Martensitic steels with carbide free microstructures containing retained austenite

Abstract

The concept of employing martensitic microstructures containing controlled quantities of carbon enriched retained austenite as a new route to high tonnage steels with improved properties is developed through an introduction to the novel non-equilibrium heat treatment procedure which has become known as quenching and partitioning (Q&P). This builds upon the earlier development of steels containing carbide free bainite and retained austenite, enabled by alloying with Si to suppress carbide precipitation, embracing a philosophy to produce refined ferritic microstructures by transformation to acicular forms, with the ferrite protected from the more damaging effects of carbon, which is partitioned to the austenite phase where it acts as a chemical stabiliser. This route offers enhanced strength from the martensite structure along with the promise of new properties from the behaviour of the retained austenite phase which could potentially contain a very high controlled concentration of carbon.