Austenitic Steels: Mechanical Properties at Cryogenic Temperatures
We have discussed the maximum service temperatures of common Austentinic Steels in
Engineering Bulletin # 106 and in today's issue we'll look at how mechanical properties of Austentinic Steels are influenced by very low (cryogenic) temperaures and what types of SS alloys are best suited for low temperature applications.
Experience with brittle fracture of steel ships during the World War II demonstrated that while many metals have good "room-temperature" characteristics they would not perform adequately at low temperatures. For example Ferritic (405, 409, 430), Martensitic (403, 410, 414, 416) and Duplex stainless steels (329, 2205) tend to become brittle as the temperature is reduced and fracture (sometimes with catastrophic results) can occur without any warning by stretching, bulging as in some plastic failures. Therefore alloys for low-temperature service must retain suitable properties such as yield and tensile strength and of course ductility.
The austenitic stainless steels such as 304 and 316 retain abovementioned engineering properties at cryogenic temperatures and can be classified as 'cryogenic steels', they are commonly used in arctic locations and in the handling and storage of liquid gases like nitrogen with a temperatures been below -321°F (-196 °C), stainless steel 321 on the other hand (with ferrite stabilising additions), somewhat less suitable at very low temperatures, but can be used "up to" about -200°C)
Table below shows some mechanical properties of stainless steels at low temperatures. Note, these alloys show not only good ductily (by means of elongation) at temperatures up to -423F° (-253°C), but they also show an increase in tensile and yield strengths.
Mechanical Properties of 304, 321 and 316 Stainless Steels at
Cryogenic Temperatures.
| Alloy | Temperature | Yield Strength | Tensile Strength | Elongation in 2" | ||||
| °F | °C | ksi | MPa | ksi | MPa | % | ||
| 304 | -40 | -40 | 34 | 234 | 155 | 1069 | 47 | |
| -80 | -62 | 34 | 234 | 170 | 1172 | 39 | ||
| -320 | -196 | 39 | 269 | 221 | 1524 | 40 | ||
| -423 | -252 | 50 | 344 | 243 | 1675 | 40 | ||
| 316 | -40 | -40 | 41 | 283 | 104 | 717 | 59 | |
| -80 | -62 | 44 | 303 | 118 | 814 | 57 | ||
| -320 | -196 | 75 | 517 | 185 | 1276 | 59 | ||
| -423 | -252 | 84 | 579 | 210 | 1448 | 52 | ||
| 321 | -40 | -40 | 45 | 310 | 120 | 828 | 55 | |
| -80 | -62 | 50 | 345 | 138 | 952 | 52 | ||
| -320 | -196 | 60 | 414 | 211 | 1455 | 23 | ||
| -423 | -252 | 68 | 469 | 248 | 1710 | 34 | ||
Note: In designing a metal hose assembly for cryogenic service, care must be taken to insure that the fittings and any accessory (guard/liner) materials are suitable for the intended operating temperatures as well.
If you have any questions or comments, please contact us.
