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Author Topic: Questions about practice and procedures  (Read 12849 times)
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Ed Fowler
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« Reply #15 on: October 07, 2007, 12:44:45 PM »

David: I am going to answer all your questions, hopefully in a logical easy to understand manner.

To address one in the last post: Does the steel get denser or does pacing occur? Not really packing as normally thought of, but homogenising, promoting uniformity at the right stage and refining of the grain. Does it increase or decrease in volume? I really don't know. There was a time before the 30 second post forging quenches that the length of the cutting edge became shorter, drawing the tip down. This produced warp. It does not happen any more. Why? again an unknown, I only have to guess that the 30 second post forging quenches provide uniformity and the entire blade responds in a similar manner.
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Ed Fowler
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« Reply #16 on: October 08, 2007, 09:06:16 AM »

You ask does steel mature? We are fairly certain that blade made 100 years ago are not the same as they were when they were made. For this reason testing an old blade tells us what it is today, but not how it preformed the day it was completed.

One reason is that Martensite is the most relaxed form of steel. When a blade is hardenend there is some retained austenite, the steel seeks to "realx" retained austenite becomes untempered martensite and the blade may become more brittle. This is one variable with quite a bit of literature supporting it.

There seems to be more to it. in 1923 F.C. Lea worked with "The Effects of Repetition Stresses on Materials". He found that stress below the maximum limit extended the maximum limit in future tests. I have not found an explanation for this in literature, but it does occur.

We have found the 24 hour cycles we subject our 52100 blades through definately contribute to the condition of the finished blades.
There is no measurable retained austenite in our finished blades, according to Rex and his work in the laboratory.

I bleieve that these numerous cycles and time between cycles promote stability in our blades and they will probably not change much in the next 100 years. I don't believe I will be around to discuss this variable. Maybe one of your grandchildren will comment.?
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Ed Fowler High Performance Knives
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radicat
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« Reply #17 on: October 08, 2007, 10:52:22 AM »

Maturing of steel - just a quick search of some snippets of old research papers and books was interesting.
In the early engineering books there is talk about compensating for the on-going expansion and contraction of metals in precise devices such as very accurate clocks. The use of different metals in the rods of pendulums with each type moving parts to maintain an exact length of the arc is interesting.

It is known that molecules in metals re-align to the earth's magnetic field in time and this process is affected by changes in temperature and pressure.  I think I'm re-aligning myself after reading some of this stuff.

Anyway, some old papers have now been digitized, such as F. C. Lea's work. Some stuff is only available to members of research societies. I won't give specific references, but I will direct you to a good way to find stuff to read. The advanced search narrows your search down to manageable. Search for info on a particular steel, or a subject, and by time period, if you want.

http://books.google.com/
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Ed Fowler
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« Reply #18 on: October 08, 2007, 07:47:22 PM »

Thanks for the information Cal: The book that I find the most useful is the one I reffer to the most, "Prevention of the Failure of Metals Under Repeated Stress" by the Battelle Memorial Institute. You can find used copies for as little as $5.00 from Abe Books and Amazon.
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davidm
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« Reply #19 on: October 09, 2007, 04:08:26 AM »

Ed,
Another question I had, was in the video you mentioned you made a knife that cut better than any knife you had made but dropped it on a piece of steel and it blew out a chip the size of a dime.  In the video you said that the knife had been overheated and there was more forging done on one side of the blade, which contributed to the failure.
My question is, is the steel rod/brass rod tests for edge flexes a good or accurate test for how much shock the blade can withstand, such as the knife edge hitting something hard laterally, or on the side of the blade?
David
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Larrin
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« Reply #20 on: October 09, 2007, 07:57:32 AM »

Here's a quote from Crucible: "No matter how tool steels are quenched, the resulting structure, martensite, is extremely brittle, and under great stress."

http://www.crucibleservice.com/eselector/general/generalpart2.html
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Ed Fowler
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« Reply #21 on: October 09, 2007, 05:50:23 PM »

Larrin: you are correct, evidently Rex and I failed to communicat exactly why retained austenite so readilly wants to transform to martensite.
Thanks for bringing the lack of understanding to my attention.
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davidm
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« Reply #22 on: October 10, 2007, 05:21:51 AM »

I have just a very basic understanding about what exactly is going on in the steel.. and reading the link, I get lost somewhat.  Can someone say, in simplest terms, what are martensite, austenite and again in simplest terms what happens.

I did gather from the link, it is the tempering that relieves stresses within the steel.  So, I gather knives that are properly heat treated/tempered are not under some kind of internal stress all of the time?
David
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Ed Fowler
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« Reply #23 on: October 11, 2007, 08:23:50 AM »

David: you ask some great questions! When Rex and I get time we will answer as much as we can. In the mean time I will provide you with some references that I have found most rewarding in our quest.

From the Battelle Memorial Institute:
"Prevention of the Failure of Metals Under Repeated Stress"
"Steel and its Heat Treatment"

Both of these books are were written in the 1940's, they contain information and references that explore the many variables in steel. You can purchase them through Abebooks.com used most of the time for less than $10.00 apiece.

