Microstructure evolution in the context of fracture in austenitic steels under complex loads at cryogenic temperatures
Autor
Nalepka, Kinga
Skoczeń, Błażej
Schmidt, Rafał
Ciepielowska, Marlena
Schmidt, Elwira
Chulist, Robert
Opublikowane w
Materials Characterization
Numeracja
vol. 197 (112654)
Data wydania
2023
Wydawca
Elsevier B.V.
Język
angielski
DOI
https://doi.org/10.1016/j.matchar.2023.112654
Słowa kluczowe
cryogenic temperatures; Fracture; fcc-bcc transformation; Electron backscatter diffraction; XFEM simulation
Abstrakt
The microstructure evolution and its coupling with fracture under complex load conditions at the temperature of liquid helium are investigated. Tension combined with torsion was applied to thin-walled cylindrical samples made of AISI 304 steel. The second component load is the key. The torque causes the sample to buckle, and the resulting folds and wells differentiate the conditions in which the transformation occurs. The feritoscopic examinations combined with the profilometer surface characterization revealed that martensite initiates in the slopes of elevations, where the highest shear stresses arise. The secondary phase has a special cross-lamellar microstructure, uncovered in detailed studies using the electron backscatter diffraction (EBSD) method and synchrotron X-ray diffraction. The new phase prefers the transverse direction of the cylinder surface, which remains invariant during torsion. Along it, the martensite grain develops, which then twins so as to continue growing along the second plane of the maximum shear stresses. In the advanced stage of the phase transformation, the resulting martensite has compact microstructure able to block fracture propagation and to deflect its path. The macrocrack trajectory and the secondary phase distribution coupled with it were reconstructed with high accuracy in the extended finite element method (XFEM) simulation.
