Austenitic stainless steels exhibit a wide range of properties, which enables them to be used at very low (cryogenic) temperatures. At cryogenic temperatures these steels have higher tensile strengths than those at ambient temperatures. However, their toughness is slightly degraded at this temperature.
Typical impact strengths of stainless steels are shown in Figure 1. Austenitic stainless steels have been extensively employed for applications involving the use of liquefied natural gas at temperatures of -161°C, and also in plants for generating liquefied gases. Boiling point of liquid nitrogen is -196°C and that of liquid oxygen is -183°C.
Figure 1 - illustrates the relationship between i mpact strength and temperature.
Ductile to Brittle Transition
Precipitation hardening, martensitic and ferritic steels are not preferred for use in negative temperatures as they tend to experience a fall in toughness at moderately low temperatures, and at temperatures slightly below room temperature in some cases. The duplex stainless steels have better low temperature ductility when compared to martensitic and ferritic grades. Duplex steels can be used down to at least -50°C, which makes them suitable for lower temperature applications.