The effect of microalloying elements on the properties of martensitic stainless steels

The present work investigates the influence of microalloying with yttrium, titanium, hafnium, and zirconium on the properties of precipitation-hardened martensitic stainless steel 17-4PH. Twenty laboratory heats were designed, each weighing 25 g, with microalloying additions ranging from 1 to 5 wt.% calculated and prepared using analytical balance accuracy. The charges were melted and refined in a vacuum arc remelting (VAR) installation, ensuring controlled solidification and minimized contamination. The chemical composition of the obtained alloys was verified using X-ray fluorescence (XRF) analysis to confirm the targeted additions and homogeneity of the melts. Microstructural characterization was carried out by optical and scanning electron microscopy, while mechanical behavior was evaluated through Vickers microhardness measurements. The results revealed that the addition of yttrium and titanium led to grain refinement and the formation of stable oxides and carbides, which contributed to increased hardness and improved microstructural homogeneity. Hafnium promoted the precipitation of secondary phases, enhancing hardness but with a tendency to increase brittleness when added in higher amounts. Zirconium improved the cleanliness of the steel by acting as a strong deoxidizer, leading to more uniform microstructures. Overall, the microalloyed steels exhibited significant variations in microhardness values depending on the type and concentration of the added element, indicating that precise control of microalloying content is critical for optimizing the performance of 17-4PH stainless steels. These findings contribute to the development of advanced high-performance martensitic stainless steels tailored for demanding structural applications.