This study refers to the phase composition influence on the coefficient of expansion of parts made of bearing steel. The tact is well know, that the phase that follow the hardening heat treatments: martensite, carbides and residual austenite have different volume coefficients of expansion. It was determined in this way the coefficient of expansion in limits 20°C... 200°C, of parts which were heat treated and then cooled at cryogenic temperatures of: +30°C; -60°C; 90°C; -120°C; -150°C; - 196°C. It was found that, due to the continuing of cooling at this cryogenic temperatures it was obtained a complex of properties which influence the functional limits of parts working in severe conditions, having very small plays and in conditions of abrasive wear.
