Abstract: The work hardening of Hadfield manganese steel arises mainly form two causes;1)a large amount of twinning makes perfect dislocations or Shockley dislocations to be blocked at the coherent twin boundaries.2)the deformation leads to strong unsymmetrical distortion due to the occurrence of a large number gf Mn-C pairs or Mn-vacancy carbon-carbon cluster.It has been demonstrated by TEM observation and internal friction tests.As deformation pro- ceeds,the slip constantly accomodates twinning shear giving rise to stress relaxation.Thus, the Hadfield steel exhibits both rapid work hardening and good ductility.

Key words: twin, work hardening, dislocation