A third book:
"Cats' Paws and Catapults" by Steven Vogel.

This book explores the world of nature and people. Physical structures and what makes them strong or flexable or rigid. You will come to realise why the convex blade has the properties it has and can have when you start out with a uniform structure and develop a composite as we seek to do with the 52100. Combine the informatin in these three books and you will have a new understanding not only about lady knife, but much more.

I suggest that you read then through the first time keeping notes, then the second time keep a new set of notes, then compare your notes and you will have an idea of what you have learned.

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davidm
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« Reply #24 on: October 11, 2007, 05:40:20 PM »

Ed,
If it's about science and metals I'm pretty sure I wouldn't understand any of it, but I'll take a look and see if I can find them.

I do remember you mentioning the other book, Cat's paws and catapults.

Funny thought I had while watching the video, the Nitrogen was said to have come from bat guano.. which is excrement.  So, I may have bat poop in my knives?  something good to tell the grandkids someday.
David
« Last Edit: October 11, 2007, 05:44:19 PM by David Mullikin » Logged
Ed Fowler
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« Reply #25 on: October 11, 2007, 06:44:23 PM »

David: some of the blades made before 1992 may have some Bat Guano in them, not all! It is however what you might call highly refined bat Guano.

The key is that homogenious fine grained austeinite acts differently when the steel is hardened than inhomogenious or coarse grained Austenite. "all austenite is unstable and wants to transform" this is why our efforts at fine grain. " from page 273 of the heat treat book.

I understood what Rex meant, but when I put it in my terms I missed.

As you read these books, do it for pleasure - don't try to understand every specific that is mentioned, look for direction or what they mean. The definitions will drive you nuts, without a lot of chemistry in your background. This is why Rex was and still is such a good teacher.
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davidm
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« Reply #26 on: October 12, 2007, 05:53:26 AM »

Ed,
Your old knife that you carried to the shows.  I remember more than once, seeing you drop it on concrete to show the toughness of the sheephorn.  This must have been done, over the course of the many years, maybe a several dozen times, maybe a hundred, or more? 
It must of seen a lot of shock to the blade from all that dropping.

How do you explain the instances, such as where in the video, a knife chips out from getting hit with something hard, or used in chopping bones?  You did say it was studied and found to be overheated and more forging was done on one side, after being looked at closely.  Do many, or most people have some kind of shock test to see if their knives can withstand a hit on something hard, to the side of the blade?  .. it might not be practical, i just wonder what kind of brittleness is there in most knives for a shock.
David
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Ed Fowler
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« Reply #27 on: October 12, 2007, 07:55:30 AM »

The blade that chipped when droped onto a billet of steel accidentally was the only time I have ever seen that happen on one of our forged blades. It was a great learning experience and we have deliberately put test blades through much more without experiencing a failure. This is one reason for the edge flex test. After that experience I put a number of blades in a vice, edge up and hit them with a ballpein hammer. Once we had identified the problen and made corrections in our methods to prevent it, it should never happen again.

Last sumer I loaned a test blade to the folks at our 1838 rondeavous to use in their knife throwing games. Everyone in the competition was invited to throw it, even the newcomers and kids. It completely missed the wood target many times, the blade bounced off of rocks numerous times, the only damage was some dents in the blade that I was able to sharpen out on a fine india stone in about 10 strokes.

Droping a knife onto a hard surface butt first is a tough test for natural materials in the handle, but does not influence the blade significantly. For sheep horn this is one test easily passed, sheep horn is designed by nature to withstand this kind of test, it happens every breeding season. When two bucks butt heads fighting for dominance, it sounds like a gunshot the sound actually echos.

This is why makers who understand the materials they use many times put caps on the pommels of their knives. The brass butt Bruce evans posted with the arrow head carved into the brass is one way of making less stable handle material tougher. Just do a search on Bruce Evans and you will find his work.

Jeffrey Davidson who apprenticed with me at the Willow Bow one summer caps his antler handles with sheep horn which really works well.

Some photos of one of his knives, one overall and one showing the sheep horn cap on a mule deer handle.

« Last Edit: October 12, 2007, 02:32:10 PM by Ed Fowler » Logged

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davidm
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« Reply #28 on: October 12, 2007, 09:48:41 AM »

Ed,
Just let me know when you are ready to let go of your old knife.  I have an Eastward home waiting for it.   Grin
David
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Harold Locke
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« Reply #29 on: October 12, 2007, 10:40:47 AM »



We have found the 24 hour cycles we subject our 52100 blades through definately contribute to the condition of the finished blades.
There is no measurable retained austenite in our finished blades, according to Rex and his work in the laboratory.


Ed,


Wow, this particular fact above, seems to me to be an extreme point. And would be just one of many conditions that all bladesmiths might find desirable.

It could be added to the lists of hallmarks or standards that are part of say the Mastersmiths final exam. I do think it would require an electron microscope of something along that line.

Harold Locke
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