Effects Of Foundry Process On Graphite Morphology And Mechanical Properties Of Wind Power Ductile Iron

With remarkable advantages in performance and price,the ductile iron castings extensive application prospect in diversified industries including machine tools,nuclear power,hydropower,and wind power.As fundamental components for the key national technical equipment,ductile iron castings play important roles in national economy and serve as key indicators in assessing the comprehensive industrial strength of a country.However,in manufacturing the wind power ductile iron castings for wind power equipment,some structural defects(i.e.low spheroidization rate,coarse graphite and graphite degeneration)often occur,which result in instable mechanical property of wind power ductile iron castings,and bring about adverse impact on product quality.In this paper,considering the actual manufacturing condition of the foundry company,which adopts the electric-furnace smelting process to manufacture the wind power ductile iron castings,and prepares the separated test bar of casting and test lug,the author intends to,by utilizing various test measures(i.e.spectrum,optical metallographic microscope,electron scanning microscope,low-temperature impact tester,and microprocessor-controlled electronic universal testing machine)to research the impact of several process factors(i.e.inoculation,alloying,holding time in ladle after spheroidization,and standing time and cooling speed of melted iron in furnace)on the graphite morphology and mechanical property of wind power ductile iron castings.The research results will be of great significance of guidance in formulating the manufacturing plan and controlling the structural properties for wind power ductile iron castings.Based on the metallographic structure,mechanical property,low-temperature impact property,spheroidization grade,and graphite size and roundness,the author intends to study the laws relating to the impact of different process factors(i.e.alloy element-stibium,high-temperature standing time in furnace,holding time in ladle,chiller,and casting section thickness)on the graphite morphology of wind power ductile iron castings.Under given test conditions,if 0.002%～0.01%stibium alloy is added during the spheroidization,the matrix grains will become finer,the amount of graphite nodules will be increased with smaller diameter,better spherical degree and higher spheroidization grade;if the high-temperature standing time in furnace is increased;the amount of graphite nucleus will be decreased with lower spheroidization rate and less graphite nodules;if the chiller is adopted for the cooling of wind power ductile iron castings,it’s able to obtain regular graphite nodules,promote the spheroidization grade and refine the microstructure,and avoid the degeneration and floatation of graphite.After correcting and improving the test conditions according to the said laws of impact from the said process factors,the author researches the laws of impact of spheroidization and inoculation treatment on the metallographic structure and mechanical properties of wind power ductile iron castings.Based on the characteristics of tensile fracture and the graphite crystallization nucleus,it’s found that during the metal-stream inoculation,the fading of spheroidization and inoculation is slowed down,Finally,the spheroidization rate of test lug reaches class-2,and the size of graphite nodules is basically kept at class-7,and the elongation,tensile strength,low-temperature impact property,and other mechanical properties of graphite nodules are improved.With balanced content of calcium and cerium,the inoculant-C is able to neutralize and prevent the hazardous trace elements generated by graphite nodules.After being adding to the melted iron,the little amount of sulfur and oxygen contained in inoculant-C will react with calcium and cerium to generate special components,which will generate satisfactory graphite crystallization nucleus.Characterized with stable particle,longer residence time,and excellent resistance to the fading of spheroidization and inoculation,the graphite crystallization nucleus is able to realize high spheroidization rate,and ensure stable size of graphite nodules,thus realizing high-density distribution of graphite nodules.As an instantaneous inoculant,inoculant-D has high average content of Y-element.After being added to melted iron,the Y-element in inoculant-D will be oxidized into yttrium oxide.The graphite nucleus grows on the basis of the nucleation of Y2O3.With longer residence time in melted iron,inoculant-D is able to realize effective nucleus,certain resistance to graphite degradation,high spheroidization rate,and better distribution of graphite nodules.However,in the later phase of melted iron,the resistance to graphite degradation and nucleation capacity of inoculant-D is inferior to that of inoculant-C.Therefore,it’s unable for inoculant-D to realize the high-density distribution of graphite nodules,affect the ferrite matrix,refine the matrix grain,and increase the ferrite matrix.