Truck wheel hubs are produced from cast spheroidal graphite iron. During the machining of cast wheel hub, we sometimes experienced a difficulty in milling the wheel hub to a desired dimmension. Cutting this material is not an issue but milling it is very challenging. The attached document contains the chemical composition of different batches of cast ductile iron wheel hubs which have been machined and milled - one without milling difficulty and the other with milling difficulty. Both batches have a similar chemical composition.
Can you please suggest why there is difference in milling behaviour of the cast components, despite having a similar chemical composition?
Thanks for your time and answer.
Dear Samuel,
According to your description, your product has not a homogeneous microstructure, namely - in several volumes graphitization did not occurred as required. Instead graphite nodules, a hard cementite phase formed. I propose to confirm this suggestion by a microstructure control in the problematic regions. If so, you need to check your inoculation route, as well as a die design to prevent non-uniform and/or too high cooling rate.
Thank you very much @ Alexander for your comments. My thought has been in that direction as you have mentioned. I will confirm the microstructure in the problematic area as you have suggested.
From my point of view, the problem is that different thicknesses in the piece generate a different cooling speed and, consequently, a different hardness. If you wish, for more information you can read the attached document.
Normally, the hardness difference can promote a reduction in tool life of the order of 30% to 50%.
We have a work about this problem, but it in spanish.
This is our presentation that show a case problem about turning on grey cast iron parts.
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