Observations of dynamic transformation products in a commercially hot-rolled steel

Sufficient evidence has now accumulated to show that dynamic transformation (DT) is a real phenomenon in steels and can take place overa wide range of temperatures in the austenite regime. During plastic deformation, some of the austenite is transformed to ferrite despite austenite being the chemically more stable equilibrium phase. Occurrence of DT has been demonstrated in various laboratory tests but apparently not in commercially hot-rolled steels. In this note, we review some old results on high strength low alloy strip steel that contained microstructural features that appear to have been caused by DT. We deduce that DT occurred early in the rolling schedule, leading to thin-pancaked sheets of ferrite in the final product. The presence of these pre-existing ferrite nuclei frequently gave rise to adjacent regions of coarse polygonal ferrite grains during cooling.