1. After heating to 1100°C and subsequent phase recrystallization to cycles making it possible to obtain an approximately 2 mm case depth in vacuum carburizing the mechanical properties (σt, σy, Ψ, δ) of the investigated steel and also the impact strengtha1 do not drop with the exception ofa1, of 20Kh steel, which decreases by 6.7% after heating at 1100°C for 2h. 2. The static bend strength for the steels after vacuum carburizing at 1050°C, hardening with reheating, and low temperature tempering is higher and the impact strength after vacuum carburizing at 1050 and 1100–1250°C not lower than after gas carburizing. 3. The fatigue resistance of the gear teeth after gas and vacuum (1050°C) carburizing is at the same level and the character of fracture of the teeth in fatigue tests is similar.