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Case hardened steel

trlvn

trlvn

Ultra Member
Hi:

I've got a chuck of steel that appears to be case hardened. Do I have to fully anneal it to work with it?

The piece is nearly 6 feet long and roughly 2-3/4" diameter. There are keyways and flats so I think this was probably a shaft in a machine originally.

I ruined a bandsaw blade cutting off a couple of 5 inch chunks. When I first chucked a piece in the lathe, I noticed that an old center hole was still in the one end...although nearly full of rust. I thought I would deepen the center hole a little but my HSS center drill would barely touch it. I tried carbide inserts to clean up the OD but the lathe was jumping, screeching and all-around unhappy.

Figuring I had little to lose, I tried to 'heat treat' the metal in the BBQ to lower the hardness. I ran it at max heat (over 550F) for nearly 1.5 hours. (It took about 2 hours to cool afterwards.) Trying to machine the OD might have be _slightly_ easier...but not much.

It was @CWret that pointed out that it might be case-hardened. So I turned the piece around and tried to work the saw-cut end. It machines: but only just. See below. I get quite small shreds of metal and the lathe is working pretty hard to take a pretty small depth of cut.

Case hardened IMG_5295.jpg

Any thoughts on salvaging this metal? Even if my buddy fires up his coal forge, it is going to take a long time to get the 5" pieces up to a red heat. There is no way to get the 5 foot piece in his forge.

I've seen a couple of Youtube videos where Casenite was used to case-harden a piece of low-carbon steel. I don't recall ever seeing the piece being heat-treated (tempered) afterward. Is tempering not a thing with case-hardening?

Craig
 
If it was case hardened you would be able to do the facing cut. I would venture that this chunk will have to soak at 770C or higher for at least an hour, then let cool slowly.

Case hardening is only going to produce a thin hard layer, nothing deep. Red hot, dip in casenite, reheat to red hot, dip in casenite, then quenceh in oil or water to harden the outer layer.
 
trlvn said:
Hi:

I've got a chuck of steel that appears to be case hardened. Do I have to fully anneal it to work with it?

The piece is nearly 6 feet long and roughly 2-3/4" diameter. There are keyways and flats so I think this was probably a shaft in a machine originally.

I ruined a bandsaw blade cutting off a couple of 5 inch chunks. When I first chucked a piece in the lathe, I noticed that an old center hole was still in the one end...although nearly full of rust. I thought I would deepen the center hole a little but my HSS center drill would barely touch it. I tried carbide inserts to clean up the OD but the lathe was jumping, screeching and all-around unhappy.

Figuring I had little to lose, I tried to 'heat treat' the metal in the BBQ to lower the hardness. I ran it at max heat (over 550F) for nearly 1.5 hours. (It took about 2 hours to cool afterwards.) Trying to machine the OD might have be _slightly_ easier...but not much.

It was @CWret that pointed out that it might be case-hardened. So I turned the piece around and tried to work the saw-cut end. It machines: but only just. See below. I get quite small shreds of metal and the lathe is working pretty hard to take a pretty small depth of cut.

View attachment 51634

Any thoughts on salvaging this metal? Even if my buddy fires up his coal forge, it is going to take a long time to get the 5" pieces up to a red heat. There is no way to get the 5 foot piece in his forge.

I've seen a couple of Youtube videos where Casenite was used to case-harden a piece of low-carbon steel. I don't recall ever seeing the piece being heat-treated (tempered) afterward. Is tempering not a thing with case-hardening?

Craig
Click to expand...

pardon me if I suggest something stupid... but usually case hardening does not penetrate that deeply. So if you know a shop in your area with a large lathe perhaps they'd turn off the case for you using a ceramic insert?

My heat treating oven is only 18" deep or I'd offer to try to anneal it
 
gerritv said:
If it was case hardened you would be able to do the facing cut. I would venture that this chunk will have to soak at 770C or higher for at least an hour, then let cool slowly.

Case hardening is only going to produce a thin hard layer, nothing deep. Red hot, dip in casenite, reheat to red hot, dip in casenite, then quenceh in oil or water to harden the outer layer.
Click to expand...

That's what I thought--need to heat to critical temperature (770C or 1400F) to anneal.

I'm having trouble imaging _why_ a shaft would be case-hardened. In old line shaft setups, did this prevent the loose pulley from wearing away the shaft?

