  We numerically study the dynamics after a parameter quench in the
one-dimensional transverse-field Ising model with long-range interactions
($\propto 1/r^\alpha$ with distance $r$), for finite chains and also directly
in the thermodynamic limit. In nonequilibrium, i.e., before the system settles
into a thermal state, we find a long-lived regime that is characterized by a
prethermal value of the magnetization, which in general differs from its
thermal value. We find that the ferromagnetic phase is stabilized dynamically:
as a function of the quench parameter, the prethermal magnetization shows a
transition between a symmetry-broken and a symmetric phase, even for those
values of $\alpha$ for which no finite-temperature transition occurs in
equilibrium. The dynamical critical point is shifted with respect to the
equilibrium one, and the shift is found to depend on $\alpha$ as well as on the
quench parameters.
