2. Experimental Procedures
The compression tests were performed on an MMS-200
thermo-mechanical simulator. The chemical composition of
the micro-alloyed steel is Fe-0.13C-0.39Si-1.5Mn-0.014P-
0.002S-0.034Nb-0.031V-0.016Ti-0.039Als-0.0032N-0.0048O
(mass.%). The steel was produced by a continuous casting
line. After austenitization at 1 200°C for 2 h, the steel was
hot-rolled to 12 mm at 1 150°C, followed by air cooling
to room temperature. The cylindrical specimens, whose
dimensions are 6 mm diameter and 12 mm length for ultrafast
cooling, were machined along the rolling direction of
the plate.
According to the following solubility product equation
proposed by Irvine,12) the solution temperature of the tested