grey iron

[Fender]

Ductile iron is basically gray iron that has been inoculated with an additive just before the mold is poured. This causes the casting to have a different grain stucture. When making gray iron castings they don’t use the additive. The foundries I have spoken to are doing an increasing percentage of their product in ductile vs. just a few years ago.

[Harold_V]

The additive is known as Glomag. It's magnesium and silicon. It causes the included carbon to precipitate as spheres instead of flakes. The gray iron must be low in sulfur in order for the inoculant to work.

Ductile iron is far superior to gray iron, as it has extreme ductility as compared to gray. Same alloy, which is what makes this so interesting.

H

[John Hasler]

Grey iron has better damping and lower friction than ductile iron and so may be better for purposes such as lathe beds.

[Fred_V]

i have a wheel that is so hard I can't cut it even with carbide tooling. Even a grinder won't do anything but polish it.
Can this be annealed?

[Fender]

Fred,
I’ve never tried this, but understand that if you build a charcoal fire around a chilled casting, then let the fire burn out slowly, the casting will be annealed. But if it is too low in silicon, this may not work. The fire will have to be hot enough (not a scientific statement!) for this to work.

[Fred_V]

Thanks. worth a try. It's useless and is a UK sourced wheel that is no longer made.

[gwrdriver]

Fred,
I've tried this on very small castings and it worked in most instances, but for anything larger (including wheels), I would devise some way to cover the fire, a pile of sand maybe, to slow the cooling as much as possible.

[Fred_V]

OK, i'm reading that the cooling is important.

[BClemens]

Fred,
If iron cools too fast, especially from molten, it crystallizes and becomes very hard. The guys are saying to heat it up to red heat and let it cool as slowly as you can. That will 'draw' it back down to a softer state. Same as annealing tool steel after quenching it from red heat - draw it back down - annealing it.
BC

[Fender]

Probably, wood ashes would make a better insulating cover than sand.

[BClemens]

Probably, wood ashes would make a better insulating cover than sand.

I would be afraid of sand - it can melt. Then you'll have a glass coated casting.
BC

[Fred_V]

would coal or charcoal be best for heating it up?