Effects of Si and Al on acicular ferrite formation in C-Mn steel

The influences of Si and Al on the microstructure of Ti-containing C-Mn steels have been studied. Although Si addition up to I wt pet did not change the crystal structure of dominant Ti2O3 particles dispersed in these steels, the formation of an acicular ferrite microstructure was suppressed at high Si contents. It has been found that the Mn content dissolved in Ti2O3 particles decreases with increasing Si content. This seems to weaken the formation of Mn-depleted zones (MDZs) around Ti2O3 particles, which art as a dominant driving force for the intragranular nucleation of acicular ferrite. It has also been found that the addition of a small amount of Al greatly reduces the formation of acicular ferrite. This is attributed to the change of dominant oxide particles from Ti2O3, which sen es as an effective nucleant for acicular ferrite, to inert Al2O3 The result of the present study implies that it is advantageous to keep Si and Al contents in Ti-containing steels as low as possible when well-developed microstructures of acicular ferrite are desired.