Step type normalizing technology for 25Cr2Ni4MoV forged piece

Abstract

The invention discloses a stepwise normalizing process for 25Cr2Ni4MoV forgings, which includes the first step of normalizing the forging material with a cross-sectional diameter of 900mm after forging, and is characterized in that: after the first step of normalizing, the furnace is reinstalled for the second step of normalizing , at a heating rate of 150-200°C / h to a medium temperature of 840°C±10°C, soak for 12 hours and then keep warm for 6 hours, and then cool at a cooling rate of 450-500°C / h for the second time with wind and mist, and then cool down to 300 ‑320°C, hold for 5 hours; then temper, heat up to the initial temperature of the forging material at a rate of 50‑80°C / h to 650±10°C, soak for 30 hours and then hold for 15 hours; then cool with the furnace to below 200°C and leave the furnace. This step normalizing process makes the pearlite obtained by the first step normalizing austenitize again, the obtained austenite is finer and more fully transformed, the metallographic grain is finer, the structure is uniform, and the internal stress is better eliminated .

Description

technical field [0001] The invention relates to an improvement of a post-forging heat treatment process, in particular to a stepped normalizing process for 25Cr2Ni4MoV forgings suitable for the post-forging heat treatment process of hydraulic and thermal generator rotors of 25Cr2Ni4MoV steel. Background technique [0002] The high-power rotors used in hydraulic and thermal generators are often produced with 25Cr2Ni4MoV steel, and the production process is ingot casting—forging—heat treatment after forging—machining—quenching and tempering—finishing. The rotor has a complex structure and a large force, so the requirements for the forging of the rotor are very high, the interior has no defects, and the structure is uniform, which can greatly extend the service life of the rotor. At present, the post-forging heat treatment process is as follows: after forging, the cross-sectional diameter of the forging is 900mm, and the forging is heated to 920±10°C at a rate of 100-150°C / h fo...

AI Technical Summary

Problems solved by technology

The disadvantage of this heat treatment process is that: due to the large diameter of the middle platform of this rotor, the internal structure transformation is insufficient during heating and heat preservation, and the core cannot be completely austenitized. After cooling, the core structure is uneven and the grain Coarse grains and mixed crystals, there are coarse grains in the UT testing center, and the metallographic structure is not uniform in cross-section sampling, and there are coarse grains and mixed crystals

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