21CMoV5-7 alloy structural steel and its 1.7709 replacement alloys belong to the group of high temperature boiler steels for energy industries. They are used in the production of components/subassemblies for the power industry, working at the temperatures up to 550 oC for small parts and for large forgings. The main applications of these grades of steel are rotors of steam turbines, rotor blades, shaft forgings, reservoirs and covers for up to 550 ℃ temperatures, nuts, tubes for high temperatures up to 540 ℃.