Effect of Post-Weld Heat Treatment Cooling Strategies on Microstructure and Mechanical Properties of 0.3 C-Cr-Mo-V Steel Weld Joints Using GTAW Process

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications.