  K$_x$Fe$_{2-y}$Se$_2$ exhibits an iron-vacancy ordering at $T_{\rm s}
{\sim}270{\deg}$C and separates into two phases: a minor superconducting
(iron-vacancy-disordered) phase and a major non-superconducting
(iron-vacancy-ordered) phase. The microstructural and superconducting
properties of this intermixture can be tuned by an appropriate control of the
quenching process through $T_{\rm s}$. A faster quenching rate leads to a finer
microstructure and a suppression of formation of the non-superconducting phase
by up to 50%. Nevertheless, such a faster cooling rate does induce a monotonic
reduction in the superconducting transition temperature (from 30.7 K down to
26.0 K) and, simultaneously, a decrease in the iron content within the
superconducting phase such that the compositional ratio changed from
K$_{0.35}$Fe$_{1.83}$Se$_2$ to K$_{0.58}$Fe$_{1.71}$Se$_2$.
