Heat treating an old chisel

[richarddownunder]

Hi there

I was rummaging through my late-dad's tool box and stumbled upon an old battered cast steel Ward 1/2 inch chisel (with an embarrassing handle made from a bit of dowel). I thought if it was decent steel, I could turn a new handle and give it to my Bro on his birthday, as a keep-sake.

Anyway, started flattening the back and grinding an edge and found it was surprisingly soft. In fact quite useless - could file a nice bevel with a blunt file. I understand Ward were a reputable make but obviously some duds got through the system!

With nothing to loose, I had a go at re-heat treating it (well, the business end 1 inch or so) - up to cherry red and quenched it in oil. Result: it has hardened it to some reasonable extent (and it might even cut something soft) but a screwdriver can still scratch it easily (if not deeply as before), and that is before tempering.

So, is oil quenching the best approach? I have used this approach with small O1 blades I have made and have had really good results but don't know anything about these old chisels. It is possible that I haven't got it quite hot enough but my little blowtorch runs out of puff at cherry red. Is there a good 'rule of thumb' hardness test that is better than a screwdriver or file.

Thanks in advance.
Richard

 

[D_W]

Heat it a little bit past where you did before, to a bit brighter of an orange. If you see what looks like bubbling on he surface (happens slowly) as little splotches appear, then quench it (I believe that's carbon migration).

If your oil is thick, then you can pre-heat it a little bit, too - counterintuitive, but slightly warmer oil flows better - and move the chisel in the oil for a while when you quench so that it remains close contact with oil the whole time.

Yes on the oil, it's the way to go with the quench. you might get away with water, but you also may not. In order to get a little bit more out of your torch, cut a hole in the side of a small can and insert the torch through the side to hold the heat in. With the caveat here that if your torch is one of the type with an automatic igniter, that will burn it out.

If you get a good shot of hardening done, it will be almost impossible to get your chisel to be abraded on a natural sharpening stone, and files will do nothing but burnish the surface, then you can temper it back a little bit. Sometimes, you'll get lucky and hit the hardness mark you want after temper just with quenching. This is apparently not technically correct, but I've never had any issue with plane irons that I've done like that (it used to occur sometimes when I used a big weed burner on propane to heat irons and no shield around them. Now, I have a paint can forge and use a smaller torch and get to a higher temperature before quench. Always oil, though - thin cross sections of water hardening steel can crack when quenched in water.

 

[guineafowl21]

I’ve had good results with heating the end until a magnet doesn’t stick to it, then quenching in a can of oil. Move the chisel up and down (side to side might bend it), then leave it suspended in the oil till reasonably cool.

That’s hardening. For tempering, I use the oven. I can’t remember the schedule, but the internet should provide.

 

[Sheffield Tony]

Thin oil is best. Cooking oil is better (an less smelly) than engine oil.

Never have your quenching oil in a plastic pot. DAMHIKT.

I switched ot a MAPP gas torch because the regular plumbing sort of blowlamp don't really get anything large hot enough. A torch in each hand is sometimes needed !

You can look up tempering temperatures. If you use the oven for tempering, it will be at or near the maximum it goes. Putting the object in a tray of sand and giving it plenty of time makes the heating more even.

 

[The_Yellow_Ardvark]

Done a few Old chisiels for Men In Shed.

Bin the handle, clean the rust off.
Clean the blade until is a dull silver colour.

Redo the grinding angle and get the tip square.

Heat the tip about 1" from the end and let the heat travel o the tip. You are looking for a bright red even over the end.
Don't heat the end directly.
Then plunge into old engine oil. It will smoke and smell. So carry out correct safety precautions.

Remove when cold, clean the old oil off an clean up to a dull silver again.
The heat again with a softer flame, 1.5" from the tip. Keep the flame moving an watch the tempering colours travel up. Aim for a dark blue at the edge. Plunge into cold water.

Sharpen the end again and fit a replacement handle.

 

[richarddownunder]

Hi All

thanks for your help and suggestions. I did get a bit more out of my torch by making a little brick oven. This resulted in a bright red-almost orange colour for about an inch of the chisel.
I held it at that temperature for a couple of minutes and dunked it (within a second of removing the heat) in the same (warmish) vege oil and jiggled it up and down as suggested.

I still didn't think it was as hard as it should be (although definitely better than it was originally), then tempered it at ~170°C (a guess) along with the chips for dinner, and ground and honed an edge.

It takes a nice sharp edge but, on cutting a few notches in Sapele, I don't think the edge really lasts long enough to be a practically useful tool, certainly nothing like my Marples and Ashley Iles chisels, or other assorted chisels of various makes and ages, so I think I'll put it away for another day, slightly disappointed, with it's original 'handle'.

Can't win em all.

Cheers
Richard

 

[guineafowl21]

The idea of tempering is to knock back some hardness to make the chisel tougher. If you haven’t hardened it enough in the first place, the tempering will make a soft chisel softer.

Either you didn’t get it hot enough at the hardening stage (and ‘cherry red’ depends on experience and ambient light - use a magnet) or it didn’t cool down quick enough. Perhaps your pot of veg oil wasn’t big enough.

A file shouldn’t bite the chisel after the hardening stage. If it does, there’s no point in proceeding to the tempering. Disappointment will result. Have another go at some point - heat-treating opens the door to making your own tools. Good luck! (hammer)

 

[Racers]

I temper to a straw colour dark blue I'd to soft. Don't forget some of the carbon will have snuck off with the oxygen when you heated it so you will have to grind the edge back to get to the blood steel.

