Based on complex investigations into the influence of alloying elements on mechanical properties over a cross-section of large-size billets some recommendations are suggested on selecting chemical composition of economically attractive structural steels. Chromium-nickel-molybdenum steels with elevated chromium content and decreased amount of nickel are recommended to be used for production of heat treated large forgings. Optimum molybdenum concentration is shown to equal 0.25%. Low carbon steels for large welded structures should contain 1.5-2.0% Cr, 0.5-1.0% Ni, 0.2% Mo and 0.1% V. The distribution of structural constituents over cross-sections of quenched forgings of steels types 35KhN1M and 35Kh3N1M are presented.