The distance between pearlite plates is an important parameter for control of ductility and deformation strengthening of carbon steels. Most methods of optical end electronic microscopy for measuring the distances between cementite and pearlite plates in pearlite steels make definite complications when applying to high-dispersed microstructures. At present time rail steels with pearlite structure are fabricated with interlamellar distance 60-130 nm. This research used atomic force microscopy (AFM) for measuring interlamellar distances of pearlite structure in the heat-affected zone (HAZ) of rail welded joint. Qualitative evaluation of cementite and ferrite plates thickness was obtained for the first time, depending on location relating to a rail weld fusion line. The input of cementite plates in strength on the base of Hall-Petch equation was considered. Influence of the relationship between the size of pearlite colonies d p and thickness of cementite plates t c on metal destruction stress of a HAZ welded joint was assessed.