Transition Regime Fracture Toughness-temperature Properties of two Advanced Ferriticmartensitic Steels

Abstract

AbstractAdvanced martensitic steels are leading candidate materials for fusion reactor structural components due to their resistance to void swelling, and good balance of physical and mechanical properties. However, irradiations at temperatures below about 400°C result in increases in the cleavage-to-microvoid coalescence transition temperature, as well as reductions in the upper-shelf tearing toughness. This paper reports on the transition regime fracture toughness properties of two unirradiated 7-9Cr martensitic alloys, F82H and T91. Effective fracture toughness-temperature curves, Ke(T), were measured in the transition regime using relatively small pre-cracked specimens. Three sets of data obtained on different specimen sizes and geometries for the two steels are analyzed. All the data can be placed on a single so-called master-curve, when shifts due to size/geometry and material are taken into account. The results from mechanical tests, finite element method (FEM) simulations of crack tip fields and confocal microscopy-fracture reconstruction observations are presented. The link between the different mechanisms taking place at various length scales, resulting in the complex process of cleavage fracture, is discussed.