Mechanical and Microstructural Properties of Al-Added ODS Ferritic Steel

Abstract

18%Cr-oxide dispersion strengthened (ODS) ferritic steels with and without 5%Al have been produced by mechanical alloying and hot-extrusion. The microstructure of the ODS steels has been characterized by means of electron microscopy (SEM, TEM), showing that in the Al-added ODS steel, the semi-coherent and coherent oxide particles are about 75% and 10%, respectively. It was found that the coherency of oxide particles depends on the size of dispersed particles. Tensile tests performed between room temperature and 973 K denote that the ultimate tensile strength of Al-free ODS steel is higher than that of Al-added one. The ductility values of both materials are sufficiently high. Impact tests reveal that the ductile-to-brittle transition temperature of Al-free ODS steel are higher than that of Al-added ODS steel; however, the upper shelf energy of 18%Cr-ODS steel is substantially smaller in comparison to the Al-added one. It is considered that the difference in mechanical properties between Al-free and Al-added ODS steels is caused by the smaller, stable titania + yttria complex oxides dispersed in the Al-free ODS steel.