The results of my latest flex test are?

A

Allan Molstad

Banned
Joined
Feb 1, 2007
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901
What a joke....

I'm not at all sure what to think of my last flex/bend test on a 52100 ball bearing knife I just did.

The blade snapped at around 60 foot LBS of torque.

I will try to post some photos, (There will be no video of this test posted on line) that show the snapped blade.
The grain along the break appears small to the eye, I dont have a scope to look closer, but I dont see any monster grains.

I guess I should back-up and tell you what I did to this blade and ask for your thoughts and advice for next time.
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The blade steel came from a 1&1/2 inch ball bearing.
the cutting area of the blade is about 4 inches long, with a 3/4 inch Racaso and a 3 inch tang.
The blade is/was about a little over an inch wide at the widest part, and right around a 1/4 thick for much of the spine.
The shape is like a Ed Fowler "Pronghorn"
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HEAT TREATMENT?

Becacause of all the heat I took after my last flex test I decided to change things up and do a different type of Heat treatment other than my normal O/A torch and edge quench.

1 - This Time, I clay-coated the areas of the spine and sides and tang that I wanted to keep from getting too hard.

2 - I heated the Texaco type "A" quench oil to 160

3 - I placed the "whole knife" (tang and all) in the hot running forge and heated until it was nonmagnetic.

4 - I kept the blade at this temp for about 2 min, while I got a few things ready in the quench tank

5 - I dunked the whole blade in the oil, and moved it around under the oil to help speed the quench cooling.

6 - When blade was still very warm, I placed in a warmed kitchen oven set at 400 temp, for 2 hours.

7 - took out of oven and cooled outside in the winter cold

8 - did another temper in Kitchen oven for about 2 & 1/2 hours at 400 temp.

cooled in freezer over night.

The knife was finished to 400 grit, then buffed to a mirror finish.
However I decided I didn't like the final design and so I wanted to test it to see what if any advantages are found in this new HT

Blade was placed in a vise as shown in the new DVD by Fowler.
I used a torque wrench to keep track of the force needed to flex the blade.
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The Flex/Bend test?
I bent the knife a little at first and went to 20 foot LBS,
The blade returned to straight and true

I bent a little more next time, took it to 40 foot lbs,
Again the blade returned to straight and true.
I looked very close at the blade and there was no sign that I had troqued on the blade at all.

next I went to 50 ft lbs
Again no change at all, blade returned to straight and true

60 ft lbs,I admit didnt get a good look here, but I sure didnt notice any difference

65 ft lbs and the blade snapped...
Actually I never reached 65 lbs, I was going to go that high but it snapped at some point as I pulled on the wrench.

-------------------------------------
RESULTS?
I concider this concept of heat Treating an error,,,a clear error and something I will not do again.
 
I think 52100 is too deep hardening for the clay thing to work.
BTW, how did it cut? :D
 
3 - I placed the "whole knife" (tang and all) in the hot running forge and heated until it was nonmagnetic.

4 - I kept the blade at this temp for about 2 min, while I got a few things ready in the quench tank
Click to expand...

How did you maintain temperature in the forge? Are you sure it didn't get much hotter than non-magnetic? 52100 does NOT respond well to overheating.

Dave
 
Alan,

Insulating the spine of a blade with clay/refractory cement to prevent hardening will only work with shallow hardening steels like the 10xx steels or W1 and W2. I've made and tested several 52100 blades loosely following the Fowler method, but bringing the entire blade up to nonmagnetic in the forge and edge quenching. None of them passed a 90 degree flex test. I don't have my notes in front of me, but I think they Rockwelled in the mid 50s along the spine. The best way to get a 52100 blade to pass your type of flex test is to bring only the part of the blade you want to harden to critical temp.

Hope that helps,
Todd
 
Todd Robbins said:
Alan,

Insulating the spine of a blade with clay/refractory cement to prevent hardening will only work with shallow hardening steels like the 10xx steels or W1 and W2. I've made and tested several 52100 blades loosely following the Fowler method, but bringing the entire blade up to nonmagnetic in the forge and edge quenching. None of them passed a 90 degree flex test. I don't have my notes in front of me, but I think they Rockwelled in the mid 50s along the spine. The best way to get a 52100 blade to pass your type of flex test is to bring only the part of the blade you want to harden to critical temp.

Hope that helps,
Todd
Click to expand...

Todd is correct.
I haven't done much heat treating like Ed showed me lately, but the last 5160 blade I torched and edge quenched/heat treated cut like a Bad Dog.
It was very hard up to almost 1/2 of its width and I did 31 180 degree bends before the cutting edge cracked up to the transition line.
You might check on the forge temp also.
 
Abrasive said:
How did you maintain temperature in the forge? Are you sure it didn't get much hotter than non-magnetic? 52100 does NOT respond well to overheating.

Dave
Click to expand...

I think Dave is correct here, at least this is part of it.
 
Todd Robbins said:
Alan,

Insulating the spine of a blade with clay/refractory cement to prevent hardening will only work with shallow hardening steels like the 10xx steels
Click to expand...

Yes, I see that now.

I got the idea to try this from something I read in BLADE, but it clearly didnt work for me at all..
 
Abrasive said:
How did you maintain temperature in the forge?
Click to expand...
The ONLY two means I have...by eye, and with my magnet.
I checked a bunch of times and i was able to keep it from getting too hot by shutting down the burner.

I got to nonmagnetic and then went a little past that for about 30 - 40 seconds, then turned down the flame and let it cook like that for perhaps 3 mins at most.
 
Im not sure,,,the way it snapped it seems to me that my TEMPERING should have been enough to keep it from doing that...