Craig
 
TorontoBuilder said:
pardon me if I suggest something stupid... but usually case hardening does not penetrate that deeply. So if you know a shop in your area with a large lathe perhaps they'd turn off the case for you using a ceramic insert?

My heat treating oven is only 18" deep or I'd offer to try to anneal it
Click to expand...

I don't know any local shops that would have that kind of capacity. Cost is a factor too. I really don't _need_ that much stock in that diameter. I got it for cheap from an auction. (Maybe the case-hardening is why the former owner never used it!) I've found a place recently that has offcuts for under $1.50 a pound. (Beach Road Steel, Hamilton.) My thought had been to cut slices to turn into model engine flywheels. Since this stuff seems to be a bear to machine, I'm probably better off to spend a few more dollars and get something easier to work with.

Craig
 
I'm not much of a metallurgist but I think there are applications where an entire shaft may be heat treated for increased strength. Surface hardening only I would expect if it was smoothly ground & had to run in a bushing for example. But maybe the surface we are seeing has since degraded from that state. Yeah, if you are spending money on gas, carbide tooling & wear & tear on the machines, best to just buy what you know you can live with, at least for small quantities. Too bad, it looks like a nice big log.

 
If it were 4340 ( a common shaft material) and heat treated, 550F would not touch it either.

If it were to be ground then case hardening is on the table, because case hardening grows the diameter, usually a little unevenly. More common to heat treat 4340, anneal, then clean up with emery. If borax is used there is little scale to remove.

some thoughts o_O
 
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If I remember case hardening right, it generally does not leave a very thick case, memory says, maybe .010 inch.
I usually give these kind of things the old file, and hand hack saw test, if an old file and or a hack saw blade will not mark it easy, there likely will be problems. A clue would be, you wiped a bandsaw blade cutting it. Another clue are the small, almost like cast iron chips. Setup dependent. Rusted metal also seems to harden a surface slightly, to say nothing of the rust itself causing trouble.However as you did cut off some pieces it means carbide will likely machine it. Try machining 1 of the ends you cut, start in the center and work to the o.d. of piece, if case hardened, outer edge will be tougher to cut.
Just my 10 cents worth, inflation and conversion to U.S., means 2 cents.
 
The joys of mystery metal. I've had case hardening done to 50 thou, that was a 24 hour soak and the heat treater said that is about as deep as you can go. It's a function of the soak time. Cases are usually very hard as you can leave them untempered after heat treating as they are supported by the ductile material underneath. I agree with others its not case hardened if it was tough all the way through.

As for annealing, the bbq tempered it a bit however to anneal you've also got to start a LOT higher. Might vary by steel, but like 1400F and it has to be held at that for a period of time then it needs a long cool down. I've used my oven or a welded steel box full of fireplace ash to give a slow cool down, both work well, but I doubt two hours isn't enough.
 
A couple years back one of the guys at work was dumping the scrap into our shared bin with the shop next door, and noticed they had tossed out a 12' stick of 3" mystery steel that was through hard. No markings on it (that's why they were scrapping it), but it's probably in the mid rc50's hard. We dug it out (with their permission of course), and I chopped it in half with a zip wheel and snapped the rest. I split it with another cheap scrounger coworker. I always figured I could try and anneal it in one of the big annual brush fires, but have never got around to it yet.....it's only been about 8 or 9 years....I doubt I'd get it hot enough to really do anything without putting a lot more time and effort into it than it's worth.
 
If it were mine, I'd cut it into useable chunks with a torch, and then try annealling it.

I'd start with whatever furnace I had. Wood stove overnight first, and keep using hotter ovens till it cut.

What do you have to lose? Win or lose, it's more fun than a barrel of monkeys!

I've always been a fan of woodstoves...... Amazing inventions.
 
For induction hardened shafting I found if I ground a slot with the angle grinder through the hardening, I could cut it with the bandsaw into workable sizes. Induction hardening goes in about .080. You can use a tiger torch and a few firebricks to box in the piece, and then heat it up. After heating, I then bed it in floor dry and cover it with more floor dry. Leave it til the next day cause it can take 6 hours to cool down.
I have a home made propane burner I use for lead casting that I use at this time of year for annealing, cause we aren't in the heating season yet, and wood stoves are not fired up. I recently annealed a 3" x 3" piece hard throughout. Heated to 870 by the heat gun reading, and into the floor dry.
 
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