Scale with Electric Oven Heat Treat?

WinDancer

WinDancer

Joined
May 15, 1999
Messages
720
For those who actually have and use electric heat treat ovens: does this eliminate the scale?

Thanks,
Dave
 
No, it does not eliminate scale. There is some oxygen in the kiln still and that is how you get the scale when it is brought up to high temps. The scale I get is more light and feathery, not rough like in my forge. Foil will cut down on scale moreso than bare steel. Gas injection does the best at scale reduction inside a kiln. I just treat the bare blades though. I have no problems grinding off a little scale. :cool: Hope that answers your question.

-Jason
 
You may try putting an open metal box containing some charcoal or wood in the oven, it will burn consuming the oxygen inside, reducing the oxidizing power of the atmosphere.
I don't know if it will work, though...
 
You can always wrap them in foil. That certainly eliminates scale and it's essential for stainless.
 
Here's a tip, just coat your blade in whiteout, yes the stuff you use to correct mistakes on paper. It will prevent any scale from forming.
Chuck
 
Dave we are going to find out here in a couple of weeks. I ordered a new Paragon furnace w/ the digital controls and the gas set up for argon while at the show in Atlanta. Should be delivered in a couple more weeks and then we can play w/ it.
 
Greetings,

In hardening a knife blade in an electric furnace, I wrap the blade in a single layer of grocery bag paper then wrap the blade in stainless foil with seams folded and flattened to make an air tight envelope.

When the paper reaches the flash point it will burn out the oxygen. When the hardening is finished, hold one end of the envelope with a tong, snip off the other end and pull out the blade and quench.

The blade will be dark and smooth with no scale.

Bearpaw
 
As I write this my very first ATS-34 blade is in the oven comming up to the quenching temp. of 1975 F.. It is now at about 1100 degrees F. and climbing. I have wrapped it in stainless HT foil with two (one for each side) pieces of brown paper bag. I will soak at 1975 for 40 min., rapid air cool, and do the first temper at 950 F. for 2 hours. All this before removing the HT foil. I will know what it looks like early this morning. I expect discolorization and do so very much hope for NO scale.

Tommorow, if all goes well tonight, I'll fetch some dry ice and K1 kerosine for aging and then the second temper.

First time for me with stainless and I am anxious and worried.

Roger
 
whoa! Striper,

have you tried the "whiteout" procedure you described? Does it really work? any flare ups from the whiteout being cooked? fill us in?-thanks, Dan
 
RLINGER, you probably don't need that 40 minutes at critical, get too much grain growth. The long soak times claimed by industry are for large cross-section pieces, to get the internal temp at critical. With the small cross section of a blade, it may well be ready as soon as it reaches critical. I wouldn't soak for more than 5-10 minutes. Post quench, don't be surprised to find the hardness at only 57-58 or so. ATS 34 can have as much as 30% retained austentite, which only slowly converts. Hence the -78*C cryo with dry ice. Funny thing, too, about ATS 34, it gets harder as you temper it. Good luck. BTW, don't need the foil after initial quench.
 
Yes, I thought that soak time was a bit long but I am following a recipie I found for ATS-34 from a knife page. I have a new post hoping Paul Bos will respond to it. I understand the foil can be removed for the tempering but I didn't want to handle it so it would cool more uniformly. My blade came out blackened but there was no scale at all. I now have a sample piece of ATS-34 without the foil wrap in the oven to see how it scales.

Thanks for the advise.

Roger
 
I use a Kerr burn out oven left over from lost wax casting. I get scale but most of it falls off during the quench and leaves a greyish
colored blade.
Take Care
TJ Smith

I'm going to try coating my blade in borax next time and see what happens.
 
Fitzo is correct on the soak time, 40min is way to long 10 min is the norm. Also ATS-34 can be tempered at 350 and 950. If you use the 950 temper you will lose some of the corrosion resistance of the steel. 350 is actually the better of the temper temps as the steel keeps its excellent corrosion resistance properties.
 
Thanks to both on ATS-34 soak time advise. I consider it with great weight. Am still awaiting Paul Bos' opinion on this to my recent post on this forum 'Hope Mr. Bos sees this - ATS-34'. The post may now have elapsed to page two of the forum but have been advised he will respond soon.

Thanks again; RL
 
OK guys I gotta ask this then:
At what temperature does scale begin to form? Reason for asking is I wonder at what point in a HT program to turn the argon on to encapsulate w/ argon to prevent scale.
 
Oxidation is taking place as soon as the steel starts to change color. In carbon steels the nice heat coloring that people use is actually an oxide. Stainless tends to need more heat to oxidize but I'll bet it depends upon the actual chrome content of the stainless as to when it oxidation will begin to show. I'd start the inert gas blanket when I put the blade in for heat treating.
 
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