The improvement of power generation efficiency is based on the large size of the generator set, so the size and weight of turbine and generator rotor forgings are gradually required to be large, and the performance requirements of materials are also gradually improved, specifically in terms of high strength, high fracture toughness, high plastic toughness and low brittle transition temperature. In addition, the low pressure rotor has higher requirements for fatigue strength, high temperature persistence, creep performance and so on.
26nicRMOV14-5 steel is a low carbon NiCrMoV steel, belonging to ASTM A470 grade 5-7 steel, similar to 26Cr2Ni4MoV steel, it has good hardenability and strong toughness and other comprehensive properties, can be used to manufacture low-pressure rotors of subcritical and supercritical units. As the larger the ingot, the more serious the segregation and internal defects, the conventional production process is difficult to adapt to the performance requirements of large forgings under high temperature, high pressure and high speed rotor operation. The production of such material forgings needs advanced technology and strict control means.
26nicrMOV14-5 steel has good hardenability, high temperature austenite is quite stable, and no pearlite transformation occurs during air cooling. When the maximum cross-section of the forgings exceeds 2000mm, the steel may still have temper brittleness tendency. After long-term aging at 350 ~ 575℃, the Si and Mn in the steel will promote the segregation of P and harmful trace elements towards grain boundaries, resulting in the rise of FATT and the deterioration of the toughness of the material.
In the process of steel making and ingot casting, measures are taken to improve the solidification quality of steel ingot, reduce loose, and optimize the structure of steel ingot mold to improve the solidification of steel ingot. Avoid too high superheat of molten steel pouring, and accurately control the temperature of tundish to reduce the influence of temperature fluctuation on the quality of ingot. In the forging process, in order to compacting the center of the ingot, the forging process should focus on forging the center of loose and diffuse inclusion.
26NICRMOV14-5 low-pressure rotor forging thermal processing technology and other rotor thermal processing technology is generally similar, but in the implementation of the process should be more strict control of the parameters, to avoid deviation or defects, only in this way, to ensure that the rotor to obtain excellent quality.
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