NEW POST FORGING TREATMENT OF MEDIUM-CARBON MICROALLOYED STEELS

In drop forging of parts for the transport industry the classical quen ch and tempering (QT) of alloyed steels is nowadays substituted by dir ect continuous cooling (CC) of microalloyed steels with elimination of quench cracking and expensive straightening and stress relieving cycl es. Nevertheless, there are some limitations on strength and toughness achievable by this technique. On two commercial medium carbon (0.3%C) steels microalloyed with vanadium or vanadium and titanium, modified forging parameters and a new two-step cooling (TSC) strategy combined with an additional annealing were applied. Some increase in manufactur ing costs, when compared to CC, can be justified by a significant incr ease in strength and ductility. The improvements attainable through su ch a modified treatment give evidence of the large potential of multi- phase ferrite-containing microstructures as a substitute of a tempered martensite.