Machining problems with special cast iron

[niamu]

Hi,we are machining a special Cast Iron,GGL(Mn 0.50-1% and P 0.35-0.7%), 100% perlite and we cut at 100m/min.The problem is that we can't achieve de finish surface Rt8. The micoestructure is ok and our supplier has told me that he hasn't make any heat treatment to the parts but maybe if we do a normalizing of 760ºC we can have better results.¿Has this any sense? I think that with this treatment we are going to have ferrite and our client told as that the max. ferrite % should be 10%. ¿Do you know if there is any heat treatment to improve the machinability but without having too much ferrite?
Thank you very much!!!!!

 

[arunmrao]

P 0.35-0.7%. Are you sure of this value? This will render the casting more brittle. You microstructure should be full of iron phosphide eutectic. It is important for you to break this network,if you desire to improve machinability.

Please check on the machinability of high phosphorous irons, I am not too sure.

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