carburizing, neutral or oxidizing flame?

General Specific · Mar 24, 2008

Tai Goo said:
I've wondered that perhaps this forum needs to be broken down into areas,... maybe a separate "special" area for "pure metallurgy", without the philosophical B.S...

... just the "facts".

Perish the thought. Kevin would be devastated

. It's fascinating to watch the juxtapositions in play. Besides, the philosophical B.S. doesn't hold up without at least a pinch of science, otherwise I'd be blaming a bunch of pixies for the flaws in my knives, and on the other side Kevin wouldn't be imparting any of his metallurgical expertise if he had no philosophical interest in passing on the truth as he sees it. The two can't be separated completely and still be meaningfully represented in a forum.

Regards,

Dave

Tai Goo · Mar 24, 2008

General Specific said:
Perish the thought. Kevin would be devastated. It's fascinating to watch the juxtapositions in play. Besides, the philosophical B.S. doesn't hold up without at least a pinch of science, otherwise I'd be blaming a bunch of pixies for the flaws in my knives, and on the other side Kevin wouldn't be imparting any of his metallurgical expertise if he had no philosophical interest in passing on the truth as he sees it. The two can't be separated completely and still be meaningfully represented in a forum.

Regards,

Dave

O.K.

Tai Goo · Mar 24, 2008

I guess if you don't have any intuition or common sense,... then going the more scientific route, might be a good thing...

All I can say is,... good luck! LOL

Tai Goo · Mar 25, 2008

Just out of curiosity, I'd still like to hear more about the humid carburizing/decarburizing and oxidizing/carburizing flames,... and the moist gas forge chamber concept.

I think Kevin might be on to something...

I always thought fire and water didn't mix. ???

Next time I have my gas forge fired up,... I think I'll try pouring a cup of water inside and see what happens...

Tai Goo · Mar 25, 2008

... just kidding about pouring the water in my fired up gas forge chamber...

... don't try it!

I just don't want to see anyone get hurt.

... no need to thank me for that info... it's the least I could do. I'm sure you all have more sense than that anyway...

Carcara · Mar 25, 2008

Something I was told by a smith who has been smelting sand iron in Japan for the last 20 plus years is that, smelts done while it is raining outside tended to yield metal with less carbon content, compared to smelts done when the air was dry.

Tai Goo · Mar 25, 2008

Carcara said:
Something I was told by a smith who has been smelting sand iron in Japan for the last 20 plus years is that, smelts done while it is raining outside tended to yield metal with less carbon content, compared to smelts done when the air was dry.

That is interesting! Now we are getting into ambient environmental atmospheric conditions outside the forge, etcwhich is another interesting topic. Im sure it all has an effect, one way or another

However, we started off talking about controllable, practical and applicable atmospheric conditions inside the forge, and if there were any good reasons to run an oxidizing flame.

I think it is actually a very interesting concept, that we should adjust our methods according to weather conditions, moon phases, planetary alignment, the Earths magnetic field, HADO, whats on the radio, vibrations, etc

Steel is like a super sensitive recording medium it sucks it all up!

Any Cal. · Mar 27, 2008

OK, here goes. I have looked at the information, and am still trying to wrap my head around it.

An oxidizing atmosphere at temps of 15-1700F will oxidize iron faster than the carbon can leave the steel due to diffusion. As the iron oxidizes(scales), the carbon recedes into the steel, leaving a higher concentration of carbon in the surface below the scale. At higher temps, the carbon can be defused out of the steel much faster, leaving a scaled, decarburized surface. This would especially be true at forging temps.

A reducing atmosphere at lower temps will allow the CO2 in the mixture to take the carbon out of the steel, turning the carbon into more CO2. The CO present at lower temps is not helpful, due to the low diffusion at the lower temps. At higher temps, the CO can more easily add carbon to the steel, so the amount of carb/decarb, is basically the ratio of CO/CO2. The problem w/ a reducing atmosphere though, is that other gases are/can be present. Because of this, even if the CO/CO2 proportions are right, the other gases that may be there can be decarburizing. This is the condition referred to as a "wet" reducing, which is still decarburizing. In an oxidizing atmosphere, those would have been consumed.

From this, I am getting that soak time for austenitizing would be best spent in an oxidizing atmosphere, but forging should be done at a neutral or reducing atmosphere. On a wet day, neutral would be best for forging, and the time in the forge would be trying to keep the piece from scaling or decarburizing. On a dry day, a reducing atmosphere could actually be adding carbon that would be lost while the piece was in the air.

Is any of this right, or do I have to read it all over again?

On a side note, I am glad to learn what caused the sweat/boiling/melting on the surface of a couple knives I did.

Tai Goo · Mar 27, 2008

Some of these "facts" seem kind of silly, trivial, and on the fringe of applicability and practicality,... such as the effects of ambient humidity.

You are always going to get some scale and decarb from the overall forging process, inside/outside the forge with conventional methods. This is not normally a major problem and is usually remedied in the following stock reduction part of the process automatically. However, in extreme cases, and for certain specific applications, scale and decarb can become a problem if not kept in check or to a reasonable minimum...

If you aren't having a problem with decarb or scale, don't worry about it,... just be aware of what the possible and most likely causes for it are should it ever become a problem.

Under average ambient forging conditions, what Chuck originally stated is fundamentally and essentially correct.

If you have an open air shop such as mine, then you probably won't be forging under extreme adverse weather conditions anyway.

As a general rule, try to get through the forging process quickly, efficiently and with as few heats as possible,... without sacrificing your blade (or bladesmithing) concept.

Tai Goo · Mar 27, 2008

What it all boils down to is that,… it shouldn’t be necessary to make any drastic changes in our methods due to a few odd tid bits of metallurgical trivia. It’s all good, (it’s all interesting), if kept in perspective. 99.9 percent of the time, you should be fine if you just stick to the solid fundamentals of the craft and use some common sense.

However, keep the trivia in the back of your mind, because there may be a few special occasions, under certain conditions, and when working with fringe concepts that they may become useful…

Tai Goo · Mar 27, 2008

It's almost like we should talk about the LOCATION and SITUATION of our shops and how it effects our methods,... HMMMM ???