The in vitro corrosion of Fe-30Mn-1C in a Ca-modified Hanks’ balanced salt solution was investigated for biodegradable cardiovascular stents with a rotating disc electrode. A blood flow-related approach was developed to adjust laminar flow conditions. Electrochemical monitoring revealed that intermediate flow caused maximum corrosion, while static and high flow conditions led to minimal corrosion. Surface analysis indicated the formation of a non-crystalline, nanoscopic degradation layer, whereby thickness, porosity and layer-disrupting defects are strongly affected by flow conditions. The interplay between laminar flow and the degradation layer was crucial for the steel degradation and discussed by employing a hydrodynamics-based corrosion scheme.