Inclusion Control of 15-5 PH High- strength Stainless Steel through Aluminum Deoxidation

15-5PH high-strength stainless steel is an important alloy used for numerous critical components. Ultralow oxygen content and inclusion control have become urgent problems that need to be addressed for the broad application of this steel. In this study, we investigate the thermodynamic equilibrium of Al-O and inclusion morphology of 15-5PH stainless steel to understand the basic mechanism behind the results obtained after commercial production of the alloy. The deoxidation behavior of 15-5PH stainless steel depends on the dissolved Al content ([Al%]). When [Al%] < 0.001%, mixed Al-Si deoxidation occurs and the deoxidation product is Al2O3-SiO2-MnO-CrOx. When [Al%] = 0.001%, simple Al deoxidation equilibrium is dominant and the deoxidation product is MgO center dot Al2O3. The formation of Al2O3-SiO2-MnO-CrOx, low melting point inclusions, and a MgO center dot Al2O3 interface layer reduces the activity of Al2O3, which is why the calculated results of Al-O thermodynamic equilibrium are higher than the experimental results. The measured results for the Al-O equilibrium demonstrate a relatively good agreement with the calculated values. This proved that the phases formed on the crucible surfaces were in equilibrium with the Al and O contents in the molten steels after holding for 120 min.