The influence of NB on the phase transformations and mechanical properties in Al- and Si-alloyed trip-steels

The influence of Nb in Al- and Si-alloyed TRIP-steel grades oil the phase transformations and mechanical properties are studied oil four alloys melted in the laboratory. The phase transformations during the hear treatment are studied by dilatometric experiments with cold rolled material. The interpretation of phase transformations is supported by thermodynamical calculations, measurements of the content of retained austenite and metallographic investigations oil samples obtained from interrupted annealing trials. The influence of the most important annealing parameters oil the mechanical properties are Studied by laboratory annealing simulations. The stability of the retained austenite against strain induced martensitic transformation (SIMT) is evaluated for various heat treatment conditions and is discussed in combination with the phase transformations during the hear treatment and measurements of the carbon content of the retained austenite.