The thermal aging and consequent embrittlement of materials are ongoing issues in cast
and duplex stainless steel. Spinodal decomposition is largely responsible for the well known
“475°C” embrittlement that results in drastic reductions in ductility and toughness in cast
materials. This process is also operative in welds in either cast or wrought stainless steels where
delta ferrite is present. While the embrittlement can occur after several hundred hours of aging
at 475°C, it can also occur at lower temperatures where ductility reductions have been observed
after several tens of thousands of hours at 300°C. The effect of thermal aging on mechanical
properties, including tensile, toughness, fatigue and static crack growth has been investigated at
room temperature and in 288°C high purity water simulating BWR operating conditions.