EFFECTS OF THERMAL AGING ON MICRO–MECHANICAL PROPERTIES AND IMPACT FRACTURE BEHAVIOR OF Z3CN20–09M STAINLESS STEELS
LI Shilei, WANG Xitao, WANG Yanli, LI Shuxiao
State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083
Cite this article:
LI Shilei WANG Xitao WANG Yanli LI Shuxiao. EFFECTS OF THERMAL AGING ON MICRO–MECHANICAL PROPERTIES AND IMPACT FRACTURE BEHAVIOR OF Z3CN20–09M STAINLESS STEELS. Acta Metall Sin, 2011, 47(6): 751-756.
Abstract Cast austenite stainless steels (CASS) were used in the primary circuit piping of pressurized water nuclear reactors (PWRs), because of their excellent strength, corrosion resistance and good weldability. However, after long–term service at mid–temperature, CASS would suffer a loss of toughness and Charpy impact energy due to thermal aging. The micro–mechanical properties and impact fracture behavior of Z3CN20–09M stainless steel after long–term thermal aging at intermediate temperature were studied in this paper. A nano–indenter was used to study the changes of mechanical properties in the ferrite phases during the aging process. The impact behavior of the aged material was investigated by an instrumented impact tester, and the impact fractures were observed with SEM. The results indicated that long–term thermal aging caused the declining plastic deformation ability of the ferrite phases and the decrease of the impact toughness. The loss of impact energy in the aging process was mainly due to the reduction of stable crack propagation energy. The impact fracture morphology chnged from ductile dimple in the initial stage into a mixture of cleavage in ferrite alonwith tearing in austenite in the later stage. In the impact fracture process, cracks initiated firstly in the errite phases and fast propagated under impact loading, and then the ferrite phases fractured along the cleavage planes. At last, the cracks extended to the austenite phases and the cracks connected through the specimen.
