Enhanced Toughness of Microalloyed Ferritic–Pearlitic Steel via Boron‐Facilitated Pearlite Nucleation on Intragranular Ferrite

Vanadium microalloyed steel with a ferritic–pearlitic microstructure (microalloyed ferritic–pearlitic steel) is widely used in hot forging applications to eliminate the need for subsequent heat treatment processes. However, the ferritic–pearlitic microstructure obtained after high‐temperature forging typically exhibits a coarse‐grained structure and low toughness. This study presents the development of a microalloyed ferritic–pearlitic steel with enhanced strength–toughness through the incorporation of boron. This modification increases the impact energy from 33.3 to 52.7 J, tensile strength from 835 to 888 MPa and yield strength from 531 to 640 MPa. The primary factor contributing to the increased strength is the reduction in the ferrite volume fraction combined with the refinement of pearlite lamellae spacing. The improvement in toughness is attributed to a unique mechanism underlying pearlite nodule refinement. During the cooling process, boron incorporation delays the precipitation of grain boundary ferrite and promotes the nucleation of pearlite on intragranular ferrite. As a result, the number of pearlite nucleation sites increases, leading to the refinement of pearlite nodules and a decrease in the average equivalent grain size. This study thus presents a novel approach for simultaneously enhancing the strength and toughness of microalloyed ferritic–pearlitic steels designed for hot forging applications.