Hardening O1 Tool Steel - What Am I Doing Wrong?

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ecdez

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Welp, I had my first crack at making a forming tool from O-1 tool steel. It's 1/4" thick, 1 1/2" wide and about 2 1/4" long. I'm using a dental oven that get's up to 2000º so heat's not a problem. Here's what I did.

First try.
Heat steel to 1490 (or so I thought)
Quench in oil
Once it's cool enough to handle it goes straight into the oven at 300º for 2 hours
Pull it out and run a file over it,.... scratches like it's mild steel.

Do a little more research for the second try.

Second try.
Heat steel to 1490 (I think)
Test with a magnet and it's not at all attracted to the magnet (according to the internet this is an indication it's ready)
Quench in oil
Check with file and it slides right off, yea! (not until later that I remember I used the flat end of the file and not a corner)
Once it's cool enough to handle it goes straight into the over at 300º for 2 hours
Pull it out and run a file over it (corner of the file),.... I can tell it's harder, but the file still digs in


I got the temperatures right off the sleeve the steel came in from Travers.
I'm using clean motor oil (last resort I know, but it's what I have on hand)
I did use the same piece for the second try which might have been a bad idea but I figured if it didn't work the first time then it's not hardened and can be tried again.


Anyway, I was hoping someone here might have some experience and can point out my obvious flaw in my process.

Thanks in advance!
 
ecdez said:
Welp, I had my first crack at making a forming tool from O-1 tool steel. It's 1/4" thick, 1 1/2" wide and about 2 1/4" long. I'm using a dental oven that get's up to 2000º so heat's not a problem. Here's what I did.

First try.
Heat steel to 1490 (or so I thought)
Quench in oil
Once it's cool enough to handle it goes straight into the oven at 300º for 2 hours
Pull it out and run a file over it,.... scratches like it's mild steel.

Do a little more research for the second try.

Second try.
Heat steel to 1490 (I think)
Test with a magnet and it's not at all attracted to the magnet (according to the internet this is an indication it's ready)
Quench in oil
Check with file and it slides right off, yea! (not until later that I remember I used the flat end of the file and not a corner)
Once it's cool enough to handle it goes straight into the over at 300º for 2 hours
Pull it out and run a file over it (corner of the file),.... I can tell it's harder, but the file still digs in


I got the temperatures right off the sleeve the steel came in from Travers.
I'm using clean motor oil (last resort I know, but it's what I have on hand)
I did use the same piece for the second try which might have been a bad idea but I figured if it didn't work the first time then it's not hardened and can be tried again.


Anyway, I was hoping someone here might have some experience and can point out my obvious flaw in my process.

Thanks in advance!
Click to expand...

Are you using the same oven for tempering that you used to harden? From your account, it sounds like you have a fairly short period of time between hardening and placing the tool in the oven for tempering. In all likelihood, the oven temperature was still much higher than 300º.

If your tool was hard after quenching, in all probability, the hardening part of the process was correct. That leaves the tempering process. The temperature should never exceed 300º at any time. Even a brief time will draw the temper and soften the steel. I have never been super strict about tempering immediately. The danger is that the fully hard steel is brittle and can crack if mishandled but with care the tool can sit for some time.

Finally, on a larger piece, you have to continue cooling during the quench until the core temperature drops befor your tempering temperature or the residual heat may draw the temper.
 
Thanks for the response.

I used separate ovens for the two different processes.

I did not do a file test on the first try between the two processes. One the second attempt I may not have been as thorough in my filing process as I should have.

One thing I did notice that I not expect is the oil did not flame up when I first placed the piece in. It smoked like crazy and bubbled but no flames. All the examples I saw online show some flames and I was a tad disappointed.
 
Verify that your tempering temperature is correct. You are measuring 300ºF, right? 300ºC would be 572ºF which would be a spring temper and fairly soft. What temperature are you running for hardening? O1 should be hardened at around 1500ºF and quenched in warm oil. Warming the oil reduces the viscosity which will improve convection flow around the quenched part.

Rather than experiment on your tool, you might want to work out your methodology on a piece of scrap.
 
I don't know about temperatures, I heat O1 to an incandescent red heat, drop it into oil and swirl it around until it "feels right." Not temperature, just time. A piece that size, 1/4" thick, i'd draw it at 400 F for half an hour. A file would skate on it at this hardness. I no longer have access to a Rockwell tester so I don't know how hard it is.
 
I usually do O-1 with a torch and go by color for drawing down. Mainly because I don't have an oven.
 
RJSakowski said:
Verify that your tempering temperature is correct. You are measuring 300ºF, right? 300ºC would be 572ºF which would be a spring temper and fairly soft. What temperature are you running for hardening? O1 should be hardened at around 1500ºF and quenched in warm oil. Warming the oil reduces the viscosity which will improve convection flow around the quenched part.

Rather than experiment on your tool, you might want to work out your methodology on a piece of scrap.
Click to expand...


I'm using a small Accu-Therm oven and I have the temp set at 1490º for hardening. The pre-set works but the attached thermometer is not which is disappointing. It was working last year and I ran a simple test to check for the accuracy of everything by melting aluminum and confirming the pre-set and actual temp while watching for the metal hitting the melting point. I'm fairly confident it's within 50º or so.

I did not knowingly let it soak at temperature. Once it showed as non-magnetic I dunked it. Not sure how long it was non-magnetic before I tested it though. I checked it around every 20 minutes or so it could have been at that point for 1 minute or for 19; no way to know. Might try to let it soak a little. It's only 1/4" thick so from what I read it it might not even be an issue.

The tempering oven is set to 300ºF according to the oven knob but I didn't think to see if the temp on the oven setting is accurate. It's an eastwood powder coating oven (fancy toaster oven).

I have the oil in an ammocan an set it on top of the Accu-therm to pre-heat. No idea what temperature it is but I can't lift it bare handed but I wouldn't call it hot but it is at the upper end of warm.

Good idea with the scrap. I thought of that after my first failure.



T Bredehoft said:
I don't know about temperatures, I heat O1 to an incandescent red heat, drop it into oil and swirl it around until it "feels right." Not temperature, just time. A piece that size, 1/4" thick, i'd draw it at 400 F for half an hour. A file would skate on it at this hardness. I no longer have access to a Rockwell tester so I don't know how hard it is.
Click to expand...

"feels right" --- I wish I had that experience. Guess it comes with time though.
 
ecdez,

Thanks for posting this question and keeping the replies coming.
I have no experience is this area, but am very interested in learning.
Please let us know what you learn!

-brino
 
I have hardened many hundreds of things,and recommend AT LEAST a tempering temp of 400º . 60 Rockwell C is really pushing it to the upper limit of hardness that will hold a decent edge,and will not be too brittle.

Plane iron makers seem to be trying to push the envelope of permissible hardness. Several of them make 60 RC irons.

I made a knife blade that hard years ago,and it would get razor sharp,but it would not hold the sharp edge very well. The sharp edge breaks off in microscopic bits,giving the impression that the edge is dull.
 
I have an old 220v Pottery kiln I use for hardening. It can go as high as 2300*F. I put a timer on it so after 2.5 hrs at 300*F it automatically shuts off and I let it cool down overnight. Comes out just right, file skates across it.
I get my son's old Rotella T motor oil from his diesel when he changes oil and it works great and gives the metal a nice color.
Works a lot better than new oil.
 
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