Precipitation behavior of a hsla steel containing molybdenum, aluminum and trace amounts of titanium

The precipitation sequence in a HSLA steel containing 0.29% Mo, 0.065% Al and small amounts of titanium (⩽50ppm) has been studied. Samples previously deformed at various strain rates at 875°C were characterized by analytical electron microscopy. In particular, the precipitates were classified according to their chemical composition and their size which allowed the evolution of the precipitate populations as a function of strain rate to be followed. Small amounts of titanium, inadvertently introduced during steelmaking, modified considerably the expected precipitation sequence. Hence, AlN dynamic precipitation was not observed but rather a Mo-rich compound (probably a carbide) was found to precipitate during deformation. This dynamic precipitation accounts for the additional retardation of recrystallization at intermediate strain rates. These results are discussed with respect to the interaction between recrystallization and precipitation and more specifically with regard to effects of strain rate on precipitation kinetics. Nous avons étudié la séquence de précipitation dans un acier microallié contenant 0.29% Mo, 0.065% Al et une faible quantité de titane (