The effect of aluminum alloying on ductile-to-brittle transition in Hadfield steel single crystal

The ductile-to-brittle transition (DBT) in Fe-13Mn-1.3C (Hadfield steel, I) and Fe-13Mn-2.7 Al-1.3C (Hadfield steel, II) (wt.%) single crystals oriented along [011], [[`1]44]{[011], [{bar{{1}}}44]}, and [[`1]11{bar{{1}}11}] directions was investigated under tension in the temperature interval of 77 to 673 K. The DBT temperature interval was found to be independent of single crystal orientation. The DBT temperatures were estimated (1) as the mean value between the temperature corresponding to the minimum crystal ductility and the one coinciding with the onset of the plateau of the e{varepsilon}(T)-dependence (T_DBT1); and (2) as the temperature where the volume fraction of brittle failure on the fracture surfaces was 50% (T_DBT2). The DBT temperatures estimated this way, do not coincide for both steels. Mechanical twinning has been reported as the primary reason for the occurrence of the DBT in austenitic high-carbon Hadfield steel and appears to account for the difference in DBT temperatures as well. Alloying with aluminum partially suppresses twinning in steel (II). Twinning sets in only after a certain amount of dislocation slip, but still influences the fracture mechanism of steel (II).