Effects of Hf addition on the thermal stability of 16Cr-ODS steels at elevated aging temperatures

In this paper, the effects of hafnium (Hf) addition on the thermal stability of the microstructure and tensile properties of Al-containing 16Cr-ODS steels were investigated. High temperature aging tests of the ODS steels with and without Hf were conducted at 750 °C, 950 °C and 1150 °C for 100 h respectively. And the microstructure evolution after thermal aging was investigated using transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). The results indicated that Hf addition could improve the coarsening resistance of the oxide particles and the grains during aging treatment due to the formation of stable Y2Hf2O7 particles. Tensile tests on the aged-steels showed that the ultimate tensile strength and yield strength of 16Cr-Hf-ODS steel were higher than those of 16Cr-ODS steel. It was considered that the excellent thermal stability and tensile properties of 16Cr-Hf-ODS steel were related with the refined microstructure.