Quality control of the hottest rotor forgings

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Quality control of rotor forgings

quality control of rotor forgings

rotor is a key component of power plant equipment, which requires safe operation at high speed, bears complex high stress, and has strict technical requirements. However, due to the metallurgical and thermodynamic factors that affect the quality, it is difficult to control them perfectly, so there are many defects, mainly including large or dense non-metallic inclusions, residual shrinkage, white spots, looseness, cracks and unqualified mechanical properties

the forgings of steam turbine generator rotor are mostly scrapped due to unqualified ultrasonic flaw detection in production. For example, the 12MW rotor forgings described in, found two defects greater than 12mm equivalent at the shaft body during ultrasonic flaw detection. Through X-ray structure analysis, it is considered that it is non-metallic inclusion aluminosilicate, which belongs to refractory erosion. The mechanical properties and microstructure of 34crmola steel 12MW rotor forgings caused by component segregation are introduced. The defects of the rotor forgings basically retain the characteristics of ingot defects. Therefore, reducing inclusions and ingot segregation in steel should be paid attention to first. Otherwise, there are many inclusions in steel and ingot segregation is serious. It is difficult to produce high-quality rotor forgings by forging and heat treatment. Therefore, great attention should be paid to smelting and pouring of rotor steel. Strict requirements shall be made for the selection of raw materials, the baking of furnace burden, the improvement of smelting system and the cleaning of gating system

although forging can eliminate the branch of ingot and the experiment requires crystal segregation, it has little effect on the regional segregation, such as the negative segregation area at the bottom of ingot and the carbon, sulfur, phosphorus, loose and other accumulation areas at the riser end of ingot. Only by increasing the removal rate at the bottom end and riser end of ingot can its adverse effects be reduced. The riser end is generally cut off by 5% ~ 10%, and the bottom end is generally 10% ~ 20%

with the increase of ingot weight, the negative segregation of ingot becomes more serious, and the defects such as porosity and intergranular crack also increase correspondingly. This makes it more difficult to forge and weld internal defects and improve the center quality of ingots. Due to the large diameter of the rotor shaft, how to improve the forging penetration is particularly important for the forging of the rotor. Wide anvil, large reduction, drawing and center compaction are commonly used to solve this problem. If the upsetting process is required in the forging process, in order to fully weld the internal defects of the ingot, break the as cast structure and change the distribution of inclusions, the upsetting deformation degree shall be greater than 50% as long as the capacity of the hydraulic press permits, whether one upsetting or two upsetting

the axis of rotor forgings shall not deviate from the center line of steel ingot as far as possible. This requires that the ingots and billets must be thoroughly burned. During the forging process, wangcuifen, Secretary General of the waterproof materials professional committee of China Construction Association, tried to make the deformation as uniform as possible, and carefully pressed the bench to avoid confidence

in order to avoid white spots and meet the requirements of rotor mechanical properties, the best post forging cooling and heat treatment process should be optimized

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