In situ X-ray quantification of melt pool behaviour during directed energy deposition additive manufacturing of stainless steel

•In situ and operando synchrotron X-ray imaging reveal the laser induced phenomena;•How powder feedrate, laser power and traverse speed impact on surface quality.•Surface roughness is a result of melt pool surface perturbations.•Process maps quantitatively correlate build quality to process parameters.•The surface quality heavily relies on build parameter.