[TheForge] why doesn't cast iron oxidize and burn in the same way?(was: oil/wax finish, blackened steel)

[peter fels & phoebe palmer]

I inquired and got a helpful
Cast iron is endothermic, steel in exothermic...
Yeah thanks.
As a guess, and as Andy speculates, it's the clumps and lumps of carbon 
and carbon compounds
that act in a refractory manner. Think carbon arc lights.
To cut cast with a torch, one needs to feed in sacrificial exothermic 
steel above the cast.
Jim B will straighten us out on this, most likely.

On 11/1/2010 8:45 PM, Andy Gladish wrote:
> Yeah, just wondering on a chemical level exactly what's happening with the
> oxygen stream, seems to be a lot going on.
> I think of carbides as being flammable but apparently they only interfere if
> anything. Carbon content per se doesn't seem to be a factor in the burning
> reaction.
>
> -----Original Message-----
> From: Bruce Freeman
> Sent: Monday, November 01, 2010 8:10 PM
> To: Blacksmithing List Sponsored by ABANA
> Subject: [TheForge] why doesn't cast iron oxidize and burn in the same
> way?(was: oil/wax finish, blackened steel)
>
> Andy,
> Yes, when you "burn" steel, the iron is oxidizing.
> I'm not sure I follow the question about cast iron.  It certainly will
> oxidize (rust).  Does this question refer to cutting with an oxygen
> stream?
>
> On Mon, Nov 1, 2010 at 2:29 PM, Andy Gladish<gladish at cablerocket.com>
> wrote:
>> I was teaching metal fab for a wind turbine building class this past week
>> (see www.scoraigwind.com ) this past week, and in the middle of a run of
>> torch work got asked a number of times, what is actually going on when you
>> burn steel...is the iron oxidizing? If so, why doesn't cast iron oxidize
>> and
>> burn in the same way?
>> Anyone want to field that one?
>> Andy G.