Abstract Martensitic low alloy high strength steel grade of 22MnB5, used for automotive safety parts constructions, was subject of the experimental analyses of dynamic fracture behavior. The main purpose of the performed analyses was the qualitative and quantitative evaluation of heterogeneities due to the standard spot welding technology. The dynamic resistance of heat affected zones compared to uninfluenced martensitic steel were the subject of suggested methodology for the evaluation of dynamic strength; impact tensile tests were performed after simulation of heat affected zone. Dynamic strength, energy consumption and fracture mode were evaluated at different strain rate. This allows to sketch the influence of the strain rate on the weld joint load capacity. Structural and fractography analyses were focused on an induced degradation process in terms of phase transformation and fracture mode.