Purpose. During chemical and thermal treatment of parts made of complex-alloyed cemented steels after quenching, as a rule, a cold treatment is carried out to reduce the amount of residual austenite in the layer both before the release and after the completion of chemical and thermal treatment. In this case austenite is known not to affect carbide formation during tempering.The peculiarity of 13Х3НВМ2ФА steel structure after cementation and direct quenching from 1020 ... 1030 °С is the presence of 95 % residual austenite in the functional part of the layer. This makes it possible to conduct tempering at 530...540 °С with different initial structure – austenitic or martensitic. Therefore, the objective of this work is to investigate the effect of the initial structure on the carbidization processes during tempering on the secondary hardness and on the properties of the diffusion layer of steel 13Х3НВМ2ФА.Research methods. Carbidization processes were studied during tempering of cemented steel 13Х3НВМ2ФА for the secondary hardness using dilatometric, metallographic, X-ray structural, durometric methods, differential phase analysis, electron microscopy.Results. The main results of the work include:- dependence of the chemical composition of carbides on the initial structure before tempering;- the carbide phase of cemented steel 13Х3НВМ2ФА released from the initial austenitic state, is more doped with molybdenum, tungsten, and vanadium;- the carbides share in the cemented steel released from the initial austenitic state is 9,2...10,5 % (wt.), and of the initial martensitic state – 12,6...13,0 % (wt.);- higher alloyance of the carbide and α- phases explains higher hardness of steel 13Х3НВМ2ФА as per HRC 3...4 after its release from the initial austenitic state.Scientific novelty. The possibility of processing for secondary hardness is shown for the first time for this grade of steel using different structures before release – initial austenitic (IA) and initial martensitic (IM). After tempering with an IA structure in the layer a smaller, but more doped, proportion of carbides is obtained i.e. special, and more doped solid solution.Practical value. The use of tempered 13Х3НВМ2ФА steel under IA condition allows to obtain HRC 3...4 hardness and higher compared to the one tempered under IT condition. The technical requirements for the hardness of the surface of the toothed wheel of gas turbine engine being ≥ 60, the hardness of the toothed wheel with the HRC value 57...58 after tempering under IM condition does not meet these requirements. In addition, indicators of contact durability, wear resistance and endurance limits due to the advanced hardness will be higher.