to heat treatment. Hardening is possible only through cold reduction.

Advantages

1. Excellent corrosion resistance

2. Strong resistance to pitting and crevice corrosion

3. Resistant to corrosion by various chemical media

4. Good mechanical properties

5. High strength and toughness

6. Good machinability

7. Good hygienic properties

8. High surface finish

Disadvantages

1. High cost

2. High alloying element content

3. Difficult welding

4. High welding process requirements

5. Limited applicable temperature range

6. Decreased high temperature strength

SMO 254 Material Equivalent Grades

Product Forms and Relative Standards

SMO 254 is designated differently in different product forms: for wrought pipe fittings, it is ASTM A403 WPS31254; for forgings, it is ASTM A182 F44; for castings, it should be CK3MCuN or UNS J93254.

You can get an offer for SMO 254 stainless steel in below material forms:

-Pipe and Tube (EN 10216-5, ASTM A213, ASTM A249)

-Fitting and Flange (ASTM A182)

-Round bar ，Billet (ASTM A276, ASTM A479)

- Plate, Sheet, Strip(ASTM A240, EN 10028-7，A480)

-Bolting, Nuts（ASTM A193, A194）

Application range

● Chemical industry

● Corrosive chemical production and storage

● Fine chemicals

● Marine engineering

● Desalination of seawater

● Offshore oil and gas production

● Food and pharmaceutical industry

● Food processing

● Pharmaceutical equipment

● Environmental protection

● Sewage treatment

● Waste gas treatment