Photoabsorption cross sections across the K edge of Fe XVIII-Fe XXIII and electron impact K-shell excitation effective collision strengths in Fe XVIII-Fe XXIII have been computed with the Breit-Pauli R-matrix method. The target models are represented with all the fine-structure levels within the n=2 complex, built up from single-electron orbital bases obtained in a Thomas-Fermi-Dirac statistical model potential. The effects of radiation and spectator Auger dampings are taken into account by means of an optical potential. In photoabsorption, these effects cause the resonances converging to the K thresholds to display symmetric profiles of constant width that smear the edge, with important implications in spectral analysis. In collisional excitation, they attenuate resonances making their contributions to the effective collision strength practically negligible.