Heat treating in a forge vs a kiln...what is your preference?

A lot of guys seem to use torches to do their heating, but correct me if I am wrong, but does this blade (which is just going in for the quench) not look like it is too hot (white hot) in some spots? When a blade comes out of my forge, it does not look like this. I move the blade around and in and out constantly and it comes out as a single, uniform orange color from tip to choil. Maybe this blade turned out okay, I don't know, but I've watched so many videos of guys...really experienced guys...quenching blades whether out of a forge or using a torch that just looked way too hot. I guess there is some subjectivity, but still... On the other hand, about every time I see a video of a knife coming out of a heat treat furnace, it is always a single, uniform color and that is what I try to achieve, not this...

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HSC /// said:
In general a heated blade always looks “hotter” in a picture. Due to the exposure of the camera and the lighting and the angle of the photo
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I think a lot of times guys are just flat out overheating them. This is out of a heat treat oven and this is how my blades look out of my forge too... I don't see any white spots on this blade.
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Why does so few smiths who HT in their forge use the decalescence? Or at least recalescence, to judge the accuracy of they're PID forge or eye balling.
 
Joel Mercier said:
Why does so few smiths who HT in their forge use the decalescence? Or at least recalescence, to judge the accuracy of they're PID forge or eye balling.
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Not exactly sure what you are asking.

Decalescence occurs while the steel is being heated. As the internal structure transforms, there is a brief decrease in temperature. You can see the "shadows". It is the only sure sign that you are going into solution.

Recalescence is an increase in temperature that occurs while the steel is cooling down through critical and happens at a much lower temperature. It is due to the change in entropy or something like that... words... lol
 
There is no decrease in temperature, the shadow is darker because the steel emits less photons.

My point was: why not use this instead of eye balling the temperature?
 
As far as I know, there is a temperature decrease in Decalescence and an increase in Recalescence. I can't find anything that says different. Please provide a link... I have been explaining it that way for a long time and would correct myself if it wasn't true.


Wouldn't observing decalescence be eyeballing?
 
When the steel has transformed to austenite it is no longer magnetic so I would think the magnet would be easier than watching for color changes.
 
Larrin said:
When the steel has transformed to austenite it is no longer magnetic so I would think the magnet would be easier than watching for color changes.
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I always use a magnet, but I let the steel get just one shade brighter to an even orange glow all throughout. So it is about one minute past non-magnetic.
 
Rick Marchand said:
As far as I know, there is a temperature decrease in Decalescence and an increase in Recalescence. I can't find anything that says different. Please provide a link... I have been explaining it that way for a long time and would correct myself if it wasn't true.


Wouldn't observing decalescence be eyeballing?
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The way I was explained this is the phase transformation requires energy, but that energy is taken from photons, not heat. That's why a shadow appears. The shadow itself isn't any cooler or hotter than the rest of the blade. But sorry, I cannot provide literature of this at the moment.
 
Joel Mercier said:
The way I was explained this is the phase transformation requires energy, but that energy is taken from photons, not heat. That's why a shadow appears. The shadow itself isn't any cooler or hotter than the rest of the blade. But sorry, I cannot provide literature of this at the moment.
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The transformation is literally endothermic. The temperature of the steel is reduced. And on cooling the temperature of the steel literally increases during the transformation.
 
Good to know Larrin. Seems I was either misinterpreting the info I was given, or the info was just wrong. Thanks!
 
I use and sell Paragon ovens, and I also use and sell propane burners and forge gear. After switching to an electric oven there is no going back.

I've heat treated hundreds of carbon steel blades in a propane forge and got fantastic results out of it, but it is always a huge time sink, watching carefully and adjusting temperatures.

With an electric oven I can get precise temperature control and heat treating only takes a couple minutes of my time. Between putting the blades in and taking the blades out for quenching (I mostly use stainless and high alloy tool steels now which need long soak times) I am back in the office or in the workshop doing something else productive.

I met Rodrigo Sfredo early last year and it was interesting to learn that he does his heat treating in a gas forge, out of preference.
 
