Heat treat confusion

Dan Pierson

Dan Pierson

Joined
Nov 24, 2003
Messages
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It was finally time to do the first heat treat in my new shop. While the Evenheat is coming up to temp with 2 O1 blades in it (about 25 minutes to 1469 -- I'd set 1475 and it kept oscilating between those 2 for the hold time), I tried out my used Ames #2 tester on an Rc 63 test block. First test showed 62, attempts to repeat that all went down, some into the 30's and 40's. Maybe I should bring this to the hammer in and have someone show me how to use it?

In the meantime I let the blades soak for 12 minutes then quenched them in 125 degree AAA and quickly (30 seconds to a minute of quenching time) stuck them in a 425 degree toaster oven for 2 hours.

After first tempering, a file would scratch them and they tested in the Rc mid-40's, this time the test block showed about Rc 52. I don't know if I've screwed them up or not :confused:

I'm really tempted to finish grinding them and put handles on them just 'cause I want to get something done! But maybe I'd better bring them along the HI too...

Any advice? This didn't go as smoothly as I was hoping for...

Dan Pierson
 
What about decarb on the blades? Wouldn't that screw up your Rockwell test results if it's not ground off? As far as the inconsistant results on your hardness tester with the test block, I haven't a clue. I recently got a tester and had similar problems. I'm about to pay someone to come out and calibrate/check it for me. Hopefully I can get them to show me how to work it while they are there.
 
Try wrapping the blades in heat treat foil/ tool wrap (with a small piece of tissue inside), also try soaking for longer -try 30 minutes once the oven reaches 1450.

Quench in transmission fluid or olive oil. Make a basket out of chicken wire in the quench tank and raise and lower the steel in the oil for better circulation and cooling.

Temper at least twice (three times is better) at 375 for 2 hours each time, allowing the steel to return to room temperature between tempers.

Finally, make sure you really do have O1. Good luck!
 
First, get somebody to show you how to use the Rockwell tester. Don't change your quenching oil. If you're using Park's AAA, then there's no reason to go back to the stone age with tranny fluid or olive oil. Methinks you just need to soak a tad longer and make sure all decarb is off before testing for hardness.
 
Something must be really wrong here:

- you'd only need to soak for a few mins, @ 1475F, not 30. 30mins will produce SERIOUS decarb/scale problem
- don't use foil with O1 - you'd need to free up the blade be4 quench
and you only have 1-2 secs to do it. No easy task
- to fight decarb, use Brownells PCB (PBC?) powder. Look for Primos'
description of the process.
- r u sure about yer steel ? Get a smallish piece, heat it up cherry red
with propane torch or whatever, dump into water. Test w/o temper - you
should be in ~63RC range. If it is any softer than that, you have bad steel

I do feel you just decarbed the steel way too deep and that's why
tester is showing it being very soft.
 
I dont think 30 minutes is extreme at all based on what ive seen lately. O1 needs longer soak times than other carbon steels from what I have read all over....

My concern may be with the foil, too. O1 has a longer nose than others, but is it possible you didnt get it out of the foil, into the quench AND below the nose in time?

As far as decarb goes, I almost re-HT'd a blade yesterday that I thought did not harden. I put a convex edge on it, took a bit of meat off the cutting edge, and it performed perfectly. If a couple sharpenings are all resulting in the same, I'd start looking at your quench. Are you just dunking and letting it sit there? How hot is your quenchant? Take it step by step....

RC 40 seems WAY too soft for 01. Id think you could get 41 by air quenching....something is off!
 
Since every post so far seems to have an entirely different direction on how to HT the stuff, if figure heck why not give my method as well and add to the confusion:D

This is what I would do- first, the rockwell readings are meaningless until I can get the thing calibrated and reading consistantly. If I have a 63 test block and I cannot get it to read 63 then the next best thing I can do is to see if it is consistantly 62 and use that to get a ballpark as to how far off it is and compensate with some simple math. If I cannot get the thing to read the same within a 4 point range I abandon it until it is calibrated.

Next if I have Parks AAA, I am happy that I do not need to adjust this part of the equation at all, since I already have the best tool available to do this part of the job, if it is fresh and labled correctly, it is the most fool proof part of the whole works.

If I am using an oven I protect against decarb. Ovens are perhaps the worst culprits for oxidizing atmospheres since they are just superheated ambient air. I either inject some inert gas into the kiln, or I coat the blade with either foil wrap, or a compound. The foil can be done in such a way that the blade can be quickly pulled from one end and freed in the ample time one would have to quench O1. Even after it hits the oil it has around 6-8 seconds to cool below 1000F. to avoid any problems; it doesn't sound like much but in quenching it is an enormous ammount of time.

I remember that because of the open air nature of ovens, my blade will need extra time just to reach temperature and then enough time to soak. Soak time could be from 10 to 25 minutes at 1475F, depending on what I did to it, as far as heating, before this.

Most importantly I would not use my rockwell tester to determine success until I had it zeroed in and working well. Some folks say some of us rely on those HRC numbers too much, sometimes they are correct in saying this, often they are not. If we allow the numbers to mislead us, they are correct in saying that, and those numbers are only as good as the testers accuracy.
 
http://www.crucibleservice.com/eselector/prodbyapp/tooldie/ketos.html

Excerpts:

High Heat: 1450/1500F(790/815C), hold 10/30 minutes at temperature.
Quench: Quench in oil to hand warm, 150F(65C).

Temper: 350/600F(175/315C); hold one hour per inch of thickness, two hours minimum, four hours preferred.

--
According to the chart, for 58-60HRc, temper at 500F

I've not done any heat treating yet, but I'm planning on sticking a meat thermometer to the side of my quench, since all the specs are temp based...

Hope that helps.
~ Dagr
 
Thanks a lot for all the advice!

It's Precision-Marshall Presco O1 from toolanddie.com. They've got a pretty good rep.

I will bring the tester to the HI to see in anyone can show me how to use it correctly. Decarb was one of my worries -- the blades were in there for a total of 35+ minutes -- I don't know what temperature decarb starts at.

In response to a comment of Kevin's in another thread: the blades were fuming a bit but oil was dripping off visibly when I took them out of the quench. I did have one flare up on the first blade from not quenching deep enough (just the tang, I think).

Sounds like I need to soak even more. Would it be better to bring the oven to heat then put the blades in?

I just ordered some PBC from Brownells.

Parks claims that AAA should be 125-140 degrees. I plead guilty to going with 125 because I ran out of patience.

David -- I agree that the readings from the tester I don't understand sound way off. You're close to convincing me to just finish the grinding and try some empirical tests. I think I left enough steel for that (meant to), but there's clearly not enough to do it twice.

Thanks again,

Dan Pierson
 
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