A method for the low-pressure carbonitriding of steel parts, in particular parts used in the manufacture of automobiles, comprises a heating step that includes a simple heating phase (M) followed by an initial nitridation phase (Ni) from a temperature between 700° C. to 750° C. to a temperature between 860° and 1000° C. and carried out using a reduced temperature gradient relative to the simple heating phase. Additionally, alternate cementing (C1-Cn) and nitridation (N1-Nn) steps are performed at constant temperature, wherein the final nitridation step is accompanied with a decrease in temperature immediately before quenching (T).