Effect of Thermomechanical Processing on the Transformation Kinetics, Microstructure and Mechanical Properties of a Continuously Cooled Cementite-free Bainitic Steel

The combination of forming with continuous cooling bainitic steels offers a new path for reaching energy-efficient manufacturing chains. Improved energy efficiency is achievable thanks to the suppression of conventional, energy-intensive heat treatments. In the present paper, different thermomechanical processing strategies, including laboratory and industrial scale forgings, were assessed alongside their impact on the resulting microstructure. Firstly, phase transformation kinetics were assessed in precisely controlled environments via dilatometry coupled to in situ techniques. Secondly, the microstructure, mechanical properties, and forgeability of large-scale forged components were investigated in laboratory and industrial conditions. These investigations were also assisted by finite element method simulation. The comparison between controlled and industrial-scale conditions illustrates pitfalls in the transfer of knowledge to conditions approaching a real manufacturing chain. Nevertheless, alloy and process design is shown to be a key aspect to overcome the discussed challenges, allowing homogeneous bainite microstructures and mechanical properties to be achievable over a flexible range of processing conditions.