Thermomechanical warm forging of Ti-V, Ti-Nb, and Ti-B microalloyed medium carbon steels

Conventional quenched and tempered steels have long been used to fabricate mechanical components, such as plates, shafts, and axles. All of these components are mainly fabricated employing medium carbon hot forged steels in the quenched and tempered condition. In the last decade, thermomechanical forging at intermediate (warm) temperatures of microalloyed medium carbon steels is increasingly adopted to reduce or eliminate quenching and tempering heat treatments in hot forged components. However, the use of these steels is still limited, being difficult to achieve a toughness comparable to that of fully heat treated ones. In an effort to improve toughness, an experimental campaign was performed to assess strength and toughness properties of three selected microalloyed medium carbon steels after thermomechanical forging simulations at warm temperatures, performed on a thermal and mechanical Gleeble 3800® apparatus. Microstructures and mechanical properties of these steels are shown to be highly dependent upon steel composition and thermomechanical schedule. The experimental results suggest that thermomechanical schedules can be designed to produce microalloyed medium carbon steels with refined microstructures, and therefore to realize improved strength and machinability; yet, toughness is still the most critical property as compared to that of quenched and tempered steels.