Re: Hardening rails

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "zxcvbnm12330134"
<johnatl@m...> wrote:

> I bought some W-1 Water Hardening Drill Rod to use with my
> hand-me-down Thompson Super Ball Bushing linear bearings.
>
> The write-up said it was usable as-is, which I suppose it is,
> but it isn't as stiff as I was expecting. Can I heat this with
> my little propane torch, then quench it in a bucket or with a
> water hose? I probably won't be able to get the whole thing
> hot at once. Maybe I could put it in the oven at 500deg?
>
> Thanks for any advice!
>
> Regards,
> JJ

There are two processes that have to be used to harden high carbon
steel. (Case hardening is reserved for low carbon steel and is a
surface process). First you have to take the entire steel piece up
over the critical temp (varies with alloys but is 1500 to 1875 deg
F). Some of the old guys can look at the color at tell you when you
get to the magic temp. The molecular structure of the steel changes
at this temp and the crystal structure (grain) realigns. The best
way to determine critical temp is to heat the steel until a magnet
will not stick. Once you reach the critical temp it has to be very
rapidly cooled by plunging (submersing) it into water. The
entire "quenching" process should not take more than a few seconds.
This makes the metal very hard and brittle. The next step is to
anneal the piece by bringing it up to a lower temp and rapidly
quinching it again. This softens the steel but maintains the
toughness. Heating steel then letting it cool slowly will completely
anneal (maximum softness). Taking the metal up anywhere BELOW the
critical temp and quenching it will not add any hardness.

If you try to do this in sections you will get twisting and warping
of the rod. There will be soft and hard spots. You have to bring the
entire piece up to critical temp which means several torches at once.
At those tempratures scale will form on the surface of the metal
inless it is in a reduced oxygen environment. This scale will have
to be removed (normally with grinding).

For precision ways using THK slides, I would suggest you find
hardened and ground rods, ground to the correct dimension. Heat
treating steel will cause it to change size and may well be out of
spec for the bearings. Unless you are familiar with heat treating I
would not recommend it for making larger critical parts.