Research On The Solidification Morphology And Mechanical Properties Of Ferrite Ductile Cast Iron

Ferrite ductile cast iron, as an ideal engineering material, has been widely used in fields of wind-power equipment and high-speed railway, due to its advantages of low-temperature performance and high ductility. Therefore, it should be worth studying solidification morphology and microstructure of the ferrite ductile cast iron.In this study, solidification process and morphology of the ferrite ductile cast iron, in different thickness are investigated. And the effect of the two-step annealed to microstructure morphology and mechanical properties is also discussed.(1) When the thermo-modulus is small, the macro morphology showes typical characteristics of paste solidification. Its microstructure is mainly composed of ball-shape austenitic shell. Low content of small-size separated dendrites can also be found. As the thermo-module increases, solidification time becomes longer. Its macro morphology becomes spongy solidification gradually. There is enough time for the primary dendrite to grow. The content of separated dendrites increases too and the grain size becomes bigger.(2)With thermo-module increasing, the quantity of graphite decreases in its microstructure. The diameter of the graphite increase and the shape become nonuniform and irregular. As element segregation among separated dendrites increase in LTF. The content of pearlite increases in the matrix., which is deteriorated the room-temperature tensile strength, elongation and impact toughness.(3)The two-step of low and high temperature annealing treatment not only eliminate free cementite, phosphorus eutectic small graphite in the matrix, form broken austenite, but also increase the quantity of graphite and decrease the area rate of pearlite, and create fine ferrite grain. Therefore, the tensile strength, elongation and impact toughness are improved obviously.(4)The annealing treatment (920℃×2h+720x4h) eliminate the pearlite of matrix barely. However, the small amount of pearlite still exist in cast by annealing treatment (920℃×2h+740℃×4h).And the content of pearlite increased along with thermo-modulus.