Tuning microstructure and hardness via alloying elements and coiling temperature in microalloyed steel

The influence of Cr–V–Nb microalloying on the thermomechanical behavior, microstructure, and hardness of low–carbon steel was investigated using two novel microalloyed steels. Specimens underwent multi–pass thermomechanical processing (TMP) on a Gleeble–3500 simulator, with deformation both above and below the non–recrystallization temperature (T nr ), followed by cooling to coiling temperatures of 500–700 °C. Microstructures were examined using optical microscopy, SEM, STEM, EDS, APT and mechanical properties were assessed via Vickers microhardness. Steel A, with a higher Cr–V–Nb content, exhibited elevated T nr , stronger work hardening, and enhanced austenite conditioning, leading to refined ferrite grains and increased carbonitride precipitate density relative to Steel B. Both STEM–EDS and APT analyses revealed incorporation of Fe and Mn into (VCrNb)CN strain induced (SIP) and interphase precipitates (IP), indicating their complex nature. Thermo–Calc simulations indicated that the higher solute content delays diffusional transformations and shifts the CCT curves toward longer times. Coiling at 650 °C produced a maximum hardness in both steels, and Steel A consistently outperformed Steel B at 600 and 650 °C due to its higher T nr , refined microstructure, and increased precipitate density. These findings demonstrate the critical role of alloying and TMP parameters in optimization of microstructure and mechanical properties of microalloyed steels. • A thermomechanical processing schedule was designed for a new microalloyed steel. • The results confirmed Mn and Fe incorporation in VCrNb(CN) precipitates. • Softening mechanisms during deformation were investigated. • Coiling at 650 °C was identified as the optimum temperature for the desirable microstructure.