The low stacking-fault energy and high carbon content of Hadfield steel made twinning the basic deformation mechanism from the onset of plastic deformation in [111]- and [011]-oriented single crystals in tension at 77 to 300K. Alloying with aluminium (2.7wt%) resulted in an increase in stacking-fault energy from 30 to 50mJ/m2 and shifted twinning to higher degrees of deformation (>15%). In aluminium-free [¯123] crystals, twinning started after 20% strain. For [¯123], [001] orientations, aluminium additions changed the dislocation arrangement from a uniform distribution to a planar dislocation arrangement and also suppressed twinning. Intersections of dislocation pile-ups were found to be the governing factor for hardening in aluminium-alloyed [001] crystals.

The Influence of Orientation and Aluminium Content on the Deformation Mechanisms of Hadfield Steel Single Crystals. E.G.Astafurova, I.V.Kireeva, Y.I.Chumlyakov, H.J.Maier, H.Sehitoglu: International Journal of Materials Research, 2007, 98[2], 144-9