Three TRIP steels have been laboratory melted with 0.17% C, 1.4% Mn, and 1.5% Si as the base composition and additions of 0.02 or 0.04% niobium. After hot and cold rolling the effect of annealing treatment on microstructure development and resulting mechanical properties was evaluated. Niobium retards the isothermal bainite transformation and thus leads to higher retained austenite values. The mechanical properties are dependent on the grain size, the volume fraction of retained austenite, the retained austenite stability, local transformation stresses after bainite formation, and on carbide precipitates. Compared to conventional high strength steels TRIP steels offer an improved strength-ductility relationship and expand the range of cold formable steels to higher strength values.
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Bleck et al. (1998) studied this question.