What Are The Properties of 254SMO?

Introductions

254SMO (UNS S31254, ASTM F44, Din 1.4547) is a so-called super austenitic stainless steel. By increasing the molybdenum content to 6%, it achieves a pitting resistance equivalent number (PREN) > 43, which is similar to that of a super duplex stainless steel (SDSS). It demonstrates outstanding resistance to pitting, crevice corrosion stress cracking, and corrosion fatigue uniform corrosion. Alloy 254 SMO is substantially stronger than the common austenitic grades, with strength nearly twice that of 300 series stainless steel. It is also characterized by high ductility and impact strength. When comparing 254SMO to super duplex stainless steels, it is non-magnetic, potentially more straightforward to weld and has a wider operating temperature range.

With high levels of chromium, molybdenum, and nitrogen, Alloy 254 SMO is frequently used in high chloride environments, such as brackish water, seawater, pulp mill bleach plants, and other chloride process streams. In some applications it has even been found to be a more cost effective substitute for high nickel and titanium alloys. However, it is considerably more expensive due to its greater nickel and molybdenum content and has a significantly lower strength. Therefore, it will mostly be used in applications where the use of super duplex stainless steels is limited.

This could include applications at lower temperatures (>-50degC) where the impact strength of SDSS drops, or at higher temperatures (>-250degC) where there is a risk of forming deleterious phases if exposed for extended periods.Stainless steel grade 254 SMO 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. For certain applications, grade 254 SMO has been reported to be a cost-effective substitute for high nickel and titanium alloys. It is known to possess excellent workability as well.

SMO 254 Characteristics

These are the products that perform well in halide solutions with chloride and bromide ions present. The SMO 254 grade demonstrates the impact of local corrosion caused by pitting, crevices, and tension. SMO 254 is a low-carbon element material. Because of the low carbon content, there is a reduced chance of carbide precipitation during heat application during welding activity.

Resistance to corrosion

The high content of alloying elements gives Ultra 254 SMO exceptionally good resistance to uniform corrosion. It can withstand a wide range of acids due to the high alloying content of chromium and molybdenum. Resistance to pitting and crevice corrosion is determined mainly by the chromium, molybdenum, and nitrogen content. 254 SMO has high amounts of these elements and is suitable for demanding environments like chlorinated sea water. Resistance to stress corrosion cracking increases with increased content of nickel and molybdenum in particular. This means that Ultra 254 SMO has very good resistance to stress corrosion cracking.

Machinability

Due to the exceptionally high work hardening rate and lack of sulfur content, stainless steel grade 254 SMO is quite difficult to mill; however, sharp tools, powerful machine machines, positive feeds, and a substantial amount of lubrication, and slow speeds tend to offer decent machining results.

Welding

Welding stainless steel grade 254 SMO necessitates the use of filler material, which results in inferior tensile qualities. AWS A5.14 ERNiCrMo-3 and alloy 625 are approved as filler metals. The electrodes used in the process must comply with AWS A5.11 ENiCrMo-12.

Annealing

The annealing temperature for this material should be 1149-1204°C (2100-2200°F), followed by a water quench.

Working in extreme conditions

Forging, upsetting, and other operations using this material can be carried out at temperatures ranging from 982 to 1149°C (1800 to 2100°F). Temperatures above this range are not recommended since they will cause scaling and reduce the material’s workability. It is recommended to undertake post-process annealing to regain maximal corrosion resistance.

Working in the cold

Cold working can be done using any of the usual methods; however, the procedure will be difficult due to the high work hardening rate. As a result, the material will have greater strength and toughness.

Working in the hot

Forging, upsetting and other operations relating to this material can be performed at 982 – 1149°C (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.

Hardening

Heat treatment does not affect stainless steel grade 254 SMO.  Only cold reduction allows for hardening.

SMO 254 Chemical Composition

SMO 254 is a highly alloyed austenitic stainless steel that contains 6% Molybdenum, 18% Chromium, and 20% Nickel. It also has small amounts of Copper, Nitrogen, and Carbon. The high Molybdenum content makes it highly resistant to pitting, crevice corrosion, and stress corrosion cracking (SCC) in chloride environments. SMO 254 is commonly used in seawater applications, pulp and paper industries, and chemical processing.

Application

Due to its high levels of molybdenum and nickel, Alloy 254 SMO is frequently used in high chloride environments. Examples of applications that call for the used of Alloy 254 SMO include:

1. Petroleum production

2. Saltwater handling

3. Food and chemical processing equipment

4. Pulp mill bleach systems

5. Flue gas desulphurization scrubbers

6. Tall oil distillation columns

7. Offshore oil & gas production equipment

8. Desalination equipment