| Scope |
The improvement in ductility and formability due to increased strain hardening capacity as a consequence of austenite to martensite transformation has been known for decades in the case of metastable austenitic stainless steels and carbon steels, the effect termed as transformation induced plasticity (TRIP). The effect has since been commercially exploited in sheets intended to automotive applications in particular. However, with ever increasing quest for tough ductile ultra-high strength steels with excellent combinations of mechanical properties, new research efforts have been directed for developing innovative processing routes for the 3rd generation steels, such as carbide-free bainitic (CFB) steels, quenched and partitioned (Q&P), TRIP-aided bainitic and martensitic steels, etc. The commonality among these groups is the presence of a small fraction of finely divided retained austenite stabilized down to RT, essentially in a bainitic or martensitic matrix. A bainitic and/or martensitic matrix has the potential to provide the required strength, while a small fraction of retained austenite distributed very finely between the martensite/bainite laths is expected to provide improved work hardening and uniform elongation without a loss of impact toughness.
Of centre-stage in the entire ground-breaking development for the realization of innovative ultra-high strength steels with high toughness and ductility is the presence of retained austenite at a fine scale, down to nanometer level in some cases. While extra addition of austenite stabilizers may be necessary to provide enough stability to austenite down to room temperature, partitioning effect of carbon from supersaturated martensite too can facilitate retention of some finely divided carbon-enriched austenite in the final microstructure. For instance, a novel class of steels that comprises of grains that are tens of nanometres in size, achieved by transformation of high-C austenite, suitably alloyed to realize bainite at very low temperatures, thus rendering a structure of alternating films of nano-bainitic ferrite and retained austenite known as ‘superbainite’. The symposium should focus on recent developments in nanostructured bainitic steels, Q&P /DQ&P steels, medium Mn steels, TRIP assisted high strength sheet steels, etc. |