1. abnormal and degraded nodularizing
If the ductile iron castings have defects of abnormal and degraded nodularizing, the fracture surfaces will show the grey color with the small black particles. There will be large amount of flaky graphite in the microstructure.
It is mainly because the too much sulphur in melted iron, or other anti-nodularizing elements. So, we suggest to use the low sulphur coal, or use the desulphite treatment. If necessary, please try to add more nodularizing agents.
2. shrinkage holes and porosity
Shrinkage holes show the concaved surfaces, and the inside surfaces of shrinkage holes are very rough. Shrinkage porosity shows many dendritic small holes.
These defects are because of low content of carbon and silicon, too much sulphur.
Using hard molding, such as resin sand casting process. Increasing the content of Si and C.
3. graphite floatation
This defect is usually happen at the end of castings, especially at the gating head. You could see many graphite balls gathering together.
This defect is because of high content of carbon and silicon, and too much residues of nodularzing agents.
The solving method is reducing the content of C and Si, and control the nodularzing agents.
4. inverse chill
This defect will show the clear white blocks on the surfaces of fractures. Some are just like the white shiny needles.
The reason is the too quick cooling for some positions, or insu? icient nodularizing.
So, the foundries need to control the usage of nodularizing agents, not too much. At the same time, enhance the temperature of pouring.
5. slag inclusion
Slag inclusion will show the inclusion with dark color and di? erent shapes on the surfaces of fractures. From macrostructures, you could see the obvious inclusion.
One reason is because of too much sulphur in the melted iron. Another reason is too much magnesium residues.
So, iron foundry needs to reduce the content of sulphur in the pig iron, and try to reduce the residues of magnesium, and set the more gating heads at the positions of easy slag inclusion.
6. deformation and cracks
When the shrinkage stress becomes higher than resistance to deformation, then there will be deformation or even cracks to ductile iron castings. The hot cracks are brown, and cold cracks are light yellow.
The main reasons are low content of carbon, insu? icient nodularizing and too quick cooling.
So, you need to increase the content of carbon and silicon, reduce the content of sulphur and improve the nodularizing.
ABOUT KEVA
Keva Casting is a professional casting company that focuses on Construction, Machinery, Automobile, Hardware, Pipeline and many other industries.
We provide top quality products with the best service based on our complete production chain including our own mold design, advanced production techniques, and full management of the supply chain. Keva Casting has two factories located in Zhucheng, China's Shandong province.
We use "shell molding", which is a new technique that has been developed in recent years.This new technique has simplified production procedures and reduced air pollution compared with traditional sand casting and investment casting. Shell making and core making are faster to ensure production in enormous quantities. The dimensions and surface finishing are satisfactory for all kinds of industrial requirements. Besides supplying our own formwork & scaffolding systems, our casting products also supply OEM services in various industries.