Austenitic Steels: Mechanical Properties at Cryogenic Temperatures
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Since we discussed the maximum service temperatures of common austenitic steels in Engineering Bulletin #106, we’ll now look at how mechanical properties of austenitic steels are influenced by cryogenic temperatures and what types of stainless steel alloys are best suited for low temperature applications.
During World War II, experience with the brittle fracture of steel ships caused engineers to look closely at what happens to metals in cold weather. They found that though many metals have good “room-temperature” characteristics, they do not necessarily maintain those characteristics 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. Fracture can occur, sometimes with catastrophic results. While stretching or bulging may serve as an indicator of impending plastic failure, such signs are absent in the case of these metals. Therefore alloys for low-temperature service are those that retain suitable properties such as yield, tensile strength and ductility.
The austenitic stainless steels such as 304 and 316 retain these 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 such as liquid nitrogen and liquid helium. Liquid helium is the coldest material known with a boiling point of -452°F (-269 °C).
The table below shows mechanical properties of stainless steels at low temperatures. Elongation is an indication of their good ductility. There is an increase in tensile and yield strengths as the temperature decreases as well.
Mechanical Properties of 304, 321 and 316 Stainless Steels at Cryogenic Temperatures.
|Alloy||Temperature||Yield Strength||Tensile Strength||Elongation in 2″|
Note: In designing a metal hose assembly for cryogenic service, care must be taken to ensure that the fittings and any accessory (guard/liner) materials are suitable for the intended operating temperatures as well.
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Disclaimer: The info presented here has been compiled from sources believed to be reliable, including the American Society of Materials Specialty Handbook on Stainless Steels. No guarantee is implied or expressly stated here and the data given is intended as a guide only.
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