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Heat Treating and Metallurgy Discussion of heat treatment and metallurgy in knife making.

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  #46  
Old 04-09-2008, 08:20 PM
Kevin R. Cashen Kevin R. Cashen is offline
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Quote:
Originally Posted by Gary Mulkey
Kevin,

I know that this is off from the original topic of the thread but I'm going to ask anyway. I have been doing a fair amount of experimenting with getting the hamon to follow the clay (satinite) more closely. Usually I will quench 1095 in a fast oil which does fair in following the clay but not close enough to get the artistic hamons that I have been after. I am guessing that I need to do water quenches for this purpose but even with lower carbon steels the amount of fracture caused by the water quench makes it undesirable. What steel/quenchant combination do you have the most success with in closely matching the hamon with the clay application?

Gary
I, and some others who I know, get good results, use black furnace cement (I find it superior to satanite in sticking and insulating), and quenching into Parks #50, but once again any good fast quench oil in the 7 second or less range should work. One just needs to remember to adjust the clay application for oil instead of water and leave more space for the cooling to make the hard stuff.
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  #47  
Old 04-09-2008, 09:06 PM
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Gary Mulkey Gary Mulkey is offline
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I have some furnace cement which I got from Evenheatthat looks about like Satanite. I'm not familiar with black cement but will check around for it. When I was looking for quenching oils this winter I couldn't find the Parks but called a manufacturer of quenching oils and bought their fastest. I was told that it would work the same.

Thanks,

Gary
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  #48  
Old 04-10-2008, 07:40 AM
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J.Arthur Loose J.Arthur Loose is offline
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Quote:
Originally Posted by Andrew Garrett
I've not made many big knives of the type I see ABS guys bending in a vice to prove their forging skill (a practice I have never fully understood). My HT methods would likely not survive such a test.
It's really meant to demonstrate that the bladesmith can control his heat treating by achieving a specific result. It isn't meant to produce the 'best,' blade.

I someone took one of my blades and bent it in a vice with a long pipe... well, he ain't getting a refund, you know what I mean?


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  #49  
Old 04-10-2008, 07:57 AM
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Andrew Garrett Andrew Garrett is offline
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[QUOTE=J.Arthur Loose]It's really meant to demonstrate that the bladesmith can control his heat treating by achieving a specific result. It isn't meant to produce the 'best,' blade.QUOTE]

Seems an odd test then--to prove the product can do what it is never intended to do. I guess I understand..., I think, but it would seem that with the collective intelligence of the ABS, a test more representative of the intended function of a knife could be developed.

Perhaps this is another conversation altogether...


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  #50  
Old 04-10-2008, 08:08 AM
Kevin R. Cashen Kevin R. Cashen is offline
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I often say that I am very proud to say that my blades will not bend like that, I heat threat them to resist bending or any other detrimental deformation- once again, strength is good! Many times I have asked people to give me an example of where a knife blade broke when it couldn't be directly attributed to a defect in the steel, the heat treatment or gross misuse. To date I have yet to get an example (I have been told of one sword blade that came close, but no knives), telling me that the hysteria is little more than very clever marketing- invent a horrible disease out of thin air, whip the public up into a frenzy about the threat, and then start selling the cure. Another point I often drive home is that even if one wanted to totally misuse a knife as a prybar, how many prybars have you seen that will BEND? A bendable prybar is more useless than a bent knife!

I personally wish that the ABS had never adopted that test, but Mr. Loose is correct that it is meant as at test of the smith not the knife. The ABS had no way of seeing how the public would completely misconstrue the message. No one could have imagined that there would be so many people in the world that have no clue as to how metal really works and basic laws of physics. Perhaps it is another black eye for the education system in our country, but then many folks in other countries don?t get it either.

Edited to add the back to topic bit:

This is also a good reason why many of the sound heat treating practices in other industries can be ignored by bladesmiths- it makes bending steel harder to do. Undersoaking and quenching into odd sludges makes bending a blade much more easy.
True story- One year while teaching the "Intro to Bladesmithing" class at the ABS school I brought out some Parks #50 for the students to use instead of the black tarry sludge or peanut oil that they had been using. Right away all the test blades got harder to bend without cracking, although the grain looked good. I took the #50 away and told them to go back to the goops for the test. On opening day I would often tell my class that I would spend a few days teaching them how to pass the test and then for the rest of the course I would show them how to make good knives.

Last edited by Kevin R. Cashen; 04-10-2008 at 03:10 PM.
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  #51  
Old 04-10-2008, 09:26 AM
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Andrew,

When I first started getting involved with the various knife forums a few years back and reading everything I could about knifemaking, I was surprised at the ABS bend test. Why anyone would bend a perfectly good knife was (and still is) beyond me. There is a lot of bravado in such a dramatic "test."

Supposedly it is supposed to demonstrate a bladesmith's skill. But, as a scientist and one who has studied statistics a little more than he wants to, a sample size of "one" is not only laughable, it is useless. The field of statistics was developed as a means of quality control for manufacturing processes to inform the manufacturer (and the buyer!) of variance in tolerances (i.e. hardness, ductility) and the rate at which sub-standard products were being made to allow the manufacturer to make corrections to the processes used. Of course a person can argue that this was meant for mass production where less personal attention is paid to each individual piece made, unlike a hand made knife.

At the end of the day it's not so much a test as it is an initiation, I think.

Nathan
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  #52  
Old 04-10-2008, 05:19 PM
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Another note on the test...

So much for getting back to topic...ehh?

