What when wrong with my heat treatment?

Keith_H

Keith_H

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Jul 20, 2007
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I heat treated my knife today in a kiln with a thermo-couple at 1475, soaked for 15 minutes and quenched in canola oil. I then tempered at 400-500 degrees for 30 minutes, I would have tempered more but I ran out of time. I take it home, and notice that my files will still bite into it! It is hard to file but they do not skate. I need to have it heat treated for the weekend so I want to know what went wrong. Thanks!
 
What was the material? How long did you quench it for? At what temp was the canola oil when you quenched?
 
A good file will bite a bit into steel after tempering. Of course, I tried to file in a few thumb groove once as an afterthought, and though I scratched up the spine a bit with my needle file, I couldn't get it to cut. However, it didn't skate the file as it did right out of the quench. Do your quick file test out of the quench before tempering.

--nathan
 
Sorry

The steel was O1, and the oil was room temperature because I had no way of warming it at the time. I figured that it would make the canola slow enough for O1. I only left it in the oil for about a minute or two because it was cold enough to handle.
 
Put a scrap piece of steel in the heat treat oven to heat up while the blade is getting to temp for the soak, then before you soak fully, take out the scrap piece of steel and put it in the oil. that will warm it up enough. The canola is faster when it isnt warmed up.
A good thing about O1 is that it is pretty forgiving when it comes to heat treating, Just normalize and do over.
 
Ok, I thought that the oil got thinner when heated an was faster. Thanks for the tip on the scrap steel.
 
There is no settings on this oven, just a dial with numbers 1-8 and a thermometer with a needle, I tried to keep the needle between 1450 and 1500 by turning the dial. It is harder, I just don't know if it is 60rc
 
Hi Keith

The weekend is kind of short notice, so I don't know what to suggest. O1 is pretty forgiving, so you may have it OK. You mention temper at "400 - 500" According to the Crucible charts, 400 gives 62+ and 500 gives about 59 - a huge difference. I would think a file would bite a bit into 59.

How did you protect the blade from decarb? I use turco on O1 with good results. If there is decarb, the layer may be thin.

Lastly, the kiln with thermocouple may not be accurate. Occasional testing of temperatures is a good idea.

I can't do much by the weekend, but if your time frame increases, I'll be glad to Rockwell for you. (Best if you grind down to a clean spot) We generally only do our own blades with oil quench now, but if it's important and pressing, we'd give it a shot for you.

Rob!
 
Thanks Rob, I tried to keep the temperature at 400 degrees but occasionally I had to crack the door to adjust the temperature. I did not do anything to prevent decarb, maybe I should have. The school's oven may not be accurate I have never seen anyone else use it, but then again, I didn't see anyone use the milling machine for 3 years.
 
As long as your blade went from the heat to the oil fast enough to prevent it from cooling too much between the two you should have reached a respectable enough hardness after the quench. Your temper was perhaps a little short, but it should have been OK if not ideal.
Decarb can be a bugger, especially if the edge was ground quite thin before the quench. Try filing at one spot on the edge for a little and see if the file suddenly starts to skate. I've had 01 blades with thin edges that needed about almost 1/32 taken off the edge before I got back to good steel after the H/T.
 
For o-1 just re-do as stated before, I soak my o-1 at 1500 deg for 1/2 hr, temper in Olive oil if quench oil not available at 120 deg, Then check with a old file and you should see where the steel cut the file shiney area on file, no cut in steel. Then temper in a oven 300 to 350 for one hr RC 62/64 400-450 1 hr RC 58/60 800-850 1 hr RC 48/52. That is what came on the last 0-1 from Starrett lot# 8088627 for 3/16 x 1 1/2" for the RC figures and harding directions I will temper twice at 2 hours but that is just me at 400 deg. You may also check the location of your thermocouple and make sure you are getting the reading as close as possible to where the blade is located.
 
Thanks, guys. I tried comparing how well annealed o1 will centre punch vs my knife, and they were about the same, although that wasn't conclusive. I don't know if it is decarb or just a poor heat treat. Should I redo it with warm oil and to try to bring it from heat to oil faster?
 
For what it's worth, I always heated my canola oil to around 135 for quenching O-1. Heating helps improve the viscosity characteristic of the oil more than it changes the speed. A thick oil will form a vapor jacket and insulate the steel slowing the cooling perhaps too far, where a properly warmed oil will flow better and the vapor jacket will be more easily displaced by the oil with gentle tip-butt agitation.

--nathan
 
Next time I will heat it, thanks Nathan. Is there any improvised anti-decarb coating I can use?
 
A common file stops biting around 58Rc. That is why the file test is not the diffinative hardness test that many believe it to be. It is only an indicator that your blade is something over 58Rc.
 
Try tempering it longer. I tempered mines two times in a standard oven at 450 for 2 hours each (cool to room temp in between), and it came out great.
 
I am pissed off. I did it again today, the oil would hardly warm at all, and it is not very hard at all. The worst part is that the edge is warped a little in the last inch. I wish I had a new oven :grumpy:
 
Keith_H said:
I heat treated my knife today in a kiln with a thermo-couple at 1475, soaked for 15 minutes and quenched in canola oil. I then tempered at 400-500 degrees for 30 minutes, I would have tempered more but I ran out of time. I take it home, and notice that my files will still bite into it! It is hard to file but they do not skate. I need to have it heat treated for the weekend so I want to know what went wrong. Thanks!
Click to expand...

first, if you tempered THEN tried the file test, the file should bite slightly.
The file should skate on a full hard blade WITHOUT DECARB, as soon as you temper it you are no longer dealing with a full hard blade.
try fighting the decarb by putting some natural wood charcoal in the kiln with your blade,the charcoal will absorb free oxygen, producing carbon monoxide and carbon dioxide. follow the soak time and temperature reccomendations of the manufacturer. extra soak time will not hurt, too short will.
heat your oil to 130.
Be sure to leave a few thousandths extra metal to allow for decarb, also leave your edge about as thick as a dime until after HT and tempering to minimize warpage

good luck
-Page
 
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