Twin wire arc spraying is widely used in industry due to its low cost and high rate of material deposition. Much has been learned about the process over the course of its use, most recently in regard to the correlation between spray parameters and coating microstructure. The aim of this study is to investigate the behavior of steel particles in nitrogen and air jets and show how in-flight particle characteristics affect coating properties. In the experiments, an optical sensing system is used to measure the velocity, temperature, and size of carbon steel particles fired from a wire arc spray gun set at 100 A and 30V for gas flow rates of 94, 110, 122, and 144 m3/h. The particle data obtained is presented and correlated with coating microstructure, hardness, and oxide content. Paper includes a German-language abstract.