  We present an analysis of the chemical abundance properties of $\approx$650
star-forming galaxies at $z \approx0.6-1.8$. Using integral-field observations
from the $K$-band Multi-Object Spectrograph (KMOS), we quantify the
[NII]/H$\alpha$ emission-line ratio, a proxy for the gas-phase Oxygen abundance
within the interstellar medium. We define the stellar mass-metallicity relation
at $z \approx0.6-1.0$ and $z \approx1.2-1.8$ and analyse the correlation
between the scatter in the relation and fundamental galaxy properties (e.g.
H$\alpha$ star-formation rate, H$\alpha$ specific star-formation rate, rotation
dominance, stellar continuum half-light radius and Hubble-type morphology). We
find that for a given stellar mass, more highly star-forming, larger and
irregular galaxies have lower gas-phase metallicities, which may be
attributable to their lower surface mass densities and the higher gas fractions
of irregular systems. We measure the radial dependence of gas-phase metallicity
in the galaxies, establishing a median, beam smearing-corrected, metallicity
gradient of $ \Delta Z/ \Delta R=0.002 \pm0.004$ dex kpc$^{-1}$, indicating on
average there is no significant dependence on radius. The metallicity gradient
of a galaxy is independent of its rest-frame optical morphology, whilst
correlating with its stellar mass and specific star-formation rate, in
agreement with an inside-out model of galaxy evolution, as well as its rotation
dominance. We quantify the evolution of metallicity gradients, comparing the
distribution of $\Delta Z/ \Delta R$ in our sample with numerical simulations
and observations at $z \approx0-3$. Galaxies in our sample exhibit flatter
metallicity gradients than local star-forming galaxies, in agreement with
numerical models in which stellar feedback plays a crucial role redistributing
metals.
