For those that heatreat in a electric oven,after you normalize is it routine to clean the decarb from carbon steel blades?And one more question,after you normalize.Is it necessary to heattreat right away? Thanks in advance for your advise.In case it matters the steel is 15n20 and Ala Damascus.
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Thermal cycles to normalize ?
- Thread starter gredpe3
- Start date
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- Dec 21, 2006
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That is a great question. I have done both, after asking exactly the same here. This is what I do, now others may come along with better advice. I'm not always doing things properly!!!!!
During the normalizing and thermal cycling I leave the scale on.
Once the last thermal cycle is done, prior to hardening, I remove the scale.
So when it goes into the austenitizing temp and soak, it's clean.
To answer your second question, NO. It is NOT necessary to heat treat right away.
However, some smiths will quench their knives during thermal cycling. Usually this is to set up for a spher anneal. But let's say you are obsessive and want what you think is the ultimate in grain refinement, and are quenching during thermal cycling. I certainly wouldn't wait too long between that last quench and the final austenitizing!
During the normalizing and thermal cycling I leave the scale on.
Once the last thermal cycle is done, prior to hardening, I remove the scale.
So when it goes into the austenitizing temp and soak, it's clean.
To answer your second question, NO. It is NOT necessary to heat treat right away.
However, some smiths will quench their knives during thermal cycling. Usually this is to set up for a spher anneal. But let's say you are obsessive and want what you think is the ultimate in grain refinement, and are quenching during thermal cycling. I certainly wouldn't wait too long between that last quench and the final austenitizing!
- Joined
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If you are a stock remover and want to thermal cycle, do it while it is still a bar of steel.
If you forge, thermal cycle after you forge, before you clean up to shape.
Don't clean the decarb off in between cycles... you'll do that as you pre-grind before final heat treat. If you have done significant grinding or suspect that you over heated certain areas while working, run a stress relieving cycle prior to final heat treat. Heat the blade to 1200F-1300F and let cool. Check for any warping.
Like Stu mentioned, some folks like to throw a quench in the mix while thermal cycling. Here is my typical routine...
-Forge
-Heat to 1650F-1700F, cool back down to magnetic
-Heat to 1500F-1550F, cool back down to magnetic
-Heat to 1475F, oil quench
-Heat to dull red(still magnetic) 2-3 times, cool to black, quench
Once the piece becomes magnetic it has formed another structure and is ready for the next cycle. The last dull red heats are what I call a "redneck spheroidize". It is a sort of subcritical anneal or what I also call an "extreme tempering". The smart guys will know what the proper terminology is... I just know it works for me, so until I find a better way, within my means, I'm sticking to it.
I don't like using ash/vermiculite/perlite to slow cool from solution. I think that has to do with the formation of coarse pearlite and in the case of hypereutectoid(+.90% carbon content) much worse things can happen.
If you forge, thermal cycle after you forge, before you clean up to shape.
Don't clean the decarb off in between cycles... you'll do that as you pre-grind before final heat treat. If you have done significant grinding or suspect that you over heated certain areas while working, run a stress relieving cycle prior to final heat treat. Heat the blade to 1200F-1300F and let cool. Check for any warping.
Like Stu mentioned, some folks like to throw a quench in the mix while thermal cycling. Here is my typical routine...
-Forge
-Heat to 1650F-1700F, cool back down to magnetic
-Heat to 1500F-1550F, cool back down to magnetic
-Heat to 1475F, oil quench
-Heat to dull red(still magnetic) 2-3 times, cool to black, quench
Once the piece becomes magnetic it has formed another structure and is ready for the next cycle. The last dull red heats are what I call a "redneck spheroidize". It is a sort of subcritical anneal or what I also call an "extreme tempering". The smart guys will know what the proper terminology is... I just know it works for me, so until I find a better way, within my means, I'm sticking to it.
I don't like using ash/vermiculite/perlite to slow cool from solution. I think that has to do with the formation of coarse pearlite and in the case of hypereutectoid(+.90% carbon content) much worse things can happen.
I agree, if I were using an electric kiln to normalize blades (as opposed to barstock) I'd use anti-scale or foil.
- Joined
- Dec 21, 2006
- Messages
- 3,158
(Using foil and coatings with carbon steel) That is an excellent idea that was thrown my way by another good knife maker friend of mine. Go ahead and buy some SS foil to use while normalizing/thermal cycling. Take it to your final finish grit, wrap her up, and stick it in the oven! When done thermal cycling, take it out of the foil, coat it in your favorite anti-scale/anti-decarb goop (thin layer of course), and harden it!
I think that will save time for sure. Not having to worry about grinding thru a decarb layer and then polishing it. Great GREAT recommendation, and I for one thank you guys for the reminder!!!!
I know that decarb MUST be dealt with when leaving steel exposed when cycling and hardening. While preventing it in the first place is most smart, dealing with it isn't too difficult. I find that the decarb layer is very easy to recognize when doing post heat treat finishing. There is actually what resembles a lamination line when you begin to sand the decarb off and reach hard steel. The harder steel is also "brighter" in appearance, to me, and you can even "hear" and "feel" the change in hardness while grinding it off.
Great tip, thanks so much.
I think that will save time for sure. Not having to worry about grinding thru a decarb layer and then polishing it. Great GREAT recommendation, and I for one thank you guys for the reminder!!!!
I know that decarb MUST be dealt with when leaving steel exposed when cycling and hardening. While preventing it in the first place is most smart, dealing with it isn't too difficult. I find that the decarb layer is very easy to recognize when doing post heat treat finishing. There is actually what resembles a lamination line when you begin to sand the decarb off and reach hard steel. The harder steel is also "brighter" in appearance, to me, and you can even "hear" and "feel" the change in hardness while grinding it off.
Great tip, thanks so much.