Vanadium - Transforming Possibilities

Processing Characteristics and Properties of Ti-V-N Steels

Abstract:

The incentive to develop Ti-V microalloyed steels stems from the desire to combine the excellent grain-coarsening characteristics of Ti grades with the effective precipitation strengthening derived from vanadium, especially when the latter is combined with nitrogen. The present study has been undertaken to establish the degree to which V and excess N detract from the grain coarsening resistance of a Ti-steel, and to determine whether or not the presence of Ti modifies the precipitation-strengthening from V(C,N).

It is found that Ti-V-N alloys are, in the as-cast condition (strand), characterized by GCT's only marginally lower than steels based on Ti-only. However, in hot-rolled material, the presence of fine V(C,N) in addition to (Ti,V)N can result in a deterioration of the grain-growth inhibition. The effective elimination of grain growth of austenite both during and following hot rolling renders Ti-V-N grades especially suitable for recrystallization rolling, whereby relatively fine as-rolled ferrite grain sizes can be achieved via conventional schedules with finishing temperatures in the range 900-1000°C. The precipitation-strengthening potential of vanadium and nitrogen is diminished somewhat when, in addition, Ti is present. The reason for this is partly that vanadium is combined as stable (Ti,V)N-particles which are responsible for the limitation of grain growth at high temperatures, and partly that V(C,N) deposits epitaxially on pre-existing (Ti,V)N-particles in austenite following the termination of rolling. Both these effects reduce the amount of vanadium and nitrogen available for strengthening via precipitation in ferrite.

Keywords:

vanadium,  titanium, microalloyed steel, precipitation strengthening. 

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