Strain-Induced Precipitation Behavior of a Nb-Ti-V Steel in the Austenite Phase Field

The precipitation behavior of a Nb (0.041 wt%), V (0.11 wt%), and Ti (0.018 wt%) micro‐alloyed steel influenced by a deformation process in the austenite region has been investigated by transmission electron microscopy and atom probe. After solution annealing at 1250°C, nearly the entire Nb and V amount is in solid solution. Ti does not go into in solid solution and stays stable as TiN precipitates. During the cooling process to deformation temperature, these TiN precipitates act as nucleation sites for Nb and V. Precipitates with a TiN rich core and a V‐rich shell are formed. Nb is homogenously distributed over the precipitate. After deformation, strain induced precipitates occur, which consist mainly of Nb, V, and only a little Ti. Smaller strain induced precipitates have a higher N‐content than C, with growth the C‐content increases. After deformation in the austenite region and an isothermal heat treatment in this region in a 0.2 wt% carbon steel, micro‐alloyed with Nb, V, and Ti, strain induced precipitates are formed. These precipitates are carbonitrides, which mainly consists of Nb and V. For the formation process N is more important than C and for the growing process the C is more important.