Microstructure And Properties Of Silicon Solution Strengthened Ferritic Ductile Iron By Increasing Inoculation Content

Spheroidal grap hite cast iron(duc.tile iron)has a lower cost,good casting property,excellent mechanical properties and so on,which is widely used in automotive,machine tools,construction machinery and other fields.In order to meet the strength requirements,the micro-alloying method is usually used,but it is difficult to precisely and stably control the content of alloy elements so that higher strength and lower toughness often appears in the production process.Effect of a large number of silicon solution strengthened can greatly improve the strength of ductile iron and increase the ferrite content,which is expected to greatly improve the strength and toughness of ductile iron in order to replace traditional ductile iron,steel and other materials.In this paper,the ductile irons with different silicon content,including 3.0%,3.5%,4.0%and 4.5%,have been produced by increasing the amount of inoculation under production conditions.The influence of the silicon content on microstructure and mechanical properties of the iron has been explored by analyzing the phase constitution,alloy microstructure,,micro-zone analyses and testing mechanical properties.The results show that:The microstructure of silicon solution strengthening ferritic ductile iron mainly contains the ferrite with the content of more than 95%volume fraction of the matrix,spheroidal graphite and a small amount of pearlite.The titanium-riched molybdenum carbide,oxide inclusions are distributed in the ferritic grain boundaries.With increasing the silicon content,the ferrite content increases and the pearlite content increases,while titanium-riched molybdenum carbide,oxide inclusions and others is less obvious.With silicon content increasing,the carbon equivalent is higher so as to increase the deformation tendency of spherical graphite.The ferritic ductile iron is produced by increasing inoculation content,which increases ferrite content and strengthenes ferrite matrix so as to increase strength,hardness and yield ratio of ductile iron.At the same time,increasing silicon content,the elongation of feritic ductile iron is increase.When the content of silicon adds to 3.5%,the elongation of ferritic ductile iron reaches maximum and then the elongation presents the trend of decrease.Then the impact energy presents the trend of decrease.The fracture morphology transforms from dimple and cleavag e fracture into the cleavage fracture.When the content of main alloying elements are respectedly 3.5%Si,0.043%Mo,0.022%Cu and 0.041%Ni,the mechanical properties of the ferritic ductile iron are better and can meet the property requirements of QT500-18.