Monitoring of Heat Treatment Processes by High Energy Synchrotron Radiation

Advanced engineering materials are frequently based on multiphase microstructures, where the decisive step is the heat treatment adjusting the desired microstructure.A typical example are transformation-induced plasticity assisted steels, where the steel grades depend on the phase composition and the deformation-induced transformation of retained austenite into martensite.Usually methods for microstructural characterization are only applied after completion of the heat treatment process and comprise typically microscopy and X-ray analysis with laboratory tubes.Both methods can suffer from artefacts and probe a relatively small surface or volume, respectively.However, in the last decade synchrotron facilities have become available that offer very hard X-rays, which open up new possibilities for the observation of heat treatment processes owing to the unique combination of extremely high intensities with large penetration depths (mm scale).Sophisticated sample environments allow for complex in situ experiments, currently with a time resolution on the order of seconds.Only recently a commercial dilatometer of type Bähr Dil805AD has become available at the HARWI-2 beamline at the HASYLAB.This experimental setup was used for the in situ investigation of the quenching and partitioning process in transformation-induced plasticity steels.The experiments were performed in transmission at a wavelength of 0.0124 nm.The Debye-Scherrer rings were observed arising from statistical grain distributions characteristic for each microstructure.The time-resolved measurements allow conclusions about the phases present in the sample, their lattice parameters, texture and grain size.