1. Vacuum casting of open-hearth structural steel, which reduces the gas and nonmetallic inclusions content (especially those of the corundum type) of the latter, has no effect on its static strength, as determined by tensile tests at room temperature. At the same time, tensile and impact tests at sub-zero temperatures showed that vacuum-cast steel is more ductile than open-cast steel. 2. The higher ductility of vacuum-cast steel leads to an increase in its fatigue strength, especially in tests on transverse and large diameter specimens. Increased ductility and increased isotropy of mechanical properties of vacuum-cast steel produce a reduction in the size effect in fatigue tests. 3. In view of the reduced size effect in fatigue tests on higher purity steel, steels subjected to some kind of a refining treatment should be recommended for the fabrication of important parts of large dimensions.