I have a 6 foot long "digging bar" that I bought for $3 at a garage
sale. It is made out of a 1 1/8" or so hex bar. On one end of it, it
looks like a metal chisel (not wood chisel). On the other end, it is
just the hex bar cut off without any shape imparted to it.
What I would like to accomplish is, to make it into a pinch bar, with
that other end sharpened by forging also into a chisel like shape, and
slightly bent. With that, I could use it to pry big things.
Anyway, the forging part is simple and I can use my Forgemaster to
heat that end, make into a chisel shape and bend afterwards. No
problem.
My question is more about quenching. I believe that it needs to be
properly quenched so that it attains maximum strength and yet is not
brittle. Would anyone recommend a quenching procedure.
i
Digging bar - sounds like it is a pry-bar.
I have one but the far end (human end) is a nice large target for a sledge
or mallet.
I've used it to roll large logs that were 36". They are useful in a number
of operations about the yard and farm/ranch.
Martin
Ignoramus2896 wrote:
"Digging bars" came from lots of sources. I have some that were made
from car and farm machinery axles, for instance. But other than that,
if you don't know what steel they are made of, how can you hope to do a
good job of heat treating it?
You said that your "...question is more about quenching..."
Not to put too fine a point on it, but quenching is only one small
part of the heat treating process.
What you want to know is how to properly HEAT TREAT a piece of steel
with properties that are unknown to you.
"Quench" is only the process of rapidly cooling the metal after it has
been carefully brought to the correct transformation temperature for the
steel at hand, after carefully preparing the steel by normalizing, as
needed.
The quenching medium itself is very dependent upon the alloying
elements in the steel.
I think Curt Welch comes as close as any of the posts I have seen on
this thread, here on alt.crafts.blackmsithing.
If I were going to seriously approach this project, I'd start by cutting
and inch or two off of the human end, draw it out to a piece about
1/8" thick by about 1 inch wide and test it for hardenability.
Heat up 2 or 3 inches of it to the point where a magnet is no longer
attracted to it, and then immediately QUENCH it in oil. Wiggle it
around while it is in the oil. Don't do this with used motor oil that
might have a lot of gasoline in it or that has water in the bottom of
the container.
Now, place the cooled piece on the anvil with about an inch hanging
over the far edge. With a face shield on, strike down on the
overhanging piece. If it bends, it is probably too low in carbon or
alloy to be heat treatable at all. If it snaps off, it is a hardenable
steel.
If you are afraid to stike the piece, try to file it with a new file.
If this piece files about the same as the rest of the bar, then it's
not heat treatable. If it doesn't file at all, it is either water
hardening or air/oil hardening steel. If the part developed cracks, it
is probably air hardening, but, see below.
Now you are faced with determining whether the material is water
hardening, oil hardening, or air hardening.
For the time being, lets' assume that air hardening is out of the
question, because it's a relatively recent material and it's generally
pretty expensive.
Now run the same test again, using another 1/8 X 1 piece. Only this
time quench in cool, but not cold water. Did any cracks develop? If
no cracks develop, it is probably water hardening, plain carbon steel.
If cracks do develop, it may well be oil hardening steel.
So now you have at least a chance of successful heat treating of the
bar. I say this because there ar hundreds of alloys of water and oil
hardening steels, and each one has a specific optimum heat treatment
schedule.
have at LEAST a 5 gallon pail of your chosen quenching medium available.
If oil, have a well-fitting cover to drop onto the pail in case the
fire gets out of hand. (It probably won't, but why take chances.) Do
the quenching of oil outside!!!
Heat the part as Curt said and quench. Oil is VERY much slower to
cool the part than water would be. It'll take a lot of swishing the end
around to get it down to a couple of hundred °F.
Shine the quenched end up so you can see bright metal and reheat
slowly, waiting for the TEMPER colors to begin to appear. I'd heat the
piece about a foot above the area the you want if all I wanted to temper
was the end, but you didn't really want to change the characteristics of
the rest of the bar, so you will need to GENTLY heat just the part that
you hardened.
Many times, when making a chisel, etc., we heat the body of the part
and watch the temper colors run FROM the body TOWARD the tip, and when
the proper temper color reaches the tip, we cool it rapidly in water to
preserve that level of hardness.
But in you case, you will want the whole area evenly tempered to (in
my opinion) a medium blue.
This will take some doing on your part. I suggest you practice this
processe a few times on smaller things. They don't have to be tool
steel at all for the colors to form.
Heat treating properly is a very complex subject and I think I know
about 1 or 2 percent of it.
Let us know how you dealt with it,
Pete Stanaitis
--------------------
Ignoramus2896 wrote:
The "human end" you refer to is also an excellent tamper for packing the
dirt back down a post hole. One could also mix concrete with it. Pour
water into the hole, dump in concrete, plunge bar in to mix.
The ends are tempered because they get beat up by dirt and rocks, but
the majority of my bar is fairly ductile and will bend if I try to pry
with it. Found that out on a squashed steel culvert end.
snipped-for-privacy@consolidated.net says...
--
Tin Lizzie
"Elephant: A mouse built to government specifications."-Lazarus Long
Yes indeed. It is heavy to tote around, but when the mass is moving
in one focused direction - it will compress. The large flat is best
to compact as the wedge is great to separate soil and wedge it in while
the flat finishes the job if you aren't finished already!
Martin
TinLizziedl wrote:
Well, I do not have that, all I have is a abrupt end that is pretty useless.
This bar is so heavy that using it with a sledgehammer will not be
productive (unless I get a 30 lbs sledge or smoething crazy like that).
i
First thing you need to do is determine if it has enough carbon to harden
... hit it with a grinder , look for short streamers with lots of forks .
