Stainless steel grade 254 SMO (UNS S31254) 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 (UNS S31254) has been reported to be a cost-effective substitute for high nickel and titanium alloys. It is known to possess excellent workability as well.
The following sections will discuss in detail about stainless steel grade 254 SMO.
Chemical Composition
The chemical composition of stainless steel grade 254 SMO (UNS S31254) is outlined in the following table.
| Element | Content (%) |
|---|---|
| Iron, Fe | 55.69 |
| Chromium, Cr | 20 |
| Nickel, Ni | 18 |
| Molybdenum, Mo | 6.1 |
| Nitrogen, N | 0.20 |
| Carbon, C | 0.010 |
Physical Properties
The physical properties of stainless steel grade 254 SMO (UNS S31254) are tabulated below.
| Properties | Metric | Imperial |
|---|---|---|
| Density | 8 g/cm3 | 0.289 lb/in3 |
Mechanical Properties
The following table shows mechanical properties of stainless steel grade 254 SMO (UNS S31254).
| Properties | Metric | Imperial |
|---|---|---|
| Tensile strength | 680 MPa | 98600 psi |
| Yield strength | 300 MPa | 43500 psi |
| Modulus of elasticity | 195 GPa | 28300 ksi |
| Shear modulus | 75 GPa | 10900 ksi |
| Poisson’s ratio | 0.30 | 0.30 |
| Elongation at break | 50 % | 50 % |
| Hardness, Brinell | 210 | 210 |
Thermal Properties
The thermal properties of stainless steel grade 254 SMO (UNS S31254) are tabulated below.
| Properties | Metric | Imperial |
|---|---|---|
| Thermal expansion co-efficient (@20-100°C/68-212°F) | 16.5 µm/m°C | 9.17 µin/in°F |
| Thermal conductivity | 14 W/mK | 97.2 BTU in/hr.ft².°F |
Other Designations
Other designations that are equivalent to stainless steel grade 254 SMO (UNS S31254) include the following.
| ASTM A813 | ASTM A469 | ASTM A269 | ASTM A240 | ASTM A182 (F44) |
| ASTM A814 | ASTM A312 | ASTM A249 |
Fabrication and Heat Treatment
Machinability
Stainless steel grade 254 SMO (UNS S31254) is quite tough to machine due to the extremely high work hardening rate and lack of sulfur content; however using sharp tools, overpowered machine tools, positive feeds, good amount of lubrication, and slow speeds tend to provide good machining results.
Welding
Welding of stainless steel grade 254 SMO (UNS S31254) 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°C (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°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.
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 (UNS S31254) does not respond to heat treatment. Hardening is possible only through cold reduction.
Applications
Stainless steel grade 254 SMO (UNS S31254) is used in the following areas:
- Saltwater handling
- Tall oil distillation columns
- Flue gas desulfurization scrubbers
- Components used in petroleum production
- Food processing equipment
- Process equipment in chemical industry
- Bleaching equipment in the pulp and paper industry
- Flue-gas cleaning
- Desalination
- Heat exchangers
Source – wilsonpipeline Pipe Industry Co., Limited (https://www.wilsonpipeline.com)
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