Microstructural and Fractographic Characterization of a Thermally Embrittled Nuclear Grade Steel: Part I - Annealing

Abstract

A nuclear reactor pressure vessel steel was submitted to different annealing heat treatments aimed at simulating neutron irradiation damage. The obtained microstructures were mechanically tested with subsequent metallographic and fractographic characterization. The relevant microstructural and fractographic aspects were employed in the interpretation of the mechanical behavior of the microstructures in both quasi-static (J-R curve) and dynamic (Charpy impact) loading regimes. A well defined relationship was determined between the elastic-plastic fracture toughness parameter J-integral and the Charpy impact energy for very most of the microstructures

Microstructural and Fractographic Characterization of a Thermally Embrittled Nuclear Grade Steel: Part II - Quenching and Tempering

“…Nevertheless, it should be emphasized that this sensitivity was expressed in a reverse fashion than that normally observed for microalloyed steels, such as for microstructures J and L, when higher loading rates inhibits ductility. Figure 4f displays the fracture surface of the annealed microstructure H, which exhibits a predominantly ductile aspect, which greatly differs from the honeycomb morphology presented earlier 1 , with shallow microvoids denoting a lower fracture toughness 1 . This indicates that the more severely annealed microstructures assessed in Part I, as well as the Q&T, I, K and M, tend to show a reverse sensitivity to strain rate as above commented, i.e., increasing ductility by raising the loading rate.…”

“…The microstructures J and L, Figs. 3b and 3d, are characterized by a wide distribution of microvoids, resembling microstructure A 1 . The microstructure L exhibits a more planar fracture aspect, or less energetic than J.…”

“…In Part I of this study 1 , a nuclear grade steel was annealed under several soaking times and temperatures, rendering to it a broad spectrum of elastic-plastic fracture toughness in both quasi-static (J-R curve) and dynamic (Charpy impact) loading regimes. In that occasion, the feasibility of simulating the fracture toughness behavior of neutron damaged structural steels was then verified.…”

Unique Appearance of Lamellar Cleavage Patterns on Fracture Surfaces of Ti-Based Amorphous Matrix Composite

“…When these cleavage facets are observed in a high-magnification micrograph (Figure 5(d)), they are composed of somewhat flat and smooth surfaces containing many weak river patterns, which give a sign of the decreased fracture resistance. [36] IV. DISCUSSION…”