I've seen many pics of the test with the smith down on one knee and the blade at 90*. The one thing that is variable in these tests is how much of the blade is commited to the flex. If you vice up 2" of a 9" blade and set the pipe on the guard, You have 7" of steel to 'bend'. This would seem easier on each section of steel than trying to bend, say, 4" the same way--It's a more gradual bend, yes.

Is there a standard for this?


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  #53  
Old 04-10-2008, 08:51 PM
AcridSaint AcridSaint is offline
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Here's what the ABS says:

Quote:
Originally Posted by ABS Website: [url
http://www.americanbladesmith.com/ABS_JSTest.htm][/url]

The Master Smith will mark a line across the width of the blade approximately 1/3 distance from the tip of the blade. The blade will then be inserted into a vise, tip first, such that the blade is placed into the vise up to the mark on the blade. If the vise jaws are rough, smooth metal inserts shall be located on each side of the clamped portion of the blade to protect the blade, when bending the test knife.


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  #54  
Old 04-10-2008, 09:00 PM
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Cool. Now I know.

Thanks.


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  #55  
Old 04-10-2008, 09:44 PM
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Huh? They're going to put smooth metal inserts in the vice jaws to protect the blade that is going to be bent.

Tell me how that makes sense.
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  #56  
Old 04-11-2008, 06:08 AM
RandyScott RandyScott is offline
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I think it does make sense - from a safety perspective!. Sharp edges lead to scratches and gouges which lead to stress cracks or fractures which could result in a catastrophic blade failure. A chunk of broken blade edge departing with all the pent up force of the blade under tension... hmmm, shrapnel from a grenade comes to mind... and you are the closest soft skinned object to it. I therefore believe the guideline was developed to protect the bladesmith from injury and to prevent blade failure due to avoidable damage to the blade.
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  #57  
Old 04-11-2008, 07:08 AM
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Quote:
Originally Posted by RandyScott
I think it does make sense - from a safety perspective!. Sharp edges lead to scratches and gouges which lead to stress cracks or fractures which could result in a catastrophic blade failure.
I can understand that. But that just goes back to the idea that the test just does not test blade quality in terms of how it will perform under use.

Sorry to keep taking this off topic, guys. I know this is a dead horse.
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  #58  
Old 04-11-2008, 08:53 AM
Kevin R. Cashen Kevin R. Cashen is offline
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Andrew touched on an important consideration in bending a blade, that is, that radius of the bend and its relation to the thickness and length of the blade. A blade that kinks tightly in one spot has a higher chance of failing due to the concentration of force than a blade that takes the stress over its entire length. This is why distal taper can have an effect on something like this even though folks rarely get the connection, the taper can redistribute how the blade will handle the stresses along its length.

Much more important is how the cross section of the blade is configured. Thickness actually plays one of the most important roles in how the blade will react to this type of treatment. Folks much more technically nerdy that I am would refer to it as moment of inertia, but even I recoil from terms that pretentiously technical. It can be very simply visualized by picking a spot in the thickest portion of the blade and viewing it from the spine down. In the action of bending there will be tension on the outside of the bend and compression in the inside, but in the middle there will be a point where one switches to the other. I like to imagine this point as a fulcrum point on a lever with the compressive and tensile loads on either end. Just like with a lever the farther you get from the fulcrum the more force is involved in movement. Steel will have an elastic range and then a yield point and then a plastic range before totally failure. The thinner the blade vs. the length of the curve in the bend, the less the forces on the end of the lever thus it is easier to stay within the elastic range. Make the blade thicker and you will increase the distance from the fulcrum and raise the forces exerted closer to the yield point when bending will begin. Things have to exceed the yield point in order to do anything more but be a spring, so if you want to avoid breaking or bending in that test make your blade thinner! It is that simple.

All heat treating does is move the yield point up or down, it does not effect the force required to flex the steel. This is why a filet knife will flex to 90 degrees and return to true with no problem but a thick spined bowie will have real problems as it will have to either bend or break due to the distance from the fulcrum within the same length. You can test this yourself by seeing how much farther you can flex a thin steel ruler, regardless of the heat treatment, than you can flex a 12? piece of ? stock without taking a set. I have written varying descriptions of these principles so many time that people have to be tired of reading it, but I will keep describing it for as long as it takes to dispel the delusional myths that bladesmiths labor under regarding this topic.

As for the smooth protectors in the vice jaws, that is just fairness as well as safety, on a soft spined knife any sharp gouges, nicks or scratches introduced to the blade when those forces are applied will reduce it ability to resist drastically. Do a back bend and have somebody hand you a pile of weights while you are bending over backwards and then hold it there. Now have some joker come up and stick a pin in your belly and see what happens! It is not much different. You can cut the toughness of a piece of steel under impact load by at least half simply by cutting a small notch in it. It doesn?t have to be real deep, I have lowered the numbers in huge ways simply with a line from a sharp scribe.

Last edited by Kevin R. Cashen; 04-12-2008 at 08:34 AM.
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  #59  
Old 04-12-2008, 08:25 AM
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Kevin,

Thanks for all of your comments. All of my high school and college physics have come rushing back, but it is all applicable.

Your last paragraph is very interesting--not just to makers, but it's important for people using our knives as well. Take care of them and don't let them get big dings or scratches IF you have to put it under hard use.
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  #60  
Old 04-12-2008, 08:36 PM
son_of_bluegras son_of_bluegras is offline
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Quote:
Originally Posted by Kevin R. Cashen
I have written varying descriptions of these principles so many time that people have to be tired of reading it, but I will keep describing it for as long as it takes to dispel the delusional myths that bladesmiths labor under regarding this topic.
So you're planning on living to be somewhere around 300?



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