Numerical simulation and experimental study on laser micromachining of 304L stainless steel in ambient air

•Surface topography evolves from the bump to the crater as laser fluence rises.•Mass inflow caused by solid-phase oxidation of material produces “flat-topped” bumps.•Oxygen mass inflow and surface oxygen content greatly influence “M-shaped” bumps.•Surface tension considering oxygen content forms outward flows and crater topography.•Pulse width greatly influences three types of surface morphologies through heat and mass transfer as well as fluid flow.