In cryogenic machining, as a sustainable alternative to the conventional flood lubrication, harmful oil-based emulsions are replaced by cryogenic media, which are usually supplied into the cutting zone in the liquid state. Despite numerous advantages of the cryogenic machining in comparison with conventional flood lubrication, the best use of cryogenic media and their effect on various materials in different industrial branches remain open to research. Therefore, this diploma thesis is comprised of the analysis and evaluation of heat-treated steel 42CrMo4 in cryogenic milling assisted by a simultaneous single-channel supply of Liquid Carbon Dioxide (LCO2) and oil mist – MQL (Minimum Quantity lubrication – MQL). The aim of the experimental work was to determine the best possible cooling and lubricating effect of the LCO2 + MQL, which is necessary to achieve the longest tool life. Furthermore, the tool life in cryogenic machining was compared with an equivalent in conventional machining where oil-based emulsions were used. All experiments were conducted under the same machining parameters and with the same processing strategies. It has been established that cryogenic milling represents a promising alternative machining process which is also cost-comparable to conventional milling under flood lubrication conditions. In addition, it lengthens the tool life, enables greater processing control, is more environmentally friendly, and therefore suitable for the use in industry.