Subject: Re: cast iron stability question

From: [email-masked] (Craig W. Hazelbaker)
Date: 10 Aug 1995 14:40:14 GMT

In article <[email-masked]>, [email-masked] says...
>
>In article <[email-masked]>, [email-masked] (Ron Hock) 
writes:

>|>cast iron and whether or not new "green" castings are prone to warpage 
and other 
>|>anti-social acts where old, aged castings remain more stable. 

>You might also ask this question on sci.engr.metallurgy, where you
>might get more scientific answers.

Here's an anecdote for you.  We used a large 12" cast iron skillet for years 
both at home and camping.  One day last month, the wife cleaned it, and put 
it on the stove to begin to dry and re-oil (maintain seasoning) and before 
the water even evaporated on it, there was a loud KIPPOW!!! and it split 
>from  the edge of the pan right to the center, ending in a ? shape around the 
center.  Strange, after so many years of useage.  Ideas?  We've saved it... 
could it be of use to a blacksmith? Next camping trip I'll see if the Smithy 
would want it for trade for some S hooks or something.

A while ago, someone said they had a small forge they wanted to get rid of. 
Drop me a note, will you?

Craig
[email-masked]

Opinions expressed are mine, the company had nothing to do with it.
So there.

---

From: [email-masked] (Russ Kepler)
Date: Fri, 11 Aug 1995 00:10:21 GMT

In article <[email-masked]>, Ron Hock <[email-masked]> wrote:
>The question has been raised over at rec.woodworking about the stability of
>cast iron and whether or not new "green" castings are prone to warpage and other 
>anti-social acts where old, aged castings remain more stable. There's tons
>of anecdotal info but can someone please enlighten me with some more
>scientific facts/data about what's the truth and why?

Mostly for the same reasons as most other iron alloys, in that the
cooling of the alloy leaves behind local concentrations of different
forms of the alloying materials.  In a carbon steel the different
forms are austentite and martensite, in cast iron it's graphite
(carbon in an iron matrix) and cementite (carbon combined with iron). 
Since the graphite in loose form takes up more room than the combined
form, and small changes occur after cooling then stresses change
constantly while the carbon decides what to do.

You can artificially age the iron by subjecting it to cryogenic
cooling - something I'm going to do to a straight edge I'm working on
now.  I've done the rough cuts, removing most of what I want off, and
will pack the iron into a small styrofoam chest after wrapping it in
newspaper.  After supporting the iron above the bottom of the chest
I'll start pouring in liquid nitrogen until the top surface get too
close to the iron, and let it steep for an hour or so, repeating the
addition until I figure the iron is at LN temperatures. At that point
I'll let it regain room temp in the styrofoam with the lid on.  It
should do a nice job of stress relieving the cast iron.

-- 
Russ Kepler posting from home  [email-masked]

                      Please don't feed the Engineers