bending tests

Toni Oostendorp

Toni Oostendorp

Joined
Sep 3, 2004
Messages
450
The fun part about cutting competitions is that as a knifemaker you are constantly thinking about improvements. The shape of the blade, the edge geometry, the grip and the method of hardening are all topics that occupy my limited brain.

A few days ago my good friend and knifemaker Erik Markman was visiting me and we decided to test our cutting knives. Soon we decided that they could be improved upon, so what do you do with the old ones? We both wondered if our hardening was good enough. That the knives kept their sharpness more than well we already tested. But what about the rest? I wanted to break my knife to see the grain size at the edge and at the back. I also wondered how far I could bent the fully hardened, forged O1 toolsteel blade.

We placed the blade in the vise without any wooden blocks for about 1.5 inches from the tip. The blade was to strong for me so I placed a steel pipe over it. Finally Erik bent it more than 90 degrees but still it didn’t break. The blade sprung back to a 50’ish degrees. The edge is undamaged.
Next we put Erik’s blade In the vise. His knife is made out of 1.5026 (comes in the neighbourhood of 5160), selectively hardened and is more tapered than my knife. With all his weight on the knife he managed to bent it more than 90 degrees. His knife also didn’t break or crack what so ever.
You can see a difference between the two blades where the bent starts. I think it’s the hardening method and geometry of the blades that makes this happen.

We learned a lot from this test. First of all we know that our hardening is more than ok. Also we noticed the hidden/through tang construction that we both use a lot is mighty strong. When the pipe was slit over the first blade the handle bent quit a lot, but sprung back into place without any damage. The last thing we learned is that we can make a fully hardened blade out of O1 for cutting competitions and not have to worry about bending the blade during a comp (which my first cutting comp. blade did).

Here are some pics (with a bit of luck some bending pics in the coming days):


IMG_0993.JPG


Top knife is from Toni
Steel: O1
thickness: 6mm
Hardening: full
Hardness: 60/61 RC

Bottom knife is from Erik
Steel: 1.5026
Thickness: 6mm?
Hardening: Selective
Hardness: 60 RC?

IMG_0990.JPG
 
That is good.

At what approximate degree did the stop springing back and start permanently deforming?
 
well we didn't check that exactly, but it was a considerable amount of degrees. Not something you would accomplice in normal or extreme use.
 
Knives are made to cut, not be stuck in a vise and bent. Don't you know the ABS has had it wrong all these years. I can't imagine what Bill Moran was thinking. That's abusive. This test has no value. Use the proper tool for the job.

There, that should cover it.

60-61 Rc not breaking, I like that. I personally prefer fully hardened blades. I would rather work harder to eventually break a blade (which yours did not do with a cheater pipe) than have it bend at a lower force. I downloaded Tim Zowada's Ashokan demo on how steels flex based on geometry, not hardness - but that past that point, failure switches from permanent bends at low force for low hardness, to fracture, at a potentially much, much higher force for hardened steel.

To get a full test of your hardening, you still need to have a magnified view of the steel. How did you heat treat the blade?
 
I'm a simple type of person who likes to see stuff before he believes it. Assuming that you are doing things right is not my cup of tea, so I like to test my stuff. When you make a knife and a person is buying it, you should be able to tell your customer what he can and cannot expect from your product. Testing is the only way.

I expected the blade to break before reaching the more than 90 degree bend. Since it is O1 and fully hardened. A fellow knifemaker is taking the blade to a German University for further analyses.

the blade was taken up to 830 degrees celcius and then soaked for about 5 minutes, than hardened in oil. Tempered three times for one hour at 200 degrees. this should bring the blade to a 60/61 RC.
 
Anthony, That is absolutely amazing. I've never seen fully hardened steel take bend like that and not break into two pieces...can you please explain why because Im lost here??? is it the O-1 or the forging or what???

I'd like to know about the edge retention too if you can share?
 
Outstanding results. But the next time you decide to break your knives, please just send them to me instead. Those knives look awesome:thumbup:
 
Heartbeat,

The ABS doesn’t have it wrong. Go to the ABS web page, open the requirements for Journeyman Smith, read the purpose of the 90-degree flex test. It doesn't say it makes a knife better, it says the purpose of the test is to prove that the applicant knows how to selectively harden a blade.

My opinion is that most serious users would enjoy the confidence they have knowing their knife wouldn't break. Blades that are fully hardened will break at some point.

eastvillage, keep on with the testing, it gives a maker confidence in their product not gained in any other way.

Wayne
 
You can do 90 degree bends on swords, because they are longer and less curvature. There is a critical point of curvature you are not supposed to pass, and the blade would always spring back to its original position. I bent my 5160 spring steel katana 90 degrees and it springs right back to its original position. I had to put something like 300+ pounds of weight on it to bend it that much.
 
Wayne G. said:
Heartbeat,

The ABS doesn’t have it wrong. Go to the ABS web page, open the requirements for Journeyman Smith, read the purpose of the 90-degree flex test. It doesn't say it makes a knife better, it says the purpose of the test is to prove that the applicant knows how to selectively harden a blade.

My opinion is that most serious users would enjoy the confidence they have knowing their knife wouldn't break. Blades that are fully hardened will break at some point.

eastvillage, keep on with the testing, it gives a maker confidence in their product not gained in any other way.

Wayne
Click to expand...

He was being sarcastic Wayne:). There are controversial destruction tests by a particular member on these forums and it always gets someone riled up. Hardheart was just poking fun at those who get offended by such destruction tests.
 
That is quite impressive, bending that far hardened to 60-61 RC and not breaking or cracking. :thumbup:
 
Cool test, and damn impressive! Thanks for sharing!

By the way I'd be more than happy to dispose of that Erik Markman piece for you. :D
 
Wayne G. said:
Heartbeat,

The ABS doesn’t have it wrong. Go to the ABS web page, open the requirements for Journeyman Smith, read the purpose of the 90-degree flex test. It doesn't say it makes a knife better, it says the purpose of the test is to prove that the applicant knows how to selectively harden a blade.

My opinion is that most serious users would enjoy the confidence they have knowing their knife wouldn't break. Blades that are fully hardened will break at some point.

eastvillage, keep on with the testing, it gives a maker confidence in their product not gained in any other way.

Wayne
Click to expand...
As Kaizen mentioned, I was joking :) I personally prefer full hardened blades, but have no problem with testing of any sort to evaluate heat treating, as long as the maker and/or user learns something about their knives.
 
Very interesting, would seem to explain behavior I've observed with O1 in the past that I didn't quite understand.

BTW, Toni ... your knife now looks like sort of a modern, side-bend khukri. Who knows what someone might pay for it on eBay? ;)
 
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