On Thu, 08 Aug 2013 12:31:33 -0500, Tim Wescott
wrote:

On Thu, 08 Aug 2013 13:17:30 -0400, Ed Huntress wrote:

On Thu, 08 Aug 2013 11:53:17 -0500, Tim Wescott
wrote:

On Thu, 08 Aug 2013 11:40:27 -0400, Ed Huntress wrote:

On Thu, 8 Aug 2013 08:12:16 -0700 (PDT), Bob La Londe
wrote:

I am sure you are familiar with them. The flat black (sometimes
otherwise coated) wrenches that come with a lot of power tools for
changing blades, bits, discs, etc. They look like they are stamped
out of sheet. I am certainly not going to make a stamping die for one
wrench, but I am sure I could cut one out of flat stock on the mill
when I need one and a regular mechanics wrench won't fit. The thing
is I don't know what steel to use.

How about an inexpensive alloy that might be easily heat treatable. I
don't think surface hardening would help for a wrench or a spanner as
the cross section would still be softer, but maybe somebody who knows
better could speak up?

Those things are almost always made of plain carbon steel. 1070 is
common for tools and other odds and ends that need strength with a
moderate amount of ductility.

You'd be suprised how *few* things that we think of as high-strength
are actually made from alloy steels. For example, the piston rods on
shock absorbers and struts: Plain carbon, 1070.

Quality wrenches often are made from a proprietary grade of
chrome-vanadium alloy. But the advantage in most practical uses is
slight.

That depends on what you see as "practical use". If it says "chrome
vanadium steel" on the outside, and that makes the wrench sell more
without you getting sued for false advertisement, isn't that a highly
practical use from the "let's make lots of money" point of view?

Man, you're a cynic. g

I don't know what they're using now, but 30 years ago, quality hand-tool
makers -- Williams, Sears, Snap-On, etc., used either an alloy like AISI
6118 (SAE J1268) or a similar proprietary, custom steel grade.

The advantages are that they develop more hardness and strength with
less carbon, and they retain some ductility, or at least resistance to
brittle failure, even with high-strength heat-treatments.

But, again, those advantages are only meaningful in some circumstances.
If you're ham-fisted and you abuse and overstress your hand tools, the
alloys may save you some grief. But really, for most uses, plain-carbon
steel wiill give you plenty of strength and hardness.

My understanding of the whole alloy-steel thing (which may be faulty) is
that the alloys don't really change the ultimate strength to which you
can heat treat in a thin section, but they make it easier (sometimes
vastly so) to attain that strength in a piece where you can't get fast
cooling everywhere.

Well, that's one type of alloy steel, or a range of types, which are
formulated to harden at slower quench rates -- the slowest being the
air-hardening punching grades, like the A-Series.

There are many reasons for alloying steel. That's why there are so
many types. But your basic idea that many of them are no stronger, but
are easier to quench without damage, is correct. Carbon steel will
achieve hardness and ultimate strength that is as good as those of
most alloys, and fairly close to those that are formulated
specifically for maximum hardness and tensile strength. But if you
have to harden a piece that varies markedly in thickness --
particularly something like a stick punch -- it can crack right off
where the thickness transition occurs, just from quenching it. This
was a big problem in the early says of press-tooling manufacture, when
there wasn't much else besides what is, today, the W-Series of
water-hardening, plain-carbon steels.

Steel metallurgy is a very involved subject, and the field is full of
myths.


So things that are fairly constant sections, and get made in massive
enough quantities that you can afford to really fine-tune your heat-treat
process, can get made with plain high-carbon steel.

Generally true. It's also true that carbon steels are typically a bit
more tolerant of imprecise temperatures for initial heating to the
transition temperature, and they'll do different things,
satisfactorly, through a range of tempering temperatures. IOW, they're
*usually* a bit more forgiving of imprecise heat-treatment.

Any steel will suffer damage if you quench it too fast. The thing
about plain carbon is that you MUST quench it fast, or it doesn't
harden. O1 can be quenched more slowly. A1 can be quenched by just
letting it lay on the bench, cooling in ambient air. That is, if it
isn't too thick.


Forged wrenches, OTOH, have massive sections sitting right by thin
sections, and would benefit from some alloying.

No doubt that's part of it, but the big issue is the inherent
ductility of the alloy -- or its impact resistance, or other ability
to withstand overloading.

--
Ed Huntress