blade quenching fact or fiction

[BMK]

Some flex is part of what makes a blade not break when bent but why would you want the degree of flex described here in any tool?

 

[Rick Marchand]

Some flex is part of what makes a blade not break when bent but why would you want the degree of flex described here in any tool?

That is the big ?uestion, Jeff.

In an ABS performance test knife, YES! The blade MUST bend 90degs to pass the test. How it applies OUTSIDE the test is what is often argued over. There is no doubt that Ed makes one of the toughest performance knives out there... what I am wondering is if it is at the expense of strength. His future testing is going to be intersting by the sound of it.

 

[J. Hoover]

Thanks Ed for your honest answer to my questions. You do heat your blades with a torch, don't you, leaving the spine well below critical temps.
I definitely want my my blades to flex slightly before they crack, on the other hand I don't want them to bend either. I normally do a full quench with the whole blade at heat. Then temper back the spine and ricasso area with a torch if the spine was not clay coated. Like the post above stated I don't make crobars, but I know that many knives I make will get used to twist or pry at some point.

 

[Ed Fowler]

I heat all my blades with a torch when hardening, always have and always will. The reason is simple, with a torch I can heat the area I want to harden, painting the color into the blade much like an artist paints his colors. I can dictate exactly what I want hard, I edge quench for assurance that only the area I want hard gets the opportunity to harden.

I believe our testing methods may be misleading in that they are absolutely extreme in nature. We test to destruction because that is the only way you will know what your methods are producing. I fully realize that no man will be able to put 70 foot pounds of torque on a knife handle with his hands.

Destructive testing is what has led us to the methods and steel we now use.

In my DVD we show a diagram of a martensite pyramid that forms inside of the blade when we edge quench. It is the martensite pyramid and the adjacent structures between the outside of the pyramid and the outside of the blade that are most significant in developing strength, thanks to a large degree of reduction by forging we are able to develop a Wootz like structure that when flexed acts like a laminated bow in supporting the martensite. The wootz like structure does not like to stretch but does not suffer greatly from compression. Since it works from both sides of the blade we have the best of both worlds.

If we soak the blade at temperatures over critical we loose the wootz like structure and blades loose strength.

I have never been able to achieve these characteristics with a fully hardened blade and soft back draw.

I hope this answers your questions, if not ask more.

 

[me2]

Ed, since you feel the 70 ft-lb torque is more than almost anyone can manage by hand, could you reduce the thickness, from say 3/16" to 1/8", and get an increase in flexibility without trading in strength with respect to what a human hand can do? This would have a reduction in lateral strength (torque required to flex/bend it) but would increase flexibility and possibly allow more trips back and forth in the vice without cracking. You could also increase the hardness (strength) of the edge for greater edge holding.

 

[lazlo]

Ed, since you feel the 70 ft-lb torque is more than almost anyone can manage by hand, could you reduce the thickness, from say 3/16" to 1/8", and get an increase in flexibility without trading in strength with respect to what a human hand can do? This would have a reduction in lateral strength (torque required to flex/bend it) but would increase flexibility and possibly allow more trips back and forth in the vice without cracking. You could also increase the hardness (strength) of the edge for greater edge holding.

He certainly could do that -- thin the spine and draw it less for the same flexibility and strength in a thinner cross section. But Ed has designed his knives with a specific heft, and I presume that he's softening the spine for a specific level of toughness given the spine thickness.

The bend test is a measure of the toughness of the blade -- the knifemaker doesn't expect that you'll run across a leg vise in the field

Does anyone know what temper hardness steel-grey is on 5160? JR Cook had us draw our journeyman knives to steel-grey to survive the bend test. I haven't had a chance to jam a penetrator into the spine, but I'm guessing that's in the 35 HRC range...

 

[Ed Fowler]

Eldon Perkins made a thinner blade, about 1/8 inch thick, four inches long, it passed our cutting and edge flex tests, then we put it into a vice and he flexed it back and forth, 90 degrees each way, it made about 60 flexes and our vice broke. The blade got so hot you could not hold it in your hands.

This was in the days we did not use a torque wrench to measure strength of the blade. One aspect of testing, when you sacrifice a blade for testing, you want to learn as much as you can from it, this is why we now use the torque wrench. I wish we had thought of it long before we did.

The blades I like to use in the field are ground to what I call the modified Price grind for the man who made the first one I saw, I believe it was Michael Price's father. It is a complex convex grind, thinner in front of the ricasso, thickens toward the front of the blade and provides extra strength to the tip.

I like a fairly thick blade because a thin blade is tough on your thumb when you place it on the spine to increase your leverage on the blade. This is why all my blades have a rounded spine. I believe that the only sharp edge on a blade should be the cutting edge. I find that sharp edges anywhere else are only uncomfortable to the hand that uses them.

