On Thursday, November 24, 2016 at 8:49:50 PM UTC-5, DoN. Nichols wrote:
On 2016-11-24, John B Slocomb wrote:
On Wed, 23 Nov 2016 17:13:22 -0800 (PST), wrote:

On Wednesday, November 23, 2016 at 6:03:56 PM UTC-5, Bob La Londe wrote:
I have a box of rust covered bits of square bar I got along with a small
lathe I bought a few years ago. There were some carbide tipped junk junk
bits in the box, but it mostly looked like keystock.

[ ... ]

I am just curious. I've got a decent selection of insert tooling and a few
pieces of known good HSS ground for stuff I don't have inserts for.

Keystock usually is just plain carbon steel -- not very hard. Try it
and see how it performs.

Is it even *carbon* steel? I think that what I have is just
plain mild steel -- not enough carbon to harden. (I've never tried,
since I don't see any benefit to hardening a key.)

Plain "mild steel" is carbon steel. A lot of jargon common terms confuse these things. Even the mildest steel contains carbon, at least 0.08 %. The series starts with 1008, which was once used for stamped car-body parts.

1008 won't harden noticeably. When you get up to 1020 (0.2% carbon), it will work-harden a bit but barely quench-harden. Quench-hardening starts at around 1040, but even that doesn't harden much.

In theory, 1070 will get as hard from quench-hardening as any higher carbon steel. But in practice, it doesn't, supposedly because of the way carbon is distributed in the iron. 1090 (0.9% carbon) comes close but music wire runs up to around 1.2% carbon. That will draw to very high hardness, but I'm told it doesn't quench-harden any more than 1090. 'Dunno, I've never tried it, and I no longer have access to a Mitutoyo hardness tester, anyway.

Keystock comes in a variety of materials but the common ones are 1018 and 1045.


High speed steel is not only hard (typically 62 - 66 Rc), but it has a
tempering temperature of around 1,000 deg. F. Sometimes a little more
(M4, M42 and above). You can use it right up to the tempering
temperature without permanently softening it. That's why it's called
"high-speed." You can run the cutting speed up until it just barely
glows red -- in a fairly dark room, at least.

Also -- I don't think that I have ever seen HSS rust. I guess
that it is possible, but uncommon.

It is somewhat rust-resistant, but it will rust.


If you have some hard steel that's not HSS, you can do some cutting
with it at low speeds. If it's plain carbon, it ought to take 450 deg.
F. That's what was used before we had HSS. My old friend at American
Machinist used music wire for cutting tools on his Unimat. That's pretty
hard, but it's plain carbon steel.

Compare the previously mentioned (and likely now snipped)
automatic center punch test -- before and after a heat and quench cycle
to see whether it does harden at all.

We often made boring bars for one off jobs from "drill rod". Takes
very little time to forge and temper grind it to shape. Even keeping
the cutting speed down to carbon steel speeds it was still a quick way
to get a job done :-)

Sure -- drill rod is a relatively high carbon steel -- made to
be hardened. Three common flavors -- water hardening "O1" (quench in
brine, not plain water, I believe), Oil hardening "O1" (quench in oil),
and air hardening "A2" and "D2" (just let it sit in air until it cools.)

For most purposes, they all need to be tempered so they are not
*too* brittle beofre use.

Enjoy,
DoN.

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