There's probably a website with pics of various spark patterns and what
they mean ...
Sounds like my digging bar.
I think I'd try a sorta draw temper on it.
First heat the end to cherry red and quench. Shine up the end so it's
silver. Now heat it slowly with a torch or your forgemaster, if you can see
it, until it is straw colored and quench again.
The first one makes it real hard if it is tool steel. The second one takes
the brittle out and makes it real durable. If you want it softer, take it a
little past the straw color,
more to the brown.
I broke the starter spring on my Husqy chain saw, again, this winter
and tried tempering the old one to see if I could toughen it a little.
At straw yellow (I measured 480F) it was still brittle, with no sign
of deformation where it snapped.
http://www.bluebladesteel.com/temper_colors_chart.html
I think I'd take the pry bar to brown/purple, 500 - 550F. If you
soften it too much it will bend and possibly work-harden and you have
to redo it, or use it flipped over. I have a Peavey log-lifter I
overloaded and bent, which now works better.
If you don't temper it enough it will shatter while you are heaving on
it. Do you have a small piece of known carbon steel to experiment on?
Alexander Weygers suggests a "bronze" or purple color for wrenches.
jsw
Now you know why properly "tempered" springs are blue. That's the
temper color for springs made from simple carbon spring steel.
Pete Stanaitis
------------------
Jim Wilkins wrote:
<snip>
Here's what I would do....
Check to see if it's anything other than mild steel with a spark test as
the other guy said. If it is a higher carbon steel, quench in oil after
heating past non-magnetic. For something that thick, you probably won't
need to temper it.
I would only do that to the end you are going to pry with (just past the
bend you want to add) and not bother to do anything to the rest of the bar.
So only heat and quench the 6 to 12 inches. Also when quenching and end
like that, move the bar up and down so as to create a more gradual cooling
between the part which is quenched and the part which is not. If you hold
it at the same depth it will create too much stress right at the oil line
and cause it to crack there.
Also, for applications like this were I am just trying to make something
harder, and not attempting to make a cold chisel or knife, I will not leave
the piece in until it gets all the way down to the temp of the oil. I'll
get it most the way down and then remove it when it's still somewhat warm.
But for pieces that thick, there will be lots of residual heat inside that
will keep coming out to the surface and fool you. If there's too much heat
coming out, it will of course, make it soft and counteract what you were
trying to do with the heat treating. But taking it all the way down to the
oil temp will increase the risk of cracking.
Test it after quenching to see if it's too brittle by just whacking it hard
against heavy stuff and see if it chips or breaks. If it does, reforge,
heat treat again, but temper the second time. That's not wise when you
know it's a high carbon tool steel, but your bar is highly unlikely to be
that.
I don't know what these bars are normally made from, but my guess is mild
or medium carbon steel at best, and not any sort of high carbon tool steel.
Tool steel is just too expensive for a bar designed to dig in dirt. And I
would guess even pry bars get their strength from their size, and not from
being high carbon steel.
I'll have to go out now and test a few of the crow bars and digging bars I
have out in the shop...
And it turns out I was dead wrong. Both my small crow bars, and the 5 ft
1" or so bar I found burred in the ground a few years back are all some
type of high carbon tool steel based on spark tests.
For the fun of it, I forged out the end of the large rusted bar to form a
pry bar and heat treated it in oil. Bars that large have so much internal
heat that I had to keep it in the oil for multiple minutes to cool it down
to the point that it was still hot to touch. I don't think there's any
point in trying to temper such a bar becuase it doesn't cool fast enough to
get brittle - at least mine didn't seem to. I ground down a sharp edge and
banged it around a lot and didn't see any indication it was going to crack
or shatter. Testing it with a file showed it was still fairly soft after
the quench.
Iggy, find out what kind of steel it is, or you're wasting your time. A bar
like that could be purpose-made, or just a piece that was lying around -- in
which case it could be almost anything.
Take a look at these descriptions and diagrams. It's never as easy as it
looks, but you'll get an idea:
http://en.wikipedia.org/wiki/Spark_testing#Spark_characteristics
If you have a piece of low-carbon steel, you're done. There's nothing more
you can do with it. If it's high-carbon, you're in luck. It's easy to
heat-treat. If you're going to use it to pry really hard, temper near the
high end of the scale, just blue. The quick tempering that's been described
here will achieve only 1/2 to 2/3 of the toughness you can achieve with a
couple of hours of tempering, but, unless you have a big furnace, you're
stuck with quick-tempering.
Medium-carbon steel *may* be manganese or chrome-moly. Pay close attention
to the sparks. If it's plain medium-carbon, it can be hardened (and thus
strengthened a bit) with a heat-and-quench, and you won't have to worry
about tempering it carefully. Just heat it up to the bottom of blue, or
slightly below. If it's an alloy steel, look up heat-treatment for that
alloy.
Forget the straw-color stuff. That's for edged tools. It will be 'way too
brittle. If it's high-carbon steel, you need the bottom end of the blue
range, at least. Like someone else said, that's why springs are blue.
If it's purpose-made, it's probably plain-carbon steel. As others have said,
don't quench a bar that thick in water -- you may get some internal cracks,
especially if you don't have a temperature-controlled furnace. Oil quenching
won't achieve quite as much strength but it's a lot safer.
Good luck.
Yeah, what Curt and Ed said! LOL :)
It's cheap steel but definitely not mild steel.
Going to be at least medium carbon steel.
I re-heat treated a tire spoon once and -had- to
draw the temper on it but the rod was only about
5/8" and then the spoon was thin too. Drew it to
"spring blue" twice. It seems quite a bit harder
than a factory tire spoon. Had ground it down to
extra thin and it works great. :)
Alvin in AZ
ps- How's it hangin Ed? ;)
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.