 

[me2]

What about the notion of less effort to push the thinner blade through, meaning that while a 1/8" spine is a narrower area for your thumb, the thumb doesn't need to push as hard?

 

[Ed Fowler]

Good question: The geometry of a blade has a lot to do with how much pressure you need to apply. I wish I was smart enough to explain the modified Price grind. I see you live in the vicinity of Blade Show. If you can make the show next year I would love to let you run your fingers along the profile of one of our blades, trying to explain it is like trying to explain a squirrel verbally. In order to take advantage of its attributes you need adequate mass in the blade, strength is one attribute I want to maximize without sacrificing function.

Like we have been discussing, the knife is a total package designed to do what you want it to do. We each have our ideas concerning knife function and naturally our methods of using them. It does not take much of a blade to field dress most of the animals we hunt on this continent. I like to develop as much potential in my blades in case they are needed when you find yourself in an unexpected wreck.

One of my greatest fears is that one of my blades will fail when it is desperately needed, this has been one of the motivations for the testing we do.

 

[kelsil]

I heat all my blades with a torch when hardening, always have and always will. The reason is simple, with a torch I can heat the area I want to harden, painting the color into the blade much like an artist paints his colors. I can dictate exactly what I want hard, I edge quench for assurance that only the area I want hard gets the opportunity to harden.

I believe our testing methods may be misleading in that they are absolutely extreme in nature. We test to destruction because that is the only way you will know what your methods are producing. I fully realize that no man will be able to put 70 foot pounds of torque on a knife handle with his hands.

Destructive testing is what has led us to the methods and steel we now use.

In my DVD we show a diagram of a martensite pyramid that forms inside of the blade when we edge quench. It is the martensite pyramid and the adjacent structures between the outside of the pyramid and the outside of the blade that are most significant in developing strength, thanks to a large degree of reduction by forging we are able to develop a Wootz like structure that when flexed acts like a laminated bow in supporting the martensite. The wootz like structure does not like to stretch but does not suffer greatly from compression. Since it works from both sides of the blade we have the best of both worlds.

If we soak the blade at temperatures over critical we loose the wootz like structure and blades loose strength.

I have never been able to achieve these characteristics with a fully hardened blade and soft back draw.

I hope this answers your questions, if not ask more.

*** Hi there Ed, I don't know if the steel you are using requires some soaking time at critical or peak temperature but if I may ask, are you able to use a torch on steels that requires about 30 minutes soaking time before hardening? Thanks.

 

[Ed Fowler]

The only steels we have worked with are 5160 and 52100. Both call for longer soak times, but when using multiple quench the longer soak time is not beneficial and is not needed. Rex has examined our blades in his lab. and found that there is no measurable retained austenite in the martensite. The finer the grain you have developed the lower the temperature at which it can and will grow. Grain growth is a function of temperature and time. After forging and post forging quenches we anneal our blades at 988 f. when hardening they are only above critical temp for a few seconds before quench.

High quality steel is a blessing and worth seeking. We use John Deer load control shafts for our 5160, John Deer has supplied the quality control steel for us. Other sources of 5160 steel have not proven reliable. We have some high quality 52100 from Rex that we use and sell to our students. I know our techniques work with these steels, if you are using something else you will have to do your own testing to determine the best temperatures and methods for the steel you are using.

One thing we have learned is that higher temperatures and soak times are not always necessary when forging or heat treating.

I just reread your question and see I did not answer exactly what you asked. Holding a blade at critical for 30 minutes would be difficult and more expensive than other methods.

 

[kelsil]

The only steels we have worked with are 5160 and 52100. Both call for longer soak times, but when using multiple quench the longer soak time is not beneficial and is not needed. Rex has examined our blades in his lab. and found that there is no measurable retained austenite in the martensite. The finer the grain you have developed the lower the temperature at which it can and will grow. Grain growth is a function of temperature and time. After forging and post forging quenches we anneal our blades at 988 f. when hardening they are only above critical temp for a few seconds before quench.

High quality steel is a blessing and worth seeking. We use John Deer load control shafts for our 5160, John Deer has supplied the quality control steel for us. Other sources of 5160 steel have not proven reliable. We have some high quality 52100 from Rex that we use and sell to our students. I know our techniques work with these steels, if you are using something else you will have to do your own testing to determine the best temperatures and methods for the steel you are using.

One thing we have learned is that higher temperatures and soak times are not always necessary when forging or heat treating.

I just reread your question and see I did not answer exactly what you asked. Holding a blade at critical for 30 minutes would be difficult and more expensive than other methods.

