We study the interaction of single Fe atoms on Cu(111) and Ag(111) substrates with low-temperature scanning tunneling microscopy and kinetic Monte Carlo simulations. In Fe/Cu(111), a self-assembled hexagonal quasisuperlattice with perturbation of around 20% dimers/clusters is obtained. In Fe/Ag(111), however, a disorderlike structure is found even though long-range interactions among atoms are observed. In combination with kinetic Monte Carlo simulations, possible mechanisms of the superstructure formation are discussed. We find that two parameters, i.e., the ratio of adatom interaction energy (the depth of the first energy minimum) to diffusion barrier and the square of the repulsive ring radius versus the superstructure lattice constant, play important roles for superstructure formation.