Effects of grain morphology and texture on high temperature deformation in oxide dispersion strengthened ferritic steels

Abstract

Oxide Dispersion Strengthened (ODS) ferritic steel is the promising candidate alloy for long-life core materials of fast reactor. A series of experiments, such as tensile tests, creep rupture tests, texture measurements and microstructure observations, are performed for the fabricated sheets of ODS ferritic steel with simulating type of morphology and also for the cladding tube in order to clarify the origin of the peculiar strength anisotropy of the cladding tube: degraded creep rupture strength in hoop direction. From these experiments, effects of grain morphology and texture on deformation of ODS ferritic steels are evaluated. The sheets and the cladding tube have strong texture of {001}〈110〉 and {111}〈110〈, respectively. In longitudinal and transverse directions of the sheets, strength level is significantly different from each other, but crystallographic orientation is almost equivalent. From that finding, it is considered that strength anisotropy of the cladding tubes is not attributed to the texture. From the results of micro structure analysis, it is concluded that origin of the degraded creep rupture strength in transverse hoop direction of the cladding tube comes from the grain boundary sliding at the large tilt angles.