Development Of The Ductile Iron For Wind Power Casting

The ductile iron for wind power casting that appears with the development of the wind power industry is a kind of high toughness ductile iron.It is also a new direction of the development of ductile iron.Because of the low toughness,the normal ductile iron is fragile in a cold climate,so it can not meet the performance requirements of wind power casting and is not suitable for the production of wind power casting.In order to ensure the safe use of wind power casting,it must be produced by high toughness ductile iron which has the high technique content in the production.In this paper,the experiment was made around the core issue that how to improve the impact toughness of ductile iron.The relationship among the production process,the mechanical properties and the microstructure was studied.By the chemical composition measurement,the mechanical properties test,the observation of microstructure and the fracture scanning,the best chemical composition and production process were determined,and the effective way to improve the impact toughness was found.That will have a guiding role in the production of ductile iron.The research shows that the chemical composition of Si, Cu and Bi has the significant influence on the toughness of ductile iron,as well as selecting the efficient spheroidizer,the compound inoculant and two-stage graphitization annealing in the production.That also has the close relation between the microstructure and the low temperature impact toughness.The higher the level of the graphite sphere,the better the low temperature impact toughness of ductile iron. As the amount of pearlite in the matrix increases,the low temperature impact toughness decreases.In order to ensure the low temperature impact toughness of ductile iron,the content should not exceed 25%.The images were obtained by SEM show that the macrascopic topography is similar but the microcosmic topography is significantly different.When the toughness is low,the microcosmic topography has the feature of cleavage fracture.When the toughness is high,the microcosmic topography has the feature of quasi-cleavage fracture. In the course of impact fracture,the gap between the graphite sphere and the matrix is formed by separating.If the gap is sharp,it is easy to promote the formation of crack and lead to the fracture.The best chemical composition of ductile iron for wind power casting in production is WC=3.7-3.8%,WSi=1.9-2.0%,WMn＜0.2%,WP＜0.04%,WS＜0.02%,WMg=0.03-0.05%,WRe=0.01-0.02%, WBi=0.006%.It was determined by ten experiments.By adding 0.006% Bi,the level of the graphite sphere and the content of the ferrite was improved,the max impact toughness at -40℃was 17.1J,the experimental effect was obvious and the performance met the requirements.The goal of the research was achieved finally.In the production of the wind power casting,the way of adding Bi is cheap in the cost of production,and the increased cost by adding Bi is only 1/7 times than by adding Ni.Therefore,it can significantly reduce the production cost and has high practical value and generalized significance.