Heat treating small tools such as pry bar issue

S

SamaraVolk

Joined
Apr 17, 2014
Messages
93
All,
I've been making small pry bars and Kiridashis lately out of scrap carbon steel. One issue that comes up is that they do not hit "non magnetic" at the same temp range as my knives. I am at 1500f and they are still magnetic. I can not vouch for the accuracy of my oven but knives are not at issue. The only thing I can think of is the ceramic floor is a heat sink and draws heat from the items. I moved them closer to the elements and still have the same problem. Any thoughts? Thanks
 
I would say that either something has gone out of whack with your oven, or that maybe you aren't letting them soak long enough to actually get to temp. They could just not be equalized to oven temp when you are checking them. I would assume they are thicker than your blades, so they will take a bit longer to heat through. I would also suggest a blade holder for the oven so they can stand on their spine instead of lay flat. A piece of angle iron with some slots cut into it will work for that.
 
I have a blade holder. Others have said it can act like a heat sink if you put the blade edge on it and not the spine. The pry bars are 1/4"and I put them into a cold oven. They are in there until I remove them for quench.
 
How long are you letting your oven itself soak at temperature before putting any blades in? This would include a blade holder as well. If the oven has "equalized", you shouldn't have problems heating small and larger pieces alike.

Now, if it is out of calibration, that's obviously another matter. IIRC, many PID manuals suggest dunking your TC into a cup of ice water and checking that it reads 0C or 32F. If it's off a a degree or two, most modern PIDs have an adjustment to bring it within range. You'll have to consult your particular PID manual on how to do that though.
 
I put my blades in while the oven is cold. They remain in there the entire time until quench. I don't have a separate TC. I only have the one on the oven. I am looking for another TC I can check my oven against.
 
SamaraVolk said:
I put my blades in while the oven is cold. They remain in there the entire time until quench. I don't have a separate TC. I only have the one on the oven. I am looking for another TC I can check my oven against.
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I'd recommend heating the oven without the blades in it, and letting it equalize. I normally like to give my oven around an hour at temp while I'm working on the final touches of blades that will be going in. When your oven is initially warming to set point, it's going to have some swings in temp before it finds equlibrium. In the grand scheme of things, this may not effect much (I really can't say), but I don't think there's any benefit in heating the blades with the oven either. You'll get more consistency and accuracy letting your oven soak at set point (assuming your oven holds a decent amount of heat and is insulated relatively well.) If your oven loses heat quickly, there are insulating coatings you can put in it to mitigate this some.

As far as calibrating, you shouldn't need a separate TC/PID set up. Just remove the TC from your oven and calibrate it. You can get a separate set up, calibrate it, and then compare readings when your oven is at 1500F, but I don't think you'll see much benefit in doing it this way. Others may agree or disagree.

You might also try some tempil sticks at various set points and see if they melt accordingly. I think standard table salt also melts right around 1475 or 1500F, so that may be another little sanity check you can try.
 
knife to a gunfight said:
I'd recommend heating the oven without the blades in it, and letting it equalize. I normally like to give my oven around an hour at temp while I'm working on the final touches of blades that will be going in. When your oven is initially warming to set point, it's going to have some swings in temp before it finds equlibrium. In the grand scheme of things, this may not effect much (I really can't say), but I don't think there's any benefit in heating the blades with the oven either. You'll get more consistency and accuracy letting your oven soak at set point (assuming your oven holds a decent amount of heat and is insulated relatively well.) If your oven loses heat quickly, there are insulating coatings you can put in it to mitigate this some.

As far as calibrating, you shouldn't need a separate TC/PID set up. Just remove the TC from your oven and calibrate it. You can get a separate set up, calibrate it, and then compare readings when your oven is at 1500F, but I don't think you'll see much benefit in doing it this way. Others may agree or disagree.

You might also try some tempil sticks at various set points and see if they melt accordingly. I think standard table salt also melts right around 1475 or 1500F, so that may be another little sanity check you can try.
Click to expand...


Thank you very much. I'll give your suggestions a go.
 
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