  The neutron-rich isotopes $^{58-63}$Cr were produced for the first time at
the ISOLDE facility and their masses were measured with the ISOLTRAP
spectrometer. The new values are up to 300 times more precise than those in the
literature and indicate significantly different nuclear structure from the new
mass-surface trend. A gradual onset of deformation is found in this proton and
neutron mid-shell region, which is a gateway to the second island of inversion
around \emph{N}=40. In addition to comparisons with density-functional theory
and large-scale shell-model calculations, we present predictions from the
valence-space formulation of the \emph{ab initio} in-medium similarity
renormalization group, the first such results for open-shell chromium isotopes.
