I want to know, what is formation mechanism of ferrite in surface of the grey cast iron? we are producing auto parts with grey cast iron. and recently we have a problem with fractures in the area of the edge and Fulcrume and legs in the parts. Our parts are such as flywheel, pressure plates and more. Now, we want to reduces the fractures without any significant cost. If someone know that with change amounts of elements in chemical composition or exchange in raw materials or use from a particular kind of materials or one idea at how to charge or hold or how to shot blasting method or any thing do you think. And more than any thing I want articles or knowledge about how to mechanism formation ferritic phase in surface and thin areas in grey cast iron if you have? thank you so much in advance.
why ferritic phase is formed on the surface and thin areas? what's the solidification and formation mechanism?
Ferrite forms in the skin (surface) of cast iron because of carbon loss at the surface. Carbon in the iron reacts with oxygen or water vapors in the molding aggregate, resulting in a decarburized surface layer. I have published a series of papers on this subject, with the most recent one being "Occurrence and effect of casting skin in
compacted graphite iron" in Int. J. Cast Metals Res. You can download this paper and most of the others on my page.
The mechanism of formation of near-surface ferritic phase in gray cast iron rotors and the factors that make it happen are described very well in the attached thesis. If you go through it carefully you will see that improvement in ductility may come with a huge price- reduction of machinability of the surface, resulting in adverse tool wear and poor surface finish, as concluded by the author of the thesis. Dr. John Campbell has also made a similar observation in his well-known casting rules. The final decision is yours to make!
Regards,
Malur
Ferrite formation near surface and at thin areas might be due to carbon effusion at high temperatures and slow cooling rates in normal atmosphere. You might avoid carbon effusion by cooling down in carbon enriched atmosphere or you might use higher cooling rates. Of course, higher cooling rates might influence microstructure and properties of your cast iron. Then, it might be essential to use different cast iron alloys with higher silicon content to maintain the desired properties.
I do not go into the details of carbon or silicon properties of the grey cast-iron. But, I could guess that any unreacted iron or corroded/thin area surfaces with iron exposures would naturally get oxidized to form Fe2O3 and Fe3O4. Gamma Fe2O3 and Fe3O4 exhibit only spinel or ferrite phase.
Ferrite forms in the skin (surface) of cast iron because of carbon loss at the surface. Carbon in the iron reacts with oxygen or water vapors in the molding aggregate, resulting in a decarburized surface layer. I have published a series of papers on this subject, with the most recent one being "Occurrence and effect of casting skin in
compacted graphite iron" in Int. J. Cast Metals Res. You can download this paper and most of the others on my page.
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