Maximum Operating Time of Steel 25X1M1FA Metal Rotors During Prolonged Operation of 60 MW Turbines

• Published in: Power technology and engineering 2024, Vol.58 (1), p.95-104
• Main Authors: Lyubimov, A. A., Dubovskova, A. A., Gladshtein, V. I.
• Format: Article
• Language: English
• Subjects: Aging (metallurgy); Creep rupture strength; Electrical Machines and Networks; Energy; Energy Systems; Foundations; Geoengineering; Hardness; Hydraulics; Mechanical properties; Power Electronics; Recrystallization; Renewable and Green Energy; Rotors; Service life; Solid solutions; Spheroidizing; Turbines
• ISSN: 1570-145X; 1570-1468
• DOI: 10.1007/s10749-024-01781-3

A comparative experimental study of the structure and properties of 25Kh1M1FA steel rotor metal from a PT-60-90 turbine is conducted after operation for approximately 400 thousand hours and appearance of a crack in the axial channel, and from a PT-60-130 turbine after additional thermal aging equivalent 600 thousand hours at a live steam temperature of 555°C. Despite the absence of obvious signs of recrystallization within the metal microstructure, after ageing there is a significant, up to ~1.5 times, decrease in metal hardness and other short-term strength mechanical properties. Weakening is not related to the diameter and distance between relatively large (over 1 μm) particles. A negative effect of decreasing molybdenum content in solid solution on strength is demonstrated. Stress-rupture strength for 100 thousand hours at 525°C decreases by a factor of 1.4, due to which the value of the guaranteed service life of a PT-60-130 turbine rotor after ageing at 650°C decreases from 1.7 × 10 5 to 1 × 10 5 h. Brittle failure resistance increases, i.e., the metal critical brittleness temperature decreases from 56 to 42°C. It is found that appearance of a crack in an axial channel is not necessarily accompanied by a large degree of bainitic component spheroidization (more than 3 points). A reduction in PT-60-90 turbine rotor metal hardness to a lower permissible level of 180 HB occurs after about 50 thousand hours, which indicates that the PT-60-90 turbine may be operated up to 450 thousand hours.