Deformation behavior in reactor pressure vessel steels as a clue to understanding irradiation hardening.
In this paper, we examine the post-yield true stress vs true strain behavior of irradiated pressure vessel steels and iron-based alloys to reveal differences in strain-hardening behavior associated with different irradiating particles (neutrons and electrons) and different alloy chernky. It is important to understand the effects on mechanical properties caused by displacement producing radiation of nuclear reactor pressure steels. Critical embrittling effects, e.g. increases in the ductile-to-brittle-transition-temperature, are associated with irradiation-induced increases in yield strength. In addition, fatigue-life and loading-rate effects on fracture can be related to the post-irradiation strain-hardening behavior of the steels. All of these properties affect the expected service life of nuclear reactor pressure vessels. We address the characteristics of two general strengthening effects that we believe are relevant to the differing defect cluster characters produced by neutrons and electrons in four different alloys: two pressure vessel steels, A212B and A350, and two binary alloys, Fe-0.28 wt%Cu and Fe-0.74 wt%Ni. Our results show that there are differences in the post-irradiation mechanical behavior for the two kinds of irradiation and that the differences are related both to differences in damage produced and alloy chemistry. We find that while electron and neutron irradiations (at T {le} 60 C) of pressure vessel steels and binary iron-based model alloys produce similar increases in yield strength for the same dose level, they do not result in the same post-yield hardening behavior. For neutron irradiation, the true stress flow curves of the irradiated material can be made to superimpose on that of the unirradiated material, when the former are shifted appropriately along the strain axis. This behavior suggests that neutron irradiation hardening has the same effect as strain hardening for all of the materials analyzed. For electron irradiated steels, the post-yield hardening rate is clearly greater than that of the unirradiated material, and the flow curves cannot be made to superimpose. The binary iron-base model alloys studied here show a less pronounced difference in flow behavior for neutrons and electrons than exhibited by the steels, implicating the effect of alloy chemistry. Our results are analyzed in the context of classical theories dealing with the interaction between the deformation microstructure, i.e. glide dislocations, and irradiation-produced defects. Our findings provide clues about the way different alloy constituents interact with the different kinds of irradiation damage to strengthen the material differently.
- Research Organization:
- Argonne National Lab., IL (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-31-109-ENG-38
- OSTI ID:
- 750440
- Report Number(s):
- ANL/RE/CP-94733; TRN: US200221%%487
- Resource Relation:
- Conference: 6th International Conference on Nuclear Engineering, San Diego, CA (US), 05/10/1998--05/15/1998; Other Information: PBD: 25 Oct 1999
- Country of Publication:
- United States
- Language:
- English
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