The present paper analyzes the effect of low aluminum additions and the hot
forging process on the microstructure and non-metallic inclusions of high
manganese steels. Four high-manganese steels (HMnS) were obtained by adding
low aluminum contents of 1.1 and 1.5 wt. % in four medium carbon austenitic
steels (0.3 - 0.4 wt% C) with manganese contents of 17 and 22 wt. Samples of
the as-cast steels were hot forged to 1100 ?C to obtain a whole reduction of
70 %. The microstructural evolution was studied by microscopy techniques
(OM, and SEM-EDS) and X-Ray diffraction measurements for the as-cast and hot
forged steels. A typical grain columnar zone obtained during solidification
of an ingot casting was obtained in the as-cast condition where the
microstructure was constituted by non-metallic inclusions in a fully
austenitic matrix. The non-metallic inclusions were identified as Al2O3 and
MnS particles. The thermomechanical treatment allows the formation of an
austenitic microstructure characterized by twins in high manganese steels
while a duplex austenitic-martensitic microstructure was obtained for HMnS
which contained the lowest manganese contents. The highest tensile
properties were obtained for the steel 17Mn-1Al which showed the lowest
grain size and higher non-metallic inclusions content. The hardness values
were similar to those obtained in the as-cast condition.