Relation between KIc and microscopic strength for low alloy steels

Abstract

A simple model has been developed to determine K IC in terms of the microscopic cleavage strength σ f ∗ and the tensile yield strength σ Y for low temperature cleavage fracture in A302B and A533 reactor grade quenched and tempered steels. The model applies at sufliciently low temperatures or in irradiated steels where σ f ∗ ≦ 3.4 σ Y . It was determined that σ f ∗ is independent of temperature below −150°F and then increases with increasing temperature. At this time, it appears that σ ∗ is independent of irradiation. At temperatures above that at which σ f ∗ ≦ 3.4 σ Y , unstable fracture initiates when a critical plastic strain ϵ f is achieved near to the crack tip. The critical local plastic strain for unstable fracture also increases with increasing temperature.