Grain Boundary Related Deformation in ODS Ferritic Steel during Creep Test

Abstract

Oxide dispersion strengthened (ODS) ferritic steel developed as a fast breeder reactor fuel cladding is an advanced heat-resistant steel, and its high-temperature strength depends on not only transgranular deformation but also intergranular deformation. The objective of this study is to elucidate the grain boundary deformation process using 15CrODS ferritic steel. From the double logarithm plot for stress and strain rate at 800°C, the stress exponent n becomes over 10, and the real strain rate is an order of 10⁵ lower than that which suggests that the simple grain boundary sliding. The serration structure, which is aggregation of micro-cracks perpendicular to the stress axis, was clearly observed along coincident site lattice boundaries. Also, sub-grains are produced along grain boundaries. From these observations, the localized deformation near grain boundary is considered to be the dominant deformation process of 15CrODS ferritic steel.