jats:p Adiabatic shear bands represent intense plastic deformation that is localised because the rate at which the heat generated by deformation is greater than that at which it is dissipated. The structure of such bands generated by ballistic testing is examined in order to reveal the governing mechanisms. We attempt to distinguish in particular whether local reaustenitisation occurs, or if the microstructural changes are simply a reflection of intense deformation. </jats:p>