Control of the Austenite Recrystallization in Niobium Microalloyed Steels
The use of heavy gauge steel sheets for structural applications very often requires a combination of high yield strength and adequate toughness. The most cost effective way to realize a high yield strength and a high ductility in a low alloyed steel is grain refinement. In industrial practice, this refinement is realized by controlled processing. This process consists of controlling the slab reheating temperature, applying a large amount of hot deformation below the non-recrystallization temperature (Tnr) and accelerated cooling. A better knowledge of Tnr could optimize the process and the best mechanical properties could be reached against the lowest cost. Tnr can be raised by the addition of microalloying elements such as Nb. Nb can retard the static recrystallization of austenite at low temperatures either by solute drag or by precipitation pinning. In this study, the recrystallization behavior of five Nb-microalloyed model alloys with various Nb contents, was evaluated by double hit compression tests. Further, the precipitation state of the materials was investigated experimentally by Inductively Couples Mass Spectroscopy and X-ray Diffraction. The construction of recrystallization-time-temperature diagrams and precipitation-time-temperature diagrams showed that both mechanisms, i.e. recrystallization and precipitation, strongly influence each other.
T. Chandra, N. Wanderka, W. Reimers , M. Ionescu
S. Vervynckt et al., "Control of the Austenite Recrystallization in Niobium Microalloyed Steels", Materials Science Forum, Vols. 638-642, pp. 3567-3572, 2010