Influence of Oxygen Content on the Microstructure and Mechanical Properties of Hot Isostatically Pressed 30CrMnSiNi2A Ultra-High Strength Steel

Oxide inclusions introduced by oxygen on the raw powder surface play an important role in the material performance of powder metallurgy products. In this study, we report the effect of oxygen content in the powder on the microstructure and mechanical properties of hot isostatically pressed (HIPed) 30CrMnSiNi2A ultra-high strength steel (UHSS). The results indicate that, when there is more oxygen in-powder, the size of the oxide inclusions increases, and the prior particle boundaries (PPBs) become clearly visible. In addition, the main constituents of-inclusions in-PPBs changes from Al-rich oxide to Si-rich oxide. When the oxygen content increases from 200 ppm to 650 ppm, the tensile strength maintains a value about 1300 MPa, while with further increases in the oxygen content to 1700 ppm, it decreases to 1200 MPa. The impact toughness of steel is sensitive to the oxygen content in the powder, and it deteriorates as the oxygen content goes above 365 ppm. Our findings not only clarify the influence of the oxygen content in raw powders on the mechanical properties of HIPed UHSS but also shed light on the formation mechanism of PPBs and their evolution, such as oxide size, morphology, species, etc., during sintering.