Soak temp and time for 52100 and 5160?

When we started working with Rex, an ASTM grain size of 10 was considered the theoretical limit in 52100 we had already developed a #10 grain. After working with Rex and others for about 12 years we have achieved a #14.

I can't remember having Rex check for grain size before post forging quenches, normalizing, annealing, hardening and tempering, we may have but not to my memory, my file on Rex's work is extensive, I will look through it when time allows.

The significant aspect of our forging is that using low temp forging temperatures, 1,625 f as top forging temperature, starting with 5 1/2 inch round bars we have a rate of reduction by forging of about 98 + points we align the grain parallel with the blade and refine do a degree.

If you do a search on this form or some reading you can find the beneficial attributes of fine grain in many texts.

I will add that fine grain size is not the only significant variable, the fine grain must be in a matrix, our statement that the grain size is 14 and finer is as significant as the grain size. A uniform fine grain, such as is many times achieved with a vanadium alloy is usually like glass, very fragile and fails catastrophically in toughness tests.
 
Why was a #10 the limit? I presume the benefits of ultrafine grain size are the same you'd want in any knife steel: better toughness and longer edge holding. What is it about such fine grain sizes that permits these things, particularly edge holding? Can 52100 achieve a grain size of 14 with just heat treatment alone, like 5160 can? And just so I'm clear on this, are we talking about grain size or carbide size?
 
#10 was the theoretical limit according to the references we read concerning 52100.

The carbides are actually finer than #14.

I do not believe you can achieve a #14 grain through heat treatment alone, but I invite anyone to try.

I did not know and have not seen 5160 achieve a #14 grain by heat treatment alone.

The most important aspect of the statement #14 and finer is that the cutting edge is a matrix of 14 and finer. The finer is as important as the largest grain. The matrix is achieved through a significant amount of rate of reduction by forging all at low temperatures that do not promote grain growth. As the blade is used, the matrix surrounding the carbides washes out and fresh carbides come to the surface, thus ease of sharpening and cutting performance.

The finer the grain, the lower the temperature at which he can grow, thus our 1,625 f. as the highest forging temperature. The numerous thermal cycles required to forge down a large piece of steel are all a part of the end product, as is the selection of the steel we use.

What has become known as JD 5160 is held to tight specifications, thus it allows for high endurance performance blades. The 52100 we use is also top quality developed to tight specifications.
 
So the virtue of the ultrafine grain that allows improved edge holding is its lower wear resistance? Do you have any micrographs of an edge after some skinning or rope cutting testing?

After doing some digging, I would make an assumption (yea I know) that the grain size provided by the ASTM standard is an average, and there will be grains of both larger and smaller size. If the largest of the grains is #14, then wouldn't the average size be smaller?

I have some references that show size 14 and 15 for a couple of steels after heat treatement without forging. This is down from an 8 - 11 range. I checked and it was not 5160, but 5150 instead. However, I see no reason that the same results could not be achieved in 5160. Also interesting is the heat treatment involves a step above 1625 F, held there for several minutes. In any case, none are 52100. Are the references you mention for 52100 only, or more generic?

Also, my apologies to the original poster for taking thread drift to another level.

So we are talking about grain size, not carbide size. Those 2 get mixed up sometimes on the various knife related forums, and it's good to make sure everyone is on the same page. Regarding carbide size, I figured they were at least as small as the 0.2 micron size I've seen for standard industrial heat treatment. Did you have them measured recently? Reading your posts here it looks like you've had some break throughs lately.

Thanks for letting me bend your ear, or keyboard in this case.

Also, my apologies to the original poster for taking thread drift to a new level.
 
When I speak of our knives, it is we. Rex is a big part of that team, I let him do the science stuff, I am just the poor dumb cowboy making knives.

The wear resistance is actually greater, when we push we can get over 1,000 cuts on one lay of 1 1/4 inch rope. I use this because it is easier to hold. I believe our record is 1,400 cuts with out sharpening. That 5 1/4 inch blade made 14 90 degree flexes, back and forth, I would call it 7 180 degree flexes. The torque required was around 80 foot pounds. When the blade cratered it cracked in 6 stages up to the soft zone where the crack or as Rex calls it the tear bifurcated in two directions parallel to the blade. It could have been straightened and used again as a knife.

I do sometimes strop the blade on the palm of my hand to open up the micro serrates. Yes you could call it better edge holding through lesser wear resistance.

I have a microscope, but have not used it. My only testing is through performance, Rex does the rest in his lab. Presently he is working 12 hour days and until his time opens up I have not sent him any blades to examine.

