Selection of optimum quenching parameters for large rotors of steel 25KhN3MFA

Conclusions

• 1. To obtain a fine-grained structure during final heat treatment, the following are recommended:

• a) accelerated heating of forgings to austenitization temperature with 2-h holding after through heating;

• b) minimizing the austenitization temperature and choosing it with regard for the temperature—time dependence of the increase in austenite grain size across the forging, as well as in relation to the critical radius of the forging and the cooling medium;

• c) austenizing at the chosen temperature with the aim of obtaining stable properties;

• 2. In selecting the quenching parameters, it is necessary to consider the future service conditions of the parts and the property values required of them:

• a) for turbine and generator rotors, we recommend quenching from 810–850°C in water or in water and then oil, ensuring σ_0.2 = 500-650 MPa and T₅₀ below +10°C;

• b) for metallurgical equipment parts that are heavy or are up to 2 m in cross section — such as bottom dies, the cylinders of hydraulic presses, etc. — we recommend quenching from 870–900°C in oil or air, ensuring σ_0.2 = 650-800 MPa and T₅₀ no greater than +40°C.