Abstract Presented study characterizes causes of edge cracks formation in the electrotechnics dynamo steel on the base C-Mn-Si. By means of formability test was identified the temperature interval 950-1200°C in which has the material low formability. The lower formability is reached by : phase structural trasformation in the temperature interval 925-975 deg C and 750-800 deg C brittleness of Fe sulphides in temperature interval 1000-1200 deg C. On the essential of statistic analysis were derivated regression equations for the description of finish rolling temperature in roughing train as a function of Si/C proportion and edge cracks formation. The form of regression equation is following: T5 = 1,49977.[660,3-994,3.C+73,4.Si-Z] where: C, Si - carbon, silicon content Z - edge craks The rolling condition for edge cracks occurence are unfavorable during rough rolling and finish rolling is making without formability problems.