Reflection high-energy electron diffraction (RHEED) intensity studies were performed during the growth of thin Fe layers on vicinal Cr(001)/Nb(001)/Al2O3(11̅ 02) substrates. The results are compared with those of recent molecular-beam epitaxy (MBE) growth models. General agreement is found as concerns the linear relationship between the logarithm of the number of RHEED oscillations and the inverse growth temperature. In agreement with theory the RHEED oscillation damping time is found to depend algebraically on the growth rate. However, contrary to expectations, the RHEED oscillations vanish faster at higher growth temperatures and lower growth rates. This behavior can be explained by a change in the growth mode from layer-by-layer to step flow. Numerical simulations in which step bunch melting during the Fe growth on the Cr buffer is assumed reproduce well the present experimental results.