Plastic deformation of highly alloyed austenitic transformation‐induced plasticity (TRIP) steels with low stacking fault energy leads typically to the formation of ɛ‐martensite within the original austenite. The ɛ‐martensite is often described as a phase having a hexagonal close‐packed crystal structure. In this contribution, an alternative structure model is presented that describes ɛ‐martensite embedded in the austenitic matrix via clustering of stacking faults in austenite. The applicability of the model was tested on experimental X‐ray diffraction data measured on a CrMnNi TRIP steel after 15% compression. The model of clustered stacking faults was implemented in the DIFFaX routine; the faulted austenite and ɛ‐martensite were represented by different stacking fault arrangements. The probabilities of the respective stacking fault arrangements were obtained from fitting the simulated X‐ray diffraction patterns to the experimental data. The reliability of the model was proven by scanning and transmission electron microscopy. For visualization of the clusters of stacking faults, the scanning electron microscopy employed electron channelling contrast imaging and electron backscatter diffraction.

A method is presented which determines the stacking fault energy in face‐centred cubic materials from the critical stress that is induced via sample bending in the early stages of plastic deformation. The critical stress is gauged by in situ X‐ray diffraction. This method utilizes the results of Byun's consideration of the stress dependence of the partial dislocation separation [Byun (2003). Acta Mater.51, 3063–3071]. Byun showed that the separation distance of the partial dislocations increases rapidly when the critical stress is reached and that the critical stress needed for the rapid separation of the partial dislocations is directly proportional to the stacking fault energy. In the approach presented here, the partial dislocation separation and the corresponding triggering stress are monitored by using in situ X‐ray diffraction during sample bending. Furthermore, the in situ X‐ray diffraction measurement checks the possible interactions between stacking faults present on equivalent lattice planes and the interactions of the stacking faults with other microstructure defects. The capability of the proposed method was tested on highly alloyed austenitic steels containing chromium (∼16 wt%), manganese (∼7 wt%) and nickel as the main alloying elements. For the steels containing 5.9 and 3.7 wt% Ni, stacking fault energies of 17.5 ± 1.4 and 8.1 ± 0.9 mJ m−2 were obtained, respectively.

No abstract

No abstract

No abstract