The ART of heat treating

[Tai Google]

As a of late, there seems to be a growing misconception or "myth" that there is only one ?proper?, "correct" or ?ideal? way, or methodology, to heat treat knife blades.

However, I would like to suggest that heat treating knife blades is a ?specialty" which requires skill, experience, common sense and intuition. A purely ?scientific? or ?idealistic? approach may not always be the best.

One thing that is often left out of heat treating discussions these days, is the effect of ?geometry? on the heating and cooling rates of the steel (quenching mediums), soak times etc. Thinner sections cool and heat more quickly than thicker or more massive sections. We aren?t quenching 1 inch round bars or one inch diameter ball bearings. With knife blades, we are generally talking about wedged shaped or diamond shaped cross sections. So what is ideal for the spine of the blade may not be ideal for the edge, and vice versus.

With water and oil hardening steels there is going to be a chilling effect, (from the air), between the time the blade is withdrawn from the forge and the exact time of emersion into the quenching medium, which will be the most dramatic on the thinnest portions of the blade like the edge and the point. This complicates things in terms of the exact temperature a blade should be before it is withdrawn from the forge.

We also have to consider possible variations in the exact carbon content of steels, (with the same designations), from one batch to the other and the possibility of decarburization from forging.

We generally hear that ?testing? is the best way to determine if a blade has been properly heat treated. But, there is no one correct or proper set of tests for all blades. It really depends what the blade is going to be used for and the preferences of the user. For example, if one wants a blade that will go a season in the field without needing to be re-sharpened, then a set of tests needs to be designed for that purpose. On the other hand, if one wants a blade that can easily be sharpened and re-sharpened in the field with a file, then a different set of tests would apply. The important thing is being able to control the outcome and to achieve the desired results for any given blade.

With these things in mind, I really see heat treating as more of an art than a science. I?m not saying to ignore the science. It can be very helpful if kept in perspective. However, on the other hand, a purely "idealistic" approach to heat treating can be very misleading and give people a false sense of security,? if ALL the variables are not considered first.

[cdent]

Are there any recommendations on how to persue understanding the variables of heat treating a blade. I guess I'm wondering if there are tips to distinguishing between thinking what's going on and knowing what's going on.

Thanks much, Craig

[ranger1]

This is very true. I noticed what Tai is speeking of on some of my clay quenched blades. I get a very vivid hamon ( almost perfect to the clay line) at the point where the blade cools more quickly, and it will fade as it gets closer to the spine sometimes to the point that the clay pattern is lost. I found that threw trial and error by haveing the clay thinner at the tang and building depth to the point, that I get a better temper line or hamon. I could be wrong but I believe this works because it allows the thicker steel at the tang to cool more closely to the same rate as the thinner steel at the point which has the heavyer clay coat. The differance is very visable.

[Tai Google]

Craig, That's where the "art" comes in.

Same as anything else or any other art form,... Study and practice is what it takes...
... and don't take anyone's word for anything.

True science makes no value judgments, like good or bad, right or wrong,? worst, better or best. Those types of judgments fall under fields like art, philosophy, culture, engineering? and personal opinion.

[cdent]

Thanks Tai, heating cooling and quenching the wedge shape seems to be an interesting process. I guess for now I'll keep bending and breaking blade shaped objects to see if I can get the visual cues (and testing) to match up with how it's supposed to work.

Take care, Craig

[BlueSkyJaunte]

If it's one thing I have learned in my career as an engineer, it's the following:

"In theory, practice and theory are the same. In practice, they're completely different."

It seems to me that everyone is in search of the perfect recipe, when they would benefit so much more by learning through personal experience and some basic experimentation. Sure, these recipes make a good starting point, but that's all they are.

[NathanMachinist]

I have to disagree Tai. If you're not forging while wearing a space suit, you're missing the entire point of bladesmithing.

[Tai Google]

I agree Aaron.

There definitely are some fundamentals and guidelines that can help immensely. After that, I think it?s all up to the individual. I also think that once you have paid your dues and found a system that works for you and you are happy with the results,? if a babbling pack nerds comes alone and tries to tell you that your way doesn?t sound ?proper? or ?scientifically correct?,? you should just tell them where they can jam it.

Art is really dictated more by concept and personal expression that anything else.

I don?t think it?s so important what methodology you choose. The important thing is to do "IT" the best you can and try to get the very most out of it.

I totally support and will do what I can to help those who's concept it is, to "go green" with their knifemaking.

[NJStricker]

Interesting thread, Tai!

I've been wondering recently about the differences that might result between clay quench and partial quench to acheive differential hardening. In the case of the clay quench the clay prevents the spine from reaching critical temp to prevent hardening, whereas in the latter approach we allow the spine to reach critical but cool the spine down from critical more slowly than the edge. Am I explaining this correctly (correctly, not technically)?

In this sense in the case of the partial quench, are we also acheiving a differential normalizing of the spine?

I understand that blades should be normalized before hardening & tempering, but other than the cosmetic aspects of the hamon that might result, in your experience is there any benefit in one method over the other?

Or are any differences so minor that they would not be noticed by the user?

Nathan

[Tai Google]

I'm not the expert on clay hardening, but I suppose in some instances what you are saying could be true, but maybe not in all cases.

I do think that clay hardening and quench lines in general are a great example of "The ART of heat treating", and a good way to learn about some of the subtleties of the steel.

[cdent]

Oops, I hope we don't have to go too green with craft. The old carbon footprint gets a little skewed every time the forge gets fired up.

Is it possible that the art of heat treating is a bit closer to science and that the art part is more related to the esthetics of finishing.

Anyway, interesting discussion, Craig

[Tai Google]

Art and aesthetics are two very different things.

Design is another thing, and with a utilitarian craft,... good design should also include aspects of performance etc., in my opinion... but, not that it has to be utilitarian.

Whether it is utilitarian or not, or to what degree,... would be more in the realm of "concept", and again is up to the individual.

To the best of my knowledge "heat treating" metals, is not a science, but does involve science, like any other art form or "craft"...

Science is primarily concerned with collecting and accumulating new empirical data, (not with what society does with it)... and as such, could be considered an art form in and of itself.

[Raymond Richard]

Tai, Good positive thread you got started here! Makes a lot of sense to me.

[Tai Google]

Ray, I also think that salvaging, recycling and using scrap steel, is another great way to learn about the subtleties of steel and "The Art of heat treating".

The ART of heat treating requires split second timing, coordination, skill, personal human involvement and creativity,... There are a lot of things you can't get from book learning alone.

I think of the ART of heat treating more as a ?creative discipline?, and an on going learning process,? rather than as a ?closed science?. Besides,? if it was a "closed science", (or ever became one), I?d have been bored with it a long time ago?

A "closed science", is a dead science...

[brucegodlesky]

Great topic Tai.Thanks for starting it!
I'm still tryin' to figge rout how them guys dress a deer with a hamon(BOG)