Graphite grain opening in grey iron casting.
Author: Date: 2019-11-21 8:55:53
It is most common problem in grey iron casting seen after machining.
It is similar but not same look as appear as micro porosities.
Mechanical reason:if metallurgy wise,metal is ok then this is machining operation defect and it is formed by higher cutting speed & depth of cut when extra fine finish are done which is not required.
Probably causes:
Higher cutting speed
Higher depth of cut
Higher surface finish.
Metallurgical reasons:
This defects are observed in machining when imbalance of carbon/silicon%& high phosphorus%.,higher CE value and knock out time.
Remedies:
1.Reduce cooling time/knock out time:the more casting inside mould,the more sand burning.bentonite/binders becomes ash and lustrous carbon become volatile.when optimal cooling time is selected then casting have natural annealing effect and leads to better service life.
2.reduce CE value
3.make balance of carbon/silicon%
4.inrease steel scrap upto 40%& keep pig iron 10-15% in charge mix for better microstructure.
5.review inoculation practice to make A-type graphite and avoid formation of D&E type.
6.avoid superheating or long delay in pouring7.low phosphorus