Effects of the powder, laser parameters and surface conditions on the molten pool formation in the selective laser melting of IN718

•Single-track SLM experiments under different conditions and parameters were carried out.•Quantitative correlations between the molten pool (MP) and the parameters are given.•Without surface powder layer, the surface sand blasting increases the MP size.•The powder layer increases the MP size due to enhanced laser absorption.•A processing map with applicable process parameters and three types of defects is given.