Mechanical Investigations on Aged Stainless Steel and Incoloy 908 Materials at 4.2 K and 7 K

Abstract

The effects of aging at 650 C for 200 hours on the tensile properties, fracture toughness, and fatigue crack growth rates of Type 316LN austenitic steel and Incoloy 908 at 7 K have been investigated. The tests were performed on specimens machined at the final manufacturing stages of the aged jackets for the ITER central solenoid (CS) - and toroidal field (TF) - model coils so as to establish sound data bases for the products. The fracture toughness results obtained using small specimens machined from the CS-jackets with a minimum wall thickness of 4 mm have been evaluated and critically assessed with respect to the ASTM standards criteria. A new test method using EDM notched round bar specimens has been adopted for determining the elastic-plastic fracture toughness and the values obtained by this technique correlated with valid data for thick plate samples. The applicability of this test method has also been demonstrated for double notched flat tensile specimens machined from the aged TF-jacket material.