<span lang="EN-GB">Friction Stir Processing of St ۳۷ Steel: A Comprehensive Study on Microstructure Characterization and Mechanical Performance

This paper surveys the impact of Friction Stir Processing on the microstructure and mechanical properties of St ۳۷ steel, a high-strength material commonly used in pipelines and pressure vessels. FSP was applied to ۲ mm-thick plates using a cylindrical tungsten carbide tool at rotational speeds of ۵۶۰ and ۹۰۰ rpm with ZrO۲ nano/micron particles, at a constant traverse speed of ۱۰۰ mm/min. Four series were tested: FSP at ۹۰۰ rpm without particles (base reference), FSP with micron particles at ۵۶۰ rpm, and FSP with nanoparticles at ۵۶۰ and ۹۰۰ rpm. Optical and scanning electron microscopy revealed refined grain structures through dynamic recrystallization and Zener pinning, uniform phase distribution across rolling/transverse/normal planes, and distinct zones (Stir Zone, Thermo-Mechanically Affected Zone, Heat Affected Zone) with particle size reduction toward the tool axis. Mechanical tests—tensile, micro-hardness, Charpy V-Notch impact, fracture toughness, corrosion, and erosion—showed improved yield strength, hardness, corrosion/erosion resistance, and reduced crack propagation/impact damage, though fracture toughness decreased slightly due to hardening. These enhancements stem from optimized temperature/strain fields and phase transformations in St ۳۷, with nanoparticle variants yielding the best results. Innovatively, this study pioneers dry FSP on St ۳۷ with ZrO۲ nano/micron particles at varied speeds, providing a green, better hydrogen compatibility to fusion welding for defect-resistant components. Overall, FSP effectively optimizes St ۳۷'s performance, addressing vulnerabilities in high-demand industrial applications.

کلیدواژه ها:

Friction stir processing ، St ۳۷ Steel ، Microstructure ، Mechanical properties ، ZrO۲ Nanoparticles