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20

2020

-

07

Development trend of thick and large ductile iron castings and their nodularizing agents

Author:

Zhu Fusheng, Yang Yupeng, Zhong Weichang, Liu Yanping, Li Chunhong


With the increasing demand for mechanical properties of large cross-section ductile iron castings, the single weight of castings is becoming heavier and the service life requirements are becoming more and more important. The production technology, raw materials, quality standards, and other aspects of large cross-section ductile iron castings have undergone significant changes.

With the increasing demand for mechanical properties of large cross-section ductile iron castings, the single weight of castings is becoming heavier and the service life requirements are becoming more and more important. The production technology, raw materials, quality standards, and other aspects of large cross-section ductile iron castings have undergone significant changes.
Understanding of Spheroidization Decay in Thick and Large Section Ductile Iron Castings
Long solidification time is the root cause of various problems in the production of thick and large section ductile iron castings. When casting thick and large section ductile iron castings, the solidification time ranges from a few hours to several 10 hours, resulting in severe spheroidization recession, inoculation recession, coarse casting structure, and increased pearlite content caused by element segregation. There are significant differences in the understanding of the graphite decay process in thick and large section ductile iron: Ding Linpu et al. believed that the graphite morphology decay process is a process from spherical to ball like, worm like, and dendritic to sheet like. 1. Fang Keming and Zhang Suomei extracted several typical graphite from the cast iron using non-destructive testing and electrolytic separation. Transmission and scanning electron microscopy studies found that the deformed graphite in the center of the large section casting is a large number of graphite branches radiating
The spherical shape of the arranged large graphite clusters is an excessive development of spherical graphite black, rather than a product of the decay of spherical graphite towards vermicular or flake graphite. The basic law of graphite deformation is from spherical graphite, flowering graphite to hyperspheroidized graphite [2]. There are also differences in the formation mechanism of abnormal graphite in the center of thick and large section ductile iron: Karsay and ByhrBtrich believe that fragmented graphite is formed due to various reasons [3-5] Ding Linpu believes that abnormal graphite is not formed by the fragmentation of spherical graphite, but by direct nucleation and growth in eutectic iron liquid [6].