I tempered 2 times at 400 for 2 hr at a time.
 
Allan, I'm not sure what you consider a failure here? You made a 4" blade that got hard and withstood 60+ foot pounds of torque before breaking. Did you expect it to never break? That is why this type of testing is called destruction testing. It seems to me that you had a good product. I would suggest that you use a programmable oven or a forge with a temperature control to know what temperature your blade REALLY is at. Just because it was at 1350 one moment does not mean it won't be at 1650 20 seconds later. Testing for quality is only relevant if the conditions are controlled and repeatable. I do applaud your interest in determining the quality of your HT process.
Stacy
 
bladsmth said:
Allan, I'm not sure what you consider a failure here? You made a 4" blade that got hard and withstood 60+ foot pounds of torque before breaking. Did you expect it to never break?
Click to expand...

"Never" is a long time...
But it is true that the target I aim for when I do a Heat-Treatment is that I hope to end up with a knife that any guy in the field would not have to worry about.

When I sell a knife it's to one of my own friends or co-workers. I sell it to them with the idea that this knife will NOT let them down no matter what.

60 foot lbs of force and it snaps?...
Well to me thats NOT good enough.

I believe what happened was that (no matter that I covered the spine and sides with a 1/4 inch of clay), the whole blade seems to have gotten very hard anyway.

I just dont believe in the concept of a fully-hard blade on a true outdoor, working man's knife.
I believe it's not the right direction I want to go in.

At the time I felt that the clay should have slowed the cooling of the spine and allowed it to pass right by the stage where steel gets hard and ended up with a much stronger state. I thought this idea would work because of the article writen in the last BLADE, as well as some Japanese 1050 Katana I have made.

But for whatever reason, the clay didn't help me at all.

The other thing that really stunned me was that my TEMPERING seems worthless.
Tempering at 400 for up to 4+ hours just did not seem to bring the blade to the point where is had lost the fragile nature of very hard steel.

Im not going to do the clay-covering next time.
And I will return to doing my Heat-treatments with a O/A torch and doing an "edge quench" only.
But I don't really know what I should change about my tempering yet?
 
kbaknife said:
Todd is correct.
I haven't done much heat treating like Ed showed me lately, but the last 5160 blade I torched and edge quenched/heat treated cut like a Bad Dog.
It was very hard up to almost 1/2 of its width and I did 31 180 degree bends before the cutting edge cracked up to the transition line.
You might check on the forge temp also.
Click to expand...

Karl, you would be a good guy to ask about this, on the "180 degree" bend do you take the tip beyond 90 degrees until it actually is 180 degrees and parallel or even touching the tang? Or is this test actually just two 90 degree bends in opposite directions?
 
that would be cool, to bend it all the way to the tang.
but my tang is thinner than my blade steel, so Im not sure it would sit in the vise correctly and bend like you would want.

Mostly I would think that you would bend it to 90 in one direction, then turn the blade around in the vise and then bend it back up and over 90 the other direction.
 
Allan Molstad said:
6 - When blade was still very warm, I placed in a warmed kitchen oven set at 400 temp, for 2 hours.

7 - took out of oven and cooled outside in the winter cold

8 - did another temper in Kitchen oven for about 2 & 1/2 hours at 400 temp.

cooled in freezer over night.
Click to expand...

For those more metallurgically inclined:
Is it possible you put it in your oven before the blade had cooled enough to fully form martensite? If so, wouldn't that contribute to lots of retained austenite?

If you did have retained austenite, it could have transformed into fresh untempered martensite in your freezer. Or, it could have transformed from the stress of your first flexes.

Also, are you sure these bearings are even made of 52100? If you've got the wrong steel, that could make a huge difference. There was a guy here on the forums offering free analysis services a while back- you might give it a try.
 
the possum said:
Is it possible you put it in your oven before the blade had cooled enough to fully form martensite?
Click to expand...
I took the blade out and it was still warm to the skin.
The oil is heated to 160 , and so there is a limit to how cool the blade would have gotten no matter how long I left it in there.
However I have received some advice about not allowing the blade to cool totally in the quench oil from forum membership.

The blade was warm,,,you could still hold it, but you knew it was warm.

the possum said:
Also, are you sure these bearings are even made of 52100?
Click to expand...
I have never had them tested and thats one thing Ed Fowler warned me about the use of bearings. He said that even if you get a bearing from the same place, you just never know for sure what you got.

However, I can say that when I have posted about the bearing on this forum the answers I got back from guy who know all about steel was that there is a very good chance it's just normal ball bearings of 52100 steel.

also, when I did a 90 flex test on the knife I made last month that steel sure acted and etched in a way that I would have expected good 52100 to act.
++++++
What have I learned?
What I have learned from this test is that clay didnt work with my bearing quality 52100 steel.

I also learned that heating the whole blade in the forge can lead my blades to become fully hard, and thats a trouble I want to stay away from in the future.

I learned that I can HT a blade to take 25-40 or even 50 foot lbs of force and the blade will spring right back to straight, and thats nice.

But I also learned that right around 60-65 foot lbs of force when bending the blade is the point when this HT failed.
This gives me a chance to do a Edge quench HT and compare the foot lbs and see if there is any difference.
 
Kevin R. Cashen said:
Karl, you would be a good guy to ask about this, on the "180 degree" bend do you take the tip beyond 90 degrees until it actually is 180 degrees and parallel or even touching the tang? Or is this test actually just two 90 degree bends in opposite directions?
Click to expand...


I always assumed it to mean 180 from the first 90. I bent a blade 180 from straight once. :) At least the knife cut well. :D
 
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