Chemical and thermal treatment ensures high performance properties and durability of most mechanical engineering products. It is shown that the developing the possibility of surface hardening of critical parts may be associated with the use of new methods of their treatment. A model of vacuum carburizing is developed, which is based on practical results. A solution to the equation determining the carbon flux density depending on the technological saturation factors in acetylene is proposed. When developing the calculation method, the peculiarity of carburization of low-alloy steels was taken into account. Recommendations on the choice of cyclic acetylene supply are given. The cyclic mode of acetylene supply was evaluated by a number of parameters: the cycle structure in the form of time ratios of active a and diffusive (passive) d stages; the total time of active stages, the total time of diffusion stages, their ratio, the total number of n cycles during τ saturation. Two programs were studied: the first involves solving a direct diffusion problem, and the second involves solving an inverse diffusion problem. It is shown that the use of the second program is preferable.