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From: Robert Bastow <"teenut"@ hotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Case hardening
Date: Fri, 16 Jun 2000 00:10:13 GMT

Case hardening is nothing but a simple process during which soft, low carbon
iron or steel is heated in the intimate presence of a carbon donating
(carburising) material.  this can be charcoal, cyanide, acetylene gas or any of
many other materials.  The carbon, is infused into the surface layer of the soft
iron, and turns it into a HIGH CARBON STEEL.  This when quenched from a suitable
temperature, results in a thin, surface CASING of glass hard, wear resistant
material.  Case hardening is NOT a cheap man's rout to a harder material..Rather
it is a expensive and complex process done to provide the OPTIMUM of material
conditions..a soft, tough core for shock resistance, coupled to a glass hard
exterior for wear resistance.

It is the process of choice for such things as automotive transmission gears,
gun parts, etc

Your local heat treatment company will case harden parts for a reasonable fee.
They will either Gas Carburise or Cyanide (salt bath) carburise before quenching
to leave a pale grey, glass hard surface on the part.  There is some risk of
distortion with intricate or thin parts..you may want to ask about Nitriding
which is done at a lower temperature. You can specify the depth of case required
to quite narrow limits.

"Kasenit" and similar products such as "Hard N' Tuff" are used by, first,
heating the part to a dull red heat, rolling or dunking the part in the sand
like compound, until a glassy, melted coating covers it.  The component is then
brought up to a bright red heat and quenched in clear cool water.  This process
can be repeated to give a thicker coating.

Traditional Case Hardening is done by packing the soft iron or steel parts in a
cast iron box, together with a mixture of charred bone meal, leather scraps or
parings from hooves etc.  The top is wired in place and sealed with fireclay.
The entire box is then heated in forge or furnace, to a medium red heat for
several hours, after which it is removed, the wires clipped and the entire
contents dumped into clear cold water.

COLOR case hardening is a similar process to the above.  In this case however
the parts are first polished to about a 400 grit finish and CAREFULLY
DEGREASED.  They are then packed in the bone meal/leather charcoal mix and
sealed absolutely air tight.

After heating, the contents of the box are dumped into a barrel of clean, cool
water to which a small amount of nitrate may be added to enhance the color
ranges.  This tub of water will have a grill half way down to separate the box
contents and will be arranged with a vigorously bubbling supply of air from a
perforated pipe at the bottom of the tub.  Beautiful ranges and variations of
colors can be obtained..though getting CONSISTANT, REPEATABLE, PREDICTABLE
results make this the realm of a few VERY practised masters.

teenut

Stephen Young wrote:
>
> There is a product called Casenite for case hardening metals. You heat
> up your part and then drop it in this sandy-powder material. That's it.
> Don't know where to get it - maybe McMaster Carr?
>
> gfulton wrote:
>
> > Was wondering if anyone knew of a home shop method for case hardening.


From: Robert Bastow <"teenut"@ hotmail.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Case hardening
Date: Fri, 16 Jun 2000 02:31:47 GMT

Yes,

Particularly on highly stressed parts.  The "dead quenched" high carbon steel
outer layer can be treated like any other High carbon steel and tempered
according to requirement.

Often the component is allowed to cool slowly after carburising so as to give a
soft outer layer.  This can then be further machined before final heat
treatment.  Areas that one doesn't require to be carburised can be "masked" by a
variety of means..whitewash being one, copperplating another..

teenut



mulligan@advinc.com wrote:
>
> In article <Ffe25.275$5e2.2109@news1.rdc1.ga.home.com>,
>   Robert Bastow <"teenut"@ hotmail.com> wrote:
>
> > .. when quenched from a suitable
> > temperature, results in a thin, surface CASING of glass hard, wear
> resistant material.
>
> Interesting post.  Thank you.
>
> Are there ever situations where the hardness of the case is
> drawn after the initial quenching, to provide a surface hardness
> below that of glass-hard?

 
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