Formation of uniformly fine grained ferrite structure through multidirectional deformation

The grain size of ferrite transformed from deformed and unrecrystallised austenite becomes finer as the plastic strain induced in the austenite increases. A multidirectional deformation has been proposed as a method for introducing a large plastic strain widely in a specimen. The introduced plastic strain was evaluated using an explicit three-dimensional finite element technique, and a spread of the large plastic strain was predicted for unidirectional compression and bidirectional compression, respectively. A multidirection deformation thermomechanical treatment simulator was used to verify the effect of bidirectional compression with regards to the creation of a fine ferrite grain structure, as predicted by the finite element analysis. The microstructure of the unrecrystallised austenite region after unidirectional and bidirectional compressions was investigated for a Fe-0.16C-0.4Si-1.4Mn (wt-%) steel. The uniformly fine grained ferrite structure produced by the bidirectional compression covered a wider region in comparison with that produced by unidirectional compression. Multidirectional deformation can be applied to obtain ultrafine grain structure for thick products of steels.