Influence of strain ageing on fracture toughness of the pressure vessel steel A533 B at elevated temperatures

The purpose of this investigation has been to evaluate the effect of a preceding ageing treatment under stress on the fracture toughness of steel A533 B by using the methods of elastic-plastic fracture mechanics. The pre-notched samples were previously aged at temperatures (100-2880C) and stresses (180-390 MPa) which are typical for different parts of the pressure vessel, and for various times between 2 days and 4 years. The results indicate that the fracture toughness at the normal service temperature (2880C) is approximately 25% lower than the value at 1000C. Furthermore, for a given test temperature (20-2880C) there is no significant decrease in fracture toughness as a result of a preceding ageing treatment, involving ageing times up to 4 years at stresses and temperatures characteristic for operation of nuclear-reactor pressure vessels. (orig.)