Michael, everything sounds good, but I was wondering how you are cooling the blade after each thermal cycle? I usually bring 1084 up to 1550 to 1600 then air cool until black, then do the 1500 and air cool until black, then the final cycle at 1400 to 1450 and place in vermiculite until cool. Then do the rough grinding and prep for quenching and tempering. 1500 is a good temp for 1084, and tough quench should work just fine. I temper at 425 for two two hour cycles. I hope this helps, let us know.

Brion

Brian I let it air cool in between thermal cycles. I don't understand why the grain is so big.

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Brian I let it air cool in between thermal cycles. I don't understand why the grain is so big.

Having a control is very important in successful heat treat troubleshooting. Do a test piece of just the 1084 stock that has had no treatments by you, break it and check the grain. If the grain is huge on it then start calibrating your oven. If the grain is finer then start calibrating your heat treating procedure. Your normalizing and previous treatments are not out of line and it would take much higher temperatures to set your grain to a size that would still be overly large after even a single quench. Grain refinement is not the involved procedure most think it is, under normal circumstances just one heat cycle can often fix grain to an acceptable level and this is why accuracy on the quenching heat is so important.

The folks at Evenheat are pretty good to deal with but they just make kilns, steel grain size as an indicator for calibrating temperature would be a pretty alien concept to them. They would be more geared toward using another pyrometer type source to double check things. I have burned out so many PID controllers that I always have a surplus of what amounts to very expensive pyrometers to do these cross checks with. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//sad.gi f' class='bbc_emoticon' alt=':(' />

What had you done to the steel prior to using the oven?

Karl, when I did the test, I had not done anything to it, simply brought it straight out of the tube from Aldo...

thanks for all the input guys!

MichaelP

Michael,

I don't see anything obviously wrong with your technique. I don't use temps quite this high but yours aren't so much different that it should be a huge difference to what I do. Something that I immediately thought of is the amount of time bringing the blade up to temp. Are you placing the blade in a cold oven or a pre-heated one?

Hopefully Kevin will chime in here with some ideas here on this.

Gary

Gary the first test piece the oven was cold but the second piece I preheated it the grain was a lot better but not glass.

Thanks for the help!

How long was your soak time?

Gary

I soaked it 5 min.

Good question Gary.

As the oven is coming up to temp, especially if you have the oven set for FULL on the ramp setting, the coils FAR!! exceed your target temp of 1500 degrees. Enough, in fact, that you may be inadvertently increasing grain size.

I have a rule that I will do NOTHING with my oven until the temp has stabilized for a minimum of 1 hour.

The higher the temp, the longer I will have it stabilize.

I think what I would do is:

Keep in mind that when I say "soak", this is AFTER the steel has come up to temp, which in my pre-heated oven takes about 4 minutes.

Preheat the oven to about 1550 - soak steel 3-4 minutes - cool until all color is gone, about a minute, and quench to cool. (This hurts nothing, as the steel has reverted to pearlite. You're just getting the steel cool again so you can get back to your cooling-off oven.)

Stabilize oven at 1500 - soak steel 3-4 minutes - cool until all color is gone, about a minute, and quench to cool. (This hurts nothing, as the steel has reverted to pearlite. You're just getting the steel cool again so you can get back to your cooling-off oven.)

Stabilize oven at 1450 - soak steel 3-4 minutes - QUENCH!! until cool.

Let oven stabilize at 1250 and let steel soak at that temp for about 1 1/2 hours.

Pull from the oven and quench.

Thanks Karl. I was wondering about the temp possibly overshooting in the heating up process.

How long does it take for y'all's ovens to cool down to the next lower temp and re-stabilize? Do you open the door to speed things up? In general, how long does it take to go through the whole cycle/series?

Thanks Karl, that makes sense and might just be my problem. I appreciate the info from everyone, I need all the help I can get.

Thanks again

Michael P.

Phil, the temp does not "possibly overshoot". It's running full wide open!!

It gets hot in there. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//ohmy.gi f' class='bbc_emoticon' alt=':o' />

For the most part, I use my forge and temp control for my post-forging thermal cycles and have it pretty well dialed in.

I do use my oven for some other steps, however, including tempering.

I even use it for a thermal cycle during my rough grinding to dissolve my carbon that was spherodized in the last step of my post forging process.

Just take the knife out and leave the door open with the heating cycle turned off.

Re-set the target temp.

You may just have to diddle with it for a bit to get it stabilized at the next temp.

Not much choice.

Whenever I know I'm going to be using my oven at some point during the day, well in advance of this I set my oven for my desired temp sometimes hours in advance.

I really, really want the entire oven's mass stabilized at the temp I want and not just the chamber's temp.

Just think ahead a little bit.

I have never noticed the use, or non-use, of the oven reflected in my electric bill. <img src=' http://www.americanbladesmith.com/ipboard/public/style_emoticons//biggrin.gi f' class='bbc_emoticon' alt=':D' />

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Thanks Karl. I was wondering about the temp possibly overshooting in the heating up process.

How long does it take for y'all's ovens to cool down to the next lower temp and re-stabilize? Do you open the door to speed things up? In general, how long does it take to go through the whole cycle/series?