Pete

 

[D_W]

Figure some of that might just be at the edge, and is worth grinding back as mentioned above. I haven't experienced much of that, but generally do heat quickly and quench quickly (both to minimize migration/degrading of any of the steel in an open environment, and out of fuel thrift).

 

[richarddownunder]

Hi Folks

thanks again. I've made a few plane irons and various cutting tools of one sort or another out of O1 and they have worked well. I think this is the first time I haven't managed to get a properly hardened result on a small item (had problems with large old plane irons in the past, just not having enough heat). As mentioned, I ground it back a bit and honed it. The oil was about 1 litre so I think that should be plenty for a 1/2 inch chisel. Its been through the heating to various reds now, the last one bright red and a quick quench. In all cases, it hasn't quite got to that stage of the file skating over the surface as I'd have expected. It sounds like I'm doing the hardening right and this should respond like O1 does so it could be the steel composition, or maybe I'm still a few degrees under where it needs to be.

I've booked to take a forging class to make an axe head in a few weeks time (which I'm really looking forward to), so might take this along to see if it can be improved on.

Cheers
Richard

 

[Derek Cohen (Perth Oz)]

Two factors could produce a too-soft blade at the end of the process:

Firstly, you did not get the steel hot enough (bright cherry red is seen when the lights are off, not in broad daylight). Try two MAPS torches instead of one. Use a coffee can or fire bricks to retain the heat.

Secondly, try quenching in water before oil. Oil is better with more modern steels but the old vintage steels were water hardening. Quenching in oil is slower than water, and you want a quick quench to prevent the steel retaining heat and softening. This is probably why David has found that he does not need to heat treat blades after the initial quenching.

Regards from Perth

Derek

 

[richarddownunder]

Hi Derek

thanks for that suggestion, that seems to have done the trick! I water quenched it and it is a lot harder. Tempering as I type this in the oven with tonight's Quiche :roll: but it seems (pre-tempering) to hold an edge far better on the same bit of sapele and passed all the suggested hardness tests (i.e. file). The line in the photo is just where I got to with the diamond stone but it has polished up at the business end pretty well (although its not that clear in the pic).

So, next job is to make a handle! I need to borrow my mate's lathe lathe for that!

Thanks
Richard

 

[worn thumbs]

I'm glad to learn that a successful outcome was achieved.I'm also not surprised that a water quench worked as I would be reasonably sure that the overwhelming majority of tools through the ages were water quenched.I have successfully treated a gouge that was soft in much the same manner as has been described here-but with the exception of normalising it first.I know that oil,and whale oil in particular,was long prized by people forging tools and I also remember that we have learned a lot since those days. For those interested in the details I remember a little of the science behind the process being described by Prof J.E. Gordon in his excellent book "The New Science of Strong Materials". The part that remains lodged in my mind is that the advancing front of crystal precipitation travels through the steel at about three thousand miles per hour.I doubt that my great grandfather knew too much about the precise science when he worked at his forge but he made a living.

 

[dannyr]

traditionally water quench fine if the urine of a red-headed boy

 

[D_W]

David has found that he does not need to heat treat blades after the initial quenching.

Regards from Perth

Derek

Clarifying, not picking fights. That was the case with oil hardening steel where I didn't get as much heat as I probably should have.

When I get good heat, then the O1 blades have come out far harder than usable (they can't be reasonably sharpened on anything other than diamond) and they show a tiny chipping characteristic rather than smooth wear when used. Funny enough, total edge life seems to be about the same (so there isn't a great detriment to not tempering those, but there's no reason for them to be harder to sharpen to just wear the same amount and leave a less nice surface).

I'd suspect that richard's chisel was hardened in oil at the factor, but something chosen to get a faster temperature transition. I use soy oil (as far as I know) that flows well without having to be too warm. I'm sure the choice of oils makes a difference.

Razors are also water hardening steel, but quenched in oil (probably to prevent cracking).

I don't know the transition temperature requirements for various steels other than XHP (LVs V11) only because I noticed that once you get a segment of any of it hot, even cutting it, it will not be annealed easily. It turns out that it hardens with temperature transition at 50ºF per minute (!!!!) or faster. A garage hand tooler is best served to not let it get hot while working it.

 

[richarddownunder]

So, after spending some time re-heat treating this old Ward chisel that used to belong to my dad, here is the final thing after knocking out a new handle on a mate's lathe this afternoon. Before and after. Feel quite pleased with the end result and I really like the feel of this handle pattern.

Cheers
Richard

 

[gregmcateer]

Looks great, (assuming new is the top picture! :shock: )
Good work, sir

 

[AndyT]

Nice rescue job, well done.

 

[El Barto]

Interesting thread and looks great. I’d like to try this myself but have always been scared of ruining an old tool in one way or another.

Do you think the edge will hold up over use?

 

[richarddownunder]

Thanks guys. Yes, the top picture, although it's a bit hard to tell - the changes are subtle :lol: . I have used it a bit and it feels OK to sharpen and cuts well enough...edge retention seems good but haven't quantified that.

As it was, it was useless so there wasn't much to loose by trying and it doesn't seem to have suffered much from the multiple heat treatments. I suppose warping might be the biggest potential problem but this one has stayed straight (well as straight as it ever was). There are some good comments on this thread about that - I think quenching straight down into the oil (or water) may help in that regard.

Cheers
Richard