1. Microalloying with zirconium, hafnium, and REM improves the mechanical properties of α+β and β alloys due to grain refining, lower concentration of impurities in grain boundaries, and more dispersed and even decomposition of metastable phases during aging, which is associated with the increasingly negative values of the heat of formation of oxides of these elements (the ductility of weldments increases by a factor of 2–5). 2. The improvement in the mechanical properties with microalloying is larger in the heat-treated condition (as compared with the annealed) in alloys with a high concentration of impurities and a structure resulting from overheating in the β region or a cast structure (as compared with alloys having an equiaxed fine-grained structure). 3. The most effective additions are zirconium and hafnium in quantities of 0.02–0.1% for α+β alloys and 0.5–1.5% for β alloys; REM are most effective in quantities of 0.02–0.05% for α+β and β alloys.