Microstructural optimization via HIP and solution annealing to enhance impact toughness and fatigue life of 15Cr–5Ni martensitic stainless steel

15Cr–5Ni martensitic stainless steel is extensively utilized application in aerospace, defense, marine, oil and gas, and medical device industries owing to its superior mechanical strength and corrosion resistance. This study investigates the application of Hot Isostatic Pressing (HIP) treatment following forging to achieve complete elimination of internal pores and defects, with systematic evaluation of the effects solution annealing effects on microstructural evolution. Mechanical properties were assessed via Vickers hardness and Charpy impact tests, while microstructural characterization and precipitate behavior were analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). TEM analysis revealed the presence of Cr-rich M₇C₃ carbides, which exhibited progressive dissolution with increasing solution annealing time, thereby directly affecting both hardness and impact toughness. The combined forging-HIP processing route demonstrated a substantial improvement in internal defect elimination and fatigue life (3.6 times) compared to conventional casting-forging methods. This investigation establishes optimized heat treatment conditions for 15Cr–5Ni martensitic stainless steel within this advanced processing methodology.