The paper studies features of structural and phase transformations of complex alloyed high-strength martensitic, austenitic-martensitic and martensitic-ferritic steels that are resistant to carbon dioxide corrosion and have a chromium content of 13–17%. The influence of the alloying system on the crystallization and phase transformations at hot strain and thermal treatment temperatures is studied by thermodynamic modeling and experiment. The effect of the quenching temperature on the phase composition and microstructure of the steels is analyzed by the results of X-ray diffraction phase analysis and optical and transmission electron microscopy. It is found that, with an increase in the nickel content, a lot of austenite is retained in the metal microstructure, which significantly decreases the creep limit at high tensile strength and ductility. To obtain a predominantly martensitic microstructure in the martensitic-austenitic steel with a chromium content of 15%, the multistage heat treatment is proposed. This treatment includes quenching, intermediate annealing for the precipitation of dispersed carbide particles, the composition of which is estimated by X-ray microanalysis, and tempering intended to shape the final mechanical properties of steel. According to the results of the elongation tests of martensitic and martensitic ferrite steels, their necessary strengths (σ0.65 ≥ 862 MPa; σu ≥ 931 MPa) are reached after the heat treatment by quenching and tempering. The required strength properties of the steel with a large fraction of nickel and chromium content of 15% are ensured by multistage heat treatment, including quenching, intermediate annealing and final tempering.