The relationship between structure and properties (including heat resistance) in low-alloy chromium-molybdenum-vanadium and high-alloy steels of ferritic and austenite classes, designed for long-term service at high temperatures, is shown. The properties of some steels (for example, a number of steels of various classes designed to serve for 100 thousand hours, in the operating temperature range of 500-750 ° C) with different heat treatment and prolonged heating are given. They are of considerable interest, since they make it possible to establish the principles of alloying heat-resistant steels. In addition, the monograph summarizes data showing how microalloying with metals and alloys of rare-earth, alkaline-earth elements and boron affects the properties of chromium-molybdenum-vanadium and chromium-nickel-niobium steel. The book is intended for engineering and scientific workers of the metallurgical and machine-building industries, as well as power plants. Ill. 130. (Table 72. Bible. 226 titles).