Microstructure characterization and tensile properties of 18Cr–4Al-oxide dispersion strengthened ferritic steel

• Various types of secondary phase precipitates were identified.
• Two kinds of nano-sized particles (Y–Ti–O/Y–Al–O) were found in matrix.
• Nano-sized oxide particles uniformly dispersed in matrix.
• Correlation between secondary phases and tensile properties was discussed.

A microstructural characterization was performed on an 18Cr–4Al oxide dispersion strengthened (ODS) ferritic steel using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the secondary phases in the 18Cr–4Al-ODS ferritic steel can be roughly divided into three categories according to their size-level: (1) micron-sized intermetallic σ and YAl phases; (2) submicron-sized precipitates consisting of TiN and AlN precipitates; (3) nano-sized Al2O3 and Y–Ti–O/Y–Al–O complex oxide particles with diameters in a broad size range from several to dozens of nanometers. In addition, tensile testing results revealed that the 18Cr–4Al-ODS sample exhibited better tensile strength and ductility as compared with another commercial ODS steel with similar composition.

TEM BF micrographs of carbon extraction replicas of the as-heat treated 18Cr–4Al-ODS sample.Figure optionsDownload as PowerPoint slide