Hardening technique questions

[sublime9065]

was wondering if anyone knows why you would NOT carburize a part made of cast iron?

and what is the advantage of nitriding over carurizing?

 

[metengr]

To answer your first question, cast iron cannot be carburized in the sense of carburizing steel because it already contains anywhere from 2-4% carbon in the form of graphite flakes (free carbon) and iron carbides. Cast iron can be surface hardened by the local application of heat and subsequent quenching to form martensite (graphite flakes would still remain, however). Since cast iron is inherently brittle, this surface heat treatment would serve no real purpose and would result in quench cracks.

To answer your second question, I found this interesting article by Milwaukee gear that compares carburizing with nitriding and carbonitriding.

http://www.milwaukeegear.com/pdf/inserts.pdf

 

[metengr]

Sorry, bad link;
Go here;

http://www.milwaukeegear.com/heat.htm

 

[patdaly]

Metengr:

We used to flame harden a Ductile Iron hub for wear resistance. Though you had to be very careful, it did work well, though I would not want to do it for a high volume part.

 

[metengr]

patdaly;
Agreed. My focus was on gray cast iron versus nodular iron, which has increased ductility and toughness.

 

[unclesyd]

Flame hardening of Cast Iron is very beneficial if the part is subject sliding or running against itself or another metal. This is especially true for machine components.
There is an art to flame hardening cast iron and should only be undertaken by one versed in the art.

 

[arunmrao]

sliding surfaces of machine tool beds are flame hardened and they respond excellently to this treatment.

 

[saxonsvn]

Why not use electron beam to treat the cast iron parts, especially for sliding parts. You can use the beam by case hardening (without subsequent machining) or by remelting (required subsequent machining, but excellent wear resistant).