Thank you so much Ed. This is actually a very helpful response specially in my desire to make some simple, but reliable small knives in the backyard, and without those expensive kilns or ovens that other kinds of steel/alloys need for hardening or heat treating. I like what I've been reading about the CPM S30V but, you made me very interested in the kind of steels you are using. I'm really curious though, if a properly made and heat treated 5160 or 52100 blade would at least be near equal, or maybe equal to a properly made and heat treated CPM S30V in edge retention and toughness.

 

[lazlo]

The geometry of a blade has a lot to do with how much pressure you need to apply. I wish I was smart enough to explain the modified Price grind.
If you can make the show next year I would love to let you run your fingers along the profile of one of our blades, trying to explain it is like trying to explain a squirrel verbally.

Ed, will you be attending the San Antonio Blade Expo? I've read the chapter on the Price grind in your book, but I'd love to hear your explanation

 

[Ed Fowler]

Kelsil: Our blades are tough, strong, have superior edge holding and are easy to sharpen. I have never tested a CPMS30V blade so can not answer your question from experience.

lazlo: The only show on my schedule at present is Blade Show next year. I experimented with the Price grind for months and adapted it to our steel, methods and the kind of knife we want to make. We teach how to develop and test it in our seminars and every student has liked using it. You can get an idea of its geometry when you look at an old Puma White Hunter, with the exception that we blend the grind from edge to spine.

 

[kelsil]

Kelsil: Our blades are tough, strong, have superior edge holding and are easy to sharpen. I have never tested a CPMS30V blade so can not answer your question from experience.

Edited by Moderator....product info and sales discussion should be done by email, not on the open forum.

 

[butcher_block]

Ed what all steels have you tested vs your 52100 and 5160

as far as how tough. S30v is good for SS but it will never be as tough as a spring or plain carbon blade HTed right
edge holding tho will depend on hardness of bothe test steels and in this case i would say that s30v should have the edge with the V carbides doing alot of cutting work (tho if under hardened the carbides kind of jsut wash out of the steel matrix)

 

[lazlo]

I experimented with the Price grind for months and adapted it to our steel, methods and the kind of knife we want to make. We teach how to develop and test it in our seminars and every student has liked using it. You can get an idea of its geometry when you look at an old Puma White Hunter, with the exception that we blend the grind from edge to spine.

Hi Ed, from what I've read, and what you've described, your Modified Price Grind seems to be an inverted distal taper: it starts out thin in front of the ricsasso, and gets thickest under the tip.

I thought the point of the distal taper was to distribute the bending moment from the ricasso out to the tip, making the blade much more flexible The Price grind seems to sacrifice that in order to move weight to the belly?

I'm guessing, when you do your bend test, that the blade bends right in front of the ricasso?

 

[kelsil]

Edited by Moderator....product info and sales discussion should be done by email, not on the open forum.

Ooopppss....my bad. My apologies sir.

 

[kelsil]

Ed what all steels have you tested vs your 52100 and 5160

as far as how tough. S30v is good for SS but it will never be as tough as a spring or plain carbon blade HTed right
edge holding tho will depend on hardness of bothe test steels and in this case i would say that s30v should have the edge with the V carbides doing alot of cutting work (tho if under hardened the carbides kind of jsut wash out of the steel matrix)

That's a good piece of info butcher_block. Think I got it but just to clarify. Are you saying then that, if you have a blade of 1095 and CPM S30V with exactly the same dimensions or size(lets say 1/16 x 1/2 x 5 inches), and are heat treated to the "T" as per specification, that the 1095 blade would beat CPM S30V with regard to toughness but that CPM S30V would have the advantage on edge retention? Thanks

 

[Ed Fowler]

A full distal taper results in a weak tip. The Price grind provides strength to the tip where it is most needed.

When you look down on the spine of one of our blades you will only see at most a slight distal taper. The Price grind, modified in accord to steel and methods developed for the intended purpose of the blade allows the maker to dictate exactly where the blade will bend. As noted earlier they do not necessarily bend easily, 70 foot pounds is a lot and for a blade to withstand the force we applied over only 1 3/4 inches is very challenging. You are correct in that when looking at our blades from the cutting edge they represent a complex reverse distal taper.

I have only been able to test one CPM S30V and hesitate to comment on its performance as it is not necessairly a representative sample. I can state that in our blades we have achieved an ASTM grain size of 15 and finer. The "and finer" is very significant as they are not a uniform grain, but a matrix that has a very dedicated grain flow from spine to tip to provide strength and flexibility to the blade. I can state that all blades we have tested that are alloyed with vanadium have been prone to catastrophic failure, some of these blades we forged using 52100v and we were unable to develop what we feel is adequate flexibility.

Blades with a full distal taper tend weakener toward the tip where they need to be stronger.

I hope this makes sense.