Influence of aging process on microstructure and mechanical characteristics of heat-treated HSLA alloy steels

This study investigates the impact of precipitates and dislocations on the aging process of X65 High-Strength Low-Alloy (HSLA) steel through a controlled thermomechanical processing sequence. Three HSLA steel variants-HSLA-100 GPP, HSLA-100 GPT, and HSLA-65-underwent a systematic sequence of heat treatment, oil quenching (OQ), aging, and cold rolling to improve mechanical properties. Microstructural evolution was characterised using advanced techniques, including light microscopy. Charpy V-notch (CVN) impact testing assessed mechanical resilience, while hardness and ultimate tensile strength (UTS) were measured using Vickers hardness testing and tensile testing equipment, respectively. Results demonstrated that cold rolling notably enhanced strength and ductility via grain refinement and increased dislocation density. Hardness values rose with progressive aging, reaching a peak during the peak aged (IPA) stage, then declined in the over-aged (IIPA) phase due to precipitate coarsening. UTS values peaked under aged conditions, with HSLA-100 GPP reaching 1245.33 MPa. The study concludes that optimizing thermomechanical sequences can effectively tailor the mechanical properties of HSLA steels, making them suitable for industrial applications requiring high strength and impact resistance. The findings contribute to advancing understanding of processing-structure-property relationships in HSLA steels, reinforcing their application in structural and defence sectors.