Low pressure carbonitriding method and furnace

A method of carbonitriding a steel part arranged in a chamber, comprising first steps and second steps, a carburizing gas being injected into the chamber only during the first steps and a nitriding gas being injected into the chamber only during the second steps, at least one of the second steps taking place between two of the first steps, the pressure in the chamber during at least part of said two first steps being maintained at a first value and the pressure in the chamber during at least part of said second step taking place between said two first steps being at a second value greater than the first value, the pressure in chamber being kept lower than 500 hPa all along the carbonitriding process.