Difficulties in the production of heavy section ductile iron wind power castings

According to the different power generation, the quality of low temperature impact resistant wind turbine castings (especially wheel hubs and bases) ranges from 5 t to dozens of tons, and most of the wall thickness is more than 100 mm. They are typical thick large section ductile iron castings.

Wind turbines are usually installed in coastal, mountainous, Gobi and other places with strong wind, and the operating environment is very harsh (low temperature, alternating stress and impact load, humidity and salt spray corrosion). Moreover, its components are installed at an altitude of tens of meters, and the wind speed changes greatly during operation, which is prone to accidental failure. Therefore, the materials of wind power castings are required to be ferritic matrix ductile iron, and the mechanical properties meet the standard. In addition, the low-temperature impact properties are also required to meet the requirements. In addition, ductile iron castings should also pass ultrasonic (UT) testing and magnetic particle (MT) testing.

Compared with ordinary ductile iron castings, wind power castings belong to High Toughness Ductile Iron Castings, which not only have high requirements for casting defects and surface quality, but also have strict requirements for casting performance. High low temperature impact toughness is required while ensuring conventional performance. Especially in the production of large castings such as wheel hubs and bases, due to their heavy weight, large size, thick section, large heat capacity during casting, slow solidification, it is very easy to cause spheroidization recession and incubation recession, resulting in changes in graphite morphology and matrix structure of castings, especially in the center of wall thickness and hot spots of castings. The slow cooling speed at the thick wall will inevitably lead to the coarseness of graphite balls, the small number of graphite balls, the distortion of graphite balls, and the formation of various non spherical graphite and fragmented graphite. At the same time, due to the redistribution of solute elements during solidification, there will be a series of problems such as serious element segregation, intergranular carbides, shrinkage cavities and porosity. As a result, the mechanical properties of wind power ductile iron castings become worse, especially the elongation and low temperature properties are significantly reduced. With the rapid development of wind power industry, the requirements for the internal and external quality and technical conditions of thick and large section ductile iron castings are becoming higher and higher.

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