Using quality 5160 forged from 1" round bars we can come very close to the performance qualities of 52100. I have a text from the 30's that mentions multiple quench in a foot note. *This was the finest grain we have seen in 5160." they do not mention how many quenches they performed or how the stock was developed. As I remember they were working on steering rods for an automobile.

There are some things we have found our lately, for example final sanding with an X22 belt and buffing parallel to the blade results is tougher blades.

There is another experiment I want to try, this is preloading a blade: say to 50 ft lbs and letting it sit for a day, then testing it to destruction. An experiment in the 30's found an increase of about 50% in toughness. I also want to try some other quench fluids (faster) and higher tempering temperatures. Another question I want to answer is how great the rate of reductin will be enough. There remain many questions.

The benefit of multiple quench allows full transformation without holding at a temp above critical long enough where the grain will grow. Grain growth is a function of time and temperature.

If you want to read some great information, the Battelle Memorial Institute wrote a book, "The prevention of fatigue failure of metals under repeated stress" you can purchase it on line from Abe Books sometimes for as little as $7.00. If you really want to read some thoughts there are references to experiments done in Germany and America before WWII, a time when information was freely shared between us. The German steel industry was light years ahead of us. A copy of this book sits permanently beside my bed for a little treat each night.

The ASTM grain size is 14 and finer, I have not asked Rex what the average grain size is, it would have to be less.

I believe that the large degree of reduction by forging is an important aspect.

When I started forging 5160 I used 1" by 1/4 inch bar stock. When I started using 2" x 3/8ths stock performance increased. I have never had a blade forged from a 2" ball bearing out cut a blade forged from a 3" ball. We have learned a lot since those days.

We have purchased a large amount of 2" to 3 1/2 inch round bars of high qulaity 52100
that we use in seminars. Blades from this stock do very well.

I am working on a billet of 52100 from our 5 1/2 inch round bars, it has been normalized 20 times and I am ready to to start working it down with flat dies. It is my belief that starting with the largest stock you can work using quality steel it is good times. While drawing dies are faster, the performance is not up to blades forged using flat dies.

All hammer blows are to the cutting edge and sides of the blade, the future spine of the blade is never hit with a hammer.

Years ago I sent Rex some samples, he could tell which was the intended cutting edge using his microscope I marked the edges of the billet with random numbers.

As usual he informed me that I tend to forge more on the right side of the blade than on the left, a habit I am fighting.

I sent Rex 7 blades one had had no post forging quenches increasing the number of quenches to 7 post forging quenches. Out of the seven blades he found a steady progression in what he called uniformity. Since we started using the 35 second (minimum) post forging quenches we have never had a blade warp in heat treat.

I hope that I am answering your questions, it is not my intent to hold anything back.

All of what we have learned has had its beginning in performance testing of blades to destruction using methods available to any blade smith in his shop who wants to know.

There is still much to learn and I am sure that it has all been learned before.

I don't mind discussing what we have found, actually it is kind of nice to find someone who asks good questions.
 
butcher_block said:
Ed i have made razors that were tested at 64RC that had no problem flexing at the edge more then .030 with ought chipping out

i can also take a new file and grind an edge on it and have it not flex at all and not chip out ether

as much as i hate the "file skate test" it tells you more about the steels hardness then the edge flex does
Click to expand...

Hardness testing with a file and the edge flex test can both be very useful and helpful if you understand them correctly and use them logically. If not, then of course they aren't of much benefit,... like anything else.

Also, (in response to one of your other posts),... the edge flex test is not so much "for" geometry as it is "relative" to geometry.
 
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Ed Fowler said:
When we started working with Rex, an ASTM grain size of 10 was considered the theoretical limit in 52100 we had already developed a #10 grain. After working with Rex and others for about 12 years we have achieved a #14.

I can't remember having Rex check for grain size before post forging quenches, normalizing, annealing, hardening and tempering, we may have but not to my memory, my file on Rex's work is extensive, I will look through it when time allows.

The significant aspect of our forging is that using low temp forging temperatures, 1,625 f as top forging temperature, starting with 5 1/2 inch round bars we have a rate of reduction by forging of about 98 + points we align the grain parallel with the blade and refine do a degree.

If you do a search on this form or some reading you can find the beneficial attributes of fine grain in many texts.

I will add that fine grain size is not the only significant variable, the fine grain must be in a matrix, our statement that the grain size is 14 and finer is as significant as the grain size. A uniform fine grain, such as is many times achieved with a vanadium alloy is usually like glass, very fragile and fails catastrophically in toughness tests.
Click to expand...

