Ferrite grain refinement is one of the best methods to improve the mechanical properties of low carbon steels.;The present work is a continuation of this past research and was conducted using a torsion machine. The aim was to improve the understanding of the strain levels and deformation temperatures required for UFF formation, as well as the influence of silicon addition. Two steels were studied: a low silicon (LSi) steel containing 0.09% C-0.02%Si-1.3%Mn-0.07%Al-0.036%Nb and a high silicon (HSi) steel containing 0.09%C-0.48%Si-1.2%Mn-0.02%Al-0.038%Nb. In the hot torsion tests, both steels were deformed to 5 true strain levels: 2, 2.5, 3.2, 3.5 and 4 at a strain rate of 3/s. The Ar3 temperatures for the two steels were measured as 758°C for LSi and 776°C for HSi. It was found that at a strain level of 4 or above, UFF was formed. The optimum deformation temperature was just above the Ar3 and the higher the strain, the finer the ferrite grain size achieved. The results indicated that silicon addition impedes ferrite grain size refinement. (Abstract shortened by UMI.).
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