"Jay" wrote in message
...

Thanks for you response..

The tool is a bench block I made, cylindrical in shape, similar to the
Starrett blocks. The main difference is there are 6 , M6 threaded
holes around the circumference to allow clamping to the block.
Diameter 3.000"
Height 2.500"
Wall Thickness .300"
Top thickness .500"

My knowledge of heat treating is mostly theory, but not much practical
work. I was thinking about case hardening, as I have 10 pounds of
Kasenite, but I figured if I could harden it, then temper, that would
be better, as I also have a portable Rockwell tester, and I wanted the
practice.

I was reading the Machinery Handbook, and gathered that quenching in
water would not produce the desired effect, as the oxygen would cause
, more or less, uneven hardening.

Do you figure water will be better?

Here's my best guess for a short answer: given the shape of your part, no.
I'd go with oil. But that doesn't mean that oil will do the job you want. It
means that I think there's too much risk of cracking or at least building in
too much stress if you use water. You're going to do some pounding on this
thing, after all. If oil does it, you're home free. If it doesn't, at least
your bench block will be safer.

And here's the longer answer. Your bench block is an excellent example of
why slow-quenching tool steels were developed. g Fairly massive, it will
not through-harden in any plain carbon steel, anyway. And the faster quench
rates required by plain carbon steel will stress that part, potentially
causing trouble at the holes. If you've studied some heat treating you
probably know why that is. Cracks could develop at the edges of the hole(s).

The best material for that block is an air-hardening tool steel. With some
skill in heat treating, it's probably also a safe candidate for an
oil-hardening steel, which, by my guess, is what Starrett probably uses. If
you're going to make it out of carbon steel, which is what I'd do at home,
I'd make it out of 1020 and case harden it -- especially if I had as much
Kasenit around as you do.

The trouble with 1045 for this job is that it's a little high in carbon,
given the great difference in section thicknesses between the places with
holes versus those without, for water quenching -- including water quenching
for the purpose of case hardening.

On the other hand, it's a medium-carbon steel that isn't going to be subject
to the fairly extreme expansion stress (the result of conversion to
martensite) that you'd experience with a higher-carbon steel like 1095. So
you may get away with it.

If you had used 1020 or another low-carbon steel made for case hardening,
you'd probably be on safer ground because, although a rapid quench will
cause some stresses due to thermal contraction, at least you won't compound
the problem with differential expansion as a result of martensite
conversion, which would add to the thermal stress.

1045 can be hardened up to Rc 58 with a water quench. I don't have the
maximum value for oil quenching handy, but 1045 often is oil-quenched in
industry. You're probably going to have to agitate the part to get enough
heat conduction away from it to get any hardening at all, using oil, given
its mass. Oil can harden it but it may fail entirely if the heat conducted
from inside the block prevents the surface (which is all you really care
about, of course) from attaining an adequate quench rate. That's the
threshhold business I was talking about. The gentle quench can do some
hardening AS LONG AS your actual quench rate isn't impeded by heat
conduction from the mass inside. That's the classic problem with judging
which medium to use for quenching, in middle-of-the-road cases like this.

Here are some links that will clear up some of these points, given that you
know something about heat treating. The first two are from a 1920s edition
of Machinery's Handbook. The last two are from Timken. In the very first
one, scroll down until you get to the section on 1045. If you *really* want
to get into it, search on Heat Treating 1045 Steel, without quotes, on
Google. There's a regular cornucopia there.

Hey, you could leave it soft and you'll have a useful bench block;
as-delivered 1045 ain't all bad. Or you can take a chance and learn
something useful. That's what makes this amateur stuff fun.

Good luck, Jay.

http://www.zianet.com/ebear/metal/heattreat7.html#1045

http://www.zianet.com/ebear/metal/heattreat0.html

http://www.timken.com/timken_ols/ste...ook/pdm049.asp

http://www.timken.com/timken_ols/ste...book/table.asp

Ed Huntress