Ed I have a question about what you said here, but to keep from hijacking this thread I started a new one here:

http://www.bladeforums.com/forums/showthread.php?p=8835718#post8835718
 
sorry Tai im sure no wordsmith and thats also why i have not added morre to this post. im much better spoken then in the ink
 
The wear resistance is actually greater, when we push we can get over 1,000 cuts on one lay of 1 1/4 inch rope. I use this because it is easier to hold. I believe our record is 1,400 cuts with out sharpening.

How do you know when to stop cutting and record the final number of cuts?

That 5 1/4 inch blade made 14 90 degree flexes, back and forth, I would call it 7 180 degree flexes.

I prefer to think of it as 90 degree flexes when I read about these tests. 180 degrees implies a horse shoe type bend to my mind.

The torque required was around 80 foot pounds.

Do you know how thick the blade was? How closely do you control the thickness of the various blades tested in this manner?

I believe that the large degree of reduction by forging is an important aspect.

Assuming 52100 can attain a grain size in the ultrafine range (13-15) from heat treatment alone, similar to other low alloy chromium steels (5150), and the carbides are even smaller (0.2 microns), then there is still an unexplained reason to do the forging? Or has the benefit from just the forging been explained and I missed it?

As the blade is used, the matrix surrounding the carbides washes out and fresh carbides come to the surface, thus ease of sharpening and cutting performance.

Since the carbides are much harder than the surrounding martinsite, doesn't this happen regardless of grain size?
 
My computer is crashing, I will try to respone when we get it or a new one working, sorry for the delay.
 
Hey....in the mean time I'll chime in to say- take this thread and run with it! This is very useful information, so please contine.

Brad
 
I have a new computer, but no spell check and all that stuff yet, sorry.

When do I stop cutting? When the blade does, just slides and does no longer crunches through the rope.

How thick was the blade? I just measured one of our test blades, in the area of the flex or bend if you will, it measures .244 and and is 1.08" from spine to cutting edge, naturally a convex blade.

How do we control the geometry (mass) of the blades we test, we test them all sizes, unless we are doing some kind of comparison testing, then we do the best we can to make both or all blades in the experiment the same.

Eldon tested one blade about 3/16" thick, it developed an S curve and flexed over 180 times when the vice broke. It is tough to hold an complex convex blade in a vice and it kept slipping so we kept tightning the vice. The blade was so hot you could not hold it in your hand.

Also we test various complex convex geometry blades. Through the geometry of a blade you can dictate where it will flex and how resistant to flex it can be. When we come to understand the geometry that influences tough, we can play with a lot of variables.

There are many reasong to forge, I will mention the big ones as I see it. The degree of reduction by forging allows the bladesmith or metal worker to dictate the grain flow of the steel. If there is a fault in a piece of steel, the greater the degree of reduction by forging the lesser the influnece of the fault to stress running parallel to the grain. Naturally this benefit can be non existent unless forging was done right.

Years ago Wayne Goddard and I compared two knives from the same steel. One forged and one shaped by stock removal. The tripple quench forged blade out cut the triple quench stock removal blade, this experiment was reported in Blade and in the first knife talk book.

When we started our performance testing, as our grain size became finer, flex and cut performance improved. I believe that if you seek ultra high endurance blades, grain refinement is what has proven itself to work for us.

Years ago Rex send me a report that reported the differences between steels that had been shaped with a press vs steel that had been worked down with a hammer. They reported a greater degtree of grain-refinement from the hammer than the press.


Hope I answered most of your questions, if not don't be bashful!
 
Eldon tested one blade about 3/16" thick, it developed an S curve and flexed over 180 times when the vice broke. It is tough to hold an complex convex blade in a vice and it kept slipping so we kept tightning the vice. The blade was so hot you could not hold it in your hand.

How well did it cut and how much torque was required? Do you think the heat was enough to damage the blade?

If there is a fault in a piece of steel, the greater the degree of reduction by forging the lesser the influnece of the fault to stress running parallel to the grain.

Do you get steel with flaws in it often enough that this is a problem?

The degree of reduction by forging allows the bladesmith or metal worker to dictate the grain flow of the steel.

I think you said here that you start with 5.5" bars. What form are they in when you get them, i.e. hot rolled, cold rolled, as cast, etc.?

And a few without quotes.

Have you compared the torque required to bend your standard blades to that needed to flex/bend a fully hardened blade approximately 1" wide, 1/4" thick, and 5" to 6" long to point that it breaks? From my experience with high strength bolts, 80 foot-pounds doesn't seem excessive for a person to produce. I've seen people get over 250 with a wrench 12" to 14" long. In other words, is 80 ft.-lbs. enough, just right, or too much?

