ASTM Specification A 302 Grade B steel was given thermal-mechanical treatments to improve mechanical properties through development of substructure. Cold work of 0.06 followed by a 435 C heat treatment produced a 28,000 psi (35 percent) increase in lower yield strength without loss of uniform elongation. Specimens were irradiated at <100 C and 288 C to fast fluences in the range of 1 × 1018 to 5.2 × 1019 n/cnr. Standard tension tests, biaxial stress (tube) tests, and instrumented Charpy-V impact tests were performed.
Data from the biaxial tests were analyzed on the basis of uniform strain predicted from the uniaxial (simple tension) test. A mathematical analysis of the instability criteria is included. Data from the Charpy tests were analyzed to determine (1) the relation between substructure and irradiation response in terms of the nil ductility transition temperature shift and (2) the way in which the sample breaking energy is distributed between crack initiation and propagation. Major conclusions from these analyses are: The predicted instability strain in the biaxial test is not exceeded. A constant cell size (and degree of substructure) is reached at small amounts of cold work and does not appear to be exceeded. An appropriate substructure treatment may decrease radiation sensitivity and may increase energy absorption in fracture propagation in the Charpy test.