[AT] Heat treating tractor parts

[Larry D. Goss]

Standard heat treating is a two-step process.  The part needs to be
heated to a relatively high temperature and held there for considerable
time so that the crystalline structure of the iron can change to absorb
more carbon.  It then is quenched (cooled quickly) at a rate that
prevents the carbon from coming out of solution with the iron.  The part
is "hardened" at that point and is exceptionally brittle.  It then has
to be reheated to allow some of the carbon to come out of solution.
This part of the process is called "tempering."  The temperature that
the part is raised to during tempering allows more of the carbon to
disassociate from the iron and resulting changes in the physical
properties of the part occur.  It goes from being exceptionally hard and
brittle to being ductile, to being "springy", to becoming dead soft
again.  The range of temperature for tempering is between 400 and 700
degrees Fahrenheit.

There are all sorts of techniques for actually getting the job done when
the original steel is the "wrong" composition, or when the parts are
exceptionally large, or when you only need the surface hardened for wear
resistance etc, but the fundamental process takes two steps.  In some
cases, the hardening and tempering can occur "all at once" if you can
control the cooling temperature and/or the absorption of carbon well
enough, but there's an art to doing that.  Some of those techniques are
things that are being talked about in this thread.

This is probably more than anyone wanted to read about this topic.

Larry

-----Original Message-----
From: at-bounces at lists.antique-tractor.com
[mailto:at-bounces at lists.antique-tractor.com] On Behalf Of Thomas O.
Mehrkam
Sent: Thursday, March 17, 2005 6:36 AM
To: Antique tractor email discussion group
Subject: Re: [AT] Heat treating tractor parts

Heat treating will make them harder. It will also make them more 
brittle. That may not be what you want. Will they be subject to wear?

I am an electrical engineer so I should not be giving advice on this 
subject. If you know the load and tell me something about the 
application I work next door to a Mechanical Engineer. I can probably 
get some good advice from him.
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