The recrystallisation behaviour of several Nb-Ti bearing high-strength low-alloy steels was investigated during multipass deformation by torsion under continuous cooling conditions. The effect of the strain on the no-recrystallisation temperature (T nr ), the temperature at which recrystallisation is no longer complete, was determined. It was observed that the T nr decreases with increasing strain. It has been observed that for similar Nb concentrations, increasing the Ti content increases the T nr , but this effect seems to saturate at the higher Ti-concentrations and over a given Ti content there is no additional increase of the T nr . This effect can be related to the presence in the austenite of an increased amount of undissolved (Ti,Nb)(C,N) particles when the Ti/N ratio is increased by the addition of titanium. Because of this, the supersaturation level is reduced leading to a low driving force for precipitation during deformation. Additionally these undissolved particles may favour heterogeneous precipitation of carbonitrides and in consequence the precipitation on dislocations, which is the responsible for the retardation of recrystallisation, can be seriously impaired. Both effects can significantly reduce the effectiveness of the titanium addition in increasing the T nr .
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Perosanz et al. (1998) studied this question.