Sensor-controlled bainitic transformation and microstructure formation of forgings during the cooling process.

Bainitic steels are increasingly employed for manufacturing high-performance forged components because they provide several advantages over martensitically hardened and tempered steels and can obtain their desired microstructure directly from the forging heat. However, especially during the heat treatment from the forging heat, many process parameters influence the microstructure formation in the component's surface and core regions, so that reliable predictions about the transformations using continuous cooling transformation diagrams and computational simulations are challenging. Within the framework of the project 'EcoForge' a measuring system was developed, that non-destructively monitors the materials transformation as well as the phase and microstructure formation in situ during cooling from the austenite. The onset of the transformation, the current transformation level and the end of the transformation is reliably detected, so that process times can be optimised. Using characteristic signal profiles it is also possible to differentiate and classify the formation of microstructures, e.g. bainite and martensite, to regulate the cooling parameters and specifically set the component's properties. Owing to its robustness and the potential for evaluating the measured signal profiles online in real time, the testing system is also suitable for online-quality control in industrial forging and heat treatment lines. [ABSTRACT FROM AUTHOR]