<p>Deformation-induced transformation of austenite into martensite plays an important role in controlling the mechanical behaviour of metastable austenitic stainless steels. In this study, the influence of different thermomechanical processing routes on the deformation behaviour and transformation kinetics of 304 stainless steel was investigated. The results show that cold-worked and annealed steels exhibit less prominent shear band formation and slower martensite transformation compared with directly annealed steels. These differences are associated with variations in grain size, dislocation density evolution, and the dominant martensite nucleation sites. In cold-worked and annealed steels, martensite preferentially nucleates near grain boundaries, whereas in as-annealed steels, intragranular nucleation is dominant. As a result, as-annealed steels exhibit enhanced work-hardening behaviour and higher ductility due to accelerated transformation kinetics and a more uniform distribution of martensite. The study shows a strong relationship between processing-induced microstructure and deformation-induced transformation behaviour in metastable austenitic stainless steels.</p> Graphical abstract <p></p>