Microstructural Evolution in Microalloyed Steels during High-Speed Thermomechanical Bar and Rod Rolling

Bars and rods are rolled at high total deformations, high strain rates, and short inter-pass times compared to products such as plates or structural sections where extensive studies have been conducted to understand the effects of microalloying and the limited range of thermomechanical process parameters. Data are presented to illustrate how microalloying and high-speed thermomechanical processing affect the as hot-rolled microstructures for a variety of steel grades and applications. Simulations on a Gleeble®3500 using torsional deformation and controlled time-temperature schedules as well as interrupted quenching have allowed examination of the evolution of prior austenite grain size and morphology. The austenite grain characteristics, in combination with the final cooling schedule, influence final hot-rolled microstructures and can lead to significant effects on mechanical properties and subsequent heat treatment.