Creep of 304 LN and 316 L stainless steels at cryogenic temperatures

Creep behavior of Type 304 LN plate and 316 L shielded-metal-arc (SMA)-deposited stainless weld metal was investigated at 40K. Testing was performed at constant load in a creep machine with a cryostat designed for long-term stability. Both transient and steady-state creep were observed during tests lasting over 2000 hours. Steady-state creep rates were much greater than expected from extrapolations of 300-K creep data. Creep rates on the order of 10-10 s-1 were observed at stresses around the yield stress for both materials. The stress exponent under these conditions if approx.2.3. Possible creep mechanisms at this temperature and the impact of these results on the design of engineering structures for long-term structural stability at cryogenic temperatures are discussed