Abstract
The effects of rolling temperature on the mechanical properties of mild steels are expected to be complicated due to the combined effects of recovery and recrystallization of austenite.
In order to clarify these effects under certain conditions, mechanical properties and microstructures of a low carbon steel and a weldable high strength steel were investigated using transmission electron microscopy.
The results were as follows:
(1) The ferrite grain size of a low carbon steel decreased with decreasing rolling temperature insofar as it was deformed in the austenite region, but no change was observed in the dislocation structures. The rolling after the γ→α transformation increased the dislocation density.
(2) The microstructures of a high strength steel varied complicatedly, probably due to the recovery and recrystallization of austenite.
(3) The yield stress depended on the grain size and dislocation density of ferrite.
(4) The ferrite grain size, shapes of grain and dislocation structures would affect the Charpy impact properties.
