A wide range of applications, especially in the automotive industry, require both large ductility and high strength, two properties that are unfortunately antagonist. TRIP-assisted multiphase steels, i.e. steels consisting of an intercritical ferrite matrix with retained austenite, bainite and martensite dispersed phases [
] provide extremely good combination of these two properties. In TRIP steels, the mechanical contribution adds to the chemical free enthalpy as a driving force for martensitic transformation of the metastable austenite. This transformation acts like an additional work-hardening source that allows to increase both ductility and tensile strength [
]. The martensite transformation of metastable austenite has been reported to have either a beneficial or a detrimental effect on fracture toughness [
], depending probably on the complex relationship between austenite stability, austenite volume fraction and martensite brittleness.