Do you make knives for fun and for gifts, or are you selling them? I also enjoyed the process of doing my HT in my little 2 brick forge that I made myself, but I was also honest with myself about the limitations. I still have many of those knives and use them. Most turned out great, but I know there was some overheating on some!
When I began selling knives the first thing I did was purchase an oven, followed by a hardness tester. I owe it to my customers to produce the very best product I can and that requires controlled HT and testing.
 
E.Carlson said:
Do you make knives for fun and for gifts, or are you selling them? I also enjoyed the process of doing my HT in my little 2 brick forge that I made myself, but I was also honest with myself about the limitations. I still have many of those knives and use them. Most turned out great, but I know there was some overheating on some!
When I began selling knives the first thing I did was purchase an oven, followed by a hardness tester. I owe it to my customers to produce the very best product I can and that requires controlled HT and testing.
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I absolutely sell my knives. I sell them in hopes of one day being able to afford a heat treat oven. I did not just start doing this yesterday either, I have had some degree of practice heat treating in a forge. I'm sure Rodrigo Sfredo sells his knives too...and the numerous other makers who use simple carbon steels from time to time. I talked with a local well known maker where I live and he say's he always heat treats his 1080 in a forge. I met a different maker that same day who gets all of his knives heat treated professionally and he was sure to brag about that fact and cut down other makers who used a forge claiming his were superior....but in the hand his knives felt heavy and uncomfortable to hold.
 
As a knife buyer and user, I run away from forge heat treated blades, nowadays. It doesn’t mean that my forge heat treated blades are bad! Just that those blades may be not optimized. Like someone previously said, if ancient swordsmiths had access to well built furnaces and molten salt bath pots with PID and precise temperature controllers, they would use the forge to forge and the furnaces/salt pots to heat treat! Always use the best available materials and protocols to work! Want traditional look? Fine, but using modern technology.
 
R.C.Reichert said:
I absolutely sell my knives. I sell them in hopes of one day being able to afford a heat treat oven. I did not just start doing this yesterday either, I have had some degree of practice heat treating in a forge. I'm sure Rodrigo Sfredo sells his knives too...and the numerous other makers who use simple carbon steels from time to time. I talked with a local well known maker where I live and he say's he always heat treats his 1080 in a forge. I met a different maker that same day who gets all of his knives heat treated professionally and he was sure to brag about that fact and cut down other makers who used a forge claiming his were superior....but in the hand his knives felt heavy and uncomfortable to hold.
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I'm not knocking the quality of anyone's knives or am I questioning your talent. By all means do whatever you are comfortable with. Starting to sell to unknown customers is what led me to change the way I do things. Just trying to answer your original question of "what's your preference?"
 
E.Carlson said:
I'm not knocking the quality of anyone's knives or am I questioning your talent. By all means do whatever you are comfortable with. Starting to sell to unknown customers is what led me to change the way I do things. Just trying to answer your original question of "what's your preference?"
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I appreciate the input 100%. Thank you!:)
 
E.Carlson said:
I'm not knocking the quality of anyone's knives or am I questioning your talent. By all means do whatever you are comfortable with. Starting to sell to unknown customers is what led me to change the way I do things. Just trying to answer your original question of "what's your preference?"
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I bought my kiln and rockwell tester right after I had my first warranty replacement. The tip on a 52100 knife curled when the owner tried to puncture a coyote to skin it. I haven’t had a warranty return since. I had a thermocouple in my forge too. Temp was just too inconsistent to hold evenly for proper soaks. A pid forge would have been an option, but I wanted to work with stainless steels, and went with the oven.
 
Willie71 said:
I bought my kiln and rockwell tester right after I had my first warranty replacement. The tip on a 52100 knife curled when the owner tried to puncture a coyote to skin it. I haven’t had a warranty return since. I had a thermocouple in my forge too. Temp was just too inconsistent to hold evenly for proper soaks. A pid forge would have been an option, but I wanted to work with stainless steels, and went with the oven.
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Metallurgy is like bakery: PRECISE temperatures and times. After almost 10 years of Knives obsession, I now use “simple” steels (8670, S1, A8mod, K600) with precise heat treatments in a furnace. Only pm steel I use is cpm M4, in my Spyderco Gayle Bradley.
 
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