Three Keys To Improve The Spheroidization Rate And Ductile Iron Graphite Roundness

Publish Time: 06/26 2021 Author: Site Editor Visit: 12567

There are many factors that affect the spheroidization rate and roundness of ductile cast iron. The following analyzes the factors that affect the spheroidization rate from the three aspects of chemical composition, process, and solidification control:

Chemical Composition

1. Carbon equivalent and silicon

Carbon and silicon are the basic components that affect the roundness of nodular iron graphite spheres. Under a certain cooling rate and incubation conditions, increasing the carbon equivalent can increase the roundness of the graphite sphere, increase the self-feeding capacity, and reduce carbides. Under certain carbon equivalent conditions, as the amount of silicon increases, especially large section ductile iron, fragmented graphite will be produced. Therefore, in the case of no graphite floating, the carbon equivalent should be increased as much as possible; at the same time, the silicon content should be reduced as much as possible under the guarantee of incubation conditions.

2. Magnesium

The control of the effective residual magnesium content is very important to improve the roundness of the graphite spheres. When the effective residual magnesium is less than 0.045%, increasing the amount of effective residual magnesium can improve the roundness of the graphite sphere; when the effective residual magnesium is greater than 0.045%, metamorphic graphite will be produced and the roundness of the graphite sphere will be reduced.

3. Rare earth

Rare earth has two beneficial effects in molten iron: one is desulfurization and degassing, playing the role of spheroidization and indirect spheroidization; the second is interacting with trace elements to eliminate harmful aspects and play a positive side. Both of these aspects can improve the roundness of the graphite ball. However, excessive residual rare earths, especially large-section ductile iron, will deteriorate the morphology of graphite, especially lumps. The ideal range is 0.010% to 0.019%.

4. Trace elements

A certain amount of antimony and bismuth combined with a proper amount of rare earth can improve the roundness of the graphite sphere and improve the mechanical properties. Appropriate adding range: 0.0025～0.005%.

The Process

1. Spheroidization

Heavy rare earth magnesium spheroidizing agent can improve the roundness of graphite spheres better than light rare earth magnesium spheroidizing agent. Mainly because of its strong desulfurization ability and strong anti-decay ability.
If the light rare earth magnesium spheroidizing agent is well controlled and supplemented with trace elements, it can also improve the roundness of graphite spheres.
The quality of molten iron is better than the subcontracting method, so it can also improve the roundness of graphite spheres.

2. Inoculation treatment

Intensified inoculation can improve the roundness of graphite balls.
The use of anti-fading inoculants can improve the roundness of graphite balls.
Using ductile iron filings as a covering agent for spheroidization can form a passivated graphite core similar to the dispersion of non-dissolved graphite, produce long-term concentration fluctuations, greatly increase the effective nucleation rate, and improve the roundness of graphite spheres. degree.
Minimizing the pouring temperature can improve the roundness of graphite balls.

3.Coagulation Control

Using cold iron can improve the roundness of graphite balls.
The use of chromite sand can improve the roundness of graphite balls.
Other measures that can speed up the cooling and shorten the time during the eutectic transformation of ductile iron can improve the roundness of graphite spheres.

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