In-Situ Monitoring of the Material Transformation in Forged Components

In the AiF-initiative "Leittechnologien fur Morgen - Ressourcen-effiziente Prozesskette fur Hochleistungsbauteile - EcoForge ", a shortened forging process-chain for high performance components was developed with the objective of conserving resources and saving energy, orientated towards lightweight structures and inherent component safety. With respect to shortening the process chain, one aspect was the sensor-controlled and regulated bainitic transformation of high strength, ductile bainitic steels (HDB) directly from the forging heat. Within the scope of the sub-project "Sensor-controlled material transformations", a bainite-sensor measurement system was developed having a specially oriented, robust sensor technology. The system allows for detecting material transformations as well as the formation of phases and microstructures in high-performance steel components to be non-destructively and contact-free detected in situ during cooling from the austenitic region. Combined with water-air spray field cooling, it was possible to realize a regulated and individually adapted cooling of hot forged components directly from the forging heat, and to specifically adjust the microstructure and the resulting component properties. With the bainite-sensor system, one can reliably detect the start of the transformation, the current level of transformation and the end of the transformation - even under industrial conditions. One can also differentiate and classify the microstructural formation of ferrite-pearlite, bainite and martensite by using the characteristic signal profiles, as well as quantify the fractions of the microstructural constituents in the mixed structures. Owing to its robustness as well as the potential for evaluating the measured signal profiles online during the process the system developed is suitable for online-quality assurance in industrial forging and heat treatment lines. It can also be employed to detect such as edge decarburization or scaling with high sensitivity.