Scientific and methodological approaches ensuring reduction of cold brittleness tendency of pearlite and martensitic steels and metal of their welded joints are considered. The role of carbides formed after thermal improvement and additional tempering was analyzed, their growth and coagulation features were studied. It is shown that coagulation and spheroidization of cementite-type carbides allows not only to increase cold resistance of pearlite and martensitic steels, including metal of their welded joints, but also to eliminate thermal brittleness of steels after long-term operation.