  Zn induced liquid metal embrittlement (LME) is a major concern in particular
for advanced high strength steels, which often contain a significant amount of
austenite compared to established steel grades. Using density functional theory
(DFT) calculations we, therefore, compare the behaviour of Zn in ferrite (bcc)
and austenite (fcc) grain boundaries (GBs) with different magnetic ordering to
investigate the role of crystal structure as well as magnetism in LME. We
address the performance of DFT based paramagnetic calculations by utilizing the
spin space averaging relaxation approach. Our results show that both magnetic
and elastic contributions have significant influence towards segregation and
embrittling behaviour of Zn. The primary requirement is the elastic
contribution, while the presence of magnetic disorder increases the critical
concentrations for the onset of GB weakening. While Zn segregation is more
favourable in bcc compared to fcc GB, larger impact of Zn coverage on GB
weakening is observed for fcc. For both structures, the rapid decrease in
surface defect state energies is identified as the driving force behind GB
weakening. These surface defect states stabilize at lower Zn concentrations
than GB defect states.