Do you have an idea of how much pressure it would take on the edge to buckle the blade or otherwise damage the knife so it can no longer be used? I picture someone pushing down on the knife to make a press cut through a very tough material, say trying to press through some dowel rods or something.

Have you ever taken a bent blade and cut through through it along the hardening line to see how much the hardened steel springs back? I imagine using a dremel and cutoff wheel or something similar would be the easiest way to do this.
 
How well did it cut? Eldon made 500 cuts with the blade and quit, it probably could have done more. We were not using a torque wrench in those days and let a lot of data go undetected because of our lack of insight, but we did learn and now use the torque wrench on all test blades. The blade woulld have had to reached a temperature over 388f. for it to have reduced the hardness by heat. I don't know what influence the flexes had on the rockwell. Another experiment for someone to try!

Our steel is very clean, still it is not only the rate of reduction that contributes, but the thermal cycles. From 1,625f to where the steel quits moving requires a lot of thermal cycles to forge a blade. When I was using steel from jobbers I found many failures that I blamed on my technique, examining the fractures in the steel I could see faults, but did not know what I was looking at at that time. Starting with all blades comming from the same pour of quality steel was one of our best decisions as it reduced the number of variables we had to deal with. Yes it was a problem, especially due to the much lower degree of reduction by forging, remember I was using flat bar stock.

A gentleman by the name of Doc. who has been forging in a steel mill since he was a kid takes the hot rolled round bars and forges them down with a 10,000 Chambersburg hammer. When I get it it is usually in 3 x 3 bars. I cut them to length that will fit into my Paragon and give them a 1,725 f soak for 2 hours for every linear inch to the center and let them cool down slow. Then weld them onto a stick and go to work working them down to knife blades. This soak promotes uniformity in the steel and has solved a lot of problems. Not all bars are the same for many reasons. Today I am using stock that all came from the same 18 foot bar. I enjoy it a lot!!

Don't forget that a bolt is a machine, 80 pounds of torque on a bolt through the screw threads may very well result is much more stress on the steel.

A 14 inch wrench is a lot different than pulling on a 5 inch handle. I have not been able to flex a blade to 90 with my hands. They are much stronger than most folks. Not only that when they flex you have an instant warning that you are pushing the blade pretty hard.

Chris Amos pounded one of his blades that he still carries through a piece of 1/2 inch angle iron, the edge showed no damage, the spine still has the hammer marks on it.
Another reason for the soft back is that it will mushroom rather than chip, I learned that steel that chips is dangerous to folks in the area. I was working with a proto 9/16 open end wrench and had a chip come out of the jaws and got it stuck in my eyelid. Been gun shy of chipping steel ever since.

I have never tried your experimet about cutting through the hardened steel to see how far it would spring back, maybe I don't understand your question? I do have a blade that made what I call 8 180's flexes and usually take it to shows. It did not fail, but retained about a 40 degree bend. when we got back to the blade several hours later it had straightened and continues to straighten over time to about 30 degrees on its own.

When we try to flex a fully hardened blade when it fails it fails catastrophically from edge to spine. Are they stronger? Yes, but not worth the sacriface in toughness in my opinion.

I still have not found a spell check I can use in my posts so apologize for spelling errors.
You are asking some good questions!
 
Ok, so here is a question I probably should have asked before delving into the details of the bend tests. What is the purpose of such high ductility in the blades?

Do you know what size the original billets start out as before being hot rolled to 5.5"?
 
as far as the bend test i think its more jsut bragging rights as if you can do it more then one or 2 times what is the point

its like proving that it will not snap in 2 parts 12 times (whens that last time you ever heard about the need for that )
 
I guess I could see that. However, the same could be said for the way a lot of us sharpen our knives. I don't really need knives that can clip off hair above my skin. Seems like there is a lot of emphasis on it beyond passing the various ABS tests, so I just wondered what the reason was.
 
I’d be curious to see what Ed has to say.

With sharpening, heat treating, performance etc., I think it has a lot to do with curiosity… “What are the absolute limits of the steel?” On the one hand it makes a lot of sense, (splitting hairs is sort of what we do),… but on the other hand how much of it is really practical for a working knife? Some of it does get kind of silly,… but it gives us something to do. When is good enough, good enough?

We don't all have to share the same obsessions though...
 
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yep we all have our thing

i ll keep working on getting better edges on my razors and keep pushing how thin i can make a kitchen knife

as to the hair popping edge its jsut a fun trick less you are making razors
on a hunter you might be far better haveigna slightly toothy edge as meat is differet to cut then hair
but as said we all have our thing
 
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