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.
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.
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.
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.
"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.
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:
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.
I've got a large cooking pot someone gave me. Not 5 gallon, but maybe 3 gallon or so? It should be larger, especially when heat treating something as large as that bar. Don't use plastic. If it catches on fire and melts, then you have a large pool of burning oil all over the place to deal with.
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 > Digging bar - sounds like it is a pry-bar.
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!
Mart> The "human end" you refer to is also an excellent tamper for packing the
I like to sharpen 'em up on that end like a fine thin hatchet. YMMV on that.
The other end is supposed to be "pointy" for dirt and rock. :)
I used up a bunch of those things digging ditches etc on the railroad, that's why I know technical terms about them like "pointy". Ok? I'm not trying to talk down to you using such technical terms, it's just from my high level of expertice and years of their use is all. ;) LOL :)
Someone cut it off?
A tamping bar either has a round butt-plate on the end like a giant nail or has a heavy retangular shape. The rectangular ones were for pole line work seems like, anyway that's what we used them for, to tamp the dirt down around a new pole we'd installed.
Yeah, pinch-bar or as the Messcans would call 'em "peen-chay bar".
I'm wondering if it needs heat treating? Just hammer it into the shape you want. ;)