heat treating hype and reality

Mr. Fowler, I'm interested in knowing a little more about your technique and theory of low temp. forging. As I forge 5160, I do short forging cycles at fairly controlled temps. and judge more by the fine scale and ability to move the steel. What I was wondering is at what point in reduction do you start reducing your temps. to your low temp range? Or do you do the entire process at a low temp?
 
Just an update on my progress on the chart. It is going to be quite a challenging project. We all know that there are so many different ways that we knifemakers heat treat our creations. I've found much information thus far, from all of the knife books in my collection (I think I have just about all of them), to going back through past issues of Blade Magazine, to going through the threads here, to wading through Professor Verhoeven's 201 page document on heat treating knife steels.

The chart is intended to be simple, but the amount of information is vast and not always the same. I'm hoping that as I whittle the information down for each steel type and apply it to what is required for a quality heat treat for a particular knifestyles intended purpose that I can rely on our most experienced knifemakers here for feedback.

It's been fun so far, and very educational. Please be patient with me, since I have a lot of information to gather, sort, and understand.
 
Ed, thanks for joining in on this topic. No one has exemplified the point I was making about learning a specific steel inside out before jumping to lots of other steels than you have.
You are absolutely correct when you say that it is not the temperature that is important, it is knowing what state (your word - condition) the steel is in.Just like the Rc the temperature is a number, you have to know what the number corresponds to inside the steel.
Another thing that just got brought up was FULL HARDENING. Full hardening, deep hardening, shallow hardening,etc.... are another example of industrial terms that mean something different to motor block foundries than bladesmiths. A steel that is "shallow Hardening" and ONLY hardens 1 inch deep on a six inch thick piece, will be a fully hardened blade that is .160 thick.I could be wrong, but know of no normal blade steel that will not harden completely through in a proper quench. So, this is another case of WORDS that come of a chart that don't apply to out craft.
Stacy
 
Scott & Stacy: My temp gague for forging is simple and immediately available to every bladesmith. Watch the scale, scale is a functioin of time and temp.
the first heat on a billet will naturally be a little thick due the to time it takes to bring steel up to forging temp, from the first heat on, I like to see the scale come off the steel like fine snow flakes, my optical pyrometer tells me this is 1625. The finer the grain, the lower the temp that will make grain grow
when it comes to 52100 and 5160 we are safe up to 1725. This gives me a 100 degree f safety factor. I forge down through critical and continue until the steel quits moving. This is my forging range always. Our blades manifest an astm grain of 14 and finer in the first hardening zone.

Due to our multiple quench the hard zone penetrates higher than the first transitiion zone inside of the blade as seen on the etched blade, thus the pyramid I have been so interested in for the past 15 years. Wrap this hard pyramid with the bandig qualities of Wootz and you have one tough, strong blade.

This is a fairly simple explanation, but it is all there. If you want to see me do it and listen to Rex explain what is happening, it is all in our new dvd available through my website or form.
 
bladsmth said:
In a series of emails to several newer makers I have come to believe that many are reading more into the numbers than is really necessary. Here is one of my replies to get this subject going.

There is a big thing being made by a lot of makers, "Oh, my blades are all Rc 61.etc..."( I have heard boasts of Rc66). This is mostly said by those who don't understand the actual situation. An example is a piece of glass. It has a high Rc but makes a poor knife. It will get razor sharp (sharper than any steel blade is able to) but the edge will chip and the blade will break. A plain piece of unhardened steel can be honed to a very sharp edge,and will not break under most any use. It just won't be able to keep that edge from wearing away or bending over.This too would be a poor knife.The optimal knife is one that has some features of both.
The aim of making a quality knife blade is to have a hardened edge that can withstand use (and a bit of abuse), be easily sharpened, and be tough.Its edge should be tough enough not to chip out or roll over. The Rc figures found on most charts are for industrially quenched large objects and tools, not knives. A good blade will temper down to Rc 59 area, and be springy enough to withstand side pressure without bending permanently or breaking.This is the subject that Ed Fowler,mete, Kevin and others like myself discuss ( I do not put myself in their sphere of expertise). Few ABS master smith blades are hardened beyond a final Rc 59. I can assure you no Rc61 blade ever passed the JS or MS testing.
The idea is to get a particular steel and learn all you can about how it works for YOU. If you have a lab with a SEM and argon shielded ovens - that is what you should master. If it is a propane torch, a can of ATF, and a set of yard sale files - that is what you should master.
I do O-1 blades with the Ac temps for O-1 ,a quench in Heat Bath's AAA and a double temper at 400, and a spine draw to achieve a properly balanced blade of a hard edge and a soft spine. On a blade done this way the Rc will vary depending on where you test.Rc 52 on some places, Rc59 at the very edge. A blade like this will outperform almost any simple quench and temper blade.

So to make it a simple catch phrase, "Don't learn the numbers...learn what the numbers represent."

I would rather have a blade made by a smith who understood the theory of knifemaking and made his blades to do a specific purpose (with procedures designed to attain that purpose) and didn't really care what the Rc is ,than one from a person who said ,"The chart said Rc61 so I tempered for that target hardness."
Stacy
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Well also dont forget you want a temper that matches the knife and cutting chore. Think of this if all your doing is cutting fine stuff say somethign where there wont be any chopping (as in raising the blade high and striking down such as a cleaver) or side to side movement then you can have a crazy high 60+ rc on it with out worries. But when you do have the cleaver type chopping motion or alot of side to side movemnt in your cut then you want a lower rc rating. I like a general purpose knife with a 56 57 rc that why i love my little aus 8 master knife it has around a 57 to 58 rc. But it has a fairly thick blade for its length.

Now of corse there are ways to break this general rule of thumb useing ither a clay build up such as a kantana (side benifit you get a pretty hamon line when done just right) and multi layer steel such as damascus or even a simple 3 layer steel i beleive cold steel has many a knife useing 3 layers of steel out side layers mild inner layer a much higher grade that does head in to the 59 to 60 rc range.

What sucks for me is i have a fairly decent understanding of how to harden a blade and what rc is a good rc yet i have 2 things against me
1 i havent got the equipment needed to do it nor do i have the skill to do it.

Another thing to remember with heat treating steel is to remember steels all have a point at wich they become to brittle to be useable. Some steels can take a higher rc than others. Who here remembers case knives pre truesharp and how the blades were less than steller when they made the switch to truesharp? That is a perfect example of putting to high a temper in to a steel. Those blade at that time were so brittle that on smaller folders the snapping of the blade closed was enough to break or chip the blade.

As you touched on a bit softer steel is easyer to sharpen so again match the knife and cutting chore to the steel hardness/rc. Some times it better to have a soft but easy to sharpen blade just ask any one who traps what they prefer. Friend of mind traps for a living travels all over the us and he uses a little high carbon steel knife with a 1.5 inch blade and 4 inch handle. The blade dulls to the point where it wont cut about half way through a beaver skinning job but only takes 3 or 4 strokes to resharpen.

Just a little ot but i use to make those blades for him from old rubber factory knife blades. First step stick on the open fire of a stove get red hot let cool secound make the edge perfectly flat to give a needle sharp point 3rd step lay blade flat and put edge on one side last step sell the blades to him 10 for 5 bucks.
 
If every maker did semi-scientific, repeatable testing with their blades, along with "just using it," he could easily figure out the best heat treatment for his steel, application, preferences, and equipment, though it is time consuming.
 
I am always open to hearing ideas about how I can make my Heat-treatments better for my knives...

Right now, with the Ball bearing steel i use, I do mostly 2 heat/quenchings, (Just to be sure , as I always doubt I did it right the 1st time)
First I heat the blade to nonmagnetic in the forge, then allow to cool in still air.
Then I do the real hardening by heating with an O/A torch along the cutting edge only,
Get that area up to the correct temp.
Then dunk in pre-heated quench oil.
I rock the blade edge in the oil, not alloweing the spine to get wet.
Then I now temper the blade right out of the quench oil in a 350 oven.
I temper for an hour, then cool, then temper again for an hour.

Now all this is to make a blade I can trust at work.
My job has me cutting all kinds of materials, and chopping 2X4s .
Thus I would love to end up with a blade that will cut well, but mostly I fear a blade breaking, so I need a blade I can trust will just not break.

Suggestions?
Any other ideas for how I could H/T my blades to get to the place I wish to be at?
 
Ed Fowler said:
Watch the scale, scale is a functioin of time and temp.
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Hi Ed,

Isn't scale also a function of the atmosphere in your forge, too? I've been wrestling with getting my new forge to the 'reducing' environs that (I've read) is meant to reduce the formation of scale by introducing a fuel-rich atmosphere, rather than an oxidizing atmosphere. Am I misunderstanding this?
 
Ed Fowler said:
Kevin:
You area absolutely correct when you state that Rc is not as significant as performance. Another factor is that temperature is not as relevant as the condition of the steel, this is why the magnet is the most significant indicator we have. I believe actual temp requirement may change, but the magnet is always measures what we want it to. Again I speak only about 52100,5160 and sometimes L6
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Thank you Ed, I always appreciate your support, but I actually don’t recall ever using those words. You see, I see Rockwell as an integral puzzle piece that is “performance”. It shows one how a knife blade will perform against ductile deformation when penetrative type forces are brought to bear against it. I like to use it, with other tests, to tell me what the steels properties are, not what I wish them to be, and let that help develop a picture of cause and effect for the end performance. This helps me overcome the all too human tendency of developing my own unique definition of performance to suit my wishes and then slanting, or picking and choosing, tests to protect my worldview. That is a constant threat in almost any testing regimen.

As for your views on the infallibility of the Currie point (magnets), well this is what makes you such an interesting guy, and why your articles may be the main reason I still read Blade magazine. I will read some points that you and Rex have come up with that can really make one ponder the possibilities in its grasp of the technical aspects, and then you will throw something like this one out there, leaving one to scratch their head and wonder if it is the same guy. The magnet will always measure something, whether it is something we want I guess depends on who “we” are… I guess… errr… oh to heck with it, to each his own. If I ever say you are boring let me be called a liar! :D
 
Scale formation and decarburization are a function of temperature [higher T-more scale and decarb] and atmosphere [more oxidizing atmosphere - more scale and decarb ]
 
I adjust my forge to a neutral atmosphere, usually about 3 lbs propane (on my regulator which is actually who knows? but the same). I adjust the air-gas mixture until no visable flame is coming out the hole in the door. I do not remember the atmosphere in the forge influencing the scale. I believe that the atmosphere could influence scale to some degree, but at this low temp I have not found it significant.

If I needed to check, I would use a magnet to evaluate critical, then go about 100 degrees hotter. I would probably go into appoplexy if huge scale was forming at critical.

Many worry about burning out carbon through many thermal cycles. Rex shot a chemistry on a 5 1/2 inch round bar, gave it to Doc who forged it down to a 3 " square bar and sent the bar to me. I forged and heat treated some blades and sent them back to Rex. Rex polished off the surface and shot a chemistry, there was no measurable carbon loss. I question the significance of the forge atmosphere (excluding extreme variations) as an influence on blade quality.

What we have learned is that the low temp forging, 1625 f and less provides many cycles through critical temp. It is a combination of these thermal cycles (and more) and reduction by forging ratio that is the greatest influence on grain size.
 
Mete and I were posting at the same time. His comment is right on!

If your forge is running efficiently you are both saving time, money and not hurting the steel.

Kevin: I was responding to the other Kevin, did not notice the similar names until now, I will now go back and read your last post.
 
MrPurple said:
Hi Ed,

Isn't scale also a function of the atmosphere in your forge, too? I've been wrestling with getting my new forge to the 'reducing' environs that (I've read) is meant to reduce the formation of scale by introducing a fuel-rich atmosphere, rather than an oxidizing atmosphere. Am I misunderstanding this?
Click to expand...

Matt, you like to put yourself in the beginner category but, you have a pretty good handle on things and took the words right out of my mouth here. Scale is iron oxide, temperature increases this chemical reaction thus the time it takes for it to occur. At room temperature it takes days and makes rust, at forging temperature it take minutes and looks like scale, but at the heart of it is the O2. If you interfere with the amount oxygen’s available for the reaction you can greatly effect or even overcome temperatures influence. Pump an inert gas into the heating chamber and you beat it. Surround the iron with foil or a flux and you can cut it way down, or you can use the oldest method of all and lock the O2 up in incomplete combustion gasses and keep tings clean. The variables are endless for these factors. If you use the same forge with the same fuel to air mix every time then the scaling may become standard enough to judge temperature, but change any of these factors or quite a few I have not considered in this paragraph and things have to be reconsidered.

It would take some time and space to thoroughly explore here and I already fill these threads with too much of my ramblings, although I am very aware of your enthusiastic encouragement of my offering a book, I don’t have a DVD, book , or forum to push the limits of this forums advertising rules with, and I doubt I could bring myself to if I did.
 
Ed Fowler said:
.

Kevin: I was responding to the other Kevin, did not notice the similar names until now, I will now go back and read your last post.
Click to expand...

No problem, we obviously erred in the same fashion. No matter though, it has no effect on my comments, you are still one of the most fascinating figures in the business, Ed. :)
 
Heat Treating Hype & Reality. Excellent choice of titles for this thread. Like many of the Knifemakers & Bladesmiths here I come from the Tool Maker,Mold Maker,Tool & Die Trade. I have to smile sometimes at the response of new makers when they heat treat their first blade and find that it "worked", they did it ! The steel is hard ,holds an edge etc.,etc. This is science,a very refined science in fact. But.....as was said in a few posts here already,a science that the data available (the sheets so many download & print out from crucible,admiral etc) pertain to large pieces of steel(mold cavity,trim & stamping dies). Larger than a knife size piece anyway,that is where "soak times","pre-heats",etc. come in,or should I say "go out". The data is still valid, but only a guideline for the type of steel you're working. It is pretty easy to screw up a perfectly good piece of blade size steel unless you understand how to adjust the "recipe" layed down by the manufacturer. On the same note nobody should be surprised when they get good results by following the "adjusted" recipe.Most data sheets specifically say that the specs are for a given size or thickness of the steel and should be adjusted accordingly.IMHO, problems start to occur when new makers (after their first successful attempt) think(because of the "science") that they have it all figured out and move to more advanced techniques before understanding exactly what they did in the first place.In closing I would like to say that I am just a beginner and have much to learn about the "more advanced techniques". Edited to add that I speak primarily about knives made using the stock removal method and Heat Treat done in a computer controlled kiln.Both air & oil quench steels. My forging experience is limited and I am learning something new about it everyday.When I started making knives I probably made the first 6 or 8 harder than they needed to be. Just as Stacy said in the beginning,by not understanding the #'s.So much to learn.....so little time :) All info layed down by the pros is much appreciated